@article {657, title = {Bilirubin oxidase-based silica macrocellular robust catalyst for on line dyes degradation}, journal = {Enzyme and Microbial Technology}, volume = {120}, year = {2019}, month = {Jan-01-2019}, pages = {77 - 83}, abstract = {

We present a new heterogeneous biocatalyst based on the grafting of Bilirubin Oxidase from Bacillus pumilus into macrocellular Si(HIPE) materials dedicated to water treatment. Due to the host intrinsic high porosity and monolithic character, on-line catalytic process is reached. We thus used this biocatalyst toward uni-axial flux decolorization of Congo Red and Remazol Brilliant Blue (RBBR) at two different pH (4 and 8.2), both in presence or absence of redox mediator. In absence of redox mediators, 40\% decolorization efficiency was reached within 24 h at pH 4 for Congo Red and 80\% for RBBR at pH 8.2 in 24 h. In presence of 10 mu M ABTS, it respectively attained 100\% efficiency after 2h and 12h. We have also demonstrated that non-toxic species were generated upon dyes decolorization. These results show that unlike laccases, this new biocatalyst exhibits excellent decolorization properties over a wide range of pH. Beyond, this enzymatic-based heterogeneous catalyst can be reused during two months being simply stored at room temperature while maintaining its decolorization efficiency. This study shows that this biocatalyst is a promising and robust candidate toward wastewater treatments, both in acidic and alkaline conditions where in the latter efficient decolorization strategies were still missing.

}, issn = {01410229}, doi = {10.1016/j.enzmictec.2018.10.004}, url = {https://linkinghub.elsevier.com/retrieve/pii/S0141022918303466}, author = {Roucher, Armand and Roussarie, Elodie and Gauvin, R{\'e}gis M. and Rouhana, Jad and Gounel, S{\'e}bastien and Stines-Chaumeil, Claire and Mano, Nicolas and Backov, Renal} } @article {673, title = {Bitumen@SiO2 core-shell particles green synthesis towards flowable powdered bitumen and their binder applications}, journal = {Colloids and Surfaces A: Physicochemical and Engineering Aspects}, volume = {570}, year = {2019}, month = {Mars-20-2019}, pages = {531 - 543}, abstract = {

Mineralization of occulated bitumen emulsions allows producing bitumen powders, also referred to as Bitumen@SiO2 hybrid particles, that can resist storage in hard conditions, with a load up to 8 kPa at 50 \°C during 20 h, without alteration of their morphology or release of their bitumen core. Thanks to the occulation, nal Bitumen@SiO2 powders are not highly pulverulent and allow transportation and handling of bitumen at ambient temperature without the need of water as it is the case for bitumen emulsions. This \“water free\” storage par- ticularity exhibits the double advantage of reducing the cost of transport and of avoiding inhibition of bitumen adhesion at mineral aggregates through the presence of water, therefore rendering the bitumen its high quality of binder. The silica shell is responsible for the high storage stability and, when mixed with aggregates for end use of asphalt, as for example in pavement applications, serves as mineral charge to the bitumen, modifying the bitumen ow properties. Indeed, when heated at 100 \°C and crushed, the capsules break releasing thus the bitumen. This suspension made of bitumen and silica shell fragments exhibits an interesting shear-thinning behavior that can be attributed to the presence of the remnant fragments. Indeed, when shell fragments have been transferred into a silicon oil, initially exhibiting a Newtonian behavior, the mixture of fragments and oil also exhibited a shear thinning rheogram demonstrating the e ect of the silica shell fragments. The bene t of such a behavior modi cation is the possibility to reduce or avoid the usual addition of llers. Passive adhesion has been tested by generating asphalt concretes with Bitumen@SiO2 powders and showed high stability.

}, issn = {09277757}, doi = {10.1016/j.colsurfa.2019.03.048}, url = {https://linkinghub.elsevier.com/retrieve/pii/S0927775719302420}, author = {Anaclet, Pauline and Depardieu, Martin and Laurichesse, Eric and Julien, Viviane and Hung, Yvong and Schmitt, Veronique and Backov, Renal} } @article {594, title = {Investigation of mixed ionic/nonionic building blocks for the dual templating of macro-mesoporous silica}, journal = {Journal of Colloid and Interface Science}, volume = {533}, year = {2019}, month = {Jan-01-2019}, pages = {385 - 400}, abstract = {

Traditional porous monoliths Si(HIPE) (High Internal Phase Emulsion), prepared from the Tetradecyltrimethylammonium Bromide (TTAB)/dodecane/water system, offer high specific surface area, mainly due to microporosity. Aside, mesoporous materials SBA-15, prepared from Pluronic P123, have a high specific surface area, but are obtained as powder, which limits their applications. Starting from the mixed TTAB-P123 surfactant, it is expected to tune the mesoporosity of Si(HIPE), while keeping their monolithic character.

The ternary TTAB/P123/water phase diagram was established by varying the weight ratio between these two surfactants. The micellar structure as well as the structural parameters of the liquid crystal domains were determined by SAXS (Small Angle X-ray Scattering). The effect of dodecane solubilization was also investigated and concentrated emulsions were formulated from the (P123/TTAB)/dodecane/ water systems. After this soft matter dedicated study, the acquired knowledge was transferred toward the hierarchical porous silica generations, where the sol-gel process is involved.

Mixing P123 with TTAB, macro-mesoporous monolithic silica with an enhanced contribution of the specific surface area due to mesoporosity can be prepared. The variation of the TTAB/P123 weight ratio allows controlling the porosity at the mesoscale. Moreover, the macroporosity can be tuned by changing the preparation method, by mixing either the two micellar solutions or directly the two surfactants prior the emulsification process. (C) 2018 Elsevier Inc. All rights reserved.

}, issn = {00219797}, doi = {10.1016/j.jcis.2018.08.068}, url = {https://linkinghub.elsevier.com/retrieve/pii/S0021979718309883}, author = {Roucher, Armand and Emo, Melanie and Vibert, Francois and Stebe, Marie-Jose and Schmitt, Veronique and Jonas, Florian and Backov, Renal and Blin, Jean-Luc} } @article {666, title = {Modified Szeg{\"o}{\textendash}Widom Asymptotics for Block Toeplitz Matrices with Zero Modes}, journal = {Journal of Statistical Physics}, volume = {174}, year = {2019}, month = {Jan-2019}, pages = {28 - 39}, abstract = {

The Szego-Widom theorem provides an expression for the determinant of block Toeplitz matrices in the asymptotic limit of large matrix dimension n. We show that the presence of zero modes, i.e, eigenvalues that vanish as n, ||\<1, when n, requires a modification of the Szego-Widom theorem. A new asymptotic expression for the determinant of a certain class of block Toeplitz matrices with one pair of zero modes is derived. The result is inspired by one-dimensional topological superconductors, and the relation with the latter systems is discussed.

}, issn = {0022-4715}, doi = {10.1007/s10955-018-2177-8}, url = {http://link.springer.com/10.1007/s10955-018-2177-8}, author = {Basor, E. and Dubail, Jerome and Emig, Thorsten and Santachiara, Raoul} } @article {578, title = {Doping as a Way To Protect Silicate Chains in Calcium Silicate Hydrates}, journal = {ACS Sustainable Chemistry \& Engineering}, volume = {6}, year = {2018}, month = {Sep-09-2018}, pages = {15015 - 15021}, abstract = {

A critical challenge in reducing anthropogenic impacts on the environment is to decrease the carbon footprint of the cement industry. A key concern in the search for more sustainable cement designs is the understanding and control of the depolymerization process that eventually determines the integrity of their silicate chains under mechanical, chemical, or thermal stresses. Herein, we use metadynamics to show that the depolymerization of cement silicate skeletons consists of hydroxylation followed by bond-breaking. We then clarify the local effects of doping the silicate chains: a stable pentacoordinate state following hydroxylation is promoted by aluminum atoms but restrained by phosphorus additions, the presence of two dopants being related to energy landscapes less favorable to bond-breaking. The role of these dopants is explained in cement-based materials and is key to the quest for low-cost opportunities to preserve the strength of cement for high temperatures or even over time.

Abstract Image

}, keywords = {Bond-breaking; Calcium silicate hydrate; Doping; Green cement; Silicate chains}, issn = {2168-0485}, doi = {10.1021/acssuschemeng.8b03488}, url = {http://pubs.acs.org/doi/10.1021/acssuschemeng.8b03488}, author = {Dupuis, Romain and Dolado, Jorge S. and Surga, Jose and Ayuela Andr{\'e}s} } @article {580, title = {Improving the practicality and safety of artificial corneas: Pre-assembly and gamma-rays sterilization of the Boston Keratoprosthesis}, journal = {The Ocular Surface}, volume = {16}, year = {2018}, month = {Jul-2018}, pages = {322 - 330}, abstract = {

Purpose: To make the Boston keratoprosthesis (B-KPro), together with its carrier corneal graft, more easily procured, transported and stored, as well as less expensive, easier for the surgeon to implant and safer for the patient, it is proposed that the B-KPro-graft combination be pre-assembled by an expert technician, followed by sterilization with gamma ray irradiation (GI) allowing long-term storage at room temperature. For this to be possible, it must be shown that the B-KPro itself (not only the graft) remains unharmed by the irradiation.

Methods: Polymethyl methacrylate (PMMA) discs and B-KPros were submitted to either ethylene oxide sterilization or different doses of GI. Cell biocompatibility, mechanical strength and optical quality were evaluated. The feasibility of assembling the B-KPro to a corneal graft, and gamma-radiate afterwards, was also assessed.

Results: There were no differences in cell biocompatibility between the samples. The optical evaluation showed high levels of transparency for all the groups. The absorbance of ultraviolet was higher for the groups treated with GI. The mechanical evaluation by nanoindentation showed no alterations of the PMMA discs after GI. The flexure test revealed a similar mechanical behavior. Technically, pre-assembly and GI of the B-KPro revealed no problems.

Conclusions: Sterilization of B-KPro using GI has no detrimental influence on the device. The pre-assembly of B-KPro to a donor cornea, followed by gamma sterilization, emerges as an efficient and safe procedure. (C) 2018 Elsevier Inc. All rights reserved.

}, keywords = {Artificial corneas; Boston keratoprosthesis; Gamma radiation; Gamma rays; Preassembly; Sterilization; Polymethyl methacrylate}, issn = {15420124}, doi = {10.1016/j.jtos.2018.04.002}, url = {https://linkinghub.elsevier.com/retrieve/pii/S1542012418300442}, author = {Gonzalez-Andrades, Miguel and Sharifi, Roholah and Islam, Mohammad Mirazul and Divoux, Thibaut and Haist, Michael and Paschalis, Eleftherios I. and Gelfand, Larisa and Mamodaly, Shamina and Di Cecilia, Luca and Cruzat, Andrea and Franz-Josef Ulm and Chodosh, James and Delori, Francois and Dohlman, Claes H.} } @article {631, title = {A nonequilibrium force can stabilize 2D active nematics}, journal = {Proceedings of the National Academy of Sciences}, volume = {115}, year = {2018}, month = {Jul-03-2018}, pages = {6934-6939}, abstract = {

Suspensions of actively driven anisotropic objects exhibit distinctively nonequilibrium behaviors, and current theories predict that they are incapable of sustaining orientational order at high activity. By contrast, here we show that nematic suspensions on a substrate can display order at arbitrarily high activity due to a previously unreported, potentially stabilizing active force. This force moreover emerges inevitably in theories of active orientable fluids under geometric confinement. The resulting nonequilibrium ordered phase displays robust giant number fluctuations that cannot be suppressed even by an incompressible solvent. Our results apply to virtually all experimental assays used to investigate the active nematic ordering of self-propelled colloids, bacterial suspensions, and the cytoskeleton and have testable implications in interpreting their nonequilibrium behaviors.

}, issn = {0027-8424}, doi = {10.1073/pnas.1720607115}, url = {http://www.pnas.org/lookup/doi/10.1073/pnas.1720607115}, author = {Maitra, Ananyo and Srivastava, Pragya and Marchetti, M. Cristina and Lintuvuori, Juho S. and Ramaswamy, Sriram and Lenz, Martin} } @article {626, title = {Rheology of granular materials composed of crushable particles}, journal = {The European Physical Journal E}, volume = {41}, year = {2018}, month = {Apr-11-2018}, pages = { Article Number 50 }, abstract = {

We investigate sheared granular materials composed of crushable particles by means of contact dynamics simulations and the bonded-cell model for particle breakage. Each particle is paved by irregular cells interacting via cohesive forces. In each simulation, the ratio of the internal cohesion of particles to the confining pressure, the relative cohesion, is kept constant and the packing is subjected to biaxial shearing. The particles can break into two or more fragments when the internal cohesive forces are overcome by the action of compressive force chains between particles. The particle size distribution evolves during shear as the particles continue to break. We find that the breakage process is highly inhomogeneous both in the fragment sizes and their locations inside the packing. In particular, a number of large particles never break whereas a large number of particles are fully shattered. As a result, the packing keeps the memory of its initial particle size distribution, whereas a power-law distribution is observed for particles of intermediate size due to consecutive fragmentation events whereby the memory of the initial state is lost. Due to growing polydispersity, dense shear bands are formed inside the packings and the usual dilatant behavior is reduced or cancelled. Hence, the stress-strain curve no longer passes through a peak stress, and a progressive monotonic evolution towards a pseudo-steady state is observed instead. We find that the crushing rate is controlled by the confining pressure. We also show that the shear strength of the packing is well expressed in terms of contact anisotropies and force anisotropies. The force anisotropy increases while the contact orientation anisotropy declines for increasing internal cohesion of the particles. These two effects compensate each other so that the shear strength is nearly independent of the internal cohesion of particles.

}, keywords = {CONTACT DYNAMICS METHOD; DISCRETE ELEMENT METHOD; SHEAR BANDS; NUMERICAL-SIMULATION; BED COMMINUTION; FRAGMENTATION; BREAKAGE; ROCK; DEM; MODEL}, issn = {1292-8941}, doi = {10.1140/epje/i2018-11656-1}, url = {http://link.springer.com/10.1140/epje/i2018-11656-1}, author = {Duc-Hanh Nguyen and Emilien Az{\'e}ma and Philippe Sornay and Farhang Radja{\"\i}} } @article {574, title = {Role of City Texture in Urban Heat Islands at Nighttime}, journal = {Physical Review Letters}, volume = {120}, year = {2018}, month = {Mar-09-2018}, pages = {Article Number: 108701 }, abstract = {

An urban heat island (UHI) is a climate phenomenon that results in an increased air temperature in cities when compared to their rural surroundings. In this Letter, the dependence of an UHI on urban geometry is studied. Multiyear urban-rural temperature differences and building footprints data combined with a heat radiation scaling model are used to demonstrate for more than 50 cities worldwide that city texture-measured by a building distribution function and the sky view factor-explains city-to-city variations in nocturnal UHIs. Our results show a strong correlation between nocturnal UHIs and the city texture.

Figure

Figure

Figure

Figure

}, keywords = {IDEAL CONDITIONS; CLIMATE-CHANGE; CITIES; SIMULATION; GEOMETRY; ENERGY; HEALTH; IMPACT; MODEL}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.120.108701}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.120.108701}, author = {Sobstyl, Jake M. and Emig, Thorsten and Qomi, M. J. Abdolhosseini and Franz-Josef Ulm and Roland Jean-Marc Pellenq} } @article {660, title = {Sol{\textendash}gel process and complex fluids: sculpting porous matter at various lengths scales towards the Si(HIPE), Si(PHIPE), and SBA-15-Si(HIPE) series}, journal = {Journal of Sol-Gel Science and Technology}, volume = {18}, year = {2018}, month = {Sep-11-2018}, abstract = {

Taking inspiration from diatom hierarchically organized porosity, synthetic porous monoliths have been synthesized through rational designs while combining sol\–gel chemistry, emulsions, Pickering-based emulsions, and lyotropic mesophases. We have described the synthesis of the Si(HIPE) series employing traditional emulsions to tune the macroscopic void diameters and cationic surfactant molecules to both stabilize the oil/water interface at the macroscopic length scale and create vermicular poorly organized porosity at the mesoscopic length scale. In a second part, while substituting surfactant molecules with modified silica nanoparticles acting as emulsion-stabilizers, we depict the possibility of tuning independently the macroscopic cell diameters and the cell junctions via Pickering emulsions employed as templates, leading to the Si(PHIPE) series presenting both monodiperse macroscopic void and cell junction diameters. Finally taking the synergetic effect of nonionic surfactants and a kosmotrope salt effect we show that it is possible generating self-standing Si(HIPE) bearing high organized mesoporosity while addressing the SBA-15-Si(HIPE) series. Open image in new window Taking inspiration from diatom hierarchically organized porosity, synthetic porous self-standing silica foams have been obtained through rational designs where sol\–gel chemistry, emulsions, Pickering-based emulsions and lyotropic mesophases are advantageously combined.

}, issn = {0928-0707}, doi = {10.1007/s10971-018-4794-8}, url = {http://link.springer.com/10.1007/s10971-018-4794-8}, author = {Roucher, Armand and Schmitt, Veronique and Blin, Jean-Luc and Backov, Renal} } @article {624, title = {Accurate classical short-range forces for the study of collision cascades in Fe{\textendash}Ni{\textendash}Cr}, journal = {Computer Physics Communications}, volume = {219}, year = {2017}, month = {Oct-2017}, pages = {11 - 19}, abstract = {

The predictive power of a classical molecular dynamics simulation is largely determined by the physical validity of its underlying empirical potential. In the case of high-energy collision cascades, it was recently shown that correctly modeling interactions at short distances is necessary to accurately predict primary damage production. An ab initio based framework is introduced for modifying an existing embedded-atom method FeNiCr potential to handle these short-range interactions. Density functional theory is used to calculate the energetics of two atoms approaching each other, embedded in the alloy, and to calculate the equation of state of the alloy as it is compressed. The pairwise terms and the embedding terms of the potential are modified in accordance with the ab initio results. Using this reparametrized potential, collision cascades are performed in Ni50Fe50, Ni80Cr20 and Ni33Fe33Cr33. The simulations reveal that alloying Ni and NiCr to Fe reduces primary damage production, in agreement with some previous calculations. Alloying Ni and NiFe to Cr does not reduce primary damage production, in contradiction with previous calculations.

}, issn = {00104655}, doi = {10.1016/j.cpc.2017.05.001}, url = {https://linkinghub.elsevier.com/retrieve/pii/S0010465517301315}, author = {B{\'e}land, Laurent Karim and Tamm, Artur and Mu, Sai and Samolyuk, D. and Osetsky, N. and Aabloo, Alvo and Klintenberg, Mattias and Caro, Alfredo and Stoller, E.} } @article {614, title = {Conformal field theory of critical Casimir forces between surfaces with alternating boundary conditions in two dimensions}, journal = {Journal of Statistical Mechanics: Theory and Experiment}, year = {2017}, month = {Mar-2017}, pages = { Article Number 033201 }, abstract = {

Systems as diverse as binary mixtures and inclusions in biological membranes, and many more, can be described effectively by interacting spins. When the critical fluctuations in these systems are constrained by boundary conditions, critical Casimir forces (CCF) emerge. Here we analyze CCF between boundaries with alternating boundary conditions in two dimensions, employing conformal field theory (CFT). After presenting the concept of boundary changing operators, we specifically consider two different boundary configurations for a strip of critical Ising spins: (I) alternating equi-sized domains of up and down spins on both sides of the strip, with a possible lateral shift, and (II) alternating domains of up and down spins of different size on one side and homogeneously fixed spins on the other side of the strip. Asymptotic results for the CCF at small and large distances are derived. We introduce a novel modified Szego formula for determinants of real antisymmetric block Toeplitz matrices to obtain the exact CCF and the corresponding scaling functions at all distances. We demonstrate the existence of a surface renormalization group flow between universal force amplitudes of different magnitude and sign. The Casimir force can vanish at a stable equilibrium position that can be controlled by parameters of the boundary conditions. Lateral Casimir forces assume a universal simple cosine form at large separations.

}, keywords = {Casimir effect; conformal field theory; critical exponents and amplitudes}, doi = {10.1088/1742-5468/aa5a68}, url = {http://stacks.iop.org/1742-5468/2017/i=3/a=033201?key=crossref.e58e04fb8593248b573c53589bed0f1d}, author = {Dubail, Jerome and Santachiara, Raoul and Emig, Thorsten} } @article {595, title = {Heat-induced aging of agar solutions: Impact on the structural and mechanical properties of agar gels}, journal = {Food Hydrocolloids}, volume = {64}, year = {2017}, month = {Mar-2017}, pages = {59 - 69}, abstract = {

Thermoreversible gels are commonly prepared by cooling down to ambient temperature, aqueous polymer solutions first brought to a boil for a short time. Here, we study the effect of the latter duration on the subsequent gelation of an agar solution. Increasing the incubation time at high temperature (T= 80 degrees C) from hours to a few days leads to the hydrolysis and the oxidation of the polysaccharides, and results in the decrease of the viscosity and the pH of the solution. Samples withdrew at different incubation times are cooled down to form gels whose structure and mechanical properties are systematically determined. Cryoelectron microscopy and X-ray diffraction experiments reveal that agar gels formed from solutions of increasing incubation times, display a coarser microstructure composed of micron-sized foils which result from the condensation of the polysaccharides, and contrast with the fibrous-like microstructure of gels prepared from a fresh agar solution. Along with structural changes, a prolonged incubation time of the agar solution at T = 80 degrees C leads to weaker gels than those made from fresher solutions, and extensive macro-indentation experiments coupled to direct visualization show that the gel rupture scenario turns from brittle to ductile-like as the incubation time increases. Our study suggests that the incubation time of agar solutions at high temperature could be used as an external control parameter to tune the mechanical properties of agar-based gels. (C) 2016 Elsevier Ltd. All rights reserved.

}, keywords = {Agar; Aging; Gelation; Debonding; Indentation; Fracture}, issn = {0268005X}, doi = {10.1016/j.foodhyd.2016.10.020}, url = {https://linkinghub.elsevier.com/retrieve/pii/S0268005X16305793}, author = {Mao, Bosi and Bentaleb, Ahmed and Louerat, Fr{\'e}d{\'e}ric and Divoux, Thibaut and Snabre, Patrick} } @article {584, title = {Impact of saccharides on the drying kinetics of agarose gels measured by in-situ interferometry}, journal = {Scientific Reports}, volume = {7}, year = {2017}, month = {Jan-23-2017}, pages = { Article Number: 41185 }, abstract = {

Agarose gels are viscoelastic soft solids that display a porous microstructure filled with water at 90\% w/w or more. Despite an extensive use in food industry and microbiology, little is known about the drying kinetics of such squishy solids, which suffers from a lack of time-resolved local measurements. Moreover, only scattered empirical observations are available on the role of the gel composition on the drying kinetics. Here we study by in-situ interferometry the drying of agarose gels of various compositions cast in Petri dishes. The gel thinning is associated with the displacement of interference fringes that are analyzed using an efficient spatiotemporal filtering method, which allows us to assess local thinning rates as low as 10 nm/s with high accuracy. The gel thinning rate measured at the center of the dish appears as a robust observable to quantify the role of additives on the gel drying kinetics and compare the drying speed of agarose gels loaded with various non-gelling saccharides of increasing molecular weights. Our work shows that saccharides systematically decrease the agarose gel thinning rate up to a factor two, and exemplifies interferometry as a powerful tool to quantify the impact of additives on the drying kinetics of polymer gels.

}, doi = {10.1038/srep41185}, url = {http://www.nature.com/articles/srep41185}, author = {Mao, Bosi and Divoux, Thibaut and Snabre, Patrick} } @article {616, title = {Mechanisms of jamming in the Nagel-Schreckenberg model for traffic flow}, journal = {Physical Review E}, volume = {95}, year = {2017}, month = {Jan-2017}, abstract = {

We study the Nagel-Schreckenberg cellular automata model for traffic flow by both simulations and analytical techniques. To better understand the nature of the jamming transition, we analyze the fraction of stopped cars P(v=0) as a function of the mean car density. We present a simple argument that yields an estimate for the free density where jamming occurs, and show satisfying agreement with simulation results. We demonstrate that the fraction of jammed cars P(v\∈{0,1}) can be decomposed into the three factors (jamming rate, jam lifetime, and jam size) for which we derive, from random walk arguments, exponents that control their scaling close to the critical density.

}, issn = {2470-0045}, doi = {10.1103/PhysRevE.95.012311}, url = {https://link.aps.org/doi/10.1103/PhysRevE.95.012311}, author = {Bette, Henrik M. and Habel, Lars and Emig, Thorsten and Schreckenberg, Michael} } @proceedings {336, title = {Modelling Transient Dynamics of Granular Slopes: MPM and DEM}, journal = {PROCEEDINGS OF THE 1ST INTERNATIONAL CONFERENCE ON THE MATERIAL POINT METHOD (MPM 2017) Book Series: Procedia Engineering }, volume = {175}, year = {2017}, month = {Jul-17-2017}, pages = {94 - 101}, publisher = {Elsevier Ltd.}, address = {JAN 10-13, 2017, Delft, NETHERLANDS}, abstract = {

Transient granular flows, such as rock falls, debris flows, and aerial and submarine avalanches, occur very often in nature. In the geotechnical context, transient movements of large granular slopes are a substantial factor of risk due to their destructive force and the transformations the y may produce in the landscape. This paper investigates the ability of MPM, a continuum approach, to reproduce the evolution of a granular slope destabilised by an external energy source. In particular, a central issue is whether the power-law dependence of run-out distance and time observed with respect to the initial geometry or energy can be reproduced by a simple Mohr-Coulomb plastic behaviour. The effect of base friction on the run-out kinematics is studied by comparing the data obtained from the DEM and MPM simulations. The mechanism of energy dissipation is primarily through friction and the MPM is able to predict the run-out response in good agreement with the DEM simulations. At very low excitation energies, the DEM simulations show longer run-out in comparison to the MPM due to local destabilization at the flow front. At low input energies, a larger fraction of the energy is consumed in the destabilisation process, hence the amount energy available for flow is less. However, at higher input energy, where most of the energy is dissipated during the spreading phase, the run-out distance has a weak dependence on the distribution of velocity in the granular mass.

}, issn = {18777058}, doi = {10.1016/j.proeng.2017.01.032}, author = {Krishna Kumar and Kenichi Soga and Jean-Yves Delenne and Farhang Radja{\"\i}}, editor = {Rohe, A and Kenichi Soga and Teunissen, H} } @proceedings {337, title = {MPM with Frictional Contact for Application to Soft Particulate Materials}, journal = {PROCEEDINGS OF THE 1ST INTERNATIONAL CONFERENCE ON THE MATERIAL POINT METHOD (MPM 2017) Book Series: Procedia Engineering }, volume = {175}, year = {2017}, month = {Mar-23-2017}, pages = {141 - 147}, publisher = {Elsevier Ltd.}, address = {JAN 10-13, 2017, Delft, NETHERLANDS}, abstract = {

Soft particle materials are composed of discrete particles that can undergo large deformations without rupture. Most food products, many powders, colloidal pastes, vesicles and biological cells are soft particle systems. In order to model such materials, we present an efficient numerical approach combining an implicit formulation of the Material Point Method (MPM) and Contact Dynamics (CD) method. The MPM deals with bulk variables of an individual particle by discretizing it as a collection of material points, whereas the CD allows for the treatment of frictional contacts between particles. This model is applied for the simulation of the uniaxial compression of 2D soft-particle packings. The compaction is a nonlinear process in which new contacts are formed between particles and the contact areas increase. The change of particle shapes allows these materials to reach high packing fraction. We find that the contact specific surface, the orientation anisotropy and the aspect ratio of particles increase as a function of the packing fraction but at different rates. We also evidence the effect of friction, which favors strong stress chains and thus the elongation of particles, leading to larger values of the orientation anisotropy and the aspect ratio at a given level of packing fraction as compared to a frictionless particle packing.

}, issn = {18777058}, doi = {10.1016/j.proeng.2017.01.044}, author = {Saeid Nezamabadi and Thanh Hai Nguyen and Jean-Yves Delenne and Julien Averseng and Frank, Xavier and Farhang Radja{\"\i}}, editor = {Rohe, A and Kenichi Soga and Teunissen, H} } @article {590, title = {Production of H 2 by water radiolysis in cement paste under electron irradiation: A joint experimental and theoretical study}, journal = {Cement and Concrete Research}, volume = {100}, year = {2017}, month = {Oct-2017}, pages = {110 - 118}, abstract = {

Long-term confinement of nuclear waste is one of the main challenges faced by the nuclear industry. Fission products such as Sr-90 and Cs-137, both beta(-) emitters known to induce serious health hazards, represent the largest fraction of nuclear waste. Cement is a good candidate to store them, provided it can resist the effects of irradiation over time. Here, we have investigated the effects of beta(-) decay on cement by performing electron irradiation experiments on different samples. We show that H-2 production in cement, the main effect of water radiolysis, depends strongly on composition and relative humidity. First-principles calculations indicate that the water-rich interlayer regions with Ca2+ ions act as electron traps that promote the formation of H-2. They also show that holes localize in water-rich regions in low Ca content samples and are then able to participate in H-2 production. This work provides new understanding of radiolysis effects in cements.

}, issn = {00088846}, doi = {10.1016/j.cemconres.2017.05.022}, url = {https://linkinghub.elsevier.com/retrieve/pii/S0008884617302065}, author = {Le Caer, Sophie and Dezerald, Lucile and Boukari, Khaoula and Laine, Maxime and Taupin, s{\'e}bastien and Kavanagh, Ryan M. and Johnston, Conrad S.N. and Foy, Eddy and Charpentier, Thibault and Konrad J. Krakowiak and Roland Jean-Marc Pellenq and Franz-Josef Ulm and Tribello, Gareth A. and Kohanoff, Jorge J. and Andres Sa{\`u}l} } @article {605, title = {Small solar system bodies as granular systems}, journal = {EPJ Web of Conferences}, volume = {140}, year = {2017}, month = {Jun-30-2017}, pages = {Article Number 14011}, abstract = {

Asteroids and other Small Solar System Bodies (SSSBs) are currently of great scientific and even industrial interest. Asteroids exist as the permanent record of the formation of the Solar System and therefore hold many clues to its understanding as a whole, as well as insights into the formation of planetary bodies. Additionally, SSSBs are being investigated in the context of impact risks for the Earth, space situational awareness and their possible industrial exploitation (asteroid mining). In all these aspects, the knowledge of the geophysical characteristics of SSSB surface and internal structure are of great importance. Given their size, constitution, and the evidence that many SSSBs are not simple monoliths, these bodies should be studied and modelled as self-gravitating granular systems in general, or as granular systems in micro-gravity environments in particular contexts. As such, the study of the geophysical characteristics of SSSBs is a multi-disciplinary effort that lies at the crossroads between Granular Mechanics, Celestial Mechanics, Soil Mechanics, Aerospace Engineering and Computer Sciences.

}, doi = {10.1051/epjconf/201714014011}, url = {http://www.epj-conferences.org/10.1051/epjconf/201714014011}, author = {Hestroffer, Daniel and Adriano Campo Bagat{\'\i}n and Losert, Wolfgang and Opsomer, Eric and S{\'a}nchez, Paul and Scheeres, Daniel J. and Staron, Lydie and Taberlet, Nicolas and Yano, Hajime and Eggl, Siegfried and Lecomte, Charles-Edouard and Murdoch, Naomi and Farhang Radja{\"\i} and Richardson, Derek C. and Salazar, Marcos and Schwartz, Stephen R. and Tanga, Paolo}, editor = {Saeid Nezamabadi and Luding, S. and Jean-Yves Delenne} } @article {596, title = {Three-dimensional bonded-cell model for grain fragmentation}, journal = {Computational Particle Mechanics}, volume = {4}, year = {2017}, month = {Oct-2017}, pages = {441 - 450}, chapter = { Special Issue: SI }, abstract = {

We present a three-dimensional numerical method for the simulation of particle crushing in 3D. This model is capable of producing irregular angular fragments upon particle fragmentation while conserving the total volume. The particle is modeled as a cluster of rigid polyhedral cells generated by a Voronoi tessellation. The cells are bonded along their faces by a cohesive Tresca law with independent tensile and shear strengths and simulated by the contact dynamics method. Using this model, we analyze the mechanical response of a single particle subjected to diametral compression for varying number of cells, their degree of disorder, and intercell tensile and shear strength. In particular, we identify the functional dependence of particle strength on the intercell strengths. We find that two different regimes can be distinguished depending on whether intercell shear strength is below or above its tensile strength. In both regimes, we observe a power-law dependence of particle strength on both intercell strengths but with different exponents. The strong effect of intercell shear strength on the particle strength reflects an interlocking effect between cells. In fact, even at low tensile strength, the particle global strength can still considerably increase with intercell shear strength. We finally show that the Weibull statistics describes well the particle strength variability.

}, keywords = {Bonded-cell model; Fragmentation; Discrete element method; Contact dynamics method; Voronoi cell; Weibull statistics}, issn = {2196-4378}, doi = {10.1007/s40571-016-0129-0}, url = {http://link.springer.com/10.1007/s40571-016-0129-0}, author = {Cantor, D and Emilien Az{\'e}ma and Philippe Sornay and Farhang Radja{\"\i}} } @article {609, title = {A time-dependent atomistic reconstruction of severe irradiation damage and associated property changes in nuclear graphite}, journal = {Carbon}, volume = {120}, year = {2017}, month = {Aug-2017}, pages = {111 - 120}, abstract = {

Wheat grains can be considered as a natural cemented granular material. They are milled under high forces to produce food products such as flour. The major part of the grain is the so-called starchy endosperm. It contains stiff starch granules, which show a multi-modal size distribution, and a softer protein matrix that surrounds the granules. Experimental milling studies and numerical simulations are going hand in hand to better understand the fragmentation behavior of this biological material and to improve milling performance. We present a numerical study of the effect of granule size distribution on the strength of such a cemented granular material. Samples of bi-modal starch granule size distribution were created and submitted to uniaxial tension, using a peridynamics method. We show that, when compared to the effects of starch-protein interface adhesion and voids, the granule size distribution has a limited effect on the samples\’ yield stress.

}, keywords = {TRANSMISSION ELECTRON-MICROSCOPY; MOLECULAR-DYNAMICS SIMULATIONS; HIGHLY ANISOTROPIC PYROCARBONS; THERMAL-CONDUCTIVITY; NEUTRON-IRRADIATION; CARBON; GRAPHENE; DEFECTS; ENERGY; NANOSTRUCTURE}, issn = {00086223}, doi = {10.1016/j.carbon.2017.05.009}, url = {https://linkinghub.elsevier.com/retrieve/pii/S0008622317304542}, author = {Baptiste Farbos and Freeman, Helen and Hardcastle, Trevor and Da Costa, Jean-Pierre and Brydson, Rik and Scott, Andrew J. and Weisbecker, Patrick and Germain Christian and G{\'e}rard L. Vignoles and Jean-Marc Leyssale} } @article {598, title = {Wall roughness and nonlinear velocity profiles in granular shear flows}, journal = {EPJ Web of Conferences}, volume = {140}, year = {2017}, month = {Jun-30-2017}, pages = {Article Number 03090}, abstract = {

Inhomogeneous velocity profiles in granular flows are well known from both experiments and simulations, and considered as a hallmark of nonlocal behavior. By means of extensive contact dynamics simulations, we show that the sigmoidal velocity profiles in 2D flows of rigid disks are controlled by the roughness of driving boundary walls. We find that the velocity profile becomes linear for a critical value of wall roughness up to an exponential decay close to the walls with a characteristic length that does not depend on the flow thickness and rate. We describe the velocity profiles by introducing a state parameter that carries wall perturbation. By assuming that the local shear rate is a linear function of the state parameter, we obtain an analytical expression that fits velocity profiles. In this model, the nonlinear velocity profiles are explained in terms of the effects of wall roughness as boundary condition for the state parameter.

}, doi = {10.1051/epjconf/201714003090}, url = {http://www.epj-conferences.org/10.1051/epjconf/201714003090}, author = {Schuhmacher, Paul and Farhang Radja{\"\i} and St{\'e}phane Roux}, editor = {Saeid Nezamabadi and Luding, S. and Jean-Yves Delenne} } @article {643, title = {Cement As a Waste Form for Nuclear Fission Products: The Case of 90Sr and Its Daughters}, journal = {Environmental Science \& Technology}, volume = {49}, year = {2016}, month = {Nov-17-2016}, pages = {13676-13683}, abstract = {

One of the main challenges faced by the nuclear industry is the long-term confinement of nuclear waste. Because it is inexpensive and easy to manufacture, cement is the material of choice to store large volumes of radioactive materials, in particular the low-level medium-lived fission products. It is therefore of utmost importance to assess the chemical and structural stability of cement containing radioactive species. Here, we use ab initio calculations based on density functional theory (DFT) to study the effects of Sr-90 insertion and decay in C-S-H (calcium-silicate-hydrate) in order to test the ability of cement to trap and hold this radioactive fission product and to investigate the consequences of its beta-decay on the cement paste structure. We show that Sr-90 is stable when it substitutes the Ca2+ ions in C-S-H, and so is its daughter nucleus Y-90 after beta-decay. Interestingly, Zr-90, daughter of Y-90 and final product in the decay sequence, is found to be unstable compared to the bulk phase of the element at zero K but stable when compared to the solvated ion in water. Therefore, cement appears as a suitable waste form for Sr-90 storage.

}, issn = {0013-936X}, doi = {10.1021/acs.est.5b02609}, url = {http://pubs.acs.org/doi/10.1021/acs.est.5b02609}, author = {Dezerald, Lucile and Kohanoff, Jorge J. and Alfredo A. Correa and Caro, Alfredo and Roland Jean-Marc Pellenq and Franz-Josef Ulm and Andres Sa{\`u}l} } @proceedings {338, title = {Contribution of mechanical factors to the variability of root architecture: Quantifying the past history of interaction forces between growing roots and soil grains}, journal = {2016 IEEE INTERNATIONAL CONFERENCE ON FUNCTIONAL-STRUCTURAL PLANT GROWTH MODELING, SIMULATION, VISUALIZATION AND APPLICATIONS (FSPMA)}, year = {2016}, month = {Nov-11-2016}, pages = {52-60}, publisher = {I E E E}, address = {NOV 07-11, 2016, Qingdao, PEOPLES R CHINA }, abstract = {

The relation between a growing root and the soil movement has often been under-estimated. The present work aims to determine how grains in granular soils are reorganized by the action of growing roots, and in turn how the resulting forces acting on root tips modify their development. For this purpose, we have developed a 2D Discrete Element Model (DEM) able to compute a numerical growth of a single root inside a granular medium, taking into account the grain-grain and the root-grain contact forces during the growth. First in silico simulations were carried out in order to : 1-quantify the influence of the granular structure (grain diameter distribution and gaps) and root mechanical properties (root bending stiffness) on the evolution of reaction forces applied to a single root during its growth; 2-highlight \“group effects\”, e.g. how the reorganization of grains and their interaction forces due to a given growing root can affect the mechanical signal perceived by its near neighbours; 3-investigate how the presence of initial channels within the granular medium can effect the growth trajectory and minimize the resistance to penetration. All simulations were carried out assuming that root growth direction was only driven by external forces. Simlation results allowed the extraction of general physical laws that will be used further to provide mechanoperceptive indicators and analyze experimental data provided by phenotyping platforms. The final objective will be to quantify the response of plants to mechanical stresses in terms of root elongation rate, root straightness and ramification.

}, doi = {10.1109/FSPMA.2016.7818288}, author = {Fakih, Mahmoud and Jean-Yves Delenne and Farhang Radja{\"\i} and Fourcaud, Thierry} } @article {252, title = {Data analytics for simplifying thermal efficiency planning in cities}, journal = {Journal of The Royal Society Interface}, volume = {13}, year = {2016}, month = {Apr-2016}, pages = {Article Number: 20150971}, abstract = {

More than 44\% of building energy consumption in the USA is used for space heating and cooling, and this accounts for 20\% of national CO2emissions. This prompts the need to identify among the 130 million households in the USA those with the greatest energy-saving potential and the associated costs of the path to reach that goal. Whereas current solutions address this problem by analysing each building in detail, we herein reduce the dimensionality of the problem by simplifying the calculations of energy losses in buildings. We present a novel inference method that can be used via a ranking algorithm that allows us to estimate the potential energy saving for heating purposes. To that end, we only need consumption from records of gas bills integrated with a building\&$\#$39;s footprint. The method entails a statistical screening of the intricate interplay between weather, infrastructural and residents\&$\#$39; choice variables to determine building gas consumption and potential savings at a city scale. We derive a general statistical pattern of consumption in an urban settlement, reducing it to a set of the most influential buildings\&$\#$39; parameters that operate locally. By way of example, the implications are explored using records of a set of (N= 6200) buildings in Cambridge, MA, USA, which indicate that retrofitting only 16\% of buildings entails a 40\% reduction in gas consumption of the whole building stock. We find that the inferred heat loss rate of buildings exhibits a power-law data distribution akin to Zipf\&$\#$39;s law, which provides a means to map an optimum path for gas savings per retrofit at a city scale. These findings have implications for improving the thermal efficiency of cities\&$\#$39; building stock, as outlined by current policy efforts seeking to reduce home heating and cooling energy consumption and lower associated greenhouse gas emissions.

}, issn = {1742-5689}, doi = {10.1098/rsif.2015.0971}, author = {Mohammad Javad Abdolhosseini Qomi and Noshadravan, Arash and Sobstyl, Jake M. and Toole, Jameson and Ferreira, Joseph and Roland Jean-Marc Pellenq and Franz-Josef Ulm and Gonzalez, Marta C.} } @article {248, title = {Fracture toughness anomalies: Viewpoint of topological constraint theory}, journal = {Acta Materialia}, volume = {121}, year = {2016}, month = {Dec-2016}, pages = {234 - 239}, abstract = {

The relationship between composition, structure, and resistance to fracture remains poorly understood. Here, based on molecular dynamics simulations, we report that sodium silicate glasses and calcium\–silicate\–hydrates feature an anomalous maximum in fracture toughness. In the framework of topological constraint theory, this anomaly is correlated to a flexible-to-rigid transition, driven by pressure or composition for sodium silicate and calcium\–silicate\–hydrates, respectively. This topological transition, observed for an isostatic network, is also shown to correspond to a ductile-to-brittle transition. At this state, the network is rigid but free of eigen-stress and features stress relaxation through crack blunting, resulting in optimal resistance to fracture. Our topological approach could therefore enable the computational design of tough inorganic solids, which has long been a \“holy grail\” within the non-metallic materials chemistry community.

Image 1

}, issn = {13596454}, doi = {10.1016/j.actamat.2016.09.004}, author = {Mathieu Bauchy and Wang, Bu and Wang, Mengyi and Yu, Yingtian and Mohammad Javad Abdolhosseini Qomi and Smedskjaer, Morten M. and Christophe Bichara and Franz-Josef Ulm and Roland Jean-Marc Pellenq} } @article {642, title = {How Ion Condensation Occurs at a Charged Surface: A Molecular Dynamics Investigation of the Stern Layer for Water{\textendash}Silica Interfaces}, journal = {The Journal of Physical Chemistry C}, volume = {120}, year = {2016}, month = {Jan-21-2016}, pages = {963-973}, abstract = {

We investigate the Stern layer of charged silicawater interfaces by calculating the ionsurface interaction from molecular dynamics simulations. The McMillanMayer potentials of mean force between a charged oxygen site and a lithium or cesium cation have been calculated. Contact ion pairs (CIPs) are important for the adsorption and desorption of ions, especially for lithium. An activation energy appears, which can result in a large estimated relaxation time. In the case of lithium, time scales needed to bind or unbind ions to and from the surface are found to be very long (up to the order of seconds for some surfaces), which implies that molecular dynamics cannot always be fully equilibrated. This work provides a new image of the Stern layer: it is not a continuous layer but a set of Bjerrum pairs. As a matter of fact, quantitative (macroscopic) treatments of such systems with localized surface charges require a three-dimensional model, contrary to the more commonly used one- or two-dimensional theoretical treatments.

}, issn = {1932-7447}, doi = {10.1021/acs.jpcc.5b08836}, url = {http://pubs.acs.org/doi/10.1021/acs.jpcc.5b08836}, author = {Hocine, Sarah and Hartkamp, Remco and Bertrand Siboulet and Duvail, Magali and Benoit A. Coasne and Turq, P. and Jean-Francois Dufreche} } @article {323, title = {Nanochemo-mechanical signature of organic-rich shales: a coupled indentation{\textendash}EDX analysis}, journal = {Acta Geotechnica}, volume = {11}, year = {2016}, month = {Jun-2016}, pages = {559 - 572}, abstract = {

The organic\–inorganic nature of organic-rich source rocks poses several challenges for the development of functional relations that link mechanical properties with geochemical composition. With this focus in mind, we herein propose a method that enables chemo-mechanical characterization of this highly heterogeneous source rock at the micron and submicron length scale through a statistical analysis of a large array of energy-dispersive X-ray spectroscopy (EDX) data coupled with nanoindentation data. The ability to include elemental composition to the indentation probe via EDX is shown to provide a means to identify pure material phases, mixture phases, and interfaces between different phases. Employed over a large array, the statistical clustering of this set of chemo-mechanical data provides access to the properties of the fundamental building blocks of clay-dominated organic-rich source rocks. The versatility of the approach is illustrated through the application to a large number of source rocks of different origin, chemical composition, and organic content. We find that the identified properties exhibit a unique scaling relation between stiffness and hardness. This suggests that organic-rich shale properties can be reduced to their elementary constituents, with several implications for the development of predictive functional relations between chemical composition and mechanical properties of organic-rich source rocks such as the intimate interplay between clay-packing, organic maturity, and mechanical properties of porous clay/organic phase.

}, issn = {1861-1125}, doi = {10.1007/s11440-015-0426-4}, author = {Abedi, Sara and Slim, Mirna and Hofmann, Ronny and Bryndzia, Taras and Franz-Josef Ulm} } @article {322, title = {Nanomechanics of organic-rich shales: the role of thermal maturity and organic matter content on texture}, journal = {Acta Geotechnica}, volume = {11}, year = {2016}, month = {Aug-2016}, pages = {775 - 787}, abstract = {

Despite the importance of organic-rich shales, microstructural characterization and theoretical modeling of these rocks are limited due to their highly heterogeneous microstructure, complex chemistry, and multiscale mechanical properties. One of the sources of complexity in organic-rich shales is the intricate interplay between microtextural evolution and kerogen maturity. In this study, a suite of experimental and theoretical microporomechanics methods are developed to associate the mechanical properties of organic-rich shales both to their maturity level and to the organic content at micrometer and sub-micrometer length scales. Recent results from chemomechanical characterization experiments involving grid nanoindentation and energy-dispersive X-ray spectroscopy (EDX) are used in new micromechanical models to isolate the effects of maturity levels and organic content from the inorganic solids. These models enable attribution of the role of organic maturity to the texture of the indented material, with immature systems exhibiting a matrix-inclusion morphology, while mature systems exhibit a polycrystal morphology. Application of these models to the interpretation of nanoindentation results on organic-rich shales allows us to identify unique clay mechanical properties that are consistent with molecular simulation results for illite and independent of the maturity of shale formation and total organic content. The results of this investigation contribute to the design of a multiscale model of the fundamental building blocks of organic-rich shales, which can be used for the design and validation of multiscale predictive poromechanics models.

}, issn = {1861-1125}, doi = {10.1007/s11440-016-0476-2}, author = {Abedi, Sara and Slim, Mirna and Franz-Josef Ulm} } @article {195, title = {Realistic molecular model of kerogen{\textquoteright}s nanostructure}, journal = {Nature Materials}, year = {2016}, month = {Feb-01-2016}, abstract = {

Despite kerogen\’s importance as the organic backbone for hydrocarbon production from source rocks such as gas shale, the interplay between kerogen\’s chemistry, morphology and mechanics remains unexplored. As the environmental impact of shale gas rises, identifying functional relations between its geochemical, transport, elastic and fracture properties from realistic molecular models of kerogens becomes all the more important. Here, by using a hybrid experimental\–simulation method, we propose a panel of realistic molecular models of mature and immature kerogens that provide a detailed picture of kerogen\’s nanostructure without considering the presence of clays and other minerals in shales. We probe the models\’ strengths and limitations, and show that they predict essential features amenable to experimental validation, including pore distribution, vibrational density of states and stiffness. We also show that kerogen\’s maturation, which manifests itself as an increase in the sp2/sp3 hybridization ratio, entails a crossover from plastic-to-brittle rupture mechanisms.

Kerogen in organic-rich shale formations.

Reconstruction of molecular models of kerogens.

Experimental validation of the molecular models.

Elastic properties of molecular models of kerogen.

}, issn = {1476-1122}, doi = {10.1038/nmat4541}, author = {Bousige, Colin and Ghimbeu, Cam{\'e}lia Matei and Vix-Guterl, Cathie and Pomerantz, Andrew E. and Suleimenova, Assiya and Vaughan, Gavin and Garbarino, Gaston and Feygenson, Mikhail and Wildgruber, Christoph and Franz-Josef Ulm and Roland Jean-Marc Pellenq and Benoit A. Coasne} } @article {326, title = {Velocity statistics of the Nagel-Schreckenberg model}, journal = {Physical Review E}, volume = {93}, year = {2016}, month = {Feb-18-2016}, pages = {Article Number: 022305}, abstract = {

The statistics of velocities in the cellular automaton model of Nagel and Schreckenberg for traffic are studied. From numerical simulations, we obtain the probability distribution function (PDF) for vehicle velocities and the velocity-velocity (vv) correlation function. We identify the probability to find a standing vehicle as a potential order parameter that signals nicely the transition between free congested flow for sufficiently large number of velocity states. Our results for the vv correlation function resemble features of a second order phase transition. We develop a 3-body approximation that allows us to relate the PDFs for velocities and headways. Using this relation, an approximation to the velocity PDF is obtained from the headway PDF observed in simulations. We find a remarkable agreement between this approximation and the velocity PDF obtained from simulations.

}, issn = {2470-0045}, doi = {10.1103/PhysRevE.93.022305}, author = {Bain, Nicolas and Emig, Thorsten and Franz-Josef Ulm and Schreckenberg, Michael} } @article {179, title = {Advances in design and modeling of porous materials}, journal = {The European Physical Journal Special Topics}, volume = {224}, year = {2015}, month = {Jul-2015}, pages = {1653 - 1653}, abstract = {

This special issue of the European Physical Journal Special Topics is dedicated to selected papers from the symposium \“High surface area porous and granular materials\” organized in the frame of the conference \“Mat\ériaux 2014\”, held on November 24\–28, 2014 in Montpellier, France.

Porous materials and granular materials gather a wide variety of heterogeneous, isotropic or anisotropic media made of inorganic, organic or hybrid solid skeletons, with open or closed porosity, and pore sizes ranging from the centimeter scale to the sub-nanometer scale. Their technological and industrial applications cover numerous areas from building and civil engineering to microelectronics, including also metallurgy, chemistry, health, waste water and gas effluent treatment. Many emerging processes related to environmental protection and sustainable development also rely on this class of materials. Their functional properties are related to specific transfer mechanisms (matter, heat, radiation, electrical charge), to pore surface chemistry (exchange, adsorption, heterogeneous catalysis) and to retention inside confined volumes (storage, separation, exchange, controlled release). The development of innovative synthesis, shaping, characterization and modeling approaches enables the design of advanced materials with enhanced functional performance. The papers collected in this special issue offer a good overview of the state-of-the-art and science of these complex media.

We would like to thank all the speakers and participants for their contribution to the success of the symposium. We also express our gratitude to the organization committee of \“Mat\´eriaux 2014\”. We finally thank the reviewers and the staff of the European Physical Journal Special Topics who made the publication of this special issue possible.

}, issn = {1951-6355}, doi = {10.1140/epjst/e2015-02487-6}, author = {Ayral, Andre and Calas-Etienne, Sylvie and Benoit A. Coasne and Deratani, Andr{\'e} and Evstratov, Alexis and Anne Galarneau and Grande, Daniel and Hureau, Matthieu and Jobic, Herv{\'e} and Morlay, Catherine and Parmentier, Julien and Prelot, B{\'e}n{\'e}dicte and Rossignol, Sylvie and Simon-Masseron, Ang{\'e}lique and Thibault-Starzyk, Fr{\'e}d{\'e}ric} } @article {153, title = {Bonded-cell model for particle fracture}, journal = {Physical Review E}, volume = {91}, year = {2015}, month = {Feb-09-2015}, pages = {Article Number: 022203}, abstract = {

Particle degradation and fracture play an important role in natural granular flows and in many applications of granular materials. We analyze the fracture properties of two-dimensional disklike particles modeled as aggregates of rigid cells bonded along their sides by a cohesive Mohr-Coulomb law and simulated by the contact dynamics method. We show that the compressive strength scales with tensile strength between cells but depends also on the friction coefficient and a parameter describing cell shape distribution. The statistical scatter of compressive strength is well described by the Weibull distribution function with a shape parameter varying from 6 to 10 depending on cell shape distribution. We show that this distribution may be understood in terms of percolating critical intercellular contacts. We propose a random-walk model of critical contacts that leads to particle size dependence of the compressive strength in good agreement with our simulation data.

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}, issn = {1539-3755}, doi = {10.1103/PhysRevE.91.022203}, author = {Duc-Hanh Nguyen and Emilien Az{\'e}ma and Philippe Sornay and Farhang Radja{\"\i}} } @article {133, title = {Cement As a Waste Form for Nuclear Fission Products: The Case of 90 Sr and Its Daughters}, journal = {Environ Sci Technol}, volume = {49}, year = {2015}, month = {Oct-2015}, pages = {13676-83}, abstract = {

One of the main challenges faced by the nuclear industry is the long-term confinement of nuclear waste. Because it is inexpensive and easy to manufacture, cement is the material of choice to store large volumes of radioactive materials, in particular the low-level medium-lived fission products. It is therefore of utmost importance to assess the chemical and structural stability of cement containing radioactive species. Here, we use ab initio calculations based on density functional theory (DFT) to study the effects of (90)Sr insertion and decay in C-S-H (calcium-silicate-hydrate) in order to test the ability of cement to trap and hold this radioactive fission product and to investigate the consequences of its \β-decay on the cement paste structure. We show that (90)Sr is stable when it substitutes the Ca(2+) ions in C-S-H, and so is its daughter nucleus (90)Y after \β-decay. Interestingly, (90)Zr, daughter of (90)Y and final product in the decay sequence, is found to be unstable compared to the bulk phase of the element at zero K but stable when compared to the solvated ion in water. Therefore, cement appears as a suitable waste form for (90)Sr storage.

}, issn = {1520-5851}, doi = {10.1021/acs.est.5b02609}, author = {Dezerald, Lucile and Kohanoff, Jorge J and Alfredo A. Correa and Caro, Alfredo and Roland Jean-Marc Pellenq and Franz-Josef Ulm and Andres Sa{\`u}l} } @article {176, title = {Control of the Pore Texture in Nanoporous Silicon via Chemical Dissolution}, journal = {Langmuir}, volume = {31}, year = {2015}, month = {Jul-28-2015}, pages = {8121 - 8128}, abstract = {
Abstract Image

The surface and textural properties of porous silicon (pSi) control many of its physical properties essential to its performance in key applications such as optoelectronics, energy storage, luminescence, sensing, and drug delivery. Here, we combine experimental and theoretical tools to demonstrate that the surface roughness at the nanometer scale of pSi can be tuned in a controlled fashion using partial thermal oxidation followed by removal of the resulting silicon oxide layer with hydrofluoric acid (HF) solution. Such a process is shown to smooth the pSi surface by means of nitrogen adsorption, electron microscopy, and small-angle X-ray and neutron scattering. Statistical mechanics Monte Carlo simulations, which are consistent with the experimental data, support the interpretation that the pore surface is initially rough and that the oxidation/oxide removal procedure diminishes the surface roughness while increasing the pore diameter. As a specific example considered in this work, the initial roughness \ξ \∼ 3.2 nm of pSi pores having a diameter of 7.6 nm can be decreased to 1.0 nm following the simple procedure above. This study allows envisioning the design of pSi samples with optimal surface properties toward a specific process.

}, issn = {0743-7463}, doi = {10.1021/acs.langmuir.5b01518}, author = {Secret, Emilie and Wu, Chia-Chen and Chaix, Arnaud and Anne Galarneau and Gonzalez, Philippe and Cot, Didier and Sailor, Michael J. and Jestin, Jacques and Zanotti, Jean-Marc and Cunin, Fr{\'e}d{\'e}rique and Benoit A. Coasne} } @article {157, title = {Critical Casimir force between inhomogeneous boundaries}, journal = {EPL (Europhysics Letters)}, volume = {112}, year = {2015}, month = {Dec-2015}, pages = {66004}, abstract = {

To study the critical Casimir force between chemically structured boundaries immersed in a binary mixture at its demixing transition, we consider a strip of Ising spins subject to alternating fixed spin boundary conditions. The system exhibits a boundary induced phase transition as function of the relative amount of up and down boundary spins. This transition is associated with a sign change of the asymptotic force and a diverging correlation length that sets the scale for the crossover between different universal force amplitudes. Using conformal field theory and a mapping to Majorana fermions, we obtain the universal scaling function of this crossover, and the force at short distances.

}, issn = {0295-5075}, doi = {10.1209/0295-5075/112/66004}, author = {Dubail, Jerome and Santachiara, Raoul and Emig, Thorsten} } @article {163, title = {Diffusion of Interlayer Cations in Swelling Clays as a Function of Water Content: Case of Montmorillonites Saturated with Alkali Cations}, journal = {The Journal of Physical Chemistry C}, volume = {119}, year = {2015}, month = {May-14-2015}, pages = {10370 - 10378}, abstract = {
Abstract Image

Swelling clays act as ion-exchange membranes owing to the presence of extra-framework ions surrounded by water molecules. A better understanding of the motion of the ions present in the pore space is required to predict the diffusion properties in these solids. Since water molecules tend to adsorb both on ions and clay surfaces, they moderate the interactions between the ions and the framework. The hydration of ions therefore has an impact on their diffusion properties. In this paper, the MX-80 montmorillonite considered for nuclear waste disposal applications has been selected and studied using an approach combining measurements of complex impedance spectroscopy and water adsorption isotherms. The number of charge carriers has been estimated, and the diffusion coefficient for interlayer cations at various hydration states was determined. The evolution of the diffusion coefficient is subsequently correlated with the effect of the opening of the interlayer space and its hydration state. The resulting picture sheds light on the reversible or irreversible character of ion exchange. Finally, our results obtained from the difference between the interlayer diffusion coefficients extracted from conductivity measurements and those obtained at the macroscopic scale is discussed in terms of the textural parameters.

}, issn = {1932-7447}, doi = {10.1021/jp512986d}, author = {Salles, Fabrice and Douillard, Jean-Marc and Bildstein, Olivier and El Ghazi, Samira and Prelot, B{\'e}n{\'e}dicte and Zajac, Jerzy and Henri Van Damme} } @article {129, title = {Effects of shape and size polydispersity on strength properties of granular materials.}, journal = {Phys Rev E Stat Nonlin Soft Matter Phys}, volume = {91}, year = {2015}, month = {Mar-18-2015}, pages = {Article Number: 032203}, abstract = {

By means of extensive contact dynamics simulations, we analyze the combined effects of polydispersity both in particle size and in particle shape, defined as the degree of shape irregularity, on the shear strength and microstructure of sheared granular materials composed of pentagonal particles. We find that the shear strength is independent of the size span, but unexpectedly, it declines with increasing shape polydispersity. At the same time, the solid fraction is an increasing function of both the size span and the shape polydispersity. Hence, the densest and loosest packings have the same shear strength. At the scale of the particles and their contacts, we analyze the connectivity of particles, force transmission, and friction mobilization as well as their anisotropies. We show that stronger forces are carried by larger particles and propped by an increasing number of small particles. The independence of shear strength with regard to size span is shown to be a consequence of contact network self-organization, with the falloff of contact anisotropy compensated by increasing force anisotropy.

}, issn = {1550-2376}, doi = {10.1103/PhysRevE.91.032203}, author = {Duc-Hanh Nguyen and Emilien Az{\'e}ma and Philippe Sornay and Farhang Radja{\"\i}} } @proceedings {343, title = {Evolution of particle size distributions in crushable granular materials}, journal = {3rd International Symposium on Geomechanics from Micro to Macro}, volume = {Geomechanics from Micro to Macro}, year = {2015}, month = {Feb-02-2015}, pages = {275 - 280}, publisher = {CRC Press}, address = {SEP 01-03-2014 Univ Cambridge, Cambridge, ENGLAND}, abstract = {

By means of the contact dynamics method together with a particle fracture model, in which the particles are cohesive aggregates of irreducible polygonal fragments, we investigate the evolution of particle size distribution in the process of uniaxial compaction of granular materials. The case of single particle breakup under compressive stress is used to test the method and the influence of discretization (number of irreducible fragments). We show that the breaking threshold of the granular assembly scales with the internal cohesion of the particles but it depends also on the initial size distribution and irregularity of polygonal particle shapes. The evolution of size distribution proceeds by consecutive periods of intense particle crushing, characterized by local shattering instability, and periods of little breaking activity. Starting with either monodisperse or power-law distribution of particle sizes, the latter evolves towards a broad distribution of the fragmented particles with a nearly power-law distribution in the range of intermediate particle sizes. Interestingly, a finite number of large particles survive despite ongoing crushing process due to the more homogeneous distribution of forces in the presence of small fragmented particles filling the pores between larger particles.

}, isbn = {978-1-138-02707-7}, doi = {10.1201/b1739510.1201/b17395-48}, author = {Duc-Hanh Nguyen and Emilien Az{\'e}ma and Farhang Radja{\"\i} and Philippe Sornay}, editor = {Kenichi Soga and Krishna Kumar and Giovanna Biscontin and Kuo, Matthew} } @article {184, title = {Ion-specific adsorption and electroosmosis in charged amorphous porous silica}, journal = {Phys. Chem. Chem. Phys.}, volume = {17}, year = {2015}, month = {Oct-14-2015}, pages = {24683 - 24695}, abstract = {

Monovalent and divalent aqueous electrolytes confined in negatively charged porous silica are studied by means of molecular simulations including free energy calculations. Owing to the strong cation adsorption at the surface, surface charge overcompensation (overscreening) occurs which leads to an effective positive surface next to the Stern layer, followed by a negatively charged diffuse layer. A simple Poisson-Boltzmann model in which the single-ion potential of mean force is introduced is shown to capture the most prominent features of ion density profiles near an amorphous silica surface. Nevertheless, due to its mean-field nature, which fails to account for correlations, this simple model does not predict overscreening corresponding to charge inversion at the surface. Such an overscreening drastically affects the transport of confined electrolytes as it leads to flow reversal when subjected to an electric field. A simple continuum theory is shown to capture how the electro-osmotic flow is affected by overscreening and by the apparent enhanced viscosity of the confined electrolytes. Comparison with available experimental data is discussed, as well as the implications of these phenomena for \ζ-potential measurements.

}, issn = {1463-9076}, doi = {10.1039/C5CP03818A}, author = {Hartkamp, Remco and Bertrand Siboulet and Jean-Francois Dufreche and Benoit A. Coasne} } @article {645, title = {Magnetic nanopantograph in the SrCu 2 (BO 3 ) 2 Shastry{\textendash}Sutherland lattice}, journal = {Proceedings of the National Academy of Sciences}, volume = {112}, year = {2015}, month = {Feb-17-2015}, pages = { 1971-1976}, abstract = {

Magnetic materials having competing, i.e., frustrated, interactions can display magnetism prolific in intricate structures, discrete jumps, plateaus, and exotic spin states with increasing applied magnetic fields. When the associated elastic energy cost is not too expensive, this high potential can be enhanced by the existence of an omnipresent magnetoelastic coupling. Here we report experimental and theoretical evidence of a nonnegligible magnetoelastic coupling in one of these fascinating materials, SrCu2(BO3)(2) (SCBO). First, using pulsed-field transversal and longitudinal magnetostriction measurements we show that its physical dimensions, indeed, mimic closely its unusually rich field-induced magnetism. Second, using density functional-based calculations we find that the driving force behind the magnetoelastic coupling is the CuOCu superexchange angle that, due to the orthogonal Cu2+ dimers acting as pantographs, can shrink significantly (0.44\%) with minute (0.01\%) variations in the lattice parameters. With this original approach we also find a reduction of similar to 10\% in the intradimer exchange integral J, enough to make predictions for the highly magnetized states and the effects of applied pressure on SCBO.

}, issn = {0027-8424}, doi = {10.1073/pnas.1421414112}, url = {http://www.pnas.org/lookup/doi/10.1073/pnas.1421414112}, author = {Guillaume Radtke and Andres Sa{\`u}l and Dabkowska, Hanna A. and Salamon, Myron B. and Jaime, Marcelo} } @article {117, title = {Magnetic nanopantograph in the SrCu2(BO3)2 Shastry{\textendash}Sutherland lattice}, journal = {Proceedings of the National Academy of Sciences}, volume = {112}, year = {2015}, month = {Feb-02-2015}, pages = {1971-1976}, abstract = {

Magnetic materials having competing, i.e., frustrated, interactions can display magnetism prolific in intricate structures, discrete jumps, plateaus, and exotic spin states with increasing applied magnetic fields. When the associated elastic energy cost is not too expensive, this high potential can be enhanced by the existence of an omnipresent magnetoelastic coupling. Here we report experimental and theoretical evidence of a nonnegligible magnetoelastic coupling in one of these fascinating materials, SrCu2(BO3)2 (SCBO). First, using pulsed-field transversal and longitudinal magnetostriction measurements we show that its physical dimensions, indeed, mimic closely its unusually rich field-induced magnetism. Second, using density functional-based calculations we find that the driving force behind the magnetoelastic coupling is the CuOCu^ superexchange angle that, due to the orthogonal Cu2+ dimers acting as pantographs, can shrink significantly (0.44\%) with minute (0.01\%) variations in the lattice parameters. With this original approach we also find a reduction of \∼10\% in the intradimer exchange integral J, enough to make predictions for the highly magnetized states and the effects of applied pressure on SCBO.

}, doi = {10.1073/pnas.1421414112}, author = {Guillaume Radtke and Andres Sa{\`u}l and Dabkowska, Hanna A. and Salamon, Myron B. and Jaime, Marcelo} } @proceedings {351, title = {Numerical simulation of granular media composed with irregular polyhedral particles: effect of particles{\textquoteright} angularity}, journal = {2nd International Conference on Particle-Based Methods - Fundamentals and Applications (Particles)}, volume = {PARTICLE-BASED METHODS II: FUNDAMENTALS AND APPLICATIONS}, year = {2015}, month = {Feb-02-2015}, pages = {222-228}, address = {OCT 26-28 2011 Barcelona, SPAIN}, abstract = {

We use contact dynamic simulations to perform a systematic investigation of the effects of particles shape angularity on mechanicals response in sheared granular ma-terials. The particles are irregular polyhedra with varying numbers of face from spheres to \"double pyramid\" shape with a constant aspect ratio. We study the quasi-static behav-ior, structural and force anisotropies of several packings subjected to triaxial compression. An interesting finding is that the shear strength first increases with angularity up to a maximum value and then saturates as the particles become more angular. Analyzing the anisotropies induced by the angular distributions of contacts and forces orientations, we show that the saturation of the shear strength at higher angularities is a consequence of fall-off of the texture anisotropies compensated by an increase of the tangential force anisotropy. This is attributed to the fact that at higher angularity, particles are bet-ter connected (or surrounded) leading to an increase of friction mobilization in order to achieve the deformation. Moreover, the most angular particles also have very few sides so that, this effect is enhanced by the increase of the proportion of face-side and side-side contacts with angularity.

}, keywords = {angularity, force transmission, Granular Materials, particle shape, texture}, url = {https://hal.archives-ouvertes.fr/hal-01112373}, author = {Emilien Az{\'e}ma and Farhang Radja{\"\i} and Dubois, Fr{\'e}d{\'e}ric}, editor = {Onate, E and Owen, DRJ} } @proceedings {357, title = {Rheology and Micromechanical Analysis of Granular Media Composed of Platy Particles: A Step Toward the DEM Simulation of Clayey Soils}, journal = {15th Pan-American Conference on Soil Mechanics and Geotechnical Engineering (PCSMGE) / 8th South American Congress on Rock Mechanics (SCRM)}, volume = {FROM FUNDAMENTALS TO APPLICATIONS IN GEOTECHNICS }, year = {2015}, month = {2015}, pages = {1357-1364}, address = {NOV 15-18 2015 Buenos Aires, ARGENTINA}, abstract = {

This work was carried out in the framework of a larger project devoted
to the micro-mechanical modeling of clayey soils by means of discrete element
simulations. Here, we study the rheology and microstructure of granular media
composed of platy particles. The particles are three-dimensional square plates,
approximated as spheropolyhedra. Several samples composed of particles of
different levels of platyness (related to the ratio of length to thickness) were
numerically prepared and sheared up to large deformations. Specifically, we
revisit and analyze in detail an ordering phenomenon described briefly in a
previous paper [1] and investigate its consequences in terms of the alignment of
particles and cluster formation. We find that particle alignment is strongly
enhanced by the degree of platyness and leads to the formation of face-connected
clusters. Due to dynamics, this spontaneous clustering is a robust characteristic of
granular systems composed of platy particles even in the absence of attraction
forces.

}, doi = {10.3233/978-1-61499-603-3-1357}, author = {Boton, Mauricio and Estrada, Nicolas and Emilien Az{\'e}ma}, editor = {Manzanal, D and Sfriso, AO} } @article {175, title = {Solubility of Gases in Water Confined in Nanoporous Materials: ZSM-5, MCM-41, and MIL-100}, journal = {The Journal of Physical Chemistry C}, volume = {119}, year = {2015}, month = {Sep-17-2015}, pages = {21547 - 21554}, abstract = {
Abstract Image

Oversolubility, which corresponds to large apparent gas solubilities in liquids confined in nanoporous solids, has been proposed as a means to develop novel adsorption, phase separation, or catalytic processes. We report a molecular simulation study to help design such hybrid adsorbents consisting of a solvent confined in host nanoporous materials. Water is selected as the confined solvent because of its ubiquity in industrial applications, while N2, CH4, and CO2 are selected as they allow probing the effect of specific molecular interaction and polarity. For each system, we consider a zeolite, an ordered mesoporous silica, and a metal\–organic framework as the confining host as they present different morphologies, porosities, and surface chemistries. We show that oversolubility is always observed because the apparent solubility in these materials surpasses the bulk solubility. In all cases, oversolubility is an enhanced bulklike solubility in which solubility is favored in the regions of low water density formed by the layering of the solvent. Such an oversolubility mechanism, which arises from the fact that the gas\–solid interactions are weaker than the solvent\–solid interactions, leads to large uptakes as high as a few hundred times that expected from bulk solubility.

}, issn = {1932-7447}, doi = {10.1021/acs.jpcc.5b06660}, author = {Linh Ngoc Ho and Schuurman, Yves and David Farrusseng and Benoit A. Coasne} } @book {647, title = {Springer Series in Materials ScienceMolecular Dynamics Simulations of Disordered MaterialsFirst-Principles Modeling of Binary Chalcogenides: Recent Accomplishments and New Achievements}, volume = {215}, year = {2015}, pages = {313 - 344}, publisher = {Springer International Publishing}, organization = {Springer International Publishing}, address = {Cham}, abstract = {

This contribution is focussed on a set of first-principles molecular dynamics results obtained over the past fifteen years for disordered chalcogenides. In the first part, we sketch and review the historical premises underlying research efforts devoted to the understanding of structural properties in liquid and glassy GexSe1-x systems. We stress the importance of selecting well performing exchange-correlation functionals (within density functional theory) to achieve a correct description of short and intermediate range order. In the second part, we provide a specific, comparative example of structural analysis for chalcogenide GeX4 systems differing by the chemical identity of the X atom. We are able to demonstrate that the correct account of differences between the coordination environments of the two corresponding glasses requires system sizes substantially larger than similar to 100 atoms.

}, isbn = {978-3-319-15674-3}, issn = {0933-033X}, doi = {10.1007/978-3-319-15675-010.1007/978-3-319-15675-0_12}, url = {http://link.springer.com/10.1007/978-3-319-15675-0}, author = {Bouzid, A. and Le Roux, S. and Guido Ori and Tugene, Christine and Boero, M. and Carlo Massobrio}, editor = {Carlo Massobrio and Du, Jincheng and Bernasconi, Marco and Salmon, Philip S.} } @book {648, title = {Springer Series in Materials ScienceMolecular Dynamics Simulations of Disordered MaterialsMolecular Modeling of Glassy Surfaces}, volume = {215}, year = {2015}, pages = {345 - 365}, publisher = {Springer International Publishing}, organization = {Springer International Publishing}, address = {Cham}, abstract = {

Progress in computational materials science has allowed the development of realistic models for a wide range of materials including both crystalline and glassy solids. In recent years, with the growing interest in nanoparticles and porous materials, more attention has been devoted to the design of realistic models of glassy surfaces and finely divided materials. The structural disorder in glassy surfaces, however, poses a major challenge which consists of describing such surfaces using computer simulations. In this paper, we show how atomic-scale simulations can be used to develop and investigate the properties of glassy surfaces. We illustrate how both first principles calculations and classical molecular mechanics can be used to follow the trajectory at finite temperature of these systems, and obtain statistical thermodynamic averages to compare against available experiments. Both glassy oxide (silica) and non-oxide (chalcogenide) surfaces are considered.

}, isbn = {978-3-319-15674-3}, issn = {0933-033X}, doi = {10.1007/978-3-319-15675-010.1007/978-3-319-15675-0_13}, url = {http://link.springer.com/10.1007/978-3-319-15675-0}, author = {Guido Ori and Carlo Massobrio and Bouzid, A. and Benoit A. Coasne}, editor = {Carlo Massobrio and Du, Jincheng and Bernasconi, Marco and Salmon, Philip S.} } @article {152, title = {Transient dynamics of a 2D granular pile}, journal = {The European Physical Journal E}, volume = {38}, year = {2015}, month = {May-26-2015}, pages = {Article Number: 47}, abstract = {

We investigate by means of Contact Dynamics simulations the transient dynamics of a 2D granular pile set into motion by applying shear velocity during a short time interval to all particles. The spreading dynamics is directly controlled by the input energy whereas in recent studies of column collapse the dynamics scales with the initial potential energy of the column. As in column collapse, we observe a power-law dependence of the runout distance with respect to the input energy with nontrivial exponents. This suggests that the power-law behavior is a generic feature of granular dynamics, and the values of the exponents reflect the distribution of kinetic energy inside the material. We observe two regimes with different values of the exponents: the low-energy regime reflects the destabilization of the pile by the impact with a runout time independent of the input energy whereas the high-energy regime is governed by the input energy. We show that the evolution of the pile in the high-energy regime can be described by a characteristic decay time and the available energy after the pile is destabilized.

https://static-content.springer.com/image/art\%3A10.1140\%2Fepje\%2Fi2015-15047-x/MediaObjects/10189_2015_133_Figa_HTML.gif
}, issn = {1292-8941}, doi = {10.1140/epje/i2015-15047-x}, author = {Patrick Mutabaruka and Krishna Kumar and Kenichi Soga and Farhang Radja{\"\i} and Jean-Yves Delenne} } @article {72, title = {Combinatorial molecular optimization of cement hydrates}, journal = {Nat Commun}, volume = {5}, year = {2014}, month = {Sep-24-2014}, pages = {Article Number: 4960}, abstract = {

Despite its ubiquitous presence in the built environment, concrete\â\€$(1s (Bmolecular-level properties are only recently being explored using experimental and simulation studies. Increasing societal concerns about concrete\â\€$(1s (Benvironmental footprint have provided strong motivation to develop new concrete with greater specific stiffness or strength (for structures with less material). Herein, a combinatorial approach is described to optimize properties of cement hydrates. The method entails screening a computationally generated database of atomic structures of calcium-silicate-hydrate, the binding phase of concrete, against a set of three defect attributes: calcium-to-silicon ratio as compositional index and two correlation distances describing medium-range silicon-oxygen and calcium-oxygen environments. Although structural and mechanical properties correlate well with calcium-to-silicon ratio, the cross-correlation between all three defect attributes reveals an indentation modulus-to-hardness ratio extremum, analogous to identifying optimum network connectivity in glass rheology. We also comment on implications of the present findings for a novel route to optimize the nanoscale mechanical properties of cement hydrate.

Figure 1

}, doi = {10.1038/ncomms5960}, author = {Mohammad Javad Abdolhosseini Qomi and Konrad J. Krakowiak and Mathieu Bauchy and Stewart, K.L. and Rouzbeh Shahsavari and Jagannathan, D. and Brommer, D.B. and Alain Baronnet and Markus J Buehler and Sidney Yip and Franz-Josef Ulm and Krystyn J. Van Vliet and Roland Jean-Marc Pellenq} } @article {651, title = {Density functional approach for the magnetism of}, journal = {Physical Review B}, volume = {89}, year = {2014}, month = {Mar-01-2014}, abstract = {

Density functional calculations have been carried out to investigate the microscopic origin of the magnetic properties of \β-TeVO4. Two different approaches, based either on a perturbative treatment of the multiorbital Hubbard model in the strongly correlated limit or on the calculation of supercell total energy differences, have been employed to evaluate magnetic couplings in this compound. The picture provided by these two approaches is that of weakly coupled frustrated chains with ferromagnetic nearest-neighbor and antiferromagnetic second-nearest-neighbor couplings. These results, differing substantially from previous reports, should motivate further experimental investigations of the magnetic properties of this compound.

}, issn = {1098-0121}, doi = {10.1103/PhysRevB.89.104414}, url = {https://link.aps.org/doi/10.1103/PhysRevB.89.104414}, author = {Andres Sa{\`u}l and Guillaume Radtke} } @article {62, title = {A density functional approach of the magnetism of b-TeVO4}, journal = {Phys. Rev. B.}, volume = {89}, year = {2014}, month = {Mar-2014}, chapter = {104414}, abstract = {

Density functional calculations have been carried out to investigate the microscopic origin of the magnetic properties of
\β-TeVO4. Two different approaches, based either on a perturbative treatment of the multiorbital Hubbard model in the strongly correlated limit or on the calculation of supercell total energy differences, have been employed to evaluate magnetic couplings in this compound. The picture provided by these two approaches is that of weakly coupled frustrated chains with ferromagnetic nearest-neighbor and antiferromagnetic second-nearest-neighbor couplings. These results, differing substantially from previous reports, should motivate further experimental investigations of the magnetic properties of this compound.

Figure

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Figure

}, doi = {10.1103/PhysRevB.89.104414}, author = {Andres Sa{\`u}l and Guillaume Radtke} } @article {273, title = {Effect of size polydispersity versus particle shape in dense granular media}, journal = {Physical Review E}, volume = {90}, year = {2014}, month = {Jul-21-2014}, pages = {Article Number: 012202}, abstract = {

We present a detailed analysis of the morphology of granular systems composed of frictionless pentagonal particles by varying systematically both the size span and particle shape irregularity, which represent two polydispersity parameters of the system. The microstructure is characterized in terms of various statistical descriptors such as global and local packing fractions, radial distribution functions, coordination number, and fraction of floating particles. We find that the packing fraction increases with the two parameters of polydispersity, but the effect of shape polydispersity for all the investigated structural properties is significant only at low size polydispersity where the positional and/or orientational ordering of the particles prevail. We focus in more detail on the class of side/side contacts, which is the interesting feature of our system as compared to a packing of disks. We show that the proportion of such contacts has weak dependence on the polydispersity parameters. The side- side contacts do not percolate but they define clusters of increasing size as a function of size polydispersity and decreasing size as a function of shape polydispersity. The clusters have anisotropic shapes but with a decreasing aspect ratio as polydispersity increases. This feature is argued to be a consequence of strong force chains (forces above the mean), which are mainly captured by side-side contacts. Finally, the force transmission is intrinsically multiscale, with a mean force increasing linearly with particle size.

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}, issn = {1539-3755}, doi = {10.1103/PhysRevE.90.012202}, author = {Duc-Hanh Nguyen and {\'e}ma, Emilien and Farhang Radja{\"\i} and Philippe Sornay} } @proceedings {346, title = {Geomechanics from Micro to MacroInteraction between two localized fluidization cavities in granular media : Experiments and numerical simulation}, journal = {3rd International Symposium on Geomechanics from Micro to Macro}, volume = {Geomechanics from Micro to Macro}, year = {2014}, month = {Sep-2014}, pages = {1571 - 1576}, publisher = {CRC Press}, address = {SEP 01-03-2014 Univ Cambridge, Cambridge, ENGLAND}, abstract = {

In this work, we present experimental and numerical results on the interaction between two localized fluidization cavities in an immersed granular packing. According to the gap between the two locally injected upward fluid flows, each fluidized cavity will evolve independently of the another, or conversely, the two cavities can interact with each other: they merge and eventually behave like a single cavity. Combined optical techniques are used for visualization of particle motion inside the granular media (Refractive Index-Matching between liquid and beads and Planar Laser-Induced Fluorescence), the experimental results are compared to a two-dimensional simulation based on coupled Discrete Element and Lattice Boltzmann Methods (DEM-LBM).

}, isbn = {978-1-138-02707-7}, doi = {10.1201/b17395-286}, author = {Jeff Ngoma and Pierre Philippe and St{\'e}phane Bonelli and Jean-Yves Delenne and Farhang Radja{\"\i}}, editor = {Kenichi Soga and Krishna Kumar and Giovanna Biscontin and Kuo, Matthew} } @article {275, title = {Initiation of immersed granular avalanches}, journal = {Physical Review E}, volume = {89}, year = {2014}, month = {May-09-2014}, pages = {Article Number: 052203}, abstract = {

By means of coupled molecular dynamics-computational fluid dynamics simulations, we analyze the initiation of avalanches in a granular bed of spherical particles immersed in a viscous fluid and inclined above its angle of repose. In quantitative agreement with experiments, we find that the bed is unstable for a packing fraction below 0.59 but is stabilized above this packing fraction by negative excess pore pressure induced by the effect of dilatancy. From detailed numerical data, we explore the time evolution of shear strain, packing fraction, excess pore pressures, and granular microstructure in this creeplike pressure redistribution regime, and we show that they scale excellently with a characteristic time extracted from a model based on the balance of granular stresses in the presence of a negative excess pressure and its interplay with dilatancy. The cumulative shear strain at failure is found to be ≃ 0.2, in close agreement with the experiments, irrespective of the initial packing fraction and inclination angle. Remarkably, the avalanche is triggered when dilatancy vanishes instantly as a result of fluctuations while the average dilatancy is still positive (expanding bed) with a packing fraction that declines with the initial packing fraction. Another nontrivial feature of this creeplike regime is that, in contrast to dry granular materials, the internal friction angle of the bed at failure is independent of dilatancy but depends on the inclination angle, leading therefore to a nonlinear dependence of the excess pore pressure on the inclination angle. We show that this behavior may be described in terms of the contact network anisotropy, which increases with a nearly constant connectivity and levels off at a value (critical state) that increases with the inclination angle. These features suggest that the behavior of immersed granular materials is controlled not only directly by hydrodynamic forces acting on the particles but also by the influence of the fluid on the granular microstructure.

}, issn = {1539-3755}, doi = {10.1103/PhysRevE.89.052203}, author = {Patrick Mutabaruka and Jean-Yves Delenne and Kenichi Soga and Farhang Radja{\"\i}} } @proceedings {344, title = {Lattice Boltzmann modeling of liquid clusters in granular media}, journal = {3rd International Symposium on Geomechanics from Micro to Macro}, volume = {Geomechanics from Micro to Macro}, year = {2014}, month = {Dec-03-2014}, pages = {461 - 466}, publisher = {CRC Press}, address = {SEP 01-03-2014 Univ Cambridge, Cambridge, ENGLAND}, abstract = {

We use capillary condensation simulated by a multiphase Lattice Boltzmann model as a means to generate homogeneous distributions of liquid clusters in 2D granular media. Liquid droplets condense from the vapor phase between and on the grains, and they transform into capillary bonds and liquid clusters as thermodynamic equilibrium is approached. As the amount of condensed liquid is increased, liquid clusters of increasing connectivity are formed and the distribution of liquid undergoes topological transitions until the whole pore space is filled by the liquid. We investigate the cluster statistics and local grain environments. From extensive simulations, we also obtain the mean Laplace pressure as a function of the amount of liquid, which is found to be quite similar to the well-known experimental retention curve in soil mechanics.

}, isbn = {978-1-138-02707-7}, doi = {10.1201/b1739510.1201/b17395-83}, author = {Jean-Yves Delenne and Vincent Richefeu and Farhang Radja{\"\i}}, editor = {Kenichi Soga and Krishna Kumar and Giovanna Biscontin and Kuo, Matthew} } @article {109, title = {Magnetic interactions in 3d metal chains on Cu2X/Cu(001) (X = N, O): Comparison with corresponding unsupported chains}, journal = {Physical Review B}, volume = {90}, year = {2014}, month = {Nov-2014}, pages = {195423}, type = {Article}, abstract = {

In this work we present a systematic study of the magnetic interactions within 3d transition-metal chains adsorbed on Cu2N and Cu2O monolayers grown on Cu(001). We are interested in the particular geometric adsorption configuration which gives rise, after relaxation, to the development of diatomic TM-X (X = N, O) chains. By using density functional theory (DFT), we calculate the energy difference between the ferromagnetic and antiferromagnetic intrachain configurations for Ti, V, Cr, Mn, Fe, and Co. Both substrates give rise, with minor differences, to the same magnetic trends, the only chains which are ferromagnetic after adsorption are Cr chains. By performing similar calculations in unsupported chains and introducing a tight-binding-model Hamiltonian based on physically reasonable assumptions we reproduce the magnetic trends obtained from the DFT calculations.

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}, issn = {1098-0121}, doi = {10.1103/PhysRevB.90.195423}, author = {Urdaniz, M. C. and Barral, M. A. and Llois, A. M. and Andres Sa{\`u}l} } @proceedings {251, title = {Mesoscale simulation of clay aggregate formation and mechanical properties}, journal = {3rd International Symposium on Geomechanics from Micro to Macro}, volume = {Geomechanics from Micro to Macro: Granular Matter}, year = {2014}, month = {Sep-2014}, pages = {539-544}, address = {SEP 01-03 2014 Univ Cambridge, Cambridge, ENGLAND}, abstract = {

This paper proposes a novel methodology for understanding the meso-scale aggregation of clay platelets in water. We use Molecular Dynamics simulations using the CLAYFF force fields to represent the interactions between two layers of Wyoming montmorillonite (Na-smectite) in bulk water. The analyses are used to establish the potential of mean force at different spacings between the layers for edge-to-edge and face-to-face interactions. This is accomplished by finding the change in free energy as a function of the separation distance between the platelets using thermodynamic perturbation theory with a simple overlap sampling method. These nanoscale results are then used to calibrate the Gay\–Berne (GB) potential that represents each platelet as a single-site ellipsoidal body. A coarse-graining upscaling approach then uses the GB potentials and molecular dynamics to represent the meso-scale aggregation of clay platelets (at submicron length scale). Results from meso-scale simulations obtain the equilibrium/jamming configurations for mono-disperse clay platelets. The results show aggregation for a range of clay platelets dimensions and pressures with mean stack size ranging from 3 to 8 platelets. The particle assemblies become more ordered and exhibit more pronounced elastic anisotropy at higher confining pressures. The results are in good agreement with previously measured nano-indentation moduli over a wide range of clay packing densities.

}, issn = {1434-5021}, doi = {10.1007/s10035-016-0655-8}, author = {Ebrahimi, Davoud and Roland Jean-Marc Pellenq and Andrew J. Whittle}, editor = {Kenichi Soga and Krishna Kumar and Giovanna Biscontin} } @proceedings {342, title = {Modelling soft-particle materials}, journal = {3rd International Symposium on Geomechanics from Micro to Macro}, volume = {Geomechanics from Micro to Macro}, year = {2014}, month = {Aug-26-2014}, pages = {43-48}, publisher = {CRC Press}, address = {SEP 01-03-2014 Univ Cambridge, Cambridge, ENGLAND}, abstract = {

Soft-particle materials include colloidal pastes, vesicles, many powders, microgels and suspensions. They share the common feature of being composed of particles that can undergo large deformations without rupture. For the simulation of such materials, we present a modelling approach based on an implicit formulation of the Material Point Method (MPM) interfaced with the Contact Dynamics (CD) method for the treatment of frictional contacts between particles. Each particle is discretized as a collection of material points. The information carried by the material points is projected onto a background mesh, where equations of motion are solved. The mesh solution is then used to update the material points. The implicit formulation of MPM allows for unconditional numerical stability and efficient coupling with implicit treatment of unilateral contacts and friction between the particles by the CD method. We use this model to analyse the compaction process of 2D soft-particle packings. The packing can reach high solid fractions by particle shape change and still flow plastically. The compaction is a nonlinear process in which new contacts are formed between particles and the contact areas increase. We find that the evolution of the packing fraction is a slow logarithmic function of the driving stress as a consequence of increasing contact area. We also evidence the effect of friction, which favours strong stress chains and thus the elongation of particles, leading to a larger packing fraction at a given level of compressive stress as compared to a frictionless particle packing.

}, url = {http://prodinra.inra.fr/record/370208}, author = {Saeid Nezamabadi and Farhang Radja{\"\i} and Julien Averseng}, editor = {Kenichi Soga and Krishna Kumar and Giovanna Biscontin} } @article {69, title = {Molecular dynamics simulations of the formation of 1D spin-valves from stretched Au-Co and Pt-Co nanowires}, journal = {J. Phys.: Condens. Matter}, volume = {26}, year = {2014}, month = {Oct-2014}, chapter = {474206}, abstract = {

We have performed molecular dynamics (MD) simulations of stretched Aux-Co1 - x and Ptx-Co1 - x nanowires to investigate the formation of bimetallic monoatomic wires between two electrodes. We have considered nanowires with two concentrations x = 0.2 and 0.8, aspect ratio of 13, a cross section of 1 nm(2) and a wide range of temperatures (from 10 to 400 K). For the MD simulations we have used a semi-empirical interatomic potential based on the second moment approximation (SMA) of the density of states to the tight-binding Hamiltonian.For Au-Co alloys, Au atoms tends to migrate towards the narrowed region to form almost pure Au wires. In the PtCo case the formed chains usually consist of Pt enriched alternating structures. The most striking result is probably the Au(0.2)-Co(0.8) alloy where pure monoatomic Au chains form between two Co electrodes constituting a potential 1D spin valve. Despite the known ease with which the 5d metals (Pt, Ir, and Au) form monoatomic chains (MACS), our results show that in the presence of Co (x = 0.2), the percentage of chain formation is higher than in the Pt and Au rich cases (x = 0.8).

}, doi = {10.1088/0953-8984/26/47/474206}, author = {Robinson Cortes-Huerto and T. Sondon and Andres Sa{\`u}l} } @article {70, title = {Multiphase equation of state for carbon addressing high pressures and temperatures}, journal = {Phys Rev. B}, volume = {89}, year = {2014}, month = {Jun-2014}, chapter = {224109}, abstract = {

We present a 5-phase equation of state for elemental carbon which addresses a wide range of density and temperature conditions: 3g/cc\<\ρ\<20g/cc,0K\<T\<\∞. The phases considered are diamond, BC8, simple cubic, simple hexagonal, and the liquid/plasma state. The solid phase free energies are constrained by density functional theory (DFT) calculations. Vibrational contributions to the free energy of each solid phase are treated within the quasiharmonic framework. The liquid free energy model is constrained by fitting to a combination of DFT molecular dynamics performed over the range 10000K\<T\<100000K, and path integral quantum Monte Carlo calculations for T\>100000K (both for \ρ between 3 and 12 g/cc, with select higher- \ρ DFT calculations as well). The liquid free energy model includes an atom-in-jellium approach to account for the effects of ionization due to temperature and pressure in the plasma state, and an ion-thermal model which includes the approach to the ideal gas limit. The precise manner in which the ideal gas limit is reached is greatly constrained by both the highest-temperature DFT data and the path integral data, forcing us to discard an ion-thermal model we had used previously in favor of a new one. Predictions are made for the principal Hugoniot and the room-temperature isotherm, and comparisons are made to recent experimental results.

Figure

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}, doi = {10.1103/PhysRevB.89.224109}, author = {L. X. Benedict and K. P. Driver and S. Hamel and B. Militzer and T. Qi and Alfredo A. Correa and Andres Sa{\`u}l and E. Schwegler} } @article {278, title = {Penetration test in coarse granular material using Contact Dynamics Method}, journal = {Computers and Geotechnics}, volume = {55}, year = {2014}, month = {Jan-2014}, pages = {248 - 253}, abstract = {

Field tests are widely used for soil characterization in geotechnical applications in spite of implementation difficulties. The light penetrometer is a well-known testing tool for fine soils, but the physical interpretation of the output data in the case of coarse granular materials is far less evident. Indeed, the data are considerably more sensitive in this case to various parameters such as fabric structure, particle shapes or the applied impact energy. In order to achieve a better understanding of the penetration process into a coarse granular material, a numerical study was performed by means of contact dynamics simulations. The penetration of a moving tip in a sample composed of irregular grain shapes was studied and the influence of the driving velocity and input energy on the penetration strength was analyzed. The results show that the latter grows with both the penetration rate and energy, despite the strong fluctuations occur due to a jamming\–unjamming process in which the contact network connectivity evolves intermittently in correlation with the penetration strength. This analysis suggests that the time-averaged data provided by a penetrometer is reliable information from which the bulk strength properties of coarse granular materials can be evaluated.

}, issn = {0266352X}, doi = {10.1016/j.compgeo.2013.09.006}, author = {Quezada, Juan Carlos and Breul, Pierre and Saussine, Gilles and Farhang Radja{\"\i}} } @article {274, title = {Predicting the settlement of coarse granular materials under vertical loading}, journal = {Scientific Reports}, volume = {4}, year = {2014}, month = {Jul-16-2014}, pages = {Article Number: 5707}, abstract = {

Granular materials are widely used in industrial processes despite their complex and poorly understood mechanical behaviour both in static and dynamic regimes. A prototypical example is the settlement and compaction of a granular bed under vibrational loading. The elementary mechanisms of this process are still unclear and there is presently no established theory or methodology to predict the settlement and its statistical variability. By means of a parametric study, carried out on a full-scale track, and a critical analysis of density relaxation laws, we introduce a novel settlement model in coarse granular materials under cyclic loading. Our extensive experimental data indicate that the settlement process is governed by three independent parameters strongly correlated with the vibration intensity and initial packing fraction. We show that the mean settlement is well predicted by the model with its parameter values extracted from experimental data.

Granular materials are both pressure-dependent and density-dependent materials and exhibit a broad range of intricate behaviours due to their discrete nature, dissipative interactions and generic structural disorder1. The packing fraction may vary as a result of particle rearrangements induced by shearing or vibrations and it leads to dramatic changes in the structure and mechanical response of a granular material2,3,4,5,6,7,8. A long-time logarithmic relaxation law of the packing fraction is systematically observed in experiments9,10. In simple compaction models, this behaviour is attributed to the exponentially increasing time for the particles to reach a new configuration of lower packing fraction. The case of settlement under cyclic loading has, however, been much less investigated. The settlement of granular bed occurs due to both compaction and side-wise spreading. An important industrial example is the railway ballast, which undergoes gradual settlement under the static and dynamic overloads induced by train traffics11,12,13,14. The readjustment of differential settlements requires costly operations on fast-train railways. For this reason, an improved understanding of the parameters governing the settlement process is a critical technological challenge for new developments in this field.

In this paper, we show that the total settlement N under vertical cyclic loading is governed by a logarithmic relaxation law as a function of the number N of cycles:

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where the three fitting parameters \∞, B and N0 can be evaluated from the loading parameters, namely the frequency (related to the train speed for ballast) and initial packing fraction of the material. Our experimental correlations between model and loading parameters show consistently that \∞ and B depend on the dimensionless loading intensity \Γ = (A\ω2)/(pd2/m + g), where A is the vibration amplitude, p is the confining pressure (under the sleeper for ballast), d is the average particle diameter, m is the average particle mass and g is gravitational acceleration. We also find that the parameter N0 is linked to the initial packing fraction of the material. In fact, this parameter controls the initial settlement rate, and it was systematically determined by means of a light penetrometer in our experiments on ballast material.

}, doi = {10.1038/srep05707}, author = {Quezada, Juan Carlos and Saussine, Gilles and Breul, Pierre and Farhang Radja{\"\i}} } @article {91, title = {Role of Silver Nanoparticles in Enhanced Xenon Adsorption Using Silver-Loaded Zeolites}, journal = {Journal of Physical Chemistry C }, volume = {118}, year = {2014}, month = {Oct-06-2014}, pages = {25032-25040}, type = {Article}}, abstract = {
Abstract Image

Molecular simulation is used to unravel the adsorption mechanisms of xenon on Ag-doped ZSM-5 zeolite. We show that silver nanoparticles, which form at the external surface of zeolite crystallites, are responsible for enhanced xenon physisorption at very low pressure. We also propose a simple model of adsorption on such composite materials made up of silver-exchanged zeolites and silver nanoparticles adsorbed at the zeolite surface. This model, which allows predicting the adsorption of other gases without any additional parameters, provides a tool to characterize the amount of reduced silver as well as the silver particle size distribution (in good agreement with transmission electron microscopy images). The presence of a majority of silver nanoparticles is further characterized by means of X-ray diffraction and X-ray Absorption Spectroscopy at the silver K edge.

}, issn = {1932-7447}, doi = {10.1021/jp507590a}, author = {Deliere, Ludovic and Topin, Sylvain and Benoit A. Coasne and Fontaine, Jean-Pierre and De Vito, Sophie and Den Auwer, Christophe and Solari, Pier Lorenzo and Daniel, Cecile and Schuurman, Yves and David Farrusseng} } @proceedings {345, title = {Shear flow of dense granular suspensions by computer simulations}, journal = {3rd International Symposium on Geomechanics from Micro to Macro}, volume = {Geomechanics from Micro to Macro}, year = {2014}, month = {Apr-2014}, pages = {467-472}, publisher = {CRC Press}, address = {SEP 01-03-2014 Univ Cambridge, Cambridge, ENGLAND}, abstract = {

We analyze the shear flow of dense granular materials composed of circular particles immersed in a viscous fluid by means of Molecular Dynamics simulations interfaced with the Lattice Boltzmann Method. A homogeneous flow of the suspension is obtained through periodic boundary conditions and by directly applying a confining pressure on the granular phase and shearing the fluid phase. The stead-state rheology can be described in terms of effective friction coefficient and packing fraction of the suspension as a function of the ratio of viscous shear stress to confining pressure (frictional description), on one hand, and in terms of normal and shear viscosities of the suspension as a function of the packing fraction (viscous description), on the other hand. We show that the simulation data are consistent with both descriptions and in close agreement with the corresponding scaling laws observed in recent experiments.

}, url = {http://prodinra.inra.fr/record/369542}, author = {L. Amarsid and Patrick Mutabaruka and Jean-Yves Delenne}, editor = {Kenichi Soga and Krishna Kumar and Giovanna Biscontin} } @article {276, title = {Some micromechanical aspects of failure in granular materials based on second-order work}, journal = {Comptes Rendus M{\'e}canique}, volume = {342}, year = {2014}, month = {Mar-2014}, pages = {174 - 188}, abstract = {

This paper discusses the notion of failure in a granular assembly by examining the key microstructural mechanisms which are most likely to trigger the nucleation and propagation of instabilities within a granular material. For this purpose, the key variable to predict the occurrence of failure, known as second-order work, is expressed from variables on the grain scale. The local behaviour incidents (where contacts may open or slide), compared to the global response of the assembly, are analysed by two approaches. First, numerical computations made by a discrete element model confirm the microscopic definition of the second-order work. Secondly, a micromechanical model, based on a homogenization procedure, relating the macroscopic behaviour to microscopic ingredients, namely contact planes, points to a close link between the occurrence of failure on the macroscopic scale as well as on the contact planes.

}, issn = {16310721}, doi = {10.1016/j.crme.2014.01.006}, author = {Fran{\c c}ois Nicot and Hadda, Nejib and Sibille, Luc and Farhang Radja{\"\i} and Hicher, Pierre-Yves and Darve, F{\'e}lix} } @article {67, title = {Sub-additive ionic transport across arrays of solid-state nanopores}, journal = {Physics of Fluids (1994-present)}, volume = {26}, year = {2014}, month = {Jan-31-2014}, pages = {012005}, abstract = {

Nanopores, either biological, solid-state, or ultrathin pierced graphene, are powerful tools which are central to many applications, from sensing of biological molecules to desalination and fabrication of ion selective membranes. However, the interpretation of transport through low aspect-ratio nanopores becomes particularly complex as 3D access effects outside the pores are expected to play a dominant role. Here, we report both experiments and theory showing that, in contrast to na\ïve expectations, long-range mutual interaction across an array of nanopores leads to a non-extensive, sub-linear scaling of the global conductance on the number of pores N. A scaling analysis demonstrates that the N-dependence of the conductance depends on the topology of the network. It scales like G \∼ N/log\ N for a 1D line of pores, and like G\∼\√\‾\‾N for a 2D array, in agreement with experimental measurements. Our results can be extended to alternative transport phenomena obeying Laplace equations, such as diffusive, thermal, or hydrodynamic transport. Consequences of this counter-intuitive behavior are discussed in the context of transport across thin membranes, with applications in energy harvesting.

Image of FIG. 1.
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Image of FIG. 5.
Image of FIG. 6.
}, doi = {10.1063/1.4863206}, author = {Gadaleta, A and Sempere, C and Simon Gravelle and A. Siria and Fulcrand, R and Christophe Ybert and Lyd{\'e}ric Bocquet} } @article {74, title = {Ultrahigh interlayer friction in multiwalled boron nitride nanotubes}, journal = {Nat Mater}, volume = {13}, year = {2014}, month = {Jul-2014}, pages = {688 - 693}, abstract = {

Friction at the nanoscale has revealed a wealth of behaviours that depart strongly from the long-standing macroscopic laws of Amontons\–Coulomb1, 2. Here, by using a \‘Christmas cracker\’-type of system in which a multiwalled nanotube is torn apart between a quartz-tuning-fork-based atomic force microscope (TF\–AFM) and a nanomanipulator, we compare the mechanical response of multiwalled carbon nanotubes (CNTs) and multiwalled boron nitride nanotubes (BNNTs) during the fracture and telescopic sliding of the layers. We found that the interlayer friction for insulating BNNTs results in ultrahigh viscous-like dissipation that is proportional to the contact area, whereas for the semimetallic CNTs the sliding friction vanishes within experimental uncertainty. We ascribe this difference to the ionic character of the BN, which allows charge localization. The interlayer viscous friction of BNNTs suggests that BNNT membranes could serve as extremely efficient shock-absorbing\ surfaces.

Multiwalled nanotube Christmas-cracker experimental set-up.

Frequency shift measured by the tuning fork versus the displacement of the piezoscanner during complete tensile load experiments.

}, isbn = {1476-1122}, doi = {10.1038/nmat3985}, author = {Nigues, A. and A. Siria and Vincent, P. and Poncharal, P. and Lyd{\'e}ric Bocquet} } @proceedings {365, title = {AIP Conference Proceedings A multiscale description of failure in granular materials}, journal = {7th International Conference on Micromechanics of Granular Media (Powders and Grains)}, volume = {Book Series: AIP Conference Proceedings POWDERS AND GRAINS 2013}, year = {2013}, month = {Jun-18-2013}, pages = {585-588}, publisher = {AIP}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

This paper presents conditions of initiation and development of failure in granular materials through a twodimensional discrete element model. General condition for the effective development of failure and its physical characteristics are recalled. Then relation between failure and the second order work expressed in terms of microscopic variables is discussed. Eventually, correspondence between a localized mode of failure marked with shear band patterns and space distribution of negative values of microscopic second-order work is investigated.

}, doi = {10.1063/1.4811999}, author = {Hadda, Nejib and Fran{\c c}ois Nicot and Sibille, Luc and Farhang Radja{\"\i} and Tordesillas, Antoinette and Darve, F{\'e}lix}, editor = {Yu, A and Dong, K and Yang, R} } @proceedings {367, title = {A benchmark for particle shape dependence}, journal = {7th International Conference on Micromechanics of Granular Media (Powders and Grains)}, volume = {Book Series: AIP Conference Proceedings POWDERS AND GRAINS 2013}, year = {2013}, month = {Jun-18-2013}, pages = {883-886}, publisher = {AIP}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

Particle shape is a major parameter for the space-filling and strength properties of granular materials. For a systematic investigation of shape effect, a numerical benchmark test was set up within a collaborative group using different numerical methods and particles of various shape characteristics such as elongation, angularity and nonconvexity. Extensive 2D shear simulations were performed in this framework and the shear strength and packing fraction were compared for different shapes. We show that the results may be analyzed in terms of a low-order shape parameter \η describing the degree of distortion from a perfectly circular shape. In particular, the shear strength is an increasing function of \η with nearly the same trend for all shapes, the differences being of second order compared to \η. We also observe a nontrivial behavior of packing fraction which, for all our simulated shapes, increases with \η from the random close packing fraction for disks, reaches a peak considerably higher than that for disks, and subsequently declines as \η is further increased. Finally, the analysis of contact forces for the same value of \η leads to very similar statistics regardless of our specific particle shapes.

}, doi = {10.1063/1.4812073}, author = {Gael Combe and C{\'e}cile Nouguier-Lehon and Emilien Az{\'e}ma and Krzysztof Szarf and Baptiste Saint-Cyr and Marie Chaze and Farhang Radja{\"\i} and Pascal Villard and Jean-Yves Delenne and Vincent Richefeu and Philippe Sornay and Charles Voivret and CEGEO Group}, editor = {Yu, A and Dong, K and Yang, R} } @article {281, title = {Cohesive granular materials composed of nonconvex particles}, journal = {Physical Review E}, volume = {87}, year = {2013}, month = {May-28-2013}, pages = {Article Number: 052207}, abstract = {

The macroscopic cohesion of granular materials made up of sticky particles depends on the particle shapes. We address this issue by performing contact dynamics simulations of 2D packings of nonconvex aggregates. We find that the macroscopic cohesion is strongly dependent on the strain and stress inhomogeneities developing inside the material. The largest cohesion is obtained for nearly homogeneous deformation at the beginning of unconfined axial compression and it evolves linearly with nonconvexity. Interestingly, the aggregates in a sheared packing tend to form more contacts with fewer neighboring aggregates as the degree of nonconvexity increases. We also find that shearing leads either to an isotropic distribution of tensile contacts or to the same privileged direction as that of compressive contacts.

}, issn = {1539-3755}, doi = {10.1103/PhysRevE.87.052207}, author = {Baptiste Saint-Cyr and Farhang Radja{\"\i} and Jean-Yves Delenne and Philippe Sornay} } @article {33, title = {Gas uptake in solvents confined in mesopores: adsorption versus enhanced solubility}, journal = {The Journal of Physical Chemistry Letters}, volume = {4}, year = {2013}, month = {Jun-25-2013}, pages = {2274{\textendash}2278}, abstract = {
Abstract Image

Three molecular mechanisms for gas uptake in a solvent confined in mesopores are identified. On the one hand, CO2 uptake is an adsorption-driven phenomenon that arises from the strong interaction between the gas molecules and the pore surface. On the other hand, H2 uptake is a confinement-induced enhanced solubility in which solubility is favored in the regions of low solvent density formed by the layering of the solvent. In partially filled pores, adsorption at the gas/liquid solvent interface is a third mechanism that leads to large gas uptakes. This study, which sheds light on previously reported yet unclear oversolubility in pores, provides a guide to design hybrid porous catalysts consisting of a solvent confined in a porous solid.

}, doi = {10.1021/jz401143x}, author = {Linh Ngoc Ho and St{\'e}phanie Clauzier and Schuurman, Yves and David Farrusseng and Benoit A. Coasne} } @proceedings {341, title = {Granular plastic flow and fabric-based internal variables}, journal = {3rd International Symposium on Geomechanics from Micro to Macro}, volume = {Geomechanics from Micro to Macro}, year = {2013}, month = {May-2013}, pages = {3 - 19}, publisher = {CRC Press}, address = {SEP 01-03-2014 Univ Cambridge, Cambridge, ENGLAND}, abstract = {

A microscopic approach to the quasi-static flow of granular materials requires
fabric parameters pertaining to the contact network. We show that the plastic behavior of
granular materials is correctly predicted with the approximation of perfectly rigid particles
interacting via dissipative contacts as simulated by means of the contact dynamics method.
We investigate the correlations between macroscopic variables (internal friction angle and ...

}, isbn = {978-1-138-02707-7}, doi = {10.1201/b1739510.1201/b17395-3}, url = {http://www.crcnetbase.com/doi/book/10.1201/b17395http://www.crcnetbase.com/doi/abs/10.1201/b17395-3}, author = {Farhang Radja{\"\i} and St{\'e}phane Roux}, editor = {Kenichi Soga and Krishna Kumar and Giovanna Biscontin and Kuo, Matthew} } @proceedings {370, title = {GRANULAR SLUMPING IN A FLUID : FOCUS ON RUNOUT DISTANCES}, journal = {3rd International Conference on Particle-based Methods}, volume = {PARTICLE-BASED METHODS III: FUNDAMENTALS AND APPLICATIONS}, year = {2013}, month = {Sept-2013}, pages = {115-123}, address = {SEP 18-20 2013 Stuttgart, GERMANY}, author = {Vincent Topin and Yann Monerie and Perales, F.}, editor = {Bischoff, M and Ramm, E and Onate, E} } @article {284, title = {An interdisciplinary approach towards improved understanding of soil deformation during compaction}, journal = {Soil and Tillage Research}, volume = {128}, year = {2013}, month = {Apr-2013}, pages = {61 - 80}, abstract = {

Soil compaction not only reduces available pore volume in which fluids are stored, but it alters the arrangement of soil constituents and pore geometry, thereby adversely impacting fluid transport and a range of soil ecological functions. Quantitative understanding of stress transmission and deformation processes in arable soils remains limited. Yet such knowledge is essential for better predictions of effects of soil management practices such as agricultural field traffic on soil functioning. Concepts and theory used in agricultural soil mechanics (soil compaction and soil tillage) are often adopted from conventional soil mechanics (e.g. foundation engineering). However, in contrast with standard geotechnical applications, undesired stresses applied by agricultural tyres/tracks are highly dynamic and last for very short times. Moreover, arable soils are typically unsaturated and contain important secondary structures (e.g. aggregates), factors important for affecting their soil mechanical behaviour. Mechanical processes in porous media are not only of concern in soil mechanics, but also in other fields including geophysics and granular material science. Despite similarity of basic mechanical processes, theoretical frameworks often differ and reflect disciplinary focus. We review concepts from different but complementary fields concerned with porous media mechanics and highlight opportunities for synergistic advances in understanding deformation and compaction of arable soils. We highlight the important role of technological advances in non-destructive measurement methods at pore (X-ray tomography) and soil profile (seismic) scales that not only offer new insights into soil architecture and enable visualization of soil deformation, but are becoming instrumental in the development and validation of new soil compaction models. The integration of concepts underlying dynamic processes that modify soil pore spaces and bulk properties will improve the understanding of how soil management affect vital soil mechanical, hydraulic and ecological functions supporting plant growth.

}, issn = {01671987}, doi = {10.1016/j.still.2012.10.004}, author = {Keller, T. and Lamand, M. and Peth, S. and Berli, M. and Jean-Yves Delenne and Baumgarten, W. and Rabbel, W. and Farhang Radja{\"\i} and Rajchenbach, J. and Selvadurai, A.P.S. and Or, D.} } @article {25, title = {Large pressure enhancements in confined phases: effect of surface chemistry and roughness}, journal = {J. Chem. Phys.}, volume = {139}, year = {2013}, month = {Oct-10-2013}, chapter = {144701}, abstract = {

Experiments and simulations both suggest that the pressure experienced by an adsorbed phase confined within a carbon nanoporous material can be several orders of magnitude larger than the bulk phase pressure in equilibrium with the system. To investigate this pressure enhancement, we report a molecular-simulation study of the pressure tensor of argon confined in slit-shaped nanopores with walls of various models, including carbon and silica materials. We show that the pressure is strongly enhanced by confinement, arising from the effect of strongly attractive wall forces; confinement within purely repulsive walls does not lead to such enhanced pressures. Simulations with both the Lennard-Jones and Barker-Fisher-Watts intermolecular potentials for argon-argon interactions give rise to similar results. We also show that an increase in the wall roughness significantly decreases the in-pore pressure due to its influence on the structure of the adsorbate. Finally, we demonstrate that the pressures calculated from the mechanical (direct pressure tensor calculations) and the thermodynamic (volume perturbation method) routes yield almost identical results, suggesting that both methods can be used to calculate the local pressure tensor components in the case of these planar geometries.

Image of FIG. 1.
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}, doi = {10.1063/1.4824125}, author = {Yun Long and Jeremy C. Palmer and Benoit A. Coasne and Malgorzata Sliwinska-Bartkowiak and George Jackson and Erich A. Mueller and Keith E. Gubbins} } @article {283, title = {Micromechanical analysis of second order work in granular media}, journal = {Granular Matter}, volume = {15}, year = {2013}, month = {Apr-2013}, pages = {221 - 235}, abstract = {

This paper examines instabilities in granular materials from a microscopic point of view through numerical simulations conducted using a discrete element method on two three-dimensional specimens. The detection and the tracking of grain scale deformation mechanisms constitute the key point for a better understanding the failure process and puzzling out what lies behind the vanishing of the macroscopic second order work. For this purpose, the second order work from microscopic variables, involving contact force and branch vector, was introduced and tracked numerically. Then, all contacts depicting negative values of the second order work were deeply investigated, especially their spatial distribution (homogeneity, agglomeration, dispersion\…) within the specimen according to the density of the granular assembly and to the loading direction. A set of comparisons has been considered in this context in order to highlight how a specimen is populated with such contacts whether it is loaded along a direction included within the plastic tensorial zone or along a direction for which the specimen is likely to behave elastically (elastic tensorial zone). Moreover, these comparisons concerned also loading directions within the cone of instability so that links between the vanishing of both microscopic and macroscopic second order works can be established and the local mechanisms responsible for failure occurrence may be figured out.

}, issn = {1434-5021}, doi = {10.1007/s10035-013-0402-3}, author = {Hadda, Nejib and Fran{\c c}ois Nicot and Bourrier, Franck and Sibille, Luc and Farhang Radja{\"\i} and Darve, F{\'e}lix} } @article {103, title = {On the molecular origin of high-pressure effects in nanoconfinement: The role of surface chemistry and roughness}, journal = {Journal of Chemical Physics}, volume = {139}, year = {2013}, month = {Oct-14-2013}, type = {Article}, abstract = {

Experiments and simulations both suggest that the pressure experienced by an adsorbed phase confined within a carbon nanoporous material can be several orders of magnitude larger than the bulk phase pressure in equilibrium with the system. To investigate this pressure enhancement, we report a molecular-simulation study of the pressure tensor of argon confined in slit-shaped nanopores with walls of various models, including carbon and silica materials. We show that the pressure is strongly enhanced by confinement, arising from the effect of strongly attractive wall forces; confinement within purely repulsive walls does not lead to such enhanced pressures. Simulations with both the Lennard-Jones and Barker-Fisher-Watts intermolecular potentials for argon-argon interactions give rise to similar results. We also show that an increase in the wall roughness significantly decreases the in-pore pressure due to its influence on the structure of the adsorbate. Finally, we demonstrate that the pressures calculated from the mechanical (direct pressure tensor calculations) and the thermodynamic (volume perturbation method) routes yield almost identical results, suggesting that both methods can be used to calculate the local pressure tensor components in the case of these planar geometries. (C) 2013 AIP Publishing LLC.

}, issn = {0021-9606}, doi = {10.1063/1.4824125}, author = {Yun Long and Jeremy C. Palmer and Benoit A. Coasne and Malgorzata Sliwinska-Bartkowiak and George Jackson and Erich A. Mueller and Keith E. Gubbins} } @proceedings {360, title = {Penetration strength of coarse granular materials from DEM simulations}, journal = {7th International Conference on Micromechanics of Granular Media (Powders and Grains)}, volume = {Book Series: AIP Conference Proceedings POWDERS AND GRAINS 2013 }, year = {2013}, month = {Jun-18-2013}, pages = { 241-244}, publisher = {AIP}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

Field tests are widely used for soil characterization in geotechnical applications in spite of implementation difficulties. The light penetrometer test is a well-known testing tool for fine soils, but the physical interpretation of the output data in the case of coarse granular materials is far less evident. In fact, the data are considerably more sensitive to various parameters such as fabric structure, particles shape or the applied impact energy. In order to achieve a better understanding of the underlying phenomena, we performed a numerical study by means contact dynamics DEM simulations. We consider the penetration of a moving tip into a sample composed of irregular grain shapes and we analyze the influence of the driving velocity and applied energy on the penetration strength. We find that the latter grows with both the penetration rate and energy. Force fluctuations on the tip involve a jamming-unjamming process. The typology of contact network and inter-granular friction play a major role in the fluctuations and measured values of the cone penetration strength.

}, doi = {10.1063/1.4811912}, author = {Quezada, Juan Carlos and Saussine, Gilles and Breul, Pierre and Farhang Radja{\"\i}}, editor = {Yu, A and Dong, K and Yang, R} } @article {282, title = {Rheology of three-dimensional packings of aggregates: Microstructure and effects of nonconvexity}, journal = {Physical Review E}, volume = {87}, year = {2013}, month = {May-22-2013}, pages = {Article Number: 052205}, abstract = {

We use 3D contact dynamics simulations to analyze the rheological properties of granular materials composed of rigid aggregates. The aggregates are made from four overlapping spheres and described by a nonconvexity parameter depending on the relative positions of the spheres. The macroscopic and microstructural properties of several sheared packings are analyzed as a function of the degree of nonconvexity of the aggregates. We find that the internal angle of friction increases with nonconvexity. In contrast, the packing fraction increases first to a maximum value but declines as nonconvexity further increases. At high level of nonconvexity, the packings are looser but show a higher shear strength. At the microscopic scale, the fabric and force anisotropy, as well as friction mobilization are enhanced by multiple contacts between aggregates and interlocking, revealing thus the mechanical and geometrical origins of shear strength.

}, issn = {1539-3755}, doi = {10.1103/PhysRevE.87.052205}, author = {Emilien Az{\'e}ma and Farhang Radja{\"\i} and Baptiste Saint-Cyr and Jean-Yves Delenne and Philippe Sornay} } @article {61, title = {Role of temperature in the formation and growth of gold monoatomic chains: A molecular dynamics study}, journal = {Physical Review B}, volume = {88}, year = {2013}, month = {Dec-31-2013}, pages = {235438}, abstract = {

The effect of temperature on the formation and growth of monoatomic chains is investigated by extensive molecular dynamics simulations using a semiempirical potential based on the second-moment approximation to the tight-binding Hamiltonian. Gold nanowires, with an aspect ratio of \∼13 and a cross section of \∼1 nm2, are stretched at a rate of 3 m/s in the range of temperatures 5\–600 K with 50 initial configurations per temperature. A detailed study on the probability to form monoatomic chains (MACs) is presented. Two domains are apparent in our simulations: one at T\<100 K, where MACs develop from crystalline disorder at the constriction, and the other at T\>100 K, where MACs form as a consequence of plastic deformation of the nanowire. Our results show that the average length of the formed MACs maximizes at T=150\ K, which is supported by simple energy arguments.

Figure

Figure

Figure

Figure

Figure

}, doi = {10.1103/PhysRevB.88.235438}, author = {Robinson Cortes-Huerto and T. Sondon and Andres Sa{\`u}l} } @proceedings {361, title = {Settlement statistics of a granular layer composed of polyhedral particles}, journal = {7th International Conference on Micromechanics of Granular Media (Powders and Grains)}, volume = {Book Series: AIP Conference Proceedings POWDERS AND GRAINS 2013}, year = {2013}, month = {Jun-18-2013}, pages = {333-336}, publisher = {AIP}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

We use 3D contact dynamics simulations to investigate the mechanical equilibrium and settlement of a granular material composed of irregular polyhedral particles confined between two horizontal frictional planes. We show that, as a consequence of mobilized wall-particle friction force at the top and bottom boundaries, the transient deformation induced by a constant vertical load increment is controlled by the aspect ratio (thickness over width) of the packing as well as the stress ratio. The transient deformation declines considerably for increasingly smaller aspect ratios and grows with the stress ratio. From the simulation data for a large number of independent configurations, we find that sample-to-sample fluctuations of the deformation have a broad distribution and they scale with the average deformation.

}, doi = {10.1063/1.4811935}, author = {Quezada, Juan Carlos and Saussine, Gilles and Breul, Pierre and Farhang Radja{\"\i}}, editor = {Yu, A and Dong, K and Yang, R} } @article {60, title = {Simple views on surface stress and surface energy concepts}, journal = {Advances in Natural Sciences: Nanoscience and Nanotechnology}, volume = {5}, year = {2013}, month = {Nov-27-2013}, pages = {013002}, abstract = {

Some aspects of the thermodynamics and mechanics of solid surfaces, in particular with respect to surface stress and surface energy, are reviewed. The purpose is to enlighten the deep differences between these two physical quantities. We consider successively the case of atomic flat surfaces and the case of vicinal surfaces characterized by surface stress discontinuities. Finally, experimental examples, concerning Si surfaces, are described.

}, doi = {10.1088/2043-6262/5/1/013002}, author = {M{\"u}ller, Pierre and Andres Sa{\`u}l and Leroy, Fr{\'e}d{\'e}ric} } @conference {36, title = {Water Isotherms, Shrinkage and Creep of Cement Paste: Hypotheses, Models and Experiments}, booktitle = {Mechanics and Physics of Creep, Shrinkage, and Durability of Concrete: A Tribute to Zdenek P. Ba{\.z}ant}, year = {2013}, month = {Sep-25-2013}, publisher = {ASCE Publications}, organization = {ASCE Publications}, abstract = {

Cement paste has a complex mesoscale structure, and small changes in its pore network potentially cause large variation in measurements such as the water isotherm (also nitrogen). We deconvolute the water isotherm with the help of advanced computational techniques, hypotheses, and a re-examination of published data. The pore system is divided into four different categories, each containing water with its own physical properties. By viewing the highly interdependent roles of water in each of the pore categories as a system, new insights are gained regarding possible mechanisms that control drying, shrinkage, and creep, and experimental strategies for verification.

}, doi = {10.1061/9780784413111.015}, author = {Hamlin M. Jennings and Enrico Masoero and Pinson, Matthew B and Strekalova, Elena G and Patrick A Bonnaud and Hegoi Manzano and Qing Ji and Jeffrey J. Thomas and Roland Jean-Marc Pellenq and Franz-Josef Ulm and others} } @article {216, title = {Water self-diffusion at the surface of silica glasses: effect of hydrophilic to hydrophobic transition}, journal = {Molecular Physics}, volume = {111}, year = {2013}, month = {Nov-2013}, pages = {3410 - 3417}, abstract = {

We study water dynamics at a silica aqueous interface. Both hydrophilic (hydroxylated) surfaces and hydrophobic surfaces (dehydroxylated upon irradiation) have been generated from atomistic simulations. A new method for the calculation of the normal self-diffusion coefficients based on the calculation of mean first passage times is proposed. It uses the Smoluchowski theory of Brownian motion and it takes proper account of the layering of the molecules. In the case of parallel self-diffusion coefficients, a decrease is found compared to the bulk values. It can be described in terms of hydrodynamic boundary conditions induced by the surface confinement. This hydrodynamic explanation is not enough to interpret the case of normal self-diffusion coefficients for which an important diminution is found. Normal self-diffusion coefficients appear to depend strongly on the hydrophilicity of the surface. They tend towards their bulk value only at long distances from the surfaces. The first layer of water molecules is found to be partially adsorbed.

}, issn = {0026-8976}, doi = {10.1080/00268976.2013.861084}, author = {Bertrand Siboulet and Molina, J. and Benoit A. Coasne and Turq, P. and Jean-Francois Dufreche} } @proceedings {350, title = {Effect of Particle Shape non-Convexity on the Rheology of Granular Media : 3D Contact Dynamics Simulations}, journal = {2nd International Conference on Particle-Based Methods - Fundamentals and Applications (Particles)}, volume = {PARTICLE-BASED METHODS II: FUNDAMENTALS AND APPLICATIONS}, year = {2012}, month = {Apr-10-2012}, pages = {427-434}, address = {OCT 26-28 2011 Barcelona, SPAIN}, abstract = {

We analyze the effect of particle shape non-convexity on the quasi-static behavior of granular materials by means of contact dynamics simulations. The particles are regular aggregates of four overlapping spheres described by a nonconvexity parameter depending on the relative positions of the particles. Several packings are first submitted to isotropic compression without friction. We find that, as in 2D, the solid fraction of isotropic packings increases with non-convexity up to a maximum value and then declines to be nearly equal to that of a packing composed of only spheres. It is also remarkable that the coordination number increases quickly and saturates so that the packings composed of grains with a high level of nonconvexity are looser but more strongly connected. Then, the quasi-static behavior, structural and force anisotropies are analyzed by subjecting each packing to a triaxial compression. We find that the shear strength increases with non-convexity. We show that this increase results from the presence of multiple contacts between trimers leading to enhanced frictional interlocking.

}, keywords = {force transmission, Granular Materials, non-convexity, particle shape, texture}, url = {https://hal.archives-ouvertes.fr/hal-00686453}, author = {Baptiste Saint-Cyr and Emilien Az{\'e}ma and Jean-Yves Delenne and Farhang Radja{\"\i} and Philippe Sornay}, editor = {Onate, E and Owen, DRJ} } @article {307, title = {Particle shape dependence in 2D granular media}, journal = {EPL (Europhysics Letters)}, volume = {98}, year = {2012}, month = {Apr-20-2012}, pages = {Article Number: 44008}, abstract = {

Particle shape is a key to the space-filling and strength properties of granular matter. We consider a shape parameter

describing the degree of distortion from a perfectly spherical shape. Encompassing most specific shape characteristics such as elongation, angularity and non-convexity, is a low-order but generic parameter that we used in a numerical benchmark test for a systematic investigation of shape dependence in sheared granular packings composed of particles of different shapes. We find that the shear strength is an increasing function of with nearly the same trend for all shapes, the differences appearing thus to be of second order compared to . We also observe a non-trivial behavior of packing fraction which, for all our simulated shapes, increases with from the random close packing fraction for disks, reaches a peak considerably higher than that for disks, and subsequently declines as is further increased. These findings suggest that a low-order description of particle shape accounts for the principal trends of packing fraction and shear strength. Hence, the effect of second-order shape parameters may be investigated by considering different shapes at the same level of .

}, issn = {0295-5075}, doi = {10.1209/0295-5075/98/44008}, author = {Baptiste Saint-Cyr and Krzysztof Szarf and Charles Voivret and Emilien Az{\'e}ma and Vincent Richefeu and Jean-Yves Delenne and Gael Combe and C{\'e}cile Nouguier-Lehon and Pascal Villard and Philippe Sornay and Marie Chaze and Farhang Radja{\"\i}} } @article {297, title = {Stability, deformation, and variability of granular fills composed of polyhedral particles}, journal = {Physical Review E}, volume = {86}, year = {2012}, month = {Sep-28-2012}, pages = {Article Number: 031308 Part: 1}, abstract = {

By means of extensive contact dynamics simulations, we investigate the mechanical equilibrium and deformation of a granular material composed of irregular polyhedral particles confined between two horizontal frictional planes. We show that, as a consequence of mobilized wall-particle friction forces at the top and bottom boundaries, the transient deformation induced by a constant vertical load is controlled by the aspect ratio (thickness over width) of the packing as well as the stress ratio. The transient deformation declines considerably for increasingly smaller aspect ratios and grows with the stress ratio. From the simulation data for a large number of independent configurations, we find that sample-to-sample fluctuations of the deformation have a broad distribution and they scale with the average deformation. We also analyze the evolution of particle connectivity during settlement and with the applied force. The face-face and edge-face contacts between polyhedral particles concentrate strong force chains with a growing proportion as a function of the applied force.

}, issn = {1539-3755}, doi = {10.1103/PhysRevE.86.031308}, author = {Quezada, Juan Carlos and Breul, Pierre and Saussine, Gilles and Farhang Radja{\"\i}} } @article {58, title = {Structure and properties of nanoscale materials: theory and atomistic computer simulation}, journal = {International Journal of Nanotechnology}, volume = {9}, year = {2012}, month = {2012}, pages = {576{\textendash}604}, abstract = {

We present a review of a few research topics developed within the \"Theory and Atomistic Computer Simulation\" Department at CINaM. The bottom line of the scientific activity is to use up\–to\–date theoretical and computer simulation techniques to address physics and materials science problems, often at the nanometric scale, in close contact with experimental groups. It ranges from the study of the structure and properties of molecular systems for organic electronics to metallic clusters and alloys, magnetic oxides, nuclear fuels and carbon\–based nanostructures. These studies are motivated by fundamental research questions as well as more applied goals including environmental and energy issues, or information technologies. This broad spectrum of activities requires a large range of techniques, from theory and ab initio calculations to semi\–empirical models incorporated in Monte Carlo or molecular dynamics simulations.

}, doi = {10.1504/IJNT.2012.045335 }, author = {Christophe Bichara and Marsal, P and Mottet, C and Roland Jean-Marc Pellenq and F. Ribeiro and Andres Sa{\`u}l and G. Tr{\'e}glia and Weissker, H{\textendash}Ch} } @proceedings {356, title = {Compressive strength of an unsaturated granular material during cementation}, journal = {Symposium on Science and Technology of Powders and Sintered Materials (STPMF 2009)}, volume = {POWDER TECHNOLOGY}, year = {2011}, month = {Mar-25-2011}, pages = {308 - 311}, address = {MAY 25-27 2009 Montpellier, FRANCE}, abstract = {

The cohesive behaviour of unsaturated granular materials is due to the presence of cohesive bonds between grains. These bonds can have various physico-chemical characteristics and may evolve with environmental conditions. We study the case of a granular material partially saturated by an aqueous solution. The bonds are thus initially of capillary type and the mechanical strength is weak. At low relative humidity, the phase change of water involves crystallization of the solute at the contact points between grains, generating thus solid bonds. The mechanical strength of the material is then enhanced. An experimental study of the evolution of the mechanical strength during crystallization of the solute shows clearly the transition from capillary regime to cemented regime. This transition is not correlated with the mass of the crystallized solute, but rather with the residual degree of saturation. This behavior is analyzed here in the light of discrete element simulations. We introduce a local cohesion law that accounts for transition from capillary to cemented bonding. This law is formulated in terms of the degree of crystallization as a result of the evaporation of water at the boundary of the sample. The cohesion of the packing is initially of capillary type. A crystallization front then spreads from the sample boundaries to the center of the sample, and the strength increases as a result. Uniaxial compression allows us to determine the strength at different times. The numerical strength agrees well with the experimental data, and reveals strength enhancement as the solute crystallizes, as well as the transition from capillary to cementation regime.

}, issn = {00325910}, doi = {10.1016/j.powtec.2010.08.021}, author = {Jean-Yves Delenne and Souli{\'e}, Fabien and Moulay Sa{\"\i}d El Youssoufi and Farhang Radja{\"\i}} } @proceedings {349, title = {Creep behaviour of confined layers of polyhedral grains}, journal = {2nd International Conference on Particle-Based Methods - Fundamentals and Applications (Particles)}, volume = {PARTICLE-BASED METHODS II: FUNDAMENTALS AND APPLICATIONS }, year = {2011}, month = {Oct-2011}, pages = {574-583}, address = {OCT 26-28 2011 Barcelona, SPAIN}, abstract = {

By means of contact dynamics simulations, we investigate the creep deformation of a thin granular layer composed of irregular polyhedral particles under the action of a constant vertical overload applied on a horizontal wall on top of the layer. We show that the total deformation induced by the overload increases with the ratio between the vertical and confining horizontal stresses and the aspect ratio of the sample. The effect of the aspect ratio is a consequence of the mobilized wall-grain friction forces at the top and bottom boundaries, that lead to enhanced strength by stabilizing strong force chains at the center of the sample. We also evidence the influence of loading history due to strain-induced fabric change or inertial effects resulting from the instant application of the overload. The topology of the contact network evolves in close correlation with creep. In particular, the face/face contacts between polyhedral particles concentrate largest force chains and their number is an increasing function of creep. A crucial feature of a confined granular system is the statistical variability of the mechanical response that we analyzed for creep deformations by performing a large number of simulations for independent initial configurations. Our data indicate that the distribution of fluctuations with respect to the mean creep falls off exponentially.

}, url = {https://hal.archives-ouvertes.fr/hal-00761094}, author = {Quezada, Juan Carlos and Farhang Radja{\"\i} and Breul, Pierre and Saussine, Gilles}, editor = {Onate, E and Owen, DRJ} } @article {316, title = {From liquid to solid bonding in cohesive granular media}, journal = {Mechanics of Materials}, volume = {43}, year = {2011}, month = {Oct-2011}, pages = {529 - 537}, abstract = {

We study the transition of a granular packing from liquid to solid bonding in the course of drying. The particles are initially wetted by a liquid brine and the cohesion of the packing is ensured by capillary forces, but the crystallization of the solute transforms the liquid bonds into partially cemented bonds. This transition is evidenced experimentally by measuring the compressive strength of the samples at regular intervals of times. Our experimental data reveal three regimes: (1) Up to a critical degree of saturation, no solid bonds are formed and the cohesion remains practically constant; (2) The onset of cementation occurs at the surface and a front spreads towards the center of the sample with a nonlinear increase of the cohesion; (3) All bonds are partially cemented when the cementation front reaches the center of the sample, but the cohesion increases rapidly due to the strengthening of cemented bonds. We introduce a model based on a parametric cohesion law at the bonds and a bond crystallization parameter. This model predicts correctly the phase transition and the relation between microscopic and macroscopic cohesion.

Fig. 1. (a) Photograph of the sample in the process of drying; (b) The press used for{\textellipsis}

Fig. 2. Compressive yield stress σY, normalized by the yield stress σLY due only to{\textellipsis}

Fig. 3. Photograph of a partially dried sample in the second regime

Fig. 4. Schematic representation of the evolution of bridge: from a liquid to a solid{\textellipsis}

Fig. 5. Evolution of the global crystallization index with time; solid line:{\textellipsis}

Fig. 6. The parametric adhesion law

}, issn = {01676636}, doi = {10.1016/j.mechmat.2011.06.008}, author = {Jean-Yves Delenne and Souli{\'e}, Fabien and Moulay Sa{\"\i}d El Youssoufi and Farhang Radja{\"\i}} } @proceedings {353, title = {Onset of Immersed Granular Avalanches by DEM-LBM Approach}, journal = {9th International Workshop on Buifurcation and Degradation in Geomaterials (IWBDG 2011)}, volume = {Springer Series in Geomechanics and Geoengineering - ADVANCES IN BIFURCATION AND DEGRADATION IN GEOMATERIALS}, year = {2011}, month = {May-28-2011}, pages = {109 - 115}, publisher = {Springer Netherlands}, address = {MAY 23-26 2011 Porquerolles, FRANCE}, abstract = {

We present 3D grain-fluid simulations based on the discrete element method interfaced with the lattice Boltzmann method and applied to investigate the initiation of underwater granular flows. We prepare granular beds of 800 spherical grains with different values of the initial solid fraction in a biperiodic rectangular box. In order to trigger an avalanche, the bed is instantaneously tilted to a finite slope angle above the maximum angle of stability. We simulate the dynamics of the transient flow for different solid fractions. In agreement with the experimental work of Iverson (Water Resour Res 36(7):1897\–1910, 2000) and Pailha et\ al. (Phys Fluids 20(11):111701, 2008), we find that the flow onset is controlled by the initial solid fraction.

}, isbn = {978-94-007-1420-5}, issn = {1866-8755}, doi = {10.1007/978-94-007-1421-210.1007/978-94-007-1421-2_14}, author = {Jean-Yves Delenne and Mansouri, M. and Farhang Radja{\"\i} and Moulay Sa{\"\i}d El Youssoufi and Seridi, A.}, editor = {St{\'e}phane Bonelli and Dascalu, Cristian and Fran{\c c}ois Nicot} } @article {315, title = {Rheology of granular materials composed of nonconvex particles}, journal = {Physical Review E}, volume = {84}, year = {2011}, month = {Oct-10-2011}, pages = {Article Number: 041302 Part: 1 }, abstract = {

By means of contact dynamics simulations, we investigate the shear strength and internal structure of granular materials composed of two-dimensional nonconvex aggregates. We find that the packing fraction first grows as the nonconvexity is increased but declines at higher nonconvexity. This unmonotonic dependence reflects the competing effects of pore size reduction between convex borders of aggregates and gain in porosity at the nonconvex borders that are captured in a simple model fitting nicely the simulation data both in the isotropic and sheared packings. On the other hand, the internal angle of friction increases linearly with nonconvexity and saturates to a value independent of nonconvexity. We show that fabric anisotropy, force anisotropy, and friction mobilization, all enhanced by multiple contacts between aggregates, govern the observed increase of shear strength and its saturation with increasing nonconvexity. The main effect of interlocking is to dislocate frictional dissipation from the locked double and triple contacts between aggregates to the simple contacts between clusters of aggregates. This self-organization of particle motions allows the packing to keep a constant shear strength at high nonconvexity.

Figure

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}, issn = {1539-3755}, doi = {10.1103/PhysRevE.84.041302}, author = {Baptiste Saint-Cyr and Jean-Yves Delenne and Charles Voivret and Farhang Radja{\"\i} and Philippe Sornay} } @proceedings {364, title = {Springer Series in Geomechanics and Geoengineering Multiscale and Multiphysics Processes in Geomechanics SIMULATION OF HYDRATION AND ELASTIC PROPERTIES OF MONTMORILLONITE USING MOLECULAR DYNAMICS}, journal = {International Workshop on Multiscale and Multiphysics Processes in Geomechanics}, volume = {Springer Series in Geomechanics and Geoengineering}, year = {2011}, month = {2011}, pages = {105 - 108}, publisher = {Springer Berlin Heidelberg}, address = {JUN 23-25 2010 Stanford Univ, Stanford, CA}, abstract = {

This article describes molecular-level simulations of the adsorption isotherm and elastic properties for a Wyoming Na-montmorillonite using the General Utility Lattice Program. The selected clay mineral includes isomorphous substitutions in both the silica tetrahedral and octahedral gibbsite sheets. The resulting negative charges are balanced by Na+ cations. The authors have investigated the importance of different interatomic potentials in understanding the adsorption of water molecules (at ambient temperature, 300K). A unique combination of NPT and Grand Canonical ensemble simulations using Core\–Shell potential shows intra-layer adsorption, while the same approach based on empirical CLAYFF potential produces only interlayer water adsorption. There is a correspondingly large difference in the theoretical elastic modulus normal to the clay sheets using the two different sets of force potentials. This article discusses the underlying reasons for these differences and reviews the experimental evidence supporting intra-layer water absorption in montmorillonite.

}, isbn = {978-3-642-19629-4}, issn = {1866-8755}, doi = {10.1007/978-3-642-19630-0_27}, author = {Roland Jean-Marc Pellenq and Andrew J. Whittle and Ebrahimi, Davoud}, editor = {Borja, Ronaldo I. and Wu, Wei} } @proceedings {347, title = {STRENGTH HOMOGENIZATION FOR COHESIVE-FRICTIONAL COMPOSITES: A LINEAR COMPARISON COMPOSITE APPROACH}, journal = {International Workshop on Multiscale and Multiphysics Processes in Geomechanics}, volume = {Springer Series in Geomechanics and Geoengineering}, year = {2011}, month = {Jan-2011}, pages = {57 - 60}, publisher = {Springer Berlin Heidelberg}, address = {JUN 23-25 2010 Stanford Univ, Stanford, CA}, abstract = {

In this work, we address the homogenization of cohesive-frictional strength properties of composite materials through the application of the Linear Comparison Composite (LCC) theory. The LCC methodology is implemented in a multiscale strength model relevant to geomaterials with heterogeneities associated with pore spaces and rigid-like grains. The proposed micromechanics solutions offer quantitative assessments of the effects of grain-scale properties and microstructure on the overall strength of the composite material Keywordscohesive-frictional materials\–linear comparison composite

}, isbn = {978-3-642-19629-4}, issn = {1866-8755}, doi = {10.1007/978-3-642-19630-0_15}, author = {J. Alberto Ortega and Gathier, Benjamin and Franz-Josef Ulm}, editor = {Wu, Wei and Borja, Ronaldo I.} } @article {293, title = {Empirical force fields for complex hydrated calcio-silicate layered materials}, journal = {Phys. Chem. Chem. Phys.}, volume = {13}, year = {2010}, month = {Nov-10-2010}, pages = {1002 - 1011}, abstract = {

The use of empirical force fields is now a standard approach in predicting the properties of hydrated oxides which are omnipresent in both natural and engineering applications. Transferability of force fields to analogous hydrated oxides without rigorous investigations may result in misleading property predictions. Herein, we focus on two common empirical force fields, the simple point charge ClayFF potential and the core-shell potential to study tobermorite minerals, the most prominent family of Calcium-Silicate-Hydrates that are complex hydrated oxides. We benchmark the predictive capabilities of these force fields against first principles results. While the structural information seem to be in close agreement with DFT results, we find that for higher order properties such as elastic constants, the core-shell potential quantitatively improves upon the simple point charge model, and shows a larger degree of transferability to complex materials. In return, to remedy the deficiencies of the simple point charge potential for hydrated calcio-silicates, we suggest using both structural data and elasticity data for potential calibration, a new force field potential, CSH-FF. This re-parameterized version of ClayFF is then applied to simulating an atomistic model of cement (Pellenq et al., PNAS, 2009). We demonstrate that this force field improves the predictive capabilities of ClayFF, being considerably less computational intensive than the core-shell model.

}, issn = {1463-9076}, doi = {10.1039/C0CP00516A}, author = {Rouzbeh Shahsavari and Roland Jean-Marc Pellenq and Franz-Josef Ulm} }