@article {525, title = {A reaction model for cement solidification: Evolving the C{\textendash}S{\textendash}H packing density at the micrometer-scale}, journal = {Journal of the Mechanics and Physics of Solids}, volume = {118}, year = {2018}, month = {Sep-2018}, pages = {58 - 73}, abstract = {

Cement paste is a multiphase material of complex chemistry, of which 60\% by volume is typically composed of calcium\–silicate\–hydrates (C\–S\–H), the phase that lends the material its strength and stiffness. Moreover, it has been shown that the C\–S\–H phase is a dispersion of nanometer-sized particles that are characterized by an attractive\–repulsive potential and densify in course of the hydration reaction. Herein, we model the nucleation and growth of the nanoparticles as a continuous density field subject to a reaction equation. Using this phase-field approach, we aim to reduce the parameter space present in similar hydration models and create a vehicle to upscale mechanical information from the nanometer-scale to the micrometer-scale. Despite the apparent simplification of the physics at play, we readily reproduce the cement paste reaction kinetics and microtexture\—functions of temperature, coarseness of the calcium\–silicate source particles, and initial water-to-cement ratio\—, and vet them against experimental observations. Presenting results for two-dimensional simulations, we achieve excellent agreement with measurements of hydration heat curves, pore-chord-length and solid-chord-length density functions, distributions of low- and high-density C\–S\–H products, and elasticity.

Illustration of the dissolution and nucleation and growth processes driving{\textellipsis}

A comparison between the mean coordination number ⟨z⟩ of the particles modeled{\textellipsis}

Gibb{\textquoteright}s free energy that interpolates between the source phase ψ=1 and open pore{\textellipsis}

Gibb{\textquoteright}s energy of reaction and (b) reaction rate for nanoparticle{\textellipsis}

Evolution of the mean packing fraction of C{\textendash}S{\textendash}H (〈ϕ〉V'; opaque) and the{\textellipsis}

Diagram of the volume fractions of hydrating cement paste

}, issn = {00225096}, doi = {10.1016/j.jmps.2018.05.010}, url = {https://www-sciencedirect-com.libproxy.mit.edu/science/article/pii/S0022509617308876}, author = {Petersen, Thomas and Valdenaire, Pierre-Louis and Roland Jean-Marc Pellenq and Franz-Josef Ulm} } @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.

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}, 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 {589, title = {Role of Interfaces in Elasticity and Failure of Clay{\textendash}Organic Nanocomposites: Toughening upon Interface Weakening?}, journal = {Langmuir}, volume = {33}, year = {2017}, month = {Oct-24-2017}, pages = {11457 - 11466}, abstract = {

Synthetic organic-inorganic composites constitute a new class of engineering materials finding applications in an increasing range of fields. The interface between the constituting phases plays a pivotal role in the enhancement of mechanical properties. In exfoliated clay-organic nanocomposites, individual, high aspect ratio clay sheets are dispersed in the organic matrix providing large interfaces and hence efficient stress transfer. In this study, we aim at elucidating molecular-scale reinforcing mechanisms in a series of model clay-organic composite systems by means of reactive molecular simulations. In our models, two possible locations of failure initiation are present: one is the interlayer space of the clay platelet, and the other one is the clay-organic interface. We systematically modify the cohesiveness of the interface and assess how the failure mechanism changes when the different model composites are subjected to a tensile test. Besides a change in the failure mechanism, an increase in the released energy at the interface (meaning an increased overall toughness) are observed upon weakening the interface by bond removal. We propose a theoretical analysis of these results by considering a cohesive law that captures the effect of the interface on the composite mechanics. We suggest an atomistic interpretation of this cohesive law, in particular, how it relates to the degree of bonding at the interface. In a broader perspective, this work sheds light on the importance of the orthogonal behavior of interfaces to nanocomposites.

https://pubs-acs-org.libproxy.mit.edu/appl/literatum/publisher/achs/journals/content/langd5/2017/langd5.2017.33.issue-42/acs.langmuir.7b01071/20171025/images/medium/la-2017-01071k_0008.gif

}, issn = {0743-7463}, doi = {10.1021/acs.langmuir.7b01071}, url = {http://pubs.acs.org/doi/10.1021/acs.langmuir.7b01071}, author = {Gy{\"o}rgy Hantal and Brochard, Laurent and Roland Jean-Marc Pellenq and Franz-Josef Ulm and Benoit A. Coasne} } @article {324, title = {Radial fracture in a three-phase composite: Application to wellbore cement liners at early ages}, journal = {Engineering Fracture Mechanics}, volume = {154}, year = {2016}, month = {Mar-2016}, pages = {272 - 287}, abstract = {

Little understanding exists between the early-age stress developments in a wellbore cement sheath and its risk of impairment. During hydration, the cement morphology and pore-pressure changes induce eigenstresses in the solid and pore volumes. Utilizing these stresses as the driving mechanism of fracture, this paper formalizes the inspection of a radial crack in an elastic cement sheath constrained by an inner steel casing and an outer rock formation. The solution is constructed in the framework of analytic function theory and seeks the Green\’s function for an edge dislocation in the intermediate cement phase. A dislocation pile-up along the line of fracture constructs a singular integral equation for the crack opening displacement derivative, from which the energy release rate is readily deduced.

Under the uniform development of eigenstresses, the stiffness ratios of steel-to-cement and rock-to-cement generally predict the crack to initiate along the steel-cement interface. Here, the impacts of (i) a rigid bond and (ii) a sliding interface with no shear are assessed. This leads to the primary result of the paper: the potential for radial fracture is substantially mitigated by ensuring the shear connection between the steel casing and the cement sheath.

Diagram of a wellbore cement system with a radial crack emanating from SC.

Simulated evolution of the shear modulus G, bulk modulus K, and Poisson{\textquoteright}s ratio ...

Simulated evolution of the effective hoop stress Σθθ=σθθ+p along SC (blue) and ...

Continuation of the annular region of the cement domain across SC and RC.

}, issn = {00137944}, doi = {10.1016/j.engfracmech.2016.01.005}, author = {Thomas Alexander Petersen 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 {320, title = {Risk of Pavement Fracture due to Eigenstresses at Early Ages and Beyond}, journal = {Journal of Engineering Mechanics}, volume = {142}, year = {2016}, month = {Dec-2016}, pages = {Article Number: 04016105 }, abstract = {

Tensile cracks significantly affect the durability of concrete pavements, leading to an increase in the costs of maintenance and rehabilitation. A model is developed that relates thermal, chemical, and hygral evolutions at small scales due to different distress mechanisms to the risk of fracture at the structural scale. The method is based on application of linear elastic fracture mechanics (LEFM) to eigenstresses that develop in infinite- and finite-length beams on an elastic foundation that represents the subgrade. Axial and bending contributions to the energy release rate are determined for a worst-case scenario of an entirely cracked pavement section in functions of material properties, structural dimensions, and eigenstress forces and moments. By way of example, the model is used to study the risk of fracture of concrete pavements due to two different mechanisms: (1)\ autogeneous shrinkage at early ages of placing the concrete and (2)\ thermal cycles at the short term and long term after a temperature change. In addition, scaling relationships are developed that provide insight into the improvement of different structural and material properties for minimizing the risk of fracture.

}, issn = {0733-9399}, doi = {10.1061/(ASCE)EM.1943-7889.0001167}, author = {Arghavan Louhghalam and Franz-Josef Ulm} } @article {160, title = {Reversing the critical Casimir force by shape deformation}, journal = {Physics Letters B}, volume = {743}, year = {2015}, month = {Apr-09-2015}, pages = {138 - 142}, abstract = {

The exact critical Casimir force between periodically deformed boundaries of a 2D semi-infinite strip is obtained for conformally invariant classical systems. Only two parameters (conformal charge and scaling dimension of a boundary changing operator), along withthe solution of an electrostatic problem, determine the Casimir force, rendering the theory practically applicable to any shape and arrangement. The attraction between any two mirror symmetric objects follows directly from our general result. The possibility of purely shape induced reversal of the force, as well as occurrence of stable equilibrium points, is demonstrated for certain conformally invariant models, including the tricritical Ising model.

}, issn = {03702693}, doi = {10.1016/j.physletb.2015.02.038}, author = {Bimonte, Giuseppe and Emig, Thorsten and Kardar, Mehran} } @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 {131, title = {Rigidity transition in materials: hardness is driven by weak atomic constraints.}, journal = {Phys Rev Lett}, volume = {114}, year = {2015}, month = {Mar-23-2015}, pages = {Article Number: 125502}, abstract = {

Understanding the composition dependence of the hardness in materials is of primary importance for infrastructures and handled devices. Stimulated by the need for stronger protective screens, topological constraint theory has recently been used to predict the hardness in glasses. Herein, we report that the concept of rigidity transition can be extended to a broader range of materials than just glass. We show that hardness depends linearly on the number of angular constraints, which, compared to radial interactions, constitute the weaker ones acting between the atoms. This leads to a predictive model for hardness, generally applicable to any crystalline or glassy material.

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}, issn = {1079-7114}, doi = {10.1103/PhysRevLett.114.125502}, author = {Mathieu Bauchy and Mohammad Javad Abdolhosseini Qomi and Christophe Bichara and Franz-Josef Ulm and Roland Jean-Marc Pellenq} } @article {147, title = {Roughness-Induced Vehicle Energy Dissipation: Statistical Analysis and Scaling}, journal = {Journal of Engineering Mechanics}, volume = {141}, year = {2015}, month = {Nov-2015}, pages = {Number: 04015046 }, abstract = {

The energy dissipated in a vehicle suspension system due to road roughness affects rolling resistance and the resulting fuel consumption and greenhouse gas emission. The key parameters driving this dissipation mechanism are identified via dimensional analysis. A mechanistic model is proposed that relates vehicle dynamic properties and road roughness statistics to vehicle dissipated energy and thus fuel consumption. A scaling relationship between the dissipated energy and the most commonly used road roughness index, the International Roughness Index (IRI), is also established. It is shown that the dissipated energy scales with IRI squared and scaling of dissipation with vehicle speed V depends on road waviness number w in the form of Vw\−2. The effect of marginal probability distribution of the road roughness profile on dissipated energy is examined. It is shown that although the marginal distribution of the road profile does not affect the identified scaling relationships, the multiplicative factor in these relationships does change from one distribution to another. As an example of practical application, the model is calibrated with the empirical HDM-4 model for different vehicle classes.

}, issn = {0733-9399}, doi = {10.1061/(ASCE)EM.1943-7889.0000944}, author = {Arghavan Louhghalam and Tootkaboni, Mazdak and Franz-Josef Ulm} } @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} } @article {149, title = {Roughness-induced Pavement-Vehicle Interactions Key Parameters and Impact on Vehicle Fuel Consumption}, journal = {Transportation Research Record: Journal of the Transportation Research Board}, volume = {2525}, year = {2014}, month = {Dec-30-2014}, pages = {62 - 70}, abstract = {

Pavement roughness affects rolling resistance and thus vehicle fuel consumption. When a vehicle travels at constant speed on an uneven road surface, the mechanical work dissipated in the vehicle\’s suspension system is compensated by vehicle engine power and results in excess fuel consumption. This dissipation depends on both road roughness and vehicle dynamic characteristics. This paper proposes, calibrates, and implements a mechanistic model for roughness-induced dissipation. The distinguishing feature of the model is its combination of a thermodynamic quantity (energy dissipation) with results from random vibration theory to identify the governing parameters that drive the excess fuel consumption caused by pavement roughness, namely, the international roughness index (IRI) and the waviness number, w (a power spectral density parameter). It is shown through sensitivity analysis that the sensitivity of model output, that is, excess fuel consumption, to the waviness number is significant and comparable to that of IRI. Thus, introducing the waviness number as a second roughness index, in addition to IRI, allows a more accurate quantification of the impact of surface characteristics on vehicle fuel consumption and the corresponding greenhouse gas emissions. This aspect is illustrated by application of the roughness\–fuel consumption model to two road profiles extracted from FHWA\’s Long-Term Pavement Performance database.

}, issn = {0361-1981}, doi = {10.3141/2525-07}, author = {Arghavan Louhghalam and Mehdi Akbarian and Franz-Josef Ulm} } @article {219, title = {Reactive elastomeric composites: When rubber meets cement}, journal = {Composites Science and Technology}, volume = {75}, year = {2013}, month = {Feb-11-2013}, pages = {77 - 83}, abstract = {

This paper describes a novel reactive composite material comprised of hydrogenated nitrile butadiene rubber (HNBR) compounded with slag cement. The composite initially looks and behaves like rubber, but when exposed to water it simultaneously swells and stiffens due to hydration of the cement component. The material eventually reaches a stiffness that is intermediate between that of HNBR and hydrated cement, while maintaining a relatively large ductility that is more characteristic of rubber. This behavior, which is ideal for sealing applications, differentiates this material from conventional swellable materials that become less stiff upon swelling. The development of this new type of material was motivated by the requirements of oilfield zonal isolation, where alternatives to cement are needed for some challenging sealing applications. A mechanism for the swelling and stiffening of the reactive composite is proposed: water diffuses into the HNBR matrix and is converted to bound water through hydration reactions with the cement, causing the effective solid filler content of the composite to increase. A model is proposed that treats the composite as a cellular solid with a continuous filler phase (hydrated cement). This model is able to reproduce the observed increase in the elastic modulus with time during exposure to water.

Elastic modulus ratio (current/initial) as a function of swelling, for HNBR ...

Kinetics of swelling of all three materials during approximately 1month of ...

Evolution of the elastic modulus of all three materials during approximately ...

Tensile stress{\textendash}strain curves for HNBR-cement (61{\textendash}39\% by volume, pre-exposure) ...

Schematic of the hydration process occurring inside the HNBR-cement material, ...

SEM images of HNBR-cement material before (left) and after (right) hydration. It ...

}, issn = {02663538}, doi = {10.1016/j.compscitech.2012.11.012}, author = {Robisson, Agathe and Sudeep Maheshwar and Musso, Simone and Jeffrey J. Thomas and Auzerais, Francois M. and Han, Dingzhi and Qu, Meng and Franz-Josef Ulm} } @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.

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}, doi = {10.1103/PhysRevB.88.235438}, author = {Robinson Cortes-Huerto and T. Sondon and Andres Sa{\`u}l} } @article {287, title = {Reply to {\textquotedblleft}Comment on {\textquoteleft}Determination of the bulk melting temperature of nickel using Monte Carlo simulations: Inaccuracy of extrapolation from cluster melting temperatures{\textquoteright} {\textquotedblright}}, journal = {Physical Review B}, volume = {84}, year = {2011}, month = {Sep-26-2011}, pages = { Article Number: 096103}, abstract = {

The thermodynamic integration (TI) method for determining the melting temperature has to be performed with great care to ensure accuracy. Since the slopes of the Gibbs free energy curves as a function of temperature (or pressure) are usually rather close, small shifts in the free energy curves can lead to a large change in the calculated melting temperature. In this Reply to a Comment by Harvey and Gheribi [ Phys. Rev. B 84 096102 (2011)] on our paper [ Phys. Rev. B 81 064112 (2010)], we show that the error in the calculated melting temperature of nickel induced by some technical imperfections in our application of the TI method, as noticed and described in the Comment, is small compared to the error bar given in our paper. We also clarify supposed doubts about the accuracy of the TI method based on Johnson\&$\#$39;s free energy expression and parametrization [ Johnson et al. Mol. Phys. 78 591 (1993)] of the Lennard-Jones fluid.

}, issn = {1098-0121}, doi = {10.1103/PhysRevB.84.096103}, author = {Los, J. H. and Roland Jean-Marc Pellenq} } @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.

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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} }