Accueil >
Production scientifique
Physique Statistique
(27) Production(s) de l'année 2021
|
|
Self-Induced Heterogeneity in Deeply Supercooled Liquids
Auteur(s): Berthier L.
(Article) Publié:
Physical Review Letters, vol. 127 p.088002 (2021)
Texte intégral en Openaccess :
Ref HAL: hal-03355608_v1
DOI: 10.1103/PhysRevLett.127.088002
WoS: WOS:000686914500008
Exporter : BibTex | endNote
Résumé: A theoretical treatment of deeply supercooled liquids is difficult because their properties emerge from spatial inhomogeneities that are self-induced, transient, and nanoscopic. I use computer simulations to analyse self-induced static and dynamic heterogeneity in equilibrium systems approaching the experimental glass transition. I characterise the broad sample-to-sample fluctuations of salient dynamic and thermodynamic properties in elementary mesoscopic systems. Findings regarding local lifetimes and distributions of dynamic heterogeneity are in excellent agreement with recent single molecule studies. Surprisingly broad thermodynamic fluctuations are also found, which correlate well with dynamics fluctuations, thus providing a local test of the thermodynamic origin of slow dynamics.
|
|
|
New interaction potentials for alkaline earth silicate and borate glasses
Auteur(s): Shih Yueh-Ting, Sundararaman Siddharth, Ispas S., Huang Liping
(Article) Publié:
Journal Of Non-Crystalline Solids, vol. 565 p.120853 (2021)
Texte intégral en Openaccess :
Ref HAL: hal-03323812_v1
DOI: 10.1016/j.jnoncrysol.2021.120853
WoS: WOS:000663076400005
Exporter : BibTex | endNote
Résumé: New interaction potentials were developed for molecular dynamics simulations to study the role of Mg and Ca in modifying the structure and properties of alkaline earth silicates and borates. Competition between the depolymerization of the silica network and the formation of new bonds between oxygen atoms and modifiers leads to the enhancement of the elastic moduli with increasing modifier content in alkaline earth silicate glasses. Compared with calcium silicate, the higher elastic moduli of magnesium silicate result from a higher connectivity of the overall glass network due to the incorporation of fourfold coordinated magnesium and a more rigid connection between oxygen atoms and modifiers. In contrast to the silicates, the effect of modifier on the elastic moduli of alkaline earth borates is dominated by the formation of fourfold coordinated boron (N4). Calcium borate with higher N4 shows a more rigid network structure and higher elastic moduli.
|
|
|
Experimental Test of the Edwards Volume Ensemble of Tapped Granular Packings
Auteur(s): Yuan Ye, Xing Yi, Zheng Jie, Li Zhifeng, Yuan Houfei, Zhang Shuyang, Zeng Zhikun, Xia Chengjie, Tong Hua, Kob W., Zhang Jie, Wang Yujie
(Article) Publié:
Physical Review Letters, vol. 127 p.018002 (2021)
Texte intégral en Openaccess :
Ref HAL: hal-03287898_v1
PMID 34270306
DOI: 10.1103/PhysRevLett.127.018002
Exporter : BibTex | endNote
Résumé: Using x-ray tomography, we experimentally investigate granular packings subject to mechanical tapping for three types of beads with different friction coefficients. We validate the Edwards volume ensemble in these three-dimensional granular systems and establish a granular version of thermodynamic zeroth law. Within the Edwards framework, we also explicitly clarify how friction influences granular statistical mechanics by modifying the density of states, which allows us to determine the entropy as a function of packing fraction and friction. Additionally, we obtain a granular jamming phase diagram based on geometric coordination number and packing fraction.
|
|
|
Effect of Chain Polydispersity on the Elasticity of Disordered Polymer Networks
Auteur(s): Sorichetti V., Ninarello A. S., Ruiz-Franco José, Hugouvieux Virginie, Kob W., Zaccarelli Emanuela, Rovigatti Lorenzo
(Article) Publié:
Macromolecules, vol. 54 p.3769 - 3779 (2021)
Texte intégral en Openaccess :
Ref HAL: hal-03234741_v1
DOI: 10.1021/acs.macromol.1c00176
Exporter : BibTex | endNote
Résumé: Due to their unique structural and mechanical properties, randomly cross-linked polymer networks play an important role in many different fields, ranging from cellular biology to industrial processes. In order to elucidate how these properties are controlled by the physical details of the network (e.g., chain-length and end-to-end distributions), we generate disordered phantom networks with different cross-linker concentrations C and initial densities ρ init and evaluate their elastic properties. We find that the shear modulus computed at the same strand concentration for networks with the same C, which determines the number of chains and the chain-length distribution, depends strongly on the preparation protocol of the network, here controlled by ρ init. We rationalize this dependence by employing a generic stress−strain relation for polymer networks that does not rely on the specific form of the polymer end-to-end distance distribution. We find that the shear modulus of the networks is a nonmonotonic function of the density of elastically active strands, and that this behavior has a purely entropic origin. Our results show that if short chains are abundant, as it is always the case for randomly cross-linked polymer networks, the knowledge of the exact chain conformation distribution is essential for correctly predicting the elastic properties. Finally, we apply our theoretical approach to literature experimental data, qualitatively confirming our interpretations.
|
|
|
First-principles study of the surface of silica and sodium silicate glasses
Auteur(s): Zhang Z., Kob W., Ispas S.
(Article) Publié:
Physical Review B, vol. 103 p.184201 (2021)
Texte intégral en Openaccess :
Ref HAL: hal-03223925_v1
DOI: 10.1103/PhysRevB.103.184201
Exporter : BibTex | endNote
Résumé: We use ab initio molecular dynamics simulations to investigate the properties of the dry surface of pure silicaand sodium silicate glasses. The surface layers are defined based on the atomic distributions along the direction(z direction) perpendicular to the surfaces. We show that these surfaces have a higher concentration of danglingbonds as well as two-membered (2M) rings than the bulk samples. Increasing the concentration of Na 2 O reducesthe proportion of structural defects. From the vibrational density of states, one concludes that 2M rings have aunique vibrational signature at a frequency ≈850 cm −1 , compatible with experimental findings. We also findthat, due to the presence of surfaces, the atomic vibration in the z direction is softer than for the two otherdirections. The electronic density of states shows clearly the differences between the surface and interior and wecan attribute these to specific structural units. Finally, the analysis of the electron localization function allows toget insight on the influence of local structure and the presence of Na on the nature of chemical bonding in theglasses.
|
|
|
Miles' mechanism for generating surface water waves by wind, in finite water depth and subject to constant vorticity flow
Auteur(s): Kern N., Chaubet C., Kraenkel Roberto, Manna M.
(Article) Publié:
Coastal Engineering, vol. 170 p.103976 (2021)
Texte intégral en Openaccess :
Ref HAL: hal-03184640_v1
Ref Arxiv: 2102.13214
DOI: 10.1016/j.coastaleng.2021.103976
WoS: WOS:000702874300002
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
Résumé: The Miles theory of wave amplification by wind is extended to the case of finite depth h and a shear flow with (constant) vorticity {\Omega}. Vorticity is characterised through the non-dimensional parameter {\nu} = {\Omega} U_1 /g, where g the gravitational acceleration, U_1 a characteristic wind velocity and k the wavenumber. The notion of 'wave age' is generalised to account for the effect of vorticity. Several widely used growth rates are derived analytically from the dispersion relation of the wind/water interface, and their dependence on both water depth and vorticity is derived and discussed. Vorticity is seen to shift the maximum wave age, similar to what was previously known to be the effect of water depth. At the same time, a novel effect arises and the growth coefficients, at identical wave age and depth, are shown to experience a net increase or decrease according to the shear gradient in the water flow.
|