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(317) Production(s) de KOB W.
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Granular materials flow like complex fluids 
Auteur(s): Kou Binquan, Cao Yixin, Li Jindong, Xia Chengjie, Li Zhifeng, Dong Haipeng, Zhang Ang, Zhang Jie, Kob W. , Wang Yujie
(Article) Publié:
Nature, vol. 551 p.360 (2017)
Texte intégral en Openaccess : 
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Methods to locate saddle points in complex landscapes
Auteur(s): Bonfanti S., Kob W.
(Article) Publié:
The Journal Of Chemical Physics, vol. 147 p.204104 (2017)
Texte intégral en Openaccess :
Ref HAL: hal-01656760_v1
DOI: 10.1063/1.5012271
WoS: 000416842200006
Exporter : BibTex | endNote
4 Citations
Résumé: .We present a class of simple algorithms that allows to find the reaction path in systems with a complexpotential energy landscape. The approach does not need any knowledge on the product state and doesnot require the calculation of any second derivatives. The underlying idea is to use two nearby points inconfiguration space to locate the path of slowest ascent. By introducing a weak noise term, the algorithmis able to find even low-lying saddle points that are not reachable by means of a slowest ascent path. Sincethe algorithm makes only use of the value of the potential and its gradient, the computational effort to findsaddles is linear in the number of degrees of freedom, if the potential is short-ranged. We test the performanceof the algorithm for two potential energy landscapes. For the M¨uller-Brown surface we find that the algorithmalways finds the correct saddle point. For the modified M¨uller-Brown surface, which has a saddle point thatis not reachable by means of a slowest ascent path, the algorithm is still able to find this saddle point withhigh probability
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Hard X-rays as pump and probe of atomic motion in oxide glasses
Auteur(s): Ruta Beatrice, Zotone F, Chushkin Y., Baldi G., Pintori G., Monaco G., Ruffle B., Kob W.
(Article) Publié:
Scientific Reports, vol. 7 p.3962 (2017)
Texte intégral en Openaccess : 
Ref HAL: hal-01548255_v1
DOI: 10.1038/s41598-017-04271-x
Exporter : BibTex | endNote
Résumé: Nowadays powerful X-ray sources like synchrotrons and free-electron lasers are considered as ultimate tools for probing microscopic properties in materials. However, the correct interpretation of such experiments requires a good understanding on how the beam affects the properties of the sample, knowledge that is currently lacking for intense X-rays. Here we use X-ray photon correlation spectroscopy to probe static and dynamic properties of oxide and metallic glasses. We find that although the structure does not depend on the flux, strong fluxes do induce a non-trivial microscopic motion in oxide glasses, whereas no such dependence is found for metallic glasses. These results show that high fluxes can alter dynamical properties in hard materials, an effect that needs to be considered in the analysis of X-ray data but which also gives novel possibilities to study materials properties since the beam can not only be used to probe the dynamics but also to pump it.
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Origin of Noncubic Scaling Law in Disordered Granular Packing
Auteur(s): Xia Chengjie, Li Jindong, Kou Binquan, Cao Yixin, Li Zhifeng, Xiao Xianghui, Fu Yanan, Xiao Tiqiao, Hong Liang, Zhang Jie, Kob W., Wang Yujie
(Article) Publié:
Physical Review Letters, vol. 118 p.238002 (2017)
Texte intégral en Openaccess :
Ref HAL: hal-01536101_v1
DOI: 10.1103/PhysRevLett.118.238002
WoS: 000402979400019
Exporter : BibTex | endNote
6 Citations
Résumé: Recent diffraction experiments on metallic glasses have unveiled an unexpected non-cubic scaling 14 law between density and average interatomic distance, which lead to the speculations on the presence of 15 fractal glass order. Using X-ray tomography we identify here a similar non-cubic scaling law in 16 disordered granular packing of spherical particles. We find that the scaling law is directly related to the 17 contact neighbors within first nearest neighbor shell, and therefore is closely connected to the 18 phenomenon of jamming. The seemingly universal scaling exponent around 2.5 arises due to the isostatic 19 condition with contact number around 6, and we argue that the exponent should not be universal. .
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