Ref HAL: hal-02947316_v1
DOI: 10.1039/d0sm01024c
Exporter : BibTex | endNote

Résumé:

The generating functions of degeneracies of D4-D2-D0 black holes in Type II string compactifications on Calabi-Yau threefolds are examples of (higher depth) mock modular forms. I'll explain how S-duality can be used to derive an explicit form for their modular completions, which becomes particularly simple in the presence of a refinement. This result turns out to have many applications going beyond the original context. In particular, I'll show that it can be used i) to reproduce and generalize in an easy way the known results on modular properties of the generating functions of BPS dyons in N=4 string compactifications; ii) to find Vafa-Witten invariants of arbitrary(!) rank on CP^2, Hirzebruch and del Pezzo surfaces; iii) to obtain holomorphic anomaly equations for BPS partition functions; iv) to reveal a non-commutative structure induced by the refinement on the moduli space of compactified theory.

Ref HAL: hal-02942375_v1
Ref Arxiv: 2006.09725
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
Résumé:

We review the field of the glass transition, glassy dynamics and aging from a statistical mechanics perspective. We give a brief introduction to the subject and explain the main phenomenology encountered in glassy systems, with a particular emphasis on spatially heterogeneous dynamics. We review the main theoretical approaches currently available to account for these glassy phenomena, including recent developments regarding mean-field theory of liquids and glasses, novel computational tools, and connections to the jamming transition. Finally, the physics of aging and off-equilibrium dynamics exhibited by glassy materials is discussed.

Commentaires: 50 pages, 24 figs. This is an updated version of a chapter initially written in 2009 for the Encyclopedia of Complexity and Systems Science (Springer)

Ref HAL: hal-02941539_v1
DOI: 10.1103/PhysRevFluids.5.093601
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Résumé:

Numerical simulations of a drop crossing a plane liquid-liquid interface in a centrifugal field have been performed by using the Level-Set method. The objective is to characterize the hydrodynamical parameters controlling the coating volume of the droplet, which results from the rupture of the liquid column of lighter phase entrained by the droplet during the crossing of the interface in the tailing regime. The numerical method has been first validated in two-phase flow simulations of a drop rising in a stagnant liquid, then in three-phase flow configurations to reproduce the theoretical critical condition for a drop to cross an interface in static conditions (without initial velocity). Then, in inertial conditions, extensive simulations of crossing droplets have been performed in a wide range of flow parameters and phase properties, for two types of drop: solid-like droplets (mimicking rigid particles) and deformable drops. The crossing criteria is found to remain very close to that given by the theory in static conditions, either for a spherical or a deformed droplet. For each studied case, the crossing time, the maximum length of the column of liquid pulled by the droplet and the volume encapsulating the drop after crossing have been computed and scaled as a function of an inertia parameter, which is the ratio F* between the inertial stresses pushing on the interface, defined from the minimum drop velocity reached during crossing as characteristic velocity, and the opposite stress pulling back the entrained column towards the interface. The maximal column length increases with F* (when rescaled by the minimal inertial required for crossing) under two distinct growth rates according to the flow regime in the column. For solid-like drops, the final coating volume is a unique function of F*, and grows with F* at large inertia. In the case of deformable droplets, the coating volume evolution can also be well predicted by F* but corrected by the drop-to-film viscosity ratio, which strongly affects the drainage rate of the film along the drop surface during the encapsulation process.

DOI: 10.1063/5.0022261
Résumé:

In this work, we have predicted a giant thermal magnetoresistance for the thermal photon transport based on the tunable magnetoplasmon of graphene. By applying an external magnetic field, we find that the heat flux can be modulated by approximately three orders of magnitude. Accordingly, both negative and giant relative thermal magnetoresistance ratios are achieved for magnetic fields with a maximum strength of 4 Tesla. This effect is mainly caused by the suppression and enhancement of scattering interactions mediated by a graphene magnetoplasmon. Specifically, it has never been achieved before for nanoparticles, which have no response to magnetic fields. The effect is remarkable at these reasonable strengths of fields and, thus, has considerable significance for real-life applications. It is also expected to enable technological advances for thermal measurement-based magnetic sensors and magnetically thermal management.

Ref Arxiv: 2005.06520
DOI: 10.1063/5.0015227
Ref. & Cit.: NASA ADS
Résumé:

It has recently become possible to prepare ultrastable glassy materials characterised by structural relaxation times which vastly exceed the duration of any feasible experiment. Similarly, new algorithms have led to the production of ultrastable computer glasses. Is it possible to obtain a reliable estimate of a structural relaxation time that is too long to be measured? We review, organise, and critically discuss various methods to estimate very long relaxation times. We also perform computer simulations of three dimensional ultrastable hard spheres glasses to test and quantitatively compare some of these methods for a single model system. The various estimation methods disagree significantly and it is not yet clear how to accurately estimate extremely long relaxation times.

Commentaires: 17 pages, 10 figures; version accepted for publication at J. Chem. Phys. Réf Journal: J. Chem. Phys. 153, 044501 (2020)

PMID 32909772
Ref Arxiv: 2002.01317
DOI: 10.1103/PhysRevLett.125.085505
WoS: 000561724800007
Ref. & Cit.: NASA ADS
Résumé:

We devise a generic strategy and simple numerical models for multi-component metallic glasses for which the swap Monte Carlo algorithm can produce highly stable equilibrium configurations equivalent to experimental systems cooled more than $10^7$ times slower than in conventional simulations. This paves the way for a deeper understanding of thermodynamic, dynamic, and mechanical properties of metallic glasses. As a first application, we extend configurational entropy measurements down to the experimental glass temperature, and demonstrate a qualitative evolution of the mechanical response of metallic glasses of increasing stability towards brittleness.

Commentaires: 11 pages, 9 figs. Réf Journal: Phys. Rev. Lett. 125, 085505 (2020)