Search results for "FOS"

Competition of electron-phonon mediated superconductivity and Stoner magnetism on a flat band

2018

The effective attractive interaction between electrons, mediated by electron-phonon coupling, is a well-established mechanism of conventional superconductivity. In metals exhibiting a Fermi surface, the critical temperature of superconductivity is exponentially smaller than the characteristic phonon energy. Therefore, such superconductors are found only at temperatures below a few kelvin. Systems with flat energy bands have been suggested to cure the problem and provide a route to room-temperature superconductivity, but previous studies are limited to only BCS models with an effective attractive interaction. Here we generalize Eliashberg's theory of strong-coupling superconductivity to syst…

Field dependence of the vortex-core sizes in dirty two-band superconductors

2019

We study the structure of Abrikosov vortices in two-band superconductors for different external magnetic fields and different parameters of the bands. The vortex core size determined by the coherence lengths are found to have qualitatively different behaviour from that determined by the quasiparticle density of states spatial variation. These different vortex core length scales coincide near the upper critical field, while the discrepancy between them becomes quite significant at lower fields. Within the diffusive approximation we demonstrate several generic regimes in the field dependence of the vortex core sizes determined by the disparity of diffusion constants in the two bands.

Scattering of Co-Current Surface Waves on an Analogue Black Hole

2018

We report on what is to our knowledge the first scattering experiment of surface waves on an accelerating transcritical flow, which in the analogue gravity context is described by an effective spacetime with a black-hole horizon. This spacetime has been probed by an incident co-current wave, which partially scatters into an outgoing countercurrent wave on each side of the horizon. The measured scattering amplitudes are compatible with the predictions of the hydrodynamical theory, where the kinematical description in terms of the effective metric is exact.

Phonons in MoSe2/WSe2 van der Waals heterobilayer

2021

We report first-principles calculations of the structural and vibrational properties of the synthesized two-dimensional van der Waals heterostructures formed by single-layers dichalcogenides MoSe2 and WSe2. We show that, when combining these systems in a periodic two-dimensional heterostructures, the intrinsic phonon characteristics of the free-standing constituents are to a large extent preserved but, furthermore, exhibit shear and breathing phonon modes that are not present in the individual building blocks. These peculiar modes depend strongly on the weak vdW forces and has a great contibution to the thermal properties of the layered materials. Besides these features, the departure of fl…

Anomaly-free scale symmetry and gravity

2023

In this Letter, we address the question of whether the conformal invariance can be considered as a global symmetry of a theory of fundamental interactions. To describe Nature, this theory must contain a mechanism of spontaneous breaking of the scale symmetry. Besides that, the fundamental theory must include gravity, whereas all known extensions of the conformal invariance to the curved space-time suffer from the Weyl anomaly. We show that conformal symmetry can be made free from the quantum anomaly only in the flat space. The presence of gravity would reduce the global symmetry group of the fundamental theory to the scale invariance only. We discuss how the effective Lagrangian respecting …

La Tene human burial and animal deposit at Varennes-sur-Seine (Seine-et-Marne)

2002

An adolescent was buried at the bottom of a large irregular shaped pit The body that had been lain on one side, legs tucked under, was in the centre of a ring of stones and was covered by a deposit of a dog and four horses of which two were foals and two were young adults. A thick layer of sand and a second deposit of three horses and a dog covered this first deposit. The adolescent skull had been broken and perforated which adds to the distinctiveness of this burial. Most of the horses had been skinned and the tendons had been removed. Also the four legs of one of the horses in the top deposit had been removed. With no datable finds the radiocarbon analysis gives a date corresponding to th…

Occitanie, Haute-Garonne, Grenade, Le Castelet

2019

Le lieu-dit Le Castelet à Grenade (Haute-Garonne) est situé à égale distance (1,5 km) du confluent Hers-Girou vers l’est et d’un méandre de la Garonne vers le nord-ouest. Un projet de carrière de la Société Midi-Pyrénées Granulats a permis de retrouver dans ce lieu les traces de plusieurs occupations humaines, échelonnées pour l’essentiel entre le Néolithique moyen et de la fin de l’âge du Bronze. L’ancien réseau hydrographique secondaire de la Garonne marque le paysage et draine dans le sous-sol la nappe phréatique, constituant sans doute un atout. En effet, il suffit de creuser un puits au sein d’un paléo-chenal pour créer un point d’eau au milieu d’une plaine cultivable, et réunir ainsi …

Enclos fossoyés et sépultures de l'âge du Bronze à Saint-Vulbas : la fouille du PIPA, lot 7, secteur 4000 (Ain, Auvergne-Rhône-Alpes)

2017

Numerical Recovery of Source Singularities via the Radiative Transfer Equation with Partial Data

2013

The inverse source problem for the radiative transfer equation is considered, with partial data. Here we demonstrate numerical computation of the normal operator $X_{V}^{*}X_{V}$ where $X_{V}$ is the partial data solution operator to the radiative transfer equation. The numerical scheme is based in part on a forward solver designed by F. Monard and G. Bal. We will see that one can detect quite well the visible singularities of an internal optical source $f$ for generic anisotropic $k$ and $\sigma$, with or without noise added to the accessible data $X_{V}f$. In particular, we use a truncated Neumann series to estimate $X_{V}$ and $X_{V}^{*}$, which provides a good approximation of $X_{V}^{*…

A posteriori error estimates for time-dependent reaction-diffusion problems based on the Payne-Weinberger inequality

2015

We consider evolutionary reaction-diffusion problem with mixed Dirichlet--Robin boundary conditions. For this class of problems, we derive two-sided estimates of the distance between any function in the admissible energy space and exact solution of the problem. The estimates (majorants and minorants) are explicitly computable and do not contain unknown functions or constants. Moreover, it is proved that the estimates are equivalent to the energy norm of the deviation from the exact solution.