Pressure dependence of the Boson peak in glassy As2S3 studied by Raman Scattering

A detailed pressure-dependence study of the low-energy excitations of glassy As2S3 is reported over a wide pressure range, up to 10 GPa. The spectral features of Boson peak are analysed as a function of pressure. Pressure effects on the Boson peak are manifested as an appreciable shift of its frequency to higher values, a suppression of its intensity, as well as a noticeable change of its asymmetry leading to a more symmetric shape at high pressures. The pressure-induced Boson peak frequency shift agrees very well with the predictions of the soft potential model over the whole pressure range studied. As regards the pressure dependence of the Boson peak intensity, the situation is more complicated. It is proposed that in order to reach proper conclusions the corresponding dependence of the Debye density of states must also be considered. Employing a comparison of the low energy modes of the crystalline counterpart of As2S3 as well as the experimental data concerning the pressure dependencies of the Boson peak frequency and intensity, structural or glass-to-glass transition seems to occur at the pressure ~4 GPa related to a change of local structure. Finally, the pressure-induced shape changes of the Boson peak can be traced back to the very details of the excess (over the Debye contribution) vibrational density of states.Comment: To appear in J. Non-Cryst. Solids (Proceedings of the 5th IDMRCS, Lille, July 2005

A Spectral Bernstein Theorem

We study the spectrum of the Laplace operator of a complete minimal properly immersed hypersurface $M$ in $\R^{n+1}$. (1) Under a volume growth condition on extrinsic balls and a condition on the unit normal at infinity, we prove that $M$ has only essential spectrum consisting of the half line $[0, +\infty)$. This is the case when $\lim_{\tilde{r}\to +\infty}\tilde{r}\kappa_i=0$, where $\tilde{r}$ is the extrinsic distance to a point of $M$ and $\kappa_i$ are the principal curvatures. (2) If the $\kappa_i$ satisfy the decay conditions $|\kappa_i|\leq 1/\tilde{r}$, and strict inequality is achieved at some point $y\in M$, then there are no eigenvalues. We apply these results to minimal graphic and multigraphic hypersurfaces.Comment: 16 pages. v2. Final version: minor revisions, we add Proposition 3.2. Accepted for publication in the Annali di Matematica Pura ed Applicata, on the 05/03/201

Magnetic relaxation phenomena and cluster glass properties of La{0.7-x}Y{x}Ca{0.3}MnO{3} manganites

The dynamic magnetic properties of the distorted perovskite system La{0.7-x}Y{x}Ca{0.3}MnO{3} (0 <= x <= 0.15) have been investigated by ac-susceptibility and dc magnetization measurements, with emphasis on relaxation and aging studies. They evidence for x >= 0.10 the appearance of a metallic cluster glass phase, that develops just below the ferromagnetic transition temperature. The clusters grow with decreasing temperature down to a temperature T(f0) at which they freeze due to severe intercluster frustration. The formation of these clusters is explained by the presence of yttrium induced local structural distortions that create localized spin disorder in a magnetic lattice where double-exchange ferromagnetism is dominant.Comment: Accepted for publication in Phys. Rev.

Potential health and economic impacts of dexamethasone treatment for patients with COVID-19

Acknowledgements We thank all members of the COVID-19 International Modelling Consortium and their collaborative partners. This work was supported by the COVID-19 Research Response Fund, managed by the Medical Sciences Division, University of Oxford. L.J.W. is supported by the Li Ka Shing Foundation. R.A. acknowledges funding from the Bill and Melinda Gates Foundation (OPP1193472).Peer reviewedPublisher PD