4,211 research outputs found
Inelastic X-ray scattering from valence electrons near absorption edges of FeTe and TiSe
We study resonant inelastic x-ray scattering (RIXS) peaks corresponding to
low energy particle-hole excited states of metallic FeTe and semi-metallic
TiSe for photon incident energy tuned near the absorption edge of
Fe and Ti respectively. We show that the cross section amplitudes are well
described within a renormalization group theory where the effect of the core
electrons is captured by effective dielectric functions expressed in terms of
the the atomic scattering parameters of Fe and Ti. This method can be
used to extract the dynamical structure factor from experimental RIXS spectra
in metallic systems.Comment: 6 pages, 4 figure
Temperature-mediated transition from Dyakonov-Tamm surface waves to surface-plasmon-polariton waves
The effect of changing the temperature on the propagation of electromagnetic surface waves (ESWs), guided by the planar interface of a homogeneous isotropic temperature-sensitive material (namely, InSb) and a temperature-insensitive structurally chiral material (SCM) was numerically investigated in the terahertz frequency regime. As the temperature rises, InSb transforms from a dissipative dielectric material to a \blue{dissipative} plasmonic material. Correspondingly, the ESWs transmute from Dyakonov--Tamm surface waves into surface--plasmon--polariton waves. The effects of the temperature change are clearly observed in the phase speeds, propagation distances, angular existence domains, multiplicity, and spatial profiles of energy flow of the ESWs. Remarkably large propagation distances can be achieved; in such instances the energy of an ESW is confined almost entirely within the SCM. For certain propagation directions, simultaneous excitation of two ESWs with (i) the same phase speeds but different propagation distances or (ii) the same propagation distances but different phase speeds are also indicated by our results
Estimating the potential impact of canine distemper virus on the Amur tiger population (Panthera tigris altaica) in Russia
Lethal infections with canine distemper virus (CDV) have recently been diagnosed in Amur tigers (Panthera tigris altaica), but long-term implications for the population are unknown. This study evaluates the potential impact of CDV on a key tiger population in Sikhote-Alin Biosphere Zapovednik (SABZ), and assesses how CDV might influence the extinction potential of other tiger populations of varying sizes. An individual-based stochastic, SIRD (susceptible-infected-recovered/dead) model was used to simulate infection through predation of infected domestic dogs, and/or wild carnivores, and direct tiger-to-tiger transmission. CDV prevalence and effective contact based on published and observed data was used to define plausible low- and high-risk infection scenarios. CDV infection increased the 50-year extinction probability of tigers in SABZ by 6.3% to 55.8% compared to a control population, depending on risk scenario. The most significant factors influencing model outcome were virus prevalence in the reservoir population(s) and its effective contact rate with tigers. Adjustment of the mortality rate had a proportional impact, while inclusion of epizootic infection waves had negligible additional impact. Small populations were found to be disproportionately vulnerable to extinction through CDV infection. The 50-year extinction risk in populations consisting of 25 individuals was 1.65 times greater when CDV was present than that of control populations. The effects of density dependence do not protect an endangered population from the impacts of a multi-host pathogen, such as CDV, where they coexist with an abundant reservoir presenting a persistent threat. Awareness of CDV is a critical component of a successful tiger conservation management policy
Infection urinaire à Haemophilus influenzae chez 3 enfants ayant une malformation de l’arbre urinaire
La pyélonéphrite aigue (PNA) est une des infections les plus fréquentes de l’enfant, dans laquelle le genre Haemophilus est très rarement impliqué. De janvier 2010 à octobre 2011, seulement 3 enfants âgés de moins de 15 ans ont été hospitalisés dans notre établissement pour une infection urinaire à Haemophilus influenzae. Les 3 enfants présentaient des tableaux typiques de PNA : fièvre, signes fonctionnels urinaires ou douleurs abdominales. L’examen cytobactériologique des urines (ECBU) montrait à l’examen direct une leucocyturie significative et de nombreux bacilles Gram négatifs. La culture bactériologique standard des urines des 3 patients était négative. H. influenzae a été mis en évidence secondairement après réensemencement des urines sur milieu enrichi. Les 3 enfants présentaient une uropathie : 2 syndromes de la jonction pyélo-urétérale droit et une duplicité urétérale bilatérale avec reflux de haut grade. Pendant la période étudiée, la prévalence des PNA à Haemophilus dans notre établissement a été de 0,02 % dans les infections urinaires de l’enfant. Dans la littérature, les PNA à Haemophilus sont rares (moins de 1 % chez l’enfant), fréquemment associées à une malformation de l’arbre urinaire et difficiles à mettre en évidence. Lorsque l’ECBU montre des bacilles Gram négatifs à l’examen direct non retrouvés à la culture, il faut réensemencer les urines sur gélose au sang cuit, notamment si le patient est porteur d’une uropathie
Geometric optics and instability for semi-classical Schrodinger equations
We prove some instability phenomena for semi-classical (linear or) nonlinear
Schrodinger equations. For some perturbations of the data, we show that for
very small times, we can neglect the Laplacian, and the mechanism is the same
as for the corresponding ordinary differential equation. Our approach allows
smaller perturbations of the data, where the instability occurs for times such
that the problem cannot be reduced to the study of an o.d.e.Comment: 22 pages. Corollary 1.7 adde
Predicted FeII Emission-Line Strengths from Active Galactic Nuclei
We present theoretical FeII emission line strengths for physical conditions
typical of Active Galactic Nuclei with Broad-Line Regions. The FeII line
strengths were computed with a precise treatment of radiative transfer using
extensive and accurate atomic data from the Iron Project. Excitation mechanisms
for the FeII emission included continuum fluorescence, collisional excitation,
self-fluorescence amoung the FeII transitions, and fluorescent excitation by
Lyman-alpha and Lyman-beta. A large FeII atomic model consisting of 827 fine
structure levels (including states to E ~ 15 eV) was used to predict fluxes for
approximately 23,000 FeII transitions, covering most of the UV, optical, and IR
wavelengths of astrophysical interest. Spectral synthesis for wavelengths from
1600 Angstroms to 1.2 microns is presented. Applications of present theoretical
templates to the analysis of observations are described. In particular, we
discuss recent observations of near-IR FeII lines in the 8500 Angstrom -- 1
micron region which are predicted by the Lyman-alpha fluorescence mechanism. We
also compare our UV spectral synthesis with an empirical iron template for the
prototypical, narrow-line Seyfert galaxy I Zw 1. The theoretical FeII template
presented in this work should also applicable to a variety of objects with FeII
spectra formed under similar excitation conditions, such as supernovae and
symbiotic stars.Comment: 33 pages, 15 postscript figure
Recommended from our members
Quand les ’candides’ evaluent les OGM... Nouveau modele de ’democratie technique’ ou mise en scence du debat public?
- …