25,972 research outputs found
Comment on "Large Difference in the Elastic Properties of fcc and hcp Hard-Sphere Crystals"
As is well known, hard-sphere crystals of the fcc and hcp type differ very
little in their thermodynamic properties. Nonetheless, recent computer
simulations by Pronk and Frenkel indicate that the elastic response to
mechanical deformation of the two types of crystal should be quite different.
By invoking a geometrical argument put forward by R. Martin some time ago, we
suggest that this is largely due to the different symmetries of the fcc and hcp
crystal structures. Indeed, we find that elastic constants obtained by means of
computer simulations for the fcc hard-sphere crystal can be mapped onto the
equivalent ones of the hcp crystal to very high accuracy. The same procedure
applied to density functional theoretical predictions for the elastic
properties of the fcc hard-sphere crystal also produces remarkably accurate
predictions for those of the hcp hard-sphere crystal.Comment: 7 pages, 5 figure
Quench Dynamics in a Model with Tuneable Integrability Breaking
We consider quantum quenches in an integrable quantum chain with
tuneable-integrability-breaking interactions. In the case where these
interactions are weak, we demonstrate that at intermediate times after the
quench local observables relax to a prethermalized regime, which can be
described by a density matrix that can be viewed as a deformation of a
generalized Gibbs ensemble. We present explicit expressions for the
approximately conserved charges characterizing this ensemble. We do not find
evidence for a crossover from the prethermalized to a thermalized regime on the
time scales accessible to us. Increasing the integrability-breaking
interactions leads to a behaviour that is compatible with eventual
thermalization.Comment: 22 pages, 35 figures, minor updates to manuscrip
Inclusion of turbulence in solar modeling
The general consensus is that in order to reproduce the observed solar p-mode
oscillation frequencies, turbulence should be included in solar models.
However, until now there has not been any well-tested efficient method to
incorporate turbulence into solar modeling. We present here two methods to
include turbulence in solar modeling within the framework of the mixing length
theory, using the turbulent velocity obtained from numerical simulations of the
highly superadiabatic layer of the sun at three stages of its evolution. The
first approach is to include the turbulent pressure alone, and the second is to
include both the turbulent pressure and the turbulent kinetic energy. The
latter is achieved by introducing two variables: the turbulent kinetic energy
per unit mass, and the effective ratio of specific heats due to the turbulent
perturbation. These are treated as additions to the standard thermodynamic
coordinates (e.g. pressure and temperature). We investigate the effects of both
treatments of turbulence on the structure variables, the adiabatic sound speed,
the structure of the highly superadiabatic layer, and the p-mode frequencies.
We find that the second method reproduces the SAL structure obtained in 3D
simulations, and produces a p-mode frequency correction an order of magnitude
better than the first method.Comment: 10 pages, 12 figure
Profil anthropometrique des enfants scolarises tananariviens
Les enfants tananariviens sont en Ă©tat de malnutrition chronique. Notre objectif est d'Ă©valuer l'indice de masse corporelle (IMC) pour estimer lesenfants apparemment "sains". Une enquĂȘte et une mesure de la taille et du poids des enfants scolarisĂ©s tananariviens de 6 Ă 11 ans ont Ă©tĂ© rĂ©alisĂ©es. AprĂšs leur accord, la taille et l'indice de masse corporelle des 442 enfants tirĂ©s au hasard ont Ă©tĂ© ainsi obtenus. L'analyse de la moyenne de la taille a rĂ©vĂ©lĂ© une diffĂ©rence significative Ă 8 ans, une diffĂ©rence non Ă©vidente sur l'indice de masse corporelle. La comparaison avec les valeurs de rĂ©fĂ©rence (OMS 2006) a montrĂ© un retard statural de 34% avec une tendance globale Ă la hausse et un dĂ©ficit pondĂ©ral Ă©gal Ă 5,5% selon le z score. Ainsi, au sein d'une population malnutrie, l'indice de masse corporelle pourrait ĂȘtre utilisĂ© comme un des paramĂštres Ă considĂ©rer dans l'Ă©valuation de l'Ă©tat de santĂ© pour classer ces enfants en bonne santĂ© apparente
Hamiltonian structure for dispersive and dissipative dynamical systems
We develop a Hamiltonian theory of a time dispersive and dissipative
inhomogeneous medium, as described by a linear response equation respecting
causality and power dissipation. The proposed Hamiltonian couples the given
system to auxiliary fields, in the universal form of a so-called canonical heat
bath. After integrating out the heat bath the original dissipative evolution is
exactly reproduced. Furthermore, we show that the dynamics associated to a
minimal Hamiltonian are essentially unique, up to a natural class of
isomorphisms. Using this formalism, we obtain closed form expressions for the
energy density, energy flux, momentum density, and stress tensor involving the
auxiliary fields, from which we derive an approximate, ``Brillouin-type,''
formula for the time averaged energy density and stress tensor associated to an
almost mono-chromatic wave.Comment: 68 pages, 1 figure; introduction revised, typos correcte
Immediate Psychosocial Impact on Healthcare Workers During COVID-19 Pandemic in China: A Systematic Review and Meta-Analysis
Objectives: The corona virus disease-2019 (COVID-19) pandemic spread globally, and we aimed to investigate the psychosocial impact on healthcare workers (HWs) in China during the pandemic.
Methods: In this systematic review and meta-analysis, we searched seven electronic databases for cross-sectional studies on psychosocial impact on HWs in relation to COVID-19 from January 1, 2020 to October 7, 2020. We included primary studies involving Chinese HWs during the pandemic, and data were extracted from the published articles. Our primary outcome was prevalence of anxiety, depression, and stress disorders. We pooled prevalence value with their 95% confidence interval using random effect models and assessed study quality on the basis of an 11-item checklist recommended by the Agency for Healthcare Research and Quality. The study protocol was registered in PROSPERO (CRD42020195843).
Results: We identified 25 articles comprising a total of 30,841 completed questionnaires and 22 studies for meta-analysis. The prevalence of anxiety, depression, and stress disorders was 34.4% (29.5â39.4%), 31.1% (24.5â37.7%), and 29.1% (24.3â33.8%) for HWs. The pooled prevalence of anxiety disorders for HWs from late January to early February was 46.4% (42.9â49.9%), significantly higher than those in mid-term February (28.0%, 23.9â32.1%) and after late February (27.6%, 16.0â39.2%). The pooled prevalence of depression disorders for HWs from late January to early February was 46.5% (38.8â54.2%), significantly higher than those in mid-term February (27.1%, 19.8â34.5%) and after late February (32.9%, 16.2â49.5%). HWs working in Hubei Province had a higher prevalence of anxiety (37.9 vs. 30.8%) and a lower prevalence of depression (27.5 vs. 34.7%) than those working in other regions. Nurses had a higher prevalence of anxiety (44.1 vs. 29.0%) and depression (34.1 vs. 29.2%) than other HWs.
Conclusions: About one-third of HWs in China suffered anxiety, depression, and stress at the early epidemic of COVID-19. HWs in Hubei Province, especially nurses, had a higher prevalence of psychological disorders. During the pandemic, a negative psychological state may persist in a proportion of Chinese HWs, fluctuating with the control of the pandemic. The long-term impact should continue to be observed. Attention should be paid to HWs for their psychological impact due to the pandemic.
Systematic Review Registration: The study protocol was registered with PROSPERO (CRD42020195843)
Raman and nuclear magnetic resonance investigation of alkali metal vapor interaction with alkene-based anti-relaxation coating
The use of anti-relaxation coatings in alkali vapor cells yields substantial
performance improvements by reducing the probability of spin relaxation in wall
collisions by several orders of magnitude. Some of the most effective
anti-relaxation coating materials are alpha-olefins, which (as in the case of
more traditional paraffin coatings) must undergo a curing period after cell
manufacturing in order to achieve the desired behavior. Until now, however, it
has been unclear what physicochemical processes occur during cell curing, and
how they may affect relevant cell properties. We present the results of
nondestructive Raman-spectroscopy and magnetic-resonance investigations of the
influence of alkali metal vapor (Cs or K) on an alpha-olefin, 1-nonadecene
coating the inner surface of a glass cell. It was found that during the curing
process, the alkali metal catalyzes migration of the carbon-carbon double bond,
yielding a mixture of cis- and trans-2-nonadecene.Comment: 5 pages, 6 figure
Constraining Primordial Non-Gaussianity With the Abundance of High Redshift Clusters
We show how observations of the evolution of the galaxy cluster number
abundance can be used to constrain primordial non-Gaussianity in the universe.
We carry out a maximum likelihood analysis incorporating a number of current
datasets and accounting for a wide range of sources of systematic error. Under
the assumption of Gaussianity, the current data prefer a universe with matter
density and are inconsistent with at the
level. If we assume , the predicted degree of cluster
evolution is consistent with the data for non-Gaussian models where the
primordial fluctuations have at least two times as many peaks of height
or more as a Gaussian distribution does. These results are robust to
almost all sources of systematic error considered: in particular, the
Gaussian case can only be reconciled with the data if a number of
systematic effects conspire to modify the analysis in the right direction.
Given an independent measurement of , the techniques described here
represent a powerful tool with which to constrain non-Gaussianity in the
primordial universe, independent of specific details of the non-Gaussian
physics. We discuss the prospects and strategies for improving the constraints
with future observations.Comment: Minor revisions to match published ApJ version, 14 pages emulateap
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