12,829 research outputs found
Why are very short times so long and very long times so short in elastic waves?
In a first study of thermoelastic waves, such as on the textbook of Landau
and Lifshitz, one might at first glance understand that when the given period
is very short, waves are isentropic because heat conduction does not set in,
while if the given period is very long waves are isothermal because there is
enough time for thermalization to be thoroughly accomplished. When one pursues
the study of these waves further, by the mathematical inspection of the
complete thermoelastic wave equation he finds that if the period is very short,
much shorter than a characteristic time of the material, the wave is
isothermal, while if it is very long, much longer than the characteristic time,
the wave is isentropic. One also learns that this fact is supported by
experiments: at low frequencies the elastic waves are isentropic, while they
are isothermal when the frequencies are so high that can be attained in few
cases. The authors show that there is no contradiction between the first glance
understanding and the mathematical treatment of the elastic wave equation: for
thermal effects very long periods are so short and very short periods are so
long.Comment: 7 pages, submitted to European Journal of Physic
Rapid Star Formation in the Presence of Active Galactic Nuclei
Recent observations reveal galaxies in the early Universe (2<z<6.4) with
large reservoirs of molecular gas and extreme star formation rates. For a very
large range of sources, a tight relationship exists between star formation rate
and the luminosity of the HCN J=1-0 spectral line, but sources at redshifts of
z~2 and beyond do not follow this trend. The deficit in HCN is conventionally
explained by an excess of infrared (IR) radiation due to active galactic nuclei
(AGN). We show in this letter not only that the presence of AGN cannot account
for the excess of IR over molecular luminosity, but also that the observed
abundance of HCN is in fact consistent with a population of stars forming from
near-primordial gas.Comment: 4 pages, 1 figure. Accepted by the Astrophysical Journal Letter
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Lifting the Fog: The Problem of Antipsychotic Drug Use in Nursing Facilities
With the rapid increase in the elder population nationwide, the problem of excessive dependence on risky antipsychotic drug treatment for dementia-related behavioral problems in nursing facilities must be addressed. At the federal level, the over-prescription of antipsychotics to the elderly in nursing homes is addressed first by regulation specific to nursing facilities, such as the Federal Nursing Home Reform Amendments (FNHRA), a part of the Ombudsman Budget Reconciliation Act of 1987 (OBRA ’87) as well as through the Centers for Medicare and Medicaid Services (CMS) guidelines. Secondarily, the Food and Drug Administration (FDA) has authority to issue black box warnings and regulation pertaining to off-label drug use for antipsychotics used to treat behavioral problems associated with dementia, a use that has not been approved by the FDA. Additionally, under state common law, these problems are addressed under the informed consent and right to refuse treatment doctrines. Despite the extensive multi-tiered body of law addressing this issue, no coherent and effective system has yet been devised to effectively protect patient rights. This paper suggests solutions to system failures via multi-faceted changes at federal and state levels in order to make the available framework more coherent and facilitate a shift to a nonpharmacologic treatment emphasis in the future
A three-dimensional symmetry result for a phase transition equation in the genuinely nonlocal regime
We consider bounded solutions of the nonlocal Allen-Cahn equation
(-\Delta)^s u=u-u^3\qquad{\mbox{ in }}{\mathbb{R}}^3, under the monotonicity
condition and in the genuinely nonlocal regime in
which~. Under the limit assumptions
\lim_{x_n\to-\infty} u(x',x_n)=-1\quad{\mbox{ and }}\quad \lim_{x_n\to+\infty}
u(x',x_n)=1, it has been recently shown that~ is necessarily D, i.e. it
depends only on one Euclidean variable. The goal of this paper is to obtain a
similar result without assuming such limit conditions. This type of results can
be seen as nonlocal counterparts of the celebrated conjecture formulated by
Ennio De Giorgi
The statistical distribution of magnetic field strength in G-band bright points
G-band bright points are small-sized features characterized by high
photometric contrast. Theoretical investigations indicate that these features
have associated magnetic field strengths between 1-2 kG. Results from
observations instead lead to contradictory results, indicating magnetic fields
of only kG strength in some and including hG strengths in others. In order to
understand the differences between measurements reported in the literature, and
to reconcile them with results from theory, we analyze the distribution of
magnetic field strength of G-band bright features identified on synthetic
images of the solar photosphere, and its sensitivity to observational and
methodological effects. We investigate the dependence of magnetic field
strength distributions of G-band bright points identified in 3D
magnetohydrodynamic simulations on feature selection method, data sampling,
alignment and spatial resolution. The distribution of magnetic field strength
of G-band bright features shows two peaks, one at about 1.5 kG and one below 1
hG. The former corresponds to magnetic features,the second mostly to bright
granules. Peaks at several hG are obtained only on spatially degraded or
misalligned data. Simulations show that magnetic G-band bright points have
typically associated field strengths of few kG. Field strengths in the hG range
can result from observational effects, thus explaining the discrepancies
presented in the literature. Our results also indicate that outcomes from
spectro-polarimetric inversions with imposed unit filling-factor should be
employed with great caution
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