1,308 research outputs found
Vortices in Superfluid Fermi Gases through the BEC to BCS Crossover
We have analyzed a single vortex at T=0 in a 3D superfluid atomic Fermi gas
across a Feshbach resonance. On the BCS side, the order parameter varies on two
scales: and the coherence length , while only variation on
the scale of is seen away from the BCS limit. The circulating current has
a peak value which is a non-monotonic function of
implying a maximum critical velocity at unitarity. The number of
fermionic bound states in the core decreases as we move from the BCS to BEC
regime. Remarkably, a bound state branch persists even on the BEC side
reflecting the composite nature of bosonic molecules.Comment: 4 Pages, 4 Figure
Assessing mental health literacy: What medical sciences students' know about depression
Background: Mental health literacy is an individual's knowledge and belief about mental disorders which aid their recognition, management and prevention. The aim of this study was to investigate mental health literacy among students of Tehran University of Medical Sciences. Methods: In this cross-sectional study, data were collected by the anonymous self-administered questionnaires and finally 324 students participated in the study. Random cluster sampling was used. Questions were in different areas of the mental health literacy for depression include recognition of disorder, intended actions to seek help and perceived barriers, beliefs about interventions, prevention, stigmatization and impact of media. T-test was used for statistical analysis. Results: The mean (±SD) age was 23.5±2.8. The participants were 188 (58.1) females and 136 (41.9) males. In response to the recognition of the disorder 115 (35.6) students mentioned the correct answer. In help-seeking area, 208 (64.3) gave positive answer. The majority of affected students sought for help from their friends and parents. Stigma was the greatest barrier for seeking help. Television and Internet were the most common sources of information related to mental health. Conclusion: Generally students' mental health literacy on depression was low in some areas. Appropriate educational programs specifically for reducing mental disorders stigma seems necessary. Organizing networks of co-helper students for mental health could be considered
Viscosity of strongly interacting quantum fluids: spectral functions and sum rules
The viscosity of strongly interacting systems is a topic of great interest in
diverse fields.
We focus here on the bulk and shear viscosities of \emph{non-relativistic}
quantum fluids, with particular emphasis on strongly interacting ultracold
Fermi gases. We use Kubo formulas for the bulk and shear viscosity spectral
functions, and respectively, to derive exact,
non-perturbative results. Our results include: a microscopic connection between
the shear viscosity and the normal fluid density ; sum rules for
and and their evolution through the BCS-BEC
crossover; universal high-frequency tails for and the dynamic
structure factor . We use our sum rules to show that, at
unitarity, is identically zero and thus relate
to density-density correlations. We predict that frequency-dependent shear
viscosity of the unitary Fermi gas can be experimentally
measured using Bragg spectroscopy.Comment: Published versio
Nodal Quasiparticle Dispersion in Strongly Correlated d-wave Superconductors
We analyze the effects of a momentum-dependent self-energy on the
photoemission momentum distribution curve (MDC) lineshape, dispersion and
linewidth. We illustrate this general analysis by a detailed examination of
nodal quasiparticles in high Tc cuprates. We use variational results for the
nodal quasiparticle weight Z (which varies rapidly with hole doping x) and the
low energy Fermi velocity (which is independent of x), to show that
the high energy MDC dispersion , so that it is much
larger than the bare (band structure) velocity and also increases strongly with
underdoping. We also present arguments for why the low energy Fermi velocity
and the high energy dispersion are independent of the bare band structure at
small x. All of these results are in good agreement with earlier and recent
photoemission data [Zhou et al, Nature 423, 398 (2003)].Comment: 4 pages, 3 eps fig
Deviations from Fermi-liquid behavior above in 2D short coherence length superconductors
We show that there are qualitative differences between the temperature
dependence of the spin and charge correlations in the normal state of the 2D
attractive Hubbard model using quantum Monte Carlo simulations. The
one-particle density of states shows a pseudogap above \tc with a depleted
with decreasing . The susceptibility \cs and the low frequency spin
spectral weight track , which explains the spin-gap scaling: 1/T_1T \sim
\cs(T). However the charge channel is dominated by collective behavior and the
compressibility is -independent. This anomalous ``spin-charge
separation'' is shown to exist even at intermediate where the momentum
distribution n(\bk) gives evidence for degenerate Fermi system.Comment: 4 pages (twocolumn format), 5 Postscript figure
BCS - BEC crossover at T=0: A Dynamical Mean Field Theory Approach
We study the T=0 crossover from the BCS superconductivity to Bose-Einstein
condensation in the attractive Hubbard Model within dynamical mean field
theory(DMFT) in order to examine the validity of Hartree-Fock-Bogoliubov (HFB)
mean field theory, usually used to describe this crossover, and to explore
physics beyond it. Quantum fluctuations are incorporated using iterated
perturbation theory as the DMFT impurity solver. We find that these
fluctuations lead to large quantitative effects in the intermediate coupling
regime leading to a reduction of both the superconducting order parameter and
the energy gap relative to the HFB results. A qualitative change is found in
the single-electron spectral function, which now shows incoherent spectral
weight for energies larger than three times the gap, in addition to the usual
Bogoliubov quasiparticle peaks.Comment: 11 pages,12 figures, Published versio
Can one determine the underlying Fermi surface in the superconducting state of strongly correlated superconductors?
The question of determining the underlying Fermi surface (FS) that is gapped
by superconductivity (SC) is of central importance in strongly correlated
systems, particularly in view of angle-resolved photoemission experiments. Here
we explore various definitions of the FS in the superconducting state using the
zero-energy Green's function, the excitation spectrum and the momentum
distribution. We examine (a) d-wave SC in high Tc cuprates, and (b) the s-wave
superfluid in the BCS-BEC crossover. In each case we show that the various
definitions agree, to a large extent, but all of them violate the Luttinger
count and do not enclose the total electron density. We discuss the important
role of chemical potential renormalization and incoherent spectral weight in
this violation.Comment: 4 pages, 4 figures, version 3, Added new figures, detailed discussion
of result
Epithelial/mesenchymal plasticity: how have quantitative mathematical models helped improve our understanding?
Phenotypic plasticity, the ability of cells to reversibly alter their phenotypes in response to signals, presents a significant clinical challenge to treating solid tumors. Tumor cells utilize phenotypic plasticity to evade therapies, metastasize, and colonize distant organs. As a result, phenotypic plasticity can accelerate tumor progression. A well-studied example of phenotypic plasticity is the bidirectional conversions among epithelial, mesenchymal, and hybrid epithelial/mesenchymal (E/M) phenotype(s). These conversions can alter a repertoire of cellular traits associated with multiple hallmarks of cancer, such as metabolism, immune evasion, invasion, and metastasis. To tackle the complexity and heterogeneity of these transitions, mathematical models have been developed that seek to capture the experimentally verified molecular mechanisms and act as ‘hypothesis-generating machines’. Here, we discuss how these quantitative mathematical models have helped us explain existing experimental data, guided further experiments, and provided an improved conceptual framework for understanding how multiple intracellular and extracellular signals can drive E/M plasticity at both the single-cell and population levels. We also discuss the implications of this plasticity in driving multiple aggressive facets of tumor progression
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