6,275 research outputs found
Finite-Temperature Study of Bose-Fermi Superfluid Mixtures
Ultra-cold atom experiments offer the unique opportunity to study mixing of
different types of superfluid states. Our interest is in superfluid mixtures
comprising particles with different statistics- Bose and Fermi. Such scenarios
occur naturally, for example, in dense QCD matter. Interestingly, cold atomic
experiments are performed in traps with finite spatial extent, thus critically
destabilizing the occurrence of various homogeneous phases. Critical to this
analysis is the understanding that the trapped system can undergo phase
separation, resulting in a unique situation where phase transition in either
species (bosons or fermions) can overlap with the phase separation between
possible phases. In the present work, we illustrate how this intriguing
interplay manifests in an interacting 2-species atomic mixture - one bosonic
and another fermionic with two spin components - within a realistic trap
configuration. We further show that such interplay of transitions can render
the nature of the ground state to be highly sensitive to the experimental
parameters and the dimensionality of the system.Comment: 9 pages, 7 figures; Accepted for publication in Phys. Rev.
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The occipital lateral plate mesoderm is a novel source for vertebrate neck musculature
In vertebrates, body musculature originates from somites, whereas head muscles originate from the cranial mesoderm. Neck muscles are located in the transition between these regions. We show that the chick occipital lateral plate mesoderm has myogenic capacity and gives rise to large muscles located in the neck and thorax. We present molecular and genetic evidence to show that these muscles not only have a unique origin, but additionally display a distinct temporal development, forming later than any other muscle group described to date. We further report that these muscles, found in the body of the animal, develop
like head musculature rather than deploying the programme used by the trunk muscles. Using mouse genetics we reveal that these muscles are formed in trunk muscle mutants but are absent in head muscle mutants. In concordance with this conclusion, their connective tissue is neural crest in origin. Finally, we provide evidence that the mechanism by which these neck muscles develop is conserved in vertebrates
SDSS J075101.42+291419.1: A Super-Eddington Accreting Quasar with Extreme X-ray Variability
We report the discovery of extreme X-ray variability in a type 1 quasar: SDSS
J. It has a black hole mass of
measured from reverberation mapping (RM), and the black hole is accreting with
a super-Eddington accretion rate. Its XMM-Newton observation in 2015 May
reveals a flux drop by a factor of with respect to the Swift
observation in 2013 May when it showed a typical level of X-ray emission
relative to its UV/optical emission. The lack of correlated UV variability
results in a steep X-ray-to-optical power-law slope () of
-1.97 in the low X-ray flux state, corresponding to an X-ray weakness factor of
36.2 at rest-frame 2 keV relative to its UV/optical luminosity. The mild
UV/optical continuum and emission-line variability also suggest that the
accretion rate did not change significantly. A single power-law model modified
by Galactic absorption describes well the keV spectra of the X-ray
observations in general. The spectral fitting reveals steep spectral shapes
with . We search for active galactic nuclei (AGNs) with such
extreme X-ray variability in the literature and find that most of them are
narrow-line Seyfert 1 galaxies and quasars with high accretion rates. The
fraction of extremely X-ray variable objects among super-Eddington accreting
AGNs is estimated to be . We discuss two possible scenarios,
disk reflection and partial covering absorption, to explain the extreme X-ray
variability of SDSS J. We propose a possible origin for the
partial covering absorber, which is the thick inner accretion disk and its
associated outflow in AGNs with high accretion rates.Comment: 15 pages, 9 figures, accepted for publication in Ap
Eliminating the mean-field shift in multicomponent Bose-Einstein condensates
We demonstrate that the nonlinear mean-field shift in a multi-component
Bose-Einstein condensate may be eliminated by controlling the two-body
interaction coefficients. This modification is achieved by, e.g., suitably
engineering the environment of the condensate. We consider as an example the
case of a two-component condensate in a tightly confining atom waveguide.
Modification of the atom-atom interactions is then achieved by varying
independently the transverse wave function of the two components. Eliminating
the density dependent phase shift in a high-density atomic beam has important
applications in atom interferometry and precision measurement
Phase separation of Bose-Einstein condensates
The zero-temperature system of two dilute overlapping Bose-Einstein
condensates is unstable against long wavelength excitations if the interaction
strength between the distinguishable bosons exceeds the geometric mean of the
like-boson interaction strengths. If the condensates attract each other, the
instability is similar to the instability of the negative scattering length
condensates. If the condensates repel, they separate spatially into condensates
of equal pressure. We estimate the boundary size, surface tension and energy of
the phase separated condensate system and we discuss the implications for
double condensates in atomic traps.Comment: 11 pages, 1 figur
Ab initio calculation of the KRb dipole moments
The relativistic configuration interaction valence bond method has been used
to calculate permanent and transition electric dipole moments of the KRb
heteronuclear molecule as a function of internuclear separation. The permanent
dipole moment of the ground state potential is found to be
0.30(2) at the equilibrium internuclear separation with excess negative
charge on the potassium atom. For the potential the dipole moment
is an order of magnitude smaller (1 Cm) In addition, we
calculate transition dipole moments between the two ground-state and
excited-state potentials that dissociate to the K(4s)+Rb(5p) limits. Using this
data we propose a way to produce singlet KRb molecules by a
two-photon Raman process starting from an ultracold mixture of doubly
spin-polarized ground state K and Rb atoms. This Raman process is only allowed
due to relativistic spin-orbit couplings and the absence of gerade/ungerade
selection rules in heteronuclear dimers.Comment: 16 pages, 7 figure
Filling minimality of Finslerian 2-discs
We prove that every Riemannian metric on the 2-disc such that all its
geodesics are minimal, is a minimal filling of its boundary (within the class
of fillings homeomorphic to the disc). This improves an earlier result of the
author by removing the assumption that the boundary is convex. More generally,
we prove this result for Finsler metrics with area defined as the
two-dimensional Holmes-Thompson volume. This implies a generalization of Pu's
isosystolic inequality to Finsler metrics, both for Holmes-Thompson and
Busemann definitions of Finsler area.Comment: 16 pages, v2: improved introduction and formattin
Symbiosis between the TRECVid benchmark and video libraries at the Netherlands Institute for Sound and Vision
Audiovisual archives are investing in large-scale digitisation efforts of their analogue holdings and, in parallel, ingesting an ever-increasing amount of born- digital files in their digital storage facilities. Digitisation opens up new access paradigms and boosted re-use of audiovisual content. Query-log analyses show the shortcomings of manual annotation, therefore archives are complementing these annotations by developing novel search engines that automatically extract information from both audio and the visual tracks. Over the past few years, the TRECVid benchmark has developed a novel relationship with the Netherlands Institute of Sound and Vision (NISV) which goes beyond the NISV just providing data and use cases to TRECVid. Prototype and demonstrator systems developed as part of TRECVid are set to become a key driver in improving the quality of search engines at the NISV and will ultimately help other audiovisual archives to offer more efficient and more fine-grained access to their collections. This paper reports the experiences of NISV in leveraging the activities of the TRECVid benchmark
The Influence of Molecular Adsorption on Elongating Gold Nanowires
Using molecular dynamics simulations, we study the impact of physisorbing
adsorbates on the structural and mechanical evolution of gold nanowires (AuNWs)
undergoing elongation. We used various adsorbate models in our simulations,
with each model giving rise to a different surface coverage and mobility of the
adsorbed phase. We find that the local structure and mobility of the adsorbed
phase remains relatively uniform across all segments of an elongating AuNW,
except for the thinning region of the wire where the high mobility of Au atoms
disrupts the monolayer structure, giving rise to higher solvent mobility. We
analyzed the AuNW trajectories by measuring the ductile elongation of the wires
and detecting the presence of characteristic structural motifs that appeared
during elongation. Our findings indicate that adsorbates facilitate the
formation of high-energy structural motifs and lead to significantly higher
ductile elongations. In particular, our simulations result in a large number of
monatomic chains and helical structures possessing mechanical stability in
excess of what we observe in vacuum. Conversely, we find that a molecular
species that interacts weakly (i.e., does not adsorb) with AuNWs worsens the
mechanical stability of monatomic chains.Comment: To appear in Journal of Physical Chemistry
Vortices in a Bose-Einstein Condensate
We have created vortices in two-component Bose-Einstein condensates. The
vortex state was created through a coherent process involving the spatial and
temporal control of interconversion between the two components. Using an
interference technique, we map the phase of the vortex state to confirm that it
possesses angular momentum. We can create vortices in either of the two
components and have observed differences in the dynamics and stability.Comment: 4 pages with 3 figure
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