358 research outputs found
Parametrically excited "Scars" in Bose-Einstein condensates
Parametric excitation of a Bose-Einstein condensate (BEC) can be realized by
periodically changing the interaction strength between the atoms. Above some
threshold strength, this excitation modulates the condensate density. We show
that when the condensate is trapped in a potential well of irregular shape,
density waves can be strongly concentrated ("scarred") along the shortest
periodic orbits of a classical particle moving within the confining potential.
While single-particle wave functions of systems whose classical counterpart is
chaotic may exhibit rich scarring patterns, in BEC, we show that nonlinear
effects select mainly those scars that are locally described by stripes.
Typically, these are the scars associated with self retracing periodic orbits
that do not cross themselves in real space. Dephasing enhances this behavior by
reducing the nonlocal effect of interference
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Genomic and epigenomic mapping of leptin-responsive neuronal populations involved in body weight regulation.
Genome wide association studies (GWAS) in obesity have identified a large number of noncoding loci located near genes expressed in the central nervous system. However, due to the difficulties in isolating and characterizing specific neuronal subpopulations, few obesity-associated SNPs have been functionally characterized. Leptin responsive neurons in the hypothalamus are essential in controlling energy homeostasis and body weight. Here, we combine FACS-sorting of leptin-responsive hypothalamic neuron nuclei with genomic and epigenomic approaches (RNA-seq, ChIP-seq, ATAC-seq) to generate a comprehensive map of leptin-response specific regulatory elements, several of which overlap obesity-associated GWAS variants. We demonstrate the usefulness of our leptin-response neuron regulome, by functionally characterizing a novel enhancer near Socs3, a leptin response-associated transcription factor. We envision our data to serve as a useful resource and a blueprint for functionally characterizing obesity-associated SNPs in the hypothalamus
The Irreducible Axion Background
Searches for dark matter decaying into photons constrain its lifetime to be
many orders of magnitude larger than the age of the Universe. A corollary
statement is that the abundance of any particle that can decay into photons
over cosmological timescales is constrained to be much smaller than the cold
dark-matter density. We show that an freeze-in
contribution to the relic density of axions is in violation of that statement
in a large portion of the parameter space. This allows us to set stringent
constraints on axions in the mass range . At our constraint on a photophilic axion is , almost three orders of magnitude stronger than
the bounds established using horizontal branch stars; at our
constraint on a photophobic axion coupled to electrons is , almost four orders of magnitude stronger than present
results. Although we focus on axions, our argument is more general and can be
extended to, for instance, sterile neutrinos.Comment: 7+14 pages, 2+9 figures; v2 additional references and updated to the
latest INTEGRAL constraint
Extinction Rates for Fluctuation-Induced Metastabilities : A Real-Space WKB Approach
The extinction of a single species due to demographic stochasticity is
analyzed. The discrete nature of the individual agents and the Poissonian noise
related to the birth-death processes result in local extinction of a metastable
population, as the system hits the absorbing state. The Fokker-Planck
formulation of that problem fails to capture the statistics of large deviations
from the metastable state, while approximations appropriate close to the
absorbing state become, in general, invalid as the population becomes large. To
connect these two regimes, a master equation based on a real space WKB method
is presented, and is shown to yield an excellent approximation for the decay
rate and the extreme events statistics all the way down to the absorbing state.
The details of the underlying microscopic process, smeared out in a mean field
treatment, are shown to be crucial for an exact determination of the extinction
exponent. This general scheme is shown to reproduce the known results in the
field, to yield new corollaries and to fit quite precisely the numerical
solutions. Moreover it allows for systematic improvement via a series expansion
where the small parameter is the inverse of the number of individuals in the
metastable state
Recent developments in monolithic integration of InGaAsP/InP optoelectronic devices
Monolithically integrated optoelectronic circuits combine optical devices such as light sources (injection lasers and light emitting diodes) and optical detectors with solid-state semiconductor devices such as field effect transistors, bipolar transistors, and others on a single semiconductor crystal. Here we review some of the integrated circuits that have been realized and discuss the laser structures suited for integration with emphasis on the InGaAsP/InP material system. Some results of high frequency modulation and performance of integrated devices are discussed
A genome-wide association study identifies four novel susceptibility loci underlying inguinal hernia.
Inguinal hernia repair is one of the most commonly performed operations in the world, yet little is known about the genetic mechanisms that predispose individuals to develop inguinal hernias. We perform a genome-wide association analysis of surgically confirmed inguinal hernias in 72,805 subjects (5,295 cases and 67,510 controls) and confirm top associations in an independent cohort of 92,444 subjects with self-reported hernia repair surgeries (9,701 cases and 82,743 controls). We identify four novel inguinal hernia susceptibility loci in the regions of EFEMP1, WT1, EBF2 and ADAMTS6. Moreover, we observe expression of all four genes in mouse connective tissue and network analyses show an important role for two of these genes (EFEMP1 and WT1) in connective tissue maintenance/homoeostasis. Our findings provide insight into the aetiology of hernia development and highlight genetic pathways for studies of hernia development and its treatment
Defects in Graphene : A Topological Description
Specific types of spatial defects or potentials can turn monolayer graphene
into a topological material. These topological defects are classified by a
spatial dimension and they are systematically obtained from the Hamiltonian
by means of its symbol , an
operator which generalises the Bloch Hamiltonian and contains all topological
information. This approach, when applied to Dirac operators, allows to recover
the tenfold classification of insulators and superconductors. The existence of
a stable -topology is predicted as a condition on the dimension
, similar to the classification of defects in thermodynamic phase
transitions. Kekule distortions, vacancies and adatoms in graphene are proposed
as examples of such defects and their topological equivalence is discussed.Comment: 5 pages and supplementary materia
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