21,530 research outputs found
Shear viscosity and damping for a Fermi gas in the unitarity limit
The shear viscosity of a two-component Fermi gas in the normal phase is
calculated as a function of temperature in the unitarity limit, taking into
account strong-coupling effects that give rise to a pseudogap in the spectral
density for single-particle excitations. The results indicate that recent
measurements of the damping of collective modes in trapped atomic clouds can be
understood in terms of hydrodynamics, with a decay rate given by the viscosity
integrated over an effective volume of the cloud.Comment: 7 pages, 3 figures. Discussion significantly extended. Appendix
added. To appear in PR
MicroRNAs influence reproductive responses by females to male sex peptide in Drosophila melanogaster
Across taxa, female behavior and physiology changes significantly following the receipt of ejaculate molecules during mating. For example, receipt of sex peptide (SP) in female Drosophila melanogaster significantly alters female receptivity, egg production, lifespan, hormone levels, immunity, sleep and feeding patterns. These changes are underpinned by distinct tissue- and time-specific changes in diverse sets of mRNAs. However, little is yet known about the regulation of these gene expression changes, and hence the potential role of microRNAs (miRNAs), in female post-mating responses. A preliminary screen of genomic responses in females to receipt of SP suggested that there were changes in the expression of several miRNAs. Here we tested directly whether females lacking four of the candidate miRNAs highlighted (miR-279, miR-317, miR-278 and miR-184) showed altered fecundity, receptivity and lifespan responses to receipt of SP, when mated once or continually to SP null or control males. The results showed that miRNA-lacking females mated to SP null males exhibited altered receptivity, but not reproductive output, in comparison to controls. However, these effects interacted significantly with the genetic background of the miRNA-lacking females. No significant survival effects were observed in miRNA-lacking females housed continually with SP null or control males. However, continual exposure to control males that transferred SP resulted in significantly higher variation in miRNA-lacking female lifespan than did continual exposure to SP null males. The results provide the first insight into the effects and importance of miRNAs in regulating post-mating responses in females
The nature of a gravitationally lensed sub-millimetre arc in MS0451.6-0305: two interacting galaxies at z~2.9?
We present a new SCUBA image of the cluster MS0451.6-0305, which exhibits
strong, extended sub-mm flux at 850 microns. The most striking feature in the
map is an elongated region of bright sub-mm emission, with a flux density of
>10 mJy over several beam-sizes. This region is apparently coincident with a
previously known optical arc (which turns out to be a strongly lensed Lyman
Break Galaxy at z=2.911), as well as with a newly identified multiply-imaged
ERO (Extremely Red Object) pair predicted to be at a similar, if not identical
redshift. By combing a detailed lensing model with deep images from HST,
Chandra, CFHT, JCMT, and spectra from the VLT, we conclude that both the
strongly lensed optical arc and ERO systems have properties consistent with
known sub-mm emitters. Using a simple model for the two sources, we estimate
that the multiply-lensed EROs contribute the majority of the flux in the SCUBA
lensed arc. Correcting for the lensing amplification, we estimate that the
inherent 850 micron fluxes for both objects are ~0.4 mJy. If the LBG and ERO
pair are truly at the same redshift, then they are separated by only ~10 kpc in
the source plane, and hence constitute an interacting system at z~2.9. Higher
angular resolution observations in sub-mm/mm will permit us to more accurately
separate the contribution from each candidate, and better understand the nature
of this system.Comment: Accepted for publication in MNRAS. 10 pages, 7 figures (1 in colour).
A higher resolution version can be found at
http://www.submm.caltech.edu/~borys/papers/ms0451.pd
Algebraic and combinatorial aspects of sandpile monoids on directed graphs
The sandpile group of a graph is a well-studied object that combines ideas
from algebraic graph theory, group theory, dynamical systems, and statistical
physics. A graph's sandpile group is part of a larger algebraic structure on
the graph, known as its sandpile monoid. Most of the work on sandpiles so far
has focused on the sandpile group rather than the sandpile monoid of a graph,
and has also assumed the underlying graph to be undirected. A notable exception
is the recent work of Babai and Toumpakari, which builds up the theory of
sandpile monoids on directed graphs from scratch and provides many connections
between the combinatorics of a graph and the algebraic aspects of its sandpile
monoid.
In this paper we primarily consider sandpile monoids on directed graphs, and
we extend the existing theory in four main ways. First, we give a combinatorial
classification of the maximal subgroups of a sandpile monoid on a directed
graph in terms of the sandpile groups of certain easily-identifiable subgraphs.
Second, we point out certain sandpile results for undirected graphs that are
really results for sandpile monoids on directed graphs that contain exactly two
idempotents. Third, we give a new algebraic constraint that sandpile monoids
must satisfy and exhibit two infinite families of monoids that cannot be
realized as sandpile monoids on any graph. Finally, we give an explicit
combinatorial description of the sandpile group identity for every graph in a
family of directed graphs which generalizes the family of (undirected)
distance-regular graphs. This family includes many other graphs of interest,
including iterated wheels, regular trees, and regular tournaments.Comment: v2: Cleaner presentation, new results in final section. Accepted for
publication in J. Combin. Theory Ser. A. 21 pages, 5 figure
Quitting unassisted: the 50-year research neglect of a major public health phenomenon.
Smoking cessation research today is dominated by the development and evaluation of interventions to improve the odds of quitting successfully. Yet little attention has been paid to the large majority of ex-smokers who quit without recourse to any formal assistance. To many, these unassisted quitters are of little interest other than as a comparator population against which to test the efficacy or effectiveness of pharmaceutical or behavioral interventions. The effect of this neglect is compounded by the preference for reporting intervention success as rates rather than as the numbers of ex-smokers generated across populations through such interventions. In so doing, researchers have insulated those in policy and practice from the importance of unassisted smoking cessation and the unparalleled contribution it has made and will continue to make to reducing smoking prevalence
Intermountain Meat Goat Production Calendar
This fact sheet is calendar based and contains the recommended and industry-accepted husbandry techniques that will help create a successful production environment for meat goats
Signs of Kidding and Care During and After Kids are Born
This fact sheet describes the various parts of the parturition (kidding) process and the basic signals which does usually exhibit for each three stages of the process
Quitting unassisted: the 50-year research neglect of a major public health phenomenon.
Smoking cessation research today is dominated by the development and evaluation of interventions to improve the odds of quitting successfully. Yet little attention has been paid to the large majority of ex-smokers who quit without recourse to any formal assistance. To many, these unassisted quitters are of little interest other than as a comparator population against which to test the efficacy or effectiveness of pharmaceutical or behavioral interventions. The effect of this neglect is compounded by the preference for reporting intervention success as rates rather than as the numbers of ex-smokers generated across populations through such interventions. In so doing, researchers have insulated those in policy and practice from the importance of unassisted smoking cessation and the unparalleled contribution it has made and will continue to make to reducing smoking prevalence
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