18,777 research outputs found
From simplicial Chern-Simons theory to the shadow invariant II
This is the second of a series of papers in which we introduce and study a
rigorous "simplicial" realization of the non-Abelian Chern-Simons path integral
for manifolds M of the form M = Sigma x S1 and arbitrary simply-connected
compact structure groups G. More precisely, we introduce, for general links L
in M, a rigorous simplicial version WLO_{rig}(L) of the corresponding Wilson
loop observable WLO(L) in the so-called "torus gauge" by Blau and Thompson
(Nucl. Phys. B408(2):345-390, 1993). For a simple class of links L we then
evaluate WLO_{rig}(L) explicitly in a non-perturbative way, finding agreement
with Turaev's shadow invariant |L|.Comment: 53 pages, 1 figure. Some minor changes and corrections have been mad
Measurement of the intrinsic damping constant in individual nanodisks of YIG and YIG{\textbar}Pt
We report on an experimental study on the spin-waves relaxation rate in two
series of nanodisks of diameter 300, 500 and 700~nm, patterned out of
two systems: a 20~nm thick yttrium iron garnet (YIG) film grown by pulsed laser
deposition either bare or covered by 13~nm of Pt. Using a magnetic resonance
force microscope, we measure precisely the ferromagnetic resonance linewidth of
each individual YIG and YIG{\textbar}Pt nanodisks. We find that the linewidth
in the nanostructure is sensibly smaller than the one measured in the extended
film. Analysis of the frequency dependence of the spectral linewidth indicates
that the improvement is principally due to the suppression of the inhomogeneous
part of the broadening due to geometrical confinement, suggesting that only the
homogeneous broadening contributes to the linewidth of the nanostructure. For
the bare YIG nano-disks, the broadening is associated to a damping constant
. A 3 fold increase of the linewidth is observed for
the series with Pt cap layer, attributed to the spin pumping effect. The
measured enhancement allows to extract the spin mixing conductance found to be
for our
YIG(20nm){\textbar}Pt interface, thus opening large opportunities for the
design of YIG based nanostructures with optimized magnetic losses.Comment: 4 pages, 3 figure
Loopedia, a Database for Loop Integrals
Loopedia is a new database at loopedia.org for information on Feynman
integrals, intended to provide both bibliographic information as well as
results made available by the community. Its bibliometry is complementary to
that of SPIRES or arXiv in the sense that it admits searching for integrals by
graph-theoretical objects, e.g. its topology.Comment: 16 pages, lots of screenshot
Ferrite-damped higher-order mode study in the Brookhaven energy-recovery linac cavity
A superconducting energy-recovery linac (ERL) is under construction at Brookhaven National Laboratory (BNL) to serve as a test bed for an application to upgrades of the Relativistic Heavy Ion Collider (RHIC). The damping of higher-order modes in the superconducting five-cell cavity is of paramount importance and represents the topic of this paper. Achieving the damping by the exclusive use of two ferrite absorbers and the adoption of a space-saving step instead of the conventional taper are part of the exploratory study. Absorber properties which are portable to simulation programs for the ERL cavity have been obtained by measuring the absorber as a ferrite-loaded pill-box cavity. Measured and simulated results for the lowest dipole modes in the prototype copper cavity with one absorber are discussed. First room-temperature measurements of the fully assembled niobium cavity string are presented which confirm the effective damping of higher-order modes by the ferrite absorbers, and which give credibility to the simulated R over Q's in the ERL.open1
Dynamical Polarizabilities of SU(3) Octet of Baryons
We present calculations and an analysis of the spin-independent dipole
electric and magnetic dynamical polarizabilities for the lowest in mass SU(3)
octet of baryons. These extensive calculations are made possible by the recent
implementation of semi-automatized calculations in Chiral Perturbation Theory
which allows evaluating dynamical spin-independent electromagnetic
polarizabilities from Compton scattering up to next-to-the-leading order. Our
results are in good agreement with calculations performed for nucleons found in
the literature. The dependencies for the range of photon energies up to 1 GeV,
covering the majority of the meson photo production channels, are analyzed. The
separate contributions into polarizabilities from the various baryon meson
clouds are studied.Comment: 10 pages, 7 figures, extended analysis of hyperon polarizabilitie
Discovery of the VHE gamma-ray source HESS J1641-463
A new TeV source, HESS J1641-463, has been serendipitously discovered in the
Galactic plane by the High Energy Stereoscopic System (H.E.S.S.) at a
significance level of 8.6 standard deviations. The observations of HESS
J1641-463 were performed between 2004 and 2011 and the source has a moderate
flux level of 1.7% of the Crab Nebula flux at E > 1 TeV. HESS J1641-463 has a
rather hard photon index of 1.99 +- 0.13_stat +- 0.20_sys. HESS J1641-463 is
positionally coincident with the radio supernova remnant SNR G338.5+0.1, but no
clear X-ray counterpart has been found in archival Chandra observations of the
region. Different possible VHE production scenarios will be discussed in this
contribution.Comment: 5 pages, 5 figures, 2012 Fermi Symposium proceedings - eConf C12102
Cytochrome P450 diversity and induction by gorgonian allelochemicals in the marine gastropod Cyphoma gibbosum
© The Authors, 2010. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in BMC Ecology 10 (2010): 24, doi:10.1186/1472-6785-10-24.Intense consumer pressure strongly affects the structural organization and function of marine ecosystems, while also having a profound effect on the phenotype of both predator and prey. Allelochemicals produced by prey often render their tissues unpalatable or toxic to a majority of potential consumers, yet some marine consumers have evolved resistance to host chemical defenses. A key challenge facing marine ecologists seeking to explain the vast differences in consumer tolerance of dietary allelochemicals is understanding the biochemical and molecular mechanisms underlying diet choice. The ability of marine consumers to tolerate toxin-laden prey may involve the cooperative action of biotransformation enzymes, including the inducible cytochrome P450s (CYPs), which have received little attention in marine invertebrates despite the importance of allelochemicals in their evolution. Here, we investigated the diversity, transcriptional response, and enzymatic activity of CYPs possibly involved in allelochemical detoxification in the generalist gastropod Cyphoma gibbosum, which feeds exclusively on chemically defended gorgonians. Twelve new genes in CYP family 4 were identified from the digestive gland of C. gibbosum. Laboratory-based feeding studies demonstrated a 2.7- to 5.1-fold induction of Cyphoma CYP4BK and CYP4BL transcripts following dietary exposure to the gorgonian Plexaura homomalla, which contains high concentrations of anti-predatory prostaglandins. Phylogenetic analysis revealed that C. gibbosum CYP4BK and CYP4BL were most closely related to vertebrate CYP4A and CYP4F, which metabolize pathophysiologically important fatty acids, including prostaglandins. Experiments involving heterologous expression of selected allelochemically-responsive C. gibbosum CYP4s indicated a possible role of one or more CYP4BL forms in eicosanoid metabolism. Sequence analysis further demonstrated that Cyphoma CYP4BK/4BL and vertebrate CYP4A/4F forms share identical amino acid residues at key positions within fatty acid substrate recognition sites. These results demonstrate differential regulation of CYP transcripts in a marine consumer feeding on an allelochemical-rich diet, and significantly advance our understanding of both the adaptive molecular mechanisms that marine consumers use to cope with environmental chemical pressures and the evolutionary history of allelochemical-metabolizing enzymes in the CYP superfamily.Financial
support for this work was provided by the Ocean Life Institute Tropical
Research Initiative Grant (WHOI) to KEW and MEH; the Robert H. Cole Endowed
Ocean Ventures Fund (WHOI) to KEW; the National Undersea Research Center -
Program Development Proposal (CMRC-03PRMN0103A) to KEW and a National
Science Foundation Graduate Research Fellowship to KEW
Factors Associated with the Diversification of the Gut Microbial Communities within Chimpanzees from Gombe National Park.
The gastrointestinal tract harbors large and diverse populations of bacteria that vary among individuals and within individuals over time. Numerous internal and external factors can influence the contents of these microbial communities, including diet, geography, physiology, and the extent of contact among hosts. To investigate the contributions of such factors to the variation and changes in gut microbial communities, we analyzed the distal gut microbiota of individual chimpanzees from two communities in Gombe National Park, Tanzania. These samples, which were derived from 35 chimpanzees, many of whom have been monitored for multiple years, provide an unusually comprehensive longitudinal depth for individuals of known genetic relationships. Although the composition of the great-ape microbiota has been shown to codiversify with host species, indicating that host genetics and phylogeny have played a major role in its differentiation over evolutionary timescales, the geneaological relationships of individual chimpanzees did not coincide with the similarity in their gut microbial communities. However, the inhabitants from adjacent chimpanzee communities could be distinguished based on the contents of their gut microbiota. Despite the broad similarity of community members, as would be expected from shared diet or interactions, long-term immigrants to a community often harbored the most distinctive gut microbiota, suggesting that individuals retain hallmarks of their previous gut microbial communities for extended periods. This pattern was reinforced in several chimpanzees sampled over long temporal scales, in which the major constituents of the gut microbiota were maintained for nearly a decade
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