3,835 research outputs found
Quantum effects in a superconducting glass model
We study disordered Josephson junctions arrays with long-range interaction
and charging effects. The model consists of two orthogonal sets of positionally
disordered parallel filaments (or wires) Josephson coupled at each crossing
and in the presence of a homogeneous and transverse magnetic field. The large
charging energy (resulting from small self-capacitance of the ultrathin wires)
introduces important quantum fluctuations of the superconducting phase within
each filament. Positional disorder and magnetic field frustration induce
spin-glass like ground state, characterized by not having long-range order of
the phases. The stability of this phase is destroyed for sufficiently large
charging energy. We have evaluated the temperature vs charging energy phase
diagram by extending the methods developed in the theory of infinite-range spin
glasses, in the limit of large magnetic field. The phase diagram in the
different temperature regimes is evaluated by using variety of methods, to wit:
semiclassical WKB and variational methods, Rayleigh-Schr\"{o}dinger
perturbation theory and pseudospin effective Hamiltonians. Possible
experimental consequences of these results are briefly discussed.Comment: 17 pages REVTEX. Two Postscript figures can be obtained from the
authors. To appear in PR
Allie: a database and a search service of abbreviations and long forms
Many abbreviations are used in the literature especially in the life sciences, and polysemous abbreviations appear frequently, making it difficult to read and understand scientific papers that are outside of a reader’s expertise. Thus, we have developed Allie, a database and a search service of abbreviations and their long forms (a.k.a. full forms or definitions). Allie searches for abbreviations and their corresponding long forms in a database that we have generated based on all titles and abstracts in MEDLINE. When a user query matches an abbreviation, Allie returns all potential long forms of the query along with their bibliographic data (i.e. title and publication year). In addition, for each candidate, co-occurring abbreviations and a research field in which it frequently appears in the MEDLINE data are displayed. This function helps users learn about the context in which an abbreviation appears. To deal with synonymous long forms, we use a dictionary called GENA that contains domain-specific terms such as gene, protein or disease names along with their synonymic information. Conceptually identical domain-specific terms are regarded as one term, and then conceptually identical abbreviation-long form pairs are grouped taking into account their appearance in MEDLINE. To keep up with new abbreviations that are continuously introduced, Allie has an automatic update system. In addition, the database of abbreviations and their long forms with their corresponding PubMed IDs is constructed and updated weekly
UV Bright Globular Clusters in M87: More Evidence for Super-helium-rich Stellar Populations?
We study the UV and optical properties of 38 massive GCs in M87, imaged using
the HST/STIS and WFPC2 instruments. The majority of these GCs appear extremely
bright in the FUV - roughly a magnitude brighter than their Galactic
counterparts with similar metallicities. The observed FUV flux is several times
larger than predictions of canonical old stellar population models. These
canonical models, which assume a fiducial helium enrichment parameter, dY/dZ=2,
are able to reproduce the observed FUV fluxes only if ages are 3--5 Gyr larger
than the WMAP age of the Universe, although the same models fit the UV
photometry of Galactic and M31 GCs for ages less than the WMAP age. A similar
discrepancy is found between the mass-weighted and UV-luminosity weighted ages
of the massive Galactic GC omega Cen, whose CMD (including peculiar features on
its well-populated horizontal branch) can be accurately reproduced by invoking
a small super-He-rich (dY/dZ ~ 90) stellar component. By comparison to omega
Cen, we propose that the majority of M87 GCs in our sample contain strong
signatures of similarly minor super-He-rich sub-components. Although we cannot
prove or disprove the extreme helium scenario at the moment, we show that the
same phenomenon that causes the extended horizontal branch of omega Cen
explains the UV brightness of our sample. If this is indeed due to the extreme
helium, this study would be the first to find its signatures in extragalactic
objects.Comment: 19 pages, 10 figures, accepted for publication in MNRA
The nuclear immune receptor RPS4 is required for RRS1SLH1-dependent constitutive defense activation in Arabidopsis thaliana
Plant nucleotide-binding leucine-rich repeat (NB-LRR) disease resistance (R) proteins recognize specific ‘‘avirulent’’ pathogen effectors and activate immune responses. NB-LRR proteins structurally and functionally resemble mammalian Nod-like receptors (NLRs). How NB-LRR and NLR proteins activate defense is poorly understood. The divergently transcribed Arabidopsis R genes, RPS4 (resistance to Pseudomonas syringae 4) and RRS1 (resistance to Ralstonia solanacearum 1), function together to confer recognition of Pseudomonas AvrRps4 and Ralstonia PopP2. RRS1 is the only known recessive NBLRR R gene and encodes a WRKY DNA binding domain, prompting suggestions that it acts downstream of RPS4 for transcriptional activation of defense genes. We define here the early RRS1-dependent transcriptional changes upon delivery of PopP2 via Pseudomonas type III secretion. The Arabidopsis slh1 (sensitive to low humidity 1) mutant encodes an RRS1 allele (RRS1SLH1) with a single amino acid (leucine) insertion in the WRKY DNA-binding domain. Its poor growth due to constitutive defense activation is rescued at higher temperature. Transcription profiling data indicate that RRS1SLH1-mediated defense activation overlaps substantially with AvrRps4- and PopP2-regulated responses. To better understand the genetic basis of RPS4/RRS1-dependent immunity, we performed a genetic screen to identify suppressor of slh1 immunity (sushi) mutants. We show that many sushi mutants carry mutations in RPS4, suggesting that RPS4 acts downstream or in a complex with RRS1. Interestingly, several mutations were identified in a domain C-terminal to the RPS4 LRR domain. Using an Agrobacterium-mediated transient assay system, we demonstrate that the P-loop motif of RPS4 but not of RRS1SLH1 is required for RRS1SLH1 function. We also recapitulate the dominant suppression of RRS1SLH1 defense activation by wild type RRS1 and show this suppression requires an intact RRS1 P-loop. These analyses of RRS1SLH1 shed new light on mechanisms by which NB-LRR protein pairs activate defense signaling, or are held inactive in the absence of a pathogen effector
Nonequilibrium mesoscopic transport: a genealogy
Models of nonequilibrium quantum transport underpin all modern electronic
devices, from the largest scales to the smallest. Past simplifications such as
coarse graining and bulk self-averaging served well to understand electronic
materials. Such particular notions become inapplicable at mesoscopic
dimensions, edging towards the truly quantum regime. Nevertheless a unifying
thread continues to run through transport physics, animating the design of
small-scale electronic technology: microscopic conservation and nonequilibrium
dissipation. These fundamentals are inherent in quantum transport and gain even
greater and more explicit experimental meaning in the passage to atomic-sized
devices. We review their genesis, their theoretical context, and their
governing role in the electronic response of meso- and nanoscopic systems.Comment: 21p
GALEX UV Color-Magnitude Relations and Evidence for Recent Star Formation in Early-type Galaxies
We have used the GALEX UV photometric data to construct a first
near-ultraviolet (NUV) color-magnitude relation (CMR) for the galaxies
pre-classified as early-type by SDSS studies. The NUV CMR is a powerful tool
for tracking the recent star formation history in early-type galaxies, owing to
its high sensitivity to the presence of young stellar populations. Our NUV CMR
for UV-weak galaxies shows a well-defined slope and thus will be useful for
interpreting the restframe NUV data of distant galaxies and studying their star
formation history. Compared to optical CMRs, the NUV CMR shows a substantially
larger scatter, which we interpret as evidence of recent star formation
activities. Roughly 15% of the recent epoch (z < 0.13) bright (M[r] < -22)
early-type galaxies show a sign of recent (< 1Gyr) star formation at the 1-2%
level (lower limit) in mass compared to the total stellar mass. This implies
that low level residual star formation was common during the last few billion
years even in bright early-type galaxies.Comment: This paper will be published as part of the Galaxy Evolution Explorer
(GALEX) Astrophysical Journal Letters Special Issue. Links to the full set of
papers will be available at http://www.galex.caltech.edu/PUBLICATIONS/ after
November 22, 200
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