558 research outputs found
Tunneling spectroscopy in the magnetic superconductor TmNi2B2C
We present new measurements about the tunneling conductance in the
borocarbide superconductor TmNiBC. The results show a very good
agreement with weak coupling BCS theory, without any lifetime broadening
parameter, over the whole sample surface. We detect no particular change of the
tunneling spectroscopy below 1.5K, when both the antiferromagnetic (AF) phase
and the superconducting order coexist.Comment: Submitted to Phys. Rev. B, Rapid Communication
Determination of Electromagnetic Source Direction as an Eigenvalue Problem
Low-frequency solar and interplanetary radio bursts are generated at
frequencies below the ionospheric plasma cutoff and must therefore be measured
in space, with deployable antenna systems. The problem of measuring both the
general direction and polarization of an electromagnetic source is commonly
solved by iterative fitting methods such as linear regression that deal
simultaneously with both directional and polarization parameters. We have
developed a scheme that separates the problem of deriving the source direction
from that of determining the polarization, avoiding iteration in a
multi-dimensional manifold. The crux of the method is to first determine the
source direction independently of concerns as to its polarization. Once the
source direction is known, its direct characterization in terms of Stokes
vectors in a single iteration if desired, is relatively simple. This study
applies the source-direction determination to radio signatures of flares
received by STEREO. We studied two previously analyzed radio type III bursts
and found that the results of the eigenvalue decomposition technique are
consistent with those obtained previously by Reiner et al. (Solar Phys. 259,
255, 2009). For the type III burst observed on 7 December 2007, the difference
in travel times from the derived source location to STEREO A and B is the same
as the difference in the onset times of the burst profiles measured by the two
spacecraft. This is consistent with emission originating from a single,
relatively compact source. For the second event of 29 January 2008, the
relative timing does not agree, suggesting emission from two sources separated
by 0.1 AU, or perhaps from an elongated region encompassing the apparent source
locations.Comment: 22 pages, 7 figures, Accepted in Solar Physic
Dimensional Crossover of Localisation and Delocalisation in a Quantum Hall Bar
The 2-- to 1--dimensional crossover of the localisation length of electrons
confined to a disordered quantum wire of finite width is studied in a
model of electrons moving in the potential of uncorrelated impurities. An
analytical formula for the localisation length is derived, describing the
dimensional crossover as function of width , conductance and
perpendicular magnetic field . On the basis of these results, the scaling
analysis of the quantum Hall effect in high Landau levels, and the
delocalisation transition in a quantum Hall wire are reconsidered.Comment: 12 pages, 7 figure
Very-high energy gamma-ray astronomy: A 23-year success story in high-energy astroparticle physics
Very-high energy (VHE) gamma quanta contribute only a minuscule fraction -
below one per million - to the flux of cosmic rays. Nevertheless, being neutral
particles they are currently the best "messengers" of processes from the
relativistic/ultra-relativistic Universe because they can be extrapolated back
to their origin. The window of VHE gamma rays was opened only in 1989 by the
Whipple collaboration, reporting the observation of TeV gamma rays from the
Crab nebula. After a slow start, this new field of research is now rapidly
expanding with the discovery of more than 150 VHE gamma-ray emitting sources.
Progress is intimately related with the steady improvement of detectors and
rapidly increasing computing power. We give an overview of the early attempts
before and around 1989 and the progress after the pioneering work of the
Whipple collaboration. The main focus of this article is on the development of
experimental techniques for Earth-bound gamma-ray detectors; consequently, more
emphasis is given to those experiments that made an initial breakthrough rather
than to the successors which often had and have a similar (sometimes even
higher) scientific output as the pioneering experiments. The considered energy
threshold is about 30 GeV. At lower energies, observations can presently only
be performed with balloon or satellite-borne detectors. Irrespective of the
stormy experimental progress, the success story could not have been called a
success story without a broad scientific output. Therefore we conclude this
article with a summary of the scientific rationales and main results achieved
over the last two decades.Comment: 45 pages, 38 figures, review prepared for EPJ-H special issue "Cosmic
rays, gamma rays and neutrinos: A survey of 100 years of research
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Survey of the prevalence of Salmonella species on laying hen farms in Kosovo
A survey on the prevalence of Salmonella (S.) species was carried out on 39 layer farms in Kosovo between April and September 2012. In total 367 samples, comprising feces, dust, eggs, and internal organs from dead birds, were investigated using bacteriological culture methods. Additionally, data on the location of the farm, the total number of birds on the farm, age of birds, and laying performance were collected. Salmonella were isolated from 38 samples obtained from 19 (49%) farms. The most common serovar identified was Salmonella enteritidis, found on 18 farms. The most common S. enteritidis phage type was PT29 followed by PT6, PT7, PT21, PT13a, PT8, PT14b, and PT4. One S. enteritidis isolate was not typable. Six farms had more than one phage type. Furthermore, serovar S. Bovismorbificans also was found in samples from 3 farms. Flock size or production stage was not associated with the probability of isolating Salmonella. The only flock factor found to be significantly associated was percent hen/day production: It was 2.8 times more likely to isolate Salmonella from flocks with production above 80% hen/day production compared to flocks producing at a lower level. Analysis of antimicrobial resistance patterns of 30 isolates revealed that all isolates were sensitive to gentamicin, ampicillin, sulphamethoxazole trimethoprim, and oxytetracycline, and 29 (97%) were sensitive to ciprofloxacin. All isolates showed intermediate resistance or were resistant to minocycline and cloxacillin. Twenty-six isolates (86%) had intermediate resistance to amoxicillin and 27 isolates (90%) were fully resistant to streptomycin. The present survey revealed a high prevalence of Salmonella enteritidis in layer flocks in Kosovo, indicating that table eggs have to be suspected as an important source of human salmone-llosis
An Integrated TCGA Pan-Cancer Clinical Data Resource to Drive High-Quality Survival Outcome Analytics
For a decade, The Cancer Genome Atlas (TCGA) program collected clinicopathologic annotation data along with multi-platform molecular profiles of more than 11,000 human tumors across 33 different cancer types. TCGA clinical data contain key features representing the democratized nature of the data collection process. To ensure proper use of this large clinical dataset associated with genomic features, we developed a standardized dataset named the TCGA Pan-Cancer Clinical Data Resource (TCGA-CDR), which includes four major clinical outcome endpoints. In addition to detailing major challenges and statistical limitations encountered during the effort of integrating the acquired clinical data, we present a summary that includes endpoint usage recommendations for each cancer type. These TCGA-CDR findings appear to be consistent with cancer genomics studies independent of the TCGA effort and provide opportunities for investigating cancer biology using clinical correlates at an unprecedented scale. Analysis of clinicopathologic annotations for over 11,000 cancer patients in the TCGA program leads to the generation of TCGA Clinical Data Resource, which provides recommendations of clinical outcome endpoint usage for 33 cancer types
Anisotropic flow of charged hadrons, pions and (anti-)protons measured at high transverse momentum in Pb-Pb collisions at TeV
The elliptic, , triangular, , and quadrangular, , azimuthal
anisotropic flow coefficients are measured for unidentified charged particles,
pions and (anti-)protons in Pb-Pb collisions at TeV
with the ALICE detector at the Large Hadron Collider. Results obtained with the
event plane and four-particle cumulant methods are reported for the
pseudo-rapidity range at different collision centralities and as a
function of transverse momentum, , out to GeV/.
The observed non-zero elliptic and triangular flow depends only weakly on
transverse momentum for GeV/. The small dependence
of the difference between elliptic flow results obtained from the event plane
and four-particle cumulant methods suggests a common origin of flow
fluctuations up to GeV/. The magnitude of the (anti-)proton
elliptic and triangular flow is larger than that of pions out to at least
GeV/ indicating that the particle type dependence persists out
to high .Comment: 16 pages, 5 captioned figures, authors from page 11, published
version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/186
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