32,777 research outputs found
In-medium kaon and antikaon properties in the quark-meson coupling model
The properties of the kaon, , and antikaon, \kbar, in nuclear medium are
studied in the quark-meson coupling (QMC) model. Employing a constituent
quark-antiquark (MIT bag model) picture, their excitation energies in a nuclear
medium at zero momentum are calculated within mean field approximation. The
scalar, and the vector mesons are assumed to couple directly to the nonstrange
quarks and antiquarks in the and \kbar mesons. It is demonstrated that
the meson induces different mean field potentials for each member of the
isodoublets, and \kbar, when they are embedded in asymmetric nuclear
matter. Furthermore, it is also shown that this meson potential is
repulsive for the meson in matter with a neutron excess, and renders
condensation less likely to occur.Comment: Latex, 11 pages, 4 Postscript figures, a few typos which can be
important for an interpretation (but not reflected in the results) are
corrected, as published in (E) Phys. Lett. B 436 (1998) 45
A Theory of Gamma-Ray Bursts
We present a specific scenario for the link between GRB and hypernovae, based
on Blandford-Znajek extraction of black-hole spin energy. Such a mechanism
requires a high angular momentum in the progenitor object. The observed
association of gamma-ray bursts with type Ibc supernovae leads us to consider
massive helium stars that form black holes at the end of their lives as
progenitors. We combine the numerical work of MacFadyen & Woosley with analytic
calculations, to show that about 1E53 erg each are available to drive the fast
GRB ejecta and the supernova. The GRB ejecta are driven by the power output
through the open field lines, whereas the supernova is powered by closed filed
lines and jet shocks. We also present a much simplified approximate derivation
of these energetics.
Helium stars that leave massive black-hole remnants in special ways, namely
via soft X-ray transients or very massive WNL stars. Since binaries naturally
have high angular momentum, we propose a link between black-hole transients and
gamma-ray bursts. Recent observations of one such transient, GRO J1655-40/Nova
Scorpii 1994, explicitly support this connection: its high space velocity
indicates that substantial mass was ejected in the formation of the black hole,
and the overabundance of alpha-nuclei, especially sulphur, indicates that the
explosion energy was extreme, as in SN 1998bw/GRB 980425. (abstract shortened)Comment: 32 pages, 8 figures, accepted for publication in New Astronom
Kaon mass in dense matter
The variation of kaon mass in dense, charge-neutral baryonic matter at
beta-equilibrium has been investigated. The baryon interaction has been
included by means of nonlinear Walecka model, with and without hyperons and the
interaction of kaons with the baryons has been incorporated through the
Nelson-Kaplan model. A self-consistant, one-loop level calculation has been
carried out. We find that at the mean field level, the presence of the hyperons
makes the density-dependence of the kaon mass softer. Thus, the kaon
condensation threshold is pushed up in the baryon density. The loop diagrams
tend to lower the kaon condensation point for lower values of . We
also find that the S-wave kaon-nucleon interaction plays the dominant role in
determining the on-set of kaon condensation and the contribution of the P-wave
interaction is insignificant.Comment: Four figures available on reques
A Novel Sequence-Based Antigenic Distance Measure for H1N1, with Application to Vaccine Effectiveness and the Selection of Vaccine Strains
H1N1 influenza causes substantial seasonal illness and was the subtype of the
2009 influenza pandemic. Precise measures of antigenic distance between the
vaccine and circulating virus strains help researchers design influenza
vaccines with high vaccine effectiveness. We here introduce a sequence-based
method to predict vaccine effectiveness in humans. Historical epidemiological
data show that this sequence-based method is as predictive of vaccine
effectiveness as hemagglutination inhibition (HI) assay data from ferret animal
model studies. Interestingly, the expected vaccine effectiveness is greater
against H1N1 than H3N2, suggesting a stronger immune response against H1N1 than
H3N2. The evolution rate of hemagglutinin in H1N1 is also shown to be greater
than that in H3N2, presumably due to greater immune selection pressure.Comment: 26 pages, 7 figures, 2 tables, supplemen
Accurate exchange-correlation energies for the warm dense electron gas
Density matrix quantum Monte Carlo (DMQMC) is used to sample exact-on-average
-body density matrices for uniform electron gas systems of up to 10
matrix elements via a stochastic solution of the Bloch equation. The results of
these calculations resolve a current debate over the accuracy of the data used
to parametrize finite-temperature density functionals. Exchange-correlation
energies calculated using the real-space restricted path-integral formalism and
the -space configuration path-integral formalism disagree by up to
\% at certain reduced temperatures and densities . Our calculations confirm the accuracy of the configuration
path-integral Monte Carlo results available at high density and bridge the gap
to lower densities, providing trustworthy data in the regime typical of
planetary interiors and solids subject to laser irradiation. We demonstrate
that DMQMC can calculate free energies directly and present exact free energies
for and .Comment: Accepted version: added free energy data and restructured text. Now
includes supplementary materia
A cancer cell-line titration series for evaluating somatic classification.
BackgroundAccurate detection of somatic single nucleotide variants and small insertions and deletions from DNA sequencing experiments of tumour-normal pairs is a challenging task. Tumour samples are often contaminated with normal cells confounding the available evidence for the somatic variants. Furthermore, tumours are heterogeneous so sub-clonal variants are observed at reduced allele frequencies. We present here a cell-line titration series dataset that can be used to evaluate somatic variant calling pipelines with the goal of reliably calling true somatic mutations at low allele frequencies.ResultsCell-line DNA was mixed with matched normal DNA at 8 different ratios to generate samples with known tumour cellularities, and exome sequenced on Illumina HiSeq to depths of >300×. The data was processed with several different variant calling pipelines and verification experiments were performed to assay >1500 somatic variant candidates using Ion Torrent PGM as an orthogonal technology. By examining the variants called at varying cellularities and depths of coverage, we show that the best performing pipelines are able to maintain a high level of precision at any cellularity. In addition, we estimate the number of true somatic variants undetected as cellularity and coverage decrease.ConclusionsOur cell-line titration series dataset, along with the associated verification results, was effective for this evaluation and will serve as a valuable dataset for future somatic calling algorithm development. The data is available for further analysis at the European Genome-phenome Archive under accession number EGAS00001001016. Data access requires registration through the International Cancer Genome Consortium's Data Access Compliance Office (ICGC DACO)
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