22,721 research outputs found
Gamma-ray burst host galaxies and the link to star-formation
We briefly review the current status of the study of long-duration gamma-ray
burst (GRB) host galaxies. GRB host galaxies are mainly interesting to study
for two reasons: 1) they may help us understand where and when massive stars
were formed throughout cosmic history, and 2) the properties of host galaxies
and the localisation within the hosts where GRBs are formed may give essential
clues to the precise nature of the progenitors. The main current problem is to
understand to what degree GRBs are biased tracers of star formation. If GRBs
are only formed by low-metallicity stars, then their host galaxies will not
give a representative view of where stars are formed in the Universe (at least
not a low redshifts). On the other hand, if there is no dependency on
metallicity then the nature of the host galaxies leads to the perhaps
surprising conclusion that most stars are formed in dwarf galaxies. In order to
resolve this issue and to fully exploit the potential of GRBs as probes of
star-forming galaxies throughout the observable universe it is mandatory that a
complete sample of bursts with redshifts and host galaxy detections is built.Comment: 9 pages, 3 figures. To appear in the proceedings of the Eleventh
Marcel Grossmann Meeting on General Relativity, eds. H. Kleinert, R. T.
Jantzen & R. Ruffini, World Scientific, Singapore, 200
A Minimum-Labeling Approach for Reconstructing Protein Networks across Multiple Conditions
The sheer amounts of biological data that are generated in recent years have
driven the development of network analysis tools to facilitate the
interpretation and representation of these data. A fundamental challenge in
this domain is the reconstruction of a protein-protein subnetwork that
underlies a process of interest from a genome-wide screen of associated genes.
Despite intense work in this area, current algorithmic approaches are largely
limited to analyzing a single screen and are, thus, unable to account for
information on condition-specific genes, or reveal the dynamics (over time or
condition) of the process in question. Here we propose a novel formulation for
network reconstruction from multiple-condition data and devise an efficient
integer program solution for it. We apply our algorithm to analyze the response
to influenza infection in humans over time as well as to analyze a pair of ER
export related screens in humans. By comparing to an extant, single-condition
tool we demonstrate the power of our new approach in integrating data from
multiple conditions in a compact and coherent manner, capturing the dynamics of
the underlying processes.Comment: Peer-reviewed and presented as part of the 13th Workshop on
Algorithms in Bioinformatics (WABI2013
Field-induced nematic-like magnetic transition in an iron pnictide superconductor, Ca(PtAs)((FePt)As)
We report a high magnetic field study up to 55 T of the nearly optimally
doped iron-pnictide superconductor Ca(PtAs)
((FePt)As) (x=0.078(6)) with a Tc 10 K using
magnetic torque, tunnel diode oscillator technique and transport measurements.
We determine the superconducting phase diagram, revealing an anisotropy of the
irreversibility field up to a factor of 10 near Tc and signatures of multiband
superconductivity. Unexpectedly, we find a spin-flop like anomaly in magnetic
torque at 22 T, when the magnetic field is applied perpendicular to the ab
planes, which becomes significantly more pronounced as the temperature is
lowered to 0.33 K. As our superconducting sample lies well outside the
antiferromagnetic region of the phase diagram, the observed field-induced
transition in torque indicates a spin-flop transition not of long-range ordered
moments, but of nematic-like antiferromagnetic fluctuations.Comment: Latex, 4 figure
Measurements of total alkalinity and inorganic dissolved carbon in the Atlantic Ocean and adjacent Southern Ocean between 2008 and 2010
Water column dissolved inorganic carbon and total alkalinity were measured during five hydrographic sections in the Atlantic Ocean and Drake Passage. The work was funded through the Strategic Funding Initiative of the UK's Oceans2025 programme, which ran from 2007 to 2012. The aims of this programme were to establish the regional budgets of natural and anthropogenic carbon in the North Atlantic, the South Atlantic, and the Atlantic sector of the Southern Ocean, as well as the rates of change of these budgets. This paper describes in detail the dissolved inorganic carbon and total alkalinity data collected along eastâwest sections at 47° N to 60° N, 24.5° N, and 24° S in the Atlantic and across two Drake Passage sections. Other hydrographic and biogeochemical parameters were measured during these sections, and relevant standard operating procedures are mentioned here. Over 95% of dissolved inorganic carbon and total alkalinity samples taken during the 24.5° N, 24° S, and the Drake Passage sections were analysed onboard and subjected to a first-level quality control addressing technical and analytical issues. Samples taken along 47° N to 60° N were analysed and subjected to quality control back in the laboratory. Complete post-cruise second-level quality control was performed using cross-over analysis with historical data in the vicinity of measurements, and data were submitted to the CLIVAR and Carbon Hydrographic Data Office (CCHDO), the Carbon Dioxide Information Analysis Center (CDIAC) and and will be included in the Global Ocean Data Analyses Project, version 2 (GLODAP 2), the upcoming update of Key et al. (2004)
Spectral and localization properties of the Dirichlet wave guide with two concentric Neumann discs
Bound states of the Hamiltonian describing a quantum particle living on three
dimensional straight strip of width are investigated. We impose the Neumann
boundary condition on the two concentric windows of the radii and
located on the opposite walls and the Dirichlet boundary condition on the
remaining part of the boundary of the strip. We prove that such a system
exhibits discrete eigenvalues below the essential spectrum for any .
When and tend to the infinity, the asymptotic of the eigenvalue is
derived. A comparative analysis with the one-window case reveals that due to
the additional possibility of the regulating energy spectrum the anticrossing
structure builds up as a function of the inner radius with its sharpness
increasing for the larger outer radius. Mathematical and physical
interpretation of the obtained results is presented; namely, it is derived that
the anticrossings are accompanied by the drastic changes of the wave function
localization. Parallels are drawn to the other structures exhibiting similar
phenomena; in particular, it is proved that, contrary to the two-dimensional
geometry, at the critical Neumann radii true bound states exist.Comment: 25 pages, 7 figure
Heavy maternal alcohol consumption and cerebral palsy in the offspring
AIM The aim of this study was to investigate the association between heavy maternal alcohol consumption and pre- peri- and postneonatally acquired cerebral palsy (CP). METHOD The records of all mothers with an International Classification of Diseases, revision 9 or 10 (ICD-9 â -10) alcohol-related diagnostic code, indicating heavy alcohol consumption, recorded on population-based health, mental health, and drug and alcohol data sets from 1983 to 2007, and their children were identified through the Western Australian Data-linkage System. This âexposedâ cohort was frequency matched with mothers without an alcohol-related diagnosis and their offspring (comparison group). Cases of CP were identified through linkage with the Western Australia CP Register. Analyses were undertaken using multivariate logistic regression.
RESULTS There were 23 573 live births in the exposed group (58.6% non-Aboriginal; 41.4% Aboriginal) and 292 cases of CP. The odds of pre â perinatally acquired CP were elevated for children of non-Aboriginal mothers with an alcohol-related diagnosis recorded during pregnancy (adjusted odds ratio 3.32; 95% confidence interval [CI] 1.30â8.48) and for Aboriginal children when an alcohol-related diagnosis was recorded up to 12 months before the motherâs pregnancy (adjusted odds ratio 2.49; 95% CI 0.99â6.25). Increased odds of postneonatally acquired CP following any alcohol-related diagnosis were found for non-Aboriginal children (adjusted odds ratio 7.92; 95% CI 2.23â28.14).
INTERPRETATION These results suggest that heavy maternal alcohol consumption is a direct cause of pre â perinatally acquired CP, and an indirect cause of postneonatally acquired CP, in non-Aboriginal children. The lack of an association for Aboriginal children requires further investigation but may be due to under ascertainment of alcohol use disorders during pregnancy and other aetiological pathways
Brane Gas Cosmology, M-theory and Little String Theory
We generalize the Brane Gas Cosmological Scenario to M-theory degrees of
freedom, namely and branes. Without brane intersections, the
Brandenberger Vafa(BV) arguments applied to M-theory degrees of freedom
generically predict a large 6 dimensional spacetime. We show that intersections
of and branes can instead lead to a large 4 dimensional spacetime.
One dimensional intersections in 11D is related to (2,0) little strings (LST)
on NS5 branes in type IIA. The gas regime of membranes in M-theory corresponds
to the thermodynamics of LST obtained from holography. We propose a mechanism
whereby LST living on the worldvolume of NS5 (M5)-branes wrapping a five
dimensional torus, annihilate most efficiently in 3+1 dimensions leading to a
large 3+1 dimensional spacetime. We also show that this picture is consistent
with the gas approximation in M-theory.Comment: 8 page
Superradiant Decay of Cyclotron Resonance of Two-Dimensional Electron Gases
We report on the observation of collective radiative decay, or superradiance,
of cyclotron resonance (CR) in high-mobility two-dimensional electron gases in
GaAs quantum wells using time-domain terahertz magnetospectroscopy. The decay
rate of coherent CR oscillations increases linearly with the electron density
in a wide range, which is a hallmark of superradiant damping. Our fully quantum
mechanical theory provides a universal formula for the decay rate, which
reproduces our experimental data without any adjustable parameter. These
results firmly establish the many-body nature of CR decoherence in this system,
despite the fact that the CR frequency is immune to electron-electron
interactions due to Kohn's theorem.Comment: 5 pages, 4 figure
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