531 research outputs found
Pulsar timing arrays and the challenge of massive black hole binary astrophysics
Pulsar timing arrays (PTAs) are designed to detect gravitational waves (GWs)
at nHz frequencies. The expected dominant signal is given by the superposition
of all waves emitted by the cosmological population of supermassive black hole
(SMBH) binaries. Such superposition creates an incoherent stochastic
background, on top of which particularly bright or nearby sources might be
individually resolved. In this contribution I describe the properties of the
expected GW signal, highlighting its dependence on the overall binary
population, the relation between SMBHs and their hosts, and their coupling with
the stellar and gaseous environment. I describe the status of current PTA
efforts, and prospect of future detection and SMBH binary astrophysics.Comment: 18 pages, 4 figures. To appear in the Proceedings of the 2014 Sant
Cugat Forum on Astrophysics. Astrophysics and Space Science Proceedings, ed.
C.Sopuerta (Berlin: Springer-Verlag
Differentially expressed genes reflect disease-induced rather than disease-causing changes in the transcriptome.
Comparing transcript levels between healthy and diseased individuals allows the identification of differentially expressed genes, which may be causes, consequences or mere correlates of the disease under scrutiny. We propose a method to decompose the observational correlation between gene expression and phenotypes driven by confounders, forward- and reverse causal effects. The bi-directional causal effects between gene expression and complex traits are obtained by Mendelian Randomization integrating summary-level data from GWAS and whole-blood eQTLs. Applying this approach to complex traits reveals that forward effects have negligible contribution. For example, BMI- and triglycerides-gene expression correlation coefficients robustly correlate with trait-to-expression causal effects (r <sub>BMI </sub> = 0.11, P <sub>BMI </sub> = 2.0 × 10 <sup>-51</sup> and r <sub>TG </sub> = 0.13, P <sub>TG </sub> = 1.1 × 10 <sup>-68</sup> ), but not detectably with expression-to-trait effects. Our results demonstrate that studies comparing the transcriptome of diseased and healthy subjects are more prone to reveal disease-induced gene expression changes rather than disease causing ones
Solvable Models of Domain Walls in N=1 Supergravity
A class of exactly solvable models of domain walls are worked out in D=4
supergravity. We develop a method to embed globally supersymmetric
theories with exact BPS domain wall solutions into supergravity, by introducing
a gravitationally deformed superpotential. The gravitational deformation is
natural in the spirit of maintaining the K\"ahler invariance. The solutions of
the warp factor and the Killing spinor are also obtained. We find that three
distinct behaviors of warp factors arise depending on the value of a constant
term in the superpotential : exponentially decreasing in both sides of the
wall, flat in one side and decreasing in the other, and increasing in one side
and decreasing in the other. Only the first possibility gives the localized
massless graviton zero mode. Models with multi-walls and models with runaway
vacua are also discussed.Comment: 10 pages, 3 figures; Misprints in three formulas are correcte
Low Frequency Flickering of TT Arietis:Hard and Soft X-ray Emission Region
Using archival ASCA observations of TT Arietis, X-ray energy spectra and
power spectra of the intensity time series are presented for the first time.
The energy spectra are well-fitted by a two continuum plasma emission model
with temperatures around 1 keV and 10 keV. A coherent feature at about 0.643
mHz appeared in the power spectra during the observation.Comment: 9 pages in PostScript including figures, accepted for publication in
Astrophysics and Space Science, available at
http://astroa.physics.metu.edu.tr/preprints.htm
Pulsar-wind nebulae and magnetar outflows: observations at radio, X-ray, and gamma-ray wavelengths
We review observations of several classes of neutron-star-powered outflows:
pulsar-wind nebulae (PWNe) inside shell supernova remnants (SNRs), PWNe
interacting directly with interstellar medium (ISM), and magnetar-powered
outflows. We describe radio, X-ray, and gamma-ray observations of PWNe,
focusing first on integrated spectral-energy distributions (SEDs) and global
spectral properties. High-resolution X-ray imaging of PWNe shows a bewildering
array of morphologies, with jets, trails, and other structures. Several of the
23 so far identified magnetars show evidence for continuous or sporadic
emission of material, sometimes associated with giant flares, and a few
possible "magnetar-wind nebulae" have been recently identified.Comment: 61 pages, 44 figures (reduced in quality for size reasons). Published
in Space Science Reviews, "Jets and Winds in Pulsar Wind Nebulae, Gamma-ray
Bursts and Blazars: Physics of Extreme Energy Release
Knowledge-based energy functions for computational studies of proteins
This chapter discusses theoretical framework and methods for developing
knowledge-based potential functions essential for protein structure prediction,
protein-protein interaction, and protein sequence design. We discuss in some
details about the Miyazawa-Jernigan contact statistical potential,
distance-dependent statistical potentials, as well as geometric statistical
potentials. We also describe a geometric model for developing both linear and
non-linear potential functions by optimization. Applications of knowledge-based
potential functions in protein-decoy discrimination, in protein-protein
interactions, and in protein design are then described. Several issues of
knowledge-based potential functions are finally discussed.Comment: 57 pages, 6 figures. To be published in a book by Springe
Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector
A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results
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