401 research outputs found
RNA-Seq Analysis Reveals a Six-Gene SoxR Regulon in Streptomyces coelicolor
The redox-regulated transcription factor SoxR is conserved in diverse bacteria, but emerging studies suggest that this protein plays distinct physiological roles in different bacteria. SoxR regulates a global oxidative stress response (involving \u3e100 genes) against exogenous redox-cycling drugs in Escherichia coli and related enterics. In the antibiotic producers Streptomyces coelicolor and Pseudomonas aeruginosa, however, SoxR regulates a smaller number of genes that encode membrane transporters and proteins with homology to antibiotic-tailoring enzymes. In both S. coelicolor and P. aeruginosa, SoxR-regulated genes are expressed in stationary phase during the production of endogenously-produced redox-active antibiotics. These observations suggest that SoxR evolved to sense endogenous secondary metabolites and activate machinery to process and transport them in antibiotic-producing bacteria. Previous bioinformatics analysis that searched the genome for SoxR-binding sites in putative promoters defined a five-gene SoxR regulon in S. coelicolor including an ABC transporter, two oxidoreductases, a monooxygenase and an epimerase/dehydratase. Since this in silico screen may have missed potential SoxR-targets, we conducted a whole genome transcriptome comparison of wild type S. coelicolor and a soxR-deficient mutant in stationary phase using RNA-Seq. Our analysis revealed a sixth SoxR-regulated gene in S. coelicolor that encodes a putative quinone oxidoreductase. Knowledge of the full complement of genes regulated by SoxR will facilitate studies to elucidate the function of this regulatory molecule in antibiotic producers
Filling the holes: Evolving excised binary black hole initial data with puncture techniques
We follow the inspiral and merger of equal-mass black holes (BHs) by the
moving puncture technique and demonstrate that both the exterior solution and
the asymptotic gravitational waveforms are unchanged when the initial interior
solution is replaced by constraint-violating ``junk'' initial data. We apply
this result to evolve conformal thin-sandwich (CTS) binary BH initial data by
filling their excised interiors with arbitrary, but smooth, initial data and
evolving with standard puncture gauge choices. The waveforms generated for both
puncture and filled-CTS initial data are remarkably similar, and there are only
minor differences between irrotational and corotational CTS BH binaries. Even
the interior solutions appear to evolve to the same constraint-satisfying
solution at late times, independent of the initial data.Comment: 5 pages, 5 figures, accepted by PRD Rapid Communications, RevTe
Quasiequilibrium sequences of black-hole--neutron-star binaries in general relativity
We construct quasiequilibrium sequences of black hole-neutron star binaries
for arbitrary mass ratios by solving the constraint equations of general
relativity in the conformal thin-sandwich decomposition. We model the neutron
star as a stationary polytrope satisfying the relativistic equations of
hydrodynamics, and account for the black hole by imposing equilibrium boundary
conditions on the surface of an excised sphere (the apparent horizon). In this
paper we focus on irrotational configurations, meaning that both the neutron
star and the black hole are approximately nonspinning in an inertial frame. We
present results for a binary with polytropic index n=1, mass ratio
M_{irr}^{BH}/M_{B}^{NS}=5 and neutron star compaction
M_{ADM,0}^{NS}/R_0=0.0879, where M_{irr}^{BH} is the irreducible mass of the
black hole, M_{B}^{NS} the neutron star baryon rest-mass, and M_{ADM,0}^{NS}
and R_0 the neutron star Arnowitt-Deser-Misner mass and areal radius in
isolation, respectively. Our models represent valid solutions to Einstein's
constraint equations and may therefore be employed as initial data for
dynamical simulations of black hole-neutron star binaries.Comment: 5 pages, 1 figure, revtex4, published in Phys.Rev.
Quasiequilibrium black hole-neutron star binaries in general relativity
We construct quasiequilibrium sequences of black hole-neutron star binaries
in general relativity. We solve Einstein's constraint equations in the
conformal thin-sandwich formalism, subject to black hole boundary conditions
imposed on the surface of an excised sphere, together with the relativistic
equations of hydrostatic equilibrium. In contrast to our previous calculations
we adopt a flat spatial background geometry and do not assume extreme mass
ratios. We adopt a Gamma=2 polytropic equation of state and focus on
irrotational neutron star configurations as well as approximately nonspinning
black holes. We present numerical results for ratios of the black hole's
irreducible mass to the neutron star's ADM mass in isolation of
M_{irr}^{BH}/M_{ADM,0}^{NS} = 1, 2, 3, 5, and 10. We consider neutron stars of
baryon rest mass M_B^{NS}/M_B^{max} = 83% and 56%, where M_B^{max} is the
maximum allowed rest mass of a spherical star in isolation for our equation of
state. For these sequences, we locate the onset of tidal disruption and, in
cases with sufficiently large mass ratios and neutron star compactions, the
innermost stable circular orbit. We compare with previous results for black
hole-neutron star binaries and find excellent agreement with third-order
post-Newtonian results, especially for large binary separations. We also use
our results to estimate the energy spectrum of the outgoing gravitational
radiation emitted during the inspiral phase for these binaries.Comment: 17 pages, 15 figures, published in Phys. Rev.
Black Hole-Neutron Star Binary Merger Calculations: GRB Progenitors and the Stability of Mass Transfer
We have calculated the first dynamical evolutions of merging black
hole-neutron star binaries that treat the combined spacetime in a
nonperturbative general relativistic framework. Using the conformal flatness
approximation, we have studied how the location of the tidal disruption radius
with respect to the the black hole horizon and innermost stable circular orbit
(ISCO) affects the qualitative evolution of the system. Based on simple
arguments, we show that for a binary mass ratio q>~0.24, tidal disruption
occurs outside the ISCO, while the opposite is true for q<~0.24. When tidal
disruption occurs sufficiently far outside the ISCO, mass is transferred
unstably from the neutron star to the black hole, resulting in the complete
disruption of the neutron star. When tidal disruption occurs slightly within
the ISCO, we find that some of the mass forms an extremely hot disk around the
black hole. The resulting configurations in this case are excellent candidates
for the progenitors of short-hard gamma ray bursts.Comment: 8 pages, 5 figures, in Proceedings of the Albert Einstein Century
International Conference, Paris, France, 2005, edited by Jean-Michel Alimi
and Andre Fuzf
General Relativistic Binary Merger Simulations and Short Gamma Ray Bursts
The recent localization of some short-hard gamma ray bursts (GRBs) in
galaxies with low star formation rates has lent support to the suggestion that
these events result from compact object binary mergers. We discuss how new
simulations in general relativity are helping to identify the central engine of
short-hard GRBs. Motivated by our latest relativistic black hole-neutron star
merger calculations, we discuss a scenario in which these events may trigger
short-hard GRBs, and compare this model to competing relativistic models
involving binary neutron star mergers and the delayed collapse of hypermassive
neutron stars. Distinguishing features of these models may help guide future
GRB and gravitational wave observations to identify the nature of the sources.Comment: 5 Pages, 3 figures, accepted by ApJ Let
Maintaining Treatment Fidelity of Mindfulness-Based Relapse Prevention Intervention for Alcohol Dependence: A Randomized Controlled Trial Experience
Background. Treatment fidelity is essential to methodological rigor of clinical trials evaluating behavioral interventions such as Mindfulness Meditation (MM). However, procedures for monitoring and maintenance of treatment fidelity are inconsistently applied, limiting the strength of such research. Objective. To describe the implementation and findings related to fidelity monitoring of the Mindfulness-Based Relapse Prevention for Alcohol Dependence (MBRP-A) intervention in a 26-week randomized controlled trial. Methods. 123 alcohol dependent adults were randomly assigned to MM (MBRP-A and home practice, adjunctive to usual care; N=64) or control (usual care alone; N=59). Treatment fidelity assessment strategies recommended by the National Institutes of Health Behavior Change Consortium for study/intervention design, therapist training, intervention delivery, and treatment receipt and enactment were applied. Results. Ten 8-session interventions were delivered. Therapist adherence and competence, assessed using the modified MBRP Adherence and Competence Scale, were high. Among the MM group participants, 46 attended ≥4 sessions; over 90% reported at-home MM practice at 8 weeks and 72% at 26 weeks. They also reported satisfaction with and usefulness of MM for maintaining sobriety. No adverse events were reported. Conclusions. A systematic approach to assessment of treatment fidelity in behavioral clinical trials allows determination of the degree of consistency between intended and actual delivery and receipt of intervention
Fully General Relativistic Simulations of Black Hole-Neutron Star Mergers
Black hole-neutron star (BHNS) binaries are expected to be among the leading
sources of gravitational waves observable by ground-based detectors, and may be
the progenitors of short-hard gamma ray bursts (SGRBs) as well. Here, we
discuss our new fully general relativistic calculations of merging BHNS
binaries, which use high-accuracy, low-eccentricity, conformal thin-sandwich
configurations as initial data. Our evolutions are performed using the moving
puncture method and include a fully relativistic, high-resolution
shock-capturing hydrodynamics treatment. Focusing on systems in which the
neutron star is irrotational and the black hole is nonspinning with a 3:1 mass
ratio, we investigate the inspiral, merger, and disk formation in the system.
We find that the vast majority of material is promptly accreted and no more
than 3% of the neutron star's rest mass is ejected into a tenuous,
gravitationally bound disk. We find similar results for mass ratios of 2:1 and
1:1, even when we reduce the NS compaction in the 2:1 mass ratio case. These
ambient disks reach temperatures suitable for triggering SGRBs, but their
masses may be too small to produce the required total energy output. We measure
gravitational waveforms and compute the effective strain in frequency space,
finding measurable differences between our waveforms and those produced by
binary black hole mergers within the advanced LIGO band. These differences
appear at frequencies corresponding to the emission that occurs when the NS is
tidally disrupted and accreted by the black hole. The resulting information
about the radius of the neutron star may be used to constrain the neutron star
equation of state.Comment: 22 pages, 14 figures, fixed a few typo
The Central Component of Gravitational Lens Q0957+561
In 1981, a faint radio source (G') was detected near the center of the
lensing galaxy of the famous "twin quasar" Q0957+561. It is still unknown
whether this central radio source is a third quasar image or an active nucleus
of the lensing galaxy, or a combination of both. In an attempt to resolve this
ambiguity, we observed Q0957+561 at radio wavelengths of 13cm, 18cm, and 21cm,
using the Very Long Baseline Array in combination with the phased Very Large
Array and the Green Bank Telescope. We measured the spectrum of G' for the
first time and found it to be significantly different from the spectra of the
two bright quasar images. This finding suggests that the central component is
primarily or entirely emission from the foreground lens galaxy, but the
spectrum is also consistent with the hypothesis of a central quasar image
suffering free-free absorption. In addition, we confirm the previously-reported
VLBI position of G' just north of the optical center of the lens galaxy. The
position slightly favors the hypothesis that G' originates in the lens, but is
not conclusive. We discuss the prospects for further clarification of this
issue.Comment: 18 pages, accepted for publication in A
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