43,448 research outputs found
Neutron star masses from hydrodynamical effects in obscured sgHMXBs
A population of obscured supergiant High Mass X-ray Binaries (sgHMXBs) has
been discovered by INTEGRAL. X-ray wind tomography of IGR J17252-3616 inferred
a slow wind velocity to account for the enhanced obscuration. The main goal of
this study is to understand under which conditions high obscuration could
occur. We have used an hydrodynamical code to simulate the flow of the stellar
wind around the neutron star. A grid of simulations was used to study the
dependency of the absorbing column density and of the X-ray light-curves on the
model parameters. A comparison between the simulation results and the
observations of IGR J17252-3616 provides an estimate on these parameters. We
have constrained the wind terminal velocity to 500-600 km/s and the neutron
star mass to 1.75-2.15 solar masses. We have confirmed that the initial
hypothesis of a slow wind velocity with a moderate mass loss rate is valid. The
mass of the neutron star can be constrained by studying its impact on the
accretion flow.Comment: A&A in pres
Leptonic origin of the 100 MeV gamma-ray emission from the Galactic Centre
The Galactic centre is a bright gamma-ray source with the GeV-TeV band
spectrum composed of two distinct components in the 1-10 GeV and 1-10 TeV
energy ranges. The nature of these two components is not clearly understood. We
investigate the gamma-ray properties of the Galactic centre to clarify the
origin of the observed emission. We report imaging, spectral, and timing
analysis of data from 74 months of observations of the Galactic centre by
FERMI/LAT gamma-ray telescope complemented by sub-MeV data from approximately
ten years of INTEGRAL/PICsIT observations. We find that the Galactic centre is
spatially consistent with the point source in the GeV band. The tightest 3
sigma upper limit on its radius is 0.13 degree in the 10-300 GeV energy band.
The spectrum of the source in the 100 MeV energy range does not have a
characteristic turnover that would point to the pion decay origin of the
signal. Instead, the source spectrum is consistent with a model of inverse
Compton scattering by high-energy electrons. In this a model, the GeV bump in
the spectrum originates from an episode of injection of high-energy particles,
which happened ~300 years ago. This injection episode coincides with the known
activity episode of the Galactic centre region, previously identified using
X-ray observations. The hadronic model of source activity could be still
compatible with the data if bremsstrahlung emission from high-energy electrons
was present in addition to pion decay emission.Comment: To match the accepted versio
A matrix ATP requirement for presequence translocation across the inner membrane of mitochondria
Nonequilibrium transitions induced by multiplicative noise
A new simple model exhibiting a noise-induced ordering transition (NIOT) and
a noise-induced disordering transition (NIDT), in which the noise is purely
multiplicative, is presented. Both transitions are found in two as well as in
one dimension (where they had not been previously reported). We show
analytically and numerically that the critical behavior of these two
transitions is described by the so called multiplicative noise(MN) universality
class. A computation of the set of critical exponents is presented in both
, and (where they have not been previously measured).Comment: 4 pages, 2 figures, Late
Using transonic small disturbance theory for predicting the aeroelastic stability of a flexible wind-tunnel model
The CAP-TSD (Computational Aeroelasticity Program - Transonic Small Disturbance) code, developed at the NASA - Langley Research Center, is applied to the Active Flexible Wing (AFW) wind tunnel model for prediction of the model's transonic aeroelastic behavior. Static aeroelastic solutions using CAP-TSD are computed. Dynamic (flutter) analyses are then performed as perturbations about the static aeroelastic deformations of the AFW. The accuracy of the static aeroelastic procedure is investigated by comparing analytical results to those from previous AFW wind tunnel experiments. Dynamic results are presented in the form of root loci at different Mach numbers for a heavy gas and air. The resultant flutter boundaries for both gases are also presented. The effects of viscous damping and angle-of-attack, on the flutter boundary in air, are presented as well
Dynamics of capillary spreading along hydrophilic microstripes
We have studied the capillary spreading of a Newtonian liquid along hydrophilic microstripes that are chemically defined on a hydrophobic substrate. The front of the spreading film advances in time according to a power law x=Bt1/2. This exponent of 1/2 is much larger than the value 1/10 observed in the axisymmetric spreading of a wetting droplet. It is identical to the exponent found for wicking in open or closed microchannels. Even though no wicking occurs in our system, the influence of surface curvature induced by the lateral confinement of the liquid stripe also leads to an exponent of 1/2 but with a strongly modified prefactor B. We obtain excellent experimental agreement with the predicted time dependence of the front location and the dependence of the front speed on the stripe width. Additional experiments and simulations reveal the influence of the reservoir volume, liquid material parameters, edge roughness, and nonwetting defects. These results are relevant to liquid dosing applications or microfluidic delivery systems based on free-surface flow
Mitochondrial heat shock protein 70, a molecular chaperone for proteins encoded by mitochondrial DNA
Mitochondrial heat shock protein 70 (mt-Hsp70) has been shown to play an important role in facilitating import into, as well as folding and assembly of nuclear-encoded proteins in the mitochondrial matrix. Here, we describe a role for mt-Hsp70 in chaperoning proteins encoded by mitochondrial DNA and synthesized within mitochondria. The availability of mt-Hsp70 function influences the pattern of proteins synthesized in mitochondria of yeast both in vivo and in vitro. In particular, we show that mt-Hsp70 acts in maintaining the var1 protein, the only mitochondrially encoded subunit of mitochondrial ribosomes, in an assembly competent state, especially under heat stress conditions. Furthermore, mt-Hsp70 helps to facilitate assembly of mitochondrially encoded subunits of the ATP synthase complex. By interacting with the ATP-ase 9 oligomer, mt-Hsp70 promotes assembly of ATP-ase 6, and thereby protects the latter protein from proteolytic degradation. Thus mt-Hsp70 by acting as a chaperone for proteins encoded by the mitochondrial DNA, has a critical role in the assembly of supra- molecular complexes
Efficient algorithms for tensor scaling, quantum marginals and moment polytopes
We present a polynomial time algorithm to approximately scale tensors of any
format to arbitrary prescribed marginals (whenever possible). This unifies and
generalizes a sequence of past works on matrix, operator and tensor scaling.
Our algorithm provides an efficient weak membership oracle for the associated
moment polytopes, an important family of implicitly-defined convex polytopes
with exponentially many facets and a wide range of applications. These include
the entanglement polytopes from quantum information theory (in particular, we
obtain an efficient solution to the notorious one-body quantum marginal
problem) and the Kronecker polytopes from representation theory (which capture
the asymptotic support of Kronecker coefficients). Our algorithm can be applied
to succinct descriptions of the input tensor whenever the marginals can be
efficiently computed, as in the important case of matrix product states or
tensor-train decompositions, widely used in computational physics and numerical
mathematics.
We strengthen and generalize the alternating minimization approach of
previous papers by introducing the theory of highest weight vectors from
representation theory into the numerical optimization framework. We show that
highest weight vectors are natural potential functions for scaling algorithms
and prove new bounds on their evaluations to obtain polynomial-time
convergence. Our techniques are general and we believe that they will be
instrumental to obtain efficient algorithms for moment polytopes beyond the
ones consider here, and more broadly, for other optimization problems
possessing natural symmetries
Fuel economy and exhaust emissions characteristics of diesel vehicles: Test results of a prototype Fiat 131 NA 2.4 liter automobile
The vehicle was tested on a chassis dynamometer over selected drive cycles and steady-state conditions. Two fuels were used, a U.S. no. 2 diesel and a European diesel fuel. The vehicle was tested with retarded timing and with and without an oxidation catalyst. Particulate emission rates were calculated from dilution tunnel measurements and large volume particulate samples were collected for biological and chemical analysis. It was determined that while the catalyst was generally effective in reducing hydrocarbon and carbon monoxide levels, it was also a factor in increasing particulate emissions. Increased particulate emission rates were particularly evident when the vehicle was operated on the European fuel which has a high sulfur content
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