38,927 research outputs found
A New Model for the Hard Time Lags in Black Hole X-Ray Binaries
The time-dependent Comptonized output of a cool soft X-ray source drifting
inward through an inhomogeneous hot inner disk or corona is numerically
simulated. We propose that this scenario can explain from first principles the
observed trends in the hard time lags and power spectra of the rapid aperiodic
variability of the X-ray emission of Galactic black-hole candidates.Comment: 10 pages, including 2 figures; uses epsf.sty, rotate.sty; accepted
for ApJ Letter
SIRIS: a high resolution scanning infrared camera for examining paintings
The new SIRIS (Scanning InfraRed Imaging System) camera developed at the National Gallery in London allows highresolution images of paintings to be made in the near infrared region (900–1700 nm). Images of 5000 × 5000 pixels are made by moving a 320 × 256 pixel InGaAs array across the focal plane of the camera using two orthogonal translation stages. The great advantages of this camera over scanning infrared devices are its relative portability and that image acquisition is comparatively rapid – a full 5000 × 5000 pixel image can be made in around 20 minutes. The paper describes the development of the mechanical, optical and electronic components of the camera, including the design of a new lens. The software routines used to control image capture and to assemble the individual 320 × 256 pixel frames into a seamless mosaic image are also mentioned. The optics of the SIRIS camera have been designed so that the camera can operate at a range of resolutions; from around 2.5 pixels per millimetre on large paintings of up to 2000 × 2000 mm to 10 pixels per millimetre on smaller paintings or details of paintings measuring 500 × 500 mm. The camera is primarily designed to examine underdrawings in paintings; preliminary results from test targets and paintings are presented and the quality of the images compared with those from other cameras currently used in this field
Calibration of GRB Luminosity Relations with Cosmography
For the use of Gamma-Ray Bursts (GRBs) to probe cosmology in a
cosmology-independent way, a new method has been proposed to obtain luminosity
distances of GRBs by interpolating directly from the Hubble diagram of SNe Ia,
and then calibrating GRB relations at high redshift. In this paper, following
the basic assumption in the interpolation method that objects at the same
redshift should have the same luminosity distance, we propose another approach
to calibrate GRB luminosity relations with cosmographic fitting directly from
SN Ia data. In cosmography, there is a well-known fitting formula which can
reflect the Hubble relation between luminosity distance and redshift with
cosmographic parameters which can be fitted from observation data. Using the
Cosmographic fitting results from the Union set of SNe Ia, we calibrate five
GRB relations using GRB sample at and deduce distance moduli of GRBs
at by generalizing above calibrated relations at high
redshift. Finally, we constrain the dark energy parameterization models of the
Chevallier-Polarski-Linder (CPL) model, the Jassal-Bagla-Padmanabhan (JBP)
model and the Alam model with GRB data at high redshift, as well as with the
Cosmic Microwave Background radiation (CMB) and the baryonic acoustic
oscillation (BAO) observations, and we find the CDM model is
consistent with the current data in 1- confidence region.Comment: 15 pages, 4 figures, 2 tables; accepted for publication in IJMP
Simulating Z_2 topological insulators with cold atoms in a one-dimensional optical lattice
We propose an experimental scheme to simulate and detect the properties of
time-reversal invariant topological insulators, using cold atoms trapped in
one-dimensional bichromatic optical lattices. This system is described by a
one-dimensional Aubry-Andre model with an additional SU(2) gauge structure,
which captures the essential properties of a two-dimensional Z2 topological
insulator. We demonstrate that topologically protected edge states, with
opposite spin orientations, can be pumped across the lattice by sweeping a
laser phase adiabatically. This process constitutes an elegant way to transfer
topologically protected quantum states in a highly controllable environment. We
discuss how density measurements could provide clear signatures of the
topological phases emanating from our one-dimensional system.Comment: 5 pages +, 3 figures, to appear in Physical Review
Spontaneous formation of a chiral (Mo2O2S2)2+-based cluster driven by dimeric {Te2O6}-based templates
Utilization of [Mo2S2O2(H2O)6]2+ and a tellurite anion led to the formation of three new clusters, 1–3, with unique structural features. The tellurite anion not only templated the formation of [(Mo2O2S2)4(TeO3)(OH)9]3− 1 and [(Mo2O2S2)12(TeO3)4(TeO4)2 (OH)18]10− 3, but also the in situ generation of two different types of dimeric {Te2O6} based moieties induced the spontaneous assembly of the chiral [(Mo2O2S2)10(TeO3)(Te2O6)2(OH)18]8− anionic cluster, 2
Comptonization signatures in the rapid aperiodic variability of Galactic black-hole candidates
We investigate the effect of inverse-Compton scattering of flares of soft
radiation in different geometries of a hot, Comptonizing region and a colder
accretion disk around a solar-mass black hole. The photon-energy dependent
light curves, their Fourier transforms, power spectra and Fourier-period
dependent time lags of hard photons with respect to softer photons are
discussed. On the basis of a comparison with existing data we find arguments
against Comptonization of external soft radiation as well as Comptonization in
a homogeneous medium as dominant mechanisms for the rapid aperiodic variability
in Galactic black-hole candidates. Possible further observational tests for the
influence of Comptonization on the rapid aperiodic variability of Galactic
black-hole candidates are suggested.Comment: 32 pages, including 10 figures and 2 tables; uses epsf.sty,
rotate.sty; submitted to Ap
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