7,634 research outputs found
Space telescope phase B definition study. Volume 2A: Science instruments, f24 field camera
The analysis and design of the F/24 field camera for the space telescope are discussed. The camera was designed for application to the radial bay of the optical telescope assembly and has an on axis field of view of 3 arc-minutes by 3 arc-minutes
Design of a system to achieve diagnosis of brain lesions of suspected infectious origin from a database and a radiologic software
This Brainsupporters project aims at creating an international database including an extensive collection of radiologic images of brain lesions and the relevant clinical, laboratory and microbiological data, and a software, to highlight and differentiate the minimal alteration in the radiologic footprint related to the local alterations of brain tissue produced by each individual pathogen that will become an objective diagnostic tool. Clinical parameters will be taken into account in defining a procedure to estimate the probability that the difference between an image and a template be due to a specific pathological agent
The puzzling X-ray continuum of the quasar MR 2251-178
We report on a comprehensive X-ray spectral analysis of the nearby
radio-quiet quasar MR 2251-178, based on the long-look (~ 400 ks) XMM-Newton
observation carried out in November 2011. As the properties of the multiphase
warm absorber (thoroughly discussed in a recent, complementary work) hint at a
steep photoionizing continuum, here we investigate into the nature of the
intrinsic X-ray emission of MR 2251-178 by testing several physical models. The
apparent 2-10 keV flatness as well as the subtle broadband curvature can be
ascribed to partial covering of the X-ray source by a cold, clumpy absorption
system with column densities ranging from a fraction to several x10^23 cm^-2.
As opposed to more complex configurations, only one cloud is required along the
line of sight in the presence of a soft X-ray excess, possibly arising as
Comptonized disc emission in the accretion disc atmosphere. On statistical
grounds, even reflection with standard efficiency off the surface of the inner
disc cannot be ruled out, although this tentatively overpredicts the observed ~
14-150 keV emission. It is thus possible that each of the examined physical
processes is relevant to a certain degree, and hence only a combination of
high-quality, simultaneous broadband spectral coverage and multi-epoch
monitoring of X-ray spectral variability could help disentangling the different
contributions. Yet, regardless of the model adopted, we infer for MR 2251-178 a
bolometric luminosity of ~ 5-7 x 10^45 erg/s, implying that the central black
hole is accreting at ~ 15-25 per cent of the Eddington limit.Comment: 14 pages, 9 figures, 7 tables. Accepted for publication in MNRA
Model 1738 tape recorder/reproducer. general test requirements
Test requirements of tape recorder for Mariner progra
Artifact of the phonon-induced localization by variational calculations in the spin-boson model
We present energy and free energy analyses on all variational schemes used in
the spin-boson model at both T=0 and . It is found that all the
variational schemes have fail points, at where the variational schemes fail to
provide a lower energy (or a lower free energy at ) than the
displaced-oscillator ground state and therefore the variational ground state
becomes unstable, which results in a transition from a variational ground state
to a displaced oscillator ground state when the fail point is reached. Such
transitions are always misidentied as crossover from a delocalized to localized
phases in variational calculations, leading to an artifact of phonon-induced
localization. Physics origin of the fail points and explanations for different
transition behaviors with different spectral functions are found by studying
the fail points of the variational schemes in the single mode case.Comment: 9 pages, 7 figure
Designing Dirac points in two-dimensional lattices
We present a framework to elucidate the existence of accidental contacts of
energy bands, particularly those called Dirac points which are the point
contacts with linear energy dispersions in their vicinity. A generalized
von-Neumann-Wigner theorem we propose here gives the number of constraints on
the lattice necessary to have contacts without fine tuning of lattice
parameters. By counting this number, one could quest for the candidate of Dirac
systems without solving the secular equation. The constraints can be provided
by any kinds of symmetry present in the system. The theory also enables the
analytical determination of k-point having accidental contact by selectively
picking up only the degenerate solution of the secular equation. By using these
frameworks, we demonstrate that the Dirac points are feasible in various
two-dimensional lattices, e.g. the anisotropic Kagome lattice under inversion
symmetry is found to have contacts over the whole lattice parameter space.
Spin-dependent cases, such as the spin-density-wave state in LaOFeAs with
reflection symmetry, are also dealt with in the present scheme.Comment: 15pages, 9figures (accepted to Phys. Rev. B
Multi-Wavelength Study of Sgr A*: The Short Time Scale Variability
To understand the correlation and the radiation mechanism of flare emission
in different wavelength bands, we have coordinated a number of telescopes to
observe SgrA* simultaneously. We focus only on one aspect of the preliminary
results of our multi-wavelength observing campaigns, namely, the short time
scale variability of emission from SgrA* in near-IR, X-ray and radio
wavelengths. The structure function analysis indicate most of the power
spectral density is detected on hourly time scales in all wavelength bands. We
also report minute time scale variability at 7 and 13mm placing a strong
constraint on the nature of the variable emission. The hourly time scale
variability can be explained in the context of a model in which the peak
frequency of emission shifts toward lower frequencies as a self-absorbed
synchrotron source expands adiabatically near the acceleration site. The short
time scale variability, on the other hand, places a strong constraint on the
size of the emitting region. Assuming that rapid minute time scale fluctuations
of the emission is optically thick in radio wavelength, light travel arguments
requires relativistic particle energy, thus suggesting the presence of outflow
from SgrA*.Comment: 9 pages, 4 figures, The Galactic Center: A Window on the Nuclear
Environment of Disk Galaxies ASP Conference Series, 2010 eds: M. Morris, D.
Q. Wang and F. Yua
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