13,253 research outputs found
Spin-dependent conductivity of iron-based superconductors in a magnetic field
We report the results of a study of magnetic field features of electron
transport in heterojunctions with NS boundary inside iron-based
superconductors, represented by a binary phase of - FeSe and
oxyarsenide pnictide LaO(F)FeAs. We used the ability of self magnetic field of
the transport current to partially destroy superconductivity, no matter how low
the field may be, in the NS interface area, where, due to the proximity effect,
the superconducting order parameter, , disperses from 1 to 0 within the
scale of the Ginzburg-Landau coherence length. The following features of
transport were found:(i) at , magnetoresistance in systems with
different superconductors has different sign;(ii) sign and magnitude of the
magnetoresistance depend on the magnitude of current and temperature, and (iii)
in all operating modes where the contribution from Andreev reflection is
suppressed (),the hysteresis of the magnetoresistance
is present. Based on the results of the experiment and analysis it has been
concluded that there is along-range magnetic order in th eground normal state
of the iron-based superconductors studied, in the presence of itinerant
magnetism of conduction electrons which determines the possibility of
anisotropic spin-dependent exchange interaction with the local magnetic moments
of the ions.Comment: 9 pages, 7 figure
Modelling the Extreme X-ray Spectrum of IRAS 13224-3809
The extreme NLS1 galaxy IRAS 13224-3809 shows significant variability,
frequency depended time lags, and strong Fe K line and Fe L features in the
long 2011 XMM-Newton observation. In this work we study the spectral properties
of IRAS 13224-3809 in detail, and carry out a series of analyses to probe the
nature of the source, focusing in particular on the spectral variability
exhibited. The RGS spectrum shows no obvious signatures of absorption by
partially ionised material (warm absorbers). We fit the 0.3-10.0 keV spectra
with a model that includes relativistic reflection from the inner accretion
disc, a standard powerlaw AGN continuum, and a low-temperature (~0.1 keV)
blackbody, which may originate in the accretion disc, either as direct or
reprocessed thermal emission. We find that the reflection model explains the
time-averaged spectrum well, and we also undertake flux-resolved and
time-resolved spectral analyses, which provide evidence of gravitational
light-bending effects. Additionally, the temperature and flux of the blackbody
component are found to follow the relation expected for simple
thermal blackbody emission from a constant emitting area, indicating a physical
origin for this component.Comment: 12 pages, 7 figures, accepted for publication in MNRA
Chinese–Spanish neural machine translation enhanced with character and word bitmap fonts
Recently, machine translation systems based on neural networks have reached state-of-the-art results for some pairs of languages (e.g., German–English). In this paper, we are investigating the performance of neural machine translation in Chinese–Spanish, which is a challenging language pair. Given that the meaning of a Chinese word can be related to its graphical representation, this work aims to enhance neural machine translation by using as input a combination of: words or characters and their corresponding bitmap fonts. The fact of performing the interpretation of every word or character as a bitmap font generates more informed vectorial representations. Best results are obtained when using words plus their bitmap fonts obtaining an improvement (over a competitive neural MT baseline system) of almost six BLEU, five METEOR points and ranked coherently better in the human evaluation.Peer ReviewedPostprint (published version
PAN AIR: A computer program for predicting subsonic or supersonic linear potential flows about arbitrary configurations using a higher order panel method. Volume 4: Maintenance document (version 1.1)
The Maintenance Document is a guide to the PAN AIR software system, a system which computes the subsonic or supersonic linear potential flow about a body of nearly arbitrary shape, using a higher order panel method. The document describes the over-all system and each program module of the system. Sufficient detail is given for program maintenance, updating and modification. It is assumed that the reader is familiar with programming and CDC (Control Data Corporation) computer systems. The PAN AIR system was written in FORTRAN 4 language except for a few COMPASS language subroutines which exist in the PAN AIR library. Structured programming techniques were used to provide code documentation and maintainability. The operating systems accommodated are NOS 1.2, NOS/BE and SCOPE 2.1.3 on the CDC 6600, 7600 and Cyber 175 computing systems. The system is comprised of a data management system, a program library, an execution control module and nine separate FORTRAN technical modules. Each module calculates part of the posed PAN AIR problem. The data base manager is used to communicate between modules and within modules. The technical modules must be run in a prescribed fashion for each PAN AIR problem. In order to ease the problem of supplying the many JCL cards required to execute the modules, a separate module called MEC (Module Execution Control) was created to automatically supply most of the JCL cards. In addition to the MEC generated JCL, there is an additional set of user supplied JCL cards to initiate the JCL sequence stored on the system
Improved detectivity of pyroelectric detectors
High detectivity single-element SBN pyroelectric detectors were fabricated. The theory and technology developments related to improved detector performance were identified and formulated. Improved methods of material characterization, thinning, mounting, blackening and amplifier matching are discussed. Detectors with detectivities of 1.3 x 10 to the 9th power square root of Hz/watt at 1 Hz are reported. Factors limiting performance and recommendations for future work are discussed
X-ray Lags in PDS 456 Revealed by Suzaku Observations
X-ray reverberation lags from the vicinity of supermassive black holes have
been detected in almost 30 AGN. The soft lag, which is the time delay between
the hard and soft X-ray light curves, is usually interpreted as the time
difference between the direct and reflected emission, but is alternatively
suggested to arise from the direct and scattering emission from distant clouds.
By analysing the archival Suzaku observations totalling an exposure time of ~
770 ks, we discover a soft lag of ks at Hz in
the luminous quasar PDS 456, which is the longest soft lag and lowest Fourier
frequency reported to date. In this study, we use the maximum likelihood method
to deal with non-continuous nature of the Suzaku light curves. The result
follows the mass-scaling relation for soft lags, which further supports that
soft lags originate from the innermost areas of AGN and hence are best
interpreted by the reflection scenario. Spectral analysis has been performed in
this work and we find no evidence of clumpy partial-covering absorbers. The
spectrum can be explained by a self-consistent relativistic reflection model
with warm absorbers, and spectral variations over epochs can be accounted for
by the change of the continuum, and of column density and ionization states of
the warm absorbers.Comment: accepted for publication in MNRA
Spectral Energy Distributions of Gamma Ray Bursts Energized by External Shocks
Sari, Piran, and Narayan have derived analytic formulas to model the spectra
from gamma-ray burst blast waves that are energized by sweeping up material
from the surrounding medium. We extend these expressions to apply to general
radiative regimes and to include the effects of synchrotron self-absorption.
Electron energy losses due to the synchrotron self-Compton process are also
treated in a very approximate way. The calculated spectra are compared with
detailed numerical simulation results. We find that the spectral and temporal
breaks from the detailed numerical simulation are much smoother than the
analytic formulas imply, and that the discrepancies between the analytic and
numerical results are greatest near the breaks and endpoints of the synchrotron
spectra. The expressions are most accurate (within a factor of ~ 3) in the
optical/X-ray regime during the afterglow phase, and are more accurate when
epsilon_e, the fraction of swept-up particle energy that is transferred to the
electrons, is <~ 0.1. The analytic results provide at best order-of-magnitude
accuracy in the self-absorbed radio/infrared regime, and give poor fits to the
self-Compton spectra due to complications from Klein-Nishina effects and
photon-photon opacity.Comment: 16 pages, 7 figures, ApJ, in press, 537, July 1, 2000. Minor changes
in response to referee report, corrected figure
On the Antenna Beam Shape Reconstruction Using Planet Transit
The calibration of the in-flight antenna beam shape and possible
beamdegradation is one of the most crucial tasks for the upcoming Planck
mission. We examine several effects which could significantly influence the
in-flight main beam calibration using planet transit: the problems of the
variability of the Jupiter's flux, the antenna temperature and passing of the
planets through the main beam. We estimate these effects on the antenna beam
shape calibration and calculate the limits on the main beam and far sidelobe
measurements, using observations of Jupiter and Saturn. We also discuss
possible effects of degradation of the mirror surfaces and specify
corresponding parameters which can help us to determine these effects.Comment: 10 pages, 8 figure
- …