259 research outputs found
Understanding the impact of failure modes of cables for the design of turbo-electric distributed propulsion electrical power systems.
The turbo-electric distributed propulsion (TeDP) concept has been proposed to enable future aircraft to meet ambitious, environmental targets as demand for air travel increases. In order to maximize the benefits of TeDP, the use of high temperature superconductors (HTS) has been proposed. Despite being an enabling technology for many future concepts, the use of superconductors in electrical power systems is still in the early stages of development. Hence their impact on system performance, in particular system transients, such as electrical faults or load changes, is poorly understood. Such an understanding is critical for the development of an appropriate electrical protection system for TeDP. Therefore, in order to enable appropriate protection strategies to be developed for TeDP electrical networks an understanding of how electrical faults will propagate in superconducting materials is required. An understanding of how technologies that utilize these materials may experience failure modes in ways that are uncharacteristic of their conventional counterparts is also needed. This paper presents a dynamic electrical – thermal model of a superconducting cable, at an appropriate level of fidelity for electrical power system studies, which enables the investigation of failure modes of cables. This includes the impact of designing fault tolerant cables on the electrical power system as a whole to be considered
Description of superdeformed nuclei in the interacting boson model
The interacting boson model is extended to describe the spectroscopy of
superdeformed bands. Microscopic structure of the model in the second minimum
is discussed and superdeformed bosons are introduced as the new building
blocks. Solutions of a quadrupole Hamiltonian are implemented through the
expansion method. Effects of the quadrupole parameters on dynamic moment of
inertia and electric quadrupole transition rates are discussed and the results
are used in a description of superdeformed bands in the Hg-Pb and Gd-Dy
regions.Comment: 18 pages revtex, 9 figures available upon reques
Fast variability from black-hole binaries
Currently available information on fast variability of the X-ray emission
from accreting collapsed objects constitutes a complex phenomenology which is
difficult to interpret. We review the current observational standpoint for
black-hole binaries and survey models that have been proposed to interpret it.
Despite the complex structure of the accretion flow, key observational
diagnostics have been identified which can provide direct access to the
dynamics of matter motions in the close vicinity of black holes and thus to the
some of fundamental properties of curved spacetimes, where strong-field general
relativistic effects can be observed.Comment: 20 pages, 11 figures. Accepted for publication in Space Science
Reviews. Also to appear in hard cover in the Space Sciences Series of ISSI
"The Physics of Accretion onto Black Holes" (Springer Publisher
Characterization of segmented HPGe detectors using Pulse Shape Comparison methods
In this work we present the first results of a detector characterization technique named Pulse Shape Comparison Scan (PSCS), applied to a large volume segmented HPGe detector of the AGATA array. The experimental data were collected with the Liverpool University scanning system. Processing two sets of singles scan data acquired with a 137Cs (662 keV) gamma collimated source (with the collimation lines perpendicular one in respect to the other), it has been possible to extract the position response of 4 detector segments. \ua9 2010 IEEE
Does accelerating universe indicates Brans-Dicke theory
The evolution of universe in Brans-Dicke (BD) theory is discussed in this
paper.
Considering a parameterized scenario for BD scalar field
which plays the role of gravitational "constant" ,
we apply the Markov Chain Monte Carlo method to investigate a global
constraints on BD theory with a self-interacting potential according to the
current observational data: Union2 dataset of type supernovae Ia (SNIa),
high-redshift Gamma-Ray Bursts (GRBs) data, observational Hubble data (OHD),
the cluster X-ray gas mass fraction, the baryon acoustic oscillation (BAO), and
the cosmic microwave background (CMB) data. It is shown that an expanded
universe from deceleration to acceleration is given in this theory, and the
constraint results of dimensionless matter density and parameter
are, and
which is consistent with the
result of current experiment exploration, . In
addition, we use the geometrical diagnostic method, jerk parameter , to
distinguish the BD theory and cosmological constant model in Einstein's theory
of general relativity.Comment: 16 pages, 3 figure
Fitting the integrated Spectral Energy Distributions of Galaxies
Fitting the spectral energy distributions (SEDs) of galaxies is an almost
universally used technique that has matured significantly in the last decade.
Model predictions and fitting procedures have improved significantly over this
time, attempting to keep up with the vastly increased volume and quality of
available data. We review here the field of SED fitting, describing the
modelling of ultraviolet to infrared galaxy SEDs, the creation of
multiwavelength data sets, and the methods used to fit model SEDs to observed
galaxy data sets. We touch upon the achievements and challenges in the major
ingredients of SED fitting, with a special emphasis on describing the interplay
between the quality of the available data, the quality of the available models,
and the best fitting technique to use in order to obtain a realistic
measurement as well as realistic uncertainties. We conclude that SED fitting
can be used effectively to derive a range of physical properties of galaxies,
such as redshift, stellar masses, star formation rates, dust masses, and
metallicities, with care taken not to over-interpret the available data. Yet
there still exist many issues such as estimating the age of the oldest stars in
a galaxy, finer details ofdust properties and dust-star geometry, and the
influences of poorly understood, luminous stellar types and phases. The
challenge for the coming years will be to improve both the models and the
observational data sets to resolve these uncertainties. The present review will
be made available on an interactive, moderated web page (sedfitting.org), where
the community can access and change the text. The intention is to expand the
text and keep it up to date over the coming years.Comment: 54 pages, 26 figures, Accepted for publication in Astrophysics &
Space Scienc
Relative quadrupole moments of exotic shapes at ultrahigh spin in 154Er: Calibrating the TSD/SD puzzle
Transition quadrupole moments, Qt, of two ultrahigh-spin, collective structures in 154Er have been measured for the first time using the Doppler Shift Attenuation Method (DSAM). Data were acquired at the ATLAS accelerator facility of Argonne National Laboratory, using the Gammasphere detector array. A thick, gold-backed 110Pd foil was bombarded by a beam of 48Ti ions at 215 MeV. The Qt for each band was determined from the Doppler shift of gamma rays emitted by the resulting recoil nuclei. The extracted transition quadrupole moments are significantly different in magnitude, suggesting the two structures in 154Er represent distinct exotic nuclear shapes, namely axial superdeformed (SD) with Q t 20 eb, and triaxial strongly deformed (TSD) with Qt ≈ 11 eb. Indeed, the results calibrate the quadrupole moments of TSD bands recently measured in light erbium nuclei, 157,158Er
Quadrupole moments of coexisting collective shapes at high spin in 154Er
Four high-spin collective bands have been populated in 68154Er86 via the 110Pd(48Ti,4nγ)154Er reaction. Average transition quadrupole moments Qt have been measured for three of the bands by using the Doppler-shift attenuation method. The strongest band has a value of Q t=11.0±1.0eb, similar to values found recently for four triaxial strongly deformed (TSD) bands in 157,158Er. The second band has a value of Qt=19.5±3.2eb, consistent with a predicted axially symmetric superdeformed (SD) shape, similar in deformation to the 152Dy isotone, and is used as a calibration point. The third, new band has a value of Qt=9.9±2.2eb. The results confirm the unexpectedly large Qt moments for the favored TSD bands in light erbium isotopes
High-spin yrast structure of 159Ho
An investigation of the yrast structure of the odd-Z 159Ho nucleus to high spin has been performed. The 159Ho nucleus was populated by the reaction 116Cd(48Ca,p4nγ) at a beam energy of 215 MeV, and resulting γ decays were detected by the Gammasphere spectrometer. The h11/2 yrast band has been significantly extended up to Iπ=75/2- (tentatively 79/2-). A lower frequency limit for the second (h11/ 2)2 proton alignment was extracted consistent with the systematics of this alignment frequency, indicating an increased deformation with neutron number in the Ho isotopes. The energy-level splitting between the signature partners in the h11/2 structures of the Ho isotopes and the neighboring N=92 isotones is discussed
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