12,871 research outputs found
On the reliability of electrical drives for safety-critical applications
The aim of this work is to present some issues related to fault tolerant electric drives,which are able to overcome different types of faults occurring in the sensors, in thepower converter and in the electrical machine, without compromising the overallfunctionality of the system. These features are of utmost importance in safety-criticalapplications. In this paper, the reliability of both commercial and innovative driveconfigurations, which use redundant hardware and suitable control algorithms, will beinvestigated for the most common types of fault: besides standard three phase motordrives, also multiphase topologies, open-end winding solutions, multi-machineconfigurations will be analyzed, applied to various electric motor technologies. Thecomplexity of hardware and control strategies will also be compared in this paper, sincethis has a tremendous impact on the investment costs
Criteria for Bayesian model choice with application to variable selection
In objective Bayesian model selection, no single criterion has emerged as
dominant in defining objective prior distributions. Indeed, many criteria have
been separately proposed and utilized to propose differing prior choices. We
first formalize the most general and compelling of the various criteria that
have been suggested, together with a new criterion. We then illustrate the
potential of these criteria in determining objective model selection priors by
considering their application to the problem of variable selection in normal
linear models. This results in a new model selection objective prior with a
number of compelling properties.Comment: Published in at http://dx.doi.org/10.1214/12-AOS1013 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Finite-temperature relativistic Landau problem and the relativistic quantum Hall effect
This paper presents a study of the free energy and particle density of the
relativistic Landau problem, and their relevance to the quantum Hall effect. We
study first the zero temperature Casimir energy and fermion number for Dirac
fields in a 2+1-dimensional Minkowski space-time, in the presence of a uniform
magnetic field perpendicular to the spatial manifold. Then, we go to the
finite-temperature problem, with a chemical potential, introduced as a uniform
zero component of the gauge potential. By performing a Lorentz boost, we obtain
Hall's conductivity in the case of crossed electric and magnetic fields.Comment: Final version, to appear in Journal of Physics A: Mathematical and
Genera
A constant dark matter halo surface density in galaxies
We confirm and extend the recent finding that the central surface density
r_0*rho_0 galaxy dark matter halos, where r_0 and rho_0 are the halo core
radius and central density, is nearly constant and independent of galaxy
luminosity. Based on the co-added rotation curves of about 1000 spiral
galaxies, mass models of individual dwarf irregular and spiral galaxies of late
and early types with high-quality rotation curves and, galaxy-galaxy weak
lensing signals from a sample of spiral and elliptical galaxies, we find that
log(r_0*rho_0) = 2.15 +- 0.2, in units of log(Msol/pc^2). We also show that the
observed kinematics of Local Group dwarf spheroidal galaxies are consistent
with this value. Our results are obtained for galactic systems spanning over 14
magnitudes, belonging to different Hubble Types, and whose mass profiles have
been determined by several independent methods. In the same objects, the
approximate constancy of rho_0*r_0 is in sharp contrast to the systematical
variations, by several orders of magnitude, of galaxy properties, including
rho_0 and central stellar surface density.Comment: Accepted for publication in MNRAS. 9 pages, 4 figure
Patterns of CT lung injury and toxicity after stereotactic radiotherapy delivered with helical tomotherapy in early stage medically inoperable NSCLC
To evaluate toxicity and patterns of radiologic lung injury on CT images after hypofractionated image-guided stereotactic body radiotherapy (SBRT) delivered with helical tomotherapy (HT) in medically early stage inoperable non-small-cell lung cancer (NSCLC)
Transcranial random noise stimulation (tRNS): a wide range of frequencies is needed for increasing cortical excitability
Transcranial random noise stimulation (tRNS) is a recent neuromodulation protocol. The high-frequency band (hf-tRNS) has shown to be the most effective in enhancing neural excitability. The frequency band of hf-tRNS typically spans from 100 to 640 Hz. Here we asked whether both the lower and the higher half of the high-frequency band are needed for increasing neural excitability. Three frequency ranges (100\u2013400 Hz, 400\u2013700 Hz, 100\u2013700 Hz) and Sham conditions were delivered for 10 minutes at an intensity of 1.5 mA over the primary motor cortex (M1). Single-pulse transcranial magnetic stimulation (TMS) was delivered over the same area at baseline, 0, 10, 20, 30, 45 and 60 minutes after stimulation, while motor evoked potentials (MEPs) were recorded to evaluate changes in cortical excitability. Only the full-band condition (100\u2013700 Hz) was able to modulate excitability by enhancing MEPs at 10 and 20 minutes after stimulation: neither the higher nor the lower sub-range of the high-frequency band significantly modulated cortical excitability. These results show that the efficacy of tRNS is strictly related to the width of the selected frequency range
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