35,720 research outputs found
Pulsars identified from the NRAO VLA Sky Survey
We identified 97 strong pulsars from the NRAO VLA Sky Survey (NVSS) at 1.4
GHz north of Dec(J2000) >-40\degr. The total flux density, linear
polarization intensity and polarization angle (PA) of all pulsars are extracted
from the NVSS catalog. The well-calibrated PA measurement of 5 pulsars can be
used for absolute PA calibrations in other observations. Comparing the source
positions with those in the pulsar catalog, we got the first measurement of the
proper motion upper limit of PSR B0031-07, which is and .Comment: 7 pages; 3 figures; one big table; To appear in A&A Supplement
A new model for the double well potential
A new model for the double well potential is presented in the paper. In the
new potential, the exchanging rate could be easily calculated by the
perturbation method in supersymmetric quantum mechanics. It gives good results
whether the barrier is high or sallow. The new model have many merits and may
be used in the double well problem.Comment: 3pages, 3figure
Schroedinger Cat States of a Nanomechanical Resonator
We present a scheme of generating large-amplitude Schr\"{o}dinger cat states
and entanglement in a coupled system of nanomechanical resonator and single
Cooper pair box (SCPB), without being limited by the magnitude of the coupling.
It is shown that the entanglement between the resonator and the SCPB can be
detected by a spectroscopic method.Comment: 1 figur
Nonparametric inference procedure for percentiles of the random effects distribution in meta-analysis
To investigate whether treating cancer patients with
erythropoiesis-stimulating agents (ESAs) would increase the mortality risk,
Bennett et al. [Journal of the American Medical Association 299 (2008)
914--924] conducted a meta-analysis with the data from 52 phase III trials
comparing ESAs with placebo or standard of care. With a standard parametric
random effects modeling approach, the study concluded that ESA administration
was significantly associated with increased average mortality risk. In this
article we present a simple nonparametric inference procedure for the
distribution of the random effects. We re-analyzed the ESA mortality data with
the new method. Our results about the center of the random effects distribution
were markedly different from those reported by Bennett et al. Moreover, our
procedure, which estimates the distribution of the random effects, as opposed
to just a simple population average, suggests that the ESA may be beneficial to
mortality for approximately a quarter of the study populations. This new
meta-analysis technique can be implemented with study-level summary statistics.
In contrast to existing methods for parametric random effects models, the
validity of our proposal does not require the number of studies involved to be
large. From the results of an extensive numerical study, we find that the new
procedure performs well even with moderate individual study sample sizes.Comment: Published in at http://dx.doi.org/10.1214/09-AOAS280 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Investigation of Partial Discharge in Solid Dielectric under DC Voltage
A partial discharge, or PD, is defined as an electrical discharge that is localized within only a part of the insulation between two separated conductors. Recent research on PD mainly focuses on the study of PD characteristics under AC voltage. Compared with DC, PD under AC is more serious and can be easily detected in terms of PD number. As the results of these concentrated research, the understanding of PD under AC condition has been significantly improved and features extracted from PD measurements have been used to diagnose the insulation condition of many power apparatus. Recently, rapid development in HVDC transmission and power grids connection, and widely applied DC cable and gas-insulated switchgear because of their benefit in long distance usage lead to an increasing concern about PD under DC. However, available study for the condition is little and related research is therefore necessary and essential for understanding the lifetime and reliability of apparatus. <br/
Exploring the nucleon structure through GPDs and TDAs in hard exclusive processes
Generalized Parton Distributions (GPDs) offer a new way to access the quark
and gluon nucleon structure. We review recent progress in this domain,
emphasizing the need to supplement the experimental study of deeply virtual
Compton scattering by its crossed version, timelike Compton scattering. We also
describe the extension of the GPD concept to three quark operators and the
relevance of their nucleon to meson matrix elements, namely the transition
distribution amplitudes (TDAs) which factorize in backward meson
electroproduction and related processes. We discuss the main properties of the
TDAs. \Comment: 8 pages; to be published in the proceedings of the conference "PHOTON
2011, International Conference on the Structure and the Interactions of the
Photon ", Spa, Belgium, 22-27 Mai 201
New results in exclusive hard reactions
Generalized Parton Distributions offer a new way to access the quark and
gluon nucleon structure. We review recent progress in this domain, emphasizing
the need to supplement the experimental study of DVCS by its crossed version,
timelike Compton scattering (TCS), where data at high energy should appear
thanks to the study of ultraperipheral collisions at the LHC. This will open
the access to very low skewness quark and gluon GPDs. Our leading order
estimates show that the factorization scale dependence of the amplitudes is
quite high. This fact demands the understanding of higher order contributions
with the hope that they will stabilize this scale dependence. The magnitudes of
the NLO coefficient functions are not small and neither is the difference of
the coefficient functions appearing respectively in the DVCS and TCS
amplitudes. The conclusion is that extracting the universal GPDs from both TCS
and DVCS reactions requires much care. We also describe the extension of the
GPD concept to three quark operators and the relevance of their nucleon to
meson matrix elements, namely the transition distribution amplitudes (TDAs)
which factorize in hard exclusive pion electroproduction off a nucleon in the
backward region and baryon-antibaryon annihilation into a pion and a lepton
pair. We discuss the main properties of the TDAs.Comment: 4 pages, to be published in the proceedings of the 2011 Europhysics
Conference on High Energy Physics-HEP 2011, July 21-27, 2011, Grenoble,
Rhone-Alpes, Franc
Radiance and Doppler shift distributions across the network of the quiet Sun
The radiance and Doppler-shift distributions across the solar network provide
observational constraints of two-dimensional modeling of transition-region
emission and flows in coronal funnels. Two different methods, dispersion plots
and average-profile studies, were applied to investigate these distributions.
In the dispersion plots, we divided the entire scanned region into a bright and
a dark part according to an image of Fe xii; we plotted intensities and Doppler
shifts in each bin as determined according to a filtered intensity of Si ii. We
also studied the difference in height variations of the magnetic field as
extrapolated from the MDI magnetogram, in and outside network. For the
average-profile study, we selected 74 individual cases and derived the average
profiles of intensities and Doppler shifts across the network. The dispersion
plots reveal that the intensities of Si ii and C iv increase from network
boundary to network center in both parts. However, the intensity of Ne viii
shows different trends, namely increasing in the bright part and decreasing in
the dark part. In both parts, the Doppler shift of C iv increases steadily from
internetwork to network center. The average-profile study reveals that the
intensities of the three lines all decline from the network center to
internetwork region. The binned intensities of Si ii and Ne viii have a good
correlation. We also find that the large blue shift of Ne viii does not
coincide with large red shift of C iv. Our results suggest that the network
structure is still prominent at the layer where Ne viii is formed in the quiet
Sun, and that the magnetic structures expand more strongly in the dark part
than in the bright part of this quiet Sun region.Comment: 10 pages,9 figure
Coupled ion - nanomechanical systems
We study ions in a nanotrap, where the electrodes are nanomechanical
resonantors. The ions play the role of a quantum optical system which acts as a
probe and control, and allows entanglement with or between nanomechanical
resonators.Comment: 4 pages, 2 figures, submitted for publicatio
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