16,222 research outputs found
QED radiative correction to spin-density matrix elements in exclusive vector meson production
QED radiative effects are considered in the case of measurement of
spin-density matrix elements of diffractive -meson electroproduction.
Large radiative correction for is found in the kinematics of
collider experiments at HERA.Comment: 7 pages, 5 figure
Improving particle swarm optimization convergence with spread and momentum factors
Particle Swarm Optimization (PSO) is a swarm intelligence search method based on the behavior of birds flocking and fish schooling. It is known for its ability to perform fast computation compared to other evolutionary computational methods like Genetic Algorithms. Several parameter control methods have been developed to make the PSO algorithm faster and more accurate such as linearly decreasing inertia weight (LDIW) and time-varying acceleration coefficients (TVAC). This paper presents an improvement over existing techniques by introducing spread factor and momentum factor into the PSO algorithm. Test results show that the PSO with these two factors produce superior performance and suitable for applications where speed and precision are important
Galaxy Bias and Halo-Occupation Numbers from Large-Scale Clustering
We show that current surveys have at least as much signal to noise in
higher-order statistics as in the power spectrum at weakly nonlinear scales. We
discuss how one can use this information to determine the mean of the galaxy
halo occupation distribution (HOD) using only large-scale information, through
galaxy bias parameters determined from the galaxy bispectrum and trispectrum.
After introducing an averaged, reasonably fast to evaluate, trispectrum
estimator, we show that the expected errors on linear and quadratic bias
parameters can be reduced by at least 20-40%. Also, the inclusion of the
trispectrum information, which is sensitive to "three-dimensionality" of
structures, helps significantly in constraining the mass dependence of the HOD
mean. Our approach depends only on adequate modeling of the abundance and
large-scale clustering of halos and thus is independent of details of how
galaxies are distributed within halos. This provides a consistency check on the
traditional approach of using two-point statistics down to small scales, which
necessarily makes more assumptions. We present a detailed forecast of how well
our approach can be carried out in the case of the SDSS.Comment: 16 pages, 9 figure
Constraints on z~10 Galaxies from the Deepest HST NICMOS Fields
We use all available fields with deep NICMOS imaging to search for J dropouts
(H<28) at z~10. Our primary data set for this search were the two J+H NICMOS
parallel fields taken with the ACS HUDF. The 5 sigma limiting mags were 28.6 in
J and 28.5 in H. Several shallower fields were also used: J+H NICMOS frames
available over the HDF North, the HDF South NICMOS parallel, and the ACS HUDF.
The primary selection criterion was (J-H)>1.8. 11 such sources were found in
all search fields using this criterion. 8 of these were clearly ruled out as
credible z~10 sources, either as a result of detections (>2 sigma) blueward of
J or their colors redward of the break (H-K~1.5). The nature of the 3 remaining
sources could not be determined from the data. The number appears consistent
with the expected contamination from low-z interlopers. Analysis of the stacked
images for the 3 candidates also suggests contamination. Regardless of their
true redshifts, the actual number of z~10 sources must be <=3. To assess the
significance of these results, two lower redshift samples (a z~3.8 B-dropout
and z~6 i-dropout sample) were projected to z~8-12 using a (1+z)^{-1} size
scaling. They were added to the image frames, and the selection repeated,
giving 15.6 and 4.8 J-dropouts, respectively. This suggests that to the limit
of this probe (0.3 L*) there has been evolution from z~3.8 and possibly from
z~6. This is consistent with the strong evolution already noted at z~6 and
z~7.5 relative to z~3-4. Even assuming that 3 sources from this probe are at
z~10, the rest-frame continuum UV (~1500 A) luminosity density at z~10
(integrated down to 0.3 L*) is just 0.19_{-0.09}^{+0.13}x that at z~3.8 (or
0.19_{-0.10}^{+0.15}x including cosmic variance). However, if none of our
sources is at z~10, this ratio has a 1 sigma upper limit of 0.07. (abridged)Comment: 13 pages, 3 figures, 2 tables, accepted for publication in the
Astrophysical Journal Letter
Spin-charge-lattice coupling near the metal-insulator transition in Ca3Ru2O7
We report x-ray scattering studies of the c-axis lattice parameter in
Ca3Ru2O7 as a function of temperature and magnetic field. These structural
studies complement published transport and magnetization data, and therefore
elucidate the spin-charge-lattice coupling near the metal-insulator transition.
Strong anisotropy of the structural change for field applied along orthogonal
in-plane directions is observed. Competition between a spin-polarized phase
that does not couple to the lattice, and an antiferromagnetic metallic phase,
which does, gives rise to rich behavior for B b.Comment: 6 pages, 4 figures, to appear in Phys. Rev.
Magnetic structure of the field-induced multiferroic GdFe3(BO3)4
We report a magnetic x-ray scattering study of the field-induced multiferroic
GdFe3(BO3)4. Resonant x-ray magnetic scattering at the Gd LII,III edges
indicates that the Gd moments order at TN ~ 37 K. The magnetic structure is
incommensurate below TN, with the incommensurability decreasing monotonically
with decreasing temperature until a transition to a commensurate magnetic phase
is observed at T ~ 10 K. Both the Gd and Fe moments undergo a spin
reorientation transition at TSR ~ 9 K such that the moments are oriented along
the crystallographic c axis at low temperatures. With magnetic field applied
along the a axis, our measurements suggest that the field-induced polarization
phase has a commensurate magnetic structure with Gd moments rotated ~45 degrees
toward the basal plane, which is similar to the magnetic structure of the Gd
subsystem observed in zero field between 9 and 10 K, and the Fe subsystem has a
ferromagnetic component in the basal plane.Comment: 27 pages, 7 figures, to appear in Phys. Rev.
Parental knowledge and impact on growth in children with congenital heart diseases in Aminu Kano Teaching Hospital
Abstract: Objectives: Parental knowledge of a child’s heart disease, treatment and prevention of complications may promote a better health related behavior towards the care of the child. Most of these children often present with failure to thrive which the parents may not associate with the disease. This study is aimed at determining the knowledge of parents of children with congenital heart disease (CHD) and the impact of the disease on their growth.Methods: This was a cross sectional study consisting of parents and children with CHD attending the Pediatric Cardiology Clinic of Aminu Kano Teaching Hospital. Relevant information was gotten from pre-tested questionnairescontaining data such as age, anthropometric parameters, educational level of parents and knowledge of their children’s cardiac defect.Results: Out of the one hundred and three parents recruited in this study, ninety-one (88.3%) of the parents knew the correct cardiac diagnosis. which had no statistically significant association with their educational status. There was statistically significant association between maternal educational status and ability to name the medications (X2= 27.01, df=12, p=0.008). A total of sixty nine (67%) children have a WAZ score of ≤−2 and <3 while forty five (43.7%) have an HAZ of ≤−2.Conclusion: Adequate knowledge will ensure better compliance to medications which can reduce morbidity and early mortality before surgical intervention. Therefore continuous patient/caregiver education is imperative for their long time survival because even surgery may not completely eliminate all complications associated with it.Keywords: Congenital heart disease, Parental knowledge, growth
Slow light in paraffin-coated Rb vapor cells
We present preliminary results from an experimental study of slow light in
anti-relaxation-coated Rb vapor cells, and describe the construction and
testing of such cells. The slow ground state decoherence rate allowed by coated
cell walls leads to a dual-structured electromagnetically induced transparency
(EIT) spectrum with a very narrow (<100 Hz) transparency peak on top of a broad
pedestal. Such dual-structure EIT permits optical probe pulses to propagate
with greatly reduced group velocity on two time scales. We discuss ongoing
efforts to optimize the pulse delay in such coated cell systems.Comment: 6 pages, 6 figures, submitted to Journal of Modern Optic
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