203,502 research outputs found
Parity Nonconservation in the Photodisintegration of the Deuteron at Low Energy
The parity-nonconserving asymmetry in the deuteron photodisintegration,
, is considered with the photon energy ranged up to 10
MeV above the threshold. The aim is to improve upon a schematic estimate
assuming the absence of tensor as well as spin-orbit forces in the
nucleon-nucleon interaction. The major contributions are due to the
vector-meson exchanges, and the strong suppression of the pion-exchange
contribution is confirmed. A simple argument, going beyond the observation of
an algebraic cancellation, is presented. Contributions of meson-exchange
currents are also considered, but found to be less significant.Comment: 12 pages, 6 figures, typeset by REVTeX (two-column format) and BIBTe
Supersymmetric Harry Dym Type Equations
A supersymmetric version is proposed for the well known Harry Dym system. A
general class super Lax operator which leads to consistent equations is
considered.Comment: 4 pages, latex, no figure
Parity violation in scattering and vector-meson weak-coupling constants
We calculate the parity-nonconserving longitudinal asymmetry in the elastic
scattering at the energies where experimental data are available.
In addition to the standard one-meson exchange weak potential, the variation of
the strong-coupling constants and the non-standard effects such as form factors
and -exchange description of the -exchange potential are taken
into account. With the extra effects, we investigate the compatibility of the
experimental data and the presently-known range of the vector-meson
weak-coupling constants.Comment: Contribution to the proceedings of the 3rd Asia-Pacific conference on
few-body problems in physics, Suranaree Univ. of Technology, Nakhon
Ratchasima, Thailand, July 26 - 30, 200
Extraordinary variability and sharp transitions in a maximally frustrated dynamic network
Using Monte Carlo and analytic techniques, we study a minimal dynamic network
involving two populations of nodes, characterized by different preferred
degrees. Reminiscent of introverts and extroverts in a population, one set of
nodes, labeled \textit{introverts} (), prefers fewer contacts (a lower
degree) than the other, labeled \textit{extroverts} (). As a starting point,
we consider an \textit{extreme} case, in which an simply cuts one of its
links at random when chosen for updating, while an adds a link to a random
unconnected individual (node). The model has only two control parameters,
namely, the number of nodes in each group, and ). In the steady
state, only the number of crosslinks between the two groups fluctuates, with
remarkable properties: Its average () remains very close to 0 for all
or near its maximum () if
. At the transition (), the fraction
wanders across a substantial part of , much like a pure random walk.
Mapping this system to an Ising model with spin-flip dynamics and unusual
long-range interactions, we note that such fluctuations are far greater than
those displayed in either first or second order transitions of the latter.
Thus, we refer to the case here as an `extraordinary transition.' Thanks to the
restoration of detailed balance and the existence of a `Hamiltonian,' several
qualitative aspects of these remarkable phenomena can be understood
analytically.Comment: 6 pages, 3 figures, accepted for publication in EP
Deuteron Anapole Moment with Heavy Mesons
Parity-nonconserving two-body currents due to vector meson exchange are
considered with the aim to determine the related contributions to the anapole
moment. A particular attention is given to the requirement of current
conservation which is essential for a reliable estimate of this quantity. An
application is made for the deuteron case.Comment: 23 pages, 5 EPS figures, uses REVTeX 4, v2: fixes layout problem
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Selective Fetal Growth Restriction in Dichorionic Twin Pregnancies: Diagnosis, Natural History, and Perinatal Outcome.
This study aims to evaluate the natural history, disease progression, and outcomes in dichorionic twins with selective fetal growth restriction (sFGR) according to different diagnostic criteria and time of onset. Dichorionic twins seen from the first trimester were included. sFGR was classified according to the Delphi consensus, and was compared to the outcomes of those classified by the International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) diagnostic criteria. Early sFGR occurred before 32-weeks, and late sFGR after 32-weeks. Disease progression, neonatal outcomes such as gestation at delivery, birthweight, neonatal unit (NNU) admission, and morbidities were compared. One-hundred twenty-three of 1053 dichorionic twins had sFGR, where 8.4% were classified as early sFGR, and 3.3% were late sFGR. Disease progression was seen in 36%, with a longer progression time (5 vs. 1 week) and higher progression rate (40% vs. 26%) in early sFGR. Perinatal death was significantly higher in the sFGR than the non-sFGR group (24 vs. 16 per 1000 births, p = 0.018), and those with early sFGR had more NNU admissions than late sFGR (p = 0.005). The ISUOG diagnostic criteria yielded a higher number of sFGR than the Delphi criteria, but similar outcomes. sFGR have worse perinatal outcomes, with early onset being more prevalent. Use of the Delphi diagnostic criteria can reduce over-diagnosis of sFGR and avoid unnecessary intervention
Advanced digital SAR processing study
A highly programmable, land based, real time synthetic aperture radar (SAR) processor requiring a processed pixel rate of 2.75 MHz or more in a four look system was designed. Variations in range and azimuth compression, number of looks, range swath, range migration and SR mode were specified. Alternative range and azimuth processing algorithms were examined in conjunction with projected integrated circuit, digital architecture, and software technologies. The advaced digital SAR processor (ADSP) employs an FFT convolver algorithm for both range and azimuth processing in a parallel architecture configuration. Algorithm performace comparisons, design system design, implementation tradeoffs and the results of a supporting survey of integrated circuit and digital architecture technologies are reported. Cost tradeoffs and projections with alternate implementation plans are presented
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