2,309 research outputs found
Recoil Order Chiral Corrections to Baryon Octet Axial Currents and Large QCD
We compute the chiral corrections to octet baryon axial currents through
in heavy baryon chiral perturbation theory, including both
octet and decuplet baryon intermediate states. We include the latter in a
consistent way by using the small scale expansion. We find that, in contrast to
the situation at , there exist no cancellations between octet
and decuplet contributions at . Consequently, the corrections spoil the expected scaling behavior of the chiral
expansion. We discuss this result in terms of the expansion. We also
consider the implications for determination of the strange quark contribution
to the nucleon spin from polarized deep inelastic scattering data.Comment: 7 page
Parton energy loss limits and shadowing in Drell-Yan dimuon production
A precise measurement of the ratios of the Drell-Yan cross section per
nucleon for an 800 GeV/c proton beam incident on Be, Fe and W targets is
reported. The behavior of the Drell-Yan ratios at small target parton momentum
fraction is well described by an existing fit to the shadowing observed in
deep-inelastic scattering. The cross section ratios as a function of the
incident parton momentum fraction set tight limits on the energy loss of quarks
passing through a cold nucleus
Why, what, and how? case study on law, risk, and decision making as necessary themes in built environment teaching
The paper considers (and defends) the necessity of including legal studies as a core part of built environment undergraduate and postgraduate curricula. The writer reflects upon his own experience as a lawyer working alongside and advising built environment professionals in complex land remediation and site safety management situations in the United Kingdom and explains how themes of liability, risk, and decision making can be integrated into a practical simulation in order to underpin more traditional lecture-based law teaching. Through reflection upon the writer's experiments with simulation-based teaching, the paper suggests some innovations that may better orientate law teaching to engage these themes and, thereby, enhance the relevance of law studies to the future needs of built environment professionals in practice.</p
Gear-Specific Population Demographics of Channel Catfish in a Large Midwestern River
Various gear types have been used to sample populations of channel catfish Ictalurus punctatus in lotic systems. However, these gears produce different population characteristics (i.e., recruitment, growth, and mortality). We compared the population demographics of channel catfish in the Wabash River, Indiana, sampled with baited 25- and 32-mm-bar mesh hoop nets and three-phase alternating current (AC) electrofishing. Based on catch per unit effort, the relative abundance of channel catfish sampled with 32-mm hoop nets was lower than that of fish sampled with 25-mm hoop nets and AC electrofishing. Each gear type also resulted in a different length frequency, mean length increasing progressively in sampling with 25-mm hoop nets, 32-mm hoop nets, and AC electrofishing. Similarly, age-frequency distributions differed among gears. The 25-mm hoop nets biased the age structure toward younger individuals (mean age = 2.5), whereas both 32-mm hoop nets (mean age = 4.0) and AC electrofishing (mean age = 5.8) included older fish. Catch-curve analysis generated different mortality rates for the three gear types, the mortality rate being highest (50%) in fish sampled with 25-mm hoop nets. Gear-specific size and age structures led to differences in von Bertalanffy statistics among the 25-mm hoop nets and AC electrofishing, while the results for 32-mm hoop nets were uninterpretable. Because the different gears led to conflicting parameter estimates, management practices based on sampling with single gears may be contradictory. Given the differences in gear selectivity, biologists need to approach management cautiously until calibration to the true size and age structure is conducted
Quark-Gluon String Model Description of Baryon Production in K^{\pm}N Interactions
The process of baryon production in K p collisions at high energies is
considered in the framework of the Quark-Gluon String Model. The contribution
of the string-junction mechanism to the strange baryon production is analysed.
The results of numerical calculations are in reasonable agreement with the data
on inclusive spectra of p, Lambda, bar{Lambda}, and on the bar{Lambda}/Lambda
asymmetry. The predictions for Xi and Omega baryons are presented.Comment: 19 pages, 7 figure
The rotational excitation of HCN and HNC by He: New insights on the HCN/HNC abundance ratio in molecular clouds
Modeling of molecular emission from interstellar clouds requires the
calculation of rates for excitation by collisions with the most abundant
species. The present paper focuses on the calculation of rate coefficients for
rotational excitation of the HCN and HNC molecules in their ground vibrational
state in collision with He. The calculations are based on new two-dimensional
potential energy surfaces obtained from highly correlated \textit{ab initio}
calculations. Calculations of pure rotational (de)excitation cross sections of
HCN and HNC by He were performed using the essentially exact close-coupling
method. Cross sections for transitions among the 8 first rotational levels of
HCN and HNC were calculated for kinetic energies up to 1000 cm. These
cross sections were used to determine collisional rate constants for
temperatures ranging from 5 K to 100 K. A propensity for even
transitions is observed in the case of HCN--He collisions whereas a propensity
for odd transitions is observed in the case of HNC--He collisions.
The consequences for astrophysical models are evaluated and it is shown that
the use of HCN rate coefficients to interpret HNC observations can lead to
significant inaccuracies in the determination of the HNC abundance, in
particular in cold dark clouds for which the new HNC rates show that the
line of this species will be more easily excited by collisions than
HCN. An important result of the new HNC-He rates is that the HNC/HCN abundance
ratio derived from observations in cold clouds has to be revised from 1 to
1, in good agreement with detailed chemical models available in the
literature.Comment: 8 figue
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