12,831 research outputs found
Evidence for the two pole structure of the Lambda(1405) resonance
The K^- p --> pi^0 pi^0 Sigma^0 reaction is studied within a chiral unitary
model. The distribution of pi^0 Sigma^0 states forming the Lambda(1405) shows,
in agreement with a recent experiment, a peak at 1420 MeV and a relatively
narrow width of Gamma = 38 MeV. The mechanism for the reaction is largely
dominated by the emission of a pi^0 prior to the K^- p interaction leading to
the Lambda(1405). This ensures the coupling of the Lambda(1405) to the K^- p
channel, thus maximizing the contribution of the second state found in chiral
unitary theories, which is narrow and of higher energy than the nominal
Lambda(1405). This is unlike the pi^- p --> K^0 \pi Sigma reaction, which gives
more weight to the pole at lower energy and with a larger width. The data of
these two experiments, together with the present theoretical analysis, provides
a firm evidence of the two pole structure of the Lambda(1405).Comment: 4 pages, 6 figure
The role of the resonance in the reaction
We investigate the photo-production in the reaction within the effective Lagrangian method near
threshold. In addition to the "background" contributions from the contact,
channel exchange, and channel nucleon pole terms, which were
already considered in previous works, the contribution from the nucleon
resonance (spin-parity ) is also considered. We show
that the inclusion of the nucleon resonance leads to a fairly good
description of the new LEPS differential cross section data, and that these
measurements can be used to determine some of the properties of this latter
resonance. However, serious discrepancies appear when the predictions of the
model are compared to the photon-beam asymmetry also measured by the LEPS
Collaboration.Comment: 9 pages,6 figures, 1 tabl
Differences in hearing acuity among “normal-hearing” young adults modulate the neural basis for speech comprehension
AbstractIn this paper, we investigate how subtle differences in hearing acuity affect the neural systems supporting speech processing in young adults. Auditory sentence comprehension requires perceiving a complex acoustic signal and performing linguistic operations to extract the correct meaning. We used functional MRI to monitor human brain activity while adults aged 18–41 years listened to spoken sentences. The sentences varied in their level of syntactic processing demands, containing either a subject-relative or object-relative center-embedded clause. All participants self-reported normal hearing, confirmed by audiometric testing, with some variation within a clinically normal range. We found that participants showed activity related to sentence processing in a left-lateralized frontotemporal network. Although accuracy was generally high, participants still made some errors, which were associated with increased activity in bilateral cingulo-opercular and frontoparietal attention networks. A whole-brain regression analysis revealed that activity in a right anterior middle frontal gyrus (aMFG) component of the frontoparietal attention network was related to individual differences in hearing acuity, such that listeners with poorer hearing showed greater recruitment of this region when successfully understanding a sentence. The activity in right aMFGs for listeners with poor hearing did not differ as a function of sentence type, suggesting a general mechanism that is independent of linguistic processing demands. Our results suggest that even modest variations in hearing ability impact the systems supporting auditory speech comprehension, and that auditory sentence comprehension entails the coordination of a left perisylvian network that is sensitive to linguistic variation with an executive attention network that responds to acoustic challenge.</jats:p
Getting Jobs, Keeping Jobs, and Earning a Living Wage: Can Welfare Reform Work?
Most discussions of welfare and work have focused on how demographic characteristics, schooling, training, and work experience limit welfare mothers’ employment and wages, but they have largely ignored factors such as inappropriate workplace behaviors, expectations of discrimination and harassment, depression, alcoholism, and domestic violence, all of which may affect welfare mothers and make employment difficult. In this paper we review the prevalence of these individual-level barriers and argue that they, in combination with an economy which does not pay low-skill workers well, are likely to impede employment and self-sufficiency for a large proportion of welfare mothers. At the end of the review, we summarize the current state of knowledge about barriers to the employment of welfare recipients and suggest several ways in which welfare-to-work programs might address these barriers.
Solid-Liquid Phase Diagrams for Binary Metallic Alloys: Adjustable Interatomic Potentials
We develop a new approach to determining LJ-EAM potentials for alloys and use
these to determine the solid-liquid phase diagrams for binary metallic alloys
using Kofke's Gibbs-Duhem integration technique combined with semigrand
canonical Monte Carlo simulations. We demonstrate that it is possible to
produce a wide-range of experimentally observed binary phase diagrams (with no
intermetallic phases) by reference to the atomic sizes and cohesive energies of
the two elemental materials. In some cases, it is useful to employ a single
adjustable parameter to adjust the phase diagram (we provided a good choice for
this free parameter). Next, we perform a systematic investigation of the effect
of relative atomic sizes and cohesive energies of the elements on the binary
phase diagrams. We then show that this approach leads to good agreement with
several experimental binary phase diagrams. The main benefit of this approach
is not the accurately reproduction of experimental phase diagrams, but rather
to provide a method by which material properties can be continuously changed in
simulations studies. This is one of the keys to the use of atomistic
simulations to understand mechanisms and properties in a manner not available
to experiment
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