2,814 research outputs found
Requirements Study for System Implementation of an Atmospheric Laser Propagation Experiment Program, Volume II
Program planning, ground support and airborne equipment for laser space communication syste
Energetics, Predation, and Ration Affect Size-dependent Growth and Mortality of Fish during Winter
Winter temperatures may reduce energy costs for ectotherms. However, variable mid-temperate and low-latitude winters may interact with scaling of size, metabolism, and energy reserves to cause energy deficits and require trade-offs between foraging and predation. A dynamic optimization model explored how ration, fall fat, and both non- and size-selective predation influenced foraging (i.e., fast or forage) and energy allocation (i.e., length or fat) decisions that maximize winter survival of age-0 largemouth bass (Micropterus salmoides). During a mid-latitude (38° N) winter, a pond experiment in which age-0 fish occurred with or without adult conspecific predators tested a subset of the model. In the model without predators, winter foraging occurred, with small size only reducing survival when low ration and low fall fat caused small fish to exhaust reserves. With predation, all sizes foraged to maintain mass and fat reserves when ration was sufficiently high, with small fish also growing in length. When modeled predation was nonselective, size-dependent mortality varied in complex ways. In contrast, size-selective predators consistently reduced survival of small fish. Generally consistent with the model, fish in ponds without predators gained mass and energy content, while those with predators only maintained these parameters. All small individuals grew more than large counterparts in length. Mortality in ponds never depended on size but was ~20% higher with predators. Energy deficits often demand active foraging during mid-temperate winters, with predation rather than energy depletion influencing size-dependent survival
Energetic Adaptations along a Broad Latitudinal Gradient: Implications for Widely Distributed Assemblages
Most community-based models in ecology assume that all individuals within a species respond similarly to environmental conditions and thereby exert identical effects as consumers or prey. Rather, individuals differ among systems, with important implications for population demographics and community interactions. For widely distributed assemblages made up of poikilotherms with high first-year mortality, species-specific differences in growth reaction norms as affected by both temperature and genotype will influence biotic interactions. For a broadly distributed fish assemblage, first-year growth does not vary with latitude for a planktivorous prey species, but declines with increasing latitude for a terminal piscivore. Size-based competitive interactions between these species are likely to be more intense at high latitudes, as they spend an extended time sharing resources during early life. Such patterns probably are pervasive and must be considered when seeking to understand species interactions. Improving our knowledge of how temperature and local adaptations affect size-based interactions should enhance our ability to manage and conserve widespread assemblages
Clinicians’ views on cognitive assessment with Aboriginal Australians
Background: A shortage of standardised cognitive assessment tools for use with Aboriginal Australians is evident. Clinicians also miss the range of guidelines necessary to inform test selection and interpretation for all Aboriginal clients. This mixed methods study examines clinicians’ confidence, views and current practices when conducting cognitive assessments with Aboriginal Australian clients. Methods: Clinicians were asked about factors that influence their likelihood of using standardised testing in Aboriginal vs non-Indigenous Australian people. Twenty-one health professionals with experience conducting cognitive assessments with Aboriginal and non-Aboriginal Australians participated. Clinicians were presented with a series of different scenarios per the client’s level of education and language of origin via an online survey. Clinicians rated their likelihood and confidence using standardised cognitive assessment for each scenario. Open-ended questions captured clinicians’ views and information about their current clinical practices. Results: Clients’ age, education and language of origin influence the likelihood of clinicians’ use of standardised cognitive assessment measures with Aboriginal people. Overall, clinicians reported feeling only slightly more confident working with non-Indigenous clients than Aboriginal clients. Qualitative data indicate a lack of consistency regarding test selection. Conclusion: Clinicians expressed concerns about the validity of available cognitive assessment tools for use with Aboriginal Australians and the absence of evidence to assist decision-making. Cited barriers included language, educational attainment and cultural factors
Strangeness in the nucleon and the ratio of proton-to-neutron neutrino-induced quasi-elastic yield
The electroweak form factors of the nucleon as obtained within a three flavor
pseudoscalar vector meson soliton model are employed to predict the ratio of
the proton and neutron yields from , which are induced by quasi-elastic
neutrino reactions. These predictions are found to vary only moderately in the
parameter space allowed by the model. The antineutrino flux of the up-coming
experiment determining this ratio was previously overestimated. The
corresponding correction is shown to have only a small effect on the predicted
ratio. However, it is found that the experimental result for the ratio
crucially depends on an accurate measurement of the energy of the knocked out
nucleon.Comment: 17 pages, LaTeX, 2 tables, 4 figures, Discussion on shape of strange
form factors added, Z. Phys. A, to be publishe
Probing Nucleon Strangeness with Neutrinos: Nuclear Model Dependences
The extraction of the nucleon's strangeness axial charge, Delta_s, from
inclusive, quasielastic neutral current neutrino cross sections is studied
within the framework of the plane-wave impulse approximation. We find that the
value of Delta_s can depend significantly on the choice of nuclear model used
in analyzing the quasielastic cross section. This model-dependence may be
reduced by one order of magnitude when Delta_s is extracted from the ratio of
total proton to neutron yields. We apply this analysis to the interpretation of
low-energy neutrino cross sections and arrive at a nuclear theory uncertainty
of plus/minus 0.03 on the value of Delta_s expected to be determined from the
ratio of proton and neutron yields measured by the LSND collaboration. This
error compares favorably with estimates of the SU(3)-breaking uncertainty in
the value of Delta_s extracted from inclusive, polarized deep-inelastic
structure function measurements. We also point out several general features of
the quasielastic neutral current neutrino cross section and compare them with
the analogous features in inclusive, quasielastic electron scattering.Comment: 40 pages (including 11 postscript figures), uses REVTeX and
epsfig.st
Cell non-autonomous regulation of hepatic IGF-1 and neonatal growth by Kinase Suppressor of Ras 2 (KSR2)
Individuals with poor postnatal growth are at risk for cardiovascular and metabolic problems as adults. Here we show that disruption of the molecular scaffold Kinase Suppressor of Ras 2 (KSR2) causes selective inhibition of hepatic GH signaling in neonatal mice with impaired expression of IGF-1 and IGFBP3. ksr2−/− mice are normal size at birth but show a marked increase in FGF21 accompanied by reduced body mass, shortened body length, and reduced bone mineral density (BMD) and content (BMC) first evident during postnatal development. However, disrupting FGF21 in ksr2−/− mice does not normalize mass, length, or bone density and content in fgf21−/−ksr2−/− mice. Body length, BMC and BMD, but not body mass, are rescued by infection of two-day-old ksr2−/− mice with a recombinant adenovirus encoding human IGF-1. Relative to wild-type mice, GH injections reveal a significant reduction in JAK2 and STAT5 phosphorylation in liver, but not in skeletal muscle, of ksr2−/− mice. However, primary hepatocytes isolated from ksr2−/− mice show no reduction in GH-stimulated STAT5 phosphorylation. These data indicate that KSR2 functions in a cell non-autonomous fashion to regulate GH-stimulated IGF-1 expression in the liver of neonatal mice, which plays a key role in the development of body length
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
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
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