1,142 research outputs found
Neutrino induced transitions between the ground states of the A=12 triad
Neutrino induced reactions on C, an ingredient of liquid
scintillators, have been studied in several experiments. We show that for
currently available neutrino energies, 300 MeV, calculated
exclusive cross sections CN for both muon
and electron neutrinos are essentially model independent, provided the
calculations simultaneously describe the rates of several other reactions
involving the same states or their isobar analogs. The calculations agree well
with the measured cross sections, which can be therefore used to check the
normalization of the incident neutrino spectrum and the efficiency of the
detector.Comment: 9 pages REVTEX, 2 postscript figures, text and figures available at
http://www.krl.caltech.edu/preprints/MAP.htm
Muon capture on nuclei with N > Z, random phase approximation, and in-medium renormalization of the axial-vector coupling constant
We use the random phase approximation to describe the muon capture rate on
Ca,Ca, Fe, Zr, and Pb. With
Ca as a test case, we show that the Continuum Random Phase
Approximation (CRPA) and the standard RPA give essentially equivalent
descriptions of the muon capture process. Using the standard RPA with the free
nucleon weak form factors we reproduce the experimental total capture rates on
these nuclei quite well. Confirming our previous CRPA result for the
nuclei, we find that the calculated rates would be significantly lower than the
data if the in-medium quenching of the axial-vector coupling constant were
employed.Comment: submitted to Phys. Rev.
The effects of charge transfer inefficiency (CTI) on galaxy shape measurements
(Abridged) We examine the effects of charge transfer inefficiency (CTI)
during CCD readout on galaxy shape measurements required by studies of weak
gravitational lensing. We simulate a CCD readout with CTI such as that caused
by charged particle radiation damage. We verify our simulations on data from
laboratory-irradiated CCDs. Only charge traps with time constants of the same
order as the time between row transfers during readout affect galaxy shape
measurements. We characterize the effects of CTI on various galaxy populations.
We baseline our study around p-channel CCDs that have been shown to have charge
transfer efficiency up to an order of magnitude better than several models of
n-channel CCDs designed for space applications. We predict that for galaxies
furthest from the readout registers, bias in the measurement of galaxy shapes,
Delta(e), will increase at a rate of 2.65 +/- 0.02 x 10^(-4) per year at L2 for
accumulated radiation exposure averaged over the solar cycle. If uncorrected,
this will consume the entire shape measurement error budget of a dark energy
mission within about 4 years. Software mitigation techniques demonstrated
elsewhere can reduce this by a factor of ~10, bringing the effect well below
mission requirements. CCDs with higher CTI than the ones we studeied may not
meet the requirements of future dark energy missions. We discuss ways in which
hardware could be designed to further minimize the impact of CTI.Comment: 11 pages, 6 figures, and 2 tables. Accepted for publication in PAS
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Nucleation and phase selection in undercooled melts: Magnetic alloys of industrial relevance (MAGNEPHAS)
Studies of phase selection and microstructure evolution in high-performance magnetic materials are an urgent need for optimization of production routes. Containerless solidification experiments by electromagnetic levitation and drop tube solidification were conducted in undercooled melts of Fe-Co, Fe-Ni soft magnetic, and Nd-Fe-B hard magnetic alloys. Melt undercooling under microgravity was achieved in the TEMPUS facility during parabolic flight campaigns. For Fe-Co and Fe-Ni alloys significant effects of microgravity on metastable phase formation were discovered. Microstructure modifications as well as metastable phase formation as function of undercooling and melt flow were elucidated in Nd-Fe-B. Modeling of solidification processes, fluid flow and heat transfer provide predictive tools for microstructure engineering from the melt. They were developed as a link between undercooling experiments under terrestrial and microgravity conditions and the production routes of magnetic materials
"Be active!" Revisiting the South African Food Based Dietary Guidelines for activity
The objective of this paper was to review current evidence on physical activity for health in order to support the foodbased dietary guideline (FBDG) “Be active!”. Physical activity, defined as at least 30 minutes of moderate-intensity physical activity per day for adults, and 60 minutes for children and adolescents, is advised in the FBDG because of the role it plays in maintaining energy balance, improving body composition and promoting general health and wellbeing. The reviewed outcome measures are changes in physical activity patterns and the reported prevalence of noncommunicable diseases (NCDs) in South Africa. Despite the previous set of FBDGs, no improvements in physical activity, obesity or NCDs have been reported in South Africa. Recent literature emphasises the beneficial effects of physical activity on the reduction of risk factors associated with the prevalence of NCDs. Physical activity has a positive effect on appetite and weight control, insulin sensitivity, dyslipidaemia, hypertension, stress relief and burnout. Barriers that prevent children and adults from participating in regular physical activity have been identified, and recommendations how to overcome these have been made. It has been concluded that South Africans are not sufficiently physically active for their general health status to be improved. It is recommended that methods to promote physical activity at national, provincial, district and local level need to be developed, implemented and sustained
Influence of the 6^1S_0-6^3P_1 Resonance on Continuous Lyman-alpha Generation in Mercury
Continuous coherent radiation in the vacuum-ultraviolet at 122 nm
(Lyman-alpha) can be generated using sum-frequency mixing of three fundamental
laser beams in mercury vapour. One of the fundamental beams is at 254 nm
wavelength, which is close to the 6^1S_0-6^3P_1 resonance in mercury.
Experiments have been performed to investigate the effect of this one-photon
resonance on phasematching, absorption and the nonlinear yield. The efficiency
of continuous Lyman-alpha generation has been improved by a factor of 4.5.Comment: 8 pages, 7 figure
Signatures of Nucleon Disappearance in Large Underground Detectors
For neutrons bound inside nuclei, baryon instability can manifest itself as a
decay into undetectable particles (e.g., ), i.e.,
as a disappearance of a neutron from its nuclear state. If electric charge is
conserved, a similar disappearance is impossible for a proton. The existing
experimental lifetime limit for neutron disappearance is 4-7 orders of
magnitude lower than the lifetime limits with detectable nucleon decay products
in the final state [PDG2000]. In this paper we calculated the spectrum of
nuclear de-excitations that would result from the disappearance of a neutron or
two neutrons from C. We found that some de-excitation modes have
signatures that are advantageous for detection in the modern high-mass,
low-background, and low-threshold underground detectors, where neutron
disappearance would result in a characteristic sequence of time- and
space-correlated events. Thus, in the KamLAND detector [Kamland], a
time-correlated triple coincidence of a prompt signal, a captured neutron, and
a decay of the residual nucleus, all originating from the same
point in the detector, will be a unique signal of neutron disappearance
allowing searches for baryon instability with sensitivity 3-4 orders of
magnitude beyond the present experimental limits.Comment: 13 pages including 6 figures, revised version, to be published in
Phys.Rev.
Sex-Specific Correlations of Individual Heterozygosity, Parasite Load, and Scalation Asymmetry in a Sexually Dichromatic Lizard
Heterozygosity-fitness correlations (HFCs) provide insights into the genetic bases of individual fitness variation in natural populations. However, despite decades of study, the biological significance of HFCs is still under debate. In this study, we investigated HFCs in a large population of the sexually dimorphic lizard Takydromus viridipunctatus (Lacertidae). Because of the high prevalence of parasitism from trombiculid mites in this lizard, we expect individual fitness (i.e., survival) to decrease with increasing parasite load. Furthermore, because morphological asymmetry is likely to influence individuals\u27 mobility (i.e., limb asymmetry) and male biting ability during copulation (i.e., head asymmetry) in this species, we also hypothesize that individual fitness should decrease with increasing morphological asymmetry. Although we did not formally test the relationship between morphological asymmetry and fitness in this lizard, we demonstrated that survival decreased with increasing parasite load using a capture-mark-recapture data set. We used a separate sample of 140 lizards to test the correlations between individual heterozygosity (i.e., standardized mean d2 and HL based on 10 microsatellite loci) and the two fitness traits (i.e., parasite load and morphological asymmetry). We also evaluated and excluded the possibility that single-locus effects produced spurious HFCs. Our results suggest male-only, negative correlations between individual heterozygosity and parasite load and between individual heterozygosity and asymmetry, suggesting sex-specific, positive HFCs. Male T. viridipunctatus with higher heterozygosity tend to have lower parasite loads (i.e., higher survival) and lower asymmetry, providing a rare example of HFC in reptiles
Patients' perceptions of the potential of breathing training for asthma: a qualitative study.
Poor symptom control is common in asthma. Breathing training exercises may be an effective adjunct to medication; it is therefore important to understand facilitators and barriers to uptake of breathing training exercises
Neutrino-induced neutron spallation and supernova r-process nucleosynthesis
In order to explore the consequences of the neutrino irradiation for the
supernova r-process nucleosynthesis, we calculate the rates of charged-current
and neutral-current neutrino reactions on neutron-rich heavy nuclei, and
estimate the average number of neutrons emitted in the resulting spallation.
Our results suggest that charged-current captures can be important in
breaking through the waiting-point nuclei at N=50 and 82, while still allowing
the formation of abundance peaks. Furthermore, after the r-process freezes out,
there appear to be distinctive neutral-current and charged-current
postprocessing effects. A subtraction of the neutrino postprocessing effects
from the observed solar r-process abundance distribution shows that two mass
regions, A=124-126 and 183-187, are inordinately sensitive to neutrino
postprocessing effects. This imposes very stringent bounds on the freeze-out
radii and dynamic timescales governing the r-process. Moreover, we find that
the abundance patterns within these mass windows are entirely consistent with
synthesis by neutrino interactions. This provides a strong argument that the
r-process must occur in the intense neutrino flux provided by a core-collapse
supernova.Comment: 34 pages, 4 PostScript figures, RevTe
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