2,434 research outputs found
Magic angle effects in the interlayer magnetoresistance of quasi-one-dimensional metals due to interchain incoherence
The dependence of the magnetoresistance of quasi-one-dimensional metals on
the direction of the magnetic field show dips when the field is tilted at the
so called magic angles determined by the structural dimensions of the
materials. There is currently no accepted explanation for these magic angle
effects. We present a possible explanation. Our model is based on the
assumption that, the intralayer transport in the second most conducting
direction has a small contribution from incoherent electrons. This incoherence
is modelled by a small uncertainty in momentum perpendicular to the most
conducting (chain) direction. Our model predicts the magic angles seen in
interlayer transport measurements for different orientations of the field. We
compare our results to predictions by other models and to experiment.Comment: 7 pages, 3 figures, Submitted To Phys. Rev.
The RHIC Zero Degree Calorimeter
High Energy collisions of nuclei usually lead to the emission of evaporation
neutrons from both ``beam'' and ``target'' nuclei. At the RHIC heavy ion
collider with 100GeV/u beam energy, evaporation neutrons diverge by less than
milliradians from the beam axis Neutral beam fragments can be detected
downstream of RHIC ion collisions (and a large aperture Accelerator dipole
magnet) if 4 mr but charged fragments in the same angular range
are usually too close to the beam trajectory.
In this 'zero degree' region produced particles and other secondaries deposit
negligible energy when compared with that of beam fragmentation neutrons.
The purpose of the RHIC zero degree calorimeters (ZDC's) is to detect
neutrons emitted within this cone along both beam directions and measure their
total energy (from which we calculate multiplicity). The ZDC coincidence of the
2 beam directions is a minimal bias selection of heavy ion collisions. This
makes it useful as an event trigger and a luminosity monitor\cite{baltz} and
for this reason we built identical detectors for all 4 RHIC experiments.
The neutron multiplicity is also known to be correlated with event geometry
\cite{appel} and will be used to measure collision centrality in mutual beam
int eractions.Comment: 18 pages, 12 figure
Geometric phases of scattering states in a ring geometry: adiabatic pumping in mesoscopic devices
Geometric phases of scattering states in a ring geometry are studied based on
a variant of the adiabatic theorem. Three time scales, i.e., the adiabatic
period, the system time and the dwell time, associated with adiabatic
scattering in a ring geometry plays a crucial role in determining geometric
phases, in contrast to only two time scales, i.e., the adiabatic period and the
dwell time, in an open system. We derive a formula connecting the gauge
invariant geometric phases acquired by time-reversed scattering states and the
circulating (pumping) current. A numerical calculation shows that the effect of
the geometric phases is observable in a nanoscale electronic device.Comment: 9 pages, 3 figure
The Hydrogen Exospheric Density Profile Measured with ASPERA-3/NPD
We have evaluated the Lyman-α limb emission from the exospheric hydrogen of Mars measured by the neutral particle detector of the ASPERA-3 instrument on Mars Express in 2004 at low solar activity (solar activity index = 42, F10.7=100). We derive estimates for the hydrogen exobase density, n H = 1010 m−3, and for the apparent temperature, T > 600 K. We conclude that the limb emission measurement is dominated by a hydrogen component that is considerably hotter than the bulk temperature at the exobase. The derived values for the exosphere density and temperature are compared with similar measurements done by the Mariner space probes in the 1969. The values found with Mars Express and Mariner data are brought in a broader context of exosphere models including the possibility of having two hydrogen components in the Martian exosphere. The present observation of the Martian hydrogen exosphere is the first one at high altitudes during low solar activity, and shows that for low solar activity exospheric densities are not higher than for high solar activit
Trends in levels of self-reported psychological distress among individuals who seek psychiatric services over eight years: a comparison between age groups in three population surveys in Stockholm County
BACKGROUND: Psychiatric service use has increased in Sweden and in other developed countries, particularly among young people. Possible explanations include lower threshold for help-seeking among young people, but evidence is scarce. METHODS: We analysed the 2002, 2006 and 2010 Stockholm public health surveys for changes in the mean level of psychological distress among adult users of psychiatric in- and outpatient services in four age groups: 18-24, 25-44, 45-64 and ≥65 years. Psychological distress was measured via the 12-item General Health Questionnaire (GHQ-12), using the Likert scoring method 0-1-2-3. In- and out-patient psychiatric service use within 6 months from the surveys was obtained from registers. RESULTS: The mean level of distress among young adults 18-24 years who utilize psychiatric services decreased between 2002 (mean GHQ-12 score, 95% confidence interval 20.5, 18.1-23.0) and 2010 (16.2, 14.6-17.7), while it remained fairly stable in older age groups. Results were similar in sex-stratified analyses, although the decrease was statistically significant only among young women 18-24 years. At the end of the follow-up, the level of distress among patients was similar for all age-groups. CONCLUSIONS: There were no differences between age groups in the level of distress when seeking care at the end of the follow-up period, supporting that there is no age-specific over- or under-consumption of psychiatric care in later years. However, the lowered threshold for help-seeking among young adults over time might have contributed to increases in psychiatric service use in the young age group. Public health policy and service delivery planning should consider the needs of the widening group of young users of psychiatric services
Energetic Hydrogen and Oxygen Atoms Observed on the Nightside of Mars
We present measurements of energetic hydrogen and oxygen atoms (ENAs) on the nightside of Mars detected by the neutral particle detector (NPD) of ASPERA-3 on Mars Express. We focus on the observations for which the field-of-view of NPD was directed at the nightside of Mars or at the region around the limb, thus monitoring the flow of ENAs towards the nightside of the planet. We derive energy spectra and total fluxes, and have compiled maps of hydrogen ENA outflow. The hydrogen ENA intensities reach 105 cm−2 sr−1 s−1, but no oxygen ENA signals above the detection threshold of 104 cm−2 sr−1 s−1 are observed. These intensities are considerably lower than most theoretical predictions. We explain the discrepancy as due to an overestimation of the charge-exchange processes in the models for which too high an exospheric density was assumed. Recent UV limb emission measurements (Galli et al., this issue) point to a hydrogen exobase density of 1010 m−3 and a very hot hydrogen component, whereas the models were based on a hydrogen exobase density of 1012 m−3 and a temperature of 200 K predicted by Krasnopolsky and Gladstone (1996). Finally, we estimate the global atmospheric loss rate of hydrogen and oxygen due to the production of ENA
The Arabidopsis Thylakoid Chloride Channel AtCLCe Functions in Chloride Homeostasis and Regulation of Photosynthetic Electron Transport.
Chloride ions can be translocated across cell membranes through Cl(-) channels or Cl(-)/H(+) exchangers. The thylakoid-located member of the Cl(-) channel CLC family in Arabidopsis thaliana (AtCLCe) was hypothesized to play a role in photosynthetic regulation based on the initial photosynthetic characterization of clce mutant lines. The reduced nitrate content of Arabidopsis clce mutants suggested a role in regulation of plant nitrate homeostasis. In this study, we aimed to further investigate the role of AtCLCe in the regulation of ion homeostasis and photosynthetic processes in the thylakoid membrane. We report that the size and composition of proton motive force were mildly altered in two independent Arabidopsis clce mutant lines. Most pronounced effects in the clce mutants were observed on the photosynthetic electron transport of dark-adapted plants, based on the altered shape and associated parameters of the polyphasic OJIP kinetics of chlorophyll a fluorescence induction. Other alterations were found in the kinetics of state transition and in the macro-organization of photosystem II supercomplexes, as indicated by circular dichroism measurements. Pre-treatment with KCl but not with KNO3 restored the wild-type photosynthetic phenotype. Analyses by transmission electron microscopy revealed a bow-like arrangement of the thylakoid network and a large thylakoid-free stromal region in chloroplast sections from the dark-adapted clce plants. Based on these data, we propose that AtCLCe functions in Cl(-) homeostasis after transition from light to dark, which affects chloroplast ultrastructure and regulation of photosynthetic electron transport
A First Comparison of the responses of a He4-based fast-neutron detector and a NE-213 liquid-scintillator reference detector
A first comparison has been made between the pulse-shape discrimination
characteristics of a novel He-based pressurized scintillation detector
and a NE-213 liquid-scintillator reference detector using an Am/Be mixed-field
neutron and gamma-ray source and a high-resolution scintillation-pulse
digitizer. In particular, the capabilities of the two fast neutron detectors to
discriminate between neutrons and gamma-rays were investigated. The NE-213
liquid-scintillator reference cell produced a wide range of scintillation-light
yields in response to the gamma-ray field of the source. In stark contrast, due
to the size and pressure of the He gas volume, the He-based
detector registered a maximum scintillation-light yield of 750~keV to
the same gamma-ray field. Pulse-shape discrimination for particles with
scintillation-light yields of more than 750~keV was excellent in the
case of the He-based detector. Above 750~keV its signal was
unambiguously neutron, enabling particle identification based entirely upon the
amount of scintillation light produced.Comment: 23 pages, 7 figures, Nuclear Instruments and Methods in Physics
Research Section A review addresse
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