7,001 research outputs found
Large Bychkov-Rashba spin-orbit coupling in high-mobility GaN/AlGaN heterostructures
We present low temperature magnetoconductivity measurements of a
density-tunable and high mobility two-dimensional electron gas confined in the
wide bandgap GaN/AlGaN system. We observed pronounced anti-localization minima
in the low-field conductivity, indicating the presence of strong spin-orbit
coupling. Density dependent measurements of magnetoconductivity indicate that
the coupling is mainly due to the Bychkov-Rashba mechanism. In addition, we
have derived a closed-form expression for the magnetoconductivity, allowing us
to extract reliable transport parameters for our devices. The Rashba spin-orbit
coupling constant is 6 10eVm, while the
conduction band spin-orbit splitting energy amounts to
0.3meV at n=1m.Comment: Accepted for publication in PR
Studying The Collector Performance Of Updraft Solar Chimney Power Plant
In the shadow of increasing energy consumption, renewable energy is the best choicefor a sustainable environment. The solar chimney power plant (SCPP) is a new technology, many researchers are paying their attention to improve its performance. In this study, experimental and numerical studies were used to understand the effect of the collector geometry on the SCPP performance. The SCPP prototype under our investigation is installed in Aswan city, its chimney height is 20m, its diameter is 1 m and the collector is a square which has a side length of 28.5m. Three dimensional CFD simulations were made to calculate the temperature and velocity distribution inside two different shapes of SCPP collector. The conclusion is that the square shaped collector achieved higher output power than the circular collector by 7.6 % at the same surface area exposed to solar radiation
Rethinking the QCD collisional energy loss
It is shown that to leading order the collisional energy loss of an energetic
parton in the hot quark gluon plasma reads , where
the scale of the coupling is determined by the (parametrically soft) Debye
screening mass. Compared to previous expressions derived by Bjorken and other
authors, , the rectified result takes
into account the running of the coupling, as dictated by quantum corrections
beyond tree level. As one significant consequence, due to asymptotic freedom,
the QCD collisional energy loss becomes independent of the jet energy in the
limit . It is advocated that this resummation improved perturbative
result might be useful to (re-)estimate the collisional energy loss for
temperatures relevant in heavy ion phenomenology.Comment: contribution to "Hot Quarks 2006", Villasimius, Italy, 15-20 May 200
Testing hydrostatic equilibrium in galaxy cluster MS 2137
We test the assumption of strict hydrostatic equilibrium in galaxy cluster
MS2137.3-2353 (MS 2137) using the latest CHANDRA X-ray observations and results
from a combined strong and weak lensing analysis based on optical observations.
We deproject the two-dimensional X-ray surface brightness and mass surface
density maps assuming spherical and spheroidal dark matter distributions. We
find a significant, 40%-50%, contribution from non-thermal pressure in the core
assuming a spherical model. This non-thermal pressure support is similar to
what was found by Molnar et al. (2010) using a sample of massive relaxed
clusters drawn from high resolution cosmological simulations. We have studied
hydrostatic equilibrium in MS 2137 under the assumption of elliptical cluster
geometry adopting prolate models for the dark matter density distribution with
different axis ratios. Our results suggest that the main effect of ellipticity
(compared to spherical models) is to decrease the non-thermal pressure support
required for equilibrium at all radii without changing the distribution
qualitatively. We find that a prolate model with an axis ratio of 1.25 (axis in
the line of sight over perpendicular to it) provides a physically acceptable
model implying that MS 2137 is close to hydrostatic equilibrium at about
0.04-0.15 Rvir and have an about 25% contribution from non-thermal pressure at
the center. Our results provide further evidence that there is a significant
contribution from non-thermal pressure in the core region of even relaxed
clusters, i.e., the assumption of hydrostatic equilibrium is not valid in this
region, independently of the assumed shape of the cluster.Comment: 11 pages, 4 figures, accepted for publication in Ap
Sleep disorders, depressive symptoms and health-related quality of life-a cross-sectional comparison between kidney transplant recipients and waitlisted patients on maintenance dialysis
BACKGROUND: Kidney transplantation is believed to improve health-related quality of life (HRQoL) of patients requiring renal replacement therapy (RRT). Recent studies suggested that the observed difference in HRQoL between kidney transplant recipients (Tx) vs patients treated with dialysis may reflect differences in patient characteristics. We tested if Tx patients have better HRQoL compared to waitlisted (WL) patients treated with dialysis after extensive adjustment for covariables. METHODS: Eight hundred and eighty-eight prevalent Tx patients followed at a single outpatient transplant clinic and 187 WL patients treated with maintenance dialysis in nine dialysis centres were enrolled in this observational cross-sectional study. Data about socio-demographic and clinical parameters, self-reported depressive symptoms and the most frequent sleep disorders assessed by self-reported questionnaires were collected at enrollment. HRQoL was assessed by the Kidney Disease Quality of Life Questionnaire. RESULTS: Patient characteristics were similar in the Tx vs WL groups: the proportion of males (58 vs 60%), mean +/- SD age (49 +/- 13 vs 49 +/- 12) and proportion of diabetics (17 vs 18%), respectively, were all similar. Tx patients had significantly better HRQoL scores compared to the WL group both in generic (Physical function, General health perceptions, Energy/fatigue, Emotional well-being) and in kidney disease-specific domains (Symptoms/problems, Effect- and Burden of kidney disease and Sleep). In multivariate regression models adjusting for clinical and socio-demographic characteristics, sleep disorders and depressive symptoms, the modality of RRT (WL vs Tx) remained independently associated with three (General health perceptions, Effect- and Burden of kidney disease) out of the eight HRQoL dimensions analysed. CONCLUSIONS: Kidney Tx recipients have significantly better HRQoL compared to WL dialysis patients in some, but not all, dimensions of quality of life after accounting for differences in patient characteristics. Utilizing multidimensional disease-specific questionnaires will allow better understanding of treatment, disease and patient-related factors potentially affecting quality of life in patients with chronic medical conditions
STAR Results on High Transverse Momentum, Heavy Flavor and Electromagnetic Probes
We summarize here recent results from the STAR collaboration focusing on
processes involving large momentum transfers. Measurements of angular
correlations of di-hadrons are explored in both the pseudorapidity (eta) and
azimuthal (phi) projections. In central Au+Au, an elongated structure is found
in the eta projection which persists up to the highest measured pT. After
quantifying the particle yield in this structure and subtracting it from the
near-side yield, we observe that the remainder exhibits a behavior strikingly
similar to that of the near-side yield in d+Au. For heavy flavor production,
using electron-hadron correlations in p+p collisions, we obtain an estimate of
the b-quark contribution to the non-photonic electrons in the pT region 3-6
GeV/c, and find it consistent with FONLL calculations. Together with the
observed suppression of non-photonic electrons in Au+Au, this strongly suggests
suppression of b-quark production in Au+Au collisions. We discuss results on
the mid-rapidity Upsilon cross-section in p+p collisions. Finally, we present a
proof-of-principle measurement of photon-hadron correlations in p+p collisions,
paving the way for the tomographic study of the matter produced in central
Au+Au via gamma-jet measurements.Comment: 8 pages, 4 figures. Proceedings of "Quark Matter 2006", 19th
International Conference on Ultra-Relativistic Nucleus-Nucleus Collision
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