2,259 research outputs found
Electron-Phonon Dynamics in an Ensemble of Nearly Isolated Nanoparticles
We investigate the electron population dynamics in an ensemble of nearly
isolated insulating nanoparticles, each nanoparticle modeled as an electronic
two-level system coupled to a single vibrational mode. We find that at short
times the ensemble-averaged excited-state population oscillates but has a
decaying envelope. At long times, the oscillations become purely sinusoidal
about a ``plateau'' population, with a frequency determined by the
electron-phonon interaction strength, and with an envelope that decays
algebraically as t^-{1/2} We use this theory to predict electron-phonon
dynamics in an ensemble of Y_2 O_3 nanoparticles.Comment: 11 pages, 3 figure
Association between cognitive performance and cortical glucose metabolism in patients with mild Alzheimer's disease
Background: Neuronal and synaptic function in Alzheimer's disease (AD) is measured in vivo by glucose metabolism using positron emission tomography (PET). Objective: We hypothesized that neuronal activation as measured by PET is a more sensitive index of neuronal dysfunction than activity during rest. We investigated if the correlations between dementia severity as measured with the Mini Mental State Examination (MMSE) and glucose metabolism are an artifact of brain atrophy. Method: Glucose metabolism was measured using {[}F-18]fluorodeoxyglucose PET during rest and activation due to audiovisual stimulation in 13 mild to moderate AD patients (MMSE score >= 17). PET data were corrected for brain atrophy. Results: In the rest condition, glucose metabolism was correlated with the MMSE score primarily within the posterior cingulate and parietal lobes. For the activation condition, additional correlations were within the primary and association audiovisual areas. Most local maxima remained significant after correcting for brain atrophy. Conclusion: PET activity measured during audiovisual stimulation was more sensitive to functional alterations in glucose metabolism in AD patients compared to the resting PET. The association between glucose metabolism and MMSE score was not dependent on brain atrophy. Copyright (C) 2005 S. Karger AG, Basel
The Radio Afterglow and the Host Galaxy of the X-Ray Rich GRB 981226
We report the discovery of a radio transient VLA 232937.2-235553, coincident
with the proposed X-ray afterglow for the gamma-ray burst GRB 981226. This GRB
has the highest ratio of X-ray to gamma-ray fluence of all the GRBs detected by
BeppoSAX so far and yet no corresponding optical transient was detected. The
radio light curve of VLA 232937.2-235553 is qualitatively similar to that of
several other radio afterglows. At the sub-arcsecond position provided by the
radio detection, optical imaging reveals an extended R=24.9 mag object, which
we identify as the host galaxy of GRB 981226. Afterglow models which invoke a
jet-like geometry for the outflow or require an ambient medium with a radial
density dependence, such as that produced by a wind from a massive star, are
both consistent with the radio data. Furthermore, we show that the observed
properties of the radio afterglow can explain the absence of an optical
transient without the need for large extinction local to the GRB.Comment: Accepted for publication in the Astrophysical Journal Letters.
Thirteen pages. Three Postscript figure
Benchmark Calculations of Electron Impact Electronic Excitation of the Hydrogen Molecule
We present benchmark integrated and differential cross-sections for electron
collisions with H using two different theoretical approaches, namely, the
R-matrix and molecular convergent close-coupling (MCCC). This is similar to
comparative studies conducted on electron-atom collisions for H, He and Mg.
Electron impact excitation to the , , $B \
^1\Sigma_u^+c \ ^3\Pi_uEF \ ^1\Sigma_g^+C \ ^1\Pi_ue \
^3\Sigma_u^+h \ ^3\Sigma_g^+B' \ ^1\Sigma_u^+d \ ^3\Pi_ub \ ^3\Sigma_u^+$ state. Good agreement is found for all
transitions presented. Where available, we compare with existing experimental
and recommended data.Comment: 21 pages, 25 figure
Effect of yohimbine on rat prolactin secretion
ABSTRACT It was recently proposed that yohimbine (YO
Development and validation of instruments measuring body image and body weight dissatisfaction in South African mothers and their daughters
Objective We sought to validate questionnaires concerning body image perception, body size dissatisfaction and weight-related beliefs in multi-ethnic South African mothers and their daughters. Settings and subjects: Girls attending primary school (ages 9-12 years, n = 333) and their mothers (n = 204) were interviewed regarding their demographics and body image. Weight, height and skinfold thicknesses were measured. Body image questions and body mass index (BMI) were compared with silhouettes adapted from the Pathways Study for girls and Stunkard\u27s body image figures for mothers. A Feel-Ideal Difference (FID) index score was created by subtracting the score of the silhouette selected by the participants as \u27Ideal\u27 from the one selected as most closely representing their current appearance or \u27Feel\u27. We hypothesised that a higher FID index score would be associated with greater body size dissatisfaction. Results BMI percentiles in girls (r = 0.46, P \u3c 0.05) and BMI in mothers (r = 0.68, P \u3c 0.05) were positively correlated with the selected silhouettes based on size. Participants who reported feelings of being \u27fat\u27 and those who perceived that their family and friends were more dissatisfied with their body size had significantly higher FID index scores. Scores were lower in black than white girls (all P \u3c 0.05). No differences were found in FID index scores between ethnic groups of mothers. Internal reliability of the \u27thin\u27 and \u27fat\u27 belief constructs for girls was demonstrated by standardised Cronbach\u27s α values ≥ 0.7. Conclusion Silhouettes, FID index, \u27fat\u27 and \u27thin\u27 belief constructs (in girls) are age-appropriate, culturally sensitive and can be used in further intervention studies to understand body image
Perinatal psychiatric episodes: a population-based study on treatment incidence and prevalence
Perinatal psychiatric episodes comprise various disorders and symptom severity, which are diagnosed and treated in multiple treatment settings. To date, no studies have quantified the incidence and prevalence of perinatal psychiatric episodes treated in primary and secondary care, which we aimed to do in the present study. We designed a descriptive prospective study and included information from Danish population registers to study first-time ever and recurrent psychiatric episodes during the perinatal period, including treatment at psychiatric facilities and general practitioners (GPs). This was done for all women who had records of one or more singleton births from 1998 until 2012. In total, we had information on 822 439 children born to 491 242 unique mothers. Results showed first-time psychiatric episodes treated at inpatient facilities were rare during pregnancy, but increased significantly shortly following childbirth (0.02 vs 0.25 per 1000 births). In comparison, first-time psychiatric episodes treated at outpatient facilities were more common, and showed little variation across pregnancy and postpartum. For every single birth resulting in postpartum episodes treated at inpatient psychiatric facilities, 2.5 births were followed by an episode treated at outpatient psychiatric facility and 12 births by GP-provided pharmacological treatment. We interpret our results the following way: treated severe and moderate psychiatric disorders have different risk patterns in relation to pregnancy and childbirth, which suggests differences in the underlying etiology. We further speculate varying treatment incidence and prevalence in pregnancy vs postpartum may indicate that the current Diagnostic and Statistical Manual of Mental Disorders-5 peripartum specifier not adequately describes at-risk periods across moderate and severe perinatal psychiatric episodes
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