459 research outputs found
Hourly and seasonal variation in photosynthesis and stomatal conductance of soybean grown at future CO2 and ozone concentrations for three years under fully open air conditions.
published or submitted for publicatio
Bragg spectroscopy with an accelerating Bose-Einstein condensate
We present the results of Bragg spectroscopy performed on an accelerating
Bose-Einstein condensate. The Bose condensate undergoes circular micro-motion
in a magnetic TOP trap and the effect of this motion on the Bragg spectrum is
analyzed. A simple frequency modulation model is used to interpret the observed
complex structure, and broadening effects are considered using numerical
solutions to the Gross-Pitaevskii equation.Comment: 5 pages, 3 figures, to appear in PRA. Minor changes to text and fig
Theory of coherent Bragg spectroscopy of a trapped Bose-Einstein condensate
We present a detailed theoretical analysis of Bragg spectroscopy from a
Bose-Einstein condensate at T=0K. We demonstrate that within the linear
response regime, both a quantum field theory treatment and a meanfield
Gross-Pitaevskii treatment lead to the same value for the mean evolution of the
quasiparticle operators. The observable for Bragg spectroscopy experiments,
which is the spectral response function of the momentum transferred to the
condensate, can therefore be calculated in a meanfield formalism. We analyse
the behaviour of this observable by carrying out numerical simulations in
axially symmetric three-dimensional cases and in two dimensions. An approximate
analytic expression for the observable is obtained and provides a means for
identifying the relative importance of three broadening and shift mechanisms
(meanfield, Doppler, and finite pulse duration) in different regimes. We show
that the suppression of scattering at small values of q observed by
Stamper-Kurn et al. [Phys. Rev. Lett. 83, 2876 (1999)] is accounted for by the
meanfield treatment, and can be interpreted in terms of the interference of the
u and v quasiparticle amplitudes. We also show that, contrary to the
assumptions of previous analyses, there is no regime for trapped condensates
for which the spectral response function and the dynamic structure factor are
equivalent. Our numerical calculations can also be performed outside the linear
response regime, and show that at large laser intensities a significant
decrease in the shift of the spectral response function can occur due to
depletion of the initial condensate.Comment: RevTeX4 format, 16 pages plus 7 eps figures; Update to published
version: minors changes and an additional figure. (To appear in Phys. Rev. A
Incidence of schizophrenia and other psychoses in ethnic minority groups: results from the MRC AESOP Study
Background. The incidence of schizophrenia in the African-Caribbean population in England is reported to be raised. We sought to clarify whether (a) the rates of other psychotic disorders are increased, (b) whether psychosis is increased in other ethnic minority groups, and (c) whether particular age or gender groups are especially at risk.
Method. We identified all people (n=568) aged 16-64 years presenting to secondary services with their first psychotic symptoms in three well-defined English areas (over a 2-year period in Southeast London and Nottingham and a 9-month period in Bristol). Standardized incidence rates and incidence rate ratios (IRR) for all major psychosis syndromes for all main ethnic groups were calculated.
Results. We found remarkably high IRRs for both schizophrenia and manic psychosis in both African-Caribbeans (schizophrenia 9.1, manic psychosis 8.0) and Black Africans (schizophrenia 5.8, manic psychosis 6.2) in men and women. IRRs in other ethnic minority groups were modestly increased as were rates for depressive psychosis and other psychoses in all minority groups. These raised rates were evident in all age groups in our study.
Conclusions. Ethnic minority groups are at increased risk for all psychotic illnesses but African- Caribbeans and Black Africans appear to be at especially high risk for both schizophrenia and mania. These findings suggest that (a) either additional risk factors are operating in African- Caribbeans and Black Africans or that these factors are particularly prevalent in these groups, and that (b) such factors increase risk for schizophrenia and mania in these groups
Grey matter abnormalties in first episode schizophrenia and affective psychosis
Background: Grey matter and other structural brain abnormalities are consistently reported in first-onset schizophrenia, but less is known about the extent of neuroanatomical changes in first-onset affective psychosis.
Aims: To determine which brain abnormalities are specific to (a) schizophrenia and (b) affective psychosis.
Method: We obtained dual-echo (proton density/T2-weighted) MR images and carried out voxel-based analysis on the images of 73 first-episode psychosis patients (schizophrenia=44, affective psychosis=29) and 58 healthy controls.
Results: Both patients with schizophrenia and patients with affective psychosis had enlarged lateral and third ventricle volumes. Regional cortical grey matter reductions (including bilateral anterior cingulate gyrus, left insula and left fusiform gyrus) were evident in affective psychosis but not in schizophrenia, although patients with schizophrenia displayed decreased hippocampal grey matter and increased striatal grey matter at a more liberal statistical threshold.
Conclusions: Both schizophrenia and affective psychosis are associated with volumetric abnormalities at the onset of frank psychosis, with some of these evident in common brain areas
Early sustained recovery following first episode psychosis:Evidence from the AESOP10 follow-up study
Objective: To describe the characteristics of individuals with early sustained recovery following first episode psychosis. Methods: Individuals with a first episode psychosis were followed-up for ten years. Comparisons were made between those with Early Sustained Recovery and those with Other Course types. Results: Of 345 individuals, n=43 (12.5%) had Early Sustained Recovery. They were more likely than those with Other Course types to be female (OR=2.45; 95% CI: 1.25-4.81); employed (OR=2.39; 95% CI: 1.22-4.69); in a relationship (OR=2.68; 95% CI: 1.35-5.32); have a short DUP (OR=2.86; 95% CI: 1.37-5.88); and have a diagnosis other than schizophrenia, particularly mania (OR=6.39; 95% CI: 2.52-16.18) or brief psychosis (OR=3.64; 95% CI: 1.10-12.10). Conclusions: Sustained recovery from first episode psychosis occurs in a minority. (c) 2018 Elsevier B.V. All rights reserved
Constructions of generalized complex structures in dimension four
Four-manifold theory is employed to study the existence of (twisted)
generalized complex structures. It is shown that there exist (twisted)
generalized complex structures that have more than one type change loci. In an
example-driven fashion, (twisted) generalized complex structures are
constructed on a myriad of four-manifolds, both simply and non-simply
connected, which are neither complex nor symplectic
Individualized prediction of illness course at the first psychotic episode: a support vector machine MRI study
To date, magnetic resonance imaging (MRI) has made little impact on the diagnosis and monitoring of psychoses in individual patients. In this study, we used a support vector machine (SVM) whole-brain classification approach to predict future illness course at the individual level from MRI data obtained at the first psychotic episode
Thermal Background Corrections to the Neutrino Electromagnetic Vertex in Models with Charged Scalar Bosons
We calculate the correction to the neutrino electromagnetic vertex due to
background of electrons in a large class of models, as the supersymmetric model
with explicit breaking of R-parity, where charged scalar bosons couple to
leptons and which are able to provide an astrophysically interesting value for
the neutrino magnetic (electric) moment, . We show
that the medium contribution to the chirality flipping magnetic (electric)
dipole moment is not significant, however a new chirality flipping, but
helicity conserving, term arises. It signals the presence of and
asymmetries in the medium and is associated to the longitudinal
photon and therefore disappears in the vacuum. We estimate the contribution of
this new term to the rate of the plasmon decay process in the core of degenerate stars, showing that it can be comparable with
the contribution coming from the vacuum magnetic (dipole) moment. We also
calculate the correction to the effective potential of a propagating neutrino
in presence of a magnetic field due to a chirality preserving contribution to
the diagonal magnetic moment from the medium. This contribution is identical
for particles and antiparticles and so need not to vanish for Majorana
neutrinos.Comment: DFPD 93/TH/75, SISSA 93/183/A preprint, 25 pages + 4 figures
available by e-mail reques
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