898 research outputs found
Solar wind effects on the outer ion coma of Comet Halley
A simple two-dimensional model is developed to examine the composition of the cometary ion coma in the region outside the ionopause which is strongly affected by the solar wind. Two-dimensional ion distributions are obtained assuming a cylindrically symmetric ion coma which accounts for the dynamic effects of the mass-loaded solar wind flow around the cometary ionosphere. The results of this model are discussed in the context of analyzing the GIOTTO ion data
Thermal discomfort with cold extremities in relation to age, gender, and body mass index in a random sample of a Swiss urban population
<p>Abstract</p> <p>Background</p> <p>The aim of this epidemiological study was to investigate the relationship of thermal discomfort with cold extremities (TDCE) to age, gender, and body mass index (BMI) in a Swiss urban population.</p> <p>Methods</p> <p>In a random population sample of Basel city, 2,800 subjects aged 20-40 years were asked to complete a questionnaire evaluating the extent of cold extremities. Values of cold extremities were based on questionnaire-derived scores. The correlation of age, gender, and BMI to TDCE was analyzed using multiple regression analysis.</p> <p>Results</p> <p>A total of 1,001 women (72.3% response rate) and 809 men (60% response rate) returned a completed questionnaire. Statistical analyses revealed the following findings: Younger subjects suffered more intensely from cold extremities than the elderly, and women suffered more than men (particularly younger women). Slimmer subjects suffered significantly more often from cold extremities than subjects with higher BMIs.</p> <p>Conclusions</p> <p>Thermal discomfort with cold extremities (a relevant symptom of primary vascular dysregulation) occurs at highest intensity in younger, slimmer women and at lowest intensity in elderly, stouter men.</p
Breakup of the aligned H molecule by xuv laser pulses: A time-dependent treatment in prolate spheroidal coordinates
We have carried out calculations of the triple-differential cross section for
one-photon double ionization of molecular hydrogen for a central photon energy
of ~eV, using a fully {\it ab initio}, nonperturbative approach to solve
the time-dependent \Schro equation in prolate spheroidal coordinates. The
spatial coordinates and are discretized in a finite-element
discrete-variable representation. The wave packet of the laser-driven
two-electron system is propagated in time through an effective short iterative
Lanczos method to simulate the double ionization of the hydrogen molecule. For
both symmetric and asymmetric energy sharing, the present results agree to a
satisfactory level with most earlier predictions for the absolute magnitude and
the shape of the angular distributions. A notable exception, however, concerns
the predictions of the recent time-independent calculations based on the
exterior complex scaling method in prolate spheroidal coordinates
[Phys.~Rev.~A~{\bf 82}, 023423 (2010)]. Extensive tests of the numerical
implementation were performed, including the effect of truncating the Neumann
expansion for the dielectronic interaction on the description of the initial
bound state and the predicted cross sections. We observe that the dominant
escape mode of the two photoelectrons dramatically depends upon the energy
sharing. In the parallel geometry, when the ejected electrons are collected
along the direction of the laser polarization axis, back-to-back escape is the
dominant channel for strongly asymmetric energy sharing, while it is completely
forbidden if the two electrons share the excess energy equally.Comment: 17 pages, 9 figure
Retinal neurovascular coupling in patients with glaucoma and ocular hypertension and its association with the level of glaucomatous damage
Purpose: To analyze neurovascular coupling in the retina of untreated primary open-angle glaucoma (POAG) and ocular hypertension (OHT) patients. Patients and methods: Maximal vessel dilation in response to flicker light was analyzed with Retinal Vessel Analyzer (RVA) in temporal superior/inferior arterioles and veins in 51 POAG patients, 46 OHT and 59 control subjects. RVA parameters were compared between groups, between contralateral POAG eyes, and correlated to intraocular pressure, visual field mean defect and retinal nerve fiber layer thickness. Results: POAG eyes demonstrated generally smaller response of all vessels to flicker light than the other two groups (ANOVA p = 0.026; mean arterial flicker response in percent of baseline, averaged superior and inferior was 3.48 ± 2.22% for controls , 2.35 ± 2.06 % for POAG patients , and 2.97 ± 2.35 % for OHT patients; corresponding values for venules were 3.88 ± 1.98%, 2.89 ± 1.72%, 3.45 ± 2.77%). There was no difference in flicker response between the eye with more and less advanced damage in each patient of the POAG group (ANOVA p = 0.79). Correlation of flicker response to intraocular pressure (IOP) was borderline at best, correlations to the level of glaucomatous damage were not significant. Correlation of flicker response of superior and inferior vessels of the same eye was significant for the arteries (Pearson r = 0.23, p = 0.004), as well as venules (r = 0.52, p < 0.001). Conclusion: General vessel response to flicker light was decreased in POAG patients, compared to normal controls and OHT patients. In contrast to significant correlation between the two contralateral eyes of the flicker response itself, only its borderline correlation to IOP was seen. There was no correlation to the level of damage, altogether indicating a systemic dysregulation phenomenon. Grants: Swiss National Foundation Grant 3200B0-113685, Velux Stiftung Grant, Freie Akademische Gesellschaft (FAG) Grant, Pfizer Inc. Grant Clinical trial registration reference number: ClinicalTrials.gov NCT0043020
Dynamics of retinal vessel response to flicker light in glaucoma patients and ocular hypertensives
Purpose: To analyze dynamics of retinal vessel dilation response to flicker light in patients with glaucoma and ocular hypertension. Patients and methods: Response to flicker light was measured in retinal vessels by means of Retinal Vessel Analyzer. After the baseline 50seconds long diameter recording of inferior and superior temporal artery and vein, three flicker stimulations of 20seconds duration was applied, with a 80seconds break in between. Area under the curve of the vessel diameter (AUC) was compared during 3 flicker periods in the open angle glaucoma patients group (POAG, n = 47) and ocular hypertensives (OHT, n = 46) and age-matched healthy controls (n = 56) Results: POAG eyes demonstrated smaller response of all vessels to flicker light in general than the other two groups (p = 0.0008), but the response dynamics was significantly different between the groups (p = 0.038), showing in three flicker periods a delayed increasing response in the POAG and OHT groups, and remaining stable in healthy subjects. Conclusion: General vessel response to flicker light was decreased in POAG patients despite the slow improvement in repeated flicker stimulation, indicating an altered response patter
Greybody Factors for Brane Scalar Fields in a Rotating Black-Hole Background
We study the evaporation of (4+n)-dimensional rotating black holes into
scalar degrees of freedom on the brane. We calculate the corresponding
absorption probabilities and cross-sections obtaining analytic solutions in the
low-energy regime, and compare the derived analytic expressions to numerical
results, with very good agreement. We then consider the high-energy regime,
construct an analytic high-energy solution to the scalar-field equation by
employing a new method, and calculate the absorption probability and
cross-section for this energy regime, finding again a very good agreement with
the exact numerical results. We also determine the high-energy asymptotic value
of the total cross-section, and compare it to the analytic results derived from
the application of the geometrical optics limit.Comment: Latex file, 30 pages, 5 figures, typos corrected, version published
in Phys. Rev.
Chandra's Close Encounter with the Disintegrating Comets 73P/2006 (Schwassmann--Wachmann--3) Fragment B and C/1999 S4 (LINEAR)
On May 23, 2006 we used the ACIS-S instrument on the Chandra X-ray
Observatory (CXO) to study the X-ray emission from the B fragment of comet
73P/2006 (Schwassmann-Wachmann 3) (73P/B). We obtained a total of 20 ks of CXO
observation time of Fragment B, and also investigated contemporaneous ACE and
SOHO solar wind physical data. The CXO data allow us to spatially resolve the
detailed structure of the interaction zone between the solar wind and the
fragment's coma at a resolution of ~ 1,000 km, and to observe the X-ray
emission due to multiple comet--like bodies. We detect a change in the spectral
signature with the ratio of the CV/OVII line increasing with increasing
collisional opacity as predicted by Bodewits \e (2007). The line fluxes arise
from a combination of solar wind speed, the species that populate the wind and
the gas density of the comet. We are able to understand some of the observed
X-ray morphology in terms of non-gravitational forces that act upon an actively
outgassing comet's debris field. We have used the results of the Chandra
observations on the highly fragmented 73P/B debris field to re-analyze and
interpret the mysterious emission seen from comet C/1999 S4 (LINEAR) on August
1st, 2000, after the comet had completely disrupted. We find the physical
situations to be similar in both cases, with extended X-ray emission due to
multiple, small outgassing bodies in the field of view. Nevertheless, the two
comets interacted with completely different solar winds, resulting in
distinctly different spectra.Comment: accepted by ApJ, 44 Pages, including 4 tables and 14 figure
Solutions to Maxwell's Equations using Spheroidal Coordinates
Analytical solutions to the wave equation in spheroidal coordinates in the
short wavelength limit are considered. The asymptotic solutions for the radial
function are significantly simplified, allowing scalar spheroidal wave
functions to be defined in a form which is directly reminiscent of the
Laguerre-Gaussian solutions to the paraxial wave equation in optics.
Expressions for the Cartesian derivatives of the scalar spheroidal wave
functions are derived, leading to a new set of vector solutions to Maxwell's
equations. The results are an ideal starting point for calculations of
corrections to the paraxial approximation
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Structurally-related (−)-epicatechin metabolites in humans: assessment using de novo chemically synthesized authentic standards
Accumulating data suggest that diets rich in flavanols and procyanidins are beneficial for human health. In this context, there has been a great interest in elucidating the systemic levels and metabolic profiles at which these compounds occur in humans. While recent progress has been made, there still exist considerable differences and various disagreements with regard to the mammalian metabolites of these compounds, which in turn is largely a consequence of the lack of availability of authentic standards that would allow for the directed development and validation of expedient analytical methodologies. In the present study, we developed a method for the analysis of structurally-related flavanol metabolites using a wide range of authentic standards. Applying this method in the context of a human dietary intervention study using comprehensively characterized and standardized flavanol- and procyanidin-containing cocoa, we were able to identify the structurally-related (−)-epicatechin metabolites (SREM) postprandially extant in the systemic circulation of humans. Our results demonstrate that (−)-epicatechin-3′-β-D-glucuronide, (−)-epicatechin-3′-sulfate, and a 3′-O-methyl(−)-epicatechin-5/7-sulfate are the predominant SREM in humans, and further confirm the relevance of the stereochemical configuration in the context of flavanol metabolism. In addition, we also identified plausible causes for the previously reported discrepancies regarding flavanol metabolism, consisting to a significant extent of inter-laboratory differences in sample preparation (enzymatic treatment and sample conditioning for HPLC analysis) and detection systems. Thus, these findings may also aid in the establishment of consensus on this topic
Immunohistochemical localization of angiotensin-converting enzyme, angiotensin II and AT1 receptor in human ocular tissues
We investigated the immunohistochemical distribution of 3 components of the renin-angiotensin system (RAS), angiotensin-converting enzyme (ACE), angiotensin II (AngII) and AT1 receptor (AT1), in the human eye. ACE and AngII were localized to nonpigmented epithelial cells of the ciliary body, to endothelial and epithelial cells of the cornea, to epithelial cells of the conjunctiva and to trabecular meshwork cells in the anterior part of the eye. In the posterior part of the eye, ACE and AngII were localized to ganglion cells, some cells in the inner nuclear layer, photoreceptor cells and to endothelial cells of the retinal and choroidal vessels. The overall intensity of AT1 immunoreactivity was weak in all ocular tissues, but the main localization was in ganglion cells. As a preliminary investigation, we were able to include 2 Alzheimer's disease (AD) cases. In AD, no differences from controls were found in the cellular distribution and staining intensity of all 3 antigens. The manifold localization sites of the observed antigens point to rather generalized functions of the RAS in human ocular tissues, such as regulatory effects on neuronal cells, vessels and vitreous humor homeostasis
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