3,533 research outputs found
1/n expansions for two-electron Coulomb matrix elements
The study of 1/n expansions for various atomic matrix elements, where n is the principal quantum number, plays an important role in the theoretical foundations of the quantum defect method. The paper develops an expansion in powers of 1/n 2 for hydrogenic boundstate wavefunctions which can be used to calculate 1/n expansions of matrix elements. The 1/n expansions of the two-electron direct and exchange Coulomb integrals are evaluated as an example. © 1993 IOP Publishing Ltd
Superfluid turbulence and pulsar glitch statistics
Experimental evidence is reviewed for the existence of superfluid turbulence
in a differentially rotating, spherical shell at high Reynolds numbers
(\Rey\gsim 10^3), such as the outer core of a neutron star. It is shown that
torque variability increases with \Rey, suggesting that glitch activity in
radio pulsars may be a function of \Rey as well. The \Rey distribution of
the 67 glitching radio pulsars with characteristic ages {\rm
yr} is constructed from radio timing data and cooling curves and compared with
the \Rey distribution of all 348 known pulsars with {\rm
yr}. The two distributions are different, with a Kolmogorov-Smirnov probability
. The conclusion holds for (modified) Urca and
nonstandard cooling, and for Newtonian and superfluid viscosities
Prevalence, Trends and Associated Socio-Economic Factors of Obesity in South Asia
Aim: Worldwide obesity levels have increased unprecedentedly over the past couple of decades. Although the prevalence, trends and associated socio-economic factors of the condition have been extensively reported in Western populations, less is known regarding South Asian populations. Methods: A review of articles using Medline with combinations of the MeSH terms: 'Obesity', ‘Overweight’ and ‘Abdominal Obesity’ limiting to epidemiology and South Asian countries. Results: Despite methodological heterogeneity and variation according to country, area of residence and gender, the most recent nationally representative and large regional data demonstrates that without any doubt there is an epidemic of obesity, overweight and abdominal obesity in South Asian countries. Prevalence estimates of overweight and obesity (based on Asian cut-offs: overweight ≥ 23 kg/m[superscript]2, obesity ≥ 25 kg/m[superscript]2) ranged from 3.5% in rural Bangladesh to over 65% in the Maldives. Abdominal obesity was more prevalent than general obesity in both sexes in this ethnic group. Countries with the lowest prevalence had the highest upward trend of obesity. Socio-economic factors associated with greater obesity in the region included female gender, middle age, urban residence, higher educational and economic status. Conclusion: South Asia is significantly affected by the obesity epidemic. Collaborative public health interventions to reverse these trends need to be mindful of many socio-economic constraints in order to provide long-term solutions
Dissipative dynamics of superfluid vortices at non-zero temperatures
We consider the evolution and dissipation of vortex rings in a condensate at
non-zero temperature, in the context of the classical field approximation,
based on the defocusing nonlinear Schr\"odinger equation. The temperature in
such a system is fully determined by the total number density and the number
density of the condensate. A vortex ring is introduced into a condensate in a
state of thermal equilibrium, and interacts with non-condensed particles. These
interactions lead to a gradual decrease in the vortex line density, until the
vortex ring completely disappears. We show that the square of the vortex line
length changes linearly with time, and obtain the corresponding universal decay
law. We relate this to mutual friction coefficients in the fundamental equation
of vortex motion in superfluids.Comment: 4 pages, 3 figure
Energy and nutrient intakes among Sri Lankan adults
Introduction: The epidemic of nutrition related non-communicable diseases such as type 2 diabetes mellitus and obesity has reached to epidemic portion in the Sri Lanka. However, to date, detailed data on food consumption in the Sri Lankan population is limited. The aim of this study is to identify energy and major nutrient intake among Sri Lankan adults. Methods: A nationally-representative sample of adults was selected using a multi-stage random cluster sampling technique. Results: Data from 463 participants (166 Males, 297 Females) were analyzed. Total energy intake was significantly higher in males (1913 ± 567 kcal/d) than females (1514 ± 458 kcal/d). However, there was no significant gender differences in the percentage of energy from carbohydrate (Male: 72.8 ± 6.4%, Female: 73.9 ± 6.7%), fat (Male: 19.9 ± 6.1%, Female: 18.5 ± 5.7%) and proteins (Male: 10.6 ± 2.1%, Female: 10.9 ± 5.6%). Conclusion: The present study provides the first national estimates of energy and nutrient intake of the Sri Lankan adult population
Global three-dimensional flow of a neutron superfluid in a spherical shell in a neutron star
We integrate for the first time the hydrodynamic
Hall-Vinen-Bekarevich-Khalatnikov equations of motion of a -paired
neutron superfluid in a rotating spherical shell, using a pseudospectral
collocation algorithm coupled with a time-split fractional scheme. Numerical
instabilities are smoothed by spectral filtering. Three numerical experiments
are conducted, with the following results. (i) When the inner and outer spheres
are put into steady differential rotation, the viscous torque exerted on the
spheres oscillates quasiperiodically and persistently (after an initial
transient). The fractional oscillation amplitude () increases
with the angular shear and decreases with the gap width. (ii) When the outer
sphere is accelerated impulsively after an interval of steady differential
rotation, the torque increases suddenly, relaxes exponentially, then oscillates
persistently as in (i). The relaxation time-scale is determined principally by
the angular velocity jump, whereas the oscillation amplitude is determined
principally by the gap width. (iii) When the mutual friction force changes
suddenly from Hall-Vinen to Gorter-Mellink form, as happens when a rectilinear
array of quantized Feynman-Onsager vortices is destabilized by a counterflow to
form a reconnecting vortex tangle, the relaxation time-scale is reduced by a
factor of compared to (ii), and the system reaches a stationary state
where the torque oscillates with fractional amplitude about a
constant mean value. Preliminary scalings are computed for observable
quantities like angular velocity and acceleration as functions of Reynolds
number, angular shear, and gap width. The results are applied to the timing
irregularities (e.g., glitches and timing noise) observed in radio pulsars.Comment: 6 figures, 23 pages. Accepted for publication in Astrophysical
Journa
Pleasure and pedagogy: the consumption of DVD add-ons among Irish teenagers
This article addresses the issue of young people and media use in the digital age, more specifically the interconnection between new media pleasures and pedagogy as they relate to the consumption of DVD add-ons. Arguing against the view of new media as having predominantly detrimental effects on young people, the authors claim that new media can enable young people to develop media literacy skills and are of the view that media literacy strategies must be based on an understanding and legitimating of young people's use patterns and pleasures. The discussion is based on a pilot research project on the use patterns and pleasures of use with a sample of Irish teenagers. They found that DVDs were used predominantly in the home context, and that, while there was variability in use between the groups, overall they developed critical literacy skills and competences which were interwoven into their social life and projects of identity construction. The authors suggest that these findings could be used to develop DVDs and their add-on features as a learning resource in the more formal educational setting and they go on to outline the potential teaching benefits of their use across a range of pedagogical areas
Reply to Rouder (2014) : good frequentist properties raise confidence
Established psychological results have been called into question by demonstrations that statistical significance is easy to achieve, even in the absence of an effect. One often-warned-against practice, choosing when to stop the experiment on the basis of the results, is guaranteed to produce significant results. In response to these demonstrations, Bayes factors have been proposed as an antidote to this practice, because they are invariant with respect to how an experiment was stopped. Should researchers only care about the resulting Bayes factor, without concern for how it was produced? Yu, Sprenger, Thomas, and Dougherty (2014) and Sanborn and Hills (2014) demonstrated that Bayes factors are sometimes strongly influenced by the stopping rules used. However, Rouder (2014) has provided a compelling demonstration that despite this influence, the evidence supplied by Bayes factors remains correct. Here we address why the ability to influence Bayes factors should still matter to researchers, despite the correctness of the evidence. We argue that good frequentist properties mean that results will more often agree with researchers’ statistical intuitions, and good frequentist properties control the number of studies that will later be refuted. Both help raise confidence in psychological results
SDSS J013655.91+242546.0 - an A-type hyper-velocity star from the outskirts of the Galaxy
Hyper-velocity stars (HVS) are moving so fast that they are unbound to the
Galaxy. Dynamical ejection by a supermassive black hole is favoured to explain
their origin. Locating the place of birth of an individual HVS is of utmost
importance to understanding the ejection mechanism. SDSS J013655.91+242546.0
(J0136+2425 for short) was found amongst three high-velocity stars (drawn from
a sample of more than 10000 blue stars), for which proper motions were
measured. A kinematical as well as a quantitative NLTE spectral analysis was
performed. When combined with the radial velocity (RV) and the spectroscopic
distance, the trajectory of the star in the Galactic potential was
reconstructed. J0136+2425 is found to be an A-type main-sequence star
travelling at 590 \kms, possibly unbound to the Galaxy and originating
in the outer Galactic rim nowhere near the Galactic centre. J0136+2425 is the
second HVS candidate with measured proper motion, besides the massive B star HD
271791, and also the second for which its proper motion excludes a Galactic
centre origin and, hence, the SMBH slingshot mechanism. Most known HVS are late
B-type stars of about 3 M. With a mass of 2.45 M, J0136+2425
resembles a typical HVS far more than HD 271791 does. Hence, this is the first
time that a typical HVS is found not to originate in the Galactic centre. Its
ejection velocity from the disk is so high (550 \kms) that the extreme
supernova binary scenario proposed for HD 271791 is very unlikely.Comment: 4 pages, 5 figures, accepted for publication in A&
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