199,513 research outputs found
Study to determine an improved method for Apollo propellant system decontamination and propellant tank drying Summary report
Vapor phase cleaning method for Apollo propellant system decontamination and propellant tank dryin
Binding energy corrections in positronium decays
Positronium annihilation amplitudes that are computed by assuming a
factorization approximation with on-shell intermediate leptons, do not exhibit
good analytical behavior. We propose an ansatz which allows to include binding
energy corrections and obtain the correct analytical and gauge invariance
behavior of these QED amplitudes. As a consequence of these non-perturbative
corrections, the parapositronium and orthopositronium decay rates receive
corrections of order alpha^4 and alpha^2, respectively. These new corrections
for orthopositronium are relevant in view of a precise comparison between
recent theoretical and experimental developments. Implications are pointed out
for analogous decays of quarkonia .Comment: 11 pages, 1 .ps figure, submitted for publicatio
Is subjective social status a more important determinant of health than objective social status? Evidence from a prospective observational study of Scottish men
Both subjective and objective measures of lower social position have been shown to be associated with poorer health. A psychosocial, as opposed to material, aetiology of health inequalities predicts that subjective social status should be a stronger determinant of health than objective social position. In a workplace based prospective study of 5232 Scottish men recruited in the early 1970s and followed up for 25 years we examined the association between objective and subjective indices of social position, perceived psychological stress, cardiovascular disease risk factors and subsequent health. Lower social position, whether indexed by more objective or more subjective measures, was consistently associated with an adverse profile of established disease risk factors. Perceived stress showed the opposite association. The main subjective social position measure used was based on individual perceptions of workplace status (as well as their actual occupation, men were asked whether they saw themselves as “employees”, “foremen”, or “managers”). Compared to foremen, employees had a small and imprecisely estimated increased risk of all cause mortality, whereas managers had a more marked decreased risk. The strongest predictors of increased mortality were father's manual as opposed to non-manual occupation; lack of car access and shorter stature, (an indicator of material deprivation in childhood). In the fully adjusted analyses, perceived work-place status was only weakly associated with mortality. In this population it appears that objective material circumstances, particularly in early life, are a more important determinant of health than perceptions of relative status. Conversely, higher perceived stress was not associated with poorer health, presumably because, in this population, higher stress was not associated with material disadvantage. Together these findings suggest that, rather than targeting perceptions of disadvantage and associated negative emotions, interventions to reduce health inequalities should aim to reduce objective material disadvantage, particularly that experienced in early life
Beam waveguides in the Deep Space Network
A beam waveguide is a mechanism for guiding electromagnetic radiation from one part of an antenna to another through a series of reflectors. Appropriate placement of reflectors on an antenna allows a beam to be guided around the elevation axis and/or below the alidade. The beam waveguide permits placement of all electronics in a room on the alidade below the elevation axis, or below the alidade; feed horn covers to be protected from the weather; and feed electronics to be in spacious rooms rather than in crowded cones, and always level rather than tipping with change in elevation angle. These factors can lead to lower costs in implementation such as Ka-band, better antenna performance at X-band, more efficient and stable performance of transmitters and receivers, and lower maintenance and operating costs. Studies are underway to determine methods for converting the major antennas of the Deep Space Network (DSN) to beam waveguide operations by 1995
Studies of the differential absorption rocket experiment
Investigations of the ionosphere, in the rocket program of the Aeronomy Laboratory, include a propagation experiment, the data from which may be analyzed in several modes. This report considers in detail the differential absorption experiment. The sources of error and limitations of sensitivity are discussed. Methods of enhancing the performance of the experiment are described. Some changes have been made in the system and the improvement demonstrated. Suggestions are made for further development of the experiment
Viscosity and Thermal Relaxation for a resonantly interacting Fermi gas
The viscous and thermal relaxation rates of an interacting fermion gas are
calculated as functions of temperature and scattering length, using a many-body
scattering matrix which incorporates medium effects due to Fermi blocking of
intermediate states. These effects are demonstrated to be large close to the
transition temperature to the superfluid state. For a homogeneous gas in
the unitarity limit, the relaxation rates are increased by nearly an order of
magnitude compared to their value obtained in the absence of medium effects due
to the Cooper instability at . For trapped gases the corresponding ratio
is found to be about three due to the averaging over the inhomogeneous density
distribution. The effect of superfluidity below is considered to leading
order in the ratio between the energy gap and the transition temperature.Comment: 7 pages, 3 figure
Publications in acoustics and noise control from the NASA Langley Research Center during 1940 - 1974
This document contains reference lists of published Langley Research Center papers in various areas of acoustics and noise control for the period 1940-1974. The research work was performed either in-house by the center staff or by other personnel supported entirely or in part by grants or contracts. The references are listed chronologically and are grouped under the following general headings: (1) Duct acoustics, (2) Propagation and operations, (3) Rotating blade noise, (4) Jet noise, (5) Sonic boom, (6) Flow-surface interaction noise, (7) Human response, and (8) Structural response
Individual employment histories and subsequent cause specific hospital admissions and mortality: a prospective study of a cohort of male and female workers with 21 years follow up
It is a widely held view that the labour market is demanding increased levels of flexibility, and that this is causing greater psychosocial stress among employees.1 Such stress may affect health, either through neuroendocrine pathways, or through increases in behaviours linked with poor health.2 Previously we presented evidence linking an unstable employment history, as measured by a greater number of job changes and shorter duration of current job, with a greater prevalence of smoking and greater alcohol consumption, in male and female workers.3 4 Despite this, we did not observe clear detrimental effects of such instability on health related physiological measures (body mass index, diastolic blood pressure, cholesterol, and lung function), nor on current cardiovascular health (electrocardiogram determined ischaemia and reported symptoms of angina).
Finding work is easier for healthy persons, and those persons who need to find work repeatedly will be particularly likely to drop out of the workforce if their health deteriorates. Consequently, an occupational cohort, upon which our previous work was based, is least likely to include people of poor health with an unstable work history. If such people are underrepresented, attempts to determine the association between health and individual work histories will mislead. This study links the same cohort to information on the hospitalisations and deaths experienced over a 21 year follow up period. While those people whose health deteriorated before the enrolment of this cohort must remain poorly represented, these prospective data permit unbiased observation of those cases who experienced ill health subsequently, whether or not this resulted in an exit from the workforce. We hypothesise that an employment history characterised by frequent job changes, whatever the motivation for those changes, will require the person to be more focused on work, and less focused on maintaining personal health, with consequent poorer health for such people
Analytical Behaviour of Positronium Decay Amplitudes
Positronium annihilation amplitudes that are computed by assuming a
factorization approximation with on-shell intermediate leptons do not exhibit
good analytical behaviour. Using dispersion techniques, we find new
contributions that interfere with the known results to restore analytical
properties. Those new amplitudes which cannot be obtained using standard
factorized amplitude formalism, contribute at order alpha^2. Therefore they
have to be evaluated before any theoretical conclusion can be drawn upon the
orthopositronium lifetime puzzle.Comment: LaTeX, 22 pages, 3 eps figure
Red Crossbill Invasion of Northwestern Arkansas during 2012-2013
An irruption of Red Crossbills (Loxia curvirostra) occurred in primarily northwestern Arkansas starting in November of 2012 and lasting to the end of May of 2013. Based on recordings of call notes, most birds around Fayetteville were Type 2, the large-billed ponderosa pine crossbill, associated with a variety of conifer species. Birds recorded in Carroll County were Type 3, the small-billed western hemlock crossbill, and they were associated with small cones on shortleaf pine (Pinus echinata). One recording was obtained in Fayetteville of Type 5, the lodgepole pine crossbill, only the third recording east of the Great Plains. Crossbills at the Fayetteville Country Club were observed eating algae (Cladophora sp.) during the months of December and January, a behavior rarely reported for passerines. During March, crossbills appeared at sunflower bird feeders, which is a relatively recent phenomenon associated with low conifer seed abundance. The first two Arkansas specimens of crossbills (probably Type 3) were obtained from birds that struck windows near feeders. This is only the third recorded irruption of crossbills in Arkansas in the last 43 years, suggesting that crossbills rarely travel this far south in search of cone crops
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