Relaxation of spins due to a magnetic field gradient, revisited; Identity of the Redfield and Torrey theories

There is an extensive literature on magnetic gradient induced spin relaxation. Cates, Schaefer and Happer (CSH) in a seminal paper, have solved the problem in the regime where diffusion theory (the Torrey equation is applicable using an expansion of the density matrix in diffusion equation eigenfunctions and angular momentum tensors. McGregor has solved the problem in the same regime using a slightly more general formulation using Redfield theory formulated in terms of the auto-correlation function of the fluctuating field seen by the spins and calculating the correlation functions using the diffusion theory Green's function. The results of both calculations were shown to agree for a special case. In the present work we show that the eigenfunction expansion of the Torrey equation yields the expansion of the Green's function for the diffusion equation thus showing the identity of this approach with that of Redfield theory. The general solution can also be obtained directly from the Torrey equation for the density matrix. Thus the physical content of the Redfield and Torrey approaches are identical. We then introduce a more general expression for the position autocorrelation function of particles moving in a closed cell, extending the range of applicability of the theory.Comment: 2 figure

Models of the hard X-ray spectrum of AM Herculis and implications for the accretion rate

Phenomenological fits to the hard X-ray spectrum of AM Herculis left unexplained the high equivalent width (0.8 + or - 0.1 keV) of Fe K alpha emission. A purely thermal origin implies a much steeper spectrum than was observed. With Monte Carlo calculations, scattering and fluorescent line production in a cold or partially ionized accretion column of hard X-rays emitted at the base were investigated. The strength of the iron emission and the flat spectral continuum can be explained by the effects of fluorescence and absorption within the accretion column and the surface of the white dwarf on a thermal X-ray spectrum. Thomson optical depths across the column in the range 0.2 to 0.7 are acceptable. The accretion rate and gravitational power can be deduced from the optical depth across the column, if the column size is known, and, together with the observed hard X-ray and polarized light luminosities, imply a lower limit for the luminosity in the UV to soft X-ray range, for which the observations give model-dependent values. Estimates of the column size differ by a factor of 40. Small spot sizes and low luminosities would be consistent with the soft component being the expected reprocessed bremsstrahlung and cyclotron radiation, although the constraint of matching the spectrum confines one to solutions with fluxes exceeding 20% the Eddington limits

Physical activity and psychological distress: social gradients of living in poverty

Master of Public HealthDepartment of KinesiologyEmily MaileyINTRODUCTION: Research has focused on the relationship between socioeconomic status and physical activity, yet there are limited examinations which directly address social groups dealing with major issues associated with insufficient income. Studies have neglected the role of psychosocial stressors, such as financial stress, food insecurity, availability of government assistance programs, as well as psychological distress relative to the relationship between physical activity and low-income status. The purposes of this study were threefold: 1) to describe the multidimensional characteristics of life among low-income populations; 2) to examine how psychosocial stressors and health conditions vary across subsets of low-income groups; and 3) to examine the relationship among income, psychological distress and physical activity within low-income populations. METHODS: Data from the 2015 National Health Interview Survey (NHIS) were analyzed for the purposes of this investigation. Descriptive statistics were calculated for the low-income status individuals who provide complete data for all variables of interest to this study. A series of chi-square analyses were conducted to determine whether key psychosocial stressors, health behaviors, and health conditions differed by low-income (FIPR) groups. Two stepwise logistic regression analyses were conducted to examine these factors and their relationships with moderate-intensity (MPA) and vigorous (VPA)-intensity physical activity. RESULTS: Overall, women made up 58.5% of the sample size. Blacks/African Americans accounted for 20.6% of the sample, yet 28.0% of FIPR Group 1 identified as Black/African American. FIPR Group 1 was disproportionately unemployed, with 63.5% unemployed compared to 46.9% for the sample. One-quarter (25.9%) of the entire sample reported severe psychological distress, yet 33.9% of FIPR Group 1 and 30.8% of FIPR Group 2 reported severe distress. Nearly three-quarters (70%) of the sample was overweight or obese and 44.2% lived with at least one chronic disease at the time the survey was taken. Overall, 67.9% of the sample reported zero minutes of VPA and 51.3% reported zero minutes of MPA. Both psychological distress and income showed significant relationships with VPA. Psychological distress remained significantly associated with VPA after controlling for all covariates; however, income was no longer related to VPA after demographic and health-related variables were added to the model. Income was not related to MPA. Psychological distress demonstrated a weak relationship with MPA before the other covariates were added to the model, at which point the relationship became non-significant. Only the relationship between psychological distress and VPA was significant in the final models. Although some of the psychosocial stressor, demographic, and health-related variables contributed to the relationships between income, physical activity, and psychological distress, these variables explained only a small portion of the variance in both MPA and VPA. CONCLUSION: Low-income individuals are faced with difficult decisions and are limited in the choices they can make to improve health. It is important to understand the multidimensional characteristics of life under limited income to better serve and improve the health of low-income populations. Further study of the relationships among income, physical activity and psychological distress is needed to further this understanding

The 1981 outburst of the old nova GK Persei

Old nova GK Per was observed in 1981 with the IUE, during its rise, maximum, and subsequent return to minimum. In outburst, GK Per is luminous but much redder than dwarf novae or standard model accretion disks. The observed spectrum can be explained qualitatively with the Ghosh and Lamb (1979) model for the interaction of an accretion disk with the magnetic field of the accreting white dwarf. The N V and He2 are enhanced relative to other emission lines during outburst. This can be understood with photoionization by very soft X-rays having a luminosity comparable to that of the hard X-rays

Anchoring In Action: Manual Estimates Of Slant Are Powerfully Biased Toward Initial Hand Orientation And Are Correlated With Verbal Report

People verbally overestimate hill slant by approximately 15 degrees to 25 degrees, whereas manual estimates (e. g., palm board measures) are thought to be more accurate. The relative accuracy of palm boards has contributed to the widely cited theoretical claim that they tap into an accurate, but unconscious, motor representation of locomotor space. In the current work, 4 replications (total N = 204) carried out by 2 different laboratories tested an alternative anchoring hypothesis that manual action measures give low estimates because they are always initiated from horizontal. The results of all 4 replications indicate that the bias from response anchoring can entirely account for the difference between manual and verbal estimates. Moreover, consistent correlations between manual and verbal estimates given by the same observers support the conclusion that both measures are based on the same visual representation. Concepts from the study of judgment under uncertainty apply even to action measures in information rich environments

Partisan Profiles in Presidential Policies: an Extension of Presidential Preferences for Inflation versus Unemployment

In a recent article, Zaleski does not find any clear difference between the political preferences of Republican and Democratic administrations with respect to the choice between unemployment and inflation. This paper provides empirical support for the opposite conclusion in a generalization of Zaleski's approach allowing for instrument costs