Does dynamic stability govern propulsive force generation in human walking?

Before succumbing to slower speeds, older adults may walk with a diminished push-off to prioritize stability over mobility. However, direct evidence for trade-offs between push-off intensity and balance control in human walking, independent of changes in speed, has remained elusive. As a critical first step, we conducted two experiments to investigate: (i) the independent effects of walking speed and propulsive force (FP) generation on dynamic stability in young adults, and (ii) the extent to which young adults prioritize dynamic stability in selecting their preferred combination of walking speed and FP generation. Subjects walked on a force-measuring treadmill across a range of speeds as well as at constant speeds while modulating their FP according to a visual biofeedback paradigm based on real-time force measurements. In contrast to improvements when walking slower, walking with a diminished push-off worsened dynamic stability by up to 32%. Rather, we find that young adults adopt an FP at their preferred walking speed that maximizes dynamic stability. One implication of these findings is that the onset of a diminished push-off in old age may independently contribute to poorer balance control and precipitate slower walking speeds

A W:B4C multilayer phase retarder for broadband polarization analysis of soft x-ray radiation \ud

A W:B4C multilayer phase retarder has been designed and characterized which shows a nearly constant phase retardance between 640 and 850 eV photon energies when operated near the Bragg condition. This freestanding transmission multilayer was used successfully to determine, for the first time, the full polarization vector at soft x-ray energies above 600 eV, which was not possible before due to the lack of suitable optical elements. Thus, quantitative polarimetry is now possible at the 2p edges of the magnetic substances Fe, Co, and Ni for the benefit of magnetic circular dichroism spectroscopy employing circularly polarized synchrotron radiatio

Near-Infrared Counterparts to Chandra X-ray Sources toward the Galactic Center. I. Statistics and a Catalog of Candidates

We present a catalog of 5184 candidate infrared counterparts to X-ray sources detected towards the Galactic center. The X-ray sample contains 9017 point sources detected in this region by the Chandra X-ray Observatory, including data from a recent deep survey of the central 2 x 0.8 deg of the Galactic plane. A total of 6760 of these sources have hard X-ray colors, and the majority of them lie near the Galactic center, while most of the remaining 2257 soft X-ray sources lie in the foreground. We cross-correlated the X-ray source positions with the 2MASS and SIRIUS near-infrared catalogs, which collectively contain stars with a 10-sigma limiting flux of K_s<=15.6 mag. In order to distinguish absorbed infrared sources near the Galactic center from those in the foreground, we defined red and blue sources as those which have H-K_s>=0.9 and <=0.9 mag, respectively. We find that 5.8(1.5)% of the hard X-ray sources have real infrared counterparts, of which 228(99) are red and 166(27) are blue. The red counterparts are probably comprised of WR/O stars, HMXBs, and symbiotics near the Galactic center. We also find that 39.4(1.0)% of the soft X-ray sources have blue infrared counterparts; most of these are probably coronally active dwarfs in the foreground. There is a noteworthy collection of ~20 red counterparts to hard X-ray sources near the Sagittarius-B H II region, which are probably massive binaries that have formed within the last several Myr. For each of the infrared matches to X-ray sources in our catalog we derived the probability that the association is real, based on the results of the cross-correlation analysis. The catalog will serve spectroscopic surveys to identify infrared counterparts to X-ray sources near the Galactic center.Comment: Submitted to ApJ January 16, 2009; accepted July 21, 2009; 30 pages, 6 figure

Temperature dependence of diffusivities, preliminary definition phase

During the six months definition phase of the instrument development program, research personnel at the Center for Microgravity and Materials Research of the University of Alabama in Huntsville (UAH) were to furnish all of the necessary labor, services, materials, and facilities necessary to provide science requirement definition, initiate hardware development activities, requirements and timetable for integration and experimental accommodation of the GAS payload into the Shuttle cargo bay and an updated ground-based research flight program proposal consistent with the NRA selection letter. These activities were to be accomplished in parallel and consistent with the necessary research and development work toward the accomplishment of the overall objectives of the selected proposal

Collateral and collateral-adjacent hyperemic vascular resistance changes and the ipsilateral coronary flow reserve: Documentation of a mechanism causing coronary steal in patients with coronary artery disease

Objectives: The goal of this clinical study was to assess the influence of hyperemic ipsilateral, collateral and contralateral vascular resistance changes on the coronary flow velocity reserve (CFVR) of the collateral-receiving (i.e. ipsilateral) artery, and to test the validity of a model describing the development of collateral steal. Methods: In 20 patients with one- to two-vessel coronary artery disease (CAD) undergoing angioplasty of one stenotic lesion, adenosine induced intracoronary (i.c.) CFVR during vessel patency was measured using a Doppler guidewire. During stenosis occlusion, simultaneous i.c. distal ipsilateral flow velocity and pressure (Poccl, using a pressure guidewire) as well as contralateral flow velocity measurements via a third i.c. wire were performed before and during intravenous adenosine. From those measurements and simultaneous mean aortic pressure (Pao), a collateral flow index (CFI), and the ipsilateral, collateral, and contralateral vascular resistance index (Ripsi, Rcoll, Rcontra) were calculated. The study population was subdivided into groups with CFI<0.15 and with CFI≥0.15. Results: The percentage-diameter coronary artery stenosis (%-S) to be dilated was similar in the two groups: 78±10% versus 82±12% (NS). CFVR was not associated with %-S. In the group with CFI≥0.15 but not with CFI<0.15, CFVR was directly and inversely associated with Rcoll and Rcontra, respectively. Conclusions: A hemodynamic interaction between adjacent vascular territories can be documented in patients with CAD and well developed collaterals among those regions. The CFVR of a collateralized region may, thus, be more dependent on hyperemic vascular resistance changes of the collateral and collateral-supplying area than on the ipsilateral stenosis severity, and may even fall below

Massive Stellar X-ray Sources in the Galactic Center

We present results of a spectroscopic survey of bright near-infrared counterparts to X-ray point sources from a deep Chandra survey of the Galactic nuclear bulge. K-band spectroscopy has revealed 13 new Wolf-Rayet and O-supergiant counterparts to Chandra sources in the Galactic center (GC). Although they are systematically softer in X-rays than the general GC source population of accretion powered cataclysmic variables (CVs), their X-ray colors indicate a hard component consistent with emission from plasmas with E > 2 keV. Such hard X-ray emission is not ubiquitous among single Wolf-Rayet and O stars, but is common among Wolf-Rayet+OB binaries with colliding supersonic winds. Although we regard colliding-wind binary hypothesis as the most likely scenario, it remains possible that several of these objects are wind-accreting neutron stars or black holes in supergiant high-mass X-ray binaries, or extraordinary single stars emitting hard X-rays

Genetic and environmental influences on sleep quality in middle‐aged men: a twin study

Poor sleep quality is a risk factor for a number of cognitive and physiological age-related disorders. Identifying factors underlying sleep quality are important in understanding the etiology of these age-related health disorders. We investigated the extent to which genes and the environment contribute to subjective sleep quality in middle-aged male twins using the classical twin design. We used the Pittsburgh Sleep Quality Index to measure sleep quality in 1218 middle-aged twin men from the Vietnam Era Twin Study of Aging (mean age = 55.4 years; range 51-60; 339 monozygotic twin pairs, 257 dizygotic twin pairs, 26 unpaired twins). The mean PSQI global score was 5.6 [SD = 3.6; range 0-20]. Based on univariate twin models, 34% of variability in the global PSQI score was due to additive genetic effects (heritability) and 66% was attributed to individual-specific environmental factors. Common environment did not contribute to the variability. Similarly, the heritability of poor sleep-a dichotomous measure based on the cut-off of global PSQI>5-was 31%, with no contribution of the common environment. Heritability of six of the seven PSQI component scores (subjective sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances, and daytime dysfunction) ranged from 0.15 to 0.31, whereas no genetic influences contributed to the use of sleeping medication. Additive genetic influences contribute to approximately one-third of the variability of global subjective sleep quality. Our results in middle-aged men constitute a first step towards examination of the genetic relationship between sleep and other facets of aging.Accepted manuscrip

Beauty Is in the Eye of the Beer Holder: An Initial Investigation of the Effects of Alcohol, Attractiveness, Warmth, and Competence on the Objectifying Gaze in Men

Despite literature revealing the adverse consequences of objectifying gazes for women, little work has empirically examined origins of objectifying gazes by perceivers. Integrating alcohol myopia and objectification theories, we examined the effects of alcohol as well as perceived female attractiveness, warmth, and competence on objectifying gazes. Specifically, male undergraduates (n = 49) from a large U.S. Midwestern university were administered either an alcoholic or placebo beverage. After consumption, participants were asked to focus on the appearance or personality (counterbalanced) of pictured women who were previously rated as high, average, or low in attractiveness, warmth, and competence. Replicating previous work, appearance focus increased objectifying gazes as measured by decreased visual dwell time on women’s faces and increased dwell time on women’s bodies. Additionally, alcohol increased objectifying gazes. Whereas greater perceived attractiveness increased objectifying gazes, more perceived warmth and perceived competence decreased objectifying gazes. Furthermore, the effects of warmth and competence perceptions on objectifying gazes were moderated by alcohol condition; intoxicated participants objectified women low in warmth and competence to a greater extent than did sober participants. Implications for understanding men’s objectifying perceptions of women are addressed, shedding light on potential interventions for clinicians and policymakers to reduce alcohol-involved objectification and related sexual aggression

Relation between repolarization and refractoriness in the human ventricle: Cycle length dependence and effect of procainamide

The cycle length dependence of the action potential duration and the effective refractory period of the right ventricular endocardium were investigated in 24 patients undergoing electrophysiologic studies for suspected ventricular tachycardia. The action potential duration at 90% repolarization and the effective refractory period at twice diastolic threshold strength were measured at the same catheter site at steady state cycle lengths of 350 to 600 ms. Both measurements decreased linearly with decreasing cycle length, maintaining a parallel relation. When the relation between action potential duration and effective refractory period was expressed as the effective refractory period-action potential duration difference, nearly constant values (range −12 to −15 ms) were obtained at all cycle lengths.To determine whether sodium channel blocking drugs influence the effective refractory period-action potential duration relation in humans, measurements of these two variables were obtained in 15 patients before and during the infusion of procainamide. Procainamide prolonged the action potential duration at each cycle length by a near constant amount over baseline values (p < 0.001). Procainamide also increased the effective refractory period at each cycle length but with a greater incremental increase at the shorter cycle lengths. The rate-dependent increase in the effective refractory period-action potential duration difference became significant at cycle lengths ≤400 ms; at these high rates, the effective refractory period-action potential duration difference became positive (1.6 ms, p < 0.01 compared with baseline).Thus, in the human ventricle, the action potential duration and the effective refractory period have a close relation that remains fixed over a wide range of cycle lengths. The cycle length-dependent increase in the effective refractory period relative to action potential duration induced by procainamide is consistent with use dependency of sodium channel blocking drugs observed in vitro and may be a useful marker for measuring antiarrhythmic drug activity in vivo