Low-frequency noise reduction of spacecraft structures

Low frequency noise reduction of spacecraft structure

How high the temperature of a liquid be raised without boiling?

How high the temperature of a liquid be raised beyond its boiling point without vaporizing (known as the limit of superheat) is an interesting subject of investigation. A new method of finding the limit of superheat of liquids is presented here. The superheated liquids are taken in the form of drops suspended in visco elastic gel. The nucleation is detected acoustically by a sensitive piezo-electric transducer, coupled to a multi channel scaler and the nucleation is observed as a funtion of time and with increase of temperature. The limit of superheat measured by the present method supersedes all other measurements and theoretical predictions in reaching closest to the critical temperature and warrants improved theoretical predictions.Comment: 10 pages, 1 fig. Phys, Rev. E. (2000) in pres

Superheated Microdrops as Cold Dark Matter Detectors

It is shown that under realistic background considerations, an improvement in Cold Dark Matter sensitivity of several orders of magnitude is expected from a detector based on superheated liquid droplets. Such devices are totally insensitive to minimum ionizing radiation while responsive to nuclear recoils of energies ~ few keV. They operate on the same principle as the bubble chamber, but offer unattended, continuous, and safe operation at room temperature and atmospheric pressure.Comment: 15 pgs, 4 figures include

Hippocampal Volume Differences in Gulf War Veterans with Current Versus Lifetime Posttraumatic Stress Disorder Symptoms

Background: Decreased hippocampal volume is described in posttraumatic stress disorder (PTSD) and depression. However, it is not known whether it is a risk factor for the development of PTSD or a consequence of PTSD. We sought to determine the effects of PTSD and depressive symptoms on hippocampal volume. Methods: Clinical and magnetic resonance imaging data were collected in a cross sectional study of 244 GulfWarveterans. Measures included lifetime and current Clinician Administered PTSD Scale, Hamilton Depression Scale, Life Stressor Checklist, and Lifetime Drinking History. Magnetic resonance imaging data were acquired with a 1.5-T scanner and analyzed with automated and semiautomated image processing techniques. Results: Eighty-two veterans had lifetime PTSD, 44 had current PTSD, and 38 had current depression. In the linear regression analysis, current PTSD symptoms (standardized coefficient B= .25, p =.03) but neither lifetime PTSD symptoms nor current depression were associated with smaller hippocampal volume. Gender, age, history of early life trauma, education, lifetime and current alcohol use, current marijuana use, and treatment with antidepressants did not have independent effects. Participants with chronic PTSD had, on average, a smaller hippocampus compared with those with remitted PTSD. Conclusions: The finding that current but not lifetime PTSD symptom severity explains hippocampal size raises two possibilities: either a small hippocampus is a risk factor for lack of recovery from PTSD (trait) or PTSD effects on hippocampal volume are reversible once PTSD symptoms remit and the patient recovers (state)

Independent Ion Migration in Suspensions of Strongly Interacting Charged Colloidal Spheres

We report on sytematic measurements of the low frequency conductivity in aequous supensions of highly charged colloidal spheres. System preparation in a closed tubing system results in precisely controlled number densities between 1E16/m3 and 1E19/m^3 (packing fractions between 1E-7 and 1E-2) and electrolyte concentrations between 1E-7 and 1E-3 mol/l. Due to long ranged Coulomb repulsion some of the systems show a pronounced fluid or crystalline order. Under deionized conditions we find s to depend linearily on the packing fraction with no detectable influence of the phase transitions. Further at constant packing fraction s increases sublinearily with increasing number of dissociable surface groups N. As a function of c the conductivity shows pronounced differences depending on the kind of electrolyte used. We propose a simple yet powerful model based on independent migration of all species present and additivity of the respective conductivity contributions. It takes account of small ion macro-ion interactions in terms of an effectivly transported charge. The model successfully describes our qualitatively complex experimental observations. It further facilitates quantitative estimates of conductivity over a wide range of particle and experimental parameters.Comment: 32 pages, 17 figures, 2 tables, Accepted by Physical Review

Drops in Space: Super Oscillations and Surfactant Studies

An unprecedented microgravity observation of maximal shape oscillations of a surfactant-bearing water drop the size of a ping pong ball was observed during a mission of Space Shuttle Columbia as part of the second United States Microgravity Laboratory-USML-2 (STS-73, October 20-November 5, 1995). The observation was precipitated by the action of an intense sound field which produced a deforming force on the drop. When this deforming force was suddenly reduced, the drop executed nearly free and axisymmetric oscillations for several cycles, demonstrating a remarkable amplitude of nonlinear motion. Whether arising from the discussion of modes of oscillation of the atomic nucleus, or the explosion of stars, or how rain forms, the complex processes influencing the motion, fission, and coalescence of drops have fascinated scientists for centuries. Therefore, the axisymmetric oscillations of a maximally deformed liquid drop are noteworthy, not only for their scientific value but also for their aesthetic character. Scientists from Yale University, the Jet Propulsion Laboratory (JPL) and Vanderbilt University conducted liquid drop experiments in microgravity using the acoustic positioning/manipulation environment of the Drop Physics Module (DPM). The Yale/JPL group's objectives were to study the rheological properties of liquid drop surfaces on which are adsorbed surfactant molecules, and to infer surface properties such as surface tension, Gibb's elasticity, and surface dilatational viscosity by using a theory which relies on spherical symmetry to solve the momentum and mass transport equations

Explanations for the Lower Rates of Diabetic Neuropathy in Indian Asians Versus Europeans

OBJECTIVE - Risks of diabetes and cardiovascular disease are elevated worldwide in Indian Asians. However, risks of other diabetes-related complications, i.e., foot ulceration and amputation, also with a vascular basis, are substantially lower in Asians than in white Europeans in the U.K., possibly due to less neuropathy. We therefore compared signs, symptoms, and objective quantitative measures of diabetic neuropathy and their risk factors in Indian Asians and Europeans. RESEARCH DESIGN AND METHODS - This was a cross-sectional study of a population-based sample of age- and sex-matched adults with type 2 diabetes of European (95 male and 85 female) and Asian (96 male and 84 female) descent in the U.K. Patients were assessed for neuropathic symptoms, signs, nerve conduction, autonomic function, and quantitative sensory testing. Peripheral vascular function and other potential risk factors for neuropathy were measured. RESULTS - Mean nerve conduction velocity Z scores were better in Asians (mean ± SD 0.07 ± 0.62) than in Europeans (-0.11 ± 0.60; P = 0.007) and were explained by the shorter height, fewer pack-years smoked, and higher transcutaneous oxygen levels (TCpO2) in Indian Asians (P value for ethnic comparison attenuated to 0.2). Small fiber neuropathy was less prevalent in Indian Asians compared with Europeans (odds ratio 0.58 [95% CI 0.37-0.93]; P = 0.02) and was primarily accounted for by better TCpO2 (0.70 [0.40-1.21]; P = 0.2). CONCLUSIONS - Asians with diabetes have substantially less large and small fiber neuropathy than Europeans, despite comparable traditional risk factors. Independent from smoking, the lower risk of neuropathy in Asians is due to better skin microvascularization and may help explain the substantially reduced Asian foot ulcer risk. © 2010 by the American Diabetes Association

Bio-inspired CO₂ conversion by iron sulfide catalysts under sustainable conditions

The mineral greigite presents similar surface structures to the active sites found in many modern-day enzymes. We show that particles of greigite can reduce CO2 under ambient conditions into chemicals such as methanol, formic, acetic and pyruvic acid. Our results also lend support to the Origin of Life theory on alkaline hydrothermal vents