Mobility of holes in the quaternary alloy In1?xGaxAsyP1?y

Hole mobilities have been measured at temperatures from 77 to 300 K in a wide range of quaternary alloys grown lattice-matched to InP substrates by liquid-phase epitaxy. Over most of the composition range the hole mobility at room temperature is lower than in InP itself, and is dominated by alloy scattering.     

Effects of drag reducing polymers on initiation of atherosclerosis

Results from two pilot studies using White Carneau pigeons on high cholesterol diets have demonstrated substantial reduction in arterial plaque accumulations when the birds were periodically injected with dilute aqueous solutions of a drag reducing polymer (Separan AP-30) so as to maintain circulating blood concentrations of approximately 60 ppm. Initiation of arterial plaque formation may be fluid-mechanically motivated such that regions subjected to fluid turbulence, rapidly developing boundary layers, and alternate separation and reattachment, arc; the most prone lo attack. Viscoelastic fluid response, as seen in drag reducing media, is known to alter such phenomena. Comparative documentation of plaque deposition in experimental as well as control birds shows significant differences in both the aortas and coronary arteries, at optical magnifications from 20 to 15000X.     

Operational Analysis of a Quantum Dot Optically Gated Field-Effect Transistor as a Single-Photon Detector

We report on the operation of a novel single-photon detector, where a layer of self-assembled quantum dots (QDs) is used as an optically addressable floating gate in a GaAs/Al_0.2Ga_0.8As delta-doped field-effect transistor. Photogenerated holes charge the QDs, and subsequently, change the amount of current flowing through the channel by screening the internal gate field. The photoconductive gain associated with this process makes the structure extremely sensitive to light of the appropriate wavelength. We investigate the charge storage and resulting persistent photoconductivity by performing time-resolved measurements of the channel current and of the photoluminescence emitted from the QDs under laser illumination. In addition, we characterize the response of the detector, and investigate sources of photogenerated signals by using the Poisson statistics of laser light. The device exhibits time-gated, single-shot, single-photon sensitivity at a temperature of 4 K. It also exhibits a linear response, and detects photons absorbed in its dedicated absorption layer with an internal quantum efficiency (IQE) of up to (68 plusmn18)%. Given the noise of the detection system, the device is shown to operate with an IQE of (53 plusmn 11)% and dark counts of 0.003 counts per shot for a particular discriminator level.     

Longitudinal patterns of risk for depression in dementia caregivers: Objective and subjective primary stress as predictors.

The present study examined how patterns of risk for depression over 1 year in 188 dementia caregivers (consistently asymptomatic, n ?=?88; consistently symptomatic, n ?=?40; changing risk, n ?=?60) could be predicted by objective (behavior problems of the relative) and subjective (role captivity and overload) primary stress. Results reveal that all primary stressors differentiated caregivers who remained at low levels of symptomatology over the course of 1 year from those who were at risk for experiencing a depressive disorder. In addition, caregivers' subjective experience of role captivity predicted the chronicity of risk. Findings extend prior caregiving research on patterns of depressive symptomatology by highlighting the relationship between subjective primary stressors and stability and change in caregivers' mental health. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Enhancement of composite scarf joint interface strength through carbon nanotube reinforcement

It was investigated whether there was a potentially significant improvement to scarf joint bonding that was achieved through the dispersion of carbon nanotubes (CNTs) along the interface of the composite joint. The study examined various factors that might affect CNT-reinforced joint interface strength. Each composite joint consisted of a vinyl-ester matrix base (DERAKANE 510-A) interlaced with a carbon fiber weave (TORAY T700CF). During the curing process, the research explored several variables concerning the CNT application. The testing included single-walled CNTs (SWCNT), and conventional and bamboo-structure multi-walled CNTs (MWCNT) with varying length, purity, and concentration levels along the surface area of the joint interface. This wide array of data demonstrated the effect of CNTs introduction at the joint interface, and provided the ideal type, size, purity level, and concentration level for composite scarf joint bond reinforcement using CNTs. Furthermore, a computational model was developed to predict the strength of the scarf joints. The predicted model agreed well with the experimental data.     

Preparation for cesarean delivery: A multicomponent analysis of treatment outcome.

We evaluated the effects of sensory information about cesarean delivery on prenatal maternal anxiety and on recovery subsequent to delivery by cesarean section. The 42 participants were recruited from a population of obstetric patients. Patients were assigned to either treatment or control groups and identified as sensitizers or repressors. Treatment groups viewed a slide/tape program presenting procedures involved in cesarean delivery. Control groups viewed a program presenting neutral information. Prepared patients classified as sensitizers showed less physiologic arousal during surgery and enhanced postsurgical recovery. Physiologic and self-report measures of anxiety indicated that the intervention itself was not a stressful event. The relations among arousal, subjective anxiety, coping styles, and treatment outcome are discussed and recommendations are made for further investigation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A simulation model of river ice cover thermodynamics

A model of ice cover thermodynamics was used to simulate ice growth and decay along the international section of the St. Lawrence River for winter 1980–1981. This winter was chosen because of the exceptionally cold weather in December and January, and because of the abnormally warm air temperatures during the second half of February. At the air-ice interface, the model computes the surface energy transfer components and a resulting equilibrium surface temperature. At the lower boundary, an empirical algorith simulates the turbulent transfer of heat from the water. Within the ice, and implicit numerical solution to the general heat diffusion equation is used, permitting stable solutions for a variety of time intervals and node distances within the model. The model was used to simulate ice growth and decay at five sites characterized by their flow velocity, the date of ice-cover formation, and the water temperature regime. The model adequately represented growth rates at all five sites, but produced decay rates slower than those observed. Simulated breakup was 1–7 days later than observed, presumably because mechanical weakening of the ice was not taken into consideration. During the growth period, the model is far more sensitive to the values assigned to ice properties than it is to the error range in the meteorological variables. During the breakup period, the most sensitive boundary variable is water temperature.     

Road transport energy conservation in Costa Rica

Transportation is typically the largest petroleum-using sector in less developed countries and is generally dominated by road transport. Despite this fact, energy planning and conservation assistance have concentrated on other sectors, partly because of a lack of experience with transport-energy conservation in less developed countries. Studies of short-term energy conservation in taxi and bus fleets under actual operating conditions in San Jose, Costa Rica, have shown that efficiency improvements on the order of 10% are obtainable. Training in fuel-efficient driving strategies reduced taxi-fuel use by 14% and bus-fuel use by 3% on the average. Implementation of fuel-efficient maintenance practices reduced bus-fuel consumption by an average of 6%. Radial tires were ineffective and possibly counter-productive in saving fuel. Because of the complex experimental design, the results were not readily perceived by vehicle operators. Future demonstrations should concentrate on showing monetary savings to vehicle operators.