An assessment of potential nonlinear circuit models for thecharacterization of resonant tunneling diodes

The intrinsically fast process of resonant tunneling through double barrier heterostructures along with the existence of negative differential resistance in the current-voltage characteristic of these structures has led to their implementation as sources for high frequency electromagnetic energy. While sources based upon resonant tunneling diodes (RTDs) have produced frequency of oscillations up to 712 GHz, only microwatt levels of performance has been achieved above 100 GHz. Since stability criteria plays critical role in determining the deliverable power of any oscillator, a physically accurate equivalent-circuit model for the RTD is extremely important for optimizing the dynamics of the device-cavity package. This study identifies a distinctly new equivalent circuit model for characterizing the modes of oscillation in RTD-based sources. Specifically, in order to exhibit the fundamental self-oscillations and the overall I-V characteristics (plateau structure and hysteresis) observed experimentally, an accurate circuit model of the RTD must incorporate: (i) a quantum-well inductance which directly chokes the nonlinear conductance and, (ii) a nonlinear access resistance, associated with the accumulation of charge in the injection region of the double barriers, with a nonlocal dependence on the bias across the double barrier structure     

MobGeoSen: facilitating personal geosensor data collection and visualization using mobile phones

Mobile sensing and mapping applications are becoming more prevalent because sensing hardware is becoming more portable and more affordable. However, most of the hardware uses small numbers of fixed sensors that report and share multiple sets of environmental data which raises privacy concerns. Instead, these systems can be decentralized and managed by individuals in their public and private spaces. This paper describes a robust system called MobGeoSens which enables individuals to monitor their local environment (e.g. pollution and temperature) and their private spaces (e.g. activities and health) by using mobile phones in their day to day life. The MobGeoSen is a combination of software components that facilitates the phone’s internal sensing devices (e.g. microphone and camera) and external wireless sensors (e.g. data loggers and GPS receivers) for data collection. It also adds a new dimension of spatial localization to the data collection process and provides the user with both textual and spatial cartographic displays. While collecting the data, individuals can interactively add annotations and photos which are automatically added and integrated in the visualization file/log. This makes it easy to visualize the data, photos and annotations on a spatial and temporal visualization tool. In addition, the paper will present ways in which mobile phones can be used as noise sensors using an on-device microphone. Finally, we present our experiences with school children using the above mentioned system to measure their exposure to environmental pollution.

Disinfection By-Product Formation during Long-Term Water Storage in Alaska

In many areas of Northern and Western Alaska, small streams and shallow lakes serve as community raw water supplies. These water supplies freeze completely during winter. In order to supply drinking water during the 6–9 month winter, communities store water that was treated during summer. A chlorine residual is maintained in the stored water. Raw water sources derived from surface water may be heavily laden with dissolved organic matter. At utilities where organic matter escapes treatment, the potential for accumulation of disinfection by-products (DBPs) during storage is a significant health concern. The following study was performed to evaluate this potential threat. Water was collected from five operating utilities, four that normally store water for 6–9 months and one that produces drinking water year-round. Raw, filtered (i.e., unchlorinated) and “finished” (i.e., filtered and chlorinated) water samples were collected during the summer pumping season and stored in the laboratory for 8 months. In order to mimic practice in the field, the chlorine residual was maintained in the finished water for the full storage period. While the concentration of DBPs in the finished water varied over the study period, there was not a statistically significant trend from the third to the eighth month of storage. The observed DBP values were strongly a function of the type of treatment system used. Those systems passing more organic matter had higher DBP values throughout the storage period. The ultraviolet absorbance at 254 nanometers ?start(UV254)end? decreased continuously in the finished water coincident with chlorine consumption. ?startUV254end?, often used as a surrogate for DBPs, remained constant during the entire storage periodin raw and filtered water samples. Filtered water that was stored prior to chlorination accumulated fewer DBPs than finished water that was continuously chlorinated during the storage period. This result suggests that storing filtered water instead of finished water for long periods would limit DBP exposure to consumers. This conclusion was based on a comparison of DBP formation potentials (i.e., raw and filtered water) to DBPs (i.e., finished water). It is important to note that DBP formation potentials are based on a ?start24?hend?chlorine contact time. If long term storage were provided for filtered water, a smaller volume of secondary storage would still be needed to provide contact time for disinfection.     

Use of the acute cardiac ischemia time-insensitive predictive instrument (ACI-TIPI) to assist with triage of patients with chest pain or other symptoms suggestive of acute cardiac ischemia. A multicenter, controlled clinical trial

BACKGROUND: Approximately 6 million U.S. patients present to emergency departments annually with symptoms suggesting acute cardiac ischemia. Triage decisions for these patients are important but remain difficult. OBJECTIVE: To test whether computerized prediction of the probability of acute ischemia, used with electrocardiography, improves the accuracy of triage decisions. DESIGN: Controlled clinical trial. SETTING: 10 hospital emergency departments in the midwestern, southeastern, and northeastern United States. PATIENTS: 10689 patients with chest pain or other symptoms suggestive of acute cardiac ischemia. INTERVENTION: The probability of acute ischemia predicted by the acute cardiac ischemia time-insensitive predictive instrument (ACI-TIPI), either automatically printed or not printed on patients' electrocardiograms. MEASUREMENTS: Emergency department triage to a coronary care unit (CCU), telemetry unit, ward, or home. Other measurements were the bed capacity of the CCU relative to that of the telemetry unit; training or supervision status of the triaging physician; and patient diagnoses and outcomes based on clinical, electrocardiographic, and creatine kinase data. RESULTS: For patients without cardiac ischemia, in hospitals with high-capacity CCUs and relatively low-capacity cardiac telemetry units, use of ACI-TIPI was associated with a reduction in CCU admissions from 15% to 12%, a change of -16% (95% CI, -30% to 0%), and an increase in emergency department discharges to home from 49% to 52%, a change of 6% (CI, 0% to 14%; overall P=0.09). Across all hospitals, for patients evaluated by unsupervised residents, use of ACI-TIPI was associated with a reduction in CCU admissions from 14% to 10%, a change of -32% (CI, -55% to 3%); a reduction in telemetry unit admissions from 39% to 31%, a change of -20% (CI, -34% to -2%); and an increase in discharges to home from 45% to 56%, a change of 25% (CI, 8% to 45%; overall P=0.008). Among patients with stable angina, in hospitals with high-capacity CCUs, use of ACI-TIPI was associated with a reduction in CCU admissions from 26% to 13%, a change of -50% (CI, -70% to -17%), and an increase in discharges to home from 20% to 22%, a change of 10% (CI, -29% to 71%; overall P=0.02). At hospitals with high-capacity telemetry units, use of ACI-TIPI was associated with a reduction in telemetry unit admissions from 68% to 59%, a change of -14% (CI, -27% to 1%), and an increase in emergency department discharges to home from 10% to 21%, a change of 100% (CI, 22% to 230%; overall P=0.02). Among patients with acute myocardial infarction or unstable angina, use of ACI-TIPI did not change appropriate admission (96%) to the CCU or telemetry unit at hospitals with high-capacity CCUs or telemetry units. CONCLUSIONS: Use of ACI-TIPI was associated with reduced hospitalization among emergency department patients without acute cardiac ischemia. This result varied as expected according to the CCU and cardiac telemetry unit capacities and physician supervision at individual hospitals. Appropriate admission for unstable angina or acute infarction was not affected. If ACI-TIPI is used widely in the United States, its potential incremental impact may be more than 200000 fewer unnecessary hospitalizations and more than 100000 fewer unnecessary CCU admissions.     

Brief motivational interviewing in a hospital setting for adolescent smoking: A preliminary study.

This study tested the feasibility and efficacy of a brief smoking intervention for adolescents in a hospital seeing. Forty adolescent patients were randomized to receive either brief advice or a motivational interview, a nonconfrontational therapeutic intervention. Feasibility of brief smoking interventions with teen patients was supported by high rates of recruitment, retention, and quit attempts, and long periods of continuous abstinence. Although between-groups differences on smoking measures were not significant at 3-month follow-up, an effect size of h?=?.28 was noted. The sample showed significant decreases in smoking dependence and number of days smoked. Baseline stage of change, smoking rate, and depression were significant prospective predictors of smoking outcome. Implications for smoking intervention research with adolescents are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Age differences in sensation seeking and impulsivity as indexed by behavior and self-report: Evidence for a dual systems model.

It has been hypothesized that sensation seeking and impulsivity, which are often conflated, in fact develop along different timetables and have different neural underpinnings, and that the difference in their timetables helps account for heightened risk taking during adolescence. In order to test these propositions, the authors examined age differences in sensation seeking and impulsivity in a socioeconomically and ethnically diverse sample of 935 individuals between the ages of 10 and 30, using self-report and behavioral measures of each construct. Consistent with the authors' predictions, age differences in sensation seeking, which are linked to pubertal maturation, follow a curvilinear pattern, with sensation seeking increasing between 10 and 15 and declining or remaining stable thereafter. In contrast, age differences in impulsivity, which are unrelated to puberty, follow a linear pattern, with impulsivity declining steadily from age 10 on. Heightened vulnerability to risk taking in middle adolescence may be due to the combination of relatively higher inclinations to seek excitement and relatively immature capacities for self-control that are typical of this period of development. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The tensile properties of strain‐crystallizing vulcanizates. III. The superiority of conventional over peroxide vulcanizates in terms of network microstructure

It is proposed that, when vulcanization is performed using peroxides, crosslinking leads to a simple network, whereas in conventional vulcanization crosslinking a partially interpenetrating polymer network (PIPN) is formed. Two unfilled polyisoprene networks of similar crosslink density, produced with dicumyl peroxide and 2‐bisbenzothiazole‐2,2′‐disulfide/sulfur formulations, were compared with respect to the effect of strain rate on their stress–strain and hysteresis curves at room and elevated temperatures. At high elongations, the stress–strain curves for peroxide vulcanizates show a steeper upturn than for conventional vulcanizates, but have lower tensile strength and elongation at break. On increasing the extension rate, stress–strain curves for peroxide vulcanizates rise less steeply, while conventional vulcanizates rise more steeply. For both vulcanizates the hysteresis ratio decreases on increasing the rate at which samples are extended and retracted. The effect on conventional vulcanizates is less than on peroxide vulcanizates. It is suggested that chains in peroxide networks disengage increasingly rapidly at higher strains, allowing increased strain‐induced crystallization. Rapid strain‐induced crystallization leads to low ultimate tensile strength (UTS). In more complex PIPNs, the disengagement and alignment of chains are retarded. The increased nonuniform extension of chains promotes early strain‐induced crystallization at low extensions, but overall it reduces the rate of crystallization, which occurs over a wider range of strains. This improves UTS and elongation. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 876–884, 2006     

Studies on the free sugars,water-soluble gums and hemicelluloses from barley grains and malts

The free sugars, water-soluble gums, and hemicelluloses have been isolated from four barley grain samples [Hordeum vulgare (L.)], and from their commercial malts. Arabinose, xylose, galactose, glucose, fructose, maltose and sucrose occur as free sugars in the grains and the proportions of these sugars increase on malting. Mannose also occurs as a free sugar in the malts. The water-soluble gums contain arabinose, xylose, lesser amounts of mannose and galactose, and varying amounts of glucose. The aqueous-ethanol supernatants from the hot-water extracts are glucans of low molecular weight. The hemicellulose A polymers contain arabinose, xylose, mannose and glucose. Wide variations in the mannose and glucose contents were observed in these polysaccharides. The hemicellulose B polymers are arabinoxylans, containing lesser amounts of galactose and glucose. The aqueous-ethanol supernatants from the hemicellulose B precipitations contain arabinose, xylose, mannose, galactose and glucose. These polysaccharides differ markedly from those present in the aqueous-ethanol supernatants of the hot-water extracts. All polysaccharides are modified to varying degrees during malting.