High energy Urbach characteristic observed for gallium nitride amorphous surface oxide

We have observed an “above band-gap” Urbach like characteristic for gallium nitride films (at the high energy side of the band-edge). A combination of X-ray diffraction, secondary ion mass spectroscopy and optical transmission measurements were taken for gallium nitride samples of different thickness. From this data we demonstrate that the high energy Urbach like characteristic is related to the presence of an amorphous surface oxide. It is shown to dominate the absorption spectra of thin gallium nitride samples, for which the influence of surface oxidation is strongest.     

Introduction to the special series.

The history of human civilization is marked by efforts to improve the quality of life by delegating laborious tasks to other species or to machines. The newest technological revolution, the use of electronic computers, has produced enormous changes in our lives over the last three decades. Computer technology has been widely applied to many fields of psychology. Psychological assessment, a subspecialty of psychology that served as one of the earliest proving grounds of automated technology, has advanced considerably in the last quarter-century. This Special Series highlights some of the advances in computerized psychological assessment methods and discusses some of the lingering issues and contemporary problems with automated psychological assessment approaches. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

New subscales for the MMPI-2 Social Introversion (Si) scale.

The development of three new content-homogeneous subscales for the revised Minnesota Multiphasic Personality Inventory (MMPI-2; J. N. Butcher et al, 1989) Social Introversion (Si) scale designed to replace the K. Serkownek (1975) subscales, which were not included in the revised MMPI, is described. The subscales, termed Shyness/Self-Consciousness, Social Avoidance, and Self/Other Alienation, were developed with data provided by college students (515 men and 797 women). Data analyses with this and the MMPI-2 normative sample demonstrated that the new subscales independently contribute to the assessment of nearly 90% of the variance in the full Si scale, that they display both convergent and divergent validity, and that these attributes generalize beyond the sample with which they were developed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

General linear methods for ordinary differential equations

General linear methods were introduced as the natural generalizations of the classical Runge–Kutta and linear multistep methods. They have potential applications, especially for stiff problems. This paper discusses stiffness and emphasises the need for efficient implicit methods for the solution of stiff problems. In this context, a survey of general linear methods is presented, including recent results on methods with the inherent RK stability property.     

Global synchronisation in Linda

The paper examines the ‘Distributed Summation’ problem, and its solution in Linda. A number of problems with the current set of primitives are examined, and a new primitive, collect, is proposed.     

Second law analysis of a natural gas‐fired gas turbine cogeneration system

The influence of operating conditions such as reheat, intercooling, ambient temperature and pressure ratio are analyzed from a second law perspective on the performance of a natural gas‐fired gas turbine cogeneration system. The effect of these operating parameters on carbon dioxide emissions is also discussed. The second law efficiency of gas turbine cogeneration system increases markedly with reheat option. Higher pressure ratios lead to decreased second law cogeneration efficiency but this effect can be reduced with a higher level of reheat option. The effect of intercooling on second law efficiency is strongly related to pressure ratio with higher pressure ratios significantly decreasing efficiency. The second law efficiency is not so sensitive to the environment temperature for levels of reheat or intercooling greater than 50%. Copyright © 2009 John Wiley & Sons, Ltd.     

Discrimination of aerial deposition sources of polychlorinated dibenzo-p-dioxin and polychlorinated dibenzofuran downwind from a pulp mill near Ketchikan, Alaska

Drinking water is supplied by individual roof-catchment systems for homes and businesses near a dissolving sulfite pulp mill (now closed) located just north of Ketchikan in southeast Alaska. This study was conducted to determine if polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDDs/Fs) found in the sediments of the roof-catchment cisterns resulted from historical deposition of stack emissions from the pulp mill's multi-fuel power boilers. Fly ash from the power boilers had maximum total PCDD/F concentrations of 3.08 x 10(5)-3.10 x 10(6) ng/kg, which resulted from combustion of bleach plant wastewater sludge and saltwater-soaked wood waste. Cistern sediments had maximum total PCDD/F concentrations of 7.71 x 10(4) ng/kg. Potential sources of PCDDs/Fs in the cistern sediments were considered to be automobile exhaust, heating oil combustion, and private trash burning as well as pulp mill boiler emissions. Discriminant analysis was used to analyze differences between profiles of tetra through octa homologue classes of PCDDs/ Fs (defined as proportional contributions to total concentration) from different source terms. Homologue profiles of potential sources from Ketchikan included in this analysis were fly ash collected from the mill's power boilers and soils collected from background areas (areas with similar PCDD/F sources as the residences [e.g., auto exhaust and burn barrels] near the mill but beyond the zone of aerial deposition of emissions from the mill). Profiles for emissions from automobile exhaust, fertilizers, oil heating, residential trash burning, and residential wood heating were also included in the source "training" data set (for the discriminant analysis) using data from published literature. The classification rules developed from the discriminant analysis were applied to the following test media sampled at Ketchikan: roof-catchment cistern sediments and soils collected from areas in the vicinity of the mill's power boilers (i.e., nearby residential or commercial [developed] areas, on the mill property, and nearby forestlands). The homologue profiles of cistern sediment and nearby developed area soil samples were similar to background soils, whereas the profiles for the forestland soil samples (influenced by emissions from the mill but not other anthropogenic sources) closely matched the fly ash pattern. The homologue profiles of the emission sources from published data were more similar to one another than either background soils or fly ash. Soil samples from the mill property were classified as members of all source groups. On the basis of these analyses, the composition of PCDDs/Fs detected in the cistern sediments is typical of Ketchikan background conditions and not reflective of mill emissions.     

Multimedia displays for conceptual discovery: information seeking with strand maps

This article explores the use of a multimedia search interface for digital libraries based on strand maps developed by the American Association for the Advancement of Science. As semantic-spatial displays, strand maps provide a visual organization of relevant conceptual information that may promote the use of science content during digital library use. A study was conducted to compare users' cognitive processes during information seeking tasks when using a multimedia strand maps interface, versus the textual search interface currently implemented in the Digital Library for Earth System Education. Quantitative and qualitative data from think-aloud protocols revealed that students were more likely to engage with science content (e.g., analyzing the relevance of science concepts with regard to task needs) during search when using the strand maps interface compared to those using textual searching. In contrast, students using a textual search interface engaged more frequently with surface-level information (e.g., the type of a resource regardless of its science content) during search and retrieval. As a multimedia search interface for digital libraries, strand maps appear to be promising tools to promote conceptual discovery and learning through content-based processes that promote learner engagement with relevant science knowledge.     

Influence of sympathectomy on the lateral hypothalamic lesion syndrome.

Two experiments with male Long-Evans rats examined sympathetic involvement in the lateral hypothalamic (LH) lesion syndrome. Ss were surgically or chemically sympathectomized and then given LH lesions. At 24 hrs postlesion, lesion-induced hyperglycemia but not hyperthermia was attenuated by splanchnicectomy and celiac ganglionectomy. Hyperthermia but not hyperglycemia was attenuated by adrenal demedullation, adrenalectomy, and daily neonatal guanethidine (50 mg/kg) treatment. Guanethidine-sympathectomized Ss also displayed lower basal temperatures, more perilesion chromatolysis, and more severe external symptoms than controls. No form of sympathectomy affected lesion-induced gastric pathology, plasma gastrin concentrations, or body weight loss, nor did any sympathectomy influence the recovery of ingestive behavior, daily food intake, the feeding response to 2-deoxy-dextro-glucose, or body weight maintenance in recovered LH-lesioned Ss. Results suggest that sympathetic hyperactivity contributed to some aspects of the acute LH syndrome: Hyperglycemia resulted from sympathetic outflow to the abdomen, whereas hyperthermia was determined by circulating catecholamines and extra-abdominal sympathetic innervation. Findings fail to support the hypothesis that chronic increases in sympathetic tone are responsible for the reduced food intake and body weight of the LH-lesioned Ss. (47 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)