InxGa1-xAs-AlyGa1-yAs-GaAs strained-layer quantum-well heterostructure circular ringlasers

The growth, processing, and optical characterization of a single Y-junction In_xGa_1-xAs-Al_yGa_1-y As-GaAs strained-layer quantum-well heterostructure circular ring laser (6 μm width, 11~251 μm outer radius) are described. The circular ring lasers have been grown by metalorganic chemical vapor deposition, etched by SiCl₄ reactive ion etching, and planarized by polyimide. The dependences of laser threshold current density and peak emission wavelength (950~1015 nm) on outer radius are presented. The emission spectra show that the circular ring lasers lase mainly in high-order whispering gallery modes, with smaller outer radius ring lasers operating in low-order whispering gallery modes     

Threshold current density in strained layerInxGa1-xAs-GaAs quantum-well heterostructurelasers

The authors consider the transparency carrier density in ideal and practical strained layer In_xGa_1-xAs-GaAs quantum-well heterostructure lasers. The transparency carrier density in practical structures is then related to transparency current density using realistic values for spontaneous recombination rates. These parameters are incorporated with representative structural parameters into a nonlinear model for gain in a quantum-well laser, in order to provide a complete model for the laser threshold current density in strained layer In_xGa_1-xAs-GaAs quantum-well heterostructure lasers. These results are then compared and contrasted with experimental laser results from several laboratories     

Induction of visual imagery during NREM sleep

In an attempt to induce eye movements (EMs) in non-rapid eye movement sleep, light and sound stimuli were presented to human subjects (at below-waking threshold) during stage 2 sleep. EMs were used as an indicator of ponto-geniculo-occipital (PGO) wave activity. When at least one concurrent EM in response to the stimuli was observed, the subjects were awakened and mentation reports collected. Compared to equivalent control periods with no stimulation, awakenings from the stage 2 stimulation condition showed a higher frequency of visual imagery reports, electroencephalogram alpha activity, and k-complexes. Additional control and stimulation conditions elicited from rapid eye movement sleep awakenings showed no significant differences in the frequency of visual imagery reports. When the amount of alpha activity before stage 2 awakenings from which imagery was reported was compared to that from which imagery was not reported, imagery awakenings showed significantly more alpha. Results can be interpreted as evidence for a link between PGO activity and dreaming in humans or in terms of an arousal-window hypothesis of visual hallucinations.     

The role and potential of engineering GNVQs

General National Vocational Qualifications (GNVQs) were introduced in the UK September 1992. They will offer young people the opportunity to learn to high standards in a practical and vocational context. Here, the authors describe how GNVQs prepare young people for employment in broad occupational areas, whilst also offering a route to higher education     

Progress in InGaAs-GaAs selective-area MOCVD toward photonicintegrated circuits

The progress toward integrated photonic devices by selective-area metalorganic chemical vapor deposition (MOCVD) is reviewed. Processing steps involved with fabricating buried heterostructures (BHs) by a three-step technique are outlined, and a computational model is presented that predicts the enhancement behavior of selective-area MOCVD. Results are reviewed for several discrete and integrated photonic devices. These include low-threshold BH lasers, laser diodes integrated with either intracavity or external cavity modulators, dual-channel emitters integrated with both modulators and passive y-junction waveguides, and broad-band light-emitting diodes (LEDs)     

Substantial narrowing of the Niemann-Pick C candidate interval by yeast artificial chromosome complementation

Niemann-Pick disease type C (NP-C) is an autosomal recessive lipidosis linked to chromosome 18q11-12, characterized by lysosomal accumulation of unesterified cholesterol and delayed induction of cholesterol-mediated homeostatic responses. This cellular phenotype is identifiable cytologically by filipin staining and biochemically by measurement of low-density lipoprotein-derived cholesterol esterification. The mutant Chinese hamster ovary cell line (CT60), which displays the NP-C cellular phenotype, was used as the recipient for a complementation assay after somatic cell fusions with normal and NP-C murine cells suggested that this Chinese hamster ovary cell line carries an alteration(s) in the hamster homolog(s) of NP-C. To narrow rapidly the candidate interval for NP-C, three overlapping yeast artificial chromosomes (YACs) spanning the 1 centimorgan human NP-C interval were introduced stably into CT60 cells and analyzed for correction of the cellular phenotype. Only YAC 911D5 complemented the NP-C phenotype, as evidenced by cytological and biochemical analyses, whereas no complementation was obtained from the other two YACs within the interval or from a YAC derived from chromosome 7. Fluorescent in situ hybridization indicated that YAC 911D5 was integrated at a single site per CT60 genome. These data substantially narrow the NP-C critical interval and should greatly simplify the identification of the gene responsible in mouse and man. This is the first demonstration of YAC complementation as a valuable adjunct strategy for positional cloning of a human gene.     

Ethnic minorities' ratings of ethnically similar and European American counselors: A meta-analysis.

A meta-analysis of studies that assessed ethnic minorities' perceptions of and preferences for ethnically similar counselors and European American counselors showed that ethnic minorities tended to prefer ethnically similar counselors over European American counselors. However, the perceptions of and preferences for counselors were influenced by the cultural affiliation of the participants and the research methods used. More precise methods for determining the degree to which ethnic minorities' preferences for ethnically similar counselors is a function of inferences concerning attitudes, values, and skill need to be developed. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

High-performance liquid chromatographic determination of the enantiomers of the benzoquinolinone LY191704, a human type 1 5 alpha-reductase inhibitor, in plasma

A stereoselective reversed-phase liquid chromatographic method for the determination of compounds LY300502 and LY300503 (enantiomers of LY191704) in rat and dog plasma was developed. The assay involved extraction of the compounds using a strong cation-exchange solid-phase extraction column, from which the compounds are eluted with 1% of 1 M HCI in methanol. The enantiomers were separated on a Daicel Chiralcel OD-R column. The mobile phase consisted of water-acetonitrile-methanol (50:40:10, v/v) at a flow-rate of 0.3 ml/min. UV detection was achieved at 220 nm. The disposition of the enantiomers of LY191704 in rats and dogs was found to be stereoselective and species specific.