657 research outputs found

    James Toohey: Brisbane Pioneer or first of the White Shoe Brigade

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    Eastern Arctic Waters, by M.J. Dunbar

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    Shallow currents along the northeastern coast of South America

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    It has generally been considered that the Guiana Current carries South Atlantic Central water in an uninterrupted flow along the northeastern coast of South America and then into the Caribbean Sea. Certain phenomena observed in the western tropical Atlantic and in the Caribbean indicate that the picture is not that simple...

    Eugene Gladstone O'Neill and his plays

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    Thesis (M.A.)--Boston Universit

    Temperature stabilized transistor direct current amplifier

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    A stable direct current transistor amplifier is difficult to design for use at elevated temperatures. The above is true since transistor parameters and bias conditions are affected by temperature. When transistors are incorporated in direct coupled amplifier circuits, these variations in parameters and bias conditions usually result in unstable operation. It is the purpose of this thesis to investigate this problem and to design a stable direct current transistor amplifier which will operate satisfactorily at elevated temperatures. This problem is of importance as such direct current amplifier circuits are found in airborne or missile servo systems. In such systems the weight and bulk of vacuum tubes, the power consumption, and the heat dissipation problems have focused attention upon the transistor. Unfortunately, such circuitry is subjected to extremes of operating temperature, thus prohibiting the use of transistorized circuits unless heavy air conditioning equipment is used. If means of stabilizing the transistor direct current amplifier could be found, then transistors could be used to solve a critical defense problem. This problem was first encountered when the author was employed during the summer of 1956 at the Emerson Electric Manufacturing Company of St. Louis, Missouri. During this period a temperature study of R-C coupled transistor amplifiers was made, but when the author first attempted to test a direct coupled design at high temperature the problem became evident, as the transistors proceeded to destroy themselves in a thermal runaway. The Emerson Electric Manufacturing Company, being interested in transistor direct coupled amplifiers, agreed to provide the components for subsequent investigations to be conducted as a thesis problem at the University of Missouri, School of Mines and Metallurgy. Therefore, because of this experience of unstable circuit action at high temperatures, the author became interested in this problem. The following review of literature and discussion of the design of a stable transistor direct current amplifier is written under the assumption that the reader is familiar with basic transistor concepts of operation and with the terminology generally used in this field. Only theoretical concepts dealing with the effects of temperature on the transistor and its associated circuitry will be included. Noise power supply stability, and any other such variables are considered to be irrelevant in this study of transistor circuits and temperature. The thesis consists of a review of literature featuring three topics which are: (1) transistors and temperature (2) stabilization techniques, and (3) direct current transistor amplifier designs. This is followed by a description and analysis of a direct current transistor amplifier based upon the findings in the literature review. The results of temperature tests are included for this design to substantiate the use of the included ideas --Introduction, pages 1-2

    Methanogenesis by Methanosarcina acetivorans involves two structurally and functionally distinct classes of heterodisulfide reductase

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    Biochemical studies have revealed two distinct classes of Coenzyme B-Coenzyme M heterodisulfide (CoB-S-S-CoM) reductase (Hdr), a key enzyme required for anaerobic respiration in methaneproducing archaea. A cytoplasmic HdrABC enzyme complex is found in most methanogens, whereas a membrane-bound HdrED complex is found exclusively in members of the order Methanosarcinales. Unexpectedly, genomic data indicate that multiple copies of both Hdr classes are found in all sequenced Methanosarcinales genomes. The Methanosarcina acetivorans hdrED1 operon is constitutively expressed and required for viability under all growth conditions examined, consistent with HdrED being the primary Hdr. HdrABC appears to be specifically involved in methylotrophic methanogenesis, based on reduced growth and methanogenesis rates of an hdrA1C1B1 mutant on methylotrophic substrates and downregulation of the genes during growth on acetate. This conclusion is further supported by phylogenetic analysis showing that the presence of hdrA1 in an organism is specifically correlated with the presence of genes for methylotrophic methanogenesis. Examination of mRNA abundance in methanol-grown DhdrA1C1B1 strains relative to wild-type revealed upregulation of genes required for synthesis of (di)methylsulfide and for transport and biosynthesis of CoB-SH and CoM-SH, suggesting that the mutant has a defect in electron transfer from ferredoxin to CoB-S-S-CoM that causes cofactor limitation

    Comparative genomics of actinomycetes with a focus on natural product biosynthetic genes

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    Effectiveness of intervention on physical activity of children: systematic review and meta-analysis of controlled trials with objectively measured outcomes (EarlyBird 54).

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    addresses: Department of Endocrinology and Metabolism, Peninsula College of Medicine and Dentistry, Plymouth University Campus, Plymouth, UK. [email protected]: Journal Article; Meta-Analysis; Research Support, Non-U.S. Gov't; ReviewCopyright © 2012 by the BMJ Publishing Group Ltd. This articles was first published in: BMJ, 2012, Vol. 345, pp. e5888 -To determine whether, and to what extent, physical activity interventions affect the overall activity levels of children

    An Optimal Design for Universal Multiport Interferometers

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    Universal multiport interferometers, which can be programmed to implement any linear transformation between multiple channels, are emerging as a powerful tool for both classical and quantum photonics. These interferometers are typically composed of a regular mesh of beam splitters and phase shifters, allowing for straightforward fabrication using integrated photonic architectures and ready scalability. The current, standard design for universal multiport interferometers is based on work by Reck et al (Phys. Rev. Lett. 73, 58, 1994). We demonstrate a new design for universal multiport interferometers based on an alternative arrangement of beam splitters and phase shifters, which outperforms that by Reck et al. Our design occupies half the physical footprint of the Reck design and is significantly more robust to optical losses.Comment: 8 pages, 4 figure
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