CVT法生长GaP多晶

阐述了CVT(化学气相输运)法生长GaP的基本反应和输运速度,采用CVT法生长出了GaP多晶.设计了石英管的结构以制造出一个局部的低温区域,防止了GaP在管壁的生长.生长出的GaP多晶相对密度为98;,红外透过率达到30;,努普硬度为611kg/mm2.散射颗粒测试表明主要的光散射颗粒为多晶中存在的孔隙.     

Leverage bubble

Leverage is strongly related to liquidity in a market and lack of liquidity is considered a cause and/or consequence of the recent financial crisis. A repurchase agreement is a financial instrument where a security is sold simultaneously with an agreement to buy it back at a later date. Repurchase agreement (repo) market size is a very important element in calculating the overall leverage in a financial market. Therefore, studying the behavior of repo market size can help to understand a process that can contribute to the birth of a financial crisis. We hypothesize that herding behavior among large investors led to massive over-leveraging through the use of repos, resulting in a bubble (built up over the previous years) and subsequent crash in this market in early 2008. We use the Johansen–Ledoit–Sornette (JLS) model of rational expectation bubbles and behavioral finance to study the dynamics of the repo market that led to the crash. The JLS model qualifies a bubble by the presence of characteristic patterns in the price dynamics, called log-periodic power law (LPPL) behavior. We show that there was significant LPPL behavior in the market before that crash and that the predicted range of times predicted by the model for the end of the bubble is consistent with the observations.     

An adeno-associated viral vector transduces the rat hypothalamus and amygdala more efficient than a lentiviral vector

Background  

This study compared the transduction efficiencies of an adeno-associated viral (AAV) vector, which was pseudotyped with an AAV1 capsid and encoded the green fluorescent protein (GFP), with a lentiviral (LV) vector, which was pseudotyped with a VSV-G envelop and encoded the discosoma red fluorescent protein (dsRed), to investigate which viral vector transduced the lateral hypothalamus or the amygdala more efficiently. The LV-dsRed and AAV1-GFP vector were mixed and injected into the lateral hypothalamus or into the amygdala of adult rats. The titers that were injected were 1 × 10⁸ or 1 × 10⁹ genomic copies of AAV1-GFP and 1 × 10⁵ transducing units of LV-dsRed.     

Methodology of generic modeling as applied to energy coupling of CO2 laser material interaction

Energy coupling is a key phenomenon in material processing techniques that use lasers. It is a complex physical process, which involves numerous parameters, such as material's refractive index, laser wavelength, angle of incidence, polarization, temperature, power, power intensity, surface roughness and surface coating. Although there are some empirical and theoretical models of the dependence of the energy coupling efficiency, also termed absorptivity on individual and/or blocks of parameters, to date, there is no comprehensive model that addresses the wide array of parameters that affect energy coupling for laser material interaction. To address this need, several of the available models are examined, and a generic methodology is introduced and used to de-couple, classify and re-categorize the parameters. The process of creating a general model that combines the influences of the selected crucial parameters is presented. Current limitation and restrictions of the model are addressed.     

Combinatorial synthesis of 3,5-dimethylene substituted 1,2,4-triazoles

Combinatorial cyclizations of imidates and hydrazides with methylene linked R groups, generated from the corresponding nitriles and carboxylic acids, respectively, provided a large library of 3,5-dimethylene substituted 1,2,4-trizoles. [formula: see text].     

The vierbein is irrelevant in perturbation theory

Proper gauge fixing permits the elimination of the vierbein in favor of the metric as the field variable of gravity even when fermions are present. The result is a much simpler computational formalism which is nonetheless background field invariant and possesses all the usual constraints of symmetry, locality, and canonical field dimension.     

Probing the stereochemistry of E. coli 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase (phenylalanine-sensitive)-catalyzed synthesis of KDO 8-P analogues

The five-carbon phosphorylated monosaccharide analogues, D-arabinose 5-phosphate, D-ribose 5-phosphate, and 2-deoxy-D-ribose 5-phosphate, were separately condensed with (Z)- and (E)-[3-(2)H]-phosphoenolpyruvate (PEP) in the presence of Escherichia coli 3-deoxy-D-arabino-heptulosonate 7-phosphate (DAH 7-P) synthase (phe) to give in the case of (Z)-[3-(2)H]-PEP (3S)-[3-(2)H]-3-deoxy-D-manno-octulosonate 8-phosphate, (3S)-[3-(2)H]-3-deoxy-D-altro-octulosonate 8-phosphate, and (3S)-[3-(2)H]-3,5-dideoxy-D-altro-octulosonate 8-phosphate, respectively, whereas incubation with (E)-[3-(2)H]-PEP gives the corresponding (3R)-monosaccharides. These results are in complete agreement with the observed facial selectivity of DAH 7-P synthase for its normal substrates D-erythrose 4-phosphate and PEP and provide direct evidence that DAH 7-P synthase (phe) catalyzes the si face addition of the C3 of PEP to the re face of C1 of the phosphorylated monosaccharides tested. Products formed by DAH 7-P synthase (phe)-catalyzed condensation of (Z)- and (E)-[3-F]-PEP with E 4-P were completely characterized by (1)H and (19)F NMR analysis for the first time. Results of our studies suggest that disappearence of the double bond between C2 and C3 of PEP and formation of a bond between C3 of PEP and C1 of the phosphorylated monosaccharide tested occur in concert during the DAH 7-P synthase-catalyzed condensation reaction.     

Gas-phase deprotonation of arylalkylamines. A collision-induced dissociation study

The collision-induced dissociation (CID) of deprotonated arylalkylamines of general formula R(1)C(6)H(4)CHR(2)CH(2)NR(3)(2) (where R(1) = H, OH, F or NO(2); R(2) = H or OH; R(3) = H or CH(3)) generated by negative chemical ionization with H(2)O and D(2)O as ionizing reagents, is discussed. The negative chemical ionization mass spectra show that, in the absence of a hydroxy group in the aromatic ring, deprotonation takes place at the benzylic position whereas the proton is lost from the OH group when present. The nitro compound forms only M(-.) ions. The CID spectra of the deprotonated molecules show that fragmentations are strongly dependent on the structural features of the molecules, namely the presence or absence of substituents in the aromatic ring or aliphatic chain. Copyright 1999 John Wiley & Sons, Ltd.     

Isolation of NO(3)(-)-N as 1-phenylazo-2-naphthol (Sudan-1) for measurement of delta(15)N

The conversion of nitrate (NO(3)(-)) to 1-phenylazo-2-naphthol (Sudan-1) has been examined as a method for natural abundance measurement of delta(15)N of NO(3)(-). The reaction results in dilution of NO(3)(-)-N with only one reagent-derived N and the product is readily concentrated from dilute samples by reverse phase chromatography. There is systematic isotopic fractionation during the reaction, but this can be allowed for by analysing known NO(3)(-) standards along with each sample set. Sudan-1 prepared from surface water samples containing approximately 50 &mgr;g NO(3)(-)-N can be analysed by automated continuous flow isotope ratio mass spectrometry with a precision of 0.2 per thousand (one standard deviation) and the accuracy is not affected by interference from other nitrogenous species in the sample or reagents. Copyright 1999 John Wiley & Sons, Ltd.