Three-dimensional eddy-current computation using Krylov subspace methods

This paper considers the numerical solution of a transmissionboundary-value problem for the time-harmonic Maxwell equationswith the help of a special finite-volume discretization. Applyingthis technique to several three-dimensional test problems, weobtain large, sparse, complex linear systems, which are solvedby four types of algorithm, using biconjugate gradients, squaredconjugate gradients, stabilized conjugate gradients, and generalizedminimal residuals, respectively. Wecombine these methods withsuitably chosen preconditioning matrices and compare the speedof convergence.     

Numerical Solution of Discrete Poisson--Neumann Problems with Compatible or Incompatible Data, with Reference to Flow in a Circular Cavity

Finite volume differencing, based on integral theorems, is usedto derive discrete approximations to three partial differentialequations in polar co-ordinates, which describe incompressibleviscous non-axisymmetric flow in a plane circular cavity. Thisapproach ensures the compatibility of discrete approximationsto the poisson equation for the pressure. which occur with singularmatrix, by exploiting the divergence form of the source term.Anextension of the analysis provides a means of dealing also withproblems in which the right-hand sides of the algebraic equationsare inconsistent. Results computed for the specimen flow problemare presented and discussed.     

A critical look at some point-process models for repairable systems

The use of a modeldriven approach to the analysis of repairablesystems is considered and shown to be useful as a way of understandingthe characteristics of such a system. However, considerablestatistical problems arise from the use of a set of standardmodel-building elements. In particular, identification problemsarise in many of the models. The argument is illustrated byexamples from software reliability and mechanical reliability.The conclusion is that, in many cases, the exploratory data-analysisapproach is as effective as the use of more sophisticated models.     

RING OPENING PHOTOREACTIONS OF 5-BROMOURACIL AND 5-BROMO-2''-DEOXYURIDINE WITH SELECTED ALKYLAMINES

Several studies in the literature indicate that histones (lysine rich proteins found associated with DNA in eukaryotic chromatin), as well as poly-L-lysine, can be photocross-linked by ultraviolet (UV) light to DNA in which 5-bromo-2'-deoxyuridine has been substituted for thymidine. To gain some insight into the possible nature of this cross-linking, we have studied the photoreactions occurring in deoxygenated aqueous solutions containing 5-bromouracil (I) (BrUra) or 5-bromo-2'-deoxyuridine (III) (BrdUrd) and ethylamine, a lysine side chain analog. In the case of I this reaction produced the ring opened compound N-(N'-ethylcarbamoyl)-3-amino-2-bromoacrylamide (Ia). A small amount of N-(N'-ethylcarbamoyl)-3-ethylamino-2-bromoacrylamide (Ic) was also isolated. It was found that purified Ia, standing in the presence of ethylamine, was gradually converted to Ic in a dark reaction. The beta and alpha anomers of N-(N'-ethylcarbamoyl)-3-(2'deoxyribofuranos-1'-yl) amino-2-bromoacrylamide (IIIa and IIIb respectively) were isolated as products in the photoreaction of III with ethylamine; the alpha anomer was produced in a dark reaction from the beta anomer. The identity of these anomers was established by comparison of their proton NMR spectra with those of the four corresponding alpha and beta furanosyl and pyranosyl isomeric nucleosides of thymine, which are presented in the Appendix. A study was also made of the reaction of I with methylamine; a ring opened product analogous to Ia, viz. N-(N'-methylcarbamoyl)-3-amino-2-bromoacrylamide (IIa) was formed. A similar study with 5-bromo-1-methyluracil produced N-(N'-methylcarbamoyl)-3-methylamino-2-bromoacrylamide (IIc) as a product. Likewise, the reaction of 5-chlorouracil with ethylamine was studied and N-(N'-ethylcarbamoyl)-3-amino-2-chloroacrylamide (Ie), which is analogous in structure to Ia, was found to be produced. Structural identifications were made through use of UV spectroscopy, high resolution 1H-NMR spectroscopy, mass spectrometry and, in the case of Ia and IIa, 13C-NMR spectroscopy. In the BrUra and BrdUrd reaction systems, described above, dehalogenation reactions accounted for a major portion of the products. The yields of ring opened products, determined at pH 10, ranged from a high of 10.3% in the BrUra-ethylamine system to a low of 1.7% in the MeBrUra-methylamine system.(ABSTRACT TRUNCATED AT 400 WORDS)     

THE PHOTOCHEMISTRY OF 2-ALKOXYCYTOSINES IN PHOSPHATE BUFFER AND ITS LINK TO CYTOSINE PHOTOCHEMISTRY IN ALCOHOLIC SOLUTION

The reactions occurring when 2-methoxycytosine (4-amino-2-methoxypyrimidine) (I) and 2-ethoxycytosine (II) are irradiated in aqueous phosphate buffer at pH 7 have been studied. We have verified the previous results of Moore [Can. J. Chem. 41, 1937-1950 (1963)], who studied I and indicated that the product isolatable in greatest yield is N-carbomethoxy-3-hydroxyacrylamidine (IIIa). Similarly, we have found that the product of highest yield, isolated after irradiation of II, is N-carboethoxy-3-hydroxyacrylamidine (IIIb). Evidence is presented indicating that these are secondary products, being produced through hydrolysis of the corresponding N-carboalkoxy-3-aminoacrylamidines. Spectroscopic data are given for N-carboisopropoxy-3-hydroxyacrylamidine (IIIc), as well as the N-carbomethoxy, N-carboethoxy and N-carboisopropoxy derivatives of 3-hydroxy-2-methylacrylamidine. These four compounds were obtained through hydrolysis of the corresponding N-carboalkoxy derivatives of 3-aminoacrylamidine or 3-amino-2-methylacrylamidine, isolated from the photoreaction of cytosine or 5-methylcytosine with the appropriate alcohol.     

PHOTOCHEMICAL ADDITION OF AMINO ACIDS AND PEPTIDES TO POLYURIDYLIC ACID

Abstract— The quantum yields for photochemical addition of glycine and the L-amino acids commonly occurring in proteins (excluding proline) to polyuridylic acid have been determined in deoxygenated phosphate buffer at pH 7, using a fluorescamine assay technique. All twenty amino acids were found to be reactive, with cysteine, tryptophan, phenylalanine, tyrosine, arginine, lysine and methionine being the most reactive. The analogous quantum yields for a series of eighteen dipeptides of the form glycyl X (X being one of the commonly occurring amino acids, including proline), of L-alanyl-L-tryptophan, of the tripeptides L-seryl-L-seryl-L-serine and L-threonyl-L-threonyl-L-threonine, of the tetrapeptide L-cystine- bis -glycine, and of the lysine derivative N_α-acetyllysine were also measured. All were found to be reactive toward photoaddition to poly U.     

Isomorphisms of Linear Semigroups

A linear semigroup is a subsemigroup of the semigroup of all endomorphisms of a vector space over a (not necessarily commutative) field. In this note it is shown that every isomorphism of linear semigroups that contain all rank-one-operators is induced by a semilinear bijection of the corresponding vector spaces, unless these vector spaces have dimension 1.     

12 W高功率高可靠性915 nm半导体激光器设计与制作

本文设计并制作了一种高效率、高可靠性的915 nm半导体激光器。半导体激光器是光纤激光器的关键部件,为了最大限度地提高器件的电光转换效率,在设计上采用双非对称大光腔波导结构,同时对量子阱结构、波导结构、掺杂以及器件结构进行了系统优化。器件模拟表明,在25℃环境温度下,器件的最高电光转换效率达到67%。采用金属有机气相沉积(MOCVD)法进行材料生长,随后制备了发光区域宽度为95μm、腔长为4.8 mm的激光芯片。测试表明,封装后器件的效率以及其它参数指标达到国际先进水平,在室温下阈值电流为1 A,斜率效率为1.18 W/A,最高电光转换效率达66.5%,输出功率12 W时,电光转换效率达到64.3%,测试结果与器件理论模拟高度吻合。经过约6 000 h的寿命加速测试,器件功率没有出现衰减,表明制作的高功率915 nm激光芯片具有很高的可靠性。