连续波锁模Pr3+:YLF激光器

本文报导了采用氩离子激光器来泵浦Pr³⁺:YLF晶体,应用声光调制器实现了主动锁模;同时应用振动─高反射平面镜也实现了被动锁模,两种锁模均得到了ps光脉冲.据作者了解这是这种晶体材料的第一次锁模运转.     

Solution of sparse quasi-square rectangular systems by Gaussian elimination

We present a general method for the linear least-squares solutionof overdetermined and underdetermined systems. The method isparticularly efficient when the coefficient matrix is quasi-square,that is when the number of rows and number of columns is almostthe same. The numerical methods for linear least-squares problemsand minimum-norm solutions do not generally take account ofthis special characteristic. The proposed method is based onLU factorization of the original quasi-square matrix A, assumingthat A has full rank. In the overdetermined case, the LU factorsare used to compute a basis for the null space of A^T. The right-handside vector b is then projected onto this subspace and the least-squaressolution is obtained from the solution of this reduced problem.In the case of underdetermined systems, the desired solutionis again obtained through the solution of a reduced system.The use of this method may lead to important savings in computationaltime for both dense and sparse matrices. It is also shown inthe paper that, even in cases where the matrices are quite small,sparse solvers perform better than dense solvers. Some practicalexamples that illustrate the use of the method are included.     

Crystal structure of 1-methyl-1,3,5,7-tetraazaadamantan-1-ium ammonium sulfate hydrate,a double salt containing puckered layers of hydrogen-bonded NH 4 + and SO 4 2− groups

The double salt [(CH₂)₆N₄CH₃](NH₄)SO₄·H₂O crystallizes in space groupP2₁/a, witha=12.994(2),b=6.319(1),c=15.082(2) Å, =93.78(2)^o, andZ=4. The structure was solved by the heavy-atom method and refined toR _F ²=0.051 for 2478 MoK data. The ammonium and sulfate ions are cross-linked by hydrogen bonds to form puckered layers disposed about the (001) family of planes. Each water molecule bridges a [(CH₂)₆N₄CH₃]⁺ ion and a sulfate group, so that the organic cations lying on both sides of a puckered layer have their methyl groups pointing inward and fitting into depressions. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82063 (18 pages).Carried out, in part, under contract DE-AC02-76CH00016 with the U.S. Department of Energy, Office of Basic Energy Sciences.     

Implementation of a ”data filter” for the UK National Marine Monitoring Programme

The implementation of a strategy for the assessment of the validity of environmental monitoring data – a ”data filter”– is described. The approach was developed through the UK National Marine AQC Scheme for application to data collected during the UK National Marine Monitoring Programme. Data reported for the year 1999, by nine laboratories, for 74 determinand-matrix combinations were assessed on the basis of the completeness of their supporting quality assurance and quality control information. The approach to the establishment of criteria of acceptability for quality information is described. Received: 28 August 2001 Accepted: 29 November 2001     

Streptavidin Modified Carbon Nanotube Based Graphite Electrode for Label‐Free Sequence Specific DNA Detection

Disposable graphite pencil electrodes (PGE) modified with multiwalled carbon nanotubes (MWCNTs)‐streptavidin (STR) conjugates were used for electrochemical monitoring of label‐free DNA hybridization. The surface morphology of PGE electrode before and after hybridization was characterized by scanning electron microscopy. Electrochemical impedance spectroscopy was used to monitor each step of the construction of the DNA biosensor. The biosensor was demonstrated to have excellent selectivity, being able to differentiate complementary sequences from a noncomplementary ones and in addition select the target sequence of DNA from a mixture of other DNA without loss in current sensitivity.