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981.
Dan Li Anthony D. Rands Scott C. Losee Brian C. Holt John R. Williams Stephen A. Lammert Richard A. Robison H. Dennis Tolley Milton L. Lee 《Analytica chimica acta》2013
An automated sample preparation system was developed and tested for the rapid detection of Bacillus anthracis endospores by gas chromatography–mass spectrometry (GC–MS) for eventual use in the field. This reactor is capable of automatically processing suspected bio-threat agents to release and derivatize unique chemical biomarkers by thermochemolysis (TCM). The system automatically controls the movement of sample vials from one position to another, crimping of septum caps onto the vials, precise delivery of reagents, and TCM reaction times and temperatures. The specific operations of introduction of sample vials, solid phase microextraction (SPME) sampling, injection into the GC–MS system, and ejection of used vials from the system were performed manually in this study, although they can be integrated into the automated system. Manual SPME sampling is performed by following visual and audible signal prompts for inserting the fiber into and retracting it from the sampling port. A rotating carousel design allows for simultaneous sample collection, reaction, biomarker extraction and analysis of sequential samples. Dipicolinic acid methyl ester (DPAME), 3-methyl-2-butenoic acid methyl ester (a fragment of anthrose) and two methylated sugars were used to compare the performance of the autoreactor with manual TCM. Statistical algorithms were used to construct reliable bacterial endospore signatures, and 24 out of 25 (96%) endospore-forming Bacillus species were correctly identified in a statistically designed test. 相似文献
982.
In two party elections with popular vote ratio , a theoretical model suggests replacing the so-called MacMahon cube law approximation , for the ratio of candidates elected, by the ratio of the two half sums in the binomial expansion of (p+q)2k+1 for some k. This ratio is nearly when k = 6. The success probability for the power law is shown to so closely approximate , if we choose , that for . Computationally, we avoid large binomial coefficients in computing for k>22 by expressing as the sum , whose terms decrease by the factors . Setting K = 4k+3, we compute ak for the large k using a continued fraction derived from the ratio of π to the finite Wallis product approximation. 相似文献
983.
A decrease of the light transmission with increasing excitation intensity is observed in tetraphenylporphyrin/toluene solutions irradiated with 80 ps pulses at λ=532 nm. The experimental data are compared with simulations using a rate equation model. Excited state absorption cross-sections are evaluated. 相似文献
984.
985.
986.
Dennis H. Rouvray 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》1993,105(6):962-963
987.
Harish J. Palanthandalam-Madapusi Tobin H. Van Pelt Dennis S. Bernstein 《Journal of Global Optimization》2009,45(4):533-549
We consider minimization of a quadratic objective function subject to a sign-indefinite quadratic equality constraint. We
derive necessary and sufficient conditions for the existence of solutions to the constrained minimization problem. These conditions
involve a generalized eigenvalue of the matrix pencil consisting of a symmetric positive-semidefinite matrix and a symmetric
indefinite matrix. A complete characterization of the solution set to the constrained minimization problem in terms of the
eigenspace of the matrix pencil is provided. 相似文献
988.
S. J. Lugowski Dennis C. Smith Joanna Z. Lugowski Walter Peters John Semple 《Analytical and bioanalytical chemistry》1998,360(3-4):486-488
The role of Si in nature is briefly described, especially the toxic properties of inorganic and organic Si for humans. The use of different forms of silicones in medicine and food industry is noted and potential consequences of their use are discussed. Since Si is an essential trace element there is need for establishment of the “normal” level of Si in blood, other body fluids and tissues and development of speciation of Si forms in biological samples. Numerous difficulties in the determination of Si are described and the need for SRM is stressed. The results of the determination of Si in blood of patients with Si breast implants and controls, Si in milk and blood of nursing mothers – with and without Si breast implants and extractable Si in capsules – are summarized. The obtained data reinforce the need for a reliable SRM. 相似文献
989.
990.