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J. A. Smith J. F. Winkel A. J. Stace B. J. Whitaker 《Journal of mass spectrometry : JMS》1993,28(5):523-526
A novel instrument which combines high-resolution double-focusing mass spectrometry with time-of-flight detection was applied to the study of cluster ion photofragmentation. Using this apparatus, kinetic energy measurements were made on neutral photofragments following the excitation of Ar at 532 nm. The results show that one and possibly two argon atoms with high centre of mass kinetic energies emerge from the cluster within a few picoseconds of the photon being absorbed. 相似文献
4.
The efficiency of collisional ionization of excited rubidium atoms is demonstrated for Rb★—Kr collisions. Since the power required to optically saturate the Rydberg levels is much lower than for photoionization, the technique promises to reduce the laser requirements in single-atom detection and other resonance ionizatlon experiments. 相似文献
5.
Bogert D Burnstein R Fisk R Fuess S Morfin J Ohska Stutte L Walker JK Bofill J Busza W Eldridge T Friedman JI Goodman MC Kendall HW Kostoulas IG Lyons T Magahiz R Mattison T Mukherjee A Osborne L Pitt R Rosenson L Sandacz A Tartaglia M Taylor FE Verdier R Whitaker S Yeh GP Abolins M Brock R Cohen A Ernwein J Owen D Slate J Weerts H 《Physical review letters》1985,55(6):574-577
6.
Testing shelled corn for aflatoxin, Part III: evaluating the performance of aflatoxin sampling plans
Johansson AS Whitaker TB Giesbrecht FG Hagler WM Young JH 《Journal of AOAC International》2000,83(5):1279-1284
The effects of changes in sample size and/or sample acceptance level on the performance of aflatoxin sampling plans for shelled corn were investigated. Six sampling plans were evaluated for a range of sample sizes and sample acceptance levels. For a given sample size, decreasing the sample acceptance level decreases the percentage of lots accepted while increasing the percentage of lots rejected at all aflatoxin concentrations, and decreases the average aflatoxin concentration in lots accepted and lots rejected. For a given sample size where the sample acceptance level decreases relative to a fixed regulatory guideline, the number of false positives increases and the number of false negatives decreases. For a given sample size where the sample acceptance level increases relative to a fixed regulatory guideline, the number of false positives decreases and the number of false negatives increases. For a given sample acceptance level, increasing the sample size increases the percentage of lots accepted at concentrations below the regulatory guideline while increasing the percentage of lots rejected at concentrations above the regulatory guideline, and decreases the average aflatoxin concentration in the lots accepted while increasing the average aflatoxin concentration in the rejected lots. For a given sample acceptance level that equals the regulatory guideline, increasing the sample size decreases misclassification of lots, both false positives and false negatives. 相似文献
7.
Processed food manufacturers often use acceptance sampling plans to screen out lots with unacceptable levels of contamination from incoming raw material streams. Sampling plan designs are determined by specifying sample sizes, sample preparation methods, analytical test methods, and accept/reject criteria. Sampling plan performance can be indicated by plotting acceptance probability versus contamination level as an operating characteristic (OC) curve. In practice, actual plan performance depends on the level of contamination in the incoming lot stream. This level can vary considerably over time, among different crop varieties, and among locales. To better gauge plan performance, a method of coupling an OC curve and crop distributions is proposed. The method provides a precise probabilistic statement about risk and can be easily performed with commercial spreadsheet software. 相似文献
8.
The proposed flow-injection determination of nonionic surfactants of the general type RO(CH2CH2O)nH (where R is an alkyl or alkylphenyl group and n is the number of moles of oxyethylene group) is based on extraction of the colored ion-pair product formed between the nonionic surfactant and the regent tetrabromophenolphthalein ethyl ester potassium salt (TBPE-K). The complex is extracted into 1,2-dichloroethane and measured at 609 nm. A new phase separator is described. Triton X-100 is used as a model compounds, for which response is linear in the range 2–60 mg l?1. Precision of the method is excellent with a relative standard deviation of <1.0%. The sensitivity of the method depends on the type of surfactant examined. 相似文献
9.
We report the first successful design of a self-associating antiparallel coiled coil, APH. The simultaneous application of Coulombic and hydrophobic components results in a decided preference for the antiparallel alignment as judged by HPLC, sedimentation equilibrium, and chemical denaturation data. The designed peptide is of comparable stability to naturally occurring leucine zipper peptides and can be expressed in bacteria. These properties of APH suggest potential in vivo protein fusion and biomaterials applications. 相似文献
10.
A. Whitaker 《Journal of chemical crystallography》1991,21(4):463-469
The crystal structure of CI Solvent Yellow 18, C18H18N4O, has been determined by single crystal X-ray diffraction techniques. It crystallizes in the monoclinic system witha=7.480(2) Å,b=19.184(3) Å,c=11.260(1) Å,=98.00(3)°, space groupP21/n andZ=4. The structure has been solved by direct methods, and least-squares refinement has been completed on three-dimensional data (2310 reflections, CuK radiation). The hydrogen atoms have been found, but only their positional parameters refined. Final residual 0.085 (all positive intensity data). The molecule exists as the hydrazone tautomer and intramolecular hydrogen bonding keep the molecule approximately planar. The molecules are packed in layers parallel to the (¯202) plane and in columns parallel tob. Alternate molecules within the columns are in antiparallel. The molecules are linked by van der Waals' forces. 相似文献