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1.
In multivariate discrimination of several normal populations, the optimal classification procedure is based on quadratic discriminant functions. We compare expected error rates of the quadratic classification procedure if the covariance matrices are estimated under the following four models: (i) arbitrary covariance matrices, (ii) common principal components, (iii) proportional covariance matrices, and (iv) identical covariance matrices. Using Monte Carlo simulation to estimate expected error rates, we study the performance of the four discrimination procedures for five different parameter setups corresponding to standard situations that have been used in the literature. The procedures are examined for sample sizes ranging from 10 to 60, and for two to four groups. Our results quantify the extent to which a parsimonious method reduces error rates, and demonstrate that choosing a simple method of discrimination is often beneficial even if the underlying model assumptions are wrong.The authors wish to thank the editor and three referees for their helpful comments on the first draft of this article. M. J. Schmid supported by grants no. 2.724-0.85 and 2.038-0.86 of the Swiss National Science Foundation. 相似文献
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G. C. Unnithan K. K. Nair Cathy J. Kooman 《Cellular and molecular life sciences : CMLS》1978,34(3):411-412
Summary Application of precocene II, topically or by contact method, appears to inhibit the synthetic activity of neurosecretory A-cells of the pars intercerebralis ofOncopeltus fasciatus. Treatment of precocene-treated insects with JH III apparently stimulates the secretory activity of these cells.Supported by National Research Council of Canada grant No. A4669.We thank Dr G. B. Staal, Zoecon Corporation, Palo Alto, California, for the gift of precocene II. 相似文献
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P. P. Nair 《Cellular and molecular life sciences : CMLS》1960,16(5):193-194
Résumé Un nouveau produit crystallin de l'acide folique avec l'acide molybdophosphorique est décrit. Ce produit a été soumis aux examens microscopique, électrophorétique et analyse élémentaire. Ce produit provoque une leucopénie chez les rats albines, ce qui indique une ressemblance probable aux antidotes de l'acide folique. D'autre part, l'observation a montré que ce produit a un effet inhibitif sur la croissance desStreptococcus faecalis R. dans des cultures renfermant de l'acide folique à des degrés différents. 相似文献
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Zusammenfassung Es wird die genetische Aktivität der Zellkerne in den akzessorischen Drüsen vonPeriplaneta americana durch Juvenilhormon gesteigert, ein Nachweis, der mittels Autoradiographie nach «Anfärbung» mit3H-Actinomyzin-D erbracht werden konnte.
The research was supported by National Research Council of Canada operating grant No. A4669 awarded to Dr.K. K. Nair. We thank Dr.J. B. Siddall of Zoecon for the generous gift of the juvenile hormone analogue. 相似文献
The research was supported by National Research Council of Canada operating grant No. A4669 awarded to Dr.K. K. Nair. We thank Dr.J. B. Siddall of Zoecon for the generous gift of the juvenile hormone analogue. 相似文献
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Silica nanoparticles have been prepared from tetraethylorthosilicate dissolved in ethanol followed by base-catalyzed condensation.Earlier works reported that at least four parameters,namely concentrati... 相似文献
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The myosin motor in muscle generates a smaller and slower working stroke at higher load 总被引:1,自引:0,他引:1
Reconditi M Linari M Lucii L Stewart A Sun YB Boesecke P Narayanan T Fischetti RF Irving T Piazzesi G Irving M Lombardi V 《Nature》2004,428(6982):578-581
Muscle contraction is driven by the motor protein myosin II, which binds transiently to an actin filament, generates a unitary filament displacement or 'working stroke', then detaches and repeats the cycle. The stroke size has been measured previously using isolated myosin II molecules at low load, with rather variable results, but not at the higher loads that the motor works against during muscle contraction. Here we used a novel X-ray-interference technique to measure the working stroke of myosin II at constant load in an intact muscle cell, preserving the native structure and function of the motor. We show that the stroke is smaller and slower at higher load. The stroke size at low load is likely to be set by a structural limit; at higher loads, the motor detaches from actin before reaching this limit. The load dependence of the myosin II stroke is the primary molecular determinant of the mechanical performance and efficiency of skeletal muscle. 相似文献