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61.
V. J. Harding Th. F. Nicholson G. A. Grant G. Hern C. E. Downs A. Castellani F. E. Taylor A. I. Kendall G. C. Linder D. D. van Slyke Eagle M. Somogyi A. L. Raymond J. G. Blanco Spannuth und Power Margrethe Sorensen G. Haugaard S. Fränkel C. Jellinek P. A. Levene T. Mori H. Bierry Cl. Rimington B. Lustig S. P. L. Sorensen Margrethe Høyrup W. M. Dehn K. E. Jackson D. A. Ballard und V. Boulez 《Fresenius' Journal of Analytical Chemistry》1935,101(5-6):204-214
Ohne Zusammenfassung 相似文献
62.
The reaction of 10 carboxamides activated by two beta-electron-withdrawing groups, which mostly exist completely or partially in their enol forms, with diazomethane was investigated. The main outcome is the diversity of reactions observed. With the most acidic enols 3-7, activated by at least one trifluoroethoxycarbonyl group or a cyano group, O-methylation or O,N-dimethylation takes place. With beta-dimethoxycarbonyl-activated systems 5 and 8, the C-methylation product of the amide form was one of the products. With a Meldrum's acid anilide enol 2, a cleavage took place leading to the C-alkylated imine having a CH(CO(2)Me)(2) group. Exchange of one 2,2,2-trifluoroethoxycarbonyl by a methoxycarbonyl in the C,N-dimethylation product of Me(2)CHNHC(OH)[double bond]C(CO(2)CH(2)CF(3))(2) 4 took place. The 2-anilido-1,3-cyclopentanedione 10 was methylated on a ring carbonyl while the enol of the 1,3-indanedione analogue 11 reacted with three diazomethane molecules and underwent a ring expansion and O-methylation to the 3-anilido-1,4-dimethoxynaphthalene. It is suggested that the reaction initiates by protonation of the diazomethane by the enol and an approximate qualitative relationship exists between the acidity of the enol and K(enol) and the regioselectivity of the reaction. 相似文献
63.
In this paper we discuss the conditional p-median and p-center problems on a network. Demand nodes are served by the closest facility whether existing or new. The formulation presented in this paper provided better results than those obtained by the best known formulation. 相似文献
64.
65.
Oded Berman Zvi Drezner Dmitry Krass George O. Wesolowsky 《European Journal of Operational Research》2009
In this paper we propose a covering problem where the covering radius of a facility is controlled by the decision-maker; the cost of achieving a certain covering distance is assumed to be a monotonically increasing function of the distance (i.e., it costs more to establish a facility with a greater covering radius). The problem is to cover all demand points at a minimum cost by finding optimal number, locations and coverage radii for the facilities. Both, the planar and discrete versions of the model are considered. Heuristic approaches are suggested for solving large problems in the plane. These methods were tested on a set of planar problems. Mathematical programming formulations are proposed for the discrete problem, and a solution approach is suggested and tested. 相似文献
66.
Relaxed Multifunctions and Young Multimeasures 总被引:2,自引:0,他引:2
Zvi Artstein 《Set-Valued Analysis》1998,6(3):237-255
Young-measure type limits of multifunctions are examined. The relaxed limit via selections is a multimeasure, while the relaxation as a set-valued point function yields a Young measure on sets. The paper verifies that the two processes are equivalent in the sense that the limit multimeasure consists of all the distributions selectionable with respect to the Young measure on sets. The main tool is the characterization of selectionable distributions. An illustrative application of the equivalence result is provided. 相似文献
67.
In this paper we solve the gravity (Huff) model for the competitive facility location problem. We show that the generalized Weiszfeld procedure converges to a local maximum or a saddle point. We also devise a global optimization procedure that finds the optimal solution within a given accuracy. This procedure is very efficient and finds the optimal solution for 10,000 demand points in less than six minutes of computer time. We also experimented with the generalized Weiszfeld algorithm on the same set of randomly generated problems. We repeated the algorithm from 1,000 different starting solutions and the optimum was obtained at least 17 times for all problems. 相似文献
68.
Increasing attention has been given over the last decade by the statistics, mathematics and science education communities to the development of statistical literacy and numeracy skills of all citizens and the enhancement of statistics education at all levels. This paper introduces the emerging discipline of statistics education and considers its role in the development of these important skills. The paper begins with information on the growing importance of statistics in today's society, schools and colleges, summarizes unique challenges students face as they learn statistics, and makes a case for the importance of collaboration between mathematicians and statisticians in preparing teachers to teach students how to understand and reason about data. We discuss the differences and interrelations between statistics and mathematics, recognizing that mathematics is the discipline that has traditionally included instruction in statistics. We conclude with an argument that statistics should be viewed as a bridge between mathematics and science and should be taught in both disciplines. 相似文献
69.
In cardiac elastography, the regional strain and strain rate imaging is based on displacement estimation of tissue sections within the heart muscle carried out with various block-matching techniques (cross-correlation, sum of absolute differences, sum of squared differences, etc.). The accuracy of these techniques depends on a combination of ultrasonic imaging parameters such as ultrasonic frequency of interrogation, signal-to-noise ratio, size of a kernel used in a block-matching algorithm, type of data and speckle decorrelation. In this paper, we discuss the possibility to enhance the accuracy of the displacement estimation via nonlinear filtering of B-mode images before block-matching operation. The combined effect of a filter algorithm and a kernel size on the accuracy of the displacement estimation is analyzed using a 36-frame sequence of grayscale B-mode images of a human heart acquired by an ultrasound system operating at 1.77 MHz. It is shown that the nonlinear filtering of images enables to obtain the desired accuracy (less than one pixel) of the displacement estimation with smaller kernels than without filtering. These results are obtained for two filters--an adaptive anisotropic diffusion filter and a nonlinear Gaussian filter chain. 相似文献
70.
A new method of spatial compound imaging is presented that improves image quality without the usual requirement to decrease the frame rate. The new method of imaging utilizes three transducers for data acquisition. The transducer located at the center of the transducer system is a phased array probe that acts as both transmitter and receiver. The other transducers are unfocused pistons that act only as receivers. Envelope data acquired by each transducer are combined to form a final image with improved quality (speckle contrast, target detectability and lateral resolution). It is shown that the improvement in speckle contrast depends on the correlation between individual images acquired by the transducers. The effective aperture approach is used for analytic estimation of the correlation between images in order to optimize the lateral separation between transducers. Using simulations, several compounding strategies have been performed to find the strategy that maximizes image quality. The central frequency of 2.5 MHz is used in simulations. Quantitative analysis of simulated B-mode images shows that the new method of imaging efficiently improves visibility, detectability, and lateral resolution of low contrast regions. The image frame rate is preserved because multiple scans are not required for the spatial compounding. 相似文献