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71.
Eitan Zemel 《Annals of Operations Research》1984,1(3):215-238
We analyze the behaviour of thek center and median problems forn points randomly distributed in an arbitrary regionA ofR d . Under a mild assumption on the regionA, we show that fork≦k(n)=o(n/logn), the objective function values of the discrete and continuous versions of these problems are equal to each otheralmost surely. For the two-dimensional case, both these problems can be solved by placing the centers or medians in an especially simple regular hexagonal pattern (the ‘honeycomb heuristic’ of Papadimitriou). This yields the exact asymptotic values for thek center and median problem, namely, α(|A|/k)1/2 and β(|A|/k)1/2, where |A| denotes the volume ofA, α and β are known constants, and the objective of the median problem is given in terms of the average, rather than the usual total, distance. For the 3- and 4-dimensional case, similar results can be obtained for the center problem to within an accuracy of roughly one percent. As a by-product, we also get asymptotically optimal algorithms for the 2-dimensionalp-normk median problem and for the twin problems of minimizing the maximum number of vertices served by any center and similarly for maximizing the minimum. 相似文献
72.
73.
Brian P. Kirkmeyer Richard C. Puetter Amos Yahil Karen I. Winey 《Journal of Polymer Science.Polymer Physics》2003,41(4):319-326
Previously, we studied a variety of ionomer morphologies with scanning transmission electron microscopy (STEM). Other groups have found that deconvoluting STEM images dramatically improve the overall image quality and the detection of sub‐nanometer‐scale features. In this study, STEM images of nanometer‐scale ion‐rich aggregates were deconvolved via the Pixon method with a simulated electron probe. The image models are considerably sharper with significantly decreased noise levels, thus making the size and shape of the ionic aggregates easier to distinguish relative to those in the raw STEM images. Raw and deconvoluted images of Zn‐neutralized poly(styrene‐ran‐methacrylic acid) ionomers containing spherical ionic aggregates indicate that the electron density varies smoothly from the edge to the center of the aggregates. Deconvolution also clarifies the issue of aggregate overlap in the STEM images. Furthermore, line scans across deconvoluted STEM images suggest that the three‐dimensional density distribution of these nanoaggregates compares favorably with a radially symmetric Gaussian distribution as opposed to a uniformly dense sphere. The overall result of this work is that deconvolution of STEM images provide ways in which to better investigate the morphologies of ionomers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 319–326, 2003 相似文献
74.
75.
The technique of thin-layer chromatography, as practised in the organic industrial laboratory, is described and its applications to the analysis of petroleum hydrocarbons, fuels, lubricants, polymers, plastics and their additives, non-ionic surfactants and explosives are reviewed. The role of thin-layer chromatography in the conservation of the environment is also considered. 相似文献
76.
77.
Roger D. Amos 《Chemical physics letters》1980,70(3):613-617
The components of the dipole polarizability and of the dipole-quadrupole polarizability A of the carbon monoxide molecule have been calculated as a function of the internuclear distance using both SCF and CI wavefunctions. The resulting values of , A and then derivatives should be the most accurate ab initio estimates available for these quantities. A comparison of the SCF and CI results shows significant differences in the values obtained. 相似文献
78.
The total synthesis of (±)-desepoxy-4,5-didehydromethylenomycin A employing a retrolactonization strategy has been achieved. 相似文献
79.
K.-H. Speidel G.J. Kumbartzki W. Knauer R. Kuhnen G. Kraft J. Gerber M.B. Goldberg G. Goldring A. Zemel 《Nuclear Physics A》1980,344(1):176-184
Energy levels in 160Er and 159Er were excited in the reactions 28Si(136Xe, 4n)160Er and 28Si(136Xe, 5n)159Er, and the product nuclei, recoiling with a velocity v = 0.07c were stopped in a plunger instrument after traversing a volume of hydrogen gas. The angular distribution of de-excitation γ-rays was studied as a function of flight time and gas pressure. Appreciable perturbations were detected in 160Er at times as short as 2 ps and in an angular momentum region as high as 12?. No perturbation could be detected in the level of 159Er even after 12 ps, signifying a low value for the g-factor of this level. 相似文献
80.
Differential cross sections and analyzing powers from the inelastic scattering of 65 MeV protons leading to the 1+T=0 (12.71 MeV) and 1+T = 1 (15.11 MeV) states in 12C have been analysed as tests of a model two-nucleon t-matrix. 相似文献