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981.
F. Y. Phillips 《The Journal of the Operational Research Society》1994,45(8):901-915
The brand shifting problem is reviewed. A new allocation of brand shifting volume is shown to be compatible with a posited hierarchical (nested) market structure, unlike previous allocations. Like the Sanddabs model on which it is based, the new allocation, called Sanddabs/Nest, uses purchase tracking information but does not require brand similarity data. The paper shows Sanddabs/Nest is equivalent to a principle of Kullback information. Implications for brand management are detailed. 相似文献
982.
A. F. Blinokhvatov O. V. Markovtseva M. N. Nikolaeva 《Chemistry of Heterocyclic Compounds》1992,28(3):266-268
Substituted 4H-pyrans were obtained in high preparative yields by the reaction of 1,5-diketones with acetic anhydride and boron trifluoride etherate in diethyl ether. It is assumed that the heterocyclization of 1,5-diketones includes a step involving the formation and transformations of an acyloxy carbonium ion.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 320–322, March, 1992. 相似文献
983.
A. F. Potekhin 《Russian Physics Journal》1991,34(5):396-399
The components of the gravitational field are compared in the post-Newtonian approximation in the geometric (Einstein tensor) and field (Maxwellian vector form) theories of gravitation. The fundamental difference of these fields in the motion of a test particle is shown. The feasibility of qualitative detection of the vortex component of the gravitational field is found experimentally. The scheme for an alternate experiment is given.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 15–18, May, 1990.The author thanks A. S. Lantsev for the experimental part of the article presented here. 相似文献
984.
R. Kadono R. F. Kiefl J. H. Brewer G. M. Luke T. Pfiz T. M. Riseman B. J. Sternlieb 《Hyperfine Interactions》1991,64(1-4):635-640
The diffusion rate of muonium in the III–V compound semiconductor GaAs has been determined from measurements of muon spinT
1 relaxation induced by motion in the presence of nuclear hyperfine interactions. It is shown for the first time in a semiconductor
that (a) there is a crossover of the transport mechanism at about 90 K from stochastic to zero-phonon hopping, as evidenced
by a steep rise in the hop rate at lower temperatures, and that (b) the muonium diffuses at the hop rate of 1010 s−1 (corresponding diffusion constantD≈10−6 cm2s−1) at lower temperatures as well as at room temperature. 相似文献
985.
986.
A. Buri A. Costantini G. Laudisio R. Fresa M. Catauro F. Branda 《Journal of Thermal Analysis and Calorimetry》1997,49(2):863-868
Glasses of composition expressed by the following general formula xCaO·(1?x)SiO2 (0.30≤x≤0.50) can be prepared by means of the sol-gel route starting from tetramethylorthosilicate and calcium nitrate tetrahydrate They are all difficult to prepare by means of the traditional technique of quenching the melt, because of the high liquidus temperature,T 1 t that in the case ofx=0.3 glass isT 1 =1650°C. The DTA apparatus appears a valuable tool for defining the procedure necessary to obtain the glass through the sol-gel route. The glassx=0.3 is bioactive. The experimental results suggest that the gel structures, such as obtained at room temperature, are very similar; only at high temperature do the reactions of hydrolysis and polycondensation go to completion and the structural units characteristic of each glass are obtained. 相似文献
987.
Mary F. Wheeler J. R. Whiteman 《Numerical Methods for Partial Differential Equations》1994,10(3):271-294
Superconvergent error estimates in l2(H1) and l∞(H1) norms are derived for recovered gradients of finite difference in time/piecewise linear Galerkin approximations in space for linear and quasinonlinear parabolic problems in two space dimensions. The analysis extends previous results for elliptic problems to the parabolic context, and covers problems in regions with nonsmooth boundaries under certain assumptions on the regularity of the solutions. © 1994 John Wiley & Sons, Inc. 相似文献
988.
M. Kopcewicz J. Jagielski A. Grabias F. Stobiecki T. Stobiecki 《Hyperfine Interactions》1998,112(1-4):25-28
The Ar-ion-beam mixing of Fe/Zr bi- and multilayers is studied by conversion electron Mössbauer spectroscopy as a function of ion dose ranging from 1×1014 to 1×1017 at./cm2. The mixing leads to amorphization of the Fe/Zr system. It was shown that the mixing process in bilayers depends strongly on the thickness of the Zr substrate. The amorphization is much more effective and occurs at lower ion doses in multilayers as compared to corresponding bilayers. 相似文献
989.
Time-resolved pulsed spectroscopy was used to measure the luminescence spectra of calcium fluoride. Characteristic features
of the luminescence of self-trapped excitons are discussed. It is shown that various configurations of self-trapped excitons
incorporating hole nuclei of a more complex structure, may be formed in CaF2 crystals.
Fiz. Tverd. Tela (St. Petersburg) 40, 1226–1227 (July 1998) 相似文献
990.
V. F. Babenko 《Ukrainian Mathematical Journal》1997,49(4):523-528
We solve the problem of optimization of monte Carlo methods for approximate integration over an arbitrary absolutely continuous measure. We propose a convenient model of Monte Carlo methods which uses the notion of transition probability. 相似文献