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排序方式: 共有302条查询结果,搜索用时 62 毫秒
51.
We develop differential and symplectic geometry of differentiable Deligne–Mumford stacks (orbifolds) including Hamiltonian group actions and symplectic reduction. As an application we construct new examples of symplectic toric DM stacks. 相似文献
52.
From dynamic modulus via different relaxation spectra to relaxation and creep functions 总被引:2,自引:0,他引:2
The main goal of the paper is to compare predictive power of relaxation spectra found by different methods of calculations.
The experimental data were obtained for a new family of propylene random copolymers with 1-pentene as a comonomer. The results
of measurements include flow curves, viscoelastic properties, creep curves and rubbery elasticity of copolymer melts.
Different relaxation spectra were calculated using independent methods based on different ideas. It lead to various distributions
of relaxation times and their “weights”. However, all of them correctly describe the frequency dependencies of dynamic modulus.
Besides, calculated spectra were used for finding integral characteristics of viscoelastic behaviour of a material (Newtonian
viscosity, the normal stress coefficient, steady-state compliance). In this sense all approaches are equivalent, though it
appears impossible to estimate instantaneous modulus.
The most crucial arguments in estimating the results of different approaches is calculating the other viscoelastic function
and predicting behaviour of a material in various deformation modes. It is the relaxation and creep functions. The results
of relaxation curve calculations show that all methods used give rather similar results in the central part of the curves,
but the relaxation curves begin to diverge when approaching the high-time (low-frequency) boundary of the relaxation curves.
The distributions of retardation times calculated through different approaches also appear very different. Meanwhile, predictions
of the creep curves based on these different retardation spectra are rather close to each other and coincide with the experimental
points in the wide time range. Relatively slight divergences are observed close to the upper boundary of the experimental
window.
All these results support the conclusion about a rather free choice of the relaxation time spectrum in fitting experimental
data and predicting viscoelastic behaviour of a material in different deformation modes.
Received: 15 March 2000 Accepted: 18 September 2000 相似文献
53.
By the method of the optical spectrsocopy of diffuse reflection in the region 0.5–5.0 eV, accelerated aging of pigment compositions
with synthetic materials used in restoration of paint layers of paintings is investigated. Composition containing pigments
zinc and titanium oxides (white pigments), chromium oxide and copper carbonate (green pigments), and iron oxide (brown pigment)
and reinforcing materials vinyl acetate-ethylene copolymer, fluorolon F-42L, and polyvinyl alcohol are investigated. It is
established that the appearance of color in pigment impregnation and subsequent heating is observed only in the compositions
of reinforcing materials with white pigments and occurs as a result of heterogeneous reactions that lead to the formation
in the pigment of color centers bonded by oxygen vacancies.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 4, pp. 518–522, July–August, 1997. 相似文献
54.
V. F. Tarasov G. S. Shakurov B. Z. Malkin A. I. Iskhakova J. Heber M. Altwein 《JETP Letters》1997,65(7):559-565
The ESR spectra of single and pair impurity centers of thulium and holmium ions in CsCdBr3:Tm3+ and CsCdBr3:Ho3+ crystals are measured in the frequency range 160-400 GHz. Analysis of the characteristic features of the hyperfine structure
of the ESR lines and analysis of the variations in the spectra as a function of the temperature and external magnetic field
shows that the Ln3+ ions substitute for Cd2+ ions and predominantly form symmetric pair centers of the type Ln3+-(vacancy at a neighboring Cd2+ site)-Ln3+. The ESR spectra of CsCdBr3: Ln3+ crystals are used to make a positive identification of the optical spectra of selective laser excitation.
Pis’ma Zh. éksp. Teor. Fiz. 65, No. 7, 535–540 (10 April 1997) 相似文献
55.
The temperature dependence of the spin-lattice relaxation time corresponding to the inelastic scattering of phonons by the73Ge quadrupole moment in Ge single crystals is calculated in the framework of the adiabatic bond charge model. The results obtained agree with the experimental data. 相似文献
56.
T. B. Krasieva Ya. N. Malkin V. A. Lokshin S. V. Mel'nichuk S. A. Tikhomirov V. A. Kuz'min 《Russian Chemical Bulletin》1989,38(11):2297-2302
It has been shown on the basis of determinations of the values of the quantum yields of the photocoloration of spiropyrans of the 1,3-dithiolane and benzo1,3-dithiolane series that the annelation of a benzene ring in the chromene part of the molecule results in an increase in the efficiency of photocoloration and an increase in the stability of the merocyanine forms of the compounds investigated.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2504–2510, November, 1989. 相似文献
57.
58.
We study preprojective algebras of graphs and their relationship to module categories over representations of quantum SL(2). As an application, ADE quiver varieties of Nakajima are shown to be subvarieties of the variety of representations of a certain associative algebra introduced by Lusztig. 相似文献
59.
A quantitative method of determining the quantum yield of irreversible photodegradation (C) of photochromic spiropyrans (SPP) was proposed for the first time. The C of a large number of SPP of different types (with a different heterocyclic part) were determined. It was shown that for all of the SPP studied (except for dithiolane SPP), C is almost independent of the heterocyclic part and is determined by the structure of the chromene part of the SPP. In addition to photodegradation, photooxidation takes place as a result of the reaction of the triplet state of the closed form of the SPP with O2 for nitrosubstituted SPP of all types. The value of C is determined by the efficiency of the reaction of isomer X of the colored form with the solvent or impurities, i.e., the lifetime of this isomer.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 290–298, February, 1990. 相似文献
60.
E. A. Pavlyuchkova A. Ya. Malkin S. V. Kotomin E. I. Frenkin I. D. Simonov-Emelyanov 《Polymer Science Series A》2018,60(4):515-522
The rheological properties of the acrylonitrile–styrene copolymer modified with hydrophobized montmorillonite Cloisite 30B and composites are studied in a wide range of shear rates and shear frequencies at a temperature of 230°C. It is shown that the filler insignificantly affects the viscoelastic properties of the compositions, but the viscosity of composite melts considerably increases at low shear rates and monotonically grows with increasing concentration, whereas at high shear rates the effective viscosity declines appreciably in the concentration range of about 0.3 vol %. 相似文献