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排序方式: 共有481条查询结果,搜索用时 15 毫秒
1.
Alexandre Chmel Alexy Krivda Ekatherina Mazurina Victor Shashkin Valery Zhizhenkov 《Journal of the American Ceramic Society》1993,76(6):1563-1567
The gel-to-glass transition in SiO2 xerogels prepared by inorganic sol-gel synthesis was studied. The evolution of the molecular structure is traced using the infrared and lowfrequency Raman spectroscopy methods. The elastic moduli of the samples as well as the pore wall moduli at various stages of heat treatment are determined from the data on Brillouin scattering. The formation of monolithic glass on the macroscopic level manifests itself within a narrow temperature range by the dramatic increase of Young's modulus to the accepted value for fused silica. This phenomenon coincides with structural transformations on the molecular scale: (i) the definite correlation radius (the long-range order sphere) appears; (ii) local distortions of the silica network relax. The presence of structural defects influences the kinetics of vitreous SiO2 formation during xerogel heat treatment. 相似文献
2.
The reactivity of O-, T- and R-phases of the high pressure-high temperature (HPHT) polymerized C60 towards gaseous fluorine in the temperature range of 50-250 °C was investigated. The reaction products were characterized by FTIR, powder X-ray diffraction, SEM, EDX, and VTP-EIMS to determine the bulk stoichiometries, bonding patterns, phase compositions, crystalline structures and thermal decomposition behavior of the fluorinated polymers. At 1 h isothermal treatment duration, fluorinated products with various bulk stoichiometries were obtained from different polymer phases with the R-phase showing the highest fluorine uptake. At 250 °C, all C60 polymers showed partial decomposition to unfluorinated C60 monomer under fluorine atmosphere. At 200 °C, the fluorination of R-phase yielded a pure fluoropolymer most likely having a {C60Fx}n (x = 36-44) composition. The same fluoropolymer was presumably obtained from O- and T-phases in lower yields. The linear chain structure was suggested for this new fluorocarbon polymer in agreement with the molecular mechanics modeling calculations. 相似文献
3.
Pavel P. Fedorov Alexander A. Alexandrov Valery V. Voronov Mariya N. Mayakova Alexander E. Baranchikov Vladimir K. Ivanov 《Journal of the American Ceramic Society》2021,104(6):2836-2848
Phase formation in the SrF2–LaF3 system was studied at temperatures ranging from 300°C to 450°C using nitrate flux. The solubility of LaF3 in SrF2 decreases with decreasing temperature. The equilibrium width of the solid solution region Sr1−xLaxF2+x at 400°C, it is 44.6 ± 0.4 mol% LaF3 (x = 0.446), at 350°C — 38.3 ± 0.7 mol% LaF3 (x = 0.383), and decreases almost to zero at 300°C. 相似文献
4.
In this paper we study the single machine common due date assignment and scheduling problem with the possibility to perform a rate-modifying activity (RMA) for changing the processing times of the jobs following this activity. The objective is to minimize the total weighted sum of earliness, tardiness and due date costs. Placing the RMA to some position in the schedule can decrease the objective function value. Several properties of the problem are considered which in some cases can reduce the complexity of the solution algorithm. 相似文献
5.
The theory of adiabatic invariants has a long history, and very important implications and applications in many different
branches of physics, classically and quantally, but is rarely founded on rigorous results. Here we treat the general time-dependent
one-dimensional harmonic oscillator, whose Newton equation q + ω2(t)q = 0 cannot be solved in general. We follow the time-evolution of an initial ensemble of phase points with sharply defined
energy Eo at time t = 0 and calculate rigorously the distribution of energy E1 after time t = T, which is fully (all moments, including the variance μ2) determined by the first moment Ē1. For example, μ2 = E2o[(Ē1/Eo)2 — (ω(T)/ω(0))2]/2, and all higher even moments are powers of μ2, whilst the odd ones vanish identically. This distribution function does not depend on any further details of the function
ω(t) and is in this sense universal. In ideal adiabaticity Ē1 = ω(T)Eo/ω(0), and the variance μ,2 is zero, whilst for finite T we calculate Ē1, and μ2 for the general case using exact WKB-theory to all orders. We prove that if ω(t)is of class
m (all derivatives up to and including the order m are continuous) μ, ∝ T−(m + 1)) whilst for the class
°° it is known to be exponential μ ∝ exp(—aT). 相似文献
6.
The authors present the results of analysis of material composition and experimental investigations of acid and biohydrometallurgical leaching of middlings on grain size, pH level, leaching process duration, temperature and slurry density. The rational parameters of flotation and acid-bacterial leaching of middlings providing an efficient release of valuable components from mineral complexes and recovery to flotation concentrate and leaching solution have been determined. A combined flowsheet and a beneficiation process for bulk flotation middlings of copper–molybdenum ore have been suggested, which include middlings grinding, sulfide minerals flotation, bacterial leaching of sulfide flotation tailings, liquid-phase extraction of dissolved copper and electrolysis of re-extraction eluates. The suggested combined method of cleaning of middlings of copper–molybdenum ores beneficiation provides the total copper recovery increase by 0.8% with a reduction of the cost price of saleable material by 0.5%. 相似文献
7.
8.
A new analytical approach for’ micromechanical modeling of the effective viscoelastic behavior of a’ composite material is
presented. Fractionexponential operators are. used to describe the viscoelastic properties of the constituents. To construct
the corresponding elastic solution, effective field method is used. Effective viscoelastic operators are obtained from the
Volter ra’s elasticity-viscoelasticity correspondence principle. Incompatible deformation that often occurs during the manufacturiig
process is taken intp account. All the formulas are obtained in explicit ready-to-use form. 相似文献
9.
The article is concerned with the analysis of panel flutter of heated circular clamped cylindrical shells made of functionally graded (FG) material, which are subject to a simultaneous action of the external supersonic gas flow and the internal flow of ideal compressible fluid. The effective properties of the material change throughout the thickness of the shell according to a power law and depend on temperature. The aerodynamic pressure is calculated based on the quasi-static aerodynamic theory. The behavior of the fluid is described in the framework of the potential theory. A mathematical formulation of the dynamic problem for elastic structure is developed based on the classical theory of shells and the principle of virtual displacements. Based on the results of numerical simulation the influence of different consistencies of the examined FG materials, thermal load, and internal flow velocity on the boundary of aeroelastic stability is analyzed. 相似文献
10.
Valery V. Val’kov Anton O. Zlotnikov 《Journal of Superconductivity and Novel Magnetism》2013,26(9):2885-2886
An interference of heavy-fermion superconductivity (SC) and antiferromagnetism (AFM) has been studied in the framework of the periodic Anderson model with the superexchange interaction between localized electrons. It has been shown that pressure-induced energy change of the localized states leads to modifying antiferromagnetic and superconducting order parameters. Conditions have been found for the coexistence of SC and AFM in the model. Theoretical results of the pressure effects on the ground state character of the heavy-fermion systems are in good agreement with experimental data for a rare-earth intermetallic compound CeRhIn5. The divergence of the effective electron mass produced by suppressing the long-range antiferromagnetic order has also been analyzed in the same framework. 相似文献