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111.
Constitutive modeling of cyclic relaxation and ratcheting (cumulative inelastic deformation) is developed on the basis of the distributed-element model (DEM). Although the original DEM is capable of describing general, elastic–plastic behavior for cyclically stabilized materials, it has the inadequacy of not being able to account for the effect of cyclic relaxation and ratcheting. By introducing the nonlinear kinematic hardening rule proposed by Armstrong and Frederick into element behavior of the DEM, the model becomes effective in characterizing the behavior of cyclic relaxation and ratcheting. Validation of the modified DEM is conducted by simulating cyclic behavior of various metal materials, including CS 1018, heat-treated rail steel, and Grade 60 steel. The results show that the modified DEM demonstrates realistic behavior of materials in both uniaxial and biaxial cyclic relaxation and ratcheting. Furthermore, detailed investigation of element behavior in the model provides us with additional insight into complex behavior and characteristics of materials in cyclic relaxation and ratcheting. 相似文献
112.
Chih-Wei Chiang Subrata Kumar Das 《Journal of Quantitative Spectroscopy & Radiative Transfer》2008,109(7):1187-1195
The aerosol optical thickness (AOT) is an important parameter for understanding the radiative impact of aerosols. AOT based on lidar measurements is often limited by its finite detection range. In this paper, we have reported a method of fitting and iterative calculation to derive the extinction profile of background aerosols from 0 to 30 km at 532 nm, which is virtually the AOT of the entire atmosphere. The mean extinction derived from this method at the ground level tallies with visibility measurement and it is also consistent with the sun-photometer data, within experimental error. These data have been further treated to study the dust cases. For most of the cases, transmission losses were determined to estimate the extinction as well as lidar ratio. The result of the analysis shows that for background aerosols, a mean lidar ratio of 47±15 sr was found. For dust layers, a mean lidar ratio of 44±19 sr and an optical thickness of 0.53±0.49 were determined at 532 nm. 相似文献
113.
The replacement of organometallic rhenium species (e.g., CH(3)ReO(3)) by less expensive and more readily available inorganic rhenium oxides (e.g., Re(2)O(7), ReO(3)(OH), and ReO(3)) can be accomplished using bis(trimethylsilyl) peroxide (BTSP) as oxidant in place of aqueous H(2)O(2). Using a catalytic amount of a proton source, controlled release of hydrogen peroxide helps preserve sensitive peroxorhenium species and enables catalytic turnover to take place. Systematic investigation of the oxorhenium catalyst precursors, substrate scope, and effects of various additives on olefin epoxidation with BTSP are reported in this contribution. 相似文献
114.
115.
Hau‐Chun Chiang Chia‐Hong Liu Raymond Chien‐Chao Tsiang 《Journal of polymer science. Part A, Polymer chemistry》2008,46(24):8149-8158
An acrylic–silica hybrid polymeric nanocomposite, comprising well‐distributed silica nanoparticles in acrylic matrix, has been synthesized at a markedly rapid rate from a dendritic acrylic oligomer (DAO) and an acrylic‐functionalized silica (A‐silica) via UV‐curing. A‐silica was made by functioning colloidal silica nanoparticles with 3‐methacryloxypropyltrimethoxysilane (MATMS) and DAO was formed by reacting 1,5‐diamino‐2‐methylpentane (MPMDA) with trimethylopropane triacrylate (TMPTA). The MATMS has been found either doubly or singly bonded to silica nanoparticles but not triply bonded, and the inclusion of MATMS into the siloxane network structure increases the size of silica nanoparticles. The well distribution of A‐silica and its good compatibility with DAO cause an increase in Td of the acrylic–silica hybrid material. Silica nanoparticles are too small to cause any significant light scattering, and do not have deleterious effects on transparency. The “hybrid‐on‐polyethylene terephathalate” films exhibited satisfactory hardness and surface roughness because of silica nanoparticles. The preparation as well as the characterization of the constituting species and the final hybrid material are described in detail. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 8149–8158, 2008 相似文献
116.
Efficiency decomposition in two-stage data envelopment analysis: An application to non-life insurance companies in Taiwan 总被引:1,自引:0,他引:1
The efficiency of decision processes which can be divided into two stages has been measured for the whole process as well as for each stage independently by using the conventional data envelopment analysis (DEA) methodology in order to identify the causes of inefficiency. This paper modifies the conventional DEA model by taking into account the series relationship of the two sub-processes within the whole process. Under this framework, the efficiency of the whole process can be decomposed into the product of the efficiencies of the two sub-processes. In addition to this sound mathematical property, the case of Taiwanese non-life insurance companies shows that some unusual results which have appeared in the independent model do not exist in the relational model. In other words, the relational model developed in this paper is more reliable in measuring the efficiencies and consequently is capable of identifying the causes of inefficiency more accurately. Based on the structure of the model, the idea of efficiency decomposition can be extended to systems composed of multiple stages connected in series. 相似文献
117.
S.Y. Frankie Mak Gary C.H. Chiang James E.P. Davidson John E. Davies Andrew Ayscough Gilles Pain Jonathan W. Burton Andrew B. Holmes 《Tetrahedron: Asymmetry》2009,20(6-8):921-944
The enantioselective synthesis of a number of simplified analogues of the cytotoxic natural product eleutherobin is reported. 相似文献
118.
Upon irradiation with 300-nm UV light, the photolysis of diazomalonates in benzene unexpectedly affords 2,6-dicarboxylate bicyclo[3.2.0]hepta-2,6-dienes in low yields. These products are proven to be derived from cyclohepta-1,3,5-triene intermediates presumably via a tandem 1,5-carboxylate migration/[2+2] cycloaddition sequence. 相似文献
119.
Chiang C. Mei 《Transport in Porous Media》1992,9(3):261-274
The theory of homogenization which is a rigorous method of averaging by multiple scale expansions, is applied here to the transport of a solute in a porous medium. The main assumption is that the matrix has a periodic pore structure on the local scale. Starting from the pores with the Navier-Stokes equations for the fluid motion and the usual convective-diffusion equation for the solute, we give an alternative derivation of the three-dimensional macroscale dispersion tensor for solute concentration. The original result was first found by Brenner by extending Brownian motion theory. The method of homogenization is an expedient approach based on conventional continuum equations and the technique of multiple-scale expansions, and can be extended to more complex media involving three or more contrasting scales with periodicity in every but the largest scale. 相似文献
120.
Two new cobalt phosphites, (H3NC6H4NH3)Co(HPO3)2 (1) and (NH4)2Co2(HPO3)3 (2), have been synthesized and characterized by single-crystal X-ray diffraction. All the cobalt atoms of 1 are in tetrahedral CoO4 coordination. The structure of 1 comprises twisted square chains of four-rings, which contain alternating vertex-shared CoO4 tetrahedra and HPO3 groups. These chains are interlinked with trans-1,4-diaminocyclohexane cations by hydrogen bonds. The 2-D structure of 2 comprises anionic complex sheets with ammonium cations present between them. An anionic complex sheet contains three-deck phosphite units, which are interconnected by Co2O9 to form complex layers. Magnetic susceptibility measurements of 1 and 2 showed that they have a weak antiferromagnetic interaction. 相似文献