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91.
Micromechanical consideration of tensile crack behavior based on virtual internal bond in contrast to cohesive stress 总被引:8,自引:0,他引:8
A modified version of the virtual internal bond model (VIB) is presented. This involves the introduction of a R-bond restricting the relative rotation freedom of pairwise mass particle. Such a modification allows the VIB model to consider arbitrary values of the Poisson ratio. A linear elastic cohesive law considering both the R-bond and L-bond are assumed. The constitutive relationship is derived using the Cauchy–Born rules. The derived constitutive associates the bond stiffness with the Young’s modulus and Poisson ratio of materials. This gives the bond stiffness in terms of the Young’s modulus and Poisson ratio of materials.The modified VIB model is then used to analyze the tensile crack behavior. In contrast to the cohesive stress method, the deformation-governed concept will be used. The local materials failure is assumed to coincide with the reduction of the bond density due to the local deformation rather than by the local cohesive stress. A phenomenological relationship between the bond density and the deformation is established. The criterion which is applied to determined crack initiation and propagation is built into the constitutive model. As an example, the method is used to study the crack initiation and propagation behavior under tensile loading. 相似文献
92.
93.
Koichi Omori Hisayoshi Kojima Rajesh Kakani David H. Slavit Stanley M. Blaugrund 《Journal of voice》1997,11(1):40-47
This study investigates the relationship between rough voice and the presence of Subharmonics, which correspond to smaller yet distinct peaks located between two consecutive harmonic peaks in the power spectrum. Spectrum analysis was undertaken in 389 pathologic voices, of which 20 had subharmonics. Although all 20 voices had roughness perceptually, 8 had normal jitter and/or shimmer. The degree of roughness had a significant inverse relationship with the frequency of subharmonics. By digital signal processing, sound samples with various types of subharmonics were synthesized and perceptually analyzed. Power and frequency of subharmonics in the synthesized sound also had significant relationships with the degree of roughness. Rough voice is acoustically characterized not only by jitter and shimmer but also by the presence of subharmonics in the power spectrum. Subharmonics are important acoustic properties for objective evaluation of rough voices. 相似文献
94.
Propagation of sound and weak shock waves in gas-liquid foams is investigated theoretically and experimentally. An original
physical model is developed to describe the evolution of small perturbations in a foam of polyhedral structure. The model
developed takes into account both peculiarities of interface heat transfer in foam and liquid motion through the system of
Plateau-Gibbs borders which results in the appearance of an additional hydrodynamic dissipative force. The Rayleigh equation
analog, which takes into account the latter phenomenon, is obtained. Structure and dynamics of weak shock waves are investigated.
A vertical shock tube was constructed and used to measure the parameters of weak shock wave propagation in gas-liquid foams
of polyhedral structure. Spectral analysis of the data obtained shows that there are weak dispersion and strong dissipation
of the initial signal. Comparison of the evolution of experimental and theoretical profiles permits to conclude that the suggested
model allows to describe the peculiarities of acoustical perturbations in gas-liquid foam more precisely than it follows from
the standard models.
Received 15 September 1993 / Accepted 27 December 1993 相似文献
95.
This work presents a formulation based on UPML for truncating conductive media by using a local and non-orthogonal coordinate
system to solve Maxwell’s equations by the FDTD method. The detailed procedure for obtaining the UPML equations for this case
is shown and the complete equation set is provided. 相似文献
96.
I.IntroductionWhenastructurcvibratcs,itsvibratingsurfacewillmakesurroundingmediummovetogethcrwithit.Ifthernotionissofastthatthcmediumroundthestructureproduccaloca1contractionandcxpansionandthcypropagatefaraway,thesoundradiationisformed.Itispossiblctodcscribeanalytica11ytheradiationfic1dofsimplyandregularlyshapcdsourcessuchaspointsoundsourccs,spherica1soundsourccsandinflnite1engthllnearsoundsourccs,butitisa1mostimpossib1ctosolvetheradiationfiledbyanyanalyt-ica1methodforsourcesofvcrycomplicateds… 相似文献
97.
98.
ON INTERACTION OF SHOCK AND SOUND WAVE (I) 总被引:1,自引:1,他引:0
Chen Shuxing 《数学年刊B辑(英文版)》1996,17(1):35-42
This paper studies the interaction of shock and gradient wave (sound wave) of solutions to the system of inviscid isentropic gas dynamics as a model for the corresponding problems for nonlinear hyperbolic systems. The problem can be reduced to a boundary value problem in a wedged dormain, By using the method of constructing asymptotic solutions and Newton‘siteration process it is proved that if a weak shock hits a gradient wave, then the grandient wave will split into two gradient waves, while the shock continuses propagating. In this paper the author reduces the problem to a standard form and constructs asymptotic solution of the problem. The existence of the genuine solution will he given in the following paper. 相似文献
99.
Effect of sound wave stress on antioxidant enzyme activities and lipid peroxidation of Dendrobium candidum 总被引:1,自引:0,他引:1
Li B Wei J Wei X Tang K Liang Y Shu K Wang B 《Colloids and surfaces. B, Biointerfaces》2008,65(2):269-275
The effect of sound wave stress on important medicinal plant, Dendrobium candidum Wall. ex Lindl, was investigated, including the responses on malondialdehyde (MDA) content, the activities change of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) and ascorbate peroxidase (APX). Results were found that the activities of SOD, CAT, POD and APX enhanced totally in different organs of D. candidum, as leaves, stems and roots, in response to the stress. Furthermore there happened similar shift of antioxidant enzymes activities, which increased in the initial stimulation and decreased afterwards. Data showed SOD, CAT, POD and APX activities ascended to max at day 9, 6, 9 and 12 in leaves, at day 9, 6, 12 and 9 in stems, and at day 12, 6, 9 and 9 in roots, respectively. As a lipid peroxidation parameter, MDA content in different organs increased in the beginning, dropped afterward, and increased again in the late. Anyway the total trend was the rise of MDA level compared to the control. It was interesting that the MDA content appeared the lowest levels almost when the antioxidant enzymes activities were up to the highest. Our results demonstrated the different organs of D. candidum might produce accumulation of active oxygen species (AOS) under initial treatment of sound wave stress. Later AOS might start to reduce due to the enhancement of antioxidant enzymes activities treated by the stress. The data revealed that the antioxidant metabolism was to be important in determining the ability of plants to survive in sound stress, and the up regulation of these enzymes activities would help to reduce the build up of AOS, which could protect plant cells from oxidative damage. Moreover, different cell compartments might activate different defensive system to reduce excessive amount of AOS. Finally the mechanism of this action was also discussed simply. 相似文献
100.
Relative protonation energies in the primary, secondary and tertiary aliphatic series of amines are calculated by a semiempirical
method employing the virtual charge model. The method accounts quite well for the observed differences between the gas-phase
protonation affinities and the protonation enthalpies in solution, but when allowance is made for steric shielding from the
bulk solvent for “non-edge” atoms, some anomalies in the uncorrected model are removed. The calculated solute-solvent interactions
are related to experimental enthalpies of solution and to trends expected from the Born model. 相似文献