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141.
We compute the asymptotic wave profiles for the exterior problemin elasticity with homogeneous Neumann condition. We give preciseresults on the asymptotic distribution of the elastic energyin various subsets of space. These results are obtained viathe use of a recently developed extension of the scatteringtheory of C. Wilcox (Mabrouk & Helali, 2002). 相似文献
142.
A new group (linear) representation of the propagation of waves in properly and naturally gyrotropic crystals in the general case where the nonreciprocity effect takes place has been developed. Simple expressions of the dependence of ray (group) velocities and polarization vectors of isonormal waves on the complex vector of principal velocities dual to the unitary tensor by which the optical properties of crystals are directly characterized have been obtained. The relationship between gyrotropy and anisotropy and the dipole moment and displacement current induced by the radiation in the crystal has been established. It is shown that the presence of gyrotropy and nonlinear polarization of radiation together with the elimination of conical points entails a phase ambiguity of the ray velocity of the quantummechanical type and a smearing and layering of the wave surface, as well as a discreteness of the spectrum of velocity values of isonormal waves. 相似文献
143.
An important material property in the paper industry is the anisotropic stiffness distribution due to the fibrous microstructure of paper and to processing procedures. Ultrasonic methods offer a means of determining the stiffness of sheets of paper from the anisotropic propagation characteristics of elastic Lamb waves along the machine direction and the cross direction. That is, along and perpendicular to the direction of paper production. Currently, piezoelectric ultrasonic methods are employed in the industry to measure the elastic polar diagram of paper through multiple contacting measurements made in all directions. This paper describes a new approach utilizing the INEEL Laser Ultrasonic Camera to provide a complete image of the elastic waves traveling in all directions in the plane of the paper sheet. This approach is based on optical dynamic holographic methods that record the out of plane ultrasonic motion over the entire paper surface simultaneously without scanning. The full-field imaging technique offers great potential for increasing the speed of the measurement and it ultimately provides a substantial amount of information concerning local property variations and flaws in the paper. This report shows the success of the method and the manner in which it yields the elastic polar diagram for the paper from the dispersive flexural or antisymmetric Lamb wave. 相似文献
144.
B. Lehnert 《Foundations of Physics Letters》2002,15(1):95-101
An extended electromagnetic theory has earlier been developed, as being based on the hypothesis of a nonzero electric field divergence in vacuo and the requirement of Lorentz invariance. This basis is supported by the commonly accepted fact that the vacuum is not merely an empty space, but has a ground state of nonzero energy and can become electrically polarized. The vacuum is thereby considered as electrically polarizable in the sense of being capable of supporting charge motion in the form of, e.g., space-charge waves. One result of the dynamic states of the present theory is the prediction of a purely longitudinal electric space-charge wave (S-wave) having no induced magnetic field. The behaviour of this wave type is demonstrated for a number of geometrical configurations. Some preliminary proposals are finally made for generation and detection of S waves. These waves are expected to have features which differ from those of the conventional transverse electromagnetic waves. If the S wave would come out to be physically realizable, it may thus form the basis of a new principle for telecommunication without or with very small magnetic induction effects. 相似文献
145.
高速扫描相机时间测量不确定度分析 总被引:21,自引:6,他引:15
以国内普遍使用的SJZ-30型高速扫描相机为例,用精测转速方法的结果处理数据,转速测量相对合成不确定度小于0.1%,时间间隔测量的相对扩展不确定度为0.2%.扫描速度在像面上的位置误差,采用"中值扫描速度",可予以校正.同时讨论了进一步降低转速测量不确定度和位置误差的方法. 相似文献
146.
E. Lazzaro R. Coelho 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,19(1):97-101
A major limit to steady state and advanced high operation of tokamaks of reactor class is due to the onset of tearing modes that develop magnetic and may cause loss of energy confinement or a major disruption. Here the structure of a classical problem
about the effects of external control helical fields is analysed and it is shown to offer a general paradigm of response of
low order classical and neoclassical tearing modes to a wide class of external perturbations. New results of principle on
the structural stability of the response model are obtained, leading to a clear interpretation of the role of “seed islands"
in the onset of neo-classical tearing modes and the role of finite ion larmor radius corrections to Ohm's law.
Received 12 November 2001 and Received in final form 4 January 2002 相似文献
147.
A new nonlinear three-wave equation of the sixth order for pressure in a polydisperse gas-liquid mixture with bubbles of two
sizes is obtained, and its stationary solutions are analyzed. The equation includes two nonlinear quadratic terms of different
derivative orders. These terms are of fundamental importance for obtaining good correspondence between the solutions to this
equation and the experimentally observed solitary waves in the form of two coupled solitons. 相似文献
148.
The propagation of acoustic disturbances in a porous medium crossed by numerous cracks (double porosity medium) is a complex problem that we here simplify by investigating the acoustics of a permeable channel. We consider a fluidfilled channel in two possible geometries, a slit or a cylindric pipe. The channel is surrounded by a porous medium (saturated with the same fluid) and is itself surrounded by an external medium. To simulate the average properties of the cracked rock, the external medium is either nonpermeable (few connections between cracks) or highly permeable (numerous connections). We present analytical and numerical results concerning acoustic disturbances of small amplitude generated in the channel, such as harmonic waves, step disturbanses and pulses. 相似文献
149.
C. Djurberg K. Jonason P. Nordblad 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(1):15-21
Experiments on the temperature and time dependence of the response function and the field cooled magnetisation of a Cu(Mn)
spin glass at temperatures below the zero field spin glass temperature are used to explore the non-equilibrium nature of the
underlying spin configuration. The results imply that a certain spin configuration is imprinted on the system as the temperature
is decreased at a constant cooling rate. The cooling rate governs the magnitude of the FC magnetisation ((H,T)). Any intermittent halt at a constant temperature, , imprints an extended spin configuration, a process that is reflected e.g. in a downward relaxation of . On continued cooling at the same rate, the magnitude of (T) remains at a lower level than that of a continuous cooling curve. These results are put into the context of the corresponding
behaviour of the response function as observed in measurements of the relaxation of the zero field cooled magnetisation.
Received 27 October 1998 and Received in final form 30 November 1998 相似文献
150.
Fuyong Xu Bin You Yue-e Li Keyu Zhao 《International Journal of Infrared and Millimeter Waves》2002,23(10):1545-1556
The modes TE and TM of arbitrarily trapezoidal-groove guide are analyzed by using the mode-matching method. The mode TE11 is the dominant mode of the trapezoidal-groove guide under different conditions. The bandwidth characteristic and the operation condition for the single dominant mode are discussed. The obtained conclusions are of very important significance in theoretical study and practical application of trapeziodal-groove guides for millimeter waves. 相似文献