Rayleigh decay

Several authors(22 30) have contributed to developing the formalism with which the effects of an interface on a dipole inside or near a particle can be treated. In the Rayleigh regime (/ > a), Gersten and Nitzan have made several contributions to the theory of molecular decay rates and energy transfer/22 24) Kerker et alP solved the boundary value problem for a dipole and a spherical particle of arbitrary size, and NcNulty et al.,(26) Ruppin,(27) Chew,(28) and Druger and co-workers(29,30) have used the solution to solve some of the problems of interest. 

As shown by TalkneP there is a direct connection between the Rayleigh quotient method and the reactive flux method. Two conditions must be met. The first is that phase space regions of products must be absorbing. In different terms, the trial function must decay to zero in the products region. The second condition is that the reduced barrier height pyl" 1. As already mentioned above, differences between the two methods will be of the order e P. ... 

Figure 6.2(a), which was calculated using the results to be derived here, shows the amplitudes of the longitudinal and shear components of a Rayleigh wave in fused silica, and their exponential decay below the surface. 

Thus, at negative defocus, the amplitude of the Rayleigh ray will vary as exp —2z(ao sec0R — aRtan0R). If the Rayleigh contribution to V(z) is smaller than the geometrical contribution, the amplitude of the oscillations in V(z) will follow the same exponential decay. 

Anyone who has successfully used a microscope to image properties to which it is sensitive will sooner or later find himself wanting to be able to measure those properties with the spatial resolution which that microscope affords. Since an acoustic microscope images the elastic properties of a specimen, it must be possible to use it to measure elastic properties both as a measurement technique in its own right and also in order to interpret quantitatively the contrast in images. It emerged from contrast theory that the form of V(z) could be calculated from the reflectance function of a specimen, and also that the periodicity and decay of oscillations in V(z) can be directly related to the velocity and attenuation of Rayleigh waves. Both of these observations can be inverted in order to deduce elastic properties from measured V(z). 

Hence, by measuring the period of the Rayleigh oscillations, the Rayleigh velocity may be deduced directly. Likewise, the exponential decay of the Rayleigh oscillations is often of the form (Kushibiki et al. 1982)... 

The exponential term can be thought of as a Green function, with the time dependence always implicit. Thus an excitation at x causes a response at x whose phase is delayed by the distance between them multiplied by the real part of kp (this corresponds approximately to 2 /Ar), and whose amplitude is decreased exponentially by the distance between them multiplied by the imaginary part of kp (this corresponds to the decay associated with the propagation of the leaky Rayleigh wave). The magnitude x — x is used because... 

A particular conclusion from this theoretical analysis is that, if a crack has faces that are separated by a thin layer of fluid, so that normal components of traction and displacement are transmitted across the crack but the faces are free with regard to shear components of traction and displacement, then there will be a scattered wave however thin the fluid layer is. This is perhaps not surprising. A Rayleigh wave can exist only because solids can support both longitudinal and shear waves, and the greater part of the displacement in a Rayleigh wave is shear in character ( 6.3). Of course, liquids can support shear stress over a short distance. In a liquid of viscosity r/, and density po, at a frequency o) the amplitude of a shear wave decays by a factor e over a distance... 

Band, A Period of measurement Maximum integrated intensity, Rayleighs Altitude of emission Approximate decay rate, sec-1 Type of measurement Reference... 

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