Local modes validity

Using the expressions derived above, we can give qualitative criteria for the validity of local-mode solutions on a nonuniform fiber with refractive-index profile n x,y,z). Over distance z, the change in profile varies as (d /dz)Zb, whence we deduce from Eqs. (19-3) and (19-4) that the slowness criteria are... 

The picture of almost harmonic excitonically coupled states is particularly appropriate in the localization or weak coupling limit. This limit will be valid in smaller peptides that do not have the rather strict symmetries of helices or sheets. It is very likely that the vibrational frequencies of each amide unit will be different even in the absence of any coupling. An example of this limit is found in the pentapeptide discussed below. If the frequency separations between the uncoupled modes are large compared with the individual coupling terms, IAj/( i — ej)l < E the coupled states... 

Local vibration mode dichroism makes anisotropic (110) por-Si a unique object for the assignment of vibration bands to the corresponding surface modes of porous silicon. The simultaneous examination of deformation and stretching bands makes it possible to validate the existence of H-terminated dimers in por-Si and, moreover, to state the growth of dimers amount after thermal annealing. 

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