Analytical theory, spectral calculations

It would be important to find analogous mechanism also for description of the main (librational) absorption band in water. After that it would be interesting to calculate for such molecular structures the spectral junction complex dielectric permittivity in terms of the ACF method. If this attempt will be successful, a new level of a nonheuristic molecular modeling of water and, generally, of aqueous media could be accomplished. We hope to convincingly demonstrate in the future that even a drastically simplified local-order structure of water could constitute a basis for a satisfactory description of the wideband spectra of water in terms of an analytical theory. 

A general approach (VIG, GT) to a linear-response analytical theory, which is used in our work, is viewed briefly in Section V.B. In Section V.C we consider the main features of the hat-curved model and present the formulae for its dipolar autocorrelator—that is, for the spectral function (SF) L(z). (Until Section V.E we avoid details of the derivation of this spectral function L). Being combined with the formulas, given in Section V.B, this correlator enables us to calculate the wideband spectra in liquids of interest. In Section V.D our theory is applied to polar fluids and the results obtained will be summarized and discussed. 

Chapter 3 is devoted to dipole dispersion laws for collective excitations on various planar lattices. For several orientationally inequivalent molecules in the unit cell of a two-dimensional lattice, a corresponding number of colective excitation bands arise and hence Davydov-split spectral lines are observed. Constructing the theory for these phenomena, we exemplify it by simple chain-like orientational structures on planar lattices and by the system CO2/NaCl(100). The latter is characterized by Davydov-split asymmetric stretching vibrations and two bending modes. An analytical theoretical analysis of vibrational frequencies and integrated absorptions for six spectral lines observed in the spectrum of this system provides an excellent agreement between calculated and measured data. 

Resistance functions have been evaluated in numerical compu-tations15831 for low Reynolds number flows past spherical particles, droplets and bubbles in cylindrical tubes. The undisturbed fluid may be at rest or subject to a pressure-driven flow. A spectral boundary element method was employed to calculate the resistance force for torque-free bodies in three cases (a) rigid solids, (b) fluid droplets with viscosity ratio of unity, and (c) bubbles with viscosity ratio of zero. A lubrication theory was developed to predict the limiting resistance of bodies near contact with the cylinder walls. Compact algebraic expressions were derived to accurately represent the numerical data over the entire range of particle positions in a tube for all particle diameters ranging from nearly zero up to almost the tube diameter. The resistance functions formulated are consistent with known analytical results and are presented in a form suitable for further studies of particle migration in cylindrical vessels. 

We have presented a method to calculate the mean frequency and effective diffusion coefficient of the numbers of cycles(events) in periodically driven renewal processes. Based on these two quantities one can evaluate the number of locked cycles in order to quantify stochastic synchronization. Applied to a discrete model of bistable dynamics the theory can be evaluated analytically. The system shows only 1 1 synchronization, however in contrast to spectral based stochastic resonance measures the mean number of locked cycles has a maximum at an optimal driving frequency, i.e. the system shows bona fide resonance [6]. For the discrete model of... 

The function G(t) depends on the system under study but also on the characteristics of the fluctuating physical quantity which is considered. The choice of a correct analytical form for the G(t) function is still a very difficult task. Redfield s comment on this problem (7, p. 28) remains correct, more than 15 years later, when he said that the calculation of spectral densities or correlation functions is "the most difficult problem in any relaxation theory."... 

Exact calculations of the retarded van der Waals force are usually carried out numerically using the full Lifshitz theory in combination with spectral data of the materials. For some special geometries as sphere-sphere interaction, better analytical approximations for Rm than Eq. (2.78) have been developed. For discussion of these approximations, see Ref [89]. 

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