Based on the experimental work by Boscaino et al on the EPR transient nutations (TNs) and free induction decay (FID) in solids, we propose the modified Bloch equations (MBEs). In addition to the Tomita expression for power-dependent parameter T2u, we give an original phenomenological expression for power-dependent parameter T2v and tuning Δ. Both analytical (in the form of a Torrey solution with these parameters) and numerical solutions of MBE are obtained for TN and for different FID regimes with very good agreement between theory and experiment. We also discuss the meaning and role of the instantaneous diffusion mechanism in the transient pulse experiments.

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On the grounds of Bloch equations modified by taking into account the power dependence of the dispersion and damping parameters, we give general expressions for hole shapes burnt in the absorption and polarization spectra of the two-level systems. The general expressions are used for detailed numerical calculations of the hole shapes and hole widths in a concrete paramagnetic system (quartz with [AlO4]0 centres). This system earlier was studied experimentally and theoretically through the transient nutation and free induction decay methods. The results on the hole width in our modified-Bloch-equations model are in good qualitative agreement with the FID data.

A theoretical description is given for nonlinear formation mechanisms and properties of the polarization echoes in piezoelectric powders, earlier experimentally investigated in both the radiofrequency (rf) and the microwave (mw) frequency domains. For rf echoes, a phenomenological model is elaborated for dynamics of dislocations in mechanically vibrating piezoelectric particles resonantly excited by short-duration pulses of rf electric field. The model includes both the reversible and irreversible moving groups of dislocations generated by Frank - Read sources. The amplitude-dependent frequency change and amplitude-dependent damping obtained by use of this model constitute two of the three nonlinear mechanisms responsible for the formation of the polarization echoes in piezoelectric powders with the signals naturally consisting of both the dynamic and the memory components. As a third type of nonlinearity, the field - mode interaction, we take the nonlinear electrostriction. For mw echoes, it is proposed that the lack of memory components in the echoes is a consequence of absence of mobile dislocations in the powder material used. We suggest a somewhat modified form of the nonlinear mechanisms related to the pure lattice anharmonicity: amplitude-dependent dispersion and damping. General expressions for two-pulse rf echoes and mw echoes are derived by using together all three types of nonlinear mechanism inherent in each frequency domain. The numerical analysis of these expressions as a function of the pulse amplitudes, the pulse widths and the pulse separation shows good agreement between the theory and the existing experiments in a broad range of amplitudes and widths of the pulses. As a result, several important material constants relevant to the nonlinear mechanisms in (rf domain) and in ZnO (mw domain) are estimated.

The possibility of using a gas discharge plasma for sterilization of freeze-drying products directly in the process of their vacuum packaging for long-term storage is considered. An alternating current electrical discharge was used as a source of sterilizing action. In order to increase the homogeneity of the processing of the products, sound waves were applied to the electrical discharge. The effect of acoustic effects was investigated in the pressure range from 10 to 100 Torr, and the sound frequency from 50 to 400 Hz. A noticeable effect of sound waves on the discharge behavior was identified and optimal conditions were determined for increasing the uniformity of the sterilizing effect on the processed products.