UDC 539.21We study the harmonic interaction in the nonlinear guiding layer located between two periodic layered structures. Analytical relations for the first-and second-harmonic amplitudes are obtained. It is shown that the nonlinear interaction coefficients become maximum at points where the Bragg resonance conditions are fulfilled for all structure layers of the studied waveguide including the guiding layer. The appreciable enhancement of the nonlinear interaction within the forbidden band described in experimental paper [1] is explained.

Artificial cardiac pacing is widely used nowadays for the treatment of disturbances of cardiac rhythm and conduction. In the industrially developed countries more than 700 implantations of artificlal cardiac pacemakers (ACP) per million of the population are done annually. The success rate of artificial pacing is high. Whereas previously half of all patient~ with AV block died within a year after the appearance of the first signs of the disease, nowadays the mortality among patients with implanted ACP is virtually the same as mortality amonl persons of the same age without any conduction disturbances.The method of artificial cardiac pacing for the treatment of ventricular asystole was first used clinically by Zoll in 1952 [20]. Successful implantations of the first ACP were first done in 1958 in Sweden and in 1962 in the USSR [5]. Since that time the method has spread widely and developed, and it is one of the principal methods of treatment of patients with bradycardias, and it is also beginning to be widely used for tachysystoles. The reason is that, despite great progress in the treatment of cardiac arrhythmias, the traditional methods of treatment do not alwaysgive the required effect in clinical practice. In addition, an extensive material is accumulating based on experience of the use of antiarrhythmic drugs, to show many adverse effects of this method of treatment with conduction disturbances and arrhythmias of the heart [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20].At the present time ACP to increase the heart rate are used in bradycardias due to the development of AV block or a sick sinus syndrome (SSS). The two most widely used forms of A~ form pulses at constant time intervals irrespective of the spontaneous heart rate. Operation of demand ACP is controlled by the spontaneous electrical activity of the heart. Fixed rate ACP are much simpler in design, but their use may be accompanied by certain complications. The most serious of these is competition between rhythms arising as a result of an increase in the frequency of the regular spontaneous rhythm or the appearance of extrasystoles. In turn, competition between rhythms may give rise to considerable hemodynamic disorders or may cause the development of ventricular fibrillation. The use of fixed rate ACP ought therefore to be completely abandoned now.Biocontrolled ACP can be divided into several types: R-wave demand, P-wave demand, Pwave synchronized, sequential, and universal. R-wave demand ACP are the type most frequently used both in the USSR and elsewhere. Their inbuilt program enables them to generate pulses automatically at the time of onset of bradycardia and to cease stimulation as soon as the spontaneous heart rate reaches the necessary level, so that competition between spontaneous and imposed rhythms can be avoided. Despite the undoubted advantages of this type of ACP over the fixed rate type, they still have certain disadvantages in clinical use. Loss of AV synchronization during ventricular stimulation by R-wave d...

UDC 539.21We study the influence of dissipation in a semiconducting material with the semiconductordielectric periodic layered structure on the passband boundaries for eigenwaves. It is shown that allowance for losses in the superconductor leads to appearance of a bend in dispersion curves for the electromagnetic waves propagating in such a structure. In this case, the minimum value of the phase velocity of the wave is limited. It is found that if the collision rate is high, then one of the band boundaries in the region of cyclotron waves degenerates, i.e., the band "destruction" takes place.