The efficiency and power of the martensite rotor heat engine. I

The physical aspects - mechanics and thermodynamics - of operation of martensite rotor heat engine (MRHE) on the basis of martensite-austenite structural phase transition with the transition temperature in the region of low-potential water temperatures have been studied. The engine converts the thermal energy of low-potential water into the elastic energy of working body (spring, ribbon or wire) made of the material with shape memory effect. At some simplifying assumptions, the analytical expressions are obtained for the thermal efficiency and the power of MRHE of different type. The registration of head hydraulic resistance and heat conductivity of working body material is made and the maximum value of power produced by the engine at the given mechanical and heat conditions is calculated. The recommendations are given on the optimal choice of engine parameters. On the basis of numerical estimations for nitinol, the possibility of application of MRHE is shown for efficient and ecologically pure production of electric energy both on local (geothermal waters, waste water of industrial enterprises, etc.) and global (warm ocean stream) scales.

The Efficiency of Ideal Ferrielectric Energy Converter

The article contains the calculation of the efficiency of ideal ferrielectric energy converter, the working body of which is ferrielectric and which converts the heat energy of low-potential water into the electric energy. Its operation is based on the sharp dependence of capacitivity of ferrielectric on the temperature of dielectric-ferrielectric structural phase transition in the vicinity of Curie temperature.

Formation mechanisms and relaxation of NMR spin-echo signals excited by two arbitrary duration radio-frequency pulses in magnets

The work is devoted to the problem of multiple signals of nuclear spin echoes in magnets, excited by a series of radio-frequency (RF) arbitrary duration pulses exceeding the free induction decay time. The quantum-statistical approach based on the Liouville equation solution for the statistical operator of system is developed for the investigation of echo-processes. The obtained theoretical results for the number of echo signals, time moments of their formation and their intensities are in good agreement with experiments carried out on magnets (ferrites, ferrometals, half metals, manganites). The pointed approach is general and could be applied to EPR and NQR, which is interesting also for its application for remote detection of explosives and narcotics. The application of wide RF pulses and their sequences makes it possible to accumulate weak signals, enriches the echo-response spectrum with clearly separated intensive lines, i.e. essentially increases the sensitivity of apparatus and, correspondingly, the possibilities to explore the fine details of dynamical and relaxation processes taking place in nuclear spin-systems with sufficiently long relaxation times. The work contains also results of new experiments on study of relaxation processes in these systems.

Investigation of multiple echo signals formation mechanism in magnet at excitation by two arbitrary radio-frequency pulses

The quantum-mechanical calculations of intensities and time moments of appearance of multiple spin echo signals of excitation of nuclear spin system of magnet by two arbitrary width radio-frequency pulses were carried out. This method was used by us earlier at consideration of multiple-pulse analogs of single-pulse echo in multidomain magnets upon sudden jumps of the effecting magnetic field in the rotating coordinate system during the action of radio-frequency pulse. The formation mechanisms of echo signals are discussed. The appearance of four primary stimulated echo signals is predicted. The total number of echo signals at fixed parameters of radio-frequency pulses does not exceed thirteen ones. Theoretical conclusions are in compliance with experiments carried out on lithium ferrite. As it was established by us earlier in this magnetic dielectric, in difference from ferrometals, it is observed very short relaxation times of single-pulse and two-pulse stimulated echoes, and the contribution of radio-frequency pulse fronts distribution mechanism is insignificant. For this reason lithium ferrite is a good material for the experimental verification of theoretical conclusions in experimental conditions most close to the theoretical model.

Obtaining and Application of the Reduced Bloch Equations

Well-known Bloch equations describe the spin systems (electronic and nuclear) for any scale of time, from transient processes to steady states. Usually in solids T_2 << T_1. The question arises: what are the approximations that should be made in order the roughen Bloch equations to describe the processes at the time T_2 < t < T_1? The answer to this question is given in this article. As an example, the saturation of magnetic resonance is considered under the conditions of harmonic modulation of a constant magnetic field.