Recent observations of two-photon absorption within the configuration 4f7 of Gd3+ in LaFs have indicated an anomalously high line strength for the transition 8S7,2+ 6P7,2 compared with .+ 6 P~,~ and *S7;2 -+ 6P3i2. It is shown that the standard expression for the two-photon intensity is unusually small for all three transitions and that a higher-order correction, involving matrix elements of the spin-orbit interaction within the intermediate configuration 4f65d, predominates. The principal term is scalar, implying (in the absence of J mixing by the crystal field) isotropic contributions to the various components of the AJ = 0 transition. The line strengths that have been observed can be accounted for reasonably well without having to invoke variations in the radial integral (4f lr15d) or inadequacies in the closure approximation. Expressions for the transition matrix elements are given for the general configuration iN.

LBSTPfCTMain results of the investigations performed by specialists of the Pesearch-Production £ssociation "Istok" (Russia) on creation of a parametric row of sealed-off copper vapor lasers with output powers from 1 to 100 W are presented.

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Выполнен обзор существующих методик расчета динамических характеристик рекуперативных трубчатых теплообменных аппаратов. Показано, что для повышения достоверности результатов расчета тепловых характеристик процессов теплообмена воздухоподогревателей целесообразно использовать математическую модель как объекта с распределенными параметрами. На основе модификации неявного численного метода «бегущего счета», разработан метод определения показателей нестационарных процессов теплообмена трубчатых воздухоподогревателей с многоходовой схемой движения теплоносителей. Получены кривые разгона и распределения температур стенок труб трубчатых воздухоподогревателей.

Biogas – one of the promising areas of generation and use of renewable energy resources. In manycountries, farmers are considered as promising sites for the production and use of biogas. Due to the largevariations in the quantity and quality of raw materials, modalities and goals of the design of biogas plantsare not formalized and is based on practical experience of the developers. It is shown that the criticalparameters in the design of biogas digesters are a source of raw materials, the amount of energy consumedby household and accommodation. Considered criteria (power, size, equipment, modes of operation, safety,etc.), which have a decisive influence on the structure and functional composition of BSU for farms. Variantsof technological schemes of individual bioreactors, as well as the characteristics of farms that should beconsidered when designing the BSU. Rationally designed BSU improves energy efficiency andenvironmentally friendly agricultural production.