342 research outputs found
THIACALIX[4]ARENES DERIVATIVES: FROM SELF-ASSEMBY TO FUNCTIONAL MATERIALS
This work was supported by the by Russian Science Foundation, project # 19-13-00095
Cross-relaxation and phonon bottleneck effects on magnetization dynamics in LiYF4:Ho3+
Frequency and dc magnetic field dependences of dynamic susceptibility in
diluted paramagnets LiYF:Ho have been measured at liquid helium
temperatures in the ac and dc magnetic fields parallel to the symmetry axis of
a tetragonal crystal lattice. Experimental data are analyzed in the framework
of microscopic theory of relaxation rates in the manifold of 24
electron-nuclear sublevels of the lowest non-Kramers doublet and the first
excited singlet in the Ho ground multiplet split by the crystal
field of S symmetry. The one-phonon transition probabilities were computed
using electron-phonon coupling constants calculated in the framework of
exchange charge model and were checked by optical piezospectroscopic
measurements. The specific features observed in field dependences of the in-
and out-of-phase susceptibilities (humps and dips, respectively) at the
crossings (anti-crossings) of the electron-nuclear sublevels are well
reproduced by simulations when the phonon bottleneck effect and the cross-spin
relaxation are taken into account
Self-Organization in Multimode Microwave Phonon Laser (Phaser): Experimental Observation of Spin-Phonon Cooperative Motions
An unusual nonlinear resonance was experimentally observed in a ruby phonon
laser (phaser) operating at 9 GHz with an electromagnetic pumping at 23 GHz.
The resonance is manifested by very slow cooperative self-detunings in the
microwave spectra of stimulated phonon emission when pumping is modulated at a
superlow frequency (less than 10 Hz). During the self-detuning cycle new and
new narrow phonon modes are sequentially ``fired'' on one side of the spectrum
and approximately the same number of modes are ``extinguished'' on the other
side, up to a complete generation breakdown in a certain final portion of the
frequency axis. This is usually followed by a short-time refractority, after
which the generation is fired again in the opposite (starting) portion of the
frequency axis. The entire process of such cooperative spectral motions is
repeated with high degree of regularity. The self-detuning period strongly
depends on difference between the modulation frequency and the resonance
frequency. This period is incommensurable with period of modulation. It
increases to very large values (more than 100 s) when pointed difference is
less than 0.05 Hz. The revealed phenomenon is a kind of global spin-phonon
self- organization. All microwave modes of phonon laser oscillate with the same
period, but with different, strongly determined phase shifts - as in optical
lasers with antiphase motions.Comment: LaTeX2e file (REVTeX4), 5 pages, 5 Postscript figures. Extended and
revised version of journal publication. More convenient terminology is used.
Many new bibliographic references are added, including main early theoretical
and experimental papers on microwave phonon lasers (in English and in
Russian
Calixarene-based supramolecular systems: a platform for nanomaterials design by self-assembly
Lower rim thiacalix[4]arenes derivatives in cone and 1,3-alternate conformations have many advantages to create a wide range of precursors for the design of very sophisticated supramolecular architectures. These compounds can be considered as technological platform for nanomaterials design by self-assembly method. Particular attention will be paid to the application of calixarene derivatives for the construction of various supramolecular and nanosystems, devices and smart materials: colloid nanoparticles, catalytic systems, metalcoordinated networks, Langmuir-Blodgett nanolayers, molecular magnets etc.The authors gratefully acknowledge of the RSF (19-13-00095 and 18-73-10033) for the financial support
Power quality problems and ways of modeling the electrotechnological installations for identification of negative phenomena and factors arising from the operation of this equipment
Статья описывает проблему снижения качества электроэнергии, возникающую в процессе наращивания энергетических мощностей. Снижение качества электроэнергии может быть вызвано множеством различных факторов, проявляющихся при определенных обстоятельствах, и имеют поэтому разные решения по их устранению. Наиболее остро стоит проблема влияния качества электроэнергии на энергетические параметры электрооборудования и электроприемников в металлургической отрасли и в области механической обработки, широко эксплуатирующих различные электротехнологические установки. Важным элементом при подготовке специалистов в области электроэнергетики и электротехники является формирование компетенций, направленных на выявление и устранение причин, вызывающих снижение качества электроэнергии. Наиболее эффективно эти компетенции могут быть сформированы при выполнении действий на реальном оборудовании или на физической модели.The article describes the problem of reducing power quality, arising in the process of building energy capacity. Reduced power quality can be caused by many different factors, manifested in certain circumstances, and therefore have different solutions for their elimination. The most acute problem of the influence of power quality parameters on energy and electrical power consumers in the steel industry and in the field of machining, widely different operating electrotechnological installation. An important element in the preparation of specialists in the field of electricity and electrical engineering is the formation of competences, aimed at identifying and eliminating the causes of decline in power quality. The most effective of these competencies can be formed when performing actions on real hardware or on a physical model
Development and testing the exciter of synchronous machine based on high frequency regulator of current
В статье обосновывается целесообразность применения возбудителей синхронных машин малой мощности на основе источника тока. Показаны особенности характеристик синхронных машин малой мощности. Описана блочная функциональная схема системы возбуждения, позволяющая регулировать величину тока. Описаны технологические особенности схемы, представлены преимущества такой схемы относительно традиционных систем.The article explains the usefulness of agents of low-power synchronous machines based on the current source. The features of low power characteristics of synchronous machines. Be described a functional block diagram of the excitation system, which allows to regulate the amount of current. Described technological features of the scheme, presented the benefits of such a scheme with respect to traditional systems
Application compensating devices and resonant filters to suppress the voltage higher harmonics in the electric grid
В статье обосновывается целесообразность применения компенсирующих устройств, в том числе конденсаторных батарей и резонансных фильтров высших гармоник. Описаны особенности применения данных устройств при комплексном использовании. Описана схема разработанных фильтров, приведены результаты сравнения применяемых компенсирующих устройств. Проведены расчеты по нахождению величин тока основной гармоники нагрузки и фильтра.The article proves the feasibility of compensating devices, including capacitor banks and harmonic filter resonance. The features of the application of these devices with the integrated use. The scheme developed by the filters, given the results of comparison used compensating devices. The calculations for finding the values of the fundamental harmonic current load and filter
Development intellectual of laboratory for trainees on electrical engineering courses
Проведение лабораторных практикумов является существенным этапом подготовки специалистов любого профиля. В настоящее время многими производителями предлагаются лабораторные стенды, отвечающие широкому спектру изучаемых дисциплин, как общего профиля, так и специализированных, однако охватить обширную тематику вопросов обсуждаемых в рамках дисциплин электроэнергетического профиля достаточно сложно. Некоторые вопросы специальных дисциплин требуют более пристального внимания, чем сейчас, что объясняет потребность в разработке специализированных лабораторных стендов для этих дисциплин.The article explains the usefulness of agents of low-power synchronous machines based on the current source. The features of low power characteristics of synchronous machines. Be described a functional block diagram of the excitation system, which allows to regulate the amount of current. Described technological features of the scheme, presented the benefits of such a scheme with respect to traditional systems
Modern strategies for the creation of polymer coatings. Part II
Introduction. Coatings on hard materials are widely used in many industries. Coating technologies help prevent or reduce corrosion,
contamination and biofouling, chemical and structural degradation, and wear and tear of external surfaces due to exposure to the
elements and natural environments. The range of materials used for functional coatings is wide enough: from organic polymers to
hybrid composites and inorganic nanoparticles, depending on the desired properties and functionality of the final product. Despite
the excellent anti-corrosion characteristics of non-polymer coatings, their usage causes environmental damage. Organic coatings
are among the most widely used. Such compositions are applied in liquid form; organic solvents are one of the major components.
Environmental concerns have encouraged the development of alternative technologies. The main areas for development are availability of raw materials and the cost of environmentally friendly coatings. Results and discussion. The review substantiates the
relevance of research on the development of multifunctional polymer-based coatings. The market for polymer coatings is presented.
Methods of surface protection, types of coatings formed, their main components, features of the formation of coatings, the influence of various factors on the formation of polymer coatings, including methods of preparation and pre-treatment of the protected
surface are presented. Methods for preventing corrosion are discussed in detail, as well as the primary lines in the development of
anti-corrosion coatings based on various protective mechanisms. The characteristics of the main components of protective coatings
are given. The issue of destruction of polymer coatings depending on the operating environment is considered in detail. The types
of media, their influence and mechanisms of action on protected objects are considered. Factors and mechanisms of destruction of
polymer coatings, methods for preventing degradation of coatings are listed. The latest technologies for the formation of protective polymer coatings are highlighted. Conclusion. Currently, coatings provide a wide range of quality indicators. An important
characteristic of modern coatings is minimal negative impact on the environment, which requires an integrated approach to the
design and production of coating
- …