БЕЗРЕДУКТОРНІ ВІТРОЕНЕРГЕТИЧНІ УСТАНОВКИ

The use of wind farms has great long-term potential as a highly efficient alternative source of cheap energy. The article is devoted to the development of new designs of wind power plants with the participation of the authors, which increase their energy, economic and operational efficiency. The developments concern designs that allow the use of a gearbox to be disconnected to connect a generator included in a wind farm. The principle of operation according to which depending on the magnitude of the voltage of the generator, ie the magnitude of the wind turbine speed, is connected to the thyristor rectifier one of the secondary windings of the transformer by means of switching on the corresponding pair of triacs by the device of selecting the working secondary winding. It is substantiated that any hardware logic or software-logic device, including a generator voltage sensor and threshold elements, will be used as a device for selecting the secondary transformer winding of the transformer, which will activate the corresponding pair of triacs depending on the voltage value of the generator. It is substantiated that the above-mentioned developments can be widely used in the creation of wind turbines with wind turbines of various design and purpose - with a horizontal or vertical axis of rotation, which includes generators for converting the energy of VP into electrical. It has been proved that the creation of an industrial or domestic wind turbine is one of the main tasks of ensuring an acceptable level of economic efficiency, realized by solving a number of technical problems.Применение ветроэнергетических установок имеет большой долгосрочный потенциал как высокоэффективный альтернативный источник дешевой энергии. Статья посвящена выполненным с участием авторов разработкам новых конструкций ветроэнергетических установок, которые повышают их энергетическую, экономическую и эксплуатационную эффективность. Разработки касаются конструкций, которые позволяют отказаться от использования редуктора для присоединения генератора, входящего в состав ветроэнергетической установки. Изложен принцип работы, в соответствии с которым в зависимости от величины напряжения генератора, то есть величины скорости ветротурбины, к тиристорному выпрямителю подключается одна из вторичных обмоток трансформатора при помощи включения соответствующей пары симисторов устройством выбора рабочей вторичной обмотки. Обосновано, что в качестве устройства выбора рабочей вторичной обмотки трансформатора может быть использовано любое аппаратное логическое или программно-логическое устройство, включающее в себя датчик напряжения генератора и пороговые элементы, которые будут производить включение соответствующей пары симисторов в зависимости от величины напряжения генератора. Обосновано, что приведенные  разработки могут найти широкое применение при создании ВЭУ с ветротурбинами различной конструкции и назначения – с горизонтальной или вертикальной осью вращения, в состав которых входят генераторы для преобразования энергии ВП в электрическую. Доказано, что при создании ВЭУ промышленного или бытового назначения одной из основных задач представляется обеспечение приемлемого уровня экономической эффективности, реализуемое путем решения ряда технических задач.Використання вітроенергетичних установок має великий довгостроковий потенціал, як високоефективний альтернативне джерело дешевої енергії. У статті наведено авторські розробки нових конструкцій вітроенергетичних установок, які підвищують їх енергетичну, економічну та експлуатаційну ефективність. Розробки стосуються   конструкцій, які дозволяють відмовитись від використання редукторів для приєднання генераторів, що знаходяться в установці вітроенергетичної установки. Викладено принцип роботи, відповідно до якого в залежності від величини напруги генератора, тобто величини швидкості вітротурбіни, до тиристорного випрямителя підключається одна з вторинних обмоток трансформатора за допомогою включення відповідної пари сімісторів пристроєм вибору робочої вторинної обмотки. Обгрунтовано, що в якості пристрою вибору робочої вторинної обмотки трансформатора може бути використано будь-який апаратний, логічний або програмно-логічний пристрій, що включає в себе датчик напруги генератора і порогові елементи, які будуть виробляти включення відповідної пари сімісторів в залежності від величини напруги генератора. Обґрунтовано, що наведені розробки можуть знайти широке застосування при створенні ВЕУ з вітротурбінами різної конструкції і призначення - з горизонтальною або вертикальною віссю обертання, до складу яких входять генератори для перетворення енергії ВП в електричну. Доведено, що при створенні ВЕУ промислового або побутового призначення однією з основних задач є забезпечення прийнятного рівня економічної ефективності, яке реалізується шляхом вирішення низки технічних завдань

Influence of the pseudogap on the superconductivity-induced phonon renormalization in high-Tc_c superconductors

We investigate the influence of a d-density wave (DDW) gap on the superconductivity-induced renormalization of phonon frequency and linewidth. The results are discussed with respect to Raman and inelastic neutron scattering experiments. It turns out that the DDW gap can enhance the range of frequencies for $q=0$ phonon softening depending on the underlying band structure. Moreover we show that an anisotropic 'd-wave' pseudogap can also contribute to the q-dependent linewidth broadening of the 340cm$^{-1}$ phonon in YBa$_2$Cu$_3$O$_7$.Comment: 4 page

Nernst Effect and Superconducting Fluctuations in Zn-doped YBa2_{2}Cu3_{3}O7−δ_{7-\delta}

We report the measurements of in-plane resistivity, Hall effect, and Nernst effect in Zn doped YBa$_{2}$Cu$_{3}$O$_{7-\delta}$ epitaxial thin films grown by pulsed laser deposition technique. The pseudogap temperature, $T^*$, determined from the temperature dependence of resistivity, does not change significantly with Zn doping. Meanwhile the onset temperature ($T^{\nu}$) of anomalous Nernst signal above $T_{c0}$, which is interpreted as evidence for vortex-like excitations, decreases sharply as the superconducting transition temperature $T_{c0}$ does. A significant decrease in the maximum of vortex Nernst signal in mixed state is also observed, which is consistent with the scenario that Zn impurities cause a decrease in the superfluid density and therefore suppress the superconductivity. The phase diagram of $T^*$, $T^{\nu}$, and $T_{c0}$ versus Zn content is presented and discussed.Comment: 6 pages, 5 figures, Latex; v2: to be published in PR

Superconducting Gap and Strong In-Plane Anisotropy in Untwinned YBa2Cu3O7-d

With significantly improved sample quality and instrumental resolution, we clearly identify in the (pi,0) ARPES spectra from YBa2Cu3O6.993, in the superconducting state, the long-sought `peak-dip-hump' structure. This advance allows us to investigate the large a-b anisotropy of the in-plane electronic structure including, in particular, a 50% difference in the magnitude of the superconducting gap that scales with the energy position of the hump feature. This anisotropy, likely induced by the presence of the CuO chains, raises serious questions about attempts to quantitatively explain the YBa2Cu3O7-d data from various experiments using models based on a perfectly square lattice.Comment: Phys. Rev. Lett., in press. Revtex, 4 pages, 4 postscript figures embedded in the tex

High-Q Supercavity Modes in Subwavelength Dielectric Resonators

Recent progress in nanoscale optical physics is associated with the development of a new branch of nanophotonics exploring strong Mie resonances in dielectric nanoparticles with a high refractive index. The high-index resonant dielectric nanostructures form building blocks for novel photonic metadevices with low losses and advanced functionalities. However, unlike extensively studied cavities in photonic crystals, such dielectric resonators demonstrate low quality factors (Q factors). Here, we uncover a novel mechanism for achieving giant Q factors of subwavelength nanoscale resonators by realizing the regime of bound states in the continuum. In contrast to the previously suggested multilayer structures with zero permittivity, we reveal strong mode coupling and Fano resonances in homogeneous high-index dielectric finite-length nanorods resulting in high-Q factors at the nanoscale. Thus, high-index dielectric resonators represent the simplest example of nanophotonic supercavities, expanding substantially the range of applications of all-dielectric resonant nanophotonics and meta-optics.Theoretical studies have been supported by the Ministry of Education and Science of the Russian Federation (3.1500.2017/4.6), the Russian Foundation for Basic Research (16-02-00461), and the Australian Research Council. Simulations of complex eigenmodes have been supported by the Russian Science Foundation (17-12-01581)

Inelastic Light Scattering From Correlated Electrons

Inelastic light scattering is an intensively used tool in the study of electronic properties of solids. Triggered by the discovery of high temperature superconductivity in the cuprates and by new developments in instrumentation, light scattering both in the visible (Raman effect) and the X-ray part of the electromagnetic spectrum has become a method complementary to optical (infrared) spectroscopy while providing additional and relevant information. The main purpose of the review is to position Raman scattering with regard to single-particle methods like angle-resolved photoemission spectroscopy (ARPES), and other transport and thermodynamic measurements in correlated materials. Particular focus will be placed on photon polarizations and the role of symmetry to elucidate the dynamics of electrons in different regions of the Brillouin zone. This advantage over conventional transport (usually measuring averaged properties) indeed provides new insights into anisotropic and complex many-body behavior of electrons in various systems. We review recent developments in the theory of electronic Raman scattering in correlated systems and experimental results in paradigmatic materials such as the A15 superconductors, magnetic and paramagnetic insulators, compounds with competing orders, as well as the cuprates with high superconducting transition temperatures. We present an overview of the manifestations of complexity in the Raman response due to the impact of correlations and developing competing orders. In a variety of materials we discuss which observations may be understood and summarize important open questions that pave the way to a detailed understanding of correlated electron systems.Comment: 62 pages, 48 figures, to appear in Rev. Mod. Phys. High-resolution pdf file available at http://onceler.uwaterloo.ca/~tpd/RMP.pd

Superconductivity-induced Resonance Raman Scattering in Multi-layer High-Tc Superconductors

Resonant Raman scattering below Tc has been discovered in several Bi-, Hg-, Tl-based high-Tc superconductors with three or four CuO2-layers. For Bi2Si2Ca2Cu3O10+d, we found an unexpected crossover of the pair-breaking peak in the A1g-spectrum from a broad bump at hw = 6kBTc for Eexc = 2.54eV to a sharp peak at hw = 8kBTc for Eexc = 2.18eV, together with a strong enhancement of the Ca-phonons. Under resonant conditions, the relative positions of the pair breaking peaks in A1g, B1g, and B2g channels are 2Delta(A1g) = 2Delta(B1g) > 2Delta(B2g). This relation implies that the A1g Raman channel is free from the Coulomb screening effect, just as predicted theoretically for a d-wave multi-layer superconductor but have never been observed experimentally thus far. The observed resonance effect is the evidence that the electronic state in the inner CuO2-planes is different from that of the outer CuO2-planes.Comment: 16 pages, 6 figures. submitted to Phys.Rev.

C-axis lattice dynamics in Bi-based cuprate superconductors

We present results of a systematic study of the c axis lattice dynamics in single layer Bi2Sr2CuO6 (Bi2201), bilayer Bi2Sr2CaCu2O8 (Bi2212) and trilayer Bi2Sr2Ca2Cu3O10 (Bi2223) cuprate superconductors. Our study is based on both experimental data obtained by spectral ellipsometry on single crystals and theoretical calculations. The calculations are carried out within the framework of a classical shell model, which includes long-range Coulomb interactions and short-range interactions of the Buckingham form in a system of polarizable ions. Using the same set of the shell model parameters for Bi2201, Bi2212 and Bi2223, we calculate the frequencies of the Brillouin-zone center phonon modes of A2u symmetry and suggest the phonon mode eigenvector patterns. We achieve good agreement between the calculated A2u eigenfrequencies and the experimental values of the c axis TO phonon frequencies which allows us to make a reliable phonon mode assignment for all three Bi-based cuprate superconductors. We also present the results of our shell model calculations for the Gamma-point A1g symmetry modes in Bi2201, Bi2212 and Bi2223 and suggest an assignment that is based on the published experimental Raman spectra. The superconductivity-induced phonon anomalies recently observed in the c axis infrared and resonant Raman scattering spectra in trilayer Bi2223 are consistently explained with the suggested assignment.Comment: 29 pages, 13 figure

Raman scattering in C_{60} and C_{48}N_{12} aza-fullerene: First-principles study

We carry out large scale {\sl ab initio} calculations of Raman scattering activities and Raman-active frequencies (RAFs) in ${\rm C}_{48}{\rm N}_{12}$ aza-fullerene. The results are compared with those of ${\rm C}_{60}$. Twenty-nine non-degenerate polarized and 29 doubly-degenerate unpolarized RAFs are predicted for ${\rm C}_{48}{\rm N}_{12}$. The RAF of the strongest Raman signal in the low- and high-frequency regions and the lowest and highest RAFs for ${\rm C}_{48}{\rm N}_{12}$ are almost the same as those of ${\rm C}_{60}$. The study of ${\rm C}_{60}$ reveals the importance of electron correlations and the choice of basis sets in the {\sl ab initio} calculations. Our best calculated results for ${\rm C}_{60}$ with the B3LYP hybrid density functional theory are in excellent agreement with experiment and demonstrate the desirable efficiency and accuracy of this theory for obtaining quantitative information on the vibrational properties of these molecules.Comment: submitted to Phys.Rev.