Research on optical properties of fishnet metamaterials with fractal-structured unit cell

В настоящей работе исследовались сетчатые метаматериалы с разработанной гео-метрией единичной ячейки на основе ковра Серпинского. Были обнаружены поло-сы отрицательного показателя преломления в ближнем ИК и видимом диапазоне. Наблюдалось линейное смещение спектральных особенностей в длинноволновую область с увеличением порядка фрактального разбиения. Обсуждались перспекти-вы применения рассмотренных метаматериалов в оптических устройствах – фильтрах, линзах, модуляторах и т. д., а также высокочувствительных датчиках давления, биологических и химических сенсорах с возможностью дистанционного помехоустойчивого считывания показаний.Fishnet metamaterials with proposed Sierpinski carpet geometry of unit cell were studied in this work. The spectral bands with negative refractive index were discovered in near-IR and visible regions. The linear red shift of spectral features was observed with the in-creasing partition order of fractal. We discussed the possible applications of analyzed metamaterials in optical devices (filters, lenses, modulators etc.), high-sensitive pressure meters, biomedical and chemical sensors capable of remote jam-resistant data acquisition.Программа развития УрФУ на 2013 год (п.1.2.2.3

Integration of innovation development and implementation processes in defence industry according to a demand — supply format

The purpose of this study is to investigate the development and implementation processes of defence innovation in a demand – supply format. The main research methods are the dialectical and systematic approach, the method of formalisation and modelling, logical-functional and logical-structural analysis. The result of the study is the design of a lifecycle matrix for the development and implementation phases of defence innovation that visualises the objectives, functions, indicators, key deliverables by phase and stage of the innovation lifecycle. The matrix is intended for managers as a tool to help formulate the functions of the participants in the innovation process and to monitor and analyse problem areas in the innovation system. A business model of the innovation system of the defense complex in the demand – supply format is proposed, including elements that create supply and demand for innovative products, implement mediation mechanisms between participants that generate supply and demand. The results obtained are aimed at developing a methodology for organising and managing the development and implementation of innovations in the defence industry and can be used by authorities in the innovation policy formation, in developing and improving the programmes for the defence industry development in Russia

Hall Transport in Granular Metals and Effects of Coulomb Interactions

We present a theory of Hall effect in granular systems at large tunneling conductance $g_{T}\gg 1$. Hall transport is essentially determined by the intragrain electron dynamics, which, as we find using the Kubo formula and diagrammatic technique, can be described by nonzero diffusion modes inside the grains. We show that in the absence of Coulomb interaction the Hall resistivity $\rho_{xy}$ depends neither on the tunneling conductance nor on the intragrain disorder and is given by the classical formula $\rho_{xy}=H/(n^* e c)$, where $n^*$ differs from the carrier density $n$ inside the grains by a numerical coefficient determined by the shape of the grains and type of granular lattice. Further, we study the effects of Coulomb interactions by calculating first-order in $1/g_T$ corrections and find that (i) in a wide range of temperatures T \gtrsim \Ga exceeding the tunneling escape rate \Ga, the Hall resistivity $\rho_{xy}$ and conductivity \sig_{xy} acquire logarithmic in $T$ corrections, which are of local origin and absent in homogeneously disordered metals; (ii) large-scale ``Altshuler-Aronov'' correction to \sig_{xy}, relevant at T\ll\Ga, vanishes in agreement with the theory of homogeneously disordered metals.Comment: 29 pages, 16 figure

Oscillations of Induced Magnetization in Superconductor-Ferromagnet Heterostructures

We study a change in the spin magnetization of a superconductor-ferromagnet (SF) heterostructure, when temperature is lowered below the superconducting transition temperature. It is assumed that the SF interface is smooth on the atomic scale and the mean free path is not too short. Solving the Eilenberger equation we show that the spin magnetic moment induced in the superconductor is an oscillating sign-changing function of the product $hd$ of the exchange field $h$ and the thickness $d$ of the ferromagnet. Therefore the total spin magnetic moment of the system in the superconducting state can be not only smaller (screening) but also greater (anti-screening) than that in the normal state, in contrast with the case of highly disordered (diffusive) systems, where only screening is possible. This surprising effect is due to peculiar periodic properties of localized Andreev states in the system. It is most pronounced in systems with ideal ballistic transport (no bulk disorder in the samples, smooth ideally transparent interface), however these ideal conditions are not crucial for the very existence of the effect. We show that oscillations exist (although suppressed) even for arbitrary low interface transparency and in the presence of bulk disorder, provided that $h \tau \gg 1$ ($\tau$ -- mean free path). At low interface transparency we solve the problem for arbitrary strength of disorder and obtain oscillating magnetization in ballistic regime ($h \tau \gg 1$) and nonoscillating magnetization in diffusive one ($h \tau \ll 1$) as limiting cases of one formula.Comment: 10 pages, 2 figures, accepted for publication in Phys. Rev.

Silicon-carbide semiconductors as base for active rectifier

В докладе представлена концепция построения преобразователя частоты по типу активного выпрямителя на сверхмалые массо-габаритные показатели (до 0,4 кг/кВт) с использованием карбид-кремниевых транзисторов. В основе концепции заложены принципы наращивания мощности преобразователей за счет параллельного соединения преобразователей меньшей мощности (модулей). Алгоритм управления всем преобразователем реализован на базе микроконтроллера и программируемой логической интегральной схемы (ПЛИС). Совокупность достоинств микросхем, а также ряд технических решений обеспечили независимое централизованное управление 36 транзисторами на постоянной частоте коммутации 75 кГц. Эквивалентная пульсность тока для рассматриваемого трехфазного преобразователя составляет 450 кГц. В работе представлены промежуточные результаты испытаний образца на номинальную мощность 25 кВт.The report introduces the concept of building the inverter-type active rectifier on ultra-small weight and size parameters (up to 0.4 kg / kW). The concept based on the principles of increasing converters power due to the parallel connection of lower power converters (modules). The control algorithm is implemented on microcontroller and programmable logic integrated circuits (FPGAs) co-working. Set of advantages applied digital circuits, as well as a number of technical solutions that organize synchronous and discontinuous operation of two chips in a single computational cycle, ensure the independence of the centralized management of 36 transistors on a constant switching frequency of 75 kHz. Equivalent frequencyof ripples in current for the considered three-phase inverter is 450 kHz. The paper presents the interim results of the test sample to the nominal power of 25 kW

Excitonic condensation in a double-layer graphene system

The possibility of excitonic condensation in a recently proposed electrically biased double-layer graphene system is studied theoretically. The main emphasis is put on obtaining a reliable analytical estimate for the transition temperature into the excitonic state. As in a double-layer graphene system the total number of fermionic "flavors" is equal to N=8 due to two projections of spin, two valleys, and two layers, the large-$N$ approximation appears to be especially suitable for theoretical investigation of the system. On the other hand, the large number of flavors makes screening of the bare Coulomb interactions very efficient, which, together with the suppression of backscattering in graphene, leads to an extremely low energy of the excitonic condensation. It is shown that the effect of screening on the excitonic pairing is just as strong in the excitonic state as it is in the normal state. As a result, the value of the excitonic gap \De is found to be in full agreement with the previously obtained estimate for the mean-field transition temperature $T_c$, the maximum possible value $\Delta^{\rm max},T_c^{\rm max}\sim 10^{-7} \epsilon_F$ ($\epsilon_F$ is the Fermi energy) of both being in $1{\rm mK}$ range for a perfectly clean system. This proves that the energy scale $\sim 10^{-7} \epsilon_F$ really sets the upper bound for the transition temperature and invalidates the recently expressed conjecture about the high-temperature first-order transition into the excitonic state. These findings suggest that, unfortunately, the excitonic condensation in graphene double-layers can hardly be realized experimentally.Comment: 21 pages, 5 figures, invited paper to Graphene special issue in Semiconductor Science and Technolog

Excitonic condensation in a double-layer graphene system

The possibility of excitonic condensation in a recently proposed electrically biased double-layer graphene system is studied theoretically. The main emphasis is put on obtaining a reliable analytical estimate for the transition temperature into the excitonic state. As in a double-layer graphene system the total number of fermionic "flavors" is equal to N=8 due to two projections of spin, two valleys, and two layers, the large-$N$ approximation appears to be especially suitable for theoretical investigation of the system. On the other hand, the large number of flavors makes screening of the bare Coulomb interactions very efficient, which, together with the suppression of backscattering in graphene, leads to an extremely low energy of the excitonic condensation. It is shown that the effect of screening on the excitonic pairing is just as strong in the excitonic state as it is in the normal state. As a result, the value of the excitonic gap \De is found to be in full agreement with the previously obtained estimate for the mean-field transition temperature $T_c$, the maximum possible value $\Delta^{\rm max},T_c^{\rm max}\sim 10^{-7} \epsilon_F$ ($\epsilon_F$ is the Fermi energy) of both being in $1{\rm mK}$ range for a perfectly clean system. This proves that the energy scale $\sim 10^{-7} \epsilon_F$ really sets the upper bound for the transition temperature and invalidates the recently expressed conjecture about the high-temperature first-order transition into the excitonic state. These findings suggest that, unfortunately, the excitonic condensation in graphene double-layers can hardly be realized experimentally.Comment: 21 pages, 5 figures, invited paper to Graphene special issue in Semiconductor Science and Technolog

Excitonic condensation in a double-layer graphene system

The possibility of excitonic condensation in a recently proposed electrically biased double-layer graphene system is studied theoretically. The main emphasis is put on obtaining a reliable analytical estimate for the transition temperature into the excitonic state. As in a double-layer graphene system the total number of fermionic "flavors" is equal to N=8 due to two projections of spin, two valleys, and two layers, the large-$N$ approximation appears to be especially suitable for theoretical investigation of the system. On the other hand, the large number of flavors makes screening of the bare Coulomb interactions very efficient, which, together with the suppression of backscattering in graphene, leads to an extremely low energy of the excitonic condensation. It is shown that the effect of screening on the excitonic pairing is just as strong in the excitonic state as it is in the normal state. As a result, the value of the excitonic gap \De is found to be in full agreement with the previously obtained estimate for the mean-field transition temperature $T_c$, the maximum possible value $\Delta^{\rm max},T_c^{\rm max}\sim 10^{-7} \epsilon_F$ ($\epsilon_F$ is the Fermi energy) of both being in $1{\rm mK}$ range for a perfectly clean system. This proves that the energy scale $\sim 10^{-7} \epsilon_F$ really sets the upper bound for the transition temperature and invalidates the recently expressed conjecture about the high-temperature first-order transition into the excitonic state. These findings suggest that, unfortunately, the excitonic condensation in graphene double-layers can hardly be realized experimentally.Comment: 21 pages, 5 figures, invited paper to Graphene special issue in Semiconductor Science and Technolog

Mathematical model of the starter system for a three-stage synchronous generator with a damping cage

В данной статье рассматривается математическая модель стартерной системы для газотурбинных двигателей. Модель исследуемого трехкаскадного синхронного генератора была построена в системе d-q-координат. Полученная модель позволяет сконфигурировать параметры машины в широком диапазоне, а также получить информацию о токах и напряжениях основных электрических узлов машины. Математическое моделирование показало эффективность полученной модели и адекватность предложенного алгоритма электростартерного запуска синхронной машины.This paper, considers a mathematical model the starter system for gas turbine engines. Model of the investigated three-stage synchronous generator has been built in the dq-coordinates. The obtained model allows one to configure the machine parameters in a wide range, as well as receive information about currents and voltages major electrical components of the machine. Mathematical modeling shown efficiency of the resulting model and adequacy of the proposed algorithms electric starter mode synchronous machine