Nonlinear resonance in a three-terminal carbon nanotube resonator

The RF-response of a three-terminal carbon nanotube resonator coupled to RF-transmission lines is studied by means of perturbation theory and direct numerical integration. We find three distinct oscillatory regimes, including one regime capable of exhibiting very large hysteresis loops in the frequency response. Considering a purely capacitive transduction, we derive a set of algebraic equations which can be used to find the output power (S-parameters) for a device connected to transmission lines with characteristic impedance $Z_0$.Comment: 16 pages, 8 figure

Multiple Andreev Reflections in Weak Links of Superfluid 3He-B

We calculate the current-pressure characteristics of a ballistic pinhole aperture between two volumes of B-phase superfluid 3He. The most important mechanism contributing to dissipative currents in weak links of this type is the process of multiple Andreev reflections. At low biases this process is significantly affected by relaxation due to inelastic quasiparticle-quasiparticle collisions. In the numerical calculations, suppression of the superfluid order parameter at surfaces is taken into account self-consistently. When this effect is neglected, the theory may be developed analytically like in the case of s-wave superconductors. A comparison with experimental results is presented.Comment: 12 pages, 9 figures, RevTeX

Quasiparticle states of the Hubbard model near the Fermi level

The spectra of the t-U and t-t'-U Hubbard models are investigated in the one-loop approximation for different values of the electron filling. It is shown that the four-band structure which is inherent in the case of half-filling and low temperatures persists also for some excess or deficiency of electrons. Besides, with some departure from half-filling an additional narrow band of quasiparticle states arises near the Fermi level. The dispersion of the band, its bandwidth and the variation with filling are close to those of the spin-polaron band of the t-J model. For moderate doping spectral intensities in the new band and in one of the inner bands of the four-band structure decrease as the Fermi level is approached which leads to the appearance of a pseudogap in the spectrum.Comment: 8 pages, 7 figure

High intermodulation gain in a micromechanical Duffing resonator

In this work we use a micromechanical resonator to experimentally study small signal amplification near the onset of Duffing bistability. The device consists of a PdAu beam serving as a micromechanical resonator excited by an adjacent gate electrode. A large pump signal drives the resonator near the onset of bistability, enabling amplification of small signals in a narrow bandwidth. To first order, the amplification is inversely proportional to the frequency difference between the pump and signal. We estimate the gain to be about 15dB for our device

Constructive solution of highly effective photoenergy module: development and experimental testing

Based on experimental study and computermodeling of working temperature influence on the efficiency of Chinese production silicon solar cells identified temperature dependence of efficiency shows the feasibility of using Chinese production Si-SC in the construction of photovoltaic thermal system, which together with the heat pump is part of a combined system for hot water supply, heating and air conditioning. Based on a detailed analysis of the working temperature influence on the efficiency of photovoltaic processes that determine the solar cells work, it has been developed the optimal construction and technological solution of hybrid solar generated module, the main feature ofwhich is the heat exchange block, designed to reduce the solar cells working temperature. The experimental testing of hybrid modules samples equipped with developed cooling system, high-voltage part of power take-off system demonstrates their reliability and high efficiency which allow to achieve the such module efficiency up to 18.5 %.На основе экспериментального исследования в комплексе с компьютерным моделированием влияния рабочей температуры на эффективность кремниевых солнечных элементов китайского производства выявлена температурная зависимость их эффективности. Температурная зависимость показывает целесообразность использования солнечных элементов китайского производства в составе фотоэлектрической тепловой системы, которая вместе с тепловым насосом является частью комбинированной системы горячего водоснабжения, отопления и кондиционирования воздуха. На основе детального анализа влияния рабочей температуры на эффективность фотоэлектрических процессов, определяющих работу солнечных элементов, было разработано оптимальное конструктивно-технологическое решение гибридного солнечного генерирующего модуля, основной особенностью которого является теплообменный блок, предназначен для снижения рабочей температуры солнечных элементов. Экспериментальные испытания образцов таких модулей, оснащенных разработанной системой охлаждения и высоковольтной системой отбора мощности, демонстрируют их надежность и высокую эффективность, позволяющие достичь КПД гибридного модуля до 18,5 %

Josephson effect in superconducting constrictions with hybrid SF electrodes: peculiar properties determined by the misorientation of magnetizations

Josephson current in SFcFS junctions with arbitrary transparency of the constriction (c) is investigated. The emphasis is done on the analysis of the supercurrent dependencies on the misorientation angle $\theta$ between the in-plane magnetizations of diffusive ferromagnetic layers (F). It is found that the current-phase relation $I(\phi)$ may be radically modified with the $\theta$ variation: the harmonic $I_{1}\sin \phi$ vanishes for definite value of $\theta$ provided for identical orientation of the magnetizations ($\theta =0$) the junction is in the $"\pi"$ state. The Josephson current may exhibit a nonmonotonic dependence on the misorientation angle both for realization of $"0 "$ and $"\pi "$ state at $\theta =0$. We also analyze the effect of exchange field induced enhancement of the critical current which may occur in definite range of $\theta$.Comment: 7 pages, 5 figures, submitted to JETP Letter

Semiclassical theory of weak antilocalization and spin relaxation in ballistic quantum dots

We develop a semiclassical theory for spin-dependent quantum transport in ballistic quantum dots. The theory is based on the semiclassical Landauer formula, that we generalize to include spin-orbit and Zeeman interaction. Within this approach, the orbital degrees of freedom are treated semiclassically, while the spin dynamics is computed quantum mechanically. Employing this method, we calculate the quantum correction to the conductance in quantum dots with Rashba and Dresselhaus spin-orbit interaction. We find a strong sensitivity of the quantum correction to the underlying classical dynamics of the system. In particular, a suppression of weak antilocalization in integrable systems is observed. These results are attributed to the qualitatively different types of spin relaxation in integrable and chaotic quantum cavities.Comment: 20 page