Turbulence in Binary Bose-Einstein Condensates Generated by Highly Non-Linear Rayleigh-Taylor and Kelvin-Helmholtz Instabilities

Quantum turbulence (QT) generated by the Rayleigh-Taylor instability in binary immiscible ultracold 87Rb atoms at zero temperature is studied theoretically. We show that the quantum vortex tangle is qualitatively different from previously considered superfluids, which reveals deep relations between QT and classical turbulence. The present QT may be generated at arbitrarily small Mach numbers, which is a unique property not found in previously studied superfluids. By numerical solution of the coupled Gross-Pitaevskii equations we find that the Kolmogorov scaling law holds for the incompressible kinetic energy. We demonstrate that the phenomenon may be observed in the laboratory.Comment: Revised version. 7 pages, 8 figure

Analysis of Physical Readiness of First Course Students after Self-Isolation

В статье представлены результаты исследования физической подготовленности студентов транспортного вуза после вынужденной самоизоляции. Установлено, что у большинства студентов первого курса самые низкие показатели отмечаются в силовых характеристиках плечевого пояса и работоспособности сердечно-сосудистой системы, а именно эти показатели являются профессионально значимыми в будущей профессиональной деятельности специалиста железной дороги. Правильно подобранные комплексы упражнений с учетом индивидуальных физических нагрузок смогут обеспечить оптимальный двигательный режим и внести коррекцию в кондиционную подготовленность студента

Potential detection spectral component of compromising emanations signal USB keyboard interface

Настоящая статья посвящена исследованию потенциальных возможностей обнаружения информативной и неинформативной составляющих сигнала ПЭМИ клавиатуры USB интерфейса. Проводиться цифровой эксперимент для оценки значения максимума взаимной корреляционной функции спектра сигнала ПЭМИ, снятого с двух информативных проводов, содержащего пакет опроса и ответа с данными и опорного сигнала, в зависимости от отношения сигнал/шум на входе приемного устройства для БГШ и одного из трех видов помех Джонсона с различными параметрами распределения. В результате исследования были установлены потенциальные возможности обнаружения сигнала ПЭМИ клавиатуры интерфейса USB в идеальных условиях без воздействия внешнего шума и в реальных условиях естественного и индустриального шумов. На основании полученных результатов сделан вывод о том, что излучения ПЭМИ клавиатуры интерфейса USB не являются опасными с точки зрения возможного обнаружения в реальных условиях.This article is devoted to research potential detection informative and uninformative signal components compromising emanations USB keyboard interface. Digital experiment held to assess the value of the maximum cross-correlation function of the signal spectrum compromising emanations, radiated from two informative wire containing package interrogation and response data and reference signal, depending on the signal / noise ratio at the receiver input for WGN and one of three types of interference Johnson different the parameters of the distribution. As a result, studies have established the potential of the detection signal compromising emanations keyboard USB interface in ideal conditions without the influence of external noise and the actual conditions of natural and industrial noise. Based on the results concluded that the radiation compromising emanations keyboard USB interface are not dangerous from the point of view of a possible encounter in the real conditions

Synthesis, Structure, and Magnetic Properties of an Al2O3/Ge-p/Al2O3/Co Thin-Film System

Abstract—Structural and magnetic measurements are made of an Al2O3/Ge-p/Al2O3/Co thin-film system. The structure is synthesized via ion-plasma deposition and can be used as a tunnel heterostructure. The dependences of the magnetic properties of cobalt on the rate of its deposition and the rates of deposition of preceding layers are established

Parametric resonance of capillary waves at the interface between two immiscible Bose-Einstein condensates

We study parametric resonance of capillary waves on the interface between two immiscible Bose-Einstein condensates pushed towards each other by an oscillating force. Guided by analytical models, we solve numerically the coupled Gross-Pitaevskii equations for two-component Bose-Einstein condensate at zero temperature. We show that, at moderate amplitudes of the driving force, the instability is stabilized due to non-linear modifications of the oscillation frequency. When the amplitude of the driving force is large enough, we observe detachment of droplets from the Bose-Einstein condensates, resulting in generation of quantum vortices (skyrmions). We analytically investigate the vortex dynamics, and conditions of quantized vortex generation.Comment: (Version 2) 11 resized figures. One new reference adde

Interface dynamics of a two-component Bose-Einstein condensate driven by an external force

The dynamics of an interface in a two-component Bose-Einstein condensate driven by a spatially uniform time-dependent force is studied. Starting from the Gross-Pitaevskii Lagrangian, the dispersion relation for linear waves and instabilities at the interface is derived by means of a variational approach. A number of diverse dynamical effects for different types of the driving force is demonstrated, which includes the Rayleigh-Taylor instability for a constant force, the Richtmyer-Meshkov instability for a pulse force, dynamic stabilization of the Rayleigh-Taylor instability and onset of the parametric instability for an oscillating force. Gaussian Markovian and non-Markovian stochastic forces are also considered. It is found that the Markovian stochastic force does not produce any average effect on the dynamics of the interface, while the non-Markovian force leads to exponential perturbation growth.Comment: 13 pages, 12 figure

Decoherence of Bose-Einstein condensates in microtraps

We discuss the impact of thermally excited near fields on the coherent expansion of a condensate in a miniaturized electromagnetic trap. Monte Carlo simulations are compared with a kinetic two-component theory and indicate that atom interactions can slow down decoherence. This is explained by a simple theory in terms of the condensate dynamic structure factor.Comment: 5 pages, 4 figure

Higher-order nonlinear modes and bifurcation phenomena due to degenerate parametric four-wave mixing

We demonstrate that weak parametric interaction of a fundamental beam with its third harmonic field in Kerr media gives rise to a rich variety of families of non-fundamental (multi-humped) solitary waves. Making a comprehensive comparison between bifurcation phenomena for these families in bulk media and planar waveguides, we discover two novel types of soliton bifurcations and other interesting findings. The later includes (i) multi-humped solitary waves without even or odd symmetry and (ii) multi-humped solitary waves with large separation between their humps which, however, may not be viewed as bound states of several distinct one-humped solitons.Comment: 9 pages, 17 figures, submitted to Phys. Rev.

Bragg guiding of domain-like nonlinear modes and kink arrays in lower-index core structures

We introduce a novel class of stable nonlinear modes trapped in a lower-index film core sandwiched between two optical lattices, or in the cylindrical core of a radial lattice, imprinted in defocusing media. Such family of nonlinear modes transforms into defect lattice solitons when the core width is sufficiently small or into an array of kinks when the width is large enough. We find that higher-order modes with multiple zeros inside the guiding core can be stable in one-dimensional settings.Comment: 12 pages, 3 figures, to appear in Optics Letter

Parametric localized modes in quadratic nonlinear photonic structures

We analyze two-color spatially localized modes formed by parametrically coupled fundamental and second-harmonic fields excited at quadratic (or chi-2) nonlinear interfaces embedded into a linear layered structure --- a quasi-one-dimensional quadratic nonlinear photonic crystal. For a periodic lattice of nonlinear interfaces, we derive an effective discrete model for the amplitudes of the fundamental and second-harmonic waves at the interfaces (the so-called discrete chi-2 equations), and find, numerically and analytically, the spatially localized solutions --- discrete gap solitons. For a single nonlinear interface in a linear superlattice, we study the properties of two-color localized modes, and describe both similarities and differences with quadratic solitons in homogeneous media.Comment: 9 pages, 8 figure