Microkelvin thermometry with Bose-Einstein condensates of magnons and applications to studies of the AB interface in superfluid 3^3He

Coherent precession of trapped Bose-Einstein condensates of magnons is a sensitive probe for magnetic relaxation processes in superfluid 3He-B down to the lowest achievable temperatures. We use the dependence of the relaxation rate on the density of thermal quasiparticles to implement thermometry in 3He-B at temperatures below 300 $\mu$K. Unlike popular vibrating wire or quartz tuning fork based thermometers, magnon condensates allow for contactless temperature measurement and make possible an independent in situ determination of the residual zero-temperature relaxation provided by the radiation damping. We use this magnon-condensate-based thermometry to study the thermal impedance of the interface between A and B phases of superfluid 3He. The magnon condensate is also a sensitive probe of the orbital order-parameter texture. This has allowed us to observe for the first time the non-thermal signature of the annihilation of two AB interfaces.Comment: 26 pages, 7 figures, manuscript prepared for EU Microkelvin Collaboration Workshop 2013. Accepted for publication in Journal of Low Temperature Physic

Vortex-mediated relaxation of magnon BEC into light Higgs quasiparticles

A magnon Bose-Einstein condensate (BEC) in superfluid 3He is a fine instrument for studying the surrounding macroscopic quantum system. At zero temperature, the BEC is subject to a few distinct forms of decay into other collective excitations, owing to momentum and energy conservation in a quantum vacuum. We study the vortex-Higgs mechanism: The vortices relax the requirement for momentum conservation, allowing the optical magnons of the BEC to transform into light Higgs quasiparticles. This facilitates a direct measurement of the dimensions of the B-phase double-core vortex, providing experimental access to elusive phenomena, such as the Kelvin wave cascade and core-bound Majorana fermions. Our paper expands the spectrum of possible interactions between magnetic quasiparticles in 3He-B and lays the groundwork for building magnon-based quantum devices

Rotating quantum wave turbulence

Turbulence under strong influence of rotation is described as an ensemble of interacting inertial waves across a wide range of length scales. In macroscopic quantum condensates, the quasiclassical turbulent dynamics at large scales is altered at small scales, where the quantization of vorticity is essential. The nature of this transition remains an unanswered question. Here we expand the concept of wave-driven turbulence to rotating quantum fluids where the spectrum of waves extends to microscopic scales as Kelvin waves on quantized vortices. We excite inertial waves at the largest scale by periodic modulation of the angular velocity and observe dissipation-independent transfer of energy to smaller scales and the eventual onset of the elusive Kelvin wave cascade at the lowest temperatures. We further find that energy is pumped to the system through a boundary layer distinct from the classical Ekman layer and support our observations with numerical simulations. Our experiments demonstrate a regime of turbulent motion in quantum fluids where the role of vortex reconnections can be neglected, thus stripping the transition between the classical and the quantum regimes of turbulence down to its constituent components

Quasiparticle transport in a two-dimensional boundary superfluid

The B phase of superfluid 3He can be cooled into the "pure" superfluid regime, characterised by negligible thermal quasiparticle density. Here, the bulk superfluid is bounded by a two-dimensional quantum well at the boundaries of the container, where creating quasiparticles requires much less energy. In this Article, we carry out experiments where we create a non-equilibrium state within the quantum well and show that the induced quasiparticle currents flow diffusively in the two-dimensional system. We conclude that the bulk of superfluid 3He is wrapped by an independent two-dimensional superfluid that interacts with mechanical probes instead of the bulk superfluid, only providing access to the bulk superfluid if given a sudden burst of energy. That is, superfluid 3He at the lowest temperatures and applied energies is thermo-mechanically two dimensional. Our work opens this two-dimensional quantum condensate and the interface it forms between the observer and the bulk superfluid for exploration, and provides the possibility of creating two-dimensional condensates of arbitrary topology.Comment: 11 pages, 9 figure

Apoptosis in the liver of male <em>db/db</em> mice during the development of obesity and type 2 diabetes

Obesity and diabetes mellitus are known to lead to the development of metabolic syndrome and non-alcoholic fatty liver disease (NAFLD). The mechanisms of programmed cell death are actively involved in maintaining cellular homeostasis along development of NAFLD. Proteins of the BCL-2 family are key regulators of physiological and pathological apoptosis. Homozygous males of BKS.Cg-Dock7mLeprdb/+/+/J mice (db/db mice) are characterized by progressive obesity and the development of type 2 diabetes mellitus (DM2) with severe hyperglycemia at 4–8 weeks and organ lesions at 8–10 weeks of age. The aim of this research was to study the expression of molecular cell regulators of apoptosis in liver cells of db/db mice males at different stages of obesity and diabetes development (at the age of 10 and 18 weeks). Immunohistochemical analysis (using the indirect avidin-biotin peroxidase method) and morphometric evaluation of the expression of the antiapoptotic protein Bcl-2 and the proapoptotic protein Bad in liver cells of studied animals at different stages of obesity and DM2 were carried out. An excess of the value of the Bcl-2 protein staining area over the Bad protein staining area was revealed in the liver of 10-week-old animals. The Bcl-2/Bad expression area ratio in 10-week-old animals was twice as high as in 18-week-old animals, which indicates the presence of conditions for blocking apoptosis in the liver of younger db/db mice. At the 18th week of life, db/db mice displayed an almost threefold increase in the expression area of the Bad protein against the background of an unchanged expression of the Bcl-2 protein. The decrease in the Bcl-2/Bad staining area ratio in 18-week-old animals was due to the increase in the Bad expression area, which indicates the absence of antiapoptotic cell protection and creates conditions for activation of the mitochondrial pathway of apoptosis in the liver of male db/db mice with pronounced signs of obesity and DM2

Оптимизация формы сигналов с квадратурной амплитудной модуляцией с использованием критерия заданной скорости спада уровня внеполосных излучений

Introduction. The growth in the volume of information transmitted through communication channels leads to their significant congestion. Almost all methods conventionally used to increase the data transfer rate in given frequency bands have been exhausted. In this regard, it is of interest to use new approaches aimed at improving the spectral efficiency of radio engineering and telecommunication systems by applying optimal signals that make it possible to use the bandwidth reserves of transmission channels given by Shannon's theory.Aim. Improvement of the spectral efficiency of digital messaging systems by using signals with a compact spectrum and increased volume of the channel alphabet at the same time as minimizing energy losses.Materials and methods. When searching for optimal signals, the mathematical apparatus of communication theory and functional analysis, as well as the methods of calculus of variations, were used. The evaluation of bit error rate performance of the obtained optimal signals transmitted in a channel with additive white Gaussian noise was performed in the MatLab environment. Results. It was established that, in a channel with additive white Gaussian noise, optimal signals with a signal constellation size of 64 in the case of quadrature amplitude-phase modulation provide an energy gain of more than 1 dB relative to signals obtained by narrowband filtering under the conditions of uncontrolled intersymbol interference. Optimal signals were shown to provide for an energy gain of 4.9 dB with respect to signals based on narrow-band filtering at a fixed spectral efficiency of 7 (bit/s)/Hz.Conclusion. The paper proposes a method for improving the spectral efficiency of quadrature signals with amplitudephase modulation, based on the use of optimal pulse shapes obtained as a result of solving an optimization problem. The optimization problem was solved according to the criterion of minimizing out-of-band emissions with the constraint on bit error rate performance in case of amplitude-phase modulation. The energy and spectral efficiency of signals with optimal pulse shapes and signals based on narrow-band filtering were compared.Введение. Рост объемов передаваемой информации по каналам связи приводит к их существенной перегруженности. Практически все используемые традиционные методы повышения скорости передачи данных в заданных полосах частот исчерпаны. В этой связи представляет интерес использование новых подходов, направленных на повышение спектральной эффективности радиотехнических и телекоммуникационных систем путем применения оптимальных сигналов, позволяющих задействовать резервы пропускной способности каналов передачи, которые дает теория Шеннона.Цель работы. Повышение спектральной эффективности систем передачи цифровых сообщений путем применения сигналов с компактным спектром и увеличения объема канального алфавита при минимизации энергетических потерь.Материалы и методы. При поиске оптимальных сигналов используется математический аппарат теории связи и функционального анализа, а также методы вариационного исчисления. Оценка помехоустойчивости приема полученных оптимальных сигналов при передаче в канале с аддитивным белым гауссовским шумом выполнена в среде MatLab.Результаты. Установлено, что в канале с аддитивным белым гауссовским шумом оптимальные сигналы при размере сигнального созвездия 64 в случае квадратурной амплитудно-фазовой модуляции обеспечивают энергетический выигрыш более 1 дБ относительно сигналов, которые получаются путем узкополосной фильтрации в условиях неконтролируемой межсимвольной интерференции. Показано, что оптимальные сигналы позволяют получить энергетический выигрыш 4.9 дБ по отношению к сигналам, построенным на основе узкополосной фильтрации, при фиксированной спектральной эффективности 7 (бит/с)/Гц.Заключение. Предложен метод повышения спектральной эффективности квадратурных сигналов с амплитудно-фазовой модуляцией, основанный на применении оптимальных форм импульсов, полученных в ходе решения оптимизационной задачи. Приведена процедура решения оптимизационной задачи по критерию минимизации внеполосных излучений при наличии ограничения на помехоустойчивость приема в случае амплитудно-фазовой модуляции. Выполнено сравнение энергетической и спектральной эффективности, обеспечиваемой сигналами с оптимальными формами импульсов и сигналами, построенными на основе узкополосной фильтрации

The expression of apoptosis-regulating proteins Bcl-2 and Bad in liver cells of C57Bl/6 mice under light-induced functional pinealectomy and after correction with melatonin

The presence of humans and animals under long-term continuous lighting leads to a suppression of melatonin synthesis, that is, to light-induced functional pinealectomy (LIFP), and the development of desynchronosis. To create LIFP, C57Bl/6 mice were kept under 24-hour lighting (24hL) for 14 days. The animals in the control group were kept under standard lighting conditions. In the next series of experiments, mice with LIFP received daily intragastrically either melatonin (1 mg/kg body weight in 200 μl of distilled water) or 200 μl of water as a placebo. The comparison group consisted of intact animals that received placebo under standard lighting conditions. Immunohistochemical analysis (using an indirect avidin-biotin peroxidase method) revealed the expression of the antiapoptotic protein Bcl-2 and the proapoptotic protein Bad in sinusoid liver cells (a heterogeneous population consisting of the endotheliocytes, Kupffer cells, Ito cells, and Pit cells) and in individual hepatocytes. The Bad expression area in the liver of LIFP mice increased 4 times against a background of the unchanged Bcl-2 expression area. Changes in the brightness (a parameter inversely proportional to the marker concentration) of Bad and Bcl-2 areas did not reach significance. Our results indicate a weakening of the antiapoptotic protection of liver cells of LIFP animals, which creates conditions for activation of the “mitochondrial branch” of apoptosis. Melatonin treatment of LIFP mice resulted in a 3.3-fold increase in Bcl-2 expression area and a 2.7 % decrease in Bcl-2 region brightness compared with the experimental untreated group. Bad protein parameters were unreliable. Thus, melatonin treatment of animals cancels the effect of LIFP, restoring the Bcl-2 expression area and increasing this protein concentration, which indicates an increase in antiapoptotic protection and creates conditions for blocking the development of the “mitochondrial branch” of apoptosis in liver cells