Ferrimagnetism of the magnetoelectric compound Cu2_2OSeO3_3 probed by 77^{77}Se NMR

We present a thorough $^{77}$Se NMR study of a single crystal of the magnetoelectric compound Cu$_2$OSeO$_3$. The temperature dependence of the local electronic moments extracted from the NMR data is fully consistent with a magnetic phase transition from the high-T paramagnetic phase to a low-T ferrimagnetic state with 3/4 of the Cu$^{2+}$ ions aligned parallel and 1/4 aligned antiparallel to the applied field of 14.09 T. The transition to this 3up-1down magnetic state is not accompanied by any splitting of the NMR lines or any abrupt modification in their broadening, hence there is no observable reduction of the crystalline symmetry from its high-T cubic \textit{P}2$_1$3 space group. These results are in agreement with high resolution x-ray diffraction and magnetization data on powder samples reported previously by Bos {\it et al.} [Phys. Rev. B, {\bf 78}, 094416 (2008)]. We also develop a mean field theory description of the problem based on a microscopic spin Hamiltonian with one antiferromagnetic ($J_\text{afm}\simeq 68$ K) and one ferromagnetic ($J_\text{fm}\simeq -50$ K) nearest-neighbor exchange interaction

Materials of the final reports on the joint Soviet-American experiment on the Kosmos-936 biosatellite

Biological experiments onboard the Kosmos-936 investigated the effect of weightlessness on the basic components of cells, the genetic structure and energy apparatus. Genetic studies were made on the Drosophila melanogaster. Experiments were made on higher vegetation and fungi as well. The results indicate that weightlessness cannot be the principal barrier for normal development. An experiment with ectopic osteogenesis in weightlessness was carried out. Measurements were made of cosmic radiation inside and outside the biosatellite

Simulations of stable compact proton beam acceleration from a two-ion-species ultrathin foil

We report stable laser-driven proton beam acceleration from ultrathin foils consisting of two ion species: heavier carbon ions and lighter protons. Multi-dimensional particle-in-cell (PIC) simulations show that the radiation pressure leads to very fast and complete spatial separation of the species. The laser pulse does not penetrate the carbon ion layer, avoiding the proton Rayleigh-Taylor-like (RT) instability. Ultimately, the carbon ions are heated and spread extensively in space. In contrast, protons always ride on the front of the carbon ion cloud, forming a compact high quality bunch. We introduce a simple three-interface model to interpret the instability suppression in the proton layer. The model is backed by simulations of various compound foils such as carbon-deuterium (C-D) and carbon-tritium (C-T) foils. The effects of the carbon ions' charge state on proton acceleration are also investigated. It is shown that with the decrease of the carbon ion charge state, both the RT-like instability and the Coulomb explosion degrade the energy spectrum of the protons. Finally, full 3D simulations are performed to demonstrate the robustness of the stable two-ion-species regime.Comment: 14 pages, 10figures, to be published in PO

ПЬЕЗОЭЛЕКТРИЧЕСКИЙ ВОЛНОВОДНЫЙ ДАТЧИК ДЛЯ ИЗМЕРЕНИЯ ИМПУЛЬСНОГО ДАВЛЕНИЯ В ЗАМКНУТЫХ ОБЪЕМАХ ЖИДКОСТИ ПРИ ВЫСОКОВОЛЬТНОМ ЭЛЕКТРИЧЕСКОМ РАЗРЯДЕ

Purpose. Investigations of the characteristics of pressure waves presuppose the registration of the total profile of the pressure wave at a given point in space. For these purposes, various types of «pressure to the electrical signal» transmitters (sensors) are used. Most of the common sensors are unsuitable for measuring the pulse pressure in a closed water volume at high hydrostatic pressures, in particular to study the effect of a powerful high-voltage pulse discharge on increasing the inflow of minerals and drinking water in wells. The purpose of the work was to develop antijamming piezoelectric waveguide sensor for measuring pulse pressure at a close distance from a high-voltage discharge channel in a closed volume of a liquid. Methodology. We have applied the calibration method as used as a secondary standard, the theory of electrical circuits. Results. We have selected the design and the circuit solution of the waveguide pressure sensor. We have developed a waveguide pulse-pressure sensor DTX-1 with a measuring loop. This sensor makes it possible to study the spectral characteristics of pressure waves of high-voltage pulse discharge in closed volumes of liquid at a hydrostatic pressure of up to 20 MPa and a temperature of up to 80 °C. The sensor can be used to study pressure waves with a maximum amplitude value of up to 150 MPa and duration of up to 80 µs. According to the results of the calibration, the sensitivity of the developed sensor DTX-1 with a measuring loop is 0.0346 V/MPa. Originality. We have further developed the theory of designing the waveguide piezoelectric pulse pressure sensors for measuring the pulse pressure at a close distance from a high-voltage discharge channel in a closed fluid volume by controlling the attenuation of the amplitude of the pressure signal. Practical value. We have developed, created, calibrated, used in scientific research waveguide pressure pulse sensors DTX-1. We propose sensors DTX-1 for sale in Ukraine and abroad. Sensors DTX-1 can be used to study pressure waves with a maximum amplitude value of up to 150 MPa in closed fluid volumes at a hydrostatic pressure of up to 20 MPa and a temperature of up to 80 °C.На основании проведенного анализа рынка приборов, измеряющих импульсное давление, выбрана конструкция и схемное решение помехоустойчивого волноводного датчика давления, обеспечивающего стабильность и достоверность показаний на близком расстоянии от канала высоковольтного электрического разряда в замкнутом объеме жидкости. Разработан волноводный датчик импульсного давления ДТХ-1 с измерительным шлейфом, позволяющий исследовать спектральные характеристики волн давления в закрытых объемах жидкости при гидростатическом давлении до 20 МПа и температуре до 80 °С. Датчик может быть применен для изучения волн давления с максимальным амплитудным значением до 150 МПа и длительностью до 80 мкс. Согласно результатам тарировки с использованием вторичного эталона, чувствительность датчика ДТХ-1 с измерительным трактом – 0,0346 В/МПа

Композиционные особенности и печатные проблемы двухкомпонентных маркировочных красок

Досліджено визначальні чинники стабільності друкарсько-технологічних властивостей двокомпонентних маркувальний фарб на епоксидній основі. Запропоновано науковий підхід до проблеми надання друкарсько-технологічних властивостей епоксидним лакофарбовим системам, що складаються з нетрадиційних для звичайних друкарських фарб компонентів.There were investigated determination factors of printing technological stability of two-component epoxy based marking inks. Scientific approach to the problem of impart the printing technological properties to epoxy non-traditional ink systems are suggested.Исследованы определяющие факторы стабильности печатно-технологических свойств двухкомпонентных маркировочных красок на эпоксидной основе. Предложен научный подход к проблеме придания печатно-технологических свойств эпоксидным лакокрасочным системам, состоящим из нетрадиционных для обычных печатных красок компонентов

Геоботанічні аспекти екотонізації природних ландшафтів

Vegetation is one of the main criteria for landscape differentiation of the Earth surface. The main morphological feature of the landscape is the presence or absence of the forest that is, and the gradual character of the boundaries between the natural zones causes the formation of fairly wide transitional zones bands – ecotones. They have become one of the most common subjects in landscape research in recent years. This is natural in view of the insufficient localization of ecotones and their constant drift in the light of gradual changes in climate and degradation of soil cover. In modern studies, structural-geographical ecotones are considered not as clear sharp boundaries, but as rather wide transitional bands. There are four natural zones (mixed coniferous-deciduous forests, deciduous forests, forest-steppe and steppe) and three structural and geographical strips – pasture, forest and field districted in the plain part of Ukraine. If the physical-geographical boundary of the forest-steppe and steppe is traditionally drawn along the Balta – Kropyvnytskyi – Dnipro – Izyum – Kup'yansk line, from the standpoint of constructive geography, the area of continuous predominance of the field landscapes is shifted to the north by almost 100 km. In general, the territory of the traditionally separated southern sub-zone of the forest-steppe objectively reaching the steppe zone is today. Anthropogenic factor makes its adjustments to the holding of ecotones, in particular through deforestation. The action of natural and anthropogenic factors is synergistic. On the one hand, the natural process of the steppe on the forest continues; on the other hand, one actively promotes deforestation. Therefore, the boundaries of Polissya and the Forest-Steppe are becoming less clear. Ecotones are manifested not only on the interzonal (macro- and meso scale) but also on the intra-zonal, within landscape complexes (micro levels). A striking example would be the ecotones in forest landscapes. In general, the continuous changes of the landscape environment, caused nowadays by both natural and anthropogenic factors, inevitably cause the displacement of both geobotanical and physical-geographical boundaries. However, most landscape systems are not homogeneous in their typological characteristics; the transitions between them are rather blurred. This further complicates the boundaries and suggests the leading importance of ecotones in the terrestrial landscape organization.Відзначено, що більшість сучасних ландшафтів – як натуральних природних, так і антропогенних – мають характер екотонів. Наголошено, що екотонізація виразно позначається на педобіогенному компоненті-чинникові ландшафту. Зауважено, що формування екотонів відбувається як на макро- й мезо-, так і на мікрорівні організації рослинного компоненту. Проілюстровано, що явище поступового переходу від однієї фізико-географічної зони до іншої яскраво проявляється на прикладах лісостепу Правобережної України – як у межах екотону "зона мішаних лісів" – "лісостеп", так і в смузі екотону "лісостеп" – "степ". Наголошено, що процесам екотонізації ландшафтів істотно сприяє втручання антропогенного чинника. Розглянуто різні варіанти екотонізації лісових фітоценозів, зокрема висвітлено особливості природних і антропогенних екотонів "ліс – галявина", "ліс – прогалина", "ліс – узлісся", "ліс – зруб" тощо. Відзначено високий рівень біорізноманіття, властивий лісовим ландшафтам завдяки їхній екотонізації. Проаналізовано феномен "екотону в часі", що проявляється на сукцесійних стадіях розвитку лісових фітоценозів. Окреслено основний зміст концепцій змін порід деревної лісової рослинності відповідно до поглядів В. П. Кучерявого та Г. Ф. Морозова. Зауважено, що сукупна дія природних і антропогенних чинників увиразнює розмитість меж природних регіонів і в такий спосіб підсилює екотонізацію ландшафтів, зокрема лісових. Наголошено, що дослідження екотонів становить комплексну міждисциплінарну наукову проблему, що перебуває на пограниччі географії, геоботаніки, лісознавства, ландшафтної та соціоекології

Electrically-driven phase transition in magnetite nanostructures

Magnetite (Fe$_{3}$O$_{4}$), an archetypal transition metal oxide, has been used for thousands of years, from lodestones in primitive compasses[1] to a candidate material for magnetoelectronic devices.[2] In 1939 Verwey[3] found that bulk magnetite undergoes a transition at T$_{V}$ $\approx$ 120 K from a high temperature "bad metal" conducting phase to a low-temperature insulating phase. He suggested[4] that high temperature conduction is via the fluctuating and correlated valences of the octahedral iron atoms, and that the transition is the onset of charge ordering upon cooling. The Verwey transition mechanism and the question of charge ordering remain highly controversial.[5-11] Here we show that magnetite nanocrystals and single-crystal thin films exhibit an electrically driven phase transition below the Verwey temperature. The signature of this transition is the onset of sharp conductance switching in high electric fields, hysteretic in voltage. We demonstrate that this transition is not due to local heating, but instead is due to the breakdown of the correlated insulating state when driven out of equilibrium by electrical bias. We anticipate that further studies of this newly observed transition and its low-temperature conducting phase will shed light on how charge ordering and vibrational degrees of freedom determine the ground state of this important compound.Comment: 17 pages, 4 figure

Nfluence of degradation of physical and mechanical properties on the kinetics of material damage under cyclic loading conditions

The article shows that at deformations of the material, the level of which exceeds the deformation corresponding to the limit of proportionality, the modulus of elasticity of the first kind and the homogeneity parameter of the material, which was determined by the LM-hardness method, are in a correlation relationshi

ANALYSIS AND DEVELOPMENT OF THE BUBBLE MODEL OF THE FORMATION STAGE OF HIGH-VOLTAGE BREAKDOWN OF THE WATER GAP

Purpose. A high-voltage underwater electric explosion, realized by discharging a capacitor into a water gap, is characterized by three main stages: the stage of formation of the plasma channel, the channel stage and post-discharge one. Substantially, the channel, post-discharge stages and the efficiency of energy release in the channel and the increase in the hydrodynamic effect on the object being processed depend on the parameters of the stage of formation. The purpose of the work was to review the existing mechanisms for the formation of a high-voltage discharge channel with the analysis and development of a bubble model of the stage of formation of water gap breakdown. Methodology. We have applied the analysis of existing theories on the formation of a high-voltage discharge channel, the carrying out of electrophysical studies with the processing of the obtained data. Results. A review and analysis of modern concepts of pre-breakdown processes in a high-voltage electric discharge in a liquid showed that the «bubble» model of the ignition of a discharge is applicable at an electric field strength (36 – 180) kV/cm. We have further developed the bubble model of the stage of formation of high-voltage breakdown on the results of experimental studies of the electrical characteristics of the discharge in the aqueous electrolyte with increased hydrostatic pressure and minimum voltage providing ignition of the discharge. A qualitative description of three phases of the stage of formation of the plasma channel in the liquid electrolyte is proposed. Originality. We have further developed the bubble model of the stage of formation of high-voltage breakdown of the liquid electrolyte on the results of experimental studies of the electrical characteristics of the discharge in the aqueous electrolyte with increased hydrostatic pressure and minimum voltage providing ignition of the discharge. A qualitative variation of the resistance of the gap in the pre-breakdown stage of the discharge is considered. Practical value. Determination of the scientific basis for creating a methodology for calculating the pre-breakdown characteristics of an electric discharge to improve the efficiency of electric discharge devices