Effect of plasma on the radio-technical characteristics of the Uragan-2M torsatron matching RF systems

There were carried out qualitative studies of the effect of plasma parameters during the RF disharge wall conditioning in a helium atmosphere on the quality factor of the antenna oscillating circuit at Uragan-2M torsatron. The quality factor is determined from the ratio of the electric current in the circuit to the feed current. The dependence of the quality factor of the toroidal steady magnetic field as well as on the helical field is analyzed. The dependence on the helical field is much stronger; with its increase the quality factor increases that is accompanied with reduction of the antenna load. Also, the ratio of idling current in the antenna (when the plasma even less) to the current in the antenna is measured during the discharge. The dependence of this parameter on the toroidal magnetic field and the neutral gas pressure is studied.Проведены качественные исследования влияния плазмы в режиме ВЧ-чистки в атмосфере гелия на добротность антенного колебательного контура в торсатроне Ураган-2М. Добротность определялась из отношенния тока в контуре к току подводящего фидера Q=Ik/If. Проанализирована зависимость добротности как от тороидального поля, так и от винтового. Зависимость от винтового поля значительно сильнее, с его ростом добротность увеличивается, что соответствует снижению нагрузки антенны. Также измерялся параметр Iaxx/IaL, т.е. отношение тока в антенне в момент холостого хода генератора (когда плазмы еще нет) к току в антенне в момент разряда. Приведены зависимости этого параметра от тороидального поля и от давления.Проведені якісні дослідження впливу плазми в режимі ВЧ-чистки в атмосфері гелію на добротність антенного коливального контуру в торсатроні Ураган-2М. Добротність визначалась з відношення струму в контурі до струму підвідного фідера Q=Ik / If. Показана залежність добротності як від тороїдального, так і від гвинтового полів. Залежність від гвинтового поля значно сильніше, з ростом поля добротність збільшується, що відповідає зниженню навантаження антени. Вимірювався також параметр Iaxx / IaL, тобто відношення струму в антені в момент холостого ходу генератора (коли плазми ще немає) до струму в антені в момент розряду. Виявлено також залежності цього параметру від тороїдального поля та від тиску

Effect of pressure on the magnetic properties of CrB₂

Magnetic susceptibility c of the itinerant antiferromagnet CrB₂ with TN ≃ 87K was studied as a function of the hydrostatic pressure up to 2 kbar at fixed temperatures 78 and 300 K. The pressure effect on c is found to be negative in sign and weakly dependent on the magnetic state of the compound. In addition, the measured pressure dependence of the Néel temperature, dTN / dP = (0.1 ± 0.1) K/kbar, is roughly two orders of magnitude smaller than the corresponding value for the pure chromium. The main contributions to c and their volume dependence are calculated ab initio within the local spin density approximation, and appeared to be in close agreement with the experimental data

Pressure effects on electronic structure and magnetic properties of anisotropic metallic compounds

Pressure effects on electronic structure and magnetic properties of anisotropic metallic materials (CrB₂, FeGe₂, LaFeAsO) are investigated. Magnetic susceptibilities of CrB₂ and FeGe₂ compounds were studied under hydrostatic pressure at fixed temperatures, 77 and 300 K. In order to analyze the experimental magnetovolume effects, the electronic structures were calculated ab initio in external magnetic field as a function of atomic volume by employing a full-potential LMTO method. The calculated field-induced magnetic moments and their volume derivatives compare favorably with the experimental pressure effects in magnetic properties of CrB₂ and FeGe₂. The main role of pressure in high-Tc superconductivity of LaFeAsO is found to reduce density of states at the Fermi level and to suppress ferromagnetic spin fluctuations

The Origin, Early Evolution and Predictability of Solar Eruptions

Coronal mass ejections (CMEs) were discovered in the early 1970s when space-borne coronagraphs revealed that eruptions of plasma are ejected from the Sun. Today, it is known that the Sun produces eruptive flares, filament eruptions, coronal mass ejections and failed eruptions; all thought to be due to a release of energy stored in the coronal magnetic field during its drastic reconfiguration. This review discusses the observations and physical mechanisms behind this eruptive activity, with a view to making an assessment of the current capability of forecasting these events for space weather risk and impact mitigation. Whilst a wealth of observations exist, and detailed models have been developed, there still exists a need to draw these approaches together. In particular more realistic models are encouraged in order to asses the full range of complexity of the solar atmosphere and the criteria for which an eruption is formed. From the observational side, a more detailed understanding of the role of photospheric flows and reconnection is needed in order to identify the evolutionary path that ultimately means a magnetic structure will erupt

Measurement of CP asymmetries and branching fraction ratios of B− decays to two charm mesons

The $CP$ asymmetries of seven $B^-$ decays to two charm mesons are measured using data corresponding to an integrated luminosity of $9\text{fb}^{-1}$ of proton-proton collisions collected by the LHCb experiment. Decays involving a $D^{*0}$ or $D^{*-}_s$ meson are analysed by reconstructing only the $D^0$ or $D^-_s$ decay products. This paper presents the first measurement of $\mathcal{A}^{CP}(B^- \rightarrow D^{*-}_s D^0)$ and $\mathcal{A}^{CP}(B^- \rightarrow D^{-}_s D^{*0})$, and the most precise measurement of the other five $CP$ asymmetries. There is no evidence of $CP$ violation in any of the analysed decays. Additionally, two ratios between branching fractions of selected decays are measured.The CP asymmetries of seven B$^{−}$ decays to two charm mesons are measured using data corresponding to an integrated luminosity of 9 fb$^{−1}$ of proton-proton collisions collected by the LHCb experiment. Decays involving a D$^{*0}$ or ${D}_s^{\ast -}$ meson are analysed by reconstructing only the D$^{0}$ or ${D}_s^{-}$ decay products. This paper presents the first measurement of $\mathcal{A} ^{CP}$(B$^{−}$→${D}_s^{\ast -}$D$^{0}$) and $\mathcal{A} ^{CP}$(B$^{−}$→${D}_s^{-}$D$^{∗0}$), and the most precise measurement of the other five CP asymmetries. There is no evidence of CP violation in any of the analysed decays. Additionally, two ratios between branching fractions of selected decays are measured.[graphic not available: see fulltext]The $CP$ asymmetries of seven $B^-$ decays to two charm mesons are measured using data corresponding to an integrated luminosity of $9\text{ fb}^{-1}$ of proton-proton collisions collected by the LHCb experiment. Decays involving a $D^{*0}$ or $D^{*-}_s$ meson are analysed by reconstructing only the $D^0$ or $D^-_s$ decay products. This paper presents the first measurement of $\mathcal{A}^{CP}(B^- \rightarrow D^{*-}_s D^0)$ and $\mathcal{A}^{CP}(B^- \rightarrow D^{-}_s D^{*0})$, and the most precise measurement of the other five $CP$ asymmetries. There is no evidence of $CP$ violation in any of the analysed decays. Additionally, two ratios between branching fractions of selected decays are measured

The primary phase part in microstructure formation of in-situ eutectic composite of LaB₆-ZrB₂

The crystal orientation relationships (COR) of LaB₆-ZrB₂ eutectic phase produced by directional solidification (DS) correspond to non-optimum coherency conditions of phase boundaries. Another peculiar feature of this eutectic is the dominant role of primary low temperature phase (LaB₆) in the cooperative eutectic growth. As a rule, it is just the high-temperature phase that plays a leading role in the crystallization and promotes heterogeneous nucleation of the second phase. In contrast, in LaB₆-ZrB₂ eutectic system, the high-temperature ZrB₂ whiskers start to grow on (100) faces of low-temperature LaB₆ phase. A possibility of discrete changes in growth direction of the composite regular structure up to 90⁰ has been revealed. It is suggested that all above mentioned features are defined mainly by the nucleation processes during the eutectic co-crystallization process, rather than by the ordinary fundamental criteria of interface surface energy minimization that occurs due to the semi-coherent habit facets formation.Установлено, что кристаллические ориентационные соотношения фаз эвтектики LaB₆-ZrB₂, полученной методом направленной кристаллизации, соответствуют не самым выгодным условиям когерентности межфазных границ. Особенностью этой эвтектики является также превалирующая роль матричной, низкотемпературной фазы в процессе кооперативного эвтектического роста. В отличие от обычного случая, когда высокотемпературная фаза играет ведущую роль при эвтектической кристаллизации и является зародышеобразующей для второй фазы, в эвтектической системе LaB₆-ZrB₂ кооперативный эвтектический рост волокон высокотемпературной фазы ZrB₂ начинается на фасетах (100) низкотемпературной фазы LaB₆. Обнаружена способность дискретного изменения направления роста регулярной структуры композита вплоть до 90⁰. Предполагается, что все упомянутые особенности определяются в основном процессами зародышеобразования во время кооперативной эвтектической сокристаллизации, а не привычными фундаментальными критериями минимизации энергии поверхности межфазных границ за счет формирования их полукогерентных габитусных поверхностей.Встановлено, що кристалiчнi орiєнтацiйнi спiввiдношення фаз евтектики LaB₆-ZrB₂, що отримана методом спрямованої кристалiзацiї, вiдповiдають не найбiльш вигiдним умовам когерентностi мiжфазових меж. Особливiстю цiєї евтектики також є головуюча роль матричної, низькотемпературної фази у процесi кооперативного евтектичного росту. На вiдмiну вiд звичайного випадку, коли високотемпературна фаза є ведучою евтектичну кристалiзацiю i зародкоутворюючою для другої фази, в евтектичнiй системi LaB₆-ZrB₂ кооперативний евтектичний рiст волокнин високотемпературної фази ZrB₂ починається на (100) фасетах низькотемпературної фази LaB₆. Виявлено здатнiсть дискретної змiни напрямку росту регулярної структури композиту на кути до 90⁰. Припускається, що усi згаданi особливостi визначаються в загалом зародкоутворюючими процесами кооперативної евтектичної кристалiзацiї, а не звичними, фундаментальними критерiями мiнiмiзацiї енергiї поверхнi мiжфазових меж за рахунок формування їх напiвкогерентних габiтусних фасет

Valence electron distribution in zirconium dodecaboride

First-principles calculations of the valence electron distribution in ZrB₁₂ have been performed by the modified Thomas-Fermi statistical method. The charge destiny maps for some planes across Zr and B atoms are presented and discussed. Directional bonding intoduced by born atoms in the crystal lattice explains the superhardness of the material

Andreev-reflection spectroscopy of the gap in ZrB12 single crystals

We present the first results of point-contact spectroscopy (PCS) in single crystals of the boride superconductor ZrB12. The material was first characterized by AC susceptibility and resistivity measurements that allowed us to determine several quantities of physical interest. Then we performed point-contact measurements that gave conductance curves with clear Andreev-reflection features typical of an s-wave single-gap superconductor. By measuring these conductance curves at various temperatures and in the presence of magnetic fields, we obtained the temperature dependence of the gap and of the upper critical field of ZrB12, as well as an estimate of the Fermi energy. All the results indicate that ZrB12 is a conventional s-wave weak coupling superconductor

The importance and possibilities of role playing on children surgery classes

This article analyzes the first experience in the implementation into the pedagogical process of one of the methods of active training — role playing. The need for intensification of medical education process is linked primarily to the rapid increase in the volume required to provide students with information and the lack of training time. The analysis showed that the game significantly increases the level of students' knowledge, but require substantial modernization of the educational process

Electronic structure and bulk properties of MB₆ and MB₁₂ borides

Ab initio band structure calculations have been carried out for higher boridesMB6 andMB12. High precision measurements of the elastic constants were performed for ZrB₁₂, HoB₁₂, ErB₁₂, TmB₁₂, LuB₁₂, YB₆ and LaB₆ compounds at low temperatures. The bulk properties of the borides have been analyzed on the basis of the calculated equations of states and balanced crystal orbital overlap populations. Our calculations indicate that hexaborides with divalent metals, CaB₆, SrB₆, BaB₆, and YbB₆, are semiconductors with small energy gaps. The metallic MB6 hexaborides with trivalent M atoms are found to possess larger bulk moduli values. For dodecaborides bulk moduli are found to be higher for MB₁₂ with increased filling of the conduction band (ZrB₁₂, HfB₁₂, UB₁₂), comparatively to M³+B₁₂ compounds. The total energy calculations for different magnetic configurations in YbB₁₂ point to a possibility of antiferromagnetic coupling between Yb³⁺ ions