667 research outputs found

    Piezoelectric mechanism of orientation of stripe structures in two-dimensional electron systems

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    A piezoelectric mechanism of orientation of stripes in two-dimensional quantum Hall systems in GaAs heterostructures is considered. The anisotropy of the elastic moduli and the boundary of the sample are taken into account. It is found that in the average the stripes line up with the [110] axis. In double layer systems the wave vector of the stripe structure rotates from the [110] to [100] axis if the period of density modulation becomes large than the interlayer distance. From the experimental point of view it means that in double layer systems anisotropic part of resistivity changes its sign under variation of the external magnetic field.Comment: 8 page

    Novel inferences of ionisation & recombination for particle/power balance during detached discharges using deuterium Balmer line spectroscopy

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    The physics of divertor detachment is determined by divertor power, particle and momentum balance. This work provides a novel analysis technique of the Balmer line series to obtain a full particle/power balance measurement of the divertor. This supplies new information to understand what controls the divertor target ion flux during detachment. Atomic deuterium excitation emission is separated from recombination quantitatively using Balmer series line ratios. This enables analysing those two components individually, providing ionisation/recombination source/sinks and hydrogenic power loss measurements. Probabilistic Monte Carlo techniques were employed to obtain full error propagation - eventually resulting in probability density functions for each output variable. Both local and overall particle and power balance in the divertor are then obtained. These techniques and their assumptions have been verified by comparing the analysed synthetic diagnostic 'measurements' obtained from SOLPS simulation results for the same discharge. Power/particle balance measurements have been obtained during attached and detached conditions on the TCV tokamak.Comment: The analysis results of this paper were formerly in arXiv:1810.0496

    Critical velocities in two-component superfluid Bose gases

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    On the ground of the Landau criterion we study the behavior of critical velocities in a superfluid two-component Bose gas. It is found that under motion of the components with different velocities the velocity of each component should not be lower than a minimum phase velocity of elementary excitations (s_). The Landau criterion yields a relation between the critical velocities of the components (v_{c1}, v_{c2}). The velocity of one or even both components may exceed s_. The maximum value of the critical velocity of a given component can be reached when the other component does not move. The approach is generalized for a two-component condensate confined in a cylindrical harmonic potential. PACS numbers: 03.75.Kk,03.75.MnComment: 6 pages, 1 figure

    Low-temperature phonon thermal conductivity of cuprate single crystals

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    The effect of sample size and surface roughness on the phonon thermal conductivity κp\kappa_p of Nd2_2CuO4_4 single crystals was studied down to 50 mK. At 0.5 K, κp\kappa_p is proportional to A\sqrt{A}, where AA is the cross-sectional area of the sample. This demonstrates that κp\kappa_p is dominated by boundary scattering below 0.5 K or so. However, the expected T3T^3 dependence of κp\kappa_p is not observed down to 50 mK. Upon roughing the surfaces, the T3T^3 dependence is restored, showing that departures from T3T^3 are due to specular reflection of phonons off the mirror-like sample surfaces. We propose an empirical power law fit, to κpTα\kappa_p \sim T^{\alpha} (where α<3\alpha < 3) in cuprate single crystals. Using this method, we show that recent thermal conductivity studies of Zn doping in YBa2_2Cu3_3Oy_y re-affirm the universal heat conductivity of d-wave quasiparticles at T0T \to 0.Comment: 4 pages, 4 figure

    Non-linear Simulations of MHD Instabilities in Tokamaks Including Eddy Current Effects and Perspectives for the Extension to Halo Currents

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    The dynamics of large scale plasma instabilities can strongly be influenced by the mutual interaction with currents flowing in conducting vessel structures. Especially eddy currents caused by time-varying magnetic perturbations and halo currents flowing directly from the plasma into the walls are important. The relevance of a resistive wall model is directly evident for Resistive Wall Modes (RWMs) or Vertical Displacement Events (VDEs). However, also the linear and non-linear properties of most other large-scale instabilities may be influenced significantly by the interaction with currents in conducting structures near the plasma. The understanding of halo currents arising during disruptions and VDEs, which are a serious concern for ITER as they may lead to strong asymmetric forces on vessel structures, could also benefit strongly from these non-linear modeling capabilities. Modeling the plasma dynamics and its interaction with wall currents requires solving the magneto-hydrodynamic (MHD) equations in realistic toroidal X-point geometry consistently coupled with a model for the vacuum region and the resistive conducting structures. With this in mind, the non-linear finite element MHD code JOREK has been coupled with the resistive wall code STARWALL, which allows to include the effects of eddy currents in 3D conducting structures in non-linear MHD simulations. This article summarizes the capabilities of the coupled JOREK-STARWALL system and presents benchmark results as well as first applications to non-linear simulations of RWMs, VDEs, disruptions triggered by massive gas injection, and Quiescent H-Mode. As an outlook, the perspectives for extending the model to halo currents are described.Comment: Proceeding paper for Theory of Fusion Plasmas (Joint Varenna-Lausanne International Workshop), Varenna, Italy (September 1-5, 2014); accepted for publication in: to Journal of Physics: Conference Serie

    Nonlinear absorption of surface acoustic waves by composite fermions

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    Absorption of surface acoustic waves by a two-dimensional electron gas in a perpendicular magnetic field is considered. The structure of such system at the filling factor ν\nu close to 1/2 can be understood as a gas of {\em composite fermions}. It is shown that the absorption at ν=1/2\nu =1/2 can be strongly nonlinear, while small deviation form 1/2 will restore the linear absorption. Study of nonlinear absorption allows one to determine the force acting upon the composite fermions from the acoustic wave at turning points of their trajectories.Comment: 7 pages, 1 figure, submitted to Europhysics letter

    Вплив параметрів технологічного процесу на якісні показники кулінарної продукції

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    Operating enterprises in the restaurant industry must apply various methods, methods, and means of process control, which will ensure the proper quality and safety of culinary products and dishes. One of the most critical tasks for a restaurant business manager is producing high-quality culinary products. The quality of food products is the essence of its consumer properties, determined by the satisfaction of the population's need for complete nutrition. The set of properties of culinary products is characterized by nutritional value and organoleptic indicators. However, control services periodically detect violations of sanitary, technological, and other regulatory requirements by enterprises of the restaurant industry, which indicates a possible danger to the health of consumers of culinary products. Under these circumstances, controlling the technological processes of the production of culinary products is relevant for industry institutions, requiring a constant search for the most effective methods and means of quality control. The quality and safety of dishes are the primary criteria for food, so restaurant establishments must daily practice continuous control of the processes of manufacturing products and providing services. This will help ensure the appropriate level of food quality with the analysis of the results of control operations, which can determine ways to improve the quality of products. The technical control system (control objects, control operations, their sequence, technical equipment, modes, methods, means of mechanization, and automation) is developed simultaneously with the design of the manufacturing technology of technical devices by the service of the chief technologist of the enterprise or relevant design and technological organizations with the participation of the technical control department (VTK). All technological processes of making dishes and culinary products in restaurants can be divided into two stages – mechanical culinary and thermal culinary processing. Within the framework of the study of the safety indicators of new products, an essential component is the analytical and experimental examination of minced meat products of the emulsion structure with EAGP regarding the determination of the type and content of food additives for compliance with legislative and regulatory documents on the regulation of food additives in the composition of food products. Analytical studies have established that the EAHP food additive based on sunflower oil – mono- and diacylglycerol fatty acids is a safe additive E471 of GRAS (Generally Regarded As Safe) status, which is used in the composition of food products according to technological necessity without restrictions and quantitatively not are regulated. Therefore, the minced meat semi-finished product of the emulsion structure fully meets the requirements of the current legislation of Ukraine in terms of EAHP content. Thus, studies of the general chemical composition, quality indicators, and safety of chopped meat semi-finished product of emulsion structure, made using the EAHP food additive based on sunflower oil, confirm the compliance of this product with the requirements of the state food control system.Діючі підприємства ресторанного господарства повинні застосовувати різні методи, способи і засоби контролю процесів, що забезпечить належну якість і безпечність кулінарної продукції та страв. Одним із найважливіших завдань для керівника підприємства ресторанного господарства є випуск кулінарної продукції високої якості. Якість продукції харчування – сутність її споживчих властивостей, обумовлених задоволенням потреби населення в повноцінному харчуванні. Сукупність властивостей кулінарної продукції характеризується харчовою цінністю та органолептичними показниками. Однак служби контролю періодично виявляють порушення санітарних, технологічних та інших нормативних вимог підприємствами ресторанного господарства, що вказує на ймовірну небезпеку для здоров’я споживачів кулінарної продукції. За цих обставин питання контролю технологічних процесів виготовлення кулінарної продукції є актуальним для закладів галузі, потребує постійного пошуку найефективніших методів та засобів контролю якості. Якість і безпека страв є першочерговими критеріями харчування, тому заклади ресторанного господарства повинні щоденно практикувати безперервний контроль виконуваних процесів з виготовлення продукції та надання послуг. Це допоможе забезпечити належний рівень якості страв з аналізом результатів операцій контролю, який може визначати шляхи підвищення якості продукції. Система технічного контролю (об’єкти контролю, контрольні операції, їхня послідовність, технічне оснащення, режими, методи, засоби механізації та автоматизації) розробляється одночасно з проектуванням технології виготовлення технічних пристроїв службою головного технолога підприємства або відповідними проектно-технологічними організаціями за участю відділу технічного контролю (ВТК). Усі технологічні процеси виготовлення страв та кулінарних виробів у закладах ресторанного господарства можна поділити на два етапи – механічна кулінарна і теплова кулінарна обробка. У межах дослідження показників безпечності нової продукції важливою складовою є аналітична та експериментальна експертиза м’ясних посічених виробів емульсійної структури з ЕАГП щодо визначення виду і вмісту харчових добавок на відповідність законодавчим і нормативним документам з регламентування харчових добавок у складі харчових продуктів. Аналітичними дослідженнями встановлено, що харчова добавка ЕАГП на основі соняшникової олії – моно- і діацилгліцерини жирних кислот, є безпечною добавкою Е471 статусу GRAS (Generally Regarded As Safe – абсолютно безпечно), яка використовується у складі харчових продуктів за технологічною необхідністю без обмежень і кількісно не регламентуються. Тому м’ясний посічений напівфабрикат емульсійної структури за вмістом ЕАГП повністю відповідає вимогам чинного законодавства України. Таким чином, дослідження загального хімічного складу, показників якості та безпечності м’ясного посіченого напівфабрикату емульсійної структури, виготовленого з використанням харчової добавки ЕАГП на основі соняшникової олії, підтверджують відповідність даного продукту вимогам державної системи контролю харчових продуктів

    Investigating the impact of the molecular charge-exchange rate on detached SOLPS-ITER simulations

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    Plasma-molecular interactions generate molecular ions which react with the plasma and contribute to detachment through molecular activated recombination (MAR), reducing the ion target flux, and molecular activated dissociation (MAD), both of which create excited atoms. Hydrogenic emission from these atoms have been detected experimentally in detached TCV, JET and MAST-U deuterium plasmas. The TCV findings, however, were in disagreement with SOLPS-ITER simulations for deuterium indicating a molecular ion density (D2+D_2^+) that was insufficient to lead to significant hydrogenic emission, which was attributed to underestimates of the molecular charge exchange rate (D2+D+D2++DD_2 + D^+ \rightarrow D_2^+ + D) for deuterium (obtained by rescaling the hydrogen rates by their isotope mass). In this work, we have performed new SOLPS-ITER simulations with the default rate setup and a modified rate setup where ion isotope mass rescaling was disabled. This increased the D2+D_2^+ content by >×100> \times 100. By disabling ion isotope mass rescaling: 1) the total ion sinks are more than doubled due to the inclusion of MAR; 2) the additional MAR causes the ion target flux to roll-over during detachment; 3) the total DαD\alpha emission in the divertor increases during deep detachment by roughly a factor four; 4) the neutral atom density in the divertor is doubled due to MAD, leading to a 50\% increase in neutral pressure; 5) total hydrogenic power loss is increased by up to 60\% due to MAD. These differences result in an improved agreement between the experiment and the simulations in terms of spectroscopic measurements, ion source/sink inferences and the occurrence of an ion target flux roll-over

    Density Induced Interchange of Anisotropy Axes at Half-Filled High Landau Levels

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    We observe density induced 90^{\circ} rotations of the anisotropy axes in transport measurements at half-filled high Landau levels in the two dimensional electron system, where stripe states are proposed (ν\nu=9/2, 11/2, etc). Using a field effect transistor, we find the transition density to be 2.9×10112.9\times10^{11}cm2^{-2} at ν\nu=9/2. Hysteresis is observed in the vicinity of the transition. We construct a phase boundary in the filling factor-magnetic field plane in the regime 4.4<ν<4.64.4<\nu<4.6. An in-plane magnetic field applied along either anisotropy axis always stabilizes the low density orientation of the stripes.Comment: 1 revtex file, 3 eps figure
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