The Most Efficient Target Development to Increase the 99Mo Production Using the VVR-ts Reactor Core

The article shows the possibility of increasing the 99Mo production using the modifyed target. It was shown that there is a significant reserve for increasing the production of the 99Mo isotope without a significant change in the cor

NMR in Superfluid A-like Phase of 3^3He Confined in Globally Deformed Aerogel in Tilted Magnetic Field

NMR spectra in superfluid A-like phases confined in axially deformed aerogel in presence of a magnetic field inclined with respect to deformation axis is considered. The characteristic features of dipole frequency shift in axially compressed and axially stretched cases are compared. In particular, it is shown that in axially stretched aerogel environment the stability region of coherently spin precessing mode is rather narrow due to the U(1)LIM effect.Comment: 8 pages, 2 figure

Accounting for the Local Wave and Morphodynamic Processes in Coastal Hydraulic Engineering

Purpose. Estimates of wave parameters in the coastal waters are of great practical importance for designing and operating coastal infrastructure facilities. On the example of the Saki bay-bar region (Western Crimea), the experience of studying the wave and morphodynamic processes in the coastal zone is presented being applied to the tasks of designing and building protective hydraulic structures. Methods and Results. Mathematical modeling of the wave and morphodynamic processes in the area under study was done using the following: spectral model of the wind waves SWAN, hydrodynamic model SWASH, complex morphodynamic model XBeach and integral model of the coastal zone evolution GenCade. The wave regime was analyzed using the 41-year time series (1979–2019) of wave parameters resulted from the retrospective calculations of wind waves based on the SWAN model and the ERA atmospheric reanalysis data. The operational and extreme characteristics of wind waves were obtained. The spatial structure of the wave fields for different types of wind effects was modeled. The most intense waves are shown to occur during the southwest wind. The height and length of wave run-up on the coast and the coastal zone profile deformations for the storms of different durations were estimated. The values of the total annual along-coastal sediment flow in the design area were obtained for 1979–2019. In 70% of the cases, the sediment flow was established to be directed towards the Evpatoriya coast. Conclusions. The studies have shown that neglecting scientifically based recommendations when designing coastal infrastructure facilities can lead both to disruption of the existing system of the coastal zone natural formation, and to significant negative consequences for the coastline of almost 10 km length. These consequences can be manifested in a reduction of the beach zone width, a decrease in elevation marks, and replacement of sand with the pebble-gravel fractions in some areas that worsen recreational features of the beaches. Having been analyzed and taken into account, the planned location of the base of the enclosing wall shows that in some parts, the embankment wall can be possibly washed away and damaged. These conclusions were confirmed in practice already during the facility construction. Based on the results of the performed study, the constructions contributing significantly to the changes in the coastal zone morphodynamics were recommended for exclusion from the project

The quantum dilogarithm and representations quantum cluster varieties

We construct, using the quantum dilogarithm, a series of *-representations of quantized cluster varieties. This includes a construction of infinite dimensional unitary projective representations of their discrete symmetry groups - the cluster modular groups. The examples of the latter include the classical mapping class groups of punctured surfaces. One of applications is quantization of higher Teichmuller spaces. The constructed unitary representations can be viewed as analogs of the Weil representation. In both cases representations are given by integral operators. Their kernels in our case are the quantum dilogarithms. We introduce the symplectic/quantum double of cluster varieties and related them to the representations.Comment: Dedicated to David Kazhdan for his 60th birthday. The final version. To appear in Inventiones Math. The last Section of the previous versions was removed, and will become a separate pape

Flux Confinement in Mesoscopic Superconductors

We report on flux confinement effects in superconducting submicron line, loop and dot structures. The main idea of our study was to vary the boundary conditions for confinement of the superconducting condensate by taking samples of different topology and, through that, modifying the lowest Landau level E_{LLL}(H). Since the critical temperature versus applied magnetic field T_{c}(H) is, in fact, E_{LLL}(H) measured in temperature units, it is varied as well when the sample topology is changed. We demonstrate that in all studied submicron structures the shape of the T_{c}(H) phase boundary is determined by the confinement topology in a unique way.Comment: 10 pages, 5 EPS figures, uses LaTeX's sup.sty, contribution to a special issue of "Superlattices and Microstructures

Giant vortex state in perforated aluminum microsquares

We investigate the nucleation of superconductivity in a uniform perpendicular magnetic field H in aluminum microsquares containing a few (2 and 4) submicron holes (antidots). The normal/superconducting phase boundary T_c(H) of these structures shows a quite different behavior in low and high fields. In the low magnetic field regime fluxoid quantization around each antidot leads to oscillations in T_c(H), expected from the specific sample geometry, and reminiscent of the network behavior. In high magnetic fields, the T_c(H) boundaries of the perforated and a reference non-perforated microsquare reveal cusps at the same values of Phi/Phi_0 (where Phi is the applied flux threading the total square area and Phi_0 is the superconducting flux quantum), while the background on T_c(H) becomes quasi-linear, indicating that a giant vortex state is established. The influence of the actual geometries on T_c(H) is analyzed in the framework of the linearized Ginzburg-Landau theory.Comment: 14 pages, 6 PS figures, RevTex, accepted for publication in Phys. Rev.

Numerical Simulation of Tsunami Wave Propagation to the Balaklava Bay

Purpose. To investigate the process of tsunami wave propagation from the hypothetical earthquake foci to the Balaklava Bay, and to zone the tsunami impact upon the bay coastline based on the results of numerical modeling, are the purposes of the paper. Methods and Results. The results of numerical simulation of the tsunami wave propagation to the Balaklava Bay with subsequent flooding of the coast are presented. The problem of the tsunami wave propagation from three hypothetical earthquake foci and their evolution in the Black Sea was solved using the nonlinear model of long waves. Time dependences of the sea level fluctuations at the entrance to the Balaklava Bay were obtained. They were applied as boundary conditions at the liquid boundary of the computational domain, where the SWASH model had been used to simulate numerically the tsunami wave propagation in the bay with their subsequent run-up to the coast. Conclusions. Propagation of tsunami waves in the Balaklava Bay is accompanied by formation of the sea level seiche oscillations with a period ~ 8 min which correspond to the Helmholtz mode. Inside the bay, the tsunami heights increase by 5–6 times as compared to those at the entrance to the computational domain. The sea level fluctuations are maximal at the bay top, where its rise achieves 1.4–1.5 m. The eastern coast of the Balaklava Bay and the one adjacent to its top are subject to the strongest flooding. The values of water level on land measured from the ground level, reach 1.0–1.5 m, and at the bay top – 1.8 m. At the eastern coast of the bay, the flooding maximum length constitutes 60 m, at its top – 90 m

Study of self-organizing regime of nuclear burning wave in fast reactor

An approach for description of the space-time evolution of self-organizing nuclear burning wave regime in a critical fast neutron reactor has been developed in the effective multigroup approximation. It is based on solving the non-stationary neutron diffusion equation together with the fuel burn-up equations and the equations of nuclear kinetics for delayed neutron precursor nuclei. The calculations have been carried out in the plane one-dimensional model for a two-zone homogeneous reactor with the metal U-Pu fuel, the Na coolant and constructional material Fe. The temperature effects and heat sink were not considered.В ефективному багатогруповому наближенні розвинуто підхід для опису просторово-часової еволюції хвильового режиму ядерного горіння, що самоорганізується у критичному реакторі на швидких нейтронах. Він заснований на розв’язанні нестаціонарного дифузійного рівняння переносу нейтронів разом з рівняннями вигоряння палива і кінетики попередників запізнілих нейтронів. Розрахунки проводилися у плоскій одновимірній моделі двохзонного гомогенного реактора з металевим U-Pu паливом, Na-теплоносієм та конструктційним матеріалом Fe. Температурні ефекти і відвід тепла не розглядались. Доведено, що за певних умов у реакторі можна створити хвильовий режим ядерного горіння, у якому реактор без керування протягом тривалого часу може підтримуватися у стані, близькому до критичного.В эффективном многогрупповом приближении развит подход для описания пространственно-временной эволюции самоорганизующегося волнового режима ядерного горения в критическом реакторе на быстрых нейтронах. Он основан на решении нестационарного диффузионного уравнения переноса нейтронов сов- местно с уравнениями выгорания топлива и кинетики предшественников запаздывающих нейтронов. Расче- ты проводились в плоской одномерной модели двухзонного гомогенного реактора с металлическим U-Pu топливом, Na-теплоносителем и конструкционным материалом Fe. Температурные эффекты и отвод тепла не рассматривались. Показано, что при определенных условиях в реакторе можно создать волновой режим ядерного горения, в котором реактор без управления в течение длительного времени может поддерживаться в состоянии, близком к критическому

Phase diagram of a superconductor / ferromagnet bilayer

The magnetic field (H) - temperature (T) phase diagram of a superconductor is significantly altered when domains are present in an underlying ferromagnet with perpendicular magnetic anisotropy. When the domains have a band-like shape, the critical temperature Tc of the superconductor in zero field is strongly reduced, and the slope of the upper critical field as a function of T is increased by a factor of 2.4 due to the inhomogeneous stray fields of the domains. Field compensation effects can cause an asymmetric phase boundary with respect to H when the ferromagnet contains bubble domains. For a very inhomogeneous domain structure, Tc~H^2 for low H and Tc~H for higher fields, indicating a dimensional crossover from a one-dimensional network-like to a two-dimensional behavior in the nucleation of superconductivity.Comment: 6 pages, 7 figure

Optimization of ignition zone of advanced fast reactor, working in nuclear burning wave mode

This article deals with the problem of optimizing composition and structure of the ignition zone of the fast reactor operating in the self-sustaining mode of nuclear burning wave with the purpose of its smooth start-up and reducing fissile material amount in initial assembly. The cylindrical homogeneous reactor with the ignition zone placed in the center or near the cylinder end is considered. The analysis has been performed basing on solving the non-stationary neutron diffusion equation together with the fuel burn-up equations and the equations of nuclear kinetics for precursor nuclei of delayed neutrons, with using the radial buckling approximation. An optimized structure of the ignition zone has been proposed, which ensures a smooth transition of the reactor to the self-sustaining nuclear burning wave mode, avoiding an excessive energy release, which is observed when using a simplified scheme of ignition zone. Comparison of the startup variants with the ignition zone at the cylinder end and at its center shows the benefits of the second one.Вивчається питання оптимізації складу та структури зони запалу швидкогоого реактора, працюючого в режимі самопідтримки хвилі ядерного горіння, з метою його плавного запуску та економії материалів, які діляться на цоому етапі. Розглядався гомогенний реактор ціліндричної форми з центральним або торцевим розміщенням зони запалу. Аналіз проводився на основі числового рішения нестаціонарного рівняння диффузії нейтронів разом з рівняннями вигорання і рівняннями кінетики ядер попередників запізнюющихся нейтронів. Задача рішалася з використанням наближення геометричного фактора ("баклінга"). Запропонована оптимізована структура зони запалу, яка забезпечує плавний вихід ректора на стаціонарний режим хвилі ядерного горіння, яка самопідтримується, уникаючи значного росту енерговиділення, яке спостерігається при використанні спрощеної схеми зони запалу. Проведено порівняння кількості материалу, якой ділеться, необхідного для запуску реактора, при двох варіантах розположення зони запалу: торцевої та центральної.Изучается вопрос оптимизации состава и структуры зоны запала быстрого реактора, работающего в самоподдерживающемся режиме волны ядерного горения, с целью его плавного запуска и экономии делящихся материалов на этом этапе. Рассматривался гомогенный реактор цилиндрической формы с центральным либо торцевым расположением зоной запала. Анализ проводился на основе численного решения нестационарного уравнения диффузии нейтронов вместе с уравнениями выгорания и уравнениями кинетики ядер предшественников запаздывающих нейтронов. Задача решалась с использованием приближения геометрического фактора ("баклинга"). Предложена оптимизированная структура зоны запала, обеспечивающая плавный выход реактора на стационарный самоподдерживающийся режим волны ядерного горения, избегая значительного роста энерговыделения, который наблюдается при использовании упрощенной схемы зоны запала. Проведено сравнение количества делящегося материала, необходимого для запуска реактора, при двух вариантах расположения зоны запала: торцевой и центральной