Models and phenomenology

It is evident that models of the knee should match the observational phenomenology. In this talk I discuss a few aspects of phenomenology, which are important not only for the understanding of the knee origin, but also for the general problem of the origin of cosmic rays. Among them are the shape of the energy spectrum, its irregularity, the sharpness of the knee and its fine structure. The classification of models is given and some examples of the most recent models are discussed. The most probable conclusion deduced from this examination is that the knee has an astrophysical origin and the so called 'source' models of the knee are most likely among them.Comment: 13 pages, 4 figures, overview talk at 19th European Cosmic Ray Symposium, Firenze, Italy, 30.08-4.09.2004 (to be published in the Int.J.Mod.Phys.A

Radiogenic Lead with Dominant Content of 208 Pb: New Coolant and Neutron Moderator for Innovative Nuclear Facilities

As a rule materials of small atomic weight (light and heavy water, graphite, and so on) are used as neutron moderators and reflectors. A new very heavy atomic weight moderator is proposed-radiogenic lead consisting mainly of isotope 208 Pb. It is characterized by extremely low neutron radiative capture cross-section (0.23 mbarn for thermal neutrons, i.e., less than that for graphite and deuterium) and highest albedo of thermal neutrons. It is evaluated that the use of radiogenic lead makes it possible to slow down the chain fission reaction on prompt neutrons in a fast reactor. This can increase safety of the fast reactors and reduce as well requirements pertaining to the fuel fabrication technology. Radiogenic lead with high 208 Pb content as a liquid-metal coolant of fast reactors helps to achieve a favorable (negative) reactivity coefficient on coolant temperature. It is noteworthy that radiogenic lead with high 208 Pb content may be extracted from thorium (as well as thorium-uranium) ores without isotope separation. This has been confirmed experimentally by the investigations performed at San Paulo University, Brazil

Escape of the martian protoatmosphere and initial water inventory

Latest research in planet formation indicate that Mars formed within a few million years (Myr) and remained a planetary embryo that never grew to a more massive planet. It can also be expected from dynamical models, that most of Mars' building blocks consisted of material that formed in orbital locations just beyond the ice line which could have contained ~0.1-0.2 wt. % of H2O. By using these constraints, we estimate the nebula-captured and catastrophically outgassed volatile contents during the solidification of Mars' magma ocean and apply a hydrodynamic upper atmosphere model for the study of the soft X-ray and extreme ultraviolet (XUV) driven thermal escape of the martian protoatmosphere during the early active epoch of the young Sun. The amount of gas that has been captured from the protoplanetary disk into the planetary atmosphere is calculated by solving the hydrostatic structure equations in the protoplanetary nebula. Depending on nebular properties such as the dust grain depletion factor, planetesimal accretion rates and luminosities, hydrogen envelopes with masses >=3x10^{19} g to <=6.5x10^{22} g could have been captured from the nebula around early Mars. Depending of the before mentioned parameters, due to the planets low gravity and a solar XUV flux that was ~100 times stronger compared to the present value, our results indicate that early Mars would have lost its nebular captured hydrogen envelope after the nebula gas evaporated, during a fast period of ~0.1-7.5 Myr. After the solidification of early Mars' magma ocean, catastrophically outgassed volatiles with the amount of ~50-250 bar H2O and ~10-55 bar CO2 could have been lost during ~0.4-12 Myr, if the impact related energy flux of large planetesimals and small embryos to the planet's surface lasted long enough, that the steam atmosphere could have been prevented from condensing. If this was not the case... (continued)Comment: 47 pages, 10 figures, 3 tables, submitted to PS

OMPEGAS: Optimized Relativistic Code for Multicore Architecture

The paper presents a new hydrodynamical code, OMPEGAS, for the 3D simulation of astrophysical flows on shared memory architectures. It provides a numerical method for solving the three-dimensional equations of the gravitational hydrodynamics based on Godunov’s method for solving the Riemann problem and the piecewise parabolic approximation with a local stencil. It obtains a high order of accuracy and low dissipation of the solution. The code is implemented for multicore processors with vector instructions using the OpenMP technology, Intel SDLT library, and compiler auto-vectorization tools. The model problem of simulating a star explosion was used to study the developed code. The experiments show that the presented code reproduces the behavior of the explosion correctly. Experiments for the model problem with a grid size of (Formula presented.) were performed on an 16-core Intel Core i9-12900K CPU to study the efficiency and performance of the developed code. By using the autovectorization, we achieved a 3.3-fold increase in speed in comparison with the non-vectorized program on the processor with AVX2 support. By using multithreading with OpenMP, we achieved an increase in speed of 2.6 times on a 16-core processor in comparison with the vectorized single-threaded program. The total increase in speed was up to ninefold. © 2022 by the authors.Russian Science Foundation, RSF: 18-11-00044The work of the third author (I.M.K.) and fourth author (I.G.C.) was supported by the Russian Science Foundation (project no. 18-11-00044). The first author (E.N.A.) and second author (V.E.M.) received no external funding

ИОНОХРОМАТОГРАФИЧЕСКОЕ ОПРЕДЕЛЕНИЕ ПЕРХЛОРАТОВ В ПИТЬЕВОЙ ВОДЕ С ПРЕДВАРИТЕЛЬНЫМ МИКРОЭКСТРАКЦИОННЫМ КОНЦЕНТРИРОВАНИЕМ

PURPOSE OF THE ARTICLE. Ion chromatography method with microextraction preconcentration and conductometric detection basis of domestic equipment and common reagents for determination of perchlorate ions low concentrations in different water samples was developed.METHODOLOGY. Reducing the influence of drinking water matrix components on the analytical signal was achieved by microextraction preconcentration perchlorate-ions using selective ion-pair reagent - tetraethylammonium chloride. The proposed methodological approach does not require a costly mass-spectrometric method, application of high-performance commercial columns and special cartridges.SCIENTIFIC PURPOSE. Different nature sorbents, including volume-porous anionite «Oka-1» were studied. Decreasing perchlorate-ions retention time to 12-13 minutes was estimated using «Oka-1» sorbent. The method of liquid-phase microextraction perchlorates concentration was developed. Concentrate was injected into the flow of amino acid eluent.RESULTS. The detection limit (3s- criterion) was 5∙10−4 mg/l. Perchlorate-ions were determined in the concentrations range of was 2∙10−3 - 2∙10−1 mg/l. Relative error was not exceed 20%. The content of matrix ions Cl−, SO42−, HCO3− up to 5 g/l was not interfere perchlorate-ions determination. Recommended method had been successfully tested in the determination of perchlorate-ions in different water samples and calcium hypochlorite disinfecting solutions.CONCLUSIONS. Microextraction concentration of perchlorate ions from aqueous solvents using drip extraction method can improve the selectivity determination of perchlorate-ions low concentrations by ion chromatography in isocratic elution with conductometric detection. Recommended simple and accessible method allows to determine perchlorate-ions in different water samples.Keywords: perchlorates, ion chromatography, determination, microextraction concentration. (Russian)DOI: http://dx.doi.org/10.15826/analitika.2014.18.1.008 P.N. Kulikov, E.V. Nayanova, E.V. Elipasheva, G.M. SergeevLobachevsky State University, Nizhny Novgorod, Russian FederationЦЕЛЬ СТАТЬИ. Разработка методики избирательного ионохроматографического определения низких содержаний перхлорат-ионов в питьевой воде различного солевого состава с предварительным микроэкстракционным концентрированием и кондуктометрическим детектированием на базе отечественного оборудования и распространенных реактивов.МЕТОДОЛОГИЯ. Уменьшение влияния матричных компонентов питьевой воды на величину аналитического сигнала достигнуто за счет использования селективного ион-парного реагента – хлорида тетраэтиламмония при предварительной пробоподготовке, которая заключается в микроэкстракционном концентрировании перхлорат-ионов. Предлагаемый методологический подход к решению поставленной задачи не требует затратного способа масс-спектрометрического детектирования, применения высокоэффективных коммерческих колонок и специальных картриджей.НАУЧНАЯ ЦЕЛЬ. Исследование анионитов различной природы, в том числе объемно-пористого анионообменника « OKA-1». Для этого ионита за счет более короткого диффузионного пути перхлората уменьшается его время удерживания до 12-13 мин. Реализация способа жидкофазного микроэкстракционного концентрирования перхлоратов с последующим вводом концентрата в поток аминокислотного элюента.РЕЗУЛЬТАТЫ. Предел обнаружения (3s-критерий) перхлорат-ионов равен 5∙10−4 мг/л. Диапазон определяемых концентраций перхлоратов 2∙10−3 – 2∙10−1 мг/л. Относительная погрешность не превышает 20 %. Содержание матричных ионов Cl−, SO42−, HCO3− до 5 г/л не мешает определению перхлората. Рекомендуемая методика успешно опробована при определении перхлорат-ионов в образцах питьевой воды различных водоисточников и дезинфицирующих растворах гипохлорита кальция.ВЫВОДЫ. Микроэкстракционное концентрирование перхлорат-ионов из водных сред способом капельной экстракции позволяет повысить избирательность определения низких концентраций перхлоратов методом ионной хроматографии в режиме изократического элюирования с кондуктометрическим детектированием. Представляется возможным контролировать простым и доступным способом содержание перхлоратов в воде различного солевого состава от «фоновых» значений до наступления критической ситуации.Ключевые слова: перхлораты, ионохроматографическое определение, микроэкстракционное концентрирование.DOI: http://dx.doi.org/10.15826/analitika.2014.18.1.008

The Lambda_b lifetime in the light front quark model

The enhancement of the Lambda_b decay width relative to B decay one due to the difference of Fermi motion effects in Lambda_b and B is calculated in the light--front quark model with the simplifying assumption that Lambda_b consists of the heavy quark and light scalar diquark. In order to explain the large deviation from unity in the experimental result for tau(Lambda_b)/tau(B), it is necessary that diquark be light and the ratio of the squares of the Lambda_b and B wave functions at the origin be \le 1.Comment: final journal version to appear in JETP Letter

The Tunka Experiment: Towards a 1-km^2 Cherenkov EAS Array in the Tunka Valley

The project of an EAS Cherenkov array in the Tunka valley/Siberia with an area of about 1 km^2 is presented. The new array will have a ten times bigger area than the existing Tunka-25 array and will permit a detailed study of the cosmic ray energy spectrum and the mass composition in the energy range from 10^15 to 10^18 eV.Comment: 3 pages, 2 figures, to be published in IJMP