237 research outputs found

    Collision-Induced Non-Adiabatic Transitions Between The Ion-Pair States Of Molecular Iodine: A Challenge For Experiment And Theory

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    The ion-pair states of molecular iodine provide a unique system for studying the efficiency, selectivity, and mechanisms of collision-induced non-adiabatic transitions. Non-adiabatic transitions between the first-tier ion-pair states in collisions with molecular partners and rare gases are analyzed and discussed. The qualitative features of the rate constants and product state distributions under single collision conditions are summarized and interpreted in terms of appropriate theoretical approaches. Two mechanisms for the non-adiabatic transitions are clearly identified. The first, operative for collisions involving molecular partners possessing permanent or transition electrostatic moments, is highly selective. It connects the initially prepared level in the E 0(g)(+) electronic state with the near-resonant vibronic level of the D 0(u)(+) state with a minimum change of the total angular momentum. In an extreme quasi-resonant case when the gap between initial and final rovibronic level is less than 1 cm(-1), this mechanism has a giant cross section, 40 times that of a gas kinetic collision. An electrostatic model, which includes the coupling of the giant E-D transition dipole moment with a moment of the colliding partner and the semiclassical Born approximation, provides a plausible interpretation of this mechanism. A second mechanism is shown to govern collisions with rare gas atoms. It results in population of several ion-pair states and broad distributions over rovibronic levels. This mechanism is successfully interpreted by quantum scattering calculations based on the diatomics-in-molecule diabatic potential energy surfaces and coupling matrix elements. The calculations provide good agreement with experimental measurements and reveal different mechanisms for the population of different electronic states. Unexplained features of the non-adiabatic dynamics and directions of future work are outlined

    Ballistic magnon heat conduction and possible Poiseuille flow in the helimagnetic insulator Cu2_2OSeO3_3

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    We report on the observation of magnon thermal conductivity κm\kappa_m\sim 70 W/mK near 5 K in the helimagnetic insulator Cu2_2OSeO3_3, exceeding that measured in any other ferromagnet by almost two orders of magnitude. Ballistic, boundary-limited transport for both magnons and phonons is established below 1 K, and Poiseuille flow of magnons is proposed to explain a magnon mean-free path substantially exceeding the specimen width for the least defective specimens in the range 2 K <T<<T< 10 K. These observations establish Cu2_2OSeO3_3 as a model system for studying long-wavelength magnon dynamics.Comment: 10pp, 9 figures, accepted PRB (Editor's Suggestion

    A search for massive neutral bosons in orthopositronium decay

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    We have searched for an exotic decay of orthopositronium into a single photon and a short-lived neutral boson in the hitherto unexplored mass region above 900 keV/c2{\rm keV}/{\it c}^{2}, by noting that this decay is one of few remaining candidates which could explain the discrepancy of the orthopositronium decay-rate. A high-resolution measurement of the associated photon energy spectrum was carried out with a germanium detector to search for a sharp peak from this two-body decay. Our negative result provides the upper-limits of\mbox{ }2.0×1042.0 \times 10^{-4} on the branching ratio of such a decay in the mass region from 847 to 1013 keV/c2{\rm keV}/{\it c}^{2}, and excludes the possibility of this decay mode explaining the discrepancy in the orthopositronium decay-rate.Comment: a LaTeX file (text 7 pages) and a uuencoded gz-compressed PostScript file (text 7 pages + figures 4 pages

    Magnetic-field dependence of low-energy magnons, anisotropic heat conduction, and spontaneous relaxation of magnetic domains in the cubic helimagnet ZnCr2Se4

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    Anisotropic low-temperature properties of the cubic spinel helimagnet ZnCr2Se4 in the single-domain spin-spiral state are investigated by a combination of neutron scattering, thermal conductivity, ultrasound velocity, and dilatometry measurements. In an applied magnetic field, neutron spectroscopy shows a complex and nonmonotonic evolution of the spin-wave spectrum across the quantum-critical point that separates the spin-spiral phase from the field-polarized ferromagnetic phase at high fields. A tiny spin gap of the pseudo-Goldstone magnon mode, observed at wave vectors that are structurally equivalent but orthogonal to the propagation vector of the spin helix, vanishes at this quantum critical point, restoring the cubic symmetry in the magnetic subsystem. The anisotropy imposed by the spin helix has only a minor influence on the lattice structure and sound velocity but has a much stronger effect on the heat conductivities measured parallel and perpendicular to the magnetic propagation vector. The thermal transport is anisotropic at T < 2 K, highly sensitive to an external magnetic field, and likely results directly from magnonic heat conduction. We also report long-time thermal relaxation phenomena, revealed by capacitive dilatometry, which are due to magnetic domain motion related to the destruction of the single-domain magnetic state, initially stabilized in the sample by the application and removal of magnetic field. Our results can be generalized to a broad class of helimagnetic materials in which a discrete lattice symmetry is spontaneously broken by the magnetic order.Comment: 13 pages, 8 figures + Supplemental Materia

    Myth as a Means of Ordering and Organizing Social Reality

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    This study investigates the phenomenon of social myth as a factor of forming and transforming the consciousness of social actors. It is defined that one of the factors of appealing to mythological representation of reality is the crisis of scientific orientations of modernism. In this plane, the article studies phenomenological receptions of myth as well as the process of mythologization of modern social reality. Moreover, attention is drawn to the fact that mythologization fixes an idea of social reality and its axiological (value) dimension in the consciousness of separate individuals and their groups. Myths are axiological indicators; the more controversial society values are the greater number of myths is produced by social consciousness to eliminate these contradictions. The difference between modern and archaic myth has both qualitative and quantitative aspects. Modern society generates a great number of myths with much more narrow content. This is a consequence of "specialization" of myths, their orientation towards solving particular local tasks: political, economic, etc. Functional and structural changes of social myths can be accounted for by critical, permanently transitional condition of society in which myth compensates the unformed elements of new social practices. However, the content side of myth is not a crisis but social request and values of particular culture. The question about the necessity to fight against myths probably should be answered negatively if we don’t mean the most dangerous myths posing a serious threat for society. Myths are in harmony with social consciousness and arise in places where there is a fault between current and desirable normativity. Thus, when social practices become stable social consciousness itself displaces and nullifies myths that are responsible for harmonization of new order and they become demanded

    Early functional and microcirculatory changes in patients with type 1 diabetes mellitus and no apparent diabetic retinopathy

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    BACKGROUND: Diabetic retinopathy (DR) is the leading complication of diabetes mellitus (DM) which is reported to affect more than one-third of the global diabetic population. Optical coherence tomography angiography (OCT-A) can help to reveal early biomarkers of DR to improve current diagnostic approach.AIMS: To evaluate early visual functions deficiency and OCT-A changes in patients with type 1 DM (T1DM) without clinical signs of DR.MATERIALS AND METHODS. 74 eyes of 40 T1DM patients with no apparent DR and 49 eyes of 28 healthy volunteers were included in the study. The mean duration of DM was 11,7 ± 6,1 years. All participants underwent standard ophthalmological examination, low-luminance visual acuity (LLVA) assessment, 7-field fundus photography, OCT and OCT-A. We analyzed LLVA deficit as a marker of visual function. For OCT-A scans we evaluated foveal avascular zone (FAZ) area (mm2), acircularity index (AI), vessel density (VD), skeletonized density (SD) and vessel diameter index (VDI) in superficial vascular plexus (SVP), intermediate capillary plexus (ICP) and deep capillary plexus (DCP).RESULTS: LLVA deficit was significantly higher in T1DM patients (0,16±0,05 vs 0,10±0,04, p&lt;0,0001). We also detected a significant difference in AI level (11,47 ± 0,24 vs 1,31 ± 0,15, p&lt;0,0001). VD was significantly lower in T1DM patients in SVP (25,37 ± 2,24%, vs 26,67 ± 1,81%, p=0,028) and DCP (17,22 ± 3,10 % vs 18,29 ± 1,95%, p=0,015)CONCLUSIONS: Our results demonstrate early visual functions deficiency and OCT-A changes at the preclinical stage of DR. The prognostic value of these findings will be studied during longitudinal observation

    Voltage Responses to Optical Pulses of Unbiased Normal and Superconducting Samples

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    The direct transformation of the energy of an incident high-energy photon into a measurable potential difference within an absorbing metal is investigated. Experimental evidence is presented that the effect arises from the inherent energy dependence of the electronic density of states, rather than from a simple temperature excursion. The similarities between the results on Al and YBa2Cu3O7 samples indicate that the effect is universal in nature. We assert it may be used as the basis of a fast, energy resolving, individual photon detector for the ultraviolet radiation and x-rays

    Motivation of Volunteers of the Ural Federal District of the World Youth Festival 2024

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    Статья посвящена изучению мотивации волонтеров Всемирного фестиваля молодежи 2024 года. По результатам проведенного анализа исходя из разных возрастных категорий для дальнейшего использования в рамках создания комфортных условий волонтерской деятельности были определены типы волонтеров по видам мотивации.The article is devoted to the study of the motivation of volunteers of the World Youth Festival 2024. Based on the results of the analysis, based on different age categories, types of volunteers were identified by type of motivation for further use in creating comfortable conditions for volunteer activity

    Chemomagnetism, magnetoconcentration effect and "fishtail" anomaly in chemically-induced granular superconductors

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    Within a 2D model of Josephson junction arrays (created by 2D network of twin boundary dislocations with strain fields acting as insulating barrier between hole-rich domains in underdoped crystals), a few novel effects expected to occur in intrinsically granular material are predicted including: (i) Josephson chemomagnetism (chemically induced magnetic moment in zero applied magnetic field) and its influence on a low-field magnetization (chemically induced paramagnetic Meissner effect), and (ii) magnetoconcentration effect (creation of oxygen vacancies in applied magnetic field) and its influence on a high-field magnetization (chemically induced analog of "fishtail" anomaly). The conditions under which these effects can be experimentally measured in non-stoichiometric high-T_c superconductors are discussed.Comment: 5 LaTeX pages (jetpl.sty included), 3 EPS figures. To be published in JETP Letters (January 2003

    ИЗМЕНЕНИЕ ФАУНЫ НЕКОТОРЫХ БИОГЕЛЬМИНТОВ РЫБ ОЗЕРА СЕВАН И ИХ ПРОМЕЖУТОЧНЫХ ХОЗЯЕВ В УСЛОВИЯХ ГИДРОЭКОЛОГИЧЕСКИХ ПРЕОБРАЗОВАНИЙ

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    The infeсtion of biohelminths of fishes in Sevan Lake is studied. 9 types of biohelminths are revealed: in a body cavity, intestines, heart and crystalline lenses of eyes. The analysis of changes of specific composition of the helminths in dynamics, taking into account changes of fauna of their intermediate hosts, in conditions of hydroecological transformations of the lake is conducted.Изучена зараженность рыб озера Севан гельминтами. Выявлено 9 видов биогельминтов: в полости тела, кишечнике, сердце и хрусталиках глаз. Проведен анализ изменений видового состава обнаруженных гельминтов в динамике, с учетом изменений фауны их промежуточных хозяев, в условиях гидроэкологических преобразований озера
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