THE APPLICATION OF SCANNING ELECTRON MICROSCOPY USING ENERGY- AND WAVELENGTH DISPERSIVE SPECTROMETERS FOR CHEMICAL DATING OF URANIUM MINERALIZATION ON THE EXAMPLE OF CARBONACEOUS SHALES OF THE DABANZHALGA SUITE (EAST SAYAN)

On the one hand, the widespread use of electron microprobe analysis in the version of a scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS) and, on the other hand, the comparability of the metrological characteristics of the EDS and wavelength dispersive spectrometry (WDS) in the case of determining the major components of minerals are a favourable background for investigating the possibility of using SEM-EDS for chemical dating of uranium mineralization. Carbonaceous-siliceous formations of the Dabanzhalga suite are widespread in carbonate deposits of the Lower Paleozoic in the Oka structural-formational zone of the East Sayan and represent deep-water deposits of the back-arc basin. All varieties of carbonaceous-siliceous rocks of the Dabanzhalga suite are characterized by increased U, Au, Ag, Pt, Pd, Mo, V, P, Cu. Their amounts are 5–10 times higher than those for other black shale deposits of the Eastern Sayan. Uranium forms its minerals – uraninite and brannerite, in association with carbonaceous matter and sulfides, and is also part of anhydrous phosphates – xenotime, monazite. The paper presents data on the composition and dating of brannerite and uraninite in samples of carbonaceous-siliceous shale sampled at three sites: Uber-Zhadoy, Deed-Khara-Zhalga and Erye-Khara-Zhalga. The obtained estimates of the isochronous dates of uraninite and brannerite grains for these areas are 523±26, 506±10, and 511±17 Ma, respectively. It was shown that these dates could be compared with the age of metamorphism at the Sukhoi Log deposit, estimated using modern methods of isotope geochronology. It should be noted that the average estimates of the dates of uraninite and brannerite in all studied areas of the Dabanzhalga suite are lower than the corresponding estimates of the isochronous date, which is probably due to the partial loss of radiogenic lead. For the Uber-Zhadoy site, a comparison of the EDS and WDS data was carried out, and it was shown that when using the EDS data, there is an underestimation of the Pb content in uraninite, and, as a consequence, an underestimation of the age of uraninite

A new look at acid catalyzed deacetylation of carbohydrates : A regioselective synthesis and reactivity of 2-O-acetyl aryl glycopyranosides

Abstract In the present work we report that acetyl groups of per – acetylated aryl glycosides have different reactivity during the acidic deacetylation using HCl/EtOH in CHCl3, which leads to preferential deacetylation at O-3, O-4 and O-6. Thereby, the one-step preparation of 2-O-acetyl aryl glycosides with simple aglycon was accomplished for the first time. It was proved that the found reagent is to be general and unique for the preparation of series of 2-О-acetyl aryl glycosides. We have determined the influence of both carbohydrate moiety and the aglycon on the selectivity of deacetylation reaction by kinetic experiments. Using DFT/B3LYP/6-31G(d,p) and semi-empirical АМ1 methods we have found that the highest activation barrier is for 2-О-acetyl group. This completely explains the least reactivity of 2-О-acetyl group.Peer reviewe

Renormalized Energies of Superfluorescent Bursts from an Electron-Hole Magneto-plasma with High Gain in InGaAs Quantum Wells

We study light emission properties of a population-inverted 2D electron-hole plasma in a quantizing magnetic field. We observe a series of superfluorescent bursts, discrete both in time and energy, corresponding to the cooperative recombination of electron-hole pairs from different Landau levels. The emission energies are strongly renormalized due to many-body interactions among the photogenerated carriers, exhibiting red-shifts as large as 20 meV at 15 T. However, the magnetic field dependence of the lowest Landau level emission line remains excitonic at all magnetic fields. Interestingly, our time-resolved measurements show that this lowest-energy burst occurs only after all upper states become empty, suggesting that this excitonic stability is related to the `hidden symmetry' of 2D magneto-excitons expected in the magnetic quantum limit.Comment: 5 pages, 4 figure

SEQUENCE OF AILLIKITE AND CALCITE CARBONATITE FORMATION WITHIN THE BELAYA ZIMA MASSIF, EAST SIBERIA, RUSSIA

The mineralogical and geochemical features, as well as the sequence of formation of aillikite and calcite carbonatite (CC) with pyrochlore are described for the massif of alkaline ultramafic carbonatite complexes Belaya Zima located in East Siberia. Until now, mutually exclusive information presents the temporal relationships of carbonatites and lamprophyres of the Belaya Zima massif.The sample marking the contact of aillikite and CC was comprehensive studied using analytical methods, e.g. XRF (ARL-9900XP spectrometer, ThermoFisher Scientific), ICP-MS (Element Finnigan MAT), SEM (MIRA 3 LMU (Tescan Ltd)), transmission and ore microscopy (AxioScope. A1, Zeiss), 40Ar/39Ar age determination of micas (Argus mass spectrometer, Micromass). The data obtained indicate a later formation of CC relative to aillikites and probable separation of the carbonatite melt from a single picrite-carbonatite source

Coherent radiation from neutral molecules moving above a grating

We predict and study the quantum-electrodynamical effect of parametric self-induced excitation of a molecule moving above the dielectric or conducting medium with periodic grating. In this case the radiation reaction force modulates the molecular transition frequency which results in a parametric instability of dipole oscillations even from the level of quantum or thermal fluctuations. The present mechanism of instability of electrically neutral molecules is different from that of the well-known Smith-Purcell and transition radiation in which a moving charge and its oscillating image create an oscillating dipole. We show that parametrically excited molecular bunches can produce an easily detectable coherent radiation flux of up to a microwatt.Comment: 4 page

Giant Superfluorescent Bursts from a Semiconductor Magnetoplasma

Currently, considerable resurgent interest exists in the concept of superradiance (SR), i.e., accelerated relaxation of excited dipoles due to cooperative spontaneous emission, first proposed by Dicke in 1954. Recent authors have discussed SR in diverse contexts, including cavity quantum electrodynamics, quantum phase transitions, and plasmonics. At the heart of these various experiments lies the coherent coupling of constituent particles to each other via their radiation field that cooperatively governs the dynamics of the whole system. In the most exciting form of SR, called superfluorescence (SF), macroscopic coherence spontaneously builds up out of an initially incoherent ensemble of excited dipoles and then decays abruptly. Here, we demonstrate the emergence of this photon-mediated, cooperative, many-body state in a very unlikely system: an ultradense electron-hole plasma in a semiconductor. We observe intense, delayed pulses, or bursts, of coherent radiation from highly photo-excited semiconductor quantum wells with a concomitant sudden decrease in population from total inversion to zero. Unlike previously reported SF in atomic and molecular systems that occur on nanosecond time scales, these intense SF bursts have picosecond pulse-widths and are delayed in time by tens of picoseconds with respect to the excitation pulse. They appear only at sufficiently high excitation powers and magnetic fields and sufficiently low temperatures - where various interactions causing decoherence are suppressed. We present theoretical simulations based on the relaxation and recombination dynamics of ultrahigh-density electron-hole pairs in a quantizing magnetic field, which successfully capture the salient features of the experimental observations.Comment: 21 pages, 4 figure

ПРИМЕНЕНИЕ СКАНИРУЮЩЕЙ ЭЛЕКТРОННОЙ МИКРОСКОПИИ С ИСПОЛЬЗОВАНИЕМ ЭНЕРГО- И ВОЛНОДИСПЕРСИОННОГО СПЕКТРОМЕТРОВ ДЛЯ ХИМИЧЕСКОГО ДАТИРОВАНИЯ УРАНОВОЙ МИНЕРАЛИЗАЦИИ НА ПРИМЕРЕ УГЛЕРОДИСТЫХ СЛАНЦЕВ ДАБАНЖАЛГИНСКОЙ СВИТЫ (ВОСТОЧНЫЙ САЯН)

On the one hand, the widespread use of electron microprobe analysis in the version of a scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS) and, on the other hand, the comparability of the metrological characteristics of the EDS and wavelength dispersive spectrometry (WDS) in the case of determining the major components of minerals are a favourable background for investigating the possibility of using SEM-EDS for chemical dating of uranium mineralization. Carbonaceous-siliceous formations of the Dabanzhalga suite are widespread in carbonate deposits of the Lower Paleozoic in the Oka structural-formational zone of the East Sayan and represent deep-water deposits of the back-arc basin. All varieties of carbonaceous-siliceous rocks of the Dabanzhalga suite are characterized by increased U, Au, Ag, Pt, Pd, Mo, V, P, Cu. Their amounts are 5–10 times higher than those for other black shale deposits of the Eastern Sayan. Uranium forms its minerals – uraninite and brannerite, in association with carbonaceous matter and sulfides, and is also part of anhydrous phosphates – xenotime, monazite. The paper presents data on the composition and dating of brannerite and uraninite in samples of carbonaceous-siliceous shale sampled at three sites: Uber-Zhadoy, Deed-Khara-Zhalga and Erye-Khara-Zhalga. The obtained estimates of the isochronous dates of uraninite and brannerite grains for these areas are 523±26, 506±10, and 511±17 Ma, respectively. It was shown that these dates could be compared with the age of metamorphism at the Sukhoi Log deposit, estimated using modern methods of isotope geochronology. It should be noted that the average estimates of the dates of uraninite and brannerite in all studied areas of the Dabanzhalga suite are lower than the corresponding estimates of the isochronous date, which is probably due to the partial loss of radiogenic lead. For the Uber-Zhadoy site, a comparison of the EDS and WDS data was carried out, and it was shown that when using the EDS data, there is an underestimation of the Pb content in uraninite, and, as a consequence, an underestimation of the age of uraninite. Широкое распространение электронно-зондового микроанализа в варианте сканирующего электронного микроскопа (СЭМ), оборудованного энергодисперсионным спектрометром (ЭДС), с одной стороны, и сопоставимость метрологических характеристик ЭДС и волнодисперсионного спектрометра (ВДС) в случае определения основных слагающих минерал элементов – с другой, являются благоприятным фоном для исследования возможности применения СЭМ-ЭДС с целью химического датирования урановой минерализации. Углеродистокремнистые образования дабанжалгинской свиты распространены в карбонатных отложениях нижнего палеозоя в Окинской структурно-формационной зоне Восточного Саяна и представляют собой глубоководные отложения задугового бассейна. Для всех разновидностей углеродисто-кремнистых пород дабанжалгинской свиты характерны повышенные содержания U, Au, Ag, Pt, Pd, Mo, V, P, Cu, которые в 5–10 раз превышают таковые для других черносланцевых отложений Восточного Саяна. Уран образует собственные минералы – уранинит и браннерит в ассоциации с углеродистым веществом и сульфидами, а также входит в состав безводных фосфатов – ксенотима, монацита. В работе представлены данные по изучению состава и определению возраста браннерита и уранинита в образцах углеродисто-кремнистых сланцев, отобранных на трех участках: Убэр-Жадой, Дэдэ-ХараЖалга и Эрье-Хара-Жалга. Полученные оценки изохронного возраста зерен уранинита и браннерита для рассматриваемых участков составляют 523±26, 506±10 и 511±17 млн лет соответственно. Было показано, что эти датировки могут быть сопоставлены с возрастом метаморфизма на месторождении Сухой Лог, оцененным с помощью современных методов изотопной геохронологии. Следует отметить, что средние значения оценок возраста уранинита и браннерита на всех изучаемых участках дабанжалгинской свиты меньше, чем соответствующие оценки изохронного возраста, что, вероятно, обуславливается частичной потерей радиогенного свинца. Для участка Убэр-Жадой было проведено сопоставление данных ЭДС и ВДС и показано, что при использовании ЭДС существует занижение содержания Pb в уранините и, как следствие, занижение возраста уранинита

Instabilities in the Envelopes and Winds of Very Massive Stars

The high luminosity of Very Massive Stars (VMS) means that radiative forces play an important, dynamical role both in the structure and stability of their stellar envelope, and in driving strong stellar-wind mass loss. Focusing on the interplay of radiative flux and opacity, with emphasis on key distinctions between continuum vs. line opacity, this chapter reviews instabilities in the envelopes and winds of VMS. Specifically, we discuss how: 1) the iron opacity bump can induce an extensive inflation of the stellar envelope; 2) the density dependence of mean opacity leads to strange mode instabilities in the outer envelope; 3) desaturation of line-opacity by acceleration of near-surface layers initiates and sustains a line-driven stellar wind outflow; 4) an associated line-deshadowing instability leads to extensive small-scale structure in the outer regions of such line-driven winds; 5) a star with super-Eddington luminosity can develop extensive atmospheric structure from photon bubble instabilities, or from stagnation of flow that exceeds the "photon tiring" limit; 6) the associated porosity leads to a reduction in opacity that can regulate the extreme mass loss of such continuum-driven winds. Two overall themes are the potential links of such instabilities to Luminous Blue Variable (LBV) stars, and the potential role of radiation forces in establishing the upper mass limit of VMS.Comment: 44 pages, 13 figures. Chapter to appear in the book "Very Massive Stars in the Local Universe", Springer, J.S. Vink, e

Current status of turbulent dynamo theory: From large-scale to small-scale dynamos

Several recent advances in turbulent dynamo theory are reviewed. High resolution simulations of small-scale and large-scale dynamo action in periodic domains are compared with each other and contrasted with similar results at low magnetic Prandtl numbers. It is argued that all the different cases show similarities at intermediate length scales. On the other hand, in the presence of helicity of the turbulence, power develops on large scales, which is not present in non-helical small-scale turbulent dynamos. At small length scales, differences occur in connection with the dissipation cutoff scales associated with the respective value of the magnetic Prandtl number. These differences are found to be independent of whether or not there is large-scale dynamo action. However, large-scale dynamos in homogeneous systems are shown to suffer from resistive slow-down even at intermediate length scales. The results from simulations are connected to mean field theory and its applications. Recent work on helicity fluxes to alleviate large-scale dynamo quenching, shear dynamos, nonlocal effects and magnetic structures from strong density stratification are highlighted. Several insights which arise from analytic considerations of small-scale dynamos are discussed.Comment: 36 pages, 11 figures, Spa. Sci. Rev., submitted to the special issue "Magnetism in the Universe" (ed. A. Balogh

Density correlations and dynamical Casimir emission of Bogoliubov phonons in modulated atomic Bose-Einstein condensates

We present a theory of the density correlations that appear in an atomic Bose-Einstein condensate as a consequence of the dynamical Casimir emission of pairs of Bogoliubov phonons when the atom-atom scattering length is modulated in time. Different regimes as a function of the temporal shape of the modulation are identified and a simple physical picture of the phenomenon is discussed. Analytical expressions for the density correlation function are provided for the most significant limiting cases. This theory is able to explain some unexpected features recently observed in numerical calculations of Hawking radiation from analog black holes