186 research outputs found

    Which oxidation state of uranium and thorium as point defects in xenotime is favorable?

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    Relativistic study of xenotime, YPO4_4, containing atoms thorium and uranium as point defects is performed in the framework of cluster model with using the compound-tunable embedding potential (CTEP) method proposed by us recently. The Y-(PO4_4)6_6-Y'22_{22}-O'104_{104} cluster for xenotime is considered, in which central part, [Y-(PO4_4)6_6]15^{-15}, is the main cluster, whereas outermost 22 atoms of yttrium and 104 atoms of oxygen are treated as its environment and compose electron-free CTEP with the total charge of +15+15. The P and O atoms of the orthophosphate groups nearest to the central Y atom are treated at all-electron level. The central Y, its substitutes, Th and U, together with environmental Y atoms are described within different versions of the generalized relativistic pseudopotential method. Correctness of our cluster and CTEP models, constructed in the paper, is justified by comparing the Y-O and P-O bond lengths with corresponding periodic structure values of the \ypo4 crystal, both experimental and theoretical. Using this cluster model, chemical properties of solitary point defects, X = U, Th, in xenotime are analyzed. It has been shown that the oxidation state +3{+3} is energetically more profitable than +4{+4} not only for thorium but for uranium as well (ΔE5\Delta E \approx 5 eV) despite the notably higher ionic radius of U+3^{+3} compared to Y+3^{+3}, whereas ionic radii of U+4^{+4} and Y+3^{+3} are close. This leads to notable local deformation of crystal geometry around the U+3^{+3} impurity in xenotime and contradicts to widespread opinion about favorite oxidation state of uranium in such kind of minerals.Comment: 8 pages, 4 figures, 3 table

    Underlying Event measurements in pp collisions at s=0.9 \sqrt {s} = 0.9 and 7 TeV with the ALICE experiment at the LHC

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    Comparative Study of Methods for Extraction of Highly Purified Hemagglutinin from H5N1 Influenza Virus Recombinant Strain (A/Astana/6:2/2009)

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    ABSTRACT In the present study with the objective of the surface protein hemagglutinin production for single radial immunodiffusion reaction two methods of A/H5N1 recombinant strain A/AstanaRG/6:2/2009 highly purified hemagglutinin extraction were studied. They are ion exchange chromatography and adsorption on formalinized erythrocytes using such detergents as octyl glucoside, cetyl trimethylammonium bromide, X-100 triton. Homogeneous highly purified hemagglutinin has been obtained using the ion exchange chromatography

    Direct observation of the dead-cone effect in quantum chromodynamics

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    The direct measurement of the QCD dead cone in charm quark fragmentation is reported, using iterative declustering of jets tagged with a fully reconstructed charmed hadron

    Nuclear Incoherence: Deterrence Theory and Non-Strategic Nuclear Weapons in Russia

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    Direct observation of the dead-cone effect in quantum chromodynamics

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    At particle collider experiments, elementary particle interactions with large momentum transfer produce quarks and gluons (known as partons) whose evolution is governed by the strong force, as described by the theory of quantum chromodynamics (QCD) [1]. The vacuum is not transparent to the partons and induces gluon radiation and quark pair production in a process that can be described as a parton shower [2]. Studying the pattern of the parton shower is one of the key experimental tools in understanding the properties of QCD. This pattern is expected to depend on the mass of the initiating parton, through a phenomenon known as the dead-cone effect, which predicts a suppression of the gluon spectrum emitted by a heavy quark of mass m and energy E, within a cone of angular size m/E around the emitter [3]. A direct observation of the dead-cone effect in QCD has not been possible until now, due to the challenge of reconstructing the cascading quarks and gluons from the experimentally accessible bound hadronic states. Here we show the first direct observation of the QCD dead-cone by using new iterative declustering techniques [4, 5] to reconstruct the parton shower of charm quarks. This result confirms a fundamental feature of QCD, which is derived more generally from its origin as a gauge quantum field theory. Furthermore, the measurement of a dead-cone angle constitutes the first direct experimental observation of the non-zero mass of the charm quark, which is a fundamental constant in the standard model of particle physics.The direct measurement of the QCD dead cone in charm quark fragmentation is reported, using iterative declustering of jets tagged with a fully reconstructed charmed hadron.In particle collider experiments, elementary particle interactions with large momentum transfer produce quarks and gluons (known as partons) whose evolution is governed by the strong force, as described by the theory of quantum chromodynamics (QCD). These partons subsequently emit further partons in a process that can be described as a parton shower which culminates in the formation of detectable hadrons. Studying the pattern of the parton shower is one of the key experimental tools for testing QCD. This pattern is expected to depend on the mass of the initiating parton, through a phenomenon known as the dead-cone effect, which predicts a suppression of the gluon spectrum emitted by a heavy quark of mass mQm_{\rm{Q}} and energy EE, within a cone of angular size mQm_{\rm{Q}}/EE around the emitter. Previously, a direct observation of the dead-cone effect in QCD had not been possible, owing to the challenge of reconstructing the cascading quarks and gluons from the experimentally accessible hadrons. We report the direct observation of the QCD dead cone by using new iterative declustering techniques to reconstruct the parton shower of charm quarks. This result confirms a fundamental feature of QCD. Furthermore, the measurement of a dead-cone angle constitutes a direct experimental observation of the non-zero mass of the charm quark, which is a fundamental constant in the standard model of particle physics
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