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  • Inorganic Chemistry  (9)
  • Elementary Particles and Fields  (3)
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  • 1
    Publication Date: 2015-11-26
    Description: Author(s): Jeremy Green, Oleksii Gryniuk, Georg von Hippel, Harvey B. Meyer, and Vladimir Pascalutsa We perform a lattice QCD calculation of the hadronic light-by-light scattering amplitude in a broad kinematical range. At forward kinematics, the results are compared to a phenomenological analysis based on dispersive sum rules for light-by-light scattering. The size of the pion pole contribution is… [Phys. Rev. Lett. 115, 222003] Published Wed Nov 25, 2015
    Keywords: Elementary Particles and Fields
    Print ISSN: 0031-9007
    Electronic ISSN: 1079-7114
    Topics: Physics
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  • 2
    Publication Date: 2011-03-30
    Description: Author(s): Leonardo Giusti and Harvey B. Meyer For a thermal field theory formulated in the grand canonical ensemble, the distribution of the total momentum is an observable characterizing the thermal state. We show that its cumulants are related to thermodynamic potentials. In a relativistic system, for instance, the thermal variance of the tot... [Phys. Rev. Lett. 106, 131601] Published Tue Mar 29, 2011
    Keywords: Elementary Particles and Fields
    Print ISSN: 0031-9007
    Electronic ISSN: 1079-7114
    Topics: Physics
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  • 3
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    American Physical Society (APS)
    Publication Date: 2011-08-11
    Description: Author(s): Harvey B. Meyer We present a formula that allows one to calculate the pion form factor in the timelike region 2 m π ≤√ s ≤4 m π in lattice QCD. The form factor quantifies the contribution of two-pion states to the vacuum polarization. It must be known very accurately in order to reduce the theoretical uncertainty on the a... [Phys. Rev. Lett. 107, 072002] Published Wed Aug 10, 2011
    Keywords: Elementary Particles and Fields
    Print ISSN: 0031-9007
    Electronic ISSN: 1079-7114
    Topics: Physics
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 478 (1981), S. 239-239 
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 5
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Contributions to the Investigation of Inorganic Non-stoichiometric Compounds. XX. Metastable Oxidation of a Series of Solid Solutions  -  an Access to W-rich Block Structures in the System Nb2O5/WO3The characteristical region of existence of block structures with building elements that are limited in size in two directions ends in the system Nb2O5/WO3, as was shown by previous investigations, under conditions of equilibrium at a maximum value of 2.654 O/ΣM. For the occurring phases with the ratios Nb2O5: WO3 = 6:1, = 7:3, = 8:5 and = 9:8 as well we now were successful in substituting W for Nb. The original block structure and the corresponding ratio O/ΣM were preserved. The “9:8”-phase W4/4[Nb18W7O69], for example, forms solid solutions W4/4[Nb11W14O69] leaving the size of the building elements ([5 times; 5] blocks) unchanged. Hereby the ratio W/Nb is drastically enhanced from 0.444 to 1.364. By metastable oxidation of these solid solutions at temperatures of about 500°C, for instance in air, one comes back to the system Nb2O5/WO3. In this way the region of existence of block structures could be expanded far beyond the limit at 2.654 O/ΣM to higher W/Nb values.
    Notes: Das charakteristische Existenzgebiet der Blockstrukturen mit zweidimensional begrenzten Bauelementen endet im System Nb2O5/WO3, wie bereits frühere Untersuchungen gezeigt haben, unter Gleichgewichtsbedingungen bei einem Maximalwert von 2,654 O/O/ΣM (M = Nb, W). Es gelang nun, in den mit den Verhältnissen Nb2O5: WO3 = 6:1, 7:3, 8:5 sowie 9:8 auftretenden Phasen im weiten Umfang Nb durch W zu substituieren, wobei ihre ursprüngliche Blockstruktur und das jeweilige Verhältnis O/ΣM erhalten blieben. So bildet z. B. die «9:8»-Phase W4/4[Nb18W7O69] bei unveränderter Größe der Bauelemente ([5 × 5]-Blöcke) einen Mischkristall W4/4[Nb11W14O69]; das Verhältnis W/Nb wird damit drastisch von 0,444 auf 1,364 erhöht. Durch metastabile Oxydation der so erhaltenen Mischkristalle bei Temperaturen um 500°C, z. B. an der Luft, gelangt man in das System Nb2O5/WO3 zurück. Das Existenzgebiet der Blockstrukturen konnte in dieser Weise bis weit über die Grenze bei 2,654 O/ΣM hinaus zu höheren W/Nb-Werten erweitert werden.
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  • 6
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Die Reduktion der metastabilen Oxydationsprodukte der NbOx-Phasen (2,4 〈 x 〈 2,5) mit H2O/H2-Mischungen wurde untersucht. Bei niedrigerer Temperatur (≈300°C) ist die Reduktionswirkung noch gering, sie nimmt mit steigender Temperatur beträchtlich zu. Dabei zeigen die Oxydationsprodukte der Zusammensetzung Nb2O5 ein gewisses „Erinnerungsvermögen“; in allen Fällen läft die Reduktion bis zu den ursprünglichen NbOx-Phasen zurück. Man gelangt bei um so niedrigerer Reduktionstemperatur zur Zusammensetzung x des jeweiligen Ausgangsprodukts NbOx zurück, je kleiner die Differenz 2,50-x ist. Bemerkenswert ist, daß die Rückreduktion zum monoklinen Nb12O29 über eine Zwischenstufe der Zusammensetzung 2,439-2,447 O/Nb verläuft. An dieser Stelle liegt eine neue, metastabile NbOx-Phase mit einem charakteristischen Guinierdiagramm vor.Contributions on the Investigation of Inorganic Non-stoichiometric Compounds. XII. Reduction of Metastable Nb2O5 Modifications, Oxidation Products of NbOx Phases (2.4 〈 x 〈 2.5)The reduction of metastable oxidation products of the NbOx phases (2.4 〈 x 〈 2.5) by H2O/H2 mixtures was investigated. At lower temperatures (ca 300°C) the effect of the reduction was slight. It increased considerably with rising temperature. Samples oxidized to the composition Nb2O5 showed a certain “memory of structure”. The original NbOx phases can be obtained in all cases from the oxidized products. The smaller the difference 2.50-x the lower the reaction temperature at which the composition x of the corresponding starting material NbOx is regained. It is remarkable that the re-reduction to the monoclinic Nb12O29 proceeds by way of the intermediate composition 2.439-2.447 O/Nb. At this ratio O/Nb a new metastable NbOx phase with a characteristic x-ray diagram exists.
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 484 (1982), S. 98-123 
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Contributions to the Investigation of Inorganic Non-stoichiometric Compounds. XV. Some Further Metastable Nb2O5-Modifications, Products of the Slow Oxidation of the NbOx PhasesIf in contrast to previous investigations the blue-black NbOx phases (2.4 〈 x 〈 2.5) are not oxidized in air, but in a rarefied oxygen atmosphere or with steam, five further metastable Nb2O5 forms can be obtained in addition to the numerous already known Nb2O5 modifications. Nb12O29 (mon. and orh.) and Nb47O116 lead to one new Nb2O5 form each. Nb22O54 yields two new Nb2O5 modifications. It can be deduced from the thermal behaviour that in addition to unexspected transitions between the known and the new metastable modifications in all cases H-Nb2O5 appears as final product at high temperature. The electron optical investigation of the new oxidation products of Nb12O29 (mon. and orh.) shows that their structures are determined by R-type tunnels as the characteristic structure element. By this they clearly differ from the already known oxidation products. With this for the first time sodium free niobium oxide structures occur whose structural concept is substantially shaped by R-type tunnels which are known from NaNb13O33.
    Notes: Oxydiert man die blauschwarzen NbOx-Phasen (2,4 〈 x 〈 2,5) im Unterschied zu früheren Untersuchungen nicht an der Luft, sondern in verdünnter Sauerstoffatmosphäre oder mit Wasserdampf, so werden zusätzlich zu den zahlreichen bisher bekannten Nb2O5-Modifikationen fünf weitere metastabile Formen von Nb2O5 erhalten. Nb12O29 (mon. und orh.) geht in je eine, Nb22O54 in zwei und Nb47O116 in eine neue Nb2O5-Form Über. Wie das thermische Verhalten zeigt, tritt außer unerwarteten Übergängen zwischen den bekannten und den neuen metastabilen Modifikationen in allen Fällen als Endstufe bei hoher Temperatur H-Nb2O5 auf.Aus der elektronenoptischen Untersuchung der neuen Oxydationsprodukte von Nb12O29 (mon. und orh.) geht hervor, daß ihr Aufbau durch R-Typ-Lücken als charakteristisches Strukturelement bestimmt ist, so daß sie sich von den bisher bekannten Oxydationsprodukten strukturell klar unterscheiden. Damit liegen erstmals Na-freie Nioboxidstrukturen vor, an deren Aufbau die von NaNb13O33 bekannten R-Typ-Lücken maßgeblich beteiligt sind.
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  • 8
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 484 (1982), S. 77-97 
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Contributions to the Investigation of Inorganic Non-stoichiometric Compounds. XIV. Oxidation Products of Orthorhombic Nb12O29, Electron Optical InvestigationAn electron optical investigation shows that the orthorhombic starting material Nb12O29(BII) is well ordered. The oxidation products Nb2O5(Ox1BII) and Nb2O5(Ox2BII) are different from each other in structures as well as in their reactions. Nb2O5(Ox1BII) is unstable in the electron beam and differs from BII by characteristic point-defects. The radiation load can lead to the reduction to BII or to a transition into a defect structure with R-type-tunnels. The not well ordered structure of Nb2O5(Ox2BII) is stable in the electron beam. Characteristic is the sequence of [2×5] and [3×4] blocks, the latter in two different orientations. The observed composition O/Nb = 2.500 can be described by the present structural modell assuming vacant niobium tetrahedral sites. The large structural differences between the oxidation products of the orthorhombic and the monoclinic Nb12O29 are remarkable.
    Notes: Wie die elektronenoptische Untersuchung zeigt, ist das orthorhombische Ausgangsprodukt Nb12O29(BII) gut geordnet. Die Oxydationsprodukte Nb2O5(Ox1BII) und Nb2O5(Ox2BII) sind strukturell sowie in ihrem Verhalten verschieden. Das im Elektronenstrahl instabile Nb2O5(Ox1BII) unterscheidet sich von BII durch charakteristische Punktdefekte. Die Strahlbelastung kann zu einer Reduktion zu BII oder zum Übergang in eine Defektstruktur mit R-Typ-Lücken führen. Die wenig geordnete Struktur von Nb2O5(Ox2BII) ist im Elektronenstrahl beständig; charakteristisch ist die Abfolge von [2×5]- und [3×4]-Blöcken, letztere in zwei verschiedenen Orientierungen. Die beobachtete Zusammensetzung O/Nb = 2,500 läßt sich im vorliegenden Strukturmodell mit einer Unterbesetzung der Nb-Tetraederpositionen beschreiben. Bemerkenswert sind die erheblichen strukturellen Unterschiede zwischen den Oxydationsprodukten von orthorhombischem und monoklinem Nb12O29.
    Additional Material: 9 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 484 (1982), S. 53-76 
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Contributions to the Investigation of Inorganic Non-stoichiometric Compounds. XIII. Oxidation Products of Monoclinic Nb12O29, Electron Optical InvestigationThe electron optical investigation shows that the starting material Nb12O29(mon.) is well ordered and that the oxidation products Nb2O5(Ox1BI) and Nb2O5(Ox2BI) have different structures. Nb2O5(Ox1BI) has a similar structure as Nb12O29(mon.), however differs from the latter by characteristic point defects, which in the electron microscope easily disappear by reduction. Nb2O5(Ox2BI) has not a well ordered structure; characteristic are rows of [2×n]-blocks which on the average are separated by five [3×n]-blocks. The average block length is n = 4 octahedra. The observed composition O/Nb = 2.500 can be explained by a structure model with unoccupied tetrahedral sites of Nb.
    Notes: Die elektronenoptische Untersuchung zeigt, daß das monokline Ausgangsprodukt Nb12O29(BI) gut geordnet ist und daß die bei der Oxydation entstehenden Produkte Nb2O5(Ox1BI) und Nb2O5(Ox2BI) unterschiedliche Strukturen besitzen. Nb2O5(Ox1BI) ist sehr ähnlich aufgebaut wie BI, unterscheidet sich hiervon jedoch durch charakteristische Punktdefekte, die durch Reduktion im Elektronenmikroskop leicht wieder verschwinden. Nb2O5(Ox2BI) besitzt eine wenig geordnete Struktur; charakteristisch sind Reihen von [2×n]-Blöcken, die im Mittel durch fünf [3×ln]-Blöcke voneinander getrennt sind; im Durchschnitt ist die Blocklänge n = 4. Die beobachtete Zusammensetzung O/Nb = 2,500 läßt sich im vorliegenden Strukturmodell durch eine Unterbesetzung der Nb-Tetraederpositionen erklären.
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  • 10
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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