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  • 1
    Electronic Resource
    Electronic Resource
    Models with Hopf terms (1992)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 33 (1992), S. 1272-1280 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: The geometrical structure of the Hopf term and its relation to the spin of a skyrmion is studied. An ansatz describing the most general one-skyrmion field configuration in three dimensions is introduced and various properties of the physical Hopf term for it are exhibited. The extension to seven dimensions is also made. Some comments are also made about the quantization of the coefficient of the Hopf term in the action.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.529704
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  • 2
    Electronic Resource
    Electronic Resource
    A supergroup based supersigma model (1992)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 33 (1992), S. 2357-2364 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: The supergroup UOSp(1,2) is used to construct geometrically a twice graded supersymmetric supersigma model. In an appropriate contraction limit, the model reduces to the conventional supersymmetric sigma model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.529606
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  • 3
    Electronic Resource
    Electronic Resource
    Comments on "Redox Processes on Pure Ceria and Rh/CeO2 Catalyst Monitored by X-ray Absorption (Fast Acquisition Mode) (1995)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 99 (1995), S. 11794-11796 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100030a025
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  • 4
    Electronic Resource
    Electronic Resource
    Microstructural and chemical properties of ceria-supported rhodium catalysts reduced at 773 K (1993)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 97 (1993), S. 4118-4123 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100118a031
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  • 5
    Electronic Resource
    Electronic Resource
    Anomalies from the Wess-Zumino-Witten action (1991)
    Springer
    The European physical journal 49 (1991), S. 627-632 
    Details
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We show that the two most frequent expressions for the anomalous commutators can be both derived from quantities associated with the WZW model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01483579
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  • 6
    Electronic Resource
    Electronic Resource
    Study of the interaction of two hexagonal neodymium oxides with atmospheric CO2 and H2O (1988)
    Springer
    Journal of materials science 23 (1988), S. 1474-1480 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The present work deals with the behaviour in air of two neodymia samples prepared by calcination of a hydroxynitrate phase at 1020 and 1310 K, respectively. Both oxides behave similarly so that after approximately 50 days of air exposure, at normal temperature and pressure, they are thoroughly transformed into hydroxide. When stabilization is reached the two aged samples are also carbonated in the bulk; evidence for this latter process, which is much less intense than the hydration reaction, cannot be obtained from X-ray diffraction studies. These findings indicate the existence of close analogies between the oxides investigated here and several hexagonal lanthana and monoclinic samaria samples studied earlier, which supports the classification of the rare earth oxides based on their behaviour with atmospheric CO2 and H2O, as recently proposed by us. The additional experiments of carbonation reported here suggest that the ageing in air of the hexagonal neodymium oxides leads to the formation of a hydroxycarbonate-like phase, which does not agree with the crystalline ancylite-type hydroxycarbonate, formed when these oxides are suspended in water.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01154619
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  • 7
    Electronic Resource
    Electronic Resource
    Solid state chemistry of the preparation of lanthana-supported metal catalysts — study of the impregnation step (1987)
    Springer
    Journal of materials science 22 (1987), S. 3793-3800 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The solid state reactions occurring at the support throughout the preparation process of lanthana-supported metal catalysts is reported. Specifically it is concerned with the impregnation step. When following the usual procedure, i.e. impregnation of lanthana with an aqueous solution of the precursor, heavy carbonation of the support with formation of a hydroxycarbonate phase, La(OH)CO3, was found to occur. Simulated impregnation treatments with distilled water have shown that the nucleation of the hydroxycarbonate phase, not observed on lanthana simply exposed to air, is not specifically induced by the presence of the precursor salt. Likewise, it has been found that the nucleation of La(OH)CO3 does not take place upon heating the oxide in air at 383 K, as in the drying treatment which follows the wetting step of the impregnation process. Accordingly, nucleation of the new carbonated phase must occur during the wetting step. Once the formation of La(OH)CO3 has begun, the support can slowly take up further amounts of CO2 by simple exposure to air. In this way, impregnated support phases actually consisting of as much as 80% La(OH)CO3 could be observed. It can be concluded from the present work that the occurrence of carbonation phenomena on lanthana constitutes a major feature of its behaviour as a support of the transition metals. To date, however, this is an aspect which has received very little attention.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01161496
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  • 8
    Electronic Resource
    Electronic Resource
    Microstructure and catalytic properties of Rh and Ni dispersed on TiO2-SiO2 aerogels (1994)
    Springer
    Journal of sol gel science and technology 2 (1994), S. 831-836 
    Details
    ISSN: 1573-4846
    Keywords: metal catalysts ; titania-silica ; sonogels ; n-butane hydrogenolysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The influence of the preparation method on the microstructure and catalytic behavior of Rh and Ni dispersed on TiO2-SiO2 aerogels is investigated. The autoclave method has been followed to prepare titania-silica aerogels with TiO2 contents ranging between 0 and 10 mole %. These aerogels have been used as matrices to disperse catalytically active metals: Rh and Ni. The metals can be deposited by impregnation of aerogels, or alternatively, can be added into the hydrolysis water used in the synthesis of gels. The resulting catalysts present surface areas higher than 550 m2·g−1. The percentage of titania, the method followed for the introduction of the metal, and the nature of the metal itself affect both the activities and selectivities of the catalysts in the hydrogenolysis of n-butane. Thus, the presence of titania in Rh catalysts increases the activity values, and the samples prepared by impregnation present selectivities towards ethane higher than 80%. Whereas, the rhodium catalysts in which the metal has been introduced before gelling, do not orientate the reaction in favor of a definite product. For the case of Ni, it is quite frequent to obtain high selectivities towards the breakdown of the C-C terminal bonds. In summary, the preparation methods allow to modulate into very broad limits the catalytic behavior of the samples.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00486360
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  • 9
    Electronic Resource
    Electronic Resource
    Model with solitons in (2+1) dimensions (1992)
    Springer
    The European physical journal 53 (1992), S. 177-182 
    Details
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We consider various models in (2+1) dimensions which possess soliton-like solutions. We discuss the additional terms that must be added to the conventionalS 2 model in order that its solutions are stable and so can be treated as solitons. The role of various terms is analysed and some properties of the solitonic solutions are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01483887
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  • 10
    Electronic Resource
    Electronic Resource
    Study of some aspects of the reactivity of La2O3 with CO2 and H2O (1985)
    Springer
    Journal of materials science 20 (1985), S. 537-541 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The behaviour of three different samples of La2O3 on exposure to atmoshperic CO2 and H2O and the influence of the origin is discussed. The thermal evolution of the samples, stabilized in air for months or even years, has been studied by TG, TPD, IR spectroscopy and X-ray diffraction. BET surface areas of the samples were determined from the corresponding nitrogen adsorption isotherms at 77 K. In all three samples, hydration and carbonation occur in bulk. In accordance with our results, lanthana samples stabilized in air would consist of lanthanum hydroxide, La(OH)3, partially carbonated, La2(OH)6−3x (CO3) x ,(x⪝1). When hexagonal phases of La2O3, obtained by calcining, at 1130 K, the samples stabilized in air were re-exposed, hydration and carbonation levels similar to those observed in the stabilized samples were reached after less than 24 h. Some lanthana samples were soaked in water, at 298 K, and then dried at 380 K. In this way, the evolution of the oxide when treated under similar conditions to those used in both impregnation and ion exchange techniques for preparation of supported metal phases, could be investigated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01026524
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