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Symmetry Properties (symmetry + property)
Selected AbstractsElectric/magnetic deformations of S3 and AdS3, and geometric cosets,FORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 1 2005D. Israël We analyze asymmetric marginal deformations of SU(2)k and SL(2,,)k WZW models. These appear in heterotic string backgrounds with non-vanishing Neveu,Schwarz three-forms plus electric or magnetic fields, depending on whether the deformation is elliptic, hyperbolic or parabolic. Asymmetric deformations create new families of exact string vacua. The geometries which are generated in this way, deformed S3 or AdS3, include in particular geometric cosets such as S2, AdS2 or H2. Hence, the latter are consistent, exact conformal sigma models, with electric or magnetic backgrounds. We discuss various geometric and symmetry properties of the deformations at hand as well as their spectra and partition functions, with special attention to the supersymmetric AdS2 × S2 background. We also comment on potential holographic applications. [source] Davydov's solitons in zigzag carbon nanotubesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 1 2010Larissa Brizhik Abstract Nonlinear mechanism of charge transport in low-dimensional nanosystems is considered, based on the account of the electron,phonon interaction that arises from the deformation dependencies of the on-site and the hopping interaction energies at intermediatevalues of the corresponding coupling constants. In particular, carbon-type hexagonal zigzag nanotubes are studied. It is shown that in the adiabatic approximation the electron,phonon coupling results in the self-trapping of carriers and formation of polaron (soliton) states. We show that the ground state of an electron in a nanotube is a low-dimensional polaron whose symmetry depends on the strength of the coupling. Namely, at relatively weak coupling, the polaron possesses quasi-one-dimensional properties and has an azimuthal symmetry. When the coupling constant exceeds some critical value, the azimuthal symmetry breaks down and two-dimensional polaron on the nanotube surface is formed. There are also polarons formed by the electrons in the conducting band (or by holes in the valence band) in semiconducting zigzag carbon nanotubes. Such polarons are described by the system of coupled nonlinear Schroedinger equations which admits single-band polarons, and entangled (hybridized) polarons. These two types of polarons possess different energies and symmetry properties. Single-band solutions are one-dimensional polarons: they are azimuthally symmetric and localized along the nanotube axis. The entangled polarons are also self-trapped along the nanotube axis, but possess an inner structure and are modulated around the nanotube. The entangled polarons break the azimuthal symmetry and their energy is lower than the energy of single-band polarons. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source] Styrene/1,3-butadiene copolymerization by C2 -symmetric group 4 metallocenes based catalystsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 4 2008Mariagrazia Napoli Abstract C2 -symmetric group 4 metallocenes based catalysts (rac -[CH2(3- tert -butyl-1-indenyl)2]ZrCl2(1), rac -[CH2(1-indenyl)2]ZrCl2(2) and rac -[CH2(3- tert -butyl-1-indenyl)2]TiCl2(3)) are able to copolymerize styrene and 1,3-butadiene, to give products with high molecular weight. In agreement with symmetry properties of metallocene precatalysts, styrene homosequences are in isotactic arrangements. Full determination of microstructure of copolymers was obtained by 13C NMR and FTIR analysis and it reveals that insertion of butadiene on styrene chain-end happens prevailingly with 1,4- trans configuration. In the butadiene homosequences, using zirconocene-based catalysts, the 1,4- trans arrangement is favored over 1,4- cis, but the latter is prevailing in the presence of titanocene (3). Diad composition analysis of the copolymers makes possible to estimate the reactivity ratios of copolymerization: zirconocenes (1) and (2) produced copolymers having r1 × r2 = 0.5 and 3.0, respectively (where 1 refers to styrene and 2 to butadiene); while titanocene (3) gave tendencially blocky styrene,butadiene copolymers (r1 × r2 = 8.5). The copolymers do not exhibit crystallinity, even when they contain a high molar fraction of styrene. Probably, comonomer homosequences are too short to crystallize (ns = 16, in the copolymer at highest styrene molar fraction). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1476,1487, 2008 [source] Symmetry point group description of second harmonic generation in carbon nanotubesLASER PHYSICS LETTERS, Issue 4 2004L. De Dominicis Abstract The role played by symmetry properties of a carbon nanotube in the generation of second harmonic radiation is studied by using the formalism of irreducible representation of the symmetry point group. Experimental results of second harmonic generation in a carbon nanotube sample are discusses in view of the theoretical prediction obtained. (© 2004 by ASTRO, Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] Description of band structures of armchair nanotubes using the symmetry-adapted linear augmented cylindrical wave methodPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2009P. N. D'yachkov Abstract Using a symmetry-adapted linear augmented cylindrical wave method, the total band structures and the densities of states of the armchair single-walled carbon nanotubes (SWNTs) (n,n) with 4 , n , 20, n = 30, 40, 60 and 100 are calculated. The approximations are made in the sense of muffin-tin potentials and density functional theory only. The electronic states are presented as the functions of the two quantum numbers, namely, the continuous wave vector k corresponding to the screw symmetry operations and an integer rotational quantum number L between 0 and n , 1. An account of rotational and helical symmetry properties of the armchair SWNTs and particularly an introduction of the quantum number L permit to elaborate a more detailed classification of the armchair SWNTs electronic states. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Rotation designs: orthogonal first-order designs with higher order projectivityAPPLIED STOCHASTIC MODELS IN BUSINESS AND INDUSTRY, Issue 3 2002Dizza Bursztyn Abstract In many factorial experiments, just a few of the experimental factors account for most of the variation in the response, a situation known as factor sparsity. Accurate modelling of the factor,response relationship may require use of higher-order terms in the active factors. In such settings, it may be desirable to use a design that is able, simultaneously, to screen out the important factors and to fit higher-order models in those factors. We derive a useful class of designs by rotating standard two-level fractional factorials. A special class of rotations is developed that has some appealing symmetry properties and can accommodate more factors than the rotation designs in Bursztyn and Steinberg (J. Stat. Plann. Inference 2001;97:399). A comparison of designs based on their projection properties and alias matrices shows that the new designs are better than many other alternatives. Copyright © 2002 John Wiley & Sons, Ltd. [source] | ||||||||||