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Selected AbstractsField theory on nonanticommutative superspaceFORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 4-5 2008M. Dimitrijevi Abstract We discuss a deformation of the Hopf algebra of supersymmetry (SUSY) transformations based on a special choice of a twist. As usual, algebra itself remains unchanged, but the comultiplication changes. This leads to a deformed Leibniz rule for SUSY transformations. Superfields are multiplied by using a ,-product which is noncommutative, hermitian and finite when expanded in power series of the deformation parameter. One possible deformation of the Wess-Zumino action is proposed and analysed in detail. Differently from most of the literature concerning this subject, we work in Minkowski space-time. [source] Aspects of stability and phenomenology in type IIA orientifolds with intersecting D6-branesFORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 1 2004T. OttArticle first published online: 14 JAN 200 Abstract Intersecting branes have been the subject of an elaborate string model building for several years. After a general introduction into string theory, this work introduces in detail the toroidal and -orientifolds. The picture involving D9-branes with B-fluxes is shortly reviewed, but the main discussion employs the T-dual picture of intersecting D6-branes. The derivation of the R-R and NS-NS tadpole cancellation conditions in the conformal field theory is shown in great detail. Various aspects of the open and closed chiral and non-chiral massless spectrum are discussed, involving spacetime anomalies and the generalized Green-Schwarz mechanism. An introduction into possible gauge breaking mechanisms is given, too. Afterwards, both ,, = 1 supersymmetric and non-supersymmetric approaches to low energy model building are treated. Firstly, the problem of complex structure instabilities in toroidal ,R -orientifolds is approached by a -orbifolded model. In particular, a stable non-supersymmetric standard-like model with three fermion generations is discussed. This model features the standard model gauge groups at the same time as having a massless hypercharge, but possessing an additional global B - L symmetry. The electroweak Higgs mechanism and the Yukawa couplings are not realized in the usual way. It is shown that this model descends naturally from a flipped SU(5) GUT model, where the string scale has to be at least of the order of the GUT scale. Secondly, supersymmetric models on the -orbifold are discussed, involving exceptional 3-cycles and the explicit construction of fractional D-branes. A three generation Pati-Salam model is constructed as a particular example, where several brane recombination mechanisms are used, yielding non-flat and non-factorizable branes. This model even can be broken down to a MSSM-like model with a massless hypercharge. Finally, the possibility that unstable closed and open string moduli could have played the role of the inflaton in the evolution of the universe is being explored. In the closed string sector, the important slow-rolling requirement can only be fulfilled for very specific cases, where some moduli are frozen and a special choice of coordinates is taken. In the open string sector, inflation does not seem to be possible at all. [source] Blow-up analysis, existence and qualitative properties of solutions for the two-dimensional Emden,Fowler equation with singular potentialMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 18 2007Daniele Bartolucci Abstract Motivated by the study of a two-dimensional point vortex model, we analyse the following Emden,Fowler type problem with singular potential: where V(x) = K(x)/|x|2, with ,,(0, 1), 0 Extension theorems for Stokes and Lamé equations for nearly incompressible media and their applications to numerical solution of problems with highly discontinuous coefficientsNUMERICAL LINEAR ALGEBRA WITH APPLICATIONS, Issue 2 2002N. S. Bakhvalov Abstract We prove extension theorems in the norms described by Stokes and Lamé operators for the three-dimensional case with periodic boundary conditions. For the Lamé equations, we show that the extension theorem holds for nearly incompressible media, but may fail in the opposite limit, i.e. for case of absolutely compressible media. We study carefully the latter case and associate it with the Cosserat problem. Extension theorems serve as an important tool in many applications, e.g. in domain decomposition and fictitious domain methods, and in analysis of finite element methods. We consider an application of established extension theorems to an efficient iterative solution technique for the isotropic linear elasticity equations for nearly incompressible media and for the Stokes equations with highly discontinuous coefficients. The iterative method involves a special choice for an initial guess and a preconditioner based on solving a constant coefficient problem. Such preconditioner allows the use of well-known fast algorithms for preconditioning. Under some natural assumptions on smoothness and topological properties of subdomains with small coefficients, we prove convergence of the simplest Richardson method uniform in the jump of coefficients. For the Lamé equations, the convergence is also uniform in the incompressible limit. Our preliminary numerical results for two-dimensional diffusion problems show fast convergence uniform in the jump and in the mesh size parameter. Copyright © 2002 John Wiley & Sons, Ltd. [source] Orbital Kondo effect and spin polarized transport through quantum dotsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2006S. Lipi Abstract The coherent spin dependent transport through a set of two capacitively coupled quantum dots placed in a magnetic field is considered within the equation of motion method. The magnetic field breaks the spin degeneracy. For special choices of gate voltages the dot levels are tuned to resonance and the orbital Kondo effect results. For different Zeemann splittings at the dots the Kondo resonance can be formed for only one spin channel. In this case the system operates as an efficient spin filter. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Multiplicative congruential generators, their lattice structure, its relation to lattice,sublattice transformations and applications in crystallographyACTA CRYSTALLOGRAPHICA SECTION A, Issue 6 2009Wolfgang Hornfeck An analysis of certain types of multiplicative congruential generators , otherwise known for their application to the sequential generation of pseudo-random numbers , reveals their relation to the coordinate description of lattice points in two-dimensional primitive sublattices. Taking the index of the lattice,sublattice transformation as the modulus of the multiplicative congruential generator, there are special choices for its multiplier which induce a symmetry-preserving permutation of lattice-point coordinates. From an analysis of similar sublattices with hexagonal and square symmetry it is conjectured that the cycle structure of the permutation has its crystallographic counterpart in the description of crystallographic orbits. Some applications of multiplicative congruential generators in structural chemistry and biology are discussed. [source]
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