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Results for "A. T. Ngiangia"
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On the SU(3) parametrization of qutritsNov 11 2005Parametrization of qutrits on the complex projective plane CP^2 = SU(3)/U(2) is given explicitly. A set of constraints that characterize mixed state density matrices is found. Quantum Renormalization Group for Ground-State FidelityAug 15 2011Sep 08 2011Ground-state fidelity (GSF) and quantum renormalization group theory (QRG) have proven useful tools in the study of quantum critical systems. Here we lay out a general, unified formalism of GSF and QRG; specifically, we propose a method to calculate GSF ... More Modelling hybrid Beta Cephei/SPB pulsations: Gamma PegasiSep 25 2009Recent photometric and spectroscopic observations of the hybrid variable Gamma Pegasi (Handler et al. 2009, Handler 2009) revealed 6 frequencies of the SPB type and 8 of the Beta Cep type pulsations. Standard seismic models, which have been constructed ... More Generalized Chaplygin Gas in a modified gravity approachAug 10 2004Dec 09 2004We study the generalized Chaplygin gas (GCG) scenario in a modified gravity approach. That is, we impose that our universe has a pure dust configuration, and allow for a modification of gravity that yields a GCG specific scale factor evolution. Moreover, ... More Quasi-exotic open-flavor mesonsMay 11 2016Oct 04 2016Meson states with exotic quantum numbers arise naturally in a covariant bound-state framework in QCD. We investigate the consequences of shifting quark masses such that the states are no longer restricted to certain C-parities, but only by J^P. Then, ... More Properties of MgB2 bulkDec 24 2009The review considers bulk MgB2-based materials in terms of their structure, superconducting and mechanical properties. Superconducting transition temperatures of 34.5-39.4 K, critical current densities of 1.8-1.0 x E6 A/sq.cm in self field and 103 in ... More Structure FunctionsDec 23 1998The latest structure function results, as presented at the ICHEP98 conference, are reviewed. A brief introduction to the formalism and the status of global analyses of parton distributions is given. The review focuses on three experimental areas: fixed-target ... More GR models of the X-ray spectral variability of MCG--6-30-15Mar 20 2009Dec 21 2009We study in detail the GR models of the X-ray spectral variability for various geometries of the X-ray source and with various relativistic effects being the dominant cause of spectral variability. The predicted properties are compared with the Suzaku ... More Active galaxy unification in the era of X-ray polarimetryJan 27 2010Jan 27 2010Active Galactic Nuclei (AGN), Seyfert galaxies and quasars, are powered by luminous accretion and often accompanied by winds which are powerful enough to affect the AGN mass budget, and whose observational appearance bears an imprint of processes which ... More Kondo effect in XXZ spin chainsFeb 24 1998The Kondo effect in a one-dimensional spin-1/2 XXZ model in the gapless XY regime (-1<Delta<=1) is studied both analytically and numerically. In our model an impurity spin (S=1/2) is coupled to a single spin in the XXZ spin chain. Perturbative renormalization-group ... More Brachistochrone of Entanglement for Spin ChainsSep 03 2012We analytically investigate the time-optimal unitary evolution of entanglement between indirectly coupled qubits in a trilinear Ising chain with unequal interaction couplings. The intermediate qubit is controlled via a local magnetic field. We find the ... More Diffusion equations for a Markovian jumping processApr 28 2006We consider a Markovian jumping process which is defined in terms of the jump-size distribution and the waiting-time distribution with a position-dependent frequency, in the diffusion limit. We assume the power-law form for the frequency. For small steps, ... More First detection of rotational CO line emission in an RGB starJan 10 2014Context: For stars with initial masses below about 1 solar mass, the mass loss during the first red giant branch (RGB) phase dominates mass loss in the later asymptotic giant branch (AGB) phase. Nevertheless, mass loss on the RGB is still often parameterised ... More Infrared excess around nearby RGB stars and Reimers lawMar 19 2012Mar 26 2012(Abridged) The spectral energy distributions of a well-defined sample of 54 RGB stars are constructed, and fitted with the dust radiative transfer model DUSTY. The central stars are modeled by MARCS model atmospheres. In a first step, the best-fit MARCS ... More Carbon stars in the Local GroupAug 24 2002The current status of carbon stars in the Local Group and beyond, is discussed. Although many carbon stars and late M-stars have been identified in Local Group galaxies, a coherent understanding in terms of the chemical evolution- and star formation history ... More Carbon stars in populations of different metallicityNov 09 1998Our current knowledge of carbon stars in the Local Group and beyond, is discussed. Although many carbon stars and late M-stars have been identified in external galaxies a coherent understanding in terms of the chemical evolution- and star formation rate-history ... More On some relativistic singular surfacesAug 26 2009In the current relativistic literature there are misleading considerations about some singular surfaces. An accurate geometric analysis allows to settle the question. No physical meaning is attributable to the spatial regions surrounded by the above surfaces. ... More Color confinement in Coulomb gauge QCDDec 28 2005We study the long-range behavior of the heavy quark potential in Coulomb gauge using a quenched SU(3) lattice gauge simulation with partial-length Polyakov line correlators. We show that the Coulomb heavy quark potential associated with the instantaneous ... More Skewed Parton Distributions and F_2^D at beta -> 1Oct 24 2000We show that the diffractive structure function is perturbatively calculable in the domain where the diffractive mass is small but still outside the resonance region. In this domain, which can be characterized by Lambda^2/Q^2 << 1-beta << (Lambda^2/Q^2)^1/2, ... More Reply to "Comments on Bouda and Djama's 'Quantum Newton's Law'"Jun 20 2002In this reply, we hope to bring clarifications about the reservations expressed by Floyd in his comments, give further explanations about the choice of the approach and show that our fundamental result can be reproduced by other ways. We also establish ... More Trajectories in the Context of the Quantum Newton's LawAug 06 2001May 17 2002In this paper, we apply the one dimensional quantum law of motion, that we recently formulated in the context of the trajectory representation of quantum mechanics, to the constant potential, the linear potential and the harmonic oscillator. In the classically ... More Simulation of Wilson fermion at finite isospin densityOct 22 2003For QCD with Wilson fermions at isospin chemical potential we study the finite phase transition on an $8^3\times4$ lattice at $\kappa=0.15$. We use two gauge actions: Wilson action and DBW2 action. Both actions give the same results. The phase diagram ... More On L. Schwartz's boundedness condition for kernelsDec 16 2002In previous works we analysed conditions for linearization of hermitian kernels. The conditions on the kernel turned out to be of a type considered previously by L. Schwartz in the related matter of characterizing the real space generated by positive ... More Rogers dilogarithm in integrable systemsOct 05 1992Oct 06 1992We dicuss some curious aspects of the Rogers dilogarithm and the functional relations in integrable systems in two dimensions. This is for the proceedings of the XX1 Differential Geometry Methods in Theoretical Physics, Tianjin, China, 5-9 June 1992. Adiabaticity in semiclassical nanoelectromechanical systemsJul 19 2011Oct 14 2011We compare the semiclassical description of NEMS within and beyond the adiabatic approximation. We consider a NEMS model which contains a single phonon (oscillator) mode linearly coupled to an electronic few-level system in contact with external particle ... More Goldstone Boson Normal CoordinatesJan 21 2000Jul 13 2000The phenomenon of spontaneous symmetry breaking is well known. It is known to be accompanied with the appearance of the `Goldstone boson'. In this paper we construct the canonical coordinates of the Goldstone boson, for quantum spin systems with short ... More Mathematical Structure of Magnons in Quantum FerromagnetsMar 01 1999We provide the mathematical structure and a simple, transparent and rigorous derivation of the magnons as elementary quasi-particle excitations at low temperatures and in the infinite spin limit for a large class of Heisenberg ferromagnets. The magnon ... More Non-Extensive Bose-Einstein Condensation ModelNov 28 2000The imperfect Boson gas supplemented with a gentle repulsive interaction is completely solved. In particular it is proved that it has non-extensive Bose-Einstein condensation, i.e., there is condensation without macroscopic occupation of the ground state ... More Electromagnetic response of light nucleiOct 28 1999We show examples of neutron capture, photo dissociation and Coulomb dissociation processes, relevant for studying nuclear structure properties of some light nuclei. In the case of the neutron capture, we show how interference effects among the direct ... More Singularities and stable homotopy groups of spheres IIJun 17 2015Oct 22 2017We establish a connection between Morin singularities and stable homotopy groups of spheres. This connection allows us to describe how the images of singularity strata behave around the image of a more complicated stratum. Freeness conditions for crossed squares and squared complexesApr 09 1999Following Ellis, we investigate the notion of totally free crossed squares and related square complexes. It is shown how to interpret the information in a free simplicial group given with a choice of CW-basis, in terms of the data for a totally free crossed ... More Virtual quandle for links in lens spacesFeb 20 2017We construct a virtual quandle for links in lens spaces $L(p,q)$, with $q=1$. This invariant has two valuable advantages over an ordinary fundamental quandle for links in lens spaces: the virtual quandle is an essential invariant and the presentation ... More Universal dephasing rate due to diluted Kondo impuritiesSep 22 2005May 18 2006We calculate the dephasing rate due to magnetic impurities in a weakly disordered metal as measured in a weak localization experiment. If the density n_S of magnetic impurities is sufficiently low, the dephasing rate 1/tau_phi is a universal function, ... More On the Jastrow Wave Function for N-Particles on a PlaneJul 17 1996The possibility of describing quantum mechanical particles on a plane by a Jastrow wave function is studied. We obtain the condition under which the particles interact through pair potentials. It is found that if the interparticle forces depend only on ... More Numerical Modelling of Dusty Debris DisksFeb 07 2005Infrared and submillimetre observations of nearby Vega-like stars have revealed a number of clumpy, asymmetric dust debris disks. Previous studies using semi-analytical and numerical methods have suggested planetary companions of various mass as the likely ... More Phase Diagram of Coupled LaddersFeb 27 1998The 2-leg t-J ladder forms a spin liquid at half-filling which evolves to a Luther-Emery liquid upon doping. Our aim is to obtain a complete phase diagram for isotropic coupling (i.e. rungs and legs equal) as a function of electron density n and the ratio ... More Brownian scattering of a spinon in a Luttinger liquidDec 20 2014We consider strongly interacting one-dimensional electron liquids where elementary excitations carry either spin or charge. At small temperatures a spinon created at the bottom of its band scatters off low-energy spin- and charge-excitations and follows ... More Sklyanin algebras and Hilbert schemes of pointsOct 03 2003Jan 30 2004We construct projective moduli spaces for torsion-free sheaves on noncommutative projective planes. These moduli spaces vary smoothly in the parameters describing the noncommutative plane and have good properties analogous to those of moduli spaces of ... More Clustering of Far-Infrared Galaxies in the AKARI All-Sky SurveyOct 09 2012We present the first measurement of the angular two-point correlation function for AKARI 90-$\mu$m point sources, detected outside of the Milky Way plane and other regions characterized by high Galactic extinction, and categorized as extragalactic sources ... More Score sets in oriented bipartite graphsSep 05 2006The set A of distinct scores of the vertices of an oriented bipartite graph D(U, V) is called its score set. We consider the following question: given a finite, nonempty set A of positive integers, is there an oriented bipartite graph D(U, V) such that ... More Magnetofluid Unification in the Yang-Mills LagrangianAug 30 2005Mar 19 2008The Yang-Mills magnetofluid unification is constructed using lagrangian approach by imposing certain gauge symmetry to the matter inside the fluid. The model provides a general description for relativistic fluid interacting with Abelian or non-Abelian ... More