Search results for "Matrix"
showing 10 items of 3205 documents
Hole-doped Hubbard ladders
2005
The formation of stripes in six-leg Hubbard ladders with cylindrical boundary conditions is investigated for two different hole dopings, where the amplitude of the hole density modulation is determined in the limits of vanishing DMRG truncation errors and infinitely long ladders. The results give strong evidence that stripes exist in the ground state of these systems for strong but not for weak Hubbard couplings. The doping dependence of these findings is analysed.
Spectral Function of the One-Dimensional Hubbard Model away from Half Filling
2004
We calculate the photoemission spectral function of the one-dimensional Hubbard model away from half filling using the dynamical density matrix renormalization group method. An approach for calculating momentum-dependent quantities in finite open chains is presented. Comparison with exact Bethe Ansatz results demonstrates the unprecedented accuracy of our method. Our results show that the photoemission spectrum of the quasi-one-dimensional conductor TTF-TCNQ provides evidence for spin-charge separation on the scale of the conduction band width.
The multiple slope discontinuity beam element for nonlinear analysis of RC framed structures
2018
The seismic nonlinear response of reinforced concrete structures permits to identify critical zones of an existing structure and to better plan its rehabilitation process. It is obtained by performing finite element analysis using numerical models classifiable into two categories: lumped plasticity models and distributed plasticity models. The present work is devoted to the implementation, in a finite element environment, of an elastoplastic Euler–Bernoulli beam element showing possible slope discontinuities at any position along the beam span, in the framework of a modified lumped plasticity. The differential equation of an Euler–Bernoulli beam element under static loads in presence of mul…
A Consistent Boundary/Interior Element Method for Evolutive Elastic Plastic Structural Analysis
1993
A symmetric/sign-definite formulation of the BEM to address the evolutive elastic plastic analysis of structures is presented. A wide class of material models with internal variables and thermodynamic potential is considered. Different energy methods—namely the boundary min-max principle, the Helmholtz free energy and the maximum intrinsic dissipation theorem—axe employed in order to provide the discretization operations by boundary elements and cell elements with inherent variational consistency. The resulting space-discretized equations can be solved by a step-by-step procedure and a predictor/corrector iteration scheme, with corrections operated locally cell-by-cell, just as with the FEM…
Electronic hamiltonian of diatomic molecules in the basis of coupled momenta eigenfunctions
1992
A systematic procedure has been developed to construct an electronic energy matrix for diatomics in the basis of antisymmetrized products of atomic wave functions represented as linear combinations of coupled momenta eigenfunctions. The exchange matrix element is expanded in powers of electronic interchange between atoms. General expressions of many-electron angular coefficients have been obtained for all types of products of one- and two-electron and overlap integrals in energy matrix elements. © 1992 John Wiley & Sons, Inc.
The Few-Body Coulombian Problem
1999
Recent advances in the treatment of scattering of charged composite particles are reviewed. In a first part I report on developments of the theory. Specifically I describe the recent completion of the derivation of the co-ordinate space asymptotic behaviour of the wave function for three charged particles in the continuum. This knowledge is increasingly being made use of in attempts to ‘derive’ three-Coulomb particle wave functions to be used in all of configuration space which are solutions of the Schrodinger equation, though not everywhere but at least in one or preferably all of the asymptotic regions. Their practical application in approximate calculations of ionisation and breakup proc…
Exceptional points in a non-Hermitian extension of the Jaynes-Cummings Hamiltonian
2016
We consider a generalization of the non-Hermitian \({\mathcal PT}\) symmetric Jaynes-Cummings Hamiltonian, recently introduced for studying optical phenomena with time-dependent physical parameters, that includes environment-induced decay. In particular, we investigate the interaction of a two-level fermionic system (such as a two-level atom) with a single bosonic field mode in a cavity. The states of the two-level system are allowed to decay because of the interaction with the environment, and this is included phenomenologically in our non-Hermitian Hamiltonian by introducing complex energies for the fermion system. We focus our attention on the occurrence of exceptional points in the spec…
K --> pi pi matrix elements beyond the leading-order chiral expansion
2002
We propose an approach for calculating $K\to\pi\pi$ decays to the next-to-leading order in chiral expansion. A detailed numerical study of this approach is being performed.
A three body state with J=3 in the ρB*B̅N* interaction
2016
We study the ρB * BN * system solving the Faddeev equations in the fixed center approximation. The B * BN * system will be considered forming a cluster, and using the two-body ρB * unitarized scattering amplitudes in the local Hidden Gauge approach we find a new I ( J PC ) = 1(3 −− ) state. The mass of the new state corresponds to a two particle invariant mass of the ρB * system close to the resonant energy of the B * 2 (5747), indicating that the role of this J = 2 resonance is important in the dynamical generation of the new state.
High order harmonic generation: The role of the acceleration matrix elements and of the bound and continuum transitions
2001
The electromagnetic spectrum emitted by a one-dimensional atom driven by a strong laser field is obtained by use of the acceleration form and interpreted by means of few general properties of the matrix elements of the acceleration operator. We show that the emission occurs essentially in a region near the atomic core where the acceleration is significant and we investigate the role of the various emission channels arising from interference effects between transitions involving the bare atomic levels.