The Critical Properties of One—Dimensional Extended Hubbard Model

In the framework of nonperturbative quantum field theory,the critical phenomena of one-dimensional extended Hubbard model (EHM) at half-filling are discussed from weak to intermediate interactions.After the EHM being mapped into two decoupled sine-Gordon models,the ground state phase diagram of the system is derived in an explicit way.It is confirmed that the coexisting phases appear in different interaction regimes which cannot be found by conventional theoretical methods.The diagram shows that there are seven different phase regions in the ground state,which seems not to be the same as previous discussions,especially the boundary between the phase separation and condensed phase regions.The phase transition properties of the model between various phase regions are studied in detail.     

One—Dimensional Potentials in q Space

We study one-dimensional potentials in q space and the new features that arise.In particular,we show that the probability of tunnelling of a particle through a barrier or potential step is less than that of the same particle with the same energy in ordinary space which is somehow unexpected.We also show that the tunnelling time for a particle in q space is less than that of the same particle in ordinary space.     

Hall Conductivity in a Quasi—Two—Dimensional disordered Electron System

By making use of the diagrammatic techniques in perturbation theory,we have investigated the Hall effect in a quasi-two dimensional disordered electron system.In the weakly localized regime,the analytical expression for quantum correction to Hall conductivity has been obtained using the kubo formalism and quasiclassical approximation.The relevant dimensional crossover behavior from three dimensions to two dimensions with decreasing the interlayer hopping energy is discussed.The quantum interference effect is shown to have a vanishing correction to the Hall coefficient.     

Critical Behaviour of the One—Dimensional Ferromagnetic t—J Model

The one-dimensional super-symmetric ferromagnetic t-J model is studied via the thermal Bethe ansatz.Analytic expressions of the free energy for T→O are obtained.A new critical behaviour beyond the universal class of Luttinger Liquids is found in this system.     

Three—Dimensional Propagation of Magnetohydrodynamic Waves in the Solar Chromophere and Corona

We study the three-dimensional magnetohydrodynamic(MHD) wave propagation in the solar atmosphere consisting of the chromosphere and corona.Pressure enhancement and velocity shear are implemented simultaneously at the bootom of the chromophere.The global propagation of the incurred MHD waves,including fast-mode and slow-mode magnetoacoustic waves as well as Alfven wave,can be identified,Wave front positions obtained numerically with respect to specific waves fit well with those calculated with local MHD wave speeds.     

Spin—Dependent Scattering Effects and Dimensional Crossover in a Quasi—Two—Dimensional Disordered Electron System

Two kinds of spin-dependent scattering effects (magnetic-impurity and spin-orbit scatterings) are investigated theoretically in a quasi-tow-dimensional (quasi-2D) disordered electron system.By making use of the diagrammatic techniques in perturbation theory,we have calculated the dc conductivity and magnetoresistance due to weak-localization effects,the analytical expressions of them are obtained as functions of the interlayer hopping energy and the characteristic times:elastic,inelastic,magnetic and spin-orbit scattering times.The relevant dimensional crossover behavior from 3D to 2D with decreasing the interlayer coupling is discussed,and the condition for the crossover is shown to be dependent on the aforementioned scattering times.At low temperature there exists a spin-dependent-scattering-induced dimensional crossover in this system.     

Heat Flux Boundary Conditions for a Lattice Boltzmann Equation Model

A method simplifying the external force term for the Boltzmann equation is proposed,using the Chapman-Enskog asymptotic expansion technique.The relationship between the perturbation strength parameter and the Grashof number is presented.A heat flux boundary condition for the temperature field simulation is developed according to the transforming ralations between the cold and hot particles on the boundary wall.The effects of buoyant force and the heat flux boundary condition are implemented with the two-particle systems of D2Q9 and D3Q15,and the numerical results agree well with the experimental result of silicone oil.     

Persistent Currents and Edge States in a Quasi－One－Dimensional Mesoscopic Ring with a Screened Interaction

The effect of the edge state on the persistent current in quasi-1D mesoscopic rings with a screned interaction which exists only between nearest-neighboring particles is studied with the Hartree-Fock approximation.The theoretical value of the current magnitude is greatly enhanced by both the edge state and the coulomb interaction.and pinning the electrons into a lattice is good for the enhancement if screening happens.In high dimensional systems the screening effect can make the interacting range show anisotropy,and create a tendency of gathering for particles with a repulsive potential.     

Mean—Field Calculations for the Three—Dimensional Holstein Model

The electron-phonon Holstein model is studied in three spatial dimensions.It is argued that this model can be used to account for major features of the high-Tc BaPb1-xBixO3 and BaxK1-xBiO3 systems.Mean-field calculations are performed via a path integral representation of the model.Charge-density-wave order parameters and transition temperatures are obtained.     

A Solvable Model in Two—Dimensional Gravity Coupled to a Nonlinear Matter Field

The two-dimensional gravity model with a coupling constant k=4 and a vanishing cosmological constant coupled to a nonlinear matter field is investigated.We found that the classical equations of motion are exactly solvable and the static solutions of the induced metric and scalar curvature can be obtained analytically.These soulutions may be used to describe the naked singularity at the origin.     

Big Bounce Singularity of a Simple Five—Dimensional Cosmological Model

The big bounce singularity of a simple five-dimensional cosmological model is studied.Contrary to the standard big bang space-time singularity,this big bounce singularity is found to be an event horizon at which the scale factor and the mass density of the universe are finite,while the pressure undergoes a sudden transition from negative infinity to positive infinity.By using coordinate transformation it is also shown that before the bounce the universe contracts deflationary.According to the proper-time,the universe may have existed for an infinitely long time.     

Transport Properties in a One—Dimensional Chain with Randomly Side—Coupled Impurities

We investigate the transport properties of a one-dimensional(1D) chain with randomly side-coupled impurities,By using the transfer matrix technique,we present numerical results of the transmission coefficient as a function of the electron energy,It is found that an extended state will be shown in such a random 1D system if the impurities are side-coupled to the chain with not only the nearest-neighbour bonds but also the next-nearestneighbour bonds.We present an analytical expression for the energy of this extended state,which is determined by the strength of the nearest and next-nearest couplings between the impurities and the chain.The obtained results can be used to explain the transport properties of DNA chains and other quasi-1D organic structures.     

Geometrical Method for the Generalized Moore Equations of a One—Dimensional Cavity with Two Moving Mirrors

Extending the approach proposed by Cole and Schieve (1995 Phys.Rev.A 52 4405) for a one-dimensional cavity with one moving mirror,we develop a geometrical method to solve exactly the generalized Moore (GM) equations for a one-dimensional cavity with two moving mirrors.As examples of applying our method,the GM equations are solved in detail when the two mirrors oscillate resonantly,and the dependences of the solutions on the frequency and dephasing of the mirror motions are investigated.     

A Higher Dimensional Cosmological Model in a Scale-Covariant Theory of Gravitation

Kaluza-Klein space-time is considered in the presence of a perfect fluid distribution in the scale-covariant theory of gravitation by Canuto et al. (Phys. Rev. Lett. 39:429, 1977). With the help of special law of variation for Hubble’s parameter proposed by Bermann (Nuovo Cimento 74B:182, 1983), a cosmological model in five dimensions with a negative constant deceleration parameter is presented in this theory. Some physical and kinematical properties of the model are also discussed.     

Construction of a Quadratic Model for Predicted and Measured Global Solar Radiation in Chile

Global solar radiation data for sites in Chile are analysed and presented in a form suitable for their use in engineering. A new model for monthly average data is developed to predict monthly average global radiation with acceptable accuracy by using actinographic data due to scarcing of pyranometer data. Use of the new quadratic model is proposed because of its relatively wider spectrum of values for Angstrom coefficients ao, al, and a2.     

Classical Poisson Structure for a Hierarchy of One–Dimensional Particle Systems Separable in Parabolic Coordinates

Abstract

We consider a hierarchy of many-particle systems on the line with polynomial potentials separable in parabolic coordinates. The first non-trivial member of this hierarchy is a generalization of an integrable case of the Hénon-Heiles system. We give a Lax representation in terms of 2 × 2 matrices for the whole hierarchy and construct the associated linear r-matrix algebra with the r-matrix dependent on the dynamical variables. A Yang-Baxter equation of dynamical type is proposed. Classical integration in a particular case is carried out and quantization of the system is discussed with the help of separation variables.     

A Pseudospectral Time—Domain Algorithm for Calculating the Band Structure of a Two—Dimensional Photonic Crystal

A pseudospectral time-domain (PSTD) method is developed for calculating the band structure of a two-dimensional photonic crystal.Maxwell‘s equations are rewritten in terms of period fields by using the Bloch theorem.Instead of spatial finite differences,the fast Fourier transform is used to calculate the spatial derivatives.To reach a similar accuracy,fewer sample points are required in the present PSTD method as compared to the conventional finite-difference time-domain methods.Our numerical simulation shows that the present PSTD method is an efficient and accurate method for calculating the band structure of a photonic crystal.     

Dynamic Localization of a One—Dimensional Quantum Dot Array in an ac Electric Field

We investigate the dynamics of two interaction electrons confined to one-dimensional quantum dot array in an ac electric field.We find that initially localized electrons will remain localized in the absence of coulomb interaction if the ratio of the ac field magnitude to the frequency is a root of the ordinary zero-order Bessel function.In contrast to the case without Coulomb interaction,no matter what the value is,the electrons are delocalized and the delocalization effect depends on the ratio U/ω and eaE/ω,where U is the strength of Coulomb interaction,a is the lattice constant,and E and ω are the ac field amplitude and frequency,respectively.     

On the Violation of Ohm’s Law for Bounded Interactions: a One Dimensional System

We consider an infinite Hamiltonian system in one space dimension, given by a charged particle subjected to a constant electric field and interacting with an infinitely extended system of particles. We discuss conditions on the particle/medium interaction which are necessary for the charged particle to reach a finite limiting velocity. We assume that the background system is initially in an equilibrium Gibbs state and we prove that for bounded interactions the average velocity of the charged particle increases linearly in time. This statement holds for any positive intensity of the electric field, thus contradicting Ohms law.Work partially supported by the GNFM-INDAM and the Italian Ministry of the University.