Quantization in presence of external soliton fields

Quantization of a Fermi field interacting with an external soliton potential is considered. Classes of interactions leading to unitarily equivalent representations of the canonical anticommutation relations are determined. Soliton-like potentials compared to trivial ones yield inequivalent representations.     

Self-diffusion in one-dimensional lattice gases in the presence of an external field

We study the motion of a tagged particle in a one-dimensional lattice gas with nearest-neighbor asymmetric jumps, withp (respectively,q),p > q, the probability to jump to the right (left). It was shown in Ref. 6 that the fluctuations in the position of the tagged particle behave normally; (X)²Dt. Here we compute explicitly the diffusion coefficient. We findD=(1-)(p-q). where is the gas density. The result confirms some recent conjectures based on theoretical arguments and computer experiments.Partially supported by NSF grant No. DMR81-14726.Partially supported by CNR.Partially supported by CNPq, grant No. 201682-83.     

Dependence of lattice hadron masses on external magnetic fields

We study the variation of the hadron masses in the presence of external magnetic fields of strength of the order of the masses themselves.We identify the main factors affecting the lattice simulation results:

• •- the boundary discontinuities for eB ⪡ 2π/L²a².
• •- the SU(6) choice of the hadron wave function.

We confirm qualitatively the earlier theoretical ansatz on the linear behaviour of the masses with the magnetic field and, as a by-product, we improve the lattice measurements of the nucleon magnetic moments.However our systematic and statistical errors preclude us from measuring the theoretically predicted field strength at which the proton becomes heavier than the neutron.     

Wave packet approach to lattice electrons in external galvanomagnetic fields

A closed expression for free wave packets in an homogeneous magnetic field is derived. A Gaussian function in the coordinates with time dependent coefficients is obtained, such that the mean values of position and momentum can be calculated exactly. The wave packets are found to move on a circle, their width is determined by the magnetic fieldB and independent of time. The weight function in an expansion of the wave packets in stationary solutions of the Schrödinger equation is approximately a Poisson distribution with the relative energy widthΔE/E=(B/E)^1/2.     

Thermodynamics of particle systems in the presence of external macroscopic fields

We study the grand partition function of a system of identical particles interacting via a superstable potential in the presence of an external field depending on a scale factor. We discuss the case when the scale factor increases to infinity (macroscopic limit for the external potential) and we prove rigorously a link between the so obtained pressure and the usual one (barometric formula).Research partially supported by the Consiglio Nazionale delle Ricerche.     

Thermodynamics of particle systems in the presence of external macroscopic fields

In a previous paper the statistics of a system of identical particles moving in an external field depending on a scale factor has been studied in the classical framework. In particular the case in which the scale factor increases to infinity (macroscopic limit) has been considered.In the present paper the quantum extension is discussed.Research supported in part by the Consiglio Nazionale delle Ricerche. (G.N.F.M.A.M.F.I.)     

Exact calculations of scattering and enhanced fields of electromagnetic waves on grating surfaces

We present scattered intensities and values of the electromagnetic field for p-polarized light on Ag grating surfaces using the theory of Toigo, Marvin, Celli and Hill. The theory is based on the application of the extinction theorem to Green's theorem. The program for calculations is set for any shape of the grating profile. Calculations are performed when the incident light is in resonance with the surface plasmon polariton. The shape of the scattered intensities are calculated for different grating amplitudes and it is shown that,for example, the reflectivity can present a minimum or a maximum depending on the amplitude and shape of the grating. It is shown that the enhanced field (the ratio between the modulus squared of the scattered field to the modulus squared of the incident field)(e) has a maximum when the reflectivity is a minimum as a function of the incident angle. The maximum of e is larger when the minimum in the reflectivity is smaller as a function of the grating amplitude. The value of e is calculated in a fine grid near to the grating and the values of the maxima are of the order of 250, then if the Raman cross-section is proportional to the fourth power of the field this could produce 10⁴ to 10⁵ in the cross-section and explain SERS. The width of the resonances as well as the plasmon dispersion relation will be also presented.     

On the energy of Yang-Mills fields in the presence of an external source

An expression is derived for the energy of a non-Abelian solution of the Yang-Mills equations in the presence of an external source, which permits an immediate comparison with the energy of the corresponding Coulomb-type solution, For any semisimple gauge group, a number of different field configurations are exhibited which always lead to solutions of lower energy than the Coulomb solution independent of the strength and symmetry properties of the source. The various implications of these results in view of the known instability of the Coulomb-type solution of a spherically symmetric source are discussed.     

Polarization of line radiation in the presence of external electric quadrupole and uniform magnetic fields

The polarization of emission lines formed in a medium immersed in external electric and magnetic fields is studied. The electric field is assumed to be quadrupolar in nature, while the magnetic field is uniform. We show that the quadrupole electric field produces line splitting which is characteristically different from the Zeeman effect. While the line components emitted along the quantization axis are circularly polarized in Zeeman effect, they are, in contrast, linearly polarized in the case of a pure quadrupole electric field. The emission perpendicular to the quantization axis produces three linearly polarized components in Zeeman effect, whereas only two linearly polarized components are observed in the case of quadrupole electric fields. Lack of azimuthal symmetry in the quadrupole electric field leads to polarized line components which appear quite differently for different azimuthal angles of the line of sight.     

Tracer diffusion in the presence of segregating obstacles

Tracer diffusion in an alloy in which the trajectories of one of the species is biased is examined as a model of mass transport with attendant segregation to extended defects (e.g., dynamic strain ageing, grain-boundary segregation). More specifically, we employ Monte Carlo simulation to describe the nonequilibrium diffusive behavior of the components of a two-dimensional lattice gas comprising A and B atoms wherein one of the species (B) interacts with randomly distributed line defects to create equilibrium atmospheres at late times. Various kinetic assumptions and defect densities are explored to highlight the role of B-atom mobility and defect interaction strength on the transport behavior of the A atoms. From the calculated instantaneous diffusivity, several diffusive regimes are then identified and related to evolving segregation profiles and, in particular, to the free area available for diffusion.     

Spatial distortions of the orientational structure of a ferronematic in the presence of external fields

Spatial distortions of the director field and magnetization of a ferronematic (suspension of magnetic nanoparticles in a nematic liquid crystal) that are induced by simultaneous action of electric and magnetic fields are studied with allowance for the flexoelectric polarization of the liquid-crystalline matrix. Soft coupling of liquid crystal and magnetic particles and layer boundaries is considered. The dependence of the phase lag of the transmitted light on the external magnetic field is analyzed.     

Water in the presence of inert Lennard-Jones obstacles

Water confined by the presence of a ‘sea’ of inert obstacles was examined. In the article, freely mobile two-dimensional Mercedes-Benz (MB) water put to a disordered, but fixed, matrix of Lennard-Jones disks was studied by the Monte Carlo computer simulations. For the MB water molecules in the matrix of Lennard-Jones disks, we explored the structures, hydrogen-bond-network formation and thermodynamics as a function of temperature and size and density of matrix particles. We found that the structure of model water is perturbed by the presence of the obstacles. Density of confined water, which was in equilibrium with the bulk water, was smaller than the density of the bulk water and the temperature dependence of the density of absorbed water did not show the density anomaly in the studied temperature range. The behaviour observed as a consequence of confinement is similar to that of increasing temperature, which can for a matrix lead to a process similar to capillary evaporation. At the same occupancy of space, smaller matrix molecules cause higher destruction effect on the absorbed water molecules than the bigger ones. We have also tested the hypothesis that at low matrix densities the obstacles induce an increased ordering and ‘hydrogen bonding’ of the MB model molecules, relative to pure fluid, while at high densities the obstacles reduce MB water structuring, as they prevent the fluid to form good ‘hydrogen-bonding’ networks. However, for the size of matrix molecules similar to that of water, we did not observe this effect.     

Exact calculations of p-polarized electromagnetic fields incident on grating surfaces: Surface polariton resonances

Exact calculations of the interaction of p-polarized light from grating surfaces are presented by using the theory of Toigo, Marvin, Celli and Hill. New features for the scattered field are found for light resonating with surface plasmon polaritons; the reflectivity present maxima for large amplitude gratings. The electromagnetic field is calculated on a fine grid near the grating. We find enhancements of the order of 200 to 300 for the square of the field that could partly explain SERS.     

Exact ground state density-functional theory for impurity models coupled to external reservoirs and transport calculations

A method is presented employing the density matrix renormalization group to construct exact ground state (GS) exchange correlation functionals for models of correlated electrons coupled to leads. We apply it to show that conductance calculations with Kohn-Sham GS density-functional theory can yield quantitative results in the Coulomb blockade regime. Our study is relevant for "molecular electronics" since it strongly suggests that the well documented discrepancies between theoretical and experimental transport coefficients originate (mainly) from approximations in GS functionals.     

Exact solution to the classical equation of motion for a charged particle in external electric and magnetic fields

An exact solution to the equation of classical motion of a charged particle in external uniform time-dependent electric and magnetic fields is obtained in two forms by two methods. An exact solution of a more general initial-value problem is found as well.     

Exact calculations of N-d polarization

The recent N-d polarization calculations of Doleschall and of Aarons and Sloan are compared (a]er performing the former calculation at 10·85 MeV), and are found to agree well.