Spin and pseudospin symmetries of the Dirac equation with confining central potentials

We derive the node structure of the radial functions which are solutions of the Dirac equation with scalar $S$ and vector $V$ confining central potentials, in the conditions of exact spin or pseudospin symmetry, i.e., when one has $V=\pm S+C$, where $C$ is a constant. We show that the node structure for exact spin symmetry is the same as the one for central potentials which go to zero at infinity but for exact pseudospin symmetry the structure is reversed. We obtain the important result that it is possible to have positive energy bound solutions in exact pseudospin symmetry conditions for confining potentials of any shape, including naturally those used in hadron physics, from nuclear to quark models. Since this does not happen for potentials going to zero at large distances, used in nuclear relativistic mean-field potentials or in the atomic nucleus, this shows the decisive importance of the asymptotic behavior of the scalar and vector central potentials on the onset of pseudospin symmetry and on the node structure of the radial functions. Finally, we show that these results are still valid for negative energy bound solutions for anti-fermions.Comment: 7 pages, uses revtex macro

A techniques-based framework for domain-specific synthesis of simulation models

The formal specification community has produced many languages but few structured design methods. Those which exist tend to be abstract, providing little guidance in tackling problems in particular domains. One way of devising domain -specific design methods is by reconstructing an example in the domain using the target method; then generalising the design structures to cover a class of designs in the domain and finally building an environment in which these structures may more easily be re- applied to new problems. We demonstrate this approach using animal population dynamics models as the domain and Prolog techniques as the target method.We have identified domain -specific techniques which use a parameterisation method from techniques editing but which contain information specific to the population dynamics domain; we define a problem description language which uses concepts from population dynamics; an interface which allows these concepts to be supplied; and provide an automated system which bridges between population dynamics problem description and the domain -specific techniques needed for model generation.TeMS - Techniques -based Model Synthesiser, is the system constructed as the main instrument of our research. Because it is an embodiment of our views on the issues addressed, we submitted TeMS to user evaluation by ecological modelling experts, which produced material for a broad discussion of the system itself, its approach to modelling and its potential uses on the ecological modelling scenario

New solutions of the D-dimensional Klein-Gordon equation via mapping onto the nonrelativistic one-dimensional Morse potential

New exact analytical bound-state solutions of the D-dimensional Klein-Gordon equation for a large set of couplings and potential functions are obtained via mapping onto the nonrelativistic bound-state solutions of the one-dimensional generalized Morse potential. The eigenfunctions are expressed in terms of generalized Laguerre polynomials, and the eigenenergies are expressed in terms of solutions of irrational equations at the worst. Several analytical results found in the literature, including the so-called Klein-Gordon oscillator, are obtained as particular cases of this unified approac

Reconstruction of the gradient refractive index of the crystalline lens with optimization methods

Esta tesis estudia la óptica del sistema visual y en particular la estructura del cristalino, desarrollando métodos para estimar el gradiente de índice de refracción (GRIN) del mismo. A pesar de que hay una larga tradición en modelar las propiedades refractivas del ojo, todavía se discuten la óptica del cristalino y los valores específicos de índice de refracción. El conocimiento preciso del GRIN permitirá comprender mejor las propiedades ópticas del cristalino y la contribución del mismo a la calidad óptica del ojo. En esta tesis se propone el uso de algoritmos genéticos e imágenes de tomografía de coherencia óptica (OCT) para el estudio del GRIN en cristalinos ex vivo. Se reconstruye tridimensionalmente el gradiente de índice de un cristalino porcino, se estudia la variación con la edad del GRIN en humanos y la distorsión, y posible corrección, de la cara posterior del cristalino en las imágenes de OCT

Bounded solutions of neutral fermions with a screened Coulomb potential

The intrinsically relativistic problem of a fermion subject to a pseudoscalar screened Coulomb plus a uniform background potential in two-dimensional space-time is mapped into a Sturm-Liouville. This mapping gives rise to an effective Morse-like potential and exact bounded solutions are found. It is shown that the uniform background potential determinates the number of bound-state solutions. The behaviour of the eigenenergies as well as of the upper and lower components of the Dirac spinor corresponding to bounded solutions is discussed in detail and some unusual results are revealed. An apparent paradox concerning the uncertainty principle is solved by recurring to the concepts of effective mass and effective Compton wavelength.Comment: 15 pages, 7 figure

Forced expiratory volume in one second and bronchodilator response in chronic obstructive pulmonary disease: a needless ritual?

Universidade Federal de São Paulo (UNIFESP)UNIFESPSciEL

Confinement of spinless particles by Coulomb potentials in two-dimensional space-time

The problem of confinement of spinless particles in 1+1 dimensions is approached with a linear potential by considering a mixing of Lorentz vector and scalar couplings. Analytical bound-states solutions are obtained when the scalar coupling is of sufficient intensity compared to the vector coupling.Comment: 14 pages, 2 figure