The Site-Diluted Ising Model in Four Dimension

In the literature, there are five distinct, fragmented sets of analytic predictions for the scaling behaviour at the phase transition in the random-site Ising model in four dimensions. Here, the scaling relations for logarithmic corrections are used to complete the scaling pictures for each set. A numerical approach is then used to confirm the leading scaling picture coming from these predictions and to discriminate between them at the level of logarithmic corrections.Comment: 15 pages, 5 ps figures. Accepted for publication in Phys. Rev.

Extended WKB method, resonances and supersymmetric radial barriers

Semiclassical approximations are implemented in the calculation of position and width of low energy resonances for radial barriers. The numerical integrations are delimited by t/T<<8, with t the period of a classical particle in the barrier trap and T the resonance lifetime. These energies are used in the construction of `haired' short range potentials as the supersymmetric partners of a given radial barrier. The new potentials could be useful in the study of the transient phenomena which give rise to the Moshinsky's diffraction in time.Comment: 12 pages, 4 figures, 3 table

Geometric Phases and Mielnik's Evolution Loops

The cyclic evolutions and associated geometric phases induced by time-independent Hamiltonians are studied for the case when the evolution operator becomes the identity (those processes are called {\it evolution loops}). We make a detailed treatment of systems having equally-spaced energy levels. Special emphasis is made on the potentials which have the same spectrum as the harmonic oscillator potential (the generalized oscillator potentials) and on their recently found coherent states.Comment: 11 pages, harvmac, 2 figures available upon request; CINVESTAV-FIS GFMR 11/9

Quantization of massive scalar fields over static black string backgrounds

The renormalized mean value of the corresponding components of the Energy-Momentum tensor for massive scalar fields coupled to an arbitrary gravitational field configuration having cylindrical symmetry are analytically evaluated using the Schwinger-DeWitt approximation, up to second order in the inverse mass value. The general results are employed to explicitly derive compact analytical expressions for the Energy-Momentum tensor in the particular background of the Black-String spacetime. In the case of the Black String considered in this work, we proof that a violation of the weak energy condition occur at the horizon of the space-time for values of the coupling constant, that include as particular cases the most interesting of minimal and conformal coupling.Comment: 4 page

Non-Hermitian SUSY Hydrogen-like Hamiltonians with real spectra

It is shown that the radial part of the Hydrogen Hamiltonian factorizes as the product of two not mutually adjoint first order differential operators plus a complex constant epsilon. The 1-susy approach is used to construct non-hermitian Hamiltonians with hydrogen spectra. Other non-hermitian Hamiltonians are shown to admit an extra `complex energy' at epsilon. New self-adjoint hydrogen-like Hamiltonians are also derived by using a 2-susy transformation with complex conjugate pairs epsilon, (c.c) epsilon.Comment: LaTeX2e file, 13 pages, 6 EPS figures. New references added. The present is a reorganized and simplified versio

Exactly Solvable Hydrogen-like Potentials and Factorization Method

A set of factorization energies is introduced, giving rise to a generalization of the Schr\"{o}dinger (or Infeld and Hull) factorization for the radial hydrogen-like Hamiltonian. An algebraic intertwining technique involving such factorization energies leads to derive $n$-parametric families of potentials in general almost-isospectral to the hydrogen-like radial Hamiltonians. The construction of SUSY partner Hamiltonians with ground state energies greater than the corresponding ground state energy of the initial Hamiltonian is also explicitly performed.Comment: LaTex file, 21 pages, 2 PostScript figures and some references added. To be published in J. Phys. A: Math. Gen. (1998

Quantum mechanical spectral engineering by scaling intertwining

Using the concept of spectral engineering we explore the possibilities of building potentials with prescribed spectra offered by a modified intertwining technique involving operators which are the product of a standard first-order intertwiner and a unitary scaling. In the same context we study the iterations of such transformations finding that the scaling intertwining provides a different and richer mechanism in designing quantum spectra with respect to that given by the standard intertwiningComment: 8 twocolumn pages, 5 figure

Spin splitting in a polarized quasi-two-dimensional exciton gas

We have observed a large spin splitting between "spin" $+1$ and $-1$ heavy-hole excitons, having unbalanced populations, in undoped GaAs/AlAs quantum wells in the absence of any external magnetic field. Time-resolved photoluminescence spectroscopy, under excitation with circularly polarized light, reveals that, for high excitonic density and short times after the pulsed excitation, the emission from majority excitons lies above that of minority ones. The amount of the splitting, which can be as large as 50% of the binding energy, increases with excitonic density and presents a time evolution closely connected with the degree of polarization of the luminescence. Our results are interpreted on the light of a recently developed model, which shows that, while intra-excitonic exchange interaction is responsible for the spin relaxation processes, exciton-exciton interaction produces a breaking of the spin degeneracy in two-dimensional semiconductors.Comment: Revtex, four pages; four figures, postscript file Accepted for publication in Physical Review B (Rapid Commun.

Correlation between site preference of ternary Mn addition in LaAg and superconductivity

The results of an extensive investigation of structure, surface morphology, composition and the superconducting-normal phase diagram of a new unconventional superconductor LaAg1-cMnc with nominal composition c = 0.0, 0.025, 0.05, 0.1, 0.2 and 0.3, reveal the following. The alloys with c = 0, 0.025 and 0.05 are essentially single phase alloys with the actual Mn concentration, x, same as the nominal one, i.e., c = x, whereas in the alloys with c = 0.1, 0.2 and 0.3, the actual Mn concentration of the majority phase (crystalline grains) is x = 0.050(1), 0.080(1) and 0.100(1), respectively. The ternary Mn addition does not alter the CsCl structure of the parent compound LaAg. Neither a structural phase transition occurs nor a long-range antiferromagnetic order exists at any temperature within the range 1.8K < = T < = 50K in any of the Mn containing alloys. Mn has exclusive La (Ag) site preference in the alloy (alloys) with x = c = 0.025 (x < = 0.05 or c < = 0.1) whereas in the alloy with x = c = 0.05, Mn has essentially no site preference in that all the Mn atoms either occupy the La sites or the Ag sites. In the alloys (alloy) with x < = 0.05 (x = c = 0.025), substitution of Ag (La) by Mn at the Ag (La) sub-lattice sites in LaAg host gives rise to unconventional superconductivity (destroys the conventional phonon-mediated superconductivity prevalent in the parent LaAg compound).Comment: The manuscript has 25 pages that include the text, 2 Tables and 12 Figures. The manuscript contains unpublished results which are of paramount interest to the Condensed Matter Physics Community at large and particularly to those engaged in the pursuit of research in Unconventional Superconductivit

Growth, blood metabolites and hormones in calves fed diets with different amounts of energy and protein during the pre- or post-weaning periods

We investigated the effects of diets differing in energy and protein concentrations given during pre- and post-weaning on hormone and metabolite levels in association to parameters of growth. Sixteen Aberdeen Angus calves four-day-old were allocated in individual pens during 105 days in a randomized complete design. Animals consumed ad libitum various diets differing in proportion of energy and protein (A: 80% of concentrate, 20% alfalfa hay; B: 60% concentrate, 40% of alfalfa hay; C: 40% concentrate, 60% alfalfa hay, and D: 20% concentrate, 80% alfalfa hay). Also, calves consumed milk substitute up to 60-day-old day. Serum growth hormone and cortisol levels were not altered with diet changes (P > 0.05) neither during the pre- nor the post-weaning periods. Plasma insulin concentration average daily intake, glucose and thyroid hormone levels, and concentrations of ammonia nitrogen and propionic acid were greater (P < 0.01) for diets having higher than lower energy and protein levels during the post-weaning but not during the pre-weaning period. These results suggest inclusion of higher amounts of concentrate in the diet of weaned calves.Fil: Fernández, H. T.. Universidad Nacional del Sur. Departamento de Agronomía; ArgentinaFil: Busso, Carlos Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiarida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiarida; ArgentinaFil: Laborde, Hugo Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiarida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiarida; ArgentinaFil: Torrea, M. B.. Universidad Nacional del Sur. Departamento de Agronomía; ArgentinaFil: Fernández, L. M.. Universidad Nacional del Sur. Departamento de Biología, Bioquímica y Farmacia; ArgentinaFil: López, G. H.. Universidad Nacional del Sur. Departamento de Biología, Bioquímica y Farmacia; ArgentinaFil: Delucchi, F.. Universidad Nacional del Sur. Departamento de Biología, Bioquímica y Farmacia; ArgentinaFil: García, B. N.. Universidad Nacional del Sur. Departamento de Biología, Bioquímica y Farmacia; Argentin