Showing papers by "Simón Bolívar University published in 1978"

Analysis of the influence of substrate variables on coral reef fish communities

Abstract: A simple field technique to obtain a gross estimate of the surface area of a quadrat on a coral reef is described. This measure, termed the substrate rugosity index, was determined, in conjunction with two other substrate variables (vertical relief and coral species richness), in a series of 4 quadrats (10 to 40 m depth) along 4 transects. The mean substrate rugosity and vertical relief of a quadrat were highly correlated. A correlation analysis was made of the substrate variables and several reef fish community parameters (species richness, number of fishes and diversity). Species richness was highly correlated with substrate rugosity. This relationship was tested in two experimental quadrats and the results were generally in accord with those predicted. Stratification of the fish communities by body size revealed that the correlation with substrate rugosity was scale-dependent. The fish community parameters were poorly correlated with percentage substrate cover by corals (ramose and glomerate) and by sand. A significant area effect was determined for two species of sand-dwelling goby.

Self-holograms of laser-induced surface depressions in heavy hydrocarbons

Abstract: Among applications of lasers in the petroleum industry are samples of heavy oils heated by a He–Ne laser beam. It is shown that laser power concentrations as low as 1 mW/mm2 induce noticeable changes in the form of the surface. The far-field diffraction pattern of the reflected wave can be considered as a self-hologram of the hole, with the paraxial focus of the bottom of the hole as a point reference source. Annular images corresponding to different zones of the hole are reconstructed by illuminating the hologram with a spherical wave. A geometrical model of the shape of the irradiated surface is proposed and compared with experimental data.

Studies of the mechanism of chlorination of indoles. detection of n-chloroindole and 3-chloro-3h-indole as intermediates

Abstract: Bei der Chlorierung von Indol (I) zu (IV) werden die Zwischenstufen (II) und (III) erhalten und nachgewiesen.

Initial-value problem and the Dirac-bracket relations in null gravidynamics

Abstract: Connections between the initial-value problem on characteristic hypersurfaces and null gravidynamics are analyzed in different gauges. A geometrical interpretation of the corner initial data is given in terms of the external curvature of one of the initial null hypersurfaces. The Dirac-Bracket relations between the dynamical variables of gravity are explicitly calculated in the Bondi gauge.

Statistical distribution of the phase in noncircular Gaussian speckle patterns

Abstract: We have extended the work of Goodman and of Fujii and Asakura to predict the phase distribution in noncircular Gaussian speckle patterns.

Dynamical structure of linearizedGL(4) gravities

Abstract: The physical content of the three more natural models ofGL(4) gravity is analyzed, for the case of weak fields. The first model we deal with is the linearized version of Yang's onetensor-field gravity. It is shown that this is a scalar-tensor theory, with its scalar part contained in the symmetric tensorh αν, instead of appearing explicitly, externally to the symmetric tensorh αν, as happens in Brans-Dicke type of scalar-tensor theories. The second and the third linearized models, which can both be derived from the fourth-order action postulated by Yang, turn out to be two-tensor decoupled systems. In both cases one of the tensors is the symmetric weak metric gravity tensor field. The second tensor appearing in these two models, representing theGL(4)-gauge field, is either a linearized symmetric affinity (in the second model) or a linearized but nonsymmetric affinity (for the third model). It is shown that in these last two cases the affinity contains a helicity-3 propagating field. The connection is also given between the fourth-order system which determines the dynamical structure (for the last two models) of the metric tensor and the third-order Yang model of gravity. Owing to the presence of helicity-3 fields we show that it is better to regard Yang's action as an action for a two-tensor system instead of trying to recover from it a pure gravity (one-tensor-field) action. Finally, it is shown what is the dynamical structure of the second and third linearized two-tensor models which can be derived from Yang's action.

Functional measures for the Feynman-quantized Einstein-Yang-Mills system

Abstract: A natural formulation of the Hamiltonian null dynamics of the Einstein-Yang-Mills system is given. In order to overcome difficulties which prevent the straightforward generalization of the previous results obtained by Fradkin and Vilkovisky and by Kaku for pure gravity a new null-gauge condition is introduced for the Einstein field. Using this gauge, both the action measure and the Lagrangian measure of the Einstein-Yang-Mills system are calculated. In the absence of the Yang-Mills boson vector field, both measures coincide with previous results of Fradkin and Vilkovisky.

Effects of overlap and next-nearest-neighbor interactions in tight-binding calculations

Abstract: Effects due to overlap between orbitals on neighboring atoms and to next-nearest-neighbor interactions, on the electronic structure, are investigated. As an illustration of their importance, analytic results are obtained for the density of states of a Bethe lattice and numerical calculations are carried out to obtain the band structure of a diamond lattice, starting from a realistic Hamiltonian. We show that overlap and next-nearest-neighbor interactions have important effects which are of opposite sign and tend to cancel each other in the valence band, but they are additive in the conduction band. The implications of our results for transition metals and surfaces are briefly discussed.

Absolute Stability of General Systems

Abstract: In a fundamental paper, J. Auslander and P. Seibert made an exhaustive study of prolongations in the sense of T. Ura (Cf. [12] and [13]) and their connection with the second method of Liapunov [2]. The context was that of a dynamical system on a locally compact metric space. Ever since, and with varying success, attempts to improve these results have been made in different directions. A noteworthy contribution is due to O. Hajek [4], who extended the characterization of absolute stability given in [2], to the case of closed sets in a paracompact locally compact space endowed with a dynamical system.

Asymptoticity in General Systems

Abstract: Modern trends toward extending Liapunov’s second method started with the work of D. Bushaw [6] on stability of abstract flows on uniform spaces, and of J. Auslander and P. Seibert [1–3] on stability of dynamical systems with respect to filters. Various theories following similar lines have been developed also by Nagy [10], Bushaw [5], Dana [7], Habets and Peiffer [9], Pelczar [11] and Rogers [12]. In [13–17], we have presented a theory of Liapunov stability under weakest assumptions: Stability is defined for a “system” consisting of a set endowed with a preorder (the “flow”) and two collections of subsets, or “quasifilters” (a kind of generalized neighborhood systems).