Showing papers by "National Autonomous University of Mexico published in 1979"

Massive deep-sea sulphide ore deposits discovered on the East Pacific Rise

Abstract: Massive ore-grade zinc, copper and iron sulphide deposits have been found at the axis of the East Pacific Rise. Although their presence on the deep ocean-floor had been predicted there was no supporting observational evidence. The East Pacific Rise deposits represent a modern analogue of Cyprus-type sulphide ores associated with ophiolitic rocks on land. They contain at least 29% zinc metal and 6% metallic copper. Their discovery will provide a new focus for deep-sea exploration, leading to new assessments of the concentration of metals in the upper layers of the oceanic crust.

The hydrogen atom within spherical boxes with penetrable walls

Abstract: We study a model for the hydrogen atom confined within spherical boxes with penetrable walls. The potential consists of the Coulomb potential inside the box and a constant potential outside the box; the Schrodinger equation admits analytical solutions in both regions. The energy eigenvalues and eigenfunctions for the lowest states of the system are determined numerically for boxes of different sizes and penetrabilities. In addition, we also evaluate the hyperfine splitting, nuclear magnetic shielding, polarizability and pressure of the system and investigate the effect of the confinement on these atomic properties.

Unified shell-model description of nuclear deformation

Abstract: A unified shell-model description of nuclear deformation valid throughout the periodic table is presented. Microscopic calculations for the Zr and Mo isotopes are carried out in the frameworks of the shell model and the Hartree-Fock-Bogoliubov method, respectively, to study the shape transition in these nuclei. It is shown that deformation is produced by the isoscalar component of the neutron-proton ($n\ensuremath{-}p$) interaction in this region, as in the lighter ($2s$,$1d$)-shell region. Deformation sets in when the $T=0$ $n\ensuremath{-}p$ interaction dominates over the sphericity-favoring pairing interaction between $T=1$ pairs of nucleons. When shell effects are important, as for the light and medium-weight regions mentioned above, the simultaneous occupation of neutrons and protons of spin-orbit "partner" orbitals plays a crucial role in determining the onset of deformation. However, their effect is probably less important in the rare-earth and transuranic regions due to the rapid accumulation of single-particle orbitals.NUCLEAR STRUCTURE Microscopic description of nuclear deformation; shell-model calculations of $^{96}\mathrm{Zr}$, $^{98}\mathrm{Zr}$, and $^{100}\mathrm{Zr}$; HFB calculations of $^{98}\mathrm{Mo}$-$^{110}\mathrm{Mo}$; discussion of light and heavy deformed nuclei; relation to interacting boson approximation.

The fundamental solution in dynamic poroelasticity

Abstract: Summary. In this paper we study Biot’s full, time-dependent equations of dynamic poroelasticity with a view to understanding the effect of pore fluid on seismic wave propagation. Typical values of the constants appearing in the equations which are relevant to the rock surrounding earthquake sources are estimated from values appearing in the recent literature. We investigate the disturbance due to an instantaneous point body force acting in a uniform whole space. In fact we calculate the tensor fundamental solution since this has spherical symmetry, which is strongly exploited in our method of solution. The introduction of four scalar potentials enables us to reduce the problem to two decoupled second-order systems, each consisting of two coupled wave equations with friction in one space and one time dimension. By a further transformation these systems are expressed as symmetric hyperbolic systems of the first order, which are then solved by Laplace transforms. Because the dispersion equations are of higher than second degree only the large time saddle-point contributions are calculated. From these several phenomena emerge. (a) A P wave propagating with the P-wave speed appropriate to the ‘solid’ obtained by constraining the fluid to move with the solid matrix. However, instead of a 6 pulse shape familiar in elastodynamics this P wave has the shape of a Gaussian which appears to diffuse in a frame of reference moving with the P-wave speed. (b) An S wave with similar shape to P. (c) A long-term diffusion which is what one obtains from the equations reduced by setting the inertial terms to zero as in consolidation theory. We also investigate in an appendix a special case of dynamical compatibility in which the P wave remains sharp (i.e. a 6 pulse) and one of our two systems can be solved explicitly. The pulse diffusion amounts to a dissipation of the high frequency content qf seismic waves at a rate proportional to the square of the frequency.

Ground motion on alluvial valleys under incident plane SH waves

Abstract: A method is presented to compute the scattering and diffraction of harmonic SH waves by an arbitrarily shaped alluvial valley. The problem is formulated in terms of a system of Fredholm integral equations of the first kind with the integration paths outside the boundary. A discretization scheme using line source solutions is employed and the boundary conditions are satisfied in the least-squares sense. Numerical results for amplification spectra for different geometries are presented. Agreement with known analytical solutions is excellent.

Perturbative approach to the calculation of the electric field near a metal surface

Abstract: A systematic perturbational procedure is developed for the calculation of the electric field near a metal surface when electromagnetic radiation is incident upon it. The method is worked out in detail for a particularly simple choice of the "unperturbed model" for the metal. Asymptotic forms of the expression for the electric-field components are used to obtain corrections to the Fresnel formulas for the reflectivity for both $s$- and $p$-polarized light. Surface corrections to ellipsometric parameters are also derived. Connection is made between these results and those of previous theories. The procedure is applied to a metal surface with chemisorbed impurities, and is shown to lead to a new and useful expression for the differential reflectance in the case of $p$-polarized light. The result is discussed in terms of its utility in studying experimental data on surface-reflectance spectroscopy.

Source mechanism and aftershock study of the Colima, Mexico earthquake of January 30, 1973

Abstract: The Colima earthquake (magnitude 7.5) occurred just inland from the Middle America Trench, 110 km south of the Volcan de Colima and 160 km southeast of Manzanillo, Colima, Mexico. Damage at several cities and towns was severe, 30 people were killed, and hundreds were injured. Four days after the earthquake, a six-station portable seismograph array was set up in the epicentral area as part of a cooperative program between UCSD, the University of Mexico, and the Mexican Federal Power Commission. From about 330 aftershocks recorded in the following 2 1 2 weeks, accurate locations were obtained for 50. One large aftershock had a magnitude of 6.2, the others range in local magnitude from 1.5 to 4.5. The locations outline a region approximately 90 km long and 60 km wide, in nearly the same location as the aftershock zone inferred by Kelleher et al. (1973) for the 1941 earthquake. The focal depth of the aftershocks (ranging from 2 to 30 km) and the fault-plane solutions for the main event indicated a shallow dipping thrust plane (about 30°). The seismic moment estimated from mantle rayleigh waves is 3 × 10 27 dyne-cm. The pattern of aftershocks was used to estimate the source dimensions. From the moment and source dimensions the average slip was estimated to be about 1.4 m, corresponding to a stress drop of about 8 bars. The occurrence of this earthquake is discussed in terms of the general seismicity of the Middle America Trench, the convergence rate predicted by plate tectonics, and the use of seismic gap theory for earthquake prediction. The fact that this earthquake may have been in the zone of the 1941 earthquake rather than in the adjacent seismic gap, suggests that caution must be taken in using seismic gap theory to predict earthquakes in the region. It further suggests that in the adjacent seismic gap a large earthquake may be eminent, and thus the gap may be an important area for deploying seismic instruments.

Order-disorder phenomena in oxides with rock salt structures: the system Li2TiO3-Mg0

Abstract: Li2TiO3, which belongs to the family of rock salt superstructure phases, undergoes an order-disorder phase transition at 1213° C. It forms solid solutions with MgO and the temperature of the order-disorder change falls increasingly rapidly with increasing MgO content; the ordered solid solutions could not be prepared beyond ∼40 mol % MgO. Up to ∼20% MgO, the transition may be observed as a DTA heat effect and is probably first order. At ≳25% MgO the transition is second order; no DTA heat effect occurs and, by X-ray diffraction, the order-disorder change occurs, reversibly and continuously, over a range of several hundred ° C. For 25% MgO, the disorder, δ, is given by δ=exp[−m(Tc−T)] whereTc is the critical temperature, above which only short range order exists, andm is a constant. The order, δ, is determined from the relative intensity of the (0 0 2) superstructure reflection. The mechanisms of the order-disorder processes are discussed and a method of studying the kinetics is indicated. It is likely that many other oxide phases which have rock salt superstructures will exhibit order-disorder phenomena at high temperatures.

A class of infinite-duration impulse response digital filters for sampling rate reduction

Abstract: A new class of recursive digital filters for sampling rate reduction is discussed. These filters present equiripple behavior in the magnitude response, with all their zeros located on the unit circle. These new filters bring together, to some extent, the advantages of finite-duration impulse response (FIR) and elliptic designs by having only powers of zDin the denominator (D is the decimation ratio). Only every D th output has to be computed, as in the FIR case; while some feedback terms, as in the elliptic case, are also present. The design and some optimality properties of these filters are discussed. Some characteristics of filters with only powers of zDin the denominator, such as pole-zero location, group delay, and coefficient sensitivity are discussed and compared with elliptic designs. It is shown how these new filters require significantly fewer multiplications per second than equivalent FIR and elliptic designs.

Propagating torsion and gravitation

Abstract: A theory of gravity is developed which allows for propagating torsion. The theory predicts the existence of torsion in a vacuum and torsion waves emitted by sources with varying spin. The motion of spinning test particles in combined metric and torsion background fields is discussed. A plausible procedure for quantizing the torsion and metric fields is presented.

Complex flow of viscoelastic fluids through oscillating pipes. Interesting effects and applications

Abstract: In the present communication, the flow of liquids through a straight pipe which is oscillating longitudinally about a mean position is examined. The basic flow is generated by a constant pressure gradient and the effect of the superimposed oscillations upon the flow is analyzed with particular attention to the flow rate. In the viscous case as well as for an elastic fluid with constant viscosity, no variation in the flow rate is present. This is in agreement with the theoretical analysis. Nevertheless, for viscoelastic fluids, increases in the flow rate of up to twenty times are possible when compared to purely rectilinear flow. This effect is examined for various viscoelastic fluids and relations are found with that basic properties of such fluids. The complex flow situation is analyzed using flow visualization techniques. As a result, the flow appears to be dominated by a shear-thinning effect. A numerical solution using a power-law fluid predicts increases in flow rate which agree qualitatively with the experimental data but are quantitatively different. It is therefore concluded that a more general model must be used for agreement between experiments and theory. In the light of the experimental results, applications are being presently undertaken for the flow of polymer melts in situations of industrial interest.

Construction and Properties of Canonical Transforms

Abstract: In this chapter we present a class of integral transforms which we shall call canonical transforms. These constitute a parametrized continuum of transforms which include the Fourier, Laplace, Gauss-Weierstrass, and Bargmann transforms as particular cases. As these have arisen quite recently, we shall include brief historical sketches of the developments which led to their recognition and refer the interested reader to the research literature for a more rigorous treatment. Section 9.1 deals with real linear canonical transforms, while Section 9.2 enlarges the set to complex ones. The former appeared a couple of times before Moshinsky and Quesne (1974) called attention to their significance in connection with canonical transformations in quantum mechanics. A particular case of the latter was developed by Segal (1963) and Bargmann (1961) in order to formalize Fok’s boson calculus (1928). Section 9.3 shows that canonical transforms have a hyperdifferential operator realization in addition to the usual integral form. Several examples and exercises show the economy of concepts and computation introduced by this new technique.

Ethnopharmacology and Taxonomy of Mexican Psychodysleptic Plants

Abstract: (1979). Ethnopharmacology and Taxonomy of Mexican Psychodysleptic Plants. Journal of Psychedelic Drugs: Vol. 11, Innovative Approached to Drug Abuse Treatment, pp. 71-101.

Accurate calculations for the even-parity core-excited 2 P states of neutral Li

Abstract: Nonrelativistic configuration-interaction calculations have been carried out with orbital basis specifically adapted for each one of the first seven even-parity $^{2}P$ bound states of neutral Li. The results show that the lowest four $^{2}P$ states have recently been observed by absorption spectroscopy from the $1{s}^{2}2p$ state. The calculated transition wavelengths (20.7452, 19.7613, 19.4728, and 19.4065\ifmmode\pm\else\textpm\fi{}0.0005 nm agree well with the experimental ones (20.744, 19.762, 19.474, and 19.405\ifmmode\pm\else\textpm\fi{}0.002 nm). Electric dipole transition probabilities to the $1{s}^{2}2p$, $3p$ and $4p$ states have also been calculated. The configurations for the two lowest $^{2}P(1)$ and $^{2}P(2)$ states are $1s2{p}^{2}$ and $(1s2p)^{3}P3p$, respectively. The $(1s2p)^{3}P\mathrm{np}$ and $(1s2p)^{1}P{n}^{\ensuremath{'}}p$ series almost coincide at $n=4$, ${n}^{\ensuremath{'}}=3$, and as a consequence, the $^{2}P(3)$ and $^{2}P(4)$ levels are approximately described by $(1s2p)^{3}P4p\ifmmode\pm\else\textpm\fi{}(1s2p)^{1}P3p$. This is the simplest known example of two-level series which mutually perturb each other.

Effects of solvents on schedule-controlled behavior.

Abstract: Operant conditioning techniques have been shown to be sensitive to the acute effects of industrial solvents. In the first experiment, five rats trained in a multiple schedule with a fixed-ratio (FR) 10 component and a differential reinforcement of low rates (DRL) 20-sec component, with a time out 60-sec between reinforcement periods, were exposed to 0.25, 0.50, 1 and 2 ml of toluene in the experimental chamber. The effects were dose-dependent, with an increase in rate in the DRL component and a decrease in FR responding. A second experiment assessing the effects of chronic exposure to thinner in the acquisition of a timing behavior in rats showed an impairment in DRL learning after 4, 8 or 16 weeks of exposure to the solvent: however, rats having a resting period did not differ from control animals. Whereas this finding suggests a reversible impairment in the acquisition of a complex behavior, further research is needed to achieve more definitive conclusions.

Electron affinity of helium (1s2s) /sup 3/S

Abstract: A configuration-interaction calculation with a carefully optimized orbital basis gives an upper bound E/sub u/ = -2.178 040 a.u. (He) for the nonrelativistic energy E/sub n/r of the (1s2s2p) /sup 4/P/sup 0/ metastable state of the He negative ion. Extensive studies of patterns of convergence for the energy show that E/sub n/r = -2.178 074(10), which together with Pekeris' accurate E/sub n/r He (1s2s) /sup 3/S yields a nonrelativistic electron affinity A/sub n/r = 77.4(3) meV. It is argued that the true electron affinity should not differ from A/sub n/r by more than +- 0.2 meV. Good agreement with the less-precise experimental values is obtained. The present results, by allowing a recalibration of the experiments, will permit a significant increase in the accuracy of future experimental determinations of electron affinities below 300 meV.

Deoxyribonucleic acid adenine and cytosine methylation in Salmonella typhimurium and Salmonella typhi.

Abstract: The methylations of adenine in the sequence -GATC- and of the second cytosine in the sequence - [Formula: see text] - were studied in Salmonella typhimurium and in Salmonella typhi. The study was carried out by using endonucleases which restrict the plasmid pBR322 by cleavage at the sequences -GATC- (DpnI and MboI) and - [Formula: see text] - (EcoRII). The restriction patterns obtained for this plasmid isolated from transformed S. typhimurium and S. typhi were compared with those of pBR322 isolated from Escherichia coli K-12. In E. coli K-12, adenines at the sequence -GATC- and the second cytosines at - [Formula: see text] - are met hylated by enzymes coded for by the genes dam and dem, respectively. From comparison of the restriction patterns obtained, it is concluded that S. typhimurium and S. typhi contain genes responsible for deoxyribonucleic acid methylation equivalent to E. coli K-12 genes dam and dcm.

Topographical interpretation of vacuum-deposited fine metallic particles

Abstract: Morphological features of vacuum–deposited gold particles are investigated. It is shown that the use of bright–field imaging techniques is inadequate for assessing these features but that unambiguous topographical information can be obtained through the use of a weak–beam dark-field technique. Coalesced gold particles deposited on KC1 substrates are shown to be facetted except when undergoing ooalesoence.