Showing papers by "Simón Bolívar University published in 1989"
TL;DR: In this article, the macroscopic equations that govern the processes of one and two-phase flow through heterogeneous porous media are derived by using the method of multiple scales, with the fundamental difference that the local permeabilities are replaced by effective parameters.
Abstract: The macroscopic equations that govern the processes of one- and two-phase flow through heterogeneous porous media are derived by using the method of multiple scales. The resulting equations are mathematically similar to the point equations, with the fundamental difference that the local permeabilities are replaced by effective parameters. The method allows the determination of these parameters from a knowledge of the geometrical structure of the medium and its heterogeneities. The technique is applied to determine the effective parameters for one- and two-phase flows through heterogeneous porous media made up of two homogeneous porous media.
76 citations
TL;DR: In this paper, the temperature dependence of the critical current in bulk samples of the high-T$ superconductors Y-Ba-Cu-O and Dy-Ba -cu-O was studied.
Abstract: We present a study of the temperature dependence of the critical current in bulk samples of the high-${T}_{c}$ superconductors Y-Ba-Cu-O and Dy-Ba-Cu-O. We have found that the critical current varies linearly with (${T}_{c}\ensuremath{-}T$). This result suggests a percolating network of Josephson-coupled superconducting grains. However, the critical current versus temperature curves are found to have a nonlinear tail close to the critical temperature. We have determined that the temperature at which the ${I}_{c}$ vs $T$ curves depart from the linear behavior in our samples agrees with what is expected according to theoretical models of granular superconductors.
44 citations
TL;DR: Brain morphology, with special attention to the three dimensional form of the corpora pedunculata, was studied in thirteen species of ants, representing four subfamilies of Formicidae, suggesting a divergent phylogenetic history.
Abstract: Brain morphology, with special attention to the three dimensional form of the corpora pedunculata, was studied in thirteen species of ants, representing four subfamilies of Formicidae. The results can
42 citations
TL;DR: In this paper, the effects of water deficit and rewatering on ribulose-1,5-bisphosphate carboxylase activity, chlorophyll and protein content were evaluated in plants of two cultivars of tomato.
Abstract: SummaryThe effects of water deficit and rewatering on ribulose-1,5-bis-phosphate carboxylase activity, chlorophyll and protein content were evaluated in plants of two cultivars of tomato. During the water deficit period, values of water potential, osmotic potential and relative water content decreased along with associated decreases in RuBPcase activity, protein content and chlorophyll content, being less marked for chlorophyll content. There was a significant correlation of RuBPcase activity and protein content with components of leaf water status from plants under water stress. The associated decrease of RuBPcase, chlorophyll and protein contents with decreased osmotic potential during the development of water deficit was evident. At the time the plants reached a water potential of –1.40 to –1.56 MPa (RI: first level of recovery after water stress), one group of plants was rewatered. The rest were kept under stress until the water potential reached values of –2.30 to –2.51 MPa (RII: second level of reco...
35 citations
TL;DR: Hamiltonian calculations are performed using a loop-labeled basis where the full set of identities for the SU(/ital N/) gauge models has been incorporated and the eigenvalue problem leads to a linear set of finite-difference equations easily amenable to numerical treatment.
Abstract: Hamiltonian calculations are performed using a loop-labeled basis where the full set of identities for the SU(/ital N/) gauge models has been incorporated. The loops are classified as clusterlike structures and the eigenvalue problem leads to a linear set of finite-difference equations easily amenable to numerical treatment. Encouraging results are reported for SU(2) at spatial dimension 2.
34 citations
TL;DR: The administration of the drug every eight hours yielded results which were significantly superior to those produced by administering a single dose every 24 hours, reducing both the number of larvae in the brain and their motility.
Abstract: Fifty-five mice were each infected with 800 embryonated eggs of Toxocara canis. Beginning on the second day of the infection, one group received a single 9 mg dose of albendazole every 24 hours for an eight-day period while a second group received 3 mg of albendazole every eight hours for the same period. On the tenth day of infection, mice in each treatment group and their corresponding controls were sacrificed, and the presence and motility of T. canis larvae in the brain were determined. With both therapeutical procedures the administration of albendazole reduced the number of larvae which reach the brain. However, for the same total dose, the administration of the drug every eight hours yielded results which were significantly superior to those produced by administering a single dose every 24 hours, reducing both the number of larvae in the brain and their motility.
32 citations
TL;DR: In this article, the deposition of silver on polycrystalline platinum was investigated over a wide range of potentials, covering both underpotential and over-potential regions.
30 citations
TL;DR: In this paper, a theory complete du champ de supercorde dans la jauge du cone de lumiere, including les termes de contact, is presented, and the caracteristiques non perturbative a partir de ces theories sont considerees.
27 citations
TL;DR: In this paper, a charge-sheet model for the equilibrium inversion layer charge of the thin-film SOI MOSFET is extended to account for nonequilibrium conditions, which occur under normal operation of the device.
Abstract: A previous charge-sheet model (A. Ortiz-Conde et al., Solid-State Electron., vol.31, p.1497-1500, Oct. 1988) for the equilibrium inversion layer charge of the thin-film SOI MOSFET is extended to account for nonequilibrium conditions, which occur under normal operation of the device. This is of vital importance to an analytical description of its current-voltage characteristics. The extended model is valid for all inversion conditions and accounts for the charge coupling between the front and back gates. The resulting analytical expression for the inversion-layer charge produces an error of less than 5% with respect to the numerical results obtained from the one-dimensional Poisson equation with the approximation of quasi-equilibrium. >
25 citations
17 Aug 1989
TL;DR: The analysis developed provides, for the first time, an asymptotic expression for the variance of the performance of partial match queries in kd-tree like structures.
Abstract: This paper deals with kd-tree like structures that implement the multidimensional dictionary. It presents the first efficient online reorganisation method that improves the performance of kd-trees. We propose a new variation of kd-trees, to be called kdt-trees, whereby the updating procedures guarantee that any subtree of size greater than 2t, t≥0, has at least t nodes on each side. Thus, kd-trees are a special case of kdt-trees with t=0. The analysis developed provides, for the first time, an asymptotic expression for the variance of the performance of partial match queries in kd-tree like structures. The relevance of kdt-trees is supported by the fact that they approach the performance of fully balanced kd-trees for small values of t.
21 citations
TL;DR: The properties of Prufer's enumeration of the set of completely labeled trees are used to obtain algorithms for the generation of completelylabel, as well as terminally labeled t-ary trees at random, i.e., with uniform distribution.
Abstract: Trees, and particularly binary trees, appear frequently in the classification literature. When studying the properties of the procedures that fit trees to sets of data, direct analysis can be too difficult, and Monte Carlo simulations may be necessary, requiring the implementation of algorithms for the generation of certain families of trees at random. In the present paper we use the properties of Prufer's enumeration of the set of completely labeled trees to obtain algorithms for the generation of completely labeled, as well as terminally labeled t-ary (and in particular binary) trees at random, i.e., with uniform distribution. Actually, these algorithms are general in that they can be used to generate random trees from any family that can be characterized in terms of the node degrees. The algorithms presented here are as fast as (in the case of terminally labeled trees) or faster than (in the case of completely labeled trees) any other existing procedure, and the memory requirements are minimal. Another advantage over existing algorithms is that there is no need to store pre-calculated tables.
TL;DR: In the first year, rain samples were taken daily; in the following years the samples were grouped on a monthly basis as discussed by the authors, and in addition, samples of dry deposition were collected during the dry seasons.
Abstract: Samples of bulk precipitation were collected in the Trachypogon savanna, Calabozo, Venezuela, during three consecutive years. In the first year, rain samples were taken daily; in the following years the samples were grouped on a monthly basis. In addition, samples of dry deposition were collected during the dry seasons. All samples were analyzed for the following water soluble cations and anions: P04-P, S04-S, N03-N, NH4-N, Ca+2, Mg+2, K+, Na+ and H+. The mean annual input rate of chemical constituents (Kg ha-1 year-1) was: PO4-P (0.42); SO4-S (2.62); NO3-N (0.21); NH4-N (2.03); Ca+2 (3.50); Mg+2 (11.31); K+ (3.60); Na+ (5.93) and H+ (0.03). The total mean input of particulate material to the savanna during the dry season was 2.06 Kg ha-1 year-1, with a soluble fraction of 30%. Possible sources of nutrients input were analyzed.
TL;DR: In this paper, the authors present information in the Third World: Information in the third world, 1989, Vol. 21, No. 2, pp. 177-191, International Library Review: Vol.
TL;DR: The interconnectivity metric integrates the structural as well as the textual aspects of a program in such a way that the organization of a programs can be seen graphically.
01 Jan 1989-International Journal of Radiation Applications and Instrumentation. Part D. Nuclear Tracks and Radiation Measurements
TL;DR: In this article, the potential of nuclear track detector CR-39 as a means to characterize very low current beams of accelerator protons, deuterons and alpha particles in the energy region of 6 MeV/amu is examined.
TL;DR: The osmotic fragility, the concentrations of Na, K and Ca, the osmolality and the total ATPase activity of bovine erythrocytes from uninfected and Anaplasma marginale-infected bovines were studied in an attempt to correlate these parameters with the decrease in the cellular ATP concentration reported during bovin anaplasmosis.
TL;DR: This work forms the U(1) and SU(2) lattice Hamiltonians in a loop-dependent magnetic basis and leads to a differential Schroedinger equation whose variables are angles associated with an independent set of closed contours in the lattice.
Abstract: We formulate the U(1) and SU(2) lattice Hamiltonians in a loop-dependent magnetic basis. The formulation is gauge invariant and leads to a differential Schroedinger equation whose variables are angles associated with an independent set of closed contours in the lattice. These contours are chosen by solving the Mandelstam identities obeyed by Wilson-loop functionals.
TL;DR: This paper showed hindered rotation of the monodentate TRIPHOS about the RuP bond about the triclinic space group P (No. 2) with R = 0.05 for 6635 reflections with I > 2 σ( I ) and 781 parameters.
TL;DR: For a stable map from a closed 3-manifold into the plane, its Stein Factorization gives useful information as discussed by the authors, and the main result presents the list of changes in the Stein factorization of the maps in a generic family of homotopies (the Pi-stable ones).
Abstract: For a stable map from a closed 3-manifold into the plane, its Stein Factorization gives useful information. Our main result presents the list of changes in the Stein Factorization of the maps in a generic family of homotopies (the Pi-stable ones).
01 May 1989
TL;DR: Los Horcones as discussed by the authors is a Waiden Two community which is guided by behavioral technology, and it has been recognized as an example of the potential of behavioral principles for social change in developing nations.
Abstract: The complex process of social change can be facilitated by applying the findings of behavior analysis. Los Horcones, located in Mexico, is a Waiden Two community which is guided by behavioral technology. The success of the community since it was founded in 1973 illustrates the promise of social applications of behavioral principles. Some misconceptions about behavior analysis and behaviorism as a philosophy have inhibited the application of behavioral principles to social change, especially in developing nations. A comprehensive strategy for social change can and should be derived from the science. The behavior analyst should be viewed as a shaper of a better society.
TL;DR: In this article, the thermal inactivation of trypsin and chymotrypsin inhibitors in black bean flours was studied as a function of the water activity of the product.
TL;DR: Pole figure analysis has been applied to different types of poly(vinyl chloride) (PVC) samples as discussed by the authors, showing that the presence of plasticizer at concentrations exceeding 20 pph decreases the orientation of the crystalline phase for a given draw ratio.
Abstract: Pole figure analysis has been applied to different types of poly(vinyl chloride) (PVC) samples. Drawn samples of formulations containing increasing amounts of plasticizer show that the presence of plasticizer at concentrations exceeding 20 pph decreases the orientation of the crystalline phase for a given draw ratio. Cast and pressed films of PVC show incipient orientation in the plane of the films. This orientation can be removed to a great extent by immersing the films in diethyl ether. The method is experimentally feasible and the resolution achieved is determined by the automation of the equipment.
TL;DR: In this article, a method for analysing 10−2−10−5M solutions of N-chlorobenzamides and other N−chloro derivatives is described.
Abstract: A method for analysing 10–2–10–5M solutions of N-chlorobenzamides and other N-chloro derivatives is described. The N-chloro derivative was reduced with sulphite to release chloride and the chloride concentration was determined with a chloride-selective electrode. The method was fast and had a relative error of 1% or less throughout the concentration range studied.
TL;DR: A consistent behavior of physical quantities near the critical point and a reasonable estimation of the transition point and the critical exponents are obtained by using a set of variables that improves the collective description proposed in previous related work.
Abstract: The Hamiltonian formulation of the /ital Z/(2) gauge theory at spatial dimension 2 is analyzed in gauge-invariant geometric terms by working in the loop-labeled basis of the /ital C/ representation. A consistent behavior of physical quantities near the critical point and a reasonable estimation of the transition point and the critical exponents are obtained by using a set of variables that improves the collective description proposed in previous related work.
TL;DR: In this paper, the authors prove versions of the Hahn-Banach and Steinhaus theorems for convex processes and show that each real convex process corresponds to a sublinear or superlinear functional.
Abstract: Our goal in this paper is to prove versions of the Hahn—Banach and Banach—Steinhaus theorems for convex processes. For the first theorem, we prove that each real convex process corresponds to a sublinear or superlinear functional and then we extend these. For the second theorem, we previously show that there is a seminorm naturally associated to the class of lower semi-continuous convex processes.
TL;DR: In this article, the authors measured the Stark width at half maximum at 0.058 nm at an electron density of 9 × 1015 cm-3, using the profile of the 447.1 nm transition of neutral He.
Abstract: Stark broadening of the transitions 21P→21S of neutral He at 2058.13 nm has been measured in a plasma produced with a linear discharge in a mixture of He with 0.5% H. During the time of observation, the electron density was ≈9 × 1015 cm-3, as determined by using the profile of the 447.1 nm transition of neutral He. At the times of interest, the electron temperature was ≈2.2 eV and was inferred from a line-to-continuum intensity-ratio measurement around the 501.6 nm He I line. The effects of reabsorption, together with the instrumental, Stark and Doppler broadening, are considered in a calculated profile that was constructed in order to match the experimental data. The final Stark half width at half maximum obtained is 0.058 nm at an electron density of 1016 cm-3. This measured Stark width agrees, within the experimental uncertainties, with theoretical estimates that are based on use of the isolated-line approximation.
TL;DR: In this article, an amplified isotope effect to the value of 19.10 indicated that there were two kinetically significant proton transfers and deprotonation of the σ-complex was the rate determining step.
Abstract: Observation of an amplified isotope effect to the value of 19.10 indicated that there were two kinetically significant proton transfers and deprotonation of the σ-complex was the rate determining step.
TL;DR: In this article, Mather proved that for smooth proper mappings, infinitesimal stability is equivalent to local infiniteimal stability, and extended this result to mappings of arbitrary codimensions, for it says that the (global) codimension of the mapping is the sum of all the multigerm co-imensions.
TL;DR: In this article, the transversal derivatives of the conservation equations for laminar boundary layer flow accounting for heat transfer are discretized by control volumes, and the resulting system of ordinary differential equations of first order is solved numerically by a Runge-Kutta integration process.