Showing papers by "Simón Bolívar University published in 1985"
TL;DR: A general survey of the thermodynamic data available on solid binary metallic carbides is given in this article, where the free energies of formation of carbides as a function of the temperature are presented as Ellingham diagrams.
58 citations
TL;DR: In this article, the electrodeposition of heptyl viologen (HV) and benzyl bromides onto vitreous carbon, platinum, silver, mercury and optically transparent tin oxide electrodes has been investigated.
41 citations
TL;DR: The first three techniques can also be used quantitatively to measure the degree of hydrolysis of the polymers, without the need to know accurately the weight of the sample as discussed by the authors.
Abstract: Polyacrylamides can be readily characterized using techniques such as IR spectroscopy, 13C-NMR, elementary analysis, TGA, and x-ray diffraction. The first three techniques can also be used quantitatively to measure the degree of hydrolysis of the polymers, without the need to know accurately the weight of the sample. The presence of inorganic salts, such as Na2SO4, Na4(CO3)SO4, and Na2CO3, is readily detected via IR or wide-angle x-ray diffraction. No evidence of crystallinity is found in the samples studied.
26 citations
TL;DR: In this article, the effect of temperature on the formation and reduction of the first two layers of mercuric sulphide on mercury has been studied, and the existence of two adsorption states of HgS on Hg, with opposing dipole moments, is postulated.
21 citations
TL;DR: In this paper, the aldehydes RCHCHCHO (R = Me or Ph) with competitive oxidative additions of the vinylic CH groups were used to give compounds of the type [Os 3 H(CO) 10 (RCCHCHO)], or of the acyl groups to give acyl clusters.
20 citations
TL;DR: In this paper, the electrodeposition of lead sulphide on polycrystalline lead from aqueous sulphide solutions has been investigated, and the electrochemical reactions attending the film formation process are discussed on the basis of variations in the voltammetric peak potentials with sulphide concentration and pH.
19 citations
TL;DR: Chemical recruitment with a trail pheromone from the poison gland which gives information about the presence and location of food and its concentration regulates the amount of recruitment is used.
Abstract: La fourmi T.u. possede les systemes de communication suivants: recrutement chimique avec une pheromone de piste provenant de la glande a poison, utilisation pour la prise de decision pendant le recrutement d'un systeme du type appel «autocratique», existence d'une odeur du nid specifique de chaque colonie et production par les ouvrieres, au niveau du gastre, d'une secretion de defense induisant l'attaque de tout objet qu'elle impregne
18 citations
TL;DR: The authors proposed a "chemical mass recruitment system" for Solenopsis saevissima and Atta cephalotes which has the following characteristics:
Abstract: Few is known about decision-making inside a society of social organisms. Questions like: Do optimal decision-making systems exist?, and: Are there common solutions for decision-making in the animal kingdom?; are still unanswered. The social insects seem to be an appropriate model for this kind of study (DENEUBOURG, 1977), although no comprehensive work exists on the subject. Within the social insects the ants seem to be the most suitable for this purpose because: aall ants live in complex societies (WILsON, 1971); bmost ants use some kind of recruitment (AFFE, 1984); and cdecision-making is a fundamental ingredient of recruitment in ants (AFFE, 1980). Different food recruiting mechanisms are known for ants (WILSON, 1971; HOLLDOBLER, 1978; DUMPERT, 1978; JAFFE, 1984), but in most of them, only the behaviour of the recruiting ant has been described. For Solenopsis saevissima (WILSON, 1962) and for Atta cephalotes (JAFFE & HOWSE, 1979), inferences about how the behaviour of the individuals may account for collective phenomena have been made. For both species, the authors proposed a "chemical mass recruitment system" which has the following characteristics:
17 citations
TL;DR: Comparaciones entre las diferentes etapas correspondientes al desarrollo larval de P. tonsoriu.s, P. arncatus del Atlantico y P. tridentatus de the costa del Pacifico arelly, discutiendose aquellos caracteres que pueden ser utilizados para the identificacion of las larvas de estas especies.
Abstract: [El desarrollo larval de Petrolisthes tonsorius Haig, 1960, un pequeno cangrejo porcelanido del Atlantico, es completamente descrito e ilustrado. Hay un estado de prezoea que dura menos de 2 horas, dos estados de zoea que duran de 4 a 8 dias y de 6 a 9 dias, respectivamente y un estado de megalopa que dura en promedio hasta 16 dias. La duracion exacta de este estadio no se conoce. Se establecen comparaciones entre las diferentes etapas correspondientes al desarrollo larval de P. tonsoriu.s, P. arncatus del Atlantico y P. tridentatus de la costa del Pacifico, discutiendose aquellos caracteres que pueden ser utilizados para la identificacion de las larvas de estas especies., El desarrollo larval de Petrolisthes tonsorius Haig, 1960, un pequeno cangrejo porcelanido del Atlantico, es completamente descrito e ilustrado. Hay un estado de prezoea que dura menos de 2 horas, dos estados de zoea que duran de 4 a 8 dias y de 6 a 9 dias, respectivamente y un estado de megalopa que dura en promedio hasta 16 dias. La duracion exacta de este estadio no se conoce. Se establecen comparaciones entre las diferentes etapas correspondientes al desarrollo larval de P. tonsoriu.s, P. arncatus del Atlantico y P. tridentatus de la costa del Pacifico, discutiendose aquellos caracteres que pueden ser utilizados para la identificacion de las larvas de estas especies.]
16 citations
TL;DR: In this paper, the volume-weighted mean pH as calculated, were 5.8, 5.6 and 5.4 units in 1981, 1982 and 1983, respectively.
Abstract: Bulk precipitation was daily collected and individual pH measured at the Trachypogon savannas, Venezuela, over a consecutive 3-year period. The volume-weighted mean pH as calculated, were 5.8, 5.6 and 5.8 for 1981, 1982 and 1983, respectively. The annual variation of pH ranged from 4.9 to 6.9: 4.8 to 6.3 and 5.4 to 6.8 units in 1981, 1982 and 1983, respectively. However, in this savanna area, which is relatively remote from heavy sources of industrial pollution, the annual proportion of daily rains with pH < 5.0, occurring mainly at the onset and end of the wet season, were 2.0,3.0 and 0.0% for 1981, 1982 and 1983, respectively. DOI: 10.1111/j.1600-0889.1985.tb00078.x
12 citations
TL;DR: At high temperature two peaks are reported whose maxima shift to lower temperatures as x increases, and the energies calculated for these relaxation processes are compared to the enthalpies deduced from conductivity measurements.
Abstract: Concentrated solid solutions ${\mathrm{Ba}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{La}}_{\mathrm{x}}$${\mathrm{F}}_{2+\mathrm{x}}$, x\ensuremath{\le}0.492, are studied by means of thermally stimulated depolarization [ionic thermal current (ITC)] or polarization [thermally stimulated polarization current (TSPC)] techniques. At high temperature two peaks are reported whose maxima shift to lower temperatures as x increases. The energies calculated for these relaxation processes are compared to the enthalpies deduced from conductivity measurements. The first high-temperature peak, D, has been already reported in a more restricted concentration range and has been attributed to either a space-charge accumulation near the electrodes or the polarization of the dislocations present in the crystal.We show here that it is the highest-temperature peak reported here for the first time and labeled as peak E which is best related to the displacement of free interstitial fluorines through the bulk of the crystal; that is, to the building up of a space charge near the electrodes. At low concentrations the behavior of peaks D and E is understood if the Debye-H\"uckel interaction energy among unassociated defects is taken into account. For the more concentrated region (x\ensuremath{\gtrsim}0.05), the enhanced ionic motion model proposed to explain the variation of the ionic conductivity slopes as a function of x also applies here; the parameters present in the model are calculated and are found to be in agreement with those previously reported. The energy difference observed between peaks D and E is almost constant for x\ensuremath{\ge}0.05. This energy difference equal to 0.08 eV is attributed to the binding energy of the interstitial fluorines forming the dislocation charge cloud to the dislocation line. TSPC experiments are carried out on the same crystals and they show that peak D is present in all the TSPC spectra, thus confirming the localized displacement of the charges, while the highest-temperature peak E is replaced by a steep increase of the ionic current. Therefore, the origin of peak E observed in ITC must be attributed to the accumulation of charges near the electrodes; that is, the build up of the space-charge layer.
TL;DR: The gauge principle in the loop space is invoked to produce the gauge theory of the Lorentz group and the full kinematics of gravitation is derived from this principle.
Abstract: The gauge principle in the loop space is invoked to produce the gauge theory of the Lorentz group. The full kinematics of gravitation is derived from this principle. The dynamics is introduced with a gauge ``matter field'' Lagrangian which leads to the sourceless Einstein equations. Some possibilities about quantization and implementation on the lattice are suggested.
TL;DR: The concepts of generalized homotopies and regular values are introduced, the solution sets of such generalized homOTopies are characterized and it is proved, under boundary conditions similar to Smale’s, the existence of a homotopy path which contains an odd number of solutions to the problem.
Abstract: Global Newton methods for computing solutions of nonlinear systems of equations have recently received a great deal of attention By using the theory of generalized equations, a homotopy method is proposed to solve problems arising in complementarity and mathematical programming, as well as in variational inequalities We introduce the concepts of generalized homotopies and regular values, characterize the solution sets of such generalized homotopies and prove, under boundary conditions similar to Smale’s [10], the existence of a homotopy path which contains an odd number of solutions to the problem We related our homotopy path to the Newton method for generalized equations developed by Josephy [3] An interpretation of our results for the nonlinear programming problem will be given
01 Jan 1985
01 Jan 1985
TL;DR: Rocket immunoelectrophoresis studies showed that seed lectin is reduced approximately 40-fold in comparison to the normal Phaseolus vulgaris cultivar ‘Contender’, and DNA gel blot studies suggested that the ‘Pinto’ and ’Contenders’ varieties contain similar numbers of lectin genes, although qualitative differences were observed in the gel blot banding patterns.
Abstract: The molecular basis of a lectin gene mutation in the Phaseolus vulgaris cultivar ‘Pinto’ was investigated. Rocket immunoelectrophoresis studies showed that seed lectin is reduced approximately 40-fold in comparison to the normal Phaseolus vulgaris cultivar ‘Contender’. DNA gel blot studies using a lectin cDNA probe suggested that the ‘Pinto’ and ‘Contender’ varieties contain similar numbers of lectin genes, although qualitative differences were observed in the gel blot banding patterns. Hybridization of the lectin cDNA probe to gel blots containing normal and mutant embryo mRNAs produced a 1 kb mRNA band in both mRNA populations. However, the amount of lectin mRNA was reduced approximately tenfold in the mutant ‘Pinto’ cultivar. Together, these findings suggest that the reduced seed lectin level is due, in part, to a reduction in seed lectin mRNA.
TL;DR: A plausible formula is derived for the mass of the Frenkel exciton of an exciton in an nth bound state of the electron-hole binding potential, which is finite as a consequence of the Heller-Marcus mechanism.
Abstract: A plausible formula derived in a previous paper for the mass ${M}_{n}^{\mathrm{*}}$ of an exciton in an nth bound state of the electron-hole binding potential is extended so as to include the effect of an exciton-hopping (or Heller-Marcus) mechanism upon ${M}_{n}^{\mathrm{*}}$ If ${m}_{e}^{\mathrm{*}}$ and ${m}_{h}^{\mathrm{*}}$ are the electron and hole masses, we find that ${M}_{n}^{\mathrm{*}}$= m $_{e}^{\mathrm{*}}$+${m}_{h}^{\mathrm{*}}$ / 1- ${K}_{n}$ / W + ${m}_{e}^{\mathrm{*}}$+${m}_{h}^{\mathrm{*}}$ / ${M}_{F}^{\mathrm{*}}$ ${H}_{n}$ / ${H}_{F}$, where ${K}_{n}$ and ${H}_{n}$ are, respectively, the kinetic and exciton-hopping energies in the nth bound state; W is one-half the sum of the electron and hole bandwidths, and ${H}_{F}$ is the value taken by ${H}_{n}$ for a Frenkel exciton of finite mass ${M}_{F}^{\mathrm{*}}$ For Wannier excitons, ${K}_{n}$=${H}_{n}$\ensuremath{\simeq}0, so that ${M}_{n}^{\mathrm{*}}$\ensuremath{\simeq}${m}_{e}^{\mathrm{*}}$+${m}_{h}^{\mathrm{*}}$; while for Frenkel excitons, ${K}_{n}$\ensuremath{\simeq}W and ${H}_{n}$\ensuremath{\simeq}${H}_{F}$, so that the mass of the Frenkel exciton ${M}_{F}^{\mathrm{*}}$ is finite as a consequence of the Heller-Marcus mechanism
TL;DR: An estimator of the standard deviation of the first derivative of a stationary Gaussian process with known variance and two continuous derivatives, based on the values of the relative maxima and minima, is proposed in this article.
Abstract: An estimator of the standard deviation of the first derivative of a stationary Gaussian process with known variance and two continuous derivatives, based on the values of the relative maxima and minima, is proposed, and some of its properties are considered.
TL;DR: In this paper, it was shown that the exchangeable σ-field of a homogeneous recurrent Markov chain is atomic, provided the chain is finite and satisfies certain conditions.
Abstract: Blackwell and Freedman [2] proved that the exchangeable σ-field ℰ of a homogeneous recurrent Markov chain is atomic. If the chain is finite, the atoms can be found explicitly by means of an algorithm given below. The approach in [2] cannot be extended to a non-homogeneous chain, but a description of ℰ can be obtained in this case by using coupling methods, provided the chain is finite and satisfies certain conditions.
TL;DR: In vivo activity of the soluble salt, which is a soluble derivative of the synthetic bispyrazole LC-6.2HCl, establishes the potential therapeutic value of the drug.
TL;DR: Thermally stimulated depolarization [ionic thermal current (ITC)] and thermally stimulated polarization current (TSPC) methods are compared, and the results obtained for crystals doped with La are reported.
Abstract: Thermally stimulated depolarization [ionic thermal current (ITC)] and thermally stimulated polarization current (TSPC) methods are compared, and the results obtained for ${\mathrm{SrF}}_{2}$ crystals doped with La are reported in this paper. It is shown that for normal dipolar peaks such as the low-temperature relaxation caused by the movement of the interstitial ${\mathrm{F}}_{\mathrm{i}}^{\mathrm{\ensuremath{-}}}$ bound to a ${\mathrm{La}}^{3+}$ cation to form a nearest-neighbor dipole, both techniques give the same information, provided that for the ITC case, the polarization temperature is below the temperature range where the very intense and somewhat anomalous high-temperature peak occurs. For an ITC experiment a current reversal is observed in the high-temperature tail of the dipolar peak if the sample is polarized at a temperature above the high-temperature peak. This current reversal, typical of a TSPC peak, is clearly observed and its height is useful in determining the effective polarization field applied to the sample when an ITC run is performed. The presence of the current reversal indicates the existence of a frozen-in polarization due to processes occurring in the high-temperature part of the relaxation spectrum. Also, information on the origin of the observed relaxation processes at high temperature can be deduced from a comparison of the two spectra.
TL;DR: An example of iterative dual changes in Assignment Problems which does not converge to the solution is given and properties of the Fibonacci Sequence are used.
TL;DR: Ajustement des sections transversales de photoionisation de plusieurs ions d'interet astrophysique tels que N 2+, N 3+, O 4+, Al +, Si 2+ et S 4+ as discussed by the authors.
Abstract: Ajustement des sections transversales de photoionisation de plusieurs ions d'interet astrophysique tels que N 2+ , N 3+ , O 4+ , Al + , Si 2+ et S 4+
TL;DR: It is shown that for a triangle-free graph these numbers coincide with the coefficients of the chromatic polynomial of its complement when thisPolynomial is written in factorial form.
Abstract: For the sake of brevity the absolute values of the coefficients of the matching polynomial of a graph are called matching numbers in this note. It is shown that for a triangle-free graph these numbers coincide with the coefficients of the chromatic polynomial of its complement when this polynomial is written in factorial form.
As an application it is mentioned that the coefficients of every rook polynomial are at the same time coefficients of some chromatic polynomial.
TL;DR: In this article, a Hitachi S-450 scanning electron microscope was used for the characterization of commercial polyacrylamides used in tertiary oil recovery, which revealed the presence of certain individual beads with differing morphologies.
Abstract: In the course of studies on the characterization of commercial polyacrylamides used in tertiary oil recovery, samples of BASF Sepaflood suspension polymerized polyacrylamide with varying degrees of hydrolysis were observed using a Hitachi S-450 scanning electron microscope. Figs ! and 2 show an overall view of a nonhydrolysed (CE 5093) and highly hydrolysed (CE 5095) Sepaflood sample, respectively. Although in both cases the expected bead morphology of a suspension polymer is observed, the photographs reveal the presence of certain individual beads with differing morphologies. Hollow shells (Fig. 1) and nested spheres within the beads (Fig. 2) can be seen in the samples. After having observed many samples, the following conclusions were drawn: 1. The majority of the beads are either solid (Fig. 3) or hollow with shells of different thicknesses (Fig. 4). Figure 2 Overall view of sample CE 5095. Scale bar is 620/tm. (Arrows point to nested spheres in beads).
TL;DR: In this article, a synthesis of α-stannyl α,β-unsaturated esters from lithio α-(tri-n-butyl stannyl)-α-(trimethylsilyl)acetate (2) and aldehydes is described.
Abstract: A synthesis of α-stannyl α,β-unsaturated esters from lithio α-(tri-n-butylstannyl)-α-(trimethylsilyl)acetate (2) and aldehydes is described.
01 Jan 1985
TL;DR: The multilevel control techniques used in this work distribute between two control levels the calculation of optimum set points of the system by decomposition-coordination of the overall optimization problem.
Abstract: The economical short term dispatching of hydroelectric system is a very actual problem and its resolution consists in solving a large scale optimization problem; the classic methods fail when the complexity and the dimension of the problem are very large. The multilevel control techniques used in this work distribute between two control levels the calculation of optimum set points of the system by decomposition-coordination of the overall optimization problem.
TL;DR: In this article, a microsonde electronique is used for the identification of inclusions non conductrices d'oxyde d'aluminium and de silicium in aciers.
TL;DR: A circuit based on the AM2901 bit slice processor and a serial/parallel multiplier is described along with the algorithm to compute the base-2 DIF fast Fourier transform.
Abstract: A circuit based on the AM2901 bit slice processor and a serial/parallel multiplier is described along with the algorithm to compute the base-2 DIF fast Fourier transform.