Showing papers by "Simón Bolívar University published in 1977"
TL;DR: Names for enamel cusps, cuspules, styles, lophs, folds and islands are given, in an attempt to include in an overall general nomenclature the advantages of the most valuable, already available, nomen clatorial systems.
Abstract: The primitive topography of the enamelled surface of molar teeth of the Cricetidae is described as expressed in the fossil Cricetodontinae. Morphological variations in the molar structure of different subgroups among the Cricetidae are interpreted as derivations from this cricetodontine pattern. Eleven available naming systems for such components are surveyed, and a new unifying nomenclature is proposed, based on the Cope-Osborn cusp homologies for mammals. Names for enamel cusps, cuspules, styles, lophs, folds and islands are given, in an attempt to include in an overall general nomenclature the advantages of the most valuable, already available, nomenclatorial systems. The system purports to apply to all modifications of the cricetid crown molar pattern, and it claims to fulfil the need for a uniform nomenclature.
166 citations
TL;DR: It is concluded that chromosomals evolution in the Didelphidae proceededs from low numbers to higher numbers by a process of centromeric fissioning complemented by some pericentric inversions and/or translocations.
Abstract: One hundred and seventy-seven specimens of American didelphids, representing 9 genera and 22 species have been studied for their chromosomal constitution. Didelphids are very conservative in chromosomal complements. All of the studied species can be sorted into one of three kinds of karyotypes: 2n= 14 (three species of Didelphis, one of Lutreolina, two of Philander, and one of Chironectes), 2n = 14 (eight species of Marmosa, one of Metachirus, three of Caluromys, and one of Dromiciops), and 2n= 18 (three species of Monodelphis). These karyotypes are stable, showing only minor variations within each basic pattern. It is concluded that chromosomals evolution in the Didelphidae proceededs from low numbers to higher numbers by a process of centromeric fissioning complemented by some pericentric inversions and/or translocations. The pattern of karyotypic stability is consistent with bradytely at the organismic level of evolution. This is explained by a low rate of regulatory genetic evolution promoted by epistatic selection favouring the retention of chromosomal arrangements highly advantageous for overall adaptation.
55 citations
TL;DR: A description of the lattice of hyperinvariant subspaces of a linear transformation on a finite-dimensional vector space is given, as well as implications between linear-algebraic and lattice-theoretic properties.
44 citations
TL;DR: In this article, the trilinear Hamiltonian of Tucker and Walls, governing the parametric amplification, leads to three coupled nonlinear Heisenberg equations in terms of creation and annihilation operators.
Abstract: The trilinear Hamiltonian of Tucker and Walls, governing the parametric amplification, leads to three coupled nonlinear Heisenberg equations in terms of creation and annihilation operators. Using the Manley-Rowe relations the equations are reduced to a single nonlinear equation in terms of one of the number operators. Thereafter, it is solved by means of a perturbation method around the diagonal, allowing calculation of the mean number of photons and the variance of the amplified field. The short-time approximation, the parametric approximation, and the classical limit are reobtained by suitable limiting processes.
15 citations
TL;DR: In this article, a thermal cycling technique for grain refinement of an Al-40 wt.% Zn alloy from approximately 400 μm to less than 25 μm has been developed, which consists of annealing a fully precipitated alloy in the α phase field.
14 citations
TL;DR: It is shown that the samples (proceeding from the Orinoco Belt, Venezuela) actually give rise to random speckle patterns when illuminated with a laser beam.
Abstract: A speckle technique recently developed for transient phenomena analysis is applied to the study of dynamic properties of petroleum wells. It is shown that the samples (proceeding from the Orinoco Belt, Venezuela) actually give rise to random speckle patterns when illuminated with a laser beam. Transverse displacements of the sample’s surface can then be measured by classical speckle photography. When the root mean square of the phase and intensity variations in the scattered light are small with respect to the corresponding mean values, line of sight displacements of the surface can also be measured by means of a simple modification of the original technique.
6 citations
TL;DR: In this article, a thermal cycling technique which allows grain refinement of Al-40 wt.% Zn alloys from 400 μm to less than 25 μm has been developed, which consists of alternate annealing in the α and (α + β) phase fields with intermediate quenching.
5 citations
TL;DR: The results demonstrate that closed groups of individuals exposed to similar dietary and environmental conditions exhibit closely similar trace element patterns in their hair and, consequently, in other biological tissue, which severely limits the use of trace element pattern patterns in hair for forensic comparisons.
Abstract: Thermal neutron activation analysis and instrumental gamma-ray spectrometry were used to analyze the elemental constituents in the head hair from sedentary Indian populations in the Venezuelan Amazonas region. Concentration values for 30 elements were determined quantitatively, and the presence of 7 others was detected qualitatively. The remoteness of the area and the primitive ecological conditions of the local population prevents the exposure of their biological systems to industrial and agricultural contamination, either external or metabolic. These conditions are reflected in a marked decrease of the concentration ranges of the trace elements, and a significant reduction or even the total absence of some components. The results demonstrate that closed groups of individuals exposed to similar dietary and environmental conditions exhibit closely similar trace element patterns in their hair and, consequently, in other biological tissue. This fact severely limits the use of trace element patterns in hair for forensic comparisons. The results also indicate that a large part of the constituents found in hair is probably deposited externally from ambient contamination and that any metabolic deposition occurs much more uniformly and probably in lower concentrations. Tables of analytical results in parts per million are presented, together with representative gamma-ray spectra of themore » hair. Comparison with earlier data in the literature is also shown.« less
5 citations
TL;DR: In this paper, an incoherent holographic technique is used to record the fundamental and Stokes optical waves resulting from the interaction of an inhomogeneous laser beam and a nonlinear dielectric.
Abstract: An incoherent holographic technique is used to record the fundamental and Stokes optical waves resulting from the interaction of an inhomogeneous laser beam and a nonlinear dielectric. The structure of the image of the interaction region, obtained by illuminating the hologram with a coherent wave, is discussed. This technique can be applied to the study of coherent phenomena in nonlinear media when coherent holographic methods fail because of random space-time variations of the phase of the waves.
2 citations
TL;DR: In this article, necessary and sufficient conditions for a coherent state to be a stable coherent state (SCS) are given for finding all its SCS and how to construct Hamiltonians having any previously established set of SCS.
2 citations
DOI•
14 Sep 1977
TL;DR: In this paper, an exact superposition of each pair of frames is obtained by comparing a reference speckle pattern registered in each frame with a standard, provided by an immobile auxiliary diffuser.
Abstract: One of the more widely used methods for the study of combustion phenomena is the deflexion-mapping method, in combination with Moire techniques. As combustion phenomena are essentially dynamic, multiple frames are generally needed to record the whole event. An exact superposition of each pair of frames may then be done, in order to deduce from the resulting Moire patterns, the change of the thermodynamic variables in the corresponding time interval. We present here a new technique by means of which the superposition of the pairs of frames can be done exactly. This superposition is obtained by comparing a reference speckle pattern registered in each frame with a standard. The reference speckle pattern is provided by an immobile auxiliary diffuser. After developing, a laser beam is directed through the reference region of the nearly superposed pairs of frames, and these are displaced one respect to the other until Young fringes disappear. This yields the criterion of correct superposition. A major advantage of this technique is that the filtering of the Moire patterns corresponding to each pair of frames, and the control of their correct superposition, are made simultaneously on the focal plane of a single lens in a simple optical setup.