Showing papers by "Instituto Politécnico Nacional published in 1977"
TL;DR: The sections in this article are: General Considerations, Evidence for the Existence of Primary Afferent Depolarization (PAD), and Organization of PAD.
Abstract: The sections in this article are:
1
I. Motoneurons
1.1
A. Alpha Motoneurons
1.2
Gamma Motoneurons
2
II. Interneurons
2.1
A. General Considerations
2.2
B. Functionally Identified Interneuron Systems
3
III. Tract Cells
3.1
General Considerations
3.2
B. Specific Systems
4
IV. Intraspinal Primary Afferents and Presynaptic Modulation
4.1
A. General Considerations
4.2
B. Intrinsic Properties of Intraspinal Afferents
4.3
C. Evidence for the Existence of Primary Afferent Depolarization (PAD)
4.4
D. Afferent Terminals Are Subjected Only to Depolarizing Input
4.5
E. Interneurons Are Involved in the Mechanism of PAD Generation
4.6
F. Possible Mechanisms of PAD Production by Interneurons
4.7
G. Changes in Synaptic Transmission Related to PAD
4.8
H. Possible Mechanisms for Presynaptic Inhibition
4.9
I. Consequences of Presynaptic Modulation of Synaptic Transmission
4.10
J. Organization of PAD
5
V. Concluding Comment
170 citations
TL;DR: In this paper, a screen of 61 species of Cercospora grown on a potato-agar medium showed the presence of the phytotoxin cercosporin in 24 of them, and of dothistromin in 8.
152 citations
TL;DR: In this article, a triaxial constitutive law and a failure criterion for concrete under short-term monotonic loading are derived from the analysis of available experimental data, and their representation through the octahedral normal and shear components of stresses and strains show that the deformational behavior of concrete can be described through simple analytical expressions relating the bulk moduli to the first two invariants of the strain state.
Abstract: A triaxial constitutive law and a failure criterion for concrete under short-term monotonic loading are derived from the analysis of available experimental data. Their representation through the octahedral normal and shear components of stresses and strains show that the deformational behavior of concrete can be described through simple analytical expressions relating the bulk and shear moduli to the first two invariants of the strain state. The values of the tangent moduli are then immediately obtained by differentiation. The ultimate strength criterion has been expressed as a relation between octahedral shear and normal stresses at failure involving also the third stress invariant. The proposed equations both for the constitutive law and the failure criterion are in a satisfactory agreement with experimental data and are suitable for use in numerical schemes for predicting the response of reinforced concrete three-dimensional structures.
106 citations
TL;DR: In this article, a finite element model is presented which enables the analyst to trace the history of strains, stresses, and crack propagation in reinforced concrete beams subject to a plane state of stress, for a monotonic increase of external load.
Abstract: A finite element model is presented which enables the analyst to trace the history of strains, stresses, and crack propagation in reinforced concrete beams subject to a plane state of stress, for a monotonic increase of external load. Concrete nonlinear behavior is assigned analytically, as resulting from biaxial tests. Steel-concrete interaction is described through experimental nonlinear bond-slip curves. Concrete cracking is taken into account by considering the element unable to sustain stresses in a direction normal to the crack, but capable of transmitting friction forces parallel to the crack itself, through a value of the shear stiffness fixed on the basis of experimental information on aggregate interlock. An iterative solution procedure is used. The effects of updating the tangent stiffness matrix at each iteration are considered, and provisions are included to prevent the occurrence of numerical ill conditioning. The validity of the method is demonstrated against a well-controlled set of experiments on reinforced concrete beams.
92 citations
TL;DR: The photoelectric measurements using asymmetrically aligned bacteriorhodopsin demonstrate that this protein undergoes reversible conformational changes after absorption of light, and applications of a new technique for the direct measurement of small capacitative charge displacements in oriented molecules are reported.
Abstract: BACTERIORHODOPSIN (a purple pigment) is a light-driven proton pump1,2, found in patches of the cell membrane of Halo-bacterium halobium3,4, and is chemically similar to the visual pigment rhodopsin of animal eyes4. In both molecules the chromophore retinal is linked as a protonated Schiff base to a lysine residue of the apoprotein opsin1,5,6. Light induces bacteriorhodopsin to move protons from the inside to the outside of the cell. The resulting electrochemical proton gradient across the membrane is finally used to synthesise ATP. We report here the application of a new technique for the direct measurement of small capacitative charge displacements in oriented molecules. Our photoelectric measurements using asymmetrically aligned bacteriorhodopsin demonstrate that this protein undergoes reversible conformational changes after absorption of light.
90 citations
TL;DR: In this article, the authors considered the incremental theory of plasticity with nonassociated (lacking normality) flow laws and established extremum properties and uniqueness conditions for solution of the rate problem.
80 citations
TL;DR: In this article, the experimental absorption spectrum and excitation profiles of β-carotene were analyzed using a three-dimensional model involving several molecular parameters related to the excited state's structure.
Abstract: Resonance Raman spectra for β-carotene in carbon disulphide at room temperature have been measured. The experimental absorption spectrum and excitation profiles were analysed using a three-dimensional model involving several molecular parameters related to the excited state's structure. These parameters are quite different from those reported previously in the literature. A possible explanation for this discrepancy is proposed.
67 citations
TL;DR: In this article, a variety of alternative mathematical programming procedures for first-order elastoplastic analysis at the collapse-load level for discrete structures described by piecewise-linear elastic-perfectly plastic constitutive laws are formulated and then assessed with respect to their relative computational merit.
62 citations
TL;DR: Cell-free extracts from Saccharomyces cerevisiae catalyzed the incorporation of glucosyl residues from UDP-[U- 14 C]glucose into β-1, 3-glucans which contained a significant proportion of β- 1, 6-glycosidic linkages, which formed the basis for β-Glucan synthesized by membrane and cell wall fractions.
59 citations
TL;DR: A model of visual excitation based on a light-activated and voltage-sensitive channel is presented and Rhodopsin has been incorporated into planar lipid bilayer membranes.
Abstract: Rhodopsin has been incorporated into planar lipid bilayer membranes. The effect of light is to increase the bilayer permeability in a pattern consistent with the formation of a transmembrane channel of about 10 A diameter. A model of visual excitation based on a light-activated and voltage-sensitive channel is presented.
59 citations
01 Jan 1977
TL;DR: This chapter discusses the effects and mechanism of action of molecules that upon incorporation into model and biological lipid bilayers increase the permeability of the membrane to ions.
Abstract: Publisher Summary This chapter discusses the effects and mechanism of action of molecules that upon incorporation into model and biological lipid bilayers increase the permeability of the membrane to ions. As the molecules act similarly in biological and synthetic lipid membranes, it is assumed that these compounds operate in the lipid milieu of the membrane. The biological membranes are a fluid mosaic composed of lipids arranged in a bilayer in which proteins either go across the lipid phase or are partially submerged in the membrane. The membranes formed exclusively with lipids are highly impermeable to ions and the impermeability is determined by the existence of the lipid bilayer. Compounds that lower ion permeability have been used to explore the properties and structure of biological membranes. The ATP synthesis can be driven by a proton-motive force of sufficient magnitude
TL;DR: Glucose, glycerol and DL — sodium lactate were injected in various doses by intraperitoneal (IP) and subcutaneous (SC) routes in rats accustomed previously to a 24 hr-feeding, 24 hrs-fasting schedule to establish a dose-dependent feeding depression and suggested that the hypophagia which followed IP administration was due to information of hepatic origin.
TL;DR: The absolute rate constants for the addition of alkyl radicals to acrylonitrile and methyl acrylate were determined by evaluating the ratio of ligand-transfer oxidation and addition to the double bond.
TL;DR: In this article, various factors influencing the precipitation of Fe-Mo-O systems have been investigated and the changes in the catalyst properties with respect to the temperature of calcination were examined and the following techniques were employed: chemical analysis, X-ray diffraction, scanning electron microscopy, surface area measurements, differential thermal analysis and an abrasion resistance test.
Abstract: In this paper various factors influencing the precipitation of Fe-Mo-O systems have been investigated. Stoichiometric Fe(III) molybdate, Mo-rich Fe(III) molybdate promoted with bismuth and an Fe-Mo-O system with excess of Mo obtained by precipitation at room temperature were studied and the changes in the catalyst properties with respect to the temperature of calcination were examined. The following techniques were employed: chemical analysis, X-ray diffraction, scanning electron microscopy, surface area measurements, differential thermal analysis and an abrasion resistance test. The oxidation of methanol to formaldehyde was also investigated using a fixed bed microreactor. Stoichiometric Fe(III) molybdate was confirmed as the active component. Excess of Mo had no influence on the specific activity of the investigated catalysts, but it was found to be responsible for the high coherence of the sample. The addition of Bi to this system improved mechanical properties by preserving the coherence at temperatures above 450 °C where a collapse of the structure was obtained in the absence of bismuth. Bi-promoted catalyst showed the formation of Bi molybdate 23 phase. Stoichiometric Fe(III) molybdate gave the highest conversions of methanol after prolonged treatment at high temperature.
TL;DR: In this article, the electrooptical theory of valence for the study of Raman intensities is reanalysed and extended to the case of non-cylindrical tensors.
Abstract: In this paper the electrooptical theory of valence for the study of Raman intensities is reanalysed and extended to the case of non-cylindrical tensors. The advantages of this theory with respect to other methods are described. The transferability of electrooptical parameters to other molecules (isotopic derivatives or chemically similar molecules) is discussed and some examples (methane and cyclohexane) are presented.
TL;DR: In this article, the deuterium labeling of perezone has been used to establish that its transformation into the mixture of pipitzols takes place in a concerted process, as deduced from PMR measurements.
TL;DR: In this article, the average length of the isotactic polypropylene is evaluated, and the experimental results are compared to the lengths calculated according to two statistical models of stereospecific propagation.
Abstract: Fractions of predominantly isotactic polypropylene with varying stereoregularity were examined by NMR analysis and by hot-stage optical microscopy, and the stereochemical composition and the melting point of each fraction were determined. From the stereochemical composition the average length of the isotactic stereoblocks is evaluated, and the experimental results are compared to the lengths calculated according to two statistical models of stereospecific propagation. The experimental melting points are then related to the experimental average lengths of isotactic stereoblocks, and the correlation is discussed.
TL;DR: The molecular collision diameter Rσ, location Rgmaxl of the maximum of the binary radial distribution function g(R), and location RuminI of the principal minimum of binary interaction potential u(R) are interrelated by Rσ as discussed by the authors.
TL;DR: Rhodopsin-phospholipid vesicles were formed and loaded with radioactive markers by sonication and results indicate that light induces the formation of a wide permeability pathway with an apparent cut-off diameter of about 10A.
TL;DR: In this article, the cosmic background anisotropy at the angular scale of 25 minutes of arc was investigated by means of a special isotropometer at the alpine station of Testa Grigia (3500 m above sea level) through the atmospheric window 1.0-1.4 mm.
Abstract: The cosmic-background anisotropy has been investigated at the angular scale of 25 minutes of arc by means of a special isotropometer at the alpine station of Testa Grigia (3500 m above sea level) through the atmospheric window 1.0-1.4 mm. We found an upper limit $\frac{\ensuremath{\Delta}T}{T}\ensuremath{\lesssim}1.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ at two standard deviations. Some physical implications about the origin and the rotation of superclusters and about the secondary ionization of plasma are discussed.
TL;DR: In this paper, the visible fluorescence of UF 6 excited at 374 nm has been studied in the temperature range 273 −313 K. The quenching rate has been found to change with temperature according to the Arrhenius equation.
TL;DR: In this article, the effect of substituents OH, OMe, OAc, and COMe on the chemical shifts has been studied for monosubstituted and some 1,5-and 1,8-disubstitized 9,10-AQ compounds.
TL;DR: A major breakthrough in the preparation of the rhodopsin proteolipid has been recently achieved, consisting of the direct transfer of rhodopin from retinal-rod disc-metibranes into an organic solvent, thus avoiding the deleterious effect of the residual surfactant in reconstitution studies.
TL;DR: In this paper, a new type of heterogeneous photosensitizer, methylene blue on silica gel, has been produced and tested in an elliptical, three-phase photo- reactor for the photo-oxygenation, via "singlet" molecular oxygen O 2 ( 1 Δ g ), of 2,3-timethyl-2-butene to the corresponding allylic hydroperoxide.
TL;DR: In this paper, the authors formulate the complex potential description of Einstein-Maxwell fields in a tetrad and coordinate independent manner, and generalize the formalism to take advantage of complex Killing vectors.
TL;DR: In this paper, the fundamental and industrial aspects of hetarogreous selective catalyric oxidation of hydrocarbons are presented and discussed and a review represents an attempt to offer a comprehensive critical collection of information concerning chemical reaction engineering of selective hydrocarbon catalyric oxidations.
Abstract: This review represents an attempt to offer a comprehensive critical collection of information concerning chemical reaction engineering of selective hydrocarbon catalyric oxidation. Many excellent reviews are available in which the fundamental and industrialaspects of hetarogreous selective oxidation of hydrocarbons are presented and discussed[1–11]
TL;DR: In this paper, a strain of Cercospora smilacis thum grown on potato-agar medium showed the presence of the known phytotoxin dothistromin together with the new 2-epidothromin.
TL;DR: In this article, the electron states of SnSe were discussed in connection with the results of a EPM band calculation of the crystal and with new UPS experimental results on a disordered phase which is a precursor of the crystalline one in SnSe film growth.
Abstract: The electron states of SnSe are discussed in connection with the results of a EPM band calculation of the crystal and with new UPS experimental results on a disordered phase which is a precursor of the crystalline one in SnSe film growth.
TL;DR: Pentaerythritol tetracinnamate (PTC) was obtained in several different crystalline forms, and its solid state photopolymerization induced by uv irradiation, was carried out under two different experimental conditions as mentioned in this paper.