Showing papers by "Instituto Politécnico Nacional published in 1974"
TL;DR: In this article, two primal static formulations are found in linear programming, from which the relevant dual kinematic versions are obtained via duality properties, and some considerations about the numerical efficiency of the proposed formulations are given.
145 citations
TL;DR: Radioactive 1-Azidonaphthalene and 1- Azido-4-iodobenzene added to liposomes and sarcoplasmic reticulum membranes, are able to reach the liquid hydrocarbon like core, as demonstrated by encounter quenching of perylene fluorescence.
78 citations
TL;DR: The surface and bulk chemistry of pure and mixed tin and antimony oxides prepared both by precipitation and solid state reaction have been investigated by spectroscopic and thermogravimetric techniques and by measurements of surface reactivity towards 1-butene oxidation and isomerization.
57 citations
TL;DR: INSULIN stimulates the movement across the cell membrane of a variety of substances such as glucose1, amino acids2, and alkali cations Na+ and K+ by increasing the available number of sites and the efficiency with which the sites operate.
Abstract: INSULIN stimulates the movement across the cell membrane of a variety of substances such as glucose1, amino acids2, and alkali cations Na+ and K+ (refs 3 and 4). All these substances move through specific membrane sites but it is not known whether insulin stimulates transport by increasing the available number of sites or by increasing the efficiency with which the sites operate.
56 citations
TL;DR: In this paper, it was shown that it is always possible to find a bilinear form that makes a given linear operator symmetric, and that a variational formulation requires the symmetry of the operator.
47 citations
TL;DR: Adsorption of the antibiotic X-537A to lipid bilayers increases the membrane conductance to monovalent and divalent cations up to 104 times, and the dependence of the conductance on ionophore and ion concentration suggests that the permeant species for the H+ conductance is the dimer (HA2)−, and for the Ca++ conductance the dimers (CaHA2).
Abstract: The antibiotic X-537A, already characterized as an ionophore for mono-, di- and trivalent cations across lipid membranes, inhibits ATP hydrolysis and glutamate oxidation stimulated in mitochondria by ion translocators such as monazomycin and beauvericin with the selectivity pattern: Cs+>Rb+>K+>Na+>Li+. The ionophore-mediated inhibition of both ATPase and respiration is fully reversed by concentration gradients of K+ and H+ imposed between intra-extra mitochondrial compartments. It is not reversed by modifying the concentrations of divalent or trivalent cations in the medium. These data as well as the substrate dependance of the respiratory inhibition indicate that X-537A inhibits energy transduction primarily by mediating the translocation of protons in exchange for K+ rather than by complexing divalent cations. Because of its ability to catalyze net proton transfer, concentrations of X-537A above 5×10−6
m uncouple the respiratory control of intact mitochondria. At concentrations below 10−6
m, the antibiotic releases the oligomycin-induced respiratory control of submitochondrial sonic particles with an alkali ion and proton-dependent selectivity as that shown to transport ions across lipid bilayers. It also stimulates a lanthanide-sensitive, ruthenium red-insensitive uptake of Ca2+ in submitochondrial sonic particles apparently occurring through an antiport type of electroneutral exchange diffusion of Ca2+ out/2H+ in.
39 citations
TL;DR: In this article, the proton noise decoupled 13 C spectra of flavone, 5,6,7,8-tetradeuteroflavone, 2′,3′,4′,5′,6′-pentadeuter-of-lavone and 4′-brom oflavone were compared.
36 citations
TL;DR: A tunable dye laser which generates pulses of high intensity and short duration was used in an experimental set-up for cytofluorometry, which allows, for the first time, the fluorescence decay time to be measured directly in the cell.
Abstract: A tunable dye laser which generates pulses of high intensity (107 W cm−2) and short duration (2 nsec) was used in an experimental set-up for cytofluorometry. The fluorescence signal given by a single cell (frog erythrocytes stained by a conventional Feulgen reaction for the demonstration of DNA) has been studied. This system allows, for the first time, the fluorescence decay time to be measured directly in the cell. The system has the following advantages compared to the conventional methods: (i) absence of appreciable photodecomposition; and (ii) a potential increase in sensitivity by several orders of magnitude.
29 citations
TL;DR: The 70 eV mass spectra of a number of derivatives of 3,5-diphenul-1,2,4-oxadiazole substituted either in the 5-phenyl (fifteen) or in the 3-, 4-, and four positions were studied using exact mass measurements and metastable determinations by the defocusing technique as discussed by the authors.
Abstract: The 70 eV mass spectra of a number of derivatives of 3,5-diphenul-1,2,4-oxadiazole substituted either in the 5-phenyl (fifteen) or in the 3-phenyl (four) position, have been studied using exact mass measurements and metastable determinations by the defocusing technique. The substituent effects on the heterocyclic cleavage are not very important for electron-withdrawing and weak electron-donating groups. The main cleavage is the formal retro 1,3-dipolar cycloaddition with the positive charge retained by the C7H5NO (orYC7H4NO in the case of the 3-substituted derivatives) fragment specifically containing the 3-phenyl, as oreviously observed for 3,5-diphenyl-1,2,4-oxadiazole using labelling experiments. Two other minor primary processes leading to benzoyl and nitrile ions, both containing the 5-phenyl, become important in the case of the electron-donating substituted compounds. Correlation of the abundance of these fragmednts and of the molecular ions with σ+(para) Brown constants is discussed. Proximity effets are shown by some ortho derivatives.
28 citations
26 citations
TL;DR: Nidification is always distinct from the formation of burrows for shelter and food storage and seems to be stimulated solely by ovarian maturation and the construction of a burrow by a bisexual couple in either P. mexicanus or P. palliatus is considered an example of incipient subsocial behavior.
Abstract: Food collection and pairing habits of 3 Mexican species of Phanaeus are examined. In Phanaeus , dung is usually buried near the animal dropping, but P. daphnis Harold, P. mexicanus Harold and P. palliatus Sturm very often reduce the effects of inter-specific competition with other Scarabaeinae by rolling a piece of dung a considerable distance away from the animal dropping. This behavior assists in the formation of bisexual couples because males are attracted to females who are rolling a ball of dung. The newly formed couple works together in the construction and provisioning of a burrow, but their relationship is not sexual until ovarian maturation occurs. Most individuals of P. palliatus and many of the other 2 species dig burrows under or near the edge of the dropping; such burrows are usually occupied by a single individual of either sex, not by a bisexual couple.
Nidification is always distinct from the formation of burrows for shelter and food storage and seems to be stimulated solely by ovarian maturation. The construction of a burrow (“home”) by a bisexual couple in either P. daphnis of P. mexicanus is considered an example of incipient subsocial behavior. With the concurrent reduction in competition, more individuals can feed on a single dropping, the excrement is dispersed more rapidly and over a wider area, and flies do not have a chance to breed in the dung.
TL;DR: The presynaptic and postsynaptic focal potentials recorded in the motor nucleus after stimulation of the ventrolateral tract, as well as the corresponding synaptic potentials electrotonically recorded from the ventral roots, are not depressed during conditioning stimulations which produce primary afferent depolarization.
TL;DR: Chromaffin cells were identified in the liver of mouse, rat, and rabbit and could be important for the adrenergic-induced hepatic glucose output.
TL;DR: The lethal effect is the same for both wild type and streptomycin-resistant mutants, indicating that the mutants are not selected by the irradiation, and the inactivation and mutagenicity show a large shoulder, suggesting the existence of repair systems.
Abstract: Near-ultraviolet (UV) light (325 to 400 nm), in the presence of air and the absence of exogenous photosensitizing compounds, is lethal and mutagenic for Haemophilus influenzae. The lethal effect is the same for both wild type and streptomycin-resistant mutants, indicating that the mutants are not selected by the irradiation. The inactivation and mutagenicity show a large shoulder, suggesting the existence of repair systems. Filters were used to eliminate the possibility of short-UV irradiation. The effective radiation is between 325 to 400 nm. The lethal and mutagenic effects are higher during mid and late log phase than during early log or stationary phase.
TL;DR: In this article, the overlap integrals for ($s\ensuremath{-}f$), ($p\ensuredmath{)-f$, and ($d\enuremath {-} f$) interactions have been calculated using the two-center approximation and considering first and second-nearest-neighbor contributions.
Abstract: In order to make tight-binding calculations possible for substances with $f$ electrons, the overlap (or energy) integrals for ($s\ensuremath{-}f$), ($p\ensuremath{-}f$), and ($d\ensuremath{-}f$) interactions have been calculated. Using the two-center approximation and considering first- and second-nearest-neighbor contributions the results have been applied to the fcc lattice.
TL;DR: In this article, a generalized formulation of the imposed rotation method for the inelastic analysis of multistory frames is presented. But this method is not applicable to the analysis of multi-dimensional structures.
Abstract: The imposed rotation method for the inelastic analysis of frames rests on the interpretation of the actual bending moment distribution as the superposition of linear elastic moment responses to loads and to unknown plastic rotations regarded as imposed strains. The method given herein is a generalized formulation, covering second-order geometric effects and moment-axial force interaction. Finite element models of frames and piecewise linear moment-rotation laws for critical sections are assumed. Recent algorithms for solving quadratic programming and linear complementarity problems are shown to be efficiently applicable to the analysis of multistory frames. The safety factor with respect to local failure because of “brittle” flexural behavior turns out to be attainable by a suitably modified linear programming procedure.
01 Jan 1974
TL;DR: Most authors in the field of feeding behavior have adopted the point of view that the control of food intake is “multifactorial”, but this only reflects a lack of knowledge about the main factor controlling hunger and satiety, and a certain misunderstanding about the operation of regulatory systems.
Abstract: Most authors in the field of feeding behavior have adopted the point of view that the control of food intake is “multifactorial” (Adolph, 1943, 1947; Stellar 1954; Brobeck, 1960; Stevenson, 1964). In our opinion this only reflects our lack of knowledge about the main factor controlling hunger and satiety, and a certain misunderstanding about the operation of regulatory systems.
TL;DR: In this article, 1-Acryloylbenzotriazole was prepared and polymerized and gave pure polyacrylic esters and polyacrylamides by reaction under mild conditions with alcohols and amines.
Abstract: 1-Acryloylbenzotriazole was prepared and polymerized. The resulting poly-1-acryloylbenzotriazole gave pure polyacrylic esters and polyacrylamides by reaction under mild conditions with alcohols and amines.
TL;DR: This paper showed that the nitroaromatic, C-6-C-1 unit of the antibiotic aureothin (9) biologically derives by degradation of the phenylpropanoid precursor D,L -p-aminophenylalanine (1) through hydroxylation β to the nitrogen to erythro and threo p-amino group to p-nitro.
TL;DR: In this article, the process of retro-1,3-dipolar cycloaddition of 2,5-diaryl 1,3,4-dioxazoles induced by electron impact is discussed.
Abstract: The process of retro-1,3-dipolar cycloaddition of 2,5-diaryl-1,3,4-dioxazoles induced by electron-impact is discussed. For this purpose, 2-phenyl-5-p-chlorophenyl-1,3,4-dioxazole was prepared, labelled with 18O in position 1; the spectrum of this compound showed clear evidence of retro-cycloaddition, the dipole fragment retaining the positive charge. This labelled compound also provides a reliable interpretation of other cleavage modes of the heterocyclic ring. The elemental compositions of the ions considered were determined by exact mass measurements and the metastable transitions were detected through the defocusing technique of the electrostatic sector.
TL;DR: In this paper, the proton spectra of thietane-1,oxide and -1,1-dioxide have been analyzed at 300 and 100 MHz and the results indicate a preferred puckered structure with the sulphinyl oxygen in the equatorial orientation.
TL;DR: In this paper, a homolytic t-butylation of 3-substituted pyridines was performed with complete selectivity m position 6, and the relative rates correlate with the Hammett σ p constants (ϱ = 5·5).
TL;DR: In this paper, a thorough examination of the main sources of error and delay distribution distortion in time measurements employing time-to-amplitude converters (TACs) is made.
TL;DR: A PMR study of ten poly-(2,4-dinitrophenoxy)benzenes and naphthalenes together with appropriate reference compounds, showed that relatively long-range anisotropic effects are observed as discussed by the authors.
TL;DR: In this article, the authors used the nuclei in the nuclear table as members of an ensemble of hamiltonianas and showed that, once nuclei with a systematic behaviour are eliminated, the nearest-neighbour spacings between states with the same spin and parity follow, in the ground state region, a distribution which is roughly consistent with that predicted by the gaussian orthogonal ensemble (GOE).
TL;DR: Cell walls from Morchella sp.
Abstract: Cell walls from Morchella sp. were isolated after mechanical breakage of the fungus. Analysis of the material revealed that the most prominent compound was protein, phosphate being present in lesser amounts. Non-nitrogenous polysaccharides accounted for 17%. They were mostly soluble in hot HCl. The following monosaccharides were identified by chromatography of hydrolyzed samples: glucose, mannose and galactose. No lipids were detected in the purified cell walls. Chitin was present in a concentration of 16%. It was identified by cytochemical reactions, infrared spectra, and X-ray diffraction analysis. The cell wall of Morchella did not contain chitosan nor cellulose.
TL;DR: The position of the angeloyl moiety in 2c was independently tested by its conversion to O-methyl hydroxyperezone (1d) identified with a sample synthesised from perezone.