Showing papers by "Instituto Politécnico Nacional published in 1986"
TL;DR: Two design procedures are presented for monomode solid-state laser resonators with large mode volume and low sensitivity both to focal length fluctuations and to misalignment.
Abstract: Resonators containing a focusing rod are thoroughly analyzed. It is shown that, as a function of the dioptric power of the rod, two stability zones of the same width exist and that the mode volume in the rod always presents a stationary point. At this point, the output power is insensitive to the focal length fluctuations, and the mode volume inside the rod is inversely proportional to the range of the input power for which the resonator is stable. The two zones are markedly different with respect to misalignment sensitivity, which is, in general, much greater in one zone than in the other. Two design procedures are presented for monomode solid-state laser resonators with large mode volume and low sensitivity both to focal length fluctuations and to misalignment.
278 citations
01 May 1986
TL;DR: In this article, a mathematical model containing three population balance equations has been defined for precipitation of titanium dioxide by thermal hydrolysis from concentrated sulfuric acid solutions by considering all the factors which have influence on the rates of the process and on the characteristics of the precipitate.
Abstract: Precipitation of titanium dioxide by thermal hydrolysis from concentrated sulfuric acid solutions has been studied by considering all the factors which have influence on the rates of the process and on the characteristics of the precipitate. For this purpose a mathematical model containing three population balance equations has been defined. A population balance equation is related to the free particles that are present at any time in the system, another to the agglomerates, and the last to the total particles, that is free particles plus particles bounded into the agglomerates. In this model kinetic laws for nucleation and growth, respectively, have been introduced by considering the experimental observations that precipitation is a strongly activated process and that sulfuric acid concentration negatively affects precipitation rate. The following assumptions have then been introduced: coalescence is possible only for very small free particles; and elementary particles in aggregates can grow independently without losing their identity. The above-mentioned population balance equations have been solved by employing the method of moments and give the amount of titanium precipitated during the time, the average size of the elementary particles and of the aggregates during the time, and the evolution of the corresponding distribution function. The reliability of the mathematical model has been tested on kinetic runs performed under different conditions of temperature, titanium concentration, and sulfuric acid concentration.
108 citations
TL;DR: The morphological and electrophysiological characteristics described for the A-V canal cells, could help to explain their slow conduction properties and the atrioventricular delay.
86 citations
TL;DR: Both adherence of trophozoites to target cells and toxin activity of crude extracts of amoebae seem to be necessary factors for the expression of the virulence of this parasite.
Abstract: We have used chemical mutagenesis to isolate 10 independent phagocytosis-deficient mutants of Entamoeba histolytica from a highly virulent clone (strain HM1:IMSS). Phagocytosis-deficient mutants were characterized by several biologic properties related to amoebic pathogenic mechanisms: virulence, adhesion to red blood cells, cytopathic effect of live trophozoites on cell culture monolayers, ability of amoebic extracts to destroy cell culture monolayers, and growth in semisolid agar. All of these mutants were also deficient in in vivo virulence and in vitro cytopathic effect. Three were also deficient in adhesion, and the extracts of three others were unable to destroy cell culture monolayers. These findings suggest a strong correlation between phagocytosis and in vivo and in vitro cytopathogenicity. Both adherence of trophozoites to target cells and toxin activity of crude extracts of amoebae seem to be necessary factors for the expression of the virulence of this parasite. Traits responsible for growth in semisolid agar do not seem to be involved in virulence.
66 citations
TL;DR: Pedro Lehmann lists what constitutes a full description of a drug's stereostructure, discusses chiral drugs as the most important and interesting representatives of stereoisomeric ligands, and draws attention to the need for a stereoselectivity database in rational drug design.
64 citations
TL;DR: In this article, the interpretation of the infrared intensities in terms of atomic polar tensors and of electrooptical parameters allows to derive rich information on the charge distribution in the molecules, and it is possible to derive information on intramolecular and intermolecular interactions even from poor data such as absolute intensities of whole regions in the spectrum or even from relative intensities.
61 citations
TL;DR: ATPase Cytochrome oxidase Enzyme stability Organic solvent Thermostability Water content
59 citations
TL;DR: In this article, the penicillinacylase was used to catalyzes the conversion at pH 7.5 of N-phenacetyl aspartame (4 ) into phenylacetic acid.
49 citations
TL;DR: In the presence of immobilized benzylpenicillin acylase of the N-phenacetyl derivatives of the primary amines, the hydroxy amines (6 )-( 8 ), key intermediates in the synthesis of optically active forms of carnitin and propranalol, of ca 04, 03 and 08 ee, respectively as mentioned in this paper.
44 citations
TL;DR: The structures of melleolides B-D, three new protoilludene sesquiterpenoid O-methylorsellinates isolated from a culture of Armillaria mellea, have been elucidated on the basis of chemical and spectral data.
43 citations
TL;DR: The results demonstrate that G. lamblia trophozoites do not invade epithelial monolayers, and under the in vitro conditions described here, giardias showed no toxic or invasive effect.
TL;DR: The contribution of the CH bond to the total intensity in the CH stretching region (Astr) and the CH deformation region (Adef) can be easily measured for several compounds.
TL;DR: In this article, a comparison of aptitudes technologiques d'isolats proteiques obtenus par two techniques (micellisation, precipitation isoelectrique) is presented.
Abstract: Comparaison des aptitudes technologiques d'isolats proteiques obtenus par 2 techniques (micellisation, precipitation isoelectrique) a partir soit de tourteau delipide en laboratoire, soit de tourteau industriel
TL;DR: Comparaison des proteines obtenues par 2 techniques : micellisation ou precipitation isoelectrique, la composition est semblable, seule la couleur est differente.
Abstract: Comparaison des proteines obtenues par 2 techniques : micellisation ou precipitation isoelectrique. La composition est semblable, seule la couleur est differente
TL;DR: In this article, the authors study the transformation produced on optical phase space by an arbitrary refracting surface and show that this factorizes into two root canonical transformations, one representing the propagation from a reference plane to the refractive surface in the first medium, and the other, the inverse propagation back to the reference plane in the second medium.
Abstract: We study the transformation produced on optical phase space by an arbitrary refracting surface. We show that this factorizes into two root canonical transformations, one representing the propagation from a reference plane to the refracting surface in the first medium, and the other, the inverse propagation back to the reference surface in the second medium. This factorization allows for a simple parameterization of the effect of a refracting surface to some aberration order, illustrated for cubic surfaces and Dragt’s Lie-algebraic description of a quartic surface and its Seidel aberration coefficients.
TL;DR: Results suggest that only half of the surface-immunoprecipitated antigens are enriched in the cap, similar to that from iodinated cell-surface proteins and polypeptides from isolated plasma membranes.
Abstract: Polyspecific antibodies bound to the cell surface of Entamoeba histolytica are polarized toward the uroid region and spontaneously released by the amoeba as supramolecular aggregate or cap. We purified these exfoliated structures and analyzed them by electron microscopy and sodium dodecyl sulfate electrophoresis. Isolated caps were mainly composed of membranes and contained five major [35S]methionine-labeled bands; many more bands appeared (together with immunoglobulins) after silver staining. Surface immunoprecipitates contained about twelve major [35S]methionine-labeled polypeptides, five of which had molecular weights similar to those of radiolabeled polypeptides in the cap. Some proteins in the caps had the same electrophoretic migration pattern as that from iodinated cell-surface proteins and polypeptides from isolated plasma membranes. Results suggest that only half of the surface-immunoprecipitated antigens are enriched in the cap.
TL;DR: In this paper, an analysis of the resonator sensitivity to mirror misalignment in solid-state lasers is presented, considering the rod as a focusing lens with a limited aperture, and it is shown both theoretically and experimentally that two stability ranges labeled zone I and II exist, with markedly different Si values; in particular, near one of the two boundaries of zone II, Si rapidly diverges.
TL;DR: In this article, a carbon centered radical is generated by reduction of methyl phenyl-glyoxalate with Ti(III) ion, which adds to the carbonyl carbon of ketones to afford pinacols.
TL;DR: Improved approaches to critical topics in the solution of systems of nonlinear equations are presented in this paper, including a new objective function, defined to ensure more reliable convergence tests; an efficient procedure for updating the Jacobian matrix; a bidimensional search, proposed to replace Newton's iteration when it fails; and finally, a procedure avoiding difficulties due to ill-conditioned Jacobians.
TL;DR: In this paper, the flexo-electric effect in a hybrid aligned nematic cell containing 4-methoxybenzylidene-4'-n-butylaniline (MBBA) subject to d.c. excitation was investigated.
Abstract: We present evidence for the flexo-electric effect in a hybrid aligned nematic cell containing 4-methoxybenzylidene-4'-n-butylaniline (MBBA) subject to d.c. excitation, by comparing the theoretical curve derived by including the flexo-electric term in the free energy with the experimental points. The agreement appears to be very good for MBBA doped with a small amount of an additive which shows reversible electrochemical reactions at very low redox potential; this allows us to determine the sum of the flexo-electric coefficients and the anchoring energy on the planar wall. For undoped MBBA the experimental results can be justified only by assuming a low voltage screening of the electric field, due to the presence of ionic impurities in the material.
TL;DR: A new design procedure for solid-state laser resonators operating in the fundamental mode is applied to the optimization of the mode volume and stability of a cw Nd:YAG laser, providing the highest power in the mode-locking regime reported to date.
Abstract: A new design procedure for solid-state laser resonators operating in the fundamental mode is applied to the optimization of the mode volume and stability of a cw Nd:YAG laser. The optimized laser provides the highest power in the mode-locking regime reported to date.
TL;DR: The reaction of the title carbanions with several aldehydes and ketones to afford the corresponding ketene dithioketals was studied in this paper, where it was found that the PO organolithium reagent reacted with both types of carbonyl substrates in good to excellent yields.
TL;DR: In a distorted nematic texture, with boundaries at fixed potential, the electric field is nonlocal as mentioned in this paper, which allows in particular the flexoelectric effect to give a volume contribution.
Abstract: In a distorted nematic texture, with boundaries at fixed potential, the electric field is nonlocal. This allows in particular the flexoelectric effect to give a volume contribution. Most calculations predicting large distortions must be revised.
TL;DR: A model for the electron transport in thylakoids, in which cyt c553, plastoquinone and FNR participate in both photosynthesis and respiration is proposed, which assumes the presence of an electron transport segment common to the photosynthetic and the respiratory chains.
Abstract: Dark and light oxidation of NADPH was measured in Spirulina maxima thylakoid membranes. The dark reaction was more cyanide sensitive than the light reaction. In light, 83% of the electrons from NADPH produced H2O2 on reducing oxygen, whereas in the dark this number was only 36%. These results are explained by assuming the presence of an electron transport segment common to the photosynthetic and the respiratory chains, so that electrons flowing through the cyanide sensitive oxidase in the dark are diverted to the photosytem (PS) I reaction center (P700). In addition, cytochrome (cyt) c 553 was found to be an electron donor for both cyt oxidase and P700. Half maximum reduction rates were obtained with 7 μM cyt c 553. The intrathylakoidal concentration of cyt c 553 was determined to be 83 μM. About 60% of the respiratory NADPH oxidation activity was lost by extracting the membranes with pentane and was restored by adding plastoquinone (the main photosythetic quinone). NADPH oxidation activity was also inhibited upon washing the membranes with a low salt buffer. This activity was restored by adding partially purified ferredoxin-NADP(+) oxido-reductase (FNR). A model for the electron transport in thylakoids, in which cyt c 553, plastoquinone and FNR participate in both photosynthesis and respiration is proposed.
TL;DR: In this paper, an analysis of the effects of the rod position on the TEM00 mode volume and on the resonator stability is presented, and experiments performed on a cw mode-locked Nd:YAG laser with a standard convex-concave resonator confirm the theoretical predictions.
TL;DR: Outside of a relatively narrow range of geometry ratios (layer thickness over a typical discretization length) certain submatrices to invert are bound to become ill-conditioned, causing significant inaccuracies in the resulting tractions; this intrinsic limitation of applicability strongly depends on the adopted computation precision.
TL;DR: Coupled submitochondrial particles from bovine heart with ATP synthases devoid of control by the inhibitor protein of Pullman and Monroy can be prepared by incubation of Mg-ATP particles in 50 mM phosphate, 250 mM sucrose, and greater than 95% D2O at 38 degrees C.
Abstract: Coupled submitochondrial particles from bovine heart with ATP synthases devoid of control by the inhibitor protein of Pullman and Monroy [J. Biol. Chem. 238, 3762-3769 (1963)] can be prepared by incubation of Mg-ATP particles in 50 mM phosphate, 250 mM sucrose, and greater than 95% D2O (pD 7.8) at 38 degrees C. As monitored with oxonol, the respiring particles build up and maintain a delta psi about 5-10% lower than that of the starting preparation. With oligomycin delta psi of the two preparations is the same. In the presence of an ATP trap (hexokinase and glucose), the two types of particles carry out oxidative phosphorylation at comparable rates. Low concentrations of oligomycin induce a small enhancement of the rate of ATP synthesis in non-controlled particles. In the absence of an ATP trap, net accumulation of ATP, as driven by electron transport in particles without control by the inhibitor protein, is low. Apparently this is due to lack of control by the inhibitor protein of ATP hydrolysis that occurs during oxidative phosphorylation.
TL;DR: In this article, the authors examined the hydrodynamic modelling of a liquid in a cocurrent two-phase upflow packed bed reactor and interpreted the dynamic response curves using the piston dispersion exchange model.
TL;DR: In this article, the boundary integral equation (BIE) was used for the solution of the plane strain visco-elastic problem with reference to a generalized Kelvin model consisting of the series of any number of simple kelvin elements, having both volumetric and deviatoric components.
Abstract: On the basis of the correspondence principle of visco-elasticity, an application is discussed of the boundary integral equation method to the solution of time-dependent stress analysis problems. The adopted solution technique, in addition to the time-dependent stress and strain distributions, enables the determination of a measure of the error affecting the numerical results. The governing equations for the plane strain visco-elastic problem are derived with reference to a generalized Kelvin model consisting of the series of any number of simple kelvin elements, having both volumetric and deviatoric components. To get some insight into the overall performance of the technique, the results obtained in the solution of some test examples are discussed and compared with those dering from the available closed from solutions.
DOI•
01 Jan 1986TL;DR: The ecology and distribution of 564 species of fungi from the Valley of Mexico is discussed, based in the material deposited in the Herbarium of the National School of Biological Sciences (ENCB), collected from 136 localities as discussed by the authors.
Abstract: The ecology and distribution of 564 species of fungi from the Valley of Mexico is discussed, based in the material deposited in the Herbarium of the National School of Biological Sciences (ENCB), collected from 136 localities. Forty five species mentioned in the bibliography and not deposited in the ENCB are also included.