Showing papers by "Instituto Politécnico Nacional published in 1996"
TL;DR: It is demonstrated that the extracts of Aloe vera gel have antiinflammatory activity and suggested its inhibitory action on the arachidonic acid pathway via cyclooxygenase.
361 citations
Book•
27 Jun 1996TL;DR: In this paper, generalisations of complex analysis have been studied in the context of hypercomplex factorization, systems of non-linear partial differential equations generated by Futer-type operators.
Abstract: Introduction and some remarks on generalisations of complex analysis a-holomorphic function theory Electrodynamical models Massive spinor fields Hypercomplex factorization, systems of non-linear partial differential equations generated by Futer-type operators.
290 citations
TL;DR: In this paper, the physicico-chemical characteristics and the reactivity of sub-monolayer V2O5-WO3/TiO2 deNOx catalysts are investigated by EPR, FT-IR and reactivity tests under transient conditions.
168 citations
TL;DR: The theory of Grobner bases is used to characterise the design ideal and the quotient, and the theory is tested using some simple examples, including the popular LI8 design.
Abstract: Many problems of confounding and identifiability for polynomial and multidimensional polynomial models can be solved using methods of algebraic geometry aided by the fact that modern computational algebra packages such as MAPLE can be used. The problem posed here is to give a description of the identifiable models given a particular experimental design. The method is to represent the design as a variety V, namely the solution of a set of algebraic equations. An equivalent description is the corresponding ideal I which is the set of all polynomials which are zero on the design points. Starting with a class of models M the quotient vector space M/I yields a class of identifiable monomial terms of the models. The theory of Grobner bases is used to characterise the design ideal and the quotient. The theory is tested using some simple examples, including the popular LI8 design.
124 citations
TL;DR: A comprehensive review of the work done by our group, during the last few years, on diode-pumped cw operating bulk Er : Yb phosphate glass is presented in this paper.
Abstract: A comprehensive review of the work done by our group, during the last few years, on diode-pumped cw operating bulk Er : Yb phosphate glass is presented. The high performance of this laser in terms of output power, laser slope efficiency, single longitudinal and transverse mode operation, laser tunability and frequency stability, amplitude noise, and active mode-locking operation, are considered. The combination of this high performance and potential low cost makes these laser devices attractive for a variety of applications including spectroscopy, metrology, optical radars, optical communications, and all optical switching.
115 citations
24 Mar 1996
TL;DR: An effective EPRCA implementation in which each source computes its input rate based on the maximum VC queue length along the path, and theoretical and experimental results show that high throughput is achieved even with queue sizes independent of the round trip delay.
Abstract: Presents a feedback control algorithm for ATM congestion control in which source rates are adjusted according to VC queue lengths at intermediate nodes along the path. The goal is to "fill in" the residual bandwidth, without exceeding a specified queue threshold. In order to obtain this, we propose a simple and classical proportional controller, plus a Smith predictor to overcome instabilities due to large propagation delays, as well as to avoid cell loss. We propose an effective EPRCA implementation in which each source computes its input rate based on the maximum VC queue length along the path. Theoretical and experimental results show that high throughput is achieved even with queue sizes independent of the round trip delay.
109 citations
TL;DR: In this article, a dynamic mathematical model of the industrial SCR monolith reactor has been derived, using the results of the transient study of NH 3 adsorption as well as other independently estimated parameters.
106 citations
TL;DR: In this article, the formation, the interaction and erasure of localised structures in a passive non-linear resonator is studied. But the results indicate the possibility of realizing optical memories based on localised structure arrays.
Abstract: We show the possibility of controlling the formation, the interaction and erasure of localised structures in a passive non-linear resonator. The localised structures , which have the character of stable 2D spatial solitons, are highly degenerate solutions which develop in the presence of modulational instabilities and their position in the transverse profile of the field can be decided by suitably tailoring the driving external field. The results indicate the possibility of realizing optical memories based on localised structures arrays.
106 citations
23 Jun 1996
TL;DR: New decoding algorithms to be embedded in the iterative decoding strategy of parallel concatenated convolutional codes are derived from the optimum maximum-a-posteriori algorithm and permit a continuous decoding of the coded sequence without requiring trellis termination of the constituent codes.
Abstract: We propose new decoding algorithms to be embedded in the iterative decoding strategy of parallel concatenated convolutional codes. They are derived from the optimum maximum-a-posteriori algorithm and permit a continuous decoding of the coded sequence without requiring trellis termination of the constituent codes. Two basic versions of the continuous algorithm and their suboptimum simplifications are described. Simulation results refer to the applications of the new algorithms to a highly efficient rate 1/3 concatenated code; they show performance only 0.6 dB worse than the Shannon limit.
100 citations
TL;DR: In this paper, a potential range where the cobalt deposition on glassy carbon electrode (GCE) occurs independently of HER, from an aqueous solution of 10 −2 M CoCl 2, in 1 M NH 4 C1 ( pH = 4.66), was found, and the nucleation kinetic parameters, using the potentiostatic method and existing theoretical formalism, were determined.
96 citations
TL;DR: It is found that a significant change in the local structure of La{sub 2/3}Ca{sub 1/3]MnO{sub 3} occurs between 80 K and temperatures above the Curie temperature, {ital T}{sub {ital c}}=270 K.
Abstract: We have found that a significant change in the local structure of ${\mathrm{La}}_{\frac{2}{3}}{\mathrm{Ca}}_{\frac{1}{3}}\mathrm{Mn}{\mathrm{O}}_{3}$ occurs between 80 K and temperatures above the Curie temperature, ${T}_{c}=270$ K. Near-edge x-ray-absorption spectra exhibits changes between 80 K and above ${T}_{c}$. X-ray-absorption fine structure reveals differences between the nearest-neighbor Mn-O bond distributions at 80 K and above ${T}_{c}$. The single-site distribution at low temperature becomes a complex, multi-site distribution above ${T}_{c}$. The observed change is consistent with proposed small polaron related local Jahn-Teller distortions for $Tg{T}_{c}$.
Journal Article•
TL;DR: In animal experiments for acute, subchronic and chronic toxicity, reproduction, mutagenicity, and teratogenicity the algae did not cause body or organ toxicity, and the Spirulina administered to the animals were at much higher amounts than those expected for human consumption.
Abstract: Spirulina, a unicellular filamentous blue-green alga has been consumed by man since ancient times in Mexico and central Africa. It is currently grown in many countries by synthetic methods. Initially the interest in Spirulina was on its nutritive value: it was found almost equal to other plant proteins. More recently, some preclinical testing suggests it has several therapeutic properties such as hypocholesterolemic, immunological, antiviral and antimutagenic. This has led to more detailed evaluations such as nucleic acid content and presence of toxic metals, biogenic toxins and organic chemicals: they have shown absence or presence at tolerable levels according to the recommendations of international regulatory agencies. In animal experiments for acute, subchronic and chronic toxicity, reproduction, mutagenicity, and teratogenicity the algae did not cause body or organ toxicity. In all instances, the Spirulina administered to the animals were at much higher amounts than those expected for human consumption. On the other hand there is scant information of the effects of the algae in humans. This area needs more research.
01 Mar 1996-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this article, the photoemission from CsI into gas has been investigated in He-, Ar- and CH 4 -based gas mixtures as a function of the electric field at the photocathode surface measurements were made both in laboratory, with a UV source, and in a beam with a RICH detector.
Abstract: The photoemission from solid surfaces into gas is important in view of the application of solid photocathodes in fast-RICH devices The photoemission from CsI into gas has been investigated in He-, Ar- and CH 4 -based gas mixtures as a function of the electric field at the photocathode surface measurements were made both in laboratory, with a UV source, and in a beam with a RICH detector The results are interpreted in terms of current models of electron transport in gas The electron collection efficiency, below gas ionization threshold, is reduced by backscattering This phenomenon is particularly important in He-based gas mixtures In CH 4 and Ar/CH 4 mixtures the backscattering is very low At high electric field, under charge multiplication, a full collection efficiency, similar to that in vacuum, is obtained in all gases investigated We discuss the parameters governing the choice of the gas mixture in this kind of photon detectors
TL;DR: It is concluded that human involucrin 5′-noncoding region contains at least three regulatory domains, a distal CaCl-responsive enhancer, a putative transcriptional silencer ( that interacts with AP-1 and YY1), and a proximal enhancer/promoter (that interacts withAP-1).
TL;DR: It was concluded that animal by-product meal can be used as a sole protein source in commercial diets for Nile tilapia fry, without affecting growth and food utilization of the fish, improving the economics of feeding in comparison with fish meal.
Abstract: Animal by-product meals (ABM) were substituted for fish meal in five experimental diets for Nile tilapia fry, Oreochromis niloticus (L), with 25%, 50%, 75% and 100% substitution. Two diets with 100% ABM were tested, one with 50:50 animal lipid:soybean oil, and the other with 100% fish oil as attractant. In general, the best growth and feeding performance was obtained with a control diet based on fish meal as the sole protein, but the results were not statistically different from those obtained with 75% and 100% ABM with soybean oil. A simple cost analysis suggested better economic efficiency when tilapia were fed with 100% ABM. It was concluded that animal by-product meal can be used as a sole protein source in commercial diets for Nile tilapia fry, without affecting growth and food utilization of the fish, improving the economics of feeding in comparison with fish meal.
TL;DR: In this paper, a free-radical mechanism for the oxidation of alkanes by aromatic peracids was proposed, which involves hydrogen abstraction from the OH group of peracides by an a...
Abstract: Evidences concerning a novel free-radical mechanism for the oxidation of alkanes by aromatic peracids are reported. The mechanism involves hydrogen abstraction from the OH group of peracids by an a...
TL;DR: Spirulina maxima, an edible micro-organism useful in human nutrition, was examined for its effect on general reproductive performance and for peri- and postnatal toxicity in rats at levels of 0, 10, 20 and 30% incorporated into the diet.
TL;DR: In this article, a complex Swift-Hohenberg equation was proposed to capture the main wave-vector selection rules for both degenerate and non-degenerate OPOs.
Abstract: Pattern formation near threshold in single longitudinal mode and large aspect ratio optical parametric oscillators (OPOs) operating near resonance are shown to be described by a complex Swift-Hohenberg equation. Such an equation is capable of capturing the main wave-vector selection rules for both degenerate and nondegenerate OPOs. \textcopyright{} 1996 The American Physical Society.
TL;DR: In this paper, a finite-time thermodynamics model for an Otto thermal cycle is proposed, which considers global losses in a simplified way lumped into a friction-like term, and takes into account the departure from an endoreversible regime through a parameter (R) arising from the Clausius inequality.
Abstract: We propose a finite-time thermodynamics model for an Otto thermal cycle. Our model considers global losses in a simplified way lumped into a friction-like term, and takes into account the departure from an endoreversible regime through a parameter (R) arising from the Clausius inequality. Our numerical results suggest that the cycle's power output and efficiency are very sensitive to that parameter. We find that R is the ratio of the constant-volume heat capacities of the reactants and products in the combustion reaction occurring inside the working fluid. Our results have implications in the search for new fuels for internal combustion engines.
TL;DR: In this article, a reaction mechanism involving the physical adsorption of water vapor molecules on the SiO2 surface and reaction between adspecies and SiO-Si species is proposed and discussed to interpret the logarithmic kinetics of residual stress evolution in evaporated SiO 2 films exposed to room air.
Abstract: Deposition of silicon dioxide thin films on silicon, germanium, and glass substrates has been accomplished by electron gun evaporation under various experimental conditions. The level of compressive residual stresses in evaporated SiO2 films determined just after deposition of films on Si or Ge substrates and the mass density of silica were found to be dependent on the substrate temperature and oxygen partial pressure in the evaporation chamber. Moreover, the intensity of compressive residual stresses decreased linearly as the logarithm of the exposure time of films to room air (aging time) was increased. After a compressive–tensile stress transition observed at a given aging time for films with relatively low densities, the intensity of tensile stresses continued to increase progressively with increasing aging time. The relative variation of residual stresses in SiO2 films was dependent on the mass density of the deposited material. Since the intensity of the absorption band of Si–OH radicals in the infrared spectra of SiO2 films exposed to room air increased with increasing aging time, the evolution of residual stresses was attributed to the effect of the hydration of silica by water vapor contained in room air. A reaction mechanism involving the physical adsorption of water vapor molecules on the SiO2 surface and reaction between adspecies and Si–O–Si species is proposed and discussed to interpret the logarithmic kinetics of residual stress evolution in evaporated SiO2 films exposed to room air.
TL;DR: In this paper, a procedure for the evaluation of the double integrals involved in the symmetric BE method is proposed, which consists in a regularization via integration by parts and in a successive numerical evaluation of weakly singular integrals.
Abstract: A procedure for the evaluation of the double integrals involved in the symmetric BE method is proposed, which consists in a regularization via integration by parts and in a successive numerical evaluation of weakly singular integrals. The procedure is applicable to curved elements and higher order shape functions and lends itself to a fairly straightforward implementation. Continuity is required for displacement modelling, while tractions may be modelled as piece-wise continuous. Some example problems characterized by the presence of curved boundaries or of cracks are analyzed using the proposed technique to demonstrate its effectiveness.
TL;DR: In this paper, the Co(II)-catalysed oxidation of alkyl- and aryl-sulfides was achieved under homogeneous and heterogeneous conditions using oxygen or air as the oxidant in the presence of excess aldehyde.
Abstract: The Co(II)-catalysed oxidation of alkyl- and aryl-sulfides was achieved under homogeneous and heterogeneous conditions using oxygen or air as the oxidant in the presence of excess aldehyde. The reactions in the homogeneous phase were carried out using the soluble Co(acac) 2 or Co(AAEMA) 2 complexes (AAEMA − = deprotonated form of 2-(acetoacetoxy)ethyl methacrylate) whereas the heterogeneous catalytic tests were carried out using the copolymers obtained by reaction of Co(AAEMA) 2 with acrylamides. Under suitable conditions excellent conversions and very good selectivities were achieved both in homogeneous and in heterogeneous phase. The supported complexes were recyclable with negligible loss of efficiency and did not suffer from metal leaching.
TL;DR: In this article, the authors studied the infiltration of an incompressible liquid in an initially dry (or partially dry), deformable sponge-like material made of a component in the slug-flow approximation.
TL;DR: In this article, the pump-and-probe technique was applied to a series of substituted oligothiophenes in solution and the observed dynamics were assigned to the intraband population relaxation associated with the internal energy redistribution process.
TL;DR: In this article, aromatic aldehydes are coupled to dl-hydrobenzoins on treatment with anhydrous TiCl3/CH2Cl2 solution at room temperature.
TL;DR: A cAMP regulated K+-selective channel from sea urchin sperm plasma membranes fused into planar bilayers that may have a role in sperm responses to the egg outer layer and/or the acrosome reaction is described.
TL;DR: In this article, the authors reviewed the convenience and possibility of utilizing thallium-based superconductors for power applications and discussed the basic properties of Tl-based systems such as the crystal structure, phase stability, weak-links, pinning problems and irreversibility lines.
Abstract: We have reviewed the convenience and possibility of utilizing thallium-based superconductors for power applications. Some basic properties of Tl-based systems such as the crystal structure, phase stability, weak-links, pinning problems and irreversibility lines are discussed first. Two basic approaches to conductor preparation are then described, the closed and the open one. Special attention is focused on the fabrication of Tl-1223 and Tl-2223 superconductors. In the case of the more successful open approach a two-step technological procedure is usually chosen: first, the basic precursor material without Tl is synthesized, then second, the precursor is thallinated in a one- or two-zone reaction chamber. The most important precursor preparation techniques are described including aerosol deposition from either solution or ink, electro-deposition, sol-gel methods such as spin- and dip-coating and screen-printing and painting. Finally, some properties of the produced conductors important for power applications are presented.
TL;DR: Chemical analysis showed that composition of yeast and mycelial walls was similar, and electrophoretic patterns of proteins extracted with SDS, beta 1, 3-glucanase, or chitinase were similar in walls of both morphologies, although some differential bands were identified.
TL;DR: The apparent slip velocity was a constant fraction of the maximal velocity for a given contraction ratio as mentioned in this paper, and was independent of L/D but was strongly influenced by the wall stress, the observed apparent slip velocities being comparable with those determined using the Mooney analysis on capillary flows.
Abstract: Nuclear magnetic resonance imaging has been used to investigate the flow of 0.2% aqueous solutions of xanthan gum. Apparent slip was observed in solutions made from the material supplied by UNAM but not in that supplied by Aldrich or Kelco. The apparent slip velocity was a constant fraction of the maximal velocity for a given contraction ratio. The apparent slip velocity also appeared to be independent of L/D but was strongly influenced by the wall stress, the observed apparent slip velocities being comparable with those determined using the Mooney analysis on capillary flows. After exposure to the action of a syringe pump, which reduced the mean molecular weight of the xanthan, the UNAM xanthan solution no longer exhibited apparent slip. Slip appears to be a function of molecular weight, possibly through sensitivity to the aspect ratio of the molecule.
TL;DR: In this paper, a geometrical technique is proposed to solve explicitly the critical conditions at localization for a quite general constitutive behaviour with isotropic elastic properties, which is closely related to the spectral properties (eigenvalues and eigenvectors) of the sum and difference of two tensors describing the inelastic effects.