Showing papers by "Instituto Politécnico Nacional published in 1993"
287 citations
TL;DR: Probably, the most workable solution to the hardening phenomenon may be the development of materials less prone to HTC phenomenon, and decreasing cooking time, increasing nutritive value, and improving sensory properties of seeds with HTC defect would have great nutritional and economical impact.
Abstract: Legumes are one of the world's most important sources of food supply, especially in developing countries, in terms of food energy as well as nutrients. Common beans are a good source of proteins, vitamins (thiamine, riboflavin, niacin, vitamin B6) and certain minerals (Ca, Fe, Cu, Zn, P, K, and Mg). They are an excellent source of complex carbohydrates and polyunsaturated free fatty acids (linoleic, linolenic). However, common beans have several undesirable attributes, such as long cooking times, being enzyme inhibitors, phytates, flatus factors, and phenolic compounds, having a "beany" flavor, and being lectins and allergens, which should be removed or eliminated for effective utilization. Grain quality of common beans is determined by factors such as acceptability by the consumer, soaking characteristics, cooking quality, and nutritive value. Acceptability characteristics include a wide variety of attributes, such as grain size, shape, color, appearance, stability under storage conditions, cooking properties, quality of the product obtained, and flavor. Storage of common beans under adverse conditions of high temperature and high humidity renders them susceptible to a hardening phenomenon, also known as the hard-to-cook (HTC) defect. Beans with this defect are characterized by extended cooking times for cotyledon softening, are less acceptable to the consumer, and are of lower nutritive value. Mechanisms involved in the HTC defect have not been elucidated satisfactorily. Attempts to provide a definitive explanation of this phenomenon have not been successful. The most important hypotheses that have been proposed to explain the cause of bean hardening are (1) lipid oxidation and/or polymerization, (2) formation of insoluble pectates, (3) lignification of middle lamella, and (4) multiple mechanisms. Most researchers have reported that the defect develops in the cotyledons. Recently, some authors have suggested that the seed coat plays a significant role in the process of common bean hardening. A better knowledge of cotyledon and seed coat microstructure may lead to a better understanding of the causes of seed hardness. In order to prevent the development of the HTC defect several procedures have been proposed: (1) appropriate storage, (2) controlled atmospheres, and (3) pretreatments. Probably, the most workable solution to the hardening phenomenon may be the development of materials less prone to HTC phenomenon. Decreasing cooking time, increasing nutritive value, and improving sensory properties of seeds with HTC defect would have great nutritional and economical impact.(ABSTRACT TRUNCATED AT 400 WORDS)
272 citations
TL;DR: An efficient computational implementation of a path deletion K shortest paths algorithm and a new algorithm for the same problem that avoids the last K−1 executions of a shortest path algorithm are presented, resulting in a suprising and very substantial reduction in the execution time.
239 citations
TL;DR: In this article, a numerical integration method for the interface constitutive laws is proposed, and the related consistent tangent modulus is derived, and an algorithm for the structural analysis in the presence of softening interfaces is presented.
212 citations
TL;DR: In this article, a simple preparation method for barium hexaaluminate-based catalysts to be used in catalytic combustion is described, which provides stable materials with a surface area of 15 m2/g after calcination at 1400°C.
Abstract: A simple preparation method for barium hexaaluminate-based catalysts to be used in catalytic combustion is described. Morphological and physico-chemical characterization data are given for Ba-Al-O (withBa/Al = 1/12) and for Ba-Mn-Al-O (with Ba/Mn/Al = 1/0.5/11.5; 1/1/11; 1/2/10) samples calcined at different temperatures. The preparation method here proposed provides stable materials with a surface area of 15 m2/g after calcination at 1400°C. The structural and morphological properties, as well as the results of activity tests in methane combustion, compare well with those reported in the literature for samples with the same composition and prepared according to a more complex preparation route.
170 citations
TL;DR: In this article, a nonlinear ABCD matrix derived from the aberrationless theory of self-focusing is introduced to treat the propagation of gaussian beams in materials with Kerr nonlinearity.
155 citations
TL;DR: Different signals after contact with either epithelial cell type leads to the morphological transformation and/or induction of adhesin synthesis by T. vaginalis, and parasites adhering to either VECs or HeLa cells were induced to synthesize greater amounts of the four previously described adhesins.
Abstract: Summary
The cytoadherence of Trichomonas vaginalis, the sexually transmitted flagellated protozoan, to vaginal epithelial cells (VECs) is the key to infection. Electron microscopy revealed that in vitro-grown parasites having typical globular shape transformed rapidly after contact with VECs into thin, flat, amoeboid cells, maximizing the area of adhesion to the surface of VECs. Amoebic trichomonads formed filopodia and pseudopodia, which interdigitated at distinct sites on the plasma membrane of target cells. In contrast, the amoeboid transformation did not occur for T. vaginalis interacting with He La cells, the previously used in vitro host model cell. Initial parasitism of VECs by a single organism was followed by establishment of a monolayer of trichomonads on the host cell. Finally, parasites adhering to either VECs or HeLa cells were induced to synthesize greater amounts of the four previously described adhesins. Therefore, distinct signals after contact with either epithelial cell type leads to the morphological transformation and/or induction of adhesin synthesis by T. vaginalis.
134 citations
TL;DR: In this paper, the effect of K-doping on the surface and catalytic properties of sub-monolayer vanadia/titania de-NOxing catalysts is carried out.
Abstract: An investigation of the effect of K-doping on the surface and catalytic properties of sub-monolayer vanadia/titania de-NOxing catalysts is carried out Samples having different vanadium and potassium loadings have been investigated by means of Fourier-transform infrared spectroscopy (FT-IR), temperature-programmed desorption (TPD), temperature-programmed surface reaction (TPSR) and temperature-programmed reaction (TPR) techniques Isolated vanadyls and polymeric metavanadate species are present on the surface of undoped catalysts; both species increase on increasing the V2O5 loading in the range 028–53% w/w TPSR and TPR data provide evidence for a greater reactivity of polymeric metavanadate species as compared to isolated vanadyls Besides, a different type of isolated vanadyl appears to form at high loadings Ammonia is adsorbed at vanadium sites in the form of molecularly coordinated species and of ammonium ions Coordinated species show a higher thermal stability than ammonium ions Ammonia is also coordinated at titanium sites to give a more weakly held species Upon K-doping the stretching frequencies of surface vanadyls are lowered due to the production of strong oxide basic anions on the catalyst surface This reduces the Lewis acidity of vanadium ions IR and TPD experiments indicate that both molecularly chemisorbed ammonia and ammonium ions are present in much lower amounts and are less strongly held on K-doped samples TPD and TPSR data further indicate that the alkali dopant poisons preferentially Lewis acid sites associated with vanadium rather than with Ti4+ ions TPSR and TPR data show that alkali doping reduces markedly the nitric oxide conversion (associated with the number of active sites), but not the temperature threshold of the SCR reaction (associated with the intrinsic reactivity of the active sites) The lower number of active sites on alkali-doped catalyst can be related to the poisoning of both Bronsted and Lewis vanadium acid sites due to alkali addition, which results in a lower ammonia surface coverage
102 citations
TL;DR: A single-frequency, diode-pumped, Er-Yb:glass microchip laser at a 1530-nm wavelength has been designed and operated and a slope efficiency of 22% has been obtained.
Abstract: A single-frequency, diode-pumped, Er-Yb:glass microchip laser at a 1530-nm wavelength has been designed and operated. An output power of greater than 25 mW, a linewidth narrower than 1 kHz, and a slope efficiency of 22% have been obtained.
98 citations
TL;DR: In this paper, the ABCD law is extended to resonators of femtosecond self-mode-locked solid-state lasers containing a self-focusing Kerr medium, and simple closed-form results valid for arbitrary resonator configurations are obtained and criteria for designing and optimizing resonators for selfmode locked lasers are discussed.
97 citations
TL;DR: A new experimental model to assess analgesic activity of both analgesic and non‐steroidal antiinflammatory drugs in described uses the unilateral intra‐articular knee injection of an uric acid suspension in mineral oil to produce acute inflammation, pain, and functional motor impairment.
Abstract: A new experimental model to assess analgesic activity of both analgesic and non-steroidal antiinflammatory drugs in described It uses the unilateral intra-articular knee injection of an uric acid suspension in mineral oil to produce acute inflammation, pain, and functional motor impairment The model, named “pain-induced functional impairment in the rat” (PIFIR) assesses analgesic activity by measuring the capacity to walk with the injured extremity The procedure determines both the potencies of analgesic drugs and the time course of the effect Analgesia of selected reference agents was followed for 4 h and the effect versus time curves were constructed The area under the curve (effect versus time), an expression of the overall activity during the observation period, increased in a dose-dependent manner The area under the curve, Emax, TEmax, and ED50 of reference agents tested are reported The PIFIR procedure was sensitive to opiate and nonopiate analgetics (nonsteroidal antiinflammatory drugs) and possibly steroidal antiinflammatory drugs These characteristics make it suitable for screening purposes © 1993 Wiley-Liss, Inc
TL;DR: The base-catalyzed isomerization of N-benzylidene derivatives of β-polyfluoro-β-aminocarboxylic esters which are hydrolyzed to corresponding amino acids in high overall yields is described in this paper.
TL;DR: In this paper, the analysis of elastic quasi-brittle structures containing cohesive cracks and contacts with friction is given a unitary formulation in the framework of incremental plasticity, where integral equations for displacements and tractions are enforced by a weighted-residual Galerkin approach so that symmetry is preserved in the key operators.
Abstract: The analysis of elastic quasi-brittle structures containing cohesive cracks and contacts with friction is given a unitary formulation in the framework of incremental plasticity. Integral equations for displacements and tractions are enforced by a weighted-residual Galerkin approach so that symmetry is preserved in the key operators (in contrast to collocation BE approaches) and cracks (either internal or edge cracks) can be dealt with by a single-domain BE formulation. The space-discrete problem in rates is expressed as a linear complementarity problem centered on a symmetric matrix or, equivalently, as a quadratic programming problem in variables pertaining to the displacement discontinuity locus only. Criteria for overall instabilities and bifurcations are derived from this formulation. The BE approach proposed and implemented by a suitable time-stepping technique, is comparatively tested by numerical solutions of cohesive-crack propagation problems.
TL;DR: In this paper, a radical process for the thermal decomposition of IBDA in the presence of sodium azide was proposed. But this method is not suitable for the case of carbon-centered radicals.
TL;DR: In this paper, a 3,3″-dialkylterthiophenes were polymerized and the effects of the presence and position of the alkoxy group on the polymerization reaction and on polymer properties were discussed.
Abstract: The polymerization of 3,3″-dialkylterthiophenes overcomes the lack of regiospecificity associated (to some extent) with all the polymerization methods in use, thus allowing the preparation of perfectly regioregular polymers endowed with enhanced electrical and optical properties. Moreover, the larger spacing of the alkyl chains achieved with the insertion of an unsubstituted thiophene unit confers to such regioregular polymers an extraordinary doping stability. Two regiochemically defined alkoxy-substituted terthiophenes were also polymerized and the effects of the effects of the presence and position of the alkoxy group on the polymerization reaction and on the polymer properties are discussed. © 1993 John Wiley & Sons, Inc.
TL;DR: The hyperholomorphic Bergmann kernel function *B for a domain R is introduced as the special quaternionic "derivative" of the Green function for R in this paper.
Abstract: The hyperholomorphic Bergmann kernel function *B for a domain R is introduced as the special quaternionic "derivative" of the Green function for R. It is shown that *B is hyperholomorphic, Hermitian symmetric and reproduces hyperholornorphic functions. We obtain an integral representation of *B as a sum of two integrals. One of them gives a smooth function, and the other describes the behaviour of +B near a boundary. To investigate the hyperholomorphic Bergmann function for some fixed class of hyperholornorphic functions we have to use not only the properties of just this class but also those of some other classes. The second fact is completely unpredictable from the complex analysis point of view. The connection between the hyperholomorphic Bergmann projector (the integral operator with the kernel $B) and some classical multidimensional singular integral operators is established. I
18 May 1993
TL;DR: A WWD- and STFT-based virtual instrument to measure instantaneous frequency and amplitude of the fundamental component of transient signals is presented and many simulations have confirmed that using the proposed low-cost VI gives measurements of good accuracy, also in the presence of noise.
Abstract: This paper deals with an application of the Wigner-Ville distribution (WVD) and with usual digital-processing techniques, such as the short-time Fourier transform (STFT), used in dedicated instrumentation for measuring nonstationary signals. The processed real signals are made analytic by means of Hilbert transformations; then suitable implementations of the windowed STFT and of the pseudo Wigner-Ville distribution (PWVD) in the time domain have been performed. Particularly, the fast Hartley transform (FHT) is used to evaluate the PWVD in the real domain. Furthermore, the use of an efficient interpolation algorithm and of a suitable flat-top windowing function is proposed in order to give accurate real-time frequency and amplitude measurements, respectively. With this aim, a dedicated digital system was set up, which uses the LabVIEW software to create virtual instruments (VI), suitable to process the data sequences. Finally, applications of the suggested techniques in analyzing noisy data were also investigated. >
TL;DR: In this article, it was shown that the angular velocity equations of a symmetric rigid body can be globally stabilized by means of linear feedback when two control torques act on the body.
TL;DR: A continuous-wave, lamp-pumped, intracavity frequency-doubled laser that provides as much as 13.5 W of power in the green, linearly polarized TEM00 output, and very low misalignment sensitivity is developed.
Abstract: We have developed a continuous-wave, lamp-pumped, intracavity frequency-doubled laser that provides as much as 13.5 W of power in the green, linearly polarized TEM00 output, and very low misalignment sensitivity. These results have been obtained with a Nd:YLF rod of large cross section, a lithium triborate frequency-doubling crystal, and a novel resonator design. We demonstrate that the problem of power fluctuations and chaos in this class of lasers (the green problem) can effectively be overcome and that fluctuations of less than ±1% on a millisecond time scale can be obtained.
TL;DR: In this paper, a quasi-continuous wave laser operation of Cr 4+ -doped Y 2 SiO 5 at room temperature was demonstrated for the first time, using a Nd:YLF laser at 1047 nm.
TL;DR: Lactobacillus curvatus SB13 biosynthetized during growth and excreted into the culture medium an inhibitor active against Listeria monocytogenes, Staphylococcus aureus, and some other Gram-positive bacteria.
Abstract: Lactobacillus curvatus SB13 biosynthetized during growth and excreted into the culture medium an inhibitor active againstListeria monocytogenes, Staphylococcus aureus, and some other Gram-positive bacteria. The native activity was linked to a non-dialyzable proteinaceous complex, destroyed by proteases, with an apparent molecular weight greater that 10 kDa. It showed a hydrophobic character, being soluble in alcohols and not denaturated by several organic solvents. The molecule was partially purified by ammonium sulfate precipitation and hydrophobic interaction chromatography.
TL;DR: The results suggest that the defect band which lies 0.13 eV below the band gap (1.48 eV in CdTe) may also be related to tellurium vacancies, and the ratio of intensities between this defect band and the 1.1-eV feature is highly variable suggests that the relationship is not simple.
Abstract: We have studied at cryogenic temperatures photoluminescence features which lie more than 0.15 eV below the band edge in ${\mathrm{Zn}}_{\mathit{x}}$${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$Te (0\ensuremath{\le}x\ensuremath{\le}0.09) crystals. The same features, namely a defect band which lies at about 0.13\char21{}0.20 eV below the band-gap energy and a peak at 1.1 eV, that are observed in pure CdTe samples are observed in these alloy materials. In annealed samples we observe that the 1.1-eV feature, which has been attributed to tellurium vacancies, increases with fast cooling. Increased concentrations of tellurium vacancies can be understood in terms of the phase diagram of CdTe which indicates that higher concentrations of excess Cd appear in CdTe quenched from high temperatures. We also observe an absorption transition near 1.1 eV by photothermal deflection spectroscopy (PTDS). The PTDS phase shifts show that the deep defect is a bulk effect rather than a surface effect. The well-defined absorption peak suggests that the states contributing to the 1.1-eV transition are both localized. Our results also suggest that the defect band which lies 0.13 eV below the band gap (1.48 eV in CdTe) may also be related to tellurium vacancies. However, the fact that the ratio of intensities between this defect band and the 1.1-eV feature is highly variable suggests that the relationship is not simple. The origin of the defect band and its phonon replicas remains controversial.
TL;DR: In this article, the authors considered local constitutive relations for the rate of change of the contact forces, the evolution of contact normals, the mechanism of local failure, and the density of contacts in a particular class.
Abstract: Micromechanically based constitutive relations for two-dimensional flow of granular materials are presented. First, overall stresses are related to the interparticle forces and microstructural parameters. Then, the overall velocity gradient is related to measures of relative sliding and rotation of granules. The notion of the class of granules with continuously evolving distribution of contact normals, is introduced. Simple local constitutive relations are considered for the rate of change of the contact forces, the evolution of the contact normals, the mechanism of local failure, and the density of contacts in a particular class. This leads to macroscopic rate constitutive equations through a Taylor averaging method. Due to nonlinearity of the rate constitutive equations, the response is computed by an incremental procedure. As an illustration, the overall response of a two-dimensional assembly of discs subjected to an overall shearing deformation is determined. In addition, explicit results are presented for the evolution of fabric, contact forces, and the history of active and inactive classes of contacts. The stress-strain relations and the evolution of fabric and contact forces are in qualitative agreement with the observed behaviour of granular materials. In light of these results, the mechanisms of failure and inelastic deformation of dense as well as loose granular materials are discussed.
TL;DR: In this paper, it was shown that thermal focusing and birefringence set an intrinsic limitation to the fundamental mode volume, such that the maximum usable TEM00 spot size in the rod is about 1 mm.
Abstract: The output characteristics of a continuous-wave lamp-pumped Nd:YAG laser using a rod of 6.4 mm diameter and stable resonators with large fundamental mode volume have been systematically investigated by testing various resonators. It is shown that, independently of the resonator, thermal focusing and birefringence set an intrinsic limitation to the fundamental mode volume, such that the maximum usable TEM00 spot size in the rod is about 1 mm, even if in principle the rod cross-section could sustain a much larger mode. A qualitative theoretical model explains the experimental data. A maximum output power of about 40 W was observed in a nearly diffractionlimited beam.
TL;DR: The trans-Pd(COOR)ClL2 (PPh3, R = Et, n-Pr, iso-Pr and iso-Bu as discussed by the authors, sec-Bu, 2-ethoxyethyl, cyclopentyl, cyclohexyl; L = 1,2-diphenylphosphinoethane and Et = Et.
TL;DR: This inhibitor belongs to the potato-I inhibitor family, showing the closest homology with the Lycopersicum peruvianum trypsin inhibitor, and with the proteinase inhibitor 5 extracted from the seeds of Cucurbita maxima.
Abstract: A protein proteinase inhibitor was purified from a seed extract of amaranth (Amaranthus hypochondriacus) by precipitation with (NH4)2SO4, gel-filtration chromatography, ion-exchange chromatography, and reverse-phase high-performance liquid chromatography. It is a 69-amino acid protein with a high content of valine, arginine, and glutamic acid, but lacking in methionine. The inhibitor has a relative molecular weight of 7400 and an isoelectric point of 7.5. It is a serine proteinase inhibitor that recognizes chymotrypsin, trypsin, and trypsin-like proteinase activities extracted from larvae of the insect Prostephanus truncatus. This inhibitor belongs to the potato-I inhibitor family, showing the closest homology (59.5%) with the Lycopersicum peruvianum trypsin inhibitor, and (51%) with the proteinase inhibitor 5 extracted from the seeds of Cucurbita maxima. The position of the lysineaspartic acid residues present in the active site of the amaranth inhibitor are found in almost the same relative position as in the inhibitor from C. maxima.
TL;DR: It was concluded that vascular and left ventricular stiffness have a close relationship with arterial hypertension but not with hypercholesterolemia, and the hypertensive patients had a higher prevalence of carotid atherosclerosis and a higher scoring grade of severity.
Abstract: Five groups of 20 patients each were studied to analyze the vascular dynamics and structure of the elastic arteries. Group I consisted of healthy young individuals (27 +/- 4 years); Group II of healthy adults (46 +/- 9 years); Group III of normotensive hypercholesterolemic adults (45 +/- 12 years and serum cholesterol > 239 mg/dl); Group IV of hypertensive normocholesterolemic adults (56 +/- 13 years); and Group V of hypertensive hypercholesterolemic adults (56 +/- 9 years). The differential arterial pressure was estimated and divided by the volume change (delta P/delta V) of the aorta and the carotid and brachial arteries. The volume change was calculated using the "cylinder formula", measuring the radius from the ultrasonographic vessel image and assigning the cylinder a height of 1 cm. The A/E index of the Doppler transmitral spectrum and the maximum velocity flow using Doppler in the above arteries were calculated. The presence of carotid atherosclerosis was observed and given an arbitrary scoring grade of 0, 1, or 2. A higher arterial and ventricular stiffness was found in the hypertensive patients regardless of the presence of hypercholesterolemia. A higher fall in Doppler velocity and an increase in atherosclerosis lesions were found in Group V. Based on the results of this study, it was concluded that vascular and left ventricular stiffness have a close relationship with arterial hypertension but not with hypercholesterolemia. The hypercholesterolemic patients had a higher prevalence of carotid atherosclerosis and a higher scoring grade of severity.
TL;DR: The metabolism of cyst-wall polymers is emphasized as a potential target to inhibit cyst formation with specific drugs that would be in principle, harmless to the host.
TL;DR: Single-mode operation of a continuous-wave Er:Yb:phosphate glass laser pumped at 980 nm by a InGaAs index-guided diode laser has been achieved for what is to the authors' knowledge the first time.
Abstract: Single-mode operation of a continuous-wave Er:Yb:phosphate glass laser pumped at 980 nm by a InGaAs index-guided diode laser has been achieved for what is to our knowledge the first time. The maximum output power obtained at 1540 nm is 10 mW, and the width of the spectral line is less than 15 kHz.
TL;DR: Ion substitution experiments indicate that the permeability to Na+, Ca2+, and Mg2+ contributes to the sperm resting membrane potential and that hyperpolarizing swollen sperm with valinomycin increases intracellular pH (pHi) in the same way as speract, thus the sPeract‐inducedhyperpolarization may be responsible for the pHi increase.