Showing papers by "Instituto Politécnico Nacional published in 1992"
477 citations
TL;DR: It was concluded that silymarin can protect against APAP intoxication through its antioxidant properties, possibly acting as a free‐radical scavenger.
Abstract: The effect of silymarin on liver damage induced by acetaminophen (APAP) intoxication was studied. Wistar male rats pretreated (72 h) with 3-methylcholanthrene (3-MC) (20 mg kg-1 body wt. i.p.) were divided into three groups: animals in group 1 were treated with acetaminophen (APAP) (500 mg kg-1 body wt. p.o.), group 2 consisted of animals that received APAP plus silymarin (200 mg kg-1 body wt. p.o.) 24 h before APAP, and rats in group 3 (control) received the equivalent amount of the vehicles. Animals were sacrificed at different times after APAP administration. Reduced glutathione (GSH), lipid peroxidation and glycogen were measured in liver and alkaline phosphatase (AP), gamma-glutamyl transpeptidase (GGTP) and glutamic pyruvic transaminase (GPT) activities were measured in serum. After APAP intoxication, GSH and glycogen decreased very fast (1 h) and remained low for 6 h. Lipid peroxidation increased three times over the control 4 and 6 h after APAP treatment. Enzyme activities increased 18 h after intoxication. In the group receiving APAP plus silymarin, levels of lipid peroxidation and serum enzyme activities remained within the control values at any time studied. The fall in GSH was not prevented by silymarin, but glycogen was restored at 18 h. It was concluded that silymarin can protect against APAP intoxication through its antioxidant properties, possibly acting as a free-radical scavenger.
316 citations
TL;DR: Preliminary antimicrobial screening against Candida albicans and selected Gram-positive and Gram-negative bacteria of methanol extracts prepared from eight Mexican medicinal plants, noted for their antiseptic properties, was conducted, finding significant activity exhibited for extracts of Ratibida latipalearis, Teloxys graveolens, Dodonaea viscosa, Hyptis albida, H. pectinata and H. verticillata.
284 citations
TL;DR: Two-and one-dimensional steady-state isothermal mathematical models of monolith reactors for selective catalytic reduction (SCR) of NOx by NH3 are compared for circular, square and triangular geometry, as well as for linear and Rideal kinetics as discussed by the authors.
Abstract: Two-and one-dimensional steady-state isothermal mathematical models of monolith reactors for selective catalytic reduction (SCR) of NOx by NH3 are compared for circular, square and triangular geometry, as well as for linear and Rideal kinetics. Solutions for the two-dimensional model demonstrate that, as the reaction rate decreases from infinity to zero, the Sherwood number varies from the values of the Nusselt number characteristic of the Graetz-Nusselt problem with constant wall temperature to those with constant wall heat flux but with peripherally varying temperature. A lumped-parameter treatment, based on similarity with the constant wall temperature heat transfer problem, agrees satisfactorily with the solutions for a far more expensive two-dimensional model. The agreement is excellent for square channels, but the NH3 slip tends to be underestimated in the triangular geometry. The one-dimensional model reproduces successfully experimental effects of the NH3/NO feed ratio, and of the area velocity and the size of monolith channels.
207 citations
TL;DR: In this article, a "symmetric" boundary element method based on a weighted residual Galerkin approach for elastoplastic analysis is revisited and its computer implementation for two-dimensional homogeneous problems is described.
Abstract: A “symmetric” boundary element method based on a weighted residual Galerkin approach for elastoplastic analysis is revisited and its computer implementation for two-dimensional homogeneous problems is described.
167 citations
TL;DR: It is hypothesized that the skilled individuals may be more adept at making subtle adjustments to landing surfaces by continual update during execution of the movement, while in unskilled subjects this capability is less evident.
Abstract: A motor performance which involves multijoint coordination and belongs to the natural repertoire of motor behavior has been studied. Displacements have been related to EMG in the lower limb when taking off and landing from a jump down (45 cm) onto two surfaces of differing compliance in two populations of teenage girls: skilled and unskilled. To evaluate the performance, an index was defined taking into account: 1) the time required for reaching stability (1 body weight) after landing, and 2) the amount of sway during the stabilization time. Despite the apparent intra and inter subject similarities in performing the jump-down, slight differences were observed in both the kinematics and electromyogram patterns. During takeoff, two strategies were identified that were not related to either skill or landing surface compliance. The most common strategy, "Push Off", is characterized by almost full joint extension when departing from the jump platform and includes a swing period during flight. The other strategy, "Roll Off", is characterized by joint flexion at departure and continual extension during midflight. While the ankle dorsiflexor, tibialis anterior, is active in preparation for the takeoff phase in both strategies, it is followed by activation of the ankle plantarflexors, lateral gastrocnemious and soleus and the hip/knee musculature, rectus femoris, biceps femoris, and vastus lateralis, only in the push off strategy. The roll off strategy is characterized by a lack of other muscle activation prior to takeoff. At landing, regardless of the strategy used in takeoff, onset of muscles followed the same sequence for both landing surfaces; ankle musculature activity began first followed by activity in the knee and hip musculature. The onset of the musculature occurred closer to landing when landing on the more compliant surface. Skilled subjects were characterized by adjustments in amount of ankle extension present at landing and concomitant flexion post-landing with respect to landing surface. When landing on the rigid surface, the ankle was more plantarflexed and onset of the dorsiflexor occurred after that of the plantarflexors; on foam, dorsiflexor activity was coincident with the plantarflexors. Ankle joint range of motion post-landing was subsequently larger when landing on the rigid surface. In contrast, unskilled individuals used a default strategy for landing on both surfaces where the ankle position and movement was between that seen for the two conditions in the skilled individual. It is suggested the landing and takeoff phases are programmed independently in both skilled and unskilled subjects.(ABSTRACT TRUNCATED AT 400 WORDS)
146 citations
TL;DR: This study demonstrates changes in cumulative burying behavior during various phases of the rat estrous cycle, including low levels of burying behavior among females tested in early proestrus, metestrus or diestrus and ovariectomized females.
105 citations
TL;DR: In this article, the X-ray structures of fifteen exocyclic Nacyl groups were compared with known structures of similar compounds and the conclusions drawn were considered relvant for a better understanding of the ever increasing role which amide groups play in stereoselective syntheses.
Abstract: The X‐ray structures of fifteen 1, 3‐imidazolidine, 1, 3‐oxazolidine, 1, 3‐dioxan‐4‐one, and hydropyrimidine‐4(1H)‐one derivatives are described (Table 2) and compared with known structures of similar compounds (Figs. 1–20). The differences between structures containing exocyclic N‐acyl groups and those lacking this structural element arise from the A1,3 effect of the amide moieties. Even t‐Bu groups are forced into axial positions of six‐ring half‐chair or into flag‐pole positions of six‐ring twist‐boat conformers by this effect (Figs. 16–20). In the N‐acylated five‐membered heterocycles, a combination of ring strain and A1, 3 strain leads to strong pyramidalizations of the amide N‐atoms (Table 1) such that the acyl groups wind up on one side and the other substituents on the opposite side of the rings (Figs. 4–9 and Scheme 3). Thus, the acyl (protecting!) groups strongly contribute to the steric bias between the two faces of the rings. Observed, at first glance surprizing stereoselectivities of reactions of these heterocycles (Schemes 1 and 2) are interpreted (Scheme 3) as an indirect consequence of the amide A1, 3 strain effect. The conclusions drawn are considered relvant for a better understanding of the ever increasing role which amide groups play in stereoselective syntheses. Copyright © 1992 Verlag GmbH & Co. KGaA, Weinheim
100 citations
TL;DR: The present results are fully consistent with the hypothesis of a hydrostatic pressure-triggered mechanism of spore germination, and revealed that the process is composed of two discrete phases separated by a variable lag: complete eversion of the polar filament, and passage of the main sporoplasm mass along the tube.
Abstract: Spores of the microsporidium Nosema algerae were stimulated to germinate in vitro while observed with video-enhanced contrast microscopy. Field-by-field playback of tape-recorded sequences yielded the first serial illustrations and kinematic analysis of the explosive discharge of the polar filament and the sporoplasm. The filament emerges from the anterior pole of the spore in a regularly pitched helicoidal course along a nearly straight axis, with a mean maximum instant velocity of 105 μm/s. Just before elongation is completed the filament tip follows a tortuous path that often results in a curved or spiralling terminal configuration. Then elongation stops and, after a lag that may vary from less than 15 to over 500 ms, the sporoplasm pours out at the filament tip forming a globule that quickly grows up to a size larger than its original volume within the spore. Concomitantly, the helical filament becomes straightened and frequently the spore body is pulled forward. Thereafter a relaxed filament, usually 5–10% shorter than when maximally extended, remains connecting the empty spore case and the sporoplasmic droplet. Experiments with hyperosmolar media produced a considerable slowdown of filament extrusion and often precluded sporoplasm discharge. The present results are fully consistent with the hypothesis of a hydrostatic pressure-triggered mechanism of spore germination, and revealed that the process is composed of two discrete phases separated by a variable lag: (1) complete eversion of the polar filament, and (2) passage of the main sporoplasm mass along the tube. The data provide a preliminary basis toward the conception of a quantitative physical model of microsporidian spore germination. © 1992 Wiley-Liss, Inc.
87 citations
TL;DR: In this article, the authors studied the characteristics associated with the activation of the N-methyl-D-aspartate (NMDA) subtype of the glutamate receptor on the release of dopamine in the striatum of awake rats as measured by brain microdialysis technique.
86 citations
TL;DR: In this paper, a semiclassical treatment is presented which allows to derive an explicit analitic expression for the contribution of nuclei relaxation in terms of vibrational spectroscopic observables.
TL;DR: In this article, a lumped parameter model of monolith SCR reactors is developed which accounts for both inter-and intra-phase transport of reactants, and implements an approximate analytical solution for diffusion and reaction inside the pores of the monolith walls suitable for specific rideal SCR kinetics.
TL;DR: A polynomial time algorithm to decide liveness for bounded free choice nets is proposed, thus proving an enlarged version of a conjecture raised by Jones (1977) about linear algebraic calculation of deadlocks and traps.
TL;DR: In this article, a broad class of elastic-plastic constitutive laws with internal variables (occuring in pairs of conjugate kinematic and static quantities) are derived for the time discretization of initial-boundary value problems.
Abstract: Reference is made to a broad class of elastic-plastic constitutive laws with internal variables (occuring in pairs of conjugate kinematic and static quantities). Their Euler backward-difference, ‘stepwise-holonomic’ formulation is derived for the time discretization of initial-boundary value problems. The space discretization is performed by systematically using the notion of ‘generalized variables’ and by generating overall, average constitutive laws for finite elements (instead of enforcing the material model in some points). Some categories of finite element models in generalized variables are comparatively discussed. Two pairs of dual extremum characterizations of the solution to the boundary value problem for a finite load step are established.
TL;DR: In this paper, a new method for numerical calculation of the zero-order Hankel (Fourier-Bessel) transform that has a high computational efficiency and an accuracy that can be 2 orders of magnitude greater than that of the standard quasi-fast Hankel procedure is described.
Abstract: We describe a new method for the numerical calculation of the zero-order Hankel (Fourier–Bessel) transform that has a high computational efficiency and an accuracy that can be 2 orders of magnitude greater than that of the standard quasi-fast Hankel procedure. The new method offers particular advantages in calculating optical beam propagation and resonator modes at high Fresnel numbers.
TL;DR: The results suggest that actin participate in calmodulin translocation to the postacrosomal region during acrosome reaction, in maintaining the acrosomes structure, and perhaps also in sperm motility.
Abstract: The presence of actin has been determined in mammalian spermatozoa. However, its function in these cells is still almost unknown. Only in boar spermatozoa has evidence for F-actin and a possible function for it been presented. In this work, actin distribution and F-actin were determined in uncapacitated, capacitated, and acrosomal-reacted guinea pig spermatozoa, by means of monoclonal and polyclonal antibodies, using an indirect immunoperoxidase technique, and by the use of rhodamine-phalloidin. With the last probe we found filamentous actin in these cells. By both techniques, actin was detected in the acrosome and in the entire tail. In some cells with acrosomal reaction, actin was also detected in the equatorial and in the postacrosomal regions. SDS-PAGE and Western blots immunostained with monoclonal and polyclonal anti-actin antibodies confirmed the presence of actin in extracts of guinea pig spermatozoa. Actin was also detected in preparations of Percoll-purified spermatozoa. We have communicated that guinea pig spermatozoa show a change on calmodulin location during the acrosome reaction. They present it first in the equatorial region and later in the postacrosomal region. To determine if F-actin participates in this calmodulin translocation, we studied the effect of cytochalasin D. It was found that the number of cells with calmodulin in the equatorial region increased in the presence of cytochalasin D while the number of cells with calmodulin in the postacrosomal region decreased. We also found that after cytochalasin D treatment acrosome loss was increased and sperm motility was slightly inhibited. Our results suggest that actin participate in calmodulin translocation to the postacrosomal region during acrosome reaction, in maintaining the acrosome structure, and perhaps also in sperm motility.
TL;DR: Comparison of activity between cysts and the total cell population in 48- and 72-h-old encysting cultures suggested that chitinase may start to accumulate in the pre-cyst forms, and like other chit inases, the cyst enzyme preferred nascent over preformed chitIn as substrate.
TL;DR: The shape of a fatigue crack tip as influenced by an air or a vacuum environment has been investigated in two stainless steels and an aluminum alloy under plane strain conditions and at crack growth rates in the Paris region, the crack tip opening displacement (CTOD) is much larger in vacuum than in air as discussed by the authors.
Abstract: The shape of a fatigue crack tip as influenced by an air or a vacuum environment has been investigated in two stainless steels and an aluminum alloy Under plane strain conditions and at crack growth rates in the Paris region, the crack tip opening displacement (CTOD) is much larger in vacuum than in air, a circumstance attributed to strain localization in air due to the presence of moisture and the absence of strain localization in vacuum In type 304 stainless steel, a strain-induced transformation from austenite to martensite occurs at the crack tip, and the extent of this strain-induced transformation in type 304 stainless steel is consistent with the degree of blunting taking place at the crack tip as influenced by the environment In air, the extent of transformation is a function of the ΔK level, and as a result, the crack opening level is found to differ in a ΔK decreasing test as compared to aAK increasing test Fatigue striations are observed in air but are absent in vacuum It is proposed that the greater extent of blunting in vacuum is responsible for the absence of striations in vacuum
TL;DR: The jelly-induced hyperpolarization may lead to the intracellular alkalinization required to trigger the AR, and, on its own or via pHi, may regulate Ca2+ transport systems involved in this process.
TL;DR: In this article, the authors provide sufficient conditions for the existence of periodic solutions to some three-body problems and find periodic solutions as minima of the associated action integral and are shown to be free of double and triple collisions.
Abstract: We provide sufficient conditions for the existence of periodic solutions to some three-body problems. Periodic solutions are found as minima of the associated action integral and are shown to be free of double and triple collisions.
TL;DR: The photoacoustic technique is used to investigate the thermal diffusivity of Ge x Te 1-x glasses as a function of composition and the observed dependence on the composition is explained on the basis of the chemically ordered network model.
Abstract: The photoacoustic technique is used to investigate the thermal diffusivity of ${\mathrm{Ge}}_{\mathit{x}}$${\mathrm{Te}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$ glasses as a function of composition. The observed dependence on the composition is explained on the basis of the chemically ordered network model. This interpretation is further supported by x-ray and electrical resistivity measurements.
TL;DR: In this paper, the effect of spraying a solution of sodium hydroxide onto sugarcane bagasse pith, in such a low volume that no free liquid was present, was evaluated with respect to Single Cell Protein production (SCP), and biological degradability.
TL;DR: In this paper, the Doppler centroid can be used to improve the computational efficiency of frequency domain focusing techniques, provided that SAR raw data are previously modified and a space-varying non-dimensional filter is applied to the focused image.
Abstract: SAR data spatially sampled at the Nyquist limit can be correctly processed if the Doppler centroid is precisely known. Whenever the Doppler centroid shows rapid variations either with range or azimuth, more care is required in order to take advantage of the computational efficiency of frequency domain techniques. It is shown that such focusing techniques can still be exploited, provided that SAR raw data are previously modified and a space-varying nondimensional filter is applied to the focused image. The computational cost increases, but it is still smaller than time-space domain processing. Results obtained with simulated SIR-C/X-SAR data and SPOTlight geometries are presented. >
TL;DR: In this paper, a macroscopic mechanical theory for ceramic-like materials undergoing isothermal deformations is presented, which describes an elastic brittle material which is damageable only under tensile loading.
TL;DR: The results support the existence of cholinergic neurotransmission within the SNc that increases the firing rate of nigrostriatal dopaminergic neurons, enhancing dopamine turnover in neostriatum without changes in AA release and suggest that the PPN could be the origin of Cholinergic afferents to theSNc that modulate the activity of dopaminergy neurons, through activation of muscarinic cholinerential receptors.
TL;DR: The reverse Perlin effects observed for all CH 1J coupling constants in 1,3-dithiane, i.e., 1J(CHa x) > 1J (CHe q), seem to support the existence of a dominant σc - s→σ*c - h stereoelectronic interaction, which leads to a weakening of the equatorial CH bonds in this heterocycle.
TL;DR: In this article, a TEM00 polarized beam was extracted from a Nd: YLF rod of large cross-section (6.35 mm diameter) by an appropriate resonator design, which uses the rod as mode selecting aperture.
Journal Article•
TL;DR: According to the information obtained in the study, brucellosis in Mexico has the following characteristics: it is related to gender but not to occupation; affects persons in all age groups, social strata and is independent of size of the community of residence.
Abstract: Brucellosis is an important and widely distributed zoonosis in Mexican cattle which also affects an unknown proportion of the human population. This report presents the brucellosis antibody levels registered in the National Seroepidemiology Survey (NAS) in sera obtained from 66,982 healthy persons from one to 98 years of age and determined by the test of plaque microagglutination. Seroprevalences by states ranged from 0.24 per cent in Morelos to 13.5 per cent in the state of Mexico. The national mean was estimated to be 3.42 per cent. The analysis showed no statistical differences for brucellosis antibody levels by urban and rural residence and by density of family sleeping areas (three or more persons vs. one or two persons per bedroom). Adults between 20 and 39 years of age had greater seropositivity and children from one to nine years had the least. Women were most affected and had 48 per cent more seropositivity than men. According to the information obtained in the study, brucellosis in Mexico has the following characteristics: it is related to gender but not to occupation; affects persons in all age groups, social strata and is independent of size of the community of residence. Historically, brucellosis has been an endemic disease in Mexico. Recently an increasing incidence has been reported, and this is possibly due to a better national notification system.