Showing papers by "Instituto Politécnico Nacional published in 1990"

Cohen-macaulay graphs

Abstract: For a graph G we consider its associated ideal I(G). We uncover large classes of Cohen-Macaulay (=CM) graphs, in particular the full subclass of CM trees is presented. A formula for the Krull dimension of the symmetric algebra of I(G) is given along with a description of when this algebra is a domain. The first Koszul homology module of a CM tree is also studied.

Prevention by silymarin of membrane alterations in acute CCl4 liver damage.

Abstract: The effect of silymarin on liver lipid peroxidation and membrane lipid alterations induced by an acute dose of CCl4 was studied. Four groups of animals were treated with CCl4, CCl4 + silymarin, silymarin and its vehicles. CCl4 was given orally (0.4 g 100 g-1 body wt.) and silymarin was administered i.p. All animals were sacrificed 24 h after the treatments. Liver lipid peroxidation was measured and plasma membranes were isolated. Alkaline phosphatase (AP) and gamma-glutamyl transpeptidase (GGTP) were measured in plasma membranes. Membrane lipids were extracted and then analysed by thin-layer chromatography by measuring the phosphorus of the phospholipids in each spot. Liver lipid peroxidation was increased about three times in the group receiving CCl4 only. Silymarin cotreatment prevented this increase. Phosphatidylethanolamine (PEA) decreased, while phosphatidylinositol (PI) increased in the plasma membranes isolated from the CCl4-treated group. Animals that received CCl4 + silymarin showed no decrease in PEA content. A partial prevention of the decrease in phosphatidylinositol content was also observed in plasma membranes of animals treated with silymarin in addition to CCl4. CCl4 decreased gamma-glutamyl transpeptidase (GGTP) and alkaline phosphatase (AP) membrane activities. Silymarin cotreatment prevented the AP (completely) and the GGTP (partially) falls caused by CCl4. Silymarin by itself increased AP membrane activity. A significant relationship between the membrane content of phosphatidylethanolamine (PEA) and the AP activity was observed in plasma membranes of treated animals and in normal liver membranes enriched with PEA. These results indicate that silymarin can protect against the alterations induced by CCl4 on the liver plasma membrane through its antioxidant properties by modifying the plasma membrane phospholipid content.

Lasers with super-Gaussian mirrors

Abstract: A systematic theoretical and experimental investigation of unstable resonators with variable reflectivity mirrors of a super-Gaussian profile is presented. The validity of a geometrical optics formalism for an algebraic mode calculation is discussed in comparison to the diffraction theory. A new method for the calculation of the output energy by means of a closed-form relationship that accounts for the effects of the transverse mode profile on gain saturation is presented. Various dielectric super-Gaussian mirrors have been fabricated, characterized, and tested in a pulsed Nd:YAG laser. Super-Gaussian resonators can provide even higher output energies than those of traditional unstable resonators and with better beam-focusing properties. >

Flavor-changing radiative decay of the t quark

Abstract: We study the loop-induced flavor-changing decay $t\ensuremath{\rightarrow}c+\ensuremath{\gamma}$ in a nonlinear ${R}_{\ensuremath{\xi}}$ gauge for the standard model with three and four generations and in models with two Higgs doublets. We find that this decay could be relevant only in a scenario with two Higgs doublets and the mass of the fourth-generation ${b}^{\ensuremath{'}}$ quark larger than ${m}_{t}$. Under these conditions, the flavor-changing electromagnetic decays ${T}_{q}^{*}\ensuremath{\rightarrow}{D}_{q}\ensuremath{\gamma}({T}_{q}\ensuremath{\rightarrow}{D}_{q}^{*}\ensuremath{\gamma})$ may surpass the standard electromagnetic transition ${T}_{q}^{*}\ensuremath{\rightarrow}{T}_{q}\ensuremath{\gamma}$.

Pattern recognition in 3D automatic human motion analysis

Abstract: The recent developments in the fields of pattern recognition and parallel computation open new possibilities to motion analysis. The quantitative analysis of movement is no longer restricted to the research, but is becoming an important tool for the assessment of patients and the therapeutic evaluation in clinical environment, as well as in industrial applications. The main features of an automatic system for motion analysis using optoelectronic sensors (special nonmetric TV cameras) and passive lightweight markers (with no limits in number) will be described herein. The system is hierarchically organized on two levels: the first provides for marker recognition and is implemented by a dedicated hardware processor and the second is devoted to the software processing of the spatial coordinates of the markers. Special attention has been paid on the description of the algorithms for 3D spatial resection and intersection. The features of the system lead to high performance with respect to noise rejection, flexibility of set-up, accuracy and easyness of use, even in critical environmental conditions.

The role of membrane composition in ATPase activities of cirrhotic rat liver: effect of silymarin.

Abstract: The activities of Ca2(+)- and Na+, K(+)-ATPases were studied in liver plasma membranes from CCl4-cirrhotic rats and from livers of rats treated with silymarin in addition to CCl4. CCl4 chronic treatment produced significant decreases in Na+, K(+)- and Ca2(+)-ATPase activities; however, the animals treated with silymarin along with CCl4 showed no differences in ATPase activities as compared to controls. The lipid analysis performed in plasma membranes revealed increases in the cholesterol/phospholipid (CH/PL) and sphingomyelin/phosphatidylcholine (SM/PC) ratios in the cirrhotic group. Again, the membranes isolated from rats receiving CCl4 + silymarin showed normal CH/PL and SM/PC values. Considering that CH/PL and SM/PC ratios are related to membrane microviscosity, this study suggests that a lower fluidity of the membrane may be responsible for the observed decreases in ATPase activities in the cirrhotic group. Additionally, the role of silymarin to improve liver function in CCl4-cirrhosis can be attributed partially to its action at membrane level by preventing the increases in CH/PL and SM/PC ratios.

Emetine resistant mutants of Entamoeba histolytica overexpress mRNAs for multidrug resistance.

Abstract: Although drug therapy is critical for control of amoebiasis, little is known about mechanisms of drug resistance by E. histolytica parasites. Here we tested the hypothesis that multidrug resistant (mdr) amoeba mutants, similar to mdr tumor cells, are drug resistant based upon overexpression of a P-glycoprotein pump that effluxes drugs from the cells. Using primers to conserved regions of the human P-glycoprotein and the polymerase chain reaction (PCR), we identified multiple 344 base par segments of amoeba DNA similar to the mammalian P glycoprotein. The amino acid sequences of amoeba mdr-like PCR products were from 53 to 97 identical with each other, 55 to identical to human mdr1 sequences, and 41-44% identical with P. falciparum mdr-like sequences. On northern blots, the mdr-like PCR products identified amoeba mRNAs 4.5-5 kilobases long, similar to the 5 kilobase mRNAs reported for the mammalian mdr gene. These mRNAs were increased at least seven times in emetine resistant mutant clone C2 amoebae versus wild-type clone A parasites. Further, the expression of the mdr-like mRNAs was increased three to four times when clone C2 mutants were grown under drug pressure versus the same parasites grown without emetine. In contrast, the number of genomic copies of the mdr-like DNA segments was not increased in the mutant clone C2 versus the wild-type clone A amoebae, and no rearrangements of the mdr-like DNA segments by the mutant were identified on Southern blots. In conclusion there appears to be a family of mdr-like genes in E. histolytica, which may be involved in drug resistance by the parasite.

Focusing SAR data with time-varying Doppler centroid

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. >

Prediction of slug frequency in horizontal two‐phase slug flow

Abstract: Available data on slug frequency in horizontal two-phase intermittent flow are predicted with adequate accuracy by assuming that the slug frequency is one half of the frequency of the unstable waves precursors of slugs, as determined according to published analyses of finite amplitude waves in conduits. The experimental effects of gas and liquid flow rates, pipe diameter, gas density and liquid viscosity on slug frequency are explained by modifications of the wave properties due to changes in the liquid level of the stratified flow existing in the pipe inlet region prior to slug formation. Simple generalized equations are provided to estimate the slug frequency for engineering calculations.

Heat transfer analysis during water spray cooling of steel rods.

Abstract: A mathematical model has been developed to predict the rod cooling behavior of steel rods under the action of water sprays in the precooling system of a Stelmor machine. The main objective of this work was to study the influence of operation parameters such as rod size, rod speed, rod temperature at the finishing mill, water flow-rate and spray cooling sequence on the final temperature distribution within the rod before it enters into the transformation conveyor.This heat transfer analysis indicates that the spray cooling sequence affects, considerably, the temperature distribution inside the rod. Besides, water flow-rate failures in the spray cooling system disturb drastically its cooling efficiency. Finally, reheating phenomena which go from 150 to 200°C at rod surface are predicted. The calculations were validated with in situ experimental measurements carried out at HyLSA's (Puebla Plant) Stelmor machine. Very good agreement was found between predicted and experimentally measured rod surface temperatures.

Hormonal regulation of potassium currents in single myometrial cells.

Abstract: Three potassium currents (IK) were recorded from myometrial cells isolated from the uterus of rats at estrus and diestrus and kept in culture for 1-6 days. IK were differentiated by their modulation with norepinephrine and/or by their onset kinetics. At +50 mV the activation time constants were about 0.7 ms, 6 ms, and 15 ms for the fast, the intermediate, and the slow IK, respectively. Norepinephrine (1 microM) potentiated the fast IK and reduced the intermediate IK. In addition, differences were found with respect to cells from animals at estrus and diestrus. The fast IK was preferentially expressed in cultures from animals at estrus, whereas the intermediate IK was more frequent in cells from rats at diestrus. These results indicate that K+ channels from myometrial cells are multiregulated. Regulation may occur by short-term signals (neurotransmitters) and/or by preferentially expressing distinct types of channels depending on the hormonal status of the animal.

Antigens in electron-dense granules from Entamoeba histolytica as possible markers for pathogenicity.

Abstract: In vitro interaction of Entamoeba histolytica with collagen induces intracellular formation and release of electron-dense granules (EDG) and stimulation of collagenolytic activity Purified EDG contain 166 U of collagenase per mg of protein Thus, EDG may participate in tissue destruction during invasive amebiasis Monoclonal antibodies (MAbs) L11 and L71 reacted specifically with EDG in enzyme-linked immunosorbent assay (ELISA) and immunofluorescence and immunoelectron microscopy MAb L71 immunoprecipitated three polypeptides with molecular weights of 95,000, 68,000, and 28,000 from lysates of biosynthetically labeled E histolytica Both MAbs recognized the pathogenic E histolytica axenic strains HM1:IMSS, HM38:IMSS, and HK-9 but failed to react in ELISA with Entamoeba moshkovskii, Entamoeba invadens, and E histolytica-like Laredo In addition, MAb L71 reacted with one E histolytica isolate from a symptomatic patient but did not react with four of five isolates from asymptomatic patients EDG antigens were detected by a MAb L71-based ELISA in E histolytica-containing fecal samples from symptomatic, but not asymptomatic, individuals These results suggest that the EDG antigen detected with MAb L71 may be differentially expressed in pathogenic and nonpathogenic E histolytica Images

Robust design of cascade control

Abstract: A design concept for cascade control that ensures enhanced robustness by minimizing the mutual influence among the cascaded loops is proposed. This is achieved by complete decoupling of the design and performance of two (or more) cascaded control loops. The decoupling applies not only to static aspects (windup and saturations) but also to possible degradation of dynamic performance. The practical impact of the design is illustrated by both analytic and numerical examples. >