Showing papers by "National Autonomous University of Mexico published in 1989"

Global patterns of tectonic stress

Abstract: Regional patterns of present-day tectonic stress can be used to evaluate the forces acting on the lithosphere and to investigate intraplate seismicity. Most intraplate regions are characterized by a compressional stress regime; extension is limited almost entirely to thermally uplifted regions. In several plates the maximum horizontal stress is subparallel to the direction of absolute plate motion, suggesting that the forces driving the plates also dominate the stress distribution in the plate interior.

Recent accretion in mangrove ecosystems based on137Cs and210Pb

Abstract: Accretion rates were measured in fringe and basin mangrove forests in river and tidally dominated sites in Terminos Lagoon, Mexico, and a basin mangrove forest in Rookery Bay, Florida, USA. Accretion rates were determined using the radionuclides210Pb and137Cs. Consolidation-corrected accretion rates for the Rookery Bay cores, ranged from 1.4 to 1.7 mm yr−1, with an average rate of 1.6 mm yr−1. Rates at the Mexico sites ranged from 1.0 to 4.4 mm yr−1, with an average of 2.4 mm yr−1. Determination of rates in these mangrove forests was greatly affected by the consolidation corrections which decreased the apparent accretion rate by over 50% in one case. Accretion rates at basin sites compare favorably with a reported 1.4 to 1.6 mm yr−1 rate of sea-level rise, indicating little or no subsidence at inland locations. Accretion rates in fringe sites are generally greater than basin sites, indicating greater subsidence rates in these sediments over longer time intervals.

Destructive strong ground motion in Mexico city: Source, path, and site effects during great 1985 Michoacán earthquake

Abstract: Simultaneous consideration of source, path, and site effects on ground motion during the Michoacan earthquake of 1985 allows us to draw coherent conclusions regarding the roles played for the disaster in Mexico City by the rupture process, the mode of propagation of the waves between the epicentral zone and Mexico City, and the local amplification. In contrast to the horizontal component which showed dramatic amplification for the 2 to 3 sec motion at lake sediment sites, we observe almost identical vertical displacement seismograms containing ripples with 2 to 3 sec period throughout the Mexico City valley whether the recording site is on the lake sediments or on hard rock. We, therefore, conclude that the 2 to 3 sec motion responsible for the destruction of Mexico City was present in the incident field. After performing a phase analysis, we interpret the signal as the superposition of long-period Rayleigh waves and short-period Lg with a dominant period of about 3 sec. The analysis of the teleseismic records indicates that the radiation of this event is enhanced for waves around the 3 sec period. Except in the case of stations for which an anomalous path effect is suspected, the records present ripples appearing a few seconds after the beginning of the signal. The characteristics of near-fault records show that the rupture process consists of the growth of a smooth crack. The numerical simulation indicates that the 3 sec period ripples can be explained by a series of changes of the rupture front velocity. We examine two alternative source models associated with different crustal models to explain the characteristics of the vertical displacements recorded in Mexico City. Our preferred model attributes the cause of the enhanced 3 sec motion to the irregularity in the rupture propagation in addition to the effect of the local conditions in Mexico City. This interpretation leads to a very coherent scenario of what happened from the start of the failure on the fault up to the destruction in Mexico City. This example illustrates the need to consider simultaneously source, path, and site effects in order to understand strong ground motions.

Quantitative assays based on the use of replicatable hybridization probes.

Abstract: Amplifiable hybridization probes--molecules with a probe sequence embedded within the sequence of a replicatable RNA--will promote the development of sensitive clinical assays. To demonstrate their utility, we prepared a recombinant RNA that contained a 30-nucleotide-long probe complementary to a conserved region of the pol gene in human immunodeficiency virus type 1 (HIV-1) mRNA. Test samples were prepared, each containing a different number of HIV-1 transcripts that served as simulated HIV-1 mRNA targets. Hybridizations were carried out in a solution containing the chaotropic salt, guanidine thiocyanate. Probe-target hybrids were isolated by reversible target capture on paramagnetic particles. The probes were then released from their targets and amplified by incubation with the RNA-directed RNA polymerase, Q beta replicase (EC 2.7.7.48). The replicase copied the probes in an exponential manner: after each round of copying, the number of RNA molecules doubled. The amount of RNA synthesized in each reaction (approximately 50 ng) was sufficient to measure without using radioisotopes. Kinetic analysis of the reactions demonstrated that the number of HIV-1 targets originally present in each sample could be determined by measuring the time it took to synthesize a particular amount of RNA (the longer the synthesis took, the fewer the number of targets originally present). The results suggest that clinical assays involving replicatable hybridization probes will be simple, accurate, sensitive, and automatable.

Release of taurine from astrocytes during potassium-evoked swelling.

Abstract: Cultured astrocytes superfused with isosmotic solutions containing high concentrations of potassium, i.e., 25, 56, 75, and 100 mM, showed a proportional increase in cell volume corresponding to 25, 36, 57, and 75% greater than the cell volume in physiological solutions. This volume increase was abolished in low chloride or hypertonic solutions. The release of 3H-taurine previously accumulated by astrocytes was stimulated by potassium at all concentrations examined. During 4-minute exposure to 25, 56, 75, or 100 mM of potassium, cells released 13.5, 15.6, 20.2, or 36.2%, respectively, of the total labeled taurine accumulated during the preloading period. The potassium-stimulated release of 3H-taurine was calcium-independent and insensitive to BaCl2 and bumetanide. Substitution of chloride by gluconate to concentrations necessary to maintain the K+ X Cl- product constant abolished the potassium-stimulated release of 3H-taurine. Superfusion with solutions made hypertonic with sucrose also decreased the potassium-elicited efflux of 3H-taurine. In both conditions, the depolarizing effect of potassium measured with 3H-TPP+ was unchanged. High potassium concentrations and hyposmotic solutions released 3H-taurine by a nonadditive mechanism. These results indicate that in cultured astrocytes high concentrations of potassium produce both swelling and depolarization, but only swelling elicits the release of taurine. These observations suggest an involvement of taurine in cell-volume regulation in astrocytes.

Is minisuperspace quantization valid?: Taub in mixmaster

Abstract: The paper addresses quantitatively the question of the validity of physical predictions based on minisuperspace quantization of Einstein's theory of gravitation. It studies a homogeneous, anisotropic cosmological model of higher symmetry (the Taub model) embedded in one of lesser symmetry (the mixmaster model). The comparison of the physical behavior of these two models is based on the construction of a non-negative probability density and the associated conserved inner product which allow a consistent probabilistic interpretation of the state function of the Universe in the interesting regime of deep channel penetration. It is shown that the respective behavior is widely different. A program is set for investigating a hierarchy of models with higher symmetry embedded in models of lesser symmetry to spell out the criteria under which minisuperspace quantum results can be expected to make meaningful predictions about full quantum gravity.

Theoretical basis for the Vogel-Fulcher-Tammann equation

Abstract: The lattice model for linear polymeric glasses proposed by Gibbs and Di Marzio several decades ago is used to calculate the average relaxation time for the structure of the model as a function of temperature. Using the fact that the model exhibits the existence of a temperature ${T}_{0}$ for which the configurational entropy of the system vanishes, we identify this temperature with the threshold of infinitely long relaxation times. Using the analytical parameter-free expression for the specific heat for temperatures above ${T}_{0}$, we show that (i) there are substances for which a Vogel-Fulcher-Tammann-like (VFT) equation is accurately obeyed in the range Tg${T}_{g}$, where ${T}_{g}$ is the experimental glass transition temperature. On the other hand, in the range ${T}_{0}$${T}_{g}$ a modified VFT equation is suggested.

On adaptive impedance control of robot manipulators

Abstract: Impedance control specifications for robot manipulators are given in terms of a desired motion trajectory and a desired dynamic relationship between position errors and interaction forces. An adaptive implementation is proposed as an alternative to reduce the design sensitivity due to model-manipulator parameter mismatch. Two adaptive controllers that globally achieve the impedance objective for the general nonlinear dynamic model are presented. The controller structures consist of a nonlinear feedback of positions, velocities, and end-effector applied forces. Computer simulations were carried out to demonstrate stability and performance control. >

Improved 13C ? 1H shift correlation spectra for indirectly bonded carbons and hydrogens: The FLOCK sequence

Abstract: Several modifications of the basic 13C1H shift correlation sequence as optimized for polarization transfer via long-range 13C1H coupling constants are described and evaluated. Modifications involve incorporation of BIRD pulse(s) at the mid-point of the evolution period and/or at the mid-point of the fixed delay prior to polarization transfer, in addition to the previously discussed incorporation of a BIRD pulse during the final fixed delay. These modifications give significantly improved sensitivity for many cross-peaks, excellent suppression of one-bond peaks and, in the case of the sequence incorporating two additional BIRD pulses, some ability to distinguish two-bond and three-bond connectivity peaks. The latter sequence is, overall, comparable in sensitivity to the fixed time sequences XCORFE and COLOC. It is also easier to parameterize and gives better suppression of one-bond peaks and other artifacts.

Identification, isolation and partial characterization of Mycobacterium tuberculosis glycoprotein antigens.

Abstract: In Mycobacterium tuberculosis culture filtrates, three concanavalin A (ConA)-binding bands of 55, 50 and 38 kilodaltons (kD) were identified by labelling blotted proteins with a ConA-peroxidase conjugate. Binding was inhibited by the competitor sugar alpha-methyl mannoside and by reduction with sodium m-periodate. Bands of 55, 50 and 38 kD stained with Coomasie blue were sensitive to digestion with proteases, thus indicating that they are proteins. Glycoproteins were isolated by lectin affinity chromatography or by elution from nitrocellulose membranes. On the isolated form, the 55-50 kD doublet glycoprotein was 65.4% protein and 34.6% sugar. The purified 38 kD molecule was 74.3% protein and 25.7% carbohydrate. By immunoblot, antibodies against mycobacterial glycoproteins were demonstrated in immunized rabbits and in patients with pulmonary tuberculosis, but not in healthy individuals. Treatment with sodium m-periodate abolished binding of rabbit antibodies to the 38 kD glycoprotein. Reactivity of the 55-50 kD doublet glycoprotein was not altered by reduction. By immunoblot with monoclonal antibodies TB71 and TB72, a carbohydrate-dependent and a carbohydrate-independent epitope could be identified on the 38 kD glycoprotein.

Deciphering western blots of tapeworm antigens (Taenia solium, Echinococcus granulosus, and Taenia crassiceps) reacting with sera from neurocysticercosis and hydatid disease patients.

Abstract: Complex antigen mixtures displayed in Western blots may be immediately and quantitatively categorized with respect to specificity and immunogenicity by immunoplotting. This involves plotting the frequency with which each antigen band reacts with a set of immune sera against the frequency of the same band when reacted with another set of immune sera. Immunoplotting has proven to be a powerful method of analyzing Western blots of reactions between vesicular fluids from the metacestodes of Taenia solium, E. granulosus, and T. crassiceps, and sera from human cases of neurocysticercosis and hydatid disease. Immunoplotting readily sorts out those antigens useful for discriminative immunodiagnosis from the multitude of bands in the sera of sick and healthy people. It aids in assessing the antigenic similarity between the human parasites and the murine parasite T. crassiceps, validating the latter as an alternative source of antigens for immunodiagnosis of cysticercosis and hydatid disease.

A 38-kD Mycobacterium tuberculosis antigen associated with infection. Its isolation and serologic evaluation.

Abstract: To identify antigens that could be specifically associated with tuberculosis infection, the antibody response to Mycobacterium tuberculosis antigens of patients with pulmonary tuberculosis and of healthy individuals were compared by immunoblot. In healthy individuals, serum antibodies were found in the majority of cases. Bands of 60 and 32-31 kilodaltons (kD) were the antigens more frequently recognized by antibodies of normal sera (55.8 and 64.7%, respectively). In patients with pulmonary tuberculosis, the number and intensity of the developed antigen bands were much higher than in normal individuals. Antigens reacting preferentially with tuberculosis sera were also identified. Furthermore, a unique disease-associated protein antigen of 38 kD was found to react with 57% of patients' sera but with none of the controls. This antigen was isolated by elution from nitrocellulose membranes and tested as an ELISA reagent in the serodiagnosis of pulmonary tuberculosis. A specificity of 0.96 and sensitivity of 0.68 were obtained.

Método para calcular la distribución de las calificaciones esperadas por azar en un examen del tipo falso, verdadero y no sé

Abstract: Multiple choice tests have been used widely in the evaluation of knowledge. The lowest passing limit is generally chosen arbitrarily. Better and more objective criteria may arise from analyzing the distribution of correct and incorrect answers as expected by chance. In order to calculate the distribution of correct answers and the difference between correct and incorrect answers (core) we propose the use of a method based on a gaussian distribution. The distribution of scores expected by chance is approximated by a gaussian distribution with a mean of zero and a standard deviation SD = square root of n(pA + pE), and the distribution of the total number of correct answers has a mean of npA and SD = square root of npApE, where n is the total number of questions, and pA and pE are the probabilities of having a correct and an incorrect answer, respectively. The formulae are applicable to questions type false/true/do not know and to the more common type of one correct in five options. Once the chance distribution is known, it can be compared with the distribution of scores or correct answers obtained, which can then be used to separate people in two groups: those that answer the test as expected or worse than expected by chance, and those that answer the test better than expected by chance. The first group should not be passed. The passing of individuals in the second group can be decided by additional criteria.

Quantitative genetics of size, shape, life-history, and fruit characteristics of the seed-heteromorphic composite heterosperma pinnatum. i. variation within and among populations.

Abstract: We document phenotypic and genetic variation within and among populations of the seed heteromorphic species Heterosperma pinnatum Cav. (Compositae) in the production of seed morphs and in a variety of life-history and morphological characteristics that might be correlated with seed and head traits. Each trait is found to have significant genetic variance in most or, usually, all populations. Significant among-population genetic variation exists for all traits except number of achenes per head and seedling shape, although some traits have much less genetic variation among than within populations. Number and percentage of intermediate achenes per head, total number of achenes per head, and lengths of central and peripheral achenes had little among-population genetic variation compared to within-population variation. Most traits had slightly less genetic variation among than within populations; however, some traits (percentage of central achenes, length of awns, date that the first flowering head opened, date that the first fruiting head opened, and death date) had more among-population genetic variation. The proportions of achene morphs produced had high broad-sense heritabilities and high among-population genetic variance, except in the case of intermediate achenes. All phenological variables had high among-population genetic variation. Within-population heritabilities were high for dates of first flowering head and fruiting head but low for death date and reproductive interval. Family and population means measured in the greenhouse for traits having high broad-sense heritability or among-population genetic variance were closely correlated with field means for the corresponding families or populations. The amounts of phenotypic variation were similar for traits that were measured in both the field and the greenhouse. These lines of evidence suggest that greenhouse results provide reasonable estimates of genetic variation in the field for this species. Numerous studies have reported variation in the proportion of seed morphs for different heteromorphic-seeded species and have discussed adaptive scenarios for the evolution of seed proportions; however, our investigation is one of only a few that have documented the amount of phenotypic and genetic variation within and among populations.

A programme to control taeniasis-cysticercosis (T. solium): experiences in a Mexican village.

Abstract: A study was carried out in a rural community of the state of Guerrero in order to find ways to control human taeniasis/cysticercosis (Taenia solium). At the beginning of the study the frequency of porcine cysticercosis was established to be around 6.6%. Fecal examination in the human population showed that of 760 persons, 24 were carriers of Taenia sp (3%). Of 440 human sera tested for antibodies against cysticercus cellulosae, 9 showed absorbance values of 0.2 or higher (2.3%). 900 persons received treatment against taeniasis. 400 soil samples and 600 flies were examined for the presence of eggs of Taenioae, all with negative results. Meetings with the adult population were organized to explain the disease and the life cycle of the parasite. Lectures and demonstrations for adults were given at the school for primary and secondary grade children. Special emphasis was given to the need to construct latrines in every home, as it was found that defaecation was practiced mainly in the open, usually at places where pigs had immediate access and ingested the faeces. One year after the initiation of the programme, pigs under the age of 1 year were inspected, to determine whether the cestocide treatment of humans has had an effect on the degree of parasitized pigs and if hygiene had improved. 11% of these animals were found to have cysticerci in their tongue. Two years after the initiation of the programme 78% of the children and 2% of adults answered questions about the lifecycle of the parasite correctly. The results of the trial are discussed and suggestions for future programmes are made.

Effect of metals on the rate of the oxidation of H2S in seawater

Abstract: Recent measurements on the oxidation of H{sub 2}S in the Black Sea yielded rates that were ten times faster than expected. To determine if this increase was due to trace metals, measurements have been made on the oxidation of H{sub 2}S in seawater with added transition metals. Below a concentration level of 100 nM, none of the metals except Fe{sup 2+} affect the rate of oxidation. At higher concentrations the rates increase for all the metals except Zn{sup 2+}. The increase in the rates followed the order Fe{sup 2+} > Pb{sup 2+} > Cu{sup 2+} > Fe{sup 3+} > Cd{sup 2+} > Ni{sup 2+} > Co{sup 2+} > Mn{sup 2+}. The increase in the rates below sulfide precipitation appears to be related to the formation of MHS{sup +} ion pairs that have a higher rate of oxidation than HS{sup {minus}}. Only Fe{sup 2+} and Mn{sup 2+} have concentrations high enough to be effective in influencing the rate of oxidation of H{sub 2}S in the waters of anoxic basins and sediments. The estimated rates of oxidation of H{sub 2}S in the Black Sea using the laboratory measurements were found to be in reasonable agreement with the measured values. Since CuHS{sup +}more » has a higher rate of oxidation than HS{sup {minus}}, it cannot be used to explain the stability of H{sub 2}S in oxic seawaters. A more likely choice is ZnHS{sup +}.« less

Geología de la cuenca de México

Abstract: A study of the geologic evolution of the Basin of Mexico located in the central part of the Trans-american Volcanic Arc (TVA) has been supported by stratigraphic, structural and petrochemical data. The results show that during the Aptian and the Turonian, carbonate sedimentation is the most significant. Changes of sedimentation from calcareous to flysch type occurred between Coniacian and Campanian times. During the Maestrichtian and Early Eocene the Cretaceous rocks were folded as a consequence of the Laramide orogeny. After the last stages of Laramide folding during Late Eocene-Early Oligocene, conjugate faulting and contemporaneous continental clastic molasse type sediments with alkaline effusive activity occurred. Calc-alkaline volcanic rocks from andesitic to ryolitic composition and Late Oligocene-Early Miocene ages are contemporaneous with ignimbritic volcan­ic activity of the Middle Tertiary Magmatic Arc. Volcanic events in genetic relation with the TVA and Plio- Quaternary faults in E-W direction are represented by: calc-alkaline basaltic andesites, andesites and dacites of Late-Middle Miocene, Early Pliocene, Late Pliocene and Quaternary age; calc-alkaline and alkaline basalts from the Plio-Quaternary; and calc-alkaline basalts, basaltic andesites and andesites of Quaternary age. The closing of the Basin of Mexico and subsequent lacustrine sedimentation of Pleistocene-Holocene ages originated as a consequence of intense volcanic activity which formed the Chichinautzin range.

Homegardens of a humid tropical region in Southeast Mexico: an example of an agroforestry cropping system in a recently established community

Abstract: The major components of the process of production in the homegardens of a tropical Mexican community are described and analyzed. Specifically, management tasks, means of production, and the amount, quality and temporal distribution of the products are discussed. The ecological, technological and productive advantages generally attributed to this kind of agroforestry cropping system in comparison to monocultures were also found in the homegardens of Balzapote. However, the area presently managed under this system is restricted, and its local and regional impact is thus very limited. Based on the detailed analysis of the functional differences in 8 homegardens and the socioeconomic roles they play in the economic organization of peasant families, the possible expansion of homegardens in the Mexican tropics is discussed.

Replicatable RNA reporters

Abstract: Elusive infectious agents such as HIV-1 can be detected by nucleic acid hybridization using special probes that are amplified by the enzyme Q-beta replicase as much as a thousand million-fold.

Young high-temperature granulites from the base of the crust in central Mexico

Abstract: CHARACTERIZATION of the lower continental crust is essential to understanding processes of crustal formation and evolution. Many workers have concluded that the lower crust is composed of granulite-facies rocks (see, for example, refs 1, 2), but many exposed granulite-facies terranes seem to have mid-crustal rather than lower-crustal origins3–5. Here we present new data from direct samples of the lower continental crust, in the form of metapelitic rock fragments brought to the surface by Quaternary volcanism in central Mexico. These xenoliths contain exsolved ternary feldspars that record extremely high minimum metamorphic temperatures of 950–1,100 °C, the highest yet known to be preserved in deep-seated metamorphic rocks. The metamorphism seems to be the result of underplating by basaltic magma and to be regional in extent. Our barometry on these samples demonstrates that granulite-facies metamorphic rocks are present in the lower crust, and provides important constraints on tectonic models and interpretations of geophysical data. Chemical and text lira I evidence suggest that the xenoliths were not able to cool to below 850–900 °C before being entrained in their host magmas, indicating that the granulite-facies metamorphism occurred no more than ~30 Myr ago.

Men's and women's emotional disclosures: The impact of disclosure recipient, culture, and the masculine role

Abstract: People vary in how willingly and how often they discuss their emotional experiences with others. A new Emotional Self-Disclosure Scale was used in three separate investigations to examine (Study I) men's and women's willingness to discuss their emotions with parents and therapists, (Study II) the impact of gender and culture on emotional disclosures to male and female friends and therapists, and (Study III) the impact of gender and the masculine role on willingness to emotionally disclose to parents and therapists. The results indicated that (a) female disclosers and female disclosure recipients, particularly mothers, were associated with greater willingness to emotionally disclose; (b) females from Mexico reported the most extensive disclosure of their emotions; and (c) the restrictive emotionality and inhibited affection aspects of the masculine role were negatively related to men's and women's willingness to be open and revealing about their emotional experiences, whereas the success dedication aspect of the masculine role was positively related to women's willingness to be emotionally open. The discussion focuses on the implications of the current findings and the relationship context of people's emotional disclosures.

Human neurocysticercosis: comparison of enzyme immunoassay capture techniques based on monoclonal and polyclonal antibodies for the detection of parasite products in cerebrospinal fluid

Abstract: Current diagnosis of neurocysticercosis relies mostly on computerized tomography and nuclear magnetic resonance, with detection of antibodies being confirmatory rather than decisive. An assay which detects parasite products in cerebrospinal fluid would conclusively demonstrate a current infection and could be important when decisions regarding treatment must be made. Cerebrospinal fluid from patients with neurocysticercosis was used in 4 enzyme immunoassay capture tests designed to detect parasite products. Of the systems tested, one, based on the use of a monoclonal antibody reactive with a surface and secretion component of the metacestode, was particularly promising, giving a sensitivity of 72%. The assay has the double advantage of a very low background and a proved specificity for the products of living cysticerci. The other 3 systems (monoclonal antivesicular fluid antibody, polyclonal antibody against a saline extract and polyclonal anti-antigen B antibody) were less sensitive. Results with the anti-antigen B system support the proposal that products of low immunogenicity are the most appropriate targets for the serological detection of the parasite.