Showing papers by "National Autonomous University of Mexico published in 1993"
TL;DR: The spectral ratio technique is a common useful way to estimate empirical transfer function to evaluate site effects in regions of moderate to high seismicity as discussed by the authors, and it can be used to study the intense S-wave part in earthquake records.
Abstract: The spectral ratio technique is a common useful way to estimate empirical transfer function to evaluate site effects in regions of moderate to high seismicity. The purpose of this paper is to show that it is possible to estimate empirical transfer function using spectral ratios between horizontal and vertical components of motion without a reference station. The technique, originally proposed by Nakamura to analyze Rayleigh waves in the microtremor records, is presented briefly and it is discussed why it may be applicable to study the intense S-wave part in earthquake records. Results are presented for three different cities in Mexico: Oaxaca, Oax., Acapulco, Gro., and Mexico City. These cities are very different by their geological and tectonic contexts and also by the very different epicentral distances to the main seismogenic zones affecting each city. Each time we compare the results of Nakamura's technique with standard spectral ratios. In all three cases the results are very encouraging. We conclude that, if site effects are caused by simple geology, a first estimate of dominant period and local amplification level can be obtained using records of only one station.
964 citations
TL;DR: In this article, a method to grow carbon microtubules with fullerene structure (buckytubes) has been identified, which consists of the catalytic decomposition of acetylene over iron particles at 700 °C.
Abstract: A method to grow carbon microtubules with fullerene structure (buckytubes) has been identified. The method consists of the catalytic decomposition of acetylene over iron particles at 700 °C. Carbon microtubules of up to 50 μm in length are synthesized by this method. Electron diffraction and high resolution electron microscopy studies demonstrate that the structure of these microtubules corresponds to the helical structure recently reported by S. Iijima, Nature 354, 56(1991), prepared using an arc‐discharge evaporation method.
672 citations
TL;DR: This review has summarized various aspects as to how prenatal protein malnutrition affects development of the brain and has attempted to integrate several broad principles, concepts, and trends in this field in relation to findings and other studies of malnutrition insults.
648 citations
TL;DR: The u54 system is widely represented in the alpha and gamma proteobacteria, and it has also been reported to be present in Bacillus subtilis and among other physiological processes controlled by C54 are nitrogen assimilation and fixation, dicarboxylic acid transport, hydrogen oxidation, alginate utilization, degradation of aromatic compounds, pilus formation and formate utilization.
Abstract: Because of their ability to stimulate gene expression from distant sites and regardless of their orientation, transcriptional enhancer elements are a puzzling class of regulatory DNA sequences (42). Although enhancers are a common feature of eukaryotic and viral genes, the mechanism by which they communicate with promoters and stimulate gene expression is still not very well understood. However, our understanding of the mechanism of gene activation at a distance has been boosted by the study of naturally occurring enhancer-like elements (ELE) in prokaryotes. The ELE are palindromic or nearly palindromic nucleotide sequences normally found between 100 and 200 bp upstream of a certain class of promoters, and, like the eukaryotic enhancers, they still stimulate transcription when moved thousands of nucleotides upstream or downstream from the transcription start and regardless of their orientation (7, 47). The extensive genetic characterization of many bacterial ELE and the development of defined in vitro transcription systems has greatly facilitated the study of activation by enhancers, and now some of the molecular details of distal activation are well established (34). It has been demonstrated that the ELE are binding sites for regulatory proteins named bacterial enhancer-binding proteins (EBPs). The best-studied EBPs are NtrC and NifA, which stimulate the expression of genes required for nitrogen assimilation and nitrogen fixation, respectively, in a number of organisms (37). These proteins activate genes transcribed by the RNA polymerase holoenzyme containing the alternative sigma factor &F4 (EO(J4). The u54 system is widely represented in the alpha and gamma proteobacteria (previously called purple bacteria), and it has also been reported to be present in Bacillus subtilis (13, 14). Among other physiological processes controlled by C54 are nitrogen assimilation and fixation, dicarboxylic acid transport, hydrogen oxidation, alginate utilization, degradation of aromatic compounds, pilus formation and formate utilization (for reviews, see references 35 and 56). A common feature of all these processes is that they are not absolutely required for cell survival, and each is activated by a different EBP interacting with a distinctive ELE nucleotide sequence. In addition to its ability to be activated at a distance, the Er54 system has several other unique characteristics that are not common among bacterial holoenzymes. E&'4 recognizes promoter DNA with unusually close boxes, centered at
419 citations
TL;DR: A new Rhizobium species that nodulates Phaseolus vulgaris L. is proposed in this paper on the basis of a sequence analysis of 16S ribosomal DNA.
Abstract: A new Rhizobium species that nodulates Phaseolus vulgaris L. is proposed on the basis of a sequence analysis of 16S ribosomal DNA. This taxon, Rhizobium etli sp. nov., was previously named Rhizobium leguminosarum biovar phaseoli (type I strains) and is characterized by the capacity to establish an effective symbiosis with bean plants, the reiteration of the nitrogenase structural genes, the organization of the common nodulation genes into two separate transcriptional units bearing nodA and nodBC, the presence of the polysaccharide inhibition gene, psi, and the 16S ribosomal DNA sequence. An analysis of the sequence of a fragment of the 16S rRNA gene shows that this gene is quite different from the gene of R. leguminosarum. In addition, all R. etli strains have identical sequences. We describe these analyses and discuss additional evidence supporting our proposal.
382 citations
TL;DR: This study focuses on the dispersal of propagules by birds to understand the movement of plants between landscape components and suggests possibilities for the management of the local species diversity of tropical rain forests.
Abstract: The tropical rain forest landscape has been transformed to a mosaic composed of patches of crops, secondary vegetation and remnant forest fragments of different shapes and sizes. Isolation of patches and fragments is a critical issue in the maintenance of local species diversity. In this study we focus on the dispersal of propagules by birds to understand the movement of plants between landscape components. Seed deposition and the behavior of frugivorous birds were monitored at four isolated fig trees (Ficus yoponensis and F. aurea) in man-made pastures. Seed deposition was measured by trapping seeds under canopy trees for six months and by direct observation of bird visits to the four trees for one year. Seed deposition densities were 465,614,632 and 1097 seeds/m2 accumulated over six months under each of the four trees. We recorded 8268 seeds of 107 species under the trees, among them, 6726 seeds (81 %) were of 56 species dispersed by vertebrate frugivores. Seeds of tree species accounted for 26% of the total species. Seventy-three species of birds perched in the observed trees, and 3344 visits were made by 47 species of frugivores. Frugivorous birds occurred in two groups: resident species nesting in the pastures and resident species nesting elsewhere. Propagule exchange between landscape components is clearly influenced by the behavior of these two groups. Structure and dynamics of the landscape depend on plant species availability within the mosaic. This availability is high and suggests possibilities for the management of the local species diversity of tropical rain forests.
241 citations
TL;DR: Reprocessed gravity data over Northern Yucatan reveal three major rings and parts of a fourth ring, spaced similarly to those observed at multiring impact basins on other planets.
Abstract: The buried Chicxulub impact structure in Mexico, which is linked to the Cretaceous- Tertiary (K-T) boundary layer, may be significantly larger than previously suspected. Reprocessed gravity data over Northern Yucatan reveal three major rings and parts of a fourth ring, spaced similarly to those observed at multiring impact basins on other planets. The outer ring, probably corresponding to the basin's topographic rim, is almost 300 kilometers in diameter, indicating that Chicxulub may be one of the largest impact structures produced in the inner solar system since the period of early bombardment ended nearly 4 billion years ago.
201 citations
TL;DR: In this paper, the pore saturation (PS) and resistivity of mortars without Cl − and with 2% Cl − were obtained, and the results showed that the mortar resistivity can prevent active state corrosion of reinforcements as effectively as passivating layers of steel in mortars.
178 citations
TL;DR: In order to establish paleoenvironmental conditions during the late Quaternary, four cores from the Basin of Mexico (central Mexico) were drilled in Chalco Lake, located in the southeastern part of the basin this paper.
175 citations
TL;DR: In this paper, the Chicxulub impact breccia was found to contain zircons that are identical in age, texture and lead loss pattern to the Colorado zircon, and to some from the Beloc section in Haiti.
Abstract: MANY lines of evidence now support the identification of the Chicxulub structure, in Mexico, as a buried impact crater and the probable source of ejecta found in Cretaceous/Tertiary (K/T) boundary sections worldwide1–8. The question remains, however, of whether there might be additional craters of K/T age, which also contributed ejecta. Shocked zircons from a K/T ejecta layer in Colorado9 preserve a primary source age of 545 ± 5 Myr, with variable degrees of isotopic resetting consistent with partial lead loss at the time of impact (65 Myr ago)10. Here we report that the impact breccia from Chicxulub contains zircons that are identical in age, texture and lead loss pattern to the Colorado zircons, and to some from the Beloc section in Haiti. U–Pb data for 18 of the 36 grains studied (from all three sites) fall on a single line as well as if they had come from a single sample. An additional source age of 418 ±6 Myr is found only in Chicxulub and Haiti, suggesting that the Haiti and Colorado ejecta might have sampled different parts of the target stratigraphy. As all the ejecta ages found so far are also found at Chicxulub, our results are consistent with this being the only significant continental K/T impact crater.
165 citations
01 Dec 1993
TL;DR: A nonlinear state observer plus state feedback control that insures exponential stability provided the desired torque does not exceed a given value is derived and it attains the field orientation objective of the highly successful “vector control” strategies.
TL;DR: In this article, a series of coprecipitated TiO 2 -Al 2 O 3 supports containing between 0 and 100% TiO2 were prepared and characterized by various methods.
Abstract: A series of coprecipitated TiO 2 -Al 2 O 3 supports containing between 0 and 100% TiO 2 were prepared and characterized by various methods. These solids were impregnated with molybdenum and tested in their sulphide form as catalysts in the hydrodesulphurization (HDS) of thiophene. The results showed that in the prepared mixed oxides supports, an interaction between TiO 2 and Al 2 O 3 exists and that the coprecipitated solid is different, in its surface properties, from a mechanical mixture of the two oxides. Acidity measurements show that Lewis and not Bronsted sites exist in the mixed oxides. The number of acid sites increases sharply at high TiO 2 content. High-resolution electron microscopy shows that a better dispersion of MoS 2 on the supports is obtained when the TiO 2 content is increased. Activity measurements in the thiophene hydrodesulphurization reaction show that the intrinsic activity, expressed on a molybdenum atom basis, increases sharply at high TiO 2 loadings in the mixed oxides supports. Comparison of the activity and acidity measurements point to a correlation between HDS activity and the number of acid sites on the support that affects the dispersion during the impregnation step and the reactivity of the MoS 2 sites.
Abstract: The Guerrero terrane makes up most of the western part of Mexico, is one of the largest terranes of the North American Cordillera, and is characterized by an Upper Jurassic-Lower Cretaceous volcanic-sedimentary sequence of are affinity. Metamorphic rocks that crop out in the western area of the terrane (Arteaga complex) may represent its basement. They are mostly composed of terrigenous sediments (Varales Formation) with minor basaltic pillow lavas, chert, tuff, and limestone. Initial ϵ Nd values (+13) and rare earth element (REE) values for pillow lavas of the Arteaga complex are characteristic of mid-ocean ridge basalts (MORB). In contrast, the Varales Formation sedimentary rocks from the Arteaga complex have negative initial ϵ Nd (-6.2 and -7.2) and are enriched in light REEs. These data indicate that the sediments of the Varales Formation were supplied from an evolved continental crust. The overlying Jurassic(?)-Cretaceous arc-related rocks have initial ϵ Nd (+7.9 to +3.9) and REE patterns similar to those of evolved intraoceanic island arcs. These data show that the evolution of the Guerrero terrane had an early pre-Cretaceous(?) stage, which consisted of an oceanic crust receiving sediments from a continental source, and a Cretaceous stage, which was the development of an island arc.The oceanic-continental isotopic signature of the Arteaga complex is different from other western North American Cordilleran terranes (e.g., Alexander, Wrangelfia) that are more completely "oceanic" in affinity. Nevertheless, the extensive Jurassic(?).Cretaceous arc represents additions of juvenile material to the western North American Cordillera.
TL;DR: The problem of electromagnetic-field quantization in time-dependent nonuniform linear nondispersive media is investigated and explicit formulas for the number of photons generated from the initial vacuum state due to the change in time of dielectric permeability of the medium are obtained.
Abstract: The problem of electromagnetic-field quantization in time-dependent nonuniform linear nondispersive media is investigated. The explicit formulas for the number of photons generated from the initial vacuum state due to the change in time of dielectric permeability of the medium are obtained in the case when the spatial and temporal dependences are factorized. The concrete time dependences include adiabatic and sudden changes of permeability, the parametric resonance at twice the eigenfrequency of the mode, Epstein's symmetric and transition profiles, «temporal Fabry-Perot resonator,» and some others
TL;DR: Dung beetles attracted to howler monkey and coati dung were studied for an annual cycle in the tropical rain forest of Los Tuxtlas, Mexico, and species overlap was high, but occurred in higher numbers between the months of March and October, when temperatures were higher.
Abstract: Dung beetles attracted to howler monkey (Alouatta palliata) and coati (Nasua narica) dung were studied for an annual cycle in the tropical rain forest of Los Tuxtlas, Mexico. Pitfall traps set for 24 h month−1 captured 1567 dung beetles of 21 species. The species Canlhidium martinto, Deltochilum pseudoparile and Canthon femoralis accounted for 62% of all individuals captured. While species overlap was high (> 80%) between diurnal and nocturnal samples and between howler monkey and coati dung baits, coati dung attracted species such as C. martinezi, D. pseudoparile and Onthophagus rhinolophus while species such as C. femoralis and Copris laeviceps were numerically dominant at howler monkey dung. Thirteen non-ball rolling dung beetle species and eight ball-rolling species accounted for 43% and for 57% of all beetles captured respectively. Dung beetles were present and active in all months of the year, but occurred in higher numbers between the months of March and October, when temperatures were higher. Relative abundance of howler monkey and coati dung in the rain forest of Los Tuxtlas was estimated at 11.2 g (fresh weight) ha−1 day−1 and at 13.0 g ha−1 day−1 respectively, a seemingly low amount for the large number of scarabs attracted to the dung.
TL;DR: The data set used by Foster and Janson (1985) to look at the relationship between seed size and establishment conditions for naturally occurring tropical trees was re-analyzed, to take into account the effect of relatedness among species.
Abstract: Within a multi-species study, species do not necessarily represent independent data points. The data set used by Foster and Janson (1985) to look at the relationship between seed size and establishment conditions for naturally occurring tropical trees was re-analyzed, to take into account the effect of relatedness among species. The re-analysis showed that 1) this data set does not support the hypothesis that large-seeded species are more likely to establish in small gaps or shade than are small-seeded species, and 2) more than 1/3 (16 of 39) of the data points were extraneous to the test of the hypothesis. It is recommended that all ecologists, and not just those interested in evolutionary questions, consider species relatedness prior to inception of any multi-species study.
TL;DR: In this paper, the morphology of the Rivera plate subducted beneath the Jalisco block in western Mexico is determined from accurately located hypocenters of locally recorded microearthquakes, and from earthquakes with magnitude mb≥4.5 recorded at teleseismic distances.
Abstract: The morphology of the Rivera plate subducted beneath the Jalisco block in western Mexico is determined from accurately located hypocenters of locally recorded microearthquakes, and from earthquakes with magnitude mb≥4.5 recorded at teleseismic distances. The hypocenters of these latter earthquakes are relocated, and for five of them the focal depth is constrained by the inversion of long-period body waves. The Wadati-Benioff zone inferred from these data indicates a steep subduction of the Rivera plate that resembles the geometry of subduction of the Cocos plate beneath Central America. It is, however, very different from the shallower and almost subhorizontal subduction of the Cocos plate observed in southern Mexico, southeast of this region. The Rivera plate is comparable to the Juan de Fuca plate in terms of the small areal extent, young seafloor age, low relative velocity, and low teleseismic activity in the subduction zone. This study shows that the dip of both the Juan de Fuca and Rivera plates are similar once they are decoupled from the overriding continental crust. The downgoing Rivera plate initially starts with a dip of ∼10° down to a depth of 20 km and then increases gradually to a constant dip of ∼50° below a depth of 40 km. Intermediate-depth seismicity is low in this zone associated with the subduction of the slow (2 cm/yr) and young (9 m.y.) Rivera plate. The maximum depth extent of earthquakes observed in the Rivera subduction zone is about 130 km. The andesitic, calc-alkaline Colima volcano appears to be directly related to the subduction of the Rivera plate. To the NW of this volcano, the observed Quaternary volcanism in the Jalisco block, which is parallel to the trench, may also be explained by the subduction of the Rivera plate.
TL;DR: Using polymer producing (ropy) strains of lactic acid bacteria it was possible to reduce considerably the syneresis of yogurt, even with 12% total milk solids as discussed by the authors.
Abstract: Using polymer producing (ropy) strains of lactic acid bacteria it was possible to reduce considerably the syneresis of yogurt, even with 12% total milk solids. The viscosities obtained with these strains were also similar to those obtained using normal strains and milk with 17% total solids content. The concentration of milk and the polymer produced by ropy starters had a synergic effect in increasing viscosity. Polymer production was not affected in most cases by milk concentration. One type of ropy culture (Wiesby) seemed to produce a different kind of polymer as it could not be determined by alcohol precipitation, in spite of being able to reduce syneresis and increase viscosity in yogurt. A limited number of yogurts were evaluated organoleptically, one prepared with a ropy starter strain (NCFB at 12, 14·5 and 17% total solids) and one prepared with a non-ropy strain (LL-I at 17% total solids). The results suggest that the ropy strain yogurts had different mouthfeel from the non-ropy strain yogurts; the most acceptable product overall was the ropy strain made with 12% total solids.
TL;DR: In this paper, the authors used a discretization scheme based on the numerical and analytical integration of exact Green's functions to study the topographical effects for incident P, SV and Rayleigh waves in an elastic half-space.
TL;DR: In this paper, the efficacy of hydroxychloroquine, 400 mg daily, for rheumatoid arthritis was evaluated in a six-month, double-blind, randomized trial.
Abstract: Objective To assess the efficacy of hydroxychloroquine, 400 mg daily, for rheumatoid arthritis. Design Six-month, double-blind, randomized trial. Setting Ambulatory referral clinic in a Mexico City, Mexico, teaching hospital. Patients A total of 126 patients with early rheumatoid arthritis were randomly assigned to receive hydroxychloroquine, 400 mg/d, or placebo; 121 patients completed the study. Results Hydroxychloroquine showed a clinically and statistically significant improvement over placebo in joint score (20% greater mean improvement; 10% more patients improved by > 50%); pain (40% greater mean improvement; 19% more patients improved by > 50%); grip strength (22% greater mean improvement; 21% more patients improved by > 50%); patient global assessment (16% more patients stated they had improved); and physician global assessment (12% more patients were judged to have improved). Side effects were mild, and no patients in the hydroxychloroquine group required discontinuation of therapy. Patient compliance with the study medication was high. Conclusion Hydroxychloroquine is moderately effective in early rheumatoid arthritis.
TL;DR: More than 6000 animals of 257 species were detected thus suggesting the existence of a rich species pool in the fragmented landscape and the value of agricultural islands as landscape features providing some degree of biotic connectivity among fragmented animal populations is discussed.
Abstract: Destruction and fragmentation of tropical rain forest result in a loss of species and of generating capacity of the ecosystem via animal vectors such as seed dispersal agents To gather quantitative data regarding this ecological problem, birds and mammals were censused in 30 forest fragments, 15 agricultural islands representing five types of vegetation (coffee, cacao, citrus, pepper and mixed-crops) and in three pastures in Los Tuxtlas, southern Veracruz, Mexico More than 6000 animals of 257 species were detected thus suggesting the existence of a rich species pool in the fragmented landscape Frugivores accounted for 60% of species, for 72% of individuals censured and for 85% of the total animal biomass recorded Clusters of small forest fragments ( 100 ha) forest islands Pastures were especially poor in forest birds and mammals While the agricultural islands studied contributed to only 1% of the total area of vegetation sampled, they contained 58% of all species detected and 34% of all individual birds and mammals censured Recaptures indicated inter-island movements of forest birds and mammals Forty percent of the species were detected in forest habitats only, the rest were detected in forest and in agricultural habitats Seeds of forest interior plants dispersed by birds and bats were detected in the agricultural habitats The value of agricultural islands as landscape features providing some degree of biotic connectivity among fragmented animal populations is discussed
TL;DR: In this paper, a boundary integral formulation is presented and applied to model the ground motion on alluvial valleys under incident P, S and Rayleigh waves, based on integral representations for the diffracted and refracted elastic waves using single-layer boundary sources.
Abstract: A boundary integral formulation is presented and applied to model the ground motion on alluvial valleys under incident P, S and Rayleigh waves. It is based on integral representations for the diffracted and the refracted elastic waves using single-layer boundary sources. This approach is called indirect BEM in the literature as the sources' strengths should be obtained as an intermediate step. Boundary conditions lead to a system of integral equations for boundary sources. A discretization scheme based on the numerical and analytical integration of exact Green's functions for displacements and tractions is used. Various examples are given for two-dimensional problems of diffraction of elastic waves by soft elastic inclusion models of alluvial deposits in an elastic half-space. Results are displayed in both frequency and time domains. These results show the significant influence of locally generated surface waves in seismic response and suggest approximations of practical interest. For shallow alluvial valleys the response and its resonant frequencies are controlled by a coupling mechanism that involves both the simple one-dimensional shear beam model and the propagation of surface waves.
TL;DR: The calculated vibrational properties of the breathing modes of the rings are found to be quite consistent with the observed frequencies, linewidths, and isotope shifts of the sharp lines D 1 and D 2 seen in the Raman spectra of α-SiO 2.
Abstract: We review the experimental evidence and qualitative arguments for the existence of small highly regular rings of bonds in amorphous (a-)${\mathrm{SiO}}_{2}$ and selected other ${\mathit{AX}}_{2}$ tetrahedral glasses. The structure and vibrations of planar 3-rings and regular puckered 4-rings in a-${\mathrm{SiO}}_{2}$ are then modeled using Born central and noncentral forces. The vibrational coupling of these rings to the more disordered glass network is modeled by attaching a Bethe lattice at each connection. The calculated vibrational properties of the breathing modes of the rings are found to be quite consistent with the observed frequencies, linewidths, and isotope shifts of the sharp lines ${\mathit{D}}_{1}$ and ${\mathit{D}}_{2}$ seen in the Raman spectra of a-${\mathrm{SiO}}_{2}$. The results support the previous assignment of ${\mathit{D}}_{2}$ (606 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$) to a planar 3-ring and ${\mathit{D}}_{1}$ (495 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$) to a regular ring. Similar calculations for a-${\mathrm{GeO}}_{2}$ are consistent with the suggestion that this material contains a substantial concentration of nearly planar 3-rings. Our methods can be generalized to treat similar forms of intermediate range order in glasses having other network connectivities.
TL;DR: The results suggest that CPK and MI measurements are useful for the prescreening of drugs with potential cytostatic activity.
Abstract: The mitotic index (MI) and cell proliferation kinetics (CPK) of human blood lymphocyte cultures were determined to evaluate the effects of six antineoplastic drugs with well known cytostatic activity: cisplatin, melphalan, bleomycin, methotrexate, 5-fluorouracil and 6-mercaptopurine. All six drugs showed a clear effect on the inhibition of MI. The first three drugs interact directly with DNA showing a dose-related retardation of CPK. Methotrexate, 5-fluorouracil and 6-mercaptopurine, which act on ribonucleotide biosynthesis, showed no significant effects on CPK. The results suggest that CPK and MI measurements are useful for the prescreening of drugs with potential cytostatic activity.
TL;DR: Neither RVD nor osmolyte fluxes were significantly reduced by removal of external Cl-, suggesting that an anion exchanger activity is not required for the volume regulatory process.
TL;DR: The results indicate that the contribution of FAA to the process of cell volume regulation is higher in astrocytes than in other cell types including renal and blood cells.
Abstract: In this work we examined the time course and the amount released, by hyposmolarity, for the most abundant free amino acids (FAA) in rat brain cortex astrocytes and neurons in culture. The aim was to evaluate their contribution to the process of cell volume regulation. Taurine, glutamate, andd-aspartate in the two types of cells, β-alanine in astrocytes and GABA in neurons were promptly released by hyposmolarity, reaching a maximum within 1–2 min. after an osmolarity change. A substantial amount of the intracellular pool of these amino acids was mobilized in response to hyposmolarity. The amount released in media with osmolarity reduced from 300 mOsm to 150 mOsm or 210 mOsm, represented 50%–65% and 13%–31%, respectively, of the total amino acid content in cells. In both astrocytes and neurons, the efflux of glutamine and alanine was higher under isosmotic conditions and increased only marginally during hyposmotic conditions.86Rb+, used as tracer for K+, was released from astrocytes, 30% and 11%, respectively, in hyposmotic media of 150 mOsm or 210 mOsm but was not transported in neurons. From these results it was calculated that FAA contribute 54% and inorganic ions 46% to the process of volume regulation in astrocytes exposed to a 150 mOsm hyposmotic medium. This contribution was 55% for FAA and 45% for K+ and Cl− in cells exposed to 210 mOsm hyposmotic solutions. These results indicate that the contribution of FAA to the process of cell volume regulation is higher in astrocytes than in other cell types including renal and blood cells.
TL;DR: In this article, the authors used historical data of an individual volcano, Colima in Mexico, to classify its eruptions by size using the Volcanic Explosivity Index (VEI).
TL;DR: The isolation of animal rotavirus variants whose infectivity is no longer dependent on the presence of sialic acids on the cell surface is reported and it is indicated that the initial interaction of the mutants with the cell occurs at a site different from the sIALic acid-binding site located on VP8, the smaller trypsin cleavage product of VP4.
Abstract: The infection of target cells by animal rotaviruses requires the presence of sialic acids on the cell surface Treatment of the cells with neuraminidases or incubation of the viruses with some sialoglycoproteins, such as glycophorin A, greatly reduces virus binding, with the consequent reduction of viral infectivity In this work, we report the isolation of animal rotavirus variants whose infectivity is no longer dependent on the presence of sialic acids on the cell surface In addition, although these variants bind to glycophorin A as efficiently as the wild-type virus, this interaction no longer inhibit viral infectivity These observations indicate that the initial interaction of the mutants with the cell occurs at a site different from the sialic acid-binding site located on VP8, the smaller trypsin cleavage product of VP4 Reassortant analysis showed that the mutant phenotype segregates with the VP4 gene Neutralizing monoclonal antibodies directed to VP4 and VP7 were tested for their ability to neutralize the variants Antibodies to VP7 and VP5, the larger trypsin cleavage product of VP4, neutralized the mutants as efficiently as the wild-type virus In contrast, although antibodies to VP8 were able to bind to the mutants, they showed little or no neutralizing activity The implications of these findings in rotavirus attachment to and penetration of epithelial cells in culture are discussed
TL;DR: The allelopathic potential of Ipomoea tricolor (Convolvulaceae), used in Mexican traditional agriculture as a weed controller, has been demonstrated by measuring the inhibitory activity of organic extracts on seedling growth of Amaranthus leucocarpus and Echinochloa crus-galli.
Abstract: The allelopathic potential of Ipomoea tricolor (Convolvulaceae), used in Mexican traditional agriculture as a weed controller, has been demonstrated by measuring the inhibitory activity of organic extracts on seedling growth of Amaranthus leucocarpus and Echinochloa crus-galli. Bioactivity-directed fractionation of the active CHCl3 extract led to the isolation of the allelopathic principle, which turned out to be a mixture of the so-called "resin glycosides" of convolvulaceous plants. The structure of tricolorin A, the major phytogrowth inhibitor present in the active fraction, was elucidated as (11S)-hydroxyhexadecanoic acid 11-O-alpha-L-rhamnopyranosyl-(1-->3)-O-alpha-L-[2-O-(2S-methylbutyryl)-4 -O- (2S-methylbutyryl)] rhamnopyranosyl-(1-->2)-O-beta-D-glucopyranosyl-(1-->2)-beta-D-fucopyran oside- (1,3"-lactone)[1], based on chemical methods and spectral analysis including 1H-1H COSY, 1H-13CHETCOR, long range 1H-13C COLOC, and selective INEPT experiments. Bioassays showed that radicle elongation of the two weed seedlings tested was inhibited by tricolorin A [1] with IC50 values ranging from 12 to 37 microM. Staphylococcus aureus was sensitive to compound 1 with an MIC value of 1.8 micrograms/ml. Significant cytotoxic activity against cultured P-388 and human breast cancer cells (ED50 2.2 micrograms/ml) was demonstrated for compound 1, and it also inhibited phorbol 12,13-dibutyrate binding using calf brain homogenate as a source of protein kinase C (IC50 43 microM).