Showing papers by "National Autonomous University of Mexico published in 1997"
TL;DR: In this paper, a method for generating aligned carbon nanotubes by pyrolysis of 2-amino-4,6-dichloro-s-triazine over thin films of a cobalt catalyst patterned on a silica substrate by laser etching is described.
Abstract: Carbon nanotubes1, 2 might be usefully employed in nanometre-scale engineering and electronics. Electrical conductivity measurements on the bulk material3, 4, on individual multi-walled5, 6 and single-walled7 nanotubes and on bundles of single-walled nanotubes8, 9 have revealed that they may behave as metallic, insulating or semiconducting nanowires, depending on the method of production—which controls the degree of graphitization, the helicity and the diameter. Measurements of Young's modulus show10 that single nanotubes are stiffer than commercial carbon fibres. Methods commonly used to generate nanotubes—carbon-arc discharge techniques1, 2, 4, catalytic pyrolysis of hydrocarbons11, 12 and condensed-phase electrolysis13, 14—generally suffer from the drawbacks that polyhedral particles are also formed and that the dimensions of the nanotubes are highly variable. Here we describe a method for generating aligned carbon nanotubes by pyrolysis of 2-amino-4,6-dichloro-s-triazine over thin films of a cobalt catalyst patterned on a silica substrate by laser etching. The use of a patterned catalyst apparently encourages the formation of aligned nanotubes. The method offers control over length (up to about 50 mum) and fairly uniform diameters (30–50 nm), as well as producing nanotubes in high yield, uncontaminated by polyhedral particles.
764 citations
TL;DR: In this article, five massive gold-cluster molecules have been isolated in high yield and have undergone separate structural characterization, and their electronic structure has been deduced by optical absorption spectroscopy.
Abstract: Five massive gold-cluster molecules have been isolated in high yield and have undergone separate structural characterization, and their electronic structure has been deduced by optical absorption spectroscopy. These new molecules are distinguished by a crystalline (or quasicrystalline) core of densely packed Au atoms, ranging in size from ∼1.1 nm (∼40 atoms) to ∼1.9 nm (∼200 atoms), surrounded by a compact monolayer of various thio (RS) adsorbates. They are obtained as the thermally and environmentally stable products of the reductive decomposition of nonmetallic (−AuS(R)−) polymer in solution, are separated according to size by fractional crystallization or column chromatography, as monitored by high-mass spectrometry, and are characterized structurally by methods including X-ray diffraction (small and large angle), high-resolution electron microscopy, and scanning tunneling microscopy. The optical absorption spectra of dilute solutions of these molecules show size-dependent steplike structure with an on...
576 citations
TL;DR: The results reconcile previous in vitro and in vivostudies by showing that D1 dopamine receptor activation can either inhibit or enhance evoked activity, depending on the level of membrane depolarization.
Abstract: Most in vitro studies of D1 dopaminergic modulation of excitability in neostriatal medium spiny neurons have revealed inhibitory effects. Yet studies made in more intact preparations have shown that D1 receptors can enhance or inhibit the responses to excitatory stimuli. One explanation for these differences is that the effects of D1 receptors on excitability are dependent on changes in the membrane potential occurring in response to cortical inputs that are seen only in intact preparations. To test this hypothesis, we obtained voltage recordings from medium spiny neurons in slices and examined the impact of D1 receptor stimulation at depolarized and hyperpolarized membrane potentials. As previously reported, evoked discharge was inhibited by D1 agonists when holding at negative membrane potentials (approximately -80 mV). However, at more depolarized potentials (approximately -55 mV), D1 agonists enhanced evoked activity. At these potentials, D1 agonists or cAMP analogs prolonged or induced slow subthreshold depolarizations and increased the duration of barium- or TEA-induced Ca2+-dependent action potentials. Both effects were blocked by L-type Ca2+ channel antagonists (nicardipine, calciseptine) and were occluded by the L-type channel agonist BayK 8644-arguing that the D1 receptor-mediated effects on evoked activity at depolarized membrane potential were mediated by enhancement of L-type Ca2+ currents. These results reconcile previous in vitro and in vivo studies by showing that D1 dopamine receptor activation can either inhibit or enhance evoked activity, depending on the level of membrane depolarization.
497 citations
TL;DR: The regulating feedback law, derived on the basis of a ‘boost’ model composed of ideal switches and ideal circuit components, is assessed, via computer simulations, on a realistic stochastically perturbed switched converter model, including parasitic resistances and parasitic voltage sources.
357 citations
TL;DR: Seventy-eight species of edible insects, representing twenty-three families from the state of Oaxaca in Mexico, were analyzed for nutrient composition, finding Hymenoptera (ants, bees, and wasps) are preferred for consumption.
335 citations
TL;DR: In this paper, the emphasis is placed on areas of intensive use interspersed with areas for conservation and catchment purposes, and a need for further interaction among foresters, ecologists, community representatives, social scientists, and economists.
Abstract: Forests are human-dominated ecosystems. Many of the seemingly lightly managed or unmanaged forests are actually in use for agroforestry or for hunting and gathering. Agroforestry does reduce biodiversity, but it can also act as an effective buffer to forest clearance and conversion to other land uses, which present the greatest threat to forested ecosystems. In forests used for logging, whole-landscape management is crucial. Here, emphasis is placed on areas of intensive use interspersed with areas for conservation and catchment purposes. Management strategies for sustainable forestry are being developed, but there is a need for further interaction among foresters, ecologists, community representatives, social scientists, and economists.
310 citations
TL;DR: In this paper, the authors review the experimental evidence, its interpretation, and what they have learnt from it, couched in the language of semiclassical scattering theory, as well as the basic features of the theory of the optical model.
305 citations
TL;DR: This review summarises a series of neuroanatomical, electrophysiological, in vivo sampling and behavioural neuropharmacological experiments carried out in sheep that have attempted to define the neural circuitry and hormonal neurotransmitter systems involved both in the control of maternal behaviour per se and in the selective olfactory recognition of lambs, which is the basis of an exclusive emotional bond between mother and offspring.
286 citations
TL;DR: Although relatively rare, odontogenic tumors are still an important cause of extensive surgical procedures in Mexico, and diagnostic criteria used in the reports are not uniform.
Abstract: Reports about the frequency of odontogenic tumors are scarce, and diagnostic criteria used in the reports are not uniform. This article presents the results of a retrospective study of odontogenic tumors recorded in four services of diagnostic pathology in Mexico City (two dental schools, one cancer hospital, and one private oral pathology service). The final diagnosis in each case was based on the 1992 histologic criteria of the World Health Organization. The frequency of odontogenic tumors, expressed as a percent of all oral and maxillofacial specimens, ranged from 0.8% in the cancer hospital (0.02% of all biopsies) to 3.7% in the private oral pathology service. The frequency was identical for the two dental schools (2.5%). We found a total of 349 odontogenic tumors; of these, 345 were benign (98.8%), and 4 (1.1%) were malignant (3 were primary intraosseous carcinomas and 1 was a malignant ameloblastoma). The most frequently occurring tumors were odontoma (34.6%), ameloblastoma (23.7%), myxoma (17.7%), adenomatoid odontogenic tumor (7.1%), and calcifying odontogenic cyst (6.8%). Although relatively rare, odontogenic tumors are still an important cause of extensive surgical procedures in Mexico.
250 citations
TL;DR: In this article, the authors describe the climatology of the near surface urban heat island of Mexico City, using hourly data from two recently installed automatic stations at a rural and an urban site.
244 citations
TL;DR: In this paper, the Chicxulub impact in Mexico has been linked to the mass extinction of species at the end of the Cretaceous period, and the diameter of the transient cavity is determined to be about 100 km.
Abstract: The Chicxulub impact in Mexico has been linked to the mass extinction of species at the end of the Cretaceous period. From seismic data collected across the offshore portion of the impact crater, the diameter of the transient cavity is determined to be about 100 km. This parameter is critical for constraining impact-related effects on the Cretaceous environment, with previous estimates of the cavity diameter spanning an order of magnitude in impact energy. The offshore seismic data indicate that the Chicxulub crater has a multi-ring basin morphology, similar to large impact structures observed on other planets, such as Venus.
TL;DR: In this paper, the chemical reactivity of boron carbide (B4C) with metallic aluminium (Al) was studied at temperatures ranging from 900 to 1273 K (627-1000 °C).
Abstract: The chemical reactivity of boron carbide (B4C) with metallic aluminium (Al) was studied at temperatures ranging from 900 to 1273 K (627–1000 °C). Al–B4C powder mixtures were cold pressed, heated for 1–450 h under 105 Pa of purified argon and characterized by X-ray diffraction (XRD) optical metallography (OM), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). Whatever the temperature in the investigated range, B4C has been observed to react with solid or liquid Al. As long as the temperature is lower than 933 K (660 °C), i.e. as long as Al is in the solid state, interaction proceeds very slowly, giving rise to the formation of ternary carbide (Al3BC) and to diboride (AlB2). At temperatures higher or equal to 933 K, Al is in the liquid state and the reaction rate increases sharply. Up to 1141 ± 4 K (868 ± 4 °C), the reaction products are Al3BC and AlB2: at temperatures higher than 1141 K, Al3 BC is still formed while Al3B48C2 (β-AlB12) replaces AlB2. In the three cases, interaction proceeds via the same mechanism including, successively, an incubation period, saturation of aluminium in B and C, nucleation and growth by dissolution–precipitation of Al3BC and a C-poor boride and, finally, the passivation of B4C by Al3BC. These results are discussed in terms of solid–liquid phase equilibria in the Al–B–C ternary system, with reference to the binary invariant transformation: α-AlB12 + L ⇔ AlB2, which has been found to occur at 1165 ± 5 K (892 ± 5 °C).
TL;DR: In this paper, the sum-over-histories framework for quantum dynamics over the observable and state-vector framework was proposed, as well as degenerate metrics over closed timelike curves to mediate topology change.
Abstract: In seeking to arrive at a theory of “quantum gravity,” one faces several choices among alternative approaches. I list some of these “forks in the road” and offer reasons for taking one alternative over the other. In particular, I advocate the following: the sum-over-histories framework for quantum dynamics over the “observable and state-vector” framework; relative probabilities over absolute ones; spacetime over space as the gravitational “substance” (4 over 3+1); a Lorentzian metric over a Riemannian (“Euclidean”) one; a dynamical topology over an absolute one; degenerate metrics over closed timelike curves to mediate topology change; “unimodular gravity” over the unrestricted functional integral; and taking a discrete underlying structure (the causal set) rather than the differentiable manifold as the basis of the theory. In connection with these choices, I also mention some results from unimodular quantum cosmology, sketch an account of the origin of black hole entropy, summarize an argument that the quantum mechanical measurement scheme breaks down for quantum field theory, and offer a reason why the cosmological constant of the present epoch might have a magnitude of around 10−120 in natural units.
TL;DR: Endophytic diazotrophic bacteria may be more prevalent than previously thought, and perhaps there are many more potentially beneficial N2-fixing bacteria which can be isolated from other agronomically important crops.
Abstract: Acetobacter diazotrophicus was isolated from coffee plant tissues and from rhizosphere soils Isolation frequencies ranged from 15 to 40% and were dependent on soil pH Attempts to isolate this bacterial species from coffee fruit, from inside vesicular-arbuscular mycorrhizal fungi spores, or from mealybugs (Planococcus citri) associated with coffee plants were not successful Other acid-producing diazotrophic bacteria were recovered with frequencies of 20% from the coffee rhizosphere These N2-fixing isolates had some features in common with the genus Acetobacter but should not be assigned to the species Acetobacter diazotrophicus because they differed from A diazotrophicus in morphological and biochemical traits and were largely divergent in electrophoretic mobility patterns of metabolic enzymes at coefficients of genetic distance as high as 0950 In addition, these N2-fixing acetobacteria differed in the small-subunit rRNA restriction fragment length polymorphism patterns obtained with EcoRI, and they exhibited very low DNA-DNA homology levels, ranging from 11 to 15% with the A diazotrophicus reference strain PAI 5T Thus, some of the diazotrophic acetobacteria recovered from the rhizosphere of coffee plants may be regarded as N2-fixing species of the genus Acetobacter other than A diazotrophicus Endophytic diazotrophic bacteria may be more prevalent than previously thought, and perhaps there are many more potentially beneficial N2-fixing bacteria which can be isolated from other agronomically important crops
TL;DR: In this paper, the authors presented new improved equations for three still widely used NaK, NaLi and SiO2 geothermometers (obtained by statistical treatment of the data and application of outlier detection and rejection as well as theory of error propagation).
TL;DR: This review of different instances of gene amplification in a variety of prokaryotes, including their mechanisms of generation and biological role, supports the concept that gene amplification be considered not as a mutation but rather as a dynamic genomic state related to the adaptation of bacterial populations to changing environmental conditions or biological interactions.
Abstract: Gene amplification is a common feature of the genome of prokaryotic organisms. In this review, we analyze different instances of gene amplification in a variety of prokaryotes, including their mechanisms of generation and biological role. Growing evidence supports the concept that gene amplification be considered not as a mutation but rather as a dynamic genomic state related to the adaptation of bacterial populations to changing environmental conditions or biological interactions. In this context, the potentially amplifiable DNA regions impose a defined dynamic structure on the genome. If such structure has indeed been selected during evolution, it is a particularly challenging hypothesis.
TL;DR: In this paper, the authors used a semianalytical approach and a CDM cosmological model to study the gravitational collapse and virialization, the structure, as well as the global and statistical properties of isolated dark matter galactic halos which emerge from primordial Gaussian fluctuations.
Abstract: We use a semianalytical approach and a CDM cosmological model to study the gravitational collapse and virialization, the structure, as well as the global and statistical properties of isolated dark matter galactic halos which emerge from primordial Gaussian fluctuations. From the statistical properties of the density fluctuation field the possible mass aggregation histories (MAHs) are generated, and these histories are used as the initial conditions of the gravitational collapse. To calculate the structure of the virialized systems we have generalized the secondary infall model. Although a range of halo structures is obtained, the average density profiles agree with the profile derived as a fitting formula to results of N-body cosmological simulations. The comparison of the density profiles with the observational data is disscused, and some possible solutions to the disagreement found in the inner regions are discussed. The results of our approach, after considering the gravitational dragging of the baryon matter that forms a central disk in centrifugal equilibrium, show that the Tully-Fisher relation and its scatter can be explained through the initial cosmological conditions. The sigma8=1 SCDM model produces galaxies with high velocities when compared to observations, but when the SCDM power spectrum is normalized to sigma8=0.57 an excellent agreement with the observable TF relation is found, suggesting that this relation is the natural extension to galactic scales of the observed galaxy distribution power spectrum. The theoretical TF scatter is close to the measured one. The slope of the TF relation is practically invariant with respect to the spin parameter lambda.
TL;DR: In this paper, the authors investigate the form of the one-point probability distribution function (pdf) for the density field of the interstellar medium using numerical simulations that successively reduce the number of physical processes included.
Abstract: We investigate the form of the one-point probability distribution function (pdf) for the density field of the interstellar medium using numerical simulations that successively reduce the number of physical processes included. Two-dimensional simulations of self-gravitating supersonic MHD and hydrodynamic turbulence, and of decaying Burgers turbulence, produce in all cases filamentary density structures and a power-law density pdf with logarithmic slope around -1.7. This suggests that the functional form of the pdf and the general filamentary morphology are the signature of the nonlinear advection operator. These results do not support previous claims that the pdf is lognormal. A series of 1D simulations of forced supersonic polytropic turbulence is used to resolve the discrepancy. They suggest that the pdf is lognormal only for effective polytropic indices $\gamma=1$ (or nearly lognormal for $\gamma
ot=1$ if the Mach number is sufficiently small), while power laws develop at high densities if $\gamma<1$. We evaluate the polytropic index for conditions relevant to the cool interstellar medium using published cooling functions and different heating sources, finding that a lognormal pdf may occur at densities between 10$^3$ and at least 10$^4$ cm$^{-3}$. Several applications are examined. First, we question a recent derivation of the IMF from the density pdf by Padoan, Nordlund & Jones because a) the pdf does not contain spatial information, and b) their derivation produces the most massive stars in the voids of the density distribution. Second, we illustrate how a distribution of ambient densities can alter the predicted form of the size distribution of expanding shells. Finally, a brief comparison is made with the density pdfs found in cosmological simulations.
TL;DR: In this article, the authors derived estimates of carbon emissions from the forest sector in Mexico for the year 1985 and for two contrasting scenarios in 2025, covering both tropical and temperate closed forests.
Abstract: Estimates of carbon emissions from the forest sector in Mexico are derived for the year 1985 and for two contrasting scenarios in 2025 The analysis covers both tropical and temperate closed forests In the mid-1980s, approximately 804,000 ha/year of closed forests suffered major perturbations, of which 668,000 ha was deforestation Seventy-five percent of total deforestation is concentrated in tropical forests The resulting annual carbon balance from land-use change is estimated at 670 × 106 tons/year, which lead to net emissions of 523 × 106 tons/year accounting for the carbon uptake in restoration plantations and degraded forest lands This last figure represents approximately 40% of the country's estimated annual total carbon emissions for 1985–1987 The annual carbon balance from the forest sector in 2025 is expected to decline to 280 × 106 t in the reference scenario and to become negative (ie, a carbon sink), 620 × 106 t in the policy scenario A number of policy changes are identified that would help achieve the carbon sequestration potential identified in this last scenario
TL;DR: It is proposed that for plants in which domestication and crop development constitute strong selection for increased growth and reproduction, reallocation of resources may result in lower defence against insects.
Abstract: Plant domestication and agronomic selection for increased yield may have an associated effect of reducing plant defence against herbivorous insects This hypothesis is based on evidence for a metabolic cost associated with defence, and on evidence that increases in yield generally come from the re-partitioning of photoassimilates rather than from fundamental increases in photosynthetic rates We propose that for plants in which domestication and crop development constitute strong selection for increased growth and reproduction, reallocation of resources may result in lower defence against insects We examine this hypothesis by means of comparative studies of growth, reproduction and resistance in a complex of maizes and closely related wild taxa, the teosintes The results of these studies are consistent with assumptions of differential investment in growth and reproduction between wild and domesticated plants A wild perennial grew slowest and had lowest grain production, while a modern cultivar grew fastest and had the highest grain yield A wild annual and a land-race cultivar were intermediate Damage from a diverse assemblage of folivorous insects, and from a specialist stemboring lepidopteran larva, fit the defence predictions closely A gradient of attack levels suggests that the wild perennial is most defended, followed in descending order by the wild annual, the land-race cultivar and the modern high-yielding variety Alternative hypotheses for this pattern are consistent with some, but not all, of our data
TL;DR: In this paper, small clusters of iron, cobalt, and nickel were studied with all-electron density functional calculations using both local and generalized gradient approximations, yielding structures where the bonding is maximized but high magnetic moments still remain, coupled ferromagneticically.
TL;DR: Relationships between alterations in the profile of urinary arsenic (As) species and the presence of cutaneous signs of arsenicism were studied in Region Lagunera, Mexico to confirm the potential relationship between metabolic alterations and overt signs of As toxicity.
Abstract: Relationships between alterations in the profile of urinary arsenic (As) species and the presence of cutaneous signs of arsenicism were studied in Region Lagunera, Mexico. The use of urinary concentrations of putative substrates and products of the As metabolism pathway, as indicators of metabolic efficiency is also discussed. Arsenic was determined by hydride generation atomic absorption spectrophotometry and separation of As species was performed by ion exchange chromatography. The exposed group had an average of 0.408 mg As/l of total As (TAs) in their drinking water, whereas `control' individuals had 0.031 mg/l. Urinary concentrations of arsenic species and TAs were 20 to 95 times higher in the exposed group. Significant increases in the relative proportions of inorganic arsenic (Asi) and monomethylarsonic acid (MMA), accompanied by decreases of dimethylarsinic acid (DMA) were also found in exposed individuals. Therefore, significant decreases in the value of the MMA/Asi, DMA/MMA and DMA/Asi ratios were observed, suggesting a decreased As methylating ability. Exposed individuals bearing cutaneous signs had a significantly longer time of exposure, higher urinary concentrations and proportions of MMA and MMA/Asi values, and significantly lower DMA/MMA than exposed individuals without cutaneous signs. Further research is needed to identify better parameters for assessing the efficiency of As metabolism in chronically exposed populations and to confirm the potential relationship between metabolic alterations and overt signs of As toxicity.
TL;DR: The type of cytogenetic damage observed gives evidence of arsenic as a clastogenic/aneugenic carcinogen in rural populations that live in the same geographical area and have similar socioeconomic status, but different degree of exposure to inorganic arsenic via drinking water.
Abstract: The cytogenetic effects of arsenic exposure were studied among rural populations that live in the same geographical area and have similar socioeconomic status, but different degree of exposure to inorganic arsenic (As) via drinking water. A group of inhabitants of Santa Ana (408.17 μg/l of As in drinking water) were considered the exposed individuals and a group of inhabitants of Nazareno (29.88 μg/l) were considered as controls. Blood and urine samples were obtained from volunteers. Past and current exposure, health, and nutritional status as well as the presence of arsenic skin lesions were ascertained in study participants through questionnaires and physical examination. The frequencies and types of chromosomal aberrations in first-division metaphases were studied in whole blood lymphocyte cultures while the presence of micronuclei (MN) was studied in exfoliated epithelial cells obtained from the oral mucosa and from urine samples. Total arsenic (TAs) content, and the relative proportions of inorganic arsenic (IAs), and the metabolites monomethylarsonic (MMA) and dimethylarsinic (DMA) acid were determined in urine samples. Exposed individuals showed a significant increase in the frequency of chromatid and isochromatid deletions in lymphocytes and of MN in oral and urinary epithelial cells. Males were more affected than females, and a higher number of micronucleated oral cells were found among those individuals with skin lesions. The type of cytogenetic damage observed gives evidence of arsenic as a clastogenic/aneugenic carcinogen
TL;DR: Insects as a major animal group possess enormous biodiversity and form a colossal biomass in nature that generally is wasted, and present a potential sustainable food source for humans.
Abstract: Insects as a major animal group possess enormous biodiversity and form a colossal biomass in nature that generally is wasted. Insects offer us many benefits, including their use in human and animal nutrition, in medicine. religion, art, and handicrafts. Also, they are efficient recyclers of organic matter and provide a source of economic gain for the poor through their commercialization. Even if insects are considered by developed nations as an emergency and non‐conventional food of low prestige, they are part of the daily diet of the larger part of humanity, that conceive them as a healthy, nutritious and savory meal, constituting sometimes the only significant source of protein of good quality. Up to date we have recorded around 2000 different edible insect species in the world. Because of their high nutritive value and ubiquitous presence, insects present a potential sustainable food source for humans. Once was select suitable species and develop appropriate breeding methods, insects can provide a reli...
TL;DR: In this paper, the authors used hydrographic data collected during four cruises to evidence upwelling on the Yucatan Shelf, and describe its structure, which suggests that the YUW is probably caused by bottom friction or other topographical mechanisms.
TL;DR: It is concluded that health education, developed along with community involvement, reduced opportunities for transmission of T. solium in the human-pig cycle.
Abstract: A comprehensive study was undertaken in a rural community in the state of Morelos, Mexico to evaluate health education as an intervention measure against Taenia solium. An educational program was developed to promote recognition and knowledge of the transmission of the parasite and to improve hygienic behavior and sanitary conditions that foster transmission. The effects of educational intervention were evaluated by measuring changes in knowledge and practices and prevalence of human taeniasis and swine cysticercosis before and after the campaign. The health education strategy was implemented with the active participation of the population based on the information obtained from a sociologic study. A questionnaire was designed and used before, immediately after the intervention, and six months later. Statistically significant improvements occurred in knowledge of the parasite, its life cycle, and how it is acquired by humans; however, changes in behavior related to transmission were less dramatic and persistent. The prevalences of cysticercosis in pigs at the start of the education intervention were 2.6% and 5.2% by lingual examination and antibody detection (immunoblot assay), respectively, and approximately one year after the intervention they were 0% and 1.2% (P < 0.05). These changes were accompanied by significant reductions in the reported access of pigs to sources of infection and freedom to roam. We conclude that health education, developed along with community involvement, reduced opportunities for transmission of T. solium in the human-pig cycle.
TL;DR: The phylogenetic analysis based on the 16S rRNA gene sequences showed that M. tianshanense was closely related to the Mesorhizobium phylogenetic branch and could be distinguished from the other four species in this branch, and confirmed that these bacteria constitute a distinct rhizobial species.
Abstract: The genetic and phylogenetic relationships for strains of Mesorhizobium tianshanense and its relatives were compared by an analysis of the results of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of whole-cell proteins, DNA-DNA hybridization, and full 16S rRNA gene sequencing. The strains of M. tianshanense formed a cluster which was distinct from those of other rhizobium species in the clustering analysis of SDS-PAGE. DNA-DNA relatedness between A-1BS (type strain of M. tianshanense) and the type or reference strains for Mesorhizobium loti, M. huakuii, M. ciceri, M. mediterraneum, and cluster U, an unnamed rhizobial group, ranged from 4.4 to 43.8%. The phylogenetic analysis based on the 16S rRNA gene sequences showed that M. tianshanense was closely related to the Mesorhizobium phylogenetic branch and could be distinguished from the other four species in this branch. These results further confirmed that these bacteria constitute a distinct rhizobial species.
Ohio State University1, University of St Andrews2, University of Colorado Boulder3, European Space Agency4, Goddard Space Flight Center5, Johns Hopkins University6, University of California, Los Angeles7, Tel Aviv University8, University of Leicester9, Max Planck Society10, New Mexico State University11, National Autonomous University of Mexico12, Sternberg Astronomical Institute13, Russian Academy of Sciences14, University of California, Berkeley15, University of Nebraska–Lincoln16, Universities Space Research Association17, Space Telescope Science Institute18, Harvard University19, University of Kentucky20, Technion – Israel Institute of Technology21, University of Michigan22, Dominion Astrophysical Observatory23, Bowling Green State University24, Spanish National Research Council25, National Institute of Standards and Technology26, University of Wisconsin-Madison27, National Central University28, European Southern Observatory29, University of Texas at Austin30, Chinese Academy of Sciences31
TL;DR: In this article, the International Ultraviolet Explorer monitored the Seyfert 1 galaxy NGC 7469 continuously in an attempt to measure time delays between the continuum and emission-line fluxes.
Abstract: From 1996 June 10 to July 29, the International Ultraviolet Explorer monitored the Seyfert 1 galaxy NGC 7469 continuously in an attempt to measure time delays between the continuum and emission-line fluxes. From the time delays, one can estimate the size of the region dominating the production of the UV emission lines in this source. We find the strong UV emission lines to respond to continuum variations with time delays of about 23-31 for Lyα, 27 for C IV λ1549, 19-24 for N V λ1240, 17-18 for Si IV λ1400, and 07-10 for He II λ1640. The most remarkable result, however, is the detection of apparent time delays between the different UV continuum bands. With respect to the UV continuum flux at 1315 A, the flux at 1485 A, 1740 A, and 1825 A lags with time delays of 021, 035, and 028, respectively. Determination of the significance of this detection is somewhat problematic since it depends on accurate estimation of the uncertainties in the lag measurements, which are difficult to assess. We attempt to estimate the uncertainties in the time delays through Monte Carlo simulations, and these yield estimates of ~007 for the 1 σ uncertainties in the interband continuum time delays. Possible explanations for the delays include the existence of a continuum-flux reprocessing region close to the central source and/or a contamination of the continuum flux with a very broad time-delayed emission feature such as the Balmer continuum or merged Fe II multiplets.
TL;DR: In summary, ABA appears to inhibit seed germination by restricting the availability of energy and metabolites, which seems consistent with other known effects of ABA.
Abstract: The addition of abscisic acid (ABA) to mature non-dormant seeds inhibits their germination. This effect of ABA might be related to its natural function as an endogenous inhibitor of precocious germination during seed formation. In this work, we studied how ABA affects the germination of mature seeds and the growth of nascent seedlings of Arabidopsis thaliana (L.) Heynh. Our findings were as follows: (i) inhibition by ABA was gradual, dose-dependent, and did not disappear after germination; (ii) inhibition of germination was relieved by the addition of metabolizable sugars or amino acids to the plating media; (iii) the effect of sugars and amino acids was cooperative, indicating that these two groups of metabolites relieve different deficiencies; (iv) ABA caused appreciable alterations in energy and nitrogen metabolism; and (v) ABA prevented the degradation of the seed storage proteins. In summary, ABA appears to inhibit seed germination by restricting the availability of energy and metabolites. This mechanism seems consistent with other known effects of ABA.
TL;DR: The giant magneto-impedance effect (GMI) as mentioned in this paper describes the large relative change of the impedance observed in magnetically very soft ribbon and wire alloys under the application of dc magnetic fields (units of kA m 1 ).
Abstract: The giant magneto-impedance effect (GMI) consists of the large relative change of the impedance (up to around 300%) observed in magnetically very soft ribbon and wire alloys under the application of dc magnetic fields (units of kA m 1 ). The phenomenology of the GMI effect is firstly described including a discussion about its origin which mainly lies in the classical skin-effect. An alternative approach to GMI phenomena considering equivalent circuits is also introduced. The main requirements to detect GMI is to count on a sample with very large circular susceptibility and reduced resistivity provided the frequency of the ac current flowing along the sample (necessary to evaluate the impedance) is high enough (roughly above 0.1 MHz for most samples here considered). The dependence on dc magnetic field, mechanical stresses and particularly on thermal treatments resulting in the induced magnetic anisotropies or in the devitrification of amorphous samples into a nanocrystalline structure are reviewed. First results on GMI in glass-coated amorphous microwires are also reported. The use of the GMI as a tool for studying the inner circular magnetization process or for evaluating the magnetostriction is introduced. Finally, a description on various aspects regarding the development of magnetic field, current, proximity and stress sensor applications is presented.