Showing papers by "National Autonomous University of Mexico published in 1988"

Exponential Amplification of Recombinant- RNA Hybridization Probes

Abstract: We have synthesized recombinant RNA molecules that function both as hybridization probes and as templates for exponential amplification by Qβ replicase. Each recombinant consists of a sequence specific for the protozoan parasite, Plasmodium falciparum, embedded within the sequence of MDV-1 RNA, which is a natural template for Qβ replicase. The probe sequence was inserted within a hairpin loop that occurs on the exterior of MDV-1 RNA. The recombinant RNAs hybridize specifically to complementary DNA, despite topological constraints on the probe domain, are replicated at the same rate as MDV-1 RNA, despite their additional length, and are able to serve as templates for the synthesis of a large number of RNA copies. A Qβ replicase reaction initiated with only 0.14 femtograms of recombinant RNA (1,000 molecules) can produce 129 nanograms of recombinant RNA product in 30 minutes. This represents a one-billion fold amplification. Our results demonstrate the feasibility of employing exponentially replicatable RNAs in bioassays, where they would serve the dual role of specific probe and amplifiable reporter.

Structure and floristic composition of the lowland rain forest of Los Tuxtlas, Mexico

Abstract: Physiognomy, structure and floristic composition of one hectare of lowland tropical rain forest was studied in detail at Los Tuxtlas, Mexico. Physiognomically, the Los Tuxtlas forest should be classified as ‘lowland tropical high evergreen rain forest’. The forest showed a closed canopy at 30–35 m. Of all woody, non-climbing species with a DBH≥1.0 cm 89.4% (94.5% of all individuals) were evergreen, 25.4% (59.5% of the individuals) had compound leaves, and over 80% of species (and individuals) had leaves in the notophyll and mesophyll size classes. The forest structure was characterized by a low density (2976 individuals with a DBH≥1.0 cm, 346 individuals with a DBH≥10.0 cm, per ha, excluding vines) with an average basal area (38.1 m2, DBH≥1.0 cm, 34.9 m2, DBH≥10.0 cm, per ha, excluding vines). This was attributed to the relative maturity of the forest on the study plot. The study plot contained 234 species (11 208 individuals with a height ≥0.5 m), of which 55.1% (34.8% of individuals) were trees, 9.4% (6.8%) shrubs, 3.4% (44.3%) palms, 20.1% (5.2%) vines, 6.8% (8.7%) herbs and 5.1% (0.3%) of unknown lifeform. Furthermore, 58 species of epiphytes and hemi-epiphytes were found. Diversity of trees, shrubs and palms with a DBH≥1.0 cm was calculated as Shannon-Wiener index (4.65), Equitability index (0.65), and Simpson index (0.10). The dominance-diversity curve showed a lognormal form, characteristic for tropical rain forest. The community structure was characterized by a relative dominance of Astrocaryum mexicanum in the understorey, Pseudolmedia oxyphyllaria in the middle storeys, and Nectandra ambigens in the canopy. Species population structures of 31 species showed three characteristic patterns, differentiated by recruitment: continuously high, discontinuously high, and continuously low recruitment. Height/diameter and crown cover/diameter diagrams suggested a very gradual shift from height growth to crown growth during tree development. Forest turnover was calculated as 138 years. Compared to other tropical rain forests the Los Tuxtlas forest had 1. similar leaf physiognomical characteristics, 2. a lower diversity, 3. a lower density, 4. an average basal area, and 5. a slow canopy turnover.

Some aspects of source characteristics of the 19 September 1985 Michoacan earthquake and ground motion amplification in and near Mexico City from strong motion data

Abstract: The Fourier amplitude ratio of the 19 September ( M s = 8.1) to the 21 September 1985 ( M s = 7.6), Michoacan earthquakes obtained from data in and near Mexico City increases from about 3.5 at 0.5 Hz to about 10 at 0.2 Hz. This increase is neither seen in the coastal data nor in the teleseismic broadband GDSN P -wave spectra. It is also not predicted by ω −2 or Gusev9s scaling laws. We tentatively attribute the increase at frequencies of less than 0.5 Hz to a special path and/or a depth of energy release effect for the 19 September earthquake. The damage to Mexico City is mostly related to 0.5 Hz energy. Since at f ≧ 0.5 Hz, the Fourier amplitude ratios in and near Mexico City, along the coast, and at teleseismic distances are nearly equal; we attribute this energy to the source characteristics of the 19 September earthquake. The evidence suggests that the 19 September was about twice more energetic at f ≃ 0.5 Hz than expected from scaling laws and from spectral regression of coastal earthquakes recorded in Mexico City. The analysis of strong motion data recorded in Mexico City shows that the ground motions in the lake bed zone are amplified by 8 to 50 times with respect to a hill zone site in Ciudad Universitaria. The frequency at which the maximum relative amplification occurs varies from site to site and lies between 0.2 and 0.7 Hz. The data suggest that f o = β/4 H , where f o = frequency at which maximum relative amplitude occurs, and β and H are the shear wave velocity and the thickness of the clay layer, respectively. Relatively small, if any, nonlinear behavior of the clay is found at strains of about 0.2 per cent during the great 19 September earthquake. For a given lake bed site, maximum relative amplitude and f o are roughly constant, independent of magnitude, depth, and azimuth of sources located more than about 200 km. Ground motion at lake bed sites in Mexico City with f o ≃ 0.5 Hz appear to be amplified 75 times with respect to hard-rock coastal sites at equal distances from the source. This is also confirmed by M L calculation of the 19 and 21 September earthquakes. For the 19 and 21 September earthquakes, the average values of M L at hard-rock coastal sites (100 ≦ distance ≦ 250 km) are 7.4 and 6.7, whereas they are 8.7 and 8.4 in the lake bed zone (distance ∼300 km), respectively.

Volume regulation in astrocytes: a role for taurine as an osmoeffector.

Abstract: Astrocytes in culture regulate their volume under anisosmotic conditions by as yet unclear mechanisms. In a number of other cells this process involves a loss of intracellular osmotically active solutes, including taurine. The possibility that taurine participates as an osmoeffector in astrocytes was examined in cultured astrocytes exposed to hyposmolar conditions. Astrocytes responded to decreases in osmolarity by rapid swelling followed by a volume regulatory phase. Hyposmotic conditions induced a dramatic increase of 3H-taurine efflux, with a time course corresponding to the cell volume regulatory phase. Decreasing osmolarity from 310 to 254, 198 or 150 m osmoles resulted in the release of 8.2%, 17%, and 54%, respectively, of 3H-taurine previously accumulated by astrocytes. Endogenous taurine concentration decreased 64%. The efflux of 3-H GABA, 3H-glycine, or 3H-D-aspartate was much less affected under similar conditions. These results suggest a role for taurine as an osmoeffector in astrocytes.

Informal Exchange Networks in Formal Systems: A Theoretical Model

Abstract: some degree from access to services provided by the modern state. Networks of reciprocity and patron-client relations have been shown to play an important role within these disadvantaged sectors, in articulating their members to the formal market system and in creating an informal social security system to survive (Lomnitz 1977, 1978, 1982). The present article proposes to examine a different aspect of "informality": the pervasive utilization of informal modes of exchange within the formal sector itself. These exchanges include various forms of trading influence and bureaucratic favors for equivalent services or cash. Depending on the political system, some forms of informal exchange may be tolerated while others may be severely repressed. Even in the latter case, however, illicit economic activities ("economic crimes") in the state bureaucracy are often seen as inevitable (if not actually useful) by members of elite groups within the formal system. I show that these activities are not random or chaotic but are based on informal networks following principles similar to those in shantytown networks: patronage, loyalty, and confianza (trust). Often the networks run underneath and parallel to the formal hierarchy. Weberian analysis of the rationality of bureaucratic systems ignored the informal activities that sprang up within formal organizations as a response to the malfunctionings of bureaucracies. Political science and anthropology, however, based on first-hand observations in underdeveloped, non-Western societies, have developed an extensive literature focusing on the discrepancies between the goals and structures of organizations and the historical and cultural specificities of the social systems in which those organizations are embedded. The main consequences of this conflict appear to be inefficiencies resulting from rigidity and corruption (arising from inefficiency). Personalistic, culturally determined loyalties to kin and local groups often defy the more nationalistic ideologies that underlie bureaucratic rationality. (For a review of this literature, see Britan and Cohen 1980; Scott 1972.) This article is generally in line with the literature mentioned above, but goes a step further in that it sees "informality" not only as a residue of traditionalism, but as an intrinsic element of "formality" insofar as it is a response to the inadequacies of formal

The effect of canopy gaps on growth and morphology of seedlings of rain forest species.

Abstract: Growth and morphology of seedlings of ten tropical rain forest species were studied at Los Tuxtlas, Mexico. Seedlings were grown in three environmental conditions: the shaded forest understorey (FU, receiving 0.9-2.3% of the daily photosynthetic photon flux, PF, above the canopy), a small canopy gap of approx. 50 m2 (SG, receiving 2.1-6.1% of daily PF), and a large canopy gap of approx. 500 m2 (LG, receiving 38.6-53.4% of daily PF). The growth of all species was enhanced in gaps, and in LG the effect was stronger than in SG. Plants grown in LG had a sunplant morphology, with a high root-shoot ratio (R/S), a high specific leaf weight (SLW) and a low leaf area ratio (LAR). Plants grown in SG or FU showed a shade-plant morphology, with a low R/S, a low SLW and a high LAR. Growth responses varied from species unable to grow in the shade but with strong growth in the sun, to species with relatively high growth rates in both shade and sun conditions. Shade tolerant species were able to grow in the shade because of a relatively high unit leaf rate. The pioneerCecropia had a high growth rate in LG because of a high LAR. Most species showed a complex growth response in which they resembled the shade intolerant extreme in some aspects of the response, and the shade tolerant extreme in other aspects.

The Mexico Earthquake of September 19, 1985—Relationships Between Soil Conditions and Earthquake Ground Motions

Abstract: Comparisons are presented between the characteristics of ground motions at five sites underlain by clay at which ground motions were recorded in Mexico City in the earthquake of September 16, 1985 and for which analyses of ground response have been made, based on the measured properties of soils and the motions recorded on hard formations at the National University of Mexico. It is shown that the ground response in areas of Mexico City underlain by clay is extremely sensitive to small changes in the shear wave velocity of the clay and it is suggested that a probabilistic approach which allows for uncertainties in shear wave velocity measurements and in the characteristics of the motions on the hard formations is desirable to assess these effects. Based on the results of such an approach it is concluded that simple ground response analyses can provide very useful data for engineering assessments of the effects of local soil conditions on the characteristics of ground motions likely to develop at s...

The Mexico Earthquake of September 19, 1985—A Study of Amplification of Seismic Waves in the Valley of Mexico with Respect to a Hill Zone Site:

Abstract: Since the installation of an extensive digital strong motion array by Fundacion Javier Barros Sierra in 1987 three moderate earthquakes have been recorded by the array and by the accelerographs operated by Instituto de Ingenieria, UNAM. Using this new data and results from the analysis of previous accelerograms we present spectral ratios at 40 sites in the valley of Mexico with respect to a hill zone site in Ciudad Universitaria (CU). Clear evidence for nonlinear behaviour of the clay is found at Central de Abastos Oficina (CDAO) site during the great Michoacan earthquake (Ms=8. 1). At four other lake bed sites this behaviour is not seen either because none occurred or because of poorer quality of data. The spectral ratio at a given site appears to be roughly independent of magnitude (except, perhaps, during great earthquakes when lake bed sites may behave nonlinearily), azimuth, and depth of earthquakes with epicenters ≥ 200 km from the city. On the lake bed sites of the valley the relative ampl...

Proterozoic and Phanerozoic basement terranes of Mexico from Nd isotopic studies

Abstract: Nd isotopic data were collected on Precambrian crystalline rocks exposed in northern, eastern, and southern Mexico, as well as from lower crustal xenoliths from central Mexico, in order to constrain the age and character of the Mexican basement. The data indicate that basement belonging to the Grenville (1.0 Ga) tectonothermal event extends from Los Filtros, in Chihuahua, northern Mexico, to Oaxaca, in southern Mexico. These rocks all have average Nd crustal residence times (TDM ages) in the range 1.60 to 1.35 Ga. We infer that this results from mixing average 1.9 Ga or older recycled continental crust with 70% to 90% newly derived mantle-crustal material during the Grenville orogeny. To the west of the Precambrian, the basement contains large amounts of Phanerozoic (probably Paleozoic) crust, identified from lower crustal xenoliths with TDM ages less than 1.0 Ga. The crust represented by these xenoliths may have been emplaced as suspect terranes in Mesozoic Cordilleran events. Alternatively, the apparent Paleozoic crust that underlies parts of central Mexico may connect to the Paleozoic metamorphic Acatlan complex in southern Mexico, and together they would constitute a continuation of the Appalachian-Caledonian orogenic belt through Mexico. Our data do not preclude either of these two models.

Genetic diversity and relationships among isolates of Rhizobium leguminosarum biovar phaseoli.

Abstract: Fifty-one isolates of Rhizobium leguminosarum biovar phaseoli from various geographic and ecological sources, largely in Mexico, were characterized by the electrophoretic mobilities of 15 metabolic enzymes, and 46 distinctive multilocus genotypes (electrophoretic types [ETs]) were distinguished on the basis of allele profiles at the enzyme loci. Mean genetic diversity per enzyme locus among the 46 ETs was 0.691, the highest value yet recorded for any species of bacterium. The occurrence of strong nonrandom associations of alleles over loci suggested a basically clonal population structure, reflecting infrequent recombination of chromosomal genes. Multilocus genotypic diversity was unusually high, with the most strongly differentiated pairs of ETs having distinctive alleles at all 15 loci and major clusters of ETs diverging at genetic distances as large as 0.89. This great diversity in the chromosomal genome raises the possibility that R. leguminosarum biovar phaseoli is a polyphyletic assemblage of strains. As other workers have suggested, the inclusion of all strains capable of nodulating beans in a single biovar or species is genetically unrealistic and taxonomically misleading. A biologically meaningful classification of Rhizobium spp. should be based on assessment of variation in the chromosomal genome rather than on phenotypic characters, especially those mediated for the most part or wholly by plasmid-borne genes, such as host relationships.

Treefall age determination and gap dynamics in a tropical forest

Abstract: (1) Most individuals of Astrocaryum mexicanum, a monopodial neotropical understorey palm, endure treefalls that form gaps in the forest, by bending under falling trees and limbs. After one year, a bent palm recovers vertical growth at its terminal meristem and forms a permanent kink in its stem. Previous detailed demographic studies have allowed us to determine with accuracy the passage of time, based on the age-constant rate of stem elongation of the palm. (2) Using this morphological feature of the palm, together with its high density (3001230 mature individuals ha-1) in a 5-ha tract of rainforest at Los Tuxtlas, Veracruz, Mx more than 50% of the quadrats suffered disturbance in the last thirty years and 28% suffered more than one disturbance in the last seventy years. These results provide evidence that canopy disturbances capable of promoting the release of suppressed seedlings and saplings of forest trees may occur at the small scale of some tens of square metres. (4) The long-term treefall patterns analysed (up to seventy years) show that canopy disturbances are a permanent ecological factor in the rainforest environment. Annual rainfall explains more than 50% of the annual variation of the proportion of forest opened to gaps per year. (5) The yearly disturbance does not indicate the gap availability for species regeneration: for example, a year of high disturbance (e.g. 6 1 % of the forest opened to gaps) may have a similar number of sizeable gaps suitable for pioneer regeneration as a year of low disturbance (e.g. 1 5% of the forest opened to gaps). (6) The results obtained in this study show that the gap-formation process operating at Los Tuxtlas forest promotes a strong temporally and spatially random variation in the physical environment of plants. This heterogeneity may be one of the factors involved in determining the high biological diversity found in most tropical rainforests.

The Mexico Earthquake of September 19, 1985—A Theoretical Investigation of Large- and Small-scale Amplification Effects in the Mexico City Valley

Abstract: The linear, large‐scale and small‐scale amplification effects in the Mexico City valley, related to both the surficial clay layer and the underlying thick sediments, are investigated with two‐dimensional (2D) models and compared with the results of simple one‐dimensional (1D) models. The deep sediments are shown to be responsible, on their own, for an amplification ranging between 3 and 7, a part of which is due to the 2D effects in case of low damping and velocity gradient. This result is consistent with the observed relative amplification around 0.5 Hz at CU stations with respect to TACY station. The amplification due to the clay layer is much larger (above 10), and the corresponding 2D effects have very peculiar characteristics. On the one hand, the local surface waves generated on any lateral heterogeneity exhibit a strong spatial decay, even in case of low damping (2%), and the motion at a given site is therefore affected only by lateral heterogeneities lying within a radius smaller than 1 k...

Mycoplasma hyopneumoniae increases the susceptibility of pigs to experimental Pasteurella multocida pneumonia.

Abstract: The interaction between Mycoplasma hyopneumoniae and Pasteurella multocida in experimental pneumonia was investigated in conventional pigs. The experimental animals were 49 days old when inoculated with M. hyopneumoniae; they were inoculated with P. multocida after 23 days, and killed 13 days later. In pigs inoculated only with P. multocida, clinical signs and lung lesions were not observed, and the agent was not recovered. Pigs inoculated with M. hyopneumoniae developed fever, moderate cough and dyspnea which tended to disappear, and small proliferative lung lesions from which M. hyopneumoniae was isolated. Pigs inoculated with both agents had higher fever, severe cough and dyspnea which tended to aggravate, and extensive exudative lung lesions from which organisms were isolated. All animals had similar growth rates, but the group infected with both agents consumed 60% more food. Therefore, M. hyopneumoniae causes mild pneumonia, whereas P. multocida is not pathogenic alone but aggravates the pneumonia initiated by M. hyopneumoniae.

Pioneer species distribution in treefall gaps in Neotropical rain forest; a gap definition and its consequences

Abstract: An attempt was made to evaluate the consequences of applying a strict definition (Brokaw 1982a) to the delimitation of forest gaps in the field. The northernmost Neotropical rain forest, at Los Tuxtlas, Mexico, was searched for young (1–2 years old) single-event gaps that would meet the criteria of the definition. In 60 ha of rain forest, only 12 such gaps containing pioneer species could be found. Thirty-three pioneer species (shrubs and trees) were used as indicator species for gap conditions. Gap size, measured as projected canopy opening (sensu Brokaw 1982a), underestimated from 44 to 515% the size of the area colonized by pioneer species. On average the size of the colonized area was 3.4 times larger than the size of the projected canopy opening. The majority of the pioneer species showed a relative preference for gap borders, an area generally not included in the projected canopy opening. Pioneer plant abundance and density, and species richness and density, did not differ significantly between gap centres and gap borders. Floristical variation was not related to gap size or location in the gap. These findings can be explained if gap environment (to which pioneer plants respond) is seen as the result of many interacting factors, of which size of the canopy opening is only one. It is concluded that the definition for delimiting gaps in the field as proposed by Brokaw (1982a) cannot be regarded a generally applicable definition, and that its value as a comparative standard is doubtful.

Globally stable adaptive controller for systems with delay

Abstract: We propose a globally stable finite spectrum assignment adaptive controller for systems with delay. It is assumed that the process is minimum phase, though not necessarily stable, and the delay is known. It is shown that the plant output asymptotically tracks a reference model output with all signals remaining bounded.

Genomic instability in Rhizobium phaseoli.

Abstract: Experience from different laboratories indicates that Rhizobium strains can generate variability in regard to some phenotypic characteristics such as colony morphology or symbiotic properties. On the other hand, several reports suggest that under certain stress conditions or genetic manipulations Rhizobium cells can present genomic rearrangements. In search of frequent genomic rearrangements, we analyzed three Rhizobium strains under laboratory conditions that are not considered to cause stress in bacterial populations. DNAs from direct descendants of a single cell were analyzed in regard to the hybridization patterns obtained, using as probes different recombinant plasmids or cosmids; while most of the probes utilized did not show differences in the hybridization patterns, some of them revealed the occurrence of frequent genomic rearrangements. The implications and possible biological significance of these observations are discussed.

Proline Accumulation as a Symptom of Drought Stress in Maize: A Tissue Differentiation Requirement

Abstract: Ibarra-Caballero, J., Villanueva-Verduzco, C, Molina-Galan, J. and Sanchez-de-Jimenez, E. 1988.Proline accumulation as a symptom of drought stress in maize: a tissue differentiation requirement—J. exp. Bot. 39: 889-897.Seedlings and callus tissue of maize (Zea mays L.) were tested for proline accumulation under droughtstress. A variety from a tropical humid region, a semi-desertic variety and its improved populationselected for drought stress resistance, were used for this study.Proline accumulation was found in green leaves of maize seedlings under drought stress; nocorrelation was found between proline accumulation in leaves and the variety or population tested.White tissue, callus and leaves of etiolated seedlings did not show this response to drought stress, nordid green callus or detached leaves (green or etiolated), even when stress caused a loss of water fromleaves similar to that observed when whole seedlings were drought-stressed. Addition of abscisic acidto green or white tissue did not result in proline accumulation. The above data indicate that prolineaccumulation caused by drought stress does not seem to be an indication of drought stress resistance,but rather a symptom of it. For this accumulation to take place it seems that fully organizedchloroplasts are required as well as the systemic development of the plant.Key words— Proline, maize, drought-stress.Correspondence to: Departamento de Bioqulmica, Facultad de Quimica, UN AM, Mexico, D.F.

The Mexico Earthquake of September 19, 1985—On the Seismic Response of the Valley of Mexico

Abstract: In order to explain damage and observed ground motions in Mexico City during the 1985 Michoaca´n earthquake, simultaneous consideration must be given to source, path, and site conditions. This is clear from teleseismic records and local vertical displacements. Incident waves had an important part of energy in the frequency band of 0.3‐1 Hz. Damage distribution and observed motion in the lake bed zone cannot be satisfactorily explained using one‐dimensional theory. The effects of lateral irregularities are required. To assess its effects we describe the stratigraphic setting of the valley and discuss some features of damage distribution with results for one‐ and two‐dimensional wave propagation models. These are useful to establish on quantitative basis the importance of lateral heterogeneity.

Sperm shape abnormality and urine mutagenicity in mice treated with niclosamide.

Abstract: Niclosamide, a widely used anthelmintic drug in underdeveloped countries, is known to be mutagenic in the Salmonella typhimurium microsomal test system. The urine obtained from mice treated with niclosamide is mutagenic in the TA98 and TA1538 strains. Its effects on mouse-sperm morphology were evaluated in CD1 and (BALB/cJ x DBA/2J) F1 mice after 5 daily oral niclosamide doses of either 60, 80, 100 or 120 mg/kg. A statistically significant increase in abnormal sperm morphology was detected in both CD1 and (BALB/cJ x DBA/2J) F1 mice. No drug-related effects on testis weight nor on sperm count were observed in either genotype. Urine samples obtained from niclosamide-treated F1 mice were assayed with the Salmonella typhimurium strain TA1538 both in the absence and presence of beta-glucuronidase. In the absence of glucuronidase, urine mutagenicity increased with increasing dose and the highest doses were toxic. In the presence of glucuronidase, urine mutagenicity and toxicity also increased. Only at the highest dose (120 mg/kg), however, was there a positive correlation between the urine mutagenic activity and an increase in the number of abnormal sperm. The results of this study suggest that the increase in abnormal sperm depends on the systemic presence of non-conjugated niclosamide metabolites.

Encephalomyelitis, reproductive failure and corneal opacity (blue eye) in pigs, associated with a paramyxovirus infection.

Abstract: A new clinicopathological disorder associated with a paramyxovirus infection in pigs is described. Central nervous system manifestations and corneal opacity are the main features in piglets two to 21 days old. Older pigs seem to be more resistant and only corneal opacity is commonly observed. In pregnant sows the virus appears to be responsible for reproductive disturbances such as stillbirth, mummification and a return to oestrus. The changes are mainly microscopic and characterised by a non-suppurative encephalomyelitis, interstitial pneumonia and anterior uveitis with corneal oedema. Experimental infection of one-day-old piglets with the virus reproduced clinical signs similar to those described in naturally infected piglets. The virus was recovered from the tonsils, lung and brain of the experimentally infected piglets between the fourth and 20th day after infection.

On multiplicative graphs and the product conjecture

Abstract: We study the following problem: which graphsG have the property that the class of all graphs not admitting a homomorphism intoG is closed under taking the product (conjunction)? Whether all undirected complete graphs have the property is a longstanding open problem due to S. Hedetniemi. We prove that all odd undirected cycles and all prime-power directed cycles have the property. The former result provides the first non-trivial infinite family of undirected graphs known to have the property, and the latter result verifies a conjecture of Nesetřil and Pultr These results allow us (in conjunction with earlier results of Nesetřil and Pultr [17], cf also [7]) to completely characterize all (finite and infinite, directed and undirected) paths and cycles having the property. We also derive the property for a wide class of 3-chromatic graphs studied by Gerards, [5].

The Mexico Earthquake of September 19, 1985—Natural Period of Sites in the Valley of Mexico from Microtremor Measurements and Strong Motion Data

Abstract: The period at which peak in the microtremor Fourier velocity spectra occurs in the transition and lake bed zones of the valley of Mexico is found to be the natural period of the site. These periods in the valley are compiled from the microtremor measurements carried out by Instituto de Ingenieri´a, UNAM and scientists from Japan (for a total of 181 sites). Using this data and the natural periods estimated from strong motion recordings (36 sites), an isoperiod contour map of the valley of Mexico is presented. This map may be useful in future design of important structures.

The Mexico Earthquake of September 19, 1985—Nonstationary Models of Seismic Ground Acceleration

Abstract: Characteristics of a nonstationary process obtained by modulating the amplitude and frequency of a stationary process differ from those of an oscillatory process. An accelerogram recorded in the soft soil of Mexico City during the 1985 earthquake serves to calibrate both nonstationary models. Responses of linear and nonlinear single‐degree‐of‐freedom systems indicate that the process with modulated amplitude and frequency is preferable for reliability studies. Coefficients of variation of ductility demands of systems excited with accelerograms generated by the model with modulated amplitude and frequency are close to those corresponding to actual accelerograms.

Neutral stellar winds that drive bipolar outflows in low-mass protostars

Abstract: The Arecibo radio telescope at the 21-cm line of atomic hydrogen has been used to detect a neutral atomic wind in the bipolar flow source HH 7-11. An atomic mass of about 0.015 solar associated with the rapidly flowing gas is deduced. The stellar mass-loss rate is roughly 3 x 10 to the -6th solar mass/yr if the crossing time of the decelerating wind is 5000 yr. The excess emission in the H I line core gives a total duration of the outflow of about 70,000 yr. A detailed analysis of the H I line shape yields a reasonable deceleration rate for the atomic wind if the stellar wind continuously entrains ambient molecular gas as it propagates from the protostar. A stellar wind with the described characteristics and a terminal velocity of 170 km/s would be more than sufficient to drive the known extended CO bipolar outflow in HH 7-11.

Macroscopic approach to universal conductance fluctuations in disordered metals.

Abstract: Recently, a macroscopic theory of N-channel disordered condeuctors showed that the statistical distribution of the transfer matrix for a system of length L evolves with L according to a diffusion equation in N dimensions. It is proved here that the recently observed universal conductance fluctuations in normal metals at very low temperatures are a rigorous consequence of that diffusion equation, in the regime in which L\ensuremath{\gg} (mean free path) and N\ensuremath{\gg}1. The value found for the fluctuation coincides with the one obtained from elaborate microscopic calculations.