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Showing papers by "National Autonomous University of Mexico published in 1977"


Book ChapterDOI
01 Jan 1977
TL;DR: The coastal zone of Mexico extends 10,000 kilometers along the borders of the Pacific, Gulf of California and Gulf of Mexico and contains approximately 125 coastal lagoons defined here as: "a coastal zone depression below MHHW, having permanent or ephemeral communication with the sea, but protected from the sea by some type of barrier".
Abstract: The coastal zone of Mexico extends 10,000 kilometers along the borders of the Pacific, Gulf of California, Gulf of Mexico and Caribbean and contains approximately 125 coastal lagoons defined here as: “a coastal zone depression below MHHW, having permanent or ephemeral communication with the sea, but protected from the sea by some type of barrier.” Mexican coastal lagoons vary widely in their physical and environmental characteristics and in their degree of man's use and modification. They are geologically classified according to origin of the depression and barrier characteristics as: I. Differential Erosion (usually drowned valleys but includes solution depressions); II. Differential Terrigenous Sedimentation (typically associated with fluvial/deltaic systems); III. Barred Inner Shelf (offshore barrier on inner continental shelf); IV. Organic (usually coralgal but includes also mangrove and other organisms); V. Tectonic-Volcanic (directly linked with faulting, folding, or volcan-ism). Many coastal lagoons are compounds of two or more basic classes. Interrelating the original geomorphic characteristics with geologic development history, coastal oceanography and regional climatology, one may predict major types of existing lagoon environmental systems. Brief case studies illustrate the main mexican coastal lagoon types.

248 citations


Journal ArticleDOI
TL;DR: Results indicated that toxicity in sponges increased with decreasing latitude, and a hypothesis is proposed which explains the relationship between species diversity of fishes and sponge toxicity with latitude.
Abstract: An investigation of the ecology of toxicity in marine sponges from different latitudes on the North American continent was made. Results indicated that toxicity in sponges increased with decreasing latitude. Three of the 34 species (9%) of sponges from San Juan Island, Washington, USA (48°N), were toxic to fishes. Nine of the 44 species (20%) of sponges from Santa Catalina Island, California, USA (33°N), were toxic. Seven of the 11 species (64%) of sponges from Zihuatanejo Bay, Guerrero, Mexico (17°N), were toxic. Twenty-seven of the 36 species (75%) of sponges from La Blanquilla, Veracruz, Mexico (19°N), were toxic. Most of these toxic sponges are openly exposed to fishes. The most common exposed sponges proved to be highly toxic to fishes. Force-feeding experiments conducted with wrasses demonstrated the effectiveness of the toxin of sponges. A hypothesis is proposed which explains the relationship between species diversity of fishes and sponge toxicity with latitude.

120 citations


Journal ArticleDOI
TL;DR: In this paper, the effects of wind and rain on surface reaeration in lakes and lagoons were analyzed and it was shown that the direct addition of oxygen from oxygen-saturated raindrops can be an important factor in re-aeration.
Abstract: Over the years, considerable research has been conducted on the subject of surface reaeration in rivers and estuaries. As a result much information is now available to determine the surface reaeration coefficient in these bodies of water. In contrast, not much is yet known about the magnitude of this coefficient in lakes and lagoons. Some studies indicate that wind action is important in establishing the rate of oxygen transfer across the surface of a lake or lagoon. In addition, it appears that the effect of rainfall may be important in reaeration in some lakes. In the present study, analyses were made of the effects of wind and rain on reaeration. Expressions were developed relating the rate and power of a rainfall to the surface reaeration coefficient. It was also determined that the direct addition of oxygen from oxygen-saturated raindrops can be an important factor in reaeration.

109 citations


Journal ArticleDOI
TL;DR: Weiner, Langley, and Ford as discussed by the authors found that the sum and difference of coexisting densities of S${\mathrm{F}}_{6}$ are consistent, within a range of 2% in reduced temperature of ${T}_{c}$, with the series of terms (revised and extended scaling) predicted by renormalization group calculations.
Abstract: The data of Weiner, Langley, and Ford on both the sum and difference of coexisting densities of S${\mathrm{F}}_{6}$ are found to be consistent, within a range of 2% in reduced temperature of ${T}_{c}$, with the series of terms (revised and extended scaling) predicted by renormalization group calculations. The hypothesis that the relatively small range of applicability of this series is due to a crossover to Van der Waals behavior is supported by further analysis.

104 citations


Journal ArticleDOI
TL;DR: Toxin γ, the major and most basic toxin, is a 62-residue protein that, unlike other scorpion toxins, contains methionine and is the first example of a fifth structural type of mammalian toxin from scorpion venom.

88 citations


Journal ArticleDOI
TL;DR: In this paper, a technique to study the shape of small metal particles (20 to 200 A in diameter) is described, which consists in high-resolution dark-field electron microscopy using weak beams under diffraction conditions in which a large number of beams are excited.
Abstract: A technique to study the shape of small metal particles (20 to 200 A in diameter) is described. This consists in high-resolution dark-field electron microscopy using weak beams under diffraction conditions in which a large number of beams are excited. Many-beam dynamical electron diffraction theory is used to explain the effect. Examples of application of this technique in the study of growth of thin films are presented. It is found that epitaxial gold particles growing on a NaCl substrate have square and rounded pyramids shapes which are very often truncated. On decrit une technique pour etudier la forme de petites particules de metal (20 a 200 A en diametre). Cette technique est celle de la microscopie electronique en champ noir de haute resolution en utilisant des faisceaux a faible intensite sous des conditions de diffraction, dans la quelle un grande nombre de faisceaux sont excites. La theorie dynamique des faisceaux est utilisee pour expliquer cet effet. On presente des examples sur l'application de cette technique en l'etude de l'agrandissement des pellicules minces. On trouve que des particules d'or du type epitaxial que croissent sur un substrat de NaCl ont une forme pyramidal carree et arrondie, cettes formes sont tres frequement tronquees.

82 citations


Journal ArticleDOI
TL;DR: In this article, a rationale for comparing obtained reliability to reliability that would result from a random-chance model is explained, and statistical procedures that could be used to determine whether obtained reliability is significantly superior to chance reliability are reviewed.
Abstract: Previous recommendations to employ occurrence, nonoccurrence, and overall estimates of interobserver reliability for interval data are reviewed. A rationale for comparing obtained reliability to reliability that would result from a random-chance model is explained. Formulae and graphic functions are presented to allow for the determination of chance agreement for each of the three indices, given any obtained per cent of intervals in which a response is recorded to occur. All indices are interpretable throughout the range of possible obtained values for the per cent of intervals in which a response is recorded. The level of chance agreement simply changes with changing values. Statistical procedures that could be used to determine whether obtained reliability is significantly superior to chance reliability are reviewed. These procedures are rejected because they yield significance levels that are partly a function of sample sizes and because there are no general rules to govern acceptable significance levels depending on the sizes of samples employed.

80 citations


Book ChapterDOI
TL;DR: In this article, the degree of occupational choice that women have within the structural margins of employment in the informal labour sector has been explored, and it is shown that the majority of those left out of the formal occupational structure are women.
Abstract: In recent years, the informal labour sector has increasingly represented a testing point for theories of development The proliferation of informal jobs in developing countries has been considered alternately a stage in the process of development and a blind alley leading a country back into underdevelopment But social scientists and policymakers have rarely recognized that the majority of those left out of the formal occupational structure are women It is, however, very difficult to establish the heuristic boundaries of the informal labour sector, particularly with respect to women Are we referring to the intermittent part-time activities of women outside the household both in cities and in rural areas? But men also engage in such activities, for example, as street peddlers Is the unpaid work of the wife and young unmarried daughters in a family enterprise such as a store an informal job? If unpaid labour is to be included in the informal labour sector, then women’s voluntary community service and their unpaid domestic labour must also be taken into account Moreover, since informal labour also comprises work not regulated through a contract, all low income, non-contractual jobs registered as formal occupations, such as paid domestic service, belong to this classification Many low income and low productivity jobs included in the formal occupational structure and registered in national censuses, even when such a contract does exist, can be considered as a continuation of informal jobs as well and thus must be analysed within the informal labour sector This paper assumes that the nature of the informal labour sector in a developing economy is a direct outgrowth of the type of industrialization a country is undergoing Within this framework, this paper explores the degree of occupational choice that women have within the structural margins of employment

70 citations



Journal ArticleDOI
TL;DR: In this paper, an approximate method is developed which replaces computation of the ellipsoid coordinates with that of a linear combination of responses to individual components, which is used to verify whether a structure is safe, at a specified reliability level, under the combined effect of several simultaneous earthquake components.
Abstract: Current design criteria are intended to provide values of structural responses to a single component of a design earthquake, at a fixed exceedance probability. It is desirable to know whether a structure is safe, at that reliability level, under the combined effect of several simultaneous earthquake components. If the component accelerograms are idealized as zero-mean Gaussian processes and the structure behaves linearly, then structural responses associated with a given exceedance probability define an ellipsoid in the response space. In this space, points falling inside the failure surface (interaction surface) correspond to survival; those outside, to failure. A structure is safe, at the specified reliability level, if the corresponding ellipsoid falls entirely within the survival region. Computations to verify this condition are, however, quite awkward. An approximate method is developed which replaces computation of the ellipsoid coordinates with that of a linear combination of responses to individual components.

66 citations


Book ChapterDOI
01 Jan 1977
TL;DR: This chapter discusses the effects and mechanism of action of molecules that upon incorporation into model and biological lipid bilayers increase the permeability of the membrane to ions.
Abstract: Publisher Summary This chapter discusses the effects and mechanism of action of molecules that upon incorporation into model and biological lipid bilayers increase the permeability of the membrane to ions. As the molecules act similarly in biological and synthetic lipid membranes, it is assumed that these compounds operate in the lipid milieu of the membrane. The biological membranes are a fluid mosaic composed of lipids arranged in a bilayer in which proteins either go across the lipid phase or are partially submerged in the membrane. The membranes formed exclusively with lipids are highly impermeable to ions and the impermeability is determined by the existence of the lipid bilayer. Compounds that lower ion permeability have been used to explore the properties and structure of biological membranes. The ATP synthesis can be driven by a proton-motive force of sufficient magnitude

Journal ArticleDOI
TL;DR: The mestizo nose, precisely because it is the product of racial mixture, is a complex entity difficult to describe.

Journal ArticleDOI
TL;DR: A comparison of Old WorldErythrina and their pollinators with New World species pollinated by orioles and hummingbirds suggests that parallel evolution has occurred, and it is clear that various New WorldIcteridae, Thraupidae, etc. are ecological equivalents ofOld WorldOriolidae, Pycnonotidae, Sturnidae, etc and that flowers pollination by these birds have similar characteristics.
Abstract: Erythrina breviflora is visited by large numbers of passerine birds of which orioles (Icterus: Icteridae) are the primary pollinators. The flowers produce large quantities of nectar but they are rarely visited by hummingbirds. Inflorescence and floral morphology, and low levels of sucrose in the nectar probably explain the rarity of foraging hummingbirds. A comparison of Old WorldErythrina and their pollinators with New World species pollinated by orioles and hummingbirds suggests that parallel evolution has occurred. When the comparison is expanded to include other species pollinated by orioles, it is clear that various New WorldIcteridae, Thraupidae, etc. are ecological equivalents of Old WorldOriolidae, Pycnonotidae, Sturnidae, etc. and that flowers pollinated by these birds have similar characteristics.

Journal ArticleDOI
TL;DR: Growth in total length of juvenile Penaeus vannamei Boone was between 0·8 and 1·4 mm per day at water temperatures between 25 and 35 °C, and growth was density dependent at densities higher than 2·5 m −2.

Journal ArticleDOI
TL;DR: It is suggested that in subcortical limbic regions and in the area of the DA cell body group innervating the limbic system, there exist muscarinic acetylcholine receptors which on activation can increase activity in inhibitory GABA interneurons, which in the midbrain can directly control activity in the ascending mesolimbic DA pathways.


Journal ArticleDOI
TL;DR: The lower Toluca Pumice bedeckt ungefahr 400 km2 and has a Volumen of rund 0,33 km3 (porenfrei gerechnet von 0,16 km3). Nach der 10-cm-Machtigkeitskurve zeigt er einen nordostgerichteten Verbreitungsfacher.
Abstract: Die Unteren und die Oberen Bimssteine des Toluca sind dacitische air fall-Ablagerungen, die vor etwa 24 500 bzw. 11 600 Jahren gefordert wurden. Der „Lower Toluca Pumice“ bedeckt ungefahr 400 km2 und hat ein Volumen von rund 0,33 km3 (porenfrei gerechnet von 0,16 km3). Nach der 10-cm-Machtigkeitskurve zeigt er einen nordostgerichteten Verbreitungsfacher. Der „Upper Toluca Pumice“ bedeckt mehr als 2000 km2; sein Volumen betragt rund 2,3 km3, wenn man die 40-cm-Machtigkeitskurve zugrundelegt. Das Gesamtvolumen durfte bei 3,5 km3 (porenfrei gerechnet bei 1,54 km3) liegen. Sein symmetrischer Verbreitungsfacher hat die Richtung N 65° E.

Journal ArticleDOI
TL;DR: It was found that both high and low doses of anisomycin decreased rapid eye movement (REM) sleep, while only high doses of ChA and V produced such a decrease.
Abstract: The present investigation sought to determine the effects of Anisomycin (A), Chloramphenicol (ChA), Vincristine (V), and Penicilline G on the sleep-wake cycle of rats. It was found that both high and low doses of anisomycin decreased rapid eye movement (REM) sleep, while only high doses of ChA and V produced such a decrease. Slow wave sleep (SWS) was unaffected by these drugs. Penicilline G, on the other hand, had no effect on the sleep-wake cycle. It was further shown that the reduction of REM sleep was the result of a decrease in the number of REM periods rather than in the duration of each individual period. These results suggest that protein synthesis may participate in the mechanisms that trigger REM sleep.


Journal ArticleDOI
TL;DR: The results are described of using the Ribi cell fractionator as an adequate disruption method for the reproducible preparation of coupled yeast mitochondria by means of a procedure that takes approximately two hours.

Journal ArticleDOI
TL;DR: Computer simulations of this model reproduced all the observed features of the enzyme behavior and showed that the free pyridoxal phosphate‐dependent activity can be abolished when either all substrate or all cofactor are in the form of Schiff base.
Abstract: — The kinetic behavior of glutamate decarboxylase from mouse brain was analyzed in a wide range of glutamate and pyridoxal 5′-phosphate concentrations, approaching three limit conditions: (I) in the absence of glutamate-pyridoxal phosphate Schiff base; (II) when all glutamate is trapped in the form of Schiff base; (III) when all pyridoxal phosphate is trapped in the form of Schiff base. The experimental results in limit condition (I) are consistent with the existence of two different enzyme activities, one dependent and the other independent of free pyridoxal phosphate. The results obtained in limit conditions (II) and (III) give further support to this postulation. These data show that the free pyridoxal phosphate-dependent activity can be abolished when either all substrate or all cofactor are in the form of Schiff base. The free pyridoxal phosphate-independent activity is also abolished when all substrate is trapped as Schiff base, but it is not affected by the conversion of free pyridoxal phosphate into the Schiff base. A kinetic and mechanistic model for brain glutamate decarboxylase activity, which accounts for these observations as well as for the results of previous dead end-inhibition studies, is postulated. Computer simulations of this model, using the experimentally obtained kinetic constants, reproduced all the observed features of the enzyme behavior. The possible implications of the kinetic model for the regulation of the enzyme activity are discussed.

Journal ArticleDOI
TL;DR: In this paper, the authors considered the low-frequency limit of cross sections for massless scalar, electromagnetic, and gravitational waves scattering on a Schwarzschild black hole and found explicit results for the scattering amplitudes.
Abstract: We consider the low-frequency limit of cross sections for massless scalar, electromagnetic, and gravitational waves scattering on a Schwarzschild black hole. Explicit results are found for the scattering amplitudes, which differ from the Born approximation results.



Journal ArticleDOI
TL;DR: In this paper, a simple way to obtain an exact closed-form expression for the vertical component of the gravitational attraction of a vertical right circular cylinder is presented, which consists of taking the Fourier-Hankel transform of Poisson's equation and looking up certain integrals and avoids tricky integrations commonly employed in obtaining such expressions.
Abstract: Summary. A simple way to obtain an exact closed-form expression for the vertical component of the gravitational attraction of a vertical right circular cylinder is presented. The method consists of taking the Fourier-Hankel transform of Poisson’s equation and looking up certain integrals and avoids tricky integrations commonly employed in obtaining such expressions.

Journal ArticleDOI
TL;DR: In this paper, all electron, restricted Hartree-Fock calculations are performed on various configurations of a molecular compounds stimulating the reaction TiCl 4 · Al(CH 3 ) 3 +C 2 H 4 → TiCl4 · Al (CH 3 ), 2 · C 3 H 7, and a minimal basis set of contracted gaussians has been used to describe the molecular orbitals.

Journal ArticleDOI
TL;DR: The ability of mitochondria to concentrate ethidium bromide may be involved in the selectivity of the dye as a mitochondrial mutagen, producing its effects at different levels of mitochondrial function.

Journal ArticleDOI
TL;DR: In this paper, the impact of agribusiness on Latin American agriculture in general and the rural proletariat in particular is discussed, and the authors take a pessimistic view of the possibilities of reversing or halting this process unless rural proletariat somehow takes political action to change the system.

Journal ArticleDOI
TL;DR: Results are consistent with previous findings suggesting the existence of two kinds of glutamate decarboxylase activity differing in their dependence on free pyridoxal phosphate, and are interpreted in terms of an ordered binding of pyridine phosphate and glutamate to the enzyme.
Abstract: — Seven N-(5′-phosphopyridoxyl) amino acids, reduced analogs of the glutamate-pyridoxal phosphate Schiff base, were synthesized and purified. All of them inhibited mouse brain glutamate decarboxylase activity. The four most potent inhibitors were the aminooxyacetate, GABA, cysteinesul-finate and glutamate derivatives, and the effect of these compounds was studied kinetically. The inhibition produced was in all cases mixed function with respect to glutamate and competitive with respect to pyridoxal phosphate. The inhibition kinetics were non-linear. These results are interpreted in terms of an ordered binding of pyridoxal phosphate and glutamate to the enzyme. Furthermore, they are consistent with previous findings suggesting the existence of two kinds of glutamate decarboxylase activity differing in their dependence on free pyridoxal phosphate.

Journal ArticleDOI
TL;DR: An abstract definition of formally symmetric operators is given and it is shown that the problem of connecting solutions of equations associated with this kind of operators leads to complete connectivity conditions, meaning the variational principles previously developed as well as a present more general one are applicable.
Abstract: A previous paper introduced the notion of complete connectivity conditions and developed variational principles for diffraction problems subjected to such restrictions. Here, an abstract definition of formally symmetric operators is given and it is shown that the problem of connecting solutions of equations associated with this kind of operators leads to complete connectivity conditions. The variational principles previously developed as well as a present more general one are thus applicable. The problem of connecting solutions defined in different regions is basic for finite element formulations. Formally symmetric operators occur in many branches of science and engineering. Applications are given here to potential theory, wave propagation, elasticity, and a general class of boundary integral equations.