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Una población relicta de Acer saccharum subsp. skutchii (Aceroideae) en el estado de Guerrero, México
Yalma L. Vargas-Rodriguez
Acta botánica mexicana , 2011,
Abstract: Se describe la estructura, composición, diversidad, relaciones ambientales y conservación de un bosque mesófilo con Acer saccharum subsp. skutchii (arce azucarero) recientemente encontrado en el municipio de Coahuayutla de José María Izazaga, Guerrero. Se registraron los individuos le osos con >1 cm dap en parcelas circulares de 10 m de radio, y la altura de plántulas y plantas juveniles del arce azucarero en parcelas de 5.6 m de radio. Para cada especie se obtuvo su valor de importancia. Se utilizó la técnica de ordenación Escalar Multidimensional No-métrica (NMDS) para explorar sus correlaciones con variables edafológicas, coordenadas geográficas, de elevación y apertura de claros. Se registraron 43 especies de plantas le osas en una superficie de 0.126 ha. Las familias mejor representadas fueron Asteraceae y Fagaceae. La distribución diamétrica de las plantas le osas mostró una forma de "J" invertida, indicando regeneración exitosa. El arce azucarero fue codominante en el dosel con Carpinus caroliniana y Quercus uxoris. Tanto en la población de Guerrero, como en las otras cinco localidades donde habita el árbol en México y Guatemala, la mayoría de las correlaciones encontradas entre la presencia y ausencia de árboles, incluyendo Acer saccharum subsp. skutchii, y los factores ambientales se refirieron a las características de suelo. De las especies registradas en el estudio, 30% están incluidas en alguna categoría de riesgo. El régimen de incendios en la zona pone en peligro la persistencia de este árbol en el sitio de estudio.
Small-scale environmental gradients in a pine-oak forest community in Nueva Colonia, Mezquitic, Jalisco, Mexico
Nieves-Hernández, Gregorio;Vázquez-García, J. Antonio;Vargas-Rodriguez, Yalma L.;Vázquez-García, Marcelino;González-Gallegos, Jesús;
Polibotánica , 2009,
Abstract: we explored environmental variables related to pine-oak forest community structure at one locality in jalisco, mexico. we used an nms ordination in conjunction with the s？rensen distance to identify the major small-scale community gradients along 25 contiguous quadrats (25 m x 25 m, 400 m2 each) of pine-oak forest in nueva colonia, mezquitic, jalisco, mexico. the main matrix (25 stands x 7 tree species) included basal area data, and the environmental matrix consisted of 19 quantitative environmental variables. community structure, through sociological ordination, showed a direct correlation with the vertical altitudinal gradient and apparent soil density, as well as with slope inclination across the horizontal gradient; it also showed an inverse correlation with cation exchange capacity, ca + mg, mg, and altitude across the horizontal gradient. direct gradient analyses showed an increase of cation exchange capacity, ca+mg, mg and k with decreasing altitude along the vertical gradient (from north to south). total nitrogen increased with decreasing altitude across the horizontal gradient (from west to east). in addition, we identified three main community groups using upgma cluster analysis; however, groups were weakly related to the ordination results and to the physical space. at the 1-hectare scale, species composition and basal area of pine-oak forest in nueva colonia can be explained by niche partitioning of altitude and soil gradients. the relevance of nitrogen for this community could be the result of habitat specialization or disturbance history.
A spherically symmetric dust-space-time with a NUT-like rotation
Hector Vargas-Rodriguez
Physics , 2004,
Abstract: A deduction of a solution of the Einstein's equations, employing the Mitskievich's field theoretic description of perfect fluids, is presented. This solution describes a dust-space-time with a spherical-like symmetry and a NUT-like rotation. This solution is of Petrov type D, and has an isometry group G4. It also admits closed timelike geodesics. It has Minkowski space-time as a limit, when both dust and rotation disappear.
The importance of scale-dependent ravine characteristics on breeding-site selection by the Burrowing Parrot, Cyanoliseus patagonus
Francisco A. Squeo,Jose-Enrique Novoa-Jerez,Myriam Ramirez-Herranz,Renzo Vargas-Rodriguez,Rodrigo S. Rios
- , 2017, DOI: 10.7717/peerj.3182
Abstract: In birds, the environmental variables and intrinsic characteristics of the nest have important fitness consequences through its influence on the selection of nesting sites. However, the extent to which these variables interact with variables that operate at the landscape scale, and whether there is a hierarchy among the different scales that influences nest-site selection, is unknown. This interaction could be crucial in burrowing birds, which depend heavily on the availability of suitable nesting locations. One representative of this group is the burrowing parrot, Cyanoliseus patagonus that breeds on specific ravines and forms large breeding colonies. At a particular site, breeding aggregations require the concentration of adequate environmental elements for cavity nesting, which are provided by within ravine characteristics. Therefore, intrinsic ravine characteristics should be more important in determining nest site selection compared to landscape level characteristics. Here, we assess this hypothesis by comparing the importance of ravine characteristics operating at different scales on nest-site selection and their interrelation with reproductive success. We quantified 12 characteristics of 105 ravines in their reproductive habitat. For each ravine we quantified morphological variables, distance to resources and disturbance as well as nest number and egg production in order to compare selected and non-selected ravines and determine the interrelationship among variables in explaining ravine differences. In addition, the number of nests and egg production for each reproductive ravine was related to ravine characteristics to assess their relation to reproductive success. We found significant differences between non-reproductive and reproductive ravines in both intrinsic and extrinsic characteristics. The multidimensional environmental gradient of variation between ravines, however, shows that differences are mainly related to intrinsic morphological characteristics followed by extrinsic variables associated to human disturbance. Likewise, within reproductive ravines, intrinsic characteristics are more strongly related to the number of nests. The probability of producing eggs, however, was related only to distance to roads and human settlements. Patterns suggest that C. patagonus mainly selects nesting sites based on intrinsic morphological characteristics of ravines. Scale differences in the importance of ravine characteristics could be a consequence of the particular orography of the breeding habitat. The arrangement of resources is associated to the
Effects of Bentonite on p-Methoxybenzyl Acetate: A Theoretical Model for Oligomerization via an Electrophilic-Substitution Mechanism
Manuel Salmón,Rene Miranda,Ines Nicolás-Vázquez,Yolanda Marina Vargas-Rodriguez,Julian Cruz-Borbolla,María Isabel Medrano,José Antonio Morales-Serna
Molecules , 2011, DOI: 10.3390/molecules16021761
Abstract: Tonsil Actisil FF, a commercial bentonitic clay, promotes the formation of a series of electrophilic-aromatic-substitution products from para-methoxybenzyl acetate in carbon disulfide. The molecules obtained correspond to linear isomeric dimers, trimers, tetramers and a pentamer, according to their spectroscopic data. A clear indication of the title mechanistic pathway for the oligomerization growth was obtained from the analysis of a set of computational-chemistry calculations using the density-functional-theory level B3LYP/6-311++G(d,p). The corresponding conclusions were based on the computed dipole moments, the HOMO/LUMO distributions, and a natural-populations analysis of the studied molecules.
Synthesis of Cycloveratrylene Macrocycles and Benzyl Oligomers Catalysed by Bentonite under Microwave/Infrared and Solvent-Free Conditions
René Miranda,Omar Valencia-Vázquez,Carlos Abel Maya-Vega,Inés Nicolás-Vázquez,Yolanda Marina Vargas-Rodriguez,José Antonio Morales-Serna,Eréndira García-Ríos,Manuel Salmón
Molecules , 2013, DOI: 10.3390/molecules181012820
Abstract: Tonsil Actisil FF, which is a commercial bentonitic clay, promotes the formation of cycloveratrylene macrocycles and benzyl oligomers from the corresponding benzyl alcohols in good yields under microwave heating and infrared irradiation in the absence of solvent in both cases. The catalytic reaction is sensitive to the type of substituent on the aromatic ring. Thus, when benzyl alcohol was substituted with a methylenedioxy, two methoxy or three methoxy groups, a cyclooligomerisation process was induced. Unsubstituted, methyl and methoxy benzyl alcohols yielded linear oligomers. In addition, computational chemistry calculations were performed to establish a validated mechanistic pathway to explain the growth of the obtained linear oligomers.
Una población relicta de Acer saccharum subsp. skutchii (Aceroideae) en el estado de Guerrero, México
Vargas-Rodríguez, Yalma L;
Acta botánica mexicana , 2011,
Abstract: structure, composition, diversity, environmental relationships, and conservation status of a cloud forest with acer saccharum subsp. skutchii (sugar maple) are described in a recently found locality at coahuayutla de josé maría izazaga municipality, state of guerrero, mexico. woody individuals ≥1 cm dbh in 10 m/radius circular plots and seedlings and saplings heights of sugar maple in 5.6 m/radius circular plots were recorded. the relative ecological importance of each species was expressed in an importance value. non-metric multidimensional scaling (nmds) ordination technique was used to explore the species correlations with edaphic, geographic coordinates, elevation, and canopy gaps variables. 43 woody species in 0.126 ha were recorded. the families with most species were asteraceae and fagaceae. the diametric distribution of woody species showed an inverted "j" shape, indicating successful regeneration. sugar maple is co-dominant with carpinus caroliniana and quercus uxoris. most correlations between presence-absence of trees, including acer saccharum subsp. skutchii, were with soil characteristics in the population of guerrero and all maple localities in mexico and guatemala. 30% of the reported species are included in some risk category. the fire regime in the zone is a major threat for the persistence of the studied species.
Subband structure comparison between n- and p-type double delta-doped GaAs quantum wells
I. Rodriguez Vargas,L.M. Gaggero Sager
Revista mexicana de física , 2004,
Abstract: Calculamos la estructura de niveles electrónicos (tipo-n), así como la de huecos (tipo-p) de pozos cuánticos ±-dopados dobles (DDD) en GaAs. Se han tomando en cuenta los efectos de intercambio en el estudio. Las aproximaciónes de Thomas-Fermi (TF) y Thomas-Fermi- Dirac (TFD) han sido implementadas para describir el doblamiento de la banda de conducción y de valencia respectivamente. El estudio de la estructura de niveles electrónicos y de huecos revela que los efectos de muchos cuerpos son más importantes en los pozos DDD tipo-p que en los DDD tipo-n. De la misma manera nuestros resultados están en buen acuerdo con los datos experimentales disponibles.
Maximum Likelihood Position Location with a Limited Number of References
Munoz-Rodriguez, D;Suarez-Robles, L;Vargas-Rosales, C;Rodriguez-Cruz, J. R.;
Journal of applied research and technology , 2011,
Abstract: a position location (pl) scheme for mobile users on the outskirts of coverage areas is presented. the proposed methodology makes it possible to obtain location information with only two land-fixed references. we introduce a general formulation and show that maximum-likelihood estimation can provide adequate pl information in this scenario. the root mean square (rms) error and error-distribution characterization are obtained for different propagation scenarios. in addition, simulation results and comparisons to another method are provided showing the accuracy and the robustness of the method proposed. we study accuracy limits of the proposed methodology for different propagation environments and show that even in the case of mismatch in the error variances, good pl estimation is feasible.
Maximum Likelihood Position Location with a Limited Number of References
D. Munoz-Rodriguez,L. Suarez-Robles,C. Vargas-Rosales,J. R. Rodriguez-Cruz
Journal of applied research and technology , 2011,
Abstract: A Position Location (PL) scheme for mobile users on the outskirts of coverage areas is presented. The proposedmethodology makes it possible to obtain location information with only two land-fixed references. We introduce ageneral formulation and show that maximum-likelihood estimation can provide adequate PL information in thisscenario. The Root Mean Square (RMS) error and error-distribution characterization are obtained for differentpropagation scenarios. In addition, simulation results and comparisons to another method are provided showing theaccuracy and the robustness of the method proposed. We study accuracy limits of the proposed methodology fordifferent propagation environments and show that even in the case of mismatch in the error variances, good PLestimation is feasible.
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