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Lvarez-Zagoya R.,Instituto Politcnico Nacional | Carrillo-Parra A.,University Jurez Del Estado Of Durango | Corral-Rivas J.J.,Autonomous University of Nuevo Leon
Southwestern Entomologist | Year: 2012

Insects that affect the quality of seeds in three seed stands of Pinus engelmannii Carr in the state of Durango, Mexico, were identified and quantified. Ten trees at each of the three sites were randomly selected, and the seeds were collected from each of 10 fully developed cones. From the total seeds harvested, 400 were randomly selected and subjected to X-ray analysis to quantify whether seeds were filled, empty, or damaged by insects. The main factors that affected seed quality were poor pollination and pest attack, especially by Leptoglossus occidentalis Heidemann. Most seeds were damaged by pests at El Encinal (42.8%) and fewest at Las Cumbres (19.4%). Damage caused by the insect Cydia latisigna Miller occurred more frequently at El Encinal (5.0%) and less frequently at Las Cumbres (2.2%). Megastigmus albifrons Walker was found most frequently at La Florida (1.1%); at Las Cumbres, no damage was caused by this insect. The greatest damage caused by Leptoglossus was observed at El Encinal (1.3%), and minor damage occurred at Las Cumbres and La Florida (0.5). Most damaged seeds were at El Encinal (61.7%), while least were at Las Cumbres (22.8%). These results showed the seed bug (L. occidentalis) is the agent that causes major damage as seeds develop.

Cohen D.H.,Swarthmore College | Wollman E.E.,Swarthmore College | Wollman E.E.,California Institute of Technology | Leutenegger M.A.,NASA | And 6 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

We quantitatively investigate the extent of wind absorption signatures in the X-ray grating spectra of all non-magnetic, effectively single O stars in the Chandra archive via line profile fitting. Under the usual assumption of a spherically symmetric wind with embedded shocks, we confirm previous claims that some objects show little or no wind absorption. However, many other objects do show asymmetric and blueshifted line profiles, indicative of wind absorption. For these stars, we are able to derive wind mass-loss rates from the ensemble of line profiles, and find values lower by an average factor of 3 than those predicted by current theoretical models, and consistent with Hα if clumping factors of fcl ≈ 20 are assumed. The same profile fitting indicates an onset radius of X-rays typically at r ≈ 1.5R*, and terminal velocities for the X-ray emitting wind component that are consistent with that of the bulk wind. We explore the likelihood that the stars in the sample that do not show significant wind absorption signatures in their line profiles have at least some X-ray emission that arises from colliding wind shocks with a close binary companion. The one clear exception is ζ Oph, a weak-wind star that appears to simply have a very low mass-loss rate. We also reanalyse the results from the canonical O supergiant ζ Pup, using a solar-metallicity wind opacity model and find Ṁ = 1.8 × 10-6 M⊙yr-1, consistent with recent multiwavelength determinations. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Salcedo J.,Instituto Politcnico Nacional | Salcedo B.,Instituto Tecnolgico Autnomo Of Mxico | Snchez-Bernabe F.J.,University Autnoma Metropolitana Iztapalapa
Computers and Mathematics with Applications | Year: 2011

In this paper we introduce a method for the numerical solutions of initial value problems, that combines finite differences with Simpson's rule. The effectiveness of the method is proved by solving, in one spatial dimension, a stiff and convection-dominated transport problem. To solve the same problem in two spatial dimensions, the proposed method was used successfully in combination with Strang's operator decomposition method. © 2010 Elsevier Ltd. All rights reserved.

Hernandez-Herrera A.,Instituto Politcnico Nacional | Martinez-Aguilar S.,Institute Nacional Of Pesca | Diaz-Uribe J.G.,Institute Nacional Of Pesca
Journal of Shellfish Research | Year: 2012

Changes in the number and abundance of the cohorts of jumbo squid are a demographic response associated with high variability in recruitment, and have implications for availability and accessibility to the fishing fleets. In this study, we analyzed the interannual changes in the size structure, recruitment, and sex ratio of jumbo squid Dosidicus gigas in the central Gulf of California, Mexico. Data were analyzed for the 2000 to 2009 fishing seasons (from March to November). The biological data were collected biweekly at the port of Santa Rosalía, Baja California Sur, during each fishing season. We recorded mantle length and mantle weight, and sex (male or female) was identified from morphochromatic properties of fresh gonads. We concluded that the mantle length structure of jumbo squid changed between 1 cohort and 3 cohorts from 2000 to 2009. In the study zone, the presence of 2 cohorts is common. The species shows positive allometric growth, and the females are more abundant than the males in the region. The comparison between the most important fishing grounds in the central Gulf of California (Santa Rosalia and Guaymas) showed similar patterns, such as the number of cohorts, sex ratios, growth pattern, and migration pattern identified between both coasts. We believe that this could be evidence of one population that is widely distributed in the central Gulf of California.

Curto-Risso P.L.,University of Montevideo | Curto-Risso P.L.,University la Rep blica Oriental | Medina A.,University of Salamanca | Calvo Hernndez A.,University of Salamanca | And 2 more authors.
Physica A: Statistical Mechanics and its Applications | Year: 2010

We study data from cycle-by-cycle variations in heat release for a simulated spark-ignited engine. Our analyses are based on nonlinear scaling properties of heat release fluctuations obtained from a turbulent combustion model. We apply monofractal and multifractal methods to characterize the fluctuations for several fuelair ratio values, φ, from lean mixtures to stoichiometric situations. The monofractal approach reveals that, for lean and stoichiometric conditions, the fluctuations are characterized by the presence of weak anticorrelations, whereas for intermediate mixtures we observe complex dynamics characterized by a crossover in the scaling exponents: for short scales, the variations display positive correlations while for large scales the fluctuations are close to white noise. Moreover, a broad multifractal spectrum is observed for intermediate fuel ratio values, while for low and high φ the fluctuations lead to a narrow spectrum. Finally, we explore the origin of correlations by using the surrogate data method to compare the findings of multifractality and scaling exponents between original simulated and randomized data. © 2010 Elsevier B.V. All rights reserved.

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