Physicochemical Foliar Traits Predict Assemblages of Litter/ Humus Detritivore Arthropods

Plant functional traits influence the decomposition of their own residues occurring underneath individual plant species. Arthropods associated to litter are critical components influencing decomposition. Nevertheless, few studies have established a direct relation between plant traits and belowground arthropods. To address this relation at the individual plant species scale, this study was conducted in the Guánica dry forest, Puerto Rico, by selecting five tree species and ten isolated trees/species where variations due to neighbor trees are reduced. Mature green leaves, litter, and associated arthropods were sampled from November 2004 through September 2005. Collected arthropods were counted and classified, and abundances were standardized to ind/m2. Arthropod abundance did not differ among plant species, but richness, and species and trophic composition were different among the plant species. Predators, omnivores, and sucking herbivores showed a similar species composition among plant species, while detritivore was the only trophic groups with a different species composition among plants. These results are further supported by canonical correspondence analysis results showing that detritivore arthropod species composition covaries with the physicochemical characteristics of mature green leaves of plants. These findings support that the plant idiosyncratic characteristics affect the structure of litter/humus arthropods up to the first consumer level

Rolling-sliding laboratory tests of friction modifiers in dry and wet wheel-rail contacts

Friction management has been carried out extensively in the majority of railway networks in the last few years. A popular practice is the application of friction modifiers to increase the adhesion level in contaminated wheel-rail contacts. Two friction modifiers have particularly been used or tested on several railway networks as adhesion enhancers to facilitate the traction and braking operation under poor adhesion conditions. However, for assessment of the performance the railway operators and infrastructure managers mostly rely on practical observations that do not elucidate completely the effectiveness and side effects of these adhesion enhancers. In this paper, the constituents of the two friction modifiers are identified and the solid components are analyzed. A twin-disk roller rig has been used to study their performance in dry and wet contacts under closely controlled laboratory conditions. The adhesion characteristics of both friction modifiers are examined for different slip ratios. Furthermore, the wheel and rail disks are examined after a series of dry tests to analyze the mass loss, the surface damage, the change in surface hardness and roughness, and the subsurface deformation caused by the friction modifiers compared to dry clean contacts. (C) 2009 Elsevier B.V. All rights reserved

A new method for the assessment of traction enhancers and the generation of organic layers in a twin-disc machine

Low adhesion presents a major concern for many rail operators. Railway vehicles under these circumstances can experience a serious loss of braking capability giving rise to dangerous situations such as platform overruns and signals passed at danger. One cause of adhesion loss is autumn leaf fall [1]. Leaves are run over by the wheels of a train and a chemical reaction occurs between the leaf and the rail steel [2]. This forms a black layer on the rail which when wet causes very low friction. These leaf layers have also been shown to be isolating and can interfere with railway signalling systems. Traction enhancers (also referred to in this paper as traction gels) have been developed as an alternative solution to using sand alone. They consist of sand particles suspended in a water based gel and are designed to be delivered to the rail by the trackside or via mobile application systems. The aim of this work was to develop a technique for generating a representative leaf layer on the surface of a twin-disc rail specimen and using this to develop a test methodology for assessing the performance of a traction gel in terms of adhesion recovery, wear and its effect on wheel/rail isolation

Manual de materiales sostenibles para la construcción de espacios públicos en Santo Domingo

El desarrollo que ha experimentado la República Dominicana en las últimas décadas se ve reflejado de manera notable en la ciudad capital del país, Santo Domingo, sobre todo en su crecimiento demográfico. Con este crecimiento surgen presiones para el medio ambiente, en materia del manejo de los residuos que genera la ciudad. Santo Domingo aún no cuenta con un sistema que los gestione de manera eficiente y cierre su ciclo de vida mediante mecanismos como la reutilización o el reciclaje. Por otro lado, encontramos la necesidad de crear un espacio público que sea sano, sostenible y diverso para sus ciudadanos. Esta preocupación va tomando auge a nivel local. La construcción y recuperación de los espacios públicos implica la inversión de una gran cantidad de recursos para el gobierno central, además de una carga ambiental significativa para el medio ambiente de la República Dominicana. Conectando estas dos realidades nace el presente trabajo, que se fundamenta en mostrar las alternativas que existen en el mercado internacional sobre materiales reciclados y recuperados, a fin de que la gestión de los residuos en la ciudad de Santo Domingo dirija sus pasos a la creación de este tipo de materiales para que sean utilizados en la construcción de nuestros espacios públicos como lo son esencialmente nuestros parques y plazas de convergencia. Así será posible que los ciudadanos puedan disfrutar de un ambiente sano, mediante la implementación de materiales y productos sostenibles que vayan a la par con nuestros tiempos

Proyectos de recuperación de zonas vulnerables con materiales de ciclo cerrado : caso de estudio La Nueva Barquita, cuenca del rio Ozama, República Dominicana

Exposición al ITeC- Desarrollo, Planes y Líneas de Investigación Tesis Doctoral (presentació PPT)Objetivos : -definir cuáles materiales existentes en el mercado de ciclo cerrado, idóneos para estas intervenciones. -proponer nuevos espacios en las áreas propensas a eventualidades catastróficas por crecidas de ríos. -plantear un nuevo uso a los desechos o residuos provenientes de la demolición de los espacios intervenidos. -plantear la mejoría en la gestión de los residuos de los nuevos espacios intervenidosPreprin

La poética colombiana contemporánea en Zamora, Michoacán (México)

El lector tiene en sus manos una antología con un abanico de temas y registros tan amplios que no tienen principio ni término. Todos estos poetas buscan, a través de señales, descifrar las claves del mundo: la identidad entendida como indagación, conflicto y redención. Identidades asumidas, perdidas, inventadas una y otra vez, muertas y renacidas identidades, recreadas a partir de los vínculos entre el individuo y la sociedad; las tensiones entre la inocencia y la lucidez, la desacralización de la realidad, el desarraigo de los lugares y seres amados y muchas veces perdidos –reencontrados por la gracia poética– y los retos de la libertad vital en este mundo y los otros mundos posibles; gracias a la imaginación

Vertical Arthropod Dynamics across Organic Matter Fractions in Relation to Microclimate and Plant Phenology

Plant diversity is a key factor influencing belowground dynamics including microclimate and decomposer arthropod communities. This study addresses the effect of individual plant species on belowground arthropods by focusing on seasonal variations in precipitation, temperature and arthropods along the vertical organic matter profile. In the Guanica Dry Forest, Puerto Rico, microclimate was described and 5 plant species and 10 trees/species were selected. Under each tree, for one year, temperature was measured and samples collected along the organic matter fractions. Collected arthropods were standardized to ind/m2, identified to Order/Family and assigned to morphotypes. The annual temperature pattern was similar for all species and OM fractions. Arthropod abundance was similar among plant species and higher in humus than in litter fractions. Richness and species composition were different among plant species and OM fractions. All plant species and OM fractions showed low arthropod abundance and richness, and similar arthropod species composition in the dry season, while in the wet season abundance and richness were higher and species composition varied across plant species and OM fractions. These data suggest that arthropods form specific assemblages under plant species and stages of decomposition that, during the dry season, represent a subgroup adapted to extreme environmental conditions

History of the technical evolution of pressurized water nuclear reactors

El complejo sistema técnico que forma un reactor nuclear es un interesante caso desde la perspectiva de los Estudios Sociales de la Ciencia y la Tecnología. Dentro de las diferentes variantes que han sido diseñadas a lo largo de la historia, la variante pressurized water reactor (pwr) ha sido la más implantada alrededor del mundo. Para acometer el estudio de su evolución técnica se desarrolla una perspectiva «combinada» de los enfoques utilizados tradicionalmente en la Historia y la Sociología de la Tecnología: (i) el determinismo tecnológico, para estudiar la evolución autónoma de la tecnología en su etapa de desarrollo (en la década de los cincuenta); (ii) el constructivismo social, para una etapa posterior de influencia social (en la década de los setenta); y (iii) el enfoque de sistemas, en una etapa de transición entre las dos anteriores, para analizar factores políticos, económicos y también para abrir la caja negra del diseño pwr./n The complex technical system forming a nuclear reactor is an interesting case from the perspective of Studies Science, Technology and Society. Among the different variants that were designed along the history, the most implemented variant has been the pressurized water reactor (pwr). To undertake the study of its technical evolution, an evolutionary perspective approach is developed within the History and Sociology of Technology: (i) the technological determinism, to study the autonomous evolution of technology in its development stage (in the fifties); (ii) the social constructivism, to study the later stage of social influence (in the seventies); and (iii) the systems approach, in a stage of transition between the two previous stages, to analyze political and economic factors, as well as to open the black box of pwr design

Quality and quantity of leaf-litter: both are important for feeding preferences and growth of an aquatic shredder

The study of leaf litter as a resource for shredders has emerged as a key topic in trophic links in ecology. However, thus far, most studies have emphasized the leaf quality as one of the main determinants of shredder behaviour and growth without simultaneously considering the leaf quantity availability. Nevertheless, the combined effects of leaf quantity and quality on shredder behaviour and growth is particularly crucial to further understand how ecosystem functioning may respond to the increasing flow intermittency due to climate change. In this study, we explore how changes in the leaf litter quality and quantity influence the feeding preferences and growth of an invertebrate shredder (Potamophylax latipennis). To do so, we used black poplar leaves conditioned in two streams with different flow regimens as a food resource. Afterwards, using a microcosm approach, we offered leaf discs that varied in terms of leaf quantity and quality to P. latipennis. Our results showed that flow intermittency had a negative effect on the quality of the food resource, and a lower quality had a negative effect on the consumption and growth rates of P. latipennis. Furthermore, we found that P. latipennis fed selectively on higher quality leaves even though the availability (quantity) of this resource was lower. In the context of climate change, with higher aridity/drier conditions/scenarios, our findings suggest that a decrease in the availability (quantity) of high-quality resources could potentially threaten links in global fluvial food webs and thus threaten ecosystem functioning