Gape size influences seasonal patterns of piscivore diets in three Neotropical rivers

We examined diets of four piscivores, two in the order Perciformes (Cichla temensis and C. orinocensis) and two in the order Characiformes (Boulengerella cuvieri and B. lucius), from the Cinaruco, La Guardia, and Ventuari rivers in Venezuela throughout the wet-dry seasonal cycle. The four piscivores consumed a phylogenetically and morphologically diverse group of fishes, reflecting the overall diversity of fish species in these rivers. At the start of the falling-water period, Cichla consumed large prey, especially the abundant, migratory, fish of the genus Semaprochilodus. As these relatively large prey became depleted during the dry season, Cichla tended to consume smaller prey. For Boulengerella, gape limitation precluded consumption of larger, seasonally abundant, fishes, and so prey sizes were more consistent throughout the seasonal cycle. Our findings show how prey abundance and gape limitations interact to influence seasonal patterns of predator-prey interactions

Propiedades acústicas de los paneles de carrizo

Reed is a plant species very similar to common cane which is widespread all over the Earth. It is an ecological and sustainable material which is low-cost, aesthetically attractive, easy to obtain and install, and can be used in different construction systems.
 
 This work analyses the acoustic properties of reed panels from the point of view of sound absorption and sound insulation against airborne noise, according to the corresponding EN ISO standards. The experimental results obtained point to the conclusion that reed panels are suitable construction systems for controlling reverberant sound within a space, and that the sound reduction index values for different thicknesses of reed panels, or reed panels used in combination with wood particle boards, demonstrate the possibility of using them in construction as an element on the facades and roofs of buildings and for interior partitions.<br><br>El carrizo es una especie vegetal, parecida a la caña común, que se encuentra ampliamente distribuida en la superficie terrestre. Es un material ecológico y sostenible de bajo coste, estéticamente aceptable, fácil de obtener y colocar, que permite generar diferentes sistemas constructivos.
 
 En este trabajo se analizan las propiedades acústicas de los paneles de carrizo en lo referente a la absorción acústica y al aislamiento acústico a ruido aéreo, para ello se han aplicado los procedimientos de las normas EN ISO correspondientes. De los resultados experimentales obtenidos se concluye que los paneles de carrizo son unos sistemas constructivos adecuados para el control del sonido reverberante en un recinto y que los valores del índice de reducción acústica de paneles de diferentes espesores o en combinación con tableros de partículas de madera muestran la posibilidad de utilizarlos en la edificación como elemento de fachada, en cubiertas de edificios y particiones interiores

Estudio de la bifurcación de ciclos límite a partir de un gráfico mediante el inverso de factor integrante

El objetivo de este trabajo consiste en estudiar el número máximo de ciclos límite que pueden bifurcar a partir de un gráfico monodrómico de un sistema diferencial autónomo en el plano con inverso de factor integrante. Demostramos que la multiplicidad de anulación del inverso de factor integrante en el gráfico da una cota superior para el número máximo de ciclos límite que pueden bifurcar del gráfico dentro de las perturbaciones uniparamétricas y analíticas que poseen un inverso de factor integrante. Además, definimos la noción de inverso de factor integrante hasta orden ` que nos permte seguir los ciclos límite bifurcados. Estudiamos varios ejemplos de sistemas en el plano que ilustran este resultado

Comparison of fish assemblages in two littoral habitats in a Neotropical morichal stream in Venezuela

Morichales are lowland streams in South American savannas with riparian forest dominated by the moriche palm (Mauritia flexuosa). We sampled littoral habitats from ten flooded vegetated patches (dominated by Mauritiella aculeate) and six sand banks in two months of the dry season (Feb-Mar 2005) in a stream in the savannas of Apure State, Venezuela. We collected samples that compromised 12,407 individual fishes of 107 species. Small-bodied fishes (\u3c 100 mm), representing diverse trophic and life history strategies, were abundant. The most abundant species were in the families Characidae and Cichlidae. Fish assemblages from flooded vegetated patches differed significantly from those on adjacent sand banks. High structural complexity along vegetated shoreline habitats of morichal streams likely contributes to species richness and affects assemblage composition

The SCUBA-2 Cosmology Legacy Survey: The EGS deep field -- III. The evolution of faint submillimeter galaxies at z<4z<4

We present a demographic analysis of the physical and morphological properties of $450/850~\mu\rm m$-selected galaxies from the deep observations of the SCUBA-2 Cosmology Legacy Survey in the Extended Groth Strip that are detected below the classical submillimeter-galaxy regime ($S_{850 \mu\rm m}\lesssim 6~\rm mJy$/beam) and compare them with a sample of optically-selected star-forming galaxies detected in the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey in the same field. We derive the evolution of the main sequence of star-forming galaxies, finding a steeper specific star formation rate versus stellar mass at $z>2.5$ than previous studies. Most faint submillimeter-galaxies fall within $3\sigma$ of the main sequence, but 40~per cent are classified as starbursts. Faint submillimeter galaxies have 50~per cent larger sizes at $2<z<3$ than optically-selected star-forming galaxies of the same mass range. This is also the redshift bin where we find the largest fraction of starbursts, and hence we could be witnessing merging processes, as confirmed by the preference for visual-morphology classifications of these systems as irregular disk galaxies and mergers. Both populations show an increment towards lower redshifts ($z<2$) of their concentration in $H$-band morphology, but faint submillimeter galaxies on average show larger concentration values at later times. These findings support the claim that faint submillimeter galaxies are mostly a population of massive dust-obscured disk-like galaxies that develop larger bulge components at later epochs. While the similarities are great, the median sizes, starburst numbers and $H$-band concentration of faint submillimeter galaxies differ from those of optically-selected star-forming galaxies of the same stellar mass.Comment: Accepted for publication in MNRA

Agricultura, campesinos y alimentos (1980-2010)

299 páginas : mapas, gráficosEste estudio que expone los resultados del análisis histórico, teórico y político de los procesos de configuración del sistema agrario en Colombia (1980-2010), enmarcado dentro de los impactos del desarrollo económico internacional de la industria de alimentos y la expansión de agroexportables, es el primero de este tipo en el campo de los estudios agrarios en Colombia. Asimismo, el enfoque en los procesos de resistencia de los diferentes sectores del campesinado ha permitido valorar sus aportes y su potencial como fuente de conocimiento para democratizar la agricultura desde lo local. Los resultados de la investigación que se exponen en este trabajo han aportado a la elaboración de la propuesta de política pública sobre Zonas de Reserva Campesina, del Sistema Nacional de Reforma Agraria e incorporada en el Punta 1 del Acuerdo de Paz, ''Hacia un nuevo campo colombiano: Reforma Rural Integral", que busca terminar un conflicto armado de más de 50 años de duración, el más prolongado en la historia de América Latina.This study exposes the results of the historical, theoretical and political analysis of the configuration of the agrarian system in Colombia (1980-2010), framed within the impacts of the international economic development of the food industry and the expansion of agro-exports. Focuses on three processes: conflicts on land distribution policies, the development of agricultural production for export and agro-industries and peasant economies and its participation in labor and food markets. The focus on the resistance processes of the different sectors of the peasantry has made it possible to assess their contributions and their potential as a source of knowledge to democratize agriculture from the local level. The results of the investigation described in this work have contributed to the elaboration of the public policy proposal on Peasant Reserve Zones, part of the National System of Agrarian Reform, incorporated in Point 1 of the Peace Agreement," Towards a newDoctor en Estudios SocialesDoctorad