Concerted changes in tropical forest structure and dynamics: evidence from 50 South American long-term plots

Several widespread changes in the ecology of old-growth tropical forests have recently been documented for the late twentieth century, in particular an increase in stem turnover (pan-tropical), and an increase in above-ground biomass (neotropical). Whether these changes are synchronous and whether changes in growth are also occurring is not known. We analysed stand-level changes within 50 long-term. monitoring plots from across South America spanning 1971-2002. We show that: (i) basal area (BA: sum of the cross-sectional areas of all trees in a plot) increased significantly over time (by 0.10 +/- 0.04 m(2) ha(-1) yr(-1), mean +/- 95% CI); as did both (ii) stand-level BA growth rates (sum of the increments of BA of surviving trees and BA of new trees that recruited into a plot); and (iii) stand-level BA mortality rates (sum of the cross-sectional areas of all trees that died in a plot). Similar patterns were observed on a per-stem basis: (i) stem density (number of stems per hectare; 1 hectare is 10(4) m(2)) increased significantly over time (0.94 +/- 0.63 stems ha(-1) yr(-1)); as did both (ii) stem recruitment rates; and (iii) stem mortality rates. In relative terms, the pools of BA and stem density increased by 0.38 +/- 0.15% and 0.18 +/- 0.12% yr(-1), respectively. The fluxes into and out of these pools-stand-level BA growth, stand-level BA mortality, stem recruitment and stem mortality rates-increased, in relative terms, by an order of magnitude more. The gain terms (BA growth, stem recruitment) consistently exceeded the loss terms (BA loss, stem mortality) throughout the period, suggesting that whatever process is driving these changes was already acting before the plot network was established. Large long-term increases in stand-level BA growth and simultaneous increases in stand BA and stem density imply a continent-wide increase in resource availability which is increasing net primary productivity and altering forest dynamics. Continent-wide changes in incoming solar radiation, and increases in atmospheric concentrations of CO2 and air temperatures may have increased resource supply over recent decades, thus causing accelerated growth and increased dynamism across the world's largest tract of tropical forest

Controlling the dominant magnetic relaxation mechanisms for magnetic hyperthermia in bimagnetic core-shell nanoparticles

We report a simple and effective way to control the heat generation of a magnetic colloid under alternate magnetic fields by changing the shell composition of bimagnetic core-shell Fe 3 O 4 /Zn x Co 1-x Fe 2 O 4 nanoparticles. The core-shell structure constitutes a magnetically-coupled biphase system, with an effective anisotropy that can be tuned by the substitution of Co 2+ by Zn 2+ ions in the shell. Magnetic hyperthermia experiments of nanoparticles dispersed in hexane and butter oil showed that the magnetic relaxation is dominated by Brown relaxation mechanism in samples with higher anisotropy (i.e., larger concentration of Co within the shell) yielding high specific power absorption values in low viscosity media as hexane. Increasing the Zn concentration of the shell, diminishes the magnetic anisotropy, which results in a change to a Néel relaxation that dominates the process when the nanoparticles are dispersed in a high-viscosity medium. We demonstrate that tuning the Zn contents at the shell of these exchange-coupled core/shell nanoparticles provides a way to control the magnetic anisotropy without loss of saturation magnetization. This ability is an essential prerequisite for most biomedical applications, where high viscosities and capturing mechanisms are present. This journal i

Donovanosis, reporte de caso

La Donovanosis es una enfermedad ulcerativa crónica y progresiva que ataca por lo común la región genital, es producida por el Calymmatobacterium granulomatis, bacteria Gram negativa. La Azitromicina ha emergido como la droga de elección para su tratamiento. Se presenta un caso de Donovanosis en un varón de 46 años, quien tenía relaciones heterosexual y homosexual, el cuál presento papula anal que evoluciono a una úlcera crónica, le realizan el diagnostico de tumoración anorrectal a descartar una neoplasia anorrectal y le realizan colostomía. El retardo en la sospecha clínica en un área no endémica concluyo con su diagnóstico con un extendido en lámina para microscopia con coloración Giemsa

Resistencia a antibióticos betalactámicos y quinolonas en Escherichia coli aislada de pollos broiler

The aim of this study was to determine the antimicrobial resistance of 176 Escherichia coli strains isolated from broiler chicken organs. The strains were challenged with beta-lactam, quinolones and fluoroquinolones, observing resistance to beta-lactam antibiotics (97.7%) and quinolones (86.7%). The results showed that 71.6% of the isolates phenotypically expressed the production of extended spectrum beta-lactamases (ESLB). By PCR, resistance genes for beta-lactams blaTEM, blaSHV, blaCTX-M1 and Amp-C and resistance genes for quinolones qnrA, qnrB, qnrS were determined. The genes Amp-C (74%), blaCTX-M (65%), blaSHV (65%), blaTEM (50%), qnrB (86.4%) and qnrS (11.9%) were found. The qnrA gene was not evident in the samples analysed. The results obtained revealed a large percentage of resistance to the studied antibiotics and the presence of resistance genes in isolates from poultry for human consumption, which constitutes a risk for Public Health.El objetivo del estudio fue determinar la resistencia antimicrobiana de 176 cepas de Escherichia. coli aisladas de órganos de pollos broiler. Las cepas fueron desafiadas con antibióticos betalactámicos, quinolonas y fluoroquinolonas, observándose resistencia a antibióticos betalactámicos (97.7%) y a quinolonas (86.7%). El 71.6% de los aislados también expresaron fenotípicamente la producción de betalactamasas de espectro extendido (ESLB). Mediante PCR se determinaron genes de resistencia para betalactámicos blaTEM, blaSHV, blaCTX-M1 y Amp-C y genes de resistencia para quinolonas qnrA, qnrB, qnrS. Se encontraron los genes Amp-C (74%), blaCTX-M (65%), blaSHV (65%), blaTEM (50%), qnrB (86.4%) y qnrS (11.9%). No se evidenció el gen qnrA en las muestras analizadas. Los resultados obtenidos revelaron un gran porcentaje de resistencia a los antibióticos estudiados y la presencia de genes de resistencia en aislados de aves para consumo humano, lo cual constituye un riesgo para la salud pública

Pattern and process in Amazon tree turnover, 1976-2001

Previous work has shown that tree turnover, tree biomass and large liana densities have increased in mature tropical forest plots in the late twentieth century. These results point to a concerted shift in forest ecological processes that may already be having significant impacts on terrestrial carbon stocks, fluxes and biodiversity. However, the findings have proved controversial, partly because a rather limited number of permanent plots have been monitored for rather short periods. The aim of this paper is to characterize regional-scale patterns of 'tree turnover' (the rate with which trees die and recruit into a population) by using improved datasets now available for Amazonia that span the past 25 years. Specifically, we assess whether concerted changes in turnover are occurring, and if so whether they are general throughout the Amazon or restricted to one region or environmental zone. In addition, we ask whether they are driven by changes in recruitment, mortality or both. We find that: (i) trees 10 cm or more in diameter recruit and die twice as fast on the richer soils of southern and western Amazonia than on the poorer soils of eastern and central Amazonia; (ii) turnover rates have increased throughout Amazonia over the past two decades; (iii) mortality and recruitment rates have both increased significantly in every region and environmental zone, with the exception of mortality in eastern Amazonia; (iv) recruitment rates have consistently exceeded mortality rates; (v) absolute increases in recruitment and mortality rates are greatest in western Amazonian sites; and (vi) mortality appears to be lagging recruitment at regional scales. These spatial patterns and temporal trends are not caused by obvious artefacts in the data or the analyses. The trends cannot be directly driven by a mortality driver (such as increased drought or fragmentation-related death) because the biomass in these forests has simultaneously increased. Our findings therefore indicate that long-acting and widespread environmental changes are stimulating the growth and productivity of Amazon forests

After trees die: quantities and determinants of necromass across Amazonia

The Amazon basin, one of the most substantial biomass carbon pools on earth, is characterised by strong macroecological gradients in biomass, mortality rates, and wood density from west to east. These gradients could affect necromass stocks, but this has not yet been tested. This study aims to assess the stocks and determinants of necromass across Amazonian forests. Field-based and literature data were used to find relationships between necromass and possible determinants. Furthermore, a simple model was applied to estimate and extrapolate necromass stocks across <i>terra firma</i> Amazonian forests. In eight northwestern and three northeastern Amazonian permanent plots, volumes of coarse woody debris (≥10 cm diameter) were measured in the field and the density of each decay class was estimated. Forest structure and historical mortality data were used to determine the factors controlling necromass. Necromass is greater in forests with low <i>stem</i> mortality rates (northeast) rather than in forests with high <i>stem</i> mortality rates (northwest) (58.5±10.6 and 27.3±3.2 Mg ha<sup>−1</sup>, respectively). Using all published necromass values, we find that necromass across <i>terra firma</i> forests in Amazonia is positively related to both forest dynamics (mortality <i>mass</i> inputs and a surrogate for decomposition rate (average wood density of living trees)) and forest structure (biomass), but is better explained by forest dynamics. We propose an improved method to estimate necromass for plots where necromass has not been measured. The estimates, together with other actual measurements of necromass, were scaled-up to project a total Amazonian necromass of 9.6±1.0 Pg C. The ratio of necromass (on average weighted by forest region) to coarse aboveground biomass is 0.127. Overall, we find (1) a strong spatial trend in necromass in parallel with other macroecological gradients and (2) that necromass is a substantial component of the carbon pool in the Amazon

Student performance assessment using clustering techniques

The application of informatics in the university system management allows managers to count with a great amount of data which, rationally treated, can offer significant help for the student programming monitoring. This research proposes the use of clustering techniques as a useful tool of management strategy to evaluate the progression of the students’ behavior by dividing the population into homogeneous groups according to their characteristics and skills. These applications can help both the teacher and the student to improve the quality of education. The selected method is the data grouping analysis by means of fuzzy logic using the Fuzzy C-means algorithm to achieve a standard indicator called Grade, through an expert system to enable segmentation.Universidad de la Costa, 2 Universidad Nacional Experimental Politécnica “Antonio José de Sucre”, Universidad Simón Bolívar, Corporación Universitaria Latinoamericana, Corporación Universitaria Minuto de Dios