Bryophyte diversity patterns in flooded and tierra firme forests in the Araracuara Region, Colombian Amazonia

We investigated patterns of bryophyte species richness and composition in two forest types of Colombian Amazonia, non-flooded tierra firme forest and floodplain forest of the Caquetá River. A total of 109 bryophyte species were recorded from 14 0.2 ha plots. Bryophyte life forms and habitats were analyzed, including the canopy and epiphylls. Bryophyte species did not show significant differences between landscapes but mosses and liverworts were different and with opposite responses balancing the overall richness. Independence test showed differences in both life form and habitat use distribution between the two forest types with more fan and mat bryophytes species in the floodplains, and more epiphytic liverworts in the tierra firme forest. Correspondence analysis showed differences in the bryophyte species assemblage between the two forest types where they may be responding to the higher humidity provided by the flooding. Despite of, the environmental differences detected, epiphyll species assemblages were not strongly affected. Apparently, epiphyll habitat is stressful enough to hide the environmental differences between the flooded and Tierra firme forests.Investigamos los patrones de riqueza de especies y composición florística de briofitos en dos tipos de bosque en la Amazonía Colombiana. Bosques no inundados de Tierra firme y bosques periódicamente inundados en los planos inundables del Rió Caquetá. Encontramos 109 especies de briofitos en 14 parcelas de 0.2 ha. Nosotros analizamos diferencias en la distribución de formas de vida y hábitat de los briofitos entre los dos tipos de bosque incluyendo especies del dosel y epifilas. El número de especies de briofitos no mostró diferencias significativas entre los dos tipos de bosque. Pero musgos y hepáticas si tuvieron diferencias con respuestas opuestas balanceando el número total de especies. Pruebas de independencia mostraron diferencias en la distribución de formas de vida y uso de hábitat entre los dos tipos de bosque con más especies de abanicos y esteras en los planos inundables, y más especies de hepáticas epifitas en el bosque de Tierra firme. El análisis de correspondencia mostró diferencias en la composición florística de briofitos entre ambos tipos de bosque, donde las comunidades de briofitos pueden estar respondiendo a un gradiente de humedad aportada por la inundación periódica de los planos inundables. La composición florística de los briofitos epifilos no mostró una separación tan clara entre los tipos de bosque como si fue detectada en los otros hábitat donde los briofitos fueron encontrados. Aparentemente, el hábitat epifilo es suficientemente estresante para ocultar el efecto de las diferentes condiciones ambientales de los bosques inundables y de Tierra firme

Interference phenomena, chiral bosons and Lorentz invariance

We have studied the theory of gauged chiral bosons and proposed a general theory, a master action, that encompasses different kinds of gauge field couplings in chiral bosonized theories with first-class chiral constraints. We have fused opposite chiral aspects of this master action using the soldering formalism and applied the final action to several well known models. The Lorentz rotation permitted us to fix conditions on the parameters of this general theory in order to preserve the relativistic invariance. We also have established some conditions on the arbitrary parameter concerned in a chiral Schwinger model with a generalized constraint, investigating both covariance and Lorentz invariance. The results obtained supplements the one that shows the soldering formalism as a new method of mass generation.Comment: 11 pages, RevTex(twocolumn). Final version to appear in Physiscal Review

Student Conceptual Difficulties in Hydrodynamics

We describe a study on the conceptual difficulties faced by college students in understanding hydrodynamics of ideal fluids. This study was based on responses obtained in hundreds of written exams and oral interviews, which were held with first-year Engineering and Science university students. Their responses allowed us to identify a series of misconceptions unreported in the literature so far. The study findings demonstrate that the most important difficulties arise from the students' inability to establish a link between the kinematics and dynamics of moving fluids, and from a lack of understanding regarding how different regions of a system interact.Comment: 12 pages, 10 figures (small corrections

Evaluating the performance of GARCH models using White´s Reality Check

time seris, GARCH models, bootstrap, reality check, volatility, financial econometrics, Monte Carlo, forecasting, riskmetrics, moving average

On Pruning for Score-Based Bayesian Network Structure Learning

Many algorithms for score-based Bayesian network structure learning (BNSL), in particular exact ones, take as input a collection of potentially optimal parent sets for each variable in the data. Constructing such collections naively is computationally intensive since the number of parent sets grows exponentially with the number of variables. Thus, pruning techniques are not only desirable but essential. While good pruning rules exist for the Bayesian Information Criterion (BIC), current results for the Bayesian Dirichlet equivalent uniform (BDeu) score reduce the search space very modestly, hampering the use of the (often preferred) BDeu. We derive new non-trivial theoretical upper bounds for the BDeu score that considerably improve on the state-of-the-art. Since the new bounds are mathematically proven to be tighter than previous ones and at little extra computational cost, they are a promising addition to BNSL methods

HYBRID RICE AND ITS IMPACT ON FOOD SECURITY AND THE PATTERN OF GLOBAL PRODUCTION AND TRADE

The hybrid rice technology is one of the many ways in which productivity of scarce resources devoted to rice production could be enhanced, with the consequent alleviation of food insecurity. The findings of this study show that the hybrid rice technology has so far made some sizable contributions to per-capita availability of rice in adopting countries with marginal spillover effects to other regions. However, at forecasted population growths, a massive intensification of adoption would be needed to maintain per-capita availability of rice at baseline levels. But even with adoption rates climbing significantly, much higher equilibrium prices are expected, which will represent a challenge for the hungry in many parts of the world. While hybrid rice has the potential to contribute significantly to improve production and food security, more efforts are needed to improve the productivity of the constraining production resources.hybrid rice, food security, technology change, Demand and Price Analysis, Food Security and Poverty, International Relations/Trade, Research and Development/Tech Change/Emerging Technologies, Q16, Q55,

Engaging Diversity Through Brain Hemispheric Orientation (BHO) Among College Students: Some Implications On Their Mathematics Performance.

This study primarily sought empirical results to be used for a more complicated future research undertaking. This study categorized the students of the College of Teacher Education according to their left, right, or confluent brain hemispheric orientation through a preference scale. Also, these college students were classified with respect to their low, average, or high level of Mathematics performance basing from the grades in Mathematics subjects. Diversity in college students‘ gender, age, and ethnicity were analysed for their effect on the brain hemispheric orientation as well as their effect on their level of Mathematics performance. Likewise, this study investigated the influence of brain hemispheric orientation on the level of Mathematics performance of the college students. Findings revealed that there were significantly more left-brained than the combined number of right-brained and confluent-brained college students. There was numerically more college students who had average level than their counterparts with low level and high level of Mathematics performance. Results indicated that female college students outnumbered their male counterparts. The college students belonged to age range 16 to 34 years while 86% belonged to age bracket 16-21 years. The Visayan-college students dominated the student population. There were: significantly more female college students who were left-brained than their male counterparts; significantly more college students at age bracket (16-21) young who were leftbrained than their counterparts in other age brackets; significantly more Visayans were left-brained than their counterparts in other ethnic groups. More female college students had high and average level of Mathematics performance than their male counterparts but the numerical difference did not show significant results. There were significantly more college students at age bracket 16-21 years with average level and low level of mathematics performance than their counterparts in other age brackets. More Visayan college students had average level and low level of mathematics performance and which outnumbered their counterparts in other ethnic groups. Gender was found to have not significantly affected the level of Mathematics performance but age, and ethnicity did significantly affect the level of Mathematics performance. Results revealed that brain hemispheric orientation of college students significantly explained their level of Mathematics performance