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Reyes J.C.,University of Los Andes, Colombia | Chopra A.K.,University of California at Berkeley
Earthquake Engineering and Structural Dynamics | Year: 2011

The modal pushover analysis (MPA) procedure, presently restricted to one horizontal component of ground motion, is extended to three-dimensional analysis of buildings-symmetric or unsymmetric in plan-subjected to two horizontal components of ground motion, simultaneously. Also presented is a variant of this method, called the practical modal pushover analysis (PMPA) procedure, which estimates seismic demands directly from the earthquake response (or design) spectrum. Its accuracy in estimating seismic demands for very tall buildings is evaluated, demonstrating that for nonlinear systems this procedure is almost as accurate as the response spectrum analysis procedure is for linear systems. Thus, for practical applications, the PMPA procedure offers an attractive alternative whereby seismic demands can be estimated directly from the (elastic) design spectrum, thus avoiding the complications of selecting and scaling ground motions for nonlinear response history analysis. © 2010 John Wiley & Sons, Ltd. Source


Maldonado-Carreno C.,University of Los Andes, Colombia | Votruba-Drzal E.,University of Pittsburgh
Child Development | Year: 2011

Despite recent growth in research highlighting the potential of teacher-child relationships to promote children's development during the early years of school, questions remain about the importance of these relationships across elementary school. Using data from the NICHD Study of Early Child Care (N=1,364), this study examines between- and within-child associations between teacher-child relationship quality and children's academic achievement and behavior problems from kindergarten (ages 4-6years) through 5th grade (ages 9-11years). Results suggest that increases in teacher-child relationship quality are associated with improvements in teacher-reported academic skills and reductions in behavior problems consistently throughout elementary school. As children progressed from kindergarten through fifth grade, the importance of teacher-child relationship quality is unchanging. © 2011 The Authors. Child Development © 2011 Society for Research in Child Development, Inc.. Source


Ateline monkeys, the largest primates in the Neotropics, may disperse more than one million seeds/km 2/d at sites where they are abundant, but it is unclear whether a reduction in their populations can alter plant diversity patterns. The species richness and composition of regenerating plants as a proxy of future plant communities were studied by comparing 16 sites with different ateline abundance in three countries in northwestern South America. A total of 3658 plots included 94,340 regenerating plants, which were assigned to species or morphospecies. Paired t-tests comparing sites in the same region but with different densities of atelines, and regression analyses showed a consistent positive relationship between ateline density and plant diversity. These results were due to the larger number of stems per area and higher evenness at sites with more atelines, suggesting higher recruitment rates for dispersed seeds. Differences were also found in plant composition, as canopy, endozoochorous, and medium seed size plants were consistently more abundant in sites with more ateline monkeys than in sites with less atelines. The findings of this study suggest that these primates play a key role in plant regeneration. In order to maintain the diversity and plant composition of tropical forests for future generations, conservation of these large frugivores and other key game species is imperative. © 2010 The Author(s). Journal compilation © 2010 by The Association for Tropical Biology and Conservation. Source


Seed dispersal is a mutualistic interaction in which frugivores gain nutrients and plants gain when seeds are transported to adequate places for establishment. However, this relationship is prone to deceit, for example, when frugivores spit-out seeds in the proximity of parental trees. Still, few hypotheses have offered explanations on why deceiving strategies are not widespread. In this study, I explore the importance of how difficult it is to mechanically separate the nutritious pulp from the seeds, as a factor that can explain the chance a seed has of being dispersed by woolly monkeys (Lagothrix lagothricha). I completed 1,440 h of focal animal follows during 2 years in order to quantify the chances plant species have of being dispersed. To do so, I evaluated the residuals from the relationship between the number of seeds manipulated and seeds dispersed by a population of woolly monkeys in Tinigua Park (Colombia). For 74 fruit species, I estimated how difficult it is to separate pulp from seeds as the time needed to separate the parts. An exponential model showed that this variable was able to predict 38% of the variation on dispersal probability, demonstrating that, when it is difficult to separate the pulp from the seeds, the probability of legitimate dispersal increases. However, when fruit parts were easy to separate, there was more variation in the outcome. My results suggest that many plants have evolved mechanisms (e. g., small seeds embedded in pulp, strong attachment, irregular seed surface, and thin pulp layer) that preclude deceit by frugivores. © 2011 Springer-Verlag. Source


Meesters R.J.,University of Los Andes, Colombia
Bioanalysis | Year: 2013

The quantitative analysis of free amino acids in human plasma has become an important and essential analysis parameter in different areas of life sciences. Free amino acid concentrations in human plasma samples are generally determined by means of GC or LC after chemical derivatization followed by UV, fluorescent or MS detection of the amino acid derivatives. Derivatization of free amino acids is done either pre-or post-column, and the amino acid derivatives obtained posess improved chromatographic behavior, increased detection sensitivity and selectivity compared with non-derivatized free amino acids. This work gives an overview of different chemical derivatization methods applied and their liquid separation techniques in bioanalytical assays for quantitative free amino acid analysis in human plasma samples. Important plasma preparation procedures, pre-and post-column derivatization, and different LC separation techniques are presented. © 2013 Future Science Ltd. Source

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