Showing papers by "Simón Bolívar University published in 2014"

Savanna Vegetation-Fire-Climate Relationships Differ Among Continents

Abstract: Ecologists have long sought to understand the factors controlling the structure of savanna vegetation. Using data from 2154 sites in savannas across Africa, Australia, and South America, we found that increasing moisture availability drives increases in fire and tree basal area, whereas fire reduces tree basal area. However, among continents, the magnitude of these effects varied substantially, so that a single model cannot adequately represent savanna woody biomass across these regions. Historical and environmental differences drive the regional variation in the functional relationships between woody vegetation, fire, and climate. These same differences will determine the regional responses of vegetation to future climates, with implications for global carbon stocks.

Experimenting with electromagnetism using augmented reality: Impact on flow student experience and educational effectiveness

Abstract: Educational researchers have recognized Augmented Reality (AR) as a technology with great potential to impact affective and cognitive learning outcomes. However, very little work has been carried out to substantiate these claims. The purpose of this study was to assess to which extent an AR learning application affects learners' level of enjoyment and learning effectiveness. The study followed an experimental/control group design using the type of the application (AR-based, web-based) as independent variable. 64 high school students were randomly assigned to the experimental or control group to learn the basic principles of electromagnetism. The participants' knowledge acquisition was evaluated by comparing pre- and post-tests. The participants' level overall-state perception on flow was measured with the Flow State Scale and their flow states were monitored throughout the learning activity. Finally, participants' perceptions of benefits and difficulties of using the augmented reality application in this study were qualitatively identified. The results showed that the augmented reality approach was more effective in promoting students' knowledge of electromagnetic concepts and phenomena. The analysis also indicated that the augmented reality application led participants to reach higher flow experience levels than those achieved by users of the web-based application. However, not all the factors seem to have influence on learners' flow state, this study found that they were limited to: concentration, distorted sense of time, sense of control, clearer direct feedback, and autotelic experience. A deeper analysis of the flow process showed that neither of the groups reported being in flow in those tasks that were very easy or too difficult. However, for those tasks that were not perceived as difficult and included visualization clues, the experimental group showed higher levels of flow that the control group. The study suggests that augmented reality can be exploited as an effective learning environment for learning the basic principles of electromagnetism at high school provided that learning designers strike a careful balance between AR support and task difficulty.

Gamification for Engaging Computer Science Students in Learning Activities: A Case Study

Abstract: Gamification is the use of game design elements in non-game settings to engage participants and encourage desired behaviors. It has been identified as a promising technique to improve students' engagement which could have a positive impact on learning. This study evaluated the learning effectiveness and engagement appeal of a gamified learning activity targeted at the learning of C-programming language. Furthermore, the study inquired into which gamified learning activities were more appealing to students. The study was conducted using the mixed-method sequential explanatory protocol. The data collected and analysed included logs, questionnaires, and pre- and post-tests. The results of the evaluation show positive effects on the engagement of students toward the gamified learning activities and a moderate improvement in learning outcomes. Students reported different motivations for continuing and stopping activities once they completed the mandatory assignment. The preferences for different gamified activities were also conditioned by academic milestones.

La Investigación Cualitativa (Síntesis conceptual)

Abstract: The Document offers an ample panorama us of the qualitative investigation. It initiates with necessary revision of the subject of the knowledge, boarded from his epistemologic nature to be able to understand the concrete totality of the reality, and in the terminology of the author, like an all polisistemico and interdisciplinariedad. In background it identifies the dynamic dimension of the qualitative investigation, as soon as it tries to identify the deep nature of the realities, his structure and relations that settle down, to fulfill the two tasks basic of all investigation: To gather data and to categorizar them and to interpret them. It makes a treatment of the referential frame, the objectives, the hypotheses and the variables, identifying several qualitative methods, as well as the instruments and procedures.

Integrated care pathways for airway diseases (AIRWAYS-ICPs).

Abstract: The objective of Integrated Care Pathways for Airway Diseases (AIRWAYS-ICPs) is to launch a collaboration to develop multi-sectoral care pathways for chronic respiratory diseases in European countries and regions. AIRWAYS-ICPs has strategic relevance to the European Union Health Strategy and will add value to existing public health knowledge by: 1) proposing a common framework of care pathways for chronic respiratory diseases, which will facilitate comparability and trans-national initiatives; 2) informing cost-effective policy development, strengthening in particular those on smoking and environmental exposure; 3) aiding risk stratification in chronic disease patients, using a common strategy; 4) having a significant impact on the health of citizens in the short term (reduction of morbidity, improvement of education in children and of work in adults) and in the long-term (healthy ageing); 5) proposing a common simulation tool to assist physicians; and 6) ultimately reducing the healthcare burden (emergency visits, avoidable hospitalisations, disability and costs) while improving quality of life. In the longer term, the incidence of disease may be reduced by innovative prevention strategies. AIRWAYS-ICPs was initiated by Area 5 of the Action Plan B3 of the European Innovation Partnership on Active and Healthy Ageing. All stakeholders are involved (health and social care, patients, and policy makers).

Nucleation, crystallization, self-nucleation and thermal fractionation of cyclic and linear poly(ε-caprolactone)s

Abstract: A series of low polydispersity cyclic PCL samples (C-PCLs), as well as their linear analogs (L-PCLs), were synthesized by click chemistry in a number average molecular weight ( M n ) range of 2–22 kg/mol. They were investigated by Polarized Light Optical Microscopy (PLOM) and Differential Scanning Calorimetry (DSC). The nucleation and overall crystallization kinetics were studied, as well as their self-nucleation behavior and SSA (Successive Self-nucleation and Annealing) thermal fractionation. Cyclic PCLs were found to nucleate and crystallize faster than linear PCLs due to: (a) faster diffusion of C-PCL chains and (b) larger supercoolings of C-PCLs at any given crystallization temperature, as compared to L-PCLs. A bell shape curve was obtained when the overall crystallization rate was examined as a function of M n , this effect is probably due to a competition between nucleation and diffusion. It was found for the first time, that since cyclic molecules have lower entanglement densities, they can quickly recover their pseudo-equilibrium compact coil conformations upon melting and therefore exhibit much smaller crystalline memory effects than their linear counterparts of identical chain lengths. SSA revealed that C-PCLs are more sensitive to annealing than L-PCLs because their ring topology and limited lamellar chain folding facilitates crystal thickening.

Black strings from minimal geometric deformation in a variable tension brane-world

Abstract: We study brane-world models with variable brane tension and compute corrections to the horizon of a black string along the extra dimension. The four-dimensional geometry of the black string on the brane is obtained by means of the minimal geometric deformation approach, and the bulk corrections are then encoded in additional terms involving the covariant derivatives of the variable brane tension. Our investigation shows that the variable brane tension strongly affects the shape and evolution of the black string horizon along the extra dimension, at least in a near-brane expansion. In particular, we apply our general analysis to a model motivated by the Eotvos branes, where the variable brane tension is related to the Friedmann–Robertson–Walker brane-world cosmology. We show that for some stages in the evolution of the universe, the black string warped horizon collapses to a point and the black string has correspondingly finite extent along the extra dimension. Furthermore, we show that in the minimal geometric deformation of a black hole on the variable tension brane, the black string has a throat along the extra dimension, whose area tends to zero as time goes to infinity.

Experimental antibiotic treatment identifies potential pathogens of white band disease in the endangered Caribbean coral Acropora cervicornis

Abstract: Coral diseases have been increasingly reported over the past few decades and are a major contributor to coral decline worldwide. The Caribbean, in particular, has been noted as a hotspot for coral disease, and the aptly named white syndromes have caused the decline of the dominant reef building corals throughout their range. White band disease (WBD) has been implicated in the dramatic loss of Acropora cervicornis and Acropora palmata since the 1970s, resulting in both species being listed as critically endangered on the International Union for Conservation of Nature Red list. The causal agent of WBD remains unknown, although recent studies based on challenge experiments with filtrate from infected hosts concluded that the disease is probably caused by bacteria. Here, we report an experiment using four different antibiotic treatments, targeting different members of the disease-associated microbial community. Two antibiotics, ampicillin and paromomycin, arrested the disease completely, and by comparing with community shifts brought about by treatments that did not arrest the disease, we have identified the likely candidate causal agent or agents of WBD. Our interpretation of the experimental treatments is that one or a combination of up to three specific bacterial types, detected consistently in diseased corals but not detectable in healthy corals, are likely causal agents of WBD. In addition, a histophagous ciliate (Philaster lucinda) identical to that found consistently in association with white syndrome in Indo-Pacific acroporas was also consistently detected in all WBD samples and absent in healthy coral. Treatment with metronidazole reduced it to below detection limits, but did not arrest the disease. However, the microscopic disease signs changed, suggesting a secondary role in disease causation for this ciliate. In future studies to identify a causal agent of WBD via tests of Henle–Koch's postulates, it will be vital to experimentally control for populations of the other potential pathogens identified in this study.

Brane-world stars from minimal geometric deformation, and black holes

Abstract: We build analytical models of spherically symmetric stars in the brane-world, in which the external space-time contains both an ADM mass and a tidal charge In order to determine the interior geometry, we apply the principle of minimal geometric deformation, which allows one to map General Relativistic solutions to solutions of the effective four-dimensional brane-world equations We further restrict our analysis to stars with a radius linearly related to the total General Relativistic mass, and obtain a general relation between the latter, the brane-world ADM mass and the tidal charge In these models, the value of the star’s radius can then be taken to zero smoothly, thus obtaining brane-world black hole metrics with a tidal charge solely determined by the mass of the source and the brane tension General conclusions regarding the minimum mass for semiclassical black holes will also be drawn

Microbial diversity in a Venezuelan orthoquartzite cave is dominated by the Chloroflexi (Class Ktedonobacterales) and Thaumarchaeota Group I.1c.

Abstract: The majority of caves are formed within limestone rock and hence our understanding of cave microbiology comes from carbonate-buffered systems. In this paper, we describe the microbial diversity of Roraima Sur Cave, an orthoquartzite (SiO4) cave within Roraima Tepui, Venezuela. The cave contains a high level of microbial activity when compared with other cave systems, as determined by an ATP-based luminescence assay and cell counting. Molecular phylogenetic analysis of microbial diversity within the cave demonstrate the dominance of Actinomycetales and Alphaproteobacteria in endolithic bacterial communities close to the entrance, while communities from deeper in the cave are dominated (82-84%) by a unique clade of Ktedonobacterales within the Chloroflexi. While members of this phylum are commonly found in caves, this is the first identification of members of the Class Ktedonobacterales. An assessment of archaeal species demonstrates the dominance of phylotypes from the Thaumarchaeota Group I.1c (100%), which have previously been associated with acidic environments. While the Thaumarchaeota have been seen in numerous cave systems, the dominance of Group I.1c in Roraima Sur Cave is unique and a departure from the traditional archaeal community structure. Geochemical analysis of the cave environment suggests that water entering the cave, rather than the nutrient-limited orthoquartzite rock, provides the carbon and energy necessary for microbial community growth and subsistence, while the poor buffering capacity of quartzite or the low pH of the environment may be selecting for this unusual community structure. Together these data suggest that pH, imparted by the geochemistry of the host rock, can play as important a role in niche-differentiation in caves as in other environmental systems.

Nucleation and Antinucleation Effects of Functionalized Carbon Nanotubes on Cyclic and Linear Poly(ε-caprolactones)

Abstract: Novel nanocomposites were prepared by blending linear or cyclic poly(e-caprolactones) with two types of chemically modified carbon nanotubes (CNTs). The low-polydispersity cyclic PCL samples (C-PCLs) were synthesized by click chemistry with a number-average molecular weight (Mn) of 22 kg/mol. Linear analogues (L-PCLs) with the same Mn value were also prepared. Two types of CNTs were employed (with 1% w/w content): single wall CNTs functionalized with octadecylamine (SWNT-ODA) and multiwall carbon nanotubes grafted with linear PCL chains (i.e., MWNT-g-PCL prepared by ring-opening polymerization on previously functionalized MWNTs with a composition of 10% MWNT and 90% L-PCL). The nanocomposites were characterized by transmission electron microscopy (TEM), polarized light optical microscopy (PLOM), and differential scanning calorimetry (DSC). A nucleating effect was detected in both PCLs when SWNT-ODAs were employed. However, in the case of MWNT-g-PCL, the nanofiller nucleated L-PCL but caused an unexpected ...

LP-based heuristics for cost-optimal planning

Abstract: Many heuristics for cost-optimal planning are based on linear programming. We cover several interesting heuristics of this type by a common framework that fixes the objective function of the linear program. Within the framework, constraints from different heuristics can be combined in one heuristic estimate which dominates the maximum of the component heuristics. Different heuristics of the framework can be compared on the basis of their constraints. With this new method of analysis, we show dominance of the recent LP-based state-equation heuristic over optimal cost partitioning on single-variable abstractions. We also show that the previously suggested extension of the state-equation heuristic to exploit safe variables cannot lead to an improved heuristic estimate. We experimentally evaluate the potential of the proposed framework on an extensive suite of benchmark tasks.

Global invasion of Lantana camara: has the climatic niche been conserved across continents?

Abstract: Lantana camara, a native plant from tropical America, is considered one of the most harmful invasive species worldwide. Several studies have identified potentially invasible areas under scenarios of global change, on the assumption that niche is conserved during the invasion process. Recent studies, however, suggest that many invasive plants do not conserve their niches. Using Principal Components Analyses (PCA), we tested the hypothesis of niche conservatism for L. camara by comparing its native niche in South America with its expressed niche in Africa, Australia and India. Using MaxEnt, the estimated niche for the native region was projected onto each invaded region to generate potential distributions there. Our results demonstrate that while L. camara occupied subsets of its original native niche in Africa and Australia, in India its niche shifted significantly. There, 34% of the occurrences were detected in warmer habitats nonexistent in its native range. The estimated niche for India was also projected onto Africa and Australia to identify other vulnerable areas predicted from the observed niche shift detected in India. As a result, new potentially invasible areas were identified in central Africa and southern Australia. Our findings do not support the hypothesis of niche conservatism for the invasion of L. camara. The mechanisms that allow this species to expand its niche need to be investigated in order to improve our capacity to predict long-term geographic changes in the face of global climatic changes.

Confined crystallization of polymers within anodic aluminum oxide templates

Abstract: In this article, a review of recent literature on confined crystallization within nanoporous anodic aluminum oxide (AAO) templates is presented. For almost all infiltrated polymeric materials, crystal orientation within the nanopores is a function of pore diameter. Tc and Tm usually decrease and are a function of pore size. When no pore interconnection remains, the crystallization occur at large supercoolings in heterogeneity free environments. Hence, the nucleation mechanism changes from heterogeneous to surface or homogeneous nucleation. The crystallization kinetics of infiltrated polymers should be close to first order, since in confined environments nucleation is the determining step of the overall crystallization and Avrami indexes (n) of ∼1 (or lower in some cases) should be obtained. Examples are provided where these conditions have been met and first order kinetics (n = 1) were measured as opposed to higher orders (n = 3−4) for the same polymer in the bulk. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 1179–1194

Food Insecurity in Children but Not in Their Mothers Is Associated with Altered Activities, School Absenteeism, and Stunting

Abstract: Household food insecurity has substantial detrimental effects on children, but little is known about the mechanisms through which these effects occur. This study investigated some possible mechanisms by examining associations of food insecurity reported by children and mothers with daily activities, school absenteeism, and stunting. We conducted a cross-sectional study in a nonprobabilistic sample of 131 mother-child pairs from a poor peri-urban area in Miranda State, Venezuela. We assessed food insecurity in children by using an instrument developed through a naturalistic approach that had 10 items for food insecurity and 9 items for management strategies. To obtain mothers' reports of food insecurity, a previously validated 12-item instrument was used. Children's daily activities, school absenteeism, and stunting were measured. Chi-square tests for contingency tables and logistic and multiple regression analyses were used to test associations of food insecurity with outcomes. There was no association between mothers' reports of food-insecurity and any child outcome. Children's reports of food insecurity were associated with higher odds of doing passive home chores (OR: 1.17; 95% CI: 1.02, 1.32), cooking at home (OR: 1.21; 95% CI: 1.05, 1,38), taking care of siblings (OR: 1.15; 95% CI: 1.01, 1.31), and doing labor (OR: 1.22; 95% CI: 1.04, 1.42) and lower odds of playing video games (OR: 0.86; 95% CI: 0.76, 0.98) (all P < 0.03). Children's reports of management strategies were associated with 5 of 7 work activities measured. Labor in food-insecure children was the main activity that explained school absenteeism. Food insecurity reported by children can be assessed by pediatricians, school personnel, and other practitioners by using a simple instrument to identify food-insecure children and to respond to mitigate their food insecurity and its consequences.

Experimental tests of the new plastic scintillator with pulse shape discrimination capabilities EJ-299-33

Abstract: We have studied the prototype of a new plastic scintillator material (EJ-299-33) engineered for gamma-neutron discrimination. Energy and time resolutions as well as pulse shape discrimination capability have been compared with those of standard plastic and liquid scintillators. EJ-299-33 characteristics are somewhat poorer compared to standard scintillators. However, results obtained with the new plastic material suggest its possible use in basic research (time-of-flight measurements) as well as in Homeland Security applications (neutron/gamma monitoring device).

Understanding the Coexistence of Food Insecurity and Obesity

Abstract: Coexistence of food insecurity and obesity is expected given that both are consequences of economic and social disadvantage. Food insecurity and obesity are positively associated in adult women but not men. There is some evidence of association in adolescents, but mixed results for children. Distinct from adults, children experience cognitive, emotional, and physical awareness of food insecurity and take responsibility for it by participating in adult strategies, initiating their own strategies, and taking action to obtain additional food or money for food. Food insecurity is detrimental for children, being associated with behavior problems, disrupted social interactions, compromised school performance and attendance, poor dietary intake and physical activity, altered daily activities, and poor health. Some of these outcomes increase the risk of developing obesity. From life course, cumulative inequality, and developmental perspectives, child food insecurity may have long-term effects, including on risk of obesity. Pediatricians can help identify and respond to children who are food-insecure and at risk of obesity.

A TiO2 surface modified with copper(II) phthalocyanine-tetrasulfonic acid tetrasodium salt as a catalyst during photoinduced dichlorvos mineralization by visible solar light

Abstract: Two consecutive Langmuir isotherms were used in this study to describe copper(II) phthalocyanine-tetrasulfonic acid-tetrasodium salt (CuPc) adsorption by TiO2-Degussa-P25. UV–vis reflectance spectroscopy confirmed CuPc adsorption on the TiO2 surface. FTIR spectra revealed less TiO–sulfonic interactions for maximum CuPc surface coverage (39 mg g−1) of the second Langmuir than the maximum coverage (8 mg g−1) of the first Langmuir. This finding indicates that there is more than one TiO–sulfonic interaction per CuPc molecule. Dichlorvos (DDVP)-water solutions were degraded with the modified TiO2 catalyst and visible simulated solar light. The highest degradation rates were obtained using 8 mg g−1 CuPc at a neutral pH with a maximum kobs = 0.0072 min−1. Under this condition, a rate vs. DDVP concentration (CDDVP) bell-shaped profile was observed. This tendency can be explained in terms of dissolved oxygen singlet formation via visible light surface sensitization. This process was diminished at high CDDVP because of DDVP competition with dissolved oxygen to reach the catalyst surface. DDVP degradation and mineralization have the same rate limiting step. Therefore, there is no intermediate accumulation during treatment. The modified TiO2-CuPc catalyst activity was further improved when solar simulated light (including UV) was used to degrade DDVP. In fact, the fastest degradation rate constant (kobs = 0.011 min−1) was obtained using high CuPc coverage (39 mg g−1).

A review of diode and solar cell equivalent circuit model lumped parameter extraction procedures

Abstract: This article presents an up-to-date review of several methods used for extraction of diode and solar cell model parameters. In order to facilitate the choice of the most appropriate method for the given particular application, the methods are classified according to their lumped parameter equivalent circuit model: single-exponential, double-exponential, multiple-exponential, with and without series and parallel resistances. In general, methods based on numerical integration or optimization are recommended to reduce the possible uncertainties arising from measurement noise .

Drug-Target Interaction Prediction Using Semantic Similarity and Edge Partitioning

Abstract: The ability to integrate a wealth of human-curated knowledge from scientific datasets and ontologies can benefit drug-target interaction prediction. The hypothesis is that similar drugs interact with the same targets, and similar targets interact with the same drugs. The similarities between drugs reflect a chemical semantic space, while similarities between targets reflect a genomic semantic space. In this paper, we present a novel method that combines a data mining framework for link prediction, semantic knowledge (similarities) from ontologies or semantic spaces, and an algorithmic approach to partition the edges of a heterogeneous graph that includes drug-target interaction edges, and drug-drug and target-target similarity edges. Our semantics based edge partitioning approach, semEP, has the advantages of edge based community detection which allows a node to participate in more than one cluster or community. The semEP problem is to create a minimal partitioning of the edges such that the cluster density of each subset of edges is maximal. We use semantic knowledge (similarities) to specify edge constraints, i.e., specific drug-target interaction edges that should not participate in the same cluster. Using a well-known dataset of drug-target interactions, we demonstrate the benefits of using semEP predictions to improve the performance of a range of state-of-the-art machine learning based prediction methods. Validation of the novel best predicted interactions of semEP against the STITCH interaction resource reflect both accurate and diverse predictions.

Pulsing hydrology determines top‐down control of basal resources in a tropical river–floodplain ecosystem

Abstract: Variable hydrology of rivers strongly affects biophysical factors that influence primary production and population densities, thereby affecting the relative influence of bottom-up and top-down processes in trophic networks. Many tropical floodplain rivers have sustained seasonal flood pulses driven by precipitation patterns of the Intertropical Convergence Zone. These changes in flow alter concentrations of dissolved nutrients, aquatic primary productivity, and per-unit-area densities of aquatic organisms. Therefore, one would predict that the strength of top-down effects of animals on basal resources should shift as the annual flood pulse progresses. We conducted a series of field experiments in a Neotropical lowland river to test for effects of hydrologic phase, habitat (in-channel vs. floodplain aquatic habitat), and benthic-feeding fish and meiofauna on particulate organic matter, chlorophyll, and benthic microalgae. Net ecosystem productivity of this oligotrophic river is higher during the low phase ...

Belief tracking for planning with sensing: width, complexity and approximations

Abstract: We consider the problem of belief tracking in a planning setting where states are valuations over a set of variables that are partially observable, and beliefs stand for the sets of states that are possible. While the problem is intractable in the worst case, it has been recently shown that in deterministic conformant and contingent problems, belief tracking is exponential in a width parameter that is often bounded and small. In this work, we extend these results in two ways. First, we introduce a width notion that applies to non-deterministic problems as well, develop a factored belief tracking algorithm that is exponential in the problem width, and show how it applies to existing benchmarks. Second, we introduce a meaningful, powerful, and sound approximation scheme, beam tracking, that is exponential in a smaller parameter, the problem causal width, and has much broader applicability. We illustrate the value of this algorithm over large instances of problems such as Battleship, Minesweeper, and Wumpus, where it yields state-of-the-art performance in real-time.

Influence of Chain Branching and Molecular Weight on Melt Rheology and Crystallization of Polyethylene/Carbon Nanotube Nanocomposites

Abstract: In this paper, the synergistic effects that carbon nanotubes (CNTs) produce on the basic rheological properties and crystallization of polyethylenes with different branch contents and molecular weights was investigated. Multiwalled carbon nanotubes coated with polyethylene (as produced by in situ polymerization) were blended in the melt (in a 1% wt. ratio) with three polyethylene matrices of different molecular weights and branch contents. Transmission electron micrographs demonstrated excellent carbon nanotube dispersion in all samples and the existence of a geometrical percolation network. The rheological and calorimetric properties of the nanocomposites were determined and the results compared to those obtained for neat polyethylene resins. Both Newtonian viscosity and steady-state shear recoverable compliance increased with the addition of CNTs in all cases. However, the increase was strongly dependent on the molecular weight (and dispersity index) of the matrices regardless of the branch content. A n...