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Strubinger A.,Simon Bolivar University of Venezuela | Ehrmann U.,Simon Bolivar University of Venezuela | Leon V.,Fundacion Institute Estudios Avanzados IDEA
Energy and Fuels

In the petroleum industry, the implementation of new methodologies requires a validation procedure in order to guarantee compliance with the specifications. This study presents a comparison between the methodology proposed for the determination of the API gravity using a gas pycnometer with a standard and an internationally recognized method such as the one described in ASTM D1298. One of the main advantages of the gas pycnometer technique is related to the use of a hydrometer, which requires a minimum amount of sample. This makes it an ideal method to monitor API gravity in research laboratory-scale processes. In addition, it is a simple and reasonably fast methodology for small samples and therefore attractive for processes with limited sample availability like biotechnological applications. Although the validation parameters reported in the literature are varied, only the results obtained by using the new method as compared with those obtained by using the standard methodology, such as those related to precision and accuracy, are presented. For the API gravity values obtained by using gas pycnometer to be equivalent to the results obtained by using the ASTM D1298 standard method, which would allow the use of both methodologies without this resulting in a deviation of the API gravity specification value of the sample, it is necessary to carry out a correction using the linear correlation data obtained. However, taking into account the precision data, reproducibility limits specifically, both methodologies are comparable. © 2012 American Chemical Society. Source

Torres-Alruiz M.D.,Fundacion Institute Estudios Avanzados IDEA | Rodriguez D.J.,Central University of Venezuela
Ecological Modelling

Topological studies of trophic webs have shown that a community's extinction risk can be influenced by the positional properties of its species. For example, networks are more robust after the deletion of high degree species, than after the deletion of species with high values of other centrality indexes. The effects of other positional attributes of the species, such as betweenness and closeness, have not been explored as deeply. There is also an evidence that community dynamics is affected by properties such as geometry, connectance, and the connection patterns between species. Most publications on community network models have analyzed the importance of species based on the number of species left unconnected after species deletions (topological criterion). However it is also important to analyze this importance in terms of community dynamics resulting after the deletion (dynamical criterion). To answer these questions we studied the importance of species for indirect interactions and the persistence of the community in network models with various levels of species number, connectance and geometries. We used a topo-dynamical criterion using two new indexes proposed in the present work: (a) the Index of importance of species i, Ii, which is a combined measure of centrality and the consequence in terms of secondary extinctions of the species' deletion; and (b) the species deletion resistance, SDR, which measures the resistance of the whole community to species deletions. We found that: (a) the mean index of importance of species in a community increases with connectance and/or species richness; (b) in webs with high connectance and/or high species richness, keystone species are less frequent; (c) the SDR of a community decreases with connectance and species richness; (d) communities with rectangular geometry do not behave differently than those with triangular geometry; (e) the number of tri-trophic chains and/or trophic loops increases with connectance and/or species richness. The possible effect of these last two modules is discussed. © 2012 Elsevier B.V. Source

Moraes Barros R.R.,University of Sao Paulo | Marini M.M.,University of Sao Paulo | Antonio C.R.,University of Sao Paulo | Cortez D.R.,University of Sao Paulo | And 6 more authors.
BMC Genomics

Background: The subtelomeres of many protozoa are highly enriched in genes with roles in niche adaptation. T. cruzi trypomastigotes express surface proteins from Trans-Sialidase (TS) and Dispersed Gene Family-1 (DGF-1) superfamilies which are implicated in host cell invasion. Single populations of T. cruzi may express different antigenic forms of TSs. Analysis of TS genes located at the telomeres suggests that chromosome ends could have been the sites where new TS variants were generated. The aim of this study is to characterize telomeric and subtelomeric regions of T. cruzi available in TriTrypDB and connect the sequences of telomeres to T. cruzi working draft sequence.Results: We first identified contigs carrying the telomeric repeat (TTAGGG). Of 49 contigs identified, 45 have telomeric repeats at one end, whereas in four contigs the repeats are located internally. All contigs display a conserved telomeric junction sequence adjacent to the hexamer repeats which represents a signature of T. cruzi chromosome ends. We found that 40 telomeric contigs are located on T. cruzi chromosome-sized scaffolds. In addition, we were able to map several telomeric ends to the chromosomal bands separated by pulsed-field gel electrophoresis.The subtelomeric sequence structure varies widely, mainly as a result of large differences in the relative abundance and organization of genes encoding surface proteins (TS and DGF-1), retrotransposon hot spot genes (RHS), retrotransposon elements, RNA-helicase and N-acetyltransferase genes. While the subtelomeric regions are enriched in pseudogenes, they also contain complete gene sequences matching both known and unknown expressed genes, indicating that these regions do not consist of nonfunctional DNA but are instead functional parts of the expressed genome. The size of the subtelomeric regions varies from 5 to 182 kb; the smaller of these regions could have been generated by a recent chromosome breakage and telomere healing event.Conclusions: The lack of synteny in the subtelomeric regions suggests that genes located in these regions are subject to recombination, which increases their variability, even among homologous chromosomes. The presence of typical subtelomeric genes can increase the chance of homologous recombination mechanisms or microhomology-mediated end joining, which may use these regions for the pairing and recombination of free ends. © 2012 Moraes Barros et al.; licensee BioMed Central Ltd. Source

Today it is estimated that half world population can be infected by malaria and there is not an available vaccine, however, there is hope with vaccine RTS,S/AS02. For this reason, we must continue to develop computer methodologies and strategies that will allow the rational design of potentially effective vaccines. We propose a new computational approach to predict linear B-cell epitopes from the whole genome sequencing of Plasmodium falciparum 3D7, obtained from IEDB database. Those that were repeated were discarded and were grouped into blocks according to the obtained results by Redundancy and Nomad programs. Subsequently, the possible antigenic character was predicted using the programs BepiPred, BcePred and BCPred. Three potentially antigenic sequences out of the 45 predicted were obtained with this methodology, but it is not possible to say which one the most antigenic without experimental evidence. Source

Romay G.,French National Institute for Agricultural Research | Romay G.,Fundacion Institute Estudios Avanzados IDEA | Lecoq H.,French National Institute for Agricultural Research | Desbiez C.,French National Institute for Agricultural Research
Journal of Plant Pathology

Cucurbit crops are cultivated throughout the world. Melon (Cucumis melo L.), cucumber (Cucumis sativus L.), watermelon (Citrullus lanatus (Thumb.) Mat. et Nak.), squash and pumpkin (Cucurbita spp.) are the major crops. In Latin America and the Caribbean islands (LAC) cucurbits are consumed as a part of the daily diet since pre-Columbian times, when some species such as Cucurbita pepo L., Cucurbita moschata Duch. and Cucurbita maxima Duch. were domesticated by American Indians. In LAC, cucurbit crops have become export commodities and a source of income for several countries, in addition to their role in local consumption. The increase of area devoted to cucurbit crops and the intensification of production has led to the emergence of severe viral epidemics that threaten the sustainability of these cultures. This paper reviews the cucurbit viruses described in the region and their impact. In addition, the potential of different measures to control the most frequent cucurbit viruses in LAC is discussed. Source

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