Study of CdS/CdS Nanoparticles Thin Films Deposited by Soft Chemistry for Optoelectronic Applications.

Chalcogenides semiconductors are currently being studied as active layers in the development of electronic devices in the field of applied technology. In the present paper, cadmium sulfide (CdS) thin films containing nanoparticles of the same material as the active layer were produced and analyzed for their application in fabricating optoelectronic devices. CdS thin films and CdS nanoparticles were obtained via soft chemistry at low temperatures. The CdS thin film was deposited via chemical bath deposition (CBD); the CdS nanoparticles were synthesized via the precipitation method. The construction of a homojunction was completed by incorporating CdS nanoparticles on CdS thin films deposited via CBD. CdS nanoparticles were deposited using the spin coating technique, and the effect of thermal annealing on the deposited films was investigated. In the modified thin films with nanoparticles, a transmittance of about 70% and a band gap between 2.12 eV and 2.35 eV were obtained. The two characteristic phonons of the CdS were observed via Raman spectroscopy, and the CdS thin films/CdS nanoparticles showed a hexagonal and cubic crystalline structure with average crystallite size of 21.3-28.4 nm, where hexagonal is the most stable for optoelectronic applications, with roughness less than 5 nm, indicating that CdS is relatively smooth, uniform and highly compact. In addition, the characteristic curves of current-voltage for as-deposited and annealed thin films showed that the metal-CdS with the CdS nanoparticle interface exhibits ohmic behavior.

Dating the cyanobacterial ancestor of the chloroplast.

Cyanobacteria have had a pivotal role in the history of life on Earth being the first organisms to perform oxygenic photosynthesis, which changed the atmospheric chemistry and allowed the evolution of aerobic Eukarya. Chloroplasts are the cellular organelles of photoautotrophic eukaryotes in which most portions of photosynthesis occur. Although the initial suggestion that cyanobacteria are the ancestors of chloroplasts was greeted with skepticism, the idea is now widely accepted. Here we attempt to resolve and date the cyanobacterial ancestry of the chloroplast using phylogenetic analysis and molecular clocks. We found that chloroplasts form a monophyletic lineage, are most closely related to subsection-I, N(2)-fixing unicellular cyanobacteria (Order Chroococcales), and heterocyst-forming Order Nostocales cyanobacteria are their sister group. Nostocales and Chroococcales appeared during the Paleoproterozoic and chloroplasts appeared in the mid-Proterozoic. The capability of N(2) fixation in cyanobacteria may have appeared only once during the late Archaean and early Proterozoic eons. Furthermore, we found that oxygen-evolving cyanobacteria could have appeared in the Archaean. Our results suggest that a free-living cyanobacterium with the capacity to store starch through oxygenic CO(2) fixation, and to fix atmospheric N(2), would be a very important intracellular acquisition, which, as can be recounted today from several lines of evidence, would have become the chloroplast by endosymbiosis.

A operacionalização das ações do programa de controle da tuberculose na rede básica de saúde do município de Porto Velho, RO

O objetivo deste estudo foi descrever a operacionalização das ações e serviços do Plano de Controle da Tuberculose oferecido aos usuários na rede básica de saúde no município de Porto Velho. Optou-se pela pesquisa de natureza descritiva com enfoque exploratório. Foram estudadas 10 Unidades Básicas de Saúde (UBS) da área urbana do município. Fizeram parte do estudo os profissionais de saúde que realizam o atendimento aos usuários das unidades de saúde após concordarem em participar da pesquisa. No total foram 10 enfermeiros, 10 médicos generalistas, seis bioquímicos/biomédicos e três agentes comunitários de saúde. Os resultados do estudo sugerem que os profissionais, mesmo treinados, têm dificuldade de operacionalizar as ações de controle para a tuberculose, devido à não adequação da estrutura das unidades aos parâmetros propostos pelo Ministério da Saúde. Apontam também a necessidade da implementação efetiva da estratégia DOTS e aumento da cobertura da Estratégia Saúde da Família. (AU)

Angiosperm diversification through time.

The extraordinary diversity of angiosperms is the ultimate outcome of the interplay of speciation and extinction, which determine the net diversification of different lineages. We document the temporal trends of angiosperm diversification rates during their early history. Absolute diversification rates were estimated for order-level clades using ages derived from relaxed molecular clock analyses that included or excluded a maximal constraint to angiosperm age. Diversification rates for angiosperms as a whole ranged from 0.0781 to 0.0909 net speciation events per million years, with dates from the constrained analysis. Diversification through time plots show an inverse relationship between clade age and rate, where the younger clades tend to have the highest rates. Angiosperm diversity is found to have mixed origins: slightly less than half of the living species belong to lineages with low to moderate diversification rates, which appeared between 130 and 102 Mya (Barremian-uppermost Albian; Lower Cretaceous). Slightly over half of the living species belong to lineages with moderate to high diversification rates, which appeared between 102 and 77 Mya (Cenomanian-mid Campanian; Upper Cretaceous). Terminal lineages leading to living angiosperm species, however, may have originated soon or long after the phylogenetic differentiation of the clade to which they belong.

Molecular diversity of rabies viruses associated with bats in Mexico and other countries of the Americas.

Bat rabies and its transmission to humans and other species in Mexico were investigated. Eighty-nine samples obtained from rabid livestock, cats, dogs, and humans in Mexico were studied by antigenic typing and partial sequence analysis. Samples were further compared with enzootic rabies associated with different species of bats in the Americas. Patterns of nucleotide variation allowed the definition of at least 20 monophyletic clusters associated with 9 or more different bat species. Several lineages associated with distinctive antigenic patterns were found in rabies viruses related to rabies in vampire bats in Mexico. Vampire bat rabies virus lineages associated with antigenic variant 3 are widely spread from Mexico to South America, suggesting these lineages as the most likely ancestors of vampire bat rabies and the ones that have been moved by vampire bat populations throughout the Americas. Rabies viruses related to Lasiurus cinereus, Histiotus montanus, and some other not yet identified species of the genus Lasiurus were found circulating in Mexico. Long-range dissemination patterns of rabies are not necessarily associated with migratory bat species, as in the case of rabies in Desmodus rotundus and Histiotus montanus. Human rabies was associated with vampire bat transmission in most cases, and in one case, rabies transmission from free-tailed bats was inferred. The occurrence of rabies spillover from bats to domestic animals was also demonstrated. Genetic typing of rabies viruses allowed us to distinguish trends of disease dissemination and to address, in a preliminary fashion, aspects of the complex evolution of rabies viruses in different host-reservoir species.

Molecular epizootiology of rabies associated with terrestrial carnivores in Mexico.

Epizootiological patterns of rabies are described, using antigenic and genetic analysis of samples obtained from infected domestic and wild mammals in 20 Mexican states during 1976-2002. Two independent origins are suggested for rabies in Mexican carnivores. One group shares ancestry with canine rabies, while the other group appears to share a common origin with bat rabies in North America. More than 12 sublineages were found in rabid dog populations, suggesting at least six major spatio-temporal foci. Coyote rabies was found as independent enzootic foci that probably emerged via spillover from dog rabies, translocated from major foci in the southcentral and western regions of Mexico. One focus of gray fox rabies was widely distributed in northwestern Mexico, overlapping with a focus in the same species in the southwestern United States. A skunk rabies focus distributed in the northcentral Mexican states appears to share a common origin with bat rabies foci in North America, and is a close relative of southcentral skunk and raccoon rabies in the United States. Two other skunk foci share a common ancestor with canine rabies and were distributed in northwest Mexico and Yucatan.

A genomic population genetics analysis of the pathogenic enterocyte effacement island in Escherichia coli: the search for the unit of selection.

Comparative genomic analysis is a powerful tool for understanding the history and organization of complete genomes. The mathematical tools of population genetics combined with genomic analysis provide a powerful approach to dissect heterogeneities in genome evolution. This study presents a hierarchical analysis of the enterocyte and effacement island (35 kb), which is found in the enteropathogenic and enterohemorrhagic strains in Escherichia coli and in Citrobacter rodentium. The locus of enterocyte and effacement in E. coli is considered to be a clonal unit inside a clonal organism and is expected to evolve as a single unit. This analysis examines the clonal assumption by determining genetic diversity, GC content, and the substitution rates at the different functional levels of (i) the complete pathogenic island, (ii) the five operons in which the island is organized, and (iii) for each of the individual 41 genes that comprise the locus. We find that there is a conserved region that is composed of genes that belong to the type III secretion system and that may be products of horizontal transfer. A more diverse region is composed of genes for secreted proteins and genes that we infer to be original components of the E. coli genome. This genetic mosaic seems to be differentially affected by selection and mutation. Our results suggest that recombination and selection may be breaking this structure so that different elements are, at best, weakly coupled in their evolution. These observations suggest that the units of selection are not the complete island, but rather, much smaller units that comprise the island.

Evolución molecular y genómica en angiospermas / Molecular and genomic evolution in angiosperms

Se revisaron, sintetizaron y compararon aspectos de la evolución de los genomas en las angioespermas. Las plantas con flores tres genomas: el del cloroplasto, el de la mitocondria y el nuclear. El genoma del cloroplasto tiene una estructura muy conservada (120-217kb) que incluye 110-113 genes. El genoma de la mitocondria es mayor (300-600kb) y contiene cerca de 60 genes, es un genoma muy dinámico ya que gana y pierde fácilmente secuencias nucleares y del cloroplasto. Los genomas nucleares de las angioespermas se encuentran entre los más grandes conocidos. El genoma nuclear de Arabidopsis thailiana tiene 125Mb que comprenden 25498 genes. Del arroz (oryza sativa) se han secuenciado dos variedades y su genoma es casi 4 veces más grande que el de A. thaliana y comprenden de 32000 a 55615 genes. Para el maíz (Zea mays), aunque no secuenciado, se tiene mucha información y se estima que 60 a 80 por ciento de su genoma nuclear está constituido por elementos móviles. Las substituciones sinónimas de los genes de cloroplasto son de 2 a 3 veces más rápidas que en las mitocondrias, y los genes nucleares cambian de 10 a 15 veces más rápido que los mitocondriales. Sin embargo, las tasas de substitución de los sitios no sinónimos son similares entre mitocondria y cloroplasto, y son un poco más altas en el núcleo. Los estudios detallados de estos tres genomas permiten avanzar en el entendimiento de las complejidades genéticas y evolutivas de este grupo de plantas

Ecología evolutiva de escherichia coli / Evolutive ecology of escherichia coli

Escherichia coli es el organismo mejor conocido en términos de su genética y fisiología. Sin embargo, se sabe poco de su ecología y biología evolutiva. En este trabajo revisamos aspectos de su biología, genómica, ecología genética de poblaciones. Estudios clásicos, basados principalmente en cepas aisladas de humanos, sugerían que E.coli es una especie con una fuerte estructura clonal, con poca o ninguna recombinación. Nosotros hemos ensamblado y analizado una colección llamada IECOL, con más de 2000 cepas provenientes de animales de varios lugares del mundo, de humanos de México y de cepas silvestres de diferentes ambientes. En este trabajo se presentan datos sobre genética de poblaciones y evolución molecular de E.coli obtenidos a partir de esta colección. Estos, junto con otros datos de la literatura reciente, indican que E.coli es un organismo muy diverso, con un genoma extraordinariamente dinámico donde la recobinación es importante, y que las combinaciones exitosas pueden dispersarse de manera epidémica en las poblaciones humanas o animales, dando una falsa señal de clonalidad. Finalmente, se ilustra el potencial de uso de la colección (IECOL) en estudios que estamos realizando sobre la evolución de tasas de mutación, y sobre la evolución de genes patogénicos en la especie

Estudios dieteticos en El Salvador : II. Canton Platanillos, Municipio de Quezaltepeque, Departamento de La Libertad

Publicacion Cientifica INCAP E-109