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Search Results: 1 - 10 of 97562 matches for " Marco Antonio David "
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Ellipsometric Study of SiOx Thin Films by Thermal Evaporation  [PDF]
David Salazar, Roberto Soto-Molina, Eder German Lizarraga-Medina, Marco Antonio Felix, Nicola Radnev, Heriberto Márquez
Open Journal of Inorganic Chemistry (OJIC) , 2016, DOI: 10.4236/ojic.2016.63013
Abstract: This paper presents a study of amorphous SiOx thin films by means of Variable Angle Spectroscopic Ellipsometry (VASE) technique. Tauc Lorentz, Lorentz and Cauchy models have been used to obtain physical thickness and complex refractive index (n and k) from experimental data. In order to obtain a wide range to x stoichiometry values, the films were prepared by vacuum thermal evaporation of SiO on glass substrates, under different and controlled deposition conditions.
The Effects of Negative Values of Apparent Resistivity in TEM Surveys  [PDF]
Cassiano Antonio Bortolozo, Julian David Realpe Campa?a, Marco Antonio Couto Junior, Jorge Luis Porsani, Fernando Acácio Monteiro dos Santos
International Journal of Geosciences (IJG) , 2016, DOI: 10.4236/ijg.2016.710088
Abstract: The calculation of apparent resistivity in electrical methods is relatively simple and consolidated in the literature. Furthermore, in the case of DC methods, the apparent resistivity values are for the most part, intuitive and enable an initial interpretation of the results. On the other hand, in TEM method the apparent resistivity values are not very intuitive and interpretation based only on the apparent resistivity values cannot be done reasonably. In this way, this paper presents a discussion about the reasons and effects of the negatives values of apparent resistivity in TEM soundings. The main objective of this paper is to clarify the meanings of these negatives values and the possible effects in TEM inversion.
Análise do emprego do cálculo amostral e do erro do método em pesquisas científicas publicadas na literatura ortod?ntica nacional e internacional
Normando, David;Almeida, Marco Antonio de Oliveira;Quint?o, Cátia Cardoso Abdo;
Dental Press Journal of Orthodontics , 2011, DOI: 10.1590/S2176-94512011000600006
Abstract: introduction: reliable sample size and an appropriate analysis of error are important steps to validate the data obtained in a scientific study, in addition to the ethical and economic issues. objective: to evaluate, quantitatively, how often the researchers of orthodontic science have used the calculation of sample size and evaluated the method error in studies published in brazil and in the united states of america. methods: two major journals, according to capes (brazilian federal agency for support and evaluation of graduate education), were analyzed through a hand search: revista dental press de ortodontia e ortopedia facial and the american journal of orthodontics and dentofacial orthopedics (ajo-do). only papers published between 2005 and 2008 were examined. results: most of surveys published in both journals employed some method of error analysis, when this methodology can be applied. on the other hand, only a very small number of articles published in these journals have any description of how sample size was calculated. this proportion was 21.1% for the journal published in the united states (ajo-do), and was significantly lower (p= 0.008) for the journal of orthodontics published in brazil (3.9%). conclusion: researchers and the editorial board of both journals should drive greater concern for the examination of errors inherent in the absence of such analyses in scientific research, particularly the errors related to the use of an inadequate sample size.
Biooxidación de concentrados de arsenopirita por Acidithiobacillus ferrooxidans en erlenmeyer agitados
Ospina Juan David,Mejía Restrepo Erica,Osorno Bedoya Laura,Márquez Marco Antonio
Revista Colombiana de Biotecnología , 2012,
Abstract: Título en ingles: Biooxidation of arsenopyrite concentrates by Acidithiobacillus ferrooxidans in shake flasks Resumen Se evaluó el proceso de biooxidación de concentrados de arsenopirita por A. ferrooxidans ATCC 23270, previa adaptación de los microorganismos al mineral y dos tama os de partícula, pasante malla Tyler 200 (~75μm) y 325 (~45μm). También, se determinó el grado de concentración del mineral mediante DRX y MOLPP/LR, bajo norma ASTM D 2799 de 2009. Los microorganismos fueron adaptados mediante disminución gradual, en etapas sucesivas, de sulfato ferroso y posterior aumento en el contenido de arsenopirita. Finalmente, se llevó a cabo el proceso de biooxidación del mineral sin adición de Fe2+. Después de treinta días de proceso, la disolución de arsénico para la malla Tyler 200 fue de 7550 mgL-1 (18,7%) y para la malla Tyler 325 fue de 2850 mgL-1 (7,1%). Por otra parte, la curva de crecimiento bacteriano mostró que entre los días 6 y 21 de proceso la población bacteriana promedio fue de 1,70x108 cel.mL‐1 y de 8,00x107 cel.mL‐1 para las mallas Tyler 200 y 325, respectivamente. Por lo tanto, el tama o de partícula jugó un papel fundamental en la cinética de adaptación de los microorganismos, sugiriendo que a menor tama o del sustrato empleado mayor dificultad se le presenta al microorganismo para oxidar el mineral. Palabras clave: arsénico; lixiviación; quimiolitótrofos; ATP. Abstract Arsenopyrite biooxidation process was evaluated with A. ferrooxidans ATCC 23270. The microorganisms were previously adapted to mineral and two different Tyler mesh sizes, 200 (~75μm) and 325 (~45μm). Also, the mineral concentration was made by DRX and MOLPP/LR under ASTM D 2799. The microorganisms were adapted through gradual decreasing of ferrous sulphate in successive state and subsequent arsenopyrite concentration increase. Finally, biooxidation process was carried out without Fe2+. After thirty days of process, Arsenic bioleaching was 7550 mgL-1(18,7%) and 2850 mgL-1 (7,1%) for the 200 and 325 Tyler meshes, respectively. On the other hand, bacterial growth curve showed, between 6 and 21 days of process that the average bacterial population was 1,70x108 cel.mL‐1 y de 8,00x107 cel.mL‐1for 200 and 325 Tyler mesh respectively. For this reason, the particle size played an important role in the adaption kinetics of microorganism. The results showed that the microorganism oxide the larger particle size of the mineral easier. Keywords: arsenic; lixiviation; chemolithoautotrophic; ATP.
EFFECT OF SINGLE SUPERPHOSPHATE AND ORGANIC MATTER DOSES ON THE GROWTH OF YELLOW PASSION FRUIT SEEDLINGS EFEITO DE DOSES DE SUPERFOSFATO SIMPLES E DE MATéRIA ORG NICA SOBRE O CRESCIMENTO DE MUDAS DE MARACUJAZEIRO 'AMARELO'
Marco Antonio David,Vander Mendon?a,Luis Lessi dos Reis,Elisangela Aparecida da Silva
Pesquisa Agropecuária Tropical , 2008, DOI: 10.5216/pat.v38i3.3783
Abstract: The objective of this research was to evaluate the effect of doses of organic matter and single superphosphate on the production of yellow passion fruit (Passiflora edulis Sims f. flavicarpa Deg) seedlings. An experiment was carried out in a screen nursery at 50% shading, at the Agricultural Production Sector , Universidade Estadual do Mato Grosso do Sul, Cassilandia (UUC), Brazil. Four doses of single superphosphate (0.0 kg.m-3; 2.5 kg.m-3; 5.0 kg.m-3; and 10.0 kg.m-3 of substratum), and three doses of organic matter (0%; 20%, and 40%) of the total volume of the substratum were tested. The organic matter was applied as poultry litter. A randomized block design with a 4 x 3 factorial scheme was used, with four replications and seven plants per plot. It was observed that the single superphosphate application at 7.7 kg.m-3 and 40% of organic matter per 1.0 m3 of substratum, provided more vigorous yellow passion fruit seedlings. KEY-WORDS: Passiflora edulis f. flavicarpa; nutrition; propagation. O objetivo desta pesquisa foi avaliar o efeito de diferentes doses de superfosfato simples e matéria organica na produ o de mudas de maracujazeiro ‘amarelo’. Conduziu-se um experimento, em condi o de viveiro telado, com sombrite 50%, no Setor de Produ o Agrícola da Universidade Estadual do Mato Grosso do Sul, Unidade Universitária de Cassilandia-MS (UUC). Foram testadas quatro doses de superfosfato simples (0,0 kg.m-3; 2,5 kg.m-3; 5,0 kg.m-3; e 10,0 kg.m-3 de substrato) e três doses de matéria organica (0%, 20% e 40%) do volume total do substrato. A matéria organica foi aplicada na forma de cama de frango. O delineamento experimental utilizado foi o de blocos ao acaso, em esquema fatorial 4 x 3, com quatro repeti es e sete plantas por parcela. Verificou-se que a aplica o de superfosfato simples, na dose de 7,7 kg.m-3 e de 40% de cama de frango por 1,0 m3 de substrato, proporcionou a obten o de mudas mais vigorosas do maracujazeiro amarelo. PALAVRAS-CHAVE: Passiflora edulis f. flavicarpa; nutri o; propaga o.
Ethane Internal Rotation -Vibrational Hamiltonian
David Ricardo Hidalgo Olguín,María Villa,María Luisa Senent,Marco Antonio Mora Delgado
Revista de la Sociedad Química de México , 2008,
Abstract: Uno de los objetivos principales de un espectroscopísta teórico es generar un modelo que reproduzca los espectros experimentales con la mayor precisión e información física posible. En este caso se estudió el espectro en el Infrarrojo lejano e Infrarrojo de moléculas no rígidas introduciendo en el potencial vibracional su dependencia de las variables de gran amplitud. La molécula de etano fue seleccionada para comprobar nuestro Hamiltoniano propuesto, ya que es una molécula ampliamente estudiada.; además de ser una molécula no rígida cuyo espectro experimental ha sido reportado en la literatura.
Mineralogia del proceso de oxidación bacteriana de la galena (PbS) por Acidithiobacillus ferrooxidans, mediante análisis de microscopia electrónica de barrido, FTIR y DRX
Erica Mejía Restrepo,Juan David Ospina Correa,Marco Antonio Márquez G
Scientia Et Technica , 2007,
Abstract: Se caracterizaron mineralógicamente dos muestras de galena, pasante malla 200 y 325, provenientes del proceso de oxidación bacteriana mediante la utilización de una cepa compatible con Acidithiobacillus ferrooxidans. Los experimentos se realizaron previa adaptación de los microorganismos sobre el mineral como única fuente de energía. Para cada ensayo se hizo además blanco (abiótico) y réplica. Se midió pH y Eh diariamente durante 21 días, tomando muestras cada 4 días para el monitoreo mineralógico del proceso. La muestra -325 oxidó completamente, mientras que la -200 mostró oxidación parcial. La anglesita (PbSO4) fue el principal producto del proceso.
Inhibition of Acinetobacter baumannii Biofilm Formation by Methanolic Extract of Nothoscordum bivalve  [PDF]
Hernández-Marín David Alejandro, Mu?oz-Ortega Martín Humberto, Guevara-Lara Fidel, Gúzman-Lucio Marco Antonio, Sánchez-García Eduardo
Advances in Microbiology (AiM) , 2018, DOI: 10.4236/aim.2018.85028
Abstract: Acinetobacter baumannii is one of the most prevalent pathogens in nosocomial infections and has been cause of concern in recent years because, it has presented multiresistance to antibiotics and besides can form biofilms on biotic and abiotic surfaces like tissues and medical devices. Therefore, the search for new alternatives of natural origin to inhibit biofilm formation is being conducted. In the present investigation, sub-lethal concentrations (5.61 mg/mL, 3.74 mg/mL and 1.87 mg/mL) of methanolic extract of Nothoscordum bivalve were evaluated, showing biofilm formation inhibition up to 40.8%, in one nosocomial isolated of A. baumannii by the microtiter biofilm formation assay using crystal violet. On the other hand, the concentrations of 5.61 mg/mL and 3.74 mg/mL, caused an overexpression (up to 15.4 times) in the genes involved in the formation of biofilm (abaI, bap and csuE); due to this, the interaction of the extract with the bacteria was analyzed by scanning electron microscopy (SEM) and cellular damage was observed in the structure and stability of biofilm.
Sex-biased expression of microRNAs in Drosophila melanogaster
Antonio Marco
Quantitative Biology , 2013, DOI: 10.1098/rsob.140024
Abstract: Most animals have separate sexes. The differential expression of gene products, in particular that of gene regulators, is underlying sexual dimorphism. Analyses of sex-biased expression have focused mostly in protein coding genes. Several lines of evidence indicate that microRNAs, a class of major gene regulators, are likely to have a significant role in sexual dimorphism. This role has not been systematically explored so far. Here I study the sex-biased expression pattern of microRNAs in the model species Drosophila melanogaster. As with protein coding genes, sex biased microRNAs are associated with the reproductive function. Strikingly, contrary to protein-coding genes, male biased microRNAs are enriched in the X chromosome whilst female microRNAs are mostly autosomal. I propose that the chromosomal distribution is a consequence of high rates of de novo emergence, and a preference of new microRNAs to be expressed in the testis. I also suggest that demasculinization of the X chromosome may not affect microRNAs. Interestingly, female biased microRNAs are often encoded within protein coding genes that are also expressed in females. MicroRNAs with sex-biased expression do not preferentially target sex-biased gene transcripts. These results strongly suggest that the sex-biased expression of microRNAs is mainly a consequence of high rates of microRNA emergence in the X (male bias) or hitch-hiked expression by host genes (female bias).
Suppression subtractive hybridization analysis reveals expression of conserved and novel genes in male accessory glands of the ant Leptothorax gredleri
Angelika Oppelt, Fernanda C Humann, Marion Fuessl, Sergio V Azevedo, David S Marco Antonio, Jürgen Heinze, Klaus Hartfelder
BMC Evolutionary Biology , 2010, DOI: 10.1186/1471-2148-10-273
Abstract: By a suppression subtractive hybridization protocol we obtained 20 unique sequences (USs). Twelve had mutual best matches with genes predicted for Apis mellifera and Nasonia vitripennis. Functional information (Gene Ontology) was available only for seven of these, including intracellular signaling, energy-dependent transport and metabolic enzyme activities. The remaining eight USs did not match sequences from other species. Six genes were further analyzed by quantitative RT-PCR in three life cycle stages of male ants. A gene with carboxy-lyase activity and one of unpredicted function were significantly overexpressed in accessory glands of sexually mature males.Our study is the first one to investigate differential gene expression in ants in a context related to mating. Our findings indicate that male accessory glands of L. gredleri express a series of genes that are unique to this species, possibly representing novel genes, in addition to conserved ones for which functions can be predicted. Identifying differentially expressed genes might help to better understand molecular mechanisms involved in reproductive processes in eusocial Hymenoptera. While the novel genes could account for rapidly evolving ones driven by intra-sexual conflict between males, conserved genes imply that rather beneficial traits might get fixed by a process described as inter-sexual cooperation between males and females.Substances produced by the male accessory glands (MAGs) of insects and transferred into the female genital tract during mating are known to reduce pathogen transmission, to form mating plugs or spermatophores, and to be important in sperm competition. In addition, they trigger fundamental changes in female physiology, behavior, and reproduction [1-4]. The major biologically active components of MAG secretions are carbohydrates, lipids, and in particular accessory gland proteins (Acps) [1].In Drosophila melanogaster, more than 100 Acps have been identified [5]. They play roles i
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