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Emissões de N2 e N2O provenientes do fertilizante aplicado a solos cultivados com cana-de-açúcar pelo método do traçador 15N; N2 and N2O emissions from fertilizer applied on soil cultivated with sugarcane measured by 15N tracer method

Milagres, João José de Miranda
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 29/08/2014 PT
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26.44%
Emissões de N2 e N2O reduzem a eficiência da adubação e podem causar danos ambientais. O método do traçador isotópico (15N) é indicado para medições de N2 e N2O, masnão há relatos de sua utilização no Brasil na quantificação desses gases.O objetivo deste estudo foi adaptar o método do traçador 15N às condições brasileiras para quantificar N2 e N2O derivados do fertilizante aplicado à cana-de-açúcar. Para o ajuste do métodoforam conduzidos três experimentos: um em condições controladas e dois em condições de campo. Em ambiente controlado foram utilizados três solos com diferentes classes texturais. A influência da umidade (40, 60 e 80% da capacidade máxima de retenção de água - CMRA) e da adição ou não de dextrose (500 mgkg-1 de C), foram outros parâmetros avaliados. O K15NO3enriquecido em 23,24% em átomos de 15N foi a fonte de N (100 mg kg-1 de N) utilizada. Os trabalhos de campo foram realizados em Latossolo Vermelho da região de Piracicaba-SP, em área de canade- açúcar sem despalha a fogo. No segundo experimento, foram testadas: fontes de N (15ureia e 15NH4 15NO3, ambos com 31,9% em átomos de 15N); doses de N (55 e 110 kg ha-1); com e sem vinhaça (100 m3 ha-1). No terceiro foram testadas doses de N (70 e 140 kg ha-1)na forma de 15NH4 15NO3; doses de vinhaça (75 e 150 m3 ha-1); com e sem a cobertura de palha (11 Mg ha-1). Em cada experimento...

Avaliação da reatividade ao CO2 de chars obtidos em atmosferas convenional (O2/N2) e de oxi-combustão (O2/CO2) com vistas à aplicação no alto-forno

Pohlmann, Juliana Gonçalves
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Dissertação Formato: application/pdf
POR
Relevância na Pesquisa
26.14%
A injeção de carvão pulverizado - PCI - é praticada nas ventaneiras dos altos-fornos com o objetivo de substituir parcialmente o coque, provendo energia e gases redutores ao processo. Em geral, as melhorias desse processo ocorrem no sentido de diminuir o fuel rate e aumentar a produtividade do alto-forno. A tecnologia de oxi-combustão consiste na queima de carvão em uma atmosfera livre de N2, o qual é substituído por um gás rico em CO2. Visando a possibilidade de aplicação desta tecnologia em PCI, chars de três carvões de diferentes ranks utilizados para injeção e chars de um coque de petróleo foram obtidos em atmosferas convencional (O2/N2) e de oxi-combustão (O2/CO2) em forno de queda livre O objetivo do presente trabalho foi avaliar a reatividade ao CO2 desses chars por termogravimetria via método isotérmico a 1000°C. Resultados de eficiência da combustão (burnout), de área superficial e a morfologia dos chars antes da gaseificação auxiliaram a análise da reatividade. A reatividade foi, em geral, mais alta quanto mais baixo o rank do carvão e tendeu a aumentar com o burnout, o qual foi associado ao aumento na área superficial BET. Em geral, as reatividades ao CO2 dos chars de atmosferas O2/N2 e O2/CO2...

Modelagem numérica bidimensional de combustão de partículas de carvão em atmosferas de O2/N2 e O2/Co2

García Sierra, Juan Esteban
Fonte: Universidade de Brasília Publicador: Universidade de Brasília
Tipo: Dissertação
POR
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26.18%
Dissertação (mestrado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Mecânica, Brasília, 2013.; Confirmando-se as previsões de esgotamento das grandes reservas de petróleo e gás natural, o carvão poderá mais uma vez tornar-se a fonte principal de combustível fóssil no mundo. Mas, com seu emprego em larga escala será necessário o desenvolvimento de técnicas de captura e armazenamento de dióxido de carbono. Recentemente vem-se desenvolvendo pesquisas sobre novas tecnologias para a produção de energia mais limpa a base de carvão e uma delas é a oxi-combustão. Esta tecnologia é baseada na queima de combustíveis em uma atmosfera oxidante (livre de nitrogênio). A combustão de carvão com oxigênio puro produz um gás rico em CO2 e vapor de água, com substancialmente baixas concentrações de NOx. Permitindo assim, uma fácil separação e captura do CO2 para depois ser comprimido, transportado e armazenado. Dentro deste contexto, este trabalho apresenta um estudo detalhado da combustão de partículas de carvão colombiano betuminoso em atmosferas O2/NO2 (ar atmosférico) e O2/CO2 (oxi-combustão), através de simulações numéricas computacionais mostrando o efeito da substituição de N2 por CO2 na combustão de carvão em partículas. As equações de conservação de massa...

Bound state solutions of schrödinger equation for a more general exponential screened coulomb potential via Nikiforov-Uvarov method

Ita,Benedict I; Ekuri,P; Isaac,Idongesit O; James,Abosede O
Fonte: Fundação Editora da Universidade Estadual Paulista Júlio de Mesquita Filho - UNESP Publicador: Fundação Editora da Universidade Estadual Paulista Júlio de Mesquita Filho - UNESP
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2010 EN
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35.85%
The arbitrary angular momentum solutions of the Schrödinger equation for a diatomic molecule with the general exponential screened coulomb potential of the form V(r) = (- a / r){1+ (1+ b )e-2b } has been presented. The energy eigenvalues and the corresponding eigenfunctions are calculated analytically by the use of Nikiforov-Uvarov (NU) method which is related to the solutions in terms of Jacobi polynomials. The bounded state eigenvalues are calculated numerically for the 1s state of N2 CO and NO

Stimulation of Symbiotic N2 Fixation in Trifolium repens L. under Elevated Atmospheric pCO2 in a Grassland Ecosystem.

Zanetti, S.; Hartwig, U. A.; Luscher, A.; Hebeisen, T.; Frehner, M.; Fischer, B. U.; Hendrey, G. R.; Blum, H.; Nosberger, J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /10/1996 EN
Relevância na Pesquisa
26.14%
Symbiotic N2 fixation is one of the main processes that introduces N into terrestrial ecosystems. As such, it may be crucial for the sequestration of the extra C available in a world of continuously increasing atmospheric CO2 partial pressure (pCO2). The effect of elevated pCO2 (60 Pa) on symbiotic N2 fixation (15N-isotope dilution method) was investigated using Free-Air-CO2-Enrichment technology over a period of 3 years. Trifolium repens was cultivated either alone or together with Lolium perenne (a nonfixing reference crop) in mixed swards. Two different N fertilization levels and defoliation frequencies were applied. The total N yield increased consistently and the percentage of plant N derived from symbiotic N2 fixation increased significantly in T. repens under elevated pCO2. All additionally assimilated N was derived from symbiotic N2 fixation, not from the soil. In the mixtures exposed to elevated pCO2, an increased amount of symbiotically fixed N (+7.8, 8.2, and 6.2 g m-2 a-1 in 1993, 1994, and 1995, respectively) was introduced into the system. Increased N2 fixation is a competitive advantage for T. repens in mixed swards with pasture grasses and may be a crucial factor in maintaining the C:N ratio in the ecosystem as a whole.

Enumeration, Isolation, and Characterization of N2-Fixing Bacteria from Seawater

Guerinot, Mary Lou; Colwell, Rita R.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /08/1985 EN
Relevância na Pesquisa
26.22%
Marine pelagic N2-fixing bacteria have not, in general, been identified or quantified, since low or negligible rates of N2 fixation have been recorded for seawater when blue-green algae (cyanobacteria) are absent. In the study reported here, marine N2-fixing bacteria were found in all samples of seawater collected and were analyzed by using a most-probable-number (MPN) method. Two different media were used which allowed growth of microaerophiles, as well as that of aerobes and facultative anaerobes. MPN values obtained for N2-fixing bacteria ranged from 0.4 to 1 × 103 per liter for water collected off the coast of Puerto Rico and from 2 to 5.5 × 102 per liter for Chesapeake Bay water. Over 100 strains of N2-fixing bacteria were isolated from the MPN tubes and classified, yielding four major groups of NaCl-requiring bacteria based on biochemical characteristics. Results of differential filtration studies indicate that N2-fixing bacteria may be associated with phytoplankton. In addition, when N2-fixing bacteria were inoculated into unfiltered seawater and incubated in situ, nitrogenase activity could be detected within 1 h. However, no nitrogenase activity was detected in uninoculated seawater or when bacteria were incubated in 0.2-μm-filtered (phytoplankton-free) seawater. The ability of these isolates to fix N2 at ambient conditions in seawater and the large variety of N2-fixing bacteria isolated and identified lead to the conclusion that N2 fixation in the ocean may occur to a greater degree than previously believed.

New Method of Denitrification Analysis of Bradyrhizobium Field Isolates by Gas Chromatographic Determination of 15N-Labeled N2

Sameshima-Saito, Reiko; Chiba, Kaori; Minamisawa, Kiwamu
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /05/2004 EN
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26.15%
To evaluate the denitrification abilities of many Bradyrhizobium field isolates, we developed a new 15N-labeled N2 detection methodology, which is free from interference from atmospheric N2 contamination. 30N2 (15N15N) and 29N2 (15N14N) were detected as an apparent peak by a gas chromatograph equipped with a thermal conductivity detector with N2 gas having natural abundance of 15N (0.366 atom%) as a carrier gas. The detection limit was 0.04% 30N2, and the linearity extended at least to 40% 30N2. When Bradyrhizobium japonicum USDA110 was grown in cultures anaerobically with 15NO3−, denitrification product (30N2) was detected stoichiometrically. A total of 65 isolates of soybean bradyrhizobia from two field sites in Japan were assayed by this method. The denitrification abilities were partly correlated with filed sites, Bradyrhizobium species, and the hup genotype.

Relationship between Ureide N and N2 Fixation, Aboveground N Accumulation, Acetylene Reduction, and Nodule Mass in Greenhouse and Field Studies with Glycine max L. (Merr) 1

van Berkum, Peter; Sloger, Charles; Weber, Deane F.; Cregan, Perry B.; Keyser, Harold H.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/1985 EN
Relevância na Pesquisa
26.24%
The relationship between ureide N and N2 fixation was evaluated in greenhouse-grown soybean (Glycine max L. Merr.) and lima bean (Phaseolus lunatus L.) and in field studies with soybean. In the greenhouse, plant N accumulation from N2 fixation in soybean and lima bean correlated with ureide N. In soybean, N2 fixation, ureide N, acetylene reduction, and nodule mass were correlated when N2 fixation was inhibited by applying KNO3 solutions to the plants. The ureide-N concentrations of different plant tissues and of total plant ureide N varied according to the effectiveness of the strain of Bradyrhizobium japonicum used to inoculate plants. The ureide-N concentrations in the different plant tissues correlated with N2 fixation. Ureide N determinations in field studies with soybean correlated with N2 fixation, aboveground N accumulation, nodule weight, and acetylene reduction. N2 fixation was estimated by 15N isotope dilution with nine and ten soybean genotypes in 1979 and 1980, respectively, at the V9, R2, and R5 growth stages. In 1981, we investigated the relationship between ureide N, aboveground N accumulation, acetylene reduction, and nodule mass using four soybean genotypes harvested at the V4, V6, R2, R4, R5, and R6 growth stages. Ureide N concentrations of young stem tissues or plants or aboveground ureide N content of the four soybean genotypes varied throughout growth correlating with acetylene reduction...

Detection and Quantitation of Acrolein-Derived 1,N2-Propanodeoxyguanosine Adducts in Human Lung by Liquid Chromatography-Electrospray Ionization-Tandem Mass Spectrometry

Zhang, Siyi; Villalta, Peter W.; Wang, Mingyao; Hecht, Stephen S.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
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26.2%
Acrolein, a widely distributed environmental pollutant, reacts with dGuo in DNA to form two pairs of 1,N2-propano-dGuo adducts: (6R/S)-3-(2′-deoxyribos-1′-yl)-5,6,7,8-tetrahydro-6-hydroxypyrimido[1,2-a]purine-10(3H)one (α-OH-Acr-dGuo) and (8R/S)-3-(2′-deoxyribos-1′-yl)-5,6,7,8-tetrahydro-8-hydroxypyrimido[1,2-a]purine-10(3H)one (γ-OH-Acr-dGuo). α-OH-Acr-dGuo is the more mutagenic and induces mainly G→T transversions. A recent study demonstrated that acrolein DNA adducts are preferentially formed in p53 mutational hotspots in human lung cancer, but there are no reports on the presence of these adducts in human lung. To directly investigate this question, we have developed a sensitive and specific liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) method for quantitative analysis of Acr-dGuo adducts in DNA. Our method is based on the enzymatic hydrolysis of DNA isolated from human lung in the presence of [13C10,15N5]Acr-dGuo as internal standards. Acr-dGuo adducts are enriched from the hydrolysates by solid phase extraction and analyzed by LC-ESI-MS/MS using selected reaction monitoring. The method is accurate and precise, and the identity of the adducts was confirmed by monitoring different transitions from the same parent ion...

Quantification of N2-Carboxymethyl-2’-deoxyguanosine in Calf-thymus DNA and Cultured Human Kidney Epithelial Cells by Capillary HPLC-Tandem Mass Spectrometry Coupled with Stable Isotope-dilution Method

Wang, Hongxia; Cao, Huachuan; Wang, Yinsheng
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/2010 EN
Relevância na Pesquisa
26.29%
Glyoxal is generated endogenously from the degradation of glucose and the oxidation of carbohydrates, lipids as well as the 2-deoxyribose moieties of DNA. Glyoxal is also widely used in industry and is present cigarette smoke and food. Glyoxal can conjugate with nucleobases and proteins to give advanced glycation end products. N2-carboxymethyl-2’-deoxyguanosine (N2-CMdG) and the cyclic 1,N2-glyoxal-dG are the major glyoxal adducts formed in DNA. In this study, we first assessed the stabilities of these two adducts. It turned out that 1,N2-glyoxal-dG was very unstable, with more than 70% of the adduct being decomposed to dG upon a 24-hr incubation at 37°C in phosphate buffered saline. However, N2-CMdG was very stable, less than 0.5% of the lesion was degraded to dG after a 7-day incubation under the same conditions. We further developed a sensitive capillary LC-ESI-MS/MS/MS coupled with stable isotope dilution method and quantified the formation of N2-CMdG in calf thymus DNA and 293T human kidney epithelial cells that were exposed to glyoxal and in calf thymus DNA treated with D-glucose. Our results showed that N2-CMdG was produced at 2–134 lesions per 106 nucleosides in calf thymus DNA when the surrounding glyoxal concentration was increased from 10 to 500 µM and approximately 3–27 lesions per 107 nucleosides while the D-glucose concentration changed from 2 to 50 mM. Furthermore...

Dynamic programming procedure for searching optimal models to estimate substitution rates based on the maximum-likelihood method

Zhang, Chengjun; Wang, Jia; Xie, Weibo; Zhou, Gang; Long, Manyuan; Zhang, Qifa
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
35.91%
The substitution rate in a gene can provide valuable information for understanding its functionality and evolution. A widely used method to estimate substitution rates is the maximum-likelihood method implemented in the CODEML program in the PAML package. A limited number of branch models, chosen based on a priori information or an interest in a particular lineage(s), are tested, whereas a large number of potential models are neglected. A complementary approach is also needed to test all or a large number of possible models to search for the globally optional model(s) of maximum likelihood. However, the computational time for this search even in a small number of sequences becomes impractically long. Thus, it is desirable to explore the most probable spaces to search for the optimal models. Using dynamic programming techniques, we developed a simple computational method for searching the most probable optimal branch-specific models in a practically feasible computational time. We propose three search methods to find the optimal models, which explored O(n) (method 1) to O(n2) (method 2 and method 3) models when the given phylogeny has n branches. In addition, we derived a formula to calculate the number of all possible models, revealing the complexity of finding the optimal branch-specific model. We show that in a reanalysis of over 50 previously published studies...

Next-generation sequencing reveals the biological significance of the N2,3-ethenoguanine lesion in vivo

Chang, Shiou-chi; Fedeles, Bogdan I.; Wu, Jie; Delaney, James C.; Li, Deyu; Zhao, Linlin; Christov, Plamen P.; Yau, Emily; Singh, Vipender; Jost, Marco; Drennan, Catherine L.; Marnett, Lawrence J.; Rizzo, Carmelo J.; Levine, Stuart S.; Guengerich, F. Pete
Fonte: Oxford University Press Publicador: Oxford University Press
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
26.22%
Etheno DNA adducts are a prevalent type of DNA damage caused by vinyl chloride (VC) exposure and oxidative stress. Etheno adducts are mutagenic and may contribute to the initiation of several pathologies; thus, elucidating the pathways by which they induce cellular transformation is critical. Although N2,3-ethenoguanine (N2,3-εG) is the most abundant etheno adduct, its biological consequences have not been well characterized in cells due to its labile glycosidic bond. Here, a stabilized 2′-fluoro-2′-deoxyribose analog of N2,3-εG was used to quantify directly its genotoxicity and mutagenicity. A multiplex method involving next-generation sequencing enabled a large-scale in vivo analysis, in which both N2,3-εG and its isomer 1,N2-ethenoguanine (1,N2-εG) were evaluated in various repair and replication backgrounds. We found that N2,3-εG potently induces G to A transitions, the same mutation previously observed in VC-associated tumors. By contrast, 1,N2-εG induces various substitutions and frameshifts. We also found that N2,3-εG is the only etheno lesion that cannot be repaired by AlkB, which partially explains its persistence. Both εG lesions are strong replication blocks and DinB, a translesion polymerase, facilitates the mutagenic bypass of both lesions. Collectively...

Extension of the Stober method to the preparation of monodisperse resorcinol-formaldehyde resin polymer and carbon spheres

Liu, J.; Qiao, S.; Liu, H.; Chen, J.; Orpe, A.; Zhao, D.; Lu, G.
Fonte: Wiley-V C H Verlag GMBH Publicador: Wiley-V C H Verlag GMBH
Tipo: Artigo de Revista Científica
Publicado em //2011 EN
Relevância na Pesquisa
35.85%
Sphere we go: Monodisperse resorcinol formaldehyde (RF) resin polymer spheres with finely tunable particle size ranging from 200 to 1000 nm (see pictures) are prepared by an extension of the Stöber method. Pyrolysis of the RF spheres at 600 °C under N2 atmosphere yields uniform carbon spheres with a volume shrinkage of 19 %.; Jian Liu, Shi Zhang Qiao, Hao Liu, Jun Chen, Ajay Orpe, Dongyuan Zhao, and Gao Qing (Max) Lu

Análise estática não linear de um edifício em betão armado

Teixeira, Diogo Miguel Guerreiro
Fonte: Instituto Politécnico de Lisboa Publicador: Instituto Politécnico de Lisboa
Tipo: Dissertação de Mestrado
Publicado em /12/2014 POR
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46.15%
A crescente preocupação com os efeitos da atividade sísmica nas construções a par das novas formas que a arquitetura moderna proporciona, impõe à engenharia desafios cada vez mais interessantes. No decorrer dos últimos anos, foi incontestavelmente reconhecido que o projeto sísmico de estruturas não pode deixar de considerar a capacidade de dissipação da energia por parte destes. No dimensionamento sísmico, de maneira a não encarecer o projeto e/ou obra, admite-se que as estruturas podem deformar para além do seu limite elástico, controlando o seu nível de deslocamentos local e global. No EC 8-1 [60] são apresentados diversos métodos de análise sísmica, sendo uns mais complexos e mais morosos do que outros. Dependendo das características e do tipo deestruturas, os métodos de análise possíveis são os métodos de análise linear, destacandose as análises estáticas equivalentes e as dinâmicas por espetro de resposta; e os métodos de análise não linear, destacando-se as análises estáticas de aplicação progressiva de cargas laterais e/ou deslocamentos e as análises dinâmicas de avaliação da resposta estrutural ao longo do tempo. Em termos de dimensionamento sísmico...

Étude de l'influence de la réassociation en surface des atomes N et O sur l'inactivation des spores bactériennes dans une post-décharge N2-O2 basse pression en flux

Carignan, Denis
Fonte: Université de Montréal Publicador: Université de Montréal
Tipo: Thèse ou Mémoire numérique / Electronic Thesis or Dissertation
FR
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26.23%
Le recours au plasma pour stériliser des dispositifs médicaux (DM) est un domaine de recherche ne datant véritablement que de la fin des années 1990. Les plasmas permettent, dans les conditions adéquates, de réaliser la stérilisation à basse température (≤ 65°C), tel qu’exigé par la présence de polymères dans les DM et ce contrairement aux procédés par chaleur, et aussi de façon non toxique, contrairement aux procédés chimiques comme, par exemple, l’oxyde d’éthylène (OEt). Les laboratoires du Groupe de physique des plasmas à l’Université de Montréal travaillent à l’élaboration d’un stérilisateur consistant plus particulièrement à employer les effluents d’une décharge N2-%O2 basse pression (2-8 Torrs) en flux, formant ce que l’on appelle une post-décharge en flux. Ce sont les atomes N et O de cette décharge qui viendront, dans les conditions appropriées, entrer en collisions dans la chambre de stérilisation pour y créer des molécules excitées NO*, engendrant ainsi l’émission d’une quantité appréciable de photons UV. Ceux-ci constituent, dans le cas présent, l’agent biocide qui va s’attaquer directement au bagage génétique du micro-organisme (bactéries, virus) que l’on souhaite inactiver. L’utilisation d’une lointaine post-décharge évite du même coup la présence des agents érosifs de la décharge...

The development of the N1 and N2 components in auditory oddball paradigms: a systematic review with narrative analysis and suggested normative values

Tomé, David; Barbosa, Fernando; Nowak, Kamila; Marques-Teixeira, João
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
Publicado em //2014 POR
Relevância na Pesquisa
36.18%
Auditory event-related potentials (AERPs) are widely used in diverse fields of today’s neuroscience, concerning auditory processing, speech perception, language acquisition, neurodevelopment, attention and cognition in normal aging, gender, developmental, neurologic and psychiatric disorders. However, its transposition to clinical practice has remained minimal. Mainly due to scarce literature on normative data across age, wide spectrumof results, variety of auditory stimuli used and to different neuropsychological meanings of AERPs components between authors. One of the most prominent AERP components studied in last decades was N1, which reflects auditory detection and discrimination. Subsequently, N2 indicates attention allocation and phonological analysis. The simultaneous analysis of N1 and N2 elicited by feasible novelty experimental paradigms, such as auditory oddball, seems an objective method to assess central auditory processing. The aim of this systematic review was to bring forward normative values for auditory oddball N1 and N2 components across age. EBSCO, PubMed, Web of Knowledge and Google Scholarwere systematically searched for studies that elicited N1 and/or N2 by auditory oddball paradigm. A total of 2,764 papers were initially identified in the database...

Evaluation of the Relative Ureide Content of Xylem Sap as an Indicator of N2 Fixation in Soybeans: GREENHOUSE STUDIES 1

McClure, Peter R.; Israel, Daniel W.; Volk, Richard J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /10/1980 EN
Relevância na Pesquisa
26.22%
The use of the relative ureide content of xylem sap [(ureide-N/total N) × 100] as an indicator of N2 fixation in soybeans (Merr.) was examined under greenhouse conditions. Acetylene treatments to inhibit N2 fixation were imposed upon the root systems of plants totally dependent upon N2 fixation as their source of N and of plants dependent upon both N2 fixation and uptake of exogenous nitrate. Significant decreases in the total N concentration of xylem sap from plants of the former type were observed, but no significant decrease was observed in the total N concentration of sap from the latter type of plants. In both types of plants, acetylene treatment caused significant decreases in the relative ureide content of xylem sap. The results provided further support for a link between the presence of ureides in the xylem and the occurrence of N2 fixation in soybeans. The relative ureide content of xylem sap from plants totally dependent upon N2 fixation was shown to be insensitive to changes in the exudation rate and total N concentration of xylem sap brought about by diurnal changes in environmental factors. There was little evidence of soybean cultivars or nodulating strains affecting the relative ureide content of xylem sap. `Ransom' soybeans nodulated with Rhizobium japonicum strain USDA 110 were grown under conditions to obtain plants exhibiting a wide range of dependency upon N2 fixation. The relative ureide content of xylem sap was shown to indicate reliably the N2 fixation of these plants during vegetative growth using a 15N method to measure N2 fixation activity. The use of the relative ureide content of xylem sap for quantification of N2 fixation in soybeans should be evaluated further.

Oxygen abundance in the Sloan Digital Sky Survey

Shi, F.; Kong, X.; Cheng, F. Z.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 09/03/2006
Relevância na Pesquisa
26.21%
We present two samples of $\hii$ galaxies from the Sloan Digital Sky Survey (SDSS) spectroscopic observations data release 3. The electron temperatures($T_e$) of 225 galaxies are calculated with the photoionized $\hii$ model and $T_e$ of 3997 galaxies are calculated with an empirical method. The oxygen abundances from the $T_e$ methods of the two samples are determined reliably. The oxygen abundances from a strong line metallicity indicator, such as $R_{23}$, $P$, $N2$, and $O3N2$, are also calculated. We compared oxygen abundances of $\hii$ galaxies obtained with the $T_e$ method, $R_{23}$ method, $P$ method, $N2$ method, and $O3N2$method. The oxygen abundances derived with the $T_e$ method are systematically lower by $\sim$0.2 dex than those derived with the $R_{23}$ method, consistent with previous studies based on $\hii$ region samples. No clear offset for oxygen abundance was found between $T_e$ metallicity and $P$, $N2$ and $O3N2$ metallicity. When we studied the relation between N/O and O/H, we found that in the metallicity regime of $\zoh > 7.95$, the large scatter of the relation can be explained by the contribution of small mass stars to the production of nitrogen. In the high metallicity regime, $\zoh > 8.2$, nitrogen is primarily a secondary element produced by stars of all masses.; Comment: 7 pages...

New light on the search for low metallicity galaxies I. The N2 method

Denicolo, Glenda; Terlevich, Roberto; Terlevich, Elena
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 15/10/2001
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36.07%
We present a simple metallicity estimator based on the logarithmic [NII]6584 / Halpha ratio, hereafter N2, which we envisage will become very useful for ranking galaxies in a metallicity sequence from redshift survey quality data even for moderately low spectral resolution. We have calibrated the N2 estimator using a compilation of HII galaxies having accurate oxygen abundances, plus photoionization models covering a wide range of abundances. The comparison of models and observations indicates that both primary and secondary nitrogen are important for the relevant range of metallicities. The N2 estimator follows a linear relation with log(O/H) that holds for the whole abundance range covered by the sample, from about 1/50th to twice the Solar value (7.2 < 12+log(O/H) < 9.1). We suggest that the ([SII]6717,6731 / Halpha) ratio (hereafter S2) can also be used as a rough metallicity indicator. Because of its large scatter the S2 estimator will be useful only in systems with very low metallicity, where [NII]6584 is not detected or in low resolution spectra where [NII]6584 is blended with Halpha.; Comment: 7 pages, 4 figures, accepted by MNRAS

Análise da preservação do miocárdio após administração de N-2 mercaptopropionilglicina em modelo experimental de isquemia e reperfusão em cães; Analysis of myocardial preservation after N2-mercaptopropionylglicin administration in an experimental model of ischemy and reperfusion in dogs

Ketzer, Bernardo Mazzini; Feldman, Andre; Grabarz, Rony; Abuhab, Abrão; Gun, Carlos; Luca, Fabio Augusto de; Abdo, Emílio
Fonte: Universidade de São Paulo. Faculdade de Medicina Publicador: Universidade de São Paulo. Faculdade de Medicina
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; Formato: application/pdf
Publicado em 29/06/2004 POR
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As doenças cardiovasculares representam a principal causa de morbi-mortalidade da atualidade, sendo a doença arterial coronariana seu maior expoente. Novos conhecimentosfisiopatológicos indicam outros mecanismos para injúria miocárdica, ainda pouco estudados. O objetivo desse trabalho é analisar o efeito da N2-Mercaptopropionilglicina (N2-MPG) como agente protetor do miocárdio durante a isquemia/reperfusão, com base na preservação da área denecrose. Foram utilizados 16 cães alocados em dois grupos de oito cães cada: Grupo I (N2-MPG) e Grupo II (controle). Após a reprodução experimental de infarto agudo do miocárdio, os corações foram corados (TTC/Azul de Evans) e pesados para análise da preservação do miocárdio. Os resultados, em relação à preservação da área de necrose, foram: Grupo I (73,14%) e Grupo II (49,98%) através do método de Mann-Whitney. A redução da área de necrose obtida neste estudo apresentou diferença estatística significativa entre os grupos mostrando uma reduçãomédia de 23,16%, concluindo-se que a N2-MPG possui efeito protetor durante a isquemia/reperfusão do miocárdio.; Nowadays, cardiovascular diseases are the principal cause of morbimortality, specially the coronary artery disease. New physiopathological acknowledgement indicates new mechanisms for myocardial injury...