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Evaluation of ammonium and phosphate release from intertidal and subtidal sediments of a shallow coastal lagoon (Ria Formosa – Portugal): a modelling approach

Serpa, Dalila; Falcão, Manuela; Duarte, Pedro; Cancela da Fonseca, Luís; Vale, Carlos
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
Publicado em //2007 ENG
Relevância na Pesquisa
36.8%
During an annual cycle, overlying water and sediment cores were collected simultaneously at three sites (Tavira, Culatra and Ramalhete) of Ria Formosa’s intertidal muddy and subtidal sandy sediments to determine ammonium, nitrates plus nitrites and phosphate. Organic carbon, nitrogen and phosphorus were also determined in superficial sediments. Ammonium and phosphate dissolved in porewater were positively correlated with temperature (P < 0.01) in muddy and sandy sediments, while the nitrogen-oxidized forms had a negative correlation (P < 0.02) in muddy sediments probably because mineralization and nitrification/denitrification processes vary seasonally. Porewater ammonium profiles evidenced apeak in the top-most muddy sediment (380 lM) suggesting higher mineralization rate when oxygen is more available, while maximum phosphate concentration (113 lM) occurred in the sub-oxic layer probably due to phosphorus desorption under reduced conditions. In organically poor subtidal sandy sediments, nutrient porewater concentrations were always lower than in intertidal muddy sediments, ranging annually from 20 lMto 100 lM for ammonium and from 0.05 lM to 16 lM for phosphate. Nutrient diffusive fluxes predicted by a mathematical model were higher during summer...

Study of the decomposition of phase stabilized ammonium nitrate (PSAN) by simultaneous thermal analysis: determination of kinetic parameters

Simões, P. N.; Pedroso, L. M.; Portugal, A. A.; Campos, J. L.
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Artigo de Revista Científica Formato: aplication/PDF
ENG
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36.7%
Ammonium nitrate (AN) has been extensively used both in explosive and propellant formulations. Unlike AN, there is a lack of information about the thermal decomposition and related kinetic analysis of phase stabilized ammonium nitrate (PSAN). Simultaneous thermal analysis (DSC-TG) has been used in the thermal characterisation of a specific type of PSAN containing 1.0% of NiO (stabilizing agent) and 0.5% of Petro (anti-caking agent) as additives. Repeated runs covering the nominal heating rates range from 2.5 to 20 K min-1 allowed to conclude on the good reproducibility of the main features of the thermal behavior of PSAN, i.e., two phase transitions, melting and decomposition. Non-isothermal kinetic analysis has been used to estimated the Arrhenius parameters of the decomposition process by applying both a single curve method and two isoconversion methods to the TG data. The results are discussed considering the range of applicability of the methods as well as the influence of the experimental conditions and/or techniques in the kinetic analysis results in a broader sense. A systematic approach based on the isoconversion methods results and statistical tools has been adopted to obtain reliable estimates of the Arrhenius parameters for the thermal decomposition of PSAN. Under the condition of study...

Nitrogen loss in Brachiaria decumbens after application of glyphosate or glufosinate-ammonium; Perdas de nitrogênio por Brachiaria decumbens após a aplicação de glifosato ou glufosinato de amônio

DAMIN, Virginia; FRANCO, Henrique Coutinho Junqueira; MORAES, Milton Ferreira; FRANCO, Ademir; TRIVELIN, Paulo Cesar Ocheuze
Fonte: São Paulo - Escola Superior de Agricultura "Luiz de Queiroz" Publicador: São Paulo - Escola Superior de Agricultura "Luiz de Queiroz"
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
36.7%
Nitrogen losses from the soil-plant system may be influenced by herbicide applications. In order to evaluate N loss in brachiaria (Brachiaria decumbens) after application of the herbicides glyphosate and glufosinate-ammonium, an experiment was carried out in a greenhouse as a completely randomized design, with three treatments and six replicates. Treatments were as follows: i) desiccation of brachiaria-plants with glyphosate; ii) desiccation of brachiaria-plants with glufosinate-ammonium; and iii) control, without herbicide application. The plants were cultivated in 4 kg pots of sandy soil and fertilized with ammonium sulfate- 15N, (200 mg kg-1) in order to quantify the allocation of the fertilizer-N and its recovery in the soil-plant system. Plants treated with the herbicides had less N accumulation and less recovery of the fertilizer-N (15N) relative to the control. In the soil, the greatest recovery of 15N-fertilizer occurred for treatments where N was applied, possibly due to the occurrence of other N compound losses to the soil, like root exudation and root death. The total recovery of 15N-fertilizer in the soil-plant system was higher in the control than in the treated plants showing the direct action of the herbicides on nitrogen loss...

Proporções de nitrato e amônio na nutrição e produção dos capins aruana e marandu.; Nitrate and ammonium proportions for aruana and marandu grasses nutrition and production.

Santos, Jorge Henrique da Silva
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 27/08/2003 PT
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36.9%
Foi conduzido experimento em casa-de-vegetação do Departamento de Solos e Nutrição de Plantas da ESALQ – USP, durante o período de fevereiro a maio de 2002, com o objetivo de avaliar respostas produtivas, fisiológicas e nutricionais a proporções de nitrato e amônio, das forrageiras Panicum maximum cv. Aruana e Brachiaria brizantha cv. Marandu, cultivados em solução nutritiva, utilizando sílica como substrato. Foi empregado o delineamento experimental de blocos completos ao acaso, com quatro repetições e seis tratamentos. O nitrogênio foi estudado na dose de 210 mg L -1 e nas proporções respectivas de nitrato e amônio de 100/0; 85/15;70/30; 55/45; 40/60 e 25/75%. As soluções foram preparadas a partir da solução completa de Sarruge (1975), devidamente modificada para as proporções desses íons no suprimento de nitrogênio. Dois corte foram realizados nas plantas, separando-se os componentes da parte aérea em folhas emergentes, lâminas de folhas recém-expandidas, lâminas de folhas maduras e colmos mais bainhas. Após o segundo corte, as raízes foram separadas da sílica e lavadas. Durante o crescimento das plantas foram determinados a atividade da redutase do nitrato e o valor SPAD e na ocasião dos cortes foram contados os perfilhos e as folhas das plantas e foi medida a área foliar. No material seco foi obtido a produção de massa e nas amostras moídas foram determinadas as concentrações de nitrogênio total...

Estudo da intensidade luminosa no cultivo de Arthrospira (Spirulina) platensis em reator tubular utilizando sulfato de amônio como fonte de nitrogênio por processo descontínuo alimentado; Light intensity study in the Arthrospira (Spirulina) platensis cultivation in a tubular reactor using ammonium sulfate as a nitrogen source in fed - batch process

Ferreira, Livia Seno
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 25/04/2008 PT
Relevância na Pesquisa
36.76%
A Arthrospira (Spirulina) platensis, cianobactéria fotoautotrófica, tem sido cultivada para a produção de biomassa, apresentando em sua constituição proteínas, ácidos graxos poliinsaturados, pigmentos, minerais, vitaminas e aminoácidos. O uso de fontes de nitrogênio de baixo custo, como o sulfato de amônio, pode contribuir para a viabilização da produção de A. platensis. Neste trabalho foram verificados a influência de diferentes intensidades luminosas e protocolos de alimentação utilizando o sulfato de amônio, em cultivos realizados com reatores tubulares por processo descontínuo alimentado. As variáveis dependentes selecionadas foram concentração celular máxima (Xm), produtividade em células (Px), fator de conversão de nitrogênio em células (YX/N), bem como teores de proteínas e lipídios da biomassa. Foram obtidos excelentes resultados em cultivos realizados aplicando-se um protocolo de alimentação de sulfato de amônio, considerando biomassa seca de A. platensis com teor de 7 % de nitrogênio, com valor médio de Xm igual a 11414 mg.L-1. Este protocolo de adição de sulfato de amônio com intensidade luminosa de 240 µmol fótons. m-2.s-1 levou à melhor combinação de obtenção de Xm e Px...

Aplicação de um quaternário amoniacal visando melhorar o desempenho da madeira tratada com octaborato de sódio; Application of an ammonium quaternary in order to improve the performance of treated wood with sodium octaborate

Vidal, Jackson Marcelo
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 07/02/2012 PT
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36.76%
Com a evolução da civilização, a busca pela praticidade e durabilidade dos materiais desafia a pesquisa e o desenvolvimento de novos materiais e produtos. A preservação de madeiras tal como hoje a conhecemos, iniciou-se a partir da segunda metade do século XIX e, também vem se expandindo e impulsionando a busca por novos desenvolvimentos. Neste contexto, os boratos são preservativos amplamente reconhecidos e eficazes devido às suas características apreciáveis. Custo vantajoso, reduzido impacto ambiental, largo espectro de ação, o credenciam como um preservativo potencial para o desenvolvimento de estudos no sentido de redução de sua taxa de lixiviação. O objetivo deste trabalho foi avaliar a possiblidade de redução da lixiviação de uma composição contendo octaborato dissódico tetrahidratado e um quaternário graxo amoniacal, em madeira de Pinus elliotii, tratada sob pressão. Avaliouse também a interferência da adição do quaternário graxo amoniacal, frente ao ataque de cupins de madeira seca. Amostras de madeira foram tratadas para as retenções de 2,8 kg/m3 e 4,5 kg/m3 em B2O3, variando-se a proporção do quaternário amoniacal de 0,0%, 1,0%, 1,5% e 2,0%. Um conjunto de amostras foi submetido ao ensaio de lixiviação...

Effect of nitrate and ammonium on the growth and protein concentration of Microcystis viridis Lemmermann (Cyanobacteria)

Rückert,Gabriela Von; Giani,Alessandra
Fonte: Sociedade Botânica de São Paulo Publicador: Sociedade Botânica de São Paulo
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2004 EN
Relevância na Pesquisa
36.95%
Cyanobacteria are a very important group in aquatic systems, particularly in eutrophic waters. Therefore studies about their success in the environment are essential. Many hypotheses have tried to explain the dominance of Cyanobacteria, and several emphasized the importance of various nitrogen sources for the success of the group. In this study, we measured the effect of ammonium and nitrate on the growth and protein concentration of Microcystis viridis (Cyanobacteria). This species is well-known because bloom formation in eutrophic waters. The study was carried out, in experimental batch cultures, using the WC medium with different nitrogen sources: ammonium, nitrate, ammonium + nitrate (50% ammonium + 50% nitrate) and ammonium at different concentrations (to test for possible NH4+ toxicity). Protein, ammonium and nitrate concentrations were measured at end of each experiment, whereas samples for cell counts were taken daily. Results showed that Microcystis viridis grew faster with ammonium (µ = 0.393 day-1) than with nitrate (µ = 0.263 day-1) and ammonium + nitrate (µ = 0.325 day-1). This pattern is explained by the metabolism of ammonium that presents higher uptake and assimilation rates than nitrate. Maximum cell concentration...

Synthesis of guanidine from ammonium thiocyanate in solid state

Zaia,Dimas A. M.; Santana,Henrique de; Toppan,Rodrigo; Zaia,Cássia T. B. V.
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2004 EN
Relevância na Pesquisa
36.88%
Guanidine is an important substance for modern living beings as well as for the prebiotic chemistry. We studied the reaction between ammonium and thiocyanate species in solid state with different substances (river sand, kaolin, transition metals, salts of seawater) and temperatures (80, 120 and 150 ºC). The recoveries of thiocyanate and ammonium in the samples with river sand or kaolin at 150 ºC were statistically different (p<0.05) from the recoveries of thiocyanate and ammonium in the sample without them. The decomposition of ammonium thiocyanate in the samples river sand or kaolin at 150 ºC was about 40%. Kaolin showed to have more effect on the synthesis guanidine than river sand, because, the concentrations of guanidine in the samples with kaolin were always bigger than in the samples with river sand. The decomposition of ammonium thiocyanate in the samples with transition metals plus river sand at 120 ºC was about 30%. The salts of seawater or transition metals plus ammonium thiocyanate plus river sand (120 ºC) showed to increase the concentration of thiourea (seawater: 538%; transition metals: 357%) or guanidine (seawater: 393%, transition metals: 806%) when they were compared to the samples without them. When the results obtained with sample of ammonium thiocyanate were compared to the samples of ammonium thiocyanate (at 120 ºC) plus salts of seawater or transition metals also an increased on the production of thiourea (168%) and guanidine (268%) was obtained...

Ammonium ion sensor based on SiO2/ZrO2/phosphate-NH4+ composite for quantification of ammonium ions in natural waters

Coutinho,Cláudia F. B.; Muxel,Alfredo A.; Rocha,Crystian G.; Jesus,Débora A. de; Alfaya,Rení V. S.; Almeida,Flaveli A. S.; Gushikem,Yoshitaka; Alfaya,Antonio A. S.
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2007 EN
Relevância na Pesquisa
36.8%
Ion selective-electrode was constructed and evaluated for determination of ammonium ions in natural waters. The electrode consists of paste carbon with the composite SiO2/ZrO2/phosphate-NH4+ obtained through sol-gel process. The electrode exhibits a sub-Nernstian response for ammonium concentrations between 7.7´10-7 and 4.0´10-2 mol L-1 and a detection limit of 1.58´10-7 mol L-1 (8.5´10-3 ppm). The electrode response for ammonium was fast (1 minute). The selectivity coefficients KpotA,B for several ions usually present in natural waters were determined applying the matched potential method. The potentiometric method with the ion selective electrode was validated by the Berthelot method (standard method), through the determination of ammonium ions in natural waters. The ion selective-electrode proved suitable for routine quality control of natural waters by potentiometry.

Metal-free catalytic oxidation of sulfides to sulfoxides with ammonium nitrate, ammonium hydrogen sulfate and ammonium bromide as catalyst

Ghorbani-Choghamarani,Arash; Zolfigol,Mohammad Ali; Ayazi-Nasrabadi,Roia
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2010 EN
Relevância na Pesquisa
36.86%
A general and metal-free catalytic oxidation of aliphatic and aromatic sulfides to their corresponding sulfoxides via combination of ammonium nitrate (NH4NO3), supported ammonium hydrogen sulfate on silica gel (NH4HSO4-SiO2) and a catalytic amount of ammonium bromide (NH4Br) in the presence of wet SiO2 (50%, w/w) has been investigated. The reactions were carried out heterogeneously and selectively in short reaction times in CH2Cl2 at room temperature. This protocol is mild and efficient compared to other reported methods.

Ammonium toxicity and the real cost of transport

Kronzucker, Herbert J.; Britto, Dev T.; Davenport, Romola J.; Tester, Mark Alfred
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em //2001 EN
Relevância na Pesquisa
36.76%
Recently, it has been proposed that ammonium is toxic to barley because of the energetic cost of pumping ammonium that has leaked into root cells back into the soil. This does not occur in rice because high levels of ammonium reduce the potential difference across the plasma membrane of rice – whereas the potential difference in barley appears to be ammonium insensitive. These results highlight the potentially high costs of membrane transport, and thus the central importance of transport processes in plants.; http://www.elsevier.com/wps/find/journaldescription.cws_home/30960/description#description

Soybean SAT1 (Symbiotic Ammonium Transporter 1) encodes a bHLH transcription factor involved in nodule growth and NH₄⁺ transport; Soybean SAT1 (Symbiotic Ammonium Transporter 1) encodes a bHLH transcription factor involved in nodule growth and NH(4)(+) transport

Chiasson, D.M.; Loughlin, P.C.; Mazurkiewicz, D.; Mohammadidehcheshmeh, M.; Fedorova, E.E.; Okamoto, M.; McLean, E.; Glass, A.D.M.; Smith, S.E.; Bisseling, T.; Tyerman, S.D.; Day, D.A.; Kaiser, B.N.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Publicado em //2014 EN
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36.83%
Glycine max symbiotic ammonium transporter 1 was first documented as a putative ammonium (NH4(+)) channel localized to the symbiosome membrane of soybean root nodules. We show that Glycine max symbiotic ammonium transporter 1 is actually a membrane-localized basic helix-loop-helix (bHLH) DNA-binding transcription factor now renamed Glycine max bHLH membrane 1 (GmbHLHm1). In yeast, GmbHLHm1 enters the nucleus and transcriptionally activates a unique plasma membrane NH4(+) channel Saccharomyces cerevisiae ammonium facilitator 1. Ammonium facilitator 1 homologs are present in soybean and other plant species, where they often share chromosomal microsynteny with bHLHm1 loci. GmbHLHm1 is important to the soybean rhizobium symbiosis because loss of activity results in a reduction of nodule fitness and growth. Transcriptional changes in nodules highlight downstream signaling pathways involving circadian clock regulation, nutrient transport, hormone signaling, and cell wall modification. Collectively, these results show that GmbHLHm1 influences nodule development and activity and is linked to a novel mechanism for NH4(+) transport common to both yeast and plants.; David M. Chiasson, Patrick C. Loughlin, Danielle Mazurkiewicz, Manijeh Mohammadidehcheshmeh...

Oligomerization of ammonium transporter LeAMT1;1 and its interactions with other proteins; Oligomerisierung des Ammoniumtransporters LeAMT1;1 und seine Interaktionen mit anderen Proteinen

Wu, Binghua
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
EN
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36.97%
Ammonium is one of the important nitrogen sources for plant growth and development. Ammonium uptake and retrieval mediated by high-affinity ammonium transporters at the plasma membrane is the initial step in ammonium assimilation and nitrogen metabolism. Molecular and genetic studies have revealed a large protein family of ammonium transporters functionally diverse but evolutionarily conserved in all domains of organisms. Despite the available information regarding the physiological aspects, biochemical characteristics and gene regulations of ammonium transporters, the function of the transporter proteins is still poorly understood, and the sensory/regulatory mechanism coupling ammonium transport in plants remains elusive. To test the hypothesis that plant ammonium transporters form multimeric complexes at the plasma membrane, the well-characterized plant ammonium transporters LeAMT1;1 and LeAMT1;2 from tomato were used as a model system. Protein-protein interactions between these transporters were monitored in two in vivo systems: the split ubiquitin system and the Xenopus oocyte expression system. Results firmly demonstrate that plant ammonium transporters, at least in the case of the LeAMT1;1 and LeAMT1;2, exist in homo-oligomeric forms. A dominant-negative point mutation at the conserved cytoplasmic C-termini of the LeAMT proteins...

Biochemical composition and growth of the marine microalga Dunaliella tertiolecta (Butcher) with different ammonium nitrogen concentrations as chloride, sulphate, nitrate and carbonate.

Fábregas, Jaime; Abalde Alonso, Julio Ernesto; Herrero, Concepción
Fonte: Elsevier Science Publishers Publicador: Elsevier Science Publishers
Tipo: info:eu-repo/semantics/acceptedVersion
SPA
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Cultures of the marine microalga Dunaliella tertiolecta were grown in ammonium chloride, sulphate, nitrate and carbonate at concentrations ranging from 0.25 to 16 mg.atom N/l. Cells were harvested in the stationary phase and cell density and biochemical composition determined. Biomass production at the end of the stationary phase, expressed as cell density, was affected by the concentration of ammonium-N in the medium but not by the ammonium compound used. Optimal growth conditions for obtaining maximum cell density, between 1.86×106 and 2.81×106 cells/ml, were 2, 4 and 8 mg.atom N/l. The compound and concentration of ammonium-N had little effect on the growth velocity of D. tertiolecta cultures in the logarithmic phase, with values of 0.35±0.06 doublings/day under all the conditions assayed. The ammonium compound and the concentration of nitrogen affected the concentration of different cellular constituents such as protein, carbohydrate, lipid and chlorophyll a, although these changes were not necessarily related to cell density in the culture. Protein, the most affected fraction, tended to increase with an increase in the nitrogen concentration for all the ammonium compounds used. Maximum protein/ml was obtained with ammonium carbonate at all the nitrogen concentrations used. Maximum protein/cell occurred at the higher nitrogen concentrations (16 and 32 mg/atom N/l) for all the ammonium compounds. Considering the optimum growth interval (2-8 mg.atom N/l)...

Over-expression of the rice OsAMT1-1 gene increases ammonium uptake and content, but impairs growth and development of plants under high ammonium nutrition

Hoque, Mohammed; Masle, Josette; Udvardi, Michael K; Ryan, Peter R; Upadhyaya, Narayana M
Fonte: CSIRO Publishing Publicador: CSIRO Publishing
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.86%
A transgenic approach was undertaken to investigate the role of a rice ammonium transporter (OsAMT1-1) in ammonium uptake and consequent ammonium assimilation under different nitrogen regimes. Transgenic lines overexpressing OsAMT1-1 were produced by Agro

High-temperature ammonium white mica from the Betic Cordillera (Spain)

Ruiz Cruz, María Dolores; Sanz de Galdeano, Carlos
Fonte: Mineralogical Society of America Publicador: Mineralogical Society of America
Tipo: Artículo Formato: 13824 bytes; application/vnd.ms-excel
ENG
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36.76%
High-temperature, ammonium-rich white mica has been identified for the first time in deep Paleozoic (and probably older) polymetamorphic schists from the Internal Zone of the Betic Cordillera (Spain). Ammonium-rich white mica has been characterized by optical microscopy, X-ray diffraction, infrared spectroscopy, elemental analysis, electron microprobe, and scanning and transmission electron microscopy. High-temperature, ammonium-rich white mica shows some significant chemical differences with tobelite formed in hydrothermal and low-temperature metamorphic rocks. Although the average formula, Ca0.09Na0.01K0.15(NH4)0.75(Al1.70Ti0.01Fe0.26Mg0.13)(Si2.99Al1.01)O10(OH)2, is typical of a dioctahedral mica, the chemical plots reveal a clear deviation toward the trioctahedral field. Thus, the increase in Fe + Mg contents is not accompanied by the parallel increase of Si contents, characteristic of the phengitic substitution, which is characteristic of low-pressure conditions of formation. Chemical differences are also accompanied by notable differences in the optical properties, both features suggesting that the term tobelite is not appropriate for this mica. Ammonium-rich white mica relics only persist in some graphite-rich microdomains, defining the first schistosity. Textural relations indicate that this mica formed during an older pre-Alpine metamorphic episode.; Peer reviewed

Shock compression of water and solutions of ammonium nitrate

Morley, Michael James
Fonte: University of Cambridge; Department of Physics; Fracture and Shock Physics, Cavendish Laboratory; Trinity College Publicador: University of Cambridge; Department of Physics; Fracture and Shock Physics, Cavendish Laboratory; Trinity College
Tipo: Thesis; doctoral; PhD
EN
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Modern mining explosives employ solutions of ammonium nitrate, where the solution is the oxidising component of a fuel/oxidiser mixture. This thesis is primarily concerned with the shock response of water and of aqueous solutions of ammonium nitrate. Of particular interest are the temperatures induced through shock compression. An experimental facility, using a single stage gas gun in the ?plate impact? configuration, is described, along with associated experimental diagnostics. Measurements of, and improvements to, the tilt at impact are reported. The problem of shock temperature is discussed, including a brief review of the relevant literature. It is demonstrated that direct measurement of shock temperature is a complex issue that is not yet fully understood, whereas determination of temperature from an equation of state is an established technique. In a series of experiments, plate impact techniques were utilised to determine the Hugoniot and, through shock/reload experiments, the equation of state of water and aqueous solutions of ammonium nitrate. In-situ manganin gauges were used to measure stresses in the liquids and, from the arrival times of the shock wave, determine the shock velocity. Linear shock velocity?particle velocity Hugoniots for the liquids were determined...

Nitrate reduction to ammonium in Nautilia profundicola via a proposed reverse HURM pathway

Kalis, Katie
Fonte: University of Delaware Publicador: University of Delaware
Tipo: Tese de Doutorado
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Hanson, Thomas E.; Nautilia profundicola is an epsilonproteobacterium that inhabits hydrothermal vents on the dorsal epithelium of Alvinella pompejana or as a free-living bacterium. N. profundicola was isolated with polysulfide as the electron acceptor for respiratory growth, but is also able to utilize nitrate as an electron acceptor for growth. Interestingly, the N. profundicola genome lacks homologs of known enzymes used in nitrite reduction. Therefore, the pathway of nitrate reduction is likely to be novel. Genome annotation suggested that the reverse hydroxylamine ubiquinone redox module (rHURM) may be used for anaerobic cellular respiration in N. profundicola when nitrate is the terminal electron acceptor. The proposed rHURM pathway includes rHaoA and hcp/har which catalyze the reduction of nitrite to hydroxylamine, as an intermediate, and hydroxylamine to ammonium, respectively. In this study, cell growth was monitored in batch cultures under varied concentrations of sulfide, nitrate, formate, and H2. Optimal concentrations were used for culturing cells in continuous culture and in batch culture for substrate addition assays. The four nitrogen compounds in the proposed pathway were measured in the substrate addition assays???nitrate...

Structure, function and regulation of ammonium transporters in plants

Howitt, Susan; Udvardi, Michael
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.94%
Ammonium is an important source of nitrogen for plants. It is taken up by plant cells via ammonium transporters in the plasma membrane and distributed to intracellular compartments such as chloroplasts, mitochondria and vacuoles probably via different transporters in each case. Ammonium is generally not used for long-distance transport of nitrogen within the plant. Instead, most of the ammonium transported into plant cells is assimilated locally via glutamine synthetases in the cytoplasm and plastids. Ammonium is also produced by plant cells during normal metabolism, and ammonium transporters enable it to be moved from intracellular sites of production to sites of consumption. Ammonium can be generated de novo from molecular nitrogen (N2) by nitrogen-fixing bacteria in some plant cells, such as rhizobia in legume root nodule cells, and at least one ammonium transporter is implicated in the transfer of ammonium from the bacteria to the plant cytoplasm. Plant physiologists have described many of these ammonium transport processes over the last few decades. However, the genes and proteins that underlie these processes have been isolated and studied only recently. In this review, we consider in detail the molecular structure, function and regulation of plant ammonium transporters. We also attempt to reconcile recent discoveries at the molecular level with our knowledge of ammonium transport at the whole plant level.

Kinetics and thermodynamic parameters for the manufacturing of anhydrous zirconium tetrafluoride with ammonium acid fluoride as fluorinating agent

Pretorius,C.J.; du Plessis,W.; Nel,J.T.; Crouse,P.L.
Fonte: Journal of the Southern African Institute of Mining and Metallurgy Publicador: Journal of the Southern African Institute of Mining and Metallurgy
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2012 EN
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More than 30 percent of the global demand for zircon (ZrSiC>4) is supplied by South Africa. A significant amount of the zircon is exported, and beneficiated products are then imported for industrial applications locally. Beneficiating the zircon locally could have a positive impact on the local market, since zircon is only one of many such cases. Ammonium acid fluoride serves as an alternative anhydrous fluorinating agent for zircon in the synthesis of several metal fluoridesi,2. It provides an effective dry fluorinating method and is easier to handle than hydrogen fluoride or fluorine gas. Zircon exposed to extreme plasma temperatures dissociates and becomes more reactive. The reaction of the plasma-dissociated zircon (ZrO2SiO2) with the ammonium acid fluoride (NH4FxHF, where x= 1 to 5) forms two main intermediate compounds (NH4)3ZrF7(s) and (NH4)2SiF6(s), the latter decomposing to form volatile products at relatively low temperatures, providing easy separation of the silicon and zirconium compounds. The ammonium zirconate compound decomposes to form zirconium tetrafluoride (ZrF4), which can be further manufactured into zirconium metal, to name but one product. Data on the kinetics of the reaction of ammonium acid fluoride with zircon and plasma-dissociated zircon...