996 resultados para 138-851A
Resumo:
An improved procedure for lithium isotope analysis using Li3PO4 as the ion source has been investigated for application to geological samples. The 7Li/6Li ratio is measured using double rhenium filament thermal ionization mass spectrometry in which isotopic fractionation is minimized at high temperatures. The method produces a stable, high intensity Li+ ion beam that allows measurement of nanogram quantities of lithium. This results in a reduction in sample size of up to 1000 times relative to that required for the established Li2BO2+ method while maintaining a comparable precision of better than 1? (1 sigma). Replicate analyses of the NBS L-SVEC Li2CO3 standard yielded a mean value of 12.1047+/-0.0043 (n=21), which is close to the reported absolute value of 12.02+/-0.03. Intercalibration with a wide range of geological samples shows excellent agreement between the Li3PO4 and Li2BO2+ techniques. Replicate analyses of seawater and a fresh submarine basalt display high precision results that agree with previous measurements. Taking advantage of the high ionization efficiency of the phosphate ion source, we have made the first measurements of the lithium concentration (by isotope dilution) and isotopic composition of calcareous foraminiferal tests and other marine carbonates. Preliminary results indicate that substantial lithium exchange occurs between carbonate sediments and their interstitial waters. In addition, a possible link between lithium paleoceanography and paleoclimate during the last 1000 ky may be derived from planktonic foraminiferal tests. This highly sensitive technique can be applied in the examination of low lithium reservoirs and thereby provide insight into some fundamental aspects of lithium geochemistry.
Resumo:
Global maps of sulfate and methane in marine sediments reveal two provinces of subsurface metabolic activity: a sulfate-rich open-ocean province, and an ocean-margin province where sulfate is limited to shallow sediments. Methane is produced in both regions but is abundant only in sulfate-depleted sediments. Metabolic activity is greatest in narrow zones of sulfate-reducing methane oxidation along ocean margins. The metabolic rates of subseafloor life are orders of magnitude lower than those of life on Earth's surface. Most microorganisms in subseafloor sediments are either inactive or adapted for extraordinarily low metabolic activity.
Resumo:
In a recent paper, Gordon, Muratov, and Shvartsman studied a partial differential equation (PDE) model describing radially symmetric diffusion and degradation in two and three dimensions. They paid particular attention to the local accumulation time (LAT), also known in the literature as the mean action time, which is a spatially dependent timescale that can be used to provide an estimate of the time required for the transient solution to effectively reach steady state. They presented exact results for three-dimensional applications and gave approximate results for the two-dimensional analogue. Here we make two generalizations of Gordon, Muratov, and Shvartsman’s work: (i) we present an exact expression for the LAT in any dimension and (ii) we present an exact expression for the variance of the distribution. The variance provides useful information regarding the spread about the mean that is not captured by the LAT. We conclude by describing further extensions of the model that were not considered by Gordon,Muratov, and Shvartsman. We have found that exact expressions for the LAT can also be derived for these important extensions...
Resumo:
A detailed single-crystal EPR study of phase IV of lithium potassium sulphate below -138 degrees C has been carried out using NH3+, which substitutes for K+, as the paramagnetic probe. The spin-Hamiltonian parameters have been evaluated at -140 degrees C and yield an isotropic g=2.0034; (AH)XX=(AH)YY=25.3 G and (AH)ZZ=23.8 G; (AN)XX=8.1 G, (AN)YY=21.2 G and (AN)ZZ=25.9 G. In this phase there are 12 magnetically inequivalent K+ sites and their occurrence is ascribed to the loss of a c glide.
Resumo:
A discussion has been provided for the comments raised by the discusser (Clausen, 2015)1] on the article recently published by the authors (Chakraborty and Kumar, 2015). The effect of exponent alpha for values of GSI approximately smaller than 30 becomes more critical. On the other hand, for greater values of GSI, the results obtained by the authors earlier remain primarily independent of alpha and can be easily used. (C) 2015 Elsevier Ltd. All rights reserved.
Resumo:
O Senador Mauro Benevides (PMDB-CE) assume a Presidência da Assembleia Nacional Constituinte (ANC) e preside a primeira sessão plenária do período de debates do novo anteprojeto. A Reforma Agrária terá dez artigos. A Deputada Raquel Capiberibe (PSB-AP) relata que o texto não reflete as aspirações do povo. O Deputado Vicente Bogo (PMDB-RS) relata que a reforma agrária atingirá o latifundiário e o pequeno proprietário. O Deputado Tadeu França (PMDB-PR) defende que as propriedades dos Estados do sul tenham, no máximo, mil hectares e, nas demais regiões, hum mil e quinhentos hectares. O Deputado Carlos Cardinal (PDT-RS) reivindica recursos para que hajam desapropriações rápidas. O Deputado Waldyr Pugliesi (PMDB-PR) esclarece que foram aprovados dispositivos que implicariam a derrogação de alguns artigos do Estatuto da Terra, uma lei criada no Governo Castello Branco, concluindo que a nova Constituição terá que avançar e jamais retroagir.
Resumo:
As mulheres constituintes reivindicam maior participação no Programa Diário da Constituinte e levaram esse pedido ao 1º Secretário da Assembléia Nacional Constituinte - ANC , o Deputado Marcelo Cordeiro (PMDB-BA). A Deputada Abigail Feitosa (PSB-BA) defende mais verbas para as escolas públicas. A Deputada Beth Azize (PSB-AM) pede que o Deputado Ulysses Guimarães revogue a Lei de Segurança Nacional, enquanto estiver interinamente no cargo de Presidente da República. O Deputado Ulysses Guimarães acha que este assunto cabe a Assembléia Nacional Constituinte. O projeto aprovado na Comissão de Sistematização será discutido e poderá receber emendas. O Deputado Luiz Inácio Lula da Silva (PT-SP) sugere a alteração da pauta das discussões. O projeto também começará a receber as emendas populares. O Senador Afonso Arinos (PFL-RJ) relata que as emendas populares representam um processo de democracia semi-direta. O número de artigos da nova Carta pode ser um problema para alguns constituintes, mas não preocupa o Presidente da Comissão de Sistematização, o Senador Afonso Arinos. Na sessão O Povo Pergunta, uma cidadã gostaria de saber o que está sendo feito em benefício do menor abandonado. O Deputado Farabulini Júnior (PTB-SP) responde que é necessário retirar as crianças da rua e, para isso, apresentou emenda que obriga o governo a manter o semi-internato, para crianças de 7 a 14 anos.