Especiação em solos: aspectos gerais.

Considerações sobre a especiação aplicada a solos.bitstream/CNPS/11580/1/doc47_2003_especiacao_solos.pd

Solução do solo: importância e extração por centrifugação.

Considerações sobre estudos de técnicas de extração da fase aquosa do solo

The spin glass transition of the three dimensional Heisenberg spin glass

It is shown, by means of Monte Carlo simulation and Finite Size Scaling analysis, that the Heisenberg spin glass undergoes a finite-temperature phase transition in three dimensions. There is a single critical temperature, at which both a spin glass and a chiral glass orderings develop. The Monte Carlo algorithm, adapted from lattice gauge theory simulations, makes possible to thermalize lattices of size L=32, larger than in any previous spin glass simulation in three dimensions. High accuracy is reached thanks to the use of the Marenostrum supercomputer. The large range of system sizes studied allow us to consider scaling corrections.Comment: 4 pages, 4 Postscript figures, version to be published in Physical Review Letter

The effect of two kinds of eluents on the speciation of Al, Mn, and Fe by size-exclusion chromatography of some Brazilian soil solutions.

Size-exclusion chromatography is a powerful tool for distinguishing dissolved organic matter in relation to its molecular size. However, problems may arise in the choice of the most appropriate eluent composition, regarding the gel used. In the present work, soil solution samples from four Brazilian topsoils were analyzed by high-performance liquid chromatography (HPLC) using a size-exclusion polymer-based column (Superdex 75 HR 10/30, Pharmacia). Water and 0.01 mol L-1 NaCl were investigated as mobile phases. The analysis of the UV peak distribution as well as their corresponding Fe, Mn, and Al concentrations suggested that the salt solution should be preferred since it minimizes unwanted interactions between the sample and the support material. Fe, Mn, and Al speciation calculated by the Geochem-PC program involving the Mattigod and Sposito Mixed Model was compared with the Fe, Mn, and Al-organic complex concentrations determined by SEC-HPLC/GFAAS. No correlation was found for Mn and Fe. For Al a significant non-linear correlation was observed

Hydrodynamic conditions affect the proteomic profile of marine biofilms formed by filamentous cyanobacterium

Proteomic studies on cyanobacterial biofilms can be an effective approach to unravel metabolic pathways involved in biofilm formation and, consequently, obtain more efficient biofouling control strategies. Biofilm development by the filamentous cyanobacterium Toxifilum sp. LEGE 06021 was evaluated on different surfaces, glass and perspex, and at two significant shear rates for marine environments (4 s(-1) and 40 s(-1)). Higher biofilm development was observed at 4 s(-1). Overall, about 1877 proteins were identified, and differences in proteome were more noticeable between hydrodynamic conditions than those found between surfaces. Twenty Differentially Expressed Proteins (DEPs) were found between 4 s(-1) vs. 40 s(-1). On glass, some of these DEPs include phage tail proteins, a carotenoid protein, cyanophynase glutathione-dependent formaldehyde dehydrogenase, and the MoaD/ThiS family protein, while on perspex, DEPs include transketolase, dihydroxy-acid dehydratase, iron ABC transporter substrate-binding protein and protein NusG. This study contributes to developing a standardized protocol for proteomic analysis of filamentous cyanobacterial biofilms. This kind of proteomic analysis can also be useful for different research fields, given the broad spectrum of promising secondary metabolites and added-value compounds produced by cyanobacteria, as well as for the development of new antibiofilm strategies

Ianus: an Adpative FPGA Computer

Dedicated machines designed for specific computational algorithms can outperform conventional computers by several orders of magnitude. In this note we describe {\it Ianus}, a new generation FPGA based machine and its basic features: hardware integration and wide reprogrammability. Our goal is to build a machine that can fully exploit the performance potential of new generation FPGA devices. We also plan a software platform which simplifies its programming, in order to extend its intended range of application to a wide class of interesting and computationally demanding problems. The decision to develop a dedicated processor is a complex one, involving careful assessment of its performance lead, during its expected lifetime, over traditional computers, taking into account their performance increase, as predicted by Moore's law. We discuss this point in detail

Evaluation of different extractants for copper, manganese and zinc in medical plants.

The extraction of copper, manganese and zinc by different organic solvents and aqueous solutions from powdered and droughts of nine medicinal plants were investigated as a possible way of accomplishing the speciation of these metals in such samples. The extractants were 75 g L-1 HCl, 50 g L-1 NaCl, 50 g L-1 NaOH, 50g L-1 Na2CO3, (1: 1) glicero-alkali solution, pure water, ethanol and ether. None of the organic solvents extracted significant amounts of the three elements. For Cu, only the HCl solution has shown significant extraction efficiency. On average, Zn was more efficiently extracted when H2O, NaOH, and Na2CO3 solutions were used while Mn was more efficiently extracted with the HCl and NaCl solutions. The differentiated extraction behavior of the studied elements in relation to the different aqueous extractants is an indicative of different pools of these elements in the plant substrate

The exonuclease Xrn1 activates transcription and translation of mRNAs encoding membrane proteins

The highly conserved 5'-3' exonuclease Xrn1 regulates gene expression in eukaryotes by coupling nuclear DNA transcription to cytosolic mRNA decay. By integrating transcriptome-wide analyses of translation with biochemical and functional studies, we demonstrate an unanticipated regulatory role of Xrn1 in protein synthesis. Xrn1 promotes translation of a specific group of transcripts encoding membrane proteins. Xrnl-dependence for translation is linked to poor structural RNA contexts for translation initiation, is mediated by interactions with components of the translation initiation machinery and correlates with an Xrnl-dependence for mRNA localization at the endoplasmic reticulum, the translation compartment of membrane proteins. Importantly, for this group of mRNAs, Xrn1 stimulates transcription, mRNA translation and decay. Our results uncover a crosstalk between the three major stages of gene expression coordinated by Xrn1 to maintain appropriate levels of membrane proteins

Assessing the regional impacts of Mexico City emissions on air quality and chemistry

The impact of Mexico City (MCMA) emissions is examined by studying its effects on air quality, photochemistry, and on ozone production regimes by combining model products and aircraft observations from the MILAGRO experiment during March 2006. The modeled influence of MCMA emissions to enhancements in surface level NOx [NO subscript x], CO, and O3 [O subscript 3] concentrations (10–30% increase) are confined to distances <200 km, near surface. However, the extent of the influence is significantly larger at higher altitudes. Broader MCMA impacts (some 900 km Northeast of the city) are shown for specific outflow conditions in which enhanced ozone, NOy [NO subscript y], and MTBE mixing ratios over the Gulf of Mexico are linked to MCMA by source tagged tracers and sensitivity runs. This study shows that the "footprint" of MCMA on average is fairly local, with exception to reactive nitrogen, which can be transported long range in the form of PAN, acting as a reservoir and source of NOx [NO subscript x] with important regional ozone formation implications. The simulated effect of MCMA emissions of anthropogenic aerosol on photochemistry showed a maximum regional decrease of 40% in J[NO2→NO+O] [J [NO subscript 2 → NO + O]], and resulting in the reduction of ozone production by 5–10%. Observed ozone production efficiencies are evaluated as a function of distance from MCMA, and by modeled influence from MCMA. These tend to be much lower closer to MCMA, or in those points where modeled contribution from MCMA is large. This research shows that MCMA emissions do effect on regional air quality and photochemistry, both contributing large amounts of ozone and its precursors, but with caveat that aerosol concentrations hinder formation of ozone to its potential due to its reduction in photolysis rates.United States. National Aeronautics and Space AdministrationNational Science Foundation (U. S.) (ATM award 0528227