Petrobras

About: Petrobras is a company organization based out in Rio de Janeiro, Brazil. It is known for research contribution in the topics: Catalysis & Subsea. The organization has 6539 authors who have published 7872 publications receiving 103061 citations. The organization is also known as: Petróleo Brasileiro S.A. & Petroleo Brasileiro SA.

Amazonia Through Time: Andean Uplift, Climate Change, Landscape Evolution, and Biodiversity

Abstract: The Amazonian rainforest is arguably the most species-rich terrestrial ecosystem in the world, yet the timing of the origin and evolutionary causes of this diversity are a matter of debate. We review the geologic and phylogenetic evidence from Amazonia and compare it with uplift records from the Andes. This uplift and its effect on regional climate fundamentally changed the Amazonian landscape by reconfiguring drainage patterns and creating a vast influx of sediments into the basin. On this “Andean” substrate, a region-wide edaphic mosaic developed that became extremely rich in species, particularly in Western Amazonia. We show that Andean uplift was crucial for the evolution of Amazonian landscapes and ecosystems, and that current biodiversity patterns are rooted deep in the pre-Quaternary.

NMR nomenclature. Nuclear spin properties and conventions for chemical shifts(IUPAC Recommendations 2001)

Abstract: A unified scale is recommended for reporting the NMR chemical shifts of all nuclei relative to the 1 H resonance of tetramethylsilane (TMS The unified scale is designed to provide a precise ratio, Ξ, of the resonance frequency of a given nuclide to that of the primary reference, the 1 H resonance of TMS in dilute solution (volume fraction, φ < 1%) in chloroform. Referencing procedures are discussed, including matters of practical application of the unified scale. Special attention is paid to recommended reference samples, and values of Ξ for secondary references on the unified scale are listed, many of which are the results of new measurements. Some earlier recommendations relating to the reporting of chemical shifts are endorsed. The chemical shift, δ, is redefined to avoid previous ambiguities but to leave practical usage unchanged. Relations between the unified scale and recently published recommendations for referencing in aqueous solutions (for specific use in biochemical work) are discussed, as well as the special effects of working in the solid state with magic-angle spinning. In all, nine new recommendations relating to chemical shifts are made. Standardized nuclear spin data are also presented in tabular form for the stable (and some unstable) isotopes of all elements with nonzero quantum numbers. The information given includes quantum numbers, isotopic abundances, magnetic moments, magnetogyric ratios and receptivities, together with quadrupole moments and line-width factors where appropriate.

Seismic features diagnostic of contourite drifts

Abstract: The sedimentary construction of oceanic margins is most often carried out by the combined action of gravitational processes and processes related to bottom (contour) currents. One of the major difficulties encountered in the interpretation of seismic profiles crossing such margins is the differentiation of these two types of deposit, especially where they display very complicated imbricated geometries. The aim of this paper, therefore, is to derive criteria for the recognition of contourite vs. turbidite deposits, based on the analysis of many seismic profiles from both published and unpublished sources. The following features are the most diagnostic for the recognition of contourite drifts. At the scale of the basin, four different drift types can be distinguished according to the morphostructural context, their general morphology and the hydrodynamic conditions. These are: contourite-sheeted drifts (including abyssal sheets and slope-plastered sheets), elongate-mounded drifts (detached and separated types), channel-related drifts (including lateral and axial patch drifts and downstream contourite fans), and confined drifts trapped in small, tectonically active basins. At the scale of the drift, three features provide the best diagnostic criteria for recognising contourite deposits on seismic profiles: major discontinuities that can be traced across the whole drift and represent time lines corresponding to hydrological events, lenticular, convex-upward depositional units with a variable geometry, and a specific style of progradation–aggradation of these units that is influenced by interaction of the bottom current with Coriolis force and with the morphology. At the scale of depositional units, the seismofacies show a wide variety of reflector characteristics, many of which are very similar to those observed in turbidite series. Distinction between sediment wave seismofacies deposited by turbidity currents and bottom currents still remains ambiguous.

Further conventions for NMR shielding and chemical shifts (IUPAC Recommendations 2008)

Abstract: IUPAC has published a number of recommendations regarding the reporting of nuclear magnetic resonance (NMR) data, especially chemical shifts. The most recent publication [Pure Appl. Chem. 73, 1795 (2001)] recommended that tetramethylsilane (TMS) serve as a universal reference for reporting the shifts of all nuclides, but it deferred recommendations for several aspects of this subject. This document first examines the extent to which the 1 H shielding in TMS itself is subject to change by variation in temperature, concentration, and solvent. On the basis of recently published results, it has been established that the shielding of TMS in solution [along with that of sodium-3-(trimethylsilyl)propanesulfonate, DSS, often used as a reference for aqueous solutions] varies only slightly with temperature but is subject to solvent perturbations of a few tenths of a part per million (ppm). Recommendations are given for reporting chemical shifts under most routine experimental conditions and for quantifying effects of temperature and solvent variation, including the use of magnetic susceptibility corrections and of magic-angle spinning (MAS). This document provides the first IUPAC recommendations for referencing and reporting chemical shifts in solids, based on high-resolution MAS studies. Procedures are given for relating 13 C NMR chemical shifts in solids to the scales used for high-resolution studies in the liquid phase. The notation and terminology used for describing chemical shift and shielding tensors in solids are reviewed in some detail, and recommendations are given for best practice.

An inverse-scattering series method for attenuating multiples in seismic reflection data

Abstract: We present a multidimensional multiple‐attenuation method that does not require any subsurface information for either surface or internal multiples. To derive these algorithms, we start with a scattering theory description of seismic data. We then introduce and develop several new theoretical concepts concerning the fundamental nature of and the relationship between forward and inverse scattering. These include (1) the idea that the inversion process can be viewed as a series of steps, each with a specific task; (2) the realization that the inverse‐scattering series provides an opportunity for separating out subseries with specific and useful tasks; (3) the recognition that these task‐specific subseries can have different (and more favorable) data requirements, convergence, and stability conditions than does the original complete inverse series; and, most importantly, (4) the development of the first method for physically interpreting the contribution that individual terms (and pieces of terms) in the inv...