Arsenic in rice agrosystems (water, soil and rice plants) in Guayas and Los Rios provinces, Ecuador

Geogenic arsenic (As) can accumulate and reach high concentrations in rice grains, thus representing a potential threat to human health. Ecuador is one of the main consumers of rice in South America. However, there is no information available about the concentrations of As in rice agrosystems, although some water bodies are known to contain high levels of the element. We carried out extensive sampling of water, soil, rice plants and commercial rice (obtained from local markets). Water samples were analysed to determine physico-chemical properties and concentrations of dissolved arsenic. Soil samples were analysed to determine total organic C, texture, total Fe and amorphous Fe oxyhydroxides (Fe-ox), total arsenic (tAs) and the bioavailable fraction (As-Me). The different plant parts were analysed separately to determine total (tAs), inorganic (iAs) and organic arsenic (oAs). Low concentrations of arsenic were found in samples of water (generally 80%) in all parts of the rice plants. (C) 2016 Elsevier B.V. All rights reserved

Alternating direction implicit time integrations for finite difference acoustic wave propagation: Parallelization and convergence

This work studies the parallelization and empirical convergence of two finite difference acoustic wave propagation methods on 2-D rectangular grids, that use the same alternating direction implicit (ADI) time integration. This ADI integration is based on a second-order implicit Crank-Nicolson temporal discretization that is factored out by a Peaceman-Rachford decomposition of the time and space equation terms. In space, these methods highly diverge and apply different fourth-order accurate differentiation techniques. The first method uses compact finite differences (CFD) on nodal meshes that requires solving tridiagonal linear systems along each grid line, while the second one employs staggered-grid mimetic finite differences (MFD). For each method, we implement three parallel versions: (i) a multithreaded code in Octave, (ii) a C++ code that exploits OpenMP loop parallelization, and (iii) a CUDA kernel for a NVIDIA GTX 960 Maxwell card. In these implementations, the main source of parallelism is the simultaneous ADI updating of each wave field matrix, either column-wise or row-wise, according to the differentiation direction. In our numerical applications, the highest performances are displayed by the CFD and MFD CUDA codes that achieve speedups of 7.21x and 15.81x, respectively, relative to their C++ sequential counterparts with optimal compilation flags. Our test cases also allow to assess the numerical convergence and accuracy of both methods. In a problem with exact harmonic solution, both methods exhibit convergence rates close to 4 and the MDF accuracy is practically higher. Alternatively, both convergences decay to second order on smooth problems with severe gradients at boundaries, and the MDF rates degrade in highly-resolved grids leading to larger inaccuracies. This transition of empirical convergences agrees with the nominal truncation errors in space and time.Comment: 20 pages, 5 figure

Desenvolvimento urbano contemporâneo em cidades médias do interior paulista sob o estatuto da cidade: uma análise comparada de Piracicaba, Bauru e Rio Claro

O artigo traça um quadro do desenvolvimento urbano contemporâneo em cidades médias do interior do estado de São Paulo (Brasil), sob três dimensões complementares: econômica, urbanística e políticoinstitucional. Para tanto, indica os processos interdependentes que estruturam o desenvolvimento urbano com base na análise comparativa desses municípios (Piracicaba, Bauru e Rio Claro). Nesses termos, identifica como essas cidades se inseriram nos processos de transformação da economia nacional nas décadas de 1970-90, e como essa trajetória impactou suas dinâmicas urbano-regionais. Observa-se de que maneira as determinantes econômicas – tanto as vinculadas às mudanças no padrão locacional das indústrias quanto outras associadas à dinâmica imobiliária – impactaram o ordenamento urbanístico e como ocorreram tais processos decisórios. A análise se faz no contexto institucional da promulgação e vigência do Estatuto da Cidade, no qual os municípios refizeram seus Planos Diretores e passaram a contar com novos meios de regular a produção do espaço urbano.The article focuses on contemporary urban development in medium-sized cities in the state of São Paulo (Brazil), under three complementary dimensions: economic, urban and political-institutional. Thus, it indicates the interdependent processes that shape urban development based on comparative analysis of these municipalities (Piracicaba, Bauru and Rio Claro). In these terms it identifies how these cities were inserted in the processes of transformation of the national economy in the decades of 1970-90, and how that path impacted their urban-regional dynamics. We observe how the economic determinants – changes in the industry standard locational and dynamic real estate – impacted the urban planning and decision-making processes. The analysis is done in the context of institutional effectiveness and promulgation enactment of the Statute of the City, when municipalities remade their Master Plans and have acquired new ways to regulate the production of urban space.Peer Reviewe

Interfacial States in Donor–Acceptor Organic Heterojunctions: Computational Insights into Thiophene-Oligomer/Fullerene Junctions

Donor–acceptor heterojunctions composed of thiophene oligomers and C60 fullerene were investigated with computational methods. Benchmark calculations were performed with time-dependent density functional theory. The effects of varying the density functional, the number of oligomers, the intermolecular distance, the medium polarization, and the chemical functionalization of the monomers were analyzed. The results are presented in terms of diagrams where the electronic states are classified as locally excited states, charge-transfer states, and delocalized states. The effects of each option for computational simulations of realistic heterojunctions employed in photovoltaic devices are evaluated and discussed

An R- and I-Band Photometric Variability Survey of the Cygnus OB2 Association

We present a catalog of photometrically variable stars discovered within two 21'.3 X 21'.3 fields centered on the Cygnus OB2 association. There have hitherto been no deep optical variability studies of Cyg OB2 despite it being replete with early-type massive stars, perhaps due to the high and variable extinction (up to A_V ~ 20) that permeates much of the region. Here we provide results of the first variability study with this combination of spatial coverage (~ 0.5 deg) and photometric depth (R ~ 21 mag). We find 121 stars to be variable in both R- and I-band, 116 of them newly discovered. Of the 121 variables, we identify 27 eclipsing binaries (EBs) and eclipsing binary candidates, 20 potential Herbig Ae/Be stars, and 52 pulsating variables. Confirming both the status and the cluster membership of the Herbig Ae/Be stars would address the uncertainty regarding the age and star formation history of Cyg OB2. We match our catalog to known variables and binaries in the region, 2MASS near-IR (NIR) data, and Chandra X-ray observations to find counterparts to new variables in other wavelengths.Comment: 34 pages, 12 figures, submitted to Ap