Difference Methods and Deferred Corrections for Ordinary Boundary Value Problems

Compact as possible difference schemes for systems of nth order equations are developed. Generalizations of the Mehrstellenverfahren and simple theoretically sound implementations of deferred corrections are given. It is shown that higher order systems are more efficiently solved as given rather than as reduced to larger lower order systems. Tables of coefficients to implement these methods are included and have been derived using symbolic computations

Computation of the pseudinverse of a matrix of unknown rank

Least squares solution to linear system and computation of pseudoinverse by matrix of unknown ran

Toxicity of Neem's oil, a potential biocide against the invasive mussel Limnoperna fortunei (Dunker 1857)

The golden mussel Limnoperna fortunei (Dunker 1857) is one of the most distributed Nuisance Invasive Species (NIS) in South America, and a threat of great concern for the industry of the area. In this study, we carried out toxicity tests made with a Neem's oil solution with L. fortunei larvae and benthonic adults (7, 13 and 19 ± 1 mm). Tests with non-target species (Daphnia magna, Lactuca sativa and Cnesterodon decemmculatus) were also made with the aim to evaluate the potential toxicity of the Neem's solution in the environment. The LC100 of Neem's solution obtained for larvae was 500 μl/L, a value much higher than the one obtained for D. magna and C. decemmaculatus. Thus, we recommend that it should not be used in open waters. However, since the adults were killed in 72 h and the larvae in 24 h, this product can be used in closed systems, in man-made facilities.Facultad de Ciencias Naturales y Muse

Toxicity of Neem's oil, a potential biocide against the invasive mussel Limnoperna fortunei (Dunker 1857)

The golden mussel Limnoperna fortunei (Dunker 1857) is one of the most distributed Nuisance Invasive Species (NIS) in South America, and a threat of great concern for the industry of the area. In this study, we carried out toxicity tests made with a Neem's oil solution with L. fortunei larvae and benthonic adults (7, 13 and 19 ± 1 mm). Tests with non-target species (Daphnia magna, Lactuca sativa and Cnesterodon decemmculatus) were also made with the aim to evaluate the potential toxicity of the Neem's solution in the environment. The LC100 of Neem's solution obtained for larvae was 500 μl/L, a value much higher than the one obtained for D. magna and C. decemmaculatus. Thus, we recommend that it should not be used in open waters. However, since the adults were killed in 72 h and the larvae in 24 h, this product can be used in closed systems, in man-made facilities.Facultad de Ciencias Naturales y Muse

Polarimetry of Li-rich giants

Protoplanetary nebulae typically present non-spherical envelopes. The origin of such geometry is still controversial. There are indications that it may be carried over from an earlier phase of stellar evolution, such as the AGB phase. But how early in the star's evolution does the non-spherical envelope appear? Li-rich giants show dusty circumstellar envelopes that can help answer that question. We study a sample of fourteen Li-rich giants using optical polarimetry in order to detect non-spherical envelopes around them. We used the IAGPOL imaging polarimeter to obtain optical linear polarization measurements in V band. Foreground polarization was estimated using the field stars in each CCD frame. After foreground polarization was removed, seven objects presented low intrinsic polarization (0.19 - 0.34)% and two (V859 Aql and GCSS 557) showed high intrinsic polarization values (0.87 - 1.16)%. This intrinsic polarization suggests that Li-rich giants present a non-spherical distribution of circumstellar dust. The intrinsic polarization level is probably related to the viewing angle of the envelope, with higher levels indicating objects viewed closer to edge-on. The correlation of the observed polarization with optical color excess gives additional support to the circumstellar origin of the intrinsic polarization in Li-rich giants. The intrinsic polarization correlates even better with the IRAS 25 microns far infrared emission. Analysis of spectral energy distributions for the sample show dust temperatures for the envelopes tend to be between 190 and 260 K. We suggest that dust scattering is indeed responsible for the optical intrinsic polarization in Li-rich giants. Our findings indicate that non-spherical envelopes may appear as early as the red giant phase of stellar evolution.Comment: to be published in A&A, 15 pages, 10 figures. Fig. 3 is available in ftp://astroweb.iag.usp.br/pub/antonio/4270/4270.fig3.pd

Solving two-point seismic-ray tracing problems in a heterogeneous medium. Part 1. A general adaptive finite difference method

A study of two-point seismic-ray tracing problems in a heterogeneous isotropic medium and how to solve them numerically will be presented in a series of papers. In this Part 1, it is shown how a variety of two-point seismic-ray tracing problems can be formulated mathematically as systems of first-order nonlinear ordinary differential equations subject to nonlinear boundary conditions. A general numerical method to solve such systems in general is presented and a computer program based upon it is described. High accuracy and efficiency are achieved by using variable order finite difference methods on nonuniform meshes which are selected automatically by the program as the computation proceeds. The variable mesh technique adapts itself to the particular problem at hand, producing more detailed computations where they are needed, as in tracing highly curved seismic rays. A complete package of programs has been produced which use this method to solve two- and three-dimensional ray-tracing problems for continuous or piecewise continuous media, with the velocity of propagation given either analytically or only at a finite number of points. These programs are all based on the same core program, PASVA3, and therefore provide a compact and flexible tool for attacking ray-tracing problems in seismology. In Part 2 of this work, the numerical method is applied to two- and three-dimensional velocity models, including models with jump discontinuities across interfaces

HLA-Associated viral mutations are common in human immunodeficiency virus type 1 elite controllers

Elite controllers (EC) of human immunodeficiency virus type 1 (HTV-1) maintain viremia below the limit of detection without antiretroviral treatment. Virus-specific cytotoxic CD8+ T lymphocytes are believed to play a crucial role in viral containment, but the degree of immune imprinting and compensatory mutations in EC is unclear. We obtained plasma gag, pol, and nef sequences from HLA-diverse subjects and found that 30 to 40% of the predefined HLA-associated polymorphic sites show evidence of immune selection pressure in EC., compared to approximately 50% of the sites in chronic progressors. These data indicate ongoing viral replication and escape from cytotoxic T lymphocytes are present even in strictly controlled HTV-1 infection

Characterization of LR-115 Type 2 Detectors for Monitoring Indoor Radon 222: Determination of the Calibration Factor

The city of Lima, capital of Peru, has about 11 million inhabitants. Lima has no records about the indoor Radon 222 concentration levels in dwellings. Hereby, we are planning to register the indoor radon concentrations in Lima and in other cities of Peru in the next three years. First, we will determine the calibration factor for the detectors which will be used in our measurements. For this purpose, Solid State Nuclear Tracks Detectors of nitrocellulose nitrate (LR-115 type 2) were used.The calibration process using a Radium 226 source was described to obtain the calibration factor. Linear response in tracks number was found in relation with irradiation time and its stability after time at the calibration chamber

Estudios Preliminares para la Remoción de Arsénico en Aguas Subterráneas Utilizando Métodos de Adsorción

La calidad del agua subterránea en estado natural está relacionada con las propiedades del suelo a través del cual fluye. El arsénico (As) es un elemento que resulta nocivo para la salud, tanto en concentraciones altas como en ingesta crónica en bajas concentra ciones. En esta investigación se estudiaron muestras de aguas subterráneas de la ciudad de Rafaela y Sunchales, las que poseen valores de arsénico superiores al límite establecido por el Código Alimentario Argentino (CAA). En la adsorción se utiliza un sólido para eliminar sustancias disueltas del agua. Con el fin de remover el As, se estudiaron diferentes adsorbentes tales como zeolita, bentonita, arcilla de La Rioja, suelo arcillo limoso de Santa Fe y arcilla de Misiones. Por su efectividad, se seleccionó la arcilla de Misiones y se trabajó con una columna compuesta por ésta y por arenas de filtración, obteniéndose una remoción de As aproximadamente de un 80 %

Los Suelos de La Pampa Ondulada. Características, Clasificación, Distribución y Génesis. Provincia de Buenos Aires - Argentina

Fil: Pereyra, F.X. Servicio Geológico Minero Argentino. Instituto de Geología y Recursos Minerales; Argentina.Fil: Ragas, D.B. Servicio Geológico Minero Argentino. Instituto de Geología y Recursos Minerales; Argentina.La presencia de “suelos zonales” en la Región Pampeana esencialmente asociados a las condiciones bioclimáticas confi rió una visión relativamente simplista al estudio de la génesis y evolución de los suelos de Pampa Ondulada. Sin embargo, numerosos rasgos presentes en los suelos evidencian una historia mucho más compleja y diversa para los mismos, relacionada a una historia geológica- geomorfológica caracterizada por la variabilidad y la complejidad. La zona estudiada corresponde a la denominada Pampa Ondulada en el norte y noreste de la provincia de Buenos Aires. El objetivo principal de la presente contribución es analizar las características de los suelos de la región y proponer un nuevo modelo morfo-pedológico de evolución de los suelos a partir de las variaciones geológicas y geomorfológicas. Es posible distinguir sucesivas combinaciones de materiales originarios según sea: a) divisorias (loéssicas)/ valles fl uviales; y b) marino/estuárico/deltáico. Predominan en ambos sectores los Molisoles (Argiudoles y Epiacuoles principalmente), seguidos de Entisoles (Fluventes), Vertisoles (Epiacuertes) y Alfi soles (Natracualfes). Numerosos cambios ambientales y climáticos tuvieron lugar en la región durante el Cuaternario. Se han considerado, como evidencias de los mismos, los rasgos geomorfológicos deposicionales, los eventos erosivos, como así también la presencia de diferentes superfi cies de erosión. En función de la infl uencia de ellos en los suelos, se plantea la existencia de ciclos cortos y largos de pedogénesis de acuerdo a la duración de los procesos formación de suelos actuantes, los que se superponen espacial y temporalmente. Estos fenómenos geológicos y geomorfológicos generaron la reversión de los ciclos cortos de pedogénesis y la interrupción de los ciclos largos. La superposición y coexistencia de propiedades y rasgos debidos a procesos diversos, implica una complejidad que aparta la evolución de los suelos del modelo simplista unidireccional y progresivo de los factores de formación o de estado del suelo. El escaso espesor de las unidades litológicas holocenas y la existencia de diferentes superfi cies de erosión que truncan los depósitos pleistocenos a distintos niveles son factores importantes que explican la existencia de numerosos materiales originarios combinados en un mismo perfi l. Consecuentemente, se observan suelos policíclicos, poligenéticos, compuestos y complejos en la región estudiada. Teniendo en cuenta los posibles tiempos de expresión de las diferentes propiedades como horizontes petrocálcicos y argílicos, es en Argiudoles y Argialboles, donde se evidencia mejor esta compleja historia. Esta nueva aproximación, presenta gran relevancia en el contexto de posteriores estudios sobre la co-evolución de suelos, geoformas-paisajes y ecosistemas y las respuestas de los mismos frente a cambios ambientales y variaciones climáticas