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Search Results: 1 - 10 of 720249 matches for " Mário A; "
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Acceleration of nonhyperbolic sequences of Mann
Mário M. Gra a
International Journal of Mathematics and Mathematical Sciences , 2002, DOI: 10.1155/s0161171202013340
Abstract: Mann's sequences are difficult to accelerate in the presence of a nonhyperbolic fixed point. New accelerators are constructed for Mann's sequences which are useful even for other sets of very slowly convergent sequences.
Maps for global separation of roots
Mário M. Gra?a
Mathematics , 2015,
Abstract: Two simple predicates are adopted and certain real-valued piecewise continuous functions are constructed from them. This type of maps will be called quasi-step maps and aim to separate the fixed points of an iteration map in an interval. The main properties of these maps are studied. Several worked examples are given where appropriate quasi-step maps for Newton and Halley iteration maps illustrate the main features of quasi-step maps as tools for global separation of roots.
A Simple Derivation of Newton-Cotes Formulas with Realistic Errors
Mário M. Gra?a
Mathematics , 2012,
Abstract: In order to approximate the integral $I(f)=\int_a^b f(x) dx$, where $f$ is a sufficiently smooth function, models for quadrature rules are developed using a given {\it panel} of $n (n\geq 2)$ equally spaced points. These models arise from the undetermined coefficients method, using a Newton's basis for polynomials. Although part of the final product is algebraically equivalent to the well known closed Newton-Cotes rules, the algorithms obtained are not the classical ones. In the basic model the most simple quadrature rule $Q_n$ is adopted (the so-called left rectangle rule) and a correction $\tilde E_n$ is constructed, so that the final rule $S_n=Q_n+\tilde E_n$ is interpolatory. The correction $\tilde E_n$, depending on the divided differences of the data, might be considered a {\em realistic correction} for $Q_n$, in the sense that $\tilde E_n$ should be close to the magnitude of the true error of $Q_n$, having also the correct sign. The analysis of the theoretical error of the rule $S_n$ as well as some classical properties for divided differences suggest the inclusion of one or two new points in the given panel. When $n$ is even it is included one point and two points otherwise. In both cases this approach enables the computation of a {\em realistic error} $\bar E_{S_n}$ for the {\it extended or corrected} rule $S_n$. The respective output $(Q_n,\tilde E_n, S_n, \bar E_{S_n})$ contains reliable information on the quality of the approximations $Q_n$ and $S_n$, provided certain conditions involving ratios for the derivatives of the function $f$ are fulfilled. These simple rules are easily converted into {\it composite} ones. Numerical examples are presented showing that these quadrature rules are useful as a computational alternative to the classical Newton-Cotes formulas.
Recursive families of higher order iterative maps
Mário M. Gra?a
Mathematics , 2014,
Abstract: To approximate a simple root of an equation we construct families of iterative maps of higher order of convergence. These maps are based on model functions which can be written as an inner product. The main family of maps discussed is defined recursively and is called {\it Newton-barycentric}. We illustrate the application of Newton-barycentric maps in two worked examples, one dealing with a typical least squares problem and the other showing how to locate simultaneously a great number of extrema of the Ackley's function.
Higher-order root distillers
Mário M. Gra?a
Mathematics , 2015,
Abstract: Recursive maps of high order of convergence $m$ (say $m=2^{10}$ or $m=2^{20}$) induce certain monotone step functions from which one can filter relevant information needed to globally separate and compute the real roots of a function on a given interval $[a,b]$. The process is here called a root distiller. A suitable root distiller has a powerful preconditioning effect enabling the computation, on the whole interval, of accurate roots of an high degree polynomial. Taking as model high-degree inexact Chebyshev polynomials and using the {\sl Mathematica} system, worked numerical examples are given detailing our distiller algorithm.
Quadrature as a least-squares and minimax problem
Mário M. Gra?a
Mathematics , 2012,
Abstract: The vector of weights of an interpolatory quadrature rule with $n$ preassigned nodes is shown to be the least-squares solution $\omega$ of an overdetermined linear system here called {\em the fundamental system} of the rule. It is established the relation between $\omega$ and the minimax solution $\stackrel{\ast}{z}$ of the fundamental system, and shown the constancy of the $\infty$-norms of the respective residual vectors which are equal to the {\em principal moment} of the rule. Associated to $\omega$ and $\stackrel{\ast}{z}$ we define several parameters, such as the angle of a rule, in order to assess the main properties of a rule or to compare distinct rules. These parameters are tested for some Newton-Cotes, Fej\'er, Clenshaw-Curtis and Gauss-Legendre rules.
Algumas notas acerca da consulta de psicologia clínica
Santos,Mário J. A.;
Análise Psicológica , 2004,
Abstract: the author approches the concept of clinical psychology consult with patients between three and thirteen years old. two decades of work at first in the c.s.m.i.j.l. and later at h.d.e.. clinical work has been made from psicanalitical theory and pratice. relationships analisis from the psychologist, the child and the parents is fundamental. the affective-cognitive-relational focus is seen from present life and past one, from future projects of the child, the family context and others from which depends global development. the author makes therapeutic consults with the parents to increase the adequacy of parental functions.
Oncocercose entre os índios Yanomámi
Moraes, Mário A. P.;
Cadernos de Saúde Pública , 1991, DOI: 10.1590/S0102-311X1991000400004
Abstract: the main features of the brazilian focus of onchocerciasis are reported. this focus encompasses large areas of the states of amazonas and roraima, in the densely forested highlands of northern brazil. it is not clear how the local inhabitants, indians of the group yanomámi, an isolated group that has lived in the region for centuries, acquired the infection. however, in some of their villages the prevalence rate among adults is as high as 80%. aspects of the focus, as its origins, manifestations of the illness among the indians, and the distribution and importance of the recognized vectors of o. volvulus in the region, are reviewed. the author also makes some considerations on the behavior and probable future of the focus, including the possible dissemination of onchocerciasis to some other sites of brazil. gold miners that in recent years have invaded the yanomámi territory and became infected in contact with the indians will be the cause of this dissemination. methods for controlling onchocerciasis are discussed and, besides the treatment of the infected indians with ivermectin, it is proposed the use of larvicides to eliminate the vectors. this method would be employed in some limited areas where the population is already stable and shows a very high prevalence rate.
Tityus serrulatus venom and its toxins Ts1 and Ts5 increase cytosolic Ca2+ concentration in isolated vascular smooth muscle cells  [PDF]
Mário dos A. Neto, Flávio Vasconcelos, Lusiane M. Bendhack, Eliane C. Arantes
Journal of Biophysical Chemistry (JBPC) , 2012, DOI: 10.4236/jbpc.2012.34035
Abstract: Voltage-gated Na+ channel (Nav channel) scorpion toxins are classified as α- and β-neurotoxins. Ts5 (α-neurotoxin) and Ts1 (β-neurotoxin) from Tityus serrulatus venom (TsV) interact with Nav channels, increasing Na+ influx and activating voltage-dependent Ca2+ channels. This study aimed to investigate the effect of TsV, Ts1 and Ts5 on the cytosolic Ca2+ concentration ([Ca2+]C) in rat aortic smooth muscle cells. Toxins were isolated by ion exchange chromatography (Ts1) followed by RP-HPLC (Ts5). The rat aortic smooth muscle cells were isolated in Hanks buffer pH 7.4 and loaded with 5 μmol/L of Fura-2AM (45 minutes at 37℃), in order to measure [Ca2+]C by fluorescence of Fura-2/AM (ratio 340/380 nm). The fluorescence was measured in one single cell (excitation: 340 and 380 nm; emission: 510 nm). TsV (100 and 500 mg/mL) and its toxins Ts1 and Ts5 (50 and 100 mg/mL each) led to a concentration-dependent increase in [Ca2+]C. Tetrodotoxin (1 mmol/L), a Nav channel blocker, and verapamil (1 mmol/L), a voltage-operated Ca2+ channel blocker, inhibited the increase in [Ca2+]C induced by TsV (500 mg/mL). In conclusion, TsV and its toxins induce a concentration-dependent increase in [Ca2+]C that probably occurs through interaction with Nav channels, thus inducing depolarization and consequent Ca2+ influx. This assumption is based on the fact that this effect is inhibited by tetrodotoxin and verapamil, showing a direct action of TsV toxins on aorta smooth muscle cells.
Determina??es multi-elementares de metais, Sulfato e Cloreto em amostras de águas por espectrometria de massas com fonte de plasma (ICP-MS)
Menegário, A. A.;Giné, M. F.;
Química Nova , 1998, DOI: 10.1590/S0100-40421998000400007
Abstract: the multi-element determination of al, cr, mn, ni, cu, zn, cd, ba, pb, so4= and cl- in riverine water samples was accomplished by inductively coupled plasma mass spectrometry (icp-ms). the sample passed through a column containing the anionic resin ag1-x8 and the metals were determined directly. the retained anionic species were eluted and so4= and cl- were determined at m/z 48 and 35 correspondent to the ions so+ and cl+ formed at the plasma. accuracy for metals was assessed by analysing the certified reference tm-26 (national water research institute of canada). results for so4= and cl- were in agreement with those obtained by turbidimetry and spectrophotometry. lod's of 0.1 μg l-1 for cd, ba and pb; 0.2 μg l-1 for al, mn and cu; 0.5 μg l-1 for cr; 0.9 for zn; 2.0 μg l-1for ni , 60 μg l-1 for s and 200 μg l-1 cl were attained.
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