Algumas técnicas SIG úteis à obtenção de áreas de serviço de conjuntos de pontos

Em estudos de acessibilidade, e não só, são muito úteis um tipo de estruturas que se podem obter a partir de uma rede, eventualmente multi-modal e parametrizável: as chamadas “áreas de serviço”, as quais são constituídas por polígonos, cada qual correspondente a uma zona situada entre um certo intervalo de custo, relativamente a uma certa “feature” (ponto, multiponto, etc.). Pretende-se neste estudo obter, a partir de áreas de serviço relativas a um universo de features, áreas de serviço relativas a subconjuntos dessas features. Estas técnicas envolvem manipulações relativamente complexas de polígonos e podem ser generalizadas para conjuntos de conjuntos e assim sucessivamente. Convém notar que nem sempre se dispõe da rede, podendo dispor-se das referidas estruturas; eventualmente, no caso de áreas de serviço, sob a forma de imagens (raster) a serem convertidas para formato vectorial.

The Minimum Number of Points Taking Part in k-Sets in Sets of Unaligned Points

En este trabajo se da un ejemplo de un conjunto de n puntos situados en posición general, en el que se alcanza el mínimo número de puntos que pueden formar parte de algún k-set para todo k con 1menor que=kmenor quen/2. Se generaliza también, a puntos en posición no general, el resultado de Erdõs et al., 1973, sobre el mínimo número de puntos que pueden formar parte de algún k-set. The study of k- sets is a very relevant topic in the research area of computational geometry. The study of the maximum and minimum number of k-sets in sets of points of the plane in general position, specifically, has been developed at great length in the literature. With respect to the maximum number of k-sets, lower bounds for this maximum have been provided by Erdõs et al., Edelsbrunner and Welzl, and later by Toth. Dey also stated an upper bound for this maximum number of k-sets. With respect to the minimum number of k-set, this has been stated by Erdos el al. and, independently, by Lovasz et al. In this paper the authors give an example of a set of n points in the plane in general position (no three collinear), in which the minimum number of points that can take part in, at least, a k-set is attained for every k with 1 ≤ k < n/2. The authors also extend Erdos’s result about the minimum number of points in general position which can take part in a k-set to a set of n points not necessarily in general position. That is why this work complements the classic works we have mentioned before.

Using sentinels to detect intersections of convex and nonconvex polygons

We describe finite sets of points, called sentinels, which allow us to decide if isometric copies of polygons, convex or not, intersect. As an example of the applicability of the concept of sentinel, we explain how they can be used to formulate an algorithm based on the optimization of differentiable models to pack polygons in convex sets. Mathematical subject classification: 90C53, 65K05.

Partitioning sets of triples into small planes

We study partitions of the set of all ((v)(3)) triples chosen from a v-set into pairwise disjoint planes with three points per line. Our partitions may contain copies of PG(2, 2) only (Fano partitions) or copies of AG(2, 3) only (affine partitions) or copies of some planes of each type (mixed partitions). We find necessary conditions for Fano or affine partitions to exist. Such partitions are already known in several cases: Fano partitions for v = 8 and affine partitions for v = 9 or 10. We construct such partitions for several sporadic orders, namely, Fano partitions for v = 14, 16, 22, 23, 28, and an affine partition for v = 18. Using these as starter partitions, we prove that Fano partitions exist for v = 7(n) + 1, 13(n) + 1, 27(n) + 1, and affine partitions for v = 8(n) + 1, 9(n) + 1, 17(n) + 1. In particular, both Fano and affine partitions exist for v = 3(6n) + 1. Using properties of 3-wise balanced designs, we extend these results to show that affine partitions also exist for v = 3(2n). Similarly, mixed partitions are shown to exist for v = 8(n), 9(n), 11(n) + 1.

The spectrum of minimal defining sets of some Steiner systems

For a design D, define spec(D) = {\M\ \ M is a minimal defining set of D} to be the spectrum of minimal defining sets of D. In this note we give bounds on the size of an element in spec(D) when D is a Steiner system. We also show that the spectrum of minimal defining sets of the Steiner triple system given by the points and lines of PG(3,2) equals {16,17,18,19,20,21,22}, and point out some open questions concerning the Steiner triple systems associated with PG(n, 2) in general. (C) 2002 Elsevier Science B.V. All rights reserved.

Oysters, and all about them : being a complete history of the titular subject, exhaustive on all points of necessary and curious information from the earliest writers to those of the present time, with numerous additions, facts, and notes /

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Oysters, and all about them : being a complete history of the titular subject, exhaustive on all points of necessary and curious information from the earliest writers to those of the present time, with numerous additions, facts, and notes /

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Accessibility to and utilisation of schistosomiasis-related health services in a rural area of state of Minas Gerais, Brazil

The objective of the present paper was to compare accessibility and utilisation of schistosomiasis diagnostic and treatment services in a small village and the surrounding rural area in northern part of the state of Minas Gerais Brazil. The study included 1,228 individuals: 935 central village residents and 293 rural residents of São Pedro do Jequitinhonha. Schistosoma mansoni infection rates were significantly higher in the central village than in the rural area during a survey in 2007 (44.3% and 23.5%, respectively) and during the 2002 schistosomiasis case-finding campaign (33.1% and 26.5%, respectively) (p < 0.001). However, during the 2002-2006 period, only 23.7% of the villagers and 27% of the rural residents obtained tests on their own from health centres, hospitals and private clinics in various nearby towns. In 2007, 63% of the villagers and 70.5% of the rural residents reported never having received treatment for schistosomiasis. This paper reveals considerable variation in the accessibility and utilisation of schistosomiasis-related health services between the central village and the rural area. A combination of low utilisation rates between 2002-2006 and persistently high S. mansoni infection rates suggest that the schistosomiasis control program must be more rapidly incorporated into the primary health services.

The Falls of Niagara : being a complete guide to all the points of interest around and in the immediate neighbourhood of the great cataract with views taken from sketches by Washington Friend, and from photographs. --

Includes index.

Simple Method to Evaluate and to Predict Flash Points of Organic Compounds

Flash points (T(FP)) of organic compounds are calculated from their flash point numbers, N(FP), with the relationship T(FP) = 23.369N(FP)(2/3) + 20.010N(FP)(1/3) + 31.901. In turn, the N(FP) values can be predicted from boiling point numbers (Y(BP)) and functional group counts with the equation N(FP) = 0.974Y(BP) + Sigma(i)n(i)G(i) + 0.095 where G(i) is a functional group-specific contribution to the value of N(FP) and n(i) is the number of such functional groups in the structure. For a data set consisting of 1000 diverse organic compounds, the average absolute deviation between reported and predicted flash points was less than 2.5 K.