Facets for Art Gallery Problems

The Art Gallery Problem (AGP) asks for placing a minimum number of stationary guards in a polygonal region P, such that all points in P are guarded. The problem is known to be NP-hard, and its inherent continuous structure (with both the set of points that need to be guarded and the set of points that can be used for guarding being uncountably infinite) makes it difficult to apply a straightforward formulation as an Integer Linear Program. We use an iterative primal-dual relaxation approach for solving AGP instances to optimality. At each stage, a pair of LP relaxations for a finite candidate subset of primal covering and dual packing constraints and variables is considered; these correspond to possible guard positions and points that are to be guarded. Particularly useful are cutting planes for eliminating fractional solutions. We identify two classes of facets, based on Edge Cover and Set Cover (SC) inequalities. Solving the separation problem for the latter is NP-complete, but exploiting the underlying geometric structure, we show that large subclasses of fractional SC solutions cannot occur for the AGP. This allows us to separate the relevant subset of facets in polynomial time. We also characterize all facets for finite AGP relaxations with coefficients in {0, 1, 2}. Finally, we demonstrate the practical usefulness of our approach. Our cutting plane technique yields a significant improvement in terms of speed and solution quality due to considerably reduced integrality gaps as compared to the approach by Kr\"oller et al.Comment: 29 pages, 18 figures, 1 tabl

Silicon detectors for neutrino oscillation experiments

This note describes the technique of using a target equipped with high resolution silicon microstrip detectors for the detection of the topological signature of decays in neutrino oscillation ex periments. Two detectors are presented. The first detector is installed in the NOMAD spectrometer at the CERN SPS neutrino beam. The target consists of four layers passive boron carbide plate s (total mass of 45 kg) interleaved with five layers of silicon microstrip detectors. A total of 600 single--sided silicon microstrip detectors are used amounting to a total area of 1.14 m$^2$. The silicon tracker is made with the longest ladders built to date (72 cm). During the 1997 run about 8000 charged current interactions were estimated to have occurred in the target and data tak ing will continue in 1998. For these events it will be possible to perform a precise measurement of both vertex and kinematical variables. The second detector was installed in September 1997 in a CERN PS pion beam to investigate the possibility of combining silicon detectors and nuclear emulsions. This detector consists of 72 single--sided silicon microstrip detectors with a total surfac e of 0.13 m$^2$ distributed over four layers, providing two measurements of each of the two orthogonal coordinates. This exposure will measure the precision with which the silicon tracker can p redict the position of particles in the emulsion. Both detectors provide invaluable experience towards the construction of a large scale silicon tracker for future neutrino oscillation experime nts

Evaluation of patients' discomfort regarding regional anesthesia: 8AP6‐7

Background and Goal of Study: Regional anesthesia may cause physical and psychological discomfort. 50% of patients scheduled for urologic procedures undergo regional anesthesia, and their comfort represents a concern to the anesthesiologist. This study aims to: 1. identify factors related to patients’ discomfort regarding regional anesthesia(position for anesthesia and surgery procedures, puncture site pain, room temperature, audio-visual perception, sensitive/motor blockade); 2. Evaluate patients’ satisfaction with anesthesia. Materials and Methods: Af ter approval from the Hospital Ethics Committee all patients over 18years old, scheduled for urologic surgery, understanding Portuguese and anesthetized with spinal anesthesia were included. Patients in day case surgery or with incomplete medical records were excluded. We performed a questionnaire(with closed ended questions) in the first 24 hours af ter surgery and consulted anesthesia records. We asked yes or no questions, used a 1-10 scale to evaluate pain and a 1-4 scale to evaluate satisfaction. Because there isn’t a valid questionnaire in the literature to evaluate what we aimed to, we created one based on multiple articles1,2. Results and Discussion: 50patients were included; mean age 65 years old (min.32, max.89); 78% males and 70% ASAII. 75%denied discomfort during positioning for back puncture and 58% referred cold during anesthesia or surgery. One person was uncomfortable in the surgical position and no one considered being awake uncomfortable; sensitive/motor blockade was uncomfortable for 22%. Spinal was more painful than the venous puncture for32%; for 50%venous puncture was more painful and for 18%pain was similar. Patients were satisfied or very satisfied with the anesthetic technique and would choose the same technique in the future in 98% of cases. Conclusion: Although this questionnaire is not validated, it allowed us to understand that cold during anesthesia/surgery is a problem for most patients but this is easily solved. It also showed us that most patients are not uncomfortable with positioning during procedures, being awake and not feeling the legs.Interestingly only about one third of the patients thought that the back puncture was more painful than the venous puncture. In general we consider spinal anesthesia a good choice for these patients and we are satisfied that patients don’t find it uncomfortable and are also satisfie

Cultivo do milho irrigado.

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Influência de um programa de treino da musculatura do core em jogadoras ado-lescentes de voleibol

Introdução: Apesar de na reabilitação e nas atividades da vida diária já se perceber que o treino do core tem bastantes benefícios, no desporto ainda não há provas conclusivas deste mesmo benefício e de como o treino do core deve ser elaborado. Objectivo(s): Avaliar a eficácia de um programa de intervenção sobre a musculatura do core em jogadoras de voleibol Métodos: O presente estudo quasi experimental longitudinal teve uma amostra final de 56 indivíduos – grupo controlo (GC) (n= 27), e grupo experimental (GE) (n=29). Avaliou-se os testes de endurance, e respectivos rácios, descritos por McGill. Ambos os grupos foram avaliados antes (Momento 0) e após (Momento 1) a aplicação de um programa de intervenção. Resultados: Na análise entre os 2 grupos, tanto no Momento 0 como no Momento 1, não se registou diferenças estatisticamente significativas, nem nas médias de tempo dos testes de McGill nem nos rácios. Já na análise intragrupo, o GC não apresentou resultados estatisti-camente significativos, nem nas médias de tempo dos testes do McGill nem nos rácios, enquanto o GE apenas apresentou valores estatisticamente significativos nas médias de tempo da prancha lateral direita (p = 0,04) e prancha lateral esquerda (p = 0,03). Conclusão: Atletas jovens e do sexo feminino, apresentaram um fraco de-sempenho da musculatura extensora do tronco que as torna mais passíveis de contrair lesões lumbopélvicas. Será necessário implementar um programa de intervenção, diferente do aplicado neste estudo, e com maior ênfase na musculatura extensora para equilibrar os rácios propostos por McGill, e assim, diminuir o risco de lesão

Indicações de gestão para um laboratório, a partir do cadastro de clientes e de serviços: estudo de caso da clínica fitossanitária Embrapa Clima Temperado.

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Microscopic mechanism for mechanical polishing of diamond (110) surfaces

Mechanically induced degradation of diamond, as occurs during polishing, is studied using total--energy pseudopotential calculations. The strong asymmetry in the rate of polishing between different directions on the diamond (110) surface is explained in terms of an atomistic mechanism for nano--groove formation. The post--polishing surface morphology and the nature of the polishing residue predicted by this mechanism are consistent with experimental evidence.Comment: 4 pages, 5 figure