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

Cold spray deposition of WC-Co

Tese de mestrado integrado. Engenharia Metalúrgica e de Materiais. Universidade do Porto. Faculdade de Engenharia. 201

Limb malformations in a 1982 museum collection of Pleurodeles waltl larvae

info:eu-repo/semantics/acceptedVersio

Performance of Smart Homes for participating in Electricity Markets

Devido ao crescente consumo de energia proveniente de residências, o comportamento dos consumidores de Smart Homes vem sendo estudado nos últimos anos, com o objetivo de otimizar a eficiência energética e o consumo de energia. Além disso, é necessário otimizar o consumo de energia da casa para minimizar custos e reduzir as emissões de gases. Atualmente, o Mercado de Energia Elétrica tem se mostrado muito mais competitivo devido ao surgimento de fontes renováveis ​​de energia e à participação ativa do consumidor no mercado, utilizando programas de demand response. O objetivo deste projeto é desenvolver e melhorar um código-fonte para permitir a gestão da demanda de uma casa inteligente, incluindo geração de energia renovável, veículo elétrico e outros aparelhos inteligentes e dispositivos/electrodomésticos elétricos. Além disso, a redução do custo esperado do consumo de energia e o aumento do conforto do consumidor são considerados como metas do projeto.Due to the rising energy consumption of residential consumers, smart home consumers' behaviour is being studied in the last years to achieve optimal energy efficiency and power consumption. Also, there is a need to optimize house energy consumption to minimize costs and reduce gas emissions. Nowadays, Electricity Market has been much more competitive due to the rising of renewable energy sources and consumer's active participation in the market, using demand response programs. This project aims to develop and improve a source code to allow demand management of a Smart Home, including renewable energy generation, electric vehicle and other smart appliances and electrical devices. Furthermore, the reduction of the expected cost of energy consumption and the rise of consumer's comfort are considered as goals for the project