Recursos de colección

Estudo Geral - Universidade de Coimbra (19.630 recursos)

ESTUDO GERAL é a designação do repositório digital da produção científica da Universidade de Coimbra, com o objectivo de divulgar conteúdos digitais de natureza científica de autores ligados à Universidade de Coimbra. A sua criação insere-se no movimento de Acesso Livre à Literatura científica (Open Access), ao qual o Conselho de Reitores das Universidades Portuguesas aderiu em 2006 e que a Universidade de Coimbra subscreveu. À semelhança de outras grandes universidades nacionais e internacionais, a UC tem o maior interesse em aumentar a sua presença na rede informática mundial, sendo cada vez mais - e também por essa via - um emissor de conhecimento e cultura.

FCTUC Matemática - Artigos em Revistas Internacionais

Mostrando recursos 1 - 20 de 208

  1. Automatic Polyp Detection in Pillcam Colon 2 Capsule Images and Videos: Preliminary Feasibility Report

    Figueiredo, Pedro N.; Figueiredo, Isabel N.; Prasath, Surya; Tsai, Richard
    Background. The aim of this work is to present an automatic colorectal polyp detection scheme for capsule endoscopy. Methods. PillCam COLON2 capsule-based images and videos were used in our study. The database consists of full exam videos from five patients. The algorithm is based on the assumption that the polyps show up as a protrusion in the captured images and is expressed bymeans of a P-value, defined by geometrical features. Results. Seventeen PillCamCOLON2 capsule videos are included, containing frames with polyps, flat lesions, diverticula, bubbles, and trash liquids. Polyps larger than 1 cmexpress a P-value higher than 2000, and 80% of the polyps show a...

  2. Optimizing the profit from a complex cascade of hydroelectric stations with recirculating water

    Korobeinikov, Andrei; Kovacec, Alexander; McGuinness, Mark; Pascoal, Marta; Pereira, Ana; Vilela, Sónia
    In modern reversible hydroelectric power stations it is possible to reverse the turbine and pump water up from a downstream reservoir to an upstream one. This allows the use of the same volume of water repeatedly and was specifically developed for hydro-electric stations operating with insufficient water supply. Pumping water upstream is usually done at times of low demand for electricity, to build up reserves in order to be able to produce energy during peak hours, thus balancing the load and making a profit on the price difference. In this paper, we consider a branched model for hydroelectric power stations interacting in a complex cascade arrangement. The goal of this...

  3. Local and Global Calibration of Coordinate Measuring Machines

    Antunes, S. D.; Antunes, P. M. V. C. D.; Vicente, M. A. F.
    In the last years, we assisted to the development of new high precision machine tools: the hexapod machines. We tried to use the hexapod machine as an artefact for CMM’s calibration. However, given their cost and their resolution, they are not the best solution for a transportable artefact. By modifying the hexapod structure, we develop two different artefacts: one for local CMM’s calibration and another one for global calibration. Local calibration allows us the determination of the transfer function characterizing the sensor displacement of the CMM. This local calibration is based on the measurement of a rigid artefact of a known geometry, derived from hexapod geometry, which...

  4. Sensitivity Analysis of a Nonlinear Obstacle Plate Problem

    Figueiredo, Isabel N.; Leal, Carlos F.
    We analyse the sensitivity of the solution of a nonlinear obstacle plate problem, with respect to small perturbations of the middle plane of the plate. This analysis, which generalizes the results of Rao and Sokolowski 1987, Rockafeller 1989 for the linear case, is done by application of an abstract variational result Levy 1999, where the sensitivity of parameterized variational inequalities in Banach spaces, without uniqueness of solution, is quantified in terms of a generalized derivative, that is the proto-derivative. We prove that the hypotheses required by this abstract sensitivity result are verified for the nonlinear obstacle plate problem. Namely, the...

  5. Analysis of Inexact Trust-Region SQP Algorithms

    Heinkenschloss, Matthias; Vicente, Luís N.
    In this paper we extend the design of a class of composite–step trust–region SQP methods and their global convergence analysis to allow inexact problem information. The inexact problem information can result from iterative linear systems solves within the trust–region SQP method or from approximations of first–order derivatives. Accuracy requirements in our trust–region SQP methods are adjusted based on feasibility and optimality of the iterates. Our accuracy requirements are stated in general terms, but we show how they can be enforced using information that is already available in matrix–free implementations of SQP methods. In the absence of inexactness our global convergence theory is equal to that...

  6. Numerical solution for the wave equation

    Patrício, M. F.
    In this paper we study numerical solutions for a hyperbolic system of equations using finite differences. In this setting, we propose the method of lines, with high precision in space. A class of some explicit, implicit and also semi-implicit schemes, with code variable methods, are presented. Finally, the analysis of some qualitative and quantitative proprieties of these methods is included.

  7. Lifting solutions of quasilinear convection-dominated problems

    Ferreira, J. A.; Mouro, A. P.; Oliveira, P.
    In certain cases, quasilinear convection-diffusion-reaction equations range from parabolic to almost hyperbolic, depending on the ratio between convection and diffusion coefficients. From a numerical point of view, two main difficulties can arise related to the existence of layers and/or the non-smoothness of the coefficients of such equations. In this paper we study the steady-state solution of a convection-dominated problem. We present a new numerical method based on the idea of solving an associated modified problem, whose solution corresponds to a lifting of the solution of the initial problem. The method introduced here avoids an a priori knowledge of the layer(s)...

  8. The inverse eigenvalue problem for Hermitian matrices whose graphs are cycles

    Fernandes, Rosário; Fonseca, C. M. da
    In 1979, Ferguson characterized the periodic Jacobi matrices with given eigenvalues and showed how to use the Lanzcos Algorithm to construct each such matrix. This article provides general characterizations and constructions for the complex analogue of periodic Jacobi matrices. As a consequence of the main procedure, we prove that the multiplicity of an eigenvalue of a periodic Jacobi matrix is at most 2.

  9. Portugal: network of institutions cooperate in computer graphics education

    Teixeira, José Carlos
    http://doi.acm.org/10.1145/232301.232319

  10. Algorithm 355: an algorithm for generating ising configurations [Z]

    Pereira, J. M. S. Simões
    http://doi.acm.org/10.1145/363235.363243

  11. An interface optimization and application for the numerical solution of optimal control problems

    Heinkenschloss, Matthias; Vicente, Luís N.
    An interface between the application problem and the nonlinear optimization algorithm is proposed for the numerical solution of distributed optimal control problems. By using this interface, numerical optimization algorithms can be designed to take advantage of inherent problem features like the splitting of the variables into states and controls and the scaling inherited from the functional scalar products. Further, the interface allows the optimization algorithm to make efficient use of user-provided function evaluations and derivative calculations.

  12. Generating box-constrained optimization problems

    Facchinei, Francisco; Júdice, Joaquim; Soares, João
    We present a method for generating box-constrained nonlinear programming test problems. The technique allows the user to control some properties of the generated test problems that are know to influence the behavior of algorithms for their solution. A corresponding set of Fortran 77 routines is described in a companion algorithm (774).

  13. Algorithm 774: Fortran subroutines for generating box-constrained optimization problems

    Facchinei, Francisco; Júdice, Joaquim; Soares, João
    We describe a set of Fortran routines for generatig box-constrained nonlinear programming test problems. The technique, as described by Facchinei et al. (this issue), allows the user to control relevant properties of the generated problems.

  14. Algorithm 728: FORTRAN subroutines for generating quadratic bilevel programming test problems

    Calamai, Paul H.; Vicente, Luís N.
    This paper describes software for generating test problems for quadratic bilevel programming. The algorithm constructs problems with a number of favorable properties that can be selected and controlled by the user. The intention is to provide a set of FORTRAN 77 routines that can be used for testing, verifying, and comparing solution techniques for these problems.

  15. Generating quadratic bilevel programming test problems

    Calamai, Paul H.; Vicente, Luís N.
    This paper describes a technique for generating sparse or dense quadratic bilevel programming problems with a selectable number of known global and local solutions. The technique described here does not require the solution of any subproblems. In addition, since most techniques for solving these problems begin by solving the corresponding relaxed quadratic program, the global solutions are constructed to be different than the global solution of this relaxed problem in a selectable number of upper- and lower-level variables. Finally, the problems that are generated satisfy the requirements imposed by all of the solution techniques known to the authors.

  16. Accelerating scientific computations with mixed precision algorithms

    Baboulin, Marc; Buttari, Alfredo; Dongarra, Jack; Kurzak, Jakub; Langou, Julie; Langou, Julien; Luszczek, Piotr; Tomov, Stanimire
    http://www.sciencedirect.com/science/article/B6TJ5-4TX7976-1/2/a85cf5566583a3c10996c05925efa9c9

  17. Face counting on an Acyclic Birkhoff polytope

    Costa, Liliana; Fonseca, C. M. da; Martins, Enide Andrade
    http://www.sciencedirect.com/science/article/B6V0R-4V5GD2H-1/2/5a4ab2f05e5a55a500bf0fc93554003a

  18. Ubiquitin associated protein 1 is a risk factor for frontotemporal lobar degeneration

    Rollinson, Sara; Rizzu, Patrizia; Sikkink, Stephen; Baker, Matthew; Halliwell, Nicola; Snowden, Julie; Traynor, Bryan J.; Ruano, Dina; Cairns, Nigel; Rohrer, Jonathan D.; Mead, Simon; Collinge, John; Rossor, Martin; Akay, Ela; Guerreiro, Rita; Rademakers, Rosa; Morrison, Karen E.; Pastor, Pau; Alonso, Elena; Martinez-Lage, Pablo; Graff-Radford, Neil; Neary, David; Heutink, Peter; Mann, David M. A.; Swieten, John Van; Pickering-Brown, Stuart M.
    http://www.sciencedirect.com/science/article/B6T09-4VKMW0R-1/2/c38ac7e3dcb87f1e42d35a151a3f69b2

  19. Existence and nonexistence of solutions for singular quadratic quasilinear equations

    Arcoya, David; Carmona, José; Leonori, Tommaso; Martínez-Aparicio, Pedro J.; Orsina, Luigi; Petitta, Francesco
    http://www.sciencedirect.com/science/article/B6WJ2-4VKMWDR-2/2/f35680f147d63f6297e97ebb1b4b242e

  20. Coupled vehicle-skin models for drug release

    Barbeiro, S.; Ferreira, J. A.
    http://www.sciencedirect.com/science/article/B6V29-4VM43XG-1/2/493993c9687e5ff240f132118604a862

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