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Publicações

2009

Geometrical effects on the refractive index sensitivity of Mach-Zehnder fibre modal interferometers based on long-period gratings

Autores
Caldas, P; Jorge, PAS; Araujo, FM; Ferreira, LA; Rego, G; Santos, JL;

Publicação
MEASUREMENT SCIENCE & TECHNOLOGY

Abstract
In this work a modal interferometer based on arc-induced long-period gratings (LPGs) in a Mach-Zehnder configuration is evaluated as a sensing structure for environmental refractive index measurement. To interrogate this sensing device, coherence addressing and pseudo-heterodyne processing were used. The influence of geometric effects such as stretching, bending and twisting the interferometer on the sensitivity to refractive index changes was studied. It is shown that due to the antisymmetric nature of cladding modes in arc-induced LPGs, it is possible to tune the system sensitivity to external refractive index by simple mechanical action. The experimental results show that it is possible to tune the sensitivity to external refractive index by more than 50% by control of the curvature in the Mach-Zehnder interferometer.

2009

Evaluating operational risk in a power system with a large amount of wind power

Autores
Gouveia, EM; Matos, MA;

Publicação
ELECTRIC POWER SYSTEMS RESEARCH

Abstract
Reserve definition is a compromise between economic issues (additional capacity costs) and reliability (risk of loss of load due to outages of the generators), generally approached by deterministic criteria (e.g. the percentage rule defined by UCTE in Europe) and probabilistic methods like PJM (Pennsylvania-New Jersey, Maryland) and its enhancements, based on the concept of risk. With wind power generation increasing in power systems worldwide, these operational issues gain a renewed interest due to the volatile nature of this kind of energy. The aim of this paper is therefore to address this issue from a risk evaluation point of view, showing that it is possible to extend classical probabilistic methods to this new situation, by introducing a detailed Markov model of wind parks that accounts both for machine failures and different wind power levels. This evaluation, where wind generation fluctuation and uncertainty is included, can be helpful for transmission system operators (TSO). when defining the reserve requirements for the next hours. In fact, the results obtained for the risk can be used by TSO to check if the reserve levels that results from traditional deterministic rules are acceptable or need to be increased.

2009

A fibre optic humidity sensor based on a long-period fibre grating coated with a thin film of SiO2 nanospheres

Autores
Viegas, D; Goicoechea, J; Corres, JM; Santos, JL; Ferreira, LA; Araujo, FM; Matias, IR;

Publicação
MEASUREMENT SCIENCE & TECHNOLOGY

Abstract
A novel sensing configuration for measuring humidity based on a long-period fibre grating coated with a thin film of silica nanospheres is proposed. The polymeric overlay is deposited on the grating using the electrostatic self-assembly technique. This thin film changes its optical properties when exposed to different humidity levels that translate into a shift of the resonance wavelength of the fibre grating. Wavelength shifts up to 12 nm in a relative humidity range from 20% to 80% are reported, and it is further demonstrated that such humidity sensitivity has negligible thermal dependence.

2009

Probabilistic evaluation of reserve requirements of generating systems with renewable power sources: The Portuguese and Spanish cases

Autores
Matos, M; Lopes, JP; Rosa, M; Ferreira, R; da Silva, AL; Sales, W; Resende, L; Manso, L; Cabral, P; Ferreira, M; Martins, N; Artaiz, C; Soto, F; Lopez, R;

Publicação
INTERNATIONAL JOURNAL OF ELECTRICAL POWER & ENERGY SYSTEMS

Abstract
This paper presents an application of probabilistic methodologies to evaluate the reserve requirements of generating systems with a large penetration of renewable energy sources. The idea is to investigate the behavior of reliability indices, including those from the well-being analysis, when the major portion of the renewable sources comes from wind power and other intermittent sources. A new simulation process to address operating reserve adequacy is introduced, and the correspondent reliability indices are observed. Case Studies on the Portuguese and Spanish generating systems are presented and discussed.

2009

Universality in nonlinear prediction of complex systems

Autores
Goncalves, R; Ferreira, H; Pinto, A; Stollenwerk, N;

Publicação
JOURNAL OF DIFFERENCE EQUATIONS AND APPLICATIONS

Abstract
We exploit ideas of nonlinear dynamics and statistical physics in a complex nondeterministic dynamical setting using the Ruelle-Takens embedding. We present some new insights on the quality of the prediction in the laminar regime and we exhibit the data collapse of the predicted relative first difference fluctuations to the universal Bramwell-Hodsworth-Pinton distribution. Hence, the nearest neighbour method of prediction acts as a filter that does not eliminate the randomness, but exhibits its universal character.

2009

From Plain Prolog to Logtalk Objects: Effective Code Encapsulation and Reuse

Autores
Moura, P;

Publicação
Logic Programming, 25th International Conference, ICLP 2009, Pasadena, CA, USA, July 14-17, 2009. Proceedings

Abstract
Prolog affords concise, elegant, and clean solutions for many interesting problems, but is not immune to the software engineering challenges of large-scale application development. Code modularization, using modules or objects, is a key feature to keep projects manageable. Since most literature, instruction, and practice focus exclusively on object-oriented languages derived from imperative languages, objects are perceived as alien to logic programming while modules are considered a natural fit. Logtalk is an object-oriented logic programming language that can use most Prolog implementations as a back-end compiler. Logtalk objects are about code encapsulation and reuse, providing an alternative to Prolog module systems, and enabling natural solutions for a wide range of problems that would be awkward to solve using modules. This talk presents the Logtalk design goals, followed by a tutorial on Logtalk programming and some application examples. The talk ends with a discussion on the problems and benefits of developing Logtalk as a portable Prolog application. © 2009 Springer Berlin Heidelberg.

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