Análise intervalar e projeto de controladores robustos via programação alvo

A computational optimization-based approach for designing fixed-order controllers through robust pole placement for uncertain (interval) linear time-invariant SISO plants is presented. The design objective is the minimization of the overall deviation from the desired performance for the closed-loop system, as specified by a polytope of characteristic polinomials. The robust pole placement design problem is associated with the solution of an interval Diophantine equation, whose basic properties are analysed. Robust pole placement controllers are viewed as inner solutions of the interval Diophantine equation. Simple and computationally efficient characterizations of the set of all robust pole placement controllers are then obtained and some of its geometric properties discused. Several aspects of the design of robust controllers by Interval Analysis are integrated into a linear goal programming formulation, which can incorporate addicional constraints on the controller parameters. Examples illustrate the main characteristics of the proposed approach.É apresentada uma abordagem computacional baseada em otimização para o projeto de controladores de ordem fixa através de alocação robusta de pólos para plantas lineares e invariantes no tempo, SISO, com incertezas do tipo intervalar. O objetivo do projeto é a minimização do desvio total do desempenho desejado para o sistema em malha fechada, especificado por um politopo de polinômios característicos. O problema de projeto por alocação robusta de pólos é associado à solução de uma equação Diofantina intervalar, cujas propriedades básicas são analisadas. Controladores por alocação robusta de pólos são vistos como soluções internas da equação Diofantina intervalar. Caracterizações simples e computacionalmente eficientes do conjunto de todos os controladores por alocação robusta de pólos são então obtidos e algumas das suas propriedades geométricas discutidas. Vários aspectos do projeto de controladores robustos por Análise Intervalar são integrados a uma formulação de programação alvo linear, que também pode incorporar restrições adicionais aos parâmetros do controlador. Exemplos ilustram as principais características da abordagem proposta.111123Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Modelação e avaliação da qualidade da água em sistemas hídricos urbanos. O caso da ribeira de Couros, em Guimarães (Portugal)

Os principais objetivos deste trabalho foram: a caracterização mais detalhada do impacto das descargas das redes municipais (saneamento e de drenagem urbana) na qualidade da água da Ribeira de Couros, em Guimarães; a identificação das zonas mais críticas da ribeira; a avaliação da qualidade da água em locais estratégicos, com base na modelação matemática, visando o posterior estabelecimento de um índice de qualidade da água (IQA) aplicável a meios hídricos urbanos. Face à escassez de dados, foi implementado um programa de monitorização com o objetivo de permitir a calibração e validação do modelo. Os dados obtidos constituem um contributo valioso para a construção de um IQA, integrando diferentes indicadores de qualidade, cuja graduação permitira sustentar a definição de estratégias e medidas de intervenção adequadas para a reabilitação e requalificação de cursos de água. A modelação efetuada permitiu evidenciar que a zona do novo Mercado Municipal é a mais crítica deste trecho, nomeadamente em termos de desoxigenação. Os resultados obtidos demonstram a especificidade da avaliação da qualidade da água em meio urbano, desaconselhando metodologias generalistas que ignorem a frequente variação (espacial e temporal) das características hidrodinâmicas e de qualidade da água nestes ecossistemas

A multi-criteria approach for the selection of wastewater treatment systems

The inefficiency of Wastewater Treatment Systems (WTS) might be a source of hydrological and environmental pollution, and it also causes problems to public health. The advances of technology have contributed to the development of a diversity of new WTS, but it generates a gap for decision-making regards to the correct use of these treatment systems, with a high number of available alternatives, not easily measurable and often presenting conflicting criteria. In this context, this work presents a literature review aiming to identify relevant economic, social, technical and environmental criteria, which can be used in the selection of WTS. Thus, 48 criteria were identified, as well and their importance was ranked according to a group of academics. Furthermore, an illustrative application was conducted considering 20 available WTS and 12 criteria. The ELECTRE 11 method was used to rank and allocate the most suitable WTS. This research contributes with a multi-criteria model for the evaluation of WTS and to show its relevance in a real world situation

Silk fibroin nanoparticles for drug delivery purposes : stabilization, incorporation and release design

Silk Fibroin (SF) has been extensively studied for various applications due to its impressive mechanical properties and biocompatibility. Recently, SF based-particles have been proposed as controlled drug delivery systems. A new and efficient method was developed to prepare SF nanoparticles (SF-NPs) by high pressure homogenization (HPH) emulsification, in oil-in-water emulsions (o/w). During the NPs production by HPH emulsification process, the secondary SF structure changed from random-coil conformation to a more stable structure, -sheets. To improve even more the NPs stability over time the effect of various surfactants was studied, namely poloxamer 407, transcutol, tween 80 and sodium dodecyl sulfate, in which SF nanoemulsions with 1% of transcutol demonstrated lower diameters and better polydispersity values during the 4 weeks of evaluation. The drug incorporation efficiency and release of SF-NPs was assessed using orange IV dye as model-drug. The influence of a human protease (human neutrophil elastase) on orange IV release profile was also evaluated. The encapsulation of orange IV effectively stabilized the size and size distribution of the SF-NPs over time, being evident the conformational change to -sheets. SF-NPs encapsulated with orange IV had a formation and encapsulation efficiency of 67% and 91%, respectively, with a controlled release over time. The stability and release profile induced by the SF-NPs enhances its potential for various applications, including biomedical

Parameterisation effect on the behaviour of a head-dependent hydro chain using a nonlinear model

This paper is on the problem of short-term hydro scheduling (STHS), particularly concerning a head-dependent hydro chain. We use a method based on nonlinear programming (NLP), namely quadratic programming, to consider hydroelectric power generation a function of water discharge and of the head. The method has been applied successfully to solve a test case based on a realistic cascaded hydro system with a negligible computational time requirement and is also applied to show that the role played by reservoirs in the hydro chain do not depend only on their relative position. As a new contribution to earlier studies, which presented reservoir operation rules mainly for medium and long-term planning procedures, we show that the physical data defining hydro chain parameters used in the nonlinear model have an effect on the STHS, implying different optimal storage trajectories for the reservoirs accordingly not only with their position in the hydro chain but also with the new parameterisation defining the data for the hydro system. Moreover, considering head dependency in the hydroelectric power generation, usually neglected for hydro plants with a large storage capacity, provides a better short-term management of the conversion of the potential energy available in the reservoirs into electric energy, which represents a major advantage for the hydroelectric utilities in a competitive electricity market

Short-term electricity prices forecasting in a competitive market: A neural network approach

This paper proposes a neural network approach for forecasting short-term electricity prices. Almost until the end of last century, electricity supply was considered a public service and any price forecasting which was undertaken tended to be over the longer term, concerning future fuel prices and technical improvements. Nowadays, short-term forecasts have become increasingly important since the rise of the competitive electricity markets. In this new competitive framework, short-term price forecasting is required by producers and consumers to derive their bidding strategies to the electricity market. Accurate forecasting tools are essential for producers to maximize their profits, avowing profit losses over the misjudgement of future price movements, and for consumers to maximize their utilities. A three-layered feedforward neural network, trained by the Levenberg-Marquardt algorithm, is used for forecasting next-week electricity prices. We evaluate the accuracy of the price forecasting attained with the proposed neural network approach, reporting the results from the electricity markets of mainland Spain and California

Environmental Risk Assessment Based on High-Resolution Spatial Maps of Potentially Toxic Elements Sampled on Stream Sediments of Santiago, Cape Verde

Geochemical mapping is the base knowledge to identify the regions of the planet with critical contents of potentially toxic elements from either natural or anthropogenic sources. Sediments, soils and waters are the vehicles which link the inorganic environment to life through the supply of essential macro and micro nutrients. The chemical composition of surface geological materials may cause metabolic changes which may favor the occurrence of endemic diseases in humans. In order to better understand the relationships between environmental geochemistry and public health, we present environmental risk maps of some harmful elements (As, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, V, and Zn) in the stream sediments of Santiago, Cape Verde, identifying the potentially harmful areas in this island. The Estimated Background Values (EBV) of Cd, Co, Cr, Ni and V were found to be above the Canadian guidelines for any type of use of stream sediments and also above the target values of the Dutch and United States guidelines. The Probably Effect Concentrations (PEC), above which harmful effects are likely in sediment dwelling organisms, were found for Cr and Ni. Some associations between the geological formations of the island and the composition of stream sediments were identified and confirmed by descriptive statistics and by Principal Component Analysis (PCA). The EBV spatial distribution of the metals and the results of PCA allowed us to establish relationships between the EBV maps and the geological formations. The first two PCA modes indicate that heavy metals in Santiago stream sediments are mainly originated from weathering of underlying bedrocks. The first metal association (Co, V, Cr, and Mn; first PCA mode) consists of elements enriched in basic rocks and compatible elements. The second association of variables (Zn and Cd as opposed to Ni; second PCA mode) appears to be strongly controlled by the composition of alkaline volcanic rocks and pyroclastic rocks. So, the second PCA mode is also considered as a natural lithogenic mode. The third association (Cu and Pb; third PCA mode) consists of elements of anthropogenic origin

Surface Photochemistry: 3,3′-Dialkylthia and Selenocarbocyanine Dyes Adsorbed onto Microcrystalline Cellulose

In this work, thia and selenocarbocyanines with n-alkyl chains of different length, namely with methyl, ethyl, propyl, hexyl and decyl substituents, were studied in homogeneous and heterogeneous media for comparison purposes. For both carbocyanine dyes adsorbed onto microcrystalline cellulose, a remarkable increase in the fluorescence quantum yields and lifetimes were detected, when compared with solution. Contrary to the solution behaviour, where the increase in the n-alkyl chains length increases to a certain extent the fluorescence emission ΦF and τF, on powdered solid samples a decrease of ΦF and τF was observed. The use of an integrating sphere enabled us to obtain absolute ΦF’s for all the powdered samples. The main difference for liquid homogeneous samples is that the increase of the alkyl chain strongly decreases the ΦF values, both for thiacarbocyanines and selenocarbocyanines. A lifetime distribution analysis for the fluorescence of these dyes adsorbed onto microcrystalline cellulose, evidenced location on the ordered and crystalline part of the substrate, as well as on the more disordered region where the lifetime is smaller. The increase of the n-alkyl chains length decreases the photoisomer emission for the dyes adsorbed onto microcrystalline cellulose, as detected for high fluences of the laser excitation, for most samples

Neuroanatomical pattern classification in a population-based sample of first-episode schizophrenia

AbstractRecent neuroanatomical pattern classification studies have attempted to individually classify cases with psychotic disorders using morphometric MRI data in an automated fashion. However, this approach has not been tested in population-based samples, in which variable patterns of comorbidity and disease course are typically found. We aimed to evaluate the diagnostic accuracy (DA) of the above technique to discriminate between incident cases of first-episode schizophrenia identified in a circumscribed geographical region over a limited period of time, in comparison with next-door healthy controls. Sixty-two cases of first-episode schizophrenia or schizophreniform disorder and 62 age, gender and educationally-matched controls underwent 1.5T MRI scanning at baseline, and were naturalistically followed-up over 1year. T1-weighted images were used to train a high-dimensional multivariate classifier, and to generate both spatial maps of the discriminative morphological patterns between groups and ROC curves. The spatial map discriminating first-episode schizophrenia patients from healthy controls revealed a complex pattern of regional volumetric abnormalities in the former group, affecting fronto-temporal-occipital gray and white matter regions bilaterally, including the inferior fronto-occipital fasciculus, as well as the third and lateral ventricles. However, an overall modest DA (73.4%) was observed for the individual discrimination between first-episode schizophrenia patients and controls, and the classifier failed to predict 1-year prognosis (remitting versus non-remitting course) of first-episode schizophrenia (DA=58.3%). In conclusion, using a “real world” sample recruited with epidemiological methods, the application of a neuroanatomical pattern classifier afforded only modest DA to classify first-episode schizophrenia subjects and next-door healthy controls, and poor discriminative power to predict the 1-year prognosis of first-episode schizophrenia