Paralelismo de inversores monofásicos, isolados ou em conexão com a rede, com otimização da resposta dinâmica

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Para uma gramática da produção: análise da marca mesmo sob o enfoque da teoria das operações predicativas e enunciativas

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

3D raytracing through homogeneous anisotropic media with smooth interfaces

O raio conectando dois pontos em um meio anisotrópico, homogêneo por partes e com variação lateral, é calculado utilizando-se técnicas de continuação em 3D. Se combinado com algoritmos para solução do problema de valor inicial, o método pode ser estendido para o cálculo de eventos qS₁ e qS₂. O algoritmo apresenta a mesma eficiência e robustez que implementações de técnicas de continuação em meios isotrópicos. Rotinas baseadas neste algoritmo têm várias aplicações de interesse. Primeiramente, na modelagem e inversão de parâmetros elásticos na presença de anisotropia. Em segundo lugar, as iterações de Newton-Raphson produzem atributos da frente de onda como vetor vagarosidade e a matrix hessiana do tempo de trânsito, quantidades que permitem determinar o espalhamento geométrico e aproximações de segunda ordem para o tempo de trânsito. Estes atributos permitem calcular as amplitudes ao longo do raio e investigar os efeitos da anisotropia no empilhamento CRS em modelos de velocidade simples.

Método heurístico para criação de linhas de trabalho em problemas de escalonamento de pessoal

Pós-graduação em Engenharia Mecânica - FEG

Switch allocation problems in power distribution systems

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Same-Destination-Intermediate Grouping vs. End-to-End Grouping for Waveband Switching in WDM Mesh Networks

We investigate waveband switching (WBS) with different grouping strategies in wavelength-division multiplexing (WDM) mesh networks. End-to-end waveband switching (ETEWBS) and same-destination-intermediate waveband switching (SD-IT-WBS) are analyzed and compared in terms of blocking probability and cost savings. First, an analytical model for ETEWBS is proposed to determine the network blocking probability in a mesh network. For SD-IT-WBS, a simple waveband switching algorithm is presented. An analytical model to determine the network blocking probability is proposed for SD-IT-WBS based on the algorithm. The analytical results are validated by comparing with simulation results. Both results match well and show that ETE-WBS slightly outperforms SD-IT-WBS in terms of blocking probability. On the other hand, simulation results show that SD-IT-WBS outperforms ETE-WBS in terms of cost savings.

Decision-directed feedback equalisation for QAM signals

Proposed is a symbol-based decision-directed algorithm for blind equalisation of quadrature amplitude modulation (QAM) signals using a decision feedback scheme. Independently of QAM order, it presents: (i) an error equal to zero when the equaliser output coincides with the transmitted signal; (ii) simultaneous recovery of the modulus and phase of the signal; (iii) a misadjustment close to that of the normalised least-mean squares algorithm; (iv) fast convergence; and (v) the avoidance of degenerative solutions. Additionally, its stability is ensured when the step-size is properly chosen.

Asynchronous teams for joint lot-sizing and scheduling problem in flow shops

The integrated production scheduling and lot-sizing problem in a flow shop environment consists of establishing production lot sizes and allocating machines to process them within a planning horizon in a production line with machines arranged in series. The problem considers that demands must be met without backlogging, the capacity of the machines must be respected, and machine setups are sequence-dependent and preserved between periods of the planning horizon. The objective is to determine a production schedule to minimise the setup, production and inventory costs. A mathematical model from the literature is presented, as well as procedures for obtaining feasible solutions. However, some of the procedures have difficulty in obtaining feasible solutions for large-sized problem instances. In addition, we address the problem using different versions of the Asynchronous Team (A-Team) approach. The procedures were compared with literature heuristics based on Mixed Integer Programming. The proposed A-Team procedures outperformed the literature heuristics, especially for large instances. The developed methodologies and the results obtained are presented.

An analysis of automatic gender classification

[EN]Different researches suggest that inner facial features are not the only discriminative features for tasks such as person identification or gender classification. Indeed, they have shown an influence of features which are part of the local face context, such as hair, on these tasks. However, object-centered approaches which ignore local context dominate the research in computational vision based facial analysis. In this paper, we performed an analysis to study which areas and which resolutions are diagnostic for the gender classification problem. We first demonstrate the importance of contextual features in human observers for gender classification using a psychophysical ”bubbles” technique.

Two fluid numerical model for coastal applications

Wave breaking is an important coastal process, influencing hydro-morphodynamic processes such as turbulence generation and wave energy dissipation, run-up on the beach and overtopping of coastal defence structures. During breaking, waves are complex mixtures of air and water (“white water”) whose properties affect velocity and pressure fields in the vicinity of the free surface and, depending on the breaker characteristics, different mechanisms for air entrainment are usually observed. Several laboratory experiments have been performed to investigate the role of air bubbles in the wave breaking process (Chanson & Cummings, 1994, among others) and in wave loading on vertical wall (Oumeraci et al., 2001; Peregrine et al., 2006, among others), showing that the air phase is not negligible since the turbulent energy dissipation involves air-water mixture. The recent advancement of numerical models has given valuable insights in the knowledge of wave transformation and interaction with coastal structures. Among these models, some solve the RANS equations coupled with a free-surface tracking algorithm and describe velocity, pressure, turbulence and vorticity fields (Lara et al. 2006 a-b, Clementi et al., 2007). The single-phase numerical model, in which the constitutive equations are solved only for the liquid phase, neglects effects induced by air movement and trapped air bubbles in water. Numerical approximations at the free surface may induce errors in predicting breaking point and wave height and moreover, entrapped air bubbles and water splash in air are not properly represented. The aim of the present thesis is to develop a new two-phase model called COBRAS2 (stands for Cornell Breaking waves And Structures 2 phases), that is the enhancement of the single-phase code COBRAS0, originally developed at Cornell University (Lin & Liu, 1998). In the first part of the work, both fluids are considered as incompressible, while the second part will treat air compressibility modelling. The mathematical formulation and the numerical resolution of the governing equations of COBRAS2 are derived and some model-experiment comparisons are shown. In particular, validation tests are performed in order to prove model stability and accuracy. The simulation of the rising of a large air bubble in an otherwise quiescent water pool reveals the model capability to reproduce the process physics in a realistic way. Analytical solutions for stationary and internal waves are compared with corresponding numerical results, in order to test processes involving wide range of density difference. Waves induced by dam-break in different scenarios (on dry and wet beds, as well as on a ramp) are studied, focusing on the role of air as the medium in which the water wave propagates and on the numerical representation of bubble dynamics. Simulations of solitary and regular waves, characterized by both spilling and plunging breakers, are analyzed with comparisons with experimental data and other numerical model in order to investigate air influence on wave breaking mechanisms and underline model capability and accuracy. Finally, modelling of air compressibility is included in the new developed model and is validated, revealing an accurate reproduction of processes. Some preliminary tests on wave impact on vertical walls are performed: since air flow modelling allows to have a more realistic reproduction of breaking wave propagation, the dependence of wave breaker shapes and aeration characteristics on impact pressure values is studied and, on the basis of a qualitative comparison with experimental observations, the numerical simulations achieve good results.

A novel map-matching procedure for low-sampling GPS data with applications to traffic flow analysis

An extensive sample (2%) of private vehicles in Italy are equipped with a GPS device that periodically measures their position and dynamical state for insurance purposes. Having access to this type of data allows to develop theoretical and practical applications of great interest: the real-time reconstruction of traffic state in a certain region, the development of accurate models of vehicle dynamics, the study of the cognitive dynamics of drivers. In order for these applications to be possible, we first need to develop the ability to reconstruct the paths taken by vehicles on the road network from the raw GPS data. In fact, these data are affected by positioning errors and they are often very distanced from each other (~2 Km). For these reasons, the task of path identification is not straightforward. This thesis describes the approach we followed to reliably identify vehicle paths from this kind of low-sampling data. The problem of matching data with roads is solved with a bayesian approach of maximum likelihood. While the identification of the path taken between two consecutive GPS measures is performed with a specifically developed optimal routing algorithm, based on A* algorithm. The procedure was applied on an off-line urban data sample and proved to be robust and accurate. Future developments will extend the procedure to real-time execution and nation-wide coverage.

Dynamik diabatischer Rossby-Wellen

Diabatische Rossby-Wellen (DRWs) sind zyklonale Wirbel in der unteren Troposphäre, welche sich durch einen thermodynamisch-dynamischen Mechanismus kontinuierlich regenerieren und dabei schnell propagieren können. Vorangehende Untersuchungen schreiben derartigen zyklonalen Wirbeln das Potential zu, unter Wechselwirkung mit einer Anomalie an der Tropopause eine rapide Zyklonenintensivierung und folglich extreme Wetterereignisse hervorrufen zu können. DRWs wurden bisher meist in idealisierten Studien untersucht, woraus sich noch einige offene Fragen zu diesem Phänomen, besonders in realen Modelldaten, ergeben.rnrnIm Mittelpunkt dieser Arbeit steht die Fallstudie einer DRW, die im Dezember 2005 über dem Nordatlantik auftrat. Der Lebenszyklus des Systems ist über mehrere Tage und durch verschiedene Phasen verfolgbar und resultiert in einer explosiven Druckvertiefung. Zur Untersuchung der Fallstudie wurde mit operationellen Daten eines Globalmodelles sowie mit den Resultaten eines feinskaligeren Regionalmodelles gearbeitet, auf welche unterschiedliche Analysewerkzeuge angewendet wurden. rnrnDie eingehende Untersuchung der Propagationsphase der DRW bekräftigte das Vorhandensein von genügend Feuchte und Baroklinität als essentiell für den Propagationsmechanismus und die Intensität der DRW. Während der Propagationsphase arbeitet der selbsterhaltende DRW-Mechanismus unabhängig von einer von den Wellen an der Tropopause ausgehenden Anregung. Sensitivitätsstudien mit dem Regionalmodell, in denen die Umgebungsbedingungen der DRW lokal modifiziert wurden, ergaben, dass die Propagation einen relativ robusten Ablauf darstellt. Dementsprechend war in den vier untersuchten operationellen Vorhersagen die Propagationsphase gut wiedergegeben, während die rapide Intensivierung, wie sie gemäß den Analysen aufgetreten ist, von zwei der Vorhersagen verfehlt wurde.rnrnBei der Untersuchung der Intensivierungsphase stellten sich die Position und die zeitliche Abstimmung der Bewegung der Anomalie an der Tropopause relativ zur DRW in der unteren Troposphäre sowie die Stärke der Systeme als entscheidende Einflussfaktoren heraus. In den Entwicklungen der Sensitivitätssimulationen deutete sich an, dass ein unabhängig von der DRW an geeigneter Position entstandener zyklonaler Wirbel konstruktiver zu einer starken Zyklonenintensivierung beitragen kann als die DRW.rnrnIm zweiten Teil der Arbeit wurde ein Datensatz über die Nordhemisphäre für die Jahre 2004-2008 hinsichtlich des geographischen Vorkommens und der Intensivierung von DRWs untersucht. DRWs ereigneten sich in diesem Zeitraum über dem Atlantik (255 DRWs) halb so oft wie über dem Pazifik (515 DRWs). Ihre Entstehungsgebiete befanden sich über den Ostteilen der Kontinente und den Westhälften der Ozeane. Die Zugbahnen folgten größtenteils der baroklinen Zone der mittleren Breiten. Von den erfassten DRWs intensivierten sich im Atlanik 16% zu explosiven Tiefdruckgebieten, über dem Pazifik liegt der Anteil mit 11% etwas niedriger. Damit tragen DRWs zu etwa 20% der sich explosiv intensivierenden außertropischen Zyklonen bei.

Surgical planning tool for robotically assisted hearing aid implantation

PURPOSE : For the facilitation of minimally invasive robotically performed direct cochlea access (DCA) procedure, a surgical planning tool which enables the surgeon to define landmarks for patient-to-image registration, identify the necessary anatomical structures and define a safe DCA trajectory using patient image data (typically computed tomography (CT) or cone beam CT) is required. To this end, a dedicated end-to-end software planning system for the planning of DCA procedures that addresses current deficiencies has been developed. METHODS :    Efficient and robust anatomical segmentation is achieved through the implementation of semiautomatic algorithms; high-accuracy patient-to-image registration is achieved via an automated model-based fiducial detection algorithm and functionality for the interactive definition of a safe drilling trajectory based on case-specific drill positioning uncertainty calculations was developed. RESULTS :    The accuracy and safety of the presented software tool were validated during the conduction of eight DCA procedures performed on cadaver heads. The plan for each ear was completed in less than 20 min, and no damage to vital structures occurred during the procedures. The integrated fiducial detection functionality enabled final positioning accuracies of [Formula: see text] mm. CONCLUSIONS :    Results of this study demonstrated that the proposed software system could aid in the safe planning of a DCA tunnel within an acceptable time.

Problems in the classical calculus of variations

This dissertation concerns convergence analysis for nonparametric problems in the calculus of variations and sufficient conditions for weak local minimizer of a functional for both nonparametric and parametric problems. Newton's method in infinite-dimensional space is proved to be well-defined and converges quadratically to a weak local minimizer of a functional subject to certain boundary conditions. Sufficient conditions for global converges are proposed and a well-defined algorithm based on those conditions is presented and proved to converge. Finite element discretization is employed to achieve an implementable line-search-based quasi-Newton algorithm and a proof of convergence of the discretization of the algorithm is included. This work also proposes sufficient conditions for weak local minimizer without using the language of conjugate points. The form of new conditions is consistent with the ones in finite-dimensional case. It is believed that the new form of sufficient conditions will lead to simpler approaches to verify an extremal as local minimizer for well-known problems in calculus of variations.

Reading on LCD vs e-Ink displays: effects on fatigue and visual strain

Purpose:  Most recently light and mobile reading devices with high display resolutions have become popular and they may open new possibilities for reading applications in education, business and the private sector. The ability to adapt font size may also open new reading opportunities for people with impaired or low vision. Based on their display technology two major groups of reading devices can be distinguished. One type, predominantly found in dedicated e-book readers, uses electronic paper also known as e-Ink. Other devices, mostly multifunction tablet-PCs, are equipped with backlit LCD displays. While it has long been accepted that reading on electronic displays is slow and associated with visual fatigue, this new generation is explicitly promoted for reading. Since research has shown that, compared to reading on electronic displays, reading on paper is faster and requires fewer fixations per line, one would expect differential effects when comparing reading behaviour on e-Ink and LCD. In the present study we therefore compared experimentally how these two display types are suited for reading over an extended period of time. Methods:  Participants read for several hours on either e-Ink or LCD, and different measures of reading behaviour and visual strain were regularly recorded. These dependent measures included subjective (visual) fatigue, a letter search task, reading speed, oculomotor behaviour and the pupillary light reflex. Results:  Results suggested that reading on the two display types is very similar in terms of both subjective and objective measures. Conclusions:  It is not the technology itself, but rather the image quality that seems crucial for reading. Compared to the visual display units used in the previous few decades, these more recent electronic displays allow for good and comfortable reading, even for extended periods of time.