Sistema de Posicionamento Acústico e Transmissão de Dados para Alvos Subaquáticos

With the increasing usage of unmanned underwater vehicles, the need to develop the different systems associated with them is also growing. One of the most essential systems for an unmanned vehicle is its positioning system. Due to the inherent characteristics of the medium, the most common positioning method in aquatic environments involves the use of acoustic signals that use time-of-flight measurements to locate a target, referencing it to a set of sensors. This dissertation presents an acoustic positioning system for underwater vehicles based on the measurement of arrival delays of three acoustic signals originating from emitters with known positions on the surface, providing data transmission by periodically sending a modulated signal with position information. This system includes several components. Firstly, there are three stationary emitters on the surface responsible for the periodic sending of modulated acoustic signals. Then, there is a receiver and an emitter on the target, the former being responsible for the acquisition of acoustic signals and the latter for sending an acoustic signal with the coded position. Finally, there’s a receiver on the surface responsible for capturing the signal with the coded position. The developed detection, coding and decoding algorithms are presented, as well as the hyperbolic positioning algorithm, the latter implemented with a Kalman filter for the position estimation. In addition, the development of hardware to enable the sending and reception of the acoustic signals is also analyzed. To validate the developed system, results obtained in field tests and in a simulation environment are presented.Com o crescente uso de veículos subaquáticos não tripulados, cresce também a necessidade de desenvolver os diferentes sistemas a eles associados. Um dos sistemas mais importantes para um veículo não tripulado é o seu sistema de posicionamento. Devido `as características inerentes ao meio, o método de posicionamento mais comum em ambientes aquáticos envolve o uso de sinais acústicos que usam medições de tempo de voo para localizar um alvo, referenciando-o a um conjunto de sensores. Esta dissertação apresenta um sistema de posicionamento acústico para veículos subaquáticos com base na medição das diferenças de chegada de três sinais acústicos, originários de emissores com posições conhecidas na superfície, sistema esse que possibilita também a transmissão de dados através do envio periódico de um sinal modulado com informação da última posição estimada para o alvo. Na superfície, três emissores estacionários são responsáveis pelo envio periódico de sinais acústicos modulados. O alvo possui um recetor e um emissor, sendo o recetor responsável pela aquisição dos sinais acústicos e o emissor pelo envio de um sinal acústico modulado com a posição. Por fim, um receptor na superfície é responsável por capturar o sinal com a posição codificada. São aqui apresentados os algoritmos de detecção, codificação e descodificação desenvolvidos, assim como o algoritmo de posicionamento hiperbólico usado, implementado com um filtro Kalman para possibilitar a estimação da posição. Além disso, ´e analisado o desenvolvimento de hardware para permitir o envio e a recepção dos sinais acústicos. Para validar o sistema desenvolvido, são apresentados os resultados obtidos em testes de campo e num ambiente de simulação

Modeling Biomass Substrates for Syngas Generation by Using CFD Approaches

Recent reports from top universities state that in spite of having great national importance, there are dozens of fields of study that are suffering due to a lack of funding. Perhaps the greatest tool available to assist researchers with this regard is numerical simulation. This tool allows cutting costs, decreasing the necessary design cycle and allows an enormous amount of physical insight on the process itself). Numerical model’s ability to correctly predict a complex system was tested in this chapter by drawing from a previously developed computational fluid dynamics model for biomass gasification. Numerical results were compared with both experimental results (pilot scale plant) and available literature. Results from common Portuguese biomass substrates were found to be within a satisfactory margin of error of 20%. Influence of all major operational conditions was then investigated and the model was once again able to predict all the expected trends. All the relevant process products were also analyzed. Finally, the numerical model was coupled with an optimization model. Maximum efficiency value was found at 900°C with a SBR of 1.5 for MSW and 1 for forest residues. Results showed that numerical models could have a preponderant impact on biomass gasification field

Physical activity and affect of the elderly: Contribution to the validation of the Positive and Negative Affect Shedule (PANAS) in the Portuguese population

The concept of affect corresponds to the emotional dimension of subjective well-being (Diener, Emmons, Larsen, & Griffin, 1985). It is represented by two dimensions (negative affect and positive affect), which were the basis of the development of the Positive and Negative Affect Schedule - PANAS (Watson, Clark, & Tellegen, 1988). It was translated and validated for the Portuguese population by Galinha and Pais-Ribeiro (2005b). Nevertheless, because the Portuguese version was not validated in a sample of Portuguese elderly, the goals of this study consisted in the translation of the scale (PANAS) from the original version of 20 items and the validation of its measurement model (including a shortened version) for a sample of Portuguese elderly (n = 311), aged 60 years or older (M = 68.53; DP = 6.69); it was then tested by a confirmatory factorial analysis. The results demonstrated that the measurement model (two factors and 10 items) of the shortened Portuguese version of the PANAS presented acceptable psychometric qualities, which adjusted to the data in a satisfactory way (factorial weights ranging between .57 and .70 in positive affect and between .52 and .68 in negative affect). We also concluded that older adults who practice more physical activity perceive higher levels of positive affect F(2, 297) = 3,78, p < .05; η2 = .025, and lower levels of negative affect F (2, 297) = 6,24, p < .001; η2 = .040).This project was supported by the National Funds through FCT - Portuguese Foundation for Science and Technology (UID/DTP/04045/2019) - and the European Fund for regional development (FEDER) allocated by European Union through the COMPETE 2020 Programme (POCI-01-0145-FEDER-006969).info:eu-repo/semantics/publishedVersio

Hierarchical fuzzy logic based approach for object tracking

In this paper a novel tracking approach based on fuzzy concepts is introduced. A methodology for both single and multiple object tracking is presented. The aim of this methodology is to use these concepts as a tool to, while maintaining the needed accuracy, reduce the complexity usually involved in object tracking problems. Several dynamic fuzzy sets are constructed according to both kinematic and non-kinematic properties that distinguish the object to be tracked. Meanwhile kinematic related fuzzy sets model the object's motion pattern, the non-kinematic fuzzy sets model the object's appearance. The tracking task is performed through the fusion of these fuzzy models by means of an inference engine. This way, object detection and matching steps are performed exclusively using inference rules on fuzzy sets. In the multiple object methodology, each object is associated with a confidence degree and a hierarchical implementation is performed based on that confidence degree.info:eu-repo/semantics/publishedVersio

Automatic histogram threshold using fuzzy measures

In this paper, an automatic histogram threshold approach based on a fuzziness measure is presented. This work is an improvement of an existing method. Using fuzzy logic concepts, the problems involved in finding the minimum of a criterion function are avoided. Similarity between gray levels is the key to find an optimal threshold. Two initial regions of gray levels, located at the boundaries of the histogram, are defined. Then, using an index of fuzziness, a similarity process is started to find the threshold point. A significant contrast between objects and background is assumed. Previous histogram equalization is used in small contrast images. No prior knowledge of the image is required.info:eu-repo/semantics/publishedVersio

Goal Content for the practice of physical activity and the impact on subjective well-being in older adults

The main goal of this study consisted in an analysis of the impact that the goal content that leads to the practice of physical activity in the elderly population can play on the variables that constitute subjective well-being, as well as to analyze the differences in these variables’ levels according to the amount of physical activity practiced. A total of 300 individuals participated in this study (n=300), including 238 females and 62 males, aged between 60 and 90 years old (M = 68.59; DP = 6.54), who practice differing levels of physical activity. The results enable us to conclude that the goal content for the practice of physical activity has positive effects on the perception of satisfaction with life and on affect. To the same extent, they verify that health is the motivation that has the greatest weight on the practice of physical activity. We also concluded that elderly people who practice more physical activity perceive higher levels of satisfaction with life and positive affect, and lower levels of negative affectinfo:eu-repo/semantics/publishedVersio

Analysing the effects of different types of exercise on dyspnoea and fatigue in adults through COPD - systematic review and meta-analysis of randomised clinical trials

Background: Chronic obstructive pulmonary disease (COPD) is a heterogeneous lung condition, the main symptoms of which are dyspnoea and fatigue. Though exercise has been recommended for subjects with COPD, its benefits remain unclear. The aim of this study was to summarise, through a systematic review and meta-analysis, the available evidence on the effects of aerobic, resistance, stretching, and combined exercise on the main symptoms of COPD. Methods: Search was performed using the electronic databases PubMed and Web of Science. Randomised controlled trials (RCTs) with interventions based on aerobic, resistance and/or combined exercise published until July 2022 were identified. The effects were summarised based on standardised mean differences (95% confidence intervals) using random and fixed effect models. Results: Eight studies were selected, including a total of 375 subjects. The results obtained showed that resistance exercise, aerobic exercise and combined exercise seem to improve dyspnoea and fatigue symptoms in COPD subjects. Conclusions: In general, we can conclude that exercise-based interventions appear to improve the main COPD symptoms and may benefit quality of life in this population.info:eu-repo/semantics/publishedVersio

FIRE DESIGN OF STEEL BEAMS WITH SLENDER CROSS-SECTION, The influence of loading

The present paper addresses the study of laterally unrestrained steel beams with slendercross-sections for the case of fire with special focus on the influence of loading. A numerical investigation of several beams submitted to triangular and bi-triangular end-moment distribution and uniformly distributed loads is carried out at elevated temperatures usingshell finite elements. The results are compared with the existing simplified beam design rules of Part 1.2 of Eurocode 3 and recent developments on the subject, as well as the utilization of the factor “f” which was developed to take into account the non-uniform bending diagrams but for stocky cross-sections (Class 1 and 2)

Behaviour of slender plates in case of fire of different stainless steel grades

Stainless steel has countless desirable characteristics for a structural material. Alt-hough initially more expensive than conventional carbon steel, stainless steel structures can be competitive because of their smaller or none need for thermal protection material and lower life-cycle cost, thus contributing to a more sustainable construction. Regarding structural fire re-sistance, in order to have a comprehensive understanding of the overall members’ resistance, it is important to first analyse the cross-section resistance, directly affected by local instabilities oc-currence on the composed thin plates. This work presents a numerical study on the behaviour of isolated plates at elevated temperatures, corresponded to the web (internal element) and flanges (outstand element) of I-cross sections, comparing the numerically obtained ultimate load bearing capacities with simplified calculation formulae for the application of the effective width method. Comparisons between the numerical results and the EC3 formulae for determining the effective area of thin plates is also presented.publishe