Cinemática e dinâmica de engrenagens - 6. Análise dinâmica de engrenagens

[Excerto] 6.1. INTRODUÇÃO Como é sabido, as engrenagens são sistemas mecânicos utilizados para transmitir potência e movimento entre os órgãos motor e movido. Tal como acontece em outros sistemas mecânicos de transmissão de movimento, o projeto e dimensionamento dos componentes que constituem as engrenagens assenta no conhecimento das forças que se desenvolvem durante o seu funcionamento (Shigley e Mischke, 1989; Wilson e Sadler, 1993). No caso das engrenagens, a determinação das forças que atuam nos dentes depende das condições de funcionamento e do tipo de dentado. Na verdade, o correto conhecimento da magnitude e do sentido de atuação das diversas componentes da força de engrenamento é de primordial importância, pois permite a determinação dos esforços que atuam nos dentes, nos veios que suportam as rodas dentadas, e nos respetivos apoios dos veios. Com efeito, conhecidas cargas que se desenvolvem nas engrenagens é possível efetuar o cálculo dos dentes, o dimensionamento dos veios e a seleção dos apoios (Branco et al., 2009). (...

Cinemática e dinâmica de engrenagens - 5. Engrenagens de parafuso sem-fim

[Excerto] 5.1. INTRODUÇÃO As engrenagens de parafuso sem-fim pertencem ao grupo das engrenagens torsas1, em que uma das rodas tem a forma de um parafuso (Branco et al., 2009). As engrenagens de parafuso sem-fim podem também ser consideradas como um caso particular das engrenagens helicoidais cruzadas, sendo que a capacidade de carga é maior no caso do parafuso sem-fim (Flores e Gomes, 2014c). A figura 5.1 ilustra uma engrenagem de parafuso sem-fim com roda helicoidal. Na verdade, esta é uma das formas mais simples e mais frequentemente utilizada na prática corrente e que inclui um parafuso cilíndrico e uma roda cilíndrica de dentes helicoidais, daí a designação de parafuso sem-fim roda helicoidal (Niemann, 1971; Drago, 1988). Na grande maioria das aplicações de parafusos sem-fim o ângulo formado pelos eixos do parafuso e da roda é igual a 90º. As engrenagens de parafuso sem-fim não são, em geral, reversíveis, isto é, funcionam apenas quando o veio motor aciona o parafuso sem-fim, uma vez que quando o sistema é acionado pela roda, a engrenagem tende a bloquear2 (Henriot, 1979; Shigley e Uicker, 1980). (...

Gold or silver nanoparticles decorating superparamagnetic calcium ferrite nanoparticles for application in SERS

In this work, we report the synthesis of Ag and Au nanoparticles capped with either cysteamine or cysteine. Purification of these NPs turned out to originate irreversible aggregation, so that the coupling of NH2 groups from Au (or Ag) nanoparticles to OH groups of magnetic calcium ferrite (CaFe2O4) nanoparticles (MNPs) would not work as expected. Therefore, naked metallic Ag or Au nanoparticles were produced and connection to calcium ferrite was performed by first attaching cysteine to the MNPs and then using the resulting SH pending groups to interact with the metallic surface.Financial support by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding of CF-UM-UP (UID/FIS/04650/2013).info:eu-repo/semantics/publishedVersio

Órgãos de máquinas II: exercícios de aplicação

Este documento contém um vasto conjunto de exercícios de aplicação no âmbito dos sistemas de transmissão (Correias, Correntes e Engrenagens), da unidade curricular Órgãos de Máquinas II do Mestrado Integrado em Engenharia Mecânica da Universidade do Minho

Developing scaffolds for tissue engineering using the Ca2+-induced cold gelation by an experimental design approach

The Ca2+-induced cold gelation technique was found suitable to prepare highly porous biodegradable scaffolds based on bovine serum albumin (BSA) and alpha-casein from bovine milk for tissue engineering. A 23 full factorial design was used to study the influence and impact of each factor on the several responses of the scaffolds. In vitro degradation (ID), swelling ratio (SR), porosity (PO), and pore size (PS) as well cytotoxicity (CT) were evaluated and shown to be dependent on the pH of sample preparation and on the amount of BSA and casein present, making these scaffolds tunable structures. Under optimized working conditions (4.19% of BSA, 0.69% of Casein, pH 7.07), the ID attained was 37.97%, the SR observed was 11.87, the PO was 82.11%, the PS measured was 180.63 μm at surface, and 175.91 μm at fracture, whereas maximum cell viability was 84% in comparison to controls. Moreover, the scaffold supported cell adhesion and proliferation. These results, consistent with the prediction by the experimental design approach, support the use of this methodology to develop tunable scaffolds for tissue engineering using the Ca2+-induced cold gelation.Contract grant sponsor: FEDER through POFC-COMPETE and by national funds from FCT; contract grant number: PEst-C/BIA/UI4050/201

A Hybrid Experimental-numerical Sif Determination Technique

AbstractHybrid methods, wherefore numerical and experimental data are used to calculate a critical parameter, have been used for several years with great success in Experimental Mechanics and, in particular, in Facture Mechanics. This letter reports on the development of a hybrid methodology for the determination of the stress intensity factor (SIF) parameter, which entails combining experimental and numerical procedures to compute the SIF based of linear elastic fracture-mechanics concepts

Resilience and adaptation in the face of climate change: the Douro wine bio- cultural landscape

The Douro wine region is one of the most important Portuguese wine regions, and the oldest demarcated wine region in the world. The evolving and living cultural landscape resulted from a symbiotic relationship between human and nature, that has proven, through time, to be sustainable and resilient was, in 2001, recognized as a UNESCO world heritage site. Climate change effects represent a growing/global concern, since more frequent and extreme climate events are expected, that can go beyond the natural ecosystem?s resilience, posing additional risks to vine and wine production, that may request the implementation of urgent adaptation measures. This threat has even more importance in communities that mostly depend on the wine industry, as is the case of the Douro Valley. The evaluation of natural systems resilience to different climate change scenarios, and the how to improve this natural capital, must be a starting point for wine producers, to the local economy agents, and to society at large, before considering more structural and costly adaptation measures. The aim of the present paper is to analyse the journey of the Douro Valley, to identify local resilience factors to climate change, and to discuss how they can contribute to mitigate the consequences or effects of future climate change scenarios.Financial support from National Funds of the FCT – Portuguese Foundation for Science and Technology within the project UID/ECO/03182/2019, UIDB/04011/2020 and UID/SOC/04011/2019 is acknowledged

Classifying heart sounds using multiresolution time series motifs : an exploratory study

The aim of this work is to describe an exploratory study on the use of a SAX-based Multiresolution Motif Discovery method for Heart Sound Classification. The idea of our work is to discover relevant frequent motifs in the audio signals and use the discovered motifs and their frequency as characterizing attributes. We also describe different configurations of motif discovery for defining attributes and compare the use of a decision tree based algorithm with random forests on this kind of data. Experiments were performed with a dataset obtained from a clinic trial in hospitals using the digital stethoscope DigiScope. This exploratory study suggests that motifs contain valuable information that can be further exploited for Heart Sound Classification

Classifying heart sounds using SAX motifs, random forests and text mining techniques

In this paper we describe an approach to classifying heart sounds (classes Normal, Murmur and Extra-systole) that is based on the discretization of sound signals using the SAX (Symbolic Aggregate Approximation) representation. The ability of automatically classifying heart sounds or at least support human decision in this task is socially relevant to spread the reach of medical care using simple mobile devices or digital stethoscopes. In our approach, sounds are firrst pre-processed using signal processing techniques (decimate, low-pass filter, normalize, Shannon envelope). Then the pre-processed symbols are transformed into sequences of discrete SAX symbols. These sequences are subject to a process of motif discovery. Frequent sequences of symbols (motifs) are adopted as features. Each sound is then characterized by the frequent motifs that occur in it and their respective frequency. This is similar to the term frequency (TF) model used in text mining. In this paper we compare the TF model with the application of the TFIDF (Term frequency - Inverse Document Frequency) and the use of bi-grams (frequent size two sequences of motifs). Results show the ability of the motifs based TF approach to separate classes and the relative value of the TFIDF and the bi-grams variants. The separation of the Extra-systole class is overly dificult and much better results are obtained for separating the Murmur class. Empirical validation is conducted using real data collected in noisy environments. We have also assessed the cost-reduction potential of the proposed methods by considering a fixed cost model and using a cost sensitive meta algorithm.Portuguese Funds through the FCT - Fundacao para a Ciencia e a Tecnologia (proj. FCOMP-01-0124-FEDER-037281 and FCOMP-01-0124-FEDER-PEst-OE/EEI/UI0760/2014)