Browsing by Author "Silva, Pedro"
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- Analysis and quantification of damage in polymer composite materialsPublication . Durão, Luís Miguel; Matos, João E.; Silva, PedroThe specific characteristics of composite materials, like carbon fibre reinforced plastics, have been leading to their rising importance and widespread use. As these parts are normally produced in a nearnet shape, secondary operations, like drilling, are necessary prior to their assembly in complex structures. It is still difficult to define a machining process that enables free damage holes, due to the peculiar laminar nature of these materials. So, the definition of a drilling process that minimizes delamination and increases reliability in produced parts combined with satisfactory cost and productivity is still of major importance in the composites manufacturing industry. In this paper two sets of unidirectional coupons from plates with carbon fibre as reinforcement and epoxy resin as matrix, are drilled using five different drilling tool strategies and two feed rates for uneven damage extension. One of the strategies is the use of a pre-drilling option. Then the delamination is assessed using enhanced radiography and, finally, two diverse mechanical tests are performed on the resulting coupons: three point bending and pin bearing. The results allowed establishing and modelling, with the help of statistical tools, the relations between the damaged area caused by drilling and the material’s mechanical resistance. The bending resistance does not vary greatly with the damage area. On the other hand, the bearing resistance decreases with the increase of the damaged area.
- Atividade física na gravidez e a sua influência nos ganhos ponderaisPublication . Santos, Paula Clara; Couto, Miriam; Soares, Luísa; Abreu, Sandra; Moreira, Carla; Silva, Pedro; Ferreira, Margarida; Santos, Rute; Moreira, Pedro; Montenegro, Nuno; Mota, JorgeComparativamente às grávidas com um peso saudável, as grávidas com excesso de peso ou obesidade têm um aumentado de diabetes gestacional, pré-eclâmpsia, parto induzido, cesariana, prematuridade e macrossomia. Existem várias recomendações quanto à prática de atividade física. Vários estudos revelam que esta prática tem efeitos positivos no que diz respeito ao cumprimento das recomendações do ganho ponderal na gravidez. No entanto, alguns estudos revelaram não haver diferenças no ganho ponderal materno entre grávidas que praticam e as que não praticam exercício.
- Compliance with physical activity guidelines in preschool childrenPublication . Vale, Susana; Silva, Pedro; Santos, Rute; Soares-Miranda, Luisa; Mota, JorgeThe aims of this study were (1) to document differences in physical activity (both total and moderate-to-vigorous physical activity) between the sexes on weekdays and weekend days in preschoolers, and (2) to assess compliance with recommendations for total physical activity (National Association for Sport and Physical Education guidelines) and moderate-to-vigorous physical activity on weekdays and weekend days in the same children. The sample comprised 245 preschoolers (105 girls, 140 boys) aged 3.5-6.0 years old. Physical activity was assessed using an Actigraph accelerometer. Data were analysed with specific software and activity was measured as counts per minute. An independent t-test and general linear model with repeated-measures were used to assess differences between the sexes and differences between days (weekdays and weekend days) within each sex, respectively. A chi-square test was used to determine differences between the sexes in the proportion of children complying with physical activity guidelines. In both sexes, sedentary behaviour accounted for the majority of the time on weekdays and weekend days (weekdays: 83%; weekend days: 83.9%). Boys engaged in significantly more (P < 0.05) total physical activity and moderate-to-vigorous physical activity than girls (weekdays: boys 155.4 min vs. girls 128.22 min; weekend days: boys 111.2 min vs. girls 90.5 min). On average, preschool children engaged in significantly more (P < 0.05) total physical activity and moderate-to-vigorous physical activity on weekdays than weekend days. Altogether, 74.3% and 93.5% of the children met the National Association for Sport and Physical Education guidelines and moderate-to-vigorous physical activity recommendations respectively on weekdays, whereas compliance with both recommendations was substantially less in both sexes on weekend days. The results of this study suggest that despite 83% of time during the day being spent in sedentary behaviour, most preschool children met the daily physical activity and moderate-to-vigorous physical activity recommendations on weekdays. Future research should consider the two constructs of physical activity and sedentary behaviour independently, as they might not necessarily counteract each other.
- Impact of compliance with different guidelines on physical activity during pregnancy and perceived barriers to leisure physical activityPublication . Santos, Paula Clara; Abreu, Sandra; Moreira, Carla; Lopes, Diana; Santos, Rute; Alves, Odete; Silva, Pedro; Montenegro, Nuno; Mota, JorgeThe aims of the this prospective study were to analyze physical activity (PA) engagement during the first and second trimesters, considering the different guidelines published on PA, to document the individual characteristics associated with the accomplishment of these guidelines and to examine pregnant women’s perceived barriers to leisure PA, using a socioecological framework. A sample of 133 pregnant women in two stages – at 10–12 weeks’ gestation (T1) and 20– 22 weeks’ gestation (T2) – were evaluated. PA was assessed by accelerometry during the T1 and T2 evaluation stages. Socio-demographic characteristics, lifestyle factors and barriers to leisure PA were assessed via questionnaire. A large proportion of women (ranging from 32% to 96%) did not reach the levels of PA recommended by the guidelines. There were no significant differences between T1 and T2 with regard to compliance with PA recommendations. A decrease in PA levels from T1 to T2 was noted for all recommendations. No associations were found between participants’ characteristics and adherence to the recommendations in T1 and T2. No significant differences were found in barriers to leisure PA between T1 and T2. The most commonly reported barriers to leisure PA were intrapersonal, not health related. Our results indicate that there were no differences between trimesters regarding compliance of PA recommendations, and perceived barriers were similar in both trimesters.
- Impact of drought periods on hydroelectric production in Portugal: A Study from 2015 to 2017Publication . Sousa, José; Adrego, Miguel; Silva, Pedro; Faria, Pedro; Vale, ZitaThe production of hydroelectric power is strongly affected due to periods of drought. In Portugal there are about forty-nine hydroelectric plants with installed capacity of more than 10MW. In the year 2017 the generation of electricity in Portugal was 54.52 TWh, of which about 14% was hydroelectric production reflecting a year below normal in hydroelectric power production. This article discusses the impact of drought periods on hydroelectric power production in Portugal, which address the importance of hydroelectric production in Portugal. Among the factors influencing the production of hydroelectric power, a method is presented for analysis of a dry month through the monthly precipitation indicators, energy production by monthly technology and energy price. These indicators were presented and analyzed in three case studies presented in this article. A solution is also presented to reduce the impact of drought periods on Hydro production.
- MAQUITEX 2015 - Feira de máquinas, tecnologia e acessórios para a indústria têxtil, de confeção, vestuário e bordadosPublication . Silva, PedroO objetivo deste trabalho é a realização de um estudo de caso sobre a organização de feiras e exposições b2b. Para isso, utilizou-se como base de estudo a Maquitex - Feira de Máquinas, Tecnologia e Acessórios para a Indústria Têxtil, de Confeção, Vestuário e Bordados. Este estudo de caso representa uma abordagem metodológica de investigação, utilizando múltiplas fontes de evidência qualitativas (aplicação prática de conhecimentos, observação, entrevistas) e quantitativa (breve análise através de inquéritos). Neste estudo pode perceber-se a importância do papel da organização na elaboração de uma feira e/ou exposição b2b, observando-se uma organização baseada numa sequência de quatro fases, a saber: (1) iniciação ao projeto feira; (2) planeamento; (3) execução e controlo; e (4) encerramento. Além disso, verifica-se também a relevância de uma organização assente numa estratégia focada em dois públicos paralelos: os expositores e os visitantes. Em cada uma das fases, apresentam-se detalhes pertinentes para atender simultaneamente aos interesses dos expositores e dos visitantes, promovendo a máxima interação entre ambos. Na prática, este estudo poderá ser um excelente contributo para os organizadores de feiras, disponibilizando um conjunto de informações importantes para o lançamento e estruturação de uma feira.
- Preschool children physical activity measurement: importance of epoch length choicePublication . Vale, Susana; Santos, Rute; Silva, Pedro; Soares-Miranda, Luísa; Mota, JorgeThe purpose of this study was twofold: first to document the gender differences in Moderate to Vigorous Physical Activity (MVPA) according to two epoch systems (5 vs. 60 s) in preschoolers, and, second to document the differences in physical activity (PA) patterns according to two different epoch choices. The sample comprised 59 preschoolers (31 girls) aged 2-5 years old. PA was assessed by accelerometer during school hours. The time spent in MVPA was significantly higher (p < .001) when a 5-s epoch was considered compared to the 60-s epoch, regardless gender. Further, it was found a difference of ?17 min difference between the 2 epoch systems for MVPA. Different epoch times might affect the time spent in MVPA among preschool children.
- The impact of digitalisation on entrepreneurshipPublication . Oliveira, Xavier; Silva, PedroThis article intends to analyse and critically discuss the state of the art of scientific literature concerning digitalisation and its impact on entrepreneurship. The study adopts a systematic literature review, relating the concepts, studying their impact on economic development, and enumerating the variables that may serve as indicators. Data was collected using the Prism method, which allowed a total of 561 articles (from 2006 to 2022) which 13 were used for analysis. The article guides researchers towards a better understanding of the concepts through the systematisation of several investigations carried out so far, also allowing the delineation of the relations between both and their impact on economic development. The articles are clustered into the following themes: i) the relationship between entrepreneurship and digitalisation; ii) the impact of digitalisation and entrepreneurship on economic development; iii) variables that may serve as gauges of the impact on economic development.
- The importance of physical education classes in pre-school childrenPublication . Vale, Susana; Santos, Rute; Soares-Miranda, Luísa; Silva, Pedro; Mota, JorgeThe purpose of this study was to analyse differences between total physical activity (TPA) and moderate-to-vigorous PA (MVPA) of pre-school children during daily school hours when they attended the physical education class (PED) and school days without PE class (NPED) and to assess the contribution of PE classes to TPA in school hours. The sample was composed of 193 pre-school healthy children (96 girls) aged from three to five years old and was conducted between February and December of 2008. Children wore accelerometers for at least four consecutive days during school hours. Data were analysed with specific software, age-specific counts-per-minute cut-off points and a 5 s epoch were used. Independent and general linear model repeated measures were used to assess differences between gender and differences between different days within each gender, respectively. Boys engaged more MVPA than girls (P < 0.05). During PED, pre-school children engaged significantly more in TPA and MVPA than during NPED (P < 0.05). PE class contributed, on average, 27.7% for the TPA and 32.8% of daily MVPA during PED in both gender. The results of this study suggest that structured PA such as a PE class increased the daily TPA and MVPA level of pre-school children.
- Using social media and social entrepreneur’s network to increase resources: what’s it worth?Publication . Bernardino, Susana; Santos, José de Freitas; Silva, PedroResources are scarce, but critical for social the social entrepreneur, as the lack of them may undermine the accomplishment of the activities and mission of the social venture. This investigation aims to examine the extent to which the social entrepreneur reliance on its personal network and social media affects its capacity to attract resources for the social organization. For this purpose, a structural equation model was estimated based on data collected from a survey administered to a sample of Portuguese social organizations. The results show that social entrepreneur’s network linkages have a direct and an indirect effect on resources. Directly, the governance of the social entrepreneur’s linkages with new and actual stakeholders seems to attract more resources for the social organization. The indirect impact on resources occurs via social media usage: first, by managing and establishing relationships with new stakeholders; second, by managing the personal linkages with the current network of stakeholders.