Estudo de diversos conceitos de eficiência da locomoção humana no meio aquático

Uma das áreas de interesse na linha fronteira entre a Biomecânica e a Fisiologia é o estudo da eficiência. Considerase que a eficiência expressa uma relação objectiva e quantitativa entre o trabalho mecânico realizado e o gasto energético que se lhe encontra associado. O estudo da eficiência em actividades realizadas no meio aquático torna-se ainda mais complexo devido à dificuldade de quantificar objectivamente as trocas energéticas entre o nadador e o meio envolvente. No entanto, a Natação Pura Desportiva é uma das modalidades mais profícuas no estudo das suas implicações bioenergéticas e das repercussões em termos de eficiência dos diferentes processos de locomoção. Assim, foi objectivo do presente trabalho efectuar uma revisão do actual “estado da arte” sobre o estudo da locomoção humana n

Economia de nado e tempo limite à velocidade mínima de vo2max: novas descobertas

A economia de nado é uma área de investigação que teve como pioneiros, em Portugal, Vilas- Boas (1993) e Alves (1995). Passada uma década, novos momentos experimentais foram realizados e resultados up to date foram obtidos. As mais recentes metodologias foram empregues e, inclusivamente, uma nova área de treino parece ter emergido - o tempo até à exaustão à intensidade de nado correspondente à Potencia Aeróbia, isto é, ao consumo máximo de oxigénio (VO2max)

Determinant kinantropometric factors in swimming

O objetivo deste trabalho é apresentar uma revisão bibliográfica das principais características cineantropométricas do nadador e a forma como estas influenciam a sua prestação na modalidade. As principais conclusões obtidas foram as seguintes: (i) os nadadores são mais altos e pesados do que a população em geral; (ii) os nadadores apresentam um elevado índice envergadura/altura, explicitando valores elevados do diâmetro biacromial e do comprimento dos MS; (iii) verifica-se uma elevada razão entre os diâmetros biacromial e bicristal, traduzindo um fator decisivo na modalidade: a promoção de um coeficiente de arrasto inferior; (iv) foram observados elevados valores de comprimento e superfície dos membros dos nadadores (afetando positivamente a sua capacidade propulsiva); (v) os nadadores de elite apresentam um somatótipo médio ecto-mesomorfo e as nadadoras são centrais ou mesomorfas equilibradas; (vi) como grupo, os nadadores apresentam um maior percentual de massa gorda do que outros desportistas, fator este que poderá beneficiários relativamente à sua flutuabilidade.The aim of this work is to present a bibliographic review, based on the specialized literature, of the kineantropometric characteristics of swimmers and their importance for swimming performance. The main conclusions were: (i) swimmers are taller and heavier than the general population; (ii) swimmers present an high index of arm span/height (explained by a large biacromial diameter and long the upper arm); (iii) high values for the biacromial/bicristal diameter ratio were found, offering a lower drag coefficient; (iv) high length and surface area arm and leg values were observed (which positively influence their propulsion capacity); (v) elite male swimmers presents a ectomorph-endomorph somatotype and elite female swimmers are central or balanced mesomorphs (vi) swimmers exhibit a higher percentage of body mass than other athletes, which may benefit positively their floatation

Factores biomecânicos e bioenergéticos limitativos do rendimento em natação pura desportiva

Um dos objectivos prioritários da Biomecânica do Desporto é o de, num primeiro momento, caracterizar um determinado padrão motor e, num segundo momento, intervir no sentido de incrementar a efi ciência motora. Esse incremento da efi ciência do gesto tem como fi nalidade última permitir que o seu executante aceda a níveis superiores de rendimento desportivo. Do exposto, emerge a ideia que a Biofísica encontrase numa linha fronteira entre a Mecânica Clássica e a Fisiologia. Neste contexto, a Natação Pura Desportiva é uma das modalidades mais profícuas no estudo das implicações bioenergéticas e das repercussões em termos de efi ciência dos diferentes modelos de locomoção. Foi objectivo do presente trabalho efectuar uma revisão do actual “estado da arte” sobre a relação que se estabelece entre o rendimento desportivo, as características bioenergéticas e biomecânicas em Natação Pura Desportiv

Relationships between some well known indicators of aerobic resistance of swimmers

The concept of the anaerobic threshold (AT) at swimming velocity corresponding to 4 mmol.l-1 blood lactate concentrations (v4), introduced by Mader et al. (1976) and further developed by following authors, was used by a large number of scientists and swimming coaches for training and diagnostic purposes. Although it's considered a good indicator of aerobic capacity of swimmers, some authors disagree of that fixed value, arguing that the individual AT varies a lot, namely between 2 and 5 mmol.l-1 (Madsen e Lohberg, 1987). The purpose of this study is to verify the adequacy of the v4 in swimming, comparing it with two other valid indicators of the AT: critical velocity (cv) and the mean velocity of the 30 min test (vT30). Subjects were 30 juvenile swimmers of the Porto regional swimming team (with ages between 12 and 15 years). V4 was determined according to the 2 x 400m protocol, being the first repetition performed at 85% of the personal best and the second one at maximum speed (a rest period higher than 30 min was respected between repetitions). Samples of 25 μl of capillary blood were collected at 3, 5 and 7 min of recovery and analysed for blood lactate concentration with an Accusport analyser (Boheringer Manheim). CV was assessed based in the results of maximal tests of 100 e 400m and was considered as the slope of the regression line calculated between the test distances and the respective times. The ratio between the distance achieved and the duration of the test, i.e., 30 min of continuous swimming assessed the vT30. The mean values of the different variables are presented in Table 1. These results showed that the mean values of v3, v4 and v5, cv and vT30 are very similar; only v8 is statistically different of some other parameters (v3, v4, cv and vT30). We can also see strong positive correlation (r³0.91) between all the parameters (with exception of v8) regardless the stronger values between V5 and the other two tests.info:eu-repo/semantics/publishedVersio

Síntese de grafenos por HFCVD

Mestrado em Engenharia de Materiais - 2º CicloAs técnicas de deposição comummente usadas para a síntese de grafenos são a deposição química em fase vapor por activação térmica (Thermal CVD) e a baixa pressão (Low Pressure CVD). Os catalisadores mais utilizados para a síntese de grafenos são o cobre e o níquel, que apresentam diferentes mecanismos de crescimento desta estrutura. Este trabalho teve como objectivo a síntese de grafenos por deposição química em fase vapor (CVD – Chemical Vapour Deposition) assistida por filamento quente (HF – Hot Filament), uma técnica ainda não explorada para esta finalidade. Placas de cobre e níquel bem como filmes finos destes metais depositados sobre substratos de Si/SiO2, por deposição física em fase vapor assistida com magnetrão (Magnetron Sputtering PVD) foram usados como substratos para a síntese de grafenos. Partindo de parâmetros de deposição utilizados para o crescimento de grafenos por TCVD, identificaram-se condições para o crescimento de grafenos por HFCVD. Avaliou-se o efeito da temperatura do substrato (Ts- 650-1000°C), pressão total (100-200mbar), razão de gases (2-20%CH4 e 0-40%Ar) e tempo de deposição (5-15min), mantendo constante a temperatura do filamento (Tf- 2300°C). Os substratos e os filmes metálicos foram caracterizados por microscopia electrónica de varrimento (SEM – Scanning Electronic Microscopy), microscopia de força atómica (AFM – Atomic Force Microscopy) e difracção de raios-X (XRD – X-Ray Diffraction) de forma a avaliar as alterações na morfologia, cristalinidade e estrutura de fases. As estruturas obtidas nas diversas tentativas de síntese por HFCVD, foram caracterizadas utilizando microscopia óptica (MO) e espectroscopia μ-Raman. Dos substratos escolhidos para a síntese de grafenos, apenas as placas de níquel apresentaram resultados promissores. Os filmes finos de cobre e níquel degradaram-se em condições de deposição e nas placas de cobre apenas foi possível sintetizar grafite amorfa. Desta forma, o estudo da síntese de grafenos incidiu na deposição em placas de níquel. Nestes substratos foi possível crescer grafite pirolítica com elevado grau de orientação (HOPG – Highly Oriented Pyrolitic Graphite) e grafeno identificado como FLG’s (Few layer Graphene), tendo-se obtido estruturas com apenas duas camadas de grafeno. Com este trabalho foram sintetizados pela primeira vez grafenos por HFCVD. A possibilidade de obter placas de níquel com tamanho de grão milimétrico, demonstrada neste trabalho, alarga o espectro de possibilidades que esta técnica permitirá.Graphene is a material that usually is grown using CVD techniques such as thermal CVD (TCVD) and low pressure CVD (LPCVD). Copper and nickel are common substrates used as catalyzers having different growth mechanisms. This work aimed synthesizing graphene using hot filament chemical vapor deposition (HFCVD), a technique yet to be explored for the synthesis of this material. Nickel and copper foils, and films deposited by magnetron sputtering PVD on Si/SiO2 were used as substrates for graphene growth. Starting from parameters reported on literature for TCVD, conditions have been optimized to grow graphene by HFCVD. Filament temperature (Tf - 2300°C) was kept constant while varying substrate temperature (Ts – 650-1000°C), pressure (100-200mbar), gas ratio (2-20%CH4 and 0-40%Ar) and time (5-15min). Substrates were characterized by optical microscopy (OM), scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD) to evaluate the morphology, crystallinity and phase structure. After that, carbon structures formed during the deposition process were evaluated and characterized firstly by optical microscopy followed by μ-Raman spectroscopy. From all the substrate chosen to grow graphene, only nickel foils presented the most promising results. Thin films of copper and nickel degraded during the deposition process, and on copper foils only amorphous graphite has been grown. Therefore, this work was mainly focused on graphene growth on nickel foils as substrates, where bilayer graphene as well as HOPG (Highly Oriented Pyrolitic Graphite) were grown. For the first time graphene layers were synthetized using HFCVD. The capability of producing nickel foils with grain size in the range of millimeters, also shown on this work, extends the range of possibilities allowed by this technique in future works

Anúncios de recompra e preço das ações : uma análise para o mercado brasileiro nos anos de 2007 a 2009

Trabalho de conclusão de curso (graduação)—Universidade de Brasília, Faculdade de Economia, Administração e Contabilidade, Departamento de Ciências Contábeis e Atuariais, Bacharelado em Ciências Contábeis, 2013.A recompra de ação por uma empresa faz com que aumente o preço da ação devido ao fato da quantidade de ação existente no mercado diminuir sem que o patrimônio líquido da empresa se modifique, aumentando assim a participação do acionista na empresa, além de ser um meio de distribuir fluxo de caixa livre. Algumas teorias e o conceito de políticas de dividendos são abordados nesse trabalho para facilitar a compreensão dos impactos que um anúncio de recompra pode ter nos preços das ações. Esse trabalho analisa os anúncios de recompra realizado por empresas listadas na Bolsa de Valores de São Paulo (BOVESPA) no período de 26/07/2007 a 18/12/2009 para verificar se há efeito positivo ou negativo sobre os preços das ações na presença de tal evento. Para isso, a metodologia utilizada foi o estudo de evento que calculou os retornos normais e anormais de uma amostra de 46 eventos de 31 empresas diferentes. Desses eventos, 21 apresentaram retornos anormais positivos e 25 apresentaram retornos anormais negativos e as médias desses retornos foram respectivamente de 7,89% e de -8,67%. Os resultados encontrados não apresentaram evidência de que a recompra tem efeito positivo no retorno anormal das ações

Predicting the intra-cyclic variation of the velocity of the centre of mass from segmental velocities in butterfly stroke: a pilot study

The purpose of this study was to analyze the relationship between the intra-cycle variation of the horizontal velocity of displacement of the center of mass (dV), the hand’s and feet’s velocity, as well as, to identify the variables that most predict the dV’s, in butterfly stroke. The study was divided in two parts. The aim of Part I was to investigate the behavior of variables in study at slow swimming velocities and the purpose of Part II was the same but at high swimming velocities. 3 male Portuguese swimmers and 1 female swimmer, of international level were studied in Part I. The swimmers were submitted to an incremental set of 200 m butterfly swims. In the Part II, 7 Portuguese male swimmers of national and international level were studied. Each swimmer performed two maximal 25 m butterfly swims. Both protocols were recorded from four different plans, allowing a 3D analysis. It was calculated the dV, the 3D components (Vx, Vy, Vz) of the hand’s velocity and the 2D components (Vx, Vy) of the feet’s velocity. Several variables presented significant correlation coefficients with dV at all selected velocities (high velocity ranged from r = 0.58 for Vx-out to r = 0.82 for Vy-1dwn; slow velocity ranged from r = -0.45 for Vx-1dwn to r=0.73 for Vx-ups; overall velocity ranged from r= 0.34 for Vz-ent to r = 0.82 for Vx-ins). It was also computed a regression model to predict dV. For high velocity (up to 1.75 ± 0.09 m.s-1), the variables that best predict dV were Vy during the first downbeat, Vx and Vy during the arm’s insweep (r2 = 0.93). At slow velocity (up to 1.48 m.s-1), the variables included in the forward step-bystep regression model were Vx during upsweep, Vy and Vx during insweep (r2 = 0.69). For overall velocity, the variables that most fit the regression model were Vx during upsweep, Vy during second downbeat and Vz during entry (r2= 0.94). In order to reduce dV, butterfliers should increase hand’s velocity in all orthogonal components at the end of the underwater path, should increase the vertical velocity durin

Swimming bioenergetics: integrating biomechanical and physiological data into a coherent biophysical model for performance and training

The purpose of the present paper is to synthesise a number of scientific contributions of our research group, into a coherent corpus of knowledge related to swimming biophysics, specially centred on the availability and use of energy in swimming. After an introductory part that intends to underline the relevance of this approach base on the conceptualization of the swimmer, and swimming action itself, as a thermodynamic system and its mechanical output, we will survey a number of studies and respective contributions for a more advanced understanding of swimming performance, that can be transferred into training and enhancement of swimmers’ working capacity. Most of the studies referred were conducted over samples of swimmers of both genders and of different types, from university/participative swimmers to Portuguese elite swimmers, crossing the large population of trained national level swimmers. Those swimmers were studied in the four different competitive swimming strokes, accomplishing progressive protocols based over distances of 200 m. Physiologic parameters like VO2 (and associated ventilatory and respiratory parameters), post exercise capillary blood [La-] peaks, and heart rate, were directly measured. Kinematical parameters were also measured in the different studies, ranging from simple semi-quantitative parameters, like stroke length (SL), and stroke frequency (SF), to more elaborated biomechanical data, like intracyclic speed fluctuations and propulsive segments kinematics. The focus of interest ranged from swimming economy of different strokes and genders (and of different technical alternatives of the same stroke), to the effects over energy cost of intracyclic speed fluctuations. Energetic input determinant factors, like swimming VO2 kinetics, including VO2 slow component, and VO2 time limit, and its determinants, will also be analysed

The influence of stroke mechanics into energy cost of elite swimmers

The purpose of this study was to analyze the relationships between energy cost (C), swimming velocity (v), stroke frequency (SF) and stroke length (SL) in toplevel swimmers. Eighteen elite swimmers (four freestylers, five backstrokers, five breaststrokers and four butterflyers) performed an intermittent set of n 9 200 m swims (n B 8) with increasing velocity. The oxygen consumption was measured breath-by-breath by a portable metabolic cart (K4 b2, Cosmed, Rome, Italy). A respiratory snorkel and valve system with low hydrodynamic resistance was used to measure pulmonary ventilation and collect expiratory gases. Blood samples were taken from the ear lobe before and after each swim to analyze the blood lactate concentration (YSI 1500L, Yellow Springs, OH, USA). At Backstroke, Breaststroke and Butterfly strokes, increases of SF were associated to increases of C, even when controlling the v. The increases in SL only promoted significant decreases in the C in Breaststroke. There was a significant and polynomial relationship between v and SF for all competitive swimming techniques. The polynomial relationship between v and SL was significant only in Freestyle and Butterfly stroke. Partial correlations between v and SF controlling the effect of SL and between v and SL controlling the effect of SF, were positive and significant for all techniques. It is concluded that manipulation of stroke mechanics variables (SF and SL) may be one of the factors through which C in competitive swimming can be altered for a given v