1,720,981 research outputs found
Energetics of swimming at maximal speeds in humans
No full textThe energy cost per unit of distance (C-s, kilojoules per metre) of the front-crawl, back, breast and butterfly strokes was assessed in 20 elite swimmers. At sub-maximal speeds (nu), C-s was measured dividing steady-state oxygen consumption ((V) over dot O-2) by the speed (nu, metres per second). At supra-maximal nu, C-s was calculated by dividing the total metabolic energy (E, kilojoules) spent in covering 45.7, 91.4 and 182.9 m by the distance. E was obtained as: E = E-an + alpha(V) over dot O(2max)t(p) - alpha(V) over dot O(2max)tau(1 - e(-(tp/tau))), where E-an was the amount of energy (kilojoules) derived from anaerobic sources, (V) over dot O-2max litres per second was the maximal oxygen uptake, alpha (= 20.9 kJ . 1 O-2(-1)) was the energy equivalent of O-2, tau (24 s) was the time constant assumed for the attainment of (V) O-2max at muscle level at the onset of exercise, and t(p) (seconds) was the performance time. The lactic acid component was assumed to increase exponentially with t(p) to an asymptotic value of 0.418 kJ . kg(-1) of body mass for t(p) greater than or equal to 120 s. The lactic acid component of E-an was obtained from the net increase of lactate concentration after exercise (Delta[La](b)) assuming that, when Delta[La](b) = 1 mmol . 1(-1) the net amount of metabolic energy released by lactate formation was 0.069 kJ . kg(-1). Over the entire range of nu, front crawl was the least costly stroke. For example at 1 m . s(-1), C-s amounted, on average, to 0.70, 0.54, 0.82 and 0.124 kJ . m(-1) in front crawl, backstroke, butterfly and breaststroke, respectively; at 1.5 m . s(-1), C-s was 1.23, 1.47, 1.55 and 1.87 kJ . m(-1) in the four strokes, respectively. The C-s was a continuous function of the speed in all of the four strokes. It increased exponentially in crawl and backstroke, whereas in butterfly C-s attained a minimum at the two lowest nu to increase exponentially at higher nu. The C-s in breaststroke was a linear function of the nu, probably because of the considerable amount of energy spent in this stroke for accelerating the body during the pushing phase so as to compensate for the loss of nu occurring in the non-propulsive phase
Oxygen cost of dynamic leg exercise on a cycle ergometer: effects of gravity acceleration.
No full textA model of the metabolic internal power (Ė(int)) during cycling, which includes the gravity acceleration (a(g)) as a variable, is presented. This model predicts that Ė(int) is minimal in microgravity (0 g; g = 9.81 m s-2), and increases linearly with a(g), whence the hypothesis that the oxygen uptake (V̇O2) during cycling depends on a(g). Repeated V̇O2 measurements during steady-state exercise at 50, 75 and 100 W on the cycle ergometer, performed in space (0 g) and on Earth (1 g) on two subjects, validated the model. V̇O2 was determined from the time course of decreasing O2 fraction during rebreathing. The gas volume during rebreathing was determined by the dilution principle, using an insoluble inert gas (SF6). Average V̇O2 for subject 1 at each power was 0.99, 1.21 and 1.52 L min-1 at 1 g (n = 3) and 0.91, 1.13 and 1.32 L min-1 at 0 g (n = 5). For subject 2 it was 0.90, 1.12 and 1.42 L min-1 at 1 g, and 0.76, 0.98 and 1.21 L min-1 at 0 g. These values corresponded to those predicted from the model. Although resting V̇O2 was lower at 0 g than at 1 g, the net (total minus resting) exercise V̇O2 was still smaller at 0 g than at 1 g. This difference reflects the lower Ė(int) at 0 g
Muscular exercise at high altitude. IV. Oxygen transport system before and after exposure to chronic hypoxia
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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