1,720,955 research outputs found
Still air resistance during walking and running
Full text link: In everyday life during terrestrial locomotion our body interacts with two media opposing the forward movement of the body: the ground and the air. Whereas the work done to overcome the ground reaction force has been extensively studied, the work done to overcome still air resistance has been only indirectly estimated by means of theoretical studies and by measurements of the force exerted on puppets simulating the geometry of the human body. In this study, we directly measured the force exerted by still air resistance on eight male subjects during walking and running on an instrumented treadmill with a belt moving at the same speed of a flow of laminar air facing the subject. Overall, the coefficient of proportionality between drag and velocity squared (Aeff) was smaller during running than walking. During running Aeff decreased progressively with increasing average velocity up to an apparently constant, velocity independent value, similar to that predicted in the literature using indirect methods. A predictive equation to estimate drag as a function of the speed and the height of the running subject is provided
Tidal expiratory flow-limitation induces expiratory looping of the alveolar pressure-flow relation in COPD patients
Full text linkDuring spontaneous breathing at rest the alveolar pressure (Palv) - flow (V̇) relation exhibits a prominent expiratory loop in many COPD patients. Among the possible determinants of the loop, tidal expiratory flow-limitation (tEFL) may be the main responsible. To compare the characteristics of the expiratory loop in COPD patients with flow-limitation (FL) and without flow-limitation (NFL), tEFL was assessed with the negative expiratory pressure technique in stable, mild to very severe COPD patients, undergoing body-plethysmography before and after bronchodilation (BD), an intervention which is able to reduce mechanical heterogeneity, recruitment/derecruitment and gas trapping, but rarely abolishes tEFL. The magnitude of the expiratory loop was indexed by the integral of Palv on V̇ during expiration (Aexp). Before BD, Aexp was 360% greater in FL (n=35) than in NFL (n=25) patients (P<0.001). After BD, Aexp was unchanged in NFL patients (ΔAexp 0%, P=0.882) and slightly decreased in FL patients who remained FL (n=32, ΔAexp -17%, P=0.064). Three FL patients became NFL after BD, and their Aexp decreased markedly (ΔAexp -61%), reaching values similar to those observed in NFL patients at baseline. In conclusion, the greater Aexp measured in FL relative to NFL COPD patients, its relative invariance after BD when flow-limitation persists, and its fall when flow-limitation is abolished indicate that tEFL is a major determinant of the magnitude of the expiratory loop. Furthermore, Aexp can be used as a predictor of the presence of tEFL
Heliox administration in anesthetized rabbits with spontaneous inspiratory flow limitation
Full text linkWe investigated the effects of heliox administration (80% Helium in O2) on tidal inspiratory flow limitation (tIFL) occurring in supine anesthetized spontaneously breathing rabbits, regarded as an animal model of obstructive apnea-hypopnea syndrome. 22 rabbits were instrumented to record oro-nasal mask flow, airway opening, tracheal and esophageal pressures and diaphragm and genioglossus electromyographic activities while breathing either room air or heliox, and, in 12 rabbits, also during the application of continuous positive airway pressure (CPAP; 6 cmH2O). For the group, heliox increased peak inspiratory flow, ventilation (18±11%), peak inspiratory tracheal and dynamic transpulmonary pressures, but in no animal eliminated tIFL, as instead CPAP did in all. Muscle activities were unaffected by heliox. In the presence of IFL the increase in flow with heliox (ΔV̇IFL) varied markedly among rabbits (2 to 49%), allowing the distinction between responders and non-responders. None of the baseline variables discriminated responders and non-responders. However, fitting the Rohrer equation (R=K1+K2V̇) to the tracheal pressure-flow relationship over the first 0.1s of inspiration while breathing air allowed such discrimination on the basis of larger K2 in responders (0.005±.002 vs 0.002±.001 cmH2O·s2·ml-2; p<0.001), suggesting a corresponding difference in the relative contribution of laminar and turbulent flow. The differences in ΔV̇IFL between responders and non-responders were simulated by modeling the collapsible segment of the upper airways as a non-linear resistor and varying its pressure-volume curve, length and diameter, thus showing the importance of mechanical and geometrical factors in determining the response to heliox in the presence of tIFL
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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