1,721,537 research outputs found
Effects of sitting posture and seat backrest on the biodynamic response of the human body and the prediction of spinal forces during vertical whole-body vibration
No full textBiodynamic models have been developed to predict the dynamic spinal forces induced by whole-body vibration but the effects of sitting posture and backrest conditions on these forces are unclear. The main objectives of the research reported in thesis were to advance understanding of: (i) how sitting posture and contact with a backrest affect the biodynamic responses of the human body, and (ii) the effects of sitting posture and backrests on spinal forces during exposure to vertical whole-body vibration.Experimental measurements found that the apparent mass of the body and transmissibilities to the spine (to the pelvis, L5, L3, and T5) are affected by the presence of a vertical backrest or an inclined backrest (inclined by 10º, 20º, and 30º). An inclined backrest induced a broad peak, or even two peaks, around 4 to 8 Hz in the vertical apparent mass at the seat pan, probably because the backrest separated the body modes contributing to the principal resonance around 5 Hz evident when sitting with no backrest. Sitting with either vertical or inclined backrests increased vertical motions of the pelvis and the spine.Leaning forward in an ‘anterior leaning’ sitting posture increased the frequency of the principal resonance in the vertical apparent mass at the seat, possibly due to increased tension in back muscles. Leaning forward in ‘anterior leaning’ or ‘kyphotic leaning’ postures induced a resonance around 2.5 Hz in the vertical apparent mass at the seat pan, due to excitation of body modes at frequencies less than 5 Hz associated with fore-and-aft motions of the pelvis and the spine. Changing sitting posture changes muscle activity. Tensing muscles in the lower body (including the lower lumbar spine, pelvis, and thighs), or tensing muscles in the whole body (the lower and upper torso), produces similar increases in the frequency of the principal resonance in the vertical apparent mass at the seat around 5 Hz. This suggests tensing muscles in the lower body causes a greater increase in the frequency of the principal resonance than tensing muscles in upper body. Biodynamic models of the seated human body that included forces from muscles were developed to fit the measured responses of the body (apparent mass and transmissibilities) in the various sitting conditions (normal and leaning forward, vertical and inclined backrests). The spinal forces in the vertical and fore-and-aft directions at the L5/S1 intervertebral disc were estimated from the sum of the predicted static and dynamic forces in both directions. In each sitting condition, a linear model was used to predict the frequency-dependent transfer function between the vertical seat acceleration and the dynamic forces in the spine. For the sitting conditions studied in this research, the contributions from the muscles to static spinal forces were comparable to the forces from gravity of the body mass supported on the intervertebral disc. Dynamic muscle forces were predicted to contribute significant dynamic spinal forces in the vertical and fore-and-aft directions during vertical whole-body vibration.Varying the sitting conditions varied the spinal forces predicted by the models, both with and without exposure to vibration. Transfer functions between vertical seat acceleration and dynamic spinal forces showed one or two resonances around 4 to 8 Hz. The resonance frequency in the transfer function between vertical seat acceleration and dynamic vertical spinal force increased with increasing inclination of a backrest, similar to the effect of backrest inclination on the vertical apparent mass at the seat pan. Compared to a normal sitting posture, sitting with 20º-inclined backrest increased the predicted static and dynamic spinal forces in the spine in the vertical and fore-and-aft directions, due to increased forces at the backrest and increased motion of the spine in both directions. Forward leaning sitting postures increased the fore-and-aft motions of the spine and increased the fore-and-aft dynamic spinal forces predicted by the model.It is concluded that sitting posture and contact with vertical or inclined backrests alter the biodynamic responses of the seated human body. The changes arise from several mechanisms including the backrest supporting some of the body mass, changes in static muscle activity, changes in dynamic muscle activity, and changes in the modes of vibration in the body. These mechanisms are also responsible for predicted changes in the forces in the spine during vertical whole-body vibration
Effect of backrest inclination on apparent mass at seat and the backrest during vertical whole-body vibration
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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
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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