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Optimal force profiles at the center of mass to reduce the energy cost of walking with unilaterally reduced push-off
No full textIndividuals with neurological impairments (e.g., post-stroke) exhibit elevated metabolic energy costs during walking. A substantial amount of this energy could be due to the mechanical work required to redirect the body’s center of mass (COM) with each step. It has been recently found that it is possible to reduce the metabolic cost of walking by 12% in individuals post-stroke with a waist tether. Since this passive device could not control or alter the timing, we expect that there is a lot of room for improvement by optimizing force profiles to reduce metabolic cost. The purpose of this study was to investigate the effects of sinusoidal force profiles on the metabolic cost by applying horizontal propulsive forces at the COM during walking with unilaterally reduced ankle mechanical power output. Results of a case study indicate that horizontal forces applied at the COM, which coincide with the acceleration phase of the COM reduced metabolic cost by 37% during walking with restricted ankle plantarflexion range of motion and ankle power generation. Determining the optimal assistance profiles from this study could guide the development of assistive rehabilitation devices
Effects of Ankle Exoskeleton Power and Actuation Timing on Movement Variability and Metabolic Cost of Walking
No full textWalking is one of the most primal movements and an essential part of everyday life. While humans use many strategies to reduce metabolic energy cost, walking still requires a considerable amount of metabolic energy. Lower extremity exoskeletons have become an established technology designed to reduce metabolic cost. Recently, it was reported that they might increase the variability of the locomotor system making the system more noisy and unstable, but optimal assistance properties for gait variability remain unclear. This could be a main concern for people with a mobility disorder. We investigated the effect of ankle exoskeleton power and actuation timing on gait variability and metabolic energy cost of walking. Data was collected for ten healthy participants wearing a powered ankle-foot exoskeleton during a 4-minute treadmill walking trial at 1.25 m∙s-1 in ten different assistance conditions. Largest Lyapunov exponent (LyE) was calculated to quantify the pattern of stride-to-stride fluctuations of the ankle angle kinematics. The metabolic rate and LyE were compared between conditions. Optimal assistance was achieved at 42% of the stride and average power of 0.4 W∙kg-1 for both the LyE and metabolic rate. This resulted to a 50% lower LyE and a 21% reduction in metabolic cost compared to walking with the exoskeleton deactivated. These results emphasize the importance of optimizing exoskeleton actuation properties to provide a more stable and metabolic efficient human locomotor system
Effects of Timing and Magnitude of Waist Pulling Assistance on Metabolic Cost and Joint Mechanics
No full textDuring walking, the need to generate muscular forces creates a metabolic demand. Studies showed that a constant forward traction force applied at the waist can reduce metabolic cost. However, there is limited information about the effects of non-constant traction forces. The purpose of the current study was to investigate the effects of timing and magnitude of different forward force profiles on metabolic cost. We developed an attachment structure that allows applying forward force profiles from a cable-pulling robot. We developed a controller that applied 33 force profiles as a function of step time. We measured rates of oxygen consumption and carbon dioxide production. Steady-state metabolic cost for each condition was estimated using a method for estimating instantaneous metabolic cost. Preliminary results indicate that conditions with higher horizontal forces and longer assistance durations have higher reductions in metabolic cost, and timings that overlap with the deceleration phase of the center-of-mass increased metabolic cost. Determining the optimal assistance profiles from this study could guide the development of powered walkers and assistive rehabilitation devices
Setting Expansion Characteristics of Three Phosphate-Bonded Investment Materials Used with High Fusing High-Noble Alloys, Cobalt-Chrome Alloys and Heat-Pressed Lithium Disilicate Ceramics
Get PDFThe purpose of this study was to investigate the setting expansion characteristics of three commercially available phosphate bonded investment materials for casting high fusing alloys and heat pressed lithium disilicate. The experimental groups in this study were P90 (Powercast 90% Special Liquid for Cobalt-Chrome alloys), P60 (Powercast 60% Special Liquid for High Noble Gold alloys), FF75 (FastFire 15 75% Special Liquid for Cobalt-Chrome alloys), FF50 (FastFire 15 50% Special Liquid for High Noble Gold alloys), and PVS (PressVest Speed 60% Special Liquid for Lithium Disilicate Veneers, Partial Crowns and Single Crowns). Twenty specimens per group were poured in a trough that conformed to ADA Specification No. 2 for the measurement of the linear setting expansion of gypsum bonded investments. Measurements of the setting expansion were taken at 2, 4, 6, 8, 12, and 24 hours after mixing.
A one sample T-Test revealed that the setting expansion measured for all of the groups was statistically significant and that all of the groups exhibited statistically significant differences in setting expansion at the manufacturer���s recommended burn-out time from the setting expansion reported by the manufacturer (P���0.01).
P90, P60, FF50 and PVS showed less expansion than is required in order to fully compensate for solidification shrinkage during the casting procedures. FF75 was the only group that managed to fully compensate for the solidification shrinkage of the alloy it is intended for (P���0.01).
The delayed burn-out times evaluated in this study resulted in significantly different setting expansion for PVS. A statistically significant difference was detected after 4 hours. The dimension of the PVS specimens did not change significantly after 4 hours. No such difference in setting expansion at delayed burn-out times could be detected for P90, P60, FF75 & FF50 (P���0.01).
Within the limitations of this study, the setting expansion of the phosphate bonded investment materials tested could not fully compensate for the solidification shrinkage of the alloys except for FF75. Delayed burn-out times resulted in significantly different setting expansion for PVS. Significant differences at delayed burn-out times could not be detected for the rest of the groups
Energetics of Walking with Waist Pulling Assistance
No full textDuring walking, the need to generate muscular forces creates a metabolic demand. Changes in energy requirements during locomotion have been examined on uphill and downhill gradients and at different speeds. One interesting walking condition occurs when an external force is applied in the horizontal direction such that the propulsion required for locomotion is reduced. The purpose of this study is to investigate the effects of waist pulling assistance on metabolic energy cost during walking. It is hypothesized that a horizontal assist force in the direction of walking will result in metabolic energy cost reduction, and external work from the waist tether will be correlated to reduction in metabolic cost
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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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