The Experts below are selected from a list of 255 Experts worldwide ranked by ideXlab platform
Jill L. Mcnitt-gray - One of the best experts on this subject based on the ideXlab platform.
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Modification of Impulse Generation During Pirouette Turns With Increased Rotational Demands
Journal of applied biomechanics, 2016Co-Authors: Antonia M. Zaferiou, Rand R. Wilcox, Jill L. Mcnitt-grayAbstract:This study determined how dancers regulated angular and linear impulse during the initiation of pirouettes of increased rotation. Skilled dancers (n = 11) performed single and double pirouette turns with each foot supported by a force plate. Linear and angular impulses generated by each leg were quantified and compared between turn types using probability-based statistical methods. As rotational demands increased, dancers increased the net angular impulse generated. The contribution of each leg to net angular impulse in both single and double pirouettes was influenced by stance configuration strategies. Dancers who generated more angular impulse with the push leg than with the turn leg initiated the turn with the center of mass positioned closer to the turn leg than did other dancers. As rotational demands increased, dancers tended to increase the Horizontal Reaction force magnitude at one or both feet; however, they used subject-specific mechanisms. By coordinating the generation of Reaction forces between legs, changes in net Horizontal impulse remained minimal, despite impulse regulation at each leg used to achieve more rotations. Knowledge gained regarding how an individual coordinates the generation of linear and angular impulse between both legs as rotational demand increased can help design tools to improve that individual's performance.
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Modification of impulse generation during piqué turns with increased rotational demands.
Human movement science, 2016Co-Authors: Antonia M. Zaferiou, Rand R. Wilcox, Jill L. Mcnitt-grayAbstract:During initiation of a pique turn, a dancer generates impulse to achieve the desired lateral translation and whole-body rotation. The goal of this study was to determine how individuals regulate impulse generation when initiating pique turns with increased rotational demands. Skilled dancers (n=10) performed single (∼360°) and double (∼720°) pique turns from a stationary position. Linear and angular impulse generated by the push and turn legs were quantified using ground Reaction forces and compared across turn conditions as a group and within a dancer using probability-based statistical methods. The results indicate that as the rotation demands of the pique turn increased, the net angular impulse generated increased whereas net lateral impulse decreased. Early during turn initiation, the free moment contributed to angular impulse generation. Later during turn initiation, Horizontal Reaction forces were controlled to generate angular impulse. As rotational demands increased, the moment applied increased primarily from redirection of the Horizontal Reaction force (RFh) at the push leg and a combination of RFh magnitude and moment arm increases at the turn leg. RFh at each leg were coordinated to limit unwanted net linear impulse. Knowledge of observed subject-specific mechanisms is important to inform the design of turning performance training tools.
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Angular Impulse and Balance Regulation During the Golf Swing.
Journal of applied biomechanics, 2016Co-Authors: Travis J. Peterson, Rand R. Wilcox, Jill L. Mcnitt-grayAbstract:Our aim was to determine how skilled players regulate linear and angular impulse while maintaining balance during the golf swing. Eleven highly-skilled golf players performed swings with a 6-iron and driver. Components contributing to linear and angular impulse generated by the rear and target legs (resultant Horizontal Reaction force [RFh], RFh-angle, and moment arm) were quantified and compared across the group and within a player (α = .05). Net angular impulse generated by both the rear and target legs was greater for the driver than the 6-iron. Mechanisms used to regulate angular impulse generation between clubs varied across players and required coordination between the legs. Increases in net angular impulse with a driver involved increases in target leg RFh. Rear leg RFh-angle was maintained between clubs whereas target leg RFh became more aligned with the target line. Net linear impulse perpendicular to the target line remained near zero, preserving balance, while net linear impulse along the target line decreased in magnitude. These results indicate that the net angular impulse was regulated between clubs by coordinating force generation of the rear and target legs while sustaining balance throughout the task.
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Regulation of Reaction forces during the golf swing.
Sports biomechanics, 2013Co-Authors: Jill L. Mcnitt-gray, Joseph M. Munaretto, Antonia M. Zaferiou, Philip S. Requejo, Henryk FlashnerAbstract:During the golf swing, the Reaction forces applied at the feet control translation and rotation of the body-club system. In this study, we hypothesized that skilled players using a 6-iron would regulate shot distance by scaling the magnitude of the resultant Horizontal Reaction force applied to the each foot with minimal modifications in force direction. Skilled players (n = 12) hit golf balls using a 6-iron. Shot distance was varied by hitting the ball as they would normally and when reducing shot distance using the same club. During each swing, Reaction forces were measured using dual force plates (1200 Hz) and three-dimensional kinematics were simultaneously captured (110 Hz). The results indicate that, on average, the peak resultant Horizontal Reaction forces of the target leg were significantly less than normal (5%, p < 0.05) when reducing shot distance. No significant differences in the orientation of the peak resultant Horizontal Reaction forces were observed. Resultant Horizontal Reaction force-angle relationships within leg and temporal relationships between target and rear legs during the swing were consistent within player across shot conditions. Regulation of force magnitude with minimal modification in force direction is expected to provide advantages from muscle activation, coordination, and performance points of view.
Kang Yong Lee - One of the best experts on this subject based on the ideXlab platform.
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Effect of Horizontal Reaction force on the deflection of short simply supported beams under transverse loadings
International Journal of Mechanical Sciences, 2015Co-Authors: Kang Yong LeeAbstract:Abstract In the classical analysis of bending of a beam resting on simple supports, the effect of the Horizontal component of Reaction force is often neglected for small deflection analysis. This paper presents an adequate analysis of a simply supported beam with emphasis on the effect of the Horizontal Reaction force. Based on Timoshenko׳s kinematic relation, a governing equation is derived. Three typical cases including uniformly distributed loading, three-point bending and four-point bending are analyzed. Expressions for the bending deflection and the cross-section rotation are obtained and a non-linear load–deflection relation is derived. When neglecting the Horizontal force, the results available for Euler–Bernoulli and Timoshenko beams are recovered from the present. The influences of shear deformation and loading position on the transverse deflection are discussed. The deflection and load–maximum displacement curve are graphically presented. A comparison of the deflections with and without the Horizontal Reaction force and with experimental data is made. Obtained results are useful in safety design of linear and non-linear beams under complicated loading.
G.r. Olbright - One of the best experts on this subject based on the ideXlab platform.
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Trimethylamine alane for MOVPE of AlGaAs and vertical-cavity surface-emitting laser structures
Journal of Crystal Growth, 1992Co-Authors: Richard P. Schneider, R. P. Bryan, Eric D. Jones, Robert M. Biefeld, G.r. OlbrightAbstract:The use of trimethylamine alane (TMAAl) as an alternative to trimethylaluminum (TMAl) for low-pressure metalorganic vapor-phase epitaxy (MOVPE) of AlGaAs thin films has been studied in detail. AlGaAs layers were grown in a Horizontal Reaction chamber at 20–110 mbar with linear flow velocities as high as 3 m/s and growth temperatures in the range 650 ≤Tg≤750°C. Wafer thickness uniformity is acceptable only for the highest linear flow velocities. The 12 K photoluminescence spectra of the layers exhibit intense and narrow bound-exciton emission throughout the growth temperature range investigated. The luminescence linewidths observed are the narrowest to date for MOVPE-grown AlxGa1-xAs with x≥0.25. To assess the viability of this new source for the growth of advanced optoelectronic devices, several optically-pumped vertical-cavity surface-emitting laser structures were grown using TMAAl extensively. Room temperature lasing at 850 nm was reproducibly obtained, with a threshold pumping power comparable to similar structures grown by molecular beam epitaxy in our laboratories.
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Trimethylamine Alane for Low-Pressure Movpe Growth of AlGaAs-Based Materials and Device Structures
MRS Online Proceedings Library, 1991Co-Authors: Richard P. Schneider, R. P. Bryan, Eric D. Jones, Robert M. Biefeld, G.r. OlbrightAbstract:The use of trimethylamine alane (TMAAl) as an alternative to trimethylaluminum (TMAl) for low-pressure metalorganic vapor-phase epitaxy (MOVPE) of AlGaAs thin films as well as complex optoelectronic device structures has been studied in detail. AlGaAs layers were grown in a Horizontal Reaction chamber at 20–110 mbar with growth temperatures in the range 650°C≤T_G≤750°C. Wafer thickness uniformity is strongly dependent on growth pressure, and is acceptable only for the highest linear flow velocities. The 12K photoluminescence (PL) spectra of AlGaAs layers grown using TMAAl and TEGa exhibit uniformly intense and narrow bound-exciton emission throughout the growth temperature range investigated. To assess the viability of this new source for the low-pressure OMVPE growth of advanced optoelectronic devices, several optically-pumped vertical-cavity surface-emitting laser (VCSEL) structures were grown using TMAAl extensively. Room temperature lasing at 850 nm was reproducibly obtained from the VCSEL structures, with a threshold pumping power comparable to similar structures grown by molecular beam epitaxy in our laboratories.
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Trimethylamine alane for low-pressure MOVPE growth of AlGaAs-based materials and device structures
MRS Proceedings, 1991Co-Authors: Richard P. Schneider, R. P. Bryan, Eric D. Jones, R.m. Biefield, G.r. OlbrightAbstract:The use of trimethylamine alane (TMAA1) as an alternative to trimethylaluminum (TMA1) for low-pressure metalorganic vapor-phase epitaxy (MOVPE) of AlGaAs thin films as well as complex optoelectronic device structures has been studied in detail. AlGaAs layers were grown in a Horizontal Reaction chamber at 20--110 mbar with growth temperatures in the range 650{degrees}C {le} T{sub G} {le} 750{degrees}C. Wafer thickness uniformity is strongly dependent on growth pressure, and is acceptable only for the highest linear flow velocities. The 12K photoluminescence (PL) spectra of AlGaAs layers grown using TMAA1 and TEGa exhibit uniformly intense and narrow bound-exciton emission throughout the growth temperature range investigated. To assess the viability of this new source for the low-pressure OMVPE growth of advanced optoelectronic devices, several optically-pumped vertical-cavity surface-emitting laser (VCSEL) structures were grown using TMAA1 extensively. Room temperature lasing at 850 nm was reproducibly obtained from the VCSEL structures, with a threshold pumping power comparable to similar structures grown by molecular beam epitaxy in our laboratories.
Antonia M. Zaferiou - One of the best experts on this subject based on the ideXlab platform.
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Modification of Impulse Generation During Pirouette Turns With Increased Rotational Demands
Journal of applied biomechanics, 2016Co-Authors: Antonia M. Zaferiou, Rand R. Wilcox, Jill L. Mcnitt-grayAbstract:This study determined how dancers regulated angular and linear impulse during the initiation of pirouettes of increased rotation. Skilled dancers (n = 11) performed single and double pirouette turns with each foot supported by a force plate. Linear and angular impulses generated by each leg were quantified and compared between turn types using probability-based statistical methods. As rotational demands increased, dancers increased the net angular impulse generated. The contribution of each leg to net angular impulse in both single and double pirouettes was influenced by stance configuration strategies. Dancers who generated more angular impulse with the push leg than with the turn leg initiated the turn with the center of mass positioned closer to the turn leg than did other dancers. As rotational demands increased, dancers tended to increase the Horizontal Reaction force magnitude at one or both feet; however, they used subject-specific mechanisms. By coordinating the generation of Reaction forces between legs, changes in net Horizontal impulse remained minimal, despite impulse regulation at each leg used to achieve more rotations. Knowledge gained regarding how an individual coordinates the generation of linear and angular impulse between both legs as rotational demand increased can help design tools to improve that individual's performance.
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Modification of impulse generation during piqué turns with increased rotational demands.
Human movement science, 2016Co-Authors: Antonia M. Zaferiou, Rand R. Wilcox, Jill L. Mcnitt-grayAbstract:During initiation of a pique turn, a dancer generates impulse to achieve the desired lateral translation and whole-body rotation. The goal of this study was to determine how individuals regulate impulse generation when initiating pique turns with increased rotational demands. Skilled dancers (n=10) performed single (∼360°) and double (∼720°) pique turns from a stationary position. Linear and angular impulse generated by the push and turn legs were quantified using ground Reaction forces and compared across turn conditions as a group and within a dancer using probability-based statistical methods. The results indicate that as the rotation demands of the pique turn increased, the net angular impulse generated increased whereas net lateral impulse decreased. Early during turn initiation, the free moment contributed to angular impulse generation. Later during turn initiation, Horizontal Reaction forces were controlled to generate angular impulse. As rotational demands increased, the moment applied increased primarily from redirection of the Horizontal Reaction force (RFh) at the push leg and a combination of RFh magnitude and moment arm increases at the turn leg. RFh at each leg were coordinated to limit unwanted net linear impulse. Knowledge of observed subject-specific mechanisms is important to inform the design of turning performance training tools.
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Regulation of Reaction forces during the golf swing.
Sports biomechanics, 2013Co-Authors: Jill L. Mcnitt-gray, Joseph M. Munaretto, Antonia M. Zaferiou, Philip S. Requejo, Henryk FlashnerAbstract:During the golf swing, the Reaction forces applied at the feet control translation and rotation of the body-club system. In this study, we hypothesized that skilled players using a 6-iron would regulate shot distance by scaling the magnitude of the resultant Horizontal Reaction force applied to the each foot with minimal modifications in force direction. Skilled players (n = 12) hit golf balls using a 6-iron. Shot distance was varied by hitting the ball as they would normally and when reducing shot distance using the same club. During each swing, Reaction forces were measured using dual force plates (1200 Hz) and three-dimensional kinematics were simultaneously captured (110 Hz). The results indicate that, on average, the peak resultant Horizontal Reaction forces of the target leg were significantly less than normal (5%, p < 0.05) when reducing shot distance. No significant differences in the orientation of the peak resultant Horizontal Reaction forces were observed. Resultant Horizontal Reaction force-angle relationships within leg and temporal relationships between target and rear legs during the swing were consistent within player across shot conditions. Regulation of force magnitude with minimal modification in force direction is expected to provide advantages from muscle activation, coordination, and performance points of view.
K. Mori - One of the best experts on this subject based on the ideXlab platform.
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Application of a quasi-static stalk bending analysis to the dynamic response of rice and wheat stalks gathered by a combine harvester reel
Biosystems Engineering, 2004Co-Authors: Yasumaru Hirai, Eiji Inoue, K. MoriAbstract:Horizontal and vertical Reaction forces of rice and wheat stalks gathered by a combine harvester reel were measured by the experiment system, newly developed in order to clarify dynamic response of the crop stalks related to the gathering performance and to discuss the application of a quasi-static stalk bending analysis to the determination of the Reaction force of crop stalks under dynamic loading conditions. The experiment was conducted under five different loading speeds, and the effect of the loading speed on the Reaction force was investigated. As the loading speed increased, the Horizontal force had a large positive peak value, while the vertical force involved the change in the force direction and had a negative peak value, depending on the initial deflection shape of crop stalks. Thus, the results simulated by the stalk bending analysis involved a large amount of error, and limitations of the analytical method were identified. The experimental results were examined in terms of acceleration at the loading point during the gathering operation. The location of a positive peak in the Horizontal Reaction force and a negative peak in the vertical one coincided with that of the negative peak in the Horizontal acceleration and the positive peak in the vertical one, respectively. These results indicated that the peak values under high loading speeds were due to the effect of the inertial force of the crop stalks. Further, the error in the simulated results under high loading speeds was investigated in terms of the direction of the acceleration force determined by the difference between the simulated and measured values. The direction of the acceleration force coincided with the loading direction during the gathering operation, and the error was shown to be the force required for the accelerated motion.
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Analysis of Reaction Forces and Posture of a Bunch of Crop Stalks during Reel Operations of a Combine Harvester
Agricultural Engineering International: The CIGR Journal, 2002Co-Authors: Yasumaru Hirai, Eiji Inoue, K. Mori, Kouichi HashiguchiAbstract:The purpose of the present study is to clarify reel operations appropriate to crop conditions, such as a crop’s physico-mechanical properties and the extent of lodging, from the viewpoint of the mechanical interactions between the crops and a combine harvester reel. First, because the gathering processes by the reel involve mechanical op-erations of forced displacement, the Horizontal and vertical Reaction forces of a bunch of crop stalks (rice and wheat stalks) undergoing the forced displacement were measured. Further, a bunch of crop stalks, which has conventionally been complicated in dealing, was considered as a composition of a single crop stalk, and the Reaction forces of crop stalks were analyzed numerically using a differential equation describing deflection, which was derived based on a mechanical model of a crop stalk. As the results, the Horizontal Reaction forces increased linearly with the in-crement of forced displacement (deflection), while the vertical ones changed its direc-tion and magnitude depending on relationship between crop posture and frictional force. The simulated results of the trends of the Reaction forces agreed approximately with measured ones. This suggested that the analytical method of determining Reaction forces based on the derived equation could be utilize for investigating reel-crop interactions. This paper also presents posture analysis of a bunch of crop stalks during gathering op-erations.
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Reaction FORCE OF WHEAT STALKS DURING THE REEL OPERATION OF A COMBINE HARVESTER
International Conference on Crop Harvesting and Processing, 1Co-Authors: Yasumaru Hirai, Eiji Inoue, K. MoriAbstract:The purpose of this study is to clarify gathering operations appropriate to crop conditions, such as a crop’s physical properties and the extent of lodging, from viewpoint of the mechanical interactions between crops and a combine harvester reel. Because the gathering process by the reel involve the mechanical operation of forced displacement, the Reaction force of a bunch of wheat stalks undergoing forced displacement was analyzed in our previous study, and the result has been verified by the experiment under a quasi-static loading rate. In the present study, in order to investigate the effect of loading rate and to discuss the application of the analytical method, which is valid under a quasi-static loading condition, to the actual reel operation, the Reaction force of a bunch of wheat stalks was measured under several different loading rates by the experiment involving gathering operation of the reel. As the results, the Horizontal Reaction force increased its values in the negative x direction together with an increase in loading rates, and the analytical results had a large amount of error under high loading rates. The above result was examined in terms of the acceleration of forced displacement during the gathering operation. The acceleration increased its values in the positive x direction together with the increase in loading rates, and the peak of acceleration coincided with that of Reaction force. From these results, the main reason for the increase in the Reaction force was considered to be an effect of the inertia force of a wheat stalk caused by forced displacement involving the acceleration, and a subject of the current analytical method for applying to the actual reel operation was clarified.