The Experts below are selected from a list of 50346 Experts worldwide ranked by ideXlab platform
Timothy Bretl - One of the best experts on this subject based on the ideXlab platform.
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Manipulation planning with contacts for an extensible elastic rod by sampling on the submanifold of Static Equilibrium configurations
2015Co-Authors: Olivier Roussel, Andy Borum, Michel Taïx, Timothy BretlAbstract:We consider the manipulation planning problem of an extensible elastic rod in collision-free or contact space. We assume the rod can be handled by grippers either at both or at only one of its extremities and during the manipulation, the grasped end may change. We show that the use of both quasi-Static and dynamic models can be coupled efficiently with sampling-based methods. By sampling directly on the submanifold of Static Equilibrium and contact-free configurations, we can take advantage of the dynamic model to improve the exploration in the state space. We show the necessity of considering contacts for this type of problems with several simulation experiments on various scenarios.
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ICRA - Manipulation planning with contacts for an extensible elastic rod by sampling on the submanifold of Static Equilibrium configurations
2015 IEEE International Conference on Robotics and Automation (ICRA), 2015Co-Authors: Olivier Roussel, Andy Borum, Michel Taïx, Timothy BretlAbstract:We consider the manipulation planning problem of an extensible elastic rod in collision-free or contact space. We assume the rod can be handled by grippers either at both or at only one of its extremities and during the manipulation, the grasped end may change. We show that the use of both quasi-Static and dynamic models can be coupled efficiently with sampling-based methods. By sampling directly on the submanifold of Static Equilibrium and contact-free configurations, we can take advantage of the dynamic model to improve the exploration in the state space. We show the necessity of considering contacts for this type of problems with several simulation experiments on various scenarios.
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Testing Static Equilibrium for Legged Robots
IEEE Transactions on Robotics, 2008Co-Authors: Timothy Bretl, Sanjay LallAbstract:Consider a legged robot at fixed foot placements. Where can the robot move its center of mass (CM) while remaining in Static Equilibrium? If the terrain is flat, the CM must lie above the convex hull of the robot's feet. If the terrain is not flat, this often-used approximation can be arbitrarily bad. Instead, the CM must lie above the projection of a nonlinear convex set that is defined by the properties of each foot placement. This paper presents an algorithm to compute the shape of this projection and gives a tight bound on the algorithm's running time. It also presents a method of amortizing the cost of this computation when it is only necessary to test Static Equilibrium at particular CM positions--that is, when it is only necessary to test the membership of points in the projection of a convex set rather than find its shape.
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a fast and adaptive test of Static Equilibrium for legged robots
International Conference on Robotics and Automation, 2006Co-Authors: Timothy Bretl, Sanjay LallAbstract:A legged robot walking on uneven terrain can avoid falling only by applying contact forces with its feet on the ground that compensate for gravity without causing slip. To plan safe motions, it is necessary to test this constraint at every posture explored at each set of foot placements. Since a huge number of postures may be explored, this test must be as fast as possible. Existing approaches either search explicitly for contact forces at each posture, or precompute the support polygon and check that the robot's center of mass lies above it. This paper presents a new algorithm that is faster than either existing approach. This algorithm is an incremental method of projection, that computes only enough of the support polygon to decide whether Static Equilibrium is possible at each posture. It takes advantage of information gained testing previous postures in order to test subsequent postures more quickly
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ICRA - A fast and adaptive test of Static Equilibrium for legged robots
Proceedings 2006 IEEE International Conference on Robotics and Automation 2006. ICRA 2006., 1Co-Authors: Timothy Bretl, Sanjay LallAbstract:A legged robot walking on uneven terrain can avoid falling only by applying contact forces with its feet on the ground that compensate for gravity without causing slip. To plan safe motions, it is necessary to test this constraint at every posture explored at each set of foot placements. Since a huge number of postures may be explored, this test must be as fast as possible. Existing approaches either search explicitly for contact forces at each posture, or precompute the support polygon and check that the robot's center of mass lies above it. This paper presents a new algorithm that is faster than either existing approach. This algorithm is an incremental method of projection, that computes only enough of the support polygon to decide whether Static Equilibrium is possible at each posture. It takes advantage of information gained testing previous postures in order to test subsequent postures more quickly
Raúl Medina - One of the best experts on this subject based on the ideXlab platform.
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a process based shape equation for a Static Equilibrium beach planform
Coastal Engineering, 2018Co-Authors: June Gainza, Ernesto Mauricio Gonzalez, Raúl MedinaAbstract:Abstract Coastal erosion is a major problem for shorelines everywhere in the world. In order to mitigate beach stability problems it is necessary to determine the Equilibrium shape of the beach planform. Current Equilibrium planform shape equations are only valid under certain simplifications; for instance, they are unable to predict the effect of nearshore islands and/or rocky bottoms, as well as the effect of several diffraction points. The aim of this paper is to present a new process-based shape equation that is able to overcome those limitations and estimate the Static Equilibrium shoreline of complex bathymetry beaches. The equation is based on the hypothesis that a pocket beach gets its Static Equilibrium planform when the mean surf-zone longshore velocity averaged over a period of time is null ( V ¯ = 0 ) in every point along the beach. Based on this hypothesis, the direction of the shoreline that nulls the mean surf zone longshore velocity along the beach is evaluated. Therefore, the shape equation is based on the longshore current velocity formula. The new Equilibrium shape equation is applied to two Spanish beaches, namely Milagro beach and Cala Millor beach. Milagro beach has a very smooth bathymetry and the parabolic shape equation developed by Hsu and Evans (1989) is able to predict the Equilibrium shoreline. Cala Millor is more complex: it has some rock outcrops along the beach and the parabolic shape equation does not work. The Equilibrium shape equation presented in this paper simulates the Equilibrium shoreline of both beaches successfully with a high R2 (around 0.96) between the modelled shoreline and the real shoreline in both case studies.
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On the design of beach nourishment projects using Static Equilibrium concepts: Application to the Spanish coast
Coastal Engineering, 2010Co-Authors: Mauricio González, Raúl Medina, Miguel A. LosadaAbstract:Abstract The concept of Equilibrium plan form and Equilibrium profile has been widely used as an engineering tool in order to design beach nourishment projects. The scope of this paper is to further explore this “Equilibrium beach” concept in crenulated bays, as a long-term tool for beach nourishment projects. The proposed methodology is based on Gonzalez and Medina (2001) and combines the Static Equilibrium plan and profile for long-term analysis. This methodology includes a modified Equilibrium plan form, which is able to define the orientation of the local wave front in the diffracting point, and also to locate the downcoast starting point of the Static Equilibrium beach from which the parabolic plan form of Hsu and Evans (1989) is valid. This methodology permits the application of any Equilibrium profile formulation. An example of the application of this methodology and long-term formulations to the design of the Spanish nourishment project of Poniente Beach (Gijon) is presented. Ten years after its construction, the beach has still got a Static Equilibrium and remains pretty close to the predicted Equilibrium beach in plan and profile.
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On the application of Static Equilibrium bay formulations to natural and man-made beaches
Coastal Engineering, 2001Co-Authors: Mauricio González, Raúl MedinaAbstract:Crenulate-shaped bays are common features found all around the world. The most widely used formulation for representing this kind of bay is the parabolic approach proposed by Hsu and Evans (Institution of Civil Engineers, Proc., London, England 87 (1989) 556), who suggested a methodology to test and predict the stability of Static Equilibrium shapes in natural and man-made bays. Based on an analytical model of null drift current and using an empirical approach, a modified methodology is proposed. The new procedure is able to locate the downcoast starting point of the Static Equilibrium beach from which the parabolic plan form of Hsu and Evans is valid. This methodology is applied with good results to different natural and man-made beaches along the Atlantic and Mediterranean coasts of Spain, including tombolo-shaped beaches.
Min Xu - One of the best experts on this subject based on the ideXlab platform.
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Sudden onset of Static Equilibrium dysfunction in patients receiving a cochlear implant
Medicine, 2017Co-Authors: Gao Y., Haifeng Yuan, Juan Hu, Qing Zhang, Min XuAbstract:Background: We investigated the sudden onset of Static Equilibrium dysfunction caused by cochlear implantation (CI) in congenital hearing loss patients.
Haifeng Yuan - One of the best experts on this subject based on the ideXlab platform.
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Sudden onset of Static Equilibrium dysfunction in patients receiving a cochlear implant
Medicine, 2017Co-Authors: Gao Y., Haifeng Yuan, Juan Hu, Qing Zhang, Min XuAbstract:Background: We investigated the sudden onset of Static Equilibrium dysfunction caused by cochlear implantation (CI) in congenital hearing loss patients.
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Sudden onset of Static Equilibrium dysfunction in patients receiving a cochlear implant.
Medicine, 2017Co-Authors: Ying Gao, Haifeng Yuan, Qing Zhang, Jing Yan, Xiaorong Niu, Peng Han, Bo LiuAbstract:BACKGROUND We investigated the sudden onset of Static Equilibrium dysfunction caused by cochlear implantation (CI) in congenital hearing loss patients. METHOD Twenty-five patients were selected from a cohort of unilateral CI recipients to form the CI group. Static posturography was performed 1 to 3 days before and 3 to 5 days after CI. Each patient underwent the test with eyes open (EO) and eyes closed (EC) for 30 seconds, separately. Another group of age- and sex-matched patients with no history of hearing impairment undergoing unrelated surgeries formed the control group, and were examined with the same tests pre- and post-surgery. A third group of patients undergoing middle ear surgery formed the otitis media (OM) group. Postural sway parameters including sway velocity (SV) in the X-axis, SV in the Y-axis, length of sway locus length (LNG), and environmental area (ENV) were measured and recorded. RESULTS Comparison of pre-surgery posturographical parameters between the CI and control groups revealed no significant differences. Significant differences were found in most parameters in pre- and post-surgery comparisons in the CI group. Mean SV values in the X-axis pre- and post-surgery were 8.48 and 11.52 mm/s, respectively, in the EO condition (P .05) except SV in the X-axis and LNG in the EO condition (P
Qing Zhang - One of the best experts on this subject based on the ideXlab platform.
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Sudden onset of Static Equilibrium dysfunction in patients receiving a cochlear implant
Medicine, 2017Co-Authors: Gao Y., Haifeng Yuan, Juan Hu, Qing Zhang, Min XuAbstract:Background: We investigated the sudden onset of Static Equilibrium dysfunction caused by cochlear implantation (CI) in congenital hearing loss patients.
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Sudden onset of Static Equilibrium dysfunction in patients receiving a cochlear implant.
Medicine, 2017Co-Authors: Ying Gao, Haifeng Yuan, Qing Zhang, Jing Yan, Xiaorong Niu, Peng Han, Bo LiuAbstract:BACKGROUND We investigated the sudden onset of Static Equilibrium dysfunction caused by cochlear implantation (CI) in congenital hearing loss patients. METHOD Twenty-five patients were selected from a cohort of unilateral CI recipients to form the CI group. Static posturography was performed 1 to 3 days before and 3 to 5 days after CI. Each patient underwent the test with eyes open (EO) and eyes closed (EC) for 30 seconds, separately. Another group of age- and sex-matched patients with no history of hearing impairment undergoing unrelated surgeries formed the control group, and were examined with the same tests pre- and post-surgery. A third group of patients undergoing middle ear surgery formed the otitis media (OM) group. Postural sway parameters including sway velocity (SV) in the X-axis, SV in the Y-axis, length of sway locus length (LNG), and environmental area (ENV) were measured and recorded. RESULTS Comparison of pre-surgery posturographical parameters between the CI and control groups revealed no significant differences. Significant differences were found in most parameters in pre- and post-surgery comparisons in the CI group. Mean SV values in the X-axis pre- and post-surgery were 8.48 and 11.52 mm/s, respectively, in the EO condition (P .05) except SV in the X-axis and LNG in the EO condition (P
