In this Technical Report we study the time evolution of the position estimates’ covariance in Cooperative Simultaneous Localization and Mapping (C-SLAM), and obtain analytical upper boundsfor the positioning uncertainty. The derived bounds provide descriptions of the asymptotic positioning performance of a team of robots in a mapping task, as a function of the characteristics of the proprioceptive and exteroceptive sensors of the robots, and of the graph of relative position measurements recorded by the robots. A study of the properties of the Riccati recursion which describes the propagation of uncertainty through time, yields (i) the guaranteed accuracyfor a robot team in a given C-SLAM application, as well as (ii) the maximum expected steady state uncertainty of the robots and landmarks, when the spatial distribution of features in the environment can be modeled by a known distribution.
{"title":"Performance Bounds for Cooperative Simultaneous Localization and Mapping (C-SLAM)","authors":"Anastasios I. Mourikis, S. Roumeliotis","doi":"10.15607/RSS.2005.I.010","DOIUrl":"https://doi.org/10.15607/RSS.2005.I.010","url":null,"abstract":"In this Technical Report we study the time evolution of the position estimates’ covariance in Cooperative Simultaneous Localization and Mapping (C-SLAM), and obtain analytical upper boundsfor the positioning uncertainty. The derived bounds provide descriptions of the asymptotic positioning performance of a team of robots in a mapping task, as a function of the characteristics of the proprioceptive and exteroceptive sensors of the robots, and of the graph of relative position measurements recorded by the robots. A study of the properties of the Riccati recursion which describes the propagation of uncertainty through time, yields (i) the guaranteed accuracyfor a robot team in a given C-SLAM application, as well as (ii) the maximum expected steady state uncertainty of the robots and landmarks, when the spatial distribution of features in the environment can be modeled by a known distribution.","PeriodicalId":87357,"journal":{"name":"Robotics science and systems : online proceedings","volume":"373 1","pages":"73-80"},"PeriodicalIF":0.0,"publicationDate":"2005-06-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84942690","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Autonomous navigation in outdoor environments with vegetation is difficult because available sensors make very indirect measurements on quantities of interest such as the supporting ground height and the location of obstacles. We introduce a terrain model that includes spatial constraints on these quantities to exploit structure found in outdoor domains and use available sensor data more effectively. The model consists of a latent variable that establishes a prior that favors vegetation of a similar height, plus multiple Markov random fields that incorporate neighborhood interactions and impose a prior on smooth ground and class continuity. These Markov random fields interact through a hidden semi-Markov model that enforces a prior on the vertical structure of elements in the environment. The system runs in real-time and has been trained and tested using real data from an agricultural setting. Results show that exploiting the 3D structure inherent in outdoor domains significantly improves ground height estimates and obstacle detection accuracy.
{"title":"Interacting Markov Random Fields for Simultaneous Terrain Modeling and Obstacle Detection","authors":"Carl K. Wellington, Aaron C. Courville, A. Stentz","doi":"10.15607/RSS.2005.I.001","DOIUrl":"https://doi.org/10.15607/RSS.2005.I.001","url":null,"abstract":"Autonomous navigation in outdoor environments with vegetation is difficult because available sensors make very indirect measurements on quantities of interest such as the supporting ground height and the location of obstacles. We introduce a terrain model that includes spatial constraints on these quantities to exploit structure found in outdoor domains and use available sensor data more effectively. The model consists of a latent variable that establishes a prior that favors vegetation of a similar height, plus multiple Markov random fields that incorporate neighborhood interactions and impose a prior on smooth ground and class continuity. These Markov random fields interact through a hidden semi-Markov model that enforces a prior on the vertical structure of elements in the environment. The system runs in real-time and has been trained and tested using real data from an agricultural setting. Results show that exploiting the 3D structure inherent in outdoor domains significantly improves ground height estimates and obstacle detection accuracy.","PeriodicalId":87357,"journal":{"name":"Robotics science and systems : online proceedings","volume":"15 1","pages":"1-8"},"PeriodicalIF":0.0,"publicationDate":"2005-06-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80913029","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We consider the efficient computation of sequences of push actions that simultaneously orient two different polygons. Our motivation for studying this problem comes from the observation that appropriately oriented parts admit simple sensorless sorting. We study the sorting of two polygonal parts by first putting them in properly selected orientations. We give an O(n2 log n)-time algorithm to enumerate all pairs of orientations for the two parts that can be realized by a sequence of push actions and admit sensorless sorting. We then propose an O(n4 log2 n)-time algorithm for finding the shortest sequence of push actions establishing a given realizable pair of orientations for the two parts. These results generalize to the sorting of k polygonal parts.
{"title":"A Polynomial-time Algorithm to Design Push Plans for Sensorless Parts Sorting","authors":"M. D. Berg, X. Goaoc, A.F. van der Stappen","doi":"10.15607/RSS.2005.I.013","DOIUrl":"https://doi.org/10.15607/RSS.2005.I.013","url":null,"abstract":"We consider the efficient computation of sequences of push actions that simultaneously orient two different polygons. Our motivation for studying this problem comes from the observation that appropriately oriented parts admit simple sensorless sorting. We study the sorting of two polygonal parts by first putting them in properly selected orientations. We give an O(n2 log n)-time algorithm to enumerate all pairs of orientations for the two parts that can be realized by a sequence of push actions and admit sensorless sorting. We then propose an O(n4 log2 n)-time algorithm for finding the shortest sequence of push actions establishing a given realizable pair of orientations for the two parts. These results generalize to the sorting of k polygonal parts.","PeriodicalId":87357,"journal":{"name":"Robotics science and systems : online proceedings","volume":"17 1","pages":"89-96"},"PeriodicalIF":0.0,"publicationDate":"2005-06-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88415674","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Subramanian, B. Vikramaditya, Lixin Dong, D. Bell, B. Nelson
The contact phase of an assembly task involving micro and nano objects is complicated by the presence of surface and intermolecular forces such as electrostatic, surface-tension and Van der Waals forces. Assembly strategies must account for the presence of these forces in order to guarantee successful repeatable micro and nanoassemblies with high precision. A detailed model for this electrostatic interaction is developed and analyzed. Based on the results of this analysis, dielectrophoretic assembly principles of MEMS/NEMS devices are proposed and experimentally verified with microtweezers for micro Ni parts and with nanoelectrodes fabricated with electron-beam lithography for carbon nanotube assembly. The successful manipulation and assembly of single carbon nanotubes (CNTs) using dielectrophoretic forces produced by nanoelectrodes will lead to a higher integration of CNTs into both nanoelectronics and NEMS.
{"title":"Micro and Nanorobotic Assembly Using Dielectrophoresis","authors":"A. Subramanian, B. Vikramaditya, Lixin Dong, D. Bell, B. Nelson","doi":"10.15607/RSS.2005.I.043","DOIUrl":"https://doi.org/10.15607/RSS.2005.I.043","url":null,"abstract":"The contact phase of an assembly task involving micro and nano objects is complicated by the presence of surface and intermolecular forces such as electrostatic, surface-tension and Van der Waals forces. Assembly strategies must account for the presence of these forces in order to guarantee successful repeatable micro and nanoassemblies with high precision. A detailed model for this electrostatic interaction is developed and analyzed. Based on the results of this analysis, dielectrophoretic assembly principles of MEMS/NEMS devices are proposed and experimentally verified with microtweezers for micro Ni parts and with nanoelectrodes fabricated with electron-beam lithography for carbon nanotube assembly. The successful manipulation and assembly of single carbon nanotubes (CNTs) using dielectrophoretic forces produced by nanoelectrodes will lead to a higher integration of CNTs into both nanoelectronics and NEMS.","PeriodicalId":87357,"journal":{"name":"Robotics science and systems : online proceedings","volume":"77 1","pages":"327-334"},"PeriodicalIF":0.0,"publicationDate":"2005-06-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83384011","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this paper we present a novel gait analysis technique which can directly be used to synthesize gaits for a broad class of mechanical systems. We build upon prior work in locomotion mechanics, however we take a different approach to generate gaits that yield absolute motion of the mechanical system. We present a systematic analysis to control all parameters of a proposed type of gait which eliminates the need for intuition and guesswork as was required in the prior work. The main contribution of the paper is relating position change or motion in the ber space to a volume integral bounded by closed curves on a two dimensional manifold embedded in the base space or shape space of the robot. Not only does our method remove the restriction of using sinusoidal gaits as was the case in the prior work but it also allows for generating optimal gaits by solving a variational problem rather than solving a dynamic programming problem as was the case in the prior work.
{"title":"Natural Gait Generation Techniques for Principally Kinematic Mechanical Systems","authors":"Elie A. Shammas, H. Choset, A. Rizzi","doi":"10.15607/RSS.2005.I.016","DOIUrl":"https://doi.org/10.15607/RSS.2005.I.016","url":null,"abstract":"In this paper we present a novel gait analysis technique which can directly be used to synthesize gaits for a broad class of mechanical systems. We build upon prior work in locomotion mechanics, however we take a different approach to generate gaits that yield absolute motion of the mechanical system. We present a systematic analysis to control all parameters of a proposed type of gait which eliminates the need for intuition and guesswork as was required in the prior work. The main contribution of the paper is relating position change or motion in the ber space to a volume integral bounded by closed curves on a two dimensional manifold embedded in the base space or shape space of the robot. Not only does our method remove the restriction of using sinusoidal gaits as was the case in the prior work but it also allows for generating optimal gaits by solving a variational problem rather than solving a dynamic programming problem as was the case in the prior work.","PeriodicalId":87357,"journal":{"name":"Robotics science and systems : online proceedings","volume":"6 1","pages":"113-120"},"PeriodicalIF":0.0,"publicationDate":"2005-06-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80170366","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Just a test. We present an algorithm for path planning for a flexible robot in complex environments. Our algorithm computes a collision free path by taking into account geometric and physical constraints, including obstacle avoidance, nonpenetration constraint, volume preservation, surface tension, and energy minimization. We describe a new algorithm for collision detection between a deformable robot and fixed obstacles using graphics processors. We also present techniques to efficiently handle complex deformable models composed of tens of thousands of polygons and obtain significant performance improvement over previous approaches. Moreover, we demonstrate a practical application of our algorithm in performing path planning of catheters in liver chemoembolization.
{"title":"Path Planning for Deformable Robots in Complex Environments","authors":"Russell Gayle, P. Segars, M. Lin, Dinesh Manocha","doi":"10.15607/RSS.2005.I.030","DOIUrl":"https://doi.org/10.15607/RSS.2005.I.030","url":null,"abstract":"Just a test. We present an algorithm for path planning for a flexible robot in complex environments. Our algorithm computes a collision free path by taking into account geometric and physical constraints, including obstacle avoidance, nonpenetration constraint, volume preservation, surface tension, and energy minimization. We describe a new algorithm for collision detection between a deformable robot and fixed obstacles using graphics processors. We also present techniques to efficiently handle complex deformable models composed of tens of thousands of polygons and obtain significant performance improvement over previous approaches. Moreover, we demonstrate a practical application of our algorithm in performing path planning of catheters in liver chemoembolization.","PeriodicalId":87357,"journal":{"name":"Robotics science and systems : online proceedings","volume":"1 1","pages":"225-232"},"PeriodicalIF":0.0,"publicationDate":"2005-06-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83143715","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper addresses the problem of resource allocation in formations of mobile robots localizing as a group. Each robot receives measurements from various sensors that provide relative (robot-to-robot) and absolute positioning information. Constraints on the sensors’ bandwidth, as well as communication and processing requirements, limit the number of measurements that are available or can be processed at each time step. The localization uncertainty of the group, determined by the covariance matrix of the equivalent continuous-time system at steady state, is expressed as a function of the sensor measurements’ frequencies. The trace of the submatrix corresponding to the position estimates is selected as the optimization criterion, under linear constraints on the measuring frequency of each sensor and the cumulative rate of EKF updates. This formulation leads to a convex optimization problem whose solution provides the sensing frequencies, for each sensor on every robot, required in order to maximize the positioning accuracy for the group. Simulation experiments are presented that demonstrate the applicability of this method and provide insight into the properties of the resource-constrained cooperative localization problem.
{"title":"Optimal Sensing Strategies for Mobile Robot Formations: Resource-Constrained Localization","authors":"Anastasios I. Mourikis, S. Roumeliotis","doi":"10.15607/RSS.2005.I.037","DOIUrl":"https://doi.org/10.15607/RSS.2005.I.037","url":null,"abstract":"This paper addresses the problem of resource allocation in formations of mobile robots localizing as a group. Each robot receives measurements from various sensors that provide relative (robot-to-robot) and absolute positioning information. Constraints on the sensors’ bandwidth, as well as communication and processing requirements, limit the number of measurements that are available or can be processed at each time step. The localization uncertainty of the group, determined by the covariance matrix of the equivalent continuous-time system at steady state, is expressed as a function of the sensor measurements’ frequencies. The trace of the submatrix corresponding to the position estimates is selected as the optimization criterion, under linear constraints on the measuring frequency of each sensor and the cumulative rate of EKF updates. This formulation leads to a convex optimization problem whose solution provides the sensing frequencies, for each sensor on every robot, required in order to maximize the positioning accuracy for the group. Simulation experiments are presented that demonstrate the applicability of this method and provide insight into the properties of the resource-constrained cooperative localization problem.","PeriodicalId":87357,"journal":{"name":"Robotics science and systems : online proceedings","volume":"409 1","pages":"281-288"},"PeriodicalIF":0.0,"publicationDate":"2005-06-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82399933","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We address the problem of building topological maps in visual space for robot navigation. The nodes of our topological maps consist of clusters along manifolds, and we propose an unsupervised learning algorithm that automatically constructs these manifolds the user need only specify the desired number of clusters and the minimum number of images per cluster. This spectral clustering like framework allows each cluster to optimize a separate set of clustering parameters, and we demonstrate empirically that this flexibility can significantly improve clustering results. We further propose a framework for servoing the robot in our manifold space, which would allow the robot to navigate from any point on one manifold (topological node) to any specified point on a second manifold. Finally, we present experimental results on indoor and outdoor image sequences demonstrating the efficacy of the proposed algorithm.
{"title":"Topological Mapping with Multiple Visual Manifolds","authors":"G. Grudic, J. Mulligan","doi":"10.15607/RSS.2005.I.025","DOIUrl":"https://doi.org/10.15607/RSS.2005.I.025","url":null,"abstract":"We address the problem of building topological maps in visual space for robot navigation. The nodes of our topological maps consist of clusters along manifolds, and we propose an unsupervised learning algorithm that automatically constructs these manifolds the user need only specify the desired number of clusters and the minimum number of images per cluster. This spectral clustering like framework allows each cluster to optimize a separate set of clustering parameters, and we demonstrate empirically that this flexibility can significantly improve clustering results. We further propose a framework for servoing the robot in our manifold space, which would allow the robot to navigate from any point on one manifold (topological node) to any specified point on a second manifold. Finally, we present experimental results on indoor and outdoor image sequences demonstrating the efficacy of the proposed algorithm.","PeriodicalId":87357,"journal":{"name":"Robotics science and systems : online proceedings","volume":"45 1","pages":"185-192"},"PeriodicalIF":0.0,"publicationDate":"2005-06-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86366524","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this paper we examine the stability of a class of simple three-dimensional point-mass hoppers, which have minimal feedback. These hoppers, with varying leg numbers, are representative of both animal and robotic runners: singlestance-leg runners such as humans, birds, and some monopod robots; double-stance-leg hoppers such as kangaroos; and triplestance-leg runners like the cockroach or the robot RHex. These models have minimal feedback: only liftoff and touchdown events are sensed and, during flight phases, legs are positioned in a predetermined manner for the ensuing touchdown. Only one model, that corresponding to cockroach running, is actuated, and then only in a feedforward fashion. The remaining hopper models form a subset of energy conserving, piecewise-holonomic point-mass models for running. Categorically, we show that the model for single-stance-leg runners is unstable; whereas the double-stance-leg and triple-stance-leg hopper models are stable. We abstract three ideas that warrant further study: 1) runners with multiple splayed legs are naturally more stable since they can produce sufficient corrective forces in all directions to perturbations. However, 2) In some systems with specialized hip joints, passive reactions to perturbations generated at the hip can be stabilizing. This scenario may be present in RHex. Finally, 3) A RHex and cockroach version of the three-stance-leg model are fundamentally different in how their individual legs act to produce net body forces, which affects their respective stability properties.
{"title":"The Stability of Point-mass Hoppers with Varying Morphology and Minimal Feedback","authors":"J. Seipel","doi":"10.15607/RSS.2005.I.040","DOIUrl":"https://doi.org/10.15607/RSS.2005.I.040","url":null,"abstract":"In this paper we examine the stability of a class of simple three-dimensional point-mass hoppers, which have minimal feedback. These hoppers, with varying leg numbers, are representative of both animal and robotic runners: singlestance-leg runners such as humans, birds, and some monopod robots; double-stance-leg hoppers such as kangaroos; and triplestance-leg runners like the cockroach or the robot RHex. These models have minimal feedback: only liftoff and touchdown events are sensed and, during flight phases, legs are positioned in a predetermined manner for the ensuing touchdown. Only one model, that corresponding to cockroach running, is actuated, and then only in a feedforward fashion. The remaining hopper models form a subset of energy conserving, piecewise-holonomic point-mass models for running. Categorically, we show that the model for single-stance-leg runners is unstable; whereas the double-stance-leg and triple-stance-leg hopper models are stable. We abstract three ideas that warrant further study: 1) runners with multiple splayed legs are naturally more stable since they can produce sufficient corrective forces in all directions to perturbations. However, 2) In some systems with specialized hip joints, passive reactions to perturbations generated at the hip can be stabilizing. This scenario may be present in RHex. Finally, 3) A RHex and cockroach version of the three-stance-leg model are fundamentally different in how their individual legs act to produce net body forces, which affects their respective stability properties.","PeriodicalId":87357,"journal":{"name":"Robotics science and systems : online proceedings","volume":"55 1","pages":"305-310"},"PeriodicalIF":0.0,"publicationDate":"2005-06-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91381534","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this paper we explore the mechanism of energy transfer between the single actuated DOF of a one-legged hopping robot and the remaining unactuated DOFs, during stable running. The concept of the energy transfer mechanism is laid out, after which follows an analytical study. Using this study, an initial controller is derived for the control of a simple SLIP model with friction in the leg and hip, using a single actuator at the hip. We show that while this controller is capable of stable motion for the SLIP model, it does not lead to stable locomotion for the full realistic robot model with pitching body, leg inertia and friction in hip and leg. This indicates that the SLIP model often used for controller design may be unsuitable for this purpose. The necessary modifications are then made to the controller to achieve stable locomotion for the full model, again with a single, easy-toimplement actuator located at the hip. Finally, results are shown from applying the controller to the full model for a wide range of parameters leading to stable motions. Index Terms one-legged hopping robot, control, underactuated.
{"title":"Single Actuator Control Analysis of a Planar 3DOF Hopping Robot","authors":"N. Cherouvim, E. Papadopoulos","doi":"10.15607/RSS.2005.I.020","DOIUrl":"https://doi.org/10.15607/RSS.2005.I.020","url":null,"abstract":"In this paper we explore the mechanism of energy transfer between the single actuated DOF of a one-legged hopping robot and the remaining unactuated DOFs, during stable running. The concept of the energy transfer mechanism is laid out, after which follows an analytical study. Using this study, an initial controller is derived for the control of a simple SLIP model with friction in the leg and hip, using a single actuator at the hip. We show that while this controller is capable of stable motion for the SLIP model, it does not lead to stable locomotion for the full realistic robot model with pitching body, leg inertia and friction in hip and leg. This indicates that the SLIP model often used for controller design may be unsuitable for this purpose. The necessary modifications are then made to the controller to achieve stable locomotion for the full model, again with a single, easy-toimplement actuator located at the hip. Finally, results are shown from applying the controller to the full model for a wide range of parameters leading to stable motions. Index Terms one-legged hopping robot, control, underactuated.","PeriodicalId":87357,"journal":{"name":"Robotics science and systems : online proceedings","volume":"28 1","pages":"145-152"},"PeriodicalIF":0.0,"publicationDate":"2005-06-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87305141","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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