961 research outputs found
Dynamical Modelling and a Decentralized Adaptive Controller for a 12-Tetrahedral Rolling Robot
The 12-tetrahedral robot is an addressable reconfigurable technology (ART)-based variable geometry truss mechanism with twenty-six extensible struts and nine nodes arranged in a tetrahedral mesh. The robot has the capability of reconfiguring shape and dimension for environment sensing requirements, which makes it suitable for space exploration and environmental perception. In this paper, we have derived a dynamics model and presented a decentralized adaptive controller for a 12-tetrahedral robot. First, the robot is divided into the node and the strut subsystems, and the kinetic and the potential energy are calculated for the two subsystems. Then, the dynamics model is achieved by applying the Lagrangian formalism on the total energy of the robot. Since the dynamics is too complicated for implementing model-based controllers, a two-layer controller is presented to control the robot, in which the planning layer determines gait and trajectory of the robot, and the executive layer adopts the decentralized adaptive control strategy and consists of twenty-six strut controllers. Each strut controller regulates the movement of the corresponding strut without information exchange with other struts. Co-simulations based on ADAMS and Matlab have been conducted to verify the feasibility and effectiveness of the proposed controller
NUMERICAL INVESTIGATION OF GAS SAMPLING FROM FLUIDIZED BEDS
Gas mixing in a tall narrow fluidized bed operated in the slugging fluidization regime is studied with the aid of computational fluid dynamics. Three-dimensional numerical simulations are performed with an Eulerian-Eulerian model. Predicted axial and radial tracer concentration profiles for various operating conditions are generally in good agreement with experimental data from the literature. Different field variables including voidage, tracer concentration, and gas velocity at upstream and downstream levels are analysed to study gas mixing. Mean tracer concentrations in the dense phase and the bubble phase are evaluated and significant differences between them are found. The time-mean concentration is weighted heavily towards the dense phase concentration which may lead to misinterpretation of sampling data in dispersion models. Caution is needed when interpreting time-mean tracer concentration data. A flux-based mean tracer concentration is introduced to characterize the gas mixing in numerical simulations of two-phase fluidized beds
Margin trading and value relevance of earnings:Evidence from China
Information asymmetry and accounting information effectiveness are important issues in the capital market. Based on a sample of China's A-share listed companies from 2007 to 2021, this paper studies the impact of China's margin trading and short-selling policy on the value relevance of earnings and the unerlying mechanisms. We find that, compared with companies that are not included in margin trading and short selling lists, the earnings value relevance of listed companies increases significantly after allowing for short selling. In addition, margin trading and short selling improve the value relevance of earnings more significantly for firms with higher agency costs and firms with lower information transparency.</p
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