In current investigations of electric arc plasmas, experiments based on modern testing technology play an important role. To enrich the testing methods and contribute to the understanding and grasping of the inherent ...In current investigations of electric arc plasmas, experiments based on modern testing technology play an important role. To enrich the testing methods and contribute to the understanding and grasping of the inherent mechanism of air switching arcs, in this paper, a nonintrusive detecting system is described that combines the magneto-optic imaging（MOI） technique with the solution to inverse electromagnetic problems. The detecting system works in a sequence of main steps as follows： MOI of the variation of the arc flux density over a plane, magnetic field information extracted from the magneto-optic（MO） images, arc current density distribution and spatial pattern reconstruction by inverting the resulting field data. Correspondingly, in the system, an MOI set-up is designed based on the Faraday effect and the polarization properties of light, and an intelligent inversion algorithm is proposed that involves simulated annealing（SA）.Experiments were carried out for high current（2 kA RMS） discharge cases in a typical low-voltage switchgear. The results show that the MO detection system possesses the advantages of visualization, high resolution and response, and electrical insulation, which provides a novel diagnostics tool for further studies of the arc.展开更多
We have developed a new three dimensional (3-D) conductivity imaging approach and have used it to detect human brain conductivity changes corresponding to acute cerebral stroke. The proposed Magnetic Resonance Electri...We have developed a new three dimensional (3-D) conductivity imaging approach and have used it to detect human brain conductivity changes corresponding to acute cerebral stroke. The proposed Magnetic Resonance Electrical Impedance Tomography (MREIT) approach is based on the J-Substitution algorithm and is expanded to imaging 3-D subject conductivity distribution changes. Computer simulation studies have been conducted to evaluate the present MREIT imaging approach. Simulations of both types of cerebral stroke, hemorrhagic stroke and ischemic stroke, were performed on a four-sphere head model. Simulation results showed that the correlation coefficient (CC) and relative error (RE) between target and estimated conductivity distributions were 0.9245±0.0068 and 8.9997%±0.0084%, for hemorrhagic stroke, and 0.6748±0.0197 and 8.8986%±0.0089%, for ischemic stroke, when the SNR (signal-to-noise radio) of added GWN (Gaussian White Noise) was 40. The convergence characteristic was also evaluated according to the changes of CC and RE with different iteration numbers. The CC increases and RE decreases monotonously with the increasing number of iterations. The present simulation results show the feasibility of the proposed 3-D MREIT approach in hemorrhagic and ischemic stroke detection and suggest that the method may become a useful alternative in clinical diagnosis of acute cerebral stroke in humans.展开更多
本文首先介绍了生物电阻抗成像(electrical impedance tomography,EIT)的数学模型、系统设计、算法分类及其存在的问题。然后介绍了由加拿大Toronto大学的Joy、Scott等人提出的电流密度成像(current density imaging,CDI)的基本原理及...本文首先介绍了生物电阻抗成像(electrical impedance tomography,EIT)的数学模型、系统设计、算法分类及其存在的问题。然后介绍了由加拿大Toronto大学的Joy、Scott等人提出的电流密度成像(current density imaging,CDI)的基本原理及发展现状,提出将CDI应用到EIT可以得到精确度与分辨率都较高的阻抗图像及实现的基本思路。最后讨论了将CDI应用到EIT的发展前景及需要解决的问题。展开更多
基金supported by the Fundamental Research Funds for the Central Universities of China(XJJ2011019)
文摘In current investigations of electric arc plasmas, experiments based on modern testing technology play an important role. To enrich the testing methods and contribute to the understanding and grasping of the inherent mechanism of air switching arcs, in this paper, a nonintrusive detecting system is described that combines the magneto-optic imaging（MOI） technique with the solution to inverse electromagnetic problems. The detecting system works in a sequence of main steps as follows： MOI of the variation of the arc flux density over a plane, magnetic field information extracted from the magneto-optic（MO） images, arc current density distribution and spatial pattern reconstruction by inverting the resulting field data. Correspondingly, in the system, an MOI set-up is designed based on the Faraday effect and the polarization properties of light, and an intelligent inversion algorithm is proposed that involves simulated annealing（SA）.Experiments were carried out for high current（2 kA RMS） discharge cases in a typical low-voltage switchgear. The results show that the MO detection system possesses the advantages of visualization, high resolution and response, and electrical insulation, which provides a novel diagnostics tool for further studies of the arc.
基金Project supported partly by the National Science Foundation (No.BES-0411898) and the National Institues of Health (No. R01EB00178) USA
文摘We have developed a new three dimensional (3-D) conductivity imaging approach and have used it to detect human brain conductivity changes corresponding to acute cerebral stroke. The proposed Magnetic Resonance Electrical Impedance Tomography (MREIT) approach is based on the J-Substitution algorithm and is expanded to imaging 3-D subject conductivity distribution changes. Computer simulation studies have been conducted to evaluate the present MREIT imaging approach. Simulations of both types of cerebral stroke, hemorrhagic stroke and ischemic stroke, were performed on a four-sphere head model. Simulation results showed that the correlation coefficient (CC) and relative error (RE) between target and estimated conductivity distributions were 0.9245±0.0068 and 8.9997%±0.0084%, for hemorrhagic stroke, and 0.6748±0.0197 and 8.8986%±0.0089%, for ischemic stroke, when the SNR (signal-to-noise radio) of added GWN (Gaussian White Noise) was 40. The convergence characteristic was also evaluated according to the changes of CC and RE with different iteration numbers. The CC increases and RE decreases monotonously with the increasing number of iterations. The present simulation results show the feasibility of the proposed 3-D MREIT approach in hemorrhagic and ischemic stroke detection and suggest that the method may become a useful alternative in clinical diagnosis of acute cerebral stroke in humans.
文摘本文首先介绍了生物电阻抗成像(electrical impedance tomography,EIT)的数学模型、系统设计、算法分类及其存在的问题。然后介绍了由加拿大Toronto大学的Joy、Scott等人提出的电流密度成像(current density imaging,CDI)的基本原理及发展现状,提出将CDI应用到EIT可以得到精确度与分辨率都较高的阻抗图像及实现的基本思路。最后讨论了将CDI应用到EIT的发展前景及需要解决的问题。
