<正> Intoduction In recent years many kinds of optimal power flow methods have been proposed. In order to meet the needs of large scale power system real-time control, it is necessary to find out a fast calculat...<正> Intoduction In recent years many kinds of optimal power flow methods have been proposed. In order to meet the needs of large scale power system real-time control, it is necessary to find out a fast calculation method of optimal power flows. Zhang (1985) proposed the concept of a kind of network flow(f_(ij)~θ=θ_(ij)/z_(ij)~θ), and expressed line loss in the network flow. Luo, Hill and Lee (1984) proposed展开更多
To speed up three-dimensional （3D） DC resistivity modeling, we present a new multigrid method, the aggregation-based algebraic multigrid method （AGMG）. We first discretize the differential equation of the secondar...To speed up three-dimensional （3D） DC resistivity modeling, we present a new multigrid method, the aggregation-based algebraic multigrid method （AGMG）. We first discretize the differential equation of the secondary potential field with mixed boundary conditions by using a seven-point finite-difference method to obtain a large sparse system of linear equations. Then, we introduce the theory behind the pairwise aggregation algorithms for AGMG and use the conjugate-gradient method with the V-cycle AGMG preconditioner （AGMG-CG） to solve the linear equations. We use typical geoelectrical models to test the proposed AGMG-CG method and compare the results with analytical solutions and the 3DDCXH algorithm for 3D DC modeling （3DDCXH）. In addition, we apply the AGMG-CG method to different grid sizes and geoelectrical models and compare it to different iterative methods, such as ILU-BICGSTAB, ILU-GCR, and SSOR-CG. The AGMG-CG method yields nearly linearly decreasing errors, whereas the number of iterations increases slowly with increasing grid size. The AGMG-CG method is precise and converges fast, and thus can improve the computational efficiency in forward modeling of three-dimensional DC resistivity.展开更多
To deal with the problem of low computational precision at the nodes near the source and satisfy the requirements for computational efficiency in inversion imaging and finite-element numerical simulations of the direc...To deal with the problem of low computational precision at the nodes near the source and satisfy the requirements for computational efficiency in inversion imaging and finite-element numerical simulations of the direct current method, we propose a new mesh refinement and recoarsement method for a two-dimensional point source. We introduce the mesh refinement and mesh recoarsement into the traditional structured mesh subdivision. By refining the horizontal grids, the singularity owing to the point source is minimized and the topography is simulated. By recoarsening the horizontal grids, the number of grid cells is reduced significantly and computational efficiency is improved. Model tests show that the proposed method solves the singularity problem and reduces the number of grid cells by 80% compared to the uniform grid refinement.展开更多
Objective To investigate the management and outcome of cerebrospinal fluid leakage(CSFL)after cervical surgery.Methods Medical records of 642 patients who underwent cervical surgery between December 1999 and December ...Objective To investigate the management and outcome of cerebrospinal fluid leakage(CSFL)after cervical surgery.Methods Medical records of 642 patients who underwent cervical surgery between December 1999 and December 2005 at our hospital were retrospectively reviewed.Five patients complicated by CSFL after surgery were enrolled,of which 4 cases were complicated after ossified posterior longitudinal ligament or posterior vertebral osteophyte resection directly injuring the dura,and 1 case after posterior cervical double-door laminoplasty without observed dural injury during surgery.Of the 5 CSFL cases,4 cases occurred at 1-3 days after operation and 1 case at 9 days after operation.All 5 postoperative CSFL cases were treated through wound drainage removal,wound sutures,prophylactic antibiotics,and continuous subarachnoid drainage in the elevated head position.Results All 5 CSFL cases experienced leakage cessation within 1-3 days and wound healing within 4-8 days,and subarachnoid drainage lasted 11-16 days with an average volume of 320 mL(range,150-410 mL).Four cases experienced headache,nausea and vomiting,1 case suffered from somnolence and hyponatremia,and symptoms subsided after symptomatic treatment and intravenous fluid administration.All patients were followed up for an average of 32 months(range,22-50 months).No occurrence of cerebrospinal fluid cyst or wound infection was observed.CSFL produced no significant negative effects upon neuromuscular function recovery.Conclusion Continuous subarachnoid cavity drainage in combination with elevated head position is a simple and safe non-surgical method in treatment of CSFL following cervical surgery.展开更多
Internet traffic classification plays an important role in network management. Many approaches have been proposed to clas-sify different categories of Internet traffic. However, these approaches have specific us-age c...Internet traffic classification plays an important role in network management. Many approaches have been proposed to clas-sify different categories of Internet traffic. However, these approaches have specific us-age contexts that restrict their ability when they are applied in the current network envi-ronment. For example, the port based ap-proach cannot identify network applications with dynamic ports; the deep packet inspec-tion approach is invalid for encrypted network applications; and the statistical based approach is time-onsuming. In this paper, a novel tech-nique is proposed to classify different catego-ries of network applications. The port based, deep packet inspection based and statistical based approaches are integrated as a multi-stage classifier. The experimental results demonstrate that this approach has high rec-ognition rate which is up to 98% and good performance of real-time for traffic identifica-tion.展开更多
Under the environment of electric power market, economic dispatch (ED) problem should consider network constraints, unit ramp rates, besides the basic constraints. For this problem, it is important to establish the ef...Under the environment of electric power market, economic dispatch (ED) problem should consider network constraints, unit ramp rates, besides the basic constraints. For this problem, it is important to establish the effective model and algorithm. This paper examines the decoupled conditions that affect the solution optimality to this problem. It proposes an effective model and solution method. Based on the look-ahead technique, it finds the number of time intervals to guarantee the solution optimality. Next, an efficient technique for finding the optimal solution via the interior point methods is described. Test cases, which include dispatching six units over 5 time intervals on the IEEE 30 test system with line flows and ramp constraints are presented. Results indicate that the computational effort as measured by iteration counts or execution time varies only modestly with the problem size.展开更多
文摘<正> Intoduction In recent years many kinds of optimal power flow methods have been proposed. In order to meet the needs of large scale power system real-time control, it is necessary to find out a fast calculation method of optimal power flows. Zhang (1985) proposed the concept of a kind of network flow(f_(ij)~θ=θ_(ij)/z_(ij)~θ), and expressed line loss in the network flow. Luo, Hill and Lee (1984) proposed
基金supported by the Natural Science Foundation of China(Nos.41404057,41674077 and 411640034)the Nuclear Energy Development Project of China,and the‘555’Project of Gan Po Excellent People
文摘To speed up three-dimensional （3D） DC resistivity modeling, we present a new multigrid method, the aggregation-based algebraic multigrid method （AGMG）. We first discretize the differential equation of the secondary potential field with mixed boundary conditions by using a seven-point finite-difference method to obtain a large sparse system of linear equations. Then, we introduce the theory behind the pairwise aggregation algorithms for AGMG and use the conjugate-gradient method with the V-cycle AGMG preconditioner （AGMG-CG） to solve the linear equations. We use typical geoelectrical models to test the proposed AGMG-CG method and compare the results with analytical solutions and the 3DDCXH algorithm for 3D DC modeling （3DDCXH）. In addition, we apply the AGMG-CG method to different grid sizes and geoelectrical models and compare it to different iterative methods, such as ILU-BICGSTAB, ILU-GCR, and SSOR-CG. The AGMG-CG method yields nearly linearly decreasing errors, whereas the number of iterations increases slowly with increasing grid size. The AGMG-CG method is precise and converges fast, and thus can improve the computational efficiency in forward modeling of three-dimensional DC resistivity.
基金financially supported by the National Natural Science Foundation of China(No.41574127 and 41174104)the National Key Technology R&D Program for the 13th five-year plan(No.2016ZX05018006-006)
文摘To deal with the problem of low computational precision at the nodes near the source and satisfy the requirements for computational efficiency in inversion imaging and finite-element numerical simulations of the direct current method, we propose a new mesh refinement and recoarsement method for a two-dimensional point source. We introduce the mesh refinement and mesh recoarsement into the traditional structured mesh subdivision. By refining the horizontal grids, the singularity owing to the point source is minimized and the topography is simulated. By recoarsening the horizontal grids, the number of grid cells is reduced significantly and computational efficiency is improved. Model tests show that the proposed method solves the singularity problem and reduces the number of grid cells by 80% compared to the uniform grid refinement.
文摘Objective To investigate the management and outcome of cerebrospinal fluid leakage(CSFL)after cervical surgery.Methods Medical records of 642 patients who underwent cervical surgery between December 1999 and December 2005 at our hospital were retrospectively reviewed.Five patients complicated by CSFL after surgery were enrolled,of which 4 cases were complicated after ossified posterior longitudinal ligament or posterior vertebral osteophyte resection directly injuring the dura,and 1 case after posterior cervical double-door laminoplasty without observed dural injury during surgery.Of the 5 CSFL cases,4 cases occurred at 1-3 days after operation and 1 case at 9 days after operation.All 5 postoperative CSFL cases were treated through wound drainage removal,wound sutures,prophylactic antibiotics,and continuous subarachnoid drainage in the elevated head position.Results All 5 CSFL cases experienced leakage cessation within 1-3 days and wound healing within 4-8 days,and subarachnoid drainage lasted 11-16 days with an average volume of 320 mL(range,150-410 mL).Four cases experienced headache,nausea and vomiting,1 case suffered from somnolence and hyponatremia,and symptoms subsided after symptomatic treatment and intravenous fluid administration.All patients were followed up for an average of 32 months(range,22-50 months).No occurrence of cerebrospinal fluid cyst or wound infection was observed.CSFL produced no significant negative effects upon neuromuscular function recovery.Conclusion Continuous subarachnoid cavity drainage in combination with elevated head position is a simple and safe non-surgical method in treatment of CSFL following cervical surgery.
基金supported by the National Key Technology R&D Program under Grant No. 2012BAH18B05
文摘Internet traffic classification plays an important role in network management. Many approaches have been proposed to clas-sify different categories of Internet traffic. However, these approaches have specific us-age contexts that restrict their ability when they are applied in the current network envi-ronment. For example, the port based ap-proach cannot identify network applications with dynamic ports; the deep packet inspec-tion approach is invalid for encrypted network applications; and the statistical based approach is time-onsuming. In this paper, a novel tech-nique is proposed to classify different catego-ries of network applications. The port based, deep packet inspection based and statistical based approaches are integrated as a multi-stage classifier. The experimental results demonstrate that this approach has high rec-ognition rate which is up to 98% and good performance of real-time for traffic identifica-tion.
文摘Under the environment of electric power market, economic dispatch (ED) problem should consider network constraints, unit ramp rates, besides the basic constraints. For this problem, it is important to establish the effective model and algorithm. This paper examines the decoupled conditions that affect the solution optimality to this problem. It proposes an effective model and solution method. Based on the look-ahead technique, it finds the number of time intervals to guarantee the solution optimality. Next, an efficient technique for finding the optimal solution via the interior point methods is described. Test cases, which include dispatching six units over 5 time intervals on the IEEE 30 test system with line flows and ramp constraints are presented. Results indicate that the computational effort as measured by iteration counts or execution time varies only modestly with the problem size.
