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A closed-form charge control model (CCM) for threshold voltage (Vth) of single-heterojunction (AlGaN/GaN) devices is developed. The CCM reveals the mechanisms of how the space charges across the barrier of a heterojunction deplete or enhance 2-D electron gas. The Vth of both depletion- and enhancement-mode heterostructure field-effect transistors may be calculated through this model. Considering the strained and relaxed states, and surface states, the calculated results for Vth are in good agreement with simulation results. The generalized form for CCM may have wide applications for theoretical-based design for Vth of AlGaN/GaN devices. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to address the de-embedding issue of millimeter-wave (mmWave) and sub-mmWave measurements and circuit design by extensively comparing several commonly used methods and by proposing a new full-matrix calculation-based de-embedding methodology. The comparison aims to investigate the impacts of different de-embedding methods on mmWave and sub-mmWave circuit design. A new de-embedding method has been proposed to achieve more accurate results on mmWave and sub-mmWave range. In this method, all possible extrinsic elements are subtracted from the measured device under test data by matrix calculation to eliminate the error from equivalent circuit. The influence of parasitic elements on the fT and fMAX are investigated. The comparison of the different de-embedding methods for transistors are performed up to 170 GHz, the results showed that the proposed method has good accuracy even at very high-frequency and it is suitable for mmWave and sub-mmWave measurements and circuit design. [ABSTRACT FROM PUBLISHER]

This paper presents a new algorithm to simulate the surge corona of power transmission lines in two dimension. The charge simulation method and the finite element method are applied to calculate the electric field, while a time-dependent upwind difference algorithm is applied to calculate the migration of the space charges. The implementation of boundary conditions and the choice of mesh size and time step are discussed to ensure the stability of the proposed algorithm. The Q-V (charge-voltage) curves of impulses applying on single conductor and bundle conductors in a cage having a square cross section are calculated. The simulation results are supported by the published experiments. [ABSTRACT FROM AUTHOR]

In this paper, based on the moment method and the circuit theory, an approach is proposed to analyze the current distribution and the electromagnetic field of a building struck by lightning. By introducing the concept of complex resistivity in the air and the soil, the approach can consider the metallic grids under the ground and above the ground altogether. Both the potential differences among the grounding parts and the electromagnetic interactions among the grids are taken into account. It shows that the resistivity of soil will affect the electromagnetic field greatly. When the electromagnetic fields around buildings near the lightning struck point are investigated, or when a building has a separated grounding system, the effect of the grounding systems must be considered. [ABSTRACT FROM AUTHOR]

There exist many recurrent neural networks for solving optimization-related problems. In this paper, we present a method for deriving such networks from existing ones by changing connections between computing blocks. Although the dynamic systems may become much different, some distinguished properties may be retained. One example is discussed to solve variational inequalities and related optimization problems with mixed linear and nonlinear constraints. A new network is obtained from two classical models by this means, and its performance is comparable to its predecessors. Thus, an alternative choice for circuits implementation is offered to accomplish such computing tasks. [ABSTRACT FROM AUTHOR]

Based on the continuity theorem of electric displacement including interface charges, the enhanced dielectric layer field (ENDIF) for silicon-on-insulator (SOI) high-voltage devices is proposed. The following three approaches for enhancing the dielectric layer electric field E1 to increase the vertical breakdown voltage of a device VB,V are presented: 1) using a thin silicon layer with a high critical electric field ES,C; 2) introducing a low-permittivity dielectric buried layer; and 3) implementing interface charges between the silicon and the dielectric layer. Considering the threshold energy of silicon εT, the formula of ES,C on silicon layer thickness tS is first obtained, which increases sharply with a decrease of tS, and reaches up to 141 V/µm at tS = 0.1 µm. Expressions for E1 and VB,V are given, which agree well with simulative and experimental results. Based on the ENDIF, the new device structures are given, and an E1 value of 300 V/µm has been experimentally obtained for double-sided trench SOI. Moreover, several conventional SOI devices are explained well by ENDIF. [ABSTRACT FROM AUTHOR]

Variations of Halbach array and Stelter array were studied to evaluate the magnetic field strength and quality. The field uniformity and skew angle were compared among the structures. It was found the circular Halbach arrays have superior field strength to the polygonal counterparts, but the polygonal Halbach arrays have better skew angle performance. For applications that require highly uniform field, the usable volume is not affected by the number of magnet segments used in Halbach arrays. With OD/ID ratio of 2, Halbach arrays approach maximum field when the length is about 4 times of ID. Stelter arrays that feature tapered pole pieces provide good field uniformity by reducing fringing. The results presented in this work provide guidelines for choosing the best-suited permanent magnet dipole structure to meet specific application requirements. [ABSTRACT FROM AUTHOR]

In this paper, a new recurrent neural network is proposed for solving convex quadratic programming (QP) problems. Compared with existing neural networks, the proposed one features global convergence property under weak conditions, low structural complexity, and no calculation of matrix inverse. It serves as a competitive alternative in the neural network family for solving linear or quadratic programming problems. In addition, it is found that by some variable substitution, the proposed network turns out to be an existing model for solving minimax problems. In this sense, it can be also viewed as a special case of the minimax neural network. Based on this scheme, a k-winners-take-all (k-WTA) network with O(n) complexity is designed, which is characterized by simple structure, global convergence, and capability to deal with some ill cases. Numerical simulations are provided to validate the theoretical results obtained. More importantly, the network design method proposed in this paper has great potential to inspire other competitive inventions along the same line. [ABSTRACT FROM AUTHOR]

A novel silicon-on-insulator (SOI) high-voltage MOSFET structure and its breakdown mechanism are presented in this paper. The structure is characterized by oxide trenches on the top interface of the buried oxide layer on partial SOI (TPSOI). Inversion charges located in the trenches enhance the electric field of the buried layer in the high-voltage blocking state, and a silicon window makes the depletion region spread into the substrate. Both of them modulate the electric field in the drift region; therefore, the breakdown voltage (BV) for a TPSOI LDMOS is greatly enhanced. Moreover, the Si window alleviates the self-heating effect. The influences of the structure parameters on device characteristics are analyzed for the proposed device structure. The TPSOI LDMOS with BV > 1200 V and the buried-layer electric field of EI > 700 V/μm is obtained by the simulation on a 2-μm-thick SOI layer over 2-μm-thick buried oxide layer, and its maximal temperature reduces by 19 and 8.7 K in comparison with the conventional SOI and partial SOI devices. [ABSTRACT FROM AUTHOR]

In order to denoise Poisson count data, we introduce a variance stabilizing transform (VST) applied on a filtered discrete Poisson process, yielding a near Gaussian process with asymptotic constant variance. This new transform, which can be deemed as an extension of the Anscombe transform to filtered data, is simple, fast, and efficient in (very) low-count situations. We combine this VST with the filter banks of wavelets, ridgelets and curvelets, leading to multiscale VSTs (MS-VSTs) and nonlinear decomposition schemes. By doing so, the noise-contaminated coefficients of these MS-VST-modified transforms are asymptotically normally distributed with known variances. A classical hypothesis-testing framework is adopted to detect the significant coefficients, and a sparsity-driven iterative scheme reconstructs properly the final estimate. A range of examples show the power of this MS-VST approach for recovering important structures of various morphologies in (very) low-count images. These results also demonstrate that the MS-VST approach is competitive relative to many existing denoising methods. [ABSTRACT FROM AUTHOR]

This paper analyzes the influence of coke bed on the heat dissipation around high voltage direct current grounding electrode. By using a method coupling moment method with boundary element method, the influence of coke bed on the leakage current distribution is analyzed. Then, the affected current distribution in the soil is achieved. By using a finite difference method, the temperature distribution caused by the affected current flow is achieved. Some verification samples are also presented in this paper. [ABSTRACT FROM AUTHOR]

When dc current is injected into the earth through the grounding electrodes of an HVDC system, transformers in an ac system may be under dc bias if the dc currents flowing through the transformers are large enough. In this paper, a circuit model is presented to calculate the dc current distribution in an ac power system caused by the ground return current of a dc system. A complex image method is used to calculate the ground potential rise of each substation in multilayer earth. An indirect boundary element method is used to take into account the effects of mountains, rivers, and sea. The circuit equations are used to take into account the effects of the transmission lines. By using the method, the dc current distribution and the effectiveness of restraining measure in an ac power system are analyzed. The method and the results are not only useful for analyzing the influence of the ground return current from an HVDC ground electrode on ac power systems, but also useful for analyzing the effectiveness of the restraining measure. [ABSTRACT FROM AUTHOR]

We studied electrical characteristics of p-channel polycrystalline silicon thin-film transistors (TFT) fabricated by solution-based metal-induced crystallization (SMIC). In particular, the effect of annealing conditions was systematically investigated. The current-voltage characteristics show that the performance of TFTs was dominated by the SMIC process rather than the annealing temperature up to 630 °C. All the devices exhibited good uniformity after annealing. The effects of gate stress and self-heating stress were also studied. The device performance was not affected by both stresses for all devices, p-channel SMIC poly-Si TFT has high performance, good uniformity, and satisfactory reliability with a process temperature < 600 °C. [ABSTRACT FROM AUTHOR]

The electric fields under high-voltage direct current (HVdc) transmission lines and the ions produced by corona affect each other greatly. This paper presents an iterative method to calculate ion flow fields under HVdc bipolar transmission lines in the presence of wind. Both the electric fields and the ion densities are calculated by integral equation method. The method is fast and stable. The results are in good agreement with the experimental data. The ion flow fields under a ± 800-kV bipolar direct current (dc) transmission line are analyzed. [ABSTRACT FROM AUTHOR]

When dc current is injected into the earth through the grounding electrodes of a high-voltage direct current (HVDC) system, transformers in ac system may be under dc bias if the dc currents flowing through the transformers are large enough. In this paper, a numerical method coupling the method of moments (MoM) to circuit equations is presented to calculate the dc current distribution in ac power system caused by an HVDC system. The MoM is used to calculate the electric fields in complex earth structure caused by all the grounding systems including the dc grounding electrodes, the ac substation grounding systems and the long metal pipe lines. The circuit equations are coupled to the moment method to take account of the effects of the transmission lines. By using the method, the dc current distribution in an ac power system caused by an HVDC system is analyzed. Some useful conclusions are drawn from the analyzed results. [ABSTRACT FROM AUTHOR]

An approach coupling indirect boundary element method with charge simulation method to calculate the electric fields around the head of transmission tower and its composite insulators is presented. On the composite insulators, the indirect boundary element method is used, while on the transmission tower and the transmission lines, the charge simulation method is used. Therefore, both the heterogeneous medium such as the composite insulators and the filament metal structure such as the transmission tower and the transmission lines are considered all together. The electric field distribution around a 330-kV transmission tower and its composite insulators was analyzed. The method gives the possibility to model very complex geometries. [ABSTRACT FROM AUTHOR]

In this paper, the electric-field distribution around the composite insulators and the heads of transmission towers is calculated by a model coupling the indirect boundary-element method to the moment method. The heterogeneous media, such as the composite insulators and the filament metal structures such as the transmission towers and the transmission lines, are considered altogether. The method can take into account not only the permittivity but also the resistivity of the media by using the complex resistivity in the frequency domain. The electric-field distribution around a three-phase 330-kV transmission tower with composite insulators was analyzed. The electric fields on the surfaces of the grading rings and the phase subconductors and at the ends of the composite insulators are analyzed. Both the method and the results are useful for the design of high-voltage transmission lines. [ABSTRACT FROM AUTHOR]

The design of grounding system often relies on the performance simulations. The evaluation of the current distribution of grounding system for many frequencies by using the method of moments (MoM) may take a long time since the impedance matrix must be recomputed at each new frequency. A multiobject adaptive spatial sampling approach is presented to construct the fitted model of the electric field intensity generated by a horizontal electric dipole. The [Z] matrix spatial interpolation technology with MoM is described to reduce the computational time needed for the transient characteristics analysis of a horizontal grounding system. The accuracy and computational time of the [Z] matrix interpolation method are compared with those of the direct MoM. The numerical examples show that the [Z] matrix spatial interpolation method can reduce the computation requirement effectively. [ABSTRACT FROM AUTHOR]

How to correctly obtain the structure parameters of earth is the precondition of grounding system design. Based on the local searching algorithm, an efficient method for estimating earth structure with any number of layers from the test data by Weaner configuration method is presented. In each iterative procedure, earth apparent resistivities are calculated by complex image method. A new method to directly obtain the partial derivatives of the earth apparent resistivities with respect to the earth parameters from the results of the complex image method is presented, which is more efficient than the conventional methods that arduously calculate the improper integrals with a Bessel's function and an infinite limit of integration. At the same time, a method to determine suitable initial earth parameters for the local searching algorithm is also proposed. The validity of the method is shown by several applications. [ABSTRACT FROM AUTHOR]

The influence between larger grounding grids and two-end grounded cables is a serious problem not only for the performance of the grounding grids but also for the safety and the normal operation of the cables. In this paper, a numerical method coupling the moment method with circuit equations is presented to analyze the performance of the grounding grid connected with two-end grounded coaxial-shielded cables in frequency domain. From the analyzed results by this method, the electromagnetic interference between the grounding grid and the two-end grounded coaxial-shielded cable is analyzed. Validity of the method is testified by comparing the results with those of experiments and with published ones. Both the method and the results are useful for designing safe grounding grid and for analyzing cable's electromagnetic compatibility problems. [ABSTRACT FROM PUBLISHER]

Focuses on a study which described the Method of Moment to analyze the grid fed by harmonic currents. Theory of analyzing grounding grid; Validation of the method; Diagnosis of breaks in the grid.

Proposes a method for speeding up the integer wavelet transforms constructed by a lifting scheme. Increased interest in wavelet transform in the field of image compression; Packed integer wavelet transform algorithm; Three building elements of modern wavelet-based image compression systems.

Focuses on a study that discussed the experimental verification of the metal oxide semiconductor (MOS)-controlled diode (MCD) key concept by using commercially available power MOS field effect transistors operating as MCD. Information on MCD; Theory and operation principle of the MCD; Expected MCD performance; Experimental demonstration; Conclusions.

Recurrent neural networks for solving constrained least absolute deviation (LAD) problems or L1-norm optimization problems have attracted much interest in recent years. But so far most neural networks can only deal with some special linear constraints efficiently. In this paper, two neural networks are proposed for solving LAD problems with various linear constraints including equality, two-sided inequality and bound constraints. When tailored to solve some special cases of LAD problems in which not all types of constraints are present, the two networks can yield simpler architectures than most existing ones in the literature. In particular, for solving problems with both equality and one-sided inequality constraints, another network is invented. All of the networks proposed in this paper are rigorously shown to be capable of solving the corresponding problems. The different networks designed for solving the same types of problems possess the same structural complexity, which is due to the fact these architectures share the same computing blocks and only differ in connections between some blocks. By this means, some flexibility for circuits realization is provided. Numerical simulations are carried out to illustrate the theoretical results and compare the convergence rates of the networks. [ABSTRACT FROM AUTHOR]

Manifold learning is a hot topic in the field of computer science, particularly since nonlinear dimensionality reduction based on manifold learning was proposed in Science in 2000. The work has achieved great success. The main purpose of current manifold-learning approaches is to search for independent intrinsic variables underlying high dimensional inputs which lie on a low dimensional manifold. In this paper, a new manifold is built up in the training step of the process, on which the input training samples are set to be close to each other if the values of their intrinsic variables are close to each other. Then, the process of dimensionality reduction is transformed into a procedure of preserving the continuity of the intrinsic variables. By utilizing the new manifold, the dynamic tracking of a human who can move and rotate freely is achieved. From the theoretical point of view, it is the first approach to transfer the manifold-learning framework to dynamic tracking. From the application point of view, a new and low dimensional feature for visual tracking is obtained and successfully applied to the real-time tracking of a free-moving object from a dynamic vision system. Experimental results from a dynamic tracking system which is mounted on a dynamic robot validate the effectiveness of the new algorithm. [ABSTRACT FROM AUTHOR]

Live working is important for the continuity of electricity supply in power system. Experiment results of 50% switching impulse sparkover voltages (U50) for different live working entering routes on a real tower are presented. The potential and electric-field distribution around the 750 kV straight tower window with a line worker inside, was analyzed via an approach combing charge simulation method and indirect boundary element method. The comparison demonstrates the close relationship between electric-field distribution and (U50). The sparkover voltage and the maximum electric-field strength change synchronously for a specific structure. Generally speaking, the higher the electric filed strength is, the lower the sparkover voltage will be. Thus, the experiment procedure for deciding the best entering route can be simplified according to the electric-field distribution calculation. [ABSTRACT FROM AUTHOR]

In order to analyze the lightning transient of a thinwire system, a time-domain method of reducing the thin-wire conductor system into an equivalent active multiport network based on the partial-element electric-circuit model is presented in this paper. A modified-mesh-current (MMC) approach is developed, uses node charge and mesh current as its variables, and takes into account both capacitive coupling and inductive coupling among conductors. Equations given by MMC are expressed in a statespace form. These equations are reduced to an active multiport network model using the trapezoidal scheme. The active multiport network is described by a constant-input-conductance matrix and a vector of currents that are updated using passed values. The multiport network can easily interface with linear and nonlinear components in an electromagnetic transient program. Since the proposed method requires only one-time calculation of the inverse of the system matrix, it is more efficient in comparison to the conventional full-wave method in the frequency domain. For a large system, well-established model-order-reduction techniques can be applied to the MMC formulation to reduce it to a small scale one. The proposed method is validated by comparing its results with NEC-calculated ones and published field measurements. Finally, the method is used to simulate two lightning-strike scenarios. [ABSTRACT FROM AUTHOR]

Device degradation of solution-based metal-induced laterally crystallized p-type polycrystalline silicon (poly-Si) thin—film transistors (TFTs) is studied under dc bias stresses. While typical negative bias temperature instability (NBT1) or electron injection (EI) is observed under — Vg or — Vd only stress, respectively, no typical hot carrier (HC) degradation can be identified under high —Vd stress combined with either low or high —Vg stress. Instead, mixed NBTI and EI degradation is observed under combined low — Vg, and — Vd stresses; and combined degradation of NBTI and HC occurs under high —Vd and moderate —Vg stresses. NBTI is the dominant mechanism in both cases. Grain boundary (GB) trap generation is found to correlate with the NBTI degradation with the same time exponent, suggesting the key role of GB trap generation in poly-Si TFTs' degradation. [ABSTRACT FROM AUTHOR]

This paper presents the study of a long electric arc in free air due to lightning stroke on the parallel gap lightning protection device (PGLPD) on high-voltage overhead transmission lines. Based on the latest electric arc model, the analysis method of the magnetic field generated by the current flowing through the PGLPD, electric arc, transmission lines, steel tower, and ground wires is developed, and the movement process of the long arc along the surface of the insulator strings is simulated. The simulation results are in agreement with the experimental results. The study is very helpful for the optimal design and suitable assemblage of the PGLPD. [ABSTRACT FROM AUTHOR]

Provides information on a study which developed a high squint subaperture (HSS) algorithm from the perspective of a stripmap synthetic aperture radar (SAR) system. Signal characteristics of squint mode strip-mapping SAR; Computation complexity of HSS algorithm; Simulation results and discussions.

In this paper, a multiple-ring-modulated junction termination extension (MRM-JTE) technology for large-area silicon carbide PiN rectifier rated at 4500 V is proposed and experimentally investigated using a standard two-zone JTE (TZ-JTE) process without extra process steps or masks. Multiple modulation rings embedded inside JTE region, which is similar to varied lateral doping technology widely used in silicon devices, form a gradual decrease of effective charges in the termination region. MRM combines the advantages of two termination techniques, namely, ring-assisted JTE and space-modulated JTE, to enlarge the optimum JTE-dose window with high reverse blocking voltage in comparison with conventional TZ-JTE. A breakdown voltage of 4940 V at a leakage current of 1 μA is achieved from fabricated MRM-JTE rectifiers with a 36-μm-thick N- epilayer doped to 1.8 × 1015 cm-3, which is 92% of the ideal parallel-plane value. A forward current of 50 A has been measured at a forward voltage drop of 3.9 V for devices with an active anode area of 9.2 mm2, corresponding to low differential on-resistance of 1.8 mQ · cm2. The simulation and experimental results show that the proposed device exhibits approximately 2 times JTE dose tolerance window improvement with respect to the breakdown voltage of 4500 V. [ABSTRACT FROM AUTHOR]

The development of 100 Gb/s transponder technology is progressing rapidly to meet the needs of next-generation optical/IP carrier networks. Video-driven IP traffic growth continues together with the need for ever higher-speed ports on IP routers, Ethernet switches, and OTN cross-connects, thus driving the requirements for cost-effective client and line side 100 Gb/s transponders. For a short time to market, 100 Gb/s transponders should be deployable using 10 Gb/s link-engineering rules over existing fiber and DWDM infrastructure. In this article we describe the upgrade of an installed 10 Gb/s field system to 100 Gb/s using a real-time single-carrier coherent 100G polarization multiplexed quadrature phase shift keyed (PM-QPSK) channel. Performance sufficient for error-free operation after forward error correction was achieved over installed 900 km and 1800 km links, proving the viability of 100 Gb/s upgrades to most installed systems. Excellent tolerance to fiber polarization mode dispersion and narrowband optical filtering demonstrates the applicability of this technology over the majority of installed fiber plant and through existing 50 GHz reconfigurable optical add/drop multiplexers. [ABSTRACT FROM AUTHOR]

Insulation of a coaxial high-voltage vacuum insulator used in the pulsed power generator TPG700 has been studied in this paper. When output voltage is increased from 700 to 800 kV, breakdown happens in the insulator. With transient simulation, the region of the insulator subject to the highest electric strength is concluded. According to the experimental and simulated results, the breakdown strength has been calculated. An electric-thermal model has been proposed in which factors such as local electric field (E-field) enhancement, imperfection in dielectric, and repetition working state are analyzed. A formula to calculate the effects of these factors is suggested. Moreover, the key structures on the coaxial line which influence the E-field distribution are optimized, and useful advice for designing an insulator of this kind is presented. [ABSTRACT FROM AUTHOR]

The insulation of secondary system in substation, including secondary cables and devices, have to endure the high ac power-frequency voltage during the short-circuit fault. The ac withstand characteristics of the secondary cables and devices are experimentally investigated and discussed in this paper. The insulation breakdown mechanism of relays can be classified into three modes: air gap breakdown, creeping discharge, and solid insulation breakdown, that of the microcomputer protection device is solid state component damage. The ac power-frequency breakdown voltages of the microcomputer protection device, the small-size electromagnetic and solid-state relays all are as low as about 2 kV. The statistic method to obtain the withstand voltage of long communication cable from experimental data of short cables is proposed. The minimum 3-s withstand voltages of secondary system are 6.5 kV and 2 kV, respectively, this should be considered in substation design. What's more, the volt-second characteristics of the power-frequency withstand voltage of the secondary cables and devices are analyzed and compared in detail, which would be important in the selection of secondary cables and devices. At last, the method how to guarantee high ac breakdown voltage of electromagnetic and solid-state relays and microcomputer protection device is suggested. [ABSTRACT FROM AUTHOR]

A novel silicon-on-insulator (SOI) high-voltage device structure and its eliminating back-gate bias effects are presented. The structure is characterized by a compound buried layer (CBL) made of two oxide layers and a polysilicon layer between them. At the high-voltage blocking state, holes collected on the polysilicon bottom interface shield the SOI layer and the upper buried oxide (UBO) layer from the back-gate bias Vbg, resulting in a constant breakdown voltage (BV) and the same electric field and potential distributions in the SOI layer, UBO, and polysilicon under different the back-gate biases for a CBL SOI REduced SURface Field (RESURF) Lateral Double-diffused MOS (LDMOS). Vbg only impacts the field strength and voltage drop in the lower buried oxide (LBO) layer. Moreover, based on the continuity of electric displacement, the holes enhance the field in the LBO from 80 V/ µm for the buried oxide in the conventional SOI to 457 V//µm at Vbg = 0 V, leading to a high BV in CBL SOI. A 747-V CBL SOI LDMOS is fabricated, and its eliminating back-gate bias effect is verified by measurement. In addition, the CBL SOI structure can alleviate the self-heating effects due to a window in the UBO. [ABSTRACT FROM AUTHOR]

This paper presents the study on the potential distribution of the ac 1000-kV ultra-high voltage metal-oxide arrester (MOA). Based on the idea of field-circuit combination, the 3-D finite-element method (FEM) and circuit-analytic method are applied to analyze and improve the potential distribution of the 1000-kV MOA. The 3-D FEM is used to obtain the 1000-kV MOA's potential distribution and stray capacitances to build the equivalent circuit of the MOA. With the equivalent circuit, the method to improve the potential distribution of the MOA by adding parallel capacitors is analyzed. A scheme to obtain the recommended values of parallel capacitors is achieved to improve the potential distribution coefficient within ±5%. In addition, the influences of the grading ring and mounting height of the MOA on the potential distribution are also discussed. The potential distribution of the developed 1000-kV surge arrester was tested by the photoelectricity measurement method, which is close to the analysis results. [ABSTRACT FROM AUTHOR]

Wideband frequency electromagnetic (EM) noise generated during the turn-ON and turn-OFF processes of thyristor valves in converter stations is conducted along the primary circuitry, and may interfere with secondary systems. The EM interference (EMI) problem in a ±800 kV ultra-HVdc converter station is an important issue that should be studied carefully in the design stage. A method to analyze the conducted EM disturbance (EMD) based on time-domain wideband circuit simulation is proposed here, which is verified through the field test results of a ±500 kV converter station. Models of major equipment are described. The EMD levels of a ±800 kV converter station, which is currently being planned and built in China, are calculated, and compared with those of a ±500 kV converter station. [ABSTRACT FROM AUTHOR]

The impulse characteristics of frozen soil are the fundament for the lightning protection design of the overhead transmission lines in frozen soil environments. In this paper, the conductivity and lightning impulse breakdown characteristics of the frozen soil were experimentally studied, and those key factors influencing the impulse breakdown characteristics of the frozen soils such as temperature, water content and salinity were analyzed systematically. Comparing with the normal soil, some important conclusions on the impulse breakdown characteristics of the frozen soil were proposed. The electric breakdown process accompanied by a thermal thaw process was proposed to explain the impulse breakdown mechanism of the frozen soil. [ABSTRACT FROM AUTHOR]

When lightning strikes a substation or a transmission tower near the substation, high current generated by the stroke would flow into the grounding grid of the substation and dissipate in the soil. The transient characteristic of the grounding grid is very important to the safe and reliable operation of the power system. A circuit model with a lumped time-variable parameter is proposed to calculate the transient characteristics of a grounding grid under lightning current. The ionization phenomena around the ground conductors in the soil are simulated by means of time-variable parameters under appropriate conditions. The influences of different parameters on the transient characteristics of the grounding grid subjected to lightning impulse current are analyzed and the effective usage area of the grounding grid under lightning is discussed. [ABSTRACT FROM AUTHOR]

In this paper, a simulation model is proposed to evaluate the electromagnetic transient surge current distribution in a lightning protection system (LPS) due to a direct lightning stroke. The model is based on the coupled transmission line network in the frequency domain combined with the Fourier transform technique. The conductor of the LPS is described using the coupled transmission line model, and can be reduced to an active two-port equivalent circuit. The unknown quantities are the node voltages of the LPS at the physical junction, which leads to a fast solver at each frequency. The validation of the proposed approach is performed by comparing the results with those in the technical literature. The numerical examples show the flexibility, efficiency, and accuracy of the model in the range of practical application of LPS. [ABSTRACT FROM AUTHOR]

We are carrying out a project to develop a conduction-cooled high temperature superconducting magnet system with an energy storage of 25 kJ. This magnet system will be used to investigate fast discharging performances. The magnet is constructed with 20 double pancakes. Each pancake is wound with Bi2223 tape. The magnet has an outer diameter of 212 mm and a clear bore of 108 mm. Cryogenics for the magnet system is designed to cool the coils with a GM cryocooler together with solid nitrogen. It is expected to operate the magnet system stand-alone. The operating current is designed as 110 A. It can generate a central magnetic field of 3.8 T at a temperature of 20 K. In this paper, the magnet design, coil fabrication and cryogenic system are presented. [ABSTRACT FROM AUTHOR]

This paper conducts a formal study of the shot boundary detection problem. First, a general formal framework of shot boundary detection techniques is proposed. Three critical techniques, i.e., the representation of visual content, the construction of continuity signal and the classification of continuity values, are identified and formulated in the perspective of pattern recognition. Meanwhile, the major challenges to the framework are identified. Second, a comprehensive review of the existing approaches is conducted. The representative approaches are categorized and compared according to their roles in the formal framework. Based on the comparison of the existing approaches, optimal criteria for each module of the framework are discussed, which will provide practical guide for developing novel methods. Third, with all the above issues considered, we present a unified shot boundary detection system based on graph partition model. Extensive experiments are carried out on the platform of TRECVID. The experiments not only verify the optimal criteria discussed above, but also show that the proposed approach is among the best in the evaluation of TRECVID 2005. Finally, we conclude the paper and present some further discussions on what shot boundary detection can learn from other related fields. [ABSTRACT FROM AUTHOR]

A high temperature superconducting (HTS) magnet for 10 kJ superconducting magnetic energy storage (SMES) system is designed by an improved optimal algorithm and cooled through GM cryocooler. In order to demonstrate the technology, a model HTS magnet made of Bi-2223/Ag tape to fabricate double-pancakes with the inner and outer diameters of 120 mm, 207.1 mm and height of 119 mm was fabricated and tested. The magnet is operating with GM cryocooler at 10 K. We have tested the Bi2223 HTS magnet at various ramping rates with 0.1–5.06 Ads. The experimental results show that the model HTS magnet is operating very stable. In the paper, we report the design of the HTS-SMES and fabrication technique for the model HTS magnet. [ABSTRACT FROM AUTHOR]

The grounding systems are simply handled as lumped resistances with constant values in traditional lightning transient analysis of substation. A complete transmission line model is proposed to consider the actual transient process of power network and the grounding grid of the substation and the grounding devices of transmission towers. A loss transmission line model with time-variable parameters is proposed to calculate the transient characteristics of grounding systems under lightning current in which the soil ionization phenomena around the ground conductors are considered. The analyzed results by the proposed model have large differences with those obtained by the traditional simplified method. The transient characteristics of grounding systems have strong influence on the lightning transient process of substation. [ABSTRACT FROM AUTHOR]

The transient near-field of the electrostatic discharge (ESD) is a kind of high power transient phenomenon, which is strongly affected by the discharge current waveform. In this paper, two different kinds of discharge current waveforms satisfying the definition of the LEC61000-4-2 are introduced. The alternating-direction-implicit finite-difference time-domain (ADI-FDTD) method is applied to simulate the transient near-field of the indirect ESD through the vertical couple plane (VCP). The configuration of the current source is considered carefully. The simulation results under different discharge current waveforms show different transient effects. The simulated data are compared with those measured by an optic testing system. [ABSTRACT FROM AUTHOR]

In this paper, a unified image retrieval framework based on both keyword annotations and visual features is proposed. In this framework, a set of statistical models are built based on visual features of a small set of manually labeled images to represent semantic concepts and used to propagate keywords to Other unlabeled images. These models are updated periodically when more images implicitly labeled by users become available through relevance feedback. In this sense, the keyword models serve the function of accumulation and memorization of knowledge learned from user-provided relevance feedback. Furthermore, two sets of effective and efficient similarity measures and relevance feedback schemes are proposed for query by keyword scenario and query by image example scenario, respectively. Keyword models are combined with visual features in these schemes. In particular, a new, entropy-based active learning strategy is introduced to improve the efficiency of relevance feedback for query by keyword. Furthermore, a new algorithm is proposed to estimate the keyword features of the search concept for query by image example. It is shown to be more appropriate than two existing relevance feedback algorithms. Experimental results demonstrate the effectiveness of the proposed framework. [ABSTRACT FROM AUTHOR]

A nonlinear self-consistent simulation code is employed to investigate' the behavior of the outer-slotted-coaxial waveguide gyrotron traveling-wave amplifier (gyro-TWA). The influences of the velocity pitch, frequency, and input power of the electron beam on efficiency, output power, and saturated gain are simulated and discussed in detail. It is predicted that this design with 95 GHz, TE3,1 will yield a peak output power of 2643 KW, a peak efficiency of 33.7%, and saturated gain of 44.2 dB. [ABSTRACT FROM AUTHOR]

We are carrying out a National High Technology Program in China to fabricate a magnetic separator by using a conduction-cooled Bi-based high temperature superconducting (HTS) magnet. The magnet is made of Bi-2223 pancakes, and has the inner and outer coil diameters of 120 mm and 211.2 mm and coil height of 202.8 mm. The operating current is about 80 A. This magnet is cryocooler-cooled with no liquid helium and should generate a magnetic field of 3 T at a temperature of 20 K. In the paper, we report the design and fabrication technique of the HTS magnet. [ABSTRACT FROM AUTHOR]

A method of moments solution for analyzing the electromagnetic shielding properties of rectangular metal enclosures with apertures over a lossy half space which can model the ground is presented. The objects are modeled by rectangular surface patches. The roof stop basic functions are used to expand the unknown electric and magnetic currents on the surfaces of the cavity and the apertures. An effective method based on the generalized pencil-of-function (GPOF) method is developed to calculate the generalized Sommerfeld integral (GSI). With this method, the value of Greens' function can be obtained quickly and accurately. Validation of the method is presented by comparing the calculation results with the results obtained by measurement. Finally, the method is successfully applied to calculating the shielding effectiveness of a relay cell in a substation. [ABSTRACT FROM AUTHOR]

In a high soil resistivity area, counterpoise wires are applied to decrease the grounding resistance of tower grounding devices. If the conductor of counterpoise wire is very long, although the power frequency grounding resistance of the tower grounding device ii decreased, the lightning protection performance of the transmission line is still not good. The influences of the length of grounding electrodes on the lightning transient characteristic were analyzed. The dynamic and nonlinear effect of soil ionization around the grounding electrode was considered in the analysis model of transient characteristics for the grounding electrodes under lightning impulse. The counterpoise wire has an effective length when lightning passes through it. When the length of a grounding electrode exceeds the effective length, the grounding conductor will not be utilized effectively. The simulating experiments were performed to analyze influences of the length of the counterpoise wire on the impulse characteristics. The formulae to calculate the impulse effective lengths of counterpoise wires were proposed. The model proposed in the paper has been validated by comparing the numerical results with experimental tests. [ABSTRACT FROM AUTHOR]