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The effect of a copper-embedded barrel on the performance of a helix slow-wave structure (SWS) has been studied theoretically and experimentally. The heat dissipation capability and cold-test characteristics of the SWSs with a monel barrel, a normal copper barrel, and a copper-embedded monel barrel have been analyzed and compared. With its combination of high mechanical strength and good thermal conductivity, the copper-embedded monel barrel enables better heat dissipation capability than the other barrel types and has low RF losses. [ABSTRACT FROM AUTHOR]

The effect of the plated metal film on the heat dissipation capability and cold-test characteristics of the helix slow-wave structure (SWS) have been studied in several experimental tests and computer simulations. The thermal conduction and the power losses of the helix SWS were improved by using a plated helix. A brazed SWS with end-plated rods exhibits excellent heat dissipation capability. The side-plated rods affect the cold-test characteristics of the SWS. [ABSTRACT FROM AUTHOR]

We present a method to compute the delay-constrained multicast routing tree by employing chaotic neural networks. The experimental result shows that the noisy chaotic neural network (NCNN) provides an optimal solution more often compared to the transiently chaotic neural network (TCNN) and the Hopfield neural network (HNN). Furthermore, compared with the bounded shortest multicast algorithm (BSMA), the NCNN is able to find multicast trees with lower cost. [ABSTRACT FROM AUTHOR]

Controlling thermal stress is a promising way to reduce the temperature instability of arrayed waveguide gratings (AWGs). A simple method to apply thermal stress is to attach stress plates on the arrayed waveguides. In this paper, a general analytical method to study the temperature sensitivity of the central wavelength in modified AWGs with stress plates is developed. The complete analysis shows that the temperature sensitivity can be controlled effectively by tuning the material parameters and the thickness of the stress plates. To obtain athermal AWGs, a stress plate with large positive thermal expansion coefficient and small Young's modulus should be attached on the bottom of the arrayed waveguides. The material with large negative thermal expansion coefficient suggests another potential scheme. [ABSTRACT FROM AUTHOR]

This paper presents a universal fault location technique for N-terminal (N ≧ 3) transmission lines based on synchronized phasor measurement units. The development of the technique is based on two-terminal fault location technique. The proposed algorithm is different from traditional multiterminal fault location techniques. We apply two-terminal fault location technique to N-terminal transmission lines and propose a novel fault section selector/fault locator. The proposed method has a very good tolerance. The proposed approach provides an analytical solution and its computational burden is very low since it does not require iterative operations. An extensive series of simulations were conducted to verify the accuracy of the proposed algorithm. The average fault location error under various fault conditions is well below 1%. [ABSTRACT FROM AUTHOR]

A novel and effective analytical method using ANSYS has been developed for studying the heat-dissipation capability of a helix traveling-wave-tube slow-wave structure (SWS). This method, which is based on calibrating theoretical calculations with experimental data, is able to precisely predict the SWS heat dissipation, thereby reducing material costs and saving time. The consistency and feasibility of this method have been verified by experimental tests on SWSs using copper-plated helices and both BeO and BN support rods. [ABSTRACT FROM AUTHOR]

The article examines the noisy chaotic neural networks with variable thresholds (NCNN-VT) approach in solving the frequency assignment problem in satellite communications. According to the study, the NCNN-VT approach obtains better solutions compared with gradual neural network on the benchmark examples. Compared to simulated annealing, the NCNN-VT finds optimal or suboptimal solutions with less computation costs. It also achieves better solutions with fewer iterations compared to transiently chaotic neural networks and noisy chaotic neural networks.

A hybrid method which combines four different algorithms for low-frequency oscillation parameter estimation using wide-area measurements is presented in this paper. The first algorithm is the discrete Fourier transform which is used to start the low-frequency oscillation estimation process. The second one is the finite-impulse response (FIR) window filter which is employed in filtering unwanted components, and window correction factor is provided to eliminate the side effect of FIR window filter. The third one is the prototype algorithm which is proposed to estimate low-frequency oscillation parameters, and the last one is the least-square error method which is employed to enhance the computational accuracy by varying the window size. This hybrid method has been implemented in wide-area phasor measurements system by Java language and is under test in Taiwan's power system. Matlab/Simulink simulation and field test results are provided in the present paper. [ABSTRACT FROM AUTHOR]

A new experimental evaluation method is presented for evaluating and comparing the heat dissipation capability of the slow-wave structures (SWSs) of helix traveling-wave tube (TWT). The practicality and simplicity of the evaluation method have been validated through experimental tests in some components with different assembling and processing methods, such as the cold stuffing, the heat shrink, the hot insertion, the molybdenum wrapping methods, and so on. Experimental results demonstrate that our evaluation method can be used effectively and conveniently to estimate and compare the thermal dissipation capability of the SWSs of the helix TWT. [ABSTRACT FROM AUTHOR]

This paper presents a concept of fault-location observability and a new fault-location scheme for transmission networks based on synchronized phasor measurement units (PMUs). Using the proposed scheme, minimal PMUs are installed in existing power transmission networks so that the fault, if it occurs, can be located correctly in the network. The scheme combines the fault-location algorithm and the fault-side selector. Extensive simulation results verify the proposed scheme. [ABSTRACT FROM AUTHOR]

This paper presents the application of a combined adaptive Fourier filtering technique and fault detector to fast distance protection of transmission lines. The filtering technique is extended from the Fourier filters and can be applied under arbitrary data window length. The proposed filtering technique possesses the advantage of recursive computing, and a decaying dc offset component is removed from fault signals by using an adaptive compensation method. A variable data window scheme is embedded in the technique to adaptively speed up its transient response under various system and fault conditions. A fault detector is developed to initiate the process of the technique. For the sake of speed and security, two phasor estimation methods based on the proposed technique are designed to achieve fast distance protection. An algorithm consisting of the two methods is used to detect internal faults by "OR" logic. Extensive simulation studies show that the algorithm significantly reduces tripping time of a distance relay and provides better protection performance than that of the conventional filters with fixed data windows. [ABSTRACT FROM AUTHOR]

In this correspondence, we first establish a limit theorem for averages of the functions of m + 1 variables of mth-order nonhomogeneous Markov information sources. As corollaries, we obtain several limit theorems for frequency of occurrence of the states and a limit theorem of the entropy density for this information sources. Finally, we prove the asymptotic equipartition property (AEP) for a class of nonhomogeneous Markov information sources. [ABSTRACT FROM AUTHOR]

This paper presents a new adaptive fault protection scheme for transmission lines using synchronized phasor measure merits. The work includes fault detection, direction discrimination, classification, and location. Both fault-detection and fault-location indices are derived by using two-terminal synchronized measurements incorporated with distributed line model and modal transformation theory. The fault-detection index is composed of two complex phasors and the angle difference between the two phasors determines whether the fault is internal or external to the protected zone. The fault types can be classified by the modal fault detection index. The proposed scheme also combines online parameter estimation to ensure protection scheme performance and achieve adaptive protection. Extensive simulation studies show that the proposed scheme provides a fast relay response and high accuracy in fault location under various system and fault conditions. The proposed method responds very well with regards to dependability, security, and sensitivity (high-resistance fault coverage). [ABSTRACT FROM AUTHOR]

This paper proposes a novel adaptive relaying scheme based on phasor-measurement units (PMUs) for transmission lines. The proposed adaptive relaying scheme can provide an extremely accurate discrimination between in-zone and out-of-zone faults. Two novel and composite fault discrimination indices in terms of Clarke components of synchronized voltage and current phasors at two ends of a line are derived. A line parameter estimation algorithm is developed and built in the newly designed relay to solve the uncertainty problem of line parameters. The proposed relaying scheme is independent of fault types, fault locations, fault path resistance, fault inception angles, and the variations of source impedance. The tripping decision time of the designed relay is very fast and almost held well within 6 ms for most fault events. All of the EMTP simulation results show that the proposed adaptive relaying scheme provides a high level of dependability and security. [ABSTRACT FROM AUTHOR]

Determines the minimal amount of statistical information about source signals for which blind equalization is possible for multiple-input multiple-output finite-impulse response (MIMO-FIR) channels. Condition for blind equalization when the source signals are white and spatially fourth-order uncorrelated; Criterion for blind equalization of MIMO-FIR channels; Alternative condition in terms of cumulants for the blind equalization of MIMO-FIR channels.

Examines the use of voltage and currence phasors in detecting fault in transmission line. Criteria for faulted leg identification; Occurrence of errors in fault location; Estimation of power frequency and phasor.

Examines the protection scheme for parallel transmission lines. Effects of fault inception angles on the protection performance of electric lines; Principle of the fault detection location scheme; Impact of the scheme on power system faults.

Investigates the system-theoretic foundation for blind equalization of a finite-impulse response multiple-input multiple-output channel system in a channel-filter setting. Objective of blind equalization; Factorization theorem for equalizable channel matrices; Orders and cononical structures of equalizers.

Studies the law of large numbers and the Shannon-McMillan theorem for Markov chain fields on trees. Discussion of the law of large numbers for the frequencies of occurrence of states and ordered couples of states for Markov chain fields in a Bethe tree; Proof of the Shannon-McMillan theorem; Coding theorem for a Markov chain field on a Bethe tree.

Presents a fault location algorithm based on phasor measurement units for series compensated lines. Decline of the operation mode of the series device to compute the voltage; Utility of two-step algorithm; Effects of various operation modes of the compensated device during the fault period.

Proposes a method for estimating fault sections in power substations. Knowledge representation and inference procedures based on the cause-effect networks and rule matrix transformation techniques; Testing of the method on a typical Taiwan Power Co.'s secondary substation; Superiority of the method to existing production systems in the inference speed and the process of implementation.

Proposes a precise digital algorithm, called smart discrete Fourier transforms (SDFT), to estimate the frequency of a sinusoid power system with harmonics in real-time. Prevention of errors when frequency deviates from nominal frequency; Recursive computing; Frequency estimation; Phasor measurement.

Deals with a study which presented an application of a combined the genetic algorithms (GA) and Lagrangian relaxation (LR) method for unit commitment (UC) problem. Background on both methods; Formulation of the UC problem; Analysis of the LRGA method.

Proposes a novel approach for on-line fault section estimations and fault type identification using the hybrid cause-effect network/fuzzy rule based method in distribution stations. Importance of a correct and rapid inference for on-line fault diagnosis in substations; Suitability of cause-effect network to parallel processing; Improvement in inference speed.

Proposes a series of precise digital algorithms based on Discrete Fourier Transforms (DFT) to calculate the electric power frequency and phasor in real-time. Algorithms of the basic Smart Discrete Fourier Transforms (SDFT); Claimed benefits of SDFT; Comparison between simulation results and conventional DFT method and second-order Prony method.

Presents information on a study which proposed methods for the computation of power system dynamic response for real-time transient stability prediction. Real-time prediction problem and dynamic model; Criteria for transient stability prediction; Conclusions.

Proposes a technique based on hyperrectangular composite neural networks (HRCNN) and fuzzy hyperrectangular composite neural networks (FHRCNN) for voltage security margin estimation. Symbolic representation of a two-layer HRCNN and FHRNN; Process of generalization for a rectangular concept; Comparisons of classification performance of the two system.

Responds to comments on an article appearing in the April 2000 issue of 'IEEE Transactions on Power Delivery,' which dealt with a method for the determination of power supply frequency and phase. Frequency from fundamental and nonintegral harmonics; Sensitivity of algorithms to window length.

Many applications using accelerator beams require a nearly uniform beam distribution at the target. A nested structure magnet producing a step-like magnet field has been proposed to transform an originally Gaussian or even irregular distribution into a more-or-less uniform one at targets. In this paper, the prototyping of a step-like field magnet is presented, which is based on the application in the China Spallation Neutron Source where the magnets are used to obtain a uniform beam profile from an initially irregular distribution at the spallation target. It includes the magnet design, 3D magnetic field calculation, prototype fabrication and field measurement. The prototyping confirms the technical feasibility of the magnet structure and the magnetic field quality consistent with the field calculations. The design improvements are discussed from the prototyping experience. [ABSTRACT FROM AUTHOR]

This paper proposes a position sensorless control scheme for four-switch three-phase (FSTP) brushless dc (BLDC) motor drives using a field programmable gate array (FPGA). A novel sensorless control with six commutation modes and novel pulsewidth modulation scheme is developed to drive FSTP BLDC motors. The low cost BLDC driver is achieved by the reduction of switch device count, cost down of control, and saving of hall sensors. The feasibility of the proposed sensorless control for FSTP BLDC motor drives is demonstrated by analysis and experimental results. [ABSTRACT FROM AUTHOR]

This paper proposes a variable-sampling variable structure controller (VSC) for brushless dc (BLDC) motor drives with low-resolution position sensors (Hall sensors). The variable-sampling characteristics arising from the situation where measurements depend on the path-embedded sensors will result in the uncertainty of the discrete-time models. To circumvent this issue, a modification of the conventional discrete-time VSC control law for BLDC motor drives with Hall sensors is derived to achieve the robustness of speed control. Three measurement error-mitigation methods are also presented to reduce the errors due to low-resolution position feedback. Both simulated and experimental results confirm the effectiveness of the proposed controller and error-mitigation techniques. [ABSTRACT FROM AUTHOR]

With the increasing use of nonlinear loads in power systems, the harmonic pollution becomes more and more serious. It is well known that fast Fourier transform (FFT) is a powerful tool for power signal harmonic analysis, but leakage effect, picket fence effect, and aliasing effect make FFT suffer from specific restrictions. In this paper, we proposed a new method for power signal harmonic analysis. The major components of this method are a frequency and phasor estimating algorithm, a finite-impulse-response comb filter, and a correction factor. We also combine other methods to enhance our performance, such as discrete Fourier transform and least square error (LSE) method. To verify this method, we provided the comparisons of this method with FFT. [ABSTRACT FROM AUTHOR]

Active devices, including electrostatic discharge protection devices and ring-oscillator Circuits, under CMOS I/O pads are investigated in a 130 nm full eight-level copper metal complementary metal-oxide-semiconductor process, using fluorinated silicate glass (FSG) low-k inter-metal dielectric. The high current I-V curve measured in the second breakdown trigger point ( V[sub t2], I[sub t2] ) of ESD protection devices under various metal level stack structures, shows that i) I[sub t2] depends very weakly on the number of metal levels used, as expected given specific junction power dissipation criteria; and ii) V[sub t2] increases with the number of metal level stacks of I/O pads because of increased dynamic impedance due to the presence of more metal levels, as clarified by a simple RC model. Moreover, no noticeable degradation in the speed of the ring-oscillator circuit, as measured for a variety of test structures subjected to bonding mechanical stress, thermal stress by temperature cycling and dc electrical stress by transmission line pulse, as well as ac electrical stress by capacitive-coupling experiments. Accordingly, active devices under CMOS I/O pads is independent of bonding pad metal level structures. [ABSTRACT FROM AUTHOR]

Responds to comments about a proposed fault protective scheme for transmission lines that uses synchronized phasor measurements through Global Positioning System (GPS) satellites. Real-time wide area measurements from phasor measurement units; Protection scheme with GPS for data synchronization.

This paper utilizes electrical analyses and a study of physical mechanisms to investigate metal gate structure-dependent performance in amorphous InGaZnO (a-IGZO) thin-film transistors. The effects of different shielding areas between the IGZO layer and metal gate are investigated. In devices with shorter metal gate lengths, an abnormal rise in capacitanceat the off-state in capacitance--voltage ( C-V) characteristic curves can be observed. This can be attributed to the stronger electric field induced by the edge of themetal gate under bias sweepwhen themetal gate length is shorter than the IGZO layer length. Light illumination measurements indicate a negative shift in threshold voltage and an increase in subthreshold-leakage current regardless of relative metal gate length. Moreover, negative threshold voltage shift becomes more severe with a more obvious hump in C-V characteristic curves under backlight illumination of a shorter width device, a phenomenon which has been verified by simulation. [ABSTRACT FROM AUTHOR]

Mode characteristics of AlGaInAs/InP square resonator microlasers laterally confined by a bisbenzocyclobutene layer, with an output waveguide connected to one vertex or the midpoint of one side, are investigated numerically and experimentally. Numerical simulation results indicate that the square resonator with the midpoint output waveguide has a better single-mode property, but a lower mode Q-factor than that with the vertex output waveguide. For a 20-μm-side-length square microlaser with a 1.5-μm-wide vertex output waveguide, lasing spectra with multiple transverse modes are observed with the mode wavelength intervals agreeing with the 2-D-finite difference time domain simulation results. In contrast, single-mode operation with a side-mode suppression ratio of 42 dB is obtained for a 20-μm-side-length square microlaser with a 1.5-μm-wide midpoint output waveguide. The results indicate that output waveguide can result in a mode selection in addition to realizing unidirectional emission. [ABSTRACT FROM AUTHOR]

Adaptive voltage positioning (AVP) has been used in multiphase voltage regulator module (VRM) applications. A novel scheme, called AVP+, is analyzed in this paper. Small signal model is used to look into the control performance issues such as output impedance and stability. The model has been verified in the experiments and simulations. Compared to a conventional AVP schemes, the present scheme provides better stability margin and output- impedance performance. This is especially true for the prevailing trend of using ceramic output capacitors and high switching frequency. The focus of the present paper is the small-signal modeling for control loop design using the AVP+ scheme which was never analyzed before. And the comparisons were made between AVP+ and AVP- on the stability and output impedance performance. [ABSTRACT FROM AUTHOR]