Spl Beta Research Articles

Application of Monte Carlo simulation to optimal maintenance scheduling in a parallel-redundant system

A modified distribution function is created based on the assumption that the component useful life phase is associated with an exponential distribution and the wearout period is subject to a Weibull distribution (/spl beta/>1). Using the modified distribution function, a Monte Carlo simulation approach is used to obtain the total failure frequency and optimum maintenance interval for a parallel-redundant system where each component can enter its wearout period. Two examples are used to illustrate the simulation procedure. The effect of the Weibull parameter /spl beta/ on the optimum maintenance interval for a parallel-redundant system is illustrated.

High ion-acceleration by employing a low-γ intense electron-beam

Analyses of results of ion acceleration employing intense electron-beam revealed that the nucleon energy attained per unit energy investment scaled inversely with /spl gamma/. Total energy scaling is supported by a potential well sustained over a long distance by suitable beam-duration. Following this, a low /spl gamma//spl sim/1.49, 6 kA, 40 ns FWHM electron beam from KALI-200 was focused into a short dielectric collimator and propagated in vacuum for durations of 15-150 ns, and ions were accelerated to nucleon energy over 20-30 MeV/kJ with ion current /spl sim/kA/kJ. The enhancement in ion energy was also attributed to the low-/spl gamma/ assisted peak Poisson field E/sub z//spl sim/C/sub 0/I/sub e///spl beta//sub e/c/spl delta/, small well-length /spl delta//spl prop//spl beta//sub e/, and ion-charge multiplication. The minimum /spl gamma/ is decided by desired high electric field for intense electron-beam generation by field emission and maximum multiple ionizations.

Improved hot workability and magnetic properties in NdFeCoGaB hot deformed magnets

The hot workability and the magnetic properties of die-upset and backward extruded melt-spun magnets with the composition of Nd/sub 14.2/Fe/sub 80.8/B/sub 5/ (MQP-A), and Nd/sub 13.6/Fe/sub 73.6/Co/sub 6.6/Ga/sub 0.6/B/sub 5.6/ (MQU-F) have been investigated. Magnets of MQU-F powder show an improved hot workability and better magnetic properties compared to the ternary alloy. Remanence, coercivity and energy product of die-upset MQU-F magnets were found to be B/sub /spl tau//=1.3 T, /spl mu//sub 0j/H/sub c/=1.7 T, and (BH)/sub max/=326 kJm/sup -3/, respectively. SEM and TEM investigations revealed a smaller average grain size in MQU-F magnets, which has a positive effect on the hot workability and magnetic properties. Radially oriented ring magnets were produced from both alloys and characterized magnetically. The temperature coefficients of ring magnets were determined to be /spl beta/=(dH/sub c//dT)=-0.6%//spl deg/C and /spl alpha/=(dB/sub /spl tau///dT)=-0.09%//spl deg/C. A higher deformation speed can be used for the production of MQU-F magnets, which should make the process more economic.

Polarization fatigue in ferroelectric polymers

Ferroelectric materials are characterized by a spontaneous polarization which can be switched by an applied electric field. In many ferroelectrics the magnitude of the reversed polarization is observed to decrease when the polarization is switched many times. In ferroelectric polymers a significant decrease in reversed polarization may be observed after /spl sim/3000 cycles, and the reduction can be /spl sim/50% of the initial value. Infrared and X-ray observations show a conversion of the non-polar /spl alpha/ crystal form to the ferroelectric /spl beta/ form in samples containing a mixture of the crystal phases. However there appear to be no crystalline changes of such a nature as would lead to fatigue. A decrease in dielectric loss at low frequencies is observed in all fatigued samples, suggesting that space charge trapping may be involved in the fatigue process.

PD recognition by means of statistical and fractal parameters and a neural network

A novel partial discharge (PD) defect identification method is described. Starting with PD data on different families of specimens, a suitable set of parameters are determined and then used as input variables to a neural network for the purpose of identifying the defects within the insulation. In this procedure the statistical Weibull analysis is performed on PD pulse amplitude histograms to obtain the scale parameter /spl alpha/ and the shape parameter /spl beta/. Thereafter, the two statistical operators (skewness and kurtosis) and two fractal parameters (fractal dimension and lacunarity) are evaluated from the PD phase on the discharge epoch histogram and from the 3 dimensional (pulse amplitude/phase/discharge rate) histogram, respectively. Following the exposition of the basic mathematical concepts regarding the above parameters, experimental results are reported on the recognition capability of the method in defining the defect category in a number of different specimens.

A novel approach to the design of a shunt active filter for an unbalanced three-phase four-wire system under nonsinusoidal conditions

A new approach is presented for the design of a shunt active filter in a three-phase, four-wire distribution system with unbalanced, distorted sources and unbalanced loads. The purpose of the shunt active filter is to provide compensation currents such that the source needs to supply balanced (positive-sequence) fundamental source current at unity power factor even though the load consumes harmonic currents as well as positive, negative, and zero-sequence currents. A major feature of the proposed approach is that it does not require symmetrical component transformation to transform the three-phase voltages and currents to /spl alpha/-/spl beta/-o quantities. This makes practical implementation of the proposed method easier than the symmetrical component transformation approach. In addition, the power factor of the positive-sequence fundamental component is close to unity and only positive-sequence power is supplied by the source. The effectiveness of the proposed control algorithm is demonstrated by computer simulation and experimental results of a shunt active filter for a three-phase four-wire distribution system with distorted, unbalanced source voltages and unbalanced loads.

Influence of design parameters on cogging torque in permanent magnet machines

The influence of various design parameters on the cogging torque developed by permanent magnet machines is investigated. It is shown that the slot and pole number combination has a significant effect on the cogging torque, and influences the optimal value of both skew angle and magnet arc, as well as determining the optimal number of auxiliary teeth/slots. A simple factor, which is proportional to the slot number and the pole number and inversely proportional to their smallest common multiple, has been introduced to indicate the "goodness"/spl beta/ of the slot and pole number combination. In general, the higher the "goodness" factor the larger the cogging torque.

Microwave radiation induces a heat-shock response and enhances growth in the nematode Caenorhabditis elegans

This paper shows that prolonged (overnight) exposure to continuous microwave fields (750 MHz, 0.5 W) can induce both a heat-shock response and enhanced growth in the nematode worm Caenorhabditis elegans. Exposures were conducted in a TEM cell with matched load, producing an E-field of approximately 45 V m/sup -1/ at the center (where test worms are placed). Biomonitoring of heat-shock responses has been simplified by using two transgenic strains (PC72 and PC161), which both carry stress-inducible reporter constructs, respectively, placing lacZ (/spl beta/-galactosidase) and lacZ plus green fluorescent protein expression under the control of C. elegans hsp16-1 promoters. In situ localization of reporter expression reveals a minority of test worms, which respond strongly to microwave exposure. Enzyme activity measurements average these reporter responses across many thousands of individual worms, giving a reliable indication of the overall stress imposed on a population. The temperature profile of reporter responses induced by microwave exposure parallels that induced in controls by heat alone, but is displaced down the temperature scale by some 3/spl deg/C. Length measurements were conducted at intervals in synchronized C. elegans cultures seeded with L1 larvae. Using pooled data from nine separate runs, growth was stimulated by 8.5% after overnight microwave exposure (relative to controls), and this disparity increased to 11% after 24 h of further growth without irradiation. Both heat-shock responses and increased growth would be consistent with a modest increase in temperature, raising the possibility that microwave exposure might cause limited heating in this system. However, there is no detectable rise in the temperature of either medium or worms during overnight exposure under these conditions, discounting both generalized and localized (worm-specific) heating effects. It is concluded that both growth and heat-shock responses are induced by microwave exposure through one or more nonthermal routes.

Simultaneous optical and nuclear magnetic resonance spectroscopy for monitoring cardiac energetics in vivo.

There are a number of applications in which it is useful to simultaneously collect data from what are traditionally separate instrumentation modalities. In particular, in vivo physiological investigations in which data from parallel experiments must be correlated would benefit from simultaneous data collection through 1) elimination of subject variability, 2) elimination of treatment variability, and 3) a reduction in the number of animal preparations required. Here we describe the simultaneous collection of fluo-3 optical fluorescence and 31P nuclear magnetic resonance (NMR) spectra to measure intracellular calcium levels and high-energy phosphate metabolism, respectively, in vivo. This work is part of ongoing research into the profound anoxia tolerance exhibited by the hearts of certain turtle species. An NMR compatible optical fluorescence spectrometer was constructed and tested. In the 31-cm bore of a 2 T superconducting magnet, NMR and optical spectra were collected every 10-15 min from the in situ, in vivo hearts of anesthetized turtle subjects prior to and during one to three hours of anoxia. It was found that while PCr stores became significantly depleted during anoxia, beta-adenosine triphosphate (ATP) levels remained within 20% of control values, and intracellular diastolic calcium levels did not vary by more than 10%. The ability to make simultaneous phosphorus and calcium measurements on a single subject is important to understanding the exact relationship between phosphorus energy state and maintenance of calcium homeostasis.

Experimental method for determining the second-ordercoefficient of nonlinear conductance of Gunn oscillator

An experimental method for determining the second-order coefficient (/spl beta/) of the nonlinear conductance of a Gunn diode oscillator is presented. This is obtained in a novel way by utilising the dependence of the device characteristic on the frequency response characteristic of an injection locked oscillator. /spl beta/ is found to be bias dependent and the measured values corroborate the theoretical findings.

Decoding of binary separable Goppa codes usingBerlekamp-Massey algorithm

It is shown that the Berlekamp-Massey algorithm can be applied without exceptions to decode the class of binary Goppa codes with location set /spl Gamma/={/spl gamma//sub 1/,....,/spl gamma//sub n/}/spl sube/GF(2/sup m/) and separable Goppa polynomial G(=)==+=+/spl beta/ defined over GF(2/sup m/) such that G(/spl gamma//sub i/)/spl ne/0 for 1/spl les/i/spl les/n up to the designed minimum distance 2l+1.

Worst-month rain statistics for radiowave propagationstudy in Malaysia

A study of the worst-month rainfall rate statistics for the Malaysian environment is presented. Rain rate data with 1 min integration time were collected in the Universiti Teknologi Malaysia and the Universiti Sains Malaysia. The relationship between the worst month and the yearly probabilities is presented and the ITU-R model verified. For better precision, new values are proposed for the parameters Q/sub 1/ and /spl beta/ in Malaysia.

Beam-cavity interaction circuit at W-band

In this paper, we describe the design, fabrication, and bench study of a millimeter-wave cavity employed as a relativistic klystron output structure. The oxygen-free electronic-grade copper cavity was prepared by electro-discharge machining and diffusion bonding, and cleaned and tuned to 91.4 GHz. Measured cavity characteristics are presented and compared with theory, including quality factor Q, coupling parameter /spl beta/, scattering matrix S/sub 11/, and axial electric field profile E/sub z/. This paper provides the basis for an understanding of the cavity as a transfer structure.

Optimal shape function for a bidirectional wire under Elmore delay model

In this paper, we determine the optimal shape function for a bidirectional wire under the Elmore delay model. Given a bidirectional wire of length L, let f(x) be the width of the wire at position x, 0/spl les/x/spl les/L. Let T/sub DR/ be the right-to-left delay. Let T/sub DL/ be the left-to-right delay. Let T/sub BD/=/spl alpha/T/sub D/R+/spl beta/T/sub DL/ be the total weighted delay where /spl alpha//spl ges/0 and /spl beta//spl ges/0 are given weights such that /spl alpha/+/spl beta/=1. We determine f(x) so that T/sub BD/ is minimized. Our study shows that, /spl alpha/=/spl beta/, the optimal shape function is f(x)=c, for some constant c; if /spl alpha//spl ne//spl beta/, the optimal shape function can be expressed in terms of the Lambert's W function as f(x)=-c/sub f//2c/sub 0/((1/W(-ae/sup -bx/))+1), where c/sub f/ is the unit length fringing capacitance, c/sub 0/ is the unit area capacitance, a and b are constants in terms of the given circuit parameters. If /spl alpha/=0 or /spl beta/=0, our result gives the optimal shape function for a unidirectional wire.

A detailed instantaneous harmonic and reactive compensation analysis of three-phase AC/DC converters, in abc and αβ coordinates

This paper presents a digital simulation of an active filter, in which the instantaneous harmonic and reactive compensating currents are desegregated in their different /spl alpha//spl beta/ space-trajectories, and in their time-domain waveforms of both the abc and the /spl alpha//spl beta/ system of coordinates. Departing from Akagi's generalized instantaneous reactive power theory, a complete analysis is presented, in which the counterharmonic compensating current injected to the coupling point of the AC mains feeding a six-pulse-controlled three phase AC/DC power converter is desegregated in its three components, namely: (a) fundamental reactive current; (b) oscillating harmonic reactive current; and (c) oscillating harmonic active current. It is demonstrated, in a selected number of abc and /spl alpha//spl beta/ oscillograms and current-space-trajectories that the active filter can compensate either separately or jointly the above mentioned currents.

Formation and magnetostructural characterization of the novel ternary compound Ce/sub 3/Fe/sub 29-x/Mo/sub x/

Formation and magnetostructural properties of the novel ternary ferromagnetic compound Ce/sub 3/Fe/sub 29-x/Mo/sub x/ is reported. It was obtained in alloys with nominal compositions Ce/sub 3/Fe/sub 29-x/Mo/sub x/, x=1.4, 1.5, and 1.6, prepared by arc melting and annealing during three weeks at 950/spl deg/C. The crystal structure was well resolved as monoclinic with space group A2/m (No 12). Quantitative phase analysis, based on the processing of the X-ray diffraction patterns by the Rietveld method, was performed. Ce/sub 3/Fe/sub 29-x/Mo/sub x/ is the main phase (78-72 wt.%) with lattice parameters a=10.553(1) /spl Aring/, b=8.511(1) /spl Aring/, c=9.688(1) /spl Aring/, and /spl beta/=96.78(1)/spl deg/. It coexists with Ce(Fe,Mo)/sub 12/ as main spurious phase. Atomic positions and mean Fe-Fe interatomic distances are reported. Temperature-dependent magnetic susceptibility shows well-defined transitions at 7 and 115/spl deg/C, which correspond to the 3:29 and 1:12 phases, respectively. Saturation magnetization at 4.2 K is 123 emu/g.

Frequency estimation of distorted power system signals using extended complex Kalman filter

The paper proposes an extended complex Kalman filter and employs it for the estimation of power system frequency in the presence of random noise and distortions. From the discrete values of the 3-phase voltage signals of a power system, a complex voltage vector is formed using the well known /spl alpha//spl beta/-transform. A nonlinear state space formulation is then obtained for this complex signal and an extended Kalman filtering approach is used to compute the true state of the model iteratively with significant noise and harmonic distortions. As the frequency is modeled as a state, the estimation of the state vector yields the unknown power system frequency. Several computer simulations test results are presented in the paper to highlight the usefulness of this approach in estimating near nominal and off-nominal power system frequencies.

Optimization of SiGe HBTs for operation at high current densities

A comprehensive investigation of the impact of Ge profile shape as well as the scaling of collector and base doping profiles on high-injection heterojunction barrier effects in SiGe HBTs has been conducted over the -73-85/spl deg/C temperature range. The onset of Kirk effect at high current densities is shown to expose the Si/SiGe heterojunction in the collector-base space charge region, thereby inducing a conduction band barrier which negatively impacts the collector and base currents as well as the dynamic response, leading to a premature roll-off in both /spl beta/ and f/sub T/. In light of this, careful profile optimization is critical for emerging SiGe HBT circuit applications, since they typically operate at high current densities to realize maximum performance. We first explore the experimental consequences and electrical signature of these barrier effects over the 200-358 K temperature range for a variety of Ge profiles from an advanced UHV/CVD SiGe HBT technology. We then use extensive simulations which were calibrated to measured results to explore the sensitivity of these barrier effects to both the Ge profile shape and collector profile design, and hence investigate the optimum profile design points as a function of vertical scaling.

Pulse height distributions of /spl beta/ rays in /sup 14/C measurement with liquid scintillation counting system Quantulus

To investigate the variations of the solar activity over a long time scale, we have started the measurements of /sup 14/C in an ancient tree, synthesizing 10 g benzene from the tree rings and using the liquid scintillation counting system Quantulus with ultra low background level. The background rate of the Quantulus was 1.2 cpm while the counting rate of /sup 14/C was 91.0 cpm for the ancient tree. The pulse height distribution of /spl beta/ rays from /sup 14/C was well fitted with theoretical /spl beta/ rays spectrum. The Quantulus detected /spl beta/ rays down to 7.5 keV with good detection efficiency. It was confirmed that the total counts from the /sup 14/C in the sample benzene can be measured within 0.2% accuracy on the basis of the pulse height distribution of a standard benzene sample, using the least squares fitting method.

Josephson junctions with hysteretic current voltage characteristics at high temperatures

The properties of bicrystal Josephson junctions with external capacitors are reported. It was found that the hysteresis in the current voltage (IV) characteristic was very sensitive to the wavelength of the Josephson oscillation in the dielectric and thermal noise suppression of the critical current. A McCumber parameter /spl beta//sub c/ of 1.2 at 65 K has been achieved. In addition intrinsic grain boundary capacitance has been found to give a large /spl beta//sub c/ value of 9.6 at 4.2 K.