New procedures for minimizing the torque ripple in switched reluctance motors by optimizing the phase-current profile

This paper introduces five new optimization procedures for the minimization of the torque ripple in the switched reluctance motor (SRM). These new procedures are based on the optimization of the phase-current profile. Two optimization techniques, the simplex method and the genetic algorithm, are adapted to these optimization procedures. The paper compares an older optimization procedure, the optimum harmonic current injection procedure, and the new optimization procedure, and presents conclusions.     

Cancer incidence in a cohort of infertile women

Among 2,496 infertile Israeli women treated between 1964 and 1974, 143 cancer cases were observed as compared with 116.1 expected (standardized incidence ratio (SIR) = 1.2, 95% confidence interval (CI) 1.0-1.5) through 1991. Site-specific analysis revealed 12 ovarian cancers versus 7.2 expected (SIR = 1.6, 95% CI 0.8-2.9), 21 endometrial cancers versus 4.3 expected (SIR = 4.85, 95% CI 3.0-7.4), and 59 breast cancers versus 46.6 expected (SIR = 1.3, 95% CI 0.96-1.6). Sensitivity analysis revealed that confounding was unlikely to explain the raised risk of endometrial cancer, but nulliparity might explain the increased risk of ovarian cancer. The excess of endometrial cancer was prominent among patients with normal estrogen production but progesterone deficiency (SIR = 9.4, 95% CI 5.0-16.0). The risk for ovarian cancer was similar among the total groups of treated and untreated patients (SIR = 1.7 vs. 1.6). The standardized incidence ratio for endometrial cancer was higher among the treated group than the untreated group, although not significantly. Treatment with ovulation-inducing drugs does not appear to increase the risk for ovarian cancer, but its role cannot be completely excluded.     

Platelet-activating factor in cardiovascular stress situations

Since the elucidation of its chemical structure two decades ago, platelet-activating factor (PAF) has emerged as an important mediator of various cardiovascular stress situations. Most notably, PAF was implicated as a key factor in the septic shock syndrome, based on the similarities between endotoxin and PAF biological effects, the elevation of circulating and tissue levels of PAF during endotoxemia, and the protective effect of PAF antagonists in the septic state. In addition, accumulating data suggest the involvement of PAF in the pathophysiological processes associated with ischemia, hemorrhage and trauma, where PAF exerts its effects directly on cells and blood elements or indirectly through interactions with other mediators such as cytokines and prostaglandins. Nevertheless, the relative contribution of PAF to the pathophysiological processes in endotoxemia is still unknown and should await further investigations. The primary aims of this chapter are: to delineate the effects of PAF on the cardiovascular system, to summarize the data which suggest the involvement of PAF in stress situations of the cardiovascular system, and to identify areas where future experimental efforts should be focused. Based on a paper presented at the Third International Conference on Platelet-Activating Factor and Structurally Related Alkyl Ether Lipids, Tokyo, Japan, May 1989.     

A simple evaluation of magnetic fields and eddy currents inferromagnetic straps of finite length

A simple analytical method to evaluate the electromagnetic fields in a ferromagnetic strap of finite dimensions, excited by a short coil, is presented. The method can be extended to ferromagnetic cylindrical parts of finite length, and also to nonlinear ferromagnetic materials by assuming an appropriate change of magnetic permeability with material depth. The original configuration of the finite-length strap and short excitation coil is replaced by an arrangement of many straps glued together, and magnetized by a suitable succession of excitation coils. This last configuration can be solved analytically according to the Fourier transform method. Results obtained by the proposed method are in good agreement with results obtained by a finite-element method, and also with experimental results     

Phase-shifted Discontinuous Pulse-Width Modulation Methods for Multi-level Inverters Operated in Over-modulation Range

This article presents combinations of the generic phase-shifted pulse-width modulation method with conventional discontinuous pulse-width modulation methods operated in the over-modulation range. The treated discontinuous methods are the third harmonic injection, Depenbrock's DPWM1, and Ogasawara's DPWM2. The significant advantage of the present approach over the conventional phase disposition pulse-width modulation method is the equal power flow between the H-bridges and the improved distribution of the switching operations number between them. Furthermore, they provide improved linearity in the over-modulation range. The proposed pulse-width modulation methods are analyzed by extensive simulation results. Several aspects, such as the total harmonic distortion factor of the inverter output currents and voltages, harmonic content, frequency spectrum distribution, and switchings number, are studied.     

Multi-pulse Rectifiers Feeding H-bridge Inverter

This article presents a comparative analysis of 12-, 18-, 24-, and 36-pulse rectifier topologies supplying 3-phase three-level H-bridge inverters as active loads. The analysis comprises the total harmonic distortion data of the inverter and grid currents and voltages, including inter-modulation harmonics. This article shows that the rectifier-inverter connection produces inter-modulation harmonics between the grid and inverter frequencies. As a result, inter-modulation and sub-harmonics are present in the grid currents. This article presents an analysis and comparison of these inter-modulation effects for the mentioned topologies. Moreover, it is shown that the inter-modulation effects can be reduced by increasing the capacitance of DC-link capacitors, increasing grid series inductance, and using rectifiers with high number of pulses. The analysis is validated by extensive simulation results.     

Virtual torque and inertia loading of controlled electric drive

This work presents a simple method to obtain effects similar to those obtained by real mechanical loading and real inertia variation but without any mechanical parts supplementary to the electric motor of the studied electric drive. The electric motor itself produces the load torque and the inertia variation using digital signal processing software. Therefore, the electric drive is virtually torque and inertia loaded, while its behavior is similar to that of the actual loaded drive. The present method could be used to test the implementation of control algorithms or for didactic purposes using motion control kits found on the market. The present method is used with laboratory works of the DSP Fundamentals in power electronics course at the Department of Electrical and Computer Engineering, Ben-Gurion University of the Negev, Beer-Sheva, Israel.     

Economic and health risk trade-offs of swim closures at a Lake Michigan beach

This paper presents a framework for analyzing the economic, health, and recreation implications of swim closures related to high fecal indicator bacteria (FIB) levels. The framework utilizes benefit transfer policy analysis to provide a practical procedure for estimating the effectiveness of recreational water quality policies. Evaluation criteria include the rates of intended and unintended management outcomes, whether the chosen protocols generate closures with positive net economic benefits to swimmers, and the number of predicted illnesses the policy is able to prevent. We demonstrate the framework through a case study of a Lake Michigan freshwater beach using existing water quality and visitor data from 1998 to 2001. We find that a typical closure causes a net economic loss among would-be swimmers totaling dollars 1274-37,030/day, depending on the value assumptions used. Unnecessary closures, caused by high indicator variability and a 24-h time delay between when samples are taken and the management decision can be made, occurred on 14 (12%) out of 118 monitored summer days. Days with high FIB levels when the swim area is open are also common but do relatively little economic harm in comparison. Also, even if the closure policy could be implemented daily and perfectly without error, only about 42% of predicted illnesses would be avoided. These conclusions were sensitive to the relative values and risk preferences that swimmers have for recreation access and avoiding health effects, suggesting a need for further study of the impacts of recreational water quality policies on individuals.