A decade ago, cutaneous lasers had only recently established a firm place, albeit peripheral, in the armenentarium of head and neck surgery. A combination of physical and clinico-histopathological evaluation had proved that lasers could be very effective and safe in treating very specific cutaneous 1esions.l-5 Now, in 1998, the clinician is presented with an almost overwhelming choice of different lasers and devices and also recommended indications. Much of this explosion is due to a focus on cosmetics rather than pathological lesions.6-13 This article surveys the current field of cutaneous lasers and addresses some of the difficulties confronting the clinician choosing or recommending a laser. These difficulties include the fact that in this rapidly expanding market, the ideal matching of technology to tissue effects correlated by histopathological studies, has taken second place to marketing imperatives in which lasers are advocated as appropriate for almost any clinical application. Thus, an analysis of the field by technology of laser type alone is inadequate and confusing.

A methodology is presented to determine the optimal sequence of capacitor switching in a power system for maintaining a desirable voltage profile over a load cycle. In the first part of the algorithm, the set point voltage of the generators are determined by a non-linear secondary voltage controller that is emulated by a feedforward neural network. In the second part, these generator voltages constitute the starting point to determine the optimal switching of capacitors by using a dynamic program solver. The algorithm was validated on an IEEE 57 bus test system with the individual loads varying non-uniformly between 50% and 110% of their base values.

The pulsed dye laser was developed for the treatment of vascular cutaneous lesions using single non-overlapping pulses. However, in practice, overlap and multiple pulses to the same site are commonly used. This study was undertaken to examine the effects of single vs two, three and five pulses to the same site on penetration depth of the laser beam and vascular selectivity. Two albino pigs were treated with a 577 nm, 450μs, 3 mm-diameter pulsed dye laser. The effect of multiple pulses to the same site over a range of fluences was analysed histologically from biopsies acquired immediately and at 1 and 4 days after laser irradiation. The results show that multiple pulses to the same site do not increase the penetration depth (maximum depth from the dermo-epidermal junction where damaged blood vessels are observed) of irreversible vascular injury. Cumulative pulses do increase the extent of tissue injury, including both desired vascular changes and unwanted effects such as extravasation. No clinical changes were observed following multiple pulses below 2 J cm−2. It was concluded that 577 nm, 450μs multiple pulses to the same site do not increase penetration depth of vascular injury of the laser beam.

The operation continuity of a critical sysnchronous motor load group subjected to momentary voltage sags can be enhanced by locally installing a static var compensator (SVC). A method is presented to determine the minimum capacitive SVC rating necessary for the system to be transient stable, and to apply a micro-processor based control of the SVC admittance for providing damping of the power oscillations. The results are validated by simulation of the full order nonlinear model of the drive and distribution system.

The transient stability of a critical induction machine load group during momentary as well as continuing voltage sags can be enhanced by using a fast-response voltage regulator in the form of a static VAr compensator (SVC) or a thyristor controlled tap changer (CTC). A procedure is presented for determining the minimum SVC rating or CTC off-nominal turn ratio including control of the SVC admittances or CTC taps to meet dynamic and steady-state specifications. The limitations of their effectiveness to preserve operation continuity are also shown. >

An expert system using a two-stage artificial neural network is proposed to control in real time multicap capacitors installed on a distribution system for a nonconforming load profile such that the system losses are minimized. The required input data are directly obtained from online measurements which include the active and reactive line power flows, voltage magnitudes, and the current capacitor...

The problem of large system size in the optimal design of switchable capacitors installed on a radial distribution system is solved by a piecewise method. The algorithm is based on tearing the system into smaller subsystems, optimizing the individual subsystems, and coordinating the subsystem solutions to yield the overall system optimization. Studies on a test system show the piecewise method to have satisfactory results as well as the significance of using appropriate load models.

A method is presented for finding the optimum fixed LC combination for power factor compensation of nonlinear loads where both source and load impedances are represented as randomly time-varying quantities. The distribution characteristics of these random variables at a supply bus can be experimentally determined by using a microcomputer-based parameter estimator. If maximum power factor is the main concern, the optimal LC combination corresponding to maximum average power factor is obtained for any given compensator cost. Laboratory tests show the optimization algorithm and the parameter estimator to be very efficient and accurate.< >

An optimal method to control the speed of a wound-rotor induction motor by variable external rotor impedance is presented. The rotor impedance is adjusted so that, for any desired torque and slip values, the total copper losses are minimized. Motor efficiency is improved compared with the case of conventional speed control by variable rotor resistance only. An example illustrates the copper loss reduction and dynamic behavior of the drive. Simulation study results that show the percentage copper loss reduction is generally likely to be higher for lighter loads. For constant-torque loads, the reduction percentage reaches a peak at the lower slip values, whereas for fan-type loads the most significant percentage copper-loss reduction occurs at both the higher and lower slip values. The response time of the rotor speed for startup or a sudden change in the speed setting is considerably smaller than that achieved by pure rotor resistance control.< >

The commenter argues that ignoring compensator rating in the optimal design of a shunt LC compensator for power engineering applications is neither realistic nor physically justified. Furthermore, minimization of source reactive power only with respect to either L or C results in a not necessarily global minimum. Computation and var specification errors were also found and corrected. For compariso...

A method is presented for finding the optimum LC combination for power factor compensation at linear loads in the presence of voltage source harmonics while the total voltamperes of the compensator capacitor and reactor is constrained. The end product is displayed in graph form where for any given compensator voltampere rating or cost, the maximum possible power factor and corresponding LC combination can be found. Examples are included showing that the cost of such an LC compensator may be less than that of a purely capacitive optimum compensator achieving the same power factor.

A generalized procedure to obtain the probabilistic model of power system harmonic current injection and propagation is presented. The model takes into account random variations of both the operating modes as well as the configuration of nonlinear loads connected to a distribution feeder. The method is illustrated by an example of a bus having linear as well as nonlinear loads of different types. Potential applications of the model are also discussed.

REPORT OF A CASE A 46-year-old man presented with a generalized eruption of 3½ years' duration. The rash began, without associated illness, as scattered pink papules on the flanks and progressed without remission. The eruption was mildly pruritic. The patient had no known medical problems. There was a family history of adult-onset diabetes mellitus. On examination, there was a generalized eruption of thousands of 1-mm papules with colors that ranged from skin-tone to red (Fig 1). Most of the papules coalesced to form circinate patterns without epidermal change. The soles were involved, but the palms, scalp, and mucocutaneous membranes were spared. Findings of a complete blood cell count, 12-factor automated chemical analysis, chest roentgenographic examination, and glucose tolerance test were all normal. Histopathologic examination revealed multiple foci of degenerating collagen surrounded by inflammatory infiltrates in a radial arrangement (Figs 2 and 3). What is your diagnosis? DIAGNOSIS: Generalized granuloma annulare (GA).

A partially decomposed variable-order model of the double-cage induction machine is presented and validated. The model exhibits improved computational efficiency in simulating full machine behaviour including stator transients. A state variable transformation is used to separate the electrical steady-state from the transient part of flux linkage response. The transient flux-linkage response is next decomposed into fast and slow sub-systems which constitute the boundary layers of the overall model. The fast subsystem is then reduced by neglecting the heavily damped fast transients caused by the starting cage. Each of the two decoupled boundary layer equations may be computed using different time steps and even ignored during periods when the corresponding mode is not excited, thereby effectively reducing model order and greatly decreasing computational requirements while retaining simulation accuracy.

This paper presents two numerical methods for computing the maximum overall rms current, and an algorithm to find the maximum peak of the total voltage on a transmission line under nonsinusoidal conditions. The only prerequisite is that the measured or calculated values of the individual harmonic voltages and line currents at one end of the line are assumed to be known. The proposed methods guarantee convergence to the global maxima of the rms current and peak voltage. The numerical algorithms are demonstrated by an example.

A method is presented and validated for increasing the computational efficiency in simulating double-cage induction machines where stator transients are to be included. Iterative decomposition is used to separate the flux-linkage equations into decoupled fast and slow subsystems, after which the model order of the fast subsystem is reduced by neglecting the heavily damped fast transients caused by the starting cage. The two decoupled subsystems along with the equation for the very slowly changing slip constitute a three time-scale model for the machine which resulted in more than doubling computational speed.

A mathematical nonlinear model is developed to simulate the performance of an induction watthour meter for nonsinusoidal voltage and current waves. The computation results show that for the special case where the voltage is purely sinusoidal, the measurement error causedby the nonlinear magnetic circuits is generally small unless the current wave contains a relatively large third harmonic component. However, when the voltage and current waves are both nonsinusoidal, the registration error can be relatively large even for a small voltage distortion. This is attributed not only to the nonlinearity but also to the drooping frequency response curve of the meter. In both cases, the sign of the registration error depends largely on the phase angles of voltage and current harmonics with respect to their fundamentals. A comparison shows that the computation results are consistent with the experimental ones which are available in the literature.

The paper presents a fault-location method which is insensitive to current-transformer saturation. The method requires less than one cycle of recorded fault data, which do not need filtering. A parameter estimation technique is applied where the linear part of the reference model response is described by instantaneous symmetrical components and the nonlinear part, caused by transformer saturation, described by phase variables. The parameters identified by the estimator are fault distance, fault resistance and saturation parameters. Accuracy is demonstrated by digital simulation studies.

A fault location methodby dynamic system parameter estimation is presented for a double-end fed transmission line using a 1/4 to 1 cycle window of data at one local end only. The system differential equations are based on a lumped parameter line model, Thevenin equivalents for transients at both ends of the line and an unknown fault resistance. Simplification of the equations is obtained by using instantaneous symmetrical components. The estimation algorithm does not require filtering of d.c. offset and high-frequency components from the recorded signals and its accuracy is illustrated in digital simulation studies.

Several simplified models of induction machines are presented. Included is a novel second-order model, which reduces the computational requirements previously considered necessary to predict electrical rotor transients, as well as mechanical transients. It is shown that the reduced-order models can be readily adapted to unbalanced voltage inputs without raising model order, thus providing increased flexibility. The model responses are compared for symmetrical voltage dips, start-up, and a sudden single-phasing condition.