An investigation of the drive circuit requirements for the powerinsulated gate bipolar transistor (IGBT)

The drive circuit requirements of the insulated gate bipolar transistor (IGBT) are explained with the aid of an analytical model. It is shown that nonquasi-static effects limit the influence of the drive circuit on the time rate-of-change of anode voltage. Model results are compared with measured turn-on and turn-off waveforms for different drive, load, and feedback circuits, and for different IGBT base lifetimes     

A nonlinear spatially variant object-dependent system model forprediction of partial volume effects and scatter in PET

Accurate quantitation of small lesions with positron emission tomography (PET) requires correction for the partial volume effect. Traditional methods that use Gaussian models of the PET system were found to be insufficient. A new approach that models the non-Gaussian object-dependent scatter was developed. The model consists of eight simple functions with a total of 24 parameters. Images of line and disk sources in circular and elliptical cylinders, and an anthropomorphic chest phantom were used to determine the parameter values. Empirical rules to determine these parameter values for various objects based on those for a reference object, a 21.5-cm circular cylinder, were also proposed. For seven spheroids and a 3.4-cm cylinder, pixel values predicted by the model were compared with the measured values. The model-to-measurement-ratio was 1.03±0.07 near the center of the spheroids and 0.99±0.03 near the center of the 3.4-cm cylinder. In comparison, the standard single Gaussian model had corresponding ratios of 1.27±0.09 and 1.24±0.03, respectively, and the corresponding ratios for a double Gaussian model were 1.13±0.09 and 1.05±0.01. Scatter fraction (28.5%) for a line source in the 21.5-cm cylinder was correctly estimated by our model. Because of scatter. The authors found that errors in the measurement of activity in spheroids with diameters from 0.6 to 3.4 cm were more significant than previously appreciated     

An integrated two-stage cascaded Mach-Zehnder device in GaAs

An integrated, cascaded, asymmetric GaAs-AlGaAs Mach-Zehnder (MZ) interferometer, for use in wavelength filtering and time-domain multiplexing, has been designed, fabricated, and tested, This device employs several new passive components, including height-tapered Y-branches, for uniform splitting and recombining, and index-tailored waveguide bends, for low-loss operation. The waveguide bend is designed with a predistorted index profile for minimizing both transition loss and radiation loss. The circuit is fabricated with a resistless, light-induced local etching technique, which enables rapid iterative fabrication of the device geometry to achieve the desired operating path delays. Acting as a wavelength filter, the fabricated device has a -24.3 dB minimum-to-maximum extinction ratio and a -10.5 dB side-lobe suppression ratio. Acting as a pulse-rate multiplexer, the device generates a four-pulse train with a 10-ps pulse-to-pulse separation and an amplitude uniformity of 80% for each input pulse     

Shyness and low social support as interactive diatheses, with loneliness as mediator: Testing an interpersonal-personality view of vulnerability to depressive symptoms.

Interpersonal approaches to depression are surveyed; it is suggested that interpersonal inhibition, as opposed to interpersonal excess, has been underemphasized as an antecedent of depression. It is proposed that shyness is a vulnerability factor for depressive symptoms in the absence but not in the presence of social support and that loneliness mediates the relation between shyness and depressive symptom increases. Undergraduates (N?=?172) reported on their levels of shyness, social support, loneliness, positive and negative affect, and depressive symptoms, and returned 5 weeks later to complete a similar set of assessments. Results supported hypotheses. Participants who were shy and unsupported were likely to experience increases in depressive symptoms and decreases in positive affect, whereas other students were not. This effect was partially mediated by increases in loneliness and was specific to depressive symptoms and low positive affect; it did not apply to negative affect. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Plastic ball grid array (PBGA) overview

As integrated circuit functionality and clock speed continue to rise, innovative packaging approaches are in great demand. Recently, the plastic ball grid array (PBGA) technology has been gaining industry-wide interest and commitment as the potentially lowest-cost package for high-I/O devices and even for some lower-pincount applications. Drivers include the density advantages of an area array, quickly achieving six-sigma assembly yields with existing assembly equipment, the potential for excellent electrical and thermal performance, along with the traditional low cost of plastic packages. Because some perceived weaknesses are being eradicated, worldwide evaluation of the PBGA has accelerated. Although various aspects of this technology are discussed frequently, an overall assessment is still under development. In this paper, a systematic and comprehensive evaluation of PBGA technology will be described to identify (1) its technical advantages and limitations, (2) unique application areas where PBGA is the package of choice, and (3) current major hurdles for acceptance of PBGA and possible approaches to overcome these problems. The PBGA will be compared with PQFP, CQFP and CBGA in terms of package characteristics and their impact on system assembly. The characteristics include package attributes (i.e., package size, I/O counts and lead pitch), performance (i.e., electrical, thermal) and reliability (moisture). At the system level, solder joint fatigue, board routing, solder assembly yield, solder reparability and board delay are key metrics. The cost implication of various package families will be discussed. By analogy with SMT, the infrastructure for PBGA will take time to develop. The key elements and the current status of this infrastructure will be discussed.     

Separation of cholesterol,and fatty acylglycerols,acids and amides by thin-layer chromatography

A rapid unidimensional thin-layer chromatographic (TLC) method for the separation of neutral lipids is described, using two sequential solvent systems of different polarity. Excellent separations of mono-, di- and triglycerides, fatty acids, fatty amides, and cholesterol are thereby achieved. Separation is accomplished at room temperature and requires 25 min. Reference to brand of firm name does not constitute endorsement by the United States Department of Agriculture over others of a similar nature not mentioned.     

Two-arm eccentric spiral antenna

This paper presents a free-space analysis of a planar two-arm eccentric spiral antenna. The eccentricity generates a circularly polarized wave with the main beam directed off-normal to the spiral plane. Input impedance and radiation characteristics are calculated from the current distribution generated by a method of moments solution. The radiation characteristics include power gain and axial ratio patterns. Three-dimensional (3-D) gain surface plots illustrate off-normal dependence of the eccentricity constant. The eccentric spiral antenna is found to have a significant increase in gain. This occurs when adjacent spiral arms rotating 360° have an electrical length increase of one wavelength. Thus, adjacent currents on one side of the spiral are nearly all in-phase. On the opposite side of the spiral, all neighboring currents are nearly out-of-phase. Evaluation of these currents result in a theory of operation for eccentric spiral antennas     

A new technique for measuring the constitutive parameters of planarmaterials

A technique for measuring the constitutive parameters of materials over a broad range of frequencies is developed. The technique is specifically designed for planar samples. Planar samples can be placed in the measurement fixture without any special preparation; this makes the technique more convenient than other techniques which require that the sample has to be machined to fit into a measurement fixture. Using fourth-order elements, the finite-element method provides a general, very accurate solution. The technique is experimentally verified by measuring the constitutive parameters of two materials with known properties. The measured results are compared to those of other investigators and are shown to be in good agreement