Showing papers by "General Electric published in 1989"

Optimum semiconductors for high-power electronics

Abstract: Elemental and compound semiconductors, including wide-bandgap semiconductors, are critically examined for high-power electronic applications in terms of several parameters. On the basis of an analysis applicable to a wide range of semiconducting materials and by using the available measured physical parameters, it is shown that wide-bandgap semiconductors such as SiC and diamond could offer significant advantages compared to either silicon or group III-V compound semiconductors for these applications. The analysis uses peak electric field strength at avalanche breakdown as a critical material parameter for evaluating the quality of a semiconducting material for high-power electronics. Theoretical calculations show improvement by orders of magnitude in the on-resistance, twentyfold improvement in the maximum frequency of operation, and potential for successful operation at temperatures beyond 600 degrees C for diamond high-power devices. New figures of merit for power-handling capability that emphasize electrical and thermal conductivities of the material are derived and are applied to various semiconducting materials. It is shown that an improvement in power-handling capabilities of semiconductor devices by three orders of magnitude is feasible by replacing silicon with silicon carbide; improvement in power-handling capability by six orders of magnitude is projected for diamond-based devices. >

Switching converter with pseudo-resonant DC link

Abstract: A pseudo-resonant DC link for coupling direct current from a DC source to an inverter includes a plurality of switches which are controlled so as to minimize switching loss in the DC link and in the inverter. The DC link includes a capacitor and an inductor coupled through controllable switches in a manner that momentarily reduces to zero the input voltage to the inverter each time that a switch in the inverter is commutated. The controllable switches in the DC link function to allow the capacitor to resonate through the inductor and then be recharged at the end of a commutation interval. The controllable switches in the DC link are timed to that switching generally occurs under conditions of zero current.

Three-dimensional phase contrast angiography.

Abstract: Bipolar flow-encoding gradients can be used in a three-dimensional magnetic resonance imaging procedure to provide a noninvasive measure of in vivo blood flow. The resulting volume angiogram is a three-dimensional data matrix which can be retrospectively analyzed and displayed in a variety of ways. This angiographic technique provides good suppression of signals arising from stationary tissue, thereby permitting the visualization of small vessels having relatively slow flow. This suppression is obtained by modulating the amplitude of the flow-encoding gradient pulse to either cancel the stationary tissue signal or displace it relative to the flow signal in the volume image. © 1989 Academic Press, Inc.

Electrocrystallochromic display and element

Abstract: A display changes the color of reflected light in response to the value of electrical potential applied to individual pixels of the display. Each pixel includes an array of light reflectors mounted on a corresponding array of electrostrictive elements. In the absence of energization, all the light reflector lie on a common plane and reflect light of all colors. The electrostrictive elements of each pixel in one embodiment are connected to be driven in common by a single potential. Each electrostrictive element of the array of each pixel has an effective length which differs from that of the adjoining elements so that the common voltage results in a differential expansion or contraction. The differential movement results in a separation between adjacent reflectors. When the separation is λ/4 at the wavelength of a color of light, destructive interference cancels that color, whereby physiological effects change the apparent color of the reflected light. In a second embodiment, the voltages applied to adjacent electrostructive elements differ.

Solution of the 2D Navier-Stokes equations on unstructured adaptive grids

Abstract: This paper presents a solution adaptive scheme for solving the Navier-Stokes equations on a n unstructured mixed grid of triangles and quadrilaterals. The solution procedure uses an explicit Itunge-Kutta finite volun~e time marching scheme. The solution is begun on a coarse grid and points are added adaptively during the solution procedure using criteria such as pressure and velocity gradients. In viscous regions the gradients are essentially one dimensional, and we use quadrilateral elements in these regions to facilitate the one dimensional refinement required for the efficient resolution of boundary layers and wakes. The effect of turbulence is modeled by the inclusion of a K E tubulence rnodel. When used for analyzing flows in turbomachinery blade rows, terms rrpresenting the effects of changes in strearnsheet lhicknrss and radius, and the effects of rotation are included. Axisymnletric flows with swirl can also be analyzed. Solutions are presented for several examples that illustrate the capability of the algorithm.

Human in vivo NMR spectroscopy in diagnostic medicine: clinical tool or research probe?

Abstract: In this critical review of human in vivo nuclear magnetic resonance (NMR) spectroscopy, the questions of which chemical species can be detected and with what sensitivity, their biochemical significance, and their potential clinical value are addressed. The current in vivo detectability limit is about 10(-6) of that of tissue water protons, necessitating a 1-10 cm3-volume of tissue and approximately 10-minute averaging time. This permits access to fats, membrane lipid metabolism, high-energy phosphate metabolism, glycogen, some neurotransmitters and metabolites in the citric acid cycle, and artificially introduced fluorocompounds. While hydrogen-31, phosphorus-31, carbon-13, sodium-23, and fluorine-19 in vivo results are discussed, the majority of patient studies use P-31 NMR spectroscopy. Here results from metabolic and ischemic disorders substantiate a case for spectroscopy as a diagnostic modality. The use of a broad range of spatial localization strategies is justifiable on the basis of the location and size of the pathologic condition and of NMR sensitivity. Abnormalities in spectra from many other disorders, most notably cancer, and improvements are often observed early in the course of successful therapy. Yet the potential impact of these results on clinical diagnosis and therapeutic monitoring is not always well understood, and many questions remain. Neurotransmitters and citric acid cycle metabolites exhibit high H-1 NMR sensitivities and represent major untapped potential for human clinical spectroscopy research. Studies evaluating spectroscopy in the context of existing modalities are needed. The unique ability of spectroscopy to provide noninvasive information about tissue chemistry in patients bodes well for its impact on clinical research and disease diagnosis.

Constructing stable grasps

Abstract: This paper shows how all force-closure grasps can be made stable by constructing virtual springs at the contacts, such that the grasped object has a desired stiffness matrix about its stable equili...

Pressure-temperature phase diagram of elemental carbon

Abstract: Carbon atoms form very strong bonds to each other yielding solid crystalline materials like graphite and diamond. Because of the high bonding energies, the vaporization and melting temperatures are very high. Different kinds of atom-to-atom bonding make many solid forms possible, ranging from pure graphite to pure diamond, as well as many types of molecules in liquid or gaseous carbon. Rigorous conditions of high temperature, high pressure, or both, are required to change a given elemental phase of carbon to another. Currently the vapor-pressure line of graphite, the P, T equilibrium line between graphite and diamond, and the graphite/diamond/liquid triple point are fairly well established. The triple point (or points) for graphite (or carbynes)/vapor/liquid remain controversial. At pressures less than 0.1 GPa liquid carbon seems to be a poor electric conductor while at higher pressures it is a good one. Current experimental and theoretical evidence indicate that diamond is stable against collapse to metallic forms (unlike Si and Ge) up to pressures over 350 GPa, and possibly as high as 2300 GPa. The latest static and shock compression experiments on diamond indicate that it melts to a conducting liquid at about 5000 K at pressures of 15 to 30 GPa, but does not melt at about 6000 K at 125 GPa. This suggests that the melting temperature of diamond increases with pressure, and that at the melting temperature liquid carbon is slightly less dense than diamond.

Effects of intravoxel incoherent motions (IVIM) in steady-state free precession (SSFP) imaging: application to molecular diffusion imaging.

Abstract: A theoretical analysis of the effects of diffusion and perfusion in steady-state free precession (SSFP) imaging sequences sensitized to intravoxel incoherent motions by magnetic field gradients is presented and supported by phantom studies. The capability of such sequences to image diffusion and perfusion quickly was recently demonstrated. The possible residual effects of T1 and T2 in diffusion measurements are evaluated, as are the effects of the sequence design and the acquisition parameters (repetition time, flip angle, gradient pulses). It is shown theoretically and confirmed by experiments on phantoms that diffusion coefficients can be directly measured from SSFP images when large enough diffusion gradient pulses are used.

Transferrable, self-supporting pellicle for elastomer light valve displays and method for making the same

Abstract: An elastomeric light valve has a substrate with a principal surface on which is formed a multiplicity of pixels; each pixel includes a first set of pixel electrodes interdigitated with a second set of pixel electrodes. A silicone elastomer gel is disposed over both the principal substrate surface and the two sets of pixel electrodes. At least one silicone/polycarbonate self-supporting pellicle is disposed substantially completely over the gel layer; the pellicle and elastomer gel layer are heat cured to improve the response of the layers to electrostatic forces induced in the light valve by control voltages applied during operation of the light valve. A layer of gold is disposed over the at least one pellicle and a layer of silver is disposed over the gold layer to provide an exposed specular surface which is easily deformed and resilient to transverse stresses. Address-lines are provided for applying control voltages to the first and second sets of pixel electrodes responsive to a video signal; a bias voltage is applied to the gold and silver layers to provide optimum light valve sensitivity at lower control voltages.

Alkoxy‐substituted diaryliodonium salt cationic photoinitiators

Abstract: Preparation et caracterisation (RMN, UV, point fusion, SIMS, toxicologie, solubilite) d'hexafluoroantimoniate et -phosphates d'alcoxy-4 diphenyl iodonium. Influence de leur concentration sur la cinetique du durcissement de resines epoxydes (oxyde de butadiene, dioxyde de limonene, phenyl glycidyl ether)

Fabrication of components by layered deposition

Abstract: A component is fabricated by depositing a succession of overlying beads of a material, the pattern and position of the beads being assigned the proper characteristics of the corresponding section of the desired component. Shape definition is accomplished by characterizing the component as a series of sections or slices having the thickness of the bead, and programming a computer-controlled deposition head to deposit a succession of beads with the respective patterns and positions. Deposition is preferably by precision laser welding. Complex shapes having properties comparable to properties of forged or cast material are readily prepared. The material used in successive beads may be varied, producing a component of graded composition to achieve particular properties in various regions.

Microstructural Coarsening During Sintering of Boron Carbide

Abstract: This paper reports how the sintering behavior of boron carbide was investigated with particular attention given to microstructure development at various stages in the sintering process. Hot-pressing and pressureless sintering techniques were employed and the effects of heating rate, firing atmosphere, and composition were used to characterize the sintering behavior. Pressureless sintering at temperatures up to 2300{degrees} C produces only limited densification. Microstructural coarsening is responsible for this since it leads to conditions where densification is slow. Hot-pressing and carbon additions suppressed coarsening and permitted densification to {gt} 95% of theoretical density.

Fault detection and management system for fault-tolerant switched reluctance motor drives

Abstract: The unique characteristics that promote the switched reluctance motor (SRM) for fault tolerance capability, i.e. its ability to continue operation despite faulted motor windings or inverter circuitry, are discussed. It is shown that the magnetic independence of the motor phases and the circuit independence of the inverter phases permit the SRM drive to continue operation with one or more phases disabled. Winding fault detectors indicate the existence of faulted motor windings, and control circuitry acts to block the gating signals to the semiconductor power switches of the affected phase, thus removing excitation from the faulted winding and halting damaging effects that can result from the continued excitation of a faulted winding. The drive an continue operation without the faulted phase. >

Laser beam scanning method for forming via holes in polymer materials

Abstract: The surface of a polymer dielectric layer is scanned repeatedly with a high energy continuous wave laser in a pattern to create via holes of desired size, shape and depth. This is followed by a short plasma etch. The via holes are produced at commercial production rates under direct computer control without use of masks and without damage to conductor material underlying the dielectric layer. A two-step technique usable to form a large hole to a partial depth in the dielectric layer and several smaller diameter holes within the large hole through the remainder of the dielectric layer depth allows formation of a large number of holes in a given area of a thick dielectric layer.

A very high speed switched-reluctance starter-generator for aircraft engine applications

Abstract: An electric direct-drive gearless starter-generator has been designed and built for an aircraft engine application. The system is based on a switched-reluctance motor, which was chosen for its simplicity, robustness, high-speed capability, and efficiency. The overall system configuration and the design of the switched-reluctance motor and its solid-state power converter are described. When operating as engine starter, the motor produces torque to spin the engine up to its light-off speed. Following light-off, the motor continues to produce torque to assist the engine in accelerating to idle speed. When the engine is running, the machine generates electrical power to supply engine and vehicle loads up to a peak operating speed of 50000 r/min. Key issues in the machine design are reliability, high speed, power density, and cost. Test results have verified that the system can meet the torque and generated-power requirements over its entire operating range. >

Geared counterrotating turbine/fan propulsion system

Abstract: High by-pass fan jet engine includes counterrotating turbine blade sets for receiving hot combustion gases from a core engine portion and driving the fan blades through a planetary gear-type reduction gear assembly. Lightweight, highspeed, concentric, counterrotating shafts transmit power from both turbine blade sets to the fan via the reduction gear assembly. A pair of planetary gear assemblies with fixed fing gears and a rotatable common planetary gear carrier is used to drive a single set of fan blades via the carrier, and a pair of planetary gear assemblies with a fixed common planetary gear carrier and rotatable ring gears is used to drive two or more counterrotating fan blade sets via the ring gears. A low pressure "booster" compressor feeding the core engine portion can be directly driven from one of the two high speed shafts.

Axial flow laser plasma spraying

Abstract: A laser plasma spray apparatus for depositing a feed material onto a substrate includes a nozzle having a plasma confinement chamber into which a laser beam is focused, the focal point being at a distance sufficiently far from the substrate that the substrate is not melted Finely divided feed material in a carrier gas flow is fed axially into the confinement chamber along the direction of the laser beam and melted in the plasma formed in the interaction of the laser beam, the feed material, and the gas at the focal point The melted feed material is then directed to deposit onto the substrate, while the plasma energy is largely confined within the apparatus by the confinement chamber and a constriction in the flow path upstream of the confinement chamber

Method for improving speech quality in code excited linear predictive speech coding

Abstract: By reconciling differences between the estimator and the filter of a code excited linear predictive (CELP) voice coder, higher quality is achieved in the output speech. The pulse amplitudes and pitch tap gain are solved for simultaneously to minimize the estimator bias in the CELP excitation. Increased signal to noise ratio is accomplished by modifying the pitch predictor such that the pitch synthesis filter accurately reflects the estimation procedure used to find the pitch tap gain, and by improving the excitation analysis technique such that the pitch predictor tap gain and codeword gain are solved for simultaneously, rather than sequentially. These modifications do not result in an increased transmission rate or significant increase in complexity of the CELP coding algorithm.

DC and microwave characteristics of sub-0.1- mu m gate-length planar-doped pseudomorphic HEMTs

Abstract: Analytical modeling of these very-short-channel HEMTs (high-electron-mobility transistors) using the charge-control model is given. The calculations performed using this model indicate a very high electron velocity in the device channel (3.2+or-0.2*10/sup 7/ cm/s) and clearly demonstrate the advantages of the planar-doped devices as compared to the conventional uniformly doped HEMTs. Devices with different air-bridged geometries have been fabricated to study the effect of the gate resistance on the sub-0.1- mu m HEMT performance. With reduced gate resistance in the air-bridge-drain device, noise figures as low as 0.7 and 1.9 dB were measured at 18 and 60 GHz, respectively. Maximum available gains as high as 13.0 dB at 60 GHz and 9.2 dB at 92 GHz, corresponding to an f/sub max/ of 270 GHz, have also been measured in the device. Using the planar-doped pseudomorphic structure with a high gate aspect-ratio design, a noise figure of less than 2.0 dB at 94 GHz is projected based on expected further reduction in the parasitic gate and source resistances. >

Ion flux from the cathode region of a vacuum arc

Abstract: The properties of the ion flux generated in a vacuum arc are reviewed. The structure and distribution of mass erosion from individual cathode spots and the characteristics of current carriers from the cathode region at moderate arc currents are described. An appreciable ion flux ( approximately 10% of the total arc current) is emitted from the cathode of a vacuum arc. This ion flux is strongly peaked in the direction of the anode, although some ion flux may be seen even at angles below the plane of the cathode surface. The observed spatial distribution of the ion flux is expressed quite well as an exponential function of the solid angle. The ion flux is quite energetic, with average ion potentials much larger than the arc voltage, and generally contains a considerable fraction of multiply charged ions. The average ion potential and ion multiplicity increase significantly for cathode materials with higher arc voltages but decrease with increasing arc current for a particular material. The main theories concerning ion acceleration in cathode spots are the potential hump theory and the gas dynamic theory. Experimental data indicate that these theories serve reasonably well when used to predict the mean values of the charge state, ion potential, and ion energies for the ion flux, but are quite insufficient when compared with the results for the potentials and energies of individual ions. >

Information extraction and text summarization using linguistic knowledge acquisition

Abstract: Storing and accessing texts in a conceptual format has a number of advantages over traditional document retrieval methods. A conceptual format facilitates natural language access to text information. It can support imprecise and inexact queries, conceptual information summarization, and, ultimately, document translation. The lack of extensive linguistic coverage is the major barrier to extracting useful information from large bodies of text. Current natural language processing (NLP) systems do not have rich enough lexicons to cover all the important words and phrases in extended texts. Two methods of overcoming this limitation are (1) to apply a text processing strategy that is tolerant of unknown words and gaps in linguistics knowledge, and (2) to acquire lexical information automatically from the texts. These two methods have been implemented in a prototype intelligent information retrieval system called SCISOR (System for Conceptual Information Summarization, Organization and Retrieval). This article describes the text processing, language acquisition, and summarization components of SCISOR.

Polymer mixture comprising an aromatic polycarbonate, a styrene-containing copolymer and/or graft polymer and a phosphate based flame-retardant; articles formed therefrom

Abstract: The invention relates to a polymer mixture which comprises an aromatic polycarbonate, a styrene­-containing copolymer and/or a styrene-containing graft polymer and a flame-retardant. It has been found that the use of a certain type of flame-retardants, namely oligomeric phosphates leads to a polymer mixture having improved properties. In particular to a polymer mixture having a good combination of flame retardancy, non-­juicing characteristics of the flame retardant, good plastifying effect and good heat resistance.

Trench gate structure with thick bottom oxide

Abstract: Improved trench gate field effect devices are provided by forming a thick oxide at the bottom of the trench. This thick oxide may be preferably formed by ion implantation into the bottom of the trench.

Method for producing polycrystalline compact tool blanks with flat carbide support/diamond or CBN interfaces

Abstract: The present invention relates to a method for making a supported PCD or CBN compact comprising placing in an enclosure a cup assembly having a mass of diamond or CBN particles having a surface and the mass of cemented metal carbide having a surface, and optionally a catalyst for diamond (or optionally, CBN) recrystallization, said surfaces being in adjacency to form an interface. The enclosure then is subjected to a high pressure/high temperature process which results in diamond or CBN compacts preferably characterized by diamond-to-diamond or CBN-to-CBN bonding joined to a cemented carbide support at their respective surfaces. The supported compacts are recovered from the enclosures and cup assemblies and finished. The finished supported compacts in the enclosure exhibit non-planar bonded interface resulting in PCD or CBN compacts of substantially non-uniform thickness. The improvement in process of the present invention comprises said carbide mass surface being the mirror image of the finished PCD or CBN non-planar interface for making a finished supported compact of substantially uniform diamond or CBN compact thickness. Preferably, at least two compacts are produced in the process and the catalyst for diamond recyrstallization is provided from the cemented metal carbide mass,

Polymer mixture having aromatic polycarbonate styrene I containing copolymer and/or graft polymer and a flame-retardant, articles formed therefrom

Abstract: The invention relates to a polymer mixture which comprises an aromatic polycarbonate, a styrene-containing copolymer and/or a styrene-containing graft polymer and a flame-retardant. It has been found that the use of a certain type of flame-retardants, namely oligomeric phosphates leads to a polymer mixture having improved properties. In particular to a polymer mixture having a good combination of flame retardancy, non-juicing characteristics of the flame retardant, good plastifying effect and good heat resistance.

Multichip integrated circuit packaging method

Abstract: A multichip integrated circuit package comprises a substrate to which is affixed one or more integrated circuit chips having interconnection pads. A polymer film overlying and bridging integrated circuit chips present is provided with a plurality of via openings to accommodate a layer of interconnection metallization which serves to connect various chips and chip pads within the interconnection pads disposed on the chips. A significant advantage of the packaging method and configuration of the present invention is the ability for the polymer film to be removed. This significantly improves testability and effectively provides wafer scale integration circuit packages which are free of problems associated with yield and testability.