Sharp Pinch Research Articles

MOCVD grown β-Ga2O3 metal-oxide-semiconductor field effect transistors on sapphire

We fabricated β-Ga2O3:Si metal-oxide field-effect transistors (MOSFETs) on c-plane sapphire substrates which typically showed maximum drain current of 100 mA mm−1. β-Ga2O3:Si thin films were realized on c-plane sapphire substrates through a combination of metalorganic chemical vapor deposition and post-annealing. The MOSFET device presented excellent on/off drain current ratio of ∼1011 with very low gate leakage current, sharp pinch off behavior, and a breakdown voltage of 400 V at VG = −40 V. The growth and fabrication of β-Ga2O3:Si MOSFETs on c-plane sapphire is valuable to its demonstration of the great potential for future high-power electronic devices.

Growth of AlGaN/GaN heterojunction field effect transistors on semi-insulating GaN using an AlGaN interlayer

Semi-insulating (SI) GaN layers were grown on 4H-SiC substrates by inserting an AlGaN layer between the AlN buffer and the GaN layer. Secondary ion mass spectroscopy measurements showed that the AlGaN layer prevented Si from diffusing from the substrate into the GaN layer. X-ray diffraction and atomic force microscopy analyses showed that an optimized AlGaN interlayer does not degrade the crystal quality or surface morphology of the SI GaN. The room temperature mobility of an AlGaN/GaN heterostructure using this SI GaN was 2200 cm2/V s. High electron mobility transistors (HEMTs) with 0.65 μm long gates were also fabricated on these SI GaN buffers. A power density of 19.0 W/mm with a power added efficiency of 48% was demonstrated at 10 GHz at a drain bias of 78 V. These HEMTs also exhibited sharp pinch off, low leakage, and negligible dispersion.

Spectrophotometric and tristimulus analysis of the colors of subcutaneous bleeding in living persons

The colorimetric patterns of color changes of skin bruises were examined in adult male Japanese volunteers wounded by a sharp pinch on the inside of the upper arm and forearm. In most cases the non-traumatic area near the bruise could be used for the control skin. By using a colorimeter, tristimulus and spectrophotometric methods were available to objectively analyze the skin discoloration. On the L* a* b* color space analysis, Δ b*, the difference between the lesion and control area, was useful to judge whether a bruise was recent or older. When it showed a minus value, the bruise was diagnosed as recent within 2 days. The temporal course of Δ b* changes may be a good indication of the time of bruising as measured in days, however, in actual forensic analysis situations, it is difficult to measure changes in the skin area on a living person over several days. It was hard to perform further age analyses on older bruises especially where only one or two measurements had been taken. On spectrophotometric analysis, clear differences of spectral reflectance curves in some wavelength regions were observed in recent, older and nearly healed lesions as compared with controls. The characteristics of new bruises had a peak point around 500–520 nm of the green area and absorbed light remarkably in the green, yellow and orange wavelength regions (approximately 520–640 nm). On older lesions, reflectance in the blue and one portion of the green wavelength region (440–520 nm) remained unchanged or further reduced before approximately ending similarly to the control curve. Nearly healed injuries showed slight reductions of reflectance over wide wavelength regions, but the curves were close to that of control skin. These reflectance graph patterns could cope with the temporal sequence of color changes of a bruise. As individual reflectance graph patterns depended on particular factors, such as the degree of bruising, it was difficult to correspond the patterns of all bruises to the date of bruising. However, if two measurements were taken at 1 or 2 days, their validity for classifying into recent, older and nearly healed bruises, might be shown by comparing patterns of both curves patterns including the control area. Some indices using reflectance values on certain wavelengths were not very useful to pinpoint the time of bruising. On spectrophotometric analysis, the evaluation of the age of a bruise needs to be done by a comparison of reflectance graph patterns in wide wavelengths in visible light regions.

Spectrophotometric and tristimulus analysis of the colors of subcutaneous bleeding in living persons

In forensic activities the estimation of the age of subcutaneous bleeding is very important. The evaluation of color, however, will vary according to differences of light-source, observer, size, background and so forth. The colorimetric methods using a spectrophotometer can effectively evaluate skin discoloration. In this study, the tristimulus and spectrophotometric patterns of color changes of skin bruises were examined among eight Japanese adult men volunteers wounded by a sharp pinch on the inside of the upper arm and forearm. From a series of color changes among the subjects, the tristimulus data and the spectral reflectance graphs showed variable patterns that made a comparison of absolute numerical values by a single measurement meaningless. Therefore, if we use colorimetric methods in a practical case, we should measure bruises in the same lesion twice or more at intervals of 1 or 2 days.

Observation of strong self-focusing of an intense relativistic electron beam impinging on a SiO/sub 2/ target

A substantial reduction in the spot size of an electron beam striking a SiO/sub 2/ target has been observed during a 60 ns pulse. We attribute this to the emission of positive ions, most probably protons, from the target. These are then accelerated upstream and focused along the axis by the electron beam, where they partially neutralize the space-charge of the beam, and produce a sharp pinch. A simulation of the effect with a particle-in-cell code provides an adequate quantitative description, and a simple model, based on space-charge-limited emission of protons by the target confirms qualitatively the results of the simulation. The presence of an aluminum foil on the upstream side of the target is shown to suppress the effect, probably by stopping the protons.

Strong self-focusing of a 7.2 MeV electron beam striking an aluminized mylar target

A substantial reduction in the spot size of a 7.2 MeV, 3 kA electron beam illuminating a thin aluminized mylar target has been observed during a 60 ns pulse. We attribute this to the emission of positive ions from the target, under the influence of the high energy flux of the beam, which perforates the target, These ions are then accelerated upstream and focused along the axis by the electron beam, where they partially neutralize the space-charge of the beam and produce a sharp pinch. After the pinch, the beam expands and forms filaments at the end of the pulse. By varying the initial beam transverse size, we have studied the influence of the beam density on the effect. A simulation of the effect with a particle-in-cell code provides a qualitative description and suggests that the ions responsible for the effect are Al/sup +/ and O/sup +/.

InP-based self-aligned normally-off superlattice-insulated-gate field-effect transistor

An InP-based normally-off superlattice-insulated gate field-effect transistor (SIGFET) is developed using a self-aligned implant process. The new gate structure reduces the gate current significantly and yields a sharp pinch off. A SIGFET with 0.7 μm gate length delivers more than 800 mA/mm of drain current at 2 V of forward gate bias and yields an f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> as high as 42 GHz. An explanation for a new kink effect is also proposed.

Treatment of Compulsive Hand in Mouth Behaviour in a Profoundly Retarded Child Using a Sharp Pinch as the Aversive Stimulus

A sharp pinch on the back of the hand, contingent upon hand in mouth behaviour was found to be an economical and effective aversive stimulus in a programme which successfully reduced compulsive hand in mouth behaviour related to vomiting and rumination over a 3 month period. Appropriate hand usage and absence of problem behaviour were positively reinforced with attention, praise and music on a one to one basis. To overcome problems of generalization, the programme was extended so that treatment could be carried out by staff in the ward setting throughout the day. The reduction in self-stimulatory behaviour was accompanied by general improvement in staff attitudes and in the child's social responsiveness. In light of these changes;, the relative effects of punishment and Differential Reinforcement of Other Behaviour in such programmes are considered as well as the problems of generalization.

Stability of the Sharp Pinch and Unpinch with Finite Conductivity

The stability of the sharp linear pinch and unpinch is analyzed using a model in which the magnetic fields are separated by a thin current layer of large, but finite electrical conductivity. Elsewhere the contained fluid is assumed to have zero conductivity, a model which may, for example, approximate a plasma pinch heated by the intermixing of skew magnetic fields. The perturbed radial displacement of the layer is assumed to be constant across the layer and small wavelength perturbations comparable to the layer thickness are not considered. Viscosity is also neglected. The infinitely conducting, ``stabilized'' pinch and the unpinch are now shown to be overstable to perturbations whose helices are approximately orthogonal to the helix of the mean magnetic field across the layer. The overstable growth rate is typically one tenth of the geometric mean of a fundamental, oscillatory frequency and the Ohmic diffusion rate of the layer.

Hydromagnetic stability of a diffuse linear pinch

The hydromagnetic energy principle is applied to the derivation of necessary and sufficient conditions for the hydromagnetic stability of a linear pinch with distributed plasma current (a diffuse linear pinch). The results are quite general in that the axial and azimuthal components of the magnetic field, which determine the structure of the pinch completely, are treated as arbitrary functions of distance from the axis. For purposes of illustration, the general results are applied to the limiting case of a pinch with the plasma current confined to an infinitely thin layer (a sharp pinch).