Use Of Hydrostatic Pressure Research Articles

The pressure dependence of the valence band discontinuity in quantum well structures

The use of hydrostatic pressure to determine the valence and conduction band offsets and their pressure dependence in both Type I and Type II quantum well structures will be described. Recent exper...

Analysis and design of semiconductor devices using strain

Abstract A brief review of the use of hydrostatic pressure to studies of group IV and group III-V semiconductor systems and devices is given. The internal loss mechanisms in semiconductor lasers designed for optical fibre communications are identified using hydrostatic pressure and suggestions made how inbuilt strain in quantum-well and superlattice structures may be used to fabricate much improved devices. The critical hot carrier transitions in silicon and in germanium avalanche photodiodes are examined using hydrostatic pressure and again possible improvements in strained Si, Ge and SiGe alloys are suggested.

Superplasticity in a high strength powder aluminum Alloy with and without SiC Reinforcement

The superplastic properties of a rapidly solidified, high strength P/M Al alloy and the same alloy reinforced with SiC particulates (SiCp) have been studied. To prepare superplastic test materials, a matrix alloy powder of composition 7.2Zn-2.4Mg-2Cu-0.2Zr-0.12Cr-0.2Co (Kaiser PM-64) and the powder mixed with 10 to 20 vol pct SiCp (~5 μm diameter) were thermomechanically processed to very fine equiaxed grain structures of ~6 μm and ~8 μm, respectively. Superplasticity in these materials was evaluated by characterizing (1) high temperature stability, (2) dynamic grain growth, (3) strain rate sensitivity, (4) flow stress behavior, (5) cavitation and cavitation control, and (6) total superplastic strain. It was observed that the PM-64 alloy could achieve a total elongation of over 800 pct, while the SiCp reinforced alloy could attain an elongation greater than 500 pct before failure. Also, it was shown that with the use of hydrostatic pressure during superplastic flow, cavitation could be controlled. Observations were made of the effect SiCp reinforcement particles had on the superplastic flow stress behavior. Interpretations are proposed to explain the role of particulates during superplastic straining.

Measurement of the motive force of the migrating slug ofDictyostelium discoideum by a centrifuge method

The motive force of the migrating slug of the cellular slime mouldDictyostelium discoideum was measured by the use of centrifugal force. Changes in shape of the slugs due to the use of centrifugal force were prevented by letting them migrate in an agar capillary. The motive force thus obtained was proportional to the slug volume, the value per unit volume being 5.8×106 dyne/cm3 (58 N/cm3). This is in good agreement with the value measured by the use of hydrostatic pressure.

Physics of short-gate GaAs MESFET's from hydrostatic pressure studies

The use of hydrostatic pressure to study the physics of a GaAs MESFET is reported for the first time. Two aspects of the physics of conventional 1-µm gate structures are focused upon: 1) the possible role played by hot-electron effects in the drain-current saturation and 2) the physical mechanism responsible for excess current. The pressure dependence of the low-field conductance, current-voltage characteristics, and VHF noise properties of the MESFET are examined and compared to those of a Gunn diode. The results show that hot-electron effects are similar in the two devices, thereby providing new evidence that current saturation is associated with Gunn domain formation. The results also suggest that the excess current at large gate voltages is due to electron injection into the substrate under the source side of the gate, rather than to other proposed mechanisms.

Use of Hydrostatic Pressure in Development of Stress Strain Information for Tomato Skins

Use of Hydrostatic Pressure in Development of Stress Strain Information for Tomato Skins

Use of hydrostatic pressure for pressing ceramic pieces

Use of hydrostatic pressure for pressing ceramic pieces

Measurement of Very Small Changes in the Velocity of Ultrasonic Waves in Solids

Circuit improvements for a method of measuring ultrasonic delay times or velocities [H. J. McSkimin, J. Acoust. Soc. Am. 37, 864–871 (1965)] have resulted in attained resolutions of approximately one part in 107 for high-Q materials, and with compatible long-term stability. By way of illustration, some results are presented for delay-time variations as a function of low (<250 psi) uniaxial stress in single crystals of Si and Ge. For the latter, the data are combined with results obtained previously through use of hydrostatic pressure to yield the six 3rd-order stiffness moduli. The satisfactory agreement with literature values demonstrates the usefulness of the method for materials that might be damaged by large uniaxial loads.

THE REDUCTION OF INTUSSUSCEPTION BY HYDROSTATIC PRESSURE

THE ARTICLE by Robins and Plenk which appears in this issue of Pediatrics is representative of the experience on the operative and non-operative forms of treatment of intussusception in childhood which is being reported by many others. Although the series is too small to draw any valid conclusions, the authors have attempted to show that reduction by barium enema will save about a half of these patients a surgical procedure, and they have called our attention to the advantages and disadvantages of hydrostatic reduction. The treatment is still controversial and there is uncertainty regarding the proper role, if any, of hydrostatic reduction of intussusception. Some of the proponents of the surgical treatment still maintain that operation is the only form of treatment for all cases of ileocolic intussusception, while other authors are equally adamant in the use of hydrostatic pressure as the primary method of reduction.

Observations on the ambulant correction of thoracic scoliosis and kyphosis with particular reference to the experimental use of hydrostatic pressure.

1 . The theoretical requirements for optimal correction of thoracic scoliosis and kyphosis are discussed, and observations are made on the limitations of methods in current use for their ambulant correction. 2. The experimental use of hydrostatic pressure in an endeavour to satisfy these clinical requirements is described. 3. It is suggested that the use of hydrostatic pressure as the source of corrective force has considerable advantages, and that, with refinements, the techniques described may prove a useful addition to rigid mechanical methods of correction.