Diffraction of shear waves by a rigid strip in a medium of monoclinic type

Summary The paper discusses the two dimensional problem of diffraction of shear waves by a rigid strip in an infinite medium of monoclinic type. This problem is reduced to a system of dual integral equations of which the solution provides the diffracted field. The method of steepest descent has been used in the determination of the diffracted fields at a large distance from the strip. Diffraction pattern for displacement and stress field have been computed and the effect of anisotropy is distinctly marked.With 6 Figures     

Simulation and experimental study of interharmonic performance of a Cycloconverter-FedSynchronous motor drive

High-power synchronous motor drives are usually fed from naturally commutated cycloconverters. The output voltage of the cycloconverter contains interharmonics/subharmonics which affect the power quality and restrict the allowable frequency range. Further, a practical circulating current-free cycloconverter usually gives rise to stator current discontinuities. The present paper deals with a simulation method to study the performance of a cycloconverter-fed synchronous motor drive in the presence of interharmonics/subharmonics taking into account the discontinuities in the output current as well as the effect of ripple in the output current on the input current of the cycloconverter. Interharmonics in output phase voltage, output phase current, input supply current, and the field current are estimated and verified with experimental results on a laboratory prototype. The significant oscillating torque components due to these interharmonics are identified in a typical case. The simulation results are useful in power quality studies for such drives and in devising methods for suppression of these interharmonics/subharmonics.     

Vertical p-i-n polysilicon diode with antifuse for stackable field-programmable ROM

A field-programmable, stackable memory cell using 0.15-/spl mu/m technology is demonstrated. Vertical polycrystalline silicon diodes are stacked on top of one another, with tungsten (with TiN adhesion film) interconnect wires. An SiO/sub 2/ antifuse film separates the top of each diode from the TiN-W films. The cell is programmed when sufficient biasing voltage is applied to break down the antifuse, connecting the diode to tungsten. The cell is unprogrammed when the antifuse is intact. Cell fabrication and performance are described.     

Improved EEPROM tunnel- and gate-oxide quality by integration of alow-temperature pre-tunnel-oxide RCA SC-1 clean

The effects of integration of a low-temperature RCA standard clean-1 (SC1) on the tunnel- and gate-oxide charge-to-breakdown (Q_BD) and voltage ramped dielectric breakdown (VRDB) distribution in a 0.7 μm CMOS EEPROM process technology were studied. A low-temperature (<65°C) SC1 used to clean the wafer surface prior to tunnel oxidation resulted in a significantly higher tunnel-oxide Q_BD, as well as improved gate-oxide Q_BD and mode-B failure rates compared to that for a traditional high temperature (>80°C) SC1. The reduced silicon diode etchrate of the low-temperature SC1 allowed for additional gate-oxide annealing during the gate oxidation cycle, while keeping the overall thermal budget (Dt)^1/2 for the technology equivalent to that with the higher temperature SC1. This resulted in improved gate-oxide VRDB distributions and QED values on large capacitor structures. The tunnel-oxide QBD improvement was most likely due to reduced surface roughness in the tunnel-oxide window regions with the lower temperature SC1. The process including the low-temperature SC1 was also proven to provide equivalent yield to the process with the high temperature SC1 on a 0.7 μm, 7 nS 128 macrocell EEPROM programmable logic device     

Spectroscopic study of Y210C lambda-repressor: implications for cooperative interaction

The development of a percutaneous artificial internal organ system requires a reliable biocompatible connection between the external environment and the inside of the human body. Such is necessary for the success of a permanent left ventricular assist device. However, the search for a satisfactory interface at the epidermal level has proven to be difficult. Carbon has been proposed for this application, but its texture does not typically promote ingrowth from surrounding tissue. We have therefore employed a new processing method to produce a fine trabecularized carbon implant. The method for preparing the implant involves infiltrating low temperature pyrolytic carbon into the surface of a carbon core which is wrapped with carbon fabric. This results in a tightly woven porous structure of carbon (carbon fiber diameter: 35-50 microm, maximal pore size >200 microm) with gradually increasing porosity from 15-75%. We implanted test samples percutaneously in a calf for in vivo histological evaluation. Thirty days after implantation epidermal downgrowth was minimal. Microscopic analysis revealed that a thin fibrous capsule surrounded the implant, and mature connective tissue with accompanying blood vessels filled the pores of the fine trabecularized carbon layer. From these results we suggest that fine trabecularized carbon is ideally suited for a percutaneous device system in a permanent left ventricular assist device.     

Semiconductor quantum devices

The operation of devices with small enough dimensions for electrons to exhibit wavelike behavior is explained. Two types of device are examined: vertical quantum devices, which include the resonant tunneling structure and the single-electron transistor, and lateral, which include the quantum interference transistor and the spin precession device. The advantages and drawbacks of the two types are identified     

Kinetics of alkylation of phenol with methanol over Ce-exchanged NaX zeolite

The alkylation of phenol with methanol was investigated in vapor phase over a series of cerium-exchanged NaX zeolite with Ce loadings ranging from 0 to 10.43 wt%. The catalyst MX-4 with 8.86 wt% cerium was found to be the best one with total cresols selectivity of 72% at a temperature of 573 K and MeOH to phenol mole ratio of 4:1. The catalyst was also found to be quite stable in the operating range investigated. It was established that the stronger acid sties are required for C-alkylation compared to O-alkylation. From the study of the effects of various parameters, the optimum operating condition for highest cresols selectivity were determined as: MeOH to phenol mole ratio, 4:1; temperature, 623 K; space-time, 10.2 kg h/kgmole under atmospheric pressure. From the kinetic analysis of the experimental data, the apparent activation energy for the reaction was determined as 57.2 kJ/mole.     

Effect of Zn, Sr, and Y Addition on Electrical Properties of PZT Thin Films

We have investigated methods to increase the efficiency of piezoelectric micromachined ultrasonic transducers (pMUTs). pMUTs are driven by a thin piezoelectric layer on a Si membrane. The efficiency of pMUTs can be increased using a film with better ferroelectric properties. We have used Zn, Sr, and Y doping on PZT-based thin films along the morphotropic phase boundary (MPB) composition to increase their piezoelectric properties. The results obtained were then extended to compositions on both sides of the MPB. The sol–gel method was used to prepare precursor solutions, which were then spin coated on a Pt(100)/Ti/SiO₂/Si substrate to prepare the PZT thin films. It was found that Zn and Sr together had the most significant effect on the ferroelectric properties in which a saturation polarization of 108 μC/cm² and remanent polarization of 54 μC/cm² were achieved.