Reactive ion etching of trenches in 6H-SiC

In this paper, we report the reactive ion etching (RIE) of trenches in 6H-silicon carbide using SF₆/O₂. The plasma parameters: etchant composition, gas flow rate, chamber pressure, and radio frequency power were optimized to obtain a maximum etch rate of 360Å/min. The etch rate of SiC was found to exhibit a direct correlation with the dc self bias except when the O₂ percentage was varied. Trenches were fabricated using the optimized conditions. It was found that the trench surface was extremely rough due to the aluminum micromasking effect. To overcome this effect, a Teflon^TM sheet was used to cover the cathode during the experiment. The trenches fabricated using this modification were found to have smooth etched surfaces and sidewalls. The angle of anisotropy of these trenches was approximately 80° which is suitable for device applications.     

Explicit formulas for stability radii of nonnegative and Metzlerianmatrices

We address stability issues pertaining to uncertain nonnegative and Metzlerian matrices. The problem under consideration is the computation of the stability radius when matrix perturbations are both unstructured and structured. We show that the stability radius can be obtained in the former case by computing the largest singular value of a constant matrix and in the latter case by computing the spectral radius of a constant matrix     

Power distribution system equipment overvoltage protection

Application of surge overvoltage protection devices in general is based upon rule of thumb without the benefit of understanding basic parameters, system components and configuration, and energy content of the surge. This may result in the selection of an inadequate device. Selection of surge protective devices should be based on the magnitude of surge overvoltage, and also upon the expected energy associated with the surge. Characteristics of surge arresters are reviewed from the application point of view. Fundamentals of surge energy are presented. The MOV surge arrester selection parameters are discussed. The need for industry standards for the application of DC surge arresters is contemplated     

Noise of a single-ion frequency standard

A frequency source supposed to serve as a standard requires feedback for short-term and long-term frequency control. A spectral discriminant for short-term control may be provided, in the microwave regime, by a hyperfine resonance of a multi-ion ensemble confined in an electrodynamic trap, and in the optical regime by an eigenmode of a focal Fabry-Pérot cavity. For long-term frequency control, resonances of single trapped ions are discriminants of superior accuracy although the controlled frequency shows random fluctuations caused by noise on the feedback signal. Its fundamental contribution is quantum projection noise. The detection of fluorescence for the generation of feedback is incompatible with the ions being prepared in a superposition state in the excitation by the wave emitted from the oscillator. Attempts of circumventing this limitation by preparing ensembles of correlated ions prior to the measurement (spin squeezing) are reviewed.     

Cyclohexanone oxime-blocked polyisocyanates

Cyclohexanone oxime-blocked isophorone diisocyanate and cyclohexanone oxime-blocked toluene diisocyanate were synthesized and analyzed by infrared spectra, nuclear magnetic resonance spectra, elemental analysis, etc. Decomposition temperatures of the blocked isocyanates were determined by thermogravimetry. The solubilities of blocked isocyanates in various polyols were tested. © 1993 John Wiley & Sons, Inc.     

Impedance parameters and the state-of charge. I. Nickel-cadmium battery

The problem of nondestructive determination of the state-of-charge of nickel-cadmium batteries has been examined experimentally as well as theoretically from the viewpoint of internal impedance. It is shown that the modulus of the impedance is mainly controlled by diffusion at all states of charge. Even so, a prediction of the state of charge is possible if the equivalent series/parallel capacitance or the alternating current phase shift is measured at a sufficiently low a.c. test frequency (5–30 Hz) which also avoids inductive effects. These results are explained on the basis of a uniform transmission-line analog equivalent circuit for the battery electrodes.On leave from Tamil Nadu Alkaline Batteries Ltd, Madras, India.     

Corrosion and Grounding Systems

Corrosion that occurs in the presence of dissimilar metals in the same electrolyte, or same metal in different electrolytes, or in different concentrations of the same electrolyte, has caused numerous problems in operating electric systems. This corrosion is the result of a potential difference existing between two surfaces which forces an electric current to flow. This effect is often ignored or overlooked in electrical grounding design, with the premise that electrical system protection will be hampered by the incorporation of corrosion protection. By careful design, however, both sets of requirements can be met. Some of the principles that determine corrosion and how these conditions exist in underground systems of cement plants are reviewed. The principles of grounding design are analyzed and suggestions to improve the design to minimize corrosion are discussed.     

Synthesis and characterisation of poly(N-4'-fluorophenylmethacrylamide)

Summary The monomer, N-4'-fluorophenylmethacrylamide (FPMA) was polymerized for the first time using benzoyl peroxide as the initiator. The IR and NMR spectra of FPMA and the polymer, poly(N-4'-fluorophenylmethacrylamide) (PFPMA) are discussed. Viscosity measurements of PFPMA was carried out in dimethylformamide medium at 25°C. The number average molecular weight of PFPMA was determined to be 690 using vapour pressure osmometer. The formation of low molecular weight of PFPMA is explained on the basis of intermolecular hydrogen bonding in the monomer.     

Synthesis and pharmacology of conformationally restricted raloxifene analogues: highly potent selective estrogen receptor modulators

The 2-arylbenzothiophene raloxifene, 1, is a selective estrogen receptor modulator (SERM) which is currently under clinical evaluation for the prevention and treatment of postmenopausal osteoporosis. In vivo structure-activity relationships and molecular modeling studies have indicated that the orientation of the basic amine-containing side chain of 1, relative to the stilbene plane, is an important discriminating factor for the maintenance of tissue selectivity. We have constructed a series of analogues of 1 in which this side chain is held in an orientation which is orthogonal to the stilbene plane, similar to the low-energy conformation predicted for raloxifene. Herein, we report on the synthesis of these compounds and on their activity in a series of in vitro and in vivo biological assays reflective of the SERM profile. In particular, we describe their ability to (1) bind the estrogen receptor, (2) antagonize estrogen-stimulated proliferation of MCF-7 cells in vitro, (3) stimulate TGF-beta3 gene expression in cell culture, (4) inhibit the uterine effects of ethynyl estradiol in immature rats, and (5) potently reduce serum cholesterol and protect against osteopenia in ovariectomized (OVX) rats without estrogen-like stimulation of uterine tissue. These data demonstrate that one of these compounds, LY357489,4, is among the most potent SERMs described to date with in vivo efficacy on bone and cholesterol metabolism in OVX rats at doses as low as 0.01 mg/kg/d.