The discrepancy between 99Tcm-ECD dynamic and static SPET images in patients with ischaemic lesions corresponds to reduced vasoreactivity to acetazolamide

We evaluated 99Tcm-N,N'-(1,2-ethylenediyl)bis-L-cysteine diethyl ester (99Tcm-ECD) dynamic and static SPET (single photon emission tomographic) images to examine 99Tcm-ECD kinetics under ischaemic cerebrovascular conditions. In 20 patients who showed arterial occlusion on magnetic resonance angiography, dynamic (0-10 min) and static (15-35 min) SPET images were acquired after the intravenous administration of 99Tcm-ECD. Thirteen of the patients had focal perfusion deficits that were more evident on the dynamic than on the static images; the other seven showed no such discrepancy. In those patients with a mismatch between the dynamic and static images, the extent corresponded to reduced vaso-reactivity to acetazolamide. Based on quantitative analysis of the ratio of tracer uptake in affected to that in unaffected areas, the patients with discrepant findings showed significantly different ratios on the dynamic and static images, whereas those with no such mismatch did not. Our results suggest that dynamic 99Tcm-ECD images provide circulatory information and that static images reflect a filling-in phenomenon of ECD metabolites in ischaemic lesions. 99Tcm-ECD dynamic and static SPET images offer an alternative method of detecting mild perfusion deficits without the need for acetazolamide challenge.     

Analysis of hydrofilm extrusion of elliptic shapes using perturbation method

An approximate method of solution is proposed for the hydrofilm extrusion of elliptic shapes from round billets through optimized curved dies. A modified upper-bound theorem and hydrodynamic lubrication theory are used in combination, in order to analyze metal deformation and fluid flow respectively. The fluid analysis in hydrodynamic lubrication theory is simplified by use of elliptic transformation and perturbation technique. Strain-hardening effect of billet material and viscosity variation of fluid due to pressure are taken into consideration.For several reductions of area, experiments are carried out at room temperature by using mild steel specimens and caster oil as the lubricant.The experimental extrusion pressures are in good agreement with the theoretical predictions.     

Epitaxy of silicon doped gallium arsenide by molecular beam method

The molecular beam method is a versatile experimental technique which may be used to grow high quality single crystal thin films in the range from 100Å to several microns with precise control of uniformity and thickness. Films may be doped by an additional molecular beam containing the doping material simultaneously impinging on the substrate surface with the film molecular beams. Epitaxial GaAs thin films doped with silicon were grown by the molecular beam method in an ultrahigh vacuum system in which high energy electron diffraction and mass spectrometric measurements could be made during growth or by stopping growth momentarily. The crystallinity and beam intensity parameters of these films were thus studied during growth. The doping profiles and the amount of compensation were evaluated by the Schottky barrier diode method and the photo luminescence spectra.     

Static and Dynamic Equalization of the L5 Repeatered Line

The residual transmission deviation of the L5 repeatered line can be divided into two categories, static or time invariant and dynamic or time variant. The static deviation, which is due to design limitations and manufacturing deviations of the basic and regulating repeaters, is compensated for by manually adjustable equalizers designatedE1andE2. These equalizers are composed of 28 Bode bump networks whose gains are adjusted to minimize the total mean-squared error of the transmission channel. The residual dynamic transmission deviation, caused by temperature variations of the basic and regulating repeaters, is corrected continuously by an automatic equalizerE3. The time-varying transmission deviations are detected by four pilot tones spaced across the L5 frequency spectrum. Four electronically controlled networks in the equalizer respond to the pilots to correct the dynamic transmission deviations.     

An enzyme immunoanalytical system based on sequential cross-flow chromatography

A new enzyme immunoanalytical concept that can be used for point-of-care testing has been investigated. Enzyme as a tracer requires a separate reaction step for signal generation, which follows the completion of immune complex formation with analyte (e.g., Hepatitis B surface antigen) in a sample. This has been a major factor limiting its utilization within the laboratory. We carried out such sequential processes employing chromatographic analysis, using two crosswise-arranged membrane pads in vertical and horizontal directions. The vertically arranged pads were the same as those in the usual format for pregnancy testing, for instance, with the exception of the use of horseradish peroxidase (HRP) as tracer. By placing the horizontally arranged pads on each lateral side of the signal generation pad in the vertical arrangement, they were employed to supply substrate to the enzyme present in the immune complexes. The substrate flow was initiated after the antigen-antibody bindings to produce a signal, which was typically a color change in proportion to the analyte concentration. Under optimal conditions, the use of HRP labeling increased the detection capability of the assay approximately 30 times compared to that of gold colloids. Potential advantages of using the concept investigated are (1) provision of a rapid and simple immunoassay, (2) satisfaction of a clinical need for highly sensitive determination of analyte, and (3) utilization of relatively inexpensive, portable quantitation means.     

Catalyst-free MOCVD growth of ZnO nanorods and their structural characterization

We have synthesized ZnO nanorods on ZnO-coated Si(100) substrates without a metal catalyst by a reaction of a diethylzinc (DEZn) and oxygen (O₂) mixture. By adjusting the argon (Ar)/O₂ gas flow ratio, we have obtained ZnO nanorods of various densities at a temperature of 450°C. The ZnO nanorods had an average diameter of 30–70 nm, and transmission electron microscopy (TEM) showed a single crystalline structure.     

Novel method for site-controlled surface nanodot fabrication by ion beam synthesis

By using a Ga FIB system to spatially control the implantation of Ga into SiO(2) followed by vacuum annealing, we have fabricated self-assembled surface Ga nanodots with a high degree of control of nucleation location. The morphology of the Ga nanodots is closely related to Ga dose, showing a critical dose needed for nucleation that results in Ga nanodot formation just below the surface, while at higher doses Ga nanodots form on the surface as metallic Ga droplets. Possible applications include defining nucleation sites for subsequent growth, use as Ga source for GaN or GaAs quantum dots, or as catalyst for nanowire growth.     

Effect of air-pressure on room temperature hydrogen sensing characteristics of nanocrystalline doped tin oxide MEMS-based sensor

Nanocrystalline indium oxide (In2O3)-doped tin oxide (SnO2) thin film sensor has been sol-gel dip-coated on a microelectrochemical system (MEMS) device using a sol-gel dip-coating technique. Hydrogen (H2) at ppm-level has been successfully detected at room temperature using the present MEMS-based sensor. The room temperature H2 sensing characteristics (sensitivity, response and recovery time, and recovery rate) of the present MEMS-based sensor has been investigated as a function of air-pressure (50-600 Torr) with and without the ultraviolet (UV) radiation exposure. It has been demonstrated that, the concentration of the surface-adsorbed oxygen-ions (which is related to the sensor-resistance in air), the ppm-level H2, and the oxygen (O2) partial pressure are the three major factors, which determine the variation in the room temperature H2 sensing characteristics of the present MEMS-based sensor as a function of air-pressure.     

The low-power-drain microelectronic VHF amplifier

Low-power-drain VHF amplifiers have some unique characteristics when they are miniaturized. And, if the design is special?requiring tight tolerances or intended for limited-quantity production?it is often desirable to make the RF micropower circuits from discrete components. Described in this article are the first-order device requirements and circuit considerations for such VHF amplifiers incorporating bipolar transistors operating at collector currents as low as 25 ?A. Two specific designs are offered, along with information pertinent to their construction.