Theoretical considerations in the optimization of surface waves on a planar structure

The problem of optimum excitation of surface waves on a grounded dielectric slab by means of slots in the ground plane is considered. By adopting a two-dimensional (2-D) model, analysis lead to closed forms for the power launched as surface waves and power leaked as radiation. Input admittance of a single slot source and mutual admittance between two slots are derived and utilized to design a three element Yagi array of slots to achieve a prescribed ratio of forward to backward surface wave power. As a development of the 2-D model, we allow finite extent of slot excitation by assuming a Gaussian E-field distribution across the slot. The effect of the Gaussian width on the excited surface wave power is studied. The analysis is relevant to the study of surface waves on printed circuits. Specifically, it applies to the implementation of power combiners based on quasioptical slab beam that have been recently introduced in the literature for use in the millimeter wave band.     

Comprehensive study of multiband unconditional stabilization of common-source and common-gate MESFET transistors using feedback

The use of a new feedback scheme to achieve unconditionally stable MESFET transistors from 0 GHz until cutoff is presented. The methodology is applied for both common-source and common-gate MESFET transistor configurations. Analytical formulation of the stabilization methodology is presented. In addition, two coplanar-waveguide-based amplifiers were designed to operate at Ka-band, monolithically fabricated, and tested, thus, verifying the methodology. The study includes the effects of the bias change on the feedback amplifier stability performance.     

Optoelectronic properties n:CdS:In/p-Si heterojunction photodetector

Optoelectronic properties of CdS:In/Si anisotype heterojunction photodetector fabricated by depositing of polycrystalline CdS and indium doped CdS films used thermal resistive technique on clean monocrystalline p-type silicon substrates are presented. The effect of In diffusion temperature(T _d)in CdS layer on the optoelectronic characteristics of these devices has been studied. Two peaks situated at 650 and 800 nm with values of 0.32 and 0.43 A/W, respectively, were observed in the responsivity plot. Other optoelectronics properties such as detectivity, photovoltaic, and response time are also presented.     

Nitric oxide (NO) production in mammalian non-tumorigenic epithelial cells of the small intestine and macrophages induced by individual strains of lactobacilli and bifidobacteria

Nitric oxide (NO) affects multiple gastrointestinal functions, including mucosal inflammation and antimicrobial activity. The aim of this study was to screen the ability of probiotic bacteria to stimulate NO production in porcine intestinal epithelial cells and macrophages in the presence and absence of interferon gamma (INF-γ). Production of NO in intestinal epithelium was stimulated by individual strains of lactobacilli without INF-γ priming. While none of the tested bifidobacteria were capable of inducing NO production, most constitutively secreted NO. Most tested strains induced a significant increase in NO production compared with the control cells in the macrophage cell line 3D4/21. Results support the protective role of the individual strains of the genera Lactobacillus and Bifidobacterium and may lead to new approaches for manipulating and regulating immune responses at the mucosal surfaces of the gastrointestinal tract.     

High temperature work softening yield point phenomena in polycrystalline aluminum

Work softening yield points have been studied in high purity polycrystalline aluminum tested in the temperature rangeT ₂ = 100°to 450°C at constant strain rate subsequent to prestraining in tension at a lower temperature (T1) = room temperature or 350° C) or higher strain rate. The yield drops increase with prestrain as well as with the difference between the flow stresses at the test and prestrain temperature. Reductions in the yield drop caused by annealing atT ₂ prior to testing indicate that the yield drops are the result of dynamic recovery. It is shown that dynamic recovery is accelerated by concurrent straining.     

Dietary cholesterol effects on plasma and yolk cholesterol fractions in selected lines of Japanese quail

Japanese quail from lines that had been divergently selected for high (HL) or low (LL) plasma total cholesterol and their unselected control line (CL) were fed an all vegetable diet to which 0 or 0.5% crystalline cholesterol were added. Relationships between plasma and yolk cholesterol fractions were examined at 10, 14, and 18 wk of age, which followed 2, 6, and 10 wk consumption of the cholesterol-enriched diet, respectively. Unesterified cholesterol (UC) and cholesteryl esters (CE) in plasma and yolk were analyzed using HPLC. There were no consistent correlations between yolk and plasma for UC, individual CE, total esterified cholesterol (EC), or total cholesterol in the selected lines at ages tested, whether or not 0.5% cholesterol was added to the diet. Cholesterol concentrations in milligrams per gram of yolk and in milligrams per yolk were higher in the HL than the LL at 10 and 14, but not at 18 wk of age. Yolk weights of the HL females increased from 10 to 18 wk of age, whereas those of the LL did not. Cholesterol concentrations in the LL yolks continued to increase over time, however the increases in yolk weight in the HL were not accompanied by proportional increases in cholesterol deposition in the yolk, leading to a dilution of concentration of cholesterol fractions in the HL yolk. Dietary cholesterol increased egg production rate in the selected lines but did not increase the cholesterol content of the yolk.     

Reactive polymers XIV. Hydrolysis of the epoxide groups of the copolymer glycidylmethacrylate — ethylenedimethacrylate

Hydrolysis of the epoxide groups of the copolymer glycidylmethacrylate - ethylenedi-methacrylate in variously concentrated sulphuric acid solutions was studied. An approximate activation energy of hydrolysis, 41 kJ mol^?1, was determined from the temperature dependences. For the sake of comparison the effect of pH on the degree of hydrolysis over the whole range of pH values was examined, and the importance of the results with respect to other reactions of the copolymer used was discussed.     

Conformation and electrical conductivity of poly(γ-methyl-L(LD)-glutamates) reticulate-doped with 1,3-dimethylimidazolium-7,7,8,8-tetracyano-p-quinodimethane complex salt

Polymeric composites were prepared by reticulate doping of poly(γ-methyl-L-glutamate) (PMLGA) and poly(γ-methyl-LD-glutamate) (PMLDGA, 1 : 1) having different conformation forms with 1,3-dimethylimidazolium-TCNQ complex salt. The heat induced α-helix to coil transition in PMLGA and α-helix to β-form and coil transition in PMLDGA were carried out in chlorobenzene and o-dichlorobenzene at temperatures between 70 and 150°C. The conductivity of polyglutamate composites thermally treated and prepared at 70°C is higher by approximately two orders of magnitude than that of thermally not treated films cast at ambient temperature. The conductivity of the most conductive reticulate-doped PMLGA film is higher by more than four orders of magnitude than that of the 1,3-dimethylimidazolium-TCNQ complex salt in pressed pellets.