Nonlinear distortions in the current modulation of non-self-pulsing and weakly self-pulsing GaAs/GaAlAs injection lasers

Nonlinear distortion characteristics of GaAs/GaAlAs injection lasers under analog current modulation were experimentally investigated. In non-self-pulsing lasers, relaxation oscillation (R.O.) plays a heavy role in generating harmonic distortions, in good agreement with theory. Additional distortions generated by microwave mixing in weakly self-pulsing lasers make such lasers unacceptable for wideband analog transmissions unless suitable negative feedback is applied. With such measure taken, both fundamental and the harmonic responses of a self-pulsing laser is indistinguishable from that of a laser with no R.O. resonance.     

Synthesis and characterization of a new monomer with pendant hindered amine group

A new monomer, 1,2,2,6,6-pentamethyl-4-piperidinyl m-isopropenyl-α, α-dimethylbenzyl carbamate, was synthesized by direct addition of 1,2,2,6,6-pentamethyl-4-piperidinol to m-isopropenyl-α, α-dimethylbenzyl isocyanate in the presence of dibutyltin dilaurate catalyst at elevated temperatures. It was characterized by FT-IR, ¹H-NMR. MS, and elemental analysis. It is a potential hindered amine light stabilizer as it contains the 2,2,6,6-tetraalkylpiperidine moiety and its vinylic functionality makes it polymerizable.     

High-performance liquid chromatographic method with quantitative comparisons of whole chromatograms of raw and steamed Panax notoginseng

A high-performance liquid chromatographic (HPLC) method coupled with chromatographic pattern matching was developed to differentiate whole chromatograms of raw and steamed Panax notoginseng objectively and quantitatively. The major peaks differentiating chromatograms of raw and steamed samples were also identified for the first time in this herb. The raw and steamed P. notoginseng roots and its products were successfully differentiated. The quantitative differences between the chromatograms were correlated to the duration of steaming. Chromatographic pattern matching allows rapid, simple, automated, and quantitative comparisons of complex chromatograms. It is a useful tool in ensuring safety and quality of herbal products.     

Kinetics of CoSi2 from evaporated silicon

2 MeV⁴He⁺ backscattering spectrometry and CuK x-ray diffraction were used to study CoSi₂ formed by annealing at temperatures between 405° and 500 °C from CoSi with evaporated Si films. A laterally uniform layer of CoSi₂ forms, in contrast to the laterally nonuniform CoSi₂ layer that is obtained on single crystal Si substrates. The thickness of the CoSi₂ film formed is proportional to the square root of time at a fixed temperature. The activation energy of this reaction is about 2.3 eV.     

Comparison of a modification of the ellman method to measure carbamate inhibition of acetylcholinesterase in plasma, erythrocytes and brain tissues in sprague dawley rats using two analytical systems

Inhibition of the enzyme acetylcholinesterase (AChE) using a carbamate compound was measured in 30 Crl: CD(R)BR Sprague Dawley rats. Erythrocyte, plasma, and brain tissues were analyzed using modifications of the Ellman technique(1) on two different clinical chemistry analyzers. Both EDTA and heparin anticoagulated whole blood were used for the erythrocyte and plasma tests. Results demonstrated similar inhibition of the enzyme in all three tissues between the control and dosed groups using the two technique modifications and instruments. Final inhibition of plasma and erythrocyte AChE for the control vs. treated groups (males and females combined) was 89.5% vs. 82% and 39% vs. 38% for the Technicon AutoAnalyzertrade mark vs. the Boehringer Mannheim Hitachitrade mark 704, respectively. Inhibition of the left and right brain segments for the control vs. treated groups (males and females combined) was 35% vs. 39% and 33.2% vs. 29% for the Technicon and the Hitachi, respectively. All inhibitions were significant at the 5% level using two tailed Dunnett's t-Test. Hemolysates prepared from EDTA whole blood packed cells gave more consistent results on the Hitachi 704.     

On -algebras associated with locally compact groups

Let be a locally compact group, and let denote the same group with the discrete topology. There are various associated to and We are concerned with the question of when these are isomorphic. This is intimately related to amenability. The results can be reformulated in terms of Fourier and Fourier-Stieltjes algebras and of weak containment properties of unitary representations.

     

Kinetics and mechanisms of the oxidation of phenols by a trans-dioxoruthenium(VI) complex

The kinetics of the oxidation of phenols by trans-[Ru(VI)(L)(O)(2)](2+) (L = 1,12-dimethyl-3,4:9,10-dibenzo-1,12-diaza-5,8-dioxacyclopentadecane) have been studied in aqueous acidic solutions and in acetonitrile. In H(2)O the oxidation of phenol produces the unstable 4,4'- biphenoquinone, as evidenced by a rapid increase and then a slow decrease in absorbance at 398 nm. The first step is first-order in both Ru(VI) and phenol, and rate constants are dependent on [H(+)] according to the relationship k(f) = k(x) + (k(y)K(a)/[H(+)]), where k(x) and k(y) are the rate constants for the oxidation of PhOH and PhO(-), respectively. At 298 K and I = 0.1 M, k(x) = 12.5 M(-1) s(-1) and k(y) = 8.0 x 10(8) M(-1) s(-1). At I = 0.1 M and pH = 2.98, the kinetic isotope effects are k(H(2)O)/k(D(2)O) = 4.8 and 0.74 for k(x) and k(y), respectively, and k(f)(C(6)H(5)OH)/k(f)(C(6)D(5)OH) = 1.1. It is proposed that the k(x) step occurs by a hydrogen atom abstraction mechanism, while the k(y) step occurs by an electron-transfer mechanism. In both steps the phenoxy radical is produced, which then undergoes two rapid concurrent reactions. The first is a further three-electron oxidation by Ru(VI) and Ru(V) to give p-benzoquinone and other organic products. The second is a coupling and oxidation process to give 4,4'-biphenoquinone, followed by the decay step, k(s). A similar mechanism is proposed for reactions in CH(3)CN. A plot of log k(x) vs O-H bond dissociation enthalpies (BDE) of the phenols separates those phenols with bulky tert-butyl substituents in the ortho positions from those with no 2,6-di-tert-butyl groups into two separate lines. This arises because there is steric crowding of the hydroxylic groups in 2,6-di-tert-butyl phenols, which react more slowly than phenols of similar O-H BDE but no 2,6-tert-butyl groups. This is as expected if hydrogen atom abstraction but not electron transfer is occurring.