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991.
992.
993.
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. 相似文献
994.
Ash WW Band HR Blume HT Camporesi T Chadwick GB Clearwater SH Coombes RW Delfino MC De Sangro R Fernandez E Ford WT Gettner MW Goderre GP Groom DE Heltsley BK Hurst RB Johnson JR Lau KH Lavine TL Lee HY Leedy RE Marini A Maruyama T Messner RL Moromisato JH Moss LJ Muller F Nelson HN Peruzzi I Piccolo M Prepost R Qi N Read AL Ritson DM Rosenberg LJ Shambroom WD Sleeman JC Smith JG Venuti JP von Goeler E Wald HB Weinstein R Wiser DE Zdarko RW 《Physical review letters》1985,54(23):2477-2480
995.
996.
Ash WW Band HR Bloom ED Bosman M Camporesi T Chadwick GB Delfino MC De Sangro R Ford WT Gettner MW Goderre GP Godfrey GL Groom DE Hurst RB Johnson JR Lau KH Lavine TL Leedy RE Lippi I Maruyama T Messner RL Moromisato JH Moss LJ Muller F Nelson HN Peruzzi I Piccolo M Prepost R Pyrlik J Qi N Read AL Ritson DM Rosenberg LJ Shambroom WD Sleeman JC Smith JG Venuti JP Verdini PG von Goeler E Wald HB Weinstein R Wiser DE Zdarko RW 《Physical review letters》1987,58(7):640-643
997.
Contamination in food from packaging material 总被引:10,自引:0,他引:10
Packaging has become an indispensible element in the food manufacturing process, and different types of additives, such as antioxidants, stabilizers, lubricants, anti-static and anti-blocking agents, have also been developed to improve the performance of polymeric packaging materials. Recently the packaging has been found to represent a source of contamination itself through the migration of substances from the packaging into food. Various analytical methods have been developed to analyze the migrants in the foodstuff, and migration evaluation procedures based on theoretical prediction of migration from plastic food contact material were also introduced recently. In this paper, the regulatory control, analytical methodology, factors affecting the migration and migration evaluation are reviewed. 相似文献
998.
A liquid chromatographic method using indirect conductimetric detection is proposed for the determination of low levels of organic compounds, which does not require any special functional characteristics of the analyte. The signal detected is proportional to the molar concentration of the analyte and independent of its nature. The detector response is linearly dependent on analyte concentrations over at least three orders of magnitude. The basis of the detection is to create a conducting background, which will decrease on elution of the organic compounds. The theory of the method is discussed, with special reference to the quantitative displacement of the conducting species of the mobile phase from the column by the analyte on sample injection. The proposed method has been applied to study the chromatographic behaviour of twenty-one amino acids, where a 5 -μm Econosil CN column was used as the stationary phase with a mixture of water-acetonitrile-tetrahydrofuran (70:20:3) containing 1 mM perchloric acid or trichloroacetic acid as the mobile phase. The proposed method allows as little as 10 ng of each amino acid to be determined. 相似文献
999.
C. S. Lee Wayne W. Y. Lau S. Y. Lee S. H. Goh 《Journal of polymer science. Part A, Polymer chemistry》1991,29(13):1889-1893
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. 相似文献
1000.
High-performance liquid chromatographic method with quantitative comparisons of whole chromatograms of raw and steamed Panax notoginseng 总被引:2,自引:0,他引:2
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. 相似文献