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71.
In this study, we present linear analysis of electrostatic counter-streaming instability in spin-polarized electron–positron–ion (e-p-i) plasma. With the aid of the separate spin evolution-quantum hydrodynamic (SSE-QHD) model, we derive the dispersion relation of counter-streaming instability. We numerically solve the dispersion and find four wave solutions: Langmuir wave, positron acoustic mode, and two electron and positron spin-dependent waves. It is noted that coupling of streaming and spin effects excites Langmuir instability and positron acoustic mode instability. However, in the absence of spin effect, only Langmuir instability will survive in e-p-i plasma. We have also discussed the effects of positron concentration, streaming speed, and spin polarization on the real frequency of waves and the growth rate. The present study may be helpful for understanding longitudinal wave propagation and instabilities in dense magnetized environments. 相似文献
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Three quettamine type alkaloids, which incorporate either a benzofuran or a dihydrobenzofuran moiety within the molecular framework, have been obtained from . These are dihydrosecoquettamine (), secoquettamine (), and quettamine chloride (). Alkaloids and are racemates. Hofmann degradation of quettamine () provides secoquettamine () and the styrene which has a trans relationship between the hydrogens at C-1 and C-α, thus indicating the identical stereochemistry in quettamine. Emde reduction of quettamine leads to dihydrosecoquettamine () and the stilbene . Two other polar alkaloids in the plant are (+)-armepavine methochloride () and oblongine chloride (). An oblongine type alkaloid must be the biogenetic precursor for the quettamines. Arguments are presented favoring direct oxidative coupling in the biogenesis of the cularine alkaloids. 相似文献
75.
Alan R. Katritzky Ghulam R. Khan Charles M. Marson 《Journal of heterocyclic chemistry》1987,24(3):641-644
Pyrrole, indole, carbazole and imidazole have been protected as N-[2-(4-pyridyl)ethyl] derivatives. Deprotection occurred under mild conditions after quaternisation. 3-Bromoindole was prepared by bromin-ation of the protected parent indole. 相似文献
76.
M.Iqbal Choudhary SyedGhulam Musharraf MahmudTareqHassan Khan Doaa Abdelrahman Massod Parvez Farzana Shaheen Atta‐ur‐Rahman 《Helvetica chimica acta》2003,86(10):3450-3460
The microbial transformation of (+)‐isolongifolen‐4‐one ( 4 ) by a number of fungi by means of a standard two‐stage fermentation technique afforded (7R)‐12‐hydroxyisolongifolen‐4‐one ( 5 ), (7S)‐13‐hydroxyisolongifolen‐4‐one ( 6 ), (11R)‐11‐hydroxyisolongifolen‐4‐one ( 7 ), (10R)‐10‐hydroxyisolongifolen‐4‐one ( 8 ), and (9R)‐9‐hydroxyisolongifolen‐4‐one ( 9 ) (Scheme). All five metabolites were found to be new, and metabolites 6 and 9 showed potent tyrosinase inhibitory activity (Table 1). The metabolites and their derivatives were characterized on the basis of spectroscopic and single‐crystal X‐ray‐diffraction techniques. 相似文献
77.
Fermentation of (+)-androsta-1,4-diene-3,17-dione ([structure: see text]) with Cephalosporium aphidicola for 8 days yielded oxidative and reductive metabolites, androst-4-ene-3,17-dione ([structure: see text]), 17beta-hydroxyandrosta-1,4-diene-3-one ([structure: see text]), 11alpha-hydroxyandrosta-1,4-diene-3,17-dione ([structure: see text]), 11alpha-hydroxyandrost-4-ene-3,17-dione ([structure: see text]), 11alpha,17beta-dihydroxyandrost-4-ene-3-one ([structure: see text]) and 11alpha,17beta-dihydroxyandrosta-1,4-diene-3-one ([structure: see text]). The fermentation of [structure: see text] with Fusarium lini also yielded metabolites [structure: see text]. The structures of these metabolites were elucidated on the basis of spectroscopic techniques. 相似文献
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Mixed micelle formation and interfacial properties of aqueous binary and ternary combinations of hexadecyltrimethylammonium bromide (C(16)Br), hexadecylbenzyldimethylammonium chloride (C(16)BzCl) and polyoxyethylene (20) cetyl ether (Brij58) at 25 degrees C in 30 mM aqueous NaCl have been studied in detail employing tensiometric and fluorimetric techniques. The micellar and adsorption characteristics like composition, activity coefficients, mutual interaction parameters and free energy of micellization have been estimated using the theoretical approaches of Clint, Rosen, Rubingh, Blankschtein et al., Rubingh-Holland and Maeda. A comprehensive account of the comparative performance of these models on the selected cationic-cationic-nonionic surfactant mixtures at constant ionic strength has been presented. The Blankschtein model predicted lower synergism than from Rubingh's method because it neglects the contribution due to steric interaction between surfactant head groups of different sizes and charges. Free energy of micellization calculated using Maeda's approach, which employs interaction parameter and micellar mole fraction from Rubingh's model as inputs, shows good correlation with that calculated from commonly used phase separation model. The present study also reveals that the modified Rubingh-Holland method along with the Rosen's model can be applied to analyze the interfacial characteristics of ternary surfactant mixtures with a fair degree of success thereby widening the domain of applicability of this model. 相似文献
80.
Shabir Ghulam Arooj Sama Javed Ahad Hussain Saeed Aamer Shahzad Nadia Iqbal Naseem Jabeen Erum 《Journal of fluorescence》2022,32(2):799-815
Journal of Fluorescence - Ruthenium-based metal complex dyes have been employed extensively in dye-sensitized solar cells (DSSCs) as photosensitizers, but the cost and toxicity of metal complexes... 相似文献