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101.
We show that cosmic strings moving through the plasma at the time of a first-order quark-hadron transition in the early universe
generate baryon inhomogeneities, which can survive till the nucleosynthesis epoch. We find out how these inhomogeneities actually
affect the calculated values of the light element abundances. Recently a wealth of observational data from various experiments
have helped to reduce the uncertainties in the values of these abundances. Using these we show that it is possible to derive
constraints in the presence of cosmic strings during the quark-hadron transition. 相似文献
102.
The stereochemistry of the marine eicosanoid, hybridalactone, has been determined experimentally to be as in 2, in accord with a proposed scheme of biosynthesis from eicosapentaenoic acid. 相似文献
103.
Silica chloride has been found to be an efficient catalyst for facile tosylation of alcohols directly with p-toluenesulfonic acid in methylene chloride under reflux. The process is associated with selective tosylation of secondary alcohols over primary alcohols. 相似文献
104.
Biswanath Das Maddeboina Krishnaiah Katta Venkateswarlu Vtukuri Saidi Reddy 《Helvetica chimica acta》2007,90(1):110-113
Oxiranes and aziridines efficiently undergo ring opening with bismuth nitrate at room temperature to furnish the corresponding β‐(nitrooxy)‐substituted alcohols and amines respectively. The conversions are highly regio‐ and stereoselective and afford the nitrooxy‐compounds in excellent yields within a short period of time. 相似文献
105.
Biswanath Das Joydeep Banerjee Nikhil Chowdhury Anjoy Majhi Gurram Mahender 《Helvetica chimica acta》2006,89(5):876-883
A simple and convenient synthesis of five important insect pheromones by means of Baylis–Hillman adducts is described, i.e., of (2E,4S)‐2,4‐dimethylhex‐2‐enoic acid ( 1 ), a mandibular‐gland secretion of the male carpenter ant in the genus Camponotus, of (+)‐(S)‐manicone ( 2 ) and (+)‐(S)‐normanicone ( 3 ), two mandibular‐gland constituents of Manica ants, and of (+)‐dominicalure‐I ( 6 ) and (+)‐dominicalure‐II ( 7 ), two aggregation pheromones of the lesser grain borer Rhyzopertha dominica (F). For the first time, the potential of the Baylis–Hillman chemistry for the stereoselective synthesis of trisubstituted olefins was successfully applied to the synthesis of these pheromone compounds. 相似文献
106.
Mallik B Thander A Sanyal MK 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(3):485-490
The time-dependent changes in absorbance in the case of ferrocene-doped poly(methyl methacrylate) thin films containing chloroform molecules have been investigated after photoexcitation in nitrogen atmosphere. Photoexcitations have been made by the monochromatic light (using Xe-source and a monochromator) in the UV range. An increase in absorbance associated with spectacular fluctuations in its value, has been noticed. The nature of the variation in the fluctuations has been studied as a function of time (duration) of photoexcitation, photoexcitation wavelength and concentration of ferrocene in the film. The observed results have been discussed considering the role of secondary reaction after photoexcitation as well as the diffusion of small chemical species in the polymer matrix. 相似文献
107.
Biswanath Das Nikhil Chowdhury Joydeep Banerjee Anjoy Majhi 《Tetrahedron letters》2006,47(37):6615-6618
An efficient one-pot stereoselective synthesis of trisubstituted (E)-2-methylalk-2-enoic acids has been accomplished by treatment of unactivated Baylis-Hillman adducts, 3-hydroxy-2-methylenealkanoates, with Al-NiCl2·6H2O in methanol at room temperature followed by hydrolysis. The method has been applied to the synthesis of three important insect pheromones, (4S,2E)-2,4-dimethyl-2-hexenoic acid, (+)-(S)-manicone and (+)-(S)-normanicone. 相似文献
108.
Biswanath Das Nikhil Chowdhury K. Damodar K. Ravinder Reddy 《Helvetica chimica acta》2007,90(2):340-345
A simple, mild, rapid, and highly efficient method for the conjugate addition of 1H‐indoles to electron‐deficient olefins has been developed using NaHSO4 ? SiO2 as heterogeneous catalyst. The conversion proceeds at room temperature, and the corresponding Michael adducts are formed in good‐to‐excellent yields. 相似文献
109.
Adsorption of Co2+, Ni2+, Cu2+, and Zn2+ onto amorphous hydrous manganese dioxide from simple (1-1) electrolyte solutions 总被引:7,自引:0,他引:7
Kanungo SB Tripathy SS Mishra SK Sahoo B Rajeev 《Journal of colloid and interface science》2004,269(1):11-21
The adsorption of Co2+, Ni2+, Cu2+, and Zn2+ onto amorphous hydrous manganese dioxide (delta-MnO2) has been studied using two methods, viz., isotherms at constant pH in the presence of buffer solution and pH variation in the absence of buffer solution from a fixed metal ion concentration. While the adsorption isotherm experiments were carried out in 0.5 M NaCl only, pH variation or batch titration experiments were carried out in 0.5 M NaCl, 0.01 M NaCl, and 0.01 M KNO3 solutions. The complex nature of adsorption isotherms at constant pH values indicates that adsorption of all the cations is non-Langmuirian (Freundlich) and takes place on the highly heterogeneous oxide surface with different binding energies. The proton stoichiometry derived from isotherms at two close pH values varies between 0.3 and 0.8. The variation of fractional adsorption with pH indicates that the background electrolyte solution influences the adsorption of cations through either metal-like or ligand-like complexes with Cl-, the former showing a low adsorption tendency. The proton stoichiometry values derived from the Kurbatov-type plot varies not only with the electrolyte solution but also with the adsorbate/adsorbent ratio. The variation of fractional adsorption with pH can be modeled either with the formation of the SOM+ type or with a combination of SOM+ and SOMOH type complexes, depending upon the cation and electrolyte medium. The equilibrium constants obtained from Kurbatov-type plots are found to be most suitable in these model calculations. Adsorption calculated on the basis of ternary surface metal-chlorocomplex formation exhibits very low values. 相似文献
110.
Biswanath Das Joydeep Banerjee Anjoy Majhi Gurram Mahender 《Tetrahedron letters》2004,45(50):9225-9227
A convenient and facile stereoselective synthesis of (E)- and (Z)-trisubstituted alkenes has been achieved by treatment of unactivated Baylis-Hillman adducts with NaBH4 in the presence of CuCl2·2H2O at room temperature for 15 min. 相似文献