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71.
A Mukherjee M Dasgupta DJ Hinde CR Morton AC Berriman RD Butt JO Newton H Timmers 《Pramana》2001,57(1):195-198
Fusion cross-sections for the 7Li + 12C reaction have been measured at energies above the Coulomb barrier by the direct detection of evaporation residues. The heavy
evaporation residues with energies below 3 MeV could not be separated out from the α-particles in the spectrum and hence their
contribution was estimated using statistical model calculations. The present work indicates that suppression of fusion cross-sections
due to the breakup of 7Li may not be significant for 7Li + 12C reaction at energies around the barrier. 相似文献
72.
Gerald G. Fuller Kaye Smith Wesley R. Burghardt 《Journal of statistical physics》1991,62(5-6):1025-1039
This paper presents experimental results on the use of spectroscopic optical polarimetry to study structure in dense systems of rigid particles and rigid polymer liquid crystals. These measurements probe microstructural anisotropy induced by the application of electric fields in the case of dense suspensions of rigid spheres, or flow fields in the case of polymer liquid crystals. It is demonstrated that conservative linear dichroism can measure moments of the particle pair distribution function in dense suspensions. In liquid crystals, the dichroism is a result of field-induced anisotropy in the defect structure of the material. 相似文献
73.
This paper reports some experimental results on the time development of a Couette flow following the start-up of shear flow using the technique of two-color flow birefringence. Measurements obtained on collagen solutions are consistent with two theoretical studies which predict that for some viscoelastic liquids, momentum is transferred from the moving Couette cell boundary to the interior of the fluid through a velocity wave propagating and reflecting between the cell boundaries. This non-Newtonian phenomenon, exhibited as an oscillatory response in the measured birefringence and orientation angle, is observed at shear rates above a critical value when the response time of the polymer solution approaches the flow development time in the Couette flow cell. 相似文献
74.
75.
Lithium and sodium complexes of dimethyl ether (DME) and dimethoxyethane (DXE) were produced by reactions of laser-vaporized metal atoms with organic vapors in a pulsed nozzle cluster source. The mono-ligand complexes were studied by photoionization and pulsed field ionization zero electron kinetic energy (ZEKE) spectroscopy. Vibrationally resolved ZEKE spectra were obtained for Li(DME), Na(DME) and Li(DXE) and a photoionization efficiency spectrum for Na(DXE). The ZEKE spectra were analyzed by comparing with the spectra of other metal-ether complexes and with electronic structure calculations and spectral simulations. Major vibrations measured for the M(DME) (M=Li,Na) ions were M-O and C-O stretches and M-O-C and C-O-C bends. These vibrations and additional O-Li-O and O-C-C-O bends were observed for the Li(DXE) ion. The M(DME) complexes were in C2v symmetry with the metal atom binding to oxygen, whereas Li(DXE) was in a C2 ring configuration with the Li atom attaching to both oxygen atoms. Moreover, the ionization energies of these complexes were measured from the ZEKE or photoionization spectra and bond dissociation energies were derived from a thermodynamic cycle. 相似文献
76.
J. E. Hardcastle W. H. Fuller R. J. Hannapel 《Journal of Radioanalytical and Nuclear Chemistry》1973,13(1):141-147
The Sr in plant and soil samples is converted to SrCl2 by digestion with HNO3 and HCl. The recovery of this digestion is 90% with a reproducibility of about 4%. SrCl2 is solubilized in toluene by forming a complex with di-n-propyl phosphate (DNP). The DNP-toluene reagent was found to be
a highly effective carrier of SrCl2, and to have properties suitable for highly efficient liquid scintillation counting. An efficiency of 95% was obtained for89Sr counting. The factors affecting the utility of the method are discussed. 相似文献
77.
78.
[reaction: see text] An approach to the C10-C24 ketone fragment of the inostamycin family of polyether antibiotics is described. The synthetic strategy utilizes an asymmetric Rh-catalyzed reductive aldol reaction and a stereoselective Rh-catalyzed reductive Claisen rearrangement as the key steps in formation of alkene and vinyl iodide synthons, respectively. 相似文献
79.
80.
In several synthetic problems in our laboratory it became essential to react a basic nitrogen atom with a suitable protecting group which could be subsequently removed under very mild conditions. The presence of sensitive functionality elsewhere in the molecule prevented serious consideration of most of the reagents which have been developed for dealkylation of quaternary ammonium salts2–12. One of the most recent methods involving the highly nucleophilic system, lithium n-propylmercaptide in hexamethylphosphoramide12 (HMPA) was thought to be most desirable but even in this instance demethylation of the quaternary system provided difficulties. For example, demethylation of the methiodide derivative of 18β-carbomethoxycleavamine (II, R [dbnd] CH3, 3,4-double bond) provided only a 5% yield of the desired product. It was clear that a protecting group more susceptible to nucleophilic displacement was essential. During our studies directed to this end it has been established that the benzyl group satisfies the requirements in all respects. We present some of our results since they may be of interest to others involved in research on alkaloids and other basic nitrogen compounds. 相似文献