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91.
92.
[reaction: see text] The first example of enantioselective linear homoallylic alcohol transfer reaction was revealed. In all cases, the whole rearrangement is thermodynamically favorable and a steric effect is the driving force of this reaction. The preservation of the stereocenter and olefin geometry together with the isolation of gamma-adduct homoallylic alcohols in one isomeric form have warranted the proposed mechanism. 相似文献
93.
[reaction: see text] A new method is presented for the measurement of enantiomeric excess (ee) utilizing molecularly imprinted polymers (MIPs). The method is demonstrated to be accurate and rapid, as the ee values can be calculated from straightforward concentration measurements. The MIP-based assay can also be adapted to measure the ee of samples of differing initial concentrations. 相似文献
94.
The memory effect upon glassification is studied in the glass-to-rubber transition of vulcanized rubber with the strain as a controlling parameter. A phenomenological model is proposed, taking the history of the temperature and the strain into account, by which the experimental results are interpreted. The data and the model demonstrate that the glassy state memorizes the time course of strain upon glassification, not as a single parameter but as the history itself. The data also show that the effect of irreversible deformation in the glassy state is beyond the scope of the present model. 相似文献
95.
The focus of this presentation is to describe our efforts at laser generation of high frequency surface acoustic waves and detection of the nonlinear contribution in the acoustic near-field of the source. Narrow band acoustic generation is accomplished by interfering two pulsed laser beams at the surface of the sample. A Michelson interferometer, that incorporates a high power microscope objective, is used to detect the acoustic disturbance. Detection near the source combined with high frequency generation (approximately 0.1 GHz) facilitates investigation of fundamental processes of harmonic generation on length scales comparable to grain size dimensions. 相似文献
96.
The femtosecond time-resolved two-photon photoemission (TR-2PP) and the ultra high vacuum (UHV) surface science techniques are integrated to investigate the electronic structures and the interfacial electron transfer dynamics at the atomically ordered adsorbate overlayers on TiO2 singlecrystalline surfaces. Our research into the CH3OH/TiO2 system exhibits complex dynamics, providing abundant information with regard to electron transport and solvation processes in the interfacial solvent structures. These represent the fundamentally physical, photochemical, and photocatalytic reactions of protic chemicals covered with metal-oxides. 相似文献
97.
Ken Ono 《Compositio Mathematica》1999,119(1):1-11
Let D denote the fundamental discriminant of a real quadratic field, and let h(D) denote its associated class number. If p is prime, then the Cohen and Lenstra Heuristics give a probability that ph(D). If pgt;3 is prime, then subject to a mild condition, we show that
This condition holds for each 3<p<5000. 相似文献
98.
Hirotaka Ihara Ken Shudo Chuichi Hirayama Hiroshi Hachisako Kimiho Yamada 《Liquid crystals》1996,20(6):807-809
The L-glutamic acid-derived lipids form organic gels in benzene, which show enantioselective elution of N-dansyl L-phenylalanine from organic gels to aqueous phases. Differential scanning calorimetry and circular dichroism measurements demonstrate that this enantioselectivity occurred through highly-oriented structures of aggregated lipids like those of aqueous lipid membrane systems. 相似文献
99.
Kazuo Onda Yasuo Kaga Ken Kato 《Journal of Quantitative Spectroscopy & Radiative Transfer》1983,29(3):277-278
The temperature profile in Fig. 3 of Ref. 1 is better approximated by a relation for a turbulent boundary layer than a laminar boundary layer. The critical Reynolds number is expected to be lowered in the flow train of MHD combustion gas because of large turbulence in the combustor and by roughness along the duct. 相似文献
100.
Observations are reported of the effect of the buffer gases He, Ne, and CF4, in the pressure range of 0–30 torr, on the branching ratio [HCl]/[DCl] of the unimolecular decomposition The ratio R = kH/kD has been measured in high-pressure thermal decomposition (670–1100 K) and was shown to give a unique measure of the internal energy of the decomposing molecules and hence, with RRKM theory and pressure fall-off data, a time scale for their decomposition. Applying the thermal data to the photolysis leads to the conclusion that excitation and decomposition are produced by the laser spike (high intensity, 70 ns FWHM) and also at a slower rate by the larger, less intense tail (1.6 μs). Added buffer gases quench the latter, leaving the former which, from measurements of R, is shown to correspond to excitations of 115 ± 15 kcal/mol and lifetimes of ~30 ps. No bond breaking is seen despite the high energies, in accord with theoretical expectations. The results require an enhanced rate of photon absorption by the highly excited molecules, which are about hundredfold greater than that observed for 300 K molecules. Data are also reported for C2H2F2 and the secondary multiphoton photolysis of the ethylenes produced. Effects of beam geometry and wavelength are explored. 相似文献