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91.
[reaction: see text] The successful application of CH2Cl2-Mg-TiCl4-system mediated methylenation of various esters such as tert-butyl ester and 2,5-cyclohexadiene-1-carboxylate highlights the extraordinary reactivity, selectivity, and the nonbasic nature of this new methylene-carbenoid, which serves as a practical reagent applicable to large-scale synthesis. 相似文献
92.
Optical seeding of plasma waves and the injection of electrons are key issues in self-modulated laser-wakefield accelerators. By implementing a copropagating laser prepulse with proper timing, we are able to control the growth of Raman forward scattering and the production of accelerated electrons. The dependence of the Raman intensity on prepulse timing indicates that the seeding of Raman forward scattering is dominated by the ionization-induced wakefield, and the dependence of the divergence and number of accelerated electrons further reveals that the stimulated Raman backward scattering of the prepulse plays the essential role of injecting hot electrons into the fast plasma wave driven by the main pulse. 相似文献
93.
H.-H.?Chu S.-Y.?Huang L.-S.?Yang T.-Y.?Chien Y.-F.?Xiao J.-Y.?Lin C.-H.?Lee S.-Y.?Chen J.?WangEmail author 《Applied physics. B, Lasers and optics》2004,79(2):193-201
We discuss the design, construction, and output characteristics of a versatile 10-TW Ti:sapphire laser system of high stability and spatiotemporal quality. By pumping the three amplifier stages independently and running at saturation, an energy stability of 1.3% is obtained. Controls over self-phase modulation, high-order dispersion, spatial aberration, and amplified spontaneous emission are done by robust passive methods. A time–bandwidth product of 1.2 times the Fourier-transform limit with a temporal contrast larger than 5×108 in the -10-ns scale, 2×106 in the -100-ps scale, and 104 in the -1-ps scale are achieved. The beam can be focused down to 1.2 times the diffraction limit with 80% of the energy enclosed in the Gaussian focal spot. Beam-pointing stability is <13 rad. Such high stability and spatiotemporal quality have made possible precision control over extremely nonlinear laser–plasma experiments, and the capability of computerized independent control of prepulse, pump pulse, probe pulse, and on-line diagnoses have made this system highly versatile and reliable. PACS 42.60.By; 42.65.Re; 42.60.Jf 相似文献
94.
Evidence for a current-induced spin-transfer torque effect has been investigated in a series of point contacts to single ferromagnetic layers. At specific current densities, abrupt resistance changes, similar to those attributed to current-induced spin-wave excitations in multilayers, have been observed for one current polarity. The critical current for these resistance changes depends linearly on the external field applied perpendicular to the layer. The observed effect is interpreted as a current-driven heterogeneous instability in an otherwise uniform ferromagnetic layer. 相似文献
95.
We introduce a Gaussian quadrature, based on the polynomials that are orthogonal with respect to the weight function ln(2)x on the interval [0, 1], which is suitable for the evaluation of radial integrals. The quadrature is exact if the non-Jacobian part of the integrand is a linear combination of a geometric sequence of exponential functions. We find that the new scheme is a useful alternative to existing approaches, particularly for integrands that exhibit multiexponential behavior. 相似文献
96.
Singh J Kronenthal DR Schwinden M Godfrey JD Fox R Vawter EJ Zhang B Kissick TP Patel B Mneimne O Humora M Papaioannou CG Szymanski W Wong MK Chen CK Heikes JE DiMarco JD Qiu J Deshpande RP Gougoutas JZ Mueller RH 《Organic letters》2003,5(17):3155-3158
[reaction: see text] An efficient asymmetric synthesis of the vasopeptidase inhibitor BMS-189921 was accomplished. Two short enantioselective syntheses of the common key intermediate (S)-alpha-aminoazepinone 6b were developed. Olefin 3 was converted to 6b via asymmetric hydrogenation. Alternatively, enyne 12 was converted to racemic alpha-aminoazepinone 15b, which was transformed to 6b by a practical dynamic resolution. 相似文献
97.
Vapor quenching in the phase-separating Ag-Ni system creates alloys that appear homogeneously amorphous under conventional probes. However, an atomic-level structural analysis based on extended x-ray absorption fine structures in combination with reverse Monte Carlo and molecular dynamics simulations demonstrates that these new phases are characterized by nonuniform, spinodal-like structures on an extremely fine scale. This heterogeneous nature of the structure is directly responsible for the unexpectedly low heat (and temperature) of crystallization observed in calorimetric measurements. 相似文献
98.
Wen-Hua Zhang Sheau Wei Chien T.S. Andy Hor 《Coordination chemistry reviews》2011,255(17-18):1991-2024
This review summarises some recent developments of the metal complexes of hetero-functional hybrid ligands of C-, N-, O-, P- and S-donors. It highlights the ligand designs, synthetic pathways, structural motifs and catalytic prowess of these complexes. 相似文献
99.
100.