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991.
[reaction: see text] High stereoselectivities were found in a wide range of superacid-catalyzed Pictet-Spengler cyclization reactions. Particularly in the cases of 2-alkyl-N-benzylidene-2-phenethylamines, an enhanced stereoselectivity was observed under the superacid conditions as compared with the corresponding weak acid (TFA)-catalyzed (monocationic) cyclization reaction of the N-benzylidene-2-(3',4'-dimethoxy)phenethylamines that bear electron-donating groups on the cyclizing aromatic ring. The computational study also supported the energetic favorability of the cyclization of the N,N-diprotonated imine and revealed a significantly early transition-state structure. 相似文献
992.
[reaction: see text] Arylative and alkenylative ring-opening reactions of a [2.2.1]- or [3.2.1]oxabicyclic alkene with a Grignard reagent take place in the presence of a catalytic amount of iron(III) chloride and a stoichiometric amount of TMEDA to produce a highly substituted 3-cyclohexen-1-ol or 3-cyclohepten-1-ol in good yield with high regio- and stereoselectivity. 相似文献
993.
Matsushima S Sasaki F Sarumaru S Ohta D Era S Sogami M Inaba T Kinosada Y 《Magnetic resonance imaging》2003,21(9):1045-1047
In the breast carcinamas, sentinel lymph node biopsy (SLNB) attracts attention as technique to be settled by axillary lymph node metastasis, but existence of a false negative case is a problem. Equivalent cross relaxation rate image (ECRI) is the measurement method that we can evaluate a change of organization structure quantitatively by magnetic resonance imaging. We executed axillary ECRI as a purpose with decreasing a false negative case of SLNB. ECRI related to a macroscopic image, and it was possible to evaluate yes or no of axillary lymph node metastasis. ECRI is the useful method to evaluate adaptability of SLNB. 相似文献
994.
K. Yamasaki S. Juodkazis T. Lippert M. Watanabe S. Matsuo H. Misawa 《Applied Physics A: Materials Science & Processing》2003,76(3):325-329
We report the reversible micro-structuring of a synthetic rubber polymer (cis1,4-polybutadiene (PB)) by femtosecond laser
illumination. Visco-elastic relaxation of the optically damaged region was observed. The recovery time, typically 102–104 ms, can be varied by changing the irradiation pulse energy. Multi-shot-induced damage recovers on the much longer scale of
101–102 s. It was found that the doping of PB by 4 wt. % of pentazadiene ([4-NO2]–phenyl–N=N–N(C3H7)–N=N–phenyl–[4-NO2]) reduces the threshold of light-induced photo-modification by 20%. This is explained by photo-induced (homolytic) cleavage
of the pentazadiene bonds and formation of gaseous N2, which facilitates material failure at the irradiated spot.
The recovery of optical transmission can be applied to optical memory, optical and micro-mechanical applications. The underlying
mechanism of the phenomenon is discussed in terms of anelastic α- and β-relaxation (polymer backbone and chains/coils relaxation,
respectively).
Received: 11 October 2001 / Accepted: 9 July 2002 / Published online: 25 October 2002
RID="*"
ID="*"Corresponding author. Fax: +81-88/656-7598, E-mail: misawa@eco.tokushima-u.ac.jp 相似文献
995.
K. Yamasaki S. Juodkazis S. Matsuo H. Misawa 《Applied Physics A: Materials Science & Processing》2003,77(3-4):371-373
We report on the femtosecond laser fabrication of micro-channels of sub-micrometer cross section recorded in polymethylmethacrylate (PMMA) films in a single processing step. Both axial lengths of an elliptical cross section smaller than 0.4 m were achieved for a fabrication irradiance close to the dielectric breakdown of PMMA. Femtosecond pulsed irradiation was scanned along the three-dimensional (3D) patterns inside the film. Channels have a self-formed densified cladding and can be 3D stacked into any pre-designed pattern and can extend over a mm length. These features are prospective for micro-total analysis system (-TAS) chip fabrication, micro- or nano-fluidic studies, and photonic applications such as photonic crystals . PACS 42.70.-a; 42.70.Jk; 81.16.-c; 81.40.-z; 82.35.Lr 相似文献
996.
997.
Assuming that a macrovariable follows a Markovian process, the extensive property of its probability distribution is proved to propagate. This is a generalization of the Gaussian properties of the equilibrium distribution to nonequilibrium nonstationary processes. It is basically a WKB-like asymptotic evaluation in the inverse of the size of the macrosystem. Evolution of the variable along the most probable path and fluctuation properties around the path are considered from a general point of view with an emphasis on the relation of nonlinearity of evolution and the associated fluctuation. Anomalous behavior of the fluctuation is discussed in connection with unstable, critical, or marginal states. A general treatment is given for the asymptotic properties of relaxation eigenmodes. 相似文献
998.
Manabu Node Takeo Kawabata Masaru Ueda Mayumi Fujimoto Kaoru Fuji Eiichi Fujita 《Tetrahedron letters》1982,23(39):4047-4050
The nitrogroup in primary α-nitroketones is converted into hydrogen with aluminum chloride and ethanethiol. 相似文献
999.
1000.