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排序方式: 共有643条查询结果,搜索用时 78 毫秒
41.
Dr. Yasunori Toda Takayuki Yoshida Kaoru Arisue Prof. Dr. Kazuaki Fukushima Dr. Hiroyoshi Esaki Ayaka Kikuchi Prof. Dr. Hiroyuki Suga 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(41):10578-10582
Chiral Lewis acid-catalyzed asymmetric alcohol addition reactions to cyclic carbonyl ylides generated from N-(α-diazocarbonyl)-2-oxazolidinones featuring a dual catalytic system are reported. Construction of a chiral quaternary heteroatom-substituted carbon center was accomplished in which the unique heterobicycles were obtained in good yields with high stereoselection. The alcohol adducts were successfully converted to optically active oxazolidine-2,4-diones by hydrolysis. Mechanistic studies by DFT calculations revealed that alcohols could be activated by Lewis acids, enabling enantioselective protonation of the carbonyl ylides. 相似文献
42.
Ultrasonic butt welding of aluminum,aluminum alloy and stainless steel plate specimens 总被引:3,自引:0,他引:3
Tsujino J Hidai K Hasegawa A Kanai R Matsuura H Matsushima K Ueoka T 《Ultrasonics》2002,40(1-8):371-374
Welding characteristics of aluminum, aluminum alloy and stainless steel plate specimens of 6.0 mm thickness by a 15 kHz ultrasonic butt welding system were studied. There are no detailed welding condition data of these specimens although the joining of these materials are required due to anticorrosive and high strength characteristics for not only large specimens but small electronic parts especially. These specimens of 6.0 mm thickness were welded end to end using a 15 kHz ultrasonic butt welding equipment with a vibration source using eight bolt-clamped Langevin type PZT transducers and a 50 kW static induction thyristor power amplifier. The stainless steel plate specimens electrolytically polished were joined with welding strength almost equal to the material strength under rather large vibration amplitude of 25 microm (peak-to-zero value), static pressure 70 MPa and welding time of 1.0-3.0 s. The hardness of stainless steel specimen adjacent to a welding surface increased about 20% by ultrasonic vibration. 相似文献
43.
Kaoru Ikeda 《Communications in Mathematical Physics》1996,180(3):757-777
We consider constructing the higher order Hamiltonian structures on the dual of the Lie algebra from the first Hamiltonian structure of the coadjoint orbit method. For this purpose we show that the structure of the Lie algebrag is inherited to the algebra of vector fields ong
* through the solution of the Modified Classical Yang-Baxter equation (Classicalr matrix). We study the algebra that generates the compatible Poisson brackets.This work was supported by Grant Aid for Scientific Research, the Ministry of Education. 相似文献
44.
Kaoru Hagiwara Dieter Haidt Seiji Matsumoto 《The European Physical Journal C - Particles and Fields》1998,2(1):95-122
We update our previous work on an analysis of the electroweak data by including new and partly preliminary data available
up to the 1996 summer conferences. The new results on the partial decay widths into and hadrons now offer a consistent interpretation of all data in the minimal standard model. The value extracted for the strong
interaction coupling constant agrees well with determinations in other areas. New constraints on the universal parameters , and are obtained from the updated measurements. No signal of new physics is found in the , , analysis once the SM contributions with GeV and those of not a too heavy Higgs boson are accounted for. The naive QCD-like technicolor model is now ruled out at the
99% CL even for the minimal model with . In the absence of a significant new physics effect in the electroweak observables, constraints on masses of the top quark,
, and Higgs boson, , are derived as a function of and the QED effective coupling . The preferred range of depends rather strongly on the actual value of : for , while for at 95% CL. Prospects due to forthcoming improved measurements of asymmetries, the mass of the weak boson
, and are discussed. Anticipating uncertainties of 0.00020 for , 20 MeV for , and 2 GeV for , the new physics contributions to the , , parameters will be constrained more severely, and, within the SM, the logarithm of the Higgs mass can be constrained to about
. The better constraints on , , and on within the minimal SM should be accompanied with matching precision in .
Received: 18 June 1997 相似文献
45.
A new surface-renewal technique at the solid electrode has been developed, based on continuous polishing. Well-defined and reproducible current-voltage curves similar to those obtained in polarography are given by the "polished precipitate electrode" (PPE). The method can be used for the continuous determination of electroactive substances and for the study of electrode reaction mechanisms at the solid-liquid interface. 相似文献
46.
47.
We report inelastic neutron scattering measurements on polystyrene thin films in a glassy state in the meV region. We found in elastic scattering that the mean square displacement decreased with film thickness, and hence the corresponding force constant f increased. In inelastic and quasielastic scattering, we observed the so-called boson peak at around 1.5 meV and the picosecond fast process for the first time in thin films, both of which decreased in intensity with film thickness. These results were discussed in terms of the potential hardening due to the confinement of polymer chains and/or the interfacial dead layer. 相似文献
48.
Katoh K Okabayashi T Tanimoto M Sumiyoshi Y Endo Y 《The Journal of chemical physics》2004,120(17):7927-7932
The rotational spectra of the CrF and CrCl radicals in the X 6Sigma+ state were observed by employing a Fourier transform microwave spectrometer. The CrF and CrCl radicals were generated by the reaction of laser-ablated Cr with F2 and Cl2, respectively, diluted in Ar. A chromium rod made of chromium powder pasted with epoxy resin was ablated by a Nd:YAG laser. Rotational transitions were measured in the region between 8 and 26 GHz. Several hyperfine constants due to the halogen nuclei were determined by a least-squares analysis. The electronic properties of CrF and CrCl were derived from their hyperfine constants and were compared with those of other 3d transition metal monohalides: TiF, MnF, FeF, CoF, NiF, and FeCl. 相似文献
49.
50.
Highly enantioselective catalytic carbon dioxide incorporation reaction: nickel-catalyzed asymmetric carboxylative cyclization of bis-1,3-dienes 总被引:4,自引:0,他引:4
Takimoto M Nakamura Y Kimura K Mori M 《Journal of the American Chemical Society》2004,126(19):5956-5957
A method for nickel-catalyzed asymmetric carbon dioxide (CO2) incorporation via carbon-carbon bond formation was developed. In the presence of a catalytic amount of Ni(acac)2 and MeO-MOP, various bis-1,3-dienes reacted with CO2 (1 atm) and a diorganozinc reagent (Me2Zn or Ph2Zn) to afford cyclic carboxylic acids in good yields (71-100%) and with high enantioselectivities (90-96% ee). 相似文献