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排序方式: 共有76条查询结果,搜索用时 15 毫秒
1.
Rolf Dreher 《Solid State Communications》1973,12(6):519-522
The optical reflection properties of distorted cholesteric liquid crystals are theoretically investigated. It is shown that higher-order reflection bands occur with distorted helical structures even for light propagation parallel to the twist axis. For aperiodic structures, the positions of the main reflection bands differ from that of periodic ones. Ferroelectric helical structures could be detected by reflection spectroscopy when the liquid crystal is deformed by an electric field. 相似文献
2.
Shultz CS Dreher SD Ikemoto N Williams JM Grabowski EJ Krska SW Sun Y Dormer PG Dimichele L 《Organic letters》2005,7(16):3405-3408
A novel and highly enantioselective Ru-catalyzed hydrogenation of N-sulfonylated-alpha-dehydroamino acids has been discovered and demonstrated in the synthesis of an anthrax lethal factor inhibitor (LFI). Herein, this methodology is used to prepare N-sulfonylated amino acids in up to 98% ee. This unprecedented hydrogenation uses a chiral Ru catalyst rather than Rh as typical for acylated dehydroamino acids and esters, and this work reports the first asymmetric hydrogenation of a tetrasubstituted dehydroamino acid derivative using a Ru catalyst. [reaction: see text] 相似文献
3.
Although much current research focuses on developing new boron reagents and identifying robust catalytic systems for the cross-coupling of these reagents, the fundamental preparations of the nucleophilic partners (i.e., boronic acids and derivatives) has been studied to a lesser extent. Most current methods to access boronic acids are indirect and require harsh conditions or expensive reagents. A simple and efficient palladium-catalyzed, direct synthesis of arylboronic acids from the corresponding aryl chlorides using an underutilized reagent, tetrahydroxydiboron B(2)(OH)(4), is reported. To ensure preservation of the carbon-boron bond, the boronic acids were efficiently converted to the trifluoroborate derivatives in good to excellent yields without the use of a workup or isolation. Further, the intermediate boronic acids can be easily converted to a wide range of useful boronates. Finally, a two-step, one-pot method was developed to couple two aryl chlorides efficiently in a Suzuki-Miyaura-type reaction. 相似文献
4.
Czeschka FD Dreher L Brandt MS Weiler M Althammer M Imort IM Reiss G Thomas A Schoch W Limmer W Huebl H Gross R Goennenwein ST 《Physical review letters》2011,107(4):046601
We systematically measured the dc voltage V(ISH) induced by spin pumping together with the inverse spin Hall effect in ferromagnet-platinum bilayer films. In all our samples, comprising ferromagnetic 3d transition metals, Heusler compounds, ferrite spinel oxides, and magnetic semiconductors, V(ISH) invariably has the same polarity, and scales with the magnetization precession cone angle. These findings, together with the spin mixing conductance derived from the experimental data, quantitatively corroborate the present theoretical understanding of spin pumping in combination with the inverse spin Hall effect. 相似文献
5.
We demonstrate the electrical detection of pulsed X-band electron nuclear double resonance (ENDOR) in phosphorus-doped silicon at 5 K. A pulse sequence analogous to Davies ENDOR in conventional electron spin resonance is used to measure the nuclear spin transition frequencies of the (31)P nuclear spins, where the (31)P electron spins are detected electrically via spin-dependent transitions through Si/SiO(2) interface states, thus not relying on a polarization of the electron spin system. In addition, the electrical detection of coherent nuclear spin oscillations is shown, demonstrating the feasibility to electrically read out the spin states of possible nuclear spin qubits. 相似文献
6.
C. Chevennement-Roux T. Dreher P. Alliot E. Aubry J.-P. Lainé L. Jézéquel 《Experimental Mechanics》2007,47(2):201-210
The optimization of wiper systems under various conditions and the creation of a product which is as robust as possible are
the main objectives for an equipment supplier. However, in certain conditions, instabilities can appear and generate wiping
defects due to the rubber-glass contact. To improve wiping quality and to reduce the number of test stages for design, this
study proposes a wiper system modeling method. The wiper system is represented by a rigid blade holder on which a rubber blade
is fitted. This rigid blade system is used on a flat test bench at constant wiping velocity. The model is based on modal synthesis
methods and will be validated through comparison with experimental tests under various conditions. The right correlation obtained
allows the same modelling method to be applied to the new generation of flexible wiper blades which take account of the degree
of freedom of the wiper blade flexions. So, a new computation tool will be developed and validated through experimentation
on a specific test bench. 相似文献
7.
The evaluation of elastic and inelastic electron scattering cross sections is discussed in terms of the Fourier-Bessel expansion of the nuclear ground state and transition charge density, respectively. The method allows one to deduce the charge distributions and the moments as well as the corresponding errors, which originate on the one hand from the uncertainties in the measured data and on the other hand from the lack of knowledge about the large-q behaviour of the form factors; these two contributions are determined separately. The method is described and proved with an evaluation of pseudodata and then applied to 208Pb cross sections. For this nucleus, detailed results concerning the possible structure of the charge density are presented. 相似文献
8.
9.
R.W. Wodrich E.G. Auld J.M. Bailey G.A. Beer B. Dreher U. Gastaldi H. Kalinowsky E. Klempt R. Landua K. Merle K. Neubeckef Chr. Sabev R.D. Wendling B.L. White 《Nuclear Physics A》1982,384(3):386-400
X-ray transitions to the 4F, 3D, and 2P atomic levels of p?He have been observed with antiprotons stopped in He gas at 4 and 1.1 atm NT. The population by radiative transitions of the 3D level in gas YM(4atm) = (28±14)% and YM(1.1 atm) = (43±22)% exceeds by more than one order of magnitude that measured in liquid He. The annihilation width of the 3D level Γa3D = 2.8±1.0 × 10?3eV is determined from the ratio between the numbers of X-rays feeding and depopulating the 3D level. The strong-interaction shift of the 2P level ε(2P) = ?14±6 eV is obtained by inputting the experimental X-ray yields into a cascade calculation, the results of which are in good agreement with well-established data from muonic, pionic, and kaonic helium. 相似文献
10.
The radial transition charge density and the reduced transition probability of the 3? level in 208Pb are determined model independently from inelastic e? scattering cross sections. The results are compared with (α, α') experiments and theoretical calculations. 相似文献