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51.
A titanium benzylidene complex bearing a boronate group converted resin-bound esters into enol ethers. Suzuki cross-coupling with aryl iodides followed by cleavage with acid completed the solid-phase synthesis of 2,5-disubstituted N-Boc-indoles. Also reported is the use of tert-butyllithium and 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane to convert an aryl bromide into an arylboronate in the presence of a dithiane, with simultaneous reduction of an aryl azide to an amine. 相似文献
52.
Main W.T. Garate E. Weatherall J.C. Cherry R. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1992,20(3):281-287
A high-power frequency-locked dielectric Cerenkov maser oscillator is presented. The device consists of an annular electron beam traveling down a dielectric-lined waveguide (wall radius 1.74 cm, liner thickness 2-3 mm, linear ∈=10). A 100 kW input signal is injected into the drift tube between the diode and liner, through a rectangular TE10 to cylindrical TM01 mode converter. When operated with a beam current of 500 A and a total output power of 13 MW, the device displays no RF quenching through the full width of the 100 ns beam pulse. Two higher current cases with power as high as 280 MW but severe RF quenching are presented. The results are compared with linear theory, and quenching mechanisms are discussed 相似文献
53.
54.
R.P. Taylor P.C. Main L. Eaves S.P. Beaumont S. Thoms C.D.W. Wilkinson 《Superlattices and Microstructures》1989,5(4)
We have studied electron heating in a submicron-size GaAs wire from 4.2 K to 50 K. We find that the energy relaxation rate for the electrons is of the form τE−1 = α + βTen where α, β are constants and Te is the electron temperature. We associate the temperature-independent term with a quasi-elastic surface scattering process in which an electron losses 1% of its energy at each collision. The temperature dependent term may be due to electron-phonon scattering. It is possible to fit the data to 2 < n < 3. 相似文献
55.
56.
Current-voltage characteristics have been measured for an AEI ES200B X-ray photoelectron spectrometer with both conducting and insulating samples. With the conducting sample, the flux of secondary electrons falling on the specimen and probe amounts to approximately 20 percent of the photoelectron flux, over a wide range of irradiation conditions. The results for the insulating sample, taken in conjunction with subsidiary data from charging shifts, indicate that the secondary flux incident on the specimen alone exceeds 99 percent of the photoelectron flux. 相似文献
57.
We report the existence of exceptional points for the hydrogen atom in crossed magnetic and electric fields in numerical calculations. The resonances of the system are investigated and it is shown how exceptional points can be found by exploiting characteristic properties of the degeneracies, which are branch point singularities. A possibility for the observation of exceptional points in an experiment with atoms is proposed. 相似文献
58.
K. Weibert J. Main G. Wunner 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,12(3):381-401
Harmonic inversion has already been proven to be a powerful tool for the analysis of quantum spectra and the periodic orbit
orbit quantization of chaotic systems. The harmonic inversion technique circumvents the convergence problems of the periodic
orbit sum and the uncertainty principle of the usual Fourier analysis, thus yielding results of high resolution and high precision.
Based on the close analogy between periodic orbit trace formulae for regular and chaotic systems the technique is generalized
in this paper for the semiclassical quantization of integrable systems. Thus, harmonic inversion is shown to be a universal
tool which can be applied to a wide range of physical systems. The method is further generalized in two directions: firstly,
the periodic orbit quantization will be extended to include higher order corrections to the periodic orbit sum. Secondly, the use of cross-correlated periodic orbit sums allows us to significantly
reduce the required number of orbits for semiclassical quantization, i.e., to improve the efficiency of the semiclassical method. As a representative of regular systems, we choose the circle billiard,
whose periodic orbits and quantum eigenvalues can easily be obtained.
Received 24 February 2000 and Received in final form 22 May 2000 相似文献
59.
为了明确储层沥青热演化程度与激光拉曼光谱的关系,利用拉曼光谱无损分析和流体包裹体方法,对黔西南白层地区储层沥青拉曼光谱进行了定量化描述,首先获取了储层沥青其伴生流体包裹体均一温度,然后获得了储层沥青拉曼光谱图,并对比标准沥青成熟度分布图,确定了储层沥青热演化程度及其特征.结果表明:黔西南白层地区存在晚三叠世(230 M... 相似文献
60.
Main W. Carmel Y. Ogura K. Weaver J. Nusinovich G.S. Kobayashi S. Tate J.P. Rodgers J. Bromborsky A. Watanabe S. Amin M.R. Minami K. Destler W.W. Granatstein V.L. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1994,22(5):566-577
Specific slow wave structures are needed in order to produce coherent Cherenkov radiation in overmoded relativistic generators. The electromagnetic characteristics of such slow wave, resonant, finite length structures commonly used in relativistic backward wave oscillators have been studied both experimentally and theoretically. In experiments, perturbation techniques were used to study both the fundamental and higher order symmetric transverse magnetic (TM) modes. Finite length effects lead to end reflections and quantization of the wave number. The effects of end reflections in open slow wave structures were found from the spectral broadening of the discrete resonances of the different axial modes. The measured axial and radial field distributions are in excellent agreement with the results of a 2-D code developed for the calculation of the fields in these structures 相似文献