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991.
Helmut Mäurer 《Geometriae Dedicata》1973,2(2):261-268
Ohne Zusammenfassung 相似文献
992.
The reaction between indole and N-(2-haloacyl)pyridinium salts has been studied. With dioxan as solvent 1-(2-haloacyl)indole (2) was generally the product at low temperatures and 3-(2-haloacyl)indole (1) at high temperatures, as illustrated by the following α-bromopropionylation: Product ratio (1c/2a), 20° (0·01), 40° (0·8) and 60° (8·5). The fact that the a-bromobutyrylation at 60° gave 3-{N-(2-bromobutyryl)-1,4-dihydro-4-pyridyl}indole (6) as the main product, and 3-(2-bromobutyryl)indole (1d) only as a minor product, shows that the 3-acylation is affected by steric hindrance.At high reaction temperature (> 60°) the yield of1 decreased, owing to the formation of 3-indacylpyridinium salts (4). 相似文献
993.
Optical four-wave mixing due to the resonant spin nonlinearity in n-InSb was observed in magnetic fields up to 1.4 T. The mixing of two CO-laser frequencies ω1 and ω2 = ω1 - Δω yields radiation with frequencies ω1 + 2Δω, ω1 + Δω, ω1 - 2Δω, and ω1 - 3Δω. We found the resonant contribution to the third order nonlinear susceptibility arising from the spin-flip interaction to increase by more than two orders of magnitude when ω1 is varied from 1760 cm-1 to 1896 cm-1. With the lasers working simultaneously Q-switched we observed radiation at ω1 + Δω and ω1 - 2Δω due to the mixing caused by the nonparabolicity of the conduction electrons even without an external magnetic field. At the resonant magnetic field the intensity of the mixed radiation is increased by more than one order of magnitude and is also observed when the laser pulses do not hit the sample simultaneously as long as the time difference between the two pulses does not exceed 450 ns. This points to a spin dephasing time T2 of about 100 ns. 相似文献
994.
H. Weber K. Braun E. Unsin H. Widey G. Zäpfel Peter F. Heil W. Krämer K. -W. Schulte Th. Fischer G. Fandel 《Mathematical Methods of Operations Research》1980,24(6):B199-B206
Ohne Zusammenfassung 相似文献
995.
996.
Tables are given to enable effective algorithms to be formed for computer calculation of the overlap and Coulomb integrals with Slater-type orbitals in complexes with rare-earth or transition-metal central ions. 相似文献
997.
998.
A Rank Encoder: Adaptive Analog to Digital Conversion Exploiting Time Domain Spike Signal Processing
Philipp Häfliger Elin Jørgensen Aasebø 《Analog Integrated Circuits and Signal Processing》2004,40(1):39-51
An electronic circuit is presented that encodes an array of analog input signals into a digital number. The digital output is a rank order code that reflects the relative strength of the inputs, but is independent of the absolute input intensities. In that sense, the circuit performs an adaptive analog to digital conversion, adapting to the average intensity of the inputs (i.e. effectively normalizing) and adapting the quantization levels to the spread of the inputs. Thus, it can convey essential information with a minimal amount of output bits over a huge range of input signals.As a first processing step the analog inputs are projected into the time domain, i.e. into voltage spikes. The latency of those spikes encodes the strength of the input. This conversion enables the circuit to conduct further analog processing steps by asynchronous logic. 相似文献
999.
The use of preamplified electrodes in electrocardiography (ECG) or electroencephalography (EEG) has a numbe of benefits, most importantly, the noise reduction through preamplification and the interference reduction through buffering (Fernandez and Pallas-Areny, 1997). Normally, preamplified electrodes are not used because the mismatch in amplification due to component tolerances leads to a reduced common mode rejection ration (CMRR) (Pallas-Areny and Webster, 1991). In this paper, we introduce a new technique to restore the CMRR. We do this by adapting the gain of the differential amplifier (DA) following the preamplified electrodes. The technique is based on measuring the transfer function of a chosen common mode signal. The gain of the DA is adjusted by a closed loop controller to maximize the CMRR. With this technique, there is no adverse effect on the ECG or EEG. In this way, the control loop can be operated continuously if needed. 相似文献
1000.