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71.
A. Gold 《Zeitschrift für Physik B Condensed Matter》1986,63(1):1-8
A theory for static and dynamic transport of a two-dimensional electron gas in GaAs-AlGaAs heterostructures at temperature zero is presented. Charged impurities, separated from the electron gas by a spacer layer, are considered as the dominant scattering mechanism. Finite extension of the wave function of the two-dimensional electron gas is taken into account. Multiple scattering effects are included and are shown to lead to a metal insulator transition at low electron densities. Due to plasmon dynamics the scattering is strongly frequency dependent, and this dissipative process determines the width of the cyclotron resonance. The corresponding reactive effect determines the shift of the cyclotron resonance. It is shown that a correlation between line width maximum and zero frequency shift of the cyclotron mode exists, in agreement with experimental results. 相似文献
72.
A. L. Vikharev A. M. Gorbachev O. A. Ivanov V. A. Isaev S. V. Kuzikov B. Z. Movshevich J. L. Hirshfield S. H. Gold 《Radiophysics and Quantum Electronics》2008,51(7):539-555
We present the results of studies of the active compressor of 3-cm wavelength microwave pulses, which uses a high-Q storage
Bragg resonator excited at the H01 mode and new types of plasma switches. Phase variation during a compressed pulse and phase correlation of the input and compressed
microwave pulses are studied both experimentally and theoretically. Using a single-channel compressor excited at the megawatt
power level by the magnicon radiation with frequency 11.4 GHz, a power amplification factor equal to 9 was reached for an
output-pulse duration of 40–50 ns and a peak power of up to 25 MW.
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 7, pp. 597–616, July 2008. 相似文献
73.
We analyze experimental data in order to evaluate Landau Fermi-liquid parameters. By using row data of recent Shubnikov-de
Haas measurements, we derive, as a function of the electron density n
s, results for the compressibility mass of the charged two-dimensional electron gas. The compressibility mass is nearly equal
to the transport mass even in the density region where the transport mass has the tendency to diverge. We conclude that Landau
Fermi-liquid parameter F
0s (n
s) is nearly independent of electron density and close to zero. This result is derived for silicon (100) and silicon (111)
surfaces. We also obtain the dependence of F
1s (n
s), determining the transport mass, and of F
0a (n
s), determining the spin susceptibility.
The text was submitted by the authors in English. 相似文献
74.
Topographical and surface chemical characterization of nanosecond pulsed-laser micromachining of titanium at 532-nm wavelength 总被引:1,自引:0,他引:1
H. Reimers J. Gold B. Kasemo D. Chakarov 《Applied Physics A: Materials Science & Processing》2003,77(3-4):491-498
Electropolished titanium was micromachined by single, 5-ns pulses from a frequency-doubled (532 nm) Nd:YAG laser. The focal spot size was varied from 10 to 100 m and the applied fluences varied from the melting threshold (1 J/cm2) to more than 100 J/cm2. The resulting craters were imaged by optical microscopy, topographically characterized by interferometry and chemically characterized on the surface by small-spot depth-profiling Auger electron spectroscopy and small-spot X-ray photoelectron spectroscopy. The prevailing ablation regime for the studied fluences and focal spot sizes was found to be melt ejection. The surface chemical characterization showed growing oxide thickness in the heat-affected zone (around the center spot) for increasing fluence but no difference inside the crater. Titanium nitride formation was found inside the crater. PACS 81.65; 87.80Mj 相似文献
75.
Nesset MJ Cai S Shokhireva TK Shokhirev NV Jacobson SE Jayaraj K Gold A Walker FA 《Inorganic chemistry》2000,39(3):532-540
The perchloratoiron(III) complexes of a series of 2,6-disubstituted tetraphenylporphyrin ligands, where the 2,6-phenyl substituents were -H, -F, -Cl, -Br, or -OMe, as well as two 2,4,6-phenyl-substituted complexes, where the substituents were -Me and -OMe, have been investigated as a function of temperature by 1H NMR spectroscopy. Curvature in the 1/T dependence was evident in most cases. Forced linear extrapolation of the temperature dependence observed over the range of the study yielded Curie plots that include negative slopes with very large positive 1/T intercepts (Cl approximately Br > Me > H) to negative slope with near zero intercept (tri-OMe) to positive slope with very large negative intercept (F, di-OMe). The NMR results were combined with EPR spectroscopic data and curve-fitting procedures based on an expanded Curie law to arrive at a consistent overview of the variety of temperature-dependence behaviors observed. This overview relies upon the premise that, in addition to the ground state observed by EPR spectroscopy, one (or more) thermally accessible excited state(s) are populated to varying degrees over the temperature range of the NMR measurements. If only one excited state is considered, the analysis is consistent with the ground state being a largely intermediate-spin state (S = 3/2) for the majority of the complexes but a largely high-spin state (S = 5/2) for ((2,6-F2)4TPP)FeOClO3 and ((2,6-(OMe)2)4TPP)FeOClO3. 相似文献
76.
Celliers PM Collins GW Da Silva LB Gold DM Cauble R Wallace RJ Foord ME Hammel BA 《Physical review letters》2000,84(24):5564-5567
Simultaneous measurements of shock velocity and optical reflectance at 1064, 808, and 404 nm of a high pressure shock front propagating through liquid deuterium show a continuous increase in reflectance from below 10% and saturating at approximately (40-60)% in the range of shock velocities from 12 to 20 &mgr;m/ns (pressure range 17-50 GPa). The high optical reflectance is evidence that the shocked deuterium reaches a conducting state characteristic of a metallic fluid. Above 20 &mgr;m/ns shock velocity (50 GPa pressure) reflectance is constant indicating that the transformation is substantially complete. 相似文献
77.
Richard A. Hancock Ray Walder Helmut Weigel Victor Gold Cristian M. Sghibartz 《Journal of mass spectrometry : JMS》1983,18(9):402-405
Isobutane chemical ionization mass spectrometry of crown ether acetals (M), derived from ethanal, give [MH]+ ions from which species corresponding to 44 u are successively eliminated. Mechanisms are presented in which these units correspond to (i) ethanal and (ii) oxirane. An accompanying process is the elimination of ethyne. Similar reactions occur in the chemical ionization mass spectrometry of benzo crown ether acetals. 相似文献
78.
Bela Gold 《European Journal of Operational Research》1983,14(1):13-17
This article primarily focuses on: the place of robotics within current and prospective advances in manufacturing technology, the impacts of increasing robot utilization on the productivity and costs of users, and resulting effects on the international competitiveness of domestic industries. 相似文献
79.
80.
Analysis of the molecular fluorescence spectra of several polycyclic aromatic hydrocarbons (PAH) by the technique of spectral decomposition is discussed. Peak characterization parameters obtained by this technique are utilized to obtain quantitative measurement of a mixture containing benzidiae and dibenzochrysene in solution. Application of the technique to a large number of reference compounds is discussed as an aid to routine identification of suspected carcinogens and other compounds containing fluorophores. 相似文献