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751.
In this paper, we have examined the filamentation instability of laser radiation in a GaAs sample in the negative differential
resistivity region. A dc electric field is applied to assist the laser beam transferring electrons in the conduction band
from the lower valley to upper satellite valleys, i.e. in increasing the effective mass of electrons. The instability causes
the space charge perturbations in the microwave range of frequencies. The nonlinearity arises through the energy dependence
of the effective mass and the ponderomotive force on the electrons. The instability has finite frequency and possesses large
growth rate which is greatly influenced by the dc electric field. 相似文献
752.
M. S. Sodha Prayag Chandra V. K. Tripathi 《Applied Physics A: Materials Science & Processing》1976,11(3):299-301
Using an appropriate expression for the field-dependent dielectric constant of a collisionless plasma, we have studied the
field distribution of the TM01 mode in a cylindrical waveguide. The wave equation has been solved by a Runge Kutta technique. It is seen that on account
of redistribution of carriers from the high-field regions to low-field regions a beam of frequency lower than the average
plasma frequency can be transmitted if its power is high.
Work supported by NSF 相似文献
753.
R.K. Tripathi 《Physics letters. [Part B]》1981,101(5):369-374
We investigate the effects of a selfconsistent single-particle potential and the Pauli principle on the equation of state for dense systems at low temperatures. It is found that the selfconsistent potential plays an extremely important role for the equation of state near nuclear matter density. 相似文献
754.
Elastic electron-hydrogen scattering at medium and high energies has been analysed in eikonal-Born series and modified Glauber
approach forE
i ≥ 50 eV. We have used closed form expressions for evaluating the second Born term in the fixed scatterer approximation and
for higher order terms of Glauber-eikonal series. The exchange effect has also been included via Glauber-Bonham-Ochkur type
procedure. The fixed scatterer approximation calculations are compared with results obtained using other approximations for
the second Born term available in the literature. The results compare fairly well with experimental data. 相似文献
755.
V.P. Gaur B.M. Tripathi 《Journal of Quantitative Spectroscopy & Radiative Transfer》1985,33(3):291-292
Partition functions and dissociation equilibrium constants for HeH+ have been computed for temperatures between 2,000 and 16,000 K in steps of 100 K. 相似文献
756.
757.
Recently a method has been developed which includes into the Brueckner-Hartree-Fock (BHF) approach in a finite nucleus those terms which produce the density dependence of the effective interaction between nucleons. This method is extended to the deformed open shell nuclei 12C and 20Ne. The results indicate that it is possible to describe these nuclei starting from a bare realistic nucleon-nucleon interaction (Reid soft-core potential). Binding energies, quadrupole moments, root mean square radii are improved compared to the usual BHF approach with the same force or the HF approach with a phenomenological effective force. 相似文献
758.
The temperature dependence of the fluorescence and fluorescence excitation spectra of all-trans diphenyl hexathene (DPH) and octatetraene (DPO) in six solvents confirms the S1(1Ag*) and S2(1Bu*) state assignment, and determines their energy difference ΔE. The S1 fluorescence rate parameter kF depends on ΔE, the solvent refractive index n, the S2 (n = 1) fluorescence rate parameter kF20 (2.23 × 108 s?1 for DPH, 2.33 × 108 s?1 for DPO), and the S2-S1 coupling matrix element V (745 cm?1 for DPH, 500 cm?1 for DPO). The S1 fluorescence is induced by 1Bu*-1Ag* potential interaction (PI), via a bu vibrational mode (≈ 900 cm?1), and not by vibronic coupling. The main S1 radiationless transition, rate parameter kR, is thermally-activated internal rotation through an angle θ about the central ethylenic bond(s). The PI distorts the S1 (θ) potential surface and thus influences kR. 相似文献
759.
760.
A high-power sub-millimeter wave propagating through bismuth, a semimetal with non-spherical energy surfaces, parametrically excites a space-charge mode and a back-scattered electromagnetic wave. The free carrier density perturbation associated with the space-charge wave couples with the oscillatory velocity due to the pump to derive the scattered wave. The scattered and pump waves exert a pondermotive force on electrons and holes, driving the space-charge wave. The collisional damping of the decay waves determines the threshold for the parametric instability. The threshold intensity for 20 μm wavelength pump turns out to be ∼2×1012 W/cm2. Above the threshold, the growth rate scales increase with ωo, attain a maximum around ωo=6.5ωp, and, after this, falls off. 相似文献