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991.
Radiation-induced resistance oscillation and instability in GaAS/AlGaAS heterostructure under transverse magnetic fields
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This paper studies dynamics of a modulation-doped GaAs/AlGaAs heterostructure under transverse magnetic fields and microwave radiations. It finds that negative differential conductivity, due to the real-space electron transfer and delayed dielectric relaxation of the interface potential barrier, can lead to complex behaviours when a relatively small magnetic field is applied. Quasiperiodicity, frequency-locking and the routes from period-doubling to chaos are found. Under a large magnetic field, however, two time-independent homogeneous steady states exist; and the longitudinal resistance of the system shows an interesting oscillation with period tuned by the ratio of microwave radiation frequency w to the cyclotron frequency Wc and local minima at ω/ωc = integer + 1/4. 相似文献
992.
We investigate the Bloch and dipole oscillations of a Bose Einstein condensate (BEC) in an optical superlattice. We show that,
as the effective mass increases in an optical superlattice, the BEC is localized in accordance with recent experimental observations
[J.E. Lye et. al. Phys. Rev. A 75, 061603 (2007)]. In addition, we find that the secondary optical lattice is a useful additional tool to manipulate
the dynamics of the atoms.
相似文献
993.
Both high and low frequency relaxation oscillations have been observed in an argon capacitive discharge connected to a peripheral grounded chamber through a slot with dielectric spacers. The oscillations, observed from time-varying optical emission of the main discharge chamber, show, for example, a high frequency (46 kHz) relaxation oscillation at 100 mTorr, with an absorbed power near the peripheral breakdown, and a low frequency (2.7-3.7 Hz) oscillation, at a higher absorbed power. The high frequency oscillation is found to ignite a plasma in the slot, but usually not in the periphery. The high frequency oscillation is interpreted by using an electromagnetic model of the slot impedance, combined with the circuit analysis of the system including a matching network. The model is further developed by using a parallel connection of variable peripheral capacitance to analyse the low frequency oscillation. The results obtained from the model are in agreement with the experimental observations and indicate that a variety of behaviours are dependent on the matching conditions. 相似文献
994.
Three-dimensional fully developed turbulent fluid flow and heat transfer in a square duct are numerically investigated with the author's anisotropic low-Reynolds-number k-ε turbulence model. Special attenton has been given to the regions close to the wall and the corner, which are known to influence the characteristics of secondary flow a great deal. Hence, instead of the common wall function approach, the no-slip boundary condition at the wall is directly used. Velocity and temperature profiles are predicted for fully developed turbulent flows with constant wall temperature. The predicted variations of both local wall shear stress and local wall heat flux are shown to be in close agreement with available experimental data. The present paper also presents the budget of turbulent kinetic energy equation and the systematic evaluation for existing wall function forms. The commonly adopted wall function forms that are valid for two-dimensional flows are found to be inadequate for three-dimensional turbulent flows in a square duct. 相似文献
995.
LI Fenghua LIU Jianjun LI Zhenglin & ZHANG Renhe National Laboratory of Acoustics Chinese Academy of Sciences Beijing China 《中国科学G辑(英文版)》2005,48(4):413-421
~~An oscillation phenomenon of low frequency reverberation in the shallow water and its physical explanation1 Zhang, R.. Jin. G. Normal-mode theory of average reverberation intensity in shallow water, Journal of Sound and Vibration, 1987 19(2):215-223
2. Ellis, D. D., A shallow-water normal-mode reverberation model, J. Acoust. Soc, Am., 1995, 97(5): 2804-2814.
3. McDaniel, S. T., Seafloor reverberation fluctuations, J. Acoust. Soc. Am., 1990, 88(3): 1530-1535.
4. Abraham, … 相似文献
996.
对称非线性弹簧振子的周期特性 总被引:6,自引:1,他引:5
通过计算机编程(Quick Basic)描绘对称非线性弹簧振子振动的特性曲线,使难懂的物理过程变得直观、形象。对称非线性弹簧振子的振动是一种周期性振动,但不是严格的简谐振动,其振动周期随非线性系数、振幅的变化而偏离简谐振动的周期。 相似文献
997.
Jelena V. Manojlović 《Czechoslovak Mathematical Journal》2005,55(1):41-60
New oscillation criteria are given for the second order sublinear differential equation
where a C
1 ([t
0, )) is a nonnegative function, , f C() with (x) 0, xf(x) / (x) > 0 for x 0, , f have continuous derivative on \ {0} with [f(x) / #x03C8;(x)] 0 for x 0 and q C([t
0, )) has no restriction on its sign. This oscillation criteria involve integral averages of the coefficients q and a and extend known oscillation criteria for the equation x (t) + q(t)x(t) = 0. 相似文献
998.
In this paper, oscillation criteria are established for all solutions of second-order nonlinear differential equations of the form
999.
1000.
In this paper, we have examined strings with monopole and electric field and domain walls with matter and electric field in
the spherically symmetric space-time admitting a one-parameter group of conformal motions. For this purpose, we have solved
Einstein's field equations for a spherically symmetric space-time via conformal motions. Also, we have discussed the features
of the obtained solutions. 相似文献