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11.
A new strategy is presented to explain the creation and persistence
of zonal flows widely observed in plasma edge turbulence. The core
physics in the edge regime of the magnetic-fusion tokamaks can be
described qualitatively by the one-state modified Hasegawa-Mima (MHM
for short) model, which creates enhanced zonal flows and more physically
relevant features in comparison with the familiar
Charney-Hasegawa-Mima (CHM for short) model for both plasma and
geophysical flows. The generation mechanism of zonal jets is
displayed from the secondary instability analysis via nonlinear
interactions with a background base state. Strong exponential growth
in the zonal modes is induced due to a non-zonal drift wave base
state in the MHM model, while stabilizing damping effect is shown
with a zonal flow base state. Together with the selective decay
effect from the dissipation, the secondary instability offers a
complete characterization of the convergence process to the purely
zonal structure. Direct numerical simulations with and without
dissipation are carried out to confirm the instability theory. It
shows clearly the emergence of a dominant zonal flow from pure
non-zonal drift waves with small perturbation in the initial
configuration. In comparison, the CHM model does not create
instability in the zonal modes and usually converges to homogeneous
turbulence. 相似文献
12.
We propose a method for analyzing the data for the rates of exchange of various currencies versus the U.S. dollar. The method analyzes the return time series of the data as a Markov process, and develops an effective equation which reconstructs it. We find that the Markov time scale, i.e., the time scale over which the data are Markov-correlated, is one day for the majority of the daily exchange rates that we analyze. We derive an effective Langevin equation to describe the fluctuations in the rates. The equation contains two quantities, D(1) and D(2), representing the drift and diffusion coefficients, respectively. We demonstrate how the two coefficients are estimated directly from the data, without using any assumptions or models for the underlying stochastic time series that represent the daily rates of exchange of various currencies versus the U.S. dollar. 相似文献
13.
Vassilios Fessatidis Norman J.M. Horing 《Physica E: Low-dimensional Systems and Nanostructures》2005,27(4):487-494
We examine the collective mode spectrum for a double quantum-wire system embedded in semi-infinite polar medium, taking account of the role of optical phonons in interaction with the double quantum-wire plasmons and bulk/surface plasmons. The collective mode frequencies are exhibited as functions of qx (wavenumber parallel to the wires) and as functions of z0 (distance of first wire from the interface). We also find that the region of drift instability of the collective modes is split into two disjoint regions of instability by the optical phonons, with a region of stability between them. 相似文献
14.
A three-tip array is used in the HL-2A tokamak to investigate the spectral characteristics of electrostatic turbulence inside the last closed flux surface (LCFS) about 5 cm. Two-point correlation techniques are used to analysis the turbulence structure. It is found that the drift wave turbulence mainly is composed of low-frequency and long wavelength wave packets. The poloidal propagation is mainly in electron-diamagnetic direction, sometimes it propagates in ion-diamagnetic direction, which is influenced by Doppler-frequency shift. The radial propagation velocity is outward and the sizeable fraction of the poloidal velocity, implying that the radial mode plays an important role in the cross field transport. 相似文献
15.
16.
蔡泽伟 《宁波大学学报(理工版)》1989,(2)
本文以伪随机二进制信号(PRBS)操舵,用同时测量轨迹与航向角的方法,计算得到漂角β,从而辨识了白箱模型(2.1),获得了操纵运动的水动力导数。并与PMM试验结果进行了比较,证实了本文方法的有效性。 相似文献
17.
本文通过数值求解平板模型中本征模方程,研究了安全因子q极值点附近的低频漂移波稳定性问题。数值计算结果表明,剪切随磁面的变化可以导致在q的极值点附近产生不稳定的漂移波模式。 相似文献
18.
本文提出了一种新的基于扩散过程轨道构造漂移系数样本的方法—对数增量法,通过理论及模拟分析说明了在适当条件下,特别是对于大多数金融数据,基于对数增量法获得的漂移系数估计量的收敛速度及有限样本性质均比基于传统的"直接增量法"所得到的结果要好。 相似文献
19.
The phenomenological Boltzmann–Matano (B–M) analysis allows approximating the concentration dependent interdiffusion coefficients related to infinite binary diffusion couple experiments. However, the complete understanding of the phenomenological process related to the Kirkendall plane position coupled with the B–M method is still lacking. A purpose of the present study is to generalize the Boltzmann–Matano analysis and propose a method of estimating the unique intrinsic diffusion coefficients of components from the experimental concentration profile and the positions of Matano and Kirkendall planes in multicomponent systems. The proposed physico-chemical approach is used to approximate the intrinsic diffusivities in a single phase of Ni–Pd binary and Cu–Fe–Ni ternary diffusion couples. 相似文献
20.
Some properties of a class of path-dependent options based on the α-quantiles of Brownian motion are discussed. In particular, it is shown that such options are well behaved in relation to standard options and comparatively cheaper than an equivalent class of lookback options. 相似文献