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1.
Suppression of spatiotemporal chaos in a one-dimensional nonlinear drift-wave equation driven by a sinusoidal wave is considered. Using a constant electric potential signal we demonstrate numerically that the spatiotemporal chaos can be effectively suppressed if the control parameters are properly chosen. The threshold and the controllable range of the control parameters are given. By establishing the kinetic equation of the system energy we find theoretically that an additional driving term in the energy equation is produced by the control signal and it can lead up to the frequency entrainment. Moreover, when the regular state is reached under the control, the system energy oscillates quasi-periodically, while the additional driving term decays to zero. 相似文献
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R.K. Varma 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(2):211-218
It has been shown earlier [3,6] that matter waves which are known to lie typically in the range of a few angstrom, can also
manifest in the macrodomain with a wave length of a few centimeters, for electrons propagating along a magnetic field. This
followed from the predictions of a probability amplitude theory by the author [1,2] in the classical macrodomain of the dynamics
of charged particles in a magnetic field. It is shown in this paper that this case constitutes only a special case of a generic
situation whereby composite systems such as atoms and molecules in their highly excited internal states, can exhibit matter
wave manifestation in macro and mesodomains, in one-dimensional scattering. The wave length of these waves is determined,
not by the mass of the particle as in the case of the de Broglie wave, but by the frequency ω, of the classical orbital motion
of the internal state in the correspondence limit, and is given by a nonquantal expression, λ = 2πv/ω, v being the velocity of the particle. For the electrons in a magnetic field the frequency corresponds to the gyrofrequency,
Ω and the nonquantal wave length is given by λ = 2πv
|| /Ω; v
|| being the velocity of electrons along the magnetic field.
Received 29 September 2001 / Received in final form 23 May 2002 Published online 19 July 2002 相似文献
4.
Chandu Venugopal 《Pramana》1987,28(2):181-193
A dispersion relation for the near perpendicular propagation of the electromagnetic ion cyclotron wave has been derived in
a fusion plasma that has deuterium as a majority species, hydrogen as a minority species and fully ionized oxygen as an impurity
constituent; all being modelled by loss cone distribution functions. The wave has a frequencyω around the deuterium ion gyrofrequency-ΩD and a wavelength much longer than its Larmor radiusγ
LD(k
⊥
γ
LD<1); the plasma itself being characterized by large ion plasma frequencies (ω
PD
2
>Ω
D
2
). Two modes, a low frequency (LF) and a high frequency (HF) mode of opposite electrical energy can propagate in the plasma;
the instabilities that arise are thus due to an interaction of modes of opposite energies. We find that while hydrogen tends
to destabilize the plasma, the impurity oxygen ions have the reverse effect. Also the plasma is most stable when the ratios
of the perpendicular components of oxygen-to-deuterium and hydrogen-to-deuterium temperatures are kept low. Detailed studies
of the wave propagation characteristics and energy reveal the close resemblance of a loss cone plasma containing oxygen to
a stable Maxwellian plasma in regard to wave stability, propagation and energy. 相似文献
5.
An investigation is reported of stimulated two-photon emission by Bose-condensed excitons accompanied by a coherent two-exciton
recombination, i.e., by simultaneous recombination of two excitons with opposite momenta leaving unchanged the occupation
numbers of exciton states with momenta p≠0. Raman light scattering (RLS) accompanied by a similar two-exciton recombination (or production of two excitons) is also
analyzed. The processes under consideration can occur only if a system contains Bose condensate, so their detection can be
used as a new method to reveal Bose condensation of excitons. The recoil momentum, which corresponds to a change in the momentum
of the electromagnetic field in the processes, is transferred to phonons or impurities. If the recoil momentum is transmitted
to optical phonons with frequency ω
0
s
, whose occupation numbers are negligible, and the incident light frequency satisfies ω<2Ω, where Ω_=Ω−ω
0
s
is the difference frequency and Ω is the light frequency corresponding to the recombination of an exciton with zero momentum,
stimulated two-photon emission and RLS with coherent two-exciton recombination give rise to a line at 2Ω_ −ω and an anti-Stokes component at ω+2Ω_, respectively. For ω2Ω_ the RLS spectrum contains Stokes and anti-Stokes components at frequencies ω±2Ω_, whereas stimulated two-photon emission is impossible. Formulas for the cross sections at finite temperatures are obtained
for the processes under consideration. Our estimates indicate that a spectral line at 2Ω_−ω, corresponding to the stimulated two-photon emission accompanied by coherent optical phonon-assisted two-exciton recombination
can be experimentally detected in Cu2O.
Zh. éksp. Teor. Fiz. 115, 1353–1376 (April 1999) 相似文献
6.
V. Bellani C. Bocchi T. Ciabattoni S. Franchi P. Frigeri P. Galinetto M. Geddo F. Germini G. Guizzetti L. Nasi M. Patrini L. Seravalli G. Trevisi 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,56(3):217-222
This work deals with the strain relaxation mechanism in InGaAs metamorphic buffers (MBs) grown on GaAs substrates and overgrown
by InAs quantum dots (QD). The residual strain is measured by using Raman scattering and X-ray diffraction, both in Reciprocal
Space Map and in single ω-2θ scan modes (ω and θ being the incidence angles on the sample surface and on the scattering planes,
respectively). By relating the GaAs-like longitudinal optical phonon frequency ωLO of InGaAs MBs to the in-plane residual strain ε measured by means of photoreflectance (PR), the linear ε-vs.-ωLO working curve is obtained. The results of Raman and XRD measurements, as well as those obtained by PR, are in a very satisfactory
agreement. The respective advantages of the techniques are discussed. The measurements confirm that strain relaxation depends
on the thickness t of the buffer layer following a ~t-1/2 power law, that can be explained by an energy-balance model. 相似文献
7.
A model of two-dimensional coupled complex Ginzburg-Landau oscillators driven by a rectificative feedbackcontroller is used to study controlling spatiotemporal chaos without gradient force items. By properly selecting the signalinjecting position with considering the maximum gap between signals and targets, and adjusting the control time interval,we have finally obtained the efficient chaos control via numerical simulations. 相似文献
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GAOJi-Hua ZHENGZhi-Gang TANGJiao-Ning PENGJian-Hua 《理论物理通讯》2003,40(3):315-318
A model of two-dimensional coupled complex Ginzburg-Landau oscillators driven by a rectificative feedback controller is used to study controlling spatiotemporal chaos without gradient force items. By properly selecting the signal injecting position with considering the maximum gap between signals and targets, and adjusting the control time interval,we have finally obtained the efficient chaos control via numerical simulations. 相似文献
10.
Suppression of Spiral Waves and Spatiotemporal Chaos Under Local Self-adaptive Coupling Interactions
In this paper, a close-loop feedback control is imposed locally on the Fitzhugh-Nagumo (FHN) system to suppress the stable spirals and spatiotemporal chaos according to the principle of self-adaptive coupling interaction. The simulation results show that an expanding target wave is stimulated by the spiral waves under dynamic control period when a local area of 5×5 grids is controlled, or the spiral tip is driven to the board of the system. It is also found that the
spatiotemporal chaos can be suppressed to get a stable homogeneous state
within 50 time units as two local grids are controlled mutually. The
mechanism of the scheme is briefly discussed. 相似文献
11.
Elimination of spiral waves and spatiotemporal chaos by the pulse with a specific spatiotemporal configuration 下载免费PDF全文
Spiral waves and spatiotemporal chaos are sometimes harmful and should be controlled. In this paper spiral waves and spatiotemporal chaos are successfully eliminated by the pulse with a very specific spatiotemporal configuration. The excited position D of spiral waves or spatiotemporal chaos is first recorded at an arbitrary time (to). When the system at the domain D enters a recovering state, the external pulse is injected into the domain. If the intensity and the working time of the pulse are appropriate, spiral waves and spatiotemporal chaos can finally be eliminated because counter-directional waves can be generated by the pulse. There are two advantages in the method. One is that the tip can be quickly eliminated together with the body of spiral wave, and the other is that the injected pulse may be weak and the duration can be very short so that the original system is nearly not affected, which is important for practical applications. 相似文献
12.
L. Bartosch P. Kopietz 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(1):29-36
We consider the effect of Coulomb interactions on the average density of states (DOS) of disordered low-dimensional metals
for temperatures T and frequencies ω smaller than the inverse elastic life-time 1/τ. Using the fact that long-range Coulomb interactions in two dimensions (2d) generate ln2-singularities in the DOS ν(ω) but only ln-singularities in the conductivity σ(ω), we can re-sum the most singular contributions
to the average DOS via a simple gauge-transformation. If σ(ω) > 0, then a metallic Coulomb gapν(ω) ∝ |ω|/e
4 appears in the DOS at T = 0 for frequencies below a certain crossover frequency Ω
2 which depends on the value of the DC conductivity σ(0). Here, - e is the charge of the electron. Naively adopting the same procedure to calculate the DOS in quasi 1d metals, we find ν(ω) ∝ (|ω|/Ω
1)1/2exp(- Ω
1/|ω|) at T = 0, where Ω
1 is some interaction-dependent frequency scale. However, we argue that in quasi 1d the above gauge-transformation method is on less firm grounds than in 2d. We also discuss the behavior of the DOS at finite temperatures and give numerical results for the expected tunneling conductance
that can be compared with experiments.
Received 28 August 2001 / Received in final form 28 January 2002 Published online 9 July 2002 相似文献
13.
A. I. Alekseev 《Journal of Experimental and Theoretical Physics》1997,84(1):35-50
The properties of the density matrix and the multipole moments arising in oriented and aligned atoms with zero nuclear spin
through the interaction with strong resonant ultrashort pulses with wave vector k
0 and circular or linear polarization have been found. Calculations have been made for the time-dependent light-induced magnetization
μ(t′) of a gas of pre-oriented and prealigned atoms following the passage of a weak resonant elliptically polarized pulse with
frequency ω and wave vector k collinear with k
0. It is shown that for oriented atoms, μ(t′) is an even function of the detuning from resonance, ω-ω
ba, and can be split into two terms whose directions are a consequence of symmetry and are determined by the vectors k
0 and k as well as by the direction of rotation of the electric fields corresponding to the pulses. For aligned atoms the vector
μ(t′) is collinear with k, and the first term is an even function of ω-ω
ba. However, the second term is an odd function of ω-ω
ba and reverses direction when the sign of ω-ω
ba changes, as well as when the orientation of the axes of the polarization ellipse is changed. It is shown that if a series
of weak linearly polarized pulses pass through the gas, the light-induced magnetization of the oriented and aligned gas atoms
can be decomposed into three factors: the first determines the direction and is a consequence of the symmetry; the second
(with the dimensions of magnetic moment) depends on the characteristics of the resonant transitions; and the third is a universal
function of t′ and ω-ω
ba that does not depend on the underlying characteristics of the resonant transition. These vector factors and the universal
functions are in principle different for oriented and aligned atoms.
Zh. éksp. Teor. Fiz. 111, 63–92 (January 1997) 相似文献
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G. Y. Yuan S. G. Chen S. P. Yang 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(3):331-336
Spiral waves and spatiotemporal chaos are sometimes
harmful and should be controlled. In this letter we present a
feedback scheme to eliminate them. We first collect feedback signals
at a certain time t0. Then wait for the system at the excitable
position to enter the recovering state. When the time comes, the
feedback signals are added. This scheme has two advantages. Firstly,
the tip can be eliminated together with the body of spiral wave.
Secondly, the injected feedback signals can be very weak and the
duration can be very short so that the original system is nearly not
to be affected, which is important for practical applications. 相似文献
17.
On the basis of numerical solution of the dispersion equation, we obtain the spectra of weakly damped high-frequency waves
in a hot magnetized plasma for the case where the electron cyclotron frequency ωHe
is below the plasma frequency ωpe. It is shown that the longitudinal wave propagating at an angle to the magnetic field evolves into the slow extraordinary
wave for the refractive index n ≤ 1. For n ≫ 1, the longitudinal-wave frequency increases with the refractive index, and the
wave evolves into the wave with anomalous dispersion if the angle θ between the wave vector and the magnetic field is close
to 90°. In the same range of θ angles, Bernstein modes appear in the spectrum of plasma eigenmode oscillations.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 3, pp. 258–266, March 2006. 相似文献
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19.
We study the nonlinear dynamics of the interaction of two-level atoms and a selected mode of a high-Q cavity with frequency modulation analytically and numerically. In the absence of modulation, the corresponding semiclassical
Heisenberg equations for the expectation values of the collective atomic observables and the field-mode amplitudes allow,
in the rotating wave approximation and in the strong-coupling limit, an exact solution with arbitrary detuning. Using this
solution, we detect the coherent effect of trapping of the population of atomic levels and of trapping of the number of photons
in the cavity. The explanation for this effect lies in the destructive interference of the atomic dipoles and the field mode.
The integrable version of the system of equations exhibits a separatrix near which a stochastic layer is formed when modulation
is introduced. The width of the layer is found to gradually increase with degree of modulation, and finally it fills the entire
energy-permissible volume of the phase space. We show that the rotating wave approximation does not hinder the formation of
Hamiltonian chaos in cavity semiclassical electrodynamics. The calculation of the maximum Lyapunov indices of nonlinear (in
this approximation) equations of motion as functions of the modulation frequency δ and the frequency of natural Rabi oscillations of the atom-field system, Ω, suggests that Hamiltonian chaos appears first
in the area of the fundamental parametric resonance, δ/2Ω≃1. Parametric instability increases with increasing modulation and decreasing detuning from the atom-field resonance,
generating at exact resonance new areas of chaos corresponding to multiple parametric resonances. The results of numerical
experiments and estimates of the characteristic parameters show that Rydberg atoms placed in a high-Q microwave cavity are possible objects for observing parametric instability and dynamical chaos.
Zh. éksp. Teor. Fiz. 115, 740–753 (February 1999) 相似文献