共查询到20条相似文献,搜索用时 15 毫秒
1.
The influence of long-range links on spiral waves in an excitable medium has been investigated.Spatiotemporal dynamics in an excitable small-world network transform remarkably when we increase the long-range connection probability P.Spiral waves with few perturbations,broken spiral waves,pseudo spiral turbulence,synchronous oscillations,and homogeneous rest state are discovered under different network structures.Tip number is selected to detect non-equilibrium phase transition between different spatiotemporal patterns.The Kuramoto order parameter is used to identify these patterns and explain the emergence of the rest state.Finally,we use long-range links to successfully control spiral waves and spiral turbulence. 相似文献
2.
The influence of long-range links on spiral waves in excitable medium has been investigated. Spatiotemporal dynamics in excitable small-world network transforms remarkably when we increase the long-range connection probability P. Spiral waves with few perturbations, broken spiral waves, pseudo spiral turbulence, synchronous oscillations, and homogeneous rest state are discovered under different network structures. Tip number is selected to detect non-equilibrium phase transition between different spatiotemporal patterns. The Kuramoto order parameter is used to identify these patterns and explain the emergence of the rest state. Finally, we use long-range links to control spiral wave and spiral turbulence successfully. 相似文献
3.
4.
V. V. Kuznetsov I. A. Kozulin O. V. Vitovsky 《Journal of Engineering Thermophysics》2012,21(2):136-143
Propagation of adiabatic evaporation waves arising while refrigerants R-11 rapidly transit to metastable state due to depressurization
in the rarefaction wave is experimentally investigated. New regularities of the interphase surface dynamics and the influence
of interphase heat and mass transfer in propagation of adiabatic evaporation waves are obtained. It has been found that the
phase transition in metastable liquid occurs in the conditions of developing multiscale turbulence in liquid and vapor phases
under dynamic action of a vapor flow on the interphase surface and convective heat supply to the zone of high-intensity phase
transition. The surface phase transition was visualized by a rapid video camera, its pulsating character is revealed and its
properties are determined. 相似文献
5.
A family of three-dimensional traveling waves for flow through a pipe of circular cross section is identified. The traveling waves are dominated by pairs of downstream vortices and streaks. They originate in saddle-node bifurcations at Reynolds numbers as low as 1250. All states are immediately unstable. Their dynamical significance is that they provide a skeleton for the formation of a chaotic saddle that can explain the intermittent transition to turbulence and the sensitive dependence on initial conditions in this shear flow. 相似文献
6.
A. Atipo G. Bonhomme T. Pierre 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,19(1):79-87
The spatio-temporal dynamics of self-excited ionization waves in a neon glow discharge is experimentally investigated. Various
mechanisms leading to ionization waves chaos and turbulence are identified: subharmonics cascade, Ruelle-Takens-Newhouse scenario,
and spatio-temporal intermittency. The dynamical states involved in the transition scenarios from stability to chaotic regimes
are characterized through both temporal and spatio-temporal analysis by means of the Biorthogonal Decomposition (BD).
Received 25 October 2001 相似文献
7.
利用从等离子体的实际问题引出的一些模型,研究了孤子、禁带孤波等相干结构,探索了非线性波动系统中的分岔、向混沌与湍流转变的现象、机制和控制问题. With models deduced from plasma systems, some phenomena in nonlinear wave systems are studied, such as solitons, gap solitary waves, bifurcations and transition to turbulence. The mechanism of bifurcations and control of chaos are also explored. 相似文献
8.
We show that helical turbulence produced during a first-order phase transition generates circularly polarized cosmological gravitational waves (GWs). The characteristic frequency of these GWs for an extreme case of the phase transition model is around 10(-3)-10(-2) Hz with an energy density parameter as high as 10(-12)-10(-11). The possibility of detection is briefly discussed. 相似文献
9.
Laminar-turbulent transition in circular Couette flow is discussed. Phenomenological equations are proposed describing the breakdown of azimuthal waves coherency. The correspondence is established between the flow turbulization and the stochastic attractor in the phase space of these equations. Evolution of attractor structure is investigated experimentally in terms of motion in some effective phase space. It is shown that during the transition to turbulence the increase in number of degrees of freedom is combined with the stochastic behaviour of rapid motion envelopes. 相似文献
10.
11.
One of the challenges in numerical simulation of wave–turbulence interaction is the precise setup and maintenance of wave and turbulence fields. In this paper, we investigate techniques for the generation and suppression of specific surface wave modes, the generation of turbulence in an inhomogeneous physical domain with a wavy boundary-fitted grid, and the generation and maintenance of waves and turbulence during the complex wave–turbulence interaction process. We apply surface pressure to generate and suppress waves. Based on the solution of linearized Cauchy–Poisson problem, we derive three pressure expressions, which lead to a δ-function method, a time-segment method, and a gradual method. Numerical experiments show that these methods generate waves as specified and eliminate spurious waves effectively. The nonlinear wave effect is accounted for with a time-relaxation method. For turbulence generation, we extend the linear forcing method to an inhomogeneous physical domain with a curvilinear computational grid. Effects of force distribution and computational grid distortion are examined. For wave–turbulence interaction, we develop an algorithm to instantaneously identify specific progressive and standing waves. To precisely control the wave amplitude in a complex turbulent flow field, we further develop an energy controlling method. Finally, a simulation example of wave–turbulence interaction is presented. Results show that turbulence has unique features in the presence of waves. Velocity fluctuations are found to be strongly dependent on the wave phase; variations of these fluctuations are explained by the pressure–strain correlation associated with the wave-induced strain field. 相似文献
12.
E. A. Kuznetsov 《Journal of Experimental and Theoretical Physics》2001,93(5):1052-1064
A weak turbulence of the magnetohydrodynamic waves in a strongly magnetized plasma was studied in the case when the plasma pressure is small as compared to the magnetic field pressure. In this case, the principal nonlinear mechanism is the resonance scattering of fast magnetoacoustic and Alfvén waves on slow magnetoacoustic waves. Since the former waves are high-frequency (HF) with respect to the latter, the total number of HF waves in the system is conserved (adiabatic invariant). In the weak turbulence regime, this integral of motion generates a Kolmogorov spectrum with a constant flux of the number of HF waves toward the longwave region. The shortwave region features a Kolmogorov spectrum with a constant energy flux. An exact angular dependence of the turbulence spectra is determined for the wave propagation angles close to the average magnetic field direction. 相似文献
13.
B. Eckhardt T. M. Schneider 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,64(3-4):457-462
The transition to turbulence in pipe flow does not follow the scenario familiar from Rayleigh-Benard or Taylor-Couette flow since the laminar profile is stable against infinitesimal perturbations for all Reynolds numbers. Moreover, even when the flow speed is high enough and the perturbation sufficiently strong such that turbulent flow is established, it can return to the laminar state without any indication of the imminent decay. In this parameter range, the lifetimes of perturbations show a sensitive dependence on initial conditions and an exponential distribution. The turbulence seems to be supported by threedimensional travelling waves which appear transiently in the flow field. The boundary between laminar and turbulent dynamics is formed by the stable manifold of an invariant chaotic state. We also discuss the relation between observations in short, periodically continued domains, and the dynamics in fully extended puffs. 相似文献
14.
G. V. Kolmakov 《JETP Letters》2006,83(2):58-63
Decay of the turbulence of capillary waves on the surface of a real liquid is studied in the presence of the viscous damping of the waves at all frequencies after stepwise removal of external pumping. The investigation is performed using two different models: the weak turbulence approximation and the local turbulence model in which the energy redistribution over frequencies is described by the polynomial expression in the wave-occupation number. It is shown that the decay of turbulence in the viscous liquid proceeds self-similarly and begins at high frequencies. In the decay process, the frequency distribution of the energy of waves is close to the stationary form E ω ~ ω?3/2 in a wide frequency range below the boundary frequency of the inertial range during a relatively long time after removal of the external force. The calculation results agree qualitatively with the results of the experiments on capillary turbulence on the charged surface of liquid hydrogen. 相似文献
15.
The interaction of two strong circulary polarized u.h.f. pump waves with a fully ionized homogeneous plasma is considered. If the difference Ω of their frequencies is near or smaller than twice the ion plasma frequency phonons can be parametrically excited. The threshold value (E0E1)s for this decay-process depends on Ω and the dissipative effects in the plasma. After exceeding the thermal level the phonons are stabilized due to the scattering by the ions. The evolution of the parametrically excited phonon turbulence and the transition into a stationary state are described by a nonlinear integro-differential equation for the spectral energy density of the phonons. This equation is solved analytically as well as numerically and it is shown, that the phonon turbulence is strongly influence by the propagation directions of the pump waves and the ratio of electron- to ion-temperature. 相似文献
16.
V. L. Frolov G. N. Boiko S. A. Metelev E. N. Sergeev 《Radiophysics and Quantum Electronics》1994,37(7):593-603
Results of measurements of the characteristics of stimulated electromagnetic emission induced in ionospheric plasma by pulsed high-power radio waves (diagnostic emission) presented. The dependences of the properties of diagnostic emission on the parameters of the diagnostic wave, ionospheric conditions, and the level of development of artificial ionospheric turbulence are determined, and criteria are given for selection of optimal diagnostic conditions for ionospheric-plasma sounding. Results of experiments on the sounding of artificial ionospheric turbulence by means of diagnostic emission are provided. It is established that with transition from daytime to evening conditions, the characteristic times of emission decay are sharply increased. This is attributed to an increase in the natural perturbation of the F-region.Scientific-Research Radio-Physics Institute, Nizhny Novgord. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 37, No. 7, pp. 909–928, July, 1994. 相似文献
17.
从速度v的傅里叶空间K的动力学方程出发,采用算子运算及变换方法,可较简便的算出静电湍流场中的重整化色散方程,在以有效关联时间代替湍流场的时、空关联的近似下,计算了有限关联时间效应的作用,表明它是削弱湍流场影响的。短关联时间极限可看成是湍流场影响的上限估计。讨论了湍流场对离声波、电子朗缪波和低频漂移波的影响。
关键词: 相似文献
18.
Yingle Li Jiying Huang Ruike Yang 《International Journal of Infrared and Millimeter Waves》2002,23(3):435-443
Dust storms and turbulence consist of a random medium system, its effects on milimeter waves propagation are studied. Attenuation of millimeter waves, its phase shift and cross- polar discrimination are presented. Results show that dust storms mainly effects XPD and phase shift of millimeter waves, turbulence chiefly produces attenuation, in mediocre fluctuation. 相似文献
19.
20.
Inhomogeneity and anisotropy are intrinsic characteristics of daytime and nighttime atmospheric turbulence. For example, turbulent eddies are often stretched in the direction of the mean wind, and the turbulence statistics depends on the height above the ground. Recent studies have shown that the log-amplitude and phase fluctuations of plane and spherical sound waves are significantly affected by turbulence inhomogeneity and anisotropy. The present paper is devoted to studies of the mean sound field and the coherence functions of plane and spherical sound waves propagating through inhomogeneous anisotropic turbulence with temperature and velocity fluctuations. These statistical moments of a sound field are important in many practical applications, e.g., for source detection, ranging, and recognition. Formulas are derived for the mean sound field and coherence function of initially arbitrary waveform. Using the latter formula, we also obtained formulas for the coherence functions of plane and spherical sound waves. All these formulas coincide with those known in the literature for two limiting cases: homogeneous isotropic turbulence with temperature and wind velocity fluctuations, and inhomogeneous anisotropic turbulence with temperature fluctuations only. Using the formulas obtained, we have numerically shown that turbulence inhomogeneity significantly affects the coherence functions of plane and spherical sound waves. 相似文献