共查询到20条相似文献,搜索用时 31 毫秒
1.
P. M. Lushnikov 《Journal of Experimental and Theoretical Physics》1998,86(3):614-627
A nonlinear theory is presented for the formation of hexagonal optical structures in a photorefractive medium equipped with
a feedback mirror. Oppositely directed beams in photorefractive crystals are unstable against the excitation of sideband waves.
It is shown here that as this instability evolves to its nonlinear stage, the three-wave interaction between weak sideband
beams does not stabilize it, but rather leads to explosive growth of the amplitudes of beams whose transverse wave vectors
form angles that are multiples of π/3. As a result, sideband beams at these angles are found to be correlated. A range of parameters is found in which four-wave
interactions saturate the explosive instability, which explains the appearance of stable hexagons in the experiment. Outside
this region, nonlinearities of higher order saturate the explosive instability, and the process of hexagon generation must
be studied numerically. Matrix elements are obtained for the three-and four-wave interactions as functions of the distance
to the feedback mirror, and an equation for the time evolution of the sideband wave amplitudes is derived that describes the
hexagon generation. A comparison is made with experimental results for the photorefractive crystals KNbO3 and BaTiO3.
Zh. éksp. Teor. Fiz. 113, 1122–1146 (March 1998) 相似文献
2.
Tomar G Shankar V Shukla SK Sharma A Biswas G 《The European physical journal. E, Soft matter》2006,20(2):185-200
The instability, rupture, and subsequent growth of holes in a thin Jeffreys-type viscoelastic film under the influence of
long-range van der Waals force are investigated using both linear stability analysis and nonlinear numerical solutions. The
linear stability analysis of full governing equations valid for arbitrary wave numbers shows that although fluid rheology
does not influence the dominant length scale of the instability, it significantly affects the growth rate. It is shown that
neglect of inertia and solvent dynamics results in a nonphysical singularity in the growth rate beyond a critical value of
relaxation time. We further carry out numerical simulations of a set of long-wave, nonlinear differential equations (also
derived in Rauscher et al., Eur. Phys. J. E 17, 373 (2005)) governing the evolution of the free surface. The nonlinear simulations, in their domain of validity, confirm
the results of the linear analysis. Interestingly, results from nonlinear simulations further show that both for Newtonian
and viscoelastic liquids, the shape and the dewetting dynamics of a hole are identical when examined in terms of a rescaled
time which depends on rheological parameters. Thus, viscoelasticity of Jeffreys type merely accelerates the growth rate, without
however affecting the important morphological characteristics. 相似文献
3.
Dmytro Shyshlov 《Molecular physics》2013,111(14):1912-1925
We report a rigorous computational treatment of quantum dynamics of cold ions in a double-well trap using the time-dependent Schrödinger equation. Our method employs a numerically accurate approach that avoids approximations, such as assumption of weak coupling between the wells; normal mode nature of vibrations; or harmonic approximation for energy spectrum of the double-well system. Our goal is to reproduce, from first principles, the process of energy swaps between the wells observed in the experiments at NIST [Nature 471, 196 (2011)] and Innsbruck [Nature 471, 200 (2011)]. The model parameters and the initial conditions are carefully chosen to mimic experimental conditions. We obtain accurate energies and wave functions of the system numerically, and study the evolution of motional wave packets to provide new insight. This model reproduces experimental results obtained by NIST and Innsbruck in detail. We explain the energy transfer in terms of wave packet dynamics in the asymmetric potential energy well. We also show that, for a localised initial wave packet, this phenomenon can be interpreted using the terms of classical dynamics, such as trajectory of motion governed by the well-known simple principle: the angle of reflection equals the angle of incidence. 相似文献
4.
Nonlinear vortical structures and soliton formation are investigated for electron temperature gradient instability in a two-electron temperature non-Maxwellian magnetoplasma. The inhomogeneity in magnetic field is also considered. A new set of nonlinear equations, using transport equations of Braginskii”s model, are formulated to study the nonlinear structures. A modified linear dispersion relation of coupled electron temperature gradient (ETG) mode and electron acoustic wave is derived. The ETG instability is found to increase with increase in ηec value that increases with sharp density gradients. The results are applied to auroral region of earth's magnetosphere and the calculated values of the nonlinear electric field of fast solitary waves are found to be in agreement with the Viking satellite observations. 相似文献
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8.
Nonlinear Dynamics of Circularly Polarized Laser Pulse Propagating in a Magnetized Plasma with q ‐Nonextensive Velocity Distributions
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The nonlinear dynamics of a circularly polarized laser pulse propagating in magnetized plasma contains hot nonextensive q ‐distributed electrons and ions is studied theoretically. A nonlinear equation which describes the dynamics of the slowly varying amplitude electromagnetic wave is obtained using the relativistic two‐fluids model. Some nonlinear phenomena include modulational instability, self‐focusing, soliton formation, and longitudinal and transversal evolutions of laser pulse in nonextensive plasma medium are investigated. Results show that the nonextensivity of particles can substantially change the nonlinearity of medium. The external magnetic field enhances the modulation instability growth rate of right‐hand polarization wave but for the left‐hand polarization the growth rate decreases. The spot size of the laser pulse is strongly affected by the plasma nonextensivity. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
9.
Wave properties and instabilities in a magnetized, anisotropic, collisionless, rarefied hot plasma in fluid approx‐imation are studied, using the 16‐moments set of the transport equations obtained from the Vlasov equations. These equations differ from the CGL‐MHD fluid model (single fluid equations by Chew, Goldberger, and Low [5,9]) by including two anisotropic heat flux evolution equations, where the fluxes invalidate the double polytropic CGL laws. We derived the general dispersion relation for linear compressible wave modes. Besides the classic incompressible fire hose modes there appear four types of compressible wave modes: two fast and slow mirror modes – strongly modified compared to the CGL model – and two thermal modes. In the presence of initial heat fluxes along the magnetic field the wave properties become different for the waves running forward and backward with respect to the magnetic field. The well known discrepancies between the results of the CGL‐MHD fluid model and the kinetic theory are now removed: i) The mirror slow mode instability criterion is now the same as that in the kinetic theory. ii) Similarly, in kinetic studies there appear two kinds of fire hose instabilities ‐ incompressible and compressible ones. These two instabilities can arise for the same plasma parameters, and the instability of the new compressible oblique fire hose modes can become dominant. The compressible fire hose instability is the result of the resonance coupling of three retrograde modes ‐ two thermal modes and a fast mirror mode. The results can be applied to the theory of solar and stellar coronal and wind models (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
10.
S. P. Aktershev 《Journal of Engineering Thermophysics》2012,21(1):36-51
This paper investigates two-dimensional waves in a heated liquid film in the presence of the thermocapillary effect. The waves
in the film are described using the integral model. The first part of the paper considers film instability for cases of fixed
temperature of the plate and fixed heat flux in the plate. The liquid temperature disturbance is calculated from the energy
equation for arbitrary values of Peclet number. In the second part, the evolution of waves in a heated film is modeled based
on the system of equations for film thickness, flow rate, and the energy equation. In numerical modeling of the wave evolution,
the boundary of the region of growing disturbances agrees well with results of stability analysis. The calculations show that
for a vertical film the thermocapillary effect leads to broadening of the instability region only at low Peclet numbers. 相似文献
11.
The four-magnon instability of magnetostatic surface waves (MSSWs) in yttrium iron garnet epitaxial films is investigated
experimentally. It is shown that four-magnon instability for MSSWs with wave numbers 30–600 cm−1 is a decay instability and develops for values of the wave magnetization close to the threshold level for second-order parametric
instability of a homogeneous transverse pump wave. When the supercriticality of the MSSW power is 15–20 dB, the generated
parametric spin waves themselves become unstable with respect to the four-magnon interaction, so that kinetic instability
develops in the film. It is shown that the pump signal transmitted through the signal and the length of the “nonlinear” part
of the film, where a MSSW is capable of exciting parametric spin waves, increase as the pump power is increased.
Fiz. Tverd. Tela (St. Petersburg) 38, 330–338 (February 1997) 相似文献
12.
Instability and evolution of nonlinearly interacting water waves 总被引:1,自引:0,他引:1
We consider the modulational instability of nonlinearly interacting two-dimensional waves in deep water, which are described by a pair of two-dimensional coupled nonlinear Schr?dinger equations. We derive a nonlinear dispersion relation. The latter is numerically analyzed to obtain the regions and the associated growth rates of the modulational instability. Furthermore, we follow the long term evolution of the latter by means of computer simulations of the governing nonlinear equations and demonstrate the formation of localized coherent wave envelopes. Our results should be useful for understanding the formation and nonlinear propagation characteristics of large-amplitude freak waves in deep water. 相似文献
13.
This work represents a study of the streamer formation in plasma for XeCl excimer laser at high pressure. It is based on a longitudinal mono-dimensional model of the cathodic zone. In this model, we show the possibility of the streamer development in the cathodic sheath and its propagation during the phase of plasma formation. The model gives the space and time evolution of the electron density and the discharge electric field in the presence of the streamer. The obtained results clearly indicate that, for conditions close to experiments for 50–100 ns laser pulse durations and electron power deposition in the MW/cm3 range in a 300 cm3 chamber, the streamer instability, related to the sheath evolution, patently appears. The drift velocity reaches a typical value of about 108 cm/s. 相似文献
14.
采用大涡模拟方法,对入射激波及其反射激波诱导球形重气泡的变形失稳过程进行了三维数值模拟,利用已有实验验证了计算模型的可靠性,重点考察了反射激波与已经失稳的气泡界面的再次作用,讨论了涡环的形成及其三维失稳的过程。研究结果显示:入射和反射激波与球形重气泡作用产生斜压效应,会在流场中产生旋转方向截然相反的多个涡环;反射激波诱导的涡环具有较小的强度,故更加容易失稳,甚至能完全形成具有流向涡量的复杂小尺度涡结构。 相似文献
15.
V. P. Ruban 《Journal of Experimental and Theoretical Physics》2010,110(3):529-536
The formation of rogue waves in sea states with two close spectral maxima near the wave vectors k
0 ± Δk/2 in the Fourier plane is studied through numerical simulations using a completely nonlinear model for long-crested surface
waves [24]. Depending on the angle θ between the vectors k
0 and Δk, which specifies a typical orientation of the interference stripes in the physical plane, the emerging extreme waves have
a different spatial structure. If θ ≲ arctan(1/√2), then typical giant waves are relatively long fragments of essentially
two-dimensional ridges separated by wide valleys and composed of alternating oblique crests and troughs. For nearly perpendicular
vectors k
0 and Δk, the interference minima develop into coherent structures similar to the dark solitons of the defocusing nonlinear Schroedinger
equation and a two-dimensional killer wave looks much like a one-dimensional giant wave bounded in the transverse direction
by two such dark solitons. 相似文献
16.
S. Keller 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,13(1):51-59
Triple differential cross-sections (TDCS) for (
e
,2
e
) processes on C60 have been calculated in the plane wave Born and distorted wave Born approximations using a jellium shell model to describe
the target valence states. The peculiarities of these TDCS are demonstrated by comparison with results for atomic hydrogen.
Ionisation into a resonant state leads to dramatic modifications of the TDCS. This effect could also be observed in a surface
(
e
,2
e
) experiment in specular geometry using a thin film of physisorbed C60.
Received 14 April 2000 and Received in final form 27 July 2000 相似文献
17.
T.J. Smith H. Capellmann R.K. Kremer K-U. Neumann K.R.A. Ziebeck 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(3):341-347
A polarised neutron scattering investigation has been carried out on a powder sample of CuGeO3 within the temperature range of 1.5 K to 600 K. The magnetic scattering has been separated from all other contributions by
using polarised neutrons and polarisation analysis and placed onto an absolute scale. At low temperatures the long wavelength
components of the paramagnetic response are suppressed consistent with the formation of Cu dimers in which the magnetic moments
are correlated antiferromagnetically. This form of the scattering persists to temperatures well above the dimerisation temperature
T
sp
∼ 14 K. However as the temperature is raised the intensity of the long wavelength spin fluctuations increases and above ∼150 K they are the dominant feature in the wave vector dependence of the response. At all temperatures the observed scattering
extrapolates smoothly to the Q
= 0 value given by the uniform susceptibility. Consequently the thermal variation of the uniform susceptibility arises from the
evolution of the long wavelength magnetic fluctuations. At large wave vectors the energy dependence of the scattering revealed
that the response occurs below 16 meV in agreement with the reported maximum magnetic excitation energy at the zone boundary
in the ground state. However the total magnetic scattering is significantly less than that expected for a local moment system
suggesting that the spectrum of thermal and quantum fluctuations overlap.
Received 30 May 2000 and Received in final form 22 March 2001 相似文献
18.
数值研究了平面激波冲击氮气环境中SF6气泡界面的Richtmyer-Meshkov不稳定性,重点关注其中的激波聚焦及射流的产生和发展过程。在入射激波马赫数为1.23的情况下,给出了压力、密度、数值纹影和涡量等物理量的演化图像,定量分析了流场中压力最大值、密度最大值、射流速度、环量和斜压力矩随时间的变化关系。计算结果表明,平面激波冲击SF6气泡过程有很强的聚能效应,在气泡内部靠近下游极点处发生激波近似理想聚焦和点爆炸现象,直接导致出现二次波系以及向下游运动的细长射流结构。相比入射激波,二次波系产生斜压力矩和涡量的能力要弱得多。 相似文献
19.
An Anderson model with N-fold degeneracy in the Kondo regime is considered. It is presumed that the electron-electron correlations in the system of
f electrons have their maximum strength. A criterion for instability against the formation of a weakly antiferromagnetic phase
superposed on the Kondo state is obtained by the auxiliary-boson method using the 1/N expansion. An effective interaction leading to the formation of magnetic ordering appears because of the spin fluctuations
in the system of localized electrons. The phase diagram of the system is constructed.
Zh. éksp. Teor. Fiz. 111, 600–614 (February 1997) 相似文献
20.
A. Yu. Romanov V. P. Silin S. A. Uryupin 《Journal of Experimental and Theoretical Physics》1997,84(4):687-693
We investigate the Weibel instability in a plasma with a nonstationary three-temperature electron distribution generated by
inverse bremsstrahlung of an intense elliptically polarized electromagnetic wave. We show that electron-ion collisions in
this strong high frequency field are simultaneously the cause of the development of the instability and the reason it is suppressed.
We find plasma and radiation parameters for which spontaneous quasistationary solenoidal electromagnetic fields can increase
by many times.
Zh. éksp. Teor. Fiz. 111, 1245–1257 (April 1997) 相似文献