共查询到20条相似文献,搜索用时 406 毫秒
1.
We investigate a continuous Heisenberg spin chain equation which models the local magnetization in ferromagnet with time-and site-dependent inhomogeneous bilinear interaction and timedependent spin-transfer torque.By establishing the gauge equivalence between the spin chain equation and an integrable generalized nonlinear Schr?dinger equation,we present explicitly a novel nonautonomous magnetic soliton solution for the spin chain equation.The results display how the dynamics of the magnetic soliton can be controlled by the bilinear interaction and spin-polarized current.Especially,we find that the site-dependent bilinear interaction may break some conserved quantity,and give rise to damping-like effect in the spin evolution. 相似文献
2.
Magnetization dynamics in uniformly magnetized ferromagnetic media is studied by using Landau-Lifshitz-Gilbert equation. The nonlinear evolution equation is integrable with site-dependent and biquadratic exchange interaction by means of Landau-Lifshitz (LL) equation which is well understood. In the present work, we construct the exact solitary solutions of the nonlinear evolution equation, particularly, we employ the modified extended tangent hyperbolic function method. We show the shape changing property of solitons for the given integrable system in the presence of damping as well as inhomogeneities. 相似文献
3.
The variational method is applied to the study of charge
transfer in dry DNA by using an extended Holstein small polaron
model in two cases: the site-dependent finite-chain discrete
case and the site-independent continuous one. The treatments in the two cases
are proven to be consistent in theory and calculation. Discrete
and continuous treatments of Holstein model both can yield a
nonlinear equation to describe the charge migration in an actual
long-range DNA chain. Our theoretical results of binding energy
Eb, probability amplitude of charge carrier \phi and the
relation between energy and charge--lattice coupling strength are
in accordance with the available experimental results and recent
theoretical calculations. 相似文献
4.
We study the trapping process of moving discrete solitons by linear and nonlinear impurities embedded in a one-dimensional nonlinear cubic array. We show that there exist specific values for the strength of the impurity and for the angle where a strong trapping is obtained. We introduce a criterion for studying the scattering dynamics of localized waves in nonlinear extended systems where the trapping of energy takes place. 相似文献
5.
We study a disordered, driven zero range process which models a closed system of attractive particles that hop with site-dependent rates and whose steady state shows a condensation transition with increasing density. We characterize the dynamical properties of the mass fluctuations in the steady state in one dimension both analytically and numerically and show that there is a dynamic phase transition in the density-disorder plane. We also determine the form of the scaling function which describes the growth of the condensate as a function of time, starting from a uniform density distribution. 相似文献
6.
We show theoretically that it is possible to trap light in a microresonator structure by use of four-wave mixing. The efficiency of the parametric process is substantially increased by the high group delay of light inside the structure. The energy that is trapped has a half-life of approximately 500 ps in the presence of both linear and nonlinear loss in the channel waveguides and resonators. We also demonstrate that the energy can be extracted from the cavity with a similar process. 相似文献
7.
8.
We report the experimental demonstration of a nonlinear process in a two-level system, in which the amplitude of the excited state decays, transferring irreversibly a large fraction of its energy to the ground state, while shedding a part of it into radiation states. The experiments where preformed in a nonlinear optical waveguide, supporting two or three modes. The process is general, and is expected to occur in other nonlinear few level systems such as nonlinear quantum wells and Bose-Einstein condensates. 相似文献
9.
Highly efficient nonlinear filter for femtosecond pulse contrast enhancement and pulse shortening 总被引:1,自引:0,他引:1
Jullien A Rousseau JP Mercier B Antonucci L Albert O Chériaux G Kourtev S Minkovski N Saltiel SM 《Optics letters》2008,33(20):2353-2355
We propose a highly efficient scheme for temporal filters devoted to femtosecond pulse contrast enhancement. The filter is based on cross-polarized wave generation with a spatially suger-Gaussian-shaped beam. In a single nonlinear crystal scheme the energy conversion to the cross-polarized pulse can reach 28%. We demonstrate that the process enables a significant spectral broadening. For an efficiency of 23% the pulse shortening is estimated to 2.2, leading to an intensity transmission of the nonlinear filter of 50%. 相似文献
10.
We present a detailed analysis of the modulational
instability of the zone-boundary mode for one and higher-dimensional
Fermi–Pasta–Ulam (FPU) lattices. The growth of the instability is followed by
a process of relaxation to equipartition, which we have
called the Anti-FPU problem because the energy is initially
fed into the highest frequency part of the spectrum, while in the
original FPU problem low frequency excitations of the
lattice were considered. This relaxation process leads to the formation of chaotic
breathers in both one and two space dimensions. The system then relaxes to
energy equipartition, on time scales that increase as the energy
density is decreased. We supplement this study by considering the
nonconservative case, where the FPU lattice is homogeneously driven at
high frequencies. Standing and travelling nonlinear waves and
solitonic patterns are detected in this case. Finally we investigate
the dynamics of the FPU chain when one end is driven at a frequency located
above the zone boundary. We show that this excitation stimulates
nonlinear bandgap transmission effects. 相似文献
11.
Direct measurements of nonlinear absorption and refraction in solutions of phthalocyanines 总被引:1,自引:0,他引:1
T. H. Wei D. J. Hagan M. J. Sence E. W. Van Stryland J. W. Perry D. R. Coulter 《Applied physics. B, Lasers and optics》1992,54(1):46-51
We report direct measurements of the excited singlet state absorption cross section and the associated nonlinear refractive cross section using picosecond pulses at 532 nm in solutions of phthalocyanine and naphthalocyanine dyes. By monitoring the transmittance and far field spatial beam distortion for different pulsewidths in the picosecond regime, we determine that both the nonlinear absorption and refraction are fluence (energy per unit area) rather than irradiance dependent. Thus, excited state absorption (ESA) is the dominant nonlinear absorption process, and the observed nonlinear refraction is also due to real population excitation. 相似文献
12.
D. T. Hristopulos L. Leonidakis A. Tsetsekou 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,50(1-2):83-87
The evolution of grain structures in materials is a complex and multiscale process that determines the material's final properties [1].
Understanding the dynamics of grain growth is a key factor for controlling this process.
We propose a phenomenological approach, based on a nonlinear, discrete mass transfer equation for the evolution of an arbitrary
initial grain size distribution.
Transition rates for mass transfer across grains
are assumed to follow the Arrhenius law, but
the activation energy depends on the degree of amorphization of
each grain.
We argue that the magnitude of the activation energy controls the
final (sintered) grain size distribution, and we verify this prediction
by numerical simulation of mass transfer in a one-dimensional
grain aggregate. 相似文献
13.
14.
A nonlinear chain driven by one end may propagate energy in the forbidden band gap by means of nonlinear modes. For harmonic driving at a given frequency, the process occurs at a threshold amplitude by sudden large energy flow that we call nonlinear supratransmission. The bifurcation of energy transmission is demonstrated numerically and experimentally on the chain of coupled pendula (sine-Gordon and nonlinear Klein-Gordon equations) and sustained by an extremely simple theory. 相似文献
15.
In this paper, we use a nonlinear decohering quantum model to study the initial step of photosynthesis which is an ultrafast transfer process of absorption the sunlight by light-harvesting complexes and electronic excitation transfer to the reaction center(RC). In this decohering model, the Hamiltonian of the system commutes with the systemenvironment interaction. We take B850 ring of light-harvesting complex II(LH-II) in purple bacteria as an example to calculate the efficiency of the energy transfer as a function of time. We find that the environmental noise can make the LH-II have stable energy transfer efficiency over a long time. This is to say that the environmental noise which is the decohering source has advantage of the energy transfer in the process of photosynthesis. 相似文献
16.
We study the statistical properties of homogeneous and isotropic three-dimensional (3D) turbulent flows. By introducing a novel way to make numerical investigations of Navier-Stokes equations, we show that all 3D flows in nature possess a subset of nonlinear evolution leading to a reverse energy transfer: from small to large scales. Up to now, such an inverse cascade was only observed in flows under strong rotation and in quasi-two-dimensional geometries under strong confinement. We show here that energy flux is always reversed when mirror symmetry is broken, leading to a distribution of helicity in the system with a well-defined sign at all wave numbers. Our findings broaden the range of flows where the inverse energy cascade may be detected and rationalize the role played by helicity in the energy transfer process, showing that both 2D and 3D properties naturally coexist in all flows in nature. The unconventional numerical methodology here proposed, based on a Galerkin decimation of helical Fourier modes, paves the road for future studies on the influence of helicity on small-scale intermittency and the nature of the nonlinear interaction in magnetohydrodynamics. 相似文献
17.
Jian Ping Ma Otto Nachtmann Manfred Wirbel 《Zeitschrift fur Physik C Particles and Fields》1986,30(3):407-411
We consider the decay of the intermediate vector bosonZ into two fermions and two Goldstone fermions in a model realizing supersymmetry in a nonlinear way. Since the Goldstone fermions are neutrino-like particles, the experimental signature would be two leptons or two jets together with missing energy. We show that for a scale of spontaneous supersymmetry breaking of the order 70 GeV the rate for this process should be detectable in LEP-experiments. 相似文献
18.
We shall construct a hierarchy of subclasses of the 16-vertex model having qualitatively different symmetry properties. We determine the bifurcation points in the parameter space of the model where new symmetry elements are added to the invariance group of the partition function. In this paper we restrict ourselves to the study of site-dependent transformations converting a homogeneous 16-vertex model into a different homogeneous model. Apart from a trivial transformation, resulting in a change of sign of all vertex weights, such site-dependent transformations exist only for those points in parameter space where particular relations are satisfied. The solution of these relations gives rise to three 6-parameter families of models, two of which are equivalent to the general 8-vertex model, and two families of 4-parameter models. The primary bifurcation models depending on six parameters contain three different types of secondary bifurcation models, depending on 4 parameters, one of which is equivalent to Baxter's symmetric 8-vertex model. 相似文献
19.
A unified approximation method is derived to illustrate the effect of electro-mechanical coupling on vibration-based energy harvesting systems caused by variations in damping ratio and excitation frequency of the mechanical subsystem. Vibrational energy harvesters are electro-mechanical systems that generate power from the ambient oscillations. Typically vibration-based energy harvesters employ a mechanical subsystem tuned to resonate with ambient oscillations. The piezoelectric or electromagnetic coupling mechanisms utilized in energy harvesters, transfers some energy from the mechanical subsystem and converts it to an electric energy. Recently the focus of energy harvesting community has shifted toward nonlinear energy harvesters that are less sensitive to the frequency of ambient vibrations. We consider the general class of hybrid energy harvesters that use both piezoelectric and electromagnetic energy harvesting mechanisms. Through using perturbation methods for low amplitude oscillations and numerical integration for large amplitude vibrations we establish a unified approximation method for linear, softly nonlinear, and bi-stable nonlinear energy harvesters. The method quantifies equivalent changes in damping and excitation frequency of the mechanical subsystem that resembles the backward coupling from energy harvesting. We investigate a novel nonlinear hybrid energy harvester as a case study of the proposed method. The approximation method is accurate, provides an intuitive explanation for backward coupling effects and in some cases reduces the computational efforts by an order of magnitude. 相似文献
20.
The optical limiting effect based on stimulated Brillouin scattering (SBS) in a nonlinear medium was investigated. We numerically treated the nonlinear propagation process with a theoretical model, which includes the spontaneous nature of the initiation of SBS, and obtained optical limiting effect in the process. Energy limiting, pulse reshaping and stabilization have been demonstrated on SBS mechanism with the nonlinear medium CCl_4. The input optical signals were Nd:YAG nanosecond laser pulses with width varying from 16ns to 7ns then to 2ns, the relationship between the transmitted signal and launched pump signal was shown. In the experimental regime, the most stable pulse and a superior energy stabilization of the transmitted pulse were obtained when the laser pulse-width became as short as 2ns. For the energy variation of laser pulses in a wide range of 14-88mJ, the output energy was limited in a quite narrow range 4.5-5.5mJ. 相似文献