Search results for " Nonlinear"
showing 10 items of 1224 documents
Brownian dynamics simulations of colloidal hard spheres. Effects of sample dimensionality on self-diffusion
1994
The self-diffusion coefficients of colloidal hard spheres were determined by Brownian dynamics (BD) computer simulations using a new efficient algorithm for treatment of the hard-sphere interactions. Calculations were done on an Apple PC type MacIIcx and on a Micro VAX 3000, considering samples in two and three dimensions at varying particle concentrations. Our results in three dimensions are compared with experimental results from our own group which were obtained by forced Rayleigh scattering (FRS), and with numerical results from a dynamical Monte Carlo simulation by Cichocki and Hinsen. Good agreement with the latter was found for particle volume fractions up to 0.40. Differences in the…
Multivalued solutions for the output intensity of a semilinear photorefractive oscillator and stability analysis
2007
The analysis of pump-ratio dependences of the output intensity for a semilinear photorefractive coherent oscillator reveals two domains of multivalued solutions for sufficiently large coupling strength ensured by the crystal. We show that even in a strictly degenerate case the nonzero output intensity can be reached in a broad range of pump ratios r from 10−6 to infinity, including the interval where both pump intensities coincide or are very close to each other. This does not contradict the existence of the known gap in the oscillation threshold near the equal intensities of two pump waves: in this particular region the oscillation is not self-starting. The output intensities for frequency…
Collective Effects in Random Sequential Adsorption of Diffusing Hard Squares
1992
We study by Monte Carlo computer simulations random sequential adsorption (RSA) with diffusional relaxation, of lattice hard squares in two dimensions. While for RSA without diffusion the coverage approaches its maximum jamming value (large-time fractional coverage) exponentially, added diffusion allows the deposition process to proceed to the full coverage. The approach to the full coverage is consistent with the t**(-1/2) power law reminiscent of the equilibrium cluster coarsening in models with nonconserved order-parameter dynamics.
Realization of a space reversal operator
2002
In this paper we propose the realization of a bosonic-fermionic interaction in the context of trapped ions whose effect upon the ion center of mass degrees of freedom is properly speaking a spatial inversion. The physical system and its features are accurately described and some applications are briefly discussed.
Coupled plasmonic graphene wires: theoretical study including complex frequencies and field distributions of bright and dark surface plasmons
2020
Theoretical research on localized surface plasmons (LSPs) supported by a structure formed by two parallel dielectric wires with a circular cross section wrapped with a graphene sheet has an impact in the practical realm. Here, LSPs are represented in the form of an infinite series of cylindrical multipole partial waves linked to each of the graphene wires. To obtain the kinematics (complex eigenfrequencies) and dynamic characteristics (field distributions) of the LSPs, we consider the analytic extension to the complex plane of the solution to the boundary value problem. The lower frequency LSP group is formed by four branches, two of them corresponding to bright modes and the others to dark…
Enhancement of electron spin lifetime in GaAs crystals: the benefits of dichotomous noise
2013
The electron spin relaxation process in n-type GaAs crystals driven by a fluctuating electric field is investigated. Two different sources of fluctuations are considered: (i) a symmetric dichotomous noise and (ii) a Gaussian correlated noise. Monte Carlo numerical simulations show, in both cases, an enhancement of the spin relaxation time by increasing the amplitude of the external noise. Moreover, we find that the electron spin lifetime versus the noise correlation time: (i) increases up to a plateau in the case of dichotomous random fluctuations, and (ii) shows a nonmonotonic behaviour with a maximum in the case of bulks subjected to a Gaussian correlated noise.
External Noise Effects in Doped Semiconductors Operating Under sub-THz Signals
2012
We study the noise-induced effects on the electron transport dynamics in low-doped n-type GaAs samples by using a Monte Carlo approach. The system is driven by an external periodic electric field in the presence of a random telegraph noise source. The modifications caused by the addition of external fluctuations are investigated by studying the spectral density of the electron velocity fluctuations for different values of the noise parameters. The findings indicate that the diffusion noise in low-doped semiconductors can be reduced by the addition of a fluctuating component to the driving electric field, but the effect critically depends on the features of the external noise source.
Modeling of the photorefractive nonlinear response in Sn_2P_2S_6 crystals
2007
We develop a theory of the photorefractive nonlinear response for Sn2P2S6 crystals. The theory incorporates two types of charge carrier (optically active and passive), provides explicit expressions for the characteristic buildup-relaxation rates and gain factors, explains naturally a big variety of accumulated experimental data, and facilitates characterization-optimization of this important nonlinear material.
Role of dispersion on zero-average-index bandgaps
2009
We consider periodic multilayers combining ordinary positive index materials and dispersive metamaterials with negative index in some frequency ranges. These structures can exhibit photonic bandgaps which, in contrast with the usual Bragg gaps, are not based on interference mechanisms. Changing the dispersion models for the constituent metamaterial, we investigate its role in the production of zero-average-index bandgaps. In particular, we show the effect of each constitutive parameter on both bandgap edges. Finally, we give some approximated analytical expressions in terms of average parameters for the determination of the upper and lower limits of the zero-average refractive-index bandgap…
Slowing down of light pulses using backward-wave four-wave mixing with local response
2015
The slowing down of light pulses is achieved using backward-wave four-wave mixing in a medium with local response. A Bi12TiO20 crystal with an external dc field is used in the experiment as a proof-of-concept material. The delay and shape transformation of output pulses are studied and compared for the transmitted and phase conjugate channels. It is shown that the phase conjugate pulse achieves a longer delay under typical experimental conditions with equal intensities of the pump beams. This advantage of the phase conjugate beam is especially pronounced for short pulses with half-widths smaller than the response time of the medium. The agreement of the experimental results with numerical c…