Biomedical subjects

G W Wei

Publications and source records attributed to G W Wei.

8 recordsLinked to original sources

PubMed2003

Local spectral time-domain method for electromagnetic wave propagation.

We explore the feasibility of using a local spectral time-domain (LSTD) method to solve Maxwell's equations that arise in optical and electromagnetic applications. The discrete singular convolution (DSC) algorithm is implemented in the LSTD method for spatial derivatives. Fourier analysis of the dispersive error of the DSC algorithm indicates that its grid density requirement for accurate simulations can be as low as approximately two grid points per wavelength. The analysis is further confirmed by numerical experiments. Our study reveals that the LSTD method has the potential to yield high resolution for solving large-scale electromagnetic problems.

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PubMed2002

Tailoring wavelets for chaos control.

Chaos is a class of ubiquitous phenomena and controlling chaos is of great interest and importance. In this Letter, we introduce wavelet controlled dynamics as a new paradigm of dynamical control. We find that by modifying a tiny fraction of the wavelet subspaces of a coupling matrix, we could dramatically enhance the transverse stability of the synchronous manifold of a chaotic system. Wavelet controlled Hopf bifurcation from chaos is observed. Our approach provides a robust strategy for controlling chaos and other dynamical systems in nature.

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PubMed2002

Synchronization and information processing by an on-off coupling.

This paper proposes an on-off coupling process for chaos synchronization and information processing. An in depth analysis for the net effect of a conventional coupling is performed. The stability of the process is studied. We show that the proposed controlled coupling process can locally minimize the smoothness and the fidelity of dynamical data. A digital filter expression for the on-off coupling process is derived and a connection is made to the Hanning filter. The utility and robustness of the proposed approach is demonstrated by chaos synchronization in Duffing oscillators, the spatiotemporal synchronization of noisy nonlinear oscillators, the estimation of the trend of a time series, and restoration of the contaminated solution of the nonlinear Schrödinger equation.

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PubMed2002

Transition from intermittency to periodicity in lag synchronization in coupled Rössler oscillators.

The dynamical and statistical behavior of lag synchronization in two coupled self-sustained chaotic Rössler oscillators is reexamined. The lack of uniqueness in the conventional characterization of lag synchronization based on the similarity function has caused much skepticism about the existence of lag synchronization. We provide an evidence that the emergence of lag synchronization is associated with the transition from on-off intermittency to a periodic structure in the laminar phase distribution.

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PubMed2002

Controlling wake turbulence.

This Letter introduces a control strategy for taming the wake turbulence behind a cylinder. An angular momentum injection scheme is proposed to synchronize the vertical velocity field. We show that the base suction, wake formation length, absolute instability, and the Kármán vortex street are effectively controlled by the angular momentum injection. A control equation is designed to implement the injection. The Navier-Stokes equations, along with the control equation, are solved. The occurrence of a new recirculation free zone is identified.

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PubMed2001

Synchronization of single-side locally averaged adaptive coupling and its application to shock capturing.

We propose a single-sided locally averaged adaptive coupling scheme for the synchronization of spatially extended systems. Coupling and synchronization are analyzed from the viewpoint of image filter construction and numerical dissipation. Single-sided locally averaged coupling is introduced based on the resolution argument of control process. Control sensors are adaptively selected and automatically adjusted according to the magnitude of local oscillations. We demonstrate that the present scheme can effectively suppress and control spatiotemporal oscillations and, thus, provide a powerful approach for shock capturing. Both the Navier-Stokes equation and Burgers' equation are used to illustrate the idea.

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PubMed1999

Integrating the Kuramoto-Sivashinsky equation in polar coordinates: application of the distributed approximating functional approach.

An algorithm is presented to integrate nonlinear partial differential equations, which is particularly useful when accurate estimation of spatial derivatives is required. It is based on an analytic approximation method, referred to as distributed approximating functionals (DAF's), which can be used to estimate a function and a finite number of derivatives with a specified accuracy. As an application, the Kuramoto-Sivashinsky (KS) equation is integrated in polar coordinates. Its integration requires accurate estimation of spatial derivatives, particularly close to the origin. Several stationary and nonstationary solutions of the KS equation are presented, and compared with analogous states observed in the combustion front of a circular burner. A two-ring, nonuniform counter-rotating state has been obtained in a KS model simulation of such a burner.

Journal Article↗

PubMed1999

[Effect of enkephalin on glial neurotrophic function related to the reduction of nitric oxide production].

The effect of methionine-enkephalin (ME) on glial neurotrophic function was studied in rat cortical glial-neuronal coculture. The results showed that ME-treated glia enhanced neuronal survival by 28% (P < 0.05), and increased total neurite length per neuron by 11% (P < 0.05), while the expression of GAP-43 mRNA by 26% (P < 0.05). The effect of ME on NO production of glia was also studied in rat cortical glial culture. The result showed that different concentrations of ME (10(-12), 10(-10), 10(-8), 10(-6) mol/L) inhibited glial NO production. All the above show that the increase of glial neurotrophic ability by ME may be due to the inhibition of glial NO production.

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