Biomedical subjects

C Y Soong

Publications and source records attributed to C Y Soong.

4 recordsLinked to original sources

PubMed2004

Controlling chaos with weak periodic signals optimized by a genetic algorithm.

In the present study we develop a relatively novel and effective chaos control approach with a multimode periodic disturbance applied as a control signal and perform an in-depth analysis on this nonfeedback chaos control strategy. Different from previous chaos control schemes, the present method is of two characteristic features: (1) the parameters of the controlling signal are optimized by a genetic algorithm (GA) with the largest Lyapunov exponent used as an index of the stability, and (2) the optimization is justified by a fitness function defined with the target Lyapunov exponent and the controlling power. This novel method is then tested on the noted Rössler and Lorenz systems with and without the presence of noise. The results disclosed that, compared to the existing chaos control methods, the present GA-based control needs only significantly reduced signal power and a shorter transient stage to achieve the preset control goal. The switching control ability and the robustness of the proposed method for cases with sudden change in a system parameter and/or with the presence of noise environment are also demonstrated.

Journal Article↗

PubMed2004

Analysis of rotation-driven electrokinetic flow in microscale gap regions of rotating disk systems.

In the present study, a novel theoretical model is developed for the analysis of rotating thermal-fluid flow characteristics in the presence of electrokinetic effects in the microscale gap region between two parallel disks under specified electrostatic, rotational, and thermal boundary conditions. The major flow configuration considered is a rotor-stator disk system. Axisymmetric Navier-Stokes equations with consideration of electric body force stemming from streaming potential are employed in the momentum balance. Variations of the fluid viscosity and permittivity with the local fluid temperature are considered. Between two disks, the axial distribution of the electric potential is determined by the Poisson equation with the concentration distributions of positive and negative ions obtained from Nernst-Planck equations for convection-diffusion of the ions in the flow field. Effects of disk rotation and electrostatic and thermal conditions on the electrokinetic flow and thermal characteristics are investigated. The electrohydrodynamic mechanisms are addressed with an interpretation of the coupling nature of the electric and flow fields. Finally, solutions with electric potential determined by employing nonlinear or linearized Poisson-Boltzmann equation and/or invoking assumptions of constant properties are compared with the predictions of the present model for justification of various levels of approximation in solution of the electrothermal flow behaviors in rotating microfluidic systems.

Journal Article↗

PubMed2003

Theoretical analysis of electrokinetic flow and heat transfer in a microchannel under asymmetric boundary conditions.

The main theme of the present work is to investigate the electrokinetic effects on liquid flow and heat transfer in a flat microchannel of two parallel plates under asymmetric boundary conditions including wall-sliding motion, unequal zeta potentials, and unequal heat fluxes on two walls. Based on the Debye-Huckel approximation, an electrical potential solution to the linearized Poisson-Boltzmann equation is obtained and employed in the analysis. The analytic solutions of the electrical potential, velocity distributions, streaming potential, friction coefficient, temperature distribution, and heat transfer rate are obtained, and thereby the effects of electrokinetic separation distance (K), zeta-potential level (zeta;(1)), ratio of two zeta potentials (r(zeta) identical with zeta;(2)/zeta;(1)), wall-sliding velocity (u(w)), and heat flux ratio (r(q) identical with q"(2)/q"(1)) are investigated. The present results reveal the effects of wall-sliding and zeta-potential ratio on the hydrodynamic nature of microchannel flow, and they are used to provide physical interpretations for the resultant electrokinetic effects and the underlying electro-hydrodynamic interaction mechanisms. In the final part the results of potential and velocity fields are applied in solving the energy equation. The temperature distributions and heat transfer characteristics under the asymmetrical kinematic, electric, and thermal boundary conditions considered presently are dealt with.

Journal Article↗

PubMed1991

Malignant melanoma: a clinicopathologic study of 22 cases.

To provide updated clinicopathologic information on malignant melanoma, we studied 22 cases of malignant melanoma registered at Tri-Service General Hospital, Taiwan from 1983 to 1988. About 60% (13/22) of the patients had a tumor thickness of more than 2.5 mm and 45% (10/22) of the patients of over 4 mm. No patient had a thin melanoma (tumor thickness less than 0.76mm) when first diagnosed. Forty-four percent of the patients, which was twice as many as those (22%) in a previous study done at the same hospital, were classified as stage III. Eleven patients (50%) had acral lentiginous melanoma, the most common type of malignant melanoma in Orientals as previously reported. The cumulative survival rate was 59% and 39% at 3 years and 5 years respectively. The age primary sites, clinical stage and tumor thickness were retrospectively evaluated. Due to the small sample size, the accuracy of the statistical analysis of survival is questionable. An extensive island-wide multicenter epidemiologic study is mandatory to clarify this issue.

Adult↗