Biomedical subjects

Wing Yim Tam

Publications and source records attributed to Wing Yim Tam.

5 recordsLinked to original sources

PubMed2006

Static shear modulus of electrorheological fluids.

We report measurements of the static shear modulus of electrorheological (ER) fluids consisting of water-wetted silica microspheres in silicone oil. A shear-annealing method, using creep-recovery (CR) cycles under an external electric field, is used to enhance ER properties of the fluid. The shear-annealing method enables the silica spheres in the ER fluid to form better aligned and denser column microstructures. A stable state with elastic shear deformation is obtained after a sufficient number of CR cycles, with an optimal combination of stress duration and shear strength. Static shear modulus is obtained by measuring the elastic deformations at different shear stresses for an electric field frequency from 10 to 1000 Hz. A water-bridge model is proposed to explain the enhanced shear modulus.

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PubMed2005

Photonic band gap effect and structural color from silver nanoparticle gelatin emulsion.

We have fabricated planar structures of silver nanoparticles in monochromatic gelatin emulsion with a continuous spacing ranging from 0.15-0.40 micron using a two-beam interference of a single laser source. Our planar holograms display a colorful "rainbow" pattern and photonic bandgaps covering the visible and IR ranges. We model the planar silver nanoparticle-gelatin composite system using an effective medium approach and good agreement is obtained between theory and experiment.

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PubMed2005

Structural transition in bidispersed electrorheological fluids.

We present results from finite element calculations on electrorheological fluids consisting of bidispersed dielectric microspheres and nanoparticles suspended in liquid, with one type much smaller than the other. The face-centered-cubic (fcc) structure of the larger microspheres is shown to be the ground state when the volume concentration of the nanoparticles is between 3-5 %. This is in contrast to the usual situation in which the body-centered-tetragonal (bct) structure is the lowest-energy state. As a function of the nanoparticles' concentration, the bct-fcc structural transition occurs when the nanoparticles' dielectric constant exceeds a threshold value, leading to the electrostatic energy curves of the two structures crossing each other.

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PubMed2003

Shear-enhanced yield stress in electrorheological fluids.

We report the enhancement of yield stress in electrorheological (ER) fluids by a shear-annealing method, using creep-recovery (CR) cycles under an external electric field. The enhancement depends on the duration and the strength of the applied shear stress, as well as on the number of the CR cycles. The shear-annealing method enables the particles in the ER fluid to form microstructures with an increased yield stress, manifest as better aligned and denser columns. For a sufficiently large number of CR cycles, with an optimal combination of stress duration and shear strength, a stable state can be obtained whereby shear deformation becomes elastic.

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PubMed2002

Cluster persistence of two-dimensional soap froth.

We report on the persistence decay of cell clusters in dynamical simulation of two-dimensional soap-froth as a function of the cluster volume fraction. Both slow gas diffusion and fast dynamical topological processes between cells are incorporated in the simulation. While the simulation yields decay rate in good agreement with two-dimensional soap-froth experiment, it shows a faster decay in comparison to measurements and calculations of persistence in other curvature-driven systems. The fraction of individual cells that contain persistent area also decays due to significant cell movements, confirming that the neighbor swapping T1 topological transition is important in froth coarsening.

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