Three-dimensional automated nanoparticle tracking using Mie scattering in an optical microscope.

The forward scattering of light in a conventional inverted optical microscope by nanoparticles ranging in diameter from 10 to 50nm has been used to automatically and quantitatively identify and track their location in three-dimensions with a temporal resolution of 200ms. The standard deviation of the location of nominally stationary 50-nm-diameter nanoparticles was found to be about 50nm along the light path and about 5nm in the plane perpendicular to the light path. The method is based on oscillating the microscope objective along the light path using a piezo actuator and acquiring images with the condenser aperture closed to a minimum to enhance the effects of diffraction. Data processing in the time and spatial domains allowed the location of particles to be obtained automatically so that the technique has potential applications both in the processing of nanoparticles and in their use in a variety of fields including nanobiotechnology, pharmaceuticals and food processing where a simple optical microscope maybe preferred for a variety of reasons.

Finite element analysis of a total knee replacement by using Gauss point contact constraints.

Finite element methods have been applied extensively and with much success in the analysis of orthopaedic hip and knee implants. Very recently a burgeoning interest has developed, in the finite element community, in how numerical models can be constructed for the solution of problems in contact mechanics. New developments in this area are of paramount importance in the design of implants for orthopaedic surgery. Modern techniques are described for finite element contact analysis and applied to two problems of stress analysis in a plastic tibial component. In the former, results are compared with a previous finite element analysis and with Hertzian solutions. In the latter, an estimate of the extent of convergence of the finite element solutions is provided.