Replica molding of elastomeric materials has proven to be an extremely useful new technology for the formation of complex microfluidic systems. Recent demonstrations of convenient methods for production of such systems by simple, rapid methods that do not require expensive fabrication facilities have enabled the extensive use of microsystems in research and development into a host of new application fields. This report describes a simple new method for fabricating active elastomeric components in microfluidic systems that is based on deformation of elastic materials that have been impregnated or coated with magnetic materials. Computer controlled miniature electromagnets are used to activate switching valves within microfluidics systems. Similar fabrication techniques can be easily extended to construct complex, and potentially completely integrated, microfluidic systems containing active valves, pumps, injectors, mixers, and flow controllers. Preliminary results indicate fabrication of channels approximately 200 m in width, with valves approximately 5 mm in size ͑including both valve chamber and valve actuator͒. The fabrication cycle time is on the order of one day using readily available benchtop equipment, and the valves seal hermetically against a 1.5 kPa back pressure.

Background:Online mixing for continuous highthroughput flow cytometry has not been previously described. A simple, general high-throughput method for mixing and delivery of submicroliter volumes in laminar flow at low Reynolds numbers would be widely useful. Materials and Methods:We describe a micromixing approach that is compatible with commercial autosamplers, flow cytometry, and other detection schemes that require mixing of components that have been introduced into laminar flow. The scheme is based on a previous approach to high-throughput flow cytometry (HyperCyt™, Kuckuck et al.: Cytometry 44:83-90, 2001). We showed that samples from multiwell plates that have been picked up by an autosampler can be separated during delivery by the small air bubbles introduced during the transit of the autosampler probe from well to well. Here, a particle sample flowing continuously is brought together in a Y with reagent samples from wells, which have been separated by bubbles.

A method is presented for predicting the distribution of orientation of rigid short fibers in thin compression molded parts. The method extends Folgar and Tucker's model for fiber orientation in a concentrated suspension to the case of spatially non-uniform flows and orientation states. A generalized Hele-Shaw model is used to predict flow and deformation during mold filling. Other assumptions are appropriate for sheet molding compound : fibers much longer than the part thickness and a cold material molded in a hot mold. The predictions compare favorably to experiments on sheet molding compound and on a model suspension of nylon monofilaments in silicone oil.

Composite materials remain extremely vulnerable to out-of-plane impact loads, which may lead to severe losses in strength and stiffness. Impact induced damage is often a complex mixture of transverse cracks, delaminations and fiber failures. An ex perimental investigation was undertaken to quantify damage tolerance and resistance in composite materials impacted using the drop-weight method. Tests were conducted on laminates of several different carbon-fiber composite systems such as epoxies, modified epoxies, and amorphous and semicrystalline thermoplastics. In this paper, impacted com posite specimens have been examined using destructive and nondestructive techniques to establish the characteristic damage states. Specifically, optical microscopy, ultrasonic and scanning electron microscopy techniques have been used to identify impact induced damage mechanisms. Damage propagation during post impact compression was also stud ied.