A new method for mass fabrication of metallic microstructures

 This paper reports on a new method for the production of metallic microstructures with high aspect ratios that combines the advantages of injection moulding with the high precision replication of surfaces by galvanic and electroless metal deposition. LIGA made moulding tools are used to produce plastic “lost forms”, which are partially metallized by a silver cluster beam of high directionality to achieve electrical conductivity. For structures with an interconnected Ag layer at the bottom, galvanic metal deposition is used to form massive microstructures without voids. For isolated structures where contacting is not possible, chemical deposition was used for metal build-up starting from the metallized areas. However, massive electroless deposition beyond about 3 μm was not yet possible due to problems with internal stress in the deposited metal layer that cause delamination from the template. This stress must be reduced by appropriate modifications of the electrolyte. Received: 25 August 1997/Accepted: 22 September 1997     

Development of filter functions for protein-ligand docking.

Current docking methods can generate bound conformations of a ligand close to the experimentally observed structure of a protein-ligand complex. However, the scoring functions used to evaluate the potential solutions are not yet reliable enough at giving the highest ranks to the best structure predictions. One approach to this problem is the use of filter functions that are applied to all docked conformations to remove structures with certain energetically unfavorable properties. We present a computationally efficient scheme for such a postprocessing of docking results. For each of the conformations generated for a given protein-ligand complex, four properties are calculated: the fraction of the ligand volume buried inside the binding pocket, the size of lipophilic cavities along the protein-ligand interface, the solvent-accessible surface (SAS) of nonpolar parts of the ligand, and the number of close contacts between nonhydrogen-bonded polar atoms of the ligand and the protein. These four terms were used to filter out the majority of the calculated solutions and to rescore the remaining ones. On a test set of 32 protein-ligand complexes, this protocol significantly improves the accuracy of the structure predictions.     

A game theoretic fault detection filter

The fault detection process is approximated with a disturbance attenuation problem. The solution to this problem, for both linear time-varying and time-invariant systems, leads to a game theoretic filter which bounds the transmission of all exogenous signals except the fault to be detected. In the limit, when the disturbance attenuation bound is brought to zero, a complete transmission block is achieved by embedding the nuisance inputs into an unobservable, invariant subspace. Since this is the same invariant subspace structure seen in some types of detection filters, we can claim that the asymptotic game filter is itself a detection filter. One can also make use of this subspace structure to reduce the order of the limiting game theoretic filter by factoring this invariant subspace out of the state space. The resulting lower dimensional filter will then be sensitive only to the failure to be detected. A pair of examples given at the end of the paper demonstrate the effectiveness of the filter for time-invariant and time-varying problems in both full-order and reduced-order forms     

Oxide dispersion strengthening of nickel electrodeposits for microsystem applications

Oxide dispersion strengthened nickel (ODS-Ni) electrodeposits were fabricated to net shape using the lithography, electroforming, and molding (LIGA) process in a nickel sulfamate bath containing a suspension of 10 nm diameter Al₂O₃ particulates. Mechanical properties were compared to baseline specimens fabricated using an identical sulfamate bath chemistry without the particulates. Results revealed that the as-deposited ODS-Ni exhibited significantly higher yield strength and ultimate tensile strength (∼50 pct) than the baseline material. This increase in as-deposited strength was attributed to Orowan strengthening. The ODS-Ni also showed improved retention of room-temperature strength after annealing over a range of temperatures up to 600 °C. Nanoindentation measurements revealed that the properties of the dispersion-strengthened deposit were uniform through its thickness, even in narrow, high aspect ratio structures. Microscopy revealed that this resistance to anneal softening was due to an inhibition of grain growth in the presence of the oxide dispersion. At elevated temperatures, the strength of the ODS-Ni was approximately 3 times greater than that of the baseline material although with a significant reduction in hot ductility.     

Computers in police cruisers

A typical police cruiser is filled with electronic devices, displays, and inputs, all competing for the officer's attention. The Project54 system integrates those devices, and its speech-based user interface lets officers operate them without taking their eyes off the road.     

Electrostatic actuation of three-dimensional MEMS mirrors using sidewall electrodes

We propose and demonstrate electrostatic sidewall-electrodes actuation of three-dimensional (3-D) microelectromechanical systems (MEMS) gimbal mirrors. The linearity of the mirror angle dependence on actuation voltage is improved with the sidewall-electrodes actuation. In addition, the undesired spring-softening effect commonly found in electrostatic actuation, where the mirror resonance frequency decreases with increased tilt angle, is significantly reduced. Sidewall actuation enables superior performance of 3-D MEMS mirrors including large pull-in angles, reduced actuation voltages, improved device reliability, and fast switching times.     

Simulation of dynamic systems with output saturation

This paper concerns the design of simulation schemes for dynamic systems with output saturation. The use of saturation blocks commonly available in simulation programs leads to incorrect results if the saturation is simply inserted at the output of a dynamic system model. The underlying problem is discussed on the basis of a simplified theoretical example, and a solution based on a state-space model of the system is proposed. Experimental results involving a dc motor with shaft speed saturation are presented to illustrate the inadequacy of the simple saturation model and to validate the proposed simulation scheme.     

Modelling of foam degradation in lost foam casting process

In this investigation a new model was developed to calculate gas pressure at the melt/foam interface (Gap) resulting from foam degradation during mould filling in the lost foam casting (LFC) process. Different aspects of the process, such as foam degradation, gas elimination, transient mass, heat transfer, and permeability of the refractory coating were incorporated into this model. A computational fluid dynamic (CFD) code was developed based on the numerical technique of the SOLution Algorithm-Volume of Fluid (SOLA-VOF) utilizing model, for the simulation and prediction of the fluid flow in the LFC process. In order to verify the computational results of the simulation, a thin plate of grey iron was poured into a transparent foam mould. The mould filling process was recorded using a 16 mm high-speed camera. Images were analysed frame by frame, in order to measuring foam depolymerization rate and the gap volume during mould filling. Comparison between the experimental method and the simulation results, for the LFC filling sequence, has shown a good agreement.