Biomedical subjects

Stephen D Jacobs

Publications and source records attributed to Stephen D Jacobs.

3 recordsLinked to original sources

PubMed2005

Minimizing artifact formation in magnetorheological finishing of chemical vapor deposition ZnS flats.

The polishing performance of magnetorheological (MR) fluids prepared with a variety of magnetic and nonmagnetic ingredients was studied on four types of initial surface for chemical vapor deposition (CVD) ZnS flats from domestic and foreign sources. The results showed that it was possible to greatly improve smoothing performance of magnetorheological finishing (MRF) by altering the fluid composition, with the best results obtained for nanoalumina abrasive used with soft carbonyl iron and altered MR fluid chemistry. Surface roughness did not exceed 20 nm peak to valley and 2 nm rms after removal of 2 microm of material. The formation of orange peel and the exposure of a pebblelike structure inherent in ZnS from the CVD process were suppressed.

Journal Article↗

PubMed2005

Subsurface damage in some single crystalline optical materials.

We present a nondestructive method for estimating the depth of subsurface damage (SSD) in some single crystalline optical materials (silicon, lithium niobate, calcium fluoride, magnesium fluoride, and sapphire); the method is established by correlating surface microroughness measurements, specifically, the peak-to-valley (p-v) microroughness, to the depth of SSD found by a novel destructive method. Previous methods for directly determining the depth of SSD may be insufficient when applied to single crystals that are very soft or very hard. Our novel destructive technique uses magnetorheological finishing to polish spots onto a ground surface. We find that p-v surface microroughness, appropriately scaled, gives an upper bound to SSD. Our data suggest that SSD in the single crystalline optical materials included in our study (deterministically microground, lapped, and sawed) is always less than 1.4 times the p-v surface microroughness found by white-light interferometry. We also discuss another way of estimating SSD based on the abrasive size used.

Journal Article↗

PubMed2002

Electric-field-induced motion of polymer cholesteric liquid-crystal flakes in a moderately conductive fluid.

Polymer cholesteric liquid-crystal flakes suspended in a fluid with nonnegligible conductivity can exhibit motion in the presence of an ac electric field. The plateletlike particles with a Grandjean texture initially lie parallel to the cell substrates and exhibit a strong selective reflection that is diminished or extinguished as the flakes move. Flake motion was seen within a specific frequency bandwidth in an electric field as low as 5 mV(rms)/microm. Flakes reoriented about their longest axis to align parallel to theapplied field, and a rise time of 560 ms was seen in a 40-mV(rms)/microm field at 100 Hz.

Journal Article↗