The highest frequency AT-cut fundamental r e s o n a t o r s r e p o r t e d i n t h e l i t e r a t u r e t o date have been f a b r i c a t e d by k r t e and co-workers [l] using nonreactive ion beam milling. Reactive ion beam m i l l i n g has recently been investigated by Wang 121, and is p o t e n t i a l l y u s e f u l . Both t e c h n i q u e s u t i l i z e e l a b o r a t e equipment and require fine tuning of operating parameters t o o b t a i n s a t i s f a c t o r y e t c h i n g c h a r a c t e r i s t i c s . In contrast, chemical etching, using various fluoridecontaining etchants is standard practice throughout the quartz crystal industry. It is commonly used t o remove surface and subsurface damage done by lapping processes and t o adjust blank frequency prior to electrode deposition. The depth of etch for this purpose is normally limited to several microns. Vig and colleagues 13, 41 developed chemical polishing methods f o r q u a r t z u s i n g f l u o r i d e s , and suggested that they could be used t o f a b r i c a t e VHF resonators. Development work using this technique, repeated here, has r e s u l t e d i n AT-cut crystal resonators with fundamental frequencies up t o
Electrofusion has recently become an important area of cell biology research. We studied the effects of pH of the cell medium on the electrofusion of human red blood cells. Cell fusion was monitored by observing the movement of a lipophylic dye between neighboring fused cells using a fluorescence microscope. The cells were first brought into close contact by dielectrophoresis. Fusion was then induced by three pulses of high-intensity electric field. Within minutes following the pulse application, many cells were observed to fuse together to form fusion chains of different lengths. We found that the optimal pH for cell fusion is around pH 7.5. At this pH, the fusion yield was highest (ranging from 57 to 81%) and the average number of cells within a fusion chain was also the largest. The dependence of cell fusion on pH is more sensitive at low than at high pH. The fusion yield was decreased by 40% when the pH was changed from 7.5 to 6.0, but there was only a 20% decrease in yield between pH 7.5 and 10.0. We suspect that the observed pH effects may be caused by a redistribution of fixed charges at the cell surface, or changes in amphipathicity of the surface proteins.
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