A full field, 3-D velocimeter for microgravity crystallization experiments

The programming and algorithms needed for implementing a full-field, 3-D velocimeter for laminar flow systems and the appropriate hardware to fully implement this ultimate system are discussed. It appears that imaging using a synched pair of video cameras and digitizer boards with synched rails for camera motion will provide a viable solution to the laminar tracking problem. The algorithms given here are simple, which should speed processing. On a heavily loaded VAXstation 3100 the particle identification can take 15 to 30 seconds, with the tracking taking less than one second. It seeems reasonable to assume that four image pairs can thus be acquired and analyzed in under one minute

A Context for Revision: An Ethnographic Perspective

For more than a decade, the field of composition has been studying writing as a process. More specifically, process studies are expressed in terms of cognitive psychology, the social science most prepared in the early seventies to focus on individual writers as they wrote. On the one hand, studies of writers\u27 cognitive processes have shown the value of attending not only to what people write, but also to how they go about doing so. Such research, for instance, has made it possible to imagine writing as a moment to moment affair, during which writers shift their attention from one cognitive activity to another, moving back and forth between what they\u27ve already written to what they\u27re writing. On the other hand, exclusive attention to writers\u27 cognitive activities ignores the fact that writing can also be thought about and studied as a social process. While an ethnographic perspective in no way discounts the importance of studying writing as cognition, it does raise questions about those studies of writers\u27 cognitive processes which systematically decontextualize writers from the circumstances of writing. In fact, contextualized research argues that cognition cannot be isolated as autonomous activity, for what people think about and how they think is profoundly influenced by the situations in which they find themselves