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Four mammalian Na+/H+ exchangers have recently been cloned. Despite the structural similarity, these Na+/H+ exchanger isoforms differ in kinetic characteristics and their response to external stimuli. The present review deals with the recent developments in their functional characterization and their short-term regulation.

There are a number of important applications where the accuracy of typed copy is less important than other criteria, such as the speed of entry, ease of learning, reduced keyboard size, provision for innovative keyboard designs and work methods, etc. Some of these applications include communication devices for the motor handicapped and rough drafting. The applications in question still provide single finger typing as opposed to multifinger entries for chord keyboards.One approach to keyboard design for such applications involves using a multicharacter key set. Because there is more than one character on a key, the number of keys can be reduced to a point limited only by the required accuracy of the text produced which is itself limited by the ability of “disambiguation” algorithms to decode the ambiguous text strings. Reducing the number of keys increases text entry rates and reduces learning time.Experiments with keysets of 10, 12, 14, and 16 keys have produced keystroke rates of 3.3 to 1.7 characters per second and a 6%keying error while the disambiguation programs can produce an accuracy of 85 to 95%. Learning time in the experiments was about 9 to 12 minutes.The experiments demonstrate the feasibility of increasing text entry rates and freeing the keyboard from architectural constraints.