Derailleur gears by 13 drive-train. Most road bicycles have two chainrings, and touring bicycles commonly have three. The rear derailleur serves double duty: moving the chain between rear sprockets and taking up chain slack caused by moving to a smaller sprocket at the rear or a smaller chainring by the front derailleur. In order to accomplish this second task, it is positioned in the path of the bottom, slack portion of chain. Sometimes the rear-derailleurs are re-purposed as chain tensioners for single-speed bicycles that cannot adjust chain tension by a different method. Although variations exist, as noted below, most rear derailleurs have
Word RAM RAM model, and was the original motivation for the model. Dan Willard used y-fast tries to solve this in formula_6 time. Michael Fredman and Willard also solved the problem using fusion trees in formula_7 time. Word RAM In theoretical computer science, the word RAM (word random access machine) model is a model of computation that is a random access machine able to do bitwise operations on a single word of bits. The model was created by Michael Fredman and Dan Willard in 1990 to simulate programming languages like C. The word RAM model is an abstract machine similar to a