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The bacterial flagellum is a highly complex prokaryotic organelle. It is the motor that drives bacterial motility, and despite the large amount of energy required to make and operate flagella, motile organisms have a strong adaptive advantage. Flagellar biogenesis is both complex and highly coordinated and it typically involves at least three two-component systems. Part of the flagellum is a type III secretion system, and it is via this structure that flagellar components are exported. The assembly of a flagellum occurs in a number of stages, and the ''checkpoint control'' protein FliK functions in this process by detecting when the flagellar hook substructure has reached its optimal length. FliK then terminates hook export and assembly and transmits a signal to begin filament export, the final stage in flagellar biosynthesis. As yet the exact mechanism of how FliK achieves this is not known. Here we review what is known of the FliK protein and discuss the evidence for and against the various hypotheses that have been proposed in recent years to explain how FliK controls hook length, FliK as a molecular ruler, the measuring cup theory, the role of the FliK N terminus, the infrequent molecular ruler theory, and the molecular clock theory.

There is a natural desire to make multi-user virtual environments large in spatial extent, in numbers of objects, and in numbers of users interacting with the environment. However, doing this brings up several problems: eficiently managing the flow of large amounts of data between large numbers of users, representing precise position and velocity information about objects that are arrayed across a large volume of space, and allowing designers t o create parts of a virtual environment separately and combine them together later.Locales are an eficient method for solving these problems b y breaking up a virtual world into compact chunks that can be described and communicated independently. I n addition, locales can be used to support a number of special effects that allow virtzal worlds to easily transcend reality.While having many benefits, locales introduce an. additional problem: finding something when you do not know whai locale it is in. This is solved b y the companion concept of beacons, which makes it possible t o find something no matter where it is.