that CFS is scalable: with 4,096 servers, looking up a block of data involves contacting only seven servers. The tests also demonstrate nearly perfect robustness and unimpaired performance even when as many as half the servers fail.

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This classification, to be used in a new inventory of wetlands and deepwater habitats of the United States, is intended to describe ecological taxa, arrange them in a system useful to resource managers, furnish units for mapping, and provide uniformity of concepts and terms. Wetlands are defined by plants (hydrophytes), soils (hydric soils), and frequency of flooding. Ecologically related areas of deep water, traditionally not considered wetlands, are included in the classification as deepwater habitats. Systems form the highest level of the classification hierarchy; five are defined—Marine, Estuarine, Riverine, Lacustrine, and Palustrine. Marine and Estuarine Systems each have two Subsystems, Subtidal and Intertidal; the Riverine System has four Subsystems, Tidal, Lower Perennial, Upper Perennial, and Intermittent; the Lacustrine has two, Littoral and Limnetic; and the Palustrine has no Subsystems. Within the Subsystems, Classes are based on substrate material and flooding regime, or on vegetative life form. The same Classes may appear under one or more of the Systems or Subsystems. Six Classes are based on substrate and flooding regime: (1) Rock Bottom with a substrate of bedrock, boulders, or stones; (2) Unconsolidated Bottom with a substrate of cobbles, gravel, sand, mud, or organic material; (3) Rocky Shore with the same substrates as Rock Bottom; (4) Unconsolidated Shore with the same substrates as Unconsolidated

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The flight envelope can be viewed as a set within the state space of an aircraft. For various safety considerations an aircraft is required to remain within its prescribed flight envelope. The safe set is the largest controlled invariant set within the flight envelope. Thus, if an aircraft is to remain within its envelope it must stay within the safe set. When an aircraft is impaired, e.g., a jammed elevator or an engine loss, the safe set shrinks as would be expected. In this paper we consider strategies to prevent the aircraft from departing the safe set- the envelope protection problem- and strategies to restore the aircraft to a desired trim point within the safe set should it find itself outside the safe set- the envelope restoration problem. Note that an aircraft may be driven outside of the safe set by a disturbance, a loss-of-control incident, or by a component failure in which the safe set shrinks. The problems of envelope protection and restoration are substantially different. Envelope protection requires avoiding close proximity to certain critical boundary segments of the safe set. Restoration is more straightforward involving steering the aircraft to a target trim condition along trajectories that minimize the excursion from the flight envelope. Precise formulations of both problems will be given and alternative solutions will be compared. Examples are given using a model derived from the the longitudinal

A relatively simple model of the phonological loop (A. D. Baddeley, 1986), a component of working memory, has proved capable of accommodating a great deal of experimental evidence from normal adult participants, children, and neuropsychological patients. Until recently, however, the role of this subsystem in everyday cognitive activities was unclear. In this article the authors review studies of word learning by normal adults and children, neuropsychological patients, and special developmental populations, which provide evidence that the phonological loop plays a crucial role in learning the novel phonological forms of new words. The authors propose that the primary purpose for which the phonological loop evolved is to store unfamiliar sound patterns while more permanent memory records are being constructed. Its use in retaining sequences of familiar words is, it is argued, secondary. Baddeley and Hitch (1974) considered the possibility that short-term memory (STM) may serve as a general working memory designed to support complex cognitive activities. This suggestion led to the development of a specific multicomponent model of working memory and has subsequently contributed to

when computing enduring perceptual objecthood. Unimpaired performance required the presence of accretion and deletion cues along fixed contours at the occluding boundaries. Performance was impaired when items were present on the visual field at the same times and to the same degrees as in the occlusion

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of human T cells are unimpaired in the absence of arginine. We then analyzed CD8+ T cell activation in a tumor peptide as well as a viral peptide antigen specific system: (i) CD8+ T cells with specificity against the MART-1aa26–35*A27L tumor antigen expanded with in vitro generated dendritic cells, and (ii