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Epitaxial GaAs grown by molecular beam epitaxy (MBE) at low substrate temperatures is observed to have a significantly shorter carrier lifetime than GaAs grown at normal substrate temperatures. Using femtosecond time-resolved-reflectance techniques, a subpicosecond (~0.4 ps) carrier lifetime has been measured for GaAs grown by MBE at-200°C and annealed at 600 "C. With the same material as a photoconductive switch we have measured electrical pulses with a full-width at half-maximum of 0.6 ps using the technique of electro-optic sampling. Good responsivity for a photoconductive switch is observed, corresponding to a mobility of the photoexcited carriers of-120-150 cm"/V s. GaAs grown by MBE at 200 "C! and annealed at 600 "C is also semi-insulating, which results in a low dark current in the switch application. The combination of fast recombination lifetime, high carrier mobility, and high resistivity makes this material ideal for a number of. subpicosecond photoconductive applications.

A body area network (BAN) is a wireless network of health monitoring sensors designed to deliver personalized healthcare. Securing intersensor communications within BANs is essential for preserving not only the privacy of health data, but also for ensuring safety of healthcare delivery. This paper presents physiological-signal-based key agreement (PSKA), a scheme for enabling secure intersensor communication within a BAN in a usable (plug-n-play, transparent) manner. PSKA allows neighboring nodes in a BAN to agree to a symmetric (shared) cryptographic key, in an authenticated manner, using physiological signals obtained from the subject. No initialization or predeployment is required; simply deploying sensors in a BAN is enough to make them communicate securely. Our analysis, prototyping, and comparison with the frequently used Diffie-Hellman key agreement protocol shows that PSKA is a viable intersensor key agreement protocol for BANs.

The emergence of inexpensive and low-power wireless communication hardware and various handheld, wearable, and embedded computing technologies is making computing and communication devices more mobile and ubiquitous. Due to the mobility and high-density of networkenabled devices, short range mobile ad hoc networks (MANET) are instantaneously and autonomously formed to facilitate exchange of information. In MANET, interactions among the devices are driven by constantly changing contextual and environmental conditions, rather than by the applications resident on the devices. This trend makes Autonomous Decentralized Systems (ADS) a desirable architecture for facilitating ad hoc communication among mobile devices. In this paper, Reconfigurable ContextSensitive Middleware (RCSM) is presented to facilitate ADS applications in MANET.

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