Over the years I have been continuously supported by various funding agencies. The work presented in Chapter 2 has been supported by grants from the National Institute of Health and the National Science Foundation. The work presented in Chapter 3 has been supported by grants from the Office of Naval Research, the United States Army Research Office and the Airforce Office of Scientific Research. The work presented in Chapter 4 has been supported by grants from the Airforce Office of Scientific Research and the Defense Advanced Research Project Agency.