Thesis (Ph. D.)--University of Missouri-Columbia, 2001. / Typescript. Vita. Includes bibliographical references (leaves 100-104). Also available on the Internet.

Thesis (Ph. D.)--West Virginia University, 2002. / Title from document title page. Document formatted into pages; contains viii, 135 p. : ill. Vita. Includes abstract. Includes bibliographical references.

Thesis (Ph.D. (Biochemistry, Microbiology & Biotechnology)) - Rhodes University, 2009.

Thesis (Ph. D.)--University of California, San Diego and San Diego State University, 2003. / Vita. Includes bibliographical references (leaves 203-234).

Thesis (Ph.D.)--Virginia Commonwealth University, 2009. / Prepared for: Dept. of Human Genetics. Title from title-page of electronic thesis. Bibliography: leaves 166-195.

Thesis (Ph. D.)--Hong Kong University of Science and Technology, 2003. / Includes bibliographical references (leaves 148-164). Also available in electronic version. Access restricted to campus users.

Thesis (Mechanical Engineer and M.S. in Mechanical Engineering)--Naval Postgraduate School, June 2003. / Thesis advisor(s): Young S. Shin. Includes bibliographical references (p. 161-162). Also available online.

The research presented in this thesis focuses on the modeling, design, and experimentation of systems containing negative stiffness mechanisms for both vibration and shock isolation. The negative stiffness element studied in this research is an axially compressed beam. If a beam is axially compressed past a critical value, it becomes bistable with a region of negative stiffness in the transverse direction. By constraining a buckled beam in its metastable position through attaching a stiff linear spring in mechanical parallel, the resulting system can reach a low level of dynamic stiffness and therefore provide vibration isolation at low frequencies, while also maintaining a high load-carrying capacity. In previous research, a system containing an axially compressed beam was modeled and tested for vibration isolation [7]. In the current research, variations of this model were studied and tested for both vibration and shock isolation. Furthermore, the mathematical model used to represent the compressed beam in [7] was improved and expanded in current research. Specifically, the behavior exhibited by buckled beams of transitioning into higher-mode shapes when placed under transverse displacement was incorporated into the model of the beam. The piecewise, nonlinear transverse behavior exhibited by a first-mode buckled beam with a higher-mode transition provides the ability of a system to mimic an ideal constant-force shock isolator. Prototypes manufactured through Selective Laser Sintering were dynamically tested using a shaker table. Vibration testing confirmed the ability of a system containing a constrained negative stiffness element to provide enhanced vibration isolation results with increasing axial compression on a beam. However, the results were limited by the high sensitivity of buckled beam behavior to geometrical and boundary condition imperfections. Shock testing confirmed the ability of a system containing a buckled beam with a higher-mode transition to mimic the theoretically ideal constant-force shock isolator. / text

published_or_final_version / Surgery / Doctoral / Doctor of Philosophy

The history of planet formation and evolution is strongly tied to understanding the outcomes of a wide range of impact events, from slow accretionary events to hypervelocity events that melt and vaporize large fractions of the colliding bodies. To better understand impact processes, their effects on planetary evolution, and how to interpret geochemical data, we need to improve our knowledge of the behavior of materials over the entire range of conditions accessed by collisions. Here I present experimental results from gas gun, laser driven, and pulsed power facilities. Together these facilities can access the tremendously wide range of pressure and temperature conditions achieved in natural impact events. This work focuses on the thermodynamics of impacts to better understand the phase transitions that most strongly affect the dynamics and chemical consequences of a collision. I show that the entropy generation during collisions is the most natural means of interpreting the thermodynamic processes that occur during an impact event. For materials with sufficient thermodynamic data at high pressures and temperatures, I present a method for obtaining the entropy generation during an impact. With the knowledge of the entropy, I present new shock-and-release techniques to investigate the liquid-vapor region of the phase diagram. I also show that for materials without sufficient data to calculate the entropy generation during an impact, one can use the shock-and-release techniques described here to determine the entropy in the high pressure shock state. With better equation of state models that are constrained by our experimental data, our confidence in impact models improves dramatically. Using a high fidelity equation of state for \(H_2O\). ice, I derive scaling laws for how much \(H_2O\) ice melts and vaporizes for impacts onto icy bodies. Recognizing that icy bodies are not pure ice, I have performed experiments to show how the impact energy partitions between the disparate phases. Finally, I discuss some of the uncertainties in using the laboratory experiments to directly interpret the effects of impacts in nature. / Earth and Planetary Sciences