DYNAMIC TENSILE TESTING OF SHEET MATERIAL USING THE SPLIT-HOPKINSON BAR TECHNIQUE

We have described an experimental method based on the SHPB technique which allows dynamic tensile testing of 1.0-mm-thick sheet material. The test method employs a framing camera to make strain measurements based on direct observation of the deforming test sample. Stress in the sample is determined using traditional SHPB wave analysis. This information is used to construct engineering stress-strain behavior. The stress-strain behavior determined using the test method is shown to be reasonably accurate for annealed tantalum and less accurate for annealed copper. We believe that this phenomenon is related to the constitutive behavior of the test material. Although the stress-strain behavior extracted from the test is in some cases suspect, the test technique is shown to provide highly reproducible results and thus can be employed to examine effects of microstructural features, alloying elements, etc., on dynamic deformation and fracture of ductile materials.     

Effect of collisionality on kinetic stability of the resistive wall mode

The impact of collisionless, energy-independent, and energy-dependent collisionality models on the kinetic stability of the resistive wall mode is examined for high pressure plasmas in the National Spherical Torus Experiment. Future devices will have decreased collisionality, which previous stability models predict to be universally destabilizing. In contrast, in kinetic theory reduced ion-ion collisions are shown to lead to a significant stability increase when the plasma rotation frequency is in a stabilizing resonance with the ion precession drift frequency. When the plasma is in a reduced stability state with rotation in between resonances, collisionality will have little effect on stability.     

Photoreduction of catalytic platinum particles using immobilized multilayers of Photosystem I

Using the abundance of available electrons generated by immobilized multilayers of the photoactive protein complex Photosystem I (PSI), we have photoreduced platinum particles that are catalytically active for the H(2)/H(+) redox couple. The resulting platinized PSI films were optimized using electrochemical measurements and then characterized using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and scanning electrochemical microscopy (SECM). These results demonstrate a novel method for generating immobilized platinum catalysts that are readily available on the surface of a photoactive PSI multilayer.