Tunnels in jointed rocks can be subjected to severe dynamic loads because of rock bursts, coal bumps, and large earthquakes. A series of 3-dimensional simulations was performed, based on discrete element analysis to gain insights into the parameters that influence the response of such tunnels. The simulations looked at the effect of joint set orientation, the effect of joint spacing, the effect of peak displacement for a given peak velocity, the effect of pulse peak velocity for a given displacement, the influence of using rigid versus deformable blocks in the analyses, and the effect of repeated loading. The results of this modeling were also compared to field evidence of dynamic tunnel failures. This comparison reinforced the notion that 3-dimensional discrete element analysis can capture very well the kinematics of structures in jointed rocks under dynamic loading. The paper concludes with a glimpse into the future. Results are shown for a 3-dimensional discrete element massively parallel simulation with 100 million contact elements, performed with the LLNL LDEC code.

Article discussing the development of the University of North Texas (UNT) Libraries' Portal to Texas History.

In January 2006, NASA's Stardust Mission will return with its valuable cargo of cometary dust particles, the first brought back to Earth, captured at hypervelocity speeds in silica aerogel collectors. Aerogel, a proven capture medium, is also a candidate for future sample return missions and low-earth orbit (LEO) deployments. Critical to the science return of Stardust and future missions using aerogel is the ability to efficiently extract impacted particles from collector tiles. Researchers will be eager to obtain Stardust samples as quickly as possible, and tools for the rapid extraction of particle impact tracks that require little construction, training, or investment would be an attractive asset. To this end, we have experimented with diamond and steel micro-blades. Applying ultrasonic frequency oscillations to these micro-blades via a piezo-driven holder produces rapid, clean cuts in the aerogel with minimal damage to the surrounding collector tile. With this approach, impact tracks in aerogel fragments with low-roughness cut surfaces have been extracted from aerogel tiles flown on NASA's Orbital Debris Collector Experiment. The smooth surfaces produced during cutting reduce imaging artifacts during analysis by SEM. Some tracks have been dissected to expose the main cavity for eventual isolation of individual impact debris particles and …

In this paper, we use a coupled climate and carbon cycle model to investigate the global climate and carbon cycle changes out to year 2300 that would occur if CO{sub 2} emissions from all the currently estimated fossil fuel resources were released to the atmosphere. By year 2300, the global climate warms by about 8 K and atmospheric CO{sub 2} reaches 1423 ppmv. The warming is higher than anticipated because the sensitivity to radiative forcing increases as the simulation progresses. In our simulation, the rate of emissions peak at over 30 PgC yr{sup -1} early in the 22nd century. Even at year 2300, nearly 50% of cumulative emissions remain in the atmosphere. In our simulations both soils and living biomass are net carbon sinks throughout the simulation. Despite having relatively low climate sensitivity and strong carbon uptake by the land biosphere, our model projections suggest severe long-term consequences for global climate if all the fossil-fuel carbon is ultimately released to the atmosphere.

Monocrystalline copper samples with orientations of [001] and [221] were shocked at pressures ranging from 20 GPa to 60 GPa using two techniques: direct drive lasers and explosively driven flyer plates. The pulse duration for these techniques differed substantially: 2 ns for the laser experiments and 1.1-1.4 {micro}s for the flyer-plate experiments. The residual microstructures were dependent on orientation, pressure, and shocking method. The much shorter pulse duration in laser shock yielded recovery microstructures with no or limited dislocation motion. For the flyer-plate experiments, the longer pulse duration allow shock-generated defects to reorganize into lower energy configurations. Calculations show that the post shock cooling occurs in a time scale of 0.2 s for laser shock and 1000 s for plate-impact shock, propitiating recovery and recrystallization conditions for the latter. At the higher pressure level extensive recrystallization was observed in the plate-impact samples, while it was absent in laser shock. An effect that is proposed to contribute significantly to the formation of recrystallized regions is the existence of micro-shearbands, which increase the local temperature.