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A drift-diffusion transport model has been used to examine the performance capabilities of AlGaN/GaN Npn heterojunction bipolar transistors (HBTs). The Gummel plot from the first GaN-based HBT structure recently demonstrated is adjusted with simulation by using experimental mobility and lifetime reported in the literature. Numerical results have been explored to study the effect of the p-type Mg doping and its incomplete ionization in the base. The high base resistance induced by the deep acceptor level is found to be the cause of limiting current gain values. Increasing the operating temperature of the device activates more carriers in the base. An improvement of the simulated current gain by a factor of 2 to 4 between 25 and 300 C agrees well with the reported experimental results. A preliminary analysis of high frequency characteristics indicates substantial progress of predicted rf performances by operating the device at higher temperature due to a reduced extrinsic base resistivity.

This is the final report for the Project to Enhance Student Science and Engineering Preparation at the Pre-College Level (Project ESEPP) for the period from January 1, 1996 through August 1, 1998. This report summarizes the accomplishments of the program and its ability to meet the objectives described in the original proposal (1990).

This document contains the results of the hazard analysis that has been performed to address Waste Feed Delivery operations and activities.

The resolution of ground-based telescopes is typically limited to {approx}1 second of arc because of the blurring effects of atmospheric turbulence. Adaptive optics (AO) technology senses and corrects for the optical distortions due to turbulence hundreds of times per second using high-speed sensors, computers, deformable mirror, and laser technology. The goal of this project is to make AO systems widely useful astronomical tools providing resolutions up to an order of magnitude better than current, ground-based telescopes. Astronomers at the University of California Lick Observatory at Mt. Hamilton now routinely use the LLNL developed AO system for high resolution imaging of astrophysical objects. We report here on the instrument development progress and on the science observations made with this system during this 3-year ERI project.

Nonlinear magneto-optical rotation (NMOR) is investigated at highlight powers where the rotation is significantly modified by AC Stark shifts. These shifts are shown to change the overall sign of rotation for closed F-->F+1 transitions as light power is increased. The effect is demonstrated by measurements in rubidium and density matrix calculations. The results are important for applications of nonlinear optical rotation such as sensitive magnetometry.

Sea quark distributions in the nucleon have naively been expected to be generated perturbatively by gluon splitting. In this case, there is no reason for the light quark and anti-quark sea distributions to be different. No asymmetries in the strange or heavy quark sea distributions are predicted in the improved parton model. However,recent experiments have called these naive expectations into question. A violation of the Gottfried sum rule has been measured in several experiments, suggesting that (bar u) < (bar d) in the proton. Additionally, other measurements, while not definitive, show that there may be an asymmetry in the strange and anti-strange quark sea distributions. These effects may require nonperturbative explanations. In this review we first discuss the perturbative aspects of the sea quark distributions. We then describe the experiments that could point to nonperturbative contributions to the nucleon sea. Current phenomenological models that could explain some of these effects are reviewed.

Metal-reinforced Al{sub 2}0{sub 3}-matrix composites were prepared using reactive hot pressing. The volume fraction of the reinforcing phase was controlled by the stoichiometry of the particular displacement reaction used. Dense Al{sub 2}0{sub 3}-Ni and Al{sub 2}O{sub 3}-Nb composites were fabricated using this technique. The best combination of strength, 610 MPa, and toughness, 12 MPam{sup 1/2}, was found for the Al{sub 2}O{sub 3}-Ni composites. Indentation cracks and fracture surfaces showed evidence of ductile deformation of the Ni phase. The Al{sub 2}O{sub 3}-Nb composites had high strength, but the toughness was lower than expected due to the poor bonding between the Nb and A1{sub 2}0{sub 3}phases.

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This document summarizes the Tanks Focus Area (TFA's) process of collecting, analyzing, and responding to high-level radioactive tank waste science and technology needs developed from across the DOE complex in FY 2000. The document also summarizes each science and technology need, and provides an initial prioritization of TFA's projected work scope for FY 2001 and FY 2002.

In a recent report entitled The Regional Impacts of Climate Change it was concluded that the technological capacity to adapt to climate change is likely to be readily available in North America, but its application will be realized only if the necessary information is available (sufficiently far in advance in relation to the planning horizons and lifetimes of investments) and the institutional and financial capacity to manage change exists. The report also acknowledged that one of the key factors that limit the ability to understand the vulnerability of subregions of North America to climate change, and to develop and implement adaptive strategies to reduce that vulnerability, is the lack of accurate regional projections of climate change, including extreme events. In particular, scientists need to account for the physical-geographic characteristics (e.g., the Great Lakes, coastlines, and mountain ranges) that play a significant role in the North America climate and also need to consider the feedback between the biosphere and atmosphere.

Although the magnetorotational instability (MRI) has been widely accepted as a powerful accretion mechanism in magnetized accretion disks, it has not been realized in the laboratory. The possibility of studying MRI in a rotating liquid-metal annulus (Couette flow) is explored by local and global stability analysis and magnetohydrodynamic (MHD) simulations. Stability diagrams are drawn in dimensionless parameters, and also in terms of the angular velocities at the inner and outer cylinders. It is shown that MRI can be triggered in a moderately rapidly rotating table-top apparatus, using easy-to-handle metals such as gallium. Practical issues of this proposed experiment are discussed.

We report the first observation of the reactions Au + Au {yields} Au + Au + {rho}{sup 0} and Au + Au {yields} Au* + Au* + {rho}{sup 0} with the STAR detector. The {rho} are produced at small perpendicular momentum, as expected if they couple coherently to both nuclei. We discuss models of vector meson production and the correlation with nuclear breakup, and present a fundamental test of quantum mechanics that is possible with the system.

Sampled shrews at 9.3 ha plots from logs manually removed and control plots in loblolly pine forests of the Southeastern Coastal Plain. Capture rates of Cryptotis parva were lower at plots from which deadwood was removed whereas capture rates of Blarina cavolinensis and Sorex longirostris did not differ between control and removal plots. Cryptotis may have been most sensitive to removal plots due to low population density, hence poor ability to move into areas of low reproduction. (Second Abstract, p. 37)Presentation of evidence that juvenile amphibians including Ambystomatid salamanders may disperse hundreds of meter from their natal wetlands within the weeks to months following metamorphosis. Data indicates Ambystoma trigrinum metamorphs can take at least six months to disperse and en route use non-polar lipid reserves garnished as larvae. Report suggests a land management regime that allows for both juvenile amphibian dispersal and also the consumptive use of the surrounding landscape.

Since the start of Run IIa, the RF curves for the extraction process from the Accumulator have been based on an algorithm described in Pbar Note 636. There are a number of problems with this procedure that result in a dilution of the longitudinal phase space of the extracted beam. The procedure consists of a number of steps in which the frequency curve during each process is a linear time ramp. For a constant bend field, the synchronous phase angle is given as: {Lambda} = sin({phi}{sub s}) = -h/{eta} (1/f{sub rf}){sup 2}df{sub rf}/dt/qV/pc where h is the harmonic number of the RF. Equation (1) shows that if the frequency curve consists of a number of linear time ramps with different slopes, there will be discontinuities in the synchronous phase. These discontinuities in the synchronous phase will lead to dipole oscillations of the beam in the RF bucket. The discontinuities observed for the present RF curves are about 10 degrees. In the procedure outlined in Pbar Note 636, the RF bucket is formed on the high energy edge of the rectangular momentum distribution. As the RF bucket is pulled away from the core, it is also programmed to increase in area. …

A 3-D simulation model study was run using CMG's STARS thermal model, and showed that a 122 meter (400 foot) horizontal well should produce up to 64 cubic meters per day of oil (400 B/D) when the heated oil bank hits the well.

Adaptive optics enables high resolution imaging through the atmospheric by correcting for the turbulent air's aberrations to the light waves passing through it. The Lawrence Livermore National Laboratory for a number of years has been at the forefront of applying adaptive optics technology to astronomy on the world's largest astronomical telescopes, in particular at the Keck 10-meter telescope on Mauna Kea, Hawaii. The technology includes the development of high-speed electrically driven deformable mirrors, high-speed low-noise CCD sensors, and real-time wavefront reconstruction and control hardware. Adaptive optics finds applications in many other areas where light beams pass through aberrating media and must be corrected to maintain diffraction-limited performance. We describe systems and results in astronomy, medicine (vision science), and horizontal path imaging, all active programs in our group.

The objectives of the mini airlift bubbler testing are to evaluate the impact of the bubbler on melt rate, melting behavior and cold cap structure, foam formation and stability, bubbler air venting, off gas behavior, and electrode/plenum power use. In addition, the effects of frit and plenum temperature on bubbler performance were evaluated. This report will cover the second program element, the evaluation of two lengths of mini-bubblers in Slurry Fed Melt Rate Furnaces to assess melting behavior and melt rate enhancement.

Aluminum corrosion and turbidity formation in reactors correlate with fuel sheath temperature. To further substantiate this correlation, discharged fuel elements from R-3, P-2 and K-2 cycles were examined for extent of corrosion and evidence of breaking off of the oxide film. This report discusses this study.

This report talks about Coalescence of Nanometer Silver Islands on Oxides Grown by Filtered Cathodic Arc Depostion

This report describes research into the use of complex hydrides for hydrogen storage. The synthesis of a number of alanates, (AIH4) compounds, was investigated. Both wet chemical and mechano-chemical methods were studied.

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Detailed residual stress analysis was performed for a multi-pass butt weld, representing the middle butt-girth weld of a storage tank. The analysis procedures took into account representative welding parameters, joint detail, weld pass deposition sequence, as well as temperature-dependent properties. The predicted residual stresses were then considered in stress intensity factor calculations using a three-dimensional finite element alternating model for investigating crack growth behavior for both small elliptical surface and through-wall cracks.