We present a new approach for investigating the kinetics of defect migration during annealing of low-energy, ion-implanted silicon, employing a combination of computer simulations and atomic-resolution tunneling microscopy. Using atomically-clean Si(111)-7x7 as a sink for bulk point defects created by 5 keV Xe and Ar irradiation, we observe distinct, temperature-dependent surface arrival rates for vacancies and interstitials. A combination of simulation tools provides a detailed description of the processes that underly the observed temperature-dependence of defect segregation, and the predictions of the simulations agree closely with the experimental observations.

By producing compact representations of hyperspectral image cubes (hypercubes), image storage requirements and the amount of time it takes to extract essential elements of information can both be dramatically reduced. However, these compact representations must preserve the important spectral features within hypercube pixels and the spatial structure associated with background and objects or phenomena of interest. This paper describes a novel approach for automatically and efficiently generating a particular type of compact hypercube representation, referred to as a supercube. The hypercube is segmented into regions that contain pixels with similar spectral shapes that are spatially connected, and the pixel connectivity constraint can be relaxed. Thresholds of similarity in spectral shape between pairs of pixels are derived directly from the hypercube data. One superpixel is generated for each region as some linear combination of pixels belonging to that region. The superpixels are optimal in the sense that the linear combination coefficients are computed so as to minimize the level of noise. Each hypercube pixel is represented in the supercube by applying a gain and bias to the superpixel assigned to the region containing that pixel. Examples are provided.

The magnet group at LBNL is currently in the process of developing high-field accelerator magnets for use in future colliders. One of the primary challenges is to provide a design which is cost-effective and simple to manufacture, at the same time resulting in good training performance and field quality adequate for accelerator operation. Recent studies have focused on a racetrack geometry that has the virtues of simplicity and conductor compatibility. The results have been applied to the design of a series of prototype high-field magnets based on Nb{sub 3}Sn conductor.

Cryogenic high-resolution X-ray spectrometers are typically operated with thin IR blocking windows to reduce radiative heating of the detector while allowing good x-ray transmission. We have estimated the temperature profile of these IR blocking windows under typical operating conditions. We show that the temperature in the center of the window is raised due to radiation from the higher temperature stages. This can increase the infrared photon flux onto the detector, thereby increasing the IR noise and decreasing the cryostat hold time. The increased window temperature constrains the maximum window size and the number of windows required. We discuss the consequences for IR blocking window design.

In May 1998 the Hanford Site started developing a program for characterization of transuranic (TRU) waste for shipment to the Waste Isolation Pilot Plant (WIPP) in New Mexico. After less than two years, Hanford will have a program certified by the Carlsbad Area Office (CAO). By picking a simple waste stream, taking advantage of lessons learned at the other sites, as well as communicating effectively with the CAO, Hanford was able to achieve certification in record time. This effort was further simplified by having a centralized program centered on the Waste Receiving and Processing (WRAP) Facility that contains most of the equipment required to characterize TRU waste. The use of fixed facilities for the characterization of TRU waste at sites with a long-term clean-up mission can be cost effective for several reasons. These include the ability to control the environment in which sensitive instrumentation is required to operate and ensuring that calibrations and maintenance activities are scheduled and performed as an operating routine. Other factors contributing to cost effectiveness include providing approved procedures and facilities for handling hazardous materials and anticipated contingencies and performing essential evolutions, and regulating and smoothing the work load and environmental conditions to provide maximal efficiency …

Creep of zirconium and zirconium alloys has been labeled ''anomalous.'' Researchers often report that zirconium and its alloys never reach true steady state creep and have stress exponents that continuously change with stress and temperature. Many varied interpretations have been offered explaining the creep behavior of zirconium. Some have suggested that creep is diffusion controlled, while others maintain that creep is dislocation glide controlled. Cumulative zirconium creep data will be presented based on an extensive literature review. An interpretation of results will be presented and compared to previous interpretations.

Safe interim dry storage of spent nuclear fuel (SNF) must be maintained for a minimum of twenty years according to the Code of Federal Regulations. The most important variable that must be regulated by dry storage licensees in order to meet current safety standards is the temperature of the SNF. The two currently accepted models to define the maximum allowable storage temperature for SNF are based on a diffusion controlled cavity growth (DCCG) failure mechanism for the cladding. Although these models are based on the same fundamental failure theory (DCCG), the researchers who developed the models made different assumptions, including selection of some of the most critical variables in the DCCG failure equation. These inconsistencies are discussed together with recommended modifications to the failure models based on recent data.

The fate of six volatile organic compounds (VOC) in a 150-meter deep vadose zone was examined in support of a RCRA Corrective Measures Study of the Chemical Waste Landfill at Sandia National Laboratories, Albuquerque, New Mexico. The study focused on the modeling of potential future transport of the VOCs to exposure media upon the completion of two separate voluntary corrective measures--soil vapor extraction and landfill excavation--designed to significantly reduce contaminant levels in subsurface soils. modeling was performed with R-UNSAT, a finite-difference simulator that was developed by the U.S. Geological Survey. R-UNSAT facilitated a relatively unique and comprehensive assessment of vapor transport because it (1) simulated the simultaneous movement of all six VOCs, taking into account each constituent's diffusion coefficient as affected by its mole fraction within a mixture of chemicals, and (2) permitted simultaneous assessment of risk to human health via volatilization (air) and drinking water (groundwater) pathways. Modeling results suggested that monitored natural attenuation would represent a viable remedial alternative at the landfill after both voluntary corrective measures were completed.

The purpose of this study is to investigate the quench sensitivity of mechanical properties of hot extruded 6061 and 6069 aluminum alloys. The relationship between mechanical properties and quench delzty time at various temperatures between 200-500 C was determined. It was concluded that the 6069-T6 was somewhat more quench sensitive than 6061, which may be consistent with the composition difference.

This work describes recent advances on the effects of subgrain boundaries on elevated-temperature plasticity. Particular attention is devoted to recent developments regarding internal back-stresses. This will include discussions of recent convergent beam electron diffraction (CBED) experiments on metals to evaluate internal stresses in association with dislocation heterogeneities.

We show that standard tissue phantoms can be used to mimic the intensity and polarization properties of tissue. Polarized light propagation through biologic tissue is typically studied using tissue phantoms consisting of dilute aqueous suspensions of microspheres. The dilute phantoms can empirically match tissue polarization and intensity properties. One discrepancy between the dilute phantoms and tissue exist: common tissue phantoms, such as dilute Intralipid and dilute 1-{micro}m-diameter polystyrene microsphere suspensions, depolarize linearly polarized light more quickly than circularly polarized light. In dense tissue, however, where scatterers are often located in close proximity to one another, circularly polarized light is depolarized similar to or more quickly than linearly polarized light. We also demonstrate that polarized light propagates differently in dilute versus densely packed microsphere suspensions, which may account for the differences seen between polarized light propagation in common dilute tissue phantoms versus dense biologic tissue.

We have used a two-stage gas gun to address issues relating to the accurate determination of the temperature of a shocked metal surface at a metal/LiF interface. We have investigated the light flash generated by the dynamics at the interface, the light sources at the LiF boundary that can contaminate the emission from the metal surface, and the light emitted from defects in the LiF crystal as it is being shocked. A seven-channel spectrometer with fiber-optic transmission of light from the target was used, and a Hohlraum geometry was used to increase the effective emissivity of the target. The method that yielded the best results is described and is expected to be useful for a wide range of applications.

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The positions of Ge atoms intermixed in the Si(100) surface at very low concentration are identified using empty-state imaging in scanning tunneling microscopy. A measurable degree of place exchange occurs at temperatures as low as 330 K. Contrary to earlier conclusions, good differentiation between Si atoms and Ge atoms can be achieved by proper imaging conditions.

Because of the complexity of two-phase flow phenomena, two-phase flow codes rely heavily on empirical correlations. This approach has a number of serious shortcomings. Advances in parallel computing and continuing improvements in computer speed and memory have stimulated the development of numerical simulation tools that rely less on empirical correlations and more on fundamental physics. The objective of this work is to take advantage of developments in massively parallel computing, single-phase computational fluid dynamics of complex systems, and numerical methods for front capturing in two-phase flows to develop a computer code for direct numerical simulation of two-phase flow. This includes bubble/droplet transport, interface deformation and topology change, bubble/droplet interactions, interface mass, momentum and energy transfer.

The authors recently developed an analytic theory of cumulative multibunch beam breakup that includes a linear variation of transverse focusing across the bunch train. The focusing variation saturates the exponential growth of the beam breakup and establishes an algebraic decay of the transverse bunch displacement versus bunch number. In this paper they illustrate how the focusing variation works to suppress multibunch beam breakup, as well as how the mechanism scales with accelerator and beam parameters.

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Thermally sprayed coating characteristics and mechanical properties are in part a result of the residual stress developed during the fabrication process. The total stress state in a coating/substrate is comprised of the quench stress and the coefficient of thermal expansion (CTE) mismatch stress. The quench stress is developed when molten particles impact the substrate and rapidly cool and solidify. The CTE mismatch stress results from a large difference in the thermal expansion coefficients of the coating and substrate material. It comes into effect when the substrate/coating combination cools from the equilibrated deposit temperature to room temperature. This paper describes a laser-based technique for measuring the curvature of a coated substrate and the analysis required to determine residual stress from curvature measurements. Quench stresses were determined by heating the specimen back to the deposit temperature thus removing the CTE mismatch stress. By subtracting the quench stress from the total residual stress at room temperature, the CTE mismatch stress was estimated. Residual stress measurements for thick (>1mm) spinel coatings with a Ni-Al bond coat on 304 stainless steel substrates were made. It was determined that a significant portion of the residual stress results from the quenching stress of the bond coat and …

Since 1993, the IAEA has made great progress in the implementation of remote monitoring. Equipment has been developed and tested, and installed systems are being used for safeguards purposes. The cost of equipment, the complexity of communication technology, and maintenance of the equipment are challenges that still face the IAEA. Resolution of these challenges will require significant effort. The USSP is committed to assisting the IAEA to overcome these challenges.

Electrical breakdown in thin oxides is assessed by a new bias-temperature ramp technique. No significant effect of radiation exposure on breakdown is observed for high quality thermal and nitrided oxides, up to 20 Mrad(SiO{sub 2}).

Sandia National Laboratories has been developing technologies to support person-to-person collaboration and the efforts of teams in the business and research communities. The technologies developed include knowledge-based design advisors, knowledge management systems, and streamlined manufacturing supply chains. These collaborative environments in which people can work together sharing information and knowledge have required a new approach to software development. The approach includes an emphasis on the requisite change in business practice that often inhibits user acceptance of collaborative technology. Leveraging the experience from this work, they have established a multidisciplinary approach for developing collaborative software environments. They call this approach ``A Holistic Software Development Methodology''.

Underdoped high temperature superconductors (HTS) exhibit a normal state for energies E > E{sub g} and/or temperatures T > T{sub 0}, and a pseudogap in their electronic spectrum for E < E{sub g} and/or T{sub 0} > T > {Tc}. Strikingly similar behavior occurs in the transition metal dichalcogenides (TMD) 2H-MX{sub 2}, where M = Ta, Nb, and X = S, Se, both in the normal (T > T{sub 0}) and in the incommensurate charge-density wave (T{sub ICDW} > T > T{sub c}) states. Such strikingly similar behavior has also been seen in the organic layered superconductors (OLS) {kappa}-(ET){sub 2}X, where ET is bis(ethylenedithio)tetrathiafulvalene, and X = Cu[N(CN){sub 2}]Br, and Cu(SCN){sub 2}, both in the normal region T > T{sub SDW} > {Tc} and in the spin-density wave region T{sub SDW} > T > T{sub c}. In all three materials classes, the anomalous transport and thermodynamic properties associated with the pseudogap or density-wave regime are completely independent of the applied magnetic field strength, whereas the same properties below {Tc} are all strongly field-dependent. Hence, the authors propose that the pseudogap in the HTS arises from charge- and/or spin-density waves, and not from either superconducting fluctuations or preformed charged quasiparticle pairs.

The authors report Q-switched operation from an electrically-injected monolithic coupled-resonator structure which consists of an active cavity with InGaAs quantum wells optically coupled to a passive cavity. The passive cavity contains a bulk GaAs region which is reverse-biased to provide variable absorption at the lasing wavelength of 990 nm. Cavity coupling is utilized to effect large changes in output intensity with only very small changes in passive cavity absorption. The device is shown to produce pulses as short as 150 ps at repetition rates as high 4 GHz. A rate equation approach is used to model the Q-switched operation yielding good agreement between the experimental and theoretical pulse shape. Small-signal frequency response measurements also show a transition from a slower ({approximately} 300 MHZ) forward-biased modulation regime to a faster ({approximately} 2 GHz) modulation regime under reverse-bias operation.

This paper focuses on a ten-element strategy for streamlining the NEPA process in order to achieve the Act's objectives while easing the considerable burden on agencies, the public, and the judicial system. In other words, this paper proposes a strategy for making NEPA work better and cost less. How these ten elements are timed and implemented is critical to any successful streamlining. The strategy elements discussed in this paper, in no particular order of priority, are as follows: (1) integrate the NEPA process with other environmental compliance and review procedures; (2) accelerate the decision time for determining the appropriate level of NEPA documentation; (3) conduct early and thorough internal EIS (or EA) scoping before public scoping or other public participation begins; (4) organize and implement public scoping processes that are more participatory than confrontational; (5) maintain an up-to-date compendium of environmental baseline information; (6) prepare more comprehensive, broad-scope umbrella EISs that can be used effectively for tiering; (7) encourage preparation of annotated outlines with detailed guidance that serve as a road map for preparation of each EIS or EA; (8) decrease the length and complexity of highly technical portions of NEPA documents; (9) increase and systematize NEPA compliance outreach, training, …