Publications

The Statistics and Human Factors Department at SNL has evolved as the Labs' mission has evolved from engineering designs for the non-nuclear parts of nuclear weapons, including the safety and security components, to a multi-program lab focusing on national security. Twenty years ago their client base was the engineers, scientists, and managers of the nuclear weapon stockpile program, at Sandia and other facilities within the DOE complex. Client relationships developed over years of association. Components and systems were assigned to statisticians so that they could develop a knowledge base in that area. Because of the many different component types and system designs in the stockpile, they typically juggled five or six statistical projects at a time. project participation other than statistical consulting was limited. They rarely had the time to lead project teams, and any skills or inclinations in that direction were often undeveloped. This paper describes a (hit-or-miss) selection of some early and recent efforts. This paper also presents their self-assessment metrics and their external assessment metrics. These metrics were selected to track the business aspects of the department; they are systematic (not hit-or-miss). These two types of histories should allow them to judge whether we're doing the right things, and also doing things right.

Methods are discussed for computing the sensitivity of field variables to changes in material properties and initial/boundary condition parameters for heat transfer problems. The method we focus on is termed the ''Sensitivity Equation Method'' (SEM). It involves deriving field equations for sensitivity coefficients by differentiating the original field equations with respect to the parameters of interest and numerically solving the resulting sensitivity field equations. Uncertainty in the model parameters are then propagated through the computational model using results derived from first-order perturbation theory; this technique is identical to the methodology typically used to propagate experimental uncertainty. Numerical results are presented for the design of an experiment to estimate the thermal conductivity of stainless steel using transient temperature measurements made on prototypical hardware of a companion contact conductance experiment. Comments are made relative to extending the SEM to conjugate heat transfer problems.

The investigation of a complex system is often performed using computer generated response data supplemented by system and component test results where possible. Analysts rely on an efficient use of limited experimental resources to test the physical system, evaluate the models and to assure (to the extent possible) that the models accurately simulate the system order investigation. The general problem considered here is one where only a restricted number of system simulations (or physical tests) can be performed to provide additional data necessary to accomplish the project objectives. The levels of variables used for defining input scenarios, for setting system parameters and for initializing other experimental options must be selected in an efficient way. The use of computer algorithms to support experimental design in complex problems has been a topic of recent research in the areas of statistics and engineering. This paper describes a resampling based approach to form dating this design. An example is provided illustrating in two dimensions how the algorithm works and indicating its potential on larger problems. The results show that the proposed approach has characteristics desirable of an algorithmic approach on the simple examples. Further experimentation is needed to evaluate its performance on larger problems.

AerMet 100 is a high strength, high fracture toughness alloy designed for use in aerospace applications. In previous work the welding behavior of this alloy has been evaluated, and it has been shown that a softened region in the heat-affected zone (HAZ) is a principal feature of the weld zone. A model for this softening, based on classical theories of precipitate coarsening and isothermal softening data, was developed and found to provide a reasonable description for weld thermal cycle simulation (Gleeble) experiments. Recent work has shown, however, that softening in real welds is not always well predicted by this model, so that additional effects, which are not captured in conventional Gleeble thermal cycle simulations must be addressed. In particular, the stresses associated with real weld HAZ's may modify the softening kinetics. In the current work, Gleeble simulations in both stress-free and stressed conditions have been conducted and the kinetics compared. The accuracy of the thermal model predictions have also been considered regarding their impact on estimated hardness values.

The parametric grid capability of the Knowledge Base (KBase) provides an efficient robust way to store and access interpolatable information that is needed to monitor the Comprehensive Nuclear Test Ban Treaty. To meet both the accuracy and performance requirements of operational monitoring systems, we use an approach which combines the error estimation of kriging with the speed and robustness of Natural Neighbor Interpolation. The method involves three basic steps: data preparation, data storage, and data access. In past presentations we have discussed in detail the first step. In this paper we focus on the latter two, describing in detail the type of information which must be stored and the interface used to retrieve parametric grid data from the Knowledge Base. Once data have been properly prepared, the information (tessellation and associated value surfaces) needed to support the interface functionality, can be entered into the KBase. The primary types of parametric grid data that must be stored include (1) generic header information; (2) base model, station, and phase names and associated ID's used to construct surface identifiers; (3) surface accounting information; (4) tessellation accounting information; (5) mesh data for each tessellation; (6) correction data defined for each surface at each node of the surfaces owning tessellation (7) mesh refinement calculation set-up and flag information; and (8) kriging calculation set-up and flag information. The eight data components not only represent the results of the data preparation process but also include all required input information for several population tools that would enable the complete regeneration of the data results if that should be necessary.

This work is an attempt to elucidate effects that may limit efficiency in magnetrons operated at relativistic voltages (V {approximately} 500 kV). Three-dimensional particle-in-cell simulation is used to investigate the behavior of 14 and 22 cavity, cylindrical, rising-sun magnetrons. Power is extracted radially through a single iris located at the end of every other cavity. Numerical results show that in general output power and efficiency increase approximately linearly with increasing iris width (decreasing vacuum Q) until the total Q becomes too low for stable oscillation in the n-mode to be maintained. Beyond this point mode competition and/or switching occur and efficiency decreases. Results reveal that the minimum value of Q (maximum efficiency) that can be achieved prior to the onset of mode competition is significantly affected by the magnitude of the 0-space-harmonic of the {pi}-mode, a unique characteristic of rising-suns, and by the magnitude of the electron current density (space-charge effects). By minimizing these effects, up to 3.7 GW output power has been produced at an efficiency of 40%.

The incorporation of vacancies, H atoms, and sp{sup 2} bond defects into single-crystal homoepitaxial (100)(2x1)- and(111)-oriented CVD diamond was simulated by atomic-scale kinetic Monte Carlo. Simulations were performed for substrate temperatures from 600 C to 1200 C with 0.4% CH{sub 4} in the feed gas, and for 0.4% to 7% CH{sub 4} feeds with a substrate temperature of 800 C. The concentrations of incorporated H atoms increase with increasing substrate temperature and feed gas composition, and sp{sup 2} bond trapping increases with increasing feed gas composition. Vacancy concentrations are low under all conditions. The ratio of growth rate to H atom concentration is highest around 800-900 C, and the growth rate to sp{sup 2} ratio is maximum around 1% CH{sub 4}, suggesting that these conditions are ideal for economical diamond growth under the simulated conditions.

Abstract not provided.

Under both static and common MAS conditions (< 15 kHz) the question of residual X-Y heteronuclear decoupling can become a complicating factor in the analysis of various NMR results. In our lab the impact of {sup 31}P-{sup 23}Na dipolar coupling on the observed {sup 23}Na M{sub 2} relaxation for a series of sodium phosphate glasses was recently investigated by employing continuous wave {sup 31}P decoupling during the entire pulse sequence. Initially these efforts were complicate by the inability to provide a gating pulse during the data acquisition using the standard Bruker nomenclature, go=2, for the acquisition loop. A pulse sequence to overcome these restrictions is given below. Our AMX400 instrument is configured with a 3 channel MCI, but utilizes a linear AMT amplifier on the 3rd channel (requiring gating pulse via the C4 program call during the entire time it is on). The standard acquisition loop has been replaced by direct adc and aq commands for data acquisition. Unlike the go=2 statement which does not allow a C4 gating command to be included, these individual acquisition commands can all include distinct C4 gating.

ZX is a new z-pinch accelerator planned as the next generation z-pinch driver at SNL, and as an intermediate step towards X-1. It is planned to drive either a single 50 MA z-pinch load, or two 25 to 30 MA z pinches. Three designs for the ZX accelerator are presented. All require 7 to 8 MV at the insulator stack to drive the z-pinch load to implosion in 100 to 120 ns. Two of the designs are based on the Z accelerator, and use water-line technology; a transit-time-isolated water adder, and a water transformer. The third design uses inductive-voltage adders in water. They also describe a low-inductance insulator stack design that helps minimize voltage requirements. This design is evaluated for water and vacuum break-down using JCM, THM, and magnetic-flashover-inhibition criteria.

The Z-accelerator at the Sandia National Laboratories (SNL) was modified in 1996 to deliver a 20 MA pulse to a z-pinch load in 100 ns. The pulsed-power driver is a 36-module waterline accelerator. Each waterline contains four self-break switches as part of the pulse-forming section. A study was conducted to investigate the effects of increasing the capacitance of the waterline switches on the shape of the electrical prepulse at the load. Past studies have shown that increasing the prepulse at the z-pinch load increases the x-ray output power. In this study, one set of switches with its surrounding waterline hardware was modeled in 3-D and capacitance calculated using the electrostatic code, COULOME. The capacitance values were used in a SCREAMER model of the Z-accelerator. SCREAMER an SNL developed, lumped-element circuit code was used to calculate the time-dependent current waveforms delivered to the z-pinch load. The design was changed and a new capacitance matrix and output waveforms were calculated. This paper presents the results of the COULOMB 3-D modeling, and the SCREAMER circuit-model analyses.

A suite of plate loading tests has recently been conducted by Sandia National Laboratories at the Exploratory Studies Facility at Yucca Mountain, Nevada. Fielding of these in situ tests as well as other approaches undertaken for the determination of rock mass modulus are described. The various methodologies are evaluated and their data compared. Calculation by existing empirical methods and numerical modeling are compared to each other as well as to field data.

Stress measurement test chips were flip chip assembled to organic BGA substrates containing micro-vias and epoxy build-up interconnect layers. Mechanical degradation observed during temperature cycling was correlated to a damage theory developed based on 3D finite element method analysis. Degradation included die cracking, edge delamination and radial fillet cracking.

We discuss the design and testing of a miniaturized explosives preconcentrator that can be used to enhance the capabilities of man-portable field detection systems, such as those based on ion mobility spectrometry (IMS). The preconcentrator is a smaller version of a similar device that was developed recently at Sandia National Laboratories for use in a trace detection portal that screens personnel for explosives. Like its predecessor, this preconcentrator is basically a filtering device that allows a small amount of explosive residue in a large incoming airflow to be concentrated into a much smaller air volume via adsorption and resorption, prior to delivery into a chemical detector. We discuss laboratory testing of this preconcentrator interfaced to a commercially available IMS-based detection system, with emphasis on the explosives 2,4,6-trinitrotoluene (TNT) and cyclotrimethylenetrinitramine (RDX). The issues investigated include optimization of the preconcentrator volume and inlet airflow, the use of different types of adsorbing surfaces within the preconcentrator, Wd preconcentrator efficiency and concentration factor. We discuss potential field applications of the preconcentrator, as well as avenues for further investigations and improvements.

A portable, autonomous, hand-held chemical laboratory ({mu}ChemLab{trademark}) is being developed for trace detection (ppb) of chemical warfare (CW) agents and explosives in real-world environments containing high concentrations of interfering compounds. Microfabrication is utilized to provide miniature, low-power components that are characterized by rapid, sensitive and selective response. Sensitivity and selectivity are enhanced using two parallel analysis channels, each containing the sequential connection of a front-end sample collector/concentrator, a gas chromatographic (GC) separator, and a surface acoustic wave (SAW) detector. Component design and fabrication and system performance are described.

During the development and qualification of a radiation-hardened, 0.5 {micro}m shallow trench isolation technology, several yield-limiting defects were observed. The 256K (32K x 8) static-random access memories (SRAMs) used as a technology characterization vehicle had elevated power supply current during wafer probe testing. Many of the die sites were functional, but exhibited quiescent power supply current (I{sub DDQ}) in excess of 100 {micro}A, the present limit for this particular SRAM. Initial electrical analysis indicated that many of the die sites exhibited unstable I{sub DDQ} that fluctuated rapidly. We refer to this condition as ''jitter.'' The I{sub DDQ} jitter appeared to be independent of temperature and predominantly associated with the larger 256K SRAMs and not as prevalent in the 16K SRAMs (on the same reticle set). The root cause of failure was found to be two major processing problems: salicide bridging and stress-induced dislocations in the silicon islands.

As information systems have become distributed over many computers within the enterprise, managing those applications has become increasingly important. This is an emerging area of work, recognized as such by many large organizations as well as many start-up companies. In this report, we present a summary of the move to distributed applications, some of the problems that came along for the ride, and some specific examples of the tools and techniques we have used to analyze distributed applications and gain some insight into the mechanics and politics of distributed computing.

A description and user's guide are given for a computer program, PATTRN, developed at Sandia National Laboratories for use in sensitivity analyses of complex models. This program is intended for use in the analysis of input-output relationships in Monte Carlo analyses when the input has been selected using random or Latin hypercube sampling. Procedures incorporated into the program are based upon attempts to detect increasingly complex patterns in scatterplots and involve the detection of linear relationships, monotonic relationships, trends in measures of central tendency, trends in measures of variability, and deviations from randomness. The program was designed to be easy to use and portable.

This report documents the history of Building 828 in Sandia National Laboratories' Technical Area I. Building 828 was constructed in 1946 as a mechanical test laboratory for Los Alamos' Z-Division (later Sandia) as it moved to Sandia Base. The building has undergone significant remodeling over the years and has had a variety of occupants. The building was evaluated in compliance with the National Historic Preservation Act, but was not eligible for the National Register of Historic Places. Nevertheless, for many Labs employees, it was a symbol of Sandia's roots in World War II and the Manhattan Project.

A major cause of semiconductor yield degradation is contaminant particles that deposit on wafers while they reside in processing tools during integrated circuit manufacturing. This report presents numerical models for assessing particle transport and deposition in a parallel-plate geometry characteristic of a wide range of single-wafer processing tools: uniform downward flow exiting a perforated-plate showerhead separated by a gap from a circular wafer resting on a parallel susceptor. Particles are assumed to originate either upstream of the showerhead or from a specified position between the plates. The physical mechanisms controlling particle deposition and transport (inertia, diffusion, fluid drag, and external forces) are reviewed, with an emphasis on conditions encountered in semiconductor process tools (i.e., sub-atmospheric pressures and submicron particles). Isothermal flow is assumed, although small temperature differences are allowed to drive particle thermophoresis. Numerical solutions of the flow field are presented which agree with an analytic, creeping-flow expression for Re < 4. Deposition is quantified by use of a particle collection efficiency, which is defined as the fraction of particles in the reactor that deposit on the wafer. Analytic expressions for collection efficiency are presented for the limiting case where external forces control deposition (i.e., neglecting particle diffusion and inertia). Deposition from simultaneous particle diffusion and external forces is analyzed by an Eulerian formulation; for creeping flow and particles released from a planar trap, the analysis yields an analytic, integral expression for particle deposition based on process and particle properties. Deposition from simultaneous particle inertia and external forces is analyzed by a Lagrangian formulation, which can describe inertia-enhanced deposition resulting from particle acceleration in the showerhead. An approximate analytic expression is derived for particle velocity at the showerhead exit as a function of showerhead geometry, flow rate, and gas and particle properties. The particle showerhead-exit velocity is next used as an initial condition for particle transport between the plates to determine whether the particle deposits on the wafer, as a function of shower-head-exit particle velocity, the plate separation, flow rate, and gas and particle properties. Based on the numerical analysis, recommendations of best practices are presented that should help tool operators and designers reduce particle deposition in real tools. These guidelines are not intended to replace detailed calculations, but to provide the user with a general feel for inherently-clean practices.

This LDRD project explored the fundamental physics of a new class of photonic materials, photonic bandgap structures (PBG), and examine its unique properties for the design and implementation of photonic devices on a nano-meter length scale for the control and confinement of light. The low loss, highly reflective and quantum interference nature of a PBG material makes it one of the most promising candidates for realizing an extremely high-Q resonant cavity, >10,000, for optoelectronic applications and for the exploration of novel photonic physics, such as photonic localization, tunneling and modification of spontaneous emission rate. Moreover, the photonic bandgap concept affords us with a new opportunity to design and tailor photonic properties in very much the same way we manipulate, or bandgap engineer, electronic properties through modern epitaxy.

A database of mechanical properties for weldment fusion and heat-affected zones was established for AerMet{reg_sign}100 alloy, and a study of the welding metallurgy of the alloy was conducted. The properties database was developed for a matrix of weld processes (electron beam and gas-tungsten arc) welding parameters (heat inputs) and post-weld heat treatment (PWHT) conditions. In order to insure commercial utility and acceptance, the matrix was commensurate with commercial welding technology and practice. Second, the mechanical properties were correlated with fundamental understanding of microstructure and microstructural evolution in this alloy. Finally, assessments of optimal weld process/PWHT combinations for cotildent application of the alloy in probable service conditions were made. The database of weldment mechanical properties demonstrated that a wide range of properties can be obtained in welds in this alloy. In addition, it was demonstrated that acceptable welds, some with near base metal properties, could be produced from several different initial heat treatments. This capability provides a means for defining process parameters and PWHT's to achieve appropriate properties for different applications, and provides useful flexibility in design and manufacturing. The database also indicated that an important region in welds is the softened region which develops in the heat-affected zone (HAZ) and analysis within the welding metallurgy studies indicated that the development of this region is governed by a complex interaction of precipitate overaging and austenite formation. Models and experimental data were therefore developed to describe overaging and austenite formation during thermal cycling. These models and experimental data can be applied to essentially any thermal cycle, and provide a basis for predicting the evolution of microstructure and properties during thermal processing.

The original scope of the project was to research improvements to the processes and materials used in the manufacture of wood-epoxy blades, conduct tests to qualify any new material or processes for use in blade design and subsequently build and test six blades using the improved processes and materials. In particular, ABM was interested in reducing blade cost and improving quality. In addition, ABM needed to find a replacement material for the mature Douglas fir used in the manufacturing process. The use of mature Douglas fir is commercially unacceptable because of its limited supply and environmental concerns associated with the use of mature timber. Unfortunately, the bankruptcy of FloWind in June 1997 and a dramatic reduction in AWT sales made it impossible for ABM to complete the full scope of work. However, sufficient research and testing were completed to identify several promising changes in the blade manufacturing process and develop a preliminary design incorporating these changes.

This report presents an implementation of the Berlekamp-Massey linear feedback shift-register (LFSR) synthesis algorithm in the C programming language. Two pseudo-code versions of the code are given, the operation of LFSRs is explained, C-version of the pseudo-code versions is presented, and the output of the code, when run on two input samples, is shown.

Decontamination of radioactive contaminated stainless steel using the ESR process is investigated by conducting thermophysical and thermochemical laboratory studies on the slag. The ESR base slag investigated in this research project is 60wt%CaF{sub 2}-20wt%CaO-20wt%Al{sub 2}O{sub 3}. In this report, we present the data obtained to date on relevant slag properties, capacity to incorporate the radioactive contaminant (using CeO{sub 3}) as surrogate, simulant for PUO{sub 2} and UO{sub 2}, slag-metal partition coefficient, volatilization rate and volatile species, viscosity, electrical conductivity and surface tension as a function of temperature. The impact of these properties on the ESR decontamination process is presented.

A theoretical analysis has been completed for a proposed induction logging tool designed to yield data which are used to generate three dimensional images of the region surrounding a well bore. The proposed tool consists of three mutually orthogonal magnetic dipole sources and multiple 3 component magnetic field receivers offset at different distances from the source. The initial study employs sensitivity functions which are derived by applying the Born Approximation to the integral equation that governs the magnetic fields generated by a magnetic dipole source located within an inhomogeneous medium. The analysis has shown that the standard coaxial configuration, where the magnetic moments of both the source and the receiver are aligned with the axis of the well bore, offers the greatest depth of sensitivity away from the borehole compared to any other source-receiver combination. In addition this configuration offers the best signal-to-noise characteristics. Due to the cylindrically symmetric nature of the tool sensitivity about the borehole, the data generated by this configuration can only be interpreted in terms of a two-dimensional cylindrical model. For a fill 3D interpretation the two radial components of the magnetic field that are orthogonal to each other must be measured. Coil configurations where both the source and receiver are perpendicular to the tool axis can also be employed to increase resolution and provide some directional information, but they offer no true 3D information.

Abstract not provided.

Abstract not provided.

The understanding and manipulation of the point defect structure in oxide glasses have been critical to the enhanced performance and reliability of optical-fiber-based, photosensitive photonic devices that currently found widespread application in telecommunications and remote sensing technologies. We provide a brief review of past research investigating photosensitive mechanisms in germanosilicate glasses, the primary material system used in telecommunications fibers. This discussion motivates an overview of ongoing work within our laboratories to migrate photosensitive glass technologies to a planar format for integrated photonic applications. Using reactive-atmosphere, RF-magnetron sputtering, we have demonstrated control of glass defect structure during synthesis, thereby controlling both the material photosensitivity (i. e. dispersion and magnitude of the refractive index change) and its environmental stability.

We examined the ability of a halophilic bacterium (WFP 1A) isolated from the Waste Isolation Pilot Plant (WIPP) site to accumulate uranium in order to determine the potential for biocolloid facilitated actinide transport. The bacterial cell Surface functional groups involved in the complexation of the actinide were determined by titration. Uranium, added as uranyl nitrate, was removed from solution at pH 5 by cells but at pH 7 and 9 very little uranium was removed due to its limited volubility. Although present as soluble species, uranyl citrate at pH 5, 7, and 9, and uranyl carbonate at pH 9 were not removed by the bacterium because they were not bioavailable due to their neutral or negative charge. Addition of uranyl EDTA to brine at pH 5, 7, and 9 resulted in the immediate precipitation of U. Transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS) analysis revealed that uranium was not only associated with the cell surface but also accumulated intracellulary as uranium-enriched granules. Extended X-ray absorption fine structure (EXAFS) analysis, of the bacterial cells indicated the bulk sample contained more than one uranium phase. Nevertheless these results show the potential for the formation of actinide bearing bacterial biocolloids that are strictly regulated by the speciation and bioavailability of the actinide.

Both the increased complexity of integrated circuits, resulting in six or more levels of integration, and the increasing use of flip-chip packaging have driven the development of integrated circuit (IC) failure analysis tools that can be applied to the backside of the chip. Among these new approaches are focused ion beam (FIB) tools and processes for performing chip edits/repairs from the die backside. This paper describes the use of backside FIB for a failure analysis application rather than for chip repair. Specifically, we used FIB technology to prepare an IC for inspection of voided metal interconnects (''lines'') and vias. Conventional FIB milling was combined with a super-enhanced gas assisted milling process that uses XeF{sub 2} for rapid removal of large volumes of bulk silicon. This combined approach allowed removal of the TiW underlayer from a large number of Ml lines simultaneously, enabling rapid localization and plan view imaging of voids in lines and vias with backscattered electron (BSE) imaging in a scanning electron microscope (SEM). Sequential cross sections of individual voided vias enabled us to develop a 3-d reconstruction of these voids. This information clarified how the voids were formed, helping us identify the IC process steps that needed to be changed.

As part of a collaborative effort between Sandia National Laboratories and the University of Kentucky to develop a deployable mirror for remote sensing applications, research in shape sensing and control algorithms that leverage the distributed nature of electron gun excitation for piezoelectric bimorph mirrors is summarized. A coarse shape sensing technique is developed that uses reflected light rays from the sample surface to provide discrete slope measurements. Estimates of surface profiles are obtained with a cubic spline curve fitting algorithm. Experiments on a PZT bimorph illustrate appropriate deformation trends as a function of excitation voltage. A parallel effort to effect desired shape changes through electron gun excitation is also summarized. A one dimensional model-based algorithm is developed to correct profile errors in bimorph beams. A more useful two dimensional algorithm is also developed that relies on measured voltage-curvature sensitivities to provide corrective excitation profiles for the top and bottom surfaces of bimorph plates. The two algorithms are illustrated using finite element models of PZT bimorph structures subjected to arbitrary disturbances. Corrective excitation profiles that yield desired parabolic forms are computed, and are shown to provide the necessary corrective action.

We report on recent studies of the effects of 50 keV focused ion beam (FIB) exposure on MOS transistors. We demonstrate that the changes in value of transistor parameters (such as threshold voltage, V{sub t}) are essentially the same for exposure to a Ga+ ion beam at 30 and 50 keV under the same exposure conditions. We characterize the effects of FIB exposure on test transistors fabricated in both 0.5 {micro}m and 0.225 {micro}m technologies from two different vendors. We report on the effectiveness of overlying metal layers in screening MOS transistors from FIB-induced damage and examine the importance of ion dose rate and the physical dimensions of the exposed area.

Both the increased complexity of integrated circuits, resulting in six or more levels of integration, and the increasing use of flip-chip packaging have driven the development of integrated circuit (IC) failure analysis tools that can be applied to the backside of the chip. Among these new approaches are focused ion beam (FIB) tools and processes for performing chip edits/repairs from the die backside. This paper describes the use of backside FIB for a failure analysis application rather than for chip repair. Specifically, they used FIB technology to prepare an IC for inspection of voided metal interconnects (lines) and vias. Conventional FIB milling was combined with a super-enhanced gas assisted milling process that uses XeF{sub 2} for rapid removal of large volumes of bulk silicon. This combined approach allowed removal of the TiW underlayer from a large number of Ml lines simultaneously, enabling rapid localization and plan view imaging of voids in lines and vias with backscattered electron (BSE) imaging in a scanning electron microscopy (SEM). Sequential cross sections of individual voided vias enabled them to develop a 3-d reconstruction of these voids. This information clarified how the voids were formed, helping to identify the IC process steps that needed to be changed.

Crystalline silicon continues to be the dominant semiconductor material used for terrestrial photovoltaics. This paper discusses the scientific issues associated with silicon photovoltaics processing, and cell design that may yield cell and module performance improvements that are both evolutionary and revolutionary in nature. We first survey critical issues in ''thick'' crystalline silicon photovoltaics, including novel separations processes for impurity removal, impurity and defect fundamentals, interface passivation, the role of hydrogen. Second, we outline emerging opportunities for creation of a very different ''thin-layer'' silicon cell structure, including the scientific issues and engineering challenges associated with thin-layer silicon processing and cell design.

There has been considerable interest in developing dry processes which can effectively replace wet processing in the manufacture of large area photovoltaic devices. Environmental and health issues are a driver for this activity because wet processes generally increase worker exposure to toxic and hazardous chemicals and generate large volumes of liquid hazardous waste. Our work has been directed toward improving the performance of screen-printed solar cells while using plasma processing to reduce hazardous chemical usage.

The joint USNRC/CEC consequence uncertainty study was chartered after the development of two new probabilistic accident consequence codes, MACCS in the U.S. and COSYMA in Europe. Both the USNRC and CEC had a vested interest in expanding the knowledge base of the uncertainty associated with consequence modeling, and teamed up to co-sponsor a consequence uncertainty study. The information acquired from the study was expected to provide understanding of the strengths and weaknesses of current models as well as a basis for direction of future research. This paper looks at the elicitation process implemented in the joint study and discusses some of the uncertainty distributions provided by eight panels of experts from the U.S. and Europe that were convened to provide responses to the elicitation. The phenomenological areas addressed by the expert panels include atmospheric dispersion and deposition, deposited material and external doses, food chain, early health effects, late health effects and internal dosimetry.

In this study we analyze the feasibility of three dimensional (3D) electromagnetic (EM) imaging from a single borehole. The proposed logging tool consists of three mutually orthogonal magnetic dipole sources and multiple three component magnetic field receivers. A sensitivity analysis indicates that the most important sensor configuration for providing 3D geological information about the borehole consists of a transmitter with moment aligned parallel to the axis of the borehole, and receivers aligned perpendicular to the axis. The standard coaxial logging configuration provides the greatest depth of sensitivity compared to other configurations, but offers no information regarding 3D structure. Two other tool configurations in which both the source and receiver are aligned perpendicular to the borehole axis provide some directional information and therefore better image resolution, but not true 3D information. A 3D inversion algorithm has been employed to demonstrate the plausibility of 3D inversion using data collected with the proposed logging tool. This study demonstrates that an increase in image resolution results when three orthogonal sources are incorporated into the logging tool rather than a single axially aligned source.

We report highly efficient, low-threshold-current edge-emitting lasers where both the optical waveguide and lateral current confinement are achieved by lateral selective oxidation of AlGaAs. External differential quantum efficiency in excess of 95% and 40% wall-plug efficiency are demonstrated in 600 {micro}m-long devices without facet coatings. Shorter, 300-{micro}m-long, uncoated devices have <6 mA threshold currents. This high-performance is a combined result of placement of the oxide layers so as to achieve the minimum optical mode volume and bi-parabolic grading of the Al{sub x}Ga{sub 1{minus}x}As heteroepitaxy for minimum height/potential barriers, less than 15 meV, created by the wide-energy-gap layers required for selective wet oxidation. Since the initial development of wet AlGaAs oxidation methods, a number of oxidized edge-emitting laser concepts have been tried. The most successful of these have used lateral selective oxidation of AlGaAs layers between 100 and 300 nm thickness. These layers have been used as current restricting apertures or for both current restriction and lateral waveguiding. Use of an oxide layer above and below the laser active region offers the ability to create a self-aligned waveguide with current apertures on both sides of the pn-junction in a process requiring only one epitaxial growth step. Previous use apertures for these dual purposes resulted multi-moded lasers with reduced efficiency and elevated threshold current density due to non-ideal formation of the waveguide and possibly excess stress caused by the thick (300 nm) oxide layer.

It is shown that lattice disorder induced by Nb and Ca substitution has a strong influence on the dielectric and relaxational properties of KTaO{sub 3}. Both substituents are believed to occupy off-center positions at the Ta site, and the difference in valence between the Ca{sup 2+} and Ta{sup 5+} ions leads to the formation of oxygen vacancies (V{sub 0}). Specifically, for a KTa{sub 1{minus}x}Nb{sub x}O{sub 3}:Ca crystal with x = 0.023 and with a 0.055 at.% Ca doping they observe: (1) a ferroelectric transition at atmospheric pressure (1 bar); (2) a large enhancement of the transition temperature by Ca doping; (3) a pressure-induced crossover from ferroelectric-to-relaxor behavior; (4) the impending vanishing of the relaxor phase at high pressure; (5) the reorientation of the Ca-oxygen vacancy (Ca:V{sub 0}) pair defect; and (6) the variation of the energetics and dynamics of this reorientation with pressure. Most of these effects are associated with Nb- and Ca-induced dipolar entities and appear to be general features of soft mode ferroelectrics with random-site polar nanodomains. The ferroelectric-to-relaxor crossover can be understood in terms of a large decrease with pressure in the correlation length among polar nanodomains--a unique property of soft ferroelectric mode systems.

Some time ago we presented evidence that, under nonhydrostatic loading, the F{sub R1} {r_arrow} A{sub O} polymorphic transformation of unpoled PZT 95/5-2Nb (PNZT) ceramic began when the maximum compressive stress equaled the hydro-static pressure at which the transformation otherwise took place. Recently we showed that this simple criterion did not apply to nonhydrostatically compressed, poled ceramic. However, unpoled ceramic is isotropic, whereas poled ceramic has a preferred crystallographic orientation and is mechanically anisotropic. If we further assume that the transformation depends not only on the magnitude of the compressive stress, but also its orientation relative to some feature(s) of PNZT's crystallography, then these disparate results can be qualitatively resolved. It has long been known that this transformation can be triggered in uniaxial compression. Our modified hypothesis makes two predictions for transformation of unpoled polycrystals under uniaxial stress: (i) the transformation should begin when the maximum compressive stress, {sigma}{sub 1}, equals the hydrostatic pressure for transformation, and (ii) a steadily increasing axial stress should be required to drive the transformation.

A hybrid FEM/MoM model has been implemented to compute the coupling of fields into a cavity through narrow slot apertures having depth. The model utilizes the slot model of Warne and Chen [23]-[29] which takes into account the depth of the slot, wall losses, and inhomogeneous dielectrics in the slot region. The cavity interior is modeled with the mixed-order, covariant-projection hexahedral elements of Crowley [32]. Results are given showing the accuracy and generality of the method for modeling geometrically complex slot-cavity combinations.

Characterization tools have been developed to study the performance characteristics and reliability of surface micromachined actuators. These tools include (1) the ability to electrically stimulate or stress the actuator, (2) the capability to visually inspect the devices in operation, (3) a method for capturing operational information, and (4) a method to extract performance characteristics from the operational information. Additionally, a novel test structure has been developed to measure electrostatic forces developed by a comb drive actuator.

We generally use large-scale hydrocodes to study the dynamic response of targets to influence pulsed radiation loads. However, for many applications where the desired solution does not require a detailed specification of pressure- or velocity-time histories, there are simple analytic approaches that can yield surprisingly accurate results. Examples include determining either the final velocity of a radiation-driven flying plate or the impulse delivered to a structural element. These methods are all based on relatively straightforward use of conservation of mass and momentum, but they typically need one scaling-law parameter. In this context, short pulse means short compared to the characteristic time of the desired response, which allows for the phenomena to be essentially uncoupled. High fluence means that the input energy is great enough to yield vaporization or blowoff of one or more portions of the configuration. We discuss some of these methods, give examples, and suggest limitations and criteria for their use.

Heavy ion TOF ERD combined with energy detection (E-TOF-ERD) is a powerful analytical technique taking advantage of the following facts: the scattering cross section is usually very high ({approximately}10{sup {minus}21} cm{sup 2}/sr) compared to regular He RBS ({approximately}10{sup {minus}25} cm{sup 2}/sr), contrary to what happens with the energy resolution in ordinary surface solid barrier detectors, time resolution is almost independent of the atomic mass of the detected element, and the detection in coincidence of time and energy signals allows for the mass separation of overlapping signals with the same energy (or time of flight). Measurements on several oxides have been performed with the E-TOF-ERD set up at Sandia National Laboratories using an incident beam of 10-15 MeV Au. The information on the composition of the sample is obtained from the time domain spectrum, which is converted to energy domain, and then, using existing software codes, the analysis is performed. During the quantification of the results, they have found problems related to the interaction of the beam with the sample and to the tabulated values of the stopping powers for heavy ions.

Characterization tools have been developed to study the performance characteristics and reliability of surface micromachined actuators. These tools include (1) the ability to electrically stimulate or stress the actuator, (2) the capability to visually inspect the devices in operation, (3) a method for capturing operational information, and (4) a method to extract performance characteristics from the operational information. Additionally, a novel test structure has been developed to measure electrostatic forces developed by a comb drive actuator.

Direct metal deposition technologies produce complex, near net shape components from CAD solid models. Most of these techniques fabricate a component by melting powder in a laser weld pool, rastering this weld bead to form a layer, and additively constructing subsequent layers. This talk describes a new direct metal deposition process, known as WireFeed, whereby a small diameter wire is used instead of powder as the feed material to fabricate components. Currently, parts are being fabricated from stainless steel. Microscopy studies show the WireFeed parts to be fully dense with fine microstructural features. Initial mechanical tests show stainless steel parts to have good strength values with retained ductility.

Experimental conditions are studied to optimize transient experiments for estimating temperature dependent thermal conductivity and volumetric heat capacity. Thermal properties are assumed to vary linearly with temperature; a total of four parameters describe linearly varying thermal conductivity and volumetric heat capacity. A numerical model of experimental configurations is studied to determine the optimum conditions to conduct the experiment. The criterion D-optimality is used to study the sensor locations, heating duration and magnitude, and experiment duration for finite and semi-infinite configurations. Results indicate that D-optimality is an order of magnitude larger for the finite configuration and hence will provide estimates with a smaller confidence region.

A novel solution method has been developed to solve the linear Boltzmann equation on an unstructured triangular mesh. Instead of tackling the first-order form of the equation, this approach is based on the even/odd-parity form in conjunction with the conventional mdtigroup discrete-ordinates approximation. The finite element method is used to treat the spatial dependence. The solution method is unique in that the space-direction dependence is solved simultaneously, eliminating the need for the conventional inner iterations, and the method is well suited for massively parallel computers.

Molecular dynamics (MD) simulations were performed on dense liquids of polyethylene chains of 24 and 66 united atom CH{sub 2} units. A series of models was studied ranging in atomistic detail from coarse-grained, freely-jointed, tangent site chains to realistic, overlapping site models subjected to bond angle restrictions and torsional potentials. These same models were also treated with the self-consistent, polymer reference interaction site model (PRISM) theory. The intramolecular and total structure factors, as well as, the intermolecular radial distribution functions g(r) and direct correlation functions C(r) were obtained from theory and simulation. Angular correlation functions were also simulation obtained from the MD simulations. Comparisons between theory and reveal that PRISM theory works well for computing the intermolecular structure of coarse-grained chain models, but systematically underpredicts the extent of intermolecular packing as more atomistic details are introduced into the model. A consequence of g(r) having insufficient structure is that the theory yields an isothermal compressibility that progressively becomes larger, relative to the simulations, as overlapping the PRISM sites and angular restrictions are introduced into the model. We found that theory could be considerably improved by adding a tail function to C(r) beyond the effective hard core diameter. The range of this tail function was determined by requiring the theory to yield the correct compressibility.

The authors have synthesized and characterized two novel Sr compounds: [Sr({mu}-ONc){sub 2}(HONc){sub 4}]{sub 2} (1, ONc = O{sub 2}CCH{sub 2}CMe{sub 3}), and Sr{sub 5}({mu}{sub 4}-O)({mu}{sub 3}-ONep){sub 4}({mu}-ONep){sub 4}(HONep)(solv){sub 4} [ONep = OCH{sub 2}CMe{sub 3}, solv = tetrahydrofuran (THF), 2a; 1-methyl-imidazole (MeIm), (2b)], that demonstrate increased solubility in comparison to the commercially available Sr precursors. The two metal centers of 1 share 4 unidentate bridging {mu}-ONc ligands and complete their octahedral geometry through the coordination of 4 monodentate terminal HONc ligands. The structure arrangement of the central core of 2a and b are identical, wherein 4 octahedral Sr atoms are arranged in a square geometry around a {mu}{sub 4}-O ligand. An additional 7-coordinated Sr atom sits directly atop the {mu}{sub 4}-O to form a square base pyramidal arrangement of the Sr atoms but the apical Sr-O distance is too long to be considered a bond. In solution, compound 1 is disrupted forming a monomer but 2a and b retain their structures.

Plate impact, shock wave experiments provide a unique method to investigate the time-dependent mechanisms and the kinetics associated with pressure-induced phenomena, such as chemical reactions and phase transformations. The very rapid and well defined loading conditions associated with plate-impact experiments permit real-time examination of the shock-induced changes. Further, the ability to propagate the shock wave along various crystallographic directions provides the means to perform careful analysis of the stress and orientational dependence. Recently, an experimental method has been developed to observe real-time changes in the absorption transmission of materials, with 100 or 200 ps resolution, in single-event, plate impact shock experiments [1-4]. These data can provide useful information regarding the material under investigation. In particular, the dependence of the absorption edge on photon energy can distinguish between direct and indirect electronic transitions, and can provide an estimate of the band-gap energy of the material [5]. Along with ab-initio techniques to calculate the electronic structure of a crystalline system, this electronic information can be used to gain insight regarding the crystal structure. As described in Ref. [1,2,4] the wurtzite-to-rocksalt phase transition in cadmium sulfide (CdS) is well suited to investigation through the use of fast electronic spectroscopy; the wurtzite and rocksalt phases exhibit a direct and indirect band gap with band gap energies of 2.5 and 1.5-1.7 eV, respectively [6-8]. The intent of this work was to use picosecond electronic spectroscopy and ab-initio methods to examine the real-time structural changes that occur in the initial stages of the shock-induced wurtzite-to-rocksalt phase transition in single crystal CdS.

Recently there has been a noted worldwide increase in violent actions including attempted sabotage at nuclear power plants. Several organizations, such as the International Atomic Energy Agency and the US Nuclear Regulatory Commission, have guidelines, recommendations, and formal threat- and risk-assessment processes for the protection of nuclear assets. Other examples are the former Defense Special Weapons Agency, which used a risk-assessment model to evaluate force-protection security requirements for terrorist incidents at DOD military bases. The US DOE uses a graded approach to protect its assets based on risk and vulnerability assessments. The Federal Aviation Administration and Federal Bureau of Investigation conduct joint threat and vulnerability assessments on high-risk US airports. Several private companies under contract to government agencies use formal risk-assessment models and methods to identify security requirements. The purpose of this paper is to survey these methods and present an overview of all potential types of sabotage at nuclear power plants. The paper discusses emerging threats and current methods of choice for sabotage--especially vehicle bombs and chemical attacks. Potential consequences of sabotage acts, including economic and political; not just those that may result in unacceptable radiological exposure to the public, are also discussed. Applicability of risk-assessment methods and mitigation techniques are also presented.

The vulnerability analysis methodology developed for fixed nuclear material sites has proven to be extremely effective in assessing associated transportation issues. The basic methods and techniques used are directly applicable to conducting a transportation vulnerability analysis. The purpose of this paper is to illustrate that the same physical protection elements (detection, delay, and response) are present, although the response force plays a dominant role in preventing the theft or sabotage of material. Transportation systems are continuously exposed to the general public whereas the fixed site location by its very nature restricts general public access.

To date, the Department of Energy's (DOE) Material Protection, Control, and Accountancy (MPC and A) program has assisted in the implementation of operational site-wide MPC and A systems at several nuclear facilities in Russia. Eleven sites from the civilian sector have completed the site-wide installations and two have completed sub-site installations. By the end of 1999, several additional sites will have completed site-wide and sub-site system installations through DOE assistance. the effort at the completed sites has focused primarily on the design, integration, and installation of upgraded MPC and A systems. In most cases, little work has been performed to ensure that the installed systems will be sustained. Because of concerns that the installed systems would not be operated in the future, DOE established a sustainability pilot program involving the 11 sites. The purpose of DOE's MPC and A Sustainability Program is to ensure that MPC and A upgrades installed at sites in Russia are effective and will continue to operate over the long term. The program mission is to work with sites where rapid upgrades have been completed to cultivate enduring and consistent MPC and A practices. The program attempts to assist the Russian sites to develop MPC and A organizations that will operate, maintain, and continue to improve the systems and procedures. Future assistance will strive to understand and incorporate culturally sensitive approaches so that the sites take ownership for all MPC and A matters. This paper describes the efforts of the sustainability program to date.

This work has been performed as part of the search for possible ways to utilize the capabilities of laser and particle beams techniques in shock wave and equation of state physics. The peculiarity of these techniques is that we have to deal with micron-thick targets and not well reproducible incident shock wave parameters, so all measurements should be of a high resolution and be done in one shot. Besides the Hugoniots, the experimental basis for creating the equations of state includes isentropes corresponding to unloading of shock-compressed matter. Experimental isentrope data are most important in the region of vaporization. With guns or explosive facilities, the unloading isentrope is recovered from a series of experiments where the shock wave parameters in plates of standard low-impedance materials placed behind the sample are measured [1,2]. The specific internal energy and specific volume are calculated from the measured p(u) release curve which corresponds to the Riemann integral. This way is not quite suitable for experiments with beam techniques where the incident shock waves are not well reproducible. The thick foil method [3] provides a few experimental points on the isentrope in one shot. When a higher shock impedance foil is placed on the surface of the material studied, the release phase occurs by steps, whose durations correspond to that for the shock wave to go back and forth in the foil. The velocity during the different steps, connected with the knowledge of the Hugoniot of the foil, allows us to determine a few points on the isentropic unloading curve. However, the method becomes insensitive when the low pressure range of vaporization is reached in the course of the unloading. The isentrope in this region can be measured by recording the smooth acceleration of a thin witness plate foil. With the mass of the foil known, measurements of the foil acceleration will give us the vapor pressure.

The Autoridad Regulatoria Nuclear of Argentina (ARN), the International Atomic Energy Agency (IAEA), ABACC, the US Department of Energy, and the US Support Program POTAS, cooperated in the development of a Remote Monitoring System for nuclear nonproliferation efforts. This system was installed at the Embalse Nuclear Power Station last year to evaluate the feasibility of using radiation sensors in monitoring the transfer of spent fuel from the spent fuel pond to dry storage. The key element in this process is to maintain continuity of knowledge throughout the entire transfer process. This project evaluated the fundamental design and implementation of the Remote Monitoring System in its application to regional and international safeguard efficiency. New technology has been developed to enhance the design of the system to include storage capability on board sensor platforms. This evaluation has led to design enhancements that will assure that no data loss will occur during loss of RF transmission of the sensors.

J. P. Wilcoxon and G. A. Samara Crystalline, size-selected Si nanocrystals in the size range 1.8-10 nm grown in inverse micellar cages exhibit highly structured optical absorption and photoluminescence (PL) across the visible range of the spectrum. The most intense PL for the smallest nanocrystals produced This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, make any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. to induce a useful level of visible photoluminescence (PL) from silicon (Si). The approaches understood. Visible PL has been observed from Si nanocrystals, or quantum dots, produced by a variety of techniques including aerosols,2 colloids,3 and ion implantation.4 However, all of The optical absorption spectra of our nanocrystals are much richer in spectral features spectrum of bulk Si where the spectral features reflect the details of the band structure shown in nanocrystals estimated to have a Si core diameter of 1-2 nm. These measured quantum those in the spectrum of bulk Si in Fig. 1 are striking indicating that nanocrystals of this size 8-Room temperature PL results on an HPLC size-selected, purified 2 nm nanocrystals but blue shifted by -0.4 eV due to quantum confinement. Excitation at 245 nm yields the PL shows the PL spectrum for a similar sample excited at 490 nm (2.53 eV) trapped excitons at the surface of Si nanocrystals. The excitons are obtained for dimer bonds 1.8- 10 nm. These nanocrystals retain bulk-like optical absorption and an indirect bandgap Figure 1. The absorption spectrum of d = 2 nm Si nanocrystals compared to that of bulk7 Si. Figure 2. The extinction and PL (excitation at 490 nm) spectra ford= 8-10 nm Si nanocrystals.

Multiple-energy (30-325 keV) O{sup +} implantation into GaN field-effect transistor structures (n {approximately} 10{sup 18} cm{sup {minus}3}, 3000 {angstrom} thick) can produce as-implanted sheet resistances of 4 x 10{sup 12} {Omega}/{open_square}, provided care is taken to ensure compensation of the region up to the projected range of the lowest energy implant. The sheet resistance remains above 10{sup 7} {Omega}/{open_square} to annealing temperatures of {approximately} 650 C and displays an activation energy of 0.29 eV. No diffusion of the implanted oxygen was observed for anneals up to 800 C.

The thermal oxidation of pentacontane (C{sub 50}H{sub 102}), and of the homopolymer polyisoprene, has been investigated using {sup 17}O NMR spectroscopy. By performing the oxidation using {sup 17}O labeled O{sub 2} gas, it is possible to easily identify degradation products, even at relatively low concentrations. It is demonstrated that details of the degradation mechanism can be obtained from analysis of the {sup 17}O NMR spectra as a function of total oxidation. Pentacontane reveals the widest variety of reaction products, and exhibits changes in the relative product distributions with increasing O{sub 2} consumption. At low levels of oxygen incorporation, peroxides are the major oxidation product, while at later stages of degradation these species are replaced by increasing concentrations of ketones, alcohols, carboxylic acids and esters. Analyzing the product distribution can help in identification of the different free-radical decomposition pathways of hydroperoxides, including recombination, proton abstraction and chain scission, as well as secondary reactions. The {sup 17}O NMR spectra of thermally oxidized polyisoprene reveal fewer degradation functionalities, but exhibit an increased complexity in the type of observed degradation species due to structural features such as unsaturation and methyl branching. Alcohols and ethers formed from hydrogen abstraction and free radical termination.

A new forcefield model was developed for modeling phosphate materials that have many important applications in the electronics and biomedical industries. Molecular dynamics simulations of a series of lithium phosphate glass compositions were performed using the new forcefield model. A high concentration of three member rings (P{sub 3}O{sub 3}) was found in the glass of intermediate composition (0.2 Li{sub 2}O {center_dot} 0.8 P{sub 2}O{sub 5}) that corresponds to the minimum in the glass transition temperature curve for the compositional series.

An eddy-current scanning system is being developed to allow the International Atomic Energy Agency (IAEA) to verify the integrity of nuclear material storage containers. Such a system is necessary to detect attempts to remove material from the containers in facilities where continuous surveillance of the containers is not practical. Initial tests have shown that the eddy-current system is also capable of verifying the identity of each container using the electromagnetic signature of its welds. The DOE-3013 containers proposed for use in some US facilities are made of an austenitic stainless steel alloy, which is nonmagnetic in its normal condition. When the material is cold worked by forming or by local stresses experienced in welding, it loses its austenitic grain structure and its magnetic permeability increases. This change in magnetic permeability can be measured using an eddy-current probe specifically designed for this purpose. Initial tests have shown that variations of magnetic permeability and material conductivity in and around welds can be detected, and form a pattern unique to the container. The changes in conductivity that are present around a mechanically inserted plug can also be detected. Further development of the system is currently underway to adapt the system to verifying the integrity and identity of sealable, tamper-indicating enclosures designed to prevent unauthorized access to measurement equipment used to verify international agreements.

Surface texture promotes enhanced light absorption in Si solar cells. The quality of lower cost multicrystalline-silicon (mc-Si) has increased to the point that its cell performance is close to that of single c-Si cells, with the major difference resulting from the inability to texture mc-Si affordably. This has reduced the cost-per-watt advantage of mc-Si. Surface texturing aimed at enhanced absorption in Si has been historically obtained by creating multimicrometer-sized pyramids using anisotropic wet etchants on single-crystalline silicon that take advantage of its single crystalline orientation. Since the surface feature sizes are several times the length of the incident solar wavelengths involved, the optical analysis of the reflected and absorbed light can be understood using geometrical optics. Geometrical textures reduce reflection and improve absorption by double-bounce and oblique light coupling into the semiconductor. However, geometrical texturing suffers from several disadvantages that limit its effectiveness. Some of these are listed below: (a) Wet-chemical anisotropic etching used to form random pyramids on <100> crystal orientation is not effective in the texturing of low-cost multicrystalline wafers, (b) Anti-reflection films deposited on random features to reduce reflection have a resonant structure limiting their effectiveness to a narrow range of angles and wavelengths. Various forms of surface texturing have been applied to mc-Si in research, including laser-structuring, mechanical grinding, porous-Si etching, and photolithographically defined etching. However, these may be too costly to ever be used in large-scale production. A Japanese firm has reported the development of an RIE process using Cl{sub 2} gas, which textures multiple wafers per batch, making it attractive for mass-production [1]. Using this process, they have produced a 17.1% efficient 225-cm{sup 2} mc-Si cell, which is the highest efficiency mc-Si cell of its size ever reported. This proves that RIE texturing does not cause performance-limiting damage to Si cells. In this paper, we will discuss an RIE texturing process that avoids the use of toxic and corrosive Cl{sub 2} gas.

The safe, secure and reliable application of Microelectromechanical Systems (MEMS) devices requires knowledge about the distribution in material and mechanical properties of the small-scale structures. A new testing program at Sandia is quantifying the strength distribution using polysilicon samples that reflect the dimensions of critical MEMS components. The strength of polysilicon fabricated at Sandia's Microelectronic Development Laboratory was successfully measured using samples 2.5 microns thick, 1.7 microns wide with lengths between 15 and 25 microns. These tensile specimens have a freely moving hub on one end that anchors the sample to the silicon die and allows free rotation. Each sample is loaded in uniaxial tension by pulling laterally with a flat tipped diamond in a computer-controlled Nanoindenter. The stress-strain curve is calculated using the specimen cross section and gage length dimensions verified by measuring against a standard in the SEM.

In this paper, we introduce a new approach for altering the properties of bridged polysilsesquioxane xerogels using post-processing mobilization of the polymeric network. The bridging organic group contains latent functionalities that can be liberated thermally, photochemically, or by chemical means after the gel has been processed to a xerogel. These modifications can produce changes in density, volubility, porosity, and or chemical properties of the material. Since every monomer possesses two latent functional groups, the technique allows for the introduction of high levels of functionality in hybrid organic-inorganic materials. Dialkylenecarbonate-bridged polysilsesquioxane gels were prepared by the sol-gel polymerization of bis(triethoxysilylpropyl)carbonate (1) and bis(triethoxysilylisobutyl)-carbonate (2). Thermal treatment of the resulting non-porous xerogels and aerogels at 300-350 C resulted in quantitative decarboxylation of the dialkylenecarbonate bridging groups to give new hydroxyalkyl and olefinic substituted polysilsesquioxane monolithic xerogels and aerogels that can not be directly prepared through direct sol-gel polymerization of organotrialkoxysilanes.

Sandia National Laboratories has demonstrated significant performance gains in crystalline silicon solar cell technology through the use of plasma-processing for the deposition of silicon nitride by Plasma Enhanced Chemical Vapor Deposition (PECVD), plasma-hydrogenation of the nitride layer, and reactive-ion etching of the silicon surface prior to the deposition to decrease the reflectivity of the surface. One of the major problems of implementing plasma processing into a cell production line is the batch configuration and/or low throughput of the systems currently available. This report describes the concept of a new in-line plasma processing system that could meet the industrial requirements for a high-throughput and cost effective solution for mass production of solar cells.

Surface texturing of Si to enhance absorption particularly in the IR spectral region has been extensively investigated. Previous research chiefly examined approaches based on geometrical optics. These surface textures typically consist of pyramids with dimensions much larger than optical wavelengths. We have investigated a physical optics approach that relies on surface texture features comparable to, or smaller than, the optical wavelengths inside the semiconductor material. Light interaction at this are strongly dependent on incident polarization and surface profile. Nanoscale textures can be tuned for either narrow band, or broad band absorptive behavior. Lowest broadband reflection has been observed for triangular profiles with linewidths significantly less than 100 nm. Si nanostructures have been integrated into large ({approximately}42 cm{sup 2}) area solar cells, Internal quantum efficiency measurements in comparison with polished and conventionally textured cells show lower efficiency in the UV-visible (350-680 mu), but significantly higher IR (700-1200 nm) efficiency.

This paper describes preliminary results in the development of an acoustic wave (SAW) microsensor array. The array is based on a novel configuration that allows for three sensors and a phase reference. Two configurations of the integrated array are discussed: a hybrid multichip-module based on a quartz SAW sensor with GaAs microelectronics and a fully monolithic GaAs-based SAW. Preliminary data are also presented for the use of the integrated SAW array in a gas-phase chemical micro system that incorporates microfabricated sample collectors and concentrators along with gas chromatography (GC) columns.

Chemically sensitive polymers coated on delay lines utilizing shear horizontal surface acoustic wave (SH-SAW) sensors are investigated for the detection of organic analytes in liquid environments. The SH-SAW sensor platform was designed and fabricated on 36{degree} rotated Y-cut LiTaO{sub 3}. By depositing a SiO{sub 2} dielectric layer over the entire device prior to applying the polymer film, partial electrical passivation of the interdigital transducers (IDT) is obtained while increasing the mass sensitivity of the device. Changes in the mechanical properties of the chemically sensitive polymer materials were clearly detectable through a frequency shift at least one order of magnitude larger than that of a coated-quartz crystal resonator (QCR) in a similar experiment.

Low energy electron microscopy (LEEM) and scanning tunneling microscopy (STM) have been used to investigate the faceting of W(111) as induced by Pt. The atomically rough W(111) surface, when fully covered with a monolayer film of Pt and annealed to temperatures higher than {approximately}750 K, experiences a significant morphological restructuring: the initially planar surface undergoes a faceting transition and forms three-sided pyramids with {l_brace}211{r_brace} faces. When Pt is dosed onto the heated surface, the transition from planar to faceted structure proceeds through the nucleation and growth of spatially separated faceted regions, as shown by LEEM. STM reveals the atomic structure of the partially faceted surface, with large planar regions, dotted by clusters of pyramids of various sizes.

The rotorcraft industry is constantly evaluating new types of lightweight composite materials that not only enhance the safety and reliability of rotor components, but also improve performance and extend operating life as well. The tests required for these evaluations are typically quite complex requiring massive test fixtures, in many cases, along with multiple actuators for loading test articles at various points simultaneously. This paper discusses the background for development of the facility, as well as hardware and overall system design and implementation. Additional topics that are covered include data acquisition, implementation of nondestructive inspection techniques during the test process, and some results from the initial test series performed in the facility.

The Accident Response Mobile Manipulator System (ARMMS) is a teleoperated emergency response vehicle that deploys two hydraulic manipulators, five cameras, and an array of sensors to the scene of an incident. It is operated from a remote base station that can be situated up to four kilometers away from the site. Recently, a modular telerobot control architecture called SMART (Sandia's Modular Architecture for Robotic and Teleoperation) was applied to ARMMS to improve the precision, safety, and operability of the manipulators on board. Using SMART, a prototype manipulator control system was developed in a couple of days, and an integrated working system was demonstrated within a couple of months. New capabilities such as camera teleoperation, autonomous tool changeout and dual manipulator control have been incorporated. The final system incorporates twenty-two separate modules and implements eight different behavior modes. This paper describes the integration of SMART into the ARMMS system.

This paper presents a practical approach for integrating automatically designed fixtures with automated assembly planning. Product assembly problems vary widely; here the focus is on assemblies that are characterized by a single base part to which a number of smaller parts and subassemblies are attached. This method starts with three-dimension at CAD descriptions of an assembly whose assembly tasks require a fixture to hold the base part. It then combines algorithms that automatically design assembly pallets to hold the base part with algorithms that automatically generate assembly sequences. The designed fixtures rigidly constrain and locate the part, obey task constraints, are robust to part shape variations, are easy to load, and are economical to produce. The algorithm is guaranteed to find the global optimum solution that satisfies these and other pragmatic conditions. The assembly planner consists of four main elements: a user interface, a constraint system, a search engine, and an animation module. The planner expresses all constraints at a sequencing level, specifying orders and conditions on part mating operations in a number of ways. Fast replanning enables an interactive plan-view-constrain-replan cycle that aids in constrain discovery and documentation. The combined algorithms guarantee that the fixture will hold the base part without interfering with any of the assembly operations. This paper presents an overview of the planners, the integration approach, and the results of the integrated algorithms applied to several practical manufacturing problems. For these problems initial high-quality fixture designs and assembly sequences are generated in a matter of minutes with global optimum solutions identified in just over an hour.

Automatic assembly sequencing and visualization tools are valuable in determining the best assembly sequences, but without Human Factors and Figure Models (HFFMs) it is difficult to evaluate or visualize human interaction. In industry, accelerating technological advances and shorter market windows have forced companies to turn to an agile manufacturing paradigm. This trend has promoted computerized automation of product design and manufacturing processes, such as automated assembly planning. However, all automated assembly planning software tools assume that the individual components fly into their assembled configuration and generate what appear to be perfectly valid operations, but in reality some operations cannot physically be carried out by a human. For example, the use of a ratchet may be reasoned feasible for an assembly operation; however, when a hand is placed on the tool the operation is no longer feasible, perhaps because of inaccessibility, insufficient strength or human interference with assembly components. Similarly, human figure modeling algorithms may indicate that assembly operations are not feasible and consequently force design modifications, however, if they had the capability to quickly generate alternative assembly sequences, they might have identified a feasible solution. To solve this problem, HFFMs must be integrated with automated assembly planning which allows engineers to quickly verify that assembly operations are possible and to see ways to make the designs even better. This paper presents a framework for integrating geometry-based assembly planning algorithms with commercially available human figure modeling software packages. Experimental results to selected applications along with lessons learned are presented.

A molecular-level understanding of mineral-water interactions is critical for the evaluation and prediction of the sorption properties of clay minerals that may be used in various chemical and radioactive waste disposal methods. Molecular models of metal sorption incorporate empirical energy force fields, based on molecular orbital calculations and spectroscopic data, that account for Coulombic, van der Waals attractive, and short-range repulsive energies. The summation of the non-bonded energy terms at equally-spaced grid points surrounding a mineral substrate provides a three dimensional potential energy grid. The energy map can be used to determine the optimal sorption sites of metal ions on the exposed surfaces of the mineral. By using this approach, we have evaluated the crystallographic and compositional control of metal sorption on the surfaces of kaolinite and illite. Estimates of the relative sorption energy and most stable sorption sites are derived based on a rigid ion approximation.

Environmental scientists have long appreciated that the distribution coefficient (the ''K{sub d}'' or ''constant K{sub d}'') approach predicts the partitioning of heavy metals between sediment and groundwater inaccurately; nonetheless, transport models applied to problems of environmental protection and groundwater remediation almost invariably employ this technique. To examine the consequences of this practice, we consider transport in one dimension of Pb and other heavy metals through an aquifer containing hydrous ferric oxide, onto which heavy metals sorb strongly. We compare the predictions of models calculated using the K{sub d} approach to those given by surface complexation theory, which is more realistic physically and chemically. The two modeling techniques give qualitatively differing results that lead to divergent cleanup strategies. The results for surface complexation theory show that water flushing is ineffective at displacing significant amounts of Pb from the sorbing surface. The effluent from such treatment contains a ''tail'' of small but significant levels of contamination that persists indefinitely. Subsurface zones of Pb contamination, furthermore, are largely immobile in flowing groundwater. These results stand in sharp contrast to the predictions of models constructed using the k{sub d} approach, yet are consistent with experience in the laboratory and field.

We demonstrate a ''universal solvent sensor'' constructed from a small array of carbon/polymer composite chemiresistors that respond to solvents spanning a wide range of Hildebrand volubility parameters. Conductive carbon particles provide electrical continuity in these composite films. When the polymer matrix absorbs solvent vapors, the composite film swells, the average separation between carbon particles increases, and an increase in film resistance results, as some of the conduction pathways are broken. The adverse effects of contact resistance at high solvent concentrations are reported. Solvent vapors including isooctane, ethanol, dlisopropyhnethylphosphonate (DIMP), and water are correctly identified (''classified'') using three chemiresistors, their composite coatings chosen to span the full range of volubility parameters. With the same three sensors, binary mixtures of solvent vapor and water vapor are correctly classified, following classification, two sensors suffice to determine the concentrations of both vapor components. Polyethylene vinylacetate and polyvinyl alcohol (PVA) are two such polymers that are used to classify binary mixtures of DIMP with water vapor; the PVA/carbon-particle-composite films are sensitive to less than 0.25{degree}A relative humidity. The Sandia-developed VERI (Visual-Empirical Region of Influence) technique is used as a method of pattern recognition to classify the solvents and mixtures and to distinguish them from water vapor. In many cases, the response of a given composite sensing film to a binary mixture deviates significantly from the sum of the responses to the isolated vapor components at the same concentrations. While these nonlinearities pose significant difficulty for (primarily) linear methods such as principal components analysis, VERI handles both linear and nonlinear data with equal ease. In the present study the maximum speciation accuracy is achieved by an array containing three or four sensor elements, with the addition of more sensors resulting in a measurable accuracy decrease.

We have observed discrete random telegraph signals (RTS'S) in the drain voltages of three, observed above 30 K were thermally activated. The switching rate for the only RTS observed below 30 K was thermally activated above 30 K but temperature-independent below 10 K. To our knowledge, this cross-over from thermal activation to tunneling behavior has not been previously observed for RTS's Metal-oxide-semiconductor field-effect transistors (MCEWETS) often exhibit relatively large levels of low-frequency (1/fl noise) [1,2]. Much evidence suggests that this noise is related to the capture all cases, switching rates have been thermally activated, often with different activation energies for capture and/or emission is accompanied by lattice relaxation. Though thermally activated behavior has sufficiently low temperatures [7,9]. While not observed in MOSFETS, cross-over from thermal activation to configurational tunneling has been observed for RTS's in junctions [13]. drain voltage was observed to randomly switch between two discrete levels, designated as Vup and Vdn, similar to RTS's reported by others [2,7'- 11 ]. We have characterized six RTS `S for temperatures above 30 K where thermally activated switching rates are observed. The properties of five of these have been the trap, i.e., the mean time a captured charge carrier spends in the trap before it is emitted. Similarly, we identify the mean time in the low resistance state ( trup in state Vup) as the capture time rc. F@ure 1 shows a typical time trace of the drain-voltage fluctuation &d(t)= Vd(t)+Vd>. This indicate that both the mean capture and emission times become independent of Tat low temperatures and where a= capture or emission, is temperature independent. The solid curve in Figure 3(a) (mean capture time) was obtained using a weighted nonlinear charge carriers are not in thermal equilibrium with the lattice, i.e., that while the lattice is being cooled Instead, we believe that the transition from thermally activated to temperature-independent switching rates is associated with a lattice relaxation mechanism similar to that observed in metal- insulator-metal tunnel junctions [13]. Capture and emission of carriers are mediated by lattice relaxation, which proceeds via a thermally activated process at higher temperatures and a configurational tunneling electron capture rate depended on both lattice and electron temperatures while the emission rate Fkure 2. Arrhenius plot showing the thermally-activated behavior of both the mean capture (triangle) and emission (square) times of the RTS for temperatures above 20 K'.

The Ministry of the Russian Federation for Atomic Energy (MINATOM) and the US Department of Energy (DOE) are engaged in joint, cooperative efforts to reduce the likelihood of nuclear proliferation by enhancing Material Protection, Control and Accounting (MPC&A) systems in both countries. Mayak Production Association (Mayak) is a major Russian nuclear enterprise within the nuclear complex that is operated by lylINATOM. This paper describes the nature, scope, and status of the joint, cooperative efforts to enhance existing MPC&A systems at Mayak. Current cooperative efforts are focused on enhancements to the existing MPC&A systems at two of the plants operated by Mayak that work with proliferation-sensitive nuclear materials.

A distributed temperature sensor (DTS) system, utilizing Raman backscattering to measure temperatures of optical fiber, has recently been installed in production wells at the Beowawe and Dixie Valley, NV, geothermal fields. The system has the potential to reduce the cost and complexity of acquiring temperature logs. However, the optical transmission of the initial fibers installed at Beawawe degraded over several months, resulting in temperature errors. Optical transmission spectra of the failed fibers indicate hydroxide contamination via hydrogen diffusion as a possible failure mechanism. Additional fibers with coatings designed to resist hydrogen diffusion were installed and have maintained their optical transmission over several months in the 340-360 F Beowawe wells. The same fibers installed in a 470 F Dixie Valley well rapidly failed. Possible methods to prevent fiber degradation include encasing the fiber in metallic buffer layer that resists hydrogen diffusion. Additional methods to correct temperature errors include using additional optical sources to measure fiber losses at the operating wavelengths. Although the DTS system is expected to have one degree F accuracy, we have observed an average accuracy of five degrees. The fiber connections appear to be the uncertainty source. Using connectors with greater stability should restore accuracy.

We have developed a new approach (the LQR method) for calculating the reflectivity and transmission spectra of a multilayer optical material with N interfaces, as an alternative to the matrix method. The approach allows the inclusion of the effects of interface roughness by introducing a ''rough'' element between adjacent layers. For this purpose we have developed an empirical model, which describes the effect of interface roughness on an optical beam passing through or being reflected from an interface. An assessment of the interface roughness of a multilayer structure was carried out by fitting the experimental reflectivity spectrum of GaAs/AlGaAs multiple quantum well samples with and without oxidation of the barrier layers. The refractive index and the thickness of the oxidized layers were also obtained from the fit.

SUMMiT (Sandia Ultra-planar Multi-level MEMS Technology) at the Sandia National Laboratories' MDL (Microelectronics Development Laboratory) is a standardized MEMS (Microelectromechanical Systems) technology that allows designers to fabricate concept prototypes. This technology provides four polysilicon layers plus three sacrificial oxide layers (with the third oxide layer being planarized) to enable fabrication of complex mechanical systems-on-a-chip. Quantified reproducibility of the SUMMiT process is important for process engineers as well as designers. Summary statistics for critical MEMS technology parameters such as film thickness, line width, and sheet resistance will be reported for the SUMMiT process. Additionally, data from Van der Pauw test structures will be presented. Data on film thickness, film uniformity and critical dimensions of etched line widths are collected from both process and monitor wafers during manufacturing using film thickness metrology tools and SEM tools. A standardized diagnostic module is included in each SWiT run to obtain post-processing parametric data to monitor run-to-run reproducibility such as Van der Pauw structures for measuring sheet resistance. This characterization of the SUMMiT process enables design for manufacturability in the SUMMiT technology.

The implementation of a backscattered x-ray landmine detection system has been demonstrated in laboratories at both Sandia National Laboratories (SNL) and the University of Florida (UF) The next step was to evaluate the modality by assembling a system for fieldwork and to evaluate the systems performance with real landmines. To assess the system's response to a variety of objects, buried simulated plastic and metal antitank landmines, surface simulated plastic antipersonnel landmines, and surface metal fragments were used as targets for the field test. The location of the test site was an unprepared field at SNL. The tests conducted using real landmines were held at UF using various burial depths. The field tests yielded the same levels of discrimination between soil and landmines that had been detected in laboratory experiments. The tests on the real landmines showed that the simulated landmines were a good approximation. The real landmines also contained internal features that would allow not only the detection of the landmines, but also the identification of them.

This contribution proposes strawman techniques for Security Service Discovery by ATM endsystems in ATM networks. Candidate techniques include ILMI extensions, ANS extensions and new ATM anycast addresses. Another option is a new protocol based on an IETF service discovery protocol, such as Service Location Protocol (SLP). Finally, this contribution provides strawman requirements for Security-Based Routing in ATM networks.

As a result of the Safeguards Arrangement between the US Department of Energy (DOE) and the Australian Safeguards and Non-Proliferation Office (ASNO) concerning international safeguards R and D, ASNO and Sandia National Laboratories (SNL) have agreed to jointly develop a remote monitoring system at the HIFAR reactor, Lucas Heights, Australia. The HIFAR reactor is a high flux research reactor operated by the Australian Nuclear Science and Technology Organization (ANSTO). The objective of the system is to remotely monitor the entire Material Balance Area (MBA) AS-A to include: fresh fuel the reactor core; spent fuel in the cropping/irradiation pond, international pond, dry spent fuel storage facility, and Dounreay flasks; and spent fuel during designated transport. The purpose is to reduce on-site inspection effort at the HIFAR reactor.

Improvements in the last decade in InP materials growth, device processing techniques, characterization, and circuit design have enabled solid-state power performance through 122 GHz. Although originally targeted for low-noise and power performance at mm-wave frequencies (>30 GHz), InP HEMTs could become the preferred device for frequencies as low as 800 MHz. This investment has benefited the microwave frequency regime with higher efficiency and power densities at lower operating voltages. State-of-the-art microwave performance at lower operating voltage provides a path to smaller, lighter-weight systems in the battery operated arena of commercial and defense electronics. This paper describes an InP HEMT technology being investigated for many power and low-noise amplifier applications from UHF to W-band frequencies. Specifically the technology demonstrated 640mW/mm power density, 27 dB gain, and 84% power-added efficiency at L-band with a bias of 3.0 volts. Based on the author's literature search, this is a record efficiency at L-band with an operating voltage of less than 5 volts.

Long-term nuclear material storage will require in-vault data verification, sensor testing, error and alarm response, inventory, and maintenance operations. System concept development efforts for a comprehensive nuclear material management system have identified the use of a small flexible mobile automation platform to perform these surveillance and maintenance operations. In order to have near-term wide-range application in the Complex, a mobile surveillance system must be small, flexible, and adaptable enough to allow retrofit into existing special nuclear material facilities. The objective of the Mobile Surveillance and Monitoring Robot project is to satisfy these needs by development of a human scale mobile robot to monitor the state of health, physical security and safety of items in storage and process; recognize and respond to alarms, threats, and off-normal operating conditions; and perform material handling and maintenance operations. The system will integrate a tool kit of onboard sensors and monitors, maintenance equipment and capability, and SNL developed non-lethal threat response technology with the intelligence to identify threats and develop and implement first response strategies for abnormal signals and alarm conditions. System versatility will be enhanced by incorporating a robot arm, vision and force sensing, robust obstacle avoidance, and appropriate monitoring and sensing equipment.

Two novel Group IV precursors, titanium (IV) neo-pentoxide, [Ti({mu}-ONep)(ONep){sub 3}]{sub 2} (l), and zirconium (IV) neo-pentoxide, [Zr({mu}-ONep)(ONep){sub 3}]{sub 2} (2), were reported to possess relatively high volatility at low temperatures. These compounds were therefore investigated as MOCVD precursors using a lamp-heated cold-wall CVD reactor and direct sublimation without carrier gas. The ONep derivatives proved to be competitive precursors for the production of thin films of the appropriate MO{sub 2} (M = Ti or Zr) materials in comparison to other metallo-organic precursors. Compound 1 was found to sublime at 120 C with a deposition rate of {approximately}0.350 {mu}m/min onto a substrate at 330 C forming the anatase phase with < 1% residual C found in the final film. Compound 2 was found to sublime at 160 C and deposited as crystalline material at 300 C with < 1% residual C found in the final film. A comparison to standard alkoxide and {beta}-diketonates is presented where appropriate.

Conductor inks containing silver and palladium, used in ceramic co-fired circuits, sometimes undergo an anomalously large expansion during heating in the temperature range where interdiffusion occurs. Therefore, the interdiffusion of silver and palladium was studied during heating in both air and argon using both powder and foil samples. Measurements on a powder compact made of a mixture of Ag and Pd (80% Ag) particles indicated that a very rapid expansion occurred between 375 and 400 C when heated in air but only a slight expansion occurred in Ar. A pre-alloyed powder with the same composition did not expand during heating. In situ high temperature x-ray diffraction studies indicated that both powders oxidized during heating in air, with the mixture oxidizing more and that interdiffusion occurred between 300 and 500 C. Microstructural examination indicated that larger particles with internal pores had formed in the mixture heated in air to 375 C due to rearrangement during interdiffusion. A porous region much thicker than the original silver film formed on a palladium foil sample when it was heated in air, whereas in inert atmosphere pores formed only in the silver film, indicating a Kirkendall effect occurs in both cases. Based on these results, it was concluded that the expansion of the Ag-Pd powder mixture was due to interdiffusion in the presence of oxygen, not solely to the oxidation of the Pd.

The analysis precision of any multivariate calibration method will be severely degraded if unmodeled sources of spectral variation are present in the unknown sample spectra. This paper describes a synthetic method for correcting for the errors generated by the presence of unmodeled components or other sources of unmodeled spectral variation. If the spectral shape of the unmodeled component can be obtained and mathematically added to the original calibration spectra, then a new synthetic multivariate calibration model can be generated to accommodate the presence of the unmodeled source of spectral variation. This new method is demonstrated for the presence of unmodeled temperature variations in the unknown sample spectra of dilute aqueous solutions of urea, creatinine, and NaCl. When constant-temperature PLS models are applied to spectra of samples of variable temperature, the standard errors of prediction (SEP) are approximately an order of magnitude higher than that of the original cross-validated SEPs of the constant-temperature partial least squares models. Synthetic models using the classical least squares estimates of temperature from pure water or variable-temperature mixture sample spectra reduce the errors significantly for the variable temperature samples. Spectrometer drift adds additional error to the analyte determinations, but a method is demonstrated that can minimize the effect of drift on prediction errors through the measurement of the spectra of a small subset of samples during both calibration and prediction. In addition, sample temperature can be predicted with high precision with this new synthetic model without the need to recalibrate using actual variable-temperature sample data. The synthetic methods eliminate the need for expensive generation of new calibration samples and collection of their spectra. The methods are quite general and can be applied using any known source of spectral variation and can be used with any multivariate calibration method.

Many studies have investigated the behavior of transition metal dopants in the YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} 123 superconductors. Much of this research has focused on the effects of metal ions such as Co, Fe, Zn, Ni when they are substituted for the copper ions at Cu(1) and Cu(2) sites, commonly referred to as the chain and plane sites, respectively. Trivalent ions such as Co{sup +3} and Fe{sup +3}have been shown to behave similarly in their substitution effects, displaying site preference on the Cu(1) site [3-8]. This site preference has been established with the use of techniques such as neutron diffraction and Moessbauer spectroscopy [4,5]. Thermogravimetry, electron diffraction, and analysis of lattice parameters as a function of dopant also yield results consistent with those of the structural studies with respect to the chain site preference of both Co and Fe [3,4,6-8]. The very fast convergence of a and b lattice parameters to that of the tetragonal structure, occurring at x = 0.3 Co dopant (i.e. YBa{sub 2}Cu{sub 2.7}Co{sub 0.3}O{sub 7{minus}{delta}}) for high-oxygen-content samples, coupled with information derived from diffuse scattering and oxidation behavior of these samples, has been described in detail by several authors in terms of the Co and Fe ions creating ''microchains'' at Cu(1) sites within the 123 compound [4,7-8]. The Cu(1) site dopants decrease T{sub c} at a rate of 2 to 5 K/at. %, varying to some extent with site preference [4,9].

In this paper numerical simulations of Mach 10 air flow over a hollow cylinder flare are presented in comparison with recent experimental results. The numerical study is performed using a Direct Simulation Monte Carlo code and the experimental results were obtained in the ONERA R5Ch wind tunnel. The flow phenomena involved include shock wave boundary layer interaction in hypersonic laminar flow. An analysis of the requirements on the grid resolution, number of particle simulators and run time is performed. Measured and calculated surface properties including pressure and heat transfer are compared.

In this paper, we summarize the rationale for an advanced system called Diagnostics-While-Drilling (DWD) and describe its benefits, preliminary configuration, and essential characteristics. The central concept is a closed data circuit in which downhole sensors collect information and send it to the surface via a high-speed data link, where it is combined with surface measurements and processed through drilling advisory software. The driller then uses this information to adjust the drilling process, sending control signals back downhole with real-time knowledge of their effects on performance. We outline a Program Plan for DOE, university, and industry to cooperate in the development of DWD technology.

The use of unattended monitoring systems for monitoring the status of high value assets and processes has proven to be less costly and less intrusive than the on-site inspections which they are intended to replace. However, these systems present a classic information overload problem to anyone trying to analyze the resulting sensor data. These data are typically so voluminous and contain information at such a low level that the significance of any single reading (e.g., a door open event) is not obvious. Sophisticated, automated techniques are needed to extract expected patterns in the data and isolate and characterize the remaining patterns that are due to undeclared activities. This paper describes a data analysis engine that runs a state machine model of each facility and its sensor suite. It analyzes the raw sensor data, converting and combining the inputs from many sensors into operator domain level information. It compares the resulting activities against a set of activities declared by an inspector or operator, and then presents the differences in a form comprehensible to an inspector. Although the current analysis engine was written with international nuclear material safeguards, nonproliferation, and transparency in mind, since there is no information about any particular facility in the software, there is no reason why it cannot be applied anywhere it is important to verify processes are occurring as expected, to detect intrusion into a secured area, or to detect the diversion of valuable assets.

The authors have successfully synthesized highly crystalline, size-selected indirect band-gap nanocrystals (NC) of Si, Ge and MoS{sub 2} in the size range 2-10 nm in inverse micelles and studied their optical absorption and photoluminescence (PL) properties using liquid chromatography. Room temperature, visible PL from these nanocrystals was demonstrated in the range 700-350 nm (1.8-3.5 eV). their experimental results are interpreted in terms of the corresponding electronic structure of the bulk materials and it is demonstrated that these nanocrystals retain bulk-like electronic character to sizes as small as 2 nm, but the absorbance energies are strongly blue-shifted by quantum confinement. The experimental results on Si-NCs are also compared to earlier work on Si clusters grown by other techniques and to the predictions of various model calculations. Currently, the wide variations in the theoretical predictions of the various models along with considerable uncertainties in experimental size determination for clusters less than 3-4 nm, make it difficult to select the best model.

Many applications produce three-dimensional points that must be further processed to generate a surface. Surface reconstruction algorithms that start with a set of unorganized points are extremely time-consuming. Sometimes, however, points are generated such that there is additional information available to the reconstruction algorithm. We present Spiraling Edge, a specialized algorithm for surface reconstruction that is three orders of magnitude faster than algorithms for the general case. In addition to sample point locations, our algorithm starts with normal information and knowledge of each point's neighbors. Our algorithm produces a localized approximation to the surface by creating a star-shaped triangulation between a point and a subset of its nearest neighbors. This surface patch is extended by locally triangulating each of the points along the edge of the patch. As each edge point is triangulated, it is removed from the edge and new edge points along the patch's edge are inserted in its place. The updated edge spirals out over the surface until the edge encounters a surface boundary and stops growing in that direction, or until the edge reduces to a small hole that is filled by the final triangle.

Visualization systems are complex dynamic software systems. Debugging such systems is difficult using conventional debuggers because the programmer must try to imagine the three-dimensional geometry based on a list of positions and attributes. In addition, the programmer must be able to mentally animate changes in those positions and attributes to grasp dynamic behaviors within the algorithm. In this paper we shall show that representing geometry, attributes, and relationships graphically permits visual pattern recognition skills to be applied to the debugging problem. The particular application is a particle system used for isosurface extraction from volumetric data. Coloring particles based on individual attributes is especially helpful when these colorings are viewed as animations over successive iterations in the program. Although we describe a particular application, the types of tools that we discuss can be applied to a variety of problems.

Sandia National Laboratories and the Russian Federal Nuclear Center-All Russian Research Institute for Experimental Physics (VNIIEF) (also known as Arzamas-16) are collaborating on ways to assure the highest standards of safety, security, and international accountability of fissile material. For these collaborations, sensors and information technologies have been identified as important in reaching these standards in a cost-effective manner. Specifically, Sandia and VNIIEF have established a series of remote monitoring field trials to provide a mechanism for joint research and development on storage monitoring systems. These efforts consist of the ''Container-to-Container'', ''Magazine-to-Magazine'', and ''Facility-to-Facility'' field trials. This paper will describe the evaluation exercise Sandia and VNIIEF conducted on the Magazine-to-Magazine systems. Topics covered will include a description of the evaluation philosophy, how the various sensors and system features were tested, evaluation results, and lessons learned.

The precise pore sizes defined by crystalline zeolite lattices have led to intensive research on zeolite membranes. Unfortunately zeolites have proven to be extremely difficult to prepare in a defect-free thin film form needed for membrane flux and selectivity. We introduce tetrapropylammonium (TPA), a structure-directing agent for zeolite ZSM-5, into a silica sol and exploit the development of high solvation stresses to create templated amorphous silicas with pore apertures comparable in size to those of ZSM-5. Silicon and carbon NMR experiments were performed to evaluate the efficacy of our templating approach. The {sup 29}Si NMR spectrum of the silica matrix was observed by an intermolecular cross-polarization experiment involving the {sup 1}H nuclei of TPA and the {sup 29}Si nuclei in the silica matrix. The efficiency of the cross-polarization interaction was used to investigate the degree to which the matrix formed a tight cage surrounding the template molecule. Bulk xerogels, prepared by gelation and slow drying of the corresponding sols, exhibited only weak interactions between the two sets of nuclei. Thin film xerogels, where drying stresses are greater, exhibited significantly increased interactions. Intramolecular cross-polarization experiments between the {sup 1}H and {sup 13}C nuclei of the template molecule demonstrated that much of the increased efficiency was a result of reduced rotational mobility of the TPA molecule.

The microscopic origin of compact triangular islands on close-packed surfaces is identified using kinetic Monte Carlo simulations with energy barriers obtained from density-functional calculations. In contrast to earlier accounts, corner diffusion anisotropy is found to control the shape of compact islands at intermediate temperatures. We rationalize the correlation between the orientation of dendrites grown at low temperatures and triangular islands grown at higher temperatures, and explain why in some systems dendrites grow fat before turning compact.