Publications

On September 24, 25, 28, and 29, 1998 and on October 19 and 23, 1998, transfer impedance measurements were made on Los Alamos National Laboratories TA 16 - Building 411 and TA 8-- Building 23 to characterize their interior open-circuit voltage response to a direct lightning flash attachment to the structures. The theory, history, measurement methods and equipment, and specific measured results are detailed. The measured results demonstrate that if the remaining metallic penetrations are bonded, then the rebar of the two structures is sufficiently well connected to form a Faraday cage that reduces the maximum open-circuit voltage inside the structure to a sufficiently low level that the required standoff distance to prevent arcing to explosive assemblies is 6.8 inches for TA 16 - Building 411 and is 11.5 inches for TA 8 - Building 23.

A human outpost on Mars requires plentiful power to assure survival of the astronauts. Anywhere from 50 to 500 kW of electric power (kWe) will be needed, depending on the number of astronauts, level of scientific activity, and life-cycle closure desired. This paper describes a 250-kWe power system based on a gas-cooled nuclear reactor with a recuperated closed Brayton cycle conversion system. The design draws upon the extensive data and engineering experience developed under the various high-temperature gas cooled reactor programs and under the SP-100 program. The reactor core is similar in power and size to the research reactors found on numerous university campuses. The fuel is uranium nitride clad in Nb1%Zr, which has been extensively tested under the SP-I 00 program. The fuel rods are arranged in a hexagonal array within a BeO block. The BeO softens the spectrum, allowing better use of the fuel and stabilizing the geometry against deformation during impact or other loadings. The system has a negative temperature feedback coefficient so that the power level will automatically follow a variable load without the need for continuous adjustment of control elements. Waste heat is removed by an air-cooled heat exchanger using cold Martian air. The amount of radioactivity in the reactor at launch is very small (less than a Curie, and about equal to a truckload of uranium ore). The system will need to be engineered so that criticality cannot occur for any launch accident. This system is also adaptable for electric propulsion or life-support during transit to and from Mars.

Thermally stimulated current and capacitance voltage methods are used to investigate the thermal stability of trapped electrons associated with radiation-induced trapped positive charge in metal-oxide-semiconductor capacitors. The density of deeply trapped electrons in radiation-hardened 45 nm oxides exceeds that of shallow electrons by a factor of {approximately}3 after radiation exposure, and by up to a factor of 10 or more during biased annealing. Shallow electron traps anneal faster than deep traps, and seem to be at least qualitatively consistent with the model of Lelis et al. Deeper traps maybe part of a fundamentally distinct dipole complex, and/or have shifted energy levels that inhibit charge exchange with the Si.

To date, few researchers have solved three-dimensional free-surface problems with dynamic wetting lines. This paper extends the free-surface finite element method described in a companion paper [Cairncross, R.A., P.R. Schunk, T.A. Baer, P.A. Sackinger, R.R. Rao, "A finite element method for free surface flows of incompressible fluid in three dimensions, Part I: Boundary-Fitted mesh motion.", to be published (1998)] to handle dynamic wetting. A generalization of the technique used in two dimensional modeling to circumvent double-valued velocities at the wetting line, the so-called kinematic paradox, is presented for a wetting line in three dimensions. This approach requires the fluid velocity normal to the contact line to be zero, the fluid velocity tangent to the contact line to be equal to the tangential component of web velocity, and the fluid velocity into the web to be zero. In addition, slip is allowed in a narrow strip along the substrate surface near the dynamic contact line. For realistic wetting-line motion, a contact angle which varies with wetting speed is required because contact lines in three dimensions typically advance or recede a different rates depending upon location and/or have both advancing and receding portions. The theory is applied to capillary rise of static fluid in a corner, the initial motion of a Newtonian droplet down an inclined plane, and extrusion of a Newtonian fluid from a nozzle onto a moving substrate. The extrusion results are compared to experimental visualization. Subject Categories

The band gap of AlXGal.XN is measured for the composition range 0s<0.45; the resulting bowing parameter, b=+O.69 eV, is compared to 20 previous works. A correlation is found between the measured band gaps and the methods used for epitaxial growth of the AlXGal_XN: directly nucleated or buffered growths of AlXGal-XN initiated at temperatures T>800 C on sapphire usually lead to stronger apparent bowing (b> +1.3 eV); while growths initiated using low-temperature buffers on sapphire, followed by high-temperature growth, lead to weaker bowing (b<+ 1.3 eV). Extant data suggests that the correct band-gap bowing parameter for AlXGal-XN is b=+O.62 (N.45) eV.

Let me begin with some comments about transparency. We all have some perception or vision about the use of transparency for nuclear technology and nuclear non-proliferation. Although we probably have some common understanding of what it implies, there is no precise definition that is agreed upon. One of the most significant ideas in transparency is that it is considered to be a voluntary or unilateral action. The party, or organization, or nation that wants its activities to be transparent voluntarily provides information to other parties with the expectation of receiving some acceptance or good will in return. The organization giving the information determines what information to provide, how much, how often, and when. This is in contrast to official treaties and monitoring regimes, in which specific verification information and activities are prescribed. This should have the advantage for the transparent organization of being less intrusive and less costly than a treaty monitoring regime. Information related to sensitive nuclear technology, proprietary processes, and physical security is more easily protected. The difficultly for both parties, the transparent organization and the information recipients, is in determining what information is necessary for the desired confidence building. It must be recognized that this state of transparency or confidence will only be achieved over an extended period of time, when history confirms that the information was reliable in conveying the true picture.

In industry, the need to maximize energy efficiency depends on the availability of suitable advanced materials. Ceramic composites are exemplary materials for many advanced engineering applications because they exhibit good thermal stability, oxidation resistance and enhanced toughness. Presently, ceramic composite fabrication processes are costly, often requiring high temperatures and pressures to achieve reasonable densities. Our research is focused on developing a processing technique, that will allow production of alumina/aluminum composites using relatively low temperatures and without the application of an external force, thus reducing the processing costs. Our composites were formed using Reactive Metal Penetration (RMP), which is a process involving the reaction of molten Al with a dense ceramic preform. The result is a near net shape ceramic/metal composite with interpenetrating phases. The volume fraction of metal in the composites was varied by doping an aluminosilicate ceramic preform with silica. For this study we fabricated composites using pure mullite and mullite doped with 23 and 42 weight percent silica, yielding 18, 25, and 30 volume percent metal in the composites, respectively. Optical and Scanning Electron Microscopy were used to characterize the homogeneity and scale of the microstructure. The scale of the microstructure varied with preform composition, the reaction temperature and with secondary heat treatments. Four-point bend testing was used to evaluate the influence of microstructure on strength and reliability. During these studies a gradient in the microstructure was observed, which we further characterized using microhardness testing. Alumina/aluminum composites formed by RMP show higher toughness then monolithic alumina and have the potential for improved reliability when compared to monolithic ceramics.

In May of 1998, a technical basis and implementation guidelines document for A Technique for Human Event Analysis (ATHEANA) was issued as a draft report for public comment (NUREG-1624). In conjunction with the release of draft NUREG- 1624, a peer review of the new human reliability analysis method its documentation and the results of an initial test of the method was held over a two-day period in June 1998 in Seattle, Washington. Four internationally known and respected experts in HK4 or probabilistic risk assessment were selected to serve as the peer reviewers. In addition, approximately 20 other individuals with an interest in HRA and ATHEANA also attended the peer and were invited to provide comments. The peer review team was asked to comment on any aspect of the method or the report in which improvements could be made and to discuss its strengths and weaknesses. They were asked to focus on two major aspects: Are the basic premises of ATHEANA on solid ground and is the conceptual basis adequate? Is the ATHEANA implementation process adequate given the description of the intended users in the documentation? The four peer reviewers asked questions and provided oral comments during the peer review meeting and provided written comments approximately two weeks after the completion of the meeting. This paper discusses their major comments.

This paper explores the geometrical errors that reduce heliostat tracking accuracy at Solar Two. The basic heliostat control architecture is described. Then, the three dominant error sources are described and their effect on heliostat tracking is visually illustrated. The strategy currently used to minimize, but not truly correct, these error sources is also shown. Finally, a novel approach to minimizing error is presented.

Abstract not provided.

The electrostriction of composites consisting of dielectric particles embedded in a gel or elastomer is discussed. It is shown that when these particles are organized by a uniaxial field before gelation, the resulting field-structured composites are expected to exhibit enhanced electrostriction in a uniform field applied along the same axis as the structuring field. The associated stresses might be large enough to form the basis of a polymer-based fast artificial muscle.

The advent of the 20-MA Z accelerator [R.B. Spielman, C. Deeney, G.A. Chandler, et al., Phys. Plasmas 5, 2105, (1997)] has enabled implosions of large diameter, high-wire-number arrays of titanium to begin testing Z-pinch K-shell scaling theories. The 2-cm long titanium arrays, which were mounted on a 40-mm diameter, produced between 75{+-}15 to 125{+-}20 kJ of K-shell x-rays. Mass scans indicate that, as predicted, higher velocity implosions in the series produced higher x-ray yields. Spectroscopic analyses indicate that these high velocity implosions achieved peak electron temperatures from 2.7{+-}0.1 to 3.2{+-}0.2 keV and obtained a K-shell emission mass participation of up to 12%.

Shock-wave experiments on iron preheated to 1,573 K conducted from 14 to 73 GPa, yield new data for sound velocities of the {gamma}- and liquid-phases. Melting was observed in the highest pressure ({approximately} 71 {+-} 2 GPa) experiments at calculated shock temperatures of 2,775 {+-} 160 K. This single crossing of the {gamma}-liquid boundary measured here agrees closely with the {gamma}-iron melting line determined by Boehler [1993], Saxena et al. [1993], and Jephcoat and Besedin [1997]. This {gamma}-iron melting curve is {approximately} 300 C lower than that of Shen et al. [1998b] at 80 GPa.

In this paper we describe a unified, hierarchical computational approach to aging and reliability problems caused by materials changes in the oxide layers of Si-based microelectronic devices. We apply this method to a particular low-dose-rate radiation effects problem

A response surface methodology-based technique is presented for treating discretization error in non-deterministic analysis. The response surface, or metamodel, is estimated from computer experiments which vary both uncertain physical parameters and the fidelity of the computational mesh. The resultant metamodel is then used to propagate the variabilities in the continuous input parameters, while the mesh size is taken to zero, its asymptotic limit. With respect to mesh size, the metamodel is equivalent to Richardson extrapolation, in which solutions on coarser and finer meshes are used to estimate discretization error. The method is demonstrated on a one dimensional prismatic bar, in which uncertainty in the third vibration frequency is estimated by propagating variations in material modulus, density, and bar length. The results demonstrate the efficiency of the method for combining non-deterministic analysis with error estimation to obtain estimates of total simulation uncertainty. The results also show the relative sensitivity of failure estimates to solution bias errors in a reliability analysis, particularly when the physical variability of the system is low.

In this paper we evaluate the design of the hybrid evolutionary algorithms (EAs) that are currently used to perform flexible ligand binding in the Autodock docking software. Hybrid EAs incorporate specialized operators that exploit domain-specific features to accelerate an EA's search. We consider hybrid EAs that use an integrated local search operator to reline individuals within each iteration of the search. We evaluate several factors that impact the efficacy of a hybrid EA, and we propose new hybrid EAs that provide more robust convergence to low-energy docking configurations than the methods currently available in Autodock.

Precision high aspect-ratio micro molds constructed by deep x-ray lithography have been used to batch fabricate accurately shaped bonded rare-earth based permanent magnets with features as small as 5 microns and thicknesses up to 500 microns. Maximum energy products of up to 8 MGOe have been achieved with a 20%/vol. epoxy bonded melt-spun isotropic Nd2Fe14b powder composite. Using individually processed sub- millimeter permanent sections multipole rotors have been assembled. Despite the fact that these permanent magnet structures are small, their magnetic field producing capability remains the same as at any scale. Combining permanent magnet structures with soft magnetic materials and micro-coils makes possible new and more efficient magnetic microdevices.

A test technique has been devised which is suitable for the testing of the bond strength of batch diffusion bonded LIGA or DXRL defined structures. The method uses a torsion tester constructed with the aid of LIGA fabrication and distributed torsion specimens which also make use of the high aspect ratio nature of DXRL based processing. Measurements reveal achieved bond strengths of 130MPa between electroplated nickel with a bond temperature of 450 C at 7 ksi pressure which is a sufficiently low temperature to avoid mechanical strength degradation.

A technique using diffusion bonding (or solid-state welding) has been used to achieve batch fabrication of two- level nickel LIGA structures. Interlayer alignment accuracy of less than 1 micron is achieved using press-fit gauge pins. A mini-scale torsion tester was built to measure the diffusion bond strength of LIGA formed specimens that has shown successful bonding at temperatures of 450"C at 7 ksi pressure with bond strength greater than 100 Mpa. Extensions to this basic process to allow for additional layers and thereby more complex assemblies as well as commensurate packaging are discussed.

Oxidation of layers of high-Al-content III-V materials by water vapor has become the enabling process for high-efficiency vertical cavity surface emitting lasers (VCSELS) and has potential applications for reducing substrate current leakage in GaAs-on-insulator (GOI) MESFETS. Because of the established importance of wet oxidation in optoelectronic devices and its potential applications in electronic devices, it has become increasingly important to understand the mechanism of wet oxidation and how it might be expected to affect both the fabrication and subsequent operation of devices that have been made using this technique. The mechanism of wet oxidation and the consequence of this mechanism for heterostructure design and ultimate device operation are discussed here.

Engineering systems are becoming increasingly complex as state of the art technologies am incorporated into designs. Surety modeling and analysis is an emerging science that permits an engineer to qualitatively and quantitatively predict and assess the completeness and predictability of a design. Surety is a term often used in the Department of Defense (DoD) and Department of Energy (DOE) communities, which refers to the integration of safety, security, reliability and performance aspects of design. Current risk assessment technologies for analyzing complex systems fail to adequately describe the problem, thus making assessment fragmented and non-integrated. To address this problem, we have developed a methodology and extensible software tool set to address model integration and complexity for high consequence systems. The MultiGraph Architecture (MGA) facilitates multi-domain, model-integrated modeling and analyses of complex, high-assurance systems. The MGA modeling environment allows the engineer to customize the modeling environment to match a design paradigm representative of the actual design. Previous modeling tools have a point-defined model space that forms the modeler to work in less than optimal environments. Current approaches for the problem to be bounded and constrained by requirements of the modeling tool and not the actual design problem. In some small cases, this is only maximally adequate MM facilitates the implementation of a surety methodology, which is used to represent high assurance systems with respect to safety and reliability. Formal mathematical models am used to correctly describe design safety and reliability functionality and behavioral fictional and behavioral representations of the design w then analyzed using commercial-off-the-shelf tools.

The authors have used low-energy electron microscopy to investigate the dynamics of the Si(111) 7 x 7 {r_arrow} 1 x 1 phase transition. Because the densities of the two phases differ, the phase transformation is analogous to precipitation in bulk systems: additional material must diffuse to the phase boundaries in order for the transformation to occur. By measuring the size evolution of an ensemble of domains, and comparing the results to simulations, they have identified a new mechanism of precipitate growth. The source of material necessary for the transformation is the random creation of atom/vacancy pairs at the surface. This mechanism contrasts sharply with classical theories of precipitation, in which mass transport kinetics determine the rate of transformation.

Relative concentrations of reactive ions, neutral radicals, resist and substrate etch products have been measured in dielectric etch chemistries using an uncollided beam mass spectrometer / ion extractor from Hiden Analytical. Analysis techniques employed include both electron impact ionization and dissociative ionization of neutral gas, and potential bias extraction of positive ions from the reactor discharge volume. Measurements were made in C{sub 2}F{sub 6} and CHF{sub 3} discharges in an inductively coupled plasma (ICP-GEC) research reactor operating with power densities, pressures, gas compositions and wafer materials typical of those found in etch processing tools. Wafer substrates investigated included blanket silicon wafers and silicon wafers with varying amounts of photo-resist coverage of the surface (20%, 80% and 100%). In C{sub 2}F{sub 6} discharges CF{sub 3}{sup +} was consistently the dominant fluorocarbon ion present, in agreement with published cross sections for dissociative ionization [ 1,2.3,4.5,6]. Smaller concentrations of CF+, CF{sub 2}{sup -}, and C{sub 2}F{sub 5}{sup +}, were also observed, though the dissociative ionization production of C{sub 2}F{sub 5}{sup +} was a factor of five smaller than would be expected from published cross section values. The presence of photo-resist, even in small amounts, was found to produce marked changes in the discharge composition. For example in C{sub 2}F{sub 6} discharges, concentrations of SiF{sub x} etch products relative to concentrations of C{sub x}F{sub y} species were notably diminished and larger concentrations of water vapor were observed when resist was present. In CHF{sub 3} discharges, CF{sub 3}{sup +} and CHF{sub 2}{sup +} were found to be the main species present, along with smaller concentrations of CF{sub 2}{sup +}, CF{sup +}, CHF{sup +}, CH{sup +} and F{sup -}.

We show that the signal and idler beams generated by certain types of unseeded, nanosecond optical parametric oscillators are tilted and angularly dispersed and have anomalously large bandwidths. This effect is demonstrated in both laboratory measurements and a numerical model. We show how the optical cavity design influences the tilts and how they can be eliminated or minimized. We also determine the conditions necessary to injection seed these parametric oscillators.

Galerkin methods are used in separable Hilbert spaces to construct and compute L{sup 2} [0,{pi}] solutions to large classes of differential equations. In this note a Galerkin method is used to construct series solutions of a nonhomogeneous Sturm-Liouville problem defined on [0,{pi}]. The series constructed are shown to converge to a specified du Bois-Reymond function f in L{sup 2} [0,{pi}]. It is then shown that the series solutions can be made to converge uniformly to the specified du Bois-Reymond function when averaged by the Ces{'a}ro-one summability method. Therefore, in the Ces{'a}ro-one sense, every continuous function f on [0,{pi}] is the uniform limit of solutions of nonhomogeneous Sturm-Liouville problems.

The papers in this special issue have been selected from the systems and balance-of- systems sessions at the 1998 Photovoltaic Performance and Reliability Workshop. The workshop was held November 3-5, 1998 and hosted by the Florida Solar Energy Center, Cocoa Beach, Florida under sponsorship of the US National Center for Photovoltaics (National Renewable Energy Laboratory and Sandia National Laboratories). The topics and issues addressed by these papers were identified in an invited review paper on PV systems by the guest editors. Their work was published earlier this year in Volume 7, Number 1 of Progress in Photovoltaics ('Photovoltaic Systems: An End-of-Millennium Review'). Experts in the PV community were asked to make presentations on these topics at the workshop. The papers that follow are the results of that effort. The papers are organized by topic: (1) codes and standards; (2) reliability; (3) design issues; and (4) commercialization.

Article 690, Solar Photovoltaic Power Systems, has been in the National Electrical Code (NEC) since 1984. An NFPA-appointed Task Group for Article 690 proposed changes to Article 690 for both the 1996 and 1999 codes. The Task Group, supported by more than 50 professionals from throughout the photovoltaic (PV) industry, met seven times during the 1999 code cycle to integrate the needs of the industry with the needs of electrical inspectors and end users to ensure the safety of PV systems. The Task Group proposed 57 changes to Article 690, and all the changes were accepted in the review process. The performance and cost of PV installations were always a consideration as these changes were formed but safety was the number-one priority. All of the proposals were well substantiated and coordinated throughout the PV industry and with representatives of Underwriters Laboratories, Inc (UL). The most significant changes that were made in Article 690 for the 1999 NEC along with some of the rationale are discussed in the remainder of this article.

A metal ion sensitive, fluorescent lipid-b i layer material (5oA PSIDA/DSPC) was successfully immobilized in a silica matrix using a tetramethoxysilane (TMOS) sol-gel procedure. The sol-gel immobilization method was quantitative in the entrapment of seif-assembled Iipid-bilayers and yielded thin films for facile configuration to optical fiber piatforms. The silica matrix was compatible with the solvent sensitive lipid bilayers and provided physical stabilization as well as biological protection. Immobilization in the silica sol-gel produced an added benefit of improving the bilayer's metal ion sensitivity by up to two orders of magnitude. This enhanced performance was attributed to a preconcentrator effect from the anionic surface of the silica matrix. Thin gels (193 micron thickness) were coupled to a bifurcated fiber optic bundle to produce a metal ion sensor probe. Response times of 10 - 15 minutes to 0.1 M CUCIZ were realized with complete regeneration of the sensor using an ethylenediarninetetraacetic acid (EDTA) solution.

We have developed instrumentation to enable the combination of surface acoustic wave (SAW) sensor measurements with direct, in-situ molecular spectroscopic measurements to understand the response of the SAW sensors with respect to the interfacial chemistry of surface-confined sensing films interacting with gas-phase analytes. Specifically, the instrumentation and software was developed to perform in-situ Fourier-transform infrared external-reflectance spectroscopy (FTIR-ERS) on operating SAW devices during dosing of their chemically modified surfaces with analytes. By probing the surface with IR spectroscopy during gas exposure, it is possible to understand in unprecedented detail the interaction processes between the sorptive SAW coatings and the gaseous analyte molecules. In this report, we provide details of this measurement system, and also demonstrate the utility of these combined measurements by characterizing the SAW and FTIR-ERS responses of organic thin-film sensor coatings interacting with gas-phase analytes.

Arrays of unheated chemically sensitive resistors (chemiresistors) can serve as extremely small, low-power-consumption sensors with simple read-out electronics. We report here results on carbon-loaded polymer composites, as well as polymeric ionic conductors, as chemiresistor sensors. We use the volubility parameter concept to understand and categorize the chemiresistor responses and, in particular, we compare chemiresistors fabricated from polyisobutylene (PIB) to results from PIB-coated acoustic wave sensors. One goal is to examine the possibility that a small number of diverse chemiresistors can sense all possible solvents-the "Universal Solvent Sensor Array". keywords: chemiresistor, volubility parameter, chemical sensor

The effects of nitrided SiO{sub 2}/Si(100) interfaces upon cycling endurance in silicon-oxide-nitride-oxide-silicon (SONOS) non-volatile memory transistors are investigated. Analysis of MOSFET sub-threshold characteristics indicate cycling degradation to be a manifestation of interface state (D{sub it}) generation at the tunnel oxide/silicon interface. After 10{sup 6} write/erase cycles, SONOS film stacks prepared with nitrided tunnel oxides exhibit enhanced cycling endurance with {Delta}D{sub it}=3x10{sup 12} V{sup -1}cm{sup -2}, compared to {Delta}D{sub it}=2x10{sup 13} V{sup -l}cm{sup -2} for non-nitrided tunnel oxides. Additionally, if the capping oxide is formed by steam oxidation, rather than by deposition, SONOS stacks prepared with non-nitrided tunnel oxides exhibit endurance characteristics similar to stacks with nitrided tunnel oxides. From this observation it is concluded that latent nitridation of the tunnel oxidehilicon interface occurs during steam oxide cap formation.

Growth kinetics, mechanisms, and material quality in GaN epitaxial lateral over-growth (ELO) were examined using a single mask of systematically varied patterns. A 2-D gas phase reaction/diffusion model describes how transport of the Ga precursor to the growth surface enhances the lateral rate in the early stages of growth. In agreement with SEM studies of truncated growth runs, the model also predicts the dramatic decrease in the lateral rate that occurs as GaN over-growth reduces the exposed area of the mask. At the point of convergence, a step-flow coalescence mechanism is observed to fill in the area between lateral growth-fronts. This alternative growth mode in which a secondary growth of GaN is nucleated along a single convergence line, may be responsible for producing smooth films observed to have uniform cathodoluminescence (CL) when using 1{micro}m nucleation zones. Although emission is comprised of both UV ({approximately}365nm) and yellow ({approximately}550nm) components, the spectra suggest these films have reduced concentrations of threading dislocations normally associated with non-radiative recombination centers and defects known to accompany growth-front convergence lines.

The National Electrical Code@ (NEC@) focuses primarily on electrical system installation requirements in the U.S. The NEC addresses both fire and personnel safety. This paper will describe recent efforts of the PV industry in the U.S. and the resulting requirements in the 1999 National Electrical Code-- Article 690 --Solar Photovoltaic Systems. The Article 690 requirements spell out the PV-unique requirements for safe installations of PV systems in the U.S.A. This paper provides an overview of the most significant changes that appear in Article 690 of the 1999 edition of the NEC. The related and coordinated efforts of the other standards- making groups will also be briefly reviewed.

Using surface micromachined samples, we demonstrate the accurate measurement of cantilever beam adhesion by using test structures which are adhered over long attachment lengths. We show that this configuration has a deep energy well, such that a fracture equilibrium is easily reached. When compared to the commonly used method of determining the shortest attached beam, the present method is much less sensitive to variations in surface topography or to details of capillary drying.

Abstract not provided.

Over the past decade, Sandia National Laboratories has been involved in the development of receivers to transfer energy from the focus of a parabolic dish concentrator to the heater tubes of a Stirling engine. Through the isothermal evaporation and condensation of sodium. a heat-pipe receiver can efficiently transfer energy to an engine's working fluid and compensate for irregularities in the flux distribution that is delivered by the concentrator. The operation of the heat pipe is completely passive because the liquid sodium is distributed over the solar-heated surface by capillary pumping provided by a wick structure. Tests have shown that using a heat pipe can boost the system performance by twenty percent when compared to directly illuminating the engine heater tubes. Designing heat pipe solar receivers has presented several challenges. The relatively large area ({approximately}0.2 m{sup 2}) of the receiver surface makes it difficult to design a wick that can continuously provide liquid sodium to all regions of the heated surface. Selecting a wick structure with smaller pores will improve capillary pumping capabilities of the wick, but the small pores will restrict the flow of liquid and generate high pressure drops. Selecting a wick that is comprised of very tine filaments can increase the permeability of the wick and thereby reduce flow losses, however, the fine wick structure is more susceptible to corrosion and mechanical damage. This paper provides a comprehensive review of the issues encountered in the design of heat pipe solar receivers and solutions to problems that have arisen. Topics include: flow characterization in the receiver, the design of wick systems. the minimization of corrosion and dissolution of metals in sodium systems. and the prevention of mechanical failure in high porosity wick structures.

High integrity/high consequence systems must be safe and reliable; hence it is only logical that both software safety and software reliability cases should be developed. Risk assessments in safety cases evaluate the severity of the consequences of a hazard and the likelihood of it occurring. The likelihood is directly related to system and software reliability predictions. Software reliability cases, as promoted by SAE JA 1002 and 1003, provide a practical approach to bridge the gap between hardware reliability, software reliability, and system safety and reliability by using a common methodology and information structure. They also facilitate early insight into whether or not a project is on track for meeting stated safety and reliability goals, while facilitating an informed assessment by regulatory and/or contractual authorities.

The Boeing Company's Dish Engine Critical Component (DECC) project started in April of 1998. It is a continuation of a solar energy program started by McDonnell Douglas (now Boeing) and United Stirling of Sweden in the mid 1980s. The overall objectives, schedule, and status of this project are presented in this paper. The hardware test configuration, hardware background, operation, and test plans are also discussed. A summary is given of the test data, which includes the daily power performance, generated energy, working-gas usage, mirror reflectivity, solar insolation, on-sun track time, generating time, and system availability. The system performance based upon the present test data is compared to test data from the 1984/88 McDonnell Douglas/United Stirling AB/Southem California Edison test program. The test data shows that the present power, energy, and mirror performance is comparable to when the hardware was first manufactured 14 years ago.

Motion detectors consisting of Pb(Zr{sub x}Ti{sub (1{minus}x)})O{sub 3} (PZT) thin films, between platinum electrodes, on micromachined silicon compound clamped-clamped or cantilever beam structures were fabricated using either hot KOH or High Aspect Ratio Silicon Etching (HARSE) to micromachine the silicon. The beams were designed such that a thicker region served as a test mass that produced stress at the top of the membrane springs that supported it when the object to which the detector was mounted moved. The PZT film devices were placed on these membranes to generate a charge or a voltage in response to the stress through the piezoelectric effect. Issues of integration of the PZT device fabrication process with the two etching processes are discussed. The effects of PZT composition and device geometry on the response of the detectors to motion is reported and discussed.

We have developed a variety of processes for fabricating components for micro devices based on deep x-ray lithography (DXRL). Although the techniques are applicable to many materials, we have demonstrated them using hard (Nd{sub 2}Fe{sub 14}B) and soft (Ni-Zn ferrite) magnetic materials because of the importance of these materials in magnetic micro-actuators and other devices and because of the difficulty fabricating them by other means. The simplest technique involves pressing a mixture of magnetic powder and a binder into a DXRL-formed mold. In the second technique, powder is pressed into the mold and then sintered to densify. The other two processes involve pressing at high temperature either powder or a dense bulk material into a ceramic mold that was previously made using a DXRL mold. These techniques allow arbitrary 2-dimensional shapes to be made 10 to 1000 micrometers thick with in-plane dimensions as small as 50 micrometers and dimensional tolerances in the micron range. Bonded isotropic Nd{sub 2}Fe{sub 14}B micromagnets made by these processes had an energy product of 7 MGOe.

This Institutional Plan is the most comprehensive yearly "snapshot" available of Sandia National Laboratories' major programs, facilities, human resources, and budget. The document also includes overviews of our missions, organization, capabilities, planning functions, milestones, and accomplishments. The document's purpose is to provide the above information to the US Department of Energy, key congressional committees, Sandia management, and other present and potential customers. Chapter 2 presents information about Sandia's mission and summarizes our recent revision of Sandia's Strategic Plan. Chapter 3 presents an overview of Sandia's strategic objectives, chapter 4 lists laboratory goals and milestones for FY 1999, and chapter 5 presents our accomplishments during FY 1998. Chapters 3 through 5 are organized around our eight strategic objectives. The four primary objectives cover nuclear weapons responsibilities, nonproliferation and materials control, energy and critical infrastructures, and emerging national security threats. The major programmatic initiatives are presented in chapter 7. However, the programmatic descriptions in chapter 6 and the Associated funding tables in chapter 9 continue to be presented by DOE Budget and Reporting Code, as in previous Sandia institutional plans. As an aid to the reader, the four primary strategic objectives in chapter 3 are cross-referenced to the program information in chapter 6.

Mining has always had an important influence on cultures and traditions of communities around the globe and throughout history. Today, because mining legislation places heavy emphasis on environmental protection, there is great interest in having a comprehensive understanding of ancient mining and mining sites. Multi-disciplinary approaches (i.e., Pb isotopes as tracers) are being used to explore the distribution of metals in natural environments. Another successful approach is to model solution migration numerically. A proven method to simulate solution migration in natural rock salt has been applied to project through time for 10,000 years the system performance and solution concentrations surrounding a proposed nuclear waste repository. This capability is readily adaptable to simulate solution migration around mining.

While many research and development activities take place at Sandia National Laboratories' Intelligent Systems and Robotics Center (ISRC), where the "rubber meets the road" is in the ISRC'S delivered systems. The ISRC has delivered several systems over the last few years that handle hazardous materials on a daily basis, and allow human workers to move to a safer, supervisory role than the "hands-on" operations that they used to perform. The ISRC at Sandia performs a large range of research and development activities, including development and delivery of one-of-a-kind robotic systems for use with hazardous materials. Our mission is to create systems for operations where people can't or don't want to perform the operations by hand, and the systems described in this article are several of our first-of-a-kind deliveries to achieve that mission.

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. Often, however, points are generated such that there is additional information available to the reconstruction algorithm. We present 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 fills itself in.

Hydrogen-metal interaction phenomena belong to the most exciting challenges of today's physical metallurgy and physics of solids due to the uncommon behavior of hydrogen in condensed media and to the need for understanding hydrogen's strong negative impact on properties of some high-strength steels and.alloys. The paper cites and summarizes research data on fundamental thermodynamic characteristics of hydrogen in some metals that absorb it endothermally at elevated temperatures. For a number of metal-hydrogen systems, information on some phase diagrams previously not available to the English-speaking scientific community is presented.

Experimental data on directional and bulk solidification of hydrogen-charged samples of aluminum alloy A356 and nickel alloy Inconel 718 are discussed. The solidification structure of the porous zone is shown to be dependent on many process variables. Of these variables, hydrogen content in the melt prior to solidification, and furnace atmospheric pressure during solidification play the decisive role. Also important are the furnace atmosphere composition, the solidification velocity, and the temperature distribution of the liquid metal inside the mold.

With the demonstration of the viability of using the electroslag remelting process for the decontamination of radionuclides, interest has increased in examining the unique aspects associated with melting steel pipe electrodes. These electrodes consist of several nested pipes, welded concentrically to atop plate. Since these electrodes can be half as dense as a solid electrode, they present unique challenges to the standard algorithms used in controlling the melting process. Naturally the electrode must be driven down at a dramatically increased speed. However, since the heat transfer is greatly influenced and enhanced with the increased area to volume ratio, considerable variation in the melting rate of the pipes has been found. Standard control methods can become unstable as a result of the variation at increased speeds, particularly at shallow immersion depths. The key to good control lies in the understanding of the melting process. Several experiments were conducted to observe the characteristics of the melting using two different control modes. By using a pressure transducer to monitor the pressure inside the pipes, the venting of the air trapped inside the electrode was observed. The measurements reveal that for a considerable amount of time. the pipes are not completely immersed in the slag, allowing the gas inside to escape without the formation of bubbles. This result has implications for the voltage swing as well as for the decontamination reactions.

The mission of this project was to use inverse micelle solutions to synthesize nanometer sized metal particles and test the particles as catalysts in the liquefaction of coal and other related reactions. The initial focus of the project was the synthesis of iron based materials in pseudo-homogeneous form. The frost three chapters discuss the synthesis, characterization, and catalyst testing in coal liquefaction and model coal liquefaction reactions of iron based pseudo-homogeneous materials. Later, we became interested in highly dispersed catalysts for coprocessing of coal and plastic waste. Bifunctional catalysts . to hydrogenate the coal and depolymerize the plastic waste are ideal. We began studying, based on our previously devised synthesis strategies, the synthesis of heterogeneous catalysts with a bifunctional nature. In chapter 4, we discuss the fundamental principles in heterogeneous catalysis synthesis with inverse micelle solutions. In chapter 5, we extend the synthesis of chapter 4 to practical systems and use the materials in catalyst testing. Finally in chapter 6, we return to iron and coal liquefaction now studied with the heterogeneous catalysts.

The role of additive noble gases He, Ar and Xe to C&based Inductively Coupled Plasmas for etching of GaN, AIN and InN were examined. The etch rates were a strong function of chlorine concentration, rf chuck power and ICP source power. The highest etch rates for InN were obtained with C12/Xe, while the highest rates for AIN and GaN were obtained with C12/He. Efficient breaking of the 111-nitrogen bond is crucial for attaining high etch rates. The InN etching was dominated by physical sputtering, in contrast to GaN and AIN. In the latter cases, the etch rates were limited by initial breaking of the III-nitrogen bond. Maximum selectivities of -80 for InN to GaN and InN to AIN were obtained.

Sputter-deposited W-based contacts on p-GaN (N{sub A} {approximately} 10{sup 18} cm{sup {minus}3}) display non-ohmic behavior independent of annealing temperature when measured at 25 C. The transition to ohmic behavior occurs above {approximately} 250 C as more of the acceptors become ionized. The optimum annealing temperature is {approximately} 700 C under these conditions. These contacts are much more thermally stable than the conventional Ni/Au metallization, which shows a severely degraded morphology even at 700 C. W-based contacts may be ohmic as-deposited on very heavily doped n-GaN, and the specific contact resistance improves with annealing up to {approximately} 900 C.

We show that the low-temperature conductance (G) of a quantum point contact consisting of ballistic tunnel-coupled double-layer quantum well wires is modulated by an in-layer magnetic field B{sub {parallel}} perpendicular to the wires due to the anticrossing. In a system with a small g factor, B{sub {parallel}} creates a V-shaped quantum staircase for G, causing it to decrease in steps of 2e{sup 2}/{Dirac_h} to a minimum and then increase to a maximum value, where G may saturate or decrease again at higher B{sub {parallel}}'s. The effect of B{sub {parallel}}-induced mass enhancement and spin splitting is studied. The relevance of the results to recent data is discussed.

Intramolecular cyclizations during acid-catalyzed, sol-gel polymerizations of ct,co- bis(tietioxysilyl)aWmes substintidly lengtien gelties formonomers witietiylene- (l), propylene- (2), and butylene-(3)-bridging groups. These cyclizations reactions were found, using mass spectrometry and %i NMR spectroscopy, to lead preferentially to monomeric and dimeric products based on six and seven membered disilsesquioxane rings. 1,2- Bis(triethoxysilyl)ethane (1) reacts under acidic conditions to give a bicyclic drier (5) that is composed of two annelated seven membered rings. Under the same conditions, 1,3- bis(triethoxysilyl)propane (2), 1,4-bis(triethoxysilyl)butane (3), and z-1,4- bis(triethoxysilyl)but-2-ene (10) undergo an intramolecular condensation reaction to give the six membemd and seven membered cyclic disilsesquioxanes 6, 7, and 11. Subsequently, these cyclic monomers slowly react to form the tricyclic dirners 8,9 and 12. With NaOH as polymerization catalyst these cyclic silsesquioxanes readily ~aeted to afford gels that were shown by CP MAS z%i NMR and infr=d spectroscopes to retain some cyclic structures. Comparison of the porosity and microstructwe of xerogels prepared from the cyclic monomers 6 and 7 with gels prepared directly from their acyclic precursors 2 and 3, indicate that the final pore structure of the xerogels is markedly dependent on the nature of the precursor. In addition, despite the fact that the monomeric cyclic disilsesquioxane species can not be isolated from 1-3 under basic conditions due to their rapid rate of gelation, spectroscopic techniques also detected the presence of the cyclic structures in the resulting polymeric gels.

The focus of this work will be to simulate a harsh, blast environment on a space structure. Data from a reverse Hopkinson bar (RHB) test is used to generate the response to a symmetric, distributed load. The RHB generates a high-amplitude, high-frequency content, concentrated pulse that excites components at near-blast levels. The transfer functions generated at discrete points, with the RHB, are used to generate an experimental model of the structure, which is then used in conjunction with the known pressure distribution, to estimate the component response to a blast. The shock spectrum of the predicted response and the actual response compared well in two of the three cases presented.

The objectives for the ASP large early release frequency (LERF) model development work is to build a Level 2 containment response model that would capture all of the events necessary to define LERF as outlined in Regulatory Guide 1.174, can be directly interfaced with the existing Level 1 models, is technically correct, can be readily modified to incorporate new information or to represent another plant, and can be executed in SAPHIRE. The ASP LERF models being developed will meet these objectives while providing the NRC with the capability to independently assess the risk impact of plant-specific changes proposed by the utilities that change the nuclear power plants' licensing basis. Together with the ASP Level 1 models, the ASP LERF models provide the NRC with the capability of performing equipment and event assessments to determine their impact on a plant's LERF for internal events during power operation. In addition, the ASP LERF models are capable of being updated to reflect changes in information regarding the system operations and phenomenological events, and of being updated to assess the potential for early fatalities for each LERF sequence. As the ASP Level 1 models evolve to include more analysis capabilities, the LERF models will also be refined to reflect the appropriate level of detail needed to demonstrate the new capabilities. An approach was formulated for the development of detailed LERF models using the NUREG-1150 APET models as a guide. The modifications to the SAPHIRE computer code have allowed the development of these detailed models and the ability to analyze these models in a reasonable time. Ten reference LERF plant models, including six PWR models and four BWR models, which cover a wide variety of containment and nuclear steam supply systems designs, will be complete in 1999. These reference models will be used as the starting point for developing the LERF models for the remaining nuclear power plants.

Pulsed-power-driven Z pinches, produced by imploding cylindrical arrays of many wires, have generated very high x-ray radiation powers (> 200 TW) and energies (2 MJ). Experiments have revealed a steady improvement in Z-pinch performance with increasing wire number at fixed total mass and array radius. The dominant mechanism acting to limit the performance of these devices is believed to be the Rayleigh-Taylor instability which broadens the radially imploding plasma sheath and consequently reduces the peak radiation power. A model is presented which describes an amplification over the two-dimensional Rayleigh-Taylor growth rate brought about by kink-like forces on the individual wires. This amplification factor goes to zero as the number of wires approaches infinity. This model gives results which are in good agreement with the experimental data and provides a scaling for wire-array Z pinches. © 1999 American Institute of Physics.

Small, reliable chemical sensors are needed for a wide range of applications, such as weapon state-of-health monitoring, nonproliferation activities, and manufacturing emission monitoring. Significant improvements in present surface acoustic wave sensors could be achieved by developing a flexural plate-wave (FPW) architecture, in which acoustic waves are excited in a thin sensor membrane. Further enhancement of device performance could be realized by integrating a piezoelectric thin film on top of the membrane. These new FPW-piezoelectric thin film devices would improve sensitivity, reduce size, enhance ruggedness and reduce the operating frequency so that the FPW devices would be compatible with standard digital microelectronics. Development of these piezoelectric thin film // FPW devices requires integration of (1) acoustic sensor technology, (2) silicon rnicromachining techniques to fabricate thin membranes, and (3) piezoelectric thin films. Two piezoelectric thin film technologies were emphasized in this study: Pb(Zr,Ti)O{sub 3} (PZT) and AlN. PZT thin films were of sufficient quality such that the first high frequency SAW measurements on PZT thin films were measured during the course of this study. Further, reasonable ferroelectric properties were obtained from PZT films deposited on Si surface micromachined FPW device membranes. Fundamental understanding of the effect of nanodimension interfacial layers on AlN thin film domain configurations and piezoelectric response was developed. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the US Department of Energy under contract DE-AC04-94AL85000.

As part of the Laboratory-Directed Research and Development (LDRD) Program at Sandia National Laboratories, an investigation into the existence of enhanced vapor-phase diffusion (EVD) in porous media has been conducted. A thorough literature review was initially performed across multiple disciplines (soil science and engineering), and based on this review, the existence of EVD was found to be questionable. As a result, modeling and experiments were initiated to investigate the existence of EVD. In this LDRD, the first mechanistic model of EVD was developed which demonstrated the mechanisms responsible for EVD. The first direct measurements of EVD have also been conducted at multiple scales. Measurements have been made at the pore scale, in a two- dimensional network as represented by a fracture aperture, and in a porous medium. Significant enhancement of vapor-phase transport relative to Fickian diffusion was measured in all cases. The modeling and experimental results provide additional mechanisms for EVD beyond those presented by the generally accepted model of Philip and deVries (1957), which required a thermal gradient for EVD to exist. Modeling and experimental results show significant enhancement under isothermal conditions. Application of EVD to vapor transport in the near-surface vadose zone show a significant variation between no enhancement, the model of Philip and deVries, and the present results. Based on this information, the model of Philip and deVries may need to be modified, and additional studies are recommended.

This report documents a collection of papers on a family of uniform strain tetrahedral finite elements and their connection to different element types. Also included in the report are two papers which address the general problem of connecting dissimilar meshes in two and three dimensions. Much of the work presented here was motivated by the development of the tetrahedral element described in the report "A Suitable Low-Order, Eight-Node Tetrahedral Finite Element For Solids," by S. W. Key {ital et al.}, SAND98-0756, March 1998. Two basic issues addressed by the papers are: (1) the performance of alternative tetrahedral elements with uniform strain and enhanced uniform strain formulations, and (2) the proper connection of tetrahedral and other element types when two meshes are "tied" together to represent a single continuous domain.

Optical channeling or refractive guiding processes involving the nonlinear interaction of intense femtosecond optical pulses with matter in the self-focussing regime has created exciting opportunities for next-generation laser plasma-based x-ray sources and directed energy applications. This fundamentally new form of extended paraxial electromagnetic propagation in nonlinear dispersive media such as underdense plasma is attributed to the interplay between normal optical diffraction and intensity-dependent nonlinear focussing and refraction contributions in the dielectric response. Superposition of these mechanisms on the intrinsic index profile acts to confine the propagating energy in a dynamic self-guiding longitudinal waveguide structure which is stable for power transmission and robust compression. The laser-driven channels are hypothesized to support a degree of solitonic transport behavior, simultaneously stable in the space and time domains (group velocity dispersion balances self-phase modulation), and are believed to be self-compensating for diffraction and dispersion over many Rayleigh lengths in contrast with the defining characteristics of conventional diffractive imaging and beamforming. By combining concentrated power deposition with well-ordered spatial localization, this phenomena will also create new possibilities for production and regulation of physical interactions, including electron beams, enhanced material coupling, and self-modulated plasma wakefields, over extended gain distances with unprecedented energy densities. Harmonious combination of short-pulse x-ray production with plasma channeling resulting from a relativistic charge displacement nonlinearity mechanism in the terawatt regime (10{sup 18} W/cm{sup 2}) has been shown to generate high-field conditions conducive to efficient multi-kilovolt x-ray amplification and peak spectral brightness. Channeled optical propagation with intense short-pulse lasers is expected to impact several critical mission areas at Sandia including x-ray backlighting of pinch implosions, nondestructive radiographic imaging of aging weapons components, high-power electromagnetic pulse generation, particle acceleration, and remote sensing.

This effort studied the integration of innovative methods of key management crypto synchronization, and key agility while scaling encryption speed. Viability of these methods for encryption of ATM cell payloads at the SONET OC- 192 data rate (10 Gb/s), and for operation at OC-48 rates (2.5 Gb/s) was shown. An SNL-Developed pipelined DES design was adapted for the encryption of ATM cells. A proof-of-principle prototype circuit board containing 11 Electronically Programmable Logic Devices (each holding the equivalent of 100,000 gates) was designed, built, and used to prototype a high speed encryptor.

This study evaluated multiple, long-term environmental oil-contamination risk scenarios that could result from the potential leakage of UP to 1.5 million barrels of crude oil entombed in the Weeks Island SPR mine following site decommissioning and abandonment, and up to 100 years thereafter. This risk assessment also provides continuity with similar risk evaluations performed earlier and documented in the 1995 DOE Environmental Assessment for Decommissioning the Strategic Petroleum Reserve Weeks Island Facility (EA). This current study was requested by the DOE to help them determine if their previous Finding of No Significant Impact (FONSI), in the EA, is still valid or needs to be rescinded. Based on the calculated environmental risk results (in terms of clean-up and remediation expenses) presented in this risk assessment, including the calculated average likelihoods of oil release and potential oil-leakage volumes, none of the evaluated risk events would appear to satisfy the definition of significant environmental impact in National Environmental Policy Act (NEPA) terminology. The DOE may combine these current results with their earlier evaluations and interpretations in the 1995 EA in order to assess whether the existing FONSI is still accurate, acceptable, and valid. However, from a risk evaluation standpoint, the assessment of impacts appears to be the same whether only 10,000 to 30,000 barrels of crude oil (as considered in the 1995 EA), or up to 1.5 million barrels of oil (as considered herein) are abandoned in the Weeks Island SPR facility.

The theoretical background for the finite element computer program, MPSalsa Version 1.5, is presented in detail. MPSalsa is designed to solve laminar or turbulent low Mach number, two- or three-dimensional incompressible and variable density reacting fluid flows on massively parallel computers, using a Petrov-Galerkin finite element formulation. The code has the capability to solve coupled fluid flow (with auxiliary turbulence equations), heat transport, multicomponent species transport, and finite-rate chemical reactions, and to solve coupled multiple Poisson or advection-diffusion-reaction equations. The program employs the CHEMKIN library to provide a rigorous treatment of multicomponent ideal gas kinetics and transport. Chemical reactions occurring in the gas phase and on surfaces are treated by calls to CHEMKIN and SURFACE CHEMK3N, respectively. The code employs unstructured meshes, using the EXODUS II finite element database suite of programs for its input and output files. MPSalsa solves both transient and steady flows by using fully implicit time integration, an inexact Newton method and iterative solvers based on preconditioned Krylov methods as implemented in the Aztec. solver library.

The U.S. Department of Energy (DOE) has been developing a nuclear waste disposal facility, the Waste Isolation Pilot Plant (WIPP), located approximately 42 km east of Carlsbad, New Mexico. The WIPP is designed to demonstrate the safe disposal of transuranic wastes produced by the defense nuclear-weapons program. Performance assessment analyses (U.S. DOE, 1996) indicate that human intrusion by inadvertent and intermittent drilling for resources provide the only credible mechanisms for significant releases of radionuclides horn the disposal system. These releases may occur by five mechanisms: (1) cuttings, (2) cavings, (3) spallings, (4) direct brine releases, and (5) long-term brine releases. The first four mechanisms could result in immediate release of contaminant to the accessible environment. For the last mechanism, migration pathways through the permeable layers of rock above the Salado are important, and major emphasis is placed on the Culebra Member of the Rustler Formation because this is the most transmissive geologic layer in the disposal system. For reasons of initial quantity, half-life, and specific radioactivity, certain isotopes of Th, U, Am, and Pu would dominate calculated releases from the WIPP. In order to help quanti~ parameters for the calculated releases, radionuclide transport experiments have been carried out using five intact-core columns obtained from the Culebra dolomite member of the Rustler Formation within the Waste Isolation Pilot Plant (WIPP) site in southeastern New Mexico. This report deals primarily with results of mathematical analyses related to the retardation of %J%, 24%, and 24'Am in two of these cores (B-Core - VPX26-11A and C-Core - VPX28-6C). All B-Core transport experiments were done using Culebra-simukmt brine relevant to the core recovery location (the WIPP air-intake shaft - AIS). Most experiments with C-Core were done with AIS brine with some admixture of a brine composition (ERDA-6) that simulated deeper formation brines. No significant changes in transport behavior were observed for changes in brine. Hydraulic characteristics (i.e., apparent porosity and apparent dispersion coefficient) for the cores were obtained via experiments using conservative tracer `Na. Elution experiments carried out over periods of a few days with tracers `*U and %Np indicated that these tracers were weakly retarded as indicated by delayed elution of these species. Elution experiments with tracers `%, 24'Pu, and 24'Ani were performed, but no elution of any of these species was observed in any flow experiment to date, including experiments of up to two years duration. However, B-Core was subjected to tomographic analysis from which a retardation factor can be inferred for%. Moreover, the fact of non- elution for 24*Pu and 24'Am after more than two years brine flow through C-Core can be coupled with the minimum detectable activity for each of these species to compute minimum retardation factors in C-Core. The retardation factors for all three species can then be coupled with the apparent hydraulic characteristics to estimate an apparent minimum solutionhock distribution coefficient, &, for each actinide. The specific radionuclide isotopes used in these experiments were chosen to facilitate analysis. Even though these isotopes are not necessarily the same as those that are most important to WIPP performance, they are isotopes of the same elements, and . their chemical and transport properties are therefore identical to those of isotopes in the WIPP inventory. The retardation factors and & values deduced from experimental results strongly support the contention that sorption in the Culebra provides an effective barrier to release of Th, Pu, and Am during the regulatory period.

This paper presents the Local Area Network Distributed Supervisory Control and Programming Environment (LandScape) commands set that provides a Generic Device Subsystem Application Programmers Interface (API). These commands are implemented using the Common Object Request Broker Architecture (CORBA) specification with Orbix from Iona Technologies.

The purpose of this project was to create a reliable, 3D sensing and visualization system for unattended monitoring. The system provides benefits for several of Sandia's initiatives including nonproliferation, treaty verification, national security and critical infrastructure surety. The robust qualities of the system make it suitable for both interior and exterior monitoring applications. The 3D sensing system combines two existing sensor technologies in a new way to continuously maintain accurate 3D models of both static and dynamic components of monitored areas (e.g., portions of buildings, roads, and secured perimeters in addition to real-time estimates of the shape, location, and motion of humans and moving objects). A key strength of this system is the ability to monitor simultaneous activities on a continuous basis, such as several humans working independently within a controlled workspace, while also detecting unauthorized entry into the workspace. Data from the sensing system is used to identi~ activities or conditions that can signi~ potential surety (safety, security, and reliability) threats. The system could alert a security operator of potential threats or could be used to cue other detection, inspection or warning systems. An interactive, Web-based, 3D visualization capability was also developed using the Virtual Reality Modeling Language (VRML). The intex%ace allows remote, interactive inspection of a monitored area (via the Internet or Satellite Links) using a 3D computer model of the area that is rendered from actual sensor data.

This report provides an overview of the results of the Vital the Nicaraguan Water Resources Management Initiative, Issues process as implemented for a collaborative effort between the Nicaraguan Ministry of Environment and Natural Resources and Sandia National Laboratories. This initiative is being developed to assist in the development of an efficient and sustainable water resources management system for Nicamgua. The Vital Issues process was used to provide information for developing a project that will develop and implement an advanced information system for managing Nicaragua's water resources. Three Vital Issues panel meetings were convened to 1) develop a mission statement and evaluation criteria for identifying and ranking the issues vital to water resources management in Nicaragua 2) define and rank the vital issues; and 3) identify a preliminary list of information needed to address the vital issues. The selection of panelists from the four basic institutional perspectives- government, industiy, academe, and citizens' groups (through nongovernmental organizations (NGOs))-ensured a high level of stakeholder representation on the panels. The already existing need for a water resource management information system has been magnified in the aftemnath of Hurricane Mitch. This information system would be beneficial for an early warning system in emergencies, and the modeling and simulation capabilities of the system would allow for advanced planning. Additionally, the outreach program will provide education to help Nicaraguan improve their water hygiene practices.

Materials compatibility studies of aged, engineered materials and hardware are critical to understanding and predicting component reliability, particularly for systems with extended stockpile life requirements. Nondestructive testing capabilities for component reliability would significantly enhance lifetime predictions. For example, if the detection of crack propagation through a solder joint can be demonstrated, this technique could be used to develop baseline information to statistically determine solder joint lifelengths. This report will investigate high frequency signal response techniques for nondestructively evaluating the electrical behavior of thick film hybrid transmission lines.

Parameters have been identified that can be modeled stochastically using PORFLOW and Latin Hypercube Sampling (LHS). These parameters include hydrologic and transport properties in the vadose and saturated zones, as well as source-term parameters and infiltration rates. A number of resources were used to define the parameter distributions, primarily those provided in the Retrieval Performance Evaluation Report (Jacobs, 1998). A linear rank regression was performed on the vadose-zone hydrologic parameters given in Khaleel and Freeman (1995) to determine if correlations existed between pairs of parameters. No strong correlations were found among the vadose-zone hydrologic parameters, and it was recommended that these parameters be sampled independently until future data or analyses reveal a strong correlation or functional relationship between parameters. Other distributions for source-term parameters, infiltration rates, and saturated-zone parameters that are required to stochastically analyze the performance of the AX Tank Farm using LHS/PORFLOW were adapted from distributions and values reported in Jacobs (1998) and other literature sources. Discussions pertaining to the geologic conceptualization, vadose-zone modeling, and saturated-zone modeling of the AX Tank Farm are also presented.

Abstract not provided.

Abstract not provided.

In 1989 BNL was added to the EPAs National Priorities List. The site is divided into seven operable units (OU). OU-I includes the former landfill area. The field task site is noted as the AOC 2C Glass Holes location. Beginning in the 1960s and continuing into the 1980s, BNL disposed of laboratory waste (glassware, chemicals and animal carcasses) in numerous shallow pits. The drivers for remediating the pits are; historical records that indicate hazardous materials may have been disposed of in the pits; ground water contamination down gradient of the pits; a test excavation of one of the glass holes that unearthed laboratory glass bottles with unidentified liquids still contained; and the fact that BNL rests atop an EPA designated sole-source aquifer. The specific site chosen for this demonstration was pit G-11. The requirements that lead to choosing this pit were; a well characterized pit and a relatively isolated pit where our construction operations would not impact on adjacent pits. The glass holes area, including pit G-11, was comprehensively surveyed using a suite of geophysical techniques (e.g., EM-31, EM-61, GPR). Prior to stabilizing the waste form a subsurface barrier was constructed to contain the entire waste pit. The pit contents were then stabilized using a cement grout applied via jet grouting. The stabilization was performed to make removal of the waste from the pit easier and safer in terms of worker exposure. The grouting process would mix and masticate the waste and grout and form a single monolithic waste form. This large monolith would then be subdivided into smaller 4 foot by 4 foot by 10-12 foot block using a demolition grout. The smaller blocks would then be easily removed from the site and disposed of in a CERCLA waste site.

This is the final report of an LDRD program entitled 'Scanning Probe-Based Processes for Nanometer-Scale Device Fabrication'. This program intends to expand Sandia's expertise in scanning-probe based fabrication and characterization of nanostructures. Our object is to achieve an order of magnitude decrease in feature size compared to conventional fabrication technology. We are exploring approaches to nanostructure fabrication and characterization using scanning probe-based (STM, AFM). We also are developing numerical simulations of localized electric field and emission current to explore mechanisms and characterize limits to processing techniques. We emphasize novel fabrication processes and characterization of physical, chemical and electronic effects in nanostructures.

The process of manufacturing the MC4277 Neutron Tube requires the evacuation of the device through a 4.76 mm (.1875 in.) OD copper tube. Eight tubes are simultaneously evacuated and then baked out. When the process is completed, the tubes must be separated from the system without compromising the ultra-high vacuum in the tube and the system. Previously, a manual pinch-off tool was used. This procedure required up to 3 operators with a high probability of creating defective seals or destroyed tubes. Two new identical robotic systems were built to allow a single operator to consistently produce good tubes with perfect seals. These systems have the added capability of partially pinching off tubes at jaw displacements repeatable to *0.05 mm (kO.002 in.). Both systems have operated flawlessly since their installation in January and March, 1998. A detailed description of these systems is given in this report.

The elevation change data measured at the Weeks Island SPR site over the last 16+ years has been studied and analyzed. The subsidence rate is not constant with time and while the subsidence rate may have increased slightly during the past several years, recently the rate has increased more dramatically. The most recent increase comes at a time when the Strategic Petroleum Reserve (SPR) storage mine had been emptied of oil and was in the process of being refilled with brine. Damage to surface structures that has been observed during the past 12-18 months is attributed to the continued subsidence and dtierential subsidence across structures. The recent greater subsidence rates were unanticipated according to analysis results and will be used to aid further subsidence model development.

Hydrogen was ion-implanted into wurtzite-phase GaN, and its transport, bound states, and microstructural effects during annealing up to 980°C were investigated by nuclear-reaction profiling, ion-channeling analysis, transmission electron microscopy, and infrared (IR) vibrational spectroscopy. At implanted concentrations v1 at.%, faceted H2 bubbles formed, enabling identification of energetically preferred surfaces, examination of passivating N-H states on these surfaces, and determination of the diffusivity-solubility product of the H. Additionally, the formation and evolution of point and extended defects arising from implantation and bubble formation were characterized. At implanted H concentrations λ0.1 at.%, bubble formation was not observed, and ion-channeling analysis indicated a defect-related H site located within the [0001] channel.

GaN implanted with donor(Si, S, Se, Te) or acceptor (Be, Mg, C) species was annealed at 900-1500°C using AlN encapsulation. No redistribution was measured by SIMS for any of the dopants and effective diffusion coefficients are ≤2×10-13 cm2 · s-1 at 1400°C, except Be, which displays damage-enhanced diffusion at 900°C and is immobile once the point defect concentration is removed. Activation efficiency of ∼90% is obtained for Si at 1400°C. TEM of the implanted material shows a strong reduction in lattice disorder at 1400-1500°C compared to previous results at 1100°C. There is minimal interaction of the sputtered AlN with GaN under our conditions, and it is readily removed selectively with KOH.

The organization and assembly of molecules in cellular membranes is orchestrated through the recognition and binding of specific chemical signals. A simplified version of the cellular membrane system has been developed using a synthetically prepared membrane receptor incorporated into a biologically derived lipid bilayer. Through an interplay of electrostatic and van der Waals interactions, aggregation or dispersion of molecular components could be executed on command using a specific chemical signal. A pyrene fluorophore was used as an optical probe to monitor the aggregational state of the membrane receptors in the bilayer matrix. The pyrene excimer emission to monomer emission (E/M) intensity ratio gave a relative assessment of the local concentration of receptors in the membrane. Bilayers were prepared with receptors selective for the divalent metal ions of copper, mercury, and lead. Addition of the metal ions produced a rapid dispersion of aggregated receptor components at nano- to micro-molar concentrations. The process was reversible by sequestering the metal ions with EDTA. Receptors for proteins and polyhistidine were also prepared and incorporated into phosphatidylcholine lipid bilayers. In this case, the guest molecules bound to the membrane through multiple points of interaction causing aggregation of initially dispersed receptor molecules. The rapid, selective, and sensitive fluorescence optical response of these lipid assemblies make them attractive in sensor applications for aqueous phase metal ions and polypeptides.

The microstructural evolution of heavily deformed polycrystalline Cu is simulated by coupling a constitutive model for polycrystal plasticity with the Monte Carlo Potts model for grain growth. The effects of deformation on boundary topology and grain growth kinetics are presented. Heavy deformation leads to dramatic strain-induced boundary migration and subsequent grain fragmentation. Grain growth is accelerated in heavily deformed microstructures. The implications of these results for the thermomechanical fatigue failure of eutectic solder joints are discussed.

A GaN based depletion mode metal oxide semiconductor field effect transistor (MOSFET) was demonstrated using Ga2O3(Gd2O3) as the gate dielectric. The MOS gate reverse breakdown voltage was >35 V which was significantly improved from 17 V of Pt Schottky gate on the same material. A maximum extrinsic transconductance of 15 mS/mm was obtained at Vds = 30 V and device performance was limited by the contact resistance. A unity current gain cut-off frequency, fT, and maximum frequency of oscillation, fmax of 3.1 and 10.3 GHz, respectively, were measured at Vds = 25 V and Vgs = -20 V.

Microscopic calculations of the absorption and luminescence spectra are presented for wide bandgap Ga1-xInxN/GaN quantum well systems. Whereas structures with narrow well widths exhibit the usual excitation-dependent bleaching of the exciton resonance without shifting spectral position, a significant blueshift of the exciton peak is obtained for wider quantum wells. This blueshift, which is also present in the excitation-dependent luminescence spectra, is attributed to the interplay between the screening of a strain induced piezoelectric field and the density dependence of many-body Coulomb effects. The calculations also show an over two orders of magnitude increase in the spontaneous electron-hole-pair lifetime with well width, due to the reduction of the electron-hole wave function overlap in the wider wells. The resulting decrease in spontaneous emission loss is predicted to lead to improved threshold properties in wide quantum well lasers. © 1999 The American Physical Society.

Measurement and signal intelligence (MASINT) of the battlespace has created new requirements in information management, communication and interoperability as they effect surveillance and situational awareness. In many situations, stand-off remote-sensing and hazard-interdiction techniques over realistic operational areas are often impractical and difficult to characterize. An alternative approach is to implement adaptive remote-sensing techniques with swarms of mobile agents employing collective behavior for optimization of mapping signatures and positional orientation (registration). We have expanded intelligent control theory using physics-based collective behavior models and genetic algorithms to produce a uniquely powerful implementation of distributed ground-based measurement incorporating both local collective behavior, and inter-operative global optimization for sensor fusion and mission oversight. By using a layered hierarchical control architecture to orchestrate adaptive reconfiguration of semi-autonomous robotic agents, we can improve overall robustness and functionality in dynamic tactical environments without information bottlenecking. In our concept, each sensor is equipped with a miniaturized optical reflectance modulator which is interactively monitored as a remote transponder using a laser communication protocol from a remote mothership or operative. Robot data-sharing at the ground level can be leveraged with global evaluation criteria, including terrain overlays and remote imaging data. Information sharing and distributed intelligence opens up a new class of remote sensing applications in which small single-function autonomous observers at the local level can collectively optimize and measure large scale ground-level signatures. As the need for coverage and the number of agents grows to improve spatial resolution, cooperative behavior orchestrated by a global situational awareness umbrella will be an essential ingredient to offset increasing bandwidth requirements within the net. A system of this type is being developed which will be capable of sensitively detecting, tracking, and mapping spatial distributions of measurement signatures, which are nonstationary or obscured by clutter or interfering obstacles by virtue of adaptive reconfiguration. This methodology is being used to field an adaptive ground-penetrating impulse radar from a superposition of small radiating dipoles for detection of underground structures and to detect/remediate hazardous biological or chemical species in migrating plumes.

An expression for the coarsening rate of the Pb-rich phase particles was determined through isothermal aging experiments and comparative literature data as: λ = λo+{[4.10×10-5 e-11023/T+15.6×10-8 e-3123/T (dγ/dt)]t}0.256 where γo and γ are the initial and final mean Pb-rich particle diameters, respectively (mm); T is temperature (°K); t is time (s); and dγ/dt is the strain rate (s-1). The phase coarsening behavior showed good agreement with previous literature data from isothermal aging experiments. The power-law exponent, p, for the Pb-rich phase size coarsening kinetics: γp-γop≈t increased from a value of 3.3 at the low aging temperature regime (70-100 °C) to a value of 5.1 at the high temperature regime (135-170 °C), suggesting that the number of short-circuit diffusion paths had increased with further aging. This expression provides an important basis for the microstructurally-based, constitutive equation used in the visco-plastic model for TMF in Sn-Pb solder. The revised visco-plastic model was exercised using a through-hole solder joint configuration. Initial data indicate a satisfactory compatibility between the coarsening expression and the constitutive equations.

In-situ filling through hydrolysis and condensation of silicon alkoxides dissolved into polymers has been utilized to generate nanocomposites in which the filler phase can be intimately associated with the polymer on relatively small length scales. One problem of the method has been achieving useful fill volumes without bulk phase separation of the growing inorganic component from the polymer. In this paper, we describe the preparation of a new class of nanocomposite materials in which the inorganic filler phase is pre-assembled before copolymerization with an organic monomer. Maleimide monomers, prepared from alkoxysilylpropyl amines and maleic anhydride, were protected against side reactions by forming the oxonorbornene Diels-Alder adduct with furan. The monomers were then reacted under sol-gel conditions to form oligomers or polymers making up the filler phase. The material was activated by thermal deprotection of the maleimide and reacted with organic monomers or polymers to form the filled nanocomposite.

Progress towards the development of such algorithms as been reported for waveguide analysis'-3and vertical-cavity laser simulation. In all these cases, the higher accuracy order was obtained for a single spatial dimension. More recently, this concept was extended to differencing of the Helmholtz Equation on a 2-D grid, with uniform regions treated to 4th order and dielectric interfaces to 3'd order5. No attempt was made to treat corners properly. In this talk I will describe the extension of this concept to allow differencing of the Helmholtz Equation on a 2-D grid to 6* order in uniform regions and 5* order at dielectric interfaces. In addition, the first known derivation of a finite difference equation for a dielectric comer that allows correct satisfaction of all boundary conditions will be presented. This equation is only accurate to first order, but as will be shown, results in simulations that are third-order-accurate. In contrast to a previous approach3 that utilized a generalized Douglas scheme to increase the accuracy order of the difference second derivative, the present method invokes the Helmholtz Equation itself to convert derivatives of high order in a single direction into mixed

The computing power available to scientists and engineers has increased dramatically in the past decade, due in part to progress in making massively parallel computing practical and available. The expectation for these machines has been great. The reality is that progress has been slower than expected. Nevertheless, massively parallel computing is beginning to realize its potential for enabling significant breakthroughs in science and engineering. This paper provides a perspective on the state of the field, colored by the authors' experiences using large-scale parallel machines at Sandia National Laboratories. We address trends in hardware, system software and algorithms, and we also offer our view of the forces shaping the parallel computing industry.

To physically investigate permeability upscaling, over 13,000 permeability values were measured with four different sample supports (i.e., sample volumes) on a block of Berea Sandstone. At each sample support, spatially exhaustive permeability datasets were measured, subject to consistent flow geometry and boundary conditions, with a specially adapted minipermeameter test system. Here, we present and analyze a subset of the data consisting of 2304 permeability values collected from a single block face oriented normal to stratification. Results reveal a number of distinct and consistent trends (i.e., upscaling) relating changes in key summary statistics to an increasing sample support. Examples include the sample mean and semivariogram range that increase with increasing sample support and the sample variance that decreases. To help interpret the measured mean upscaling, we compared it to theoretical models that are only available for somewhat different flow geometries. The comparison suggests that the nonuniform flow imposed by the minipermeameter coupled with permeability anisotropy at the scale of the local support (i.e., smallest sample support for which data is available) are the primary controls on the measured upscaling. This work demonstrates, experimentally, that it is not always appropriate to treat the local-support permeability as an intrinsic feature of the porous medium, that is, independent of its conditions of measurement.

Isotopic labeling experiments have revealed correlations between hydrogen reactions, Ga desorption, and ammonia decomposition in GaN CVD. Low energy electron diffraction (LEED) and temperature programmed desorption (TPD) were used to demonstrate that hydrogen atoms are available on the surface for reaction after exposing GaN(001) to deuterium at elevated temperatures. Hydrogen reactions also lowered the temperature for Ga desorption significantly. Ammonia did not decompose on the surface before hydrogen exposure. However, after hydrogen reactions altered the surface, N15H3 did undergo both reversible and irreversible decomposition. This also resulted in the desorption of N2 of mixed isotopes below the onset of GaN sublimation. This suggests that the driving force of the high nitrogen-nitrogen bond strength (226 kcal/mol) can lead to the removal of nitrogen from the substrate when the surface is nitrogen rich. Overall, these findings indicate that hydrogen can influence GaN CVD significantly, being a common factor in the reactivity of the surface, the desorption of Ga, and the decomposition of ammonia.

Advanced rechargeable lithium-ion batteries are presently being developed and commercialized worldwide for use in consumer electronics, military and space applications. The motivation behind these efforts involves, among other things, a favorable combination of energy and power density. For some of the applications the power sources may need to perform at a reasonable rate at subambient temperatures. Given the nature of the lithium-ion cell chemistry the low temperature performance of the cells may not be very good. At Sandia National Laboratories, we have used different electrochemical techniques such as impedance and charge/discharge at ambient and subambient temperatures to probe the various electrochemical processes that are occurring in Li-ion cells. The purpose of this study is to identify the component that reduces the cell performance at subambient temperatures. We carried out 3-electrode impedance measurements on the cells which allowed us to measure the anode and cathode impedances separately. Our impedance data suggests that while the variation in the electrolyte resistance between room temperature and -20°C is negligible, the cathode electrolyte interfacial resistance increases substantially in the same temperature span. We believe that the slow interfacial charge transfer kinetics at the cathode electrolyte may be responsible for the increase in cell impedance and poor cell performance. © Copyright 1999 Society of Automotive Engineers, Inc.

Thermal batteries are normally constructed using pressed-powder anode, separator, and cathode pellets (discs). However, parts less than 0.010" thick are difficult to press from the starting powders. The use of plasma spraying to deposit thin pyrite films onto a stainless steel substrate was examined as an alternative to pressed-powder cathodes. The electrodes were tested under isothermal conditions and constant-current discharge over a temperature range of 400°C to 550°C using a standard LiSi anode and a separator based on the LiCIKCI eutectic. The plasma-sprayed cathodes were also evaluated in similar 5-cell thermal batteries. Cells and batteries using pressed-powder cathodes were tested under the same conditions for comparative purposes.

This paper addresses key issues for the cost-effective use of COTS (Commercially available Off The Shelf) microelectronics in radiation environments that enable circuit or system designers to manage risks and ensure mission success. We review several factors and tradeoffs affecting the successful application of COTS parts including (1) hardness assurance and qualification issues, (2) system hardening techniques, and (3) life-cycle costs. The paper also describes several experimental studies that address trends in total-dose, transient, and single-event radiation hardness as COTS technology scales to smaller feature sizes. As an example, the level at which dose-rate upset occurs in Samsung SRAMs increases from 1.4x10s rad(Si)/s for a 256K SRAM to 7.7xl09rad(Si)/s for a 4M SRAM, indicating unintentional hardening improvements in the design or process of a commercial technology. Additional experiments were performed to quantify variations in radiation hardness for COTS parts. In one study, only small (10-15%) variations were found in the dose-rate upset and latchup thresholds for Samsung 4M SRAMs from three different date codes. In another study, irradiations of 4M SRAMs from Samsung, Hitachi, and Toshiba indicate large differences in total-dose radiation hardness. The paper attempts to carefully define terms and clear up misunderstandings about the definitions of "COTS'1 and "radiation-hardened (RH)" technology. © 1999 IEEE.

The rutile TiO2(110) (1 × 1) surface is considered the prototypical 'well-defined' system in the surface science of metal oxides. Its popularity results partly from two experimental advantages: (i) bulk-reduced single crystals do not exhibit charging, and (ii) stoichiometric surfaces, as judged by electron spectroscopies, can be prepared reproducibly by sputtering and annealing in oxygen. We present results that show that this commonly applied preparation procedure may result in a surface structure that is by far more complex than generally anticipated. Flat, (1 × 1)-terminated surfaces are obtained by sputtering and annealing in ultrahigh vacuum. When re-annealed in oxygen at moderate temperatures (470-660 K), irregular networks of partially connected, pseudohexagonal rosettes (6.5 × 6 Å wide), one-unit cell wide strands, and small (≈tens of Å) (1 × 1) islands appear. This new surface phase is formed through reaction of oxygen gas with interstitial Ti from the reduced bulk. Because it consists of an incomplete, kinetically limited (1 × 1) layer, this phenomenon has been termed 'restructuring'. We report a combined experimental and theoretical study that systematically explores this restructuring process. The influence of several parameters (annealing time, temperature, pressure, sample history, gas) on the surface morphology is investigated using STM. The surface coverage of the added phase as well as the kinetics of the restructuring process are quantified by LEIS and SSIMS measurements in combination with annealing in 18O-enriched gas. Atomic models of the essential structural elements are presented and are shown to be stable with first-principles density functional calculations. The effect of oxygen-induced restructuring on surface chemistry and its importance for TiO2 and other bulk-reduced oxide materials is briefly discussed.

We describe the microfabrication of an extremely compact optical system as a key element in an integrated capillary channel electrochromatograph with fluorescence detection. The optical system consists of a vertical cavity surface-emitting laser (VCSEL), two high performance microlenses, and a commercial photodetector. The microlenses are multilevel diffractive optics patterned by electron beam lithography and etched by reactive ion etching in fused silica. The design uses substrate-mode propagation within the fused silica substrate. Two generations of optical subsystems are described. The first generation design has a 6 mm optical length and is integrated directly onto the capillary channel-containing substrate. The second generation design separates the optical system onto its own substrate module and the optical path length is further compressed to 3.5 mm. The first generation design has been tested using direct fluorescence detection with a 750 nm VCSEL pumping a 10-4 M solution of CY-7 dye. The observed signal-to-noise ratio of better than 100:1 demonstrates that the background signal from scattered pump light is low despite the compact size of the optical system and is adequate for system sensitivity requirements. © 1999 American Vacuum Society.

A computational procedure for extracting substructure-by-substructure flexibility properties from global modal parameters is presented. The present procedure consists of two key features: an element-based direct flexibility method, which uniquely determines the global flexibility without resorting to case-dependent redundancy selections, and the projection of kinematically inadmissible modes that are contained in the iterated substructural matrices. The direct flexibility method is used as the basis of an inverse problem, whose goal is to determine substructural flexibilities given the global flexibility, geometrically determined substructural rigid-body modes, and the local-to-global assembly operators. The resulting procedure, given accurate global flexibility, extracts the exact element-by-element substructural flexibilities for determinate structures. For indeterminate structures, the accuracy depends on the iteration tolerance limits. The procedure is illustrated using both simple and complex numerical examples and appears to be effective for structural applications such as damage localization and finite element model reconciliation.

Evidence for capillary waves at a liquid-vapor interface are presented from extensive molecular dynamics simulations of a system containing up to 1.24 million Lennard-Jones particles. Careful measurements show that the total interfacial width depends logarithmically on L∥, the length of the simulation cell parallel to the interface, as predicted theoretically. The strength of the divergence of the interfacial width on L∥ depends inversely on the surface tension γ. This allows us to measure γ two ways since γ can also be obtained from the difference in the pressure parallel and perpendicular to the interface. These two independent measures of γ agree provided that the interfacial order parameter profile is fit to an error function and not a hyperbolic tangent, as often assumed. We explore why these two common fitting functions give different results for γ.

Previous photopumping studies of coupled vertical cavity laser structures have demonstrated three mode coupling (two photonic and one excitonic), dual wavelength emission, and short pulse generation. This paper reports on electrically injected coupled resonator vertical-cavity laser diodes, including two novel modulation approaches.

Consider the 2-matching problem defined on the complete graph, with edge costs which satisfy the triangle inequality. We prove that the value of a minimum cost 2-matching is bounded above by 4/3 times the value of its linear programming relaxation, the fractional 2-matching problem. This lends credibility to a long-standing conjecture that the optimal value for the traveling salesman problem is bounded above by 4/3 times the value of its linear programming relaxation, the subtour elimination problem. © Springer-Verlag 1999.

Diamond films were grown by chemical deposition of hydrocarbon species in a vapor composed predominantly of hydrogen. The rate constants of the surface reactions and the concentrations of the gas-phase species were used as input to a variable time step Monte Carlo algorithm, which simulates the evolution of the diamond growth surface by tracking the occupancies of surface sites. The results of the combined tight binding and density functional theory quantum mechanical calculations are presented, suggesting that the etching of isolated, monomolecular moieties occurred at an appreciable rate, while etching from larger carbon islands was nor favorable.

We study the low-temperature in-plane magnetoresistance of tunnel-coupled quasi-one-dimensional quantum wires. The wires are defined by two pairs of mutually aligned split gates on opposite sides of a ⩽1-μm-thick (Formula presented) double-quantum-well heterostructure, allowing independent control of the width of each quantum well. In the ballistic regime, when both wires are defined and the field is perpendicular to the current, a large resistance peak at ∼6 T is observed with a strong gate voltage dependence. The data are consistent with a counting model whereby the number of subbands crossing the Fermi level changes with field due to the formation of an anticrossing in each pair of one-dimensional subbands. © 1999 The American Physical Society.

We describe a very-low power consumption circuit for processing the pulses from a semiconductor radiation detector. The circuit was designed for use with a cadmium zinc telluride (CZT) detector for unattended monitoring of stored nuclear materials. The device is intended to be battery powered and operate at low duty-cycles over a long period of time. This system will provide adequate performance for medium resolution gamma-ray pulse-height spectroscopy applications. The circuit incorporates the functions of a charge sensitive preamplifier, shaping amplifier, and peak sample and hold circuit. An application specific integrated circuit (ASIC) version of the design has been designed, built and tested. With the exception of the input field effect transistor (FET), the circuit is constructed using bipolar components. In this paper the design philosophy and measured performance characteristics of the circuit are described.

We report the stability of TlBa2CaCu2O7 and Tl2Ba2CaCu2O8 on LaAlO3(100) epitaxial thin films, under a variety of conditions. All films are stable in acetone and methanol and with repeated thermal cycling to cryogenic temperatures. Moisture, especially vapor, degrades film quality rapidly. These materials are stable to high temperatures in either N2 or O2 ambients. While total degradation, resulting from Tl depletion, occurs at the same temperatures for both phases, 600 °C in N2 and 700 °C in O2, the onset of degradation occurs at somewhat lower temperatures for TlBa2CaCu2O7 than for Tl2Ba2CaCu2O8.