The combination of an energy dispersive x-ray spectrometer (EDS) with the ultrahigh vacuum environment of many modern electron microscopes requires the spectrometer designer to take extra precautions and presents the microscopist with the additional option of utilizing windowless spectrometers for light element detection while not worrying about contamination of the detector. UHV is generally defined as a pressure of better than 10{sup {minus}7} Pa and is necessary to prevent specimen modification by the components of the vacuum. UHV may also be defined as an environment in which the time to form a monolayer on the specimen is equal to or longer than the usual time for a laboratory measurement. This report examines performance of energy dispersion x-ray spectrometers in UHV.
The primary difficulty of computing the vibration of spinning inflated membranes arises from the low natural frequencies of such systems. When such systems are rotated near their own natural frequencies the dynamics equations must account for higher order kinematics than is necessary for more rigid structures. These complications results from the membrane loads that develop within the bodies in reaction to the accelerations of the overall body. When second order kinematics act against these membrane loads, the resulting energies become of the same order as the potential and kinetic energies of the vibrations that would be calculated by first order kinematics. These complications apply to the problem addressed here. Here we consider a spin-stabilized, inflated membrane, spinning around its minor axis. This structure is very flexible and somewhat viscoelastic, so vibrations excited by the overall motion of the structure will dissipate energy of the system, thus reducing the kinetic energy. A reduction in kinetic energy consistent with a conservation of angular momentum results in coning and, eventually, tumbling. Here we must address the excitation of vibration by the rigid-body motion and then we must address the retarding effect of the energy dissipation on the rigid-body motion.
The properties of vertical-cavity surface-emitting lasers (VCSELS) and VCSEL-based optical switches using MOCVD-grown epitaxial material are discussed and sum their performance.
Parallel computing offers new capabilities for using molecular dynamics (MD) to simulate larger numbers of atoms and longer time scales. In this paper we discuss two methods we have used to implement the embedded atom method (EAM) formalism for molecular dynamics on multiple-instruction/multiple-data (MIMD) parallel computers. The first method (atom-decomposition) is simple and suitable for small numbers of atoms. The second method (force-decomposition) is new and is particularly appropriate for the EAM because all the computations are between pairs of atoms. Both methods have the advantage of not requiring any geometric information about the physical domain being simulated. We present timing results for the two parallel methods on a benchmark EAM problem and briefly indicate how the methods can be used in other kinds of materials MD simulations.
Solutions from a Parabolized Navier-Stokes (PNS) code with an algebraic turbulence model are compared with wall functions. The wall functions represent the turbulent flow profiles in the viscous sublayer, thus removing many grid points from the solution procedure. The wall functions are intended to replace the computed profiles between the body surface and a match point in the logarithmic region. A supersonic adiabatic flow case was examined first. This adiabatic case indicates close agreement between computed velocity profiles near the wall and the wall function for a limited range of suitable match points in the logarithmic region. In an attempt to improve marching stability, a laminar to turbulent transition routine was implemented at the start of the PNS code. Implementing the wall function with the transitional routine in the PNS code is expected to reduce computational time while maintaining good accuracy in computed skin friction.
CRESLAF is a Fortran program that predicts the velocity, temperature, and species profiles in two-dimensional (planar or axisymmetric) channels. The program accounts for finite-rate gas-phase and surface chemical kinetics and molecular transport. The model employs the boundary-layer approximations for the fluid-flow equations, coupled to gas-phase and surface species continuity equations. The program runs in conjunction with the Chemkin preprocessors for the gas-phase and surface chemical reaction mechanisms and the transport properties. This report presents the equations defining the model, the method of solution, the input parameters to the program, and a sample problem illustrating its use. Applications of CRESLAF include chemical vapor deposition (CVD) reactors, heterogeneous catalysis on reactor walls, and corrosion processes.
Biometric identity research and development activities are being conducted in universities, government, and private industry. This paper discusses some of the factors that limit the performance of biometric identity devices, looks at some new developments, and speculates on future developments.
Performance projections based on the analytical model of a scannerless laser radar system are compared to laboratory simulations and to field data measurements. Data and characteristics of the system, including camera response, image spatial resolution, and contributions to the signal-to-noise ratio are presented. A discussion of range resolution for this system will also be presented, and finally, the performance characteristics of the prototype benchtop system will be summarized.
In an effort to remain regulatory compliant, it is becoming increasingly important to locate resources that can provide up to date environmental regulations and regulatory interpretations. there are many resources available to provide information and training in these areas.
Remote systems are needed to accomplish many tasks such as the clean up of waste sites in which the exposure of personnel to radiation, chemical, explosive, and other hazardous constituents is unacceptable. In addition, hazardous operations which in the past have been completed by technicians are under increased scrutiny due to high costs and low productivity associated with providing protective clothing and environments. Traditional remote operations have, unfortunately, proven to also have very low productivity when compare with unencumbered human operators. However, recent advances in the integration of sensors and computing into the control of conventional remotely operated industrial equipment has shown great promise for providing systems capable of solving difficult problems.
This work concerns preparing tailored porous carbon monoliths by pyrolyzing porous polymer precursors. Prior work in this laboratory (1) demonstrated that a low density (0.05 g/cm{sup 3}), high void fraction (97 vol%) carbon monolith could be prepared by pyrolyzing a porous poly(acrylonitrile) (PAN) precursor. A higher density, more robust carbon material is preferred for certain applications, such as electrodes for electrochemical devices. The present work demonstrates that porous carbon monoliths having mass density of 0.7 g/cm{sup 3} can be prepared from a porous PAN precursor if the pyrolysis is controlled carefully. The macropore structure of the carbon is adjusted by changing the pore structure of the PAN precursor, and the finer scale structure (such as the crystallite size L{sub c}) is adjusted by varying the pyrolysis or heat treatment temperature.
The Arrhenius approach assumes a linear relation between log time to material property change and inverse absolute temperature. For elastomers, ultimate tensile elongation results are often used to confirm Arrhenius behavior, even though the ultimate tensile strength is non-Arrhenius. This paper critically examines the Arrhenius approach. Elongation vs air-oven aging temperature for a nitrile rubber, gives an E{sub a} of 22 kcal/mol; however this does not hold for the tensile strength, indicating degradation. Modulus profiling shows heterogeneity at the earliest times at 125 C, caused by diffusion-limited oxidation (DLO). Tensile strength depends on the force at break integrated over the cross section, and nitrile rubbers aged at different temperatures experience different degrees of degradation in the interior. Modulus at the surface, however, is not affected by DLO anomalies. Severe mechanical degradation will occur when the edge modulus increases by an order of magnitude. 7 figs, 3 refs.
Critical information required for Environment, Safety, and Health (ES&H) protection can be acquired with a comprehensive cradle-to-grave tracking and information system. The cradle-to-grave concept makes two initial assumptions. First, it is more effective to gather information at the origination of a process or entry point of a material and maintain that information during the rest of its life-cycle than to collect data on an ad hoc basis. Second, the information needs of the various ES&H programs have many commonalties. A system which adheres to a methodology based upon these assumptions requires a significant technical and administrative commitment; however, this investment, will in the long-term, reduce the effort and duplication of ES&H programs, improve the efficiency of ES&H and line personnel, and increase the scope and accuracy of ES&H data. The cradle-to-grave system being developed at Sandia National Laboratories (SNL) is designed to provide useful information on materials, personnel, facilities, hazards, wastes, and processes to fulfill the mission of pollution prevention, risk management, industrial hygiene, emergency preparedness, air/water quality, and hazardous and radioactive waste management groups. SNL is currently linking system modules, which are at various stages of development and production, to realize a cradle-to-grave tracking and information system that is functional for a large research and development laboratory.
A very brief description of two ``classes`` developed for use in design optimization and sensitivity analyses are given. These classes are used in simulations of systems in early design phases as well as system response assessments. The instanciated classes were coupled to system models to demonstrate the practically and efficiency of using these objects in complex robust design processes.
The Becker-Kistiakowsky-Wilson equation of state (BKW-EOS) has been calibrated over a wide initial density range near C-J states using measured detonation properties from 62 explosives at III total initial densities. Values for the empirical BKW constants {alpha}, {beta}, {kappa}, and {theta} were 0.5, 0.298, 10.5, and 6620, respectively. Covolumes were assumed to be invariant. Model evaluation includes comparison to measurements from 91 explosives composed of combinations of Al, B, Ba, C, Ca, Cl, F, H, N, 0, P, Pb, and Si at 147 total initial densities. Adequate agreement between predictions and measurements were obtained with a few exceptions for nonideal explosives. However, detonation properties for the nonideal explosives can be predicted adequately by assuming partial equilibrium. The partial equilibrium assumption was applied to aluminized composites of RDX, HMX, TNETB, and TNT to predict detonation velocity and temperature.
The multifrequency, multisource holographic method used in the analysis of seismic data is to extended electromagnetic (EM) data within the audio frequency range. The method is applied to the secondary magnetic fields produced by a borehole, vertical electric source (VES). The holographic method is a numerical reconstruction procedure based on the double focusing principle for both the source array and the receiver array. The approach used here is to Fourier transform the constructed image from frequency space to time space and set time equal to zero. The image is formed when the in-phase part (real part) is a maximum or the out-of-phase (imaginary part) is a minimum; i.e., the EM wave is phase coherent at its origination. In the application here the secondary magnetic fields are treated as scattered fields. In the numerical reconstruction, the seismic analog of the wave vector is used; i.e., the imaginary part of the actual wave vector is ignored. The multifrequency, multisource holographic method is applied to calculated model data and to actual field data acquired to map a diesel fuel oil spill.
An essential requirement for both Vertical Seismic Profiling (VSP) and Cross-Hole Seismic Profiling (CHSP) is the rapid acquisition of high resolution borehole seismic data. Additionally, full wave-field recording using three-component receivers enables the use of both transmitted and reflected elastic wave events in the resulting seismic images of the subsurface. To this end, an advanced three- component multi-station borehole seismic receiver system has been designed and developed by Sandia National Laboratory (SNL) and OYO Geospace. The system requires data from multiple three-component wall-locking accelerometer packages and telemeters digital data to the surface in real-time. Due to the multiplicity of measurement stations and the real-time data link, acquisition time for the borehole seismic survey is significantly reduced. The system was tested at the Chevron La Habra Test Site using Chevron`s clamped axial borehole vibrator as the seismic source. Several source and receiver fans were acquired using a four-station version of the advanced system. For comparison purposes, an equivalent data set was acquired using a standard analog wall-locking geophone receiver. The test data indicate several enhancements provided by the multi-station receiver relative to the standard, drastically improved signal-to-noise ratio, increased signal bandwidth, the detection of multiple reflectors, and a true 4:1 reduction in survey time.
The introduction of rapid prototyping machines into the market place promises to revolutionize the process of producing prototype parts with production-like quality. In the age of concurrent engineering and agile manufacturing, it is necessary to exploit applicable new technologies as soon as they become available. The driving force behind integrating these evolutionary processes into the design and manufacture of prototype parts is the need to reduce lead times and fabrication costs improve efficiency, and increase flexibility without sacrificing quality. Sandia Utilizes stereolithography and selective laser sintering capabilities to support internal design and manufacturing efforts. Stereolithography (SLA) is used in the design iteration process to produce proof-of-concept models, hands-on models for design reviews, fit check models, visual aids for manufacturing, and functional parts in assemblies. Selective laser sintering (SLS) is used to produce wax patterns for the lost wax process of investment casting in support of an internal Sandia National Laboratories program called FASTCAST which integrates experimental and computational technologies into the investment casting process. This presentation will provide a brief overview of the SLA and SLS processes and address our experiences with these technologies from the standpoints of application, accuracy, surface finish, and feature definition. Also presented will be several examples of prototype parts manufactured by the stereolithography and selective laser sintering rapid prototyping machines.
Three-dimensional finite element analyses of gas-filled storage caverns in domal salt were performed to investigate the effects of cavern spacing on surface subsidence, storage loss, and cavern stability. The finite element model used for this study models a seven cavern storage field with one center cavern and six hexagonally spaced surrounding caverns. Cavern spacing is described in terms of the P/D ratio which is the pillar thickness (the width between two caverns) divided by the cavern diameter. With the stratigraphy and cavern size held constant, simulations were performed for P/D ratios of 6.0, 3.0, 2.0, 1.0, and 0.5. Ten year simulations were performed modeling a constant 400 psi gas pressure applied to the cavern lining. The calculations were performed using JAC3D, a three dimensional finite element analysis code for nonlinear quasistatic solids. For the range of P/D ratios studied, cavern deformation and storage volume were relatively insensitive to P/D ratio, while subsidence volume increased with increasing P/D ratio. A stability criterion which describes stability in terms of a limiting creep strain was used to investigate cavern stability. The stability criterion indicated that through-pillar instability was possible for the cases of P/D = 0.5 and 1.0.
One of the proposed applications of the satellite-based Global Verification and Location System (GVLS) is the Authenticated Tracking and Monitoring System (ATMS). When fully developed, ATMS will provide the capability to monitor, in a secure and authenticated fashion, the status and global tracking of selected items while in transit - in particular, proliferation sensitive items. The resulting tracking, timing, and status information can then be processed and utilized to assure compliance with, for example, various treaties. Selected items to be monitored could include, but are not limited to, Treaty Limited Items (TLIs), such as nuclear weapon components, Re-entry Vehicles (RVs), weapon delivery and launch systems, chemical and biological agents, Special Nuclear Material (SNM), and related nuclear weapons manufacturing equipment. The ATMS has potential applications in the areas of arms control, disarmament and Non-proliferation treaty verification, military asset control, as well as International Atomic Energy Agency (IAEA) and Euratom safeguards monitoring activities. The concept presented here is mainly focused on a monitoring technology for proliferation sensitive items. It should, however, be noted that the systems potential applications are numerous and broad in scope, and could easily be applied to other types of monitoring activities as well.
This bulletin presents state of the art testing technology utilized at Sandia National Laboratory. A hand-held NiCad battery tester automatically checks batteries of individual cells. Modal analysis shows the way to better process control for integrated circuit lithography. An ultrasonic system pings reentry vehicles to measure in-flight ablation. A smaller VISAR shines in detonator tests. Higher image quality is achieved at neutron radiography facility with the use of a neutron collimator.
Over the past several years the Information Technology Department at Sandia Laboratories has developed information systems based on a solid foundation of information modeling and data administration. The output of the information modeling efforts is a fifth normal form relational table structure and associated data constraints. Developers would then implement the system by creating end-user application software. Traditionally, the development process combined the code necessary for maintaining data constraints with the code to provide the user interface (i.e. forms, windows, etc.). This approach has an adverse effect on the maintainability of the software as the system (i.e. the information model) changes over time. This paper will discuss the application of a direct connection between the information model and the implementation of a database with associated code to maintain required data constraints. The automated generation of this code allows the developers to concentrate on the user interface code development. The technique involves generating database procedure code automatically from the information modeling process. The database procedure code will enforce the data constraints defined in the information model. This has resulted in a fully functional database with complete rules enforcement within days of a completed information model. This work used the Knowledge Management Extensions of the Ingres database software. Changes to the architecture of both Application By Forms (ABF) and Ingres Windows4GL client applications required by this process will also be discussed.
Leonard, J.A.; Floyd, H.L.; Goetsch, B.; Doran, L.
This bulletin describes innovative manufacturing technologies being developed at Sandia National Laboratories. Topics in this issue include: new techniques to overcome barriers to large scale fabrication of vertical cavity surface-emitting lasers (VCSELs), variability reduction in plasma etching of microcircuits, using neural networks to evaluate effectiveness of flux-cleaning methods and alternative fluxes for printed circuit boards, ion implantation to increase the strength and wear resistance of aluminium, and a collaborative project to improve processing of thin-section welded assemblies. (GH)
A technique to integrate a dense, locally non-uniform mesh into finite-difference time-domain (FDTD) codes is presented. The method is designed for the full-wave analysis of multi-material layers that are physically thin, but perhaps electrically thick. Such layers are often used for the purpose of suppressing electromagnetic reflections from conducting surfaces. Throughout the non-uniform local mesh, average values for the conductivity and permittivity are used, where as variations in permeability are accommodated by splitting H-field line integrals and enforcing continuity of the normal B field. A unique interpolation scheme provides accuracy and late-time stability for mesh discontinuities as large as 1000 to 1. Application is made to resistive sheets, the absorbing Salisbury screen, crosstalk on printed circuit boards, and apertures that are narrow both in width and depth with regard to a uniform cell. Where appropriate, comparisons are made with the MoM code CARLOS and transmission-line theory. The hybrid mesh formulation has been highly optimized for both vector and parallel-processing on Cray YMP architectures.