The authors present sufficient conditions for the design of strictly positive real (SPR), fixed-order dynamic compensators. The primary motivation for designing SPR compensators is for application to positive real (PR) plants. When an SPR compensator is connected to a PR plant in a negative feedback configuration, the closed loop is guaranteed stable for arbitrary plant variations as long as the plant remains PR. Equations that are a modified form of the optimal projection equations, with the separation principle not holding in either the full- or reduced-order case, are given. A solution to the design equations in shown to exist when the plant is PR (or just stable). Finally, the closed-loop system consisting of a PR plant and an SPR compensator is shown to be S-structured Lyapunov stable.
A Nuisance Alarm Data System (NADS) was developed to gather long-term background alarm data on exterior intrusion detectors as part of their evaluation. Since nuisance alarms play an important part in the selection of intrusion detectors for use at Department of Energy (DOE) facilities, an economical and reliable way to monitor and record these alarms was needed. NADS consists of an IBM Personal Computer and printer along with other commercial units to communicate with the detectors, to gather weather data and to record video for assessment. Each alarm, its assessment and the weather conditions occurring at alarm time are placed into a database that is used in the evaluation of the detector. The operating software is written in Turbo Pascal for easy maintenance and modification. A portable system, based on the NADS design, has been built and shipped to other DOE locations to do on-site alarm monitoring. This has been valuable for the comparison of different detectors in the on-site environment and for testing new detectors when the appropriate conditions do not exist or cannot be simulated at the Exterior Intrusion Detection Testbed.
A 2D-Laser Radar Imaging System consisting of a prototype 2D-Laser Radar Sensor and an Image Processing System is currently being developed as an intrusion detection system capable of immediate detection and quick assessment for perimeter security and surveillance. The objective of this system is to produce a thin laser wall as an invisible intrusion barrier. Since only a small space is needed to create a narrow laser radar wall, this system will work well where there is only limited or narrow zones available to create the secure perimeter. Images are created of objects which penetrate the laser radar wall for assessment and to determine the appropriate alarm response. Such a system can be used to protect against airborne threats from rooftop areas or to guard against ground threats across perimeter zones of critical facilities. This paper will discuss the operational concepts, the technology, and an initial performance of this prototype system. 2 refs., 6 figs.
Technical Digest, 1990 Solid-State Sensor and Actuator Workshop
Frye, G.C.; Brinker, C.J.; Ashley, C.S.; Martinez, S.L.; Bein, T.
The use of porous oxide coatings, formed using sol-gel chemistry routes, as the discriminating elements of acoustic wave (AW) chemical sensors, is investigated. These coatings provide several unique advantages: durability, high adsorption capacity based on large surface areas, and chemical selectivity based on both molecular size and chemical interactions. The porosity of these coatings is determined by performing nitrogen adsorption isotherms using the AW device response to monitor the uptake of nitrogen at 77 K. The chemical sensitivity and selectivity obtained with this class of coatings is demonstrated using several examples: hydrous titanate ion exchange coatings, zeolite/silicate microcomposite coatings, and surface modified silicate films.
In light sources such as tungsten filament bulbs, fluorescent tubes and gas tube type radioluminescent (RL) lamps, visible light is emitted from a thin surface layer of excited material. In contrast, neon bulbs, xenon flash tubes and lasers emit light generated throughout their volumes. The first group can be characterized as surface emitters and the latter as volumetric emitters. Theoretically, an ideal volumetric light source has definite advantages over a surface source. In reality, practical volumetric sources will have limitations as well. These advantages and limitations will be discussed with particular emphasis on comparisons between current gas tube type RL lamps and the more advanced volumetric RL lamps.
A new generation of digital multimeters was used to compare the ratios of the resistances of wire-wound reference resistors and quantized Hall resistances. The accuracies are better than 0.1 ppM for ratios as large as 4:1 if the multimeters are calibrated with a Josephson array. 9 refs.
Constitutive modeling and bifurcation analyses are combined with axisymmetric (triaxial), triaxial/torsion, and plane-strain experiments to interpret and anticipate the development of shear localization in rocks. This paper discusses preliminary results. 22 refs., 3 figs.
The US Department of Energy (DOE) has supported the development of the sodium-sulfur technology since 1973. The programs have focused on progressing core aspects of the technology and completing initial battery engineering for both mobile and stationary applications. An overview of the Office of Energy Management (OEM) activities is contained in this paper. Two major development programs have been active: the first with Ford Aerospace and Communications Corporation (1975 to 1985), and the second with Chloride Silent Power Limited (1985 to 1990). With the completion this year of the qualification of a cell suitable for initial Solar Energy Systems (SES) applications, the emphasis of future DOE/OEM sodium/sulfur programs will shift to SES-battery engineering and development. The initial effort will resolve a number of issues related to the feasibility of utilizing the sodium/sulfur technology in these large-scale applications. This multi-year activity will represent the initial phase of an integrated long-term DOE-supported program to produce a commercially viable battery system.
The integrity of many mechanical assemblies and electrical components depends on small threaded fasteners. The design standards for small (less than {1/4} inch in diameter) screws made of stainless steel are not as well developed as those for larger sizes of high strength steels. The typical design approach is based on the application of static design principals. Steady state accelerations are applied to the component or assembly and sufficient screws are installed in mounting hardware for attachment to the next assembly. These design principals have been used successfully for years in a wide variety of applications. As the parts requiring small screws have continued to decrease in size, some design requirements include greater thread depths and adherence to strict interpretation of the governing thread standards. These design requirements have their origins in the lack of adequate definitions and standards for designs using small threaded fasteners. These design practices have led to significant problems in manufacturing parts with small threaded fasteners by requiring thread depths to four and more diameters of engagement while maintaining thread heights (radial engagement) of 75 percent throughout the thread interfaces. A test program was developed to address questions regarding design and manufacturing issues involving small threaded fasteners which included tensile strength, length of engagement needed to achieve the full strengths of the screws, and verification of the static design principals in dynamic conditions. This paper summarizes the initial results obtained to date from this test program and describes the work-in-progress on the dynamic tests with their related static tests. 2 refs., 4 figs., 4 tabs.
An isotropic continuum damage theory which accounts for the degradation of material strength under quasi-static loading conditions has been developed in the present investigation. The damage mechanism in this theory has been selected to be the interaction and growth of subscale cracks. The development of the theory follows closely the strain-rate dependent dynamic model advanced by the first author and his coworkers. Briefly, the cracks are activated by the maximum principal tensile strain and the density of activated cracks is described by a Weibull statistical distribution. The moduli of a cracked solid derived by Budiansky and O'Connell are then used to represent the global material degradation due to subscale cracking. Two additional material constants have been introduced in this model. These constants are determined from uniaxial tensile test data. The model has been implemented into a finite element code. Sample calculations involving the uniaxial and biaxial responses of plain concrete panels are presented to demonstrate the utility of the model. 7 refs., 2 figs.
The first in a series of multi-factor experiments designed to optimize the chemical cleaning procedure for four types of silicon material used in solar cell fabrication has been completed. The goal of this first experiment (a twenty-two factor main-effects experiment) was to determine the factors associated with chemical cleaning procedures that are most important in obtaining high excess charge-carrier recombination lifetime following a high-temperature furnace oxidation. It was determined that the factors having the strongest influence on charge-carrier lifetime were different for the four different silicon materials considered. In general, the lower the lifetime of the material, the less sensitive the material was to different chemical cleaning steps. The stability of the lifetime was also evaluated with several factors exhibiting a significant effect for high-quality silicon. Chemical cleaning procedures were identified that resulted in stable post-oxidation lifetimes greater than 2 ms for high-resistivity float-zone silicon. 3 refs., 8 figs.
The closure measurements from a large scale, heated, in situ experimental room in salt are compared to numerical calculations using the most recent predictive technology, with very good agreement, limited potentially only by the unmodeled roof fracture and separation.
Insulations are used in metallic glass ribbon cores in pulse power applications to prevent interlaminar eddy currents due to voltages induced between adjacent laminations. These interlaminar eddy currents can greatly increase the losses in cores, and, thereby, decrease the pulse permeability at high magnetization rates. This paper reports results of experiments with various insulation materials and both low and high induced anisotropy energy iron-base metallic glass ribbons. Co-wound insulation films as well as conformal insulations were investigated. Magnetic properties and voltage hold-off strengths are reported. 11 refs., 11 figs., 5 tabs.
When quartz controlled oscillators are required for use in applications demanding precision many factors will ultimately place limitations on the ability of the oscillator to remain at the desired frequency. These factors include temperature, resonator Q, pullability, radiation, output load variability, and the electronic components. This paper addresses the subject of frequency instability of oscillator circuits due to power supply voltage variations. In particular, the primary sources of this instability are described for a Pierce oscillator employing a bipolar transistor and design techniques are presented which minimize these frequency pulling effects. 4 refs., 17 figs.
The three-dimensional structural analysis of reentry vehicles presents a considerable challenge to the analyst. This is due to the mechanics of the problem as well as the incorporation of results from several disciplines into the environmental description of the problem. Separate results from aero-analyses, frequently computed in one-dimensional format must be combined into a three-dimensional format suitable for a structural finite element analysis. Features required for the analysis include the ablated thickness of the heatshield structure, as well as pressure on the vehicle and the temperature distribution through the heatshield. By combining these environments, a complete description of all factors which affect the structural performance of reentry vehicles are included into one analysis. This paper presents a method of analyzing the structural response of reentry vehicles using the complete three-dimensional environmental load description.
Reflection Mass Spectrometry (REMS) consists of a cryo-shrouded mass spectrometer which measures mass-analyzed, line-of-sight chemical fluxes from a growing wafer. It is especially useful during III/V molecular beam epitaxy (MBE) for which there are always substantial group V fluxes and often some group III fluxes leaving the wafer during growth. These fluxes depend sensitively on the instantaneous chemical reactivity of the surface. That chemical reactivity in turn depends on instantaneous alloy composition (III/III ratio), surface stoichiometry (As coverage) and temperature. In this brief summary of our work, we describe two examples of the engineering'' usefulness of REMS, involving MBE of InAlAs and InGaAs and one example of measurements of basic scientific interest. 3 figs.
A program is under way to develop liquid metal heat pipes that can transfer energy from the focal point of a parabolic solar concentrator to the heater tubes of one or more Stirling engines. To design high performance wicks for heat pipe solar receivers, it is necessary to have an accurate assessment of the wick's properties. Procedures for measuring the flow properties of wicks before and after fabrication processes take place are presented. The testing procedures provide a useful method of determining the validity of a wick design before full-scale testing is attempted.
Significant progress is continuing in the development of photovoltaic (PV) concentrator technology. New record cell and module efficiencies have been achieved, and improvements in cells, cell assemblies, and modules are increasing reliability and decreasing cost. The number of firms actively pursuing PV concentrator module technology has increased substantially in the last three years. Two new concentrator systems were installed last year, and we are likely to see more in the near future. This paper describes the most significant developments of the last two years, including descriptions of PV concentrator module development and reliability activities, advances in concentrator cell technology, the new PV concentrator array installations, a new Concentrator Initiative Program, and results of the latest costing study. 26 refs., 9 figs., 1 tab.
Chacahoula salt dome, eight miles southwest of Thibodaux, LA, could be solution mined to create caverns for storing as much as 500 million barrels (MMB) of crude oil, should the Strategic Petroleum Reserve (SPR) require additional storage volume. The salt mass geometry is confirmed by more than 50 oil wells, and also from previous exploratory drilling for sulphur. Top of salt occurs at {minus}1100 ft, and some 1300 acres exist within the {minus}2000 ft salt contour. Frasch mining of 1.35 million long tons of sulphur caused the surface to subside about one foot on the northeastern part of the dome. Creep-induced subsidence averaging {approximately}2.7 ft over 30 yrs is estimated for a 200 MMB cavern array, which would require perimeter diking to control localized perennial flooding. Earthquakes approaching intensity MM 6 have occurred nearby and are expected to recur on the order of {approximately}100 yrs but would not affect cavern stability. Additional study of brine disposal methods and hurricane surge probabilities are needed to establish design parameters and cost estimates for storage. 11 refs., 8 figs., 2 tabs.
A Nuisance Alarm Data System (NADS) was developed to gather long- term background alarm data on exterior intrusion detectors as part of their evaluation. Since nuisance alarms play an important part in the selection of intrusion detectors for use at Department of Energy (DOE) facilities, an economical and reliable way to monitor and record there alarms was needed. NADS consists of an IBM Personal Computer and printer along with other commercial units to communicate with detectors, to gather weather data and to record video for assessment. Each alarm, its assessment and the weather conditions occurring at alarm time are placed into a database that is used in the evaluation of the detector. The operating software is written in Turbo Pascal for easy maintenance and modification. A portable system, based on the NADS design, has been built and shipped to other DOE locations to do on-site alarm monitoring. This has been valuable for the comparison of different detectors in the on-site environment and for testing new detectors when the appropriate conditions do not exist or cannot be simulated at the Exterior Intrusion Detection Testbed.
A molten salt cavity receiver was solar tested at Sandia National Laboratories during a year-long test program. Upon completion of testing, an analysis was performed to determine the effect of thermal cycling on the receiver. The results indicate substantial fatigue damage accumulation for the receiver when the relatively short test time is considered. This paper describes the methodology used to analyze the cycling, the results, and how they affect future receiver design. The test receiver was configured as a C-shaped cavity with eight multipass heat absorption panels. The tubes were Alloy 800. The heat exchange medium was a molten nitrate salt mixture (60% sodium nitrate, 40% potassium nitrate by weight). The operating temperature range was from 288°C to 566°C.
Under compressive stresses, brittle polycrystalline materials fail as the result of the growth, interaction and coalesence of microcracks. To predict the deformation of damaging material, constitutive laws developed for such materials must incorporate the effects of crack size, density, orientation, and interaction.A method of incorporating the accumulation and growth of microcracks into a continuum model is to use a measure of microcrack growth and interaction defined as damage. Although a number of damage theories have been proposed, there is no generally accepted experimental technique for detecting and measuring damage. Acoustic emissions (AE) have been correlated with microcrack nucleation and growth. We propose that AE locations and density are useful measures of damage that can be correlated with calculated damage. Our approach is to use acoustic emissions (AE) and computer modeling to study the development of damage in geomaterials.
Consideration is given to the problem of stabilizing a plant using a suboptimal stable compensator of fixed order. The resulting equations are a modified form of the optimal projection equations, with the separation principle not holding in either the full- or reduced-order case. An overbounding technique on the state covariance guarantees that the compensator is stable if nonnegative definite solutions exist to the design equations.
The Function Point (FP) concept was introduced to define'' a measure for applications development and maintenance functions avoiding the problems inherent in productivity measures in the late 1970s. At that time, Albrecht outlines three essentials elements for software size measurement: the measure must be technology independent; the technique must measure all the application functions delivered to the end customer; and the technique must measure only the application functions as delivered. Using these three attributes of a measurement, further concentrated analysis could be performed for languages, technologies, methodologies, and tools. The characterization of systems and the quality of the product are motives for subscribing to FPs. Since the inception of FPs, attempts have been made to improve the process of quantifying FPs. Some of these attempts have strayed from the intended use of FPs and have diverted valuable energy away from consistent application. The purpose of this article is to describe the process and the quantification of complexity factors for each of the five Unadjusted FPs. 4 refs.
Light ion fusion research has developed ion diodes that have unique properties when compared to other ion diodes. These diodes involve relativistic electrons, ion beam stagnation pressures that compress the magnetic field to the order of 10 Tesla, and large space-charge and particle current effects throughout the accelerating region. These diodes have required new theories and models to account for effects that previously were unimportant. One of the most important effects of the magnetic field compression and large space-charge has been impedance collapse. The impedance collapse can lead to poor energy transfer efficiency, beam debunching, and rapid change of the beam focus. This paper discusses our current understanding of these effects, some of the methods we are using to ameliorate them, and the future directions our theory and modeling will take. 40 refs., 6 figs.
A new scanning electron microscopy imaging technique has been developed to examine the logic state of conductors on passivated CMOS integrated circuits. This technique employs a modified Resistive Contrast Imaging system to acquire image data on powered devices. The image is generated by monitoring subtle shifts in the power supply current of an integrated circuit as an electron beam is scanned over the device surface. The images produced with this new technique resemble voltage contrast data from devices with the passivation removed and the surface topography subtracted. Non-destructive applications of this imaging method to functional and failed integrated circuits are described. Possible irradiation effects and methods to minimize them are also discussed. 2 refs., 1 fig.
Transit time, the time from bridgewire burst until breakout of detonation from the output pellet of an exploding bridgewire detonator, was measured as a function of burst current. From this data, in conjunction with known equations for run distance versus pressure, unreacted explosive Hugoniots, and detonation properties of the initial pressing pellet, the run distance in the initial pressing explosive pellet and shock pressure from the exploding bridgewire were determined, both as a function of burst current.
Fifteen years of solar thermal technology development have produced a considerable amount of knowledge relating to the production of electricity from central receiver power plants. This body of knowledge is under examination by researchers from the United States and the Federal Republic of Germany for the purpose of defining the next generation central receiver electricity producers. This second generation power plant is expected to represent a significant step towards commercialization of these systems. During the course of the study, specific activities needed to realize this next-step technology are being defined. The study is an international team effort. Under the International Energy Agency Small Solar Power Systems project, researchers from DLR, Interatom, Sandia National Laboratories, and Bechtel have designed a study in which technologies relating to existing systems are quantified, logical next-step systems are characterized, and future potential advances are identified. The receiver concepts under investigation are: salt-in- tube, volumetric, and direct absorption. Two plant performance levels are examined, 30 and 100 MW{sub e}. Each concept is applied with common capacity factors, solar multiples, and types and sizes of heliostats at each performance level. Availability and uncertainty analyses are also performed. Annual energy production figures are calculated using the SOLERGY computer code. Capital and Operation and Maintenance cost methodologies are mutually agreed upon in order that levelized energy cost calculations will be consistent for each power plant. During the course of this effort, further potential advances in central receiver technology have continued to become apparent. These possible areas for improvement will be described. An additional comparison is being made between central receivers and trough-based systems. 8 refs., 2 figs.
A hierarchical control architecture for telerobotic vehicles intended to yield a modular, flexible, and easily expanded control system is presented. This architecture is proposed for applications where simple teleoperation is required but where additional capabilities might be quickly added without major changes to the control system. Similarities to the NASREM architecture are noted. Results are given from hardware implementation of the control system on a telerobotic vehicle, Raybot, at Sandia National Laboratories.
A systematic study is described which addresses the technical issues associated with launching flier-plates intact to hypervelocitites. First, very high pressures are needed to launch the flier plates to hypervelocitites, and second this high pressure loading must be uniform and nearly shockless. To achieve both these criteria, a graded-density material referred to as a pillow'' is used to impact a flier plate. When this graded-density material is used to impact a flier plate at high velocities on a two-stage light-gas gun, nearly shockless megabar pressure pulses are introduced into the flier plate. Since the loading on the flier plate is shockless, melting of the flier plate is prevented. This technique has been used to launch a 2-mm thick titanium alloy (Ti-6Al-4V) plate to a velocity of 8.1 km/s, and a 1-mm thick aluminum alloy (6061-T6) plate to a velocity of 10.4 km/s. A method is described by which the flier plate velocities could be further augmented to velocities approaching 14 km/s. 18 refs., 16 figs.
A new technique is reported for the rapid determination of interstitial oxygen (O{sub i}) in heavily doped n{sup +} and p{sup +} silicon. This technique includes application of a selective electrochemical thinning (SET) process and FTIR transmittance measurement on a limited area of a silicon wafer. The O{sub i} is calculated using ASTM F1188--88 with the IOC 88 calibration factor. An advantage of SET over mechanical thinning is that the original wafer thickness and diameter are maintained for additional processing. 1 tab.
The Shippable Storage Cask Demonstration Project is intended to demonstrate casks which can be used for both shipping and storing spent nuclear fuel assemblies. The demonstration included the requirement that the casks be certified for shipping by the US Nuclear Regulatory Commission (NRC). After a lengthy review process which resulted in the resolution of several important technical issues, designs for two similar casks have been certified. This paper describes the certification phase of the demonstration. Based on experience gained during certification phase of the demonstration. Based on experience gained during certification, observations and recommendations have been developed which can benefit others seeking NRC approval of transportation cask designs.
Reviews of normal breakdown and current induced avalanche breakdown mechanisms in silicon power transistors are presented. We show the applicability of the current induced avalanche model to heavy ion induced burnouts. Finally, we present solutions to current induced avalanche in silicon power semiconductors. 7 refs., 5 figs.
The electronic properties of heavily and orderly Si-doped nipi structures in GaAs are studied theoretically using the ab-initio self-consistent pseudopotential method within the local density approximation. Two nipi configurations are considered. Besides investigating the nature of the impurity-related band edge states, the xy-planar-averaged local ionic and self-consistent potentials are also analyzed. The screening effect of the host crystal on the doping induced potential is found to be small. The effects of the doping induced electric field and the strain due to dopings are also examined. 13 refs., 9 figs., 2 tabs.
The near field surrounding buried waste in the proposed high level nuclear waste repository in Yucca Mountain, Nye County, Nevada, is a region where strongly heat driven processes can exist. These strongly heat driven processes further complicate an already very difficult problem, i.e,. predicting groundwater flow and chemical transport through unsaturated fractured, heterogeneous porous media. The coupling between fluid flow and heat emanation is central to understanding these strongly heat driven processes. Although it is important that all of couplings be investigated, the intent of this paper is to discuss the mathematical models and associated computer codes that can be used in investigating the coupled heat emanation and fluid flow in unsaturated porous media. The information in this paper should be useful to those studying these phenomena, validating these models, or investigating the coupling of fluid flow and heat emanation with the other phenomena. The codes implementing these models are commonly referred to as nonisothermal two-phase flow codes. 5 refs., 4 tabs.
The United States Department of Energy (DOE) is developing the Waste Isolation Pilot Plant (WIPP), located in southeastern New Mexico, for disposal of transuranic wastes generated by defense programs. The DOE must first demonstrate compliance with the Environmental Protection Agency's (EPA) Environmental Standards for the Management and Disposal of Spent Nuclear Fuel, High-Level and Transuranic Radioactive Wastes hereafter called the Standard. The Containment Requirements in Subpart B of the Standard set limits on the probability that cumulative radionuclide releases to the accessible environment during the 10,000 years following decommissioning of the repository will exceed certain limits. To comply with these requirements, performance assessments must construct a modeling system that can adequately simulate all realistic future states of the repository that might result in radionuclide releases. Because the regulatory limits are probabilistic, performance assessments must accurately reflect variability and uncertainty within all factors that contribute to the simulation, including variability and uncertainty within all factors that contribute to the simulation, including variability in material properties, probabilities of future human actions, and uncertainties inherent in the conceptual and numerical models that simulate reality. This paper describes conceptual and numerical improvements in the performance assessment methodology made during 1990, and summarizes the present status of WIPP performance assessment. All results to date are preliminary, and cannot be used to determine compliance or non-compliance. The DOE anticipates determining compliance after evaluating a final performance assessment in 1994. 11 refs., 3 figs.
Low pressure (200 Torr) metalorganic chemical vapor deposition (MOCVD) of InSb has been examined through variation of the Column III (TMIn) and Column V (TMSb or TESb) precursor partial pressures. The use of lower growth pressure significantly enhanced the range of allowable Column III Column V partial pressures in which specular morphology InSb could be obtained without the formation of In droplets or Sb crystals. In addition, a 70% improvement in the average hole mobility was obtained, compared to InSb grown in the same reactor at atmospheric pressure. SIMS analysis revealed that Si at the substrate/epitaxial layer interface is an important impurity that may contribute to degradation of the mobility. Substitution of TESb for TMSb did not result in any improvement in the purity of the InSb. 6 refs.
The long length and relatively small cross sectional area of the robotic arms envisioned for use inside of the underground nuclear waste storage tanks will require the control of flexible structures. This will become an important problem in the characterization and remediation of these tanks. We are developing control strategies to actively damp residual vibrations in flexible robotic arms caused by high speed motion and abrupt external forces. A planar, two-link flexible arm is currently being used to test these control strategies. In this paper, two methods of control are discussed. The first is a minimum-time control approach which utilizes a finite element model and and optimization program. These tools plan the motor torque profiles necessary for the tip of the arm to move along a straight line, in minimum time, within the motors' torque constraints, and end in a quiescent state. To account for modeling errors in the finite element model, errors in joint angles, velocities, and link curvatures are added to the optimal torque trajectory. Linear quadratic Gaussian (LQG) regulatory design theory is used to determine the feedback gains. The second method of control is a teleoperated joystick controller which uses an input shaping technique to alter the commands of the joystick so as to reduce the residual vibration of the fundamental modes. Approximating the system as linear, the natural frequency and damping ratio are estimated on-line for the complete system, which includes the structure plus a lower level proportional derivative controller. An input shaping filter is determined from the estimated natural frequency, estimated damping ratio, and the desired transfer function of the system. 11 reps., 9 figs.
Muir, J.F.; Hogan Jr., R.E.; Skocypec, R.D.; Buck, R.
The concept of solar driven chemical reactions in a commercial-scale volumetric receiver/reactor on a parabolic concentrator was successfully demonstrated in the CAtalytically Enhanced Solar Absorption Receiver (CAESAR) test. Solar reforming of methane (CH{sub 4}) with carbon dioxide (CO{sub 2}) was achieved in a 64-cm diameter direct absorption reactor on a parabolic dish capable of 150 kW solar power. The reactor was a catalytic volumetric absorber consisting of a multi-layered, porous alumina foam disk coated with rhodium (Rh) catalyst. The system was operated during both steady-state and solar transient (cloud passage) conditions. The total solar power absorbed reached values up to 97 kW and the maximum methane conversion was 70%. Receiver thermal efficiencies ranged up to 85% and chemical efficiencies peaked at 54%. The absorber performed satisfactorily in promoting the reforming reaction during the tests without carbon formation. However, problems of cracking and degradation of the porous matrix, nonuniform dispersion of the Rh through the absorber, and catalyst deactivation due to sintering and possible encapsulation, must be resolved to achieve long-term operation and eventual commercialization. 17 refs., 11 figs., 1 tab.
We have performed MD simulations of adhesive phenomena, on an atomic scale, between metals possessing both smooth and stepped-surfaces. Studies of adhesion between identical metals, consisting of either Au, Cu, or Ni, with (001) or (111) orientations, reveal the existence of adhesive avalanches as the bodies are brought to within a critical separation ({approximately}2 {angstrom}). That is, as the surfaces approach one another, one or both surface layers becomes unstable, and abruptly moves toward the other. This signals a transition from an initial system with two distinct surfaces to one possessing no identifiable surfaces. The presence of adhesive avalanches will pose difficulties in determining adhesive forces and energies by means of atomic force microscopy at sub-nanometer separations of probe tip and sample surface. 7 refs., 3 figs.
An improved standard total-dose test method is described to qualify electronics for a low-dose radiation environment typical of space systems. The method consists of {sup 60}Co irradiation at a dose rate of 1--3 Gy(Si)/s (100--300 rad(Si)/s) and a subsequent 373 K (100{degree}C) bake. New initiatives in radiation hardness assurance are also briefly discussed, including the Qualified Manufacturers List (QML) test methodology and the possible use of 1/f noise measurements as a nondestructive screen for oxide-trap charge related failure. 8 refs.
A two-stage data compression technique that provides for exact, bit-for-bit recovery is described. The first stage is a modified form of conventional linear prediction which generates an error or residue sequence in such a way that exact reconstruction of the original data sequence can be accomplished with a simple recovery algorithm. The second stage is bi-level sequence coding. Even though the residue sequence from the first stage is essential white and Gaussian with seismic or other similar waveform data, bi-level sequence coding will generally provide further compression. The complete technique is described briefly in this summary, and examples of its performance are presented. A full paper on the algorithm is available from the author. 12 refs., 2 figs., 2 tabs.
We have synthesized a new tool, a lasing phase diagram, for designing high efficiency surface-emitting laser resonators and have demonstrated its usefulness by fabricating and operating many different laser resonators. 4 refs., 4 figs.
This paper is concerned with controlling the morphology of microporous polymers prepared via thermal demixing of solutions. 2 wt % solutions of poly(acrylonitrile) in maleic anhydride, a poor solvent, are first cooled to produce separated polymer-rich and solvent-rich phases. Removing the solvent by freeze drying then produces a microporous material having a density of 33 mg/cm{sup 3}, a void fraction of 97%, and a pore size of about 10 {mu}m. We find that the morphology cannot be explained by existing models, which focus on phase diagrams and kinetics of phase transformations during cooling of the solution. In conflict with those models, we find that two radically different morphologies can be produced even when the polymer concentration and cooling path are held strictly constant. A hypothesis that polymer degradation causes the different morphologies is not supported by GPC, {sup 13}C NMR, and FTIR experiments. Instead, we offer evidence that the different microporous morphologies are caused by different polymer conformations in solutions having the same concentration and temperature. 11 refs., 3 figs.
The nuclear industry uses sensitive or classified parts and material that must be protected and accounted for. We believe there is a need for an automated system that can help protect and inventory these parts and material. In response to this need Sandia National Laboratories Division 5245 is developing a personnel and material tracking system named PAMTRAK to safeguard sensitive parts and material at selected Department of Energy facilities. This paper describes the project's background, design goals and features.