Publications

The need to improve the radiation detection architecture has given rise to increased concern over the potential of equipment or procedures to violate the Fourth Amendment. Protecting the rights guaranteed by the Constitution is a foremost value of every government agency. However, protecting U.S. residents and assets from potentially catastrophic threats is also a crucial role of government. In the absence of clear precedent, the fear of potentially violating rights could lead to the rejection of effective and reasonable means that could reduce risks, possibly savings lives and assets. The goal of this document is not to apply case law to determine what the precedent may be if it exists, but rather provide a detailed outline that defines searches and seizures, identifies what precedent exists and what precedent doesn't exist, and explore what the existing (and non-existing) precedent means for the use of radiation detection used inside the nation's borders.

A gradient array apparatus was constructed for the study of porous polymers produced using the process of chemically-induced phase separation (CIPS). The apparatus consisted of a 60 element, two-dimensional array in which a temperature gradient was placed in the y-direction and composition was varied in the x-direction. The apparatus allowed for changes in opacity of blends to be monitored as a function of temperature and cure time by taking images of the array with time. The apparatus was validated by dispense a single blend composition into all 60 wells of the array and curing them for 24 hours and doing the experiment in triplicate. Variations in micron scale phase separation were readily observed as a function of both curing time and temperature and there was very good well-to-well consistency as well as trial-to-trial consistency. Poragen of samples varying with respect to cure temperature was removed and SEM images were obtained. The results obtained showed that cure temperature had a dramatic affect on sample morphology, and combining data obtained from visual observations made during the curing process with SEM data can enable a much better understanding of the CIPS process and provide predictive capability through the relatively facile generation of composition-process-morphology relationships. Data quality could be greatly enhanced by making further improvements in the apparatus. The primary improvements contemplated include the use of a more uniform light source, an optical table, and a CCD camera with data analysis software. These improvements would enable quantification of the amount of scattered light generated from individual elements as a function of cure time. In addition to the gradient array development, porous composites were produced by incorporating metal particles into a blend of poragen, epoxy resin, and crosslinker. The variables involved in the experiment were metal particle composition, primary metal particle size, metal concentration, and poragen composition. A total of 16 different porous composites were produced and characterized using SEM. In general, the results showed that pore morphology and the distribution of metal particles was dependent on multiple factors. For example, the use of silver nanoparticles did not significantly affect pore morphology for composites derived from decanol as the poragen, but exceptionally large pores were obtained with the use of decane as the poragen. With regard to the effect of metal particle size, silver nanoparticles were essentially exclusively dispered in the polymer matrix while silver microparticles were found in pores. For nickel particles, both nanoparticles and microparticles were largely dispersed in the polymer matrix and not in the pores.

Abstract not provided.

Circuit simulation tools (e.g., SPICE) have become invaluable in the development and design of electronic circuits. However, they have been pushed to their performance limits in addressing circuit design challenges that come from the technology drivers of smaller feature scales and higher integration. Improving the performance of circuit simulation tools through exploiting new opportunities in widely-available multi-processor architectures is a logical next step. Unfortunately, not all traditional simulation applications are inherently parallel, and quickly adapting mature application codes (even codes designed to parallel applications) to new parallel paradigms can be prohibitively difficult. In general, performance is influenced by many choices: hardware platform, runtime environment, languages and compilers used, algorithm choice and implementation, and more. In this complicated environment, the use of mini-applications small self-contained proxies for real applications is an excellent approach for rapidly exploring the parameter space of all these choices. In this report we present a multi-core performance study of Xyce, a transistor-level circuit simulation tool, and describe the future development of a mini-application for circuit simulation.

A permeability model for hydrogen transport in a porous material is successfully applied to both laboratory-scale and vehicle-scale sodium alanate hydrogen storage systems. The use of a Knudsen number dependent relationship for permeability of the material in conjunction with a constant area fraction channeling model is shown to accurately predict hydrogen flow through the reactors. Generally applicable model parameters were obtained by numerically fitting experimental measurements from reactors of different sizes and aspect ratios. The degree of channeling was experimentally determined from the measurements and found to be 2.08% of total cross-sectional area. Use of this constant area channeling model and the Knudsen dependent Young & Todd permeability model allows for accurate prediction of the hydrogen uptake performance of full-scale sodium alanate and similar metal hydride systems.

We describe breakthrough results obtained in a feasibility study of a fundamentally new architecture for air-cooled heat exchangers. A longstanding but largely unrealized opportunity in energy efficiency concerns the performance of air-cooled heat exchangers used in air conditioners, heat pumps, and refrigeration equipment. In the case of residential air conditioners, for example, the typical performance of the air cooled heat exchangers used for condensers and evaporators is at best marginal from the standpoint the of achieving maximum the possible coefficient of performance (COP). If by some means it were possible to reduce the thermal resistance of these heat exchangers to a negligible level, a typical energy savings of order 30% could be immediately realized. It has long been known that a several-fold increase in heat exchanger size, in conjunction with the use of much higher volumetric flow rates, provides a straight-forward path to this goal but is not practical from the standpoint of real world applications. The tension in the market place between the need for energy efficiency and logistical considerations such as equipment size, cost and operating noise has resulted in a compromise that is far from ideal. This is the reason that a typical residential air conditioner exhibits significant sensitivity to reductions in fan speed and/or fouling of the heat exchanger surface. The prevailing wisdom is that little can be done to improve this situation; the 'fan-plus-finned-heat-sink' heat exchanger architecture used throughout the energy sector represents an extremely mature technology for which there is little opportunity for further optimization. But the fact remains that conventional fan-plus-finned-heat-sink technology simply doesn't work that well. Their primary physical limitation to performance (i.e. low thermal resistance) is the boundary layer of motionless air that adheres to and envelops all surfaces of the heat exchanger. Within this boundary layer region, diffusive transport is the dominant mechanism for heat transfer. The resulting thermal bottleneck largely determines the thermal resistance of the heat exchanger. No one has yet devised a practical solution to the boundary layer problem. Another longstanding problem is inevitable fouling of the heat exchanger surface over time by particulate matter and other airborne contaminants. This problem is especially important in residential air conditioner systems where often little or no preventative maintenance is practiced. The heat sink fouling problem also remains unsolved. The third major problem (alluded to earlier) concerns inadequate airflow to heat exchanger resulting from restrictions on fan noise. The air-cooled heat exchanger described here solves all of the above three problems simultaneously. The 'Air Bearing Heat Exchanger' provides a several-fold reduction in boundary layer thickness, intrinsic immunity to heat sink fouling, and drastic reductions in noise. It is also very practical from the standpoint of cost, complexity, ruggedness, etc. Successful development of this technology is also expected to have far reaching impact in the IT sector from the standpointpoint of solving the 'Thermal Brick Wall' problem (which currently limits CPU clocks speeds to {approx}3 GHz), and increasing concern about the the electrical power consumption of our nation's information technology infrastructure.

This report examines the interactions involved with flashover along a surface in high density electronegative gases. The focus is on fast ionization processes rather than the later time ionic drift or thermalization of the discharge. A kinetic simulation of the gas and surface is used to examine electron multiplication and includes gas collision, excitation and ionization, and attachment processes, gas photoionization and surface photoemission processes, as well as surface attachment. These rates are then used in a 1.5D fluid ionization wave (streamer) model to study streamer propagation with and without the surface in air and in SF6. The 1.5D model therefore includes rates for all these processes. To get a better estimate for the behavior of the radius we have studied radial expansion of the streamer in air and in SF6. The focus of the modeling is on voltage and field level changes (with and without a surface) rather than secondary effects, such as, velocities or changes in discharge path. An experiment has been set up to carry out measurements of threshold voltages, streamer velocities, and other discharge characteristics. This setup includes both electrical and photographic diagnostics (streak and framing cameras). We have observed little change in critical field levels (where avalanche multiplication sets in) in the gas alone versus with the surface. Comparisons between model calculations and experimental measurements are in agreement with this. We have examined streamer sustaining fields (field which maintains ionization wave propagation) in the gas and on the surface. Agreement of the gas levels with available literature is good and agreement between experiment and calculation is good also. Model calculations do not indicate much difference between the gas alone versus the surface levels. Experiments have identified differences in velocity between streamers on the surface and in the gas alone (the surface values being larger).

Abstract not provided.

Abstract not provided.

Understanding the physics of phonon transport at small length scales is increasingly important for basic research in nanoelectronics, optoelectronics, nanomechanics, and thermoelectrics. We conducted several studies to develop an understanding of phonon behavior in very small structures. This report describes the modeling, experimental, and fabrication activities used to explore phonon transport across and along material interfaces and through nanopatterned structures. Toward the understanding of phonon transport across interfaces, we computed the Kapitza conductance for {Sigma}29(001) and {Sigma}3(111) interfaces in silicon, fabricated the interfaces in single-crystal silicon substrates, and used picosecond laser pulses to image the thermal waves crossing the interfaces. Toward the understanding of phonon transport along interfaces, we designed and fabricated a unique differential test structure that can measure the proportion of specular to diffuse thermal phonon scattering from silicon surfaces. Phonon-scale simulation of the test ligaments, as well as continuum scale modeling of the complete experiment, confirmed its sensitivity to surface scattering. To further our understanding of phonon transport through nanostructures, we fabricated microscale-patterned structures in diamond thin films.

Abstract not provided.

Abstract not provided.

In a globalized world, dramatic changes within any one nation causes ripple or even tsunamic effects within neighbor nations and nations geographically far removed. Multinational interventions to prevent or mitigate detrimental changes can easily cause secondary unintended consequences more detrimental and enduring than the feared change instigating the intervention. This LDRD research developed the foundations for a flexible geopolitical and socioeconomic simulation capability that focuses on the dynamic national security implications of natural and man-made trauma for a nation-state and the states linked to it through trade or treaty. The model developed contains a database for simulating all 229 recognized nation-states and sovereignties with the detail of 30 economic sectors including consumers and natural resources. The model explicitly simulates the interactions among the countries and their governments. Decisions among governments and populations is based on expectation formation. In the simulation model, failed expectations are used as a key metric for tension across states, among ethnic groups, and between population factions. This document provides the foundational documentation for the model.

While climate-change models have done a reasonable job of forecasting changes in global climate conditions over the past decades, recent data indicate that actual climate change may be much more severe. To better understand some of the potential economic impacts of these severe climate changes, Sandia economists estimated the impacts to the U.S. economy of climate change-induced impacts to U.S. precipitation over the 2010 to 2050 time period. The economists developed an impact methodology that converts changes in precipitation and water availability to changes in economic activity, and conducted simulations of economic impacts using a large-scale macroeconomic model of the U.S. economy.

This report gives an overview of the types of economic methodologies and models used by Sandia economists in their consequence analysis work for the National Infrastructure Simulation & Analysis Center and other DHS programs. It describes the three primary resolutions at which analysis is conducted (microeconomic, mesoeconomic, and macroeconomic), the tools used at these three levels (from data analysis to internally developed and publicly available tools), and how they are used individually and in concert with each other and other infrastructure tools.

The capability of gallium nitride (GaN) high power transistors arises, in large part, due to piezoelectric polarizations that induce the formation of a carrier rich two-dimensional electron gas. These polarizations, in turn, are directly related to the strain and hence stress that is present within the transistor. As a consequence, the stress load, as well as its measurement, is extremely important to the optimization of this device class. In response, this study demonstrates a technique to quantify the magnitude of operational thermoelastic stress that evolves in a GaN transistor through simultaneous use of the Raman signal's Stokes peak position and linewidth. After verifying the technique through comparison with a finite element model, the method is then utilized in the analysis of high electron mobility transistors grown on silicon (Si) and silicon carbide (SiC) substrates. For each series of device, the major stress contributors-thermoelastic, converse piezoelectric, and residual-are acquired and compared. While the magnitudes of the components are larger in those devices grown on silicon, the resultant biaxial loads in each of the devices are comparable at high power levels as the dominant residual tensile stress is counterbalanced by the compressive thermoelastic contribution. © 2009 American Institute of Physics.

We present MEMS polysilicon microvalves for flow control of a rapid analytical microsystem (Micro-Gas-Analyzer, MGA). All valve components (boss, seat, springs, electrodes, and stops) are surface micromachined in the SUMMiT™ microfabrication process. The valves have been characterized at high flow rate when open (60 ml/min air), low leak rate when closed (<0.0025 ml/min Hydrogen, H2), and tunable closing pressures (1 to 35 psig). Active electrostatic valves have been shown to hold closed (voltage on) against a high pressure (>40 psig) for sample loading, open for gas chromatograph (GC) loading (voltage off), and reclose against low pressure 2-5 psig. ©2009 IEEE.

As tribological properties are critical factors in the reliability of microelectromechanical systems, it is important to understand the physical processes and parameters governing wear and friction in silicon structural films. Dynamic friction, wear volumes and wear morphology have been studied for polysilicon devices from the Sandia SUMMiT VTM process actuated in ambient air at μN loads. A total of seven devices were tested. Roughly half of the devices showed a peak in the friction coefficient at three times the initial value with failure after 105 cycles. The other half of the devices behaved similarly initially; however, following the friction coefficient peak they displayed a lower steady-state friction regime with no failure for millions of cycles. Additionally, the nanoscale wear coefficient and roughness increased in the first ~105 cycles and then slowly decayed over several million cycles. Transmission electron microscopy studies revealed amorphous oxygen-rich debris. These measurements show that after a short adhesive wear regime, abrasive wear is the governing mechanism with failures attributed to differences in the local nanoscale surface morphology. Changing the relative humidity, sliding speed and load was found to influence the friction coefficient, but re-oxidation of worn polysilicon surfaces was only found to have an effect after periods of inactivity. © 2009 SPIE.

Abstract not provided.

The next generation of integrated micro-system technologies can only keep up with increased functionality and performance demands by using the 3rd dimension. The primary drivers for 3D integration are miniaturization, integration of different technologies in a small form-factor, and performance. 3D integration technologies can be grouped into 3 main categories, namely 3D On-chip integration, 3D IC-stacking, and 3D-packaging. This chapter provides a detailed review of each of these categories. © 2009 Springer-Verlag US.

The sensor placement problem in contamination warning system design for municipal water distribution networks involves maximizing the protection level afforded by limited numbers of sensors, typically quantified as the expected impact of a contamination event; the issue of how to mitigate against high-consequence events is either handled implicitly or ignored entirely. Consequently, expected-case sensor placements run the risk of failing to protect against high-consequence 9/11-style attacks. In contrast, robust sensor placements address this concern by focusing strictly on high-consequence events and placing sensors to minimize the impact of these events. We introduce several robust variations of the sensor placement problem, distinguished by how they quantify the potential damage due to high-consequence events. We explore the nature of robust versus expected-case sensor placements on three real-world large-scale distribution networks. We find that robust sensor placements can yield large reductions in the number and magnitude of high-consequence events, with only modest increases in expected impact. The ability to trade-off between robust and expected-case impacts is a key unexplored dimension in contamination warning system design. © 2009 ASCE.

A global partnership between nuclear energy supplier nations and user nations could enable the safe and secure expansion of nuclear power throughout the world. Although it is likely that supplier nations and their industries would be anxious to sell reactors and fuel services as part of this partnership, their commitment to close the fuel cycle (i.e., permanently take back fuel and high-level waste) remains unclear. At the 2007 Waste Management Symposia in Tucson, Arizona, USA, a distinguished international panel explored fuel take back and waste disposal from the perspective of current and prospective user nations. This paper reports on the findings of that panel and presents a path for policy makers to move forward with the partnership vision.

Simple preconditioned iterations can provide an efficient alternative to more elaborate eigenvalue algorithms. We observe that these simple methods can be viewed as forward Euler discretizations of well-known autonomous differential equations that enjoy appealing geometric properties. This connection facilitates novel results describing convergence of a class of preconditioned eigensolvers to the leftmost eigenvalue, provides insight into the role of orthogonality and biorthogonality, and suggests the development of new methods and analyses based on more sophisticated discretizations. These results also highlight the effect of preconditioning on the convergence and stability of the continuous-time system and its discretization. © 2009 Societ y for Industrial and Applied Mathematics.

The mechanisms governing D loss in ErD2 films with and without a Mo diffusion barrier on kovar substrates were studied between 200 and 600 °C via in-situ Ion Beam Analysis (IBA). Significant intermixing between kovar and Er was observed above 450°C and between kovar and ErD2 above 500 °C. The D loss mechanism in ErD2 films was found to change from intermixing between kovar and ErD2 at low temperatures (< 500 °C) to thermal decomposition at higher temperatures (> 500 °C). Diffusion between kovar and ErD2 was measured isothermally at 500 and 550 °C. An activation energy of 2.1 eV and a pre-exponential factor of 0.071 cm2/s were determined. Diffusion between the kovar components and ErD2 film was inhibited by depositing a 200 nm Mo diffusion barrier between the kovar substrate and the ErD2 film. The processing of the Mo diffusion barrier was shown to impact its performance. Intermixing between the kovar / Mo / ErD2 stack becomes significant between 500 and 550 °C with a sputter deposited Mo diffusion barrier and between 550 and 600 °C for an electron-beam evaporated Mo diffusion barrier. Copyright © 2009 ASM International® All rights reserved.

Particle image velocimetry (PIV) data have been acquired using three different experimental configurations in the far-field of the interaction created by a transverse supersonic jet exhausting from a flat plate into a transonic crossflow. The configurations included two-component PIV in the centerline streamwise plane at two overlapping stations, as well as stereoscopic PIV in both the same streamwise plane and in the crossplane. All measurement planes intersected at a common line. Data from both two-component measurement stations and the stereoscopic streamwise configuration agreed to within the estimated uncertainty, but data from the crossplane exhibited reduced velocity and turbulent stress magnitudes by a small but significant degree. Subsequent reprocessing of the data in nominally the same manner using a newer software package brought all values into close agreement with each other, but produced substantially higher turbulent stresses. The error source associated with the choice of software was traced to the use of image deformation in the newer software to treat velocity gradients, which is shown by synthetic PIV tests to yield a more accurate result for turbulence measurements even for gradients within the recommended limits for classical PIV. These detailed comparisons of replicate data suggest that routine methods of uncertainty quantification used for a turbulent PIV experiment may not fully capture the actual error sources. © 2009 US Government.