We present results of an off-lattice simulation of a two-component planar system, as a model for lateral organization of cholesterol molecules in lipid-cholesterol assemblies. We explore the existence of 'superlattice' structures even in fluid systems, in the absence of an underlying translational long-range order, and study their coupling to hexatic or bond-orientational order. We discuss our results in context of geometric superlattice theories and 'condensation complexes' in understanding a variety of experiments in artificial lipid-cholesterol assemblies.
A grating-gated field-effect transistor fabricated from a single-quantum well in a high-mobility GaAs-AlGaAs heterostructure is shown to function as a continuously electrically tunable photodetector of terahertz radiation via excitation of resonant plasmon modes in the well. Different harmonics of the plasmon wave vector are mapped, showing different branches of the dispersion relation. As a function of temperature, the resonant response magnitude peaks at around 30 K. Both photovoltaic and photoconductive responses have been observed under different incident power and bias conditions.
As current experimental and simulation methods cannot determine the mobility of flat boundaries across the large misorientation phase space, we have developed a computational method for imposing an artificial driving force on boundaries. In a molecular dynamics simulation, this allows us to go beyond the inherent timescale restrictions of the technique and induce non-negligible motion in flat boundaries of arbitrary misorientation. For different series of symmetric boundaries, we find both expected and unexpected results. In general, mobility increases as the grain boundary plane deviates from (111), but high-coincidence and low-angle boundaries represent special cases. These results agree with and enrich experimental observations.
The overall goal of this joint research project was to develop and demonstrate advanced sensors and computational technology for continuous monitoring of the condition of components, structures, and systems in advanced and next-generation nuclear power plants (NPPs). This project included investigating and adapting several advanced sensor technologies from Korean and US national laboratory research communities, some of which were developed and applied in non-nuclear industries. The project team investigated and developed sophisticated signal processing, noise reduction, and pattern recognition techniques and algorithms. The researchers installed sensors and conducted condition monitoring tests on two test loops, a check valve (an active component) and a piping elbow (a passive component), to demonstrate the feasibility of using advanced sensors and computational technology to achieve the project goal. Acoustic emission (AE) devices, optical fiber sensors, accelerometers, and ultrasonic transducers (UTs) were used to detect mechanical vibratory response of check valve and piping elbow in normal and degraded configurations. Chemical sensors were also installed to monitor the water chemistry in the piping elbow test loop. Analysis results of processed sensor data indicate that it is feasible to differentiate between the normal and degraded (with selected degradation mechanisms) configurations of these two components from the acquired sensor signals, but it is questionable that these methods can reliably identify the level and type of degradation. Additional research and development efforts are needed to refine the differentiation techniques and to reduce the level of uncertainties.
Guidelines to Improve Airport Preparedness Against Chemical and Biological Terrorism is a 100-page document that makes concrete recommendations on improving security and assessing vulnerable areas and helps its readers understand the nature of chemical and biological attacks. The report has been turned over to Airports Council International (ACI) and the American Association of Airport Executives (AAAE), two organizations that together represent the interests of thousands of airport personnel and facilities in the U.S. and around the world.
The annual program report provides detailed information about all aspects of the SNL/CA Environmental Planning and Ecology Program for a given calendar year. It functions as supporting documentation to the SNL/CA Environmental Management System Program Manual. The 2005 program report describes the activities undertaken during the past year, and activities planned in future years to implement the Planning and Ecology Program, one of six programs that supports environmental management at SNL/CA.
Variables influencing inferences about a stranger's goal during an unsolicited social interaction were explored. Experiment 1 developed a procedure for identifying cues. Experiments 2 and 3 assessed the relative importance of various cues (space, time, characteristics of oneself, characteristics of the stranger, and the stranger's behavior) for goal judgments. Results indicated that situational context cues informed goal judgments in ways that were consistent with diagnosticity ratings and typicality ratings of those cues. Stranger characteristics and stranger behaviors affected goal judgments more than would be expected from these quantitative measures of their informativeness. Nonetheless, the results are consistent with a mental model view that assumes perceivers monitor situational cues present during interactions and that goal inferences are guided by the informativeness of these cues.
Sandia national laboratories (SNL) and lockheed martin MS2 are designing an electromagnetic missile launcher (EMML) for naval applications. The EMML uses an induction coilgun topology with the requirement of launching a 3600 lb. missile up to a velocity of 40 m/s. To demonstrate the feasibility of the electromagnetic propulsion design, a demonstrator launcher was built that consists of approximately 10% of the propulsion coils needed for a tactical design. The demonstrator verified the design by launching a 1430 lb weighted sled to a height of 24 ft in mid-December 2004 (Figure 1). This paper provides the general launcher design, specific pulsed power system component details, system operation, and demonstration results.
In this study, we perform molecular dynamics simulations of adhesive contact and friction between alkylsilane Si(OH){sub 3}(CX{sub 2}){sub 10}CX{sub 3} and alkoxylsilane Si(OH){sub 2}(CX{sub 2}){sub 10}CX{sub 3} (where X = H or F) self-assembled monolayers (SAMs) on an amorphous silica substrate. The alkylsilane SAMs are primarily hydrogen-bonded or physisorbed to the surface. The alkoxylsilane SAMs are covalently bonded or chemisorbed to the surface. Previously, we studied the chemisorbed systems. In this work, we study the physisorbed systems and compare the tribological properties with the chemisorbed systems. Furthermore, we examine how water at the interface of the SAMs and substrate affects the tribological properties of the physisorbed systems. When less than a third of a monolayer is present, very little difference in the microscopic friction coefficient {mu} or shear stresses is observed. For increasing amounts of water, the values of {mu} and the shear stresses decrease; this effect is somewhat more pronounced for fluorocarbon alkylsilane SAMs than for the hydrocarbon SAMs. The observed decrease in friction is a consequence of a slip plane that occurs in the water as the amount of water is increased. We studied the frictional behavior using relative shear velocities ranging from v = 2 cm/s to 2 m/s. Similar to previously reported results for alkoxylsilane SAMs, the values of the measured stress and {mu} for the alkylsilane SAM systems decrease monotonically with v.
We present extensive simulations modeling the casting of multiblock polymer films by evaporation. The domain structure of the resulting film is strongly affected by varying the relative stiffness of the coblocks. The morphology changes from a bicontinuous lamellar phase when both blocks are flexible to a small-scale phase-separated phase with isolated domains as the stiffness of one of the blocks increases. As the relative stiffness of the blocks changes, the rate of evaporation, interfacial width, and morphology of the system changes. The findings can be used to tailor membrane morphology of interest to fuel-cell applications where the morphology is important for proton conduction.
While it had been known for a long time how to transform an asymmetric traveling salesman (ATS) problem on the complete graph with n vertices into a symmetric traveling salesman (STS) problem on an incomplete graph with 2n vertices, no method was available for using this correspondence to derive facets of the symmetric polytope from facets of the asymmetric polytope until the work of E. Balas and M. Fischetti in [Lifted cycle inequalities for the asymmetric traveling salesman problem, Mathematics of Operations Research 24 (2) (1999) 273-292] suggested an approach. The original Balas-Fischetti method uses a standard sequential lifting procedure for the computation of the coefficient of the edges that are missing in the incomplete STS graph, which is a difficult task when addressing classes of (as opposed to single) inequalities. In this paper we introduce a systematic procedure for accomplishing the lifting task. The procedure exploits the structure of the tight STS tours and organizes them into a suitable tree structure. The potential of the method is illustrated by deriving large new classes of facet-defining STS inequalities.
We report the demonstration of distributed-feedback terahertz quantum-cascade lasers based on a first-order grating fabricated via a lateral corrugation in a double-sided metal ridge waveguide. The phase of the facet reflection was precisely set by lithographically defined facets by dry etching. Single-mode emission was observed at low to moderate injection currents, although multimode emission was observed far beyond threshold owing to spatial hole burning. Finite-element simulations were used to calculate the modal and threshold characteristics for these devices, with results in good agreement with experiments.
This document is intended to serve as a users guide for the time-domain atmospheric acoustic propagation suite (TDAAPS) program developed as part of the Department of Defense High-Performance Modernization Office (HPCMP) Common High-Performance Computing Scalable Software Initiative (CHSSI). TDAAPS performs staggered-grid finite-difference modeling of the acoustic velocity-pressure system with the incorporation of spatially inhomogeneous winds. Wherever practical the control structure of the codes are written in C++ using an object oriented design. Sections of code where a large number of calculations are required are written in C or F77 in order to enable better compiler optimization of these sections. The TDAAPS program conforms to a UNIX style calling interface. Most of the actions of the codes are controlled by adding flags to the invoking command line. This document presents a large number of examples and provides new users with the necessary background to perform acoustic modeling with TDAAPS.
Lenhart, Joseph L.; Fischer, Daniel A.; Sambasivan, Sharadha; Lin, Eric K.; Jones, Ronald L.; Soles, Christopher L.; Wu, Wen L.; Goldfarb, Dario L.; Angelopoulos, Marie
The goal of this one year LDRD was to improve the overall efficiency of InGaN LEDs by improving the extraction of light from the semiconductor chip. InGaN LEDs are currently the most promising technology for producing high efficiency blue and green semiconductor light emitters. Improving the efficiency of InGaN LEDs will enable a more rapid adoption of semiconductor based lighting. In this LDRD, we proposed to develop photonic structures to improve light extraction from nitride-based light emitting diodes (LEDs). While many advanced device geometries were considered for this work, we focused on the use of a photonic crystal for improved light extraction. Although resonant cavity LEDs and other advanced structures certainly have the potential to improve light extraction, the photonic crystal approach showed the most promise in the early stages of this short program. The photonic crystal (PX)-LED developed here incorporates a two dimensional photonic crystal, or photonic lattice, into a nitride-based LED. The dimensions of the photonic crystal are selected such that there are very few or no optical modes in the plane of the LED ('lateral' modes). This will reduce or eliminate any radiation in the lateral direction so that the majority of the LED radiation will be in vertical modes that escape the semiconductor, which will improve the light-extraction efficiency. PX-LEDs were fabricated using a range of hole diameters and lattice constants and compared to control LEDs without a photonic crystal. The far field patterns from the PX-LEDs were dramatically modified by the presence of the photonic crystal. An increase in LED brightness of 1.75X was observed for light measured into a 40 degree emission cone with a total increase in power of 1.5X for an unencapsulated LED.
STDEM is the structured mesh time-domain electromagnetic and plasma physics component of Emphasis/Nevada. This report provides a guide on using STDEM. Emphasis, the electromagnetic physics analysis system, is a suite of codes for the simulation of electromagnetic and plasma physics phenomena. The time-dependent components of Emphasis have been implemented using the Nevada framework [1]. The notation Emphasis/Nevada is used to highlight this relationship and/or distinguish the time-dependent components of Emphasis. In theory the underlying framework should have little influence on the user's interaction with the application. In practice the framework tends to be more invasive as it provides key services such as input parsing and defines fundamental concepts and terminology. While the framework offers many technological advancements from a software development point of view, from a user's perspective the key benefits of the underlying framework are the common interface for all framework physics modules as well as the ability to perform coupled physics simulations. STDEM is the structured time-domain electromagnetic and plasma physics component of Emphasis/Nevada. STDEM provides for the full-wave solution to Maxwell's equations on multi-block three-dimensional structured grids using finite-difference time-domain (FDTD) algorithms. Additionally STDEM provides for the fully relativistic, self-consistent simulation of charged particles using particle-in-cell (PIC) algorithms.
The shock compaction behavior of a tungsten carbide powder was investigated using a new experimental design for gas-gun experiments. This design allows the Hugoniot properties to be measured with reasonably good accuracy despite the inherent difficulties involved with distended powders. The experiments also provide the first reshock state for the compacted powder. Experiments were conducted at impact velocities of 245, 500, and 711 m/s. A steady shock wave was observed for some of the sample thicknesses, but the remainder were attenuated due to release from the back of the impactor or the edge of the sample. The shock velocity for the powder was found to be quite low, and the propagating shock waves were seen to be very dispersive. The Hugoniot density for the 711 m/s experiment was close to ambient crystal density for tungsten carbide, indicating nearly complete compaction. When compared with quasi-static compaction results for the same material, the dynamic compaction data is seen to be significantly stiffer for the regime over which they overlap. Based on these initial results, recommendations are made for improving the experimental technique and for future work to improve our understanding of powder compaction.
Numerical models of complex phenomena often contain approximations due to our inability to fully model the underlying physics, the excessive computational resources required to fully resolve the physics, the need to calibrate constitutive models, or in some cases, our ability to only bound behavior. Here we illustrate the relationship between approximation, calibration, extrapolation, and model validation through a series of examples that use the linear transient convective/dispersion equation to represent the nonlinear behavior of Burgers equation. While the use of these models represents a simplification relative to the types of systems we normally address in engineering and science, the present examples do support the tutorial nature of this document without obscuring the basic issues presented with unnecessarily complex models.
One critical aspect of any denuclearization of the Democratic People’s Republic of Korea (DPRK) involves dismantlement of its nuclear facilities and management of their associated radioactive wastes. The decommissioning problem for its two principal operational plutonium facilities at Yongbyun, the 5MWe nuclear reactor and the Radiochemical Laboratory reprocessing facility, alone present a formidable challenge. Dismantling those facilities will create radioactive waste in addition to existing inventories of spent fuel and reprocessing wastes. Negotiations with the DPRK, such as the Six Party Talks, need to appreciate the enormous scale of the radioactive waste management problem resulting from dismantlement. The two operating plutonium facilities, along with their legacy wastes, will result in anywhere from 50 to 100 metric tons of uranium spent fuel, as much as 500,000 liters of liquid high-level waste, as well as miscellaneous high-level waste sources from the Radiochemical Laboratory. A substantial quantity of intermediate-level waste will result from disposing 600 metric tons of graphite from the reactor, an undetermined quantity of chemical decladding liquid waste from reprocessing, and hundreds of tons of contaminated concrete and metal from facility dismantlement. Various facilities for dismantlement, decontamination, waste treatment and packaging, and storage will be needed. The shipment of spent fuel and liquid high level waste out of the DPRK is also likely to be required. Nuclear facility dismantlement and radioactive waste management in the DPRK are all the more difficult because of nuclear nonproliferation constraints, including the call by the United States for “complete, verifiable and irreversible dismantlement,” or “CVID.” It is desirable to accomplish dismantlement quickly, but many aspects of the radioactive waste management cannot be achieved without careful assessment, planning and preparation, sustained commitment, and long completion times. The radioactive waste management problem in fact offers a prospect for international participation to engage the DPRK constructively. DPRK nuclear dismantlement, when accompanied with a concerted effort for effective radioactive waste management, can be a mutually beneficial goal.
The Bryan Mound salt dome, located near Freeport, Texas, is home to one of four underground crude oil-storage facilities managed by the U. S. Department of Energy Strategic Petroleum Reserve (SPR) Program. Sandia National Laboratories, as the geotechnical advisor to the SPR, conducts site-characterization investigations and other longer-term geotechnical and engineering studies in support of the program. This report describes the conversion of two-dimensional geologic interpretations of the Bryan Mound site into three-dimensional geologic models. The new models include the geometry of the salt dome, the surrounding sedimentary units, mapped faults, and the 20 oil-storage caverns at the site. This work provides an internally consistent geologic model of the Bryan Mound site that can be used in support of future work.
Sandia is undergoing tremendous change. Sandia's executive management recognized the need for leadership development. About ten years ago the Business, Leadership, and Management Development department in partnership with executive management developed and implemented the organizational leadership Success Profile Competencies to help address some of the changes on the horizon such as workforce losses and lack of a skill set in the area of interpersonal skills. This study addresses the need for the Business, Leadership, and Management Development department to provide statistically sound data in two areas. One is to demonstrate that the organizational 360-degree success profile assessment tool has made a difference for leaders. A second area is to demonstrate the presence of high performing leaders at the Labs. The study utilized two tools to address these two areas. Study participants were made up of individuals who have solid data on Sandia's 360-degree success profile assessment tool. The second assessment tool was comprised of those leaders who participated in the Lockheed Martin Corporation Employee Preferences Survey. Statistical data supports the connection between leader indicators and the 360-degree assessment tool. The study also indicates the presence of high performing leaders at Sandia.
The thrust from a multi-cycle, pulse detonation engine operating at practical flight altitudes will vary with the surrounding environment pressure. We have carried out the first experimental study using a detonation tube hung in a ballistic pendulum arrangement within a large pressure vessel in order to determine the effect that the environment has on the single-cycle impulse. The air pressure inside the vessel surrounding the detonation tube varied between 100 and 1.4 kPa while the initial pressure of the stoichiometric ethylene-oxygen mixture inside the tube varied between 100 and 30 kPa. The original impulse model (Wintenberger et al., Journal of Propulsion and Power, Vol. 19, No. 1, 2002) was modified to predict the observed increase in impulse and blow down time as the environment pressure decreased below one atmosphere. Comparisons between the impulse from detonation tubes and ideal, steady flow rockets indicate incomplete expansion of the detonation tube exhaust, resulting in a 37% difference in impulse at a pressure ratio (ratio of pressure behind the Taylor wave to the environment pressure) of 100.
Smart polymeric materials, such as piezoelectric polymers which deform by application of an electric field, are of interest for use in controllable mirrors as large, lightweight space optics. An important consideration when using any organic material in a space application is their extreme vulnerability to the space environment. In LEO the presence of atomic oxygen, large thermal extremes, hard vacuum, short wavelength ultraviolet and particulate radiation can result in erosion, cracking and outgassing of most polymers. While much research has been performed examining the physical and chemical changes incurred by polymers exposed to actual and simulated LEO environments, little work has focused on the effects of the space environment on the performance of piezoelectric polymers. The most widely used piezoelectric polymers are those based on poly(vinylidene fluoride) (PVDF) and include copolymers synthesized from vinylidene fluoride and trifluoroethylene, hexafluoropropylene or chlorotrifluoroethylene. The presence of a comonomer group can greatly influence on the crystalline phase, melting point, Curie point, modulus and processing required for piezoelectricity. After a rigorous pre-selection process only two polymers, namely the PVDF homopolymer and a TrFE copolymer (80% comonomer content), satisfied most of the requirements for operation in the temperature/radiation environment of LEO. Based on this initial materials selection, we have now performed a detailed study of the effects of temperature, atomic oxygen and vacuum UV radiation simulating low Earth orbit conditions on these two polymers. Both polymers exhibited diminished but very stable piezoelectric performance up to 130 C despite the upper use temperatures suggested by industry of 80 C (PVDF) and 100 C (P(VDF-TrFE)). We believe that the loss of piezoelectric response in samples conditioned at 130 C compared with non-exposed samples is partly due to the depoling process which occurs when the highly stressed films undergo contraction via relaxation. The TrFE copolymer, which does not need to be stretched for the polar phase to be present, has better retention of piezoelectric properties at 130 C compared with the highly oriented homopolymer. AO/VUV exposure caused significant surface erosion and pattern development for both polymers. Erosion yields were 2.8 x 10{sup -24} cm{sup 3}/atom for PVDF and 2.5 x 10{sup -24} cm{sup 3}/atom for P(VDF-TrFE). The piezoelectric properties of the residual material for both polymers were largely unchanged after exposure, although a slight shift in the Curie transition of the P(VDF-TrFE) was observed. A lightly crosslinked network was formed in the copolymer, presumably due to penetrating VUV radiation, while the homopolymer remained uncrosslinked. These differences were attributed to different levels of crystallinity and increased VUV absorption by P(VDF-TrFE) over PVDF. In this paper a summary of the performance limiting effects of temperature, radiation, atomic oxygen and VUV on the piezoelectric response of PVDF based polymers will be presented.
With multipath routing in mobile ad hoc networks (MANETs), a source can establish multiple routes to a destination for routing data. In MANETs, mulitpath routing can be used to provide route resilience, smaller end-to-end delay, and better load balancing. However, when the multiple paths are close together, transmissions of different paths may interfere with each other, causing degradation in performance. Besides interference, the physical diversity of paths also improves fault tolerance. We present a purely distributed multipath protocol based on the AODV-Multipath (AODVM) protocol called AODVM with Path Diversity (AODVM/PD) that finds multiple paths with a desired degree of correlation between paths specified as an input parameter to the algorithm. We demonstrate through detailed simulation analysis that multiple paths with low degree of correlation determined by AODVM/PD provides both smaller end-to-end delay than AODVM in networks with low mobility and better route resilience in the presence of correlated node failures.
We report a simple, rapid approach to synthesize water-soluble and biocompatible fluorescent quantum dot (QD) micelles by encapsulation of monodisperse, hydrophobic QDs within surfactant/lipid micelles. Analyses of UV-vis and photo luminescence spectra, along with transmission electron microscopy, indicate that the water-soluble semiconductor QD micelles are monodisperse and retain the optical properties of the original hydrophobic QDs. The QD micelles were shown to be biocompatible and exhibited little or no aggregation when taken up by cultured rat hippocampal neurons.
The effects of atomic oxygen (AO) and vacuum UV radiation simulating low Earth orbit conditions on two commercially available piezoelectric polymer films, poly(vinylidene fluoride) (PVDF) and poly(vinylidene fluoride-trifluoroethylene) P(VDF-TrFE), have been studied. Surface erosion and pattern development are significant for both polymers. Erosion yields were determined as 2.8 x 10{sup -24} cm{sup 3}/atom for PVDF and 2.5 x 10{sup -24} cm{sup 3}/atom for P(VDF-TrFE). The piezoelectric properties of the residual material of both polymers were largely unchanged after exposure, although a slight shift in the Curie transition of the P(VDF-TrFE) was observed. A lightly cross-linked network was formed in the copolymer presumably because of penetrating vacuum ultraviolet (VUV) radiation, while the homopolymer remained uncross-linked. These differences were attributed to varying degrees of crystallinity and potentially greater absorption, and hence damage, of VUV radiation in P(VDF-TrFE) compared with PVDF.
Pellets of Fe/KClO{sub 4} mixtures are used as a heat source for thermally activated ('thermal') batteries. They provide the energy necessary for melting the electrolyte and bringing the battery stack to operating temperature. The effects of morphology of the Fe and the heat-pellet density and composition on both the physical properties (flowability, pelletization, and pellet strength) and the pyrotechnic performance (burn rate and ignition sensitivity) were examined using several commercial sources of Fe.
We report the demonstration of a terahertz quantum-cascade laser that operates up to 164 K in pulsed mode and 117 K in continuous-wave mode at approximately 3.0 THz. The active region was based on a resonant-phonon depopulation scheme and a metal-metal waveguide was used for modal confinement. Copper to copper thermocompression wafer bonding was used to fabricate the waveguide, which displayed improved thermal properties compared to a previous indium-gold bonding method.
Nano photonic materials are synthetically manufactured crystals at the nano scale with the target of creating a microstructure with a special electro-magnetic periodicity. Such nano photonic materials have the ability to control light propagation and thus are capable of creating photonic bandgaps in the frequency domain. We propose using nano photonic crystals as sensors to detect microdamage in composite materials. We demonstrate using a simulation model that a nano photonic sensor attached to a composite bar experiences a significant change in its bandgap profile when damage is induced in the composite bar. The model predicts the frequency response of the nano photonic sensor using the transfer matrix method. A damage metric to evaluate the change in the frequency response is developed. Successful developments of nano photonic sensors allow damage identification at scales not attainable using current sensing technologies.
This slide presentation outlines information on a technology acquisition strategy for the security of water distribution networks. The Department of Homeland Security (DHS) has tasked a multi-laboratory team to evaluate current and future needs to protect the nation's water distribution infrastructure by supporting an objective evaluation of current and new technologies. The primary deliverables from this Operational Technology Demonstration (OTD) are the following: establishment of an advisory board for review and approval of testing protocols, technology acquisition processes and recommendations for technology test and evaluation in laboratory and field settings; development of a technology acquisition process; creation of laboratory and field testing and evaluation capability; and, testing of candidate technologies for insertion into a water early warning system. The initial phase of this study involves the development of two separate but complementary strategies to be reviewed by the advisory board: a technology acquisition strategy; and, a technology evaluation strategy. Lawrence Livermore National Laboratory and Sandia National Laboratories are tasked with the first strategy, while Los Alamos, Pacific Northwest, and Oak Ridge National Laboratories are tasked with the second strategy. The first goal of the acquisition strategy is the development of a technology survey process that includes a review of current test programs and development of a method to solicit and select existing and emerging sensor technologies for evaluation and testing. The second goal is to implement the acquisition strategy to provide a set of recommendations for candidate technologies for laboratory and field testing.
We have conducted an extensive study of the evolution of surface morphology of single crystal diamond surfaces during sputtering by 20 keV Ga{sup +} and Ga{sup +} + H{sub 2}O. We observe the formation of well-ordered ripples on the surface for angles of incidence between 40 and 70{sup o}. We have also measured sputter yields as a function of angle of incidence, and ripple wavelength and amplitude dependence on angle of incidence and ion fluence. Smooth surface morphology is observed for <40{sup o}, and a transition to a step-and-terrace structure is observed for >70{sup o}. The formation and evolution of well-ordered surface ripples is well characterized by the model of Bradley and Harper, where sputter-induced roughening is balanced by surface transport smoothing. Smoothing is consistent with an ion-induced viscous relaxation mechanism. Ripple amplitude saturates at high ion fluence, confirming the effect of nonlinear processes. Differences between Ga{sup +} and Ga{sup +} + H{sub 2}O in ripple wavelength, amplitude, and time to saturation of amplitude are consistent with the increased sputter yield observed for Ga{sup +} + H{sub 2}O. For angle of incidence <40{sup o}, an ion bombardment-induced 'atomic drift' mechanism for surface smoothing may be responsible for suppression of ripple formation. For Ga{sup +} + H{sub 2}O, we observe anomalous formation of very large amplitude and wavelength, poorly ordered surface ridges for angle of incidence near 40{sup o}. Finally, we observe that ripple initiation on smooth surfaces can take place by initial stochastic roughening followed by evolution of increasingly well-ordered ripples.
Nuclear fuel cycle transparency can be defined as a confidence building approach among political entities to ensure civilian nuclear facilities are not being used for the development of nuclear weapons. Transparency concepts facilitate the transfer of nuclear technology, as the current international political climate indicates a need for increased methods of assuring non-proliferation. This research develops a system which will augment current non-proliferation assessment activities undertaken by U.S. and international regulatory agencies. It will support the export of nuclear technologies, as well as the design and construction of Gen. IV energy systems. Additionally, the framework developed by this research will provide feedback to cooperating parties, thus ensuring full transparency of a nuclear fuel cycle. As fuel handling activities become increasingly automated, proliferation or diversion potential of nuclear material still needs to be assessed. However, with increased automation, there exists a vast amount of process data to be monitored. By designing a system that monitors process data continuously, and compares this data to declared process information and plant designs, a faster and more efficient assessment of proliferation risk can be made. Figure 1 provides an illustration of the transparency framework that has been developed. As shown in the figure, real-time process data is collected at the fuel cycle facility; a reactor, a fabrication plant, or a recycle facility, etc. Data is sent to the monitoring organization and is assessed for proliferation risk. Analysis and recommendations are made to cooperating parties, and feedback is provided to the facility. The analysis of proliferation risk is based on the following factors: (1) Material attractiveness: the quantification of factors relevant to the proliferation risk of a certain material (e.g., highly enriched Pu-239 is more attractive than that of lower enrichment) (2) The static (baseline) risk: the quantification of risk factors regarding the expected value of proliferation risk under normal (not proliferating) operations. (3) The dynamic (changing) risk: the quantification of risk factors regarding the observed value of proliferation risk, based on monitor signals from facility operations. This framework could be implemented at facilities which have been exported (for instance, to third world countries), or facilities located in sensitive countries. Sandia National Laboratories is currently working with the Japan Nuclear Cycle Development Institute (JNC) to implement a demonstration of nuclear fuel cycle transparency technology at the Fuel Handling Training Model designed for the Monju Fast Reactor at the International Cooperation and Development Training Center in Japan. This technology has broad applications, both in the U.S. and abroad. Following the demonstration, we expect to begin further testing of the technology at an Enrichment Facility, a Fast Reactor, and at a Recycle Facility.
The use of a lower-melting-point molten metal to join metallic components is perhaps the earliest example of processing which employs metallurgical bonding principles, having roots as far back as 4200 BC (Peaslee 2003). More than 6000 years later, brazing occupies a prominent position in our suite of joining processes where it offers cost and/or performance advantages in the fabrication of many structures. More precisely, brazing can be described as the use of a molten filler metal to wet the closely fitting faying surfaces of a joint, leading to formation of metallurgical bonds between the filler metal and substrates. Historically, brazing processes employ filler metals whose solidus temperature exceeds 723 K, as opposed to soldering processes which use lower-melting-point temperature filler materials. In the past several decades, technological advances have facilitated a broadening of applications for brazing while simultaneously contradicting some of the traditional perceptions of the process. However, many of those tenets remain appropriate for the majority of brazing processes and products. Accordingly, this article provides a brief description of traditional brazing and some important factors to be considered when designing and producing brazed structures. An additional section describes the technical advances in the field.
The effect of critical dimension (CD) variation and metallization ratio on the efficiency of energy conversion of a surface acoustic wave (SAW) correlator is examined. We find that a 10% variation in the width of finger electrodes predicts only a 1% decrease in the efficiency of energy conversion. Furthermore, our model predicts that a metallization ratio of 0.74 represents an optimum value for energy extraction from the SAW by the interdigitated transducer (IDT).
This paper presents a 3D facial recognition algorithm based on the Hausdorff distance metric. The standard 3D formulation of the Hausdorff matching algorithm has been modified to operate on a 2D range image, enabling a reduction in computation from O(N2) to O(N) without large storage requirements. The Hausdorff distance is known for its robustness to data outliers and inconsistent data between two data sets, making it a suitable choice for dealing with the inherent problems in many 3D datasets due to sensor noise and object self-occlusion. For optimal performance, the algorithm assumes a good initial alignment between probe and template datasets. However, to minimize the error between two faces, the alignment can be iteratively refined. Results from the algorithm are presented using 3D face images from the Face Recognition Grand Challenge database version 1.0.
While loss of life is the operating concern of Department of Homeland Security (DHS), the security of the economy ultimately decides the success of the war on terrorism. This project focuses on mitigation, containment, response, and impact of terrorist events on the economy. Conventional economic methods are inadequate, but agent-based methods (Discrete Simulation) appears to uniquely capture the dynamics and emergent (human) behaviors.
Low-temperature co-fired ceramic (LTCC) enables development and testing of critical elements on microsystem boards as well as nonmicroelectronic meso-scale applications. We describe silicon-based microelectromechanical systems packaging and LTCC meso-scale applications. Microfluidic interposers permit rapid testing of varied silicon designs. The application of LTCC to micro-high-performance liquid chromatography (?-HPLC) demonstrates performance advantages at very high pressures. At intermediate pressures, a ceramic thermal cell lyser has lysed bacteria spores without damaging the proteins. The stability and sensitivity of LTCC/chemiresistor smart channels are comparable to the performance of silicon-based chemiresistors. A variant of the use of sacrificial volume materials has created channels, suspended thick films, cavities, and techniques for pressure and flow sensing. We report on inductors, diaphragms, cantilevers, antennae, switch structures, and thermal sensors suspended in air. The development of 'functional-as-released' moving parts has resulted in wheels, impellers, tethered plates, and related new LTCC mechanical roles for actuation and sensing. High-temperature metal-to-LTCC joining has been developed with metal thin films for the strong, hermetic interfaces necessary for pins, leads, and tubes.
Combinatorial algorithms have long played a pivotal enabling role in many applications of parallel computing. Graph algorithms in particular arise in load balancing, scheduling, mapping and many other aspects of the parallelization of irregular applications. These are still active research areas, mostly due to evolving computational techniques and rapidly changing computational platforms. But the relationship between parallel computing and discrete algorithms is much richer than the mere use of graph algorithms to support the parallelization of traditional scientific computations. Important, emerging areas of science are fundamentally discrete, and they are increasingly reliant on the power of parallel computing. Examples include computational biology, scientific data mining, and network analysis. These applications are changing the relationship between discrete algorithms and parallel computing. In addition to their traditional role as enablers of high performance, combinatorial algorithms are now customers for parallel computing. New parallelization techniques for combinatorial algorithms need to be developed to support these nontraditional scientific approaches. This chapter will describe some of the many areas of intersection between discrete algorithms and parallel scientific computing. Due to space limitations, this chapter is not a comprehensive survey, but rather an introduction to a diverse set of techniques and applications with a particular emphasis on work presented at the Eleventh SIAM Conference on Parallel Processing for Scientific Computing. Some topics highly relevant to this chapter (e.g. load balancing) are addressed elsewhere in this book, and so we will not discuss them here.
Red Storm is a massively parallel processor. The Red Storm design goals are: (1) Balanced system performance - CPU, memory, interconnect, and I/O; (2) Usability - functionality of hardware and software meets needs of users for Massively Parallel Computing; (3)S calability - system hardware and software scale, single cabinet system to {approx} 30,000 processor system; (4) reliability - machines tays up long enough between interrupts to make real progress on completing application run (at least 50 hours MTBI), requires full system RAS capability; (5) Upgradability - system can be upgraded with a processor swap and additional cabinets to 100T or greater; (6) red/black switching - capability to switch major portions of the machine between classified and unclassified computing environments; (7) space, power, cooling - high density, low power system; and (8) price/performance - excellent performance per dollar, use high volume commodity parts where feasible.
In this article we describe stress nets, a technique for exploring 2D tensor fields. Our method allows a user to examine simultaneously the tensors eigenvectors (both major and minor) as well as scalar-valued tensor invariants. By avoiding noise-advection techniques, we are able to display both principal directions of the tensor field as well as the derived scalars without cluttering the display. We present a CPU-only implementation of stress nets as well as a hybrid CPU/GPU approach and discuss the relative strengths and weaknesses of each. Stress nets have been used as part of an investigation into crack propagation. They were used to display the directions of maximum shear in a slab of material under tension as well as the magnitude of the shear forces acting on each point. Our methods allowed users to find new features in the data that were not visible on standard plots of tensor invariants. These features disagree with commonly accepted analytical crack propagation solutions and have sparked renewed investigation. Though developed for a materials mechanics problem, our method applies equally well to any 2D tensor field having unique characteristic directions.
Smart polymeric materials, such as piezoelectric polymers which deform by application of an electric field, are of interest for use in controllable mirrors as large, lightweight space optics. An important consideration when using any organic material in a space application is their extreme vulnerability to the space environment. In LEO the presence of atomic oxygen, large thermal extremes, hard vacuum, short wavelength ultraviolet and particulate radiation can result in erosion, cracking and outgassing of most polymers. While much research has been performed examining the physical and chemical changes incurred by polymers exposed to actual and simulated LEO environments, little work has focused on the effects of the space environment on the performance of piezoelectric polymers. The most widely used piezoelectric polymers are those based on poly(vinylidene fluoride) (PVDF) and include copolymers synthesized from vinylidene fluoride and trifluoroethylene, hexafluoropropylene or chlorotrifluoroethylene. The presence of a comonomer group can greatly influence on the crystalline phase, melting point, Curie point, modulus and processing required for piezoelectricity. After a rigorous pre-selection process only two polymers, namely the PVDF homopolymer and a TrFE copolymer (80% comonomer content), satisfied most of the requirements for operation in the temperature/radiation environment of LEO. Based on this initial materials selection, we have now performed a detailed study of the effects of temperature, atomic oxygen and vacuum UV radiation simulating low Earth orbit conditions on these two polymers. Both polymers exhibited diminished but very stable piezoelectric performance up to 130 C despite the upper use temperatures suggested by industry of 80 C (PVDF) and 100 C (P(VDF-TrFE)). We believe that the loss of piezoelectric response in samples conditioned at 130 C compared with non-exposed samples is partly due to the depoling process which occurs when the highly stressed films undergo contraction via relaxation. The TrFE copolymer, which does not need to be stretched for the polar phase to be present, has better retention of piezoelectric properties at 130 C compared with the highly oriented homopolymer. AO/VUV exposure caused significant surface erosion and pattern development for both polymers. Erosion yields were 2.8 x 10{sup -24} cm{sup 3}/atom for PVDF and 2.5 x 10{sup -24} cm{sup 3}/atom for P(VDF-TrFE). The piezoelectric properties of the residual material for both polymers were largely unchanged after exposure, although a slight shift in the Curie transition of the P(VDF-TrFE) was observed. A lightly crosslinked network was formed in the copolymer, presumably due to penetrating VUV radiation, while the homopolymer remained uncrosslinked. These differences were attributed to different levels of crystallinity and increased VUV absorption by P(VDF-TrFE) over PVDF. In this paper a summary of the performance limiting effects of temperature, radiation, atomic oxygen and VUV on the piezoelectric response of PVDF based polymers will be presented.
Empirical studies suggest that consumption is more sensitive to current income than suggested under the permanent income hypothesis, which raises questions regarding expectations for future income, risk aversion, and the role of economic confidence measures. This report surveys a body of fundamental economic literature as well as burgeoning computational modeling methods to support efforts to better anticipate cascading economic responses to terrorist threats and attacks. This is a three part survey to support the incorporation of models of economic confidence into agent-based microeconomic simulations. We first review broad underlying economic principles related to this topic. We then review the economic principle of confidence and related empirical studies. Finally, we provide a brief survey of efforts and publications related to agent-based economic simulation.
Resist substrates used in the LIGA process must provide high initial bond strength between the substrate and resist, little degradation of the bond strength during x-ray exposure, acceptable undercut rates during development, and a surface enabling good electrodeposition of metals. Additionally, they should produce little fluorescence radiation and give small secondary doses in bright regions of the resist at the substrate interface. To develop a new substrate satisfying all these requirements, we have investigated secondary resist doses due to electrons and fluorescence, resist adhesion before exposure, loss of fine features during extended development, and the nucleation and adhesion of electrodeposits for various substrate materials. The result of these studies is a new anodized aluminum substrate and accompanying methods for resist bonding and electrodeposition. We demonstrate successful use of this substrate through all process steps and establish its capabilities via the fabrication of isolated resist features down to 6 {micro}m, feature aspect ratios up to 280 and electroformed nickel structures at heights of 190 to 1400 {micro}m. The minimum mask absorber thickness required for this new substrate ranges from 7 to 15 {micro}m depending on the resist thickness.