The International Monitoring System (IMS) proposed for verifying compliance with the Comprehensive Nuclear-Test-Ban Treaty will include an infrasound network for detecting and identifying explosions in the atmosphere. As is the case with seismic monitoring, data collected from historic events of interest are vital for improving infrasonic monitoring capabilities. Unfortunately, however, infrasonic recordings of such events are rare and thus any additional data sets that might be available should be pursued. Towards that end, we will digitize, as a result of the ROA01-38 award, paper records and extract from 9-track tapes several unique data sets from Sandia National Laboratories and Los Alamos National Laboratory that have not been available to the monitoring community. These data sets include recordings of surface and atmospheric explosions representing different yields, altitudes and weather conditions, as well as bolides and other natural phenomena that may be detected by the international infrasound monitoring network. Once the data are all in digital form, we will convert them to the standard CSS format, including event and station information. The complete set of database tables and binary waveform files will be the ultimate product of our work.
In the current study we are developing an experimental fracture material property test method specific to dynamic fragmentation. This test method allows the study of fracture fragmentation in a reproducible laboratory environment under well-controlled loading conditions. Motion and fragmentation of the specimen are diagnosed using framing camera, VISAR and soft recovery methods. Fragmentation properties of several steels, nitinol, tungsten alloy, copper, aluminum, and titanium have been obtained to date. The values for fragmentation toughness, and failure threshold will be reported, as well as effects in these values as the material strain-rate is varied through changes in wall thickness and impact conditions.
Attempting to convey concepts and ideas in the subject area of robotic manipulators from within the confines of a static two-dimensional printed page can prove quite challenging to even the most gifted of authors. The inherently dynamic and multi-dimensional nature of the subject matter seems better suited to a medium of conveyance wherein a student is allowed to interactively explore topics in this multi-disciplinary field. This article describes the initial development of an online robotics course 'textbook' which seeks to leverage recent advances in Web-based technologies to enhance the learning experience in ways not possible with printed materials. The pedagogical approach employed herein is that of multi-modal reinforcement wherein key concepts are first described in words, conveyed visually, and finally reinforced by soliciting student interaction.
Memory may be the only system component that is more commoditized than a microprocessor. To simultaneously exploit this and address the impending memory wall, processing in memory (PIM) research efforts are considering ways to move processing into memory without significantly increasing the cost of the memory. As such, PIM devices may become the basis for future commodity clusters. Although these PIM devices may leverage new computational paradigms such as hardware support for multi-threading and traveling threads, they must provide support for legacy programming models if they are to supplant commodity clusters. This paper presents a prototype implementation of MPI over a traveling thread mechanism called parcels. A performance analysis indicates that the direct hardware support of a traveling thread model can lead to an efficient, lightweight MPI implementation.
Mechanisms for enhanced low-dose-rate sensitivity are described. In these mechanisms, bimolecular reactions dominate the kinetics at high dose rates thereby causing a sub-linear dependence on total dose, and this leads to a dose-rate dependence. These bimolecular mechanisms include electron-hole recombination, hydrogen recapture at hydrogen source sites, and hydrogen dimerization to form hydrogen molecules. The essence of each of these mechanisms is the dominance of the bimolecular reactions over the radiolysis reaction at high dose rates. However, at low dose rates, the radiolysis reaction dominates leading to a maximum effect of the radiation.
Properties of relevance for the equation of state for a high-density glass are discussed. We review the effects of failure waves, comminuted phase, and compaction on the validity of the Mie-Grueneisen EOS. The specific heat and the Grueneisen parameter at standard conditions for a {rho}{sub 0} = 5.085 g/cm{sup 3} glass ('Glass A') is then estimated to be 522 mJ/g/K and 0.1-0.3, respectively. The latter value is substantially smaller than the value of 2.1751 given in the SESAME tables for a high-density glass with {rho}{sub 0} = 5.46 g/cm{sup 3}. The present unusual value of the Grueneisen parameter is confirmed from the volume dependence determined from fitting the Mie-Grueneisen EOS to shock data in Ref. [2].
Scalable thermal runaway models for cook-off of energetic materials (EMs) require realistic temperature- and pressure-dependent chemical reaction rates. The Sandia Instrumented Thermal Ignition apparatus was developed to provide in situ small-scale test data that address this model requirement. Spatially and temporally resolved internal temperature measurements have provided new insight into the energetic reactions occurring in PBX 9501, LX-10-2, and PBXN-109. The data have shown previously postulated reaction steps to be incorrect and suggest previously unknown reaction steps. Model adjustments based on these data have resulted in better predictions at a range of scales.
Submovements are hypothesized building blocks of human movement, discrete ballistic movements of which more complex movements are composed. Using a novel algorithm, submovements were extracted from the point-to-point movements of 41 persons recovering from stroke. Analysis of the extracted submovements showed that, over the course of therapy, patients' submovements tended to increase in peak speed and duration. The number of submovements employed to produce a given movement decreased. The time between the peaks of adjacent submovements decreased for inpatients (those less than 1 month post-stroke), but not for outpatients (those greater than 12 months post-stroke) as a group. Submovements became more overlapped for all patients, but more markedly for inpatients. The strength and consistency with which it quantified patients' recovery indicates that analysis of submovement overlap might be a useful tool for measuring learning or other changes in motor behavior in future human movement studies.
Proposed for publication in Coordinated & Multiple Views in Exploratory Visualization, Special Issue of Information Visualization Journal, Vol 2 No. 4, Palgrave/Macmillan.
Studies of the dielectric properties and phase behavior of an {sup 18}O-substituted SrTiO{sub 3} (>97% {sup 18}O), or STO-18, crystal at 1 bar and as functions of hydrostatic pressure and applied dc biasing electric field have shed much light on the mechanism of the {sup 18}O-induced ferroelectric transition in this material. Dielectric measurements reveal an equilibrium phase transition (T{sub c} {approx_equal} 24K at 1 bar) and an enhancement of the static dielectric constant {var_epsilon} over that of normal (i.e., {sup 16}O) SrTiO{sub 3}, or STO-16, over a large temperature range above T{sub c}. This enhancement is quantitatively shown to be attributed to additional softening of the ferroelectric soft-mode frequency ({omega}{sub s}) of STO-16, in agreement with lattice dynamic calculations. Thus, in STO-18, two effects due to the heavier mass of {sup 18}O conspire to induce the transition: (i) this additional softening of {omega}{sub s} and (ii) damping of quantum fluctuations. Pressure lowers T{sub c} at the large initial rate of 20 K/kbar and completely suppresses the ferroelectric state leading to a quantum paraelectric state at 0.7 kbar, confirming earlier results. Very large effects of a biasing dc electric fields on the peak temperature and {var_epsilon} are also observed in the quantum regime reflecting the small characteristic energies of the system. The results also reveal a dielectric relaxation process near 10 K with interesting properties. The implications of all the results on our understanding of the physics of STO-18 are discussed.
Bulk migration of particles towards regions of lower shear occurs in suspensions of neutrally buoyant spheres in Newtonian fluids undergoing creeping flow in the annular region between two rotating, coaxial cylinders (a wide-gap Couette). For a monomodal suspension of spheres in a viscous fluid, dimensional analysis indicates that the rate of migration at a given concentration should scale with the square of the sphere radius. However, a previous experimental study showed that the rate of migration of spherical particles at 50% volume concentration actually scaled with the sphere radius to approximately the 2.9 power.
The Electricity Generation Cost Simulation Model (GenSim) is a user-friendly, high-level dynamic simulation model that calculates electricity production costs for variety of electricity generation technologies, including: pulverized coal, gas combustion turbine, gas combined cycle, nuclear, solar (PV and thermal), and wind. The model allows the user to quickly conduct sensitivity analysis on key variables, including: capital, O&M, and fuel costs; interest rates; construction time; heat rates; and capacity factors. The model also includes consideration of a wide range of externality costs and pollution control options for carbon dioxide, nitrogen oxides, sulfur dioxide, and mercuty. Two different data sets are included in the model; one from the US. Department of Energy (DOE) and the other from Platt's Research Group. Likely users of this model include executives and staff in the Congress, the Administration and private industry (power plant builders, industrial electricity users and electric utilities). The model seeks to improve understanding of the economic viability of various generating technologies and their emissions trade-offs. The base case results, using the DOE data, indicate that in the absence of externality costs, or renewable tax credits, pulverized coal and gas combined cycle plants are the least cost alternatives at 3.7 and 3.5 cents/kwhr, respectively. A complete sensitivity analysis on fuel, capital, and construction time shows that these results coal and gas are much more sensitive to assumption about fuel prices than they are to capital costs or construction times. The results also show that making nuclear competitive with coal or gas requires significant reductions in capital costs, to the $1000/kW level, if no other changes are made. For renewables, the results indicate that wind is now competitive with the nuclear option and is only competitive with coal and gas for grid connected applications if one includes the federal production tax credit of 1.8cents/kwhr.
Chemically prepared zinc oxide powders are fabricated for the production of high aspect ratio varistor components. Colloidal processing was performed to reduce agglomerates to primary particles, form a high solids loadingslurry, and prevent dopant migration. The milled and dispersed powder exhibited a viscoelastic to elastic behavioral transition at a volume loading of 43-46%. The origin of this transition was studied using acoustic spectroscopy, zeta potential measurements, and oscillatory rheology. The phenomenon occurs due to a volume fraction solids dependent reduction in the zeta potential of the solid phase. It is postulated to result from divalent ion binding within the polyelectrolyte dispersant chain and was mitigated using a polyethylene glycol plasticizing additive. This allowed for increased solids loading in the slurry and a green body fabrication study to be presented in our companion paper.
We report the synthesis of a new nanocrystal (NC) mesophase through self-assembly of water-soluble NC micelles with soluble silica. The mesophase comprises gold nanocrystals arranged within a silica matrix in a face-centered cubic lattice with cell dimensions that are adjustable through control of the nanocrystal diameter and/or the alkane chain lengths of the primary alkanethiol stabilizing ligands or the surrounding secondary surfactants. Under kinetically controlled silica polymerization conditions, evaporation drives self-assembly of NC micelles into ordered NC/silica thin-film mesophases during spin coating. The intermediate NC micelles are water soluble and of interest for biolabeling. Initial experiments on a metal-insulator-metal capacitor fabricated with an ordered three-dimensional gold nanocrystal/silica array as the 'insulator' demonstrated collective Coulomb blockade behavior below 100 kelvin and established the current-voltage scaling relationship for a well-defined three-dimensional array of Coulomb islands.
Interfacial force microscopy (IFM) is used to measure the electrical contact properties of electroplated gold thin films of the type used in microelectromechanical system relays. Force and current levels consistent with those present in metal-metal contact switches are examined in an atmospheric-pressure, dry-nitrogen ambient at room temperature, and the nature of a nonmetallic contamination layer which limits contact resistance and lifetime is explicitly examined mechanically, electrically and chemically. The electrical and mechanical properties of the contamination layer on the gold substrate are observed by IFM both before and after being exposed to ozone for an extended period of time. The contamination film is characterized by x-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry, and found to consist mostly of hydrocarbons; the film remains relatively stable in both composition and thickness following ozonation. However, some subtle chemical changes in the contamination layer induced by the ozonation process are found to profoundly affect the electrical properties of the gold-gold contact, reducing the resistance by more than 3 orders of magnitude and considerably reducing variability in the contact resistance between contact events. These results clearly demonstrate the critical role both positive and negative of the latent contamination present on the contact surfaces.
Chemically prepared zinc oxide powders were processed for the production of high aspect ratio varistor components (length/diameter >5). Near-net-shape casting methods including slip casting and agarose gelcasting were evaluated for effectiveness in achieving a uniform green microstructure that densifies to near theoretical values during sintering. The structure of the green parts was examined by mercury porisimetry. Agarose gelcasting produced green parts having low solids loading values and did not achieve high fired density. Isopressing the agarose cast parts after drying raised the fired density to greater than 95%, but the parts exhibited catastrophic shorting during electrical testing. Slip casting produced high green density parts, which exhibit high fired density values. The electrical characteristics of slip-cast parts are comparable with dry-pressed powder compacts.
We present results from crystal spectroscopic analysis of silicon aero-gel foams heated by dynamic hohlraums on Z. The dynamic hohlraum on Z creates a radiation source with a 230-eV average temperature over a 2.4-mm diameter. In these experiments silicon aero-gel foams with 10-mg/cm{sup 3} densities and 1.7-mm lengths were placed on both ends of the dynamic hohlraum. Several crystal spectrometers were placed both above and below the z-pinch to diagnose the temperature of the silicon aero-gel foam using the K-shell lines of silicon. The crystal spectrometers were (1) temporally integrated and spatially resolved, (2) temporally resolved and spatially integrated, and (3) both temporally and spatially resolved. The results indicate that the dynamic hohlraum heats the silicon aero-gel to approximately 150-eV at peak power. As the dynamic hohlraum source cools after peak power the silicon aero-gel continues to heat and jets axially at an average velocity of approximately 50-cm/{micro}s. The spectroscopy has also shown that the reason for the up/down asymmetry in radiated power on Z is that tungsten enters the line-of-sight on the bottom of the machine much more than on the top.
Data collection for interferometric synthetic aperture radar (IFSAR) mapping systems currently utilize two operation modes. A single-antenna, dual-pass IFSAR operation mode is the first mode in which a platform carrying a single antenna traverses a flight path by the scene of interest twice collecting data. A dual-antenna, single-pass IFSAR operation mode is the second mode where a platform possessing two antennas flies past the scene of interest collecting data. There are advantages and disadvantages associated with both of these data collection modes. The single-antenna, dual-pass IFSAR operation mode possesses an imprecise knowledge of the antenna baseline length but allows for large antenna baseline lengths. This imprecise antenna baseline length knowledge lends itself to inaccurate target height scaling. The dual-antenna, one-pass IFSAR operation mode allows for a precise knowledge of the limited antenna baseline length but this limited baseline length leads to increased target height noise. This paper presents a new, innovative dual-antenna, dual-pass IFSAR operation mode which overcomes the disadvantages of the two current IFSAR operation modes. Improved target height information is now obtained with this new mode by accurately estimating the antenna baseline length between the dual flight passes using the data itself. Consequently, this new IFSAR operation mode possesses the target height scaling accuracies of the dual-antenna, one-pass operation mode and the height-noise performance of the one-antenna, dual-pass operation mode.
We examine the total-dose radiation response of capacitors and transistors with stacked Al{sub 2}O{sub 3} on oxynitride gate dielectrics with Al and poly-Si gates after irradiation with 10 keV X-rays. The midgap voltage shift increases monotonically with dose and depends strongly on both Al{sub 2}O{sub 3} and SiO{sub x}N{sub y} thickness. The thinnest dielectrics, of most interest to industry, are extremely hard to ionizing irradiation, exhibiting only {approx}50 mV of shift at a total dose of 10 Mrad(SiO{sub 2}) for the worst case bias condition. Oxygen anneals are found to improve the total dose radiation response by {approx}50% and induce a small amount of capacitance-voltage hysteresis. Al{sub 2}O{sub 3}/SiO{sub x}N{sub y} dielectrics which receive a {approx}1000 C dopant activation anneal trap {approx}12% more of the initial charge than films annealed at 550 C. Charge pumping measurements show that the interface trap density decreases with dose up to 500 krad(SiO{sub 2}). This surprising result is discussed with respect to hydrogen effects in alternative dielectric materials, and may be the result of radiation-induced hydrogen passivation of some of the near-interfacial defects in these gate dielectrics.