The production and aging of silicone materials remains an important issue in the weapons stockpile due to their utilization in a wide variety of components and systems within the stockpile. Changes in the physical characteristics of silicone materials due to long term desiccation has been identified as one of the major aging effects observed in silicone pad components. Here we report relaxation nuclear magnetic resonance imaging (R-NMRI) spectroscopy characterization of the silica-filled and unfilled polydimethylsiloxane (PDMS) and polydiphenylsiloxane (PDPS) copolymer (M9787) silicone pads within desiccating environments. These studies were directed at providing additional details about the heterogeneity of the desiccation process. Uniform NMR spin-spin relaxation time (T2) images were observed across the pad thickness indicating that the drying process is approximately uniform, and that the desiccation of the M9787 silicone pad is not a H2O diffusion limited process. In a P2O5 desiccation environment, significant reduction of T2 was observed for the silica-filled and unfilled M9787 silicone pad for desiccation up to 225 days. A very small reduction in T2 was observed for the unfilled copolymer between 225 and 487 days. The increase in relative stiffness with desiccation was found to be higher for the unfilled copolymer. These R-NMRI results are correlated to local changes in the modulus of the material
Oxygen plasma treatment of poly(dimethylsiloxane) (PDMS) thin films produced a hydrophilic surface that was biocompatible and resistant to biofouling in microfluidic studies. Thin film coatings of PDMS were previously developed to provide protection for semiconductor-based microoptical devices from rapid degradation by biofluids. However, the hydrophobic surface of native PDMS induced rapid clogging of microfluidic channels with glial cells. To evaluate the various issues of surface hydrophobicity and chemistry on material biocompatibility, we tested both native and oxidized PDMS (ox-PDMS) coatings as well as bare silicon and hydrophobic alkane and hydrophilic oligoethylene glycol silane monolayer coated under both cell culture and microfluidic studies. For the culture studies, the observed trend was that the hydrophilic surfaces supported cell adhesion and growth, whereas the hydrophobic ones were inhibitive. However, for the fluidic studies, a glass-silicon microfluidic device coated with the hydrophilic ox-PDMS had an unperturbed flow rate over 14 min of operation, whereas the uncoated device suffered a loss in rate of 12%, and the native PDMS coating showed a loss of nearly 40%. Possible protein modification of the surfaces from the culture medium also were examined with adsorbed films of albumin, collagen, and fibrinogen to evaluate their effect on cell adhesion.
Shock wave compression of poled Pb{sub 0.99}(Zr{sub 0.95}Ti{sub 0.05}){sub 0.98}Nb{sub 0.02}O{sub 3} (PZT 95/5-2Nb) results in rapid depoling and release of bound charge. In the current study, planar-impact experiments with this material were conducted on a gas-gun facility to determine Hugoniot states, to examine constitutive mechanical properties during shock propagation, and to investigate shock-induced depoling characteristics. A previous article summarized results from the first two of these areas, and this article summarizes the depoling studies. A baseline material, similar to materials used in previous studies, was examined in detail. More limited experiments were conducted with other materials to investigate the effects of different porous microstructures. Experiments were conducted over a wide range of conditions in order to examine the effects of varying shock strength, poling orientation, input wave shape, electric field strength, porous microstructure at a fixed density, and initial density. Depoling currents were recorded in an external circuit under either short-circuit or high-field conditions, and provide a convenient means of examining the kinetics associated with the ferroelectric-to-antiferroelectric phase transition. For sufficiently strong shock waves, the measured short-circuit currents indicate that the phase transition is very rapid and essentially complete. As shock strengths are reduced, short-circuit currents show increasing rise times and decreasing final levels at the end of shock transit. These features indicate that the transition kinetics can be characterized in terms of both a transition rate and a limiting degree of transition achieved in a given shock experiment. The presence of a strong electric field does not appear to have a significant effect on transition kinetics at high shock stresses, but has a strong effect at low stresses. As was found for constitutive mechanical properties, only small effects on measured currents resulted from differences in the porous microstructure of common-density materials, but large effects were observed when initial density was varied. To examine transition kinetics in more detail, short-circuit currents obtained with the baseline material and several approximate methods were used to estimate values for the rate and degree of transition as functions of shock properties. Differences between these currents and currents measured in high-field experiments using the same impact conditions were used to examine field effects on transition kinetics and corresponding dielectric properties.
The physical and welding a metallurgy of gadolinium- (Gd-) enriched Ni-based alloys has been examined using a combination of differential thermal analysis, hot ductility testing. Varestraint testing, and various microstructural characterization techniques. Three different matrix compositions were chosen that were similar to commercial Ni-Cr-Mo base alloys (UNS N06455, N06022, and N06059). A ternary Ni-Cr-Gd alloy was also examined. The Gd level of each alloy was {approx}2 wt-%. All the alloys initiated solidification by formation of primary austenite and terminated solidification by a Liquid {gamma} + Ni{sub 5}Gd eutectic-type reaction at {approx}1270 C. The solidification temperature ranges of the alloys varied from {approx}100 to 130 C (depending on alloy composition). This is a substantial reduction compared to the solidification temperature range to Gd-enriched stainless steels (360 to 400 C) that terminate solidification by a peritectic reaction at {approx}1060 C. The higher-temperature eutectic reaction that occurs in the Ni-based alloys is accompanied by significant improvements in hot ductility and solidification cracking resistance. The results of this research demonstrate that Gd-enriched Ni-based alloys are excellent candidate materials for nuclear criticality control in spent nuclear fuel storage applications that require production and fabrication of large amounts of material through conventional ingot metallurgy and fusion welding techniques.
Atomistic simulations were performed to investigate high temperature wetting phenomena for metals. A sessile drop configuration was modeled for two systems: Ag(l) on Cu and Pb(l) on Cu. The former case is an eutectic binary and the wetting kinetics were greatly enhanced by the presence of aggressive interdiffusion between Ag and Cu. Wetting kinetics were directly dependent upon dissolution kinetics. The dissolution rate was nearly identical for Ag(l) on Cu(100) compared to Cu(111); as such, the spreading rate was very similar on both surfaces. Pb and Cu are bulk immiscible so spreading of Pb(l) on Cu occurred in the absence of significant substrate dissolution. For Pb(l) on Cu(111) a precursor wetting film of atomic thickness emerged from the partially wetting liquid drop and rapidly covered the surface. For Pb(l) on Cu(100), a foot was also observed to emerge from a partially wetting drop; however, spreading kinetics were dramatically slower for Pb(l) on Cu(100) than on Cu(111). For the former, a surface alloying reaction was observed to occur as the liquid wet the surface. The alloying reaction was associated with dramatically decreased wetting kinetics on Cu(100) versus Cu(111), where no alloying was observed. These two cases demonstrate markedly different atomistic mechanisms of wetting where, for Ag(l) on Cu, the dissolution reaction is associated with increased wetting kinetics while, for Pb(l) on Cu, the surface alloying reaction is associated with decreased wetting kinetics.
The force on and the heat flux to the NASA Mars Reconnaissance Orbiter (MRO) during drag passes are analyzed. Aerobraking takes place in the higher/rarefied levels of the Martian atmosphere, where traditional continuum flui d dynamics methods cannot be applied. Therefore, molecular gas dynamics simulations such as the Direct Simulation Monte Carlo Method are used to calculate these flow fields and provide heating and aerodynamic predictions for the vehicles. The heating and aerodynamic predictions calculated for the MRO include the heat transfer coefficient (C{sub h}), calculated for a number of angles of attack and the drag coefficient (C{sub D}) calculated for a number of altitudes and velocities. Bridging relations are sought that are applicable over the range of conditions of interest. A sensitivity analysis of the results to the chemical reaction rates, surface accommodation and temperature is also performed.
This reports tabulates the Test and Evaluation results of the Access Class Switch tests conducted by members of Department 9336. About 15 switches were reviewed for use in the enterprise network as access tier switches as defined in a three tier architecture. The Access Switch Tier has several functions including: aggregate customer desktop ports, preserve and apply QoS tags, provide switched LAN access, provide VLAN assignment, as well as others. The typical switch size is 48 or less user ports. The evaluation team reviewed network switch evaluation reports from the Tolly Group as well as other sources. We then used these reports as a starting point to identify particular switches for evaluation. In general we reviewed the products of dominant equipment manufacturers. Also, based on architectural design requirements, the majority of the switches tested were of relatively small monolithic unit variety.
The effects of ruffling on the axial ligation properties of a series of nickel(II) tetra(alkyl)porphyrins have been investigated with UV-visible absorption spectroscopy, resonance Raman spectroscopy, X-ray crystallography, classical molecular mechanics calculations, and normal-coordinate structural decomposition analysis. For the modestly nonplanar porphyrins, porphyrin ruffling is found to cause a decrease in binding affinity for pyrrolidine and piperidine, mainly caused by a decrease in the binding constant for addition of the first axial ligand; ligand binding is completely inhibited for the more nonplanar porphyrins. The lowered affinity, resulting from the large energies required to expand the core and flatten the porphyrin to accommodate the large high-spin nickel(II) ion, has implications for nickel porphyrin-based molecular devices and the function of heme proteins and methyl-coenzyme M reductase.
{sup 13}CH{sub 4} was injected with a toroidally-symmetric gas system into 22 identical lower-single-null L-mode discharges on DIII-D. The injection level was adjusted so that it did not significantly perturb the core or divertor plasmas, with a duration of {approx}3 s on each shot, for a total of {approx}300 T L of injected particles. The plasma shape remained very constant; the divertor strike points were controlled to {approx}1 cm at the divertor plate. At the beginning of the subsequent machine vent, 29 carbon tiles were removed for nuclear reaction analysis of {sup 13}C content to determine regions of carbon deposition. It was found that only the tiles inboard of the inner strike point had appreciable {sup 13}C above background. Visible spectroscopy measurements of the carbon injection and comparisons with modeling are consistent with carbon transport by means of scrape-off layer flow.
The objective of this research was the development of tools and techniques for the identification of critical nodes within critical infrastructures. These are nodes that, if disrupted through natural events or terrorist action, would cause the most widespread, immediate damage. This research focuses on one particular element of the national infrastructure: the bulk power system. Through the identification of critical elements and the quantification of the consequences of their failure, site-specific vulnerability analyses can be focused at those locations where additional security measures could be effectively implemented. In particular, with appropriate sizing and placement within the grid, distributed generation in the form of regional power parks may reduce or even prevent the impact of widespread network power outages. Even without additional security measures, increased awareness of sensitive power grid locations can provide a basis for more effective national, state and local emergency planning. A number of methods for identifying critical nodes were investigated: small-world (or network theory), polyhedral dynamics, and an artificial intelligence-based search method - particle swarm optimization. PSO was found to be the only viable approach and was applied to a variety of industry accepted test networks to validate the ability of the approach to identify sets of critical nodes. The approach was coded in a software package called Buzzard and integrated with a traditional power flow code. A number of industry accepted test networks were employed to validate the approach. The techniques (and software) are not unique to power grid network, but could be applied to a variety of complex, interacting infrastructures.
In this article we report on the electrical characteristics of single wall carbon nanotubes (SWCNTs) wrapped with single-stranded deoxyribonucleic acid (ssDNA). We fabricate these devices using a solution-based method whereby SWCNTs are dispersed in aqueous solution using 20-mer ssDNA, and are placed across pairs of Au electrodes using alternating current dielectrophoresis (ACDEP). In addition to current voltage characteristics, we evaluate our devices using scanning electron microscopy and atomic force microscopy. We find that ACDEP with ssDNA based suspensions results in individual SWCNTs bridging metal electrodes, free of carbon debris, while similar devices prepared using the Triton X-100 surfactant yield nanotube bundles, and frequently have carbon debris attached to the nanotubes. Furthermore, the presence of ssDNA around the nanotubes does not appear to appreciably affect the overall electrical characteristics of the devices. In addition to comparing the properties of several devices prepared on nominally clean Au electrodes, we also investigate the effects of self-assembled monolayers of C{sub 14}H{sub 29}-SH alkyl thiol and benzyl mercaptan on the adhesion and electrical transport across the metal/SWCNT/metal devices.
The Sandia National Laboratories Nuclear Weapons Strategic Management Unit (NWSMU) is pursuing performance excellence, by focusing on compliance with the ISO 9001:2000 standard for quality management systems. The NWSMU also intends to achieve ISO Certification and eventually reach levels of performance excellence that are consistent with those of Malcolm Baldrige National Quality Award winners. In that context, this report documents a study undertaken to answer these questions: {sm_bullet} Would achieving ISO 9001:2000 compliance or certification help an organization prepare to achieve Baldrige-level performance excellence? {sm_bullet} Would pursuing Baldrige-based performance excellence help an organization achieve ISO certification? {sm_bullet} What are the areas where the Baldrige and ISO systems are most closely aligned? The study produced answers to those questions, as well as a number of comparisons and contrasts between the ISO standard and the Baldrige criteria.
Laser-induced fluorescence-dip spectroscopy was used to measure two-dimensional (2-D) maps of the electric field present in an argon discharge above a ratio frequency-powered, nonuniform surface. Electric fields were obtained from experimentally measured Stark shifts of the energy of argon Rydberg states. The 2-D maps of the electric fields demonstrated that nonuniformities present on an electrode have long-range effects on the structure of the sheath.
We performed molecular dynamics simulations of chain systems to investigate general relationships between the system mobility and computed scalar quantities. Three quantities were found that had a simple one-to-one relationship with mobility: packing fraction, potential energy density, and the value of the static structure factor at the first peak. The chain center-of-mass mobility as a function of these three quantities could be described equally well by either a Vogel-Fulcher type or a power law equation.
Percolation theory is now standard in the analysis of polycrystalline materials where the grain boundaries can be divided into two distinct classes, namely 'good' boundaries that have favorable properties and 'bad' boundaries that seriously degrade the material performance. Grain-boundary engineering (GBE) strives to improve material behavior by engineering the volume fraction c and arrangement of good grain boundaries. Two key percolative processes in GBE materials are the onset of percolation of a strongly connected aggregate of grains, and the onset of a connected path of weak grain boundaries. Using realistic polycrystalline microstructures, we find that in two dimensions the threshold for strong aggregate percolation c{sub SAP} and the threshold for weak boundary percolation c{sub WBP} are equivalent and have the value c{sub SAP} = c{sub WBP} = 0.38(1), which is slightly higher than the threshold found for regular hexagonal grain structures, c{sub RH} = 2 sin({pi}/18) = 0.347. In three dimensions strong aggregate percolation and weak boundary percolation occur at different locations and we find c{sub SAP} = 0.12(3) and c{sub WBP} = 0.77(3). The critical current in high T{sub c} materials and the cohesive energy in structural systems are related to the critical manifold problem in statistical physics. We develop a theory of critical manifolds in GBE materials, which has three distinct regimes: (1) low concentrations, where random manifold theory applies, (2) critical concentrations where percolative scaling theory applies, and (3) high concentrations, c > c{sub SAP}, where the theory of periodic elastic media applies. Regime (3) is perhaps most important practically and is characterized by a critical length L{sub c}, which is the size of cleavage regions on the critical manifold. In the limit of high contrast {open_square} {yields} 0, we find that in two dimensions L{sub c} {proportional_to} gc/(1-c), while in three dimensions L{sub c} {proportional_to} g exp[b{sub 0}c/(1-c)]/[c(1-c)]{sup 1/2}, where g is the average grain size, {open_square} is the ratio of the bonding energy of the weak boundaries to that of the strong boundaries, and b{sub 0} is a constant which is of order 1. Many of the properties of GBE materials can be related to L{sub c}, which diverges algebraically on approach to c=1 in two dimensions, but diverges exponentially in that limit in three dimensions. We emphasize that GBE percolation processes and critical manifold behavior are very different in two dimensions as compared to three dimensions. For this reason, the use of two dimensional models to understand the behavior of bulk GBE materials can be misleading.