Investigation of bacterial transport in the large-block test, a thermally perturbed block of Topopah Spring Tuff

This study investigates the transport of bacteria in a large, thermally perturbed block of Topopah Spring tuff. The study was part of the Large-Block Test (LBT), thermochemical and physical studies conducted on a 10 ft x 10 ft x 14 ft block of volcanic tuff excavated on 5 of 6 sides out of Fran Ridge, Nevada. Two bacterial species, Bacillus subtilis and Arthrobacter oxydans, were isolated from the Yucca Mountain tuff. Natural mutants that can grow under the simultaneous presence of the two antibiotics, streptomycin and rifampicin, were selected from these species by laboratory procedures. The double-drug-resistant mutants, which could be thus distinguished from the indigenous species, were injected into the five heater boreholes of the large block hours before heating was initiated. The temperature, as measured 5 cm above one of the heater boreholes, rose slowly and steadily over a matter of months to a maximum of 142 C. Samples (cotton cloths inserted the length of the hole, glass fiber swabs, and filter papers) were collected from the boreholes that were approximately 5 ft below the injection points. Double-drug-resistant bacteria were found in the collection boreholes nine months after injection. Surprisingly, they also appeared in the heater boreholes where the temperature had been sustainably high throughout the test. These bacteria appear to be the species that were injected. The number of double-drug-resistant bacteria that were identified in the collection boreholes increased with time. An apparent homogeneous distribution among the observation boreholes and heater boreholes suggests that a random motion could be the pattern that the bacteria migrated in the block. These observations indicated the possibility of rapid bacterial transport in a thermally perturbed geologic setting

Lifetime Assessments of Weapon Organics and Polymers FY05 Annual Report

Non-nuclear organics, while not yet regarded to be at risk, figure in a large percentage of Significant Findings Investigations. Further, early application of advanced lifetime, compatibility, and base-lining assessments for LEP replacement materials and emerging materials for the Reliable Replacement Warhead (RRW) provides data for rational material choices. This task is currently assessing the chemical and mechanical characteristics of a variety of weapon organics prioritized by the risk-consequence of material aging. The majority of effort to date has been dedicated to silicone elastomer components known to lose their load resistance with age, with additional effort dedicated to urethane adhesives. This fiscal year, we have focused on initial aging studies of UNI620-3, a candidate replacement material for DC745U, and Adiprene (LW520). Aging studies of S5455, originally scheduled for testing in FY05, were postponed until FY07. We have initiated aging studies on these materials by employing accelerated aging tests with exposure to Co-60 {gamma}-radiation and elevated temperatures and studying their mechanical properties using a variety of analytical tools including nuclear magnetic resonance (NMR), dynamic mechanical analysis (DMA), and differential scanning calorimetry (DSC). Additionally, we have investigated aging signatures present in parts returned from surveillance as well as initiated long and short term stress relaxation studies for a thorough understanding of compression set occurring in silicone elastomers components. Additional investigations of aging processes in fluoropolymer binders and the combined effects of radiation and tensile set on silicone pads were performed. Finally, we have used temperature programmed desorption (TPD) studies to significantly improve the accuracy of our H{sub 2}O outgassing model in comparison with last year through the use of the isoconversion technique as well as to measure the equilibrium vapor pressure of hydrogenated DPB pellets. This report satisfies the milestones/deliverables for the L3 task 'Update chemical and mechanical aging models for cushion/pads/adhesives' and all data will be input into the L2 milestone 'Bill's token L2 milestone'

Magnetic Resonance Based Diagnostics for Polymer Production and Surveillance

In an effort to develop a magnetic resonance based diagnostic tool to be used for polymer production and surveillance, we have investigated the use of magnetic resonance imaging (MRI) and unilateral relaxometry. MRI provides a spatial map of the polymer, which can be correlated to the structure heterogeneity. Though highly detailed information can be obtained with MRI, the high equipment cost and expertise required to operate the system makes it a poor choice for a production setting. Unilateral relaxometry via the NMR MOUSE provides rapid, inexpensive polymer screening, useful in the development in new polymer parts or to identify potentially defective components. The NMR ProFiler (originally called the NMR MOUSE) was procured by Kansas City originally for production support of the W80 LEP with future applications as a surveillance diagnostic. A robotic autosampler has been designed allowing the detection of several components without the need for any human interaction. A summary of the qualification experiments and results to date from the ProFiler and the robotic unit will be presented

Evidence of gating in hundred nanometer diameter pores: an experimental and theoretical study

We report on the observation of an unexpected gating mechanism at the 100 nm scale on track-etched polycarbonate membranes. Transport measurements of methyl viologen performed by absorption spectroscopy under various pH conditions demonstrated that perfect gating was achieved for 100 nm diameter pores at pH 2, while the positively charged molecular ions moved through the membrane according to diffusion laws at pH 5. An oppositely charged molecular ion, naphthalene disulfonate, in the same membrane, showed the opposite trend: diffusion of the negative ion at pH 2 and perfect gating at pH 5. The influence of parameters such as ionic strength and membrane surface coating were also investigated. A theoretical study of the system shows that at this larger length scale the magnitude of the electric field in the vicinity of the pores is too small to account for the experimental observations, rather, it is the surface trapping of the mobile ion (Cl{sup -} or Na{sup +}) which gives rise to the gating phenomena. This surprising effect might have potential applications for high-throughput separation of large molecules and bio-organisms

Nutrient limitation and microbially mediated chemistry: studies using tuff inoculum obtained from the Exploratory Studies Facility, Yucca Mountain

Flow-through bioreactors are used to investigate the relationship between the supply (and limitation) of major nutrients required by microorganisms (C, N, P, S) and effluent chemistry to obtain data that can be useful to develop models of microbially mediated aqueous chemistry. The bioreactors were inoculated with crushed tuff from Yucca Mountain. Six of the 14 bioreactor experiments currently in operation have shown growth, which occurred in as few as 5 days and as much as a few months after initiation of the experiment. All of the bioreactors exhibiting growth contained glucose as a carbon source, but other nutritional components varied. Chemical signatures of each bioreactor were compared to each other and selected results were compared to computer simulations of the equivalent abiotic chemical reactions. At 21 C, the richest medium formulation produced a microbial community that lowered the effluent pH from 6.4 to as low as 3.9. The same medium formulation at 50 C produced no significant change in pH but caused a significant increase in Cl after a period of 200 days. Variations in concentrations of other elements, some of which appear to be periodic (Ca, Mg, etc.) also occur. Bioreactors fed with low C, N, P, S media showed growth, but had stabilized at lower cell densities. The room temperature bioreactor in this group exhibited a phospholipid fatty acid (PLFA) signature of sulfur- or iron-reducing bacteria, which produced a significant chemical signature in the effluent from that bioreactor. Growth had not been observed yet in the alkaline bioreactors, even in those containing glucose. The value of combining detailed chemical and community (e.g., ester-linked PLFA) analyses, long-duration experiments, and abiotic chemical models to distinguish chemical patterns is evident. Although all of the bioreactors contain the same initial microorganisms and mineral constituents, PLFA analysis demonstrates that both input chemistry and temperature determine the character of the long-term population of microorganisms. Where microbial growth occurs, that community can impact the chemistry of water significantly. These principles are well known, but we note their relevance to modeling microbially mediated chemistry. We recognize, in addition to microbial growth, three categories of chemical effects, each of which will require a different approach and constitutive equation(s): (1) unidirectional bacterial modification of the chemistry (i.e., pH) that is directly related to the dominance of particular species, (2) secondary impact of direct microbial modifications (i.e., increased dissolution of solids as a result of reduced pH), and (3) cyclical effects that may be attributed to internal regulation (e.g., osmoregulation or internal pH regulation) or evolution of the microbial communit

Chemical Origins of Permanent Set in a Peroxide Cured Filled Silicone Elastomer - Tensile and 1H NMR Analysis

The aging of a commercial filled siloxane polymeric composite in states of high stress and Co-60 {gamma}-radiation exposure has been studied. DC-745 is a commercially available silicone elastomer consisting of dimethyl, methyl-phenyl, and vinyl-methyl siloxane monomers crosslinked with a peroxide vinyl specific curing agent. It is filled with {approx}30 wt.% mixture of high and low surface area silicas. This filled material is shown to be subject to permanent set if exposed to radiation while under tensile stress. Tensile modulus measurements show that the material gets marginally softer with combined radiation exposure and tensile strain as compared to material exposed to radiation without tensile strain. In addition, the segmental dynamics as measured by both uniaxial NMR relaxometry and Multiple Quantum NMR methods indicate that the material is undergoes radiatively-induced crosslinking in the absence of tensile strain and a combination of crosslinking and strain dependent increase in dynamic order parameter for the network chains. The MQ-NMR also suggests a small change in the number of polymer chains associated with the silica filler surface. Comparison of the prediction of the relative change in crosslink density from the NMR data as well as solvent swelling data and from that predicted from the Tobolsky model suggest that degradation leads to a deviation from Gaussian chain statistics and the formation of increased numbers of elastically ineffective network chains

Influence of Surface Composition on Electronic Transport through Naked Nanocrystal Networks

Influence of Surface Composition on Electronic Transport through Naked Nanocrystal Network

Nanocrystal-based active layers with tailored interfaces and architectures for advanced energy applications

The properties of tasked nanocrystals in energy-related devices are strongly dependent on the presence and chem. nature of ligands at their surface, and the architectures they assume in electroactive layers. Here we will describe an exceptionally versatile class of reagents for native ligand stripping of carboxylate-, phosphonate- and amine- passivated nanocrystals, resulting in either bare or BF4-/DMF-passivated surfaces depending on the material used. These reagents were effective both for thin films of nanocrystals as well as their dispersions. Significantly, no etching of the nanocrystals was obsd. We will also show that dispersions of ligand stripped nanocrystals are useful as nanoinks and are amenable to architecturing at the mesoscale using suitable macromol. tamplating agents that make particular use of specific and dynamic mol. interactions at the nanocrystal surface. Structured electroactive layers as such are poised to overcome challenges assocd. with electrochem. reactions occurring at accessible interfaces

Modulation of Carrier Type in Nanocrystal-in-Matrix Composites by Interfacial Doping

Inorganic nanocomposites synthesized by combination of colloidal nanocrystals (NCs) and inorganic clusters have recently emerged as new materials with novel and unique functionalities. Much of the demonstrated promise of nanocomposites derives from the unique interactions between NC and matrix components - this generates new material properties, which direct unique transport behavior in the overall solid or nanocomposite - be it mass, charge, or heat. While measured empirically, it has remained largely impossible to take an a priori look at material properties and use those as a guideline to design desired transport behavior. Fundamentally, this is because the structural and electronic changes manifest at those interfaces have remained hidden from examination. Here, we provide experimental evidence that transport behavior in nanocrystal-in-matrix (NIM) composites is dictated primarily by interfacial charge transfer associated with electronic and structural reconstructions as the composite forms. Our approach building continuous composite superlattices serves as a starting point for systematic probing of the nanointerface of NIM composites via ultrathin films. A combination of field effect transistor device characterization and photoemission spectroscopy reveals the systematic dependence of the polarity of charge transfer on the selection of matrix materials in NIM composites. We use this insight to combine, by design, different components to tune the carrier type in NIM composites