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Conformation of Single Pentablock Ionomer Chains in Dilute Solutions

Sandia journal manuscript; Not yet accepted for publication

Aryal, Dipak; Perahia, Dvora; Grest, Gary S.

The conformation of single chain pentablock ionomers (A-B-C-B-A) containing randomly sulfonated polystyrene in the center block, tethered to poly-ethylene-r-propylene end-capped by poly-t-butyl styrene is studied in dilute solutions by molecular dynamics simulations. Multi-block copolymers offer a means to tailor several properties into one molecule, taking advantage of their rich phase diagram together with unique properties of specific blocks. For this pentablock the ionic block facilitates transport while the A and B components are incorporated for mechanical stability. The present study investigates the confirmation of a single chain of pentablock ionomer of molecular weight Mw ~ 50,000 g/mol and sulfonated polystyrene of the same molecular weight as that of the center block for six sulfonation fractions f from f=0.0-0.55. For the sulfonated systems Na+ counterions are included. Results for the equilibrium conformation of the chains and the three blocks in water and 1:1 mixture of cyclohexane and n-heptane are compared to simulations in implicit poor solvents with dielectric constants ε =1.0 and 77.73. In water, the pentablock is collapsed with sulfonated groups on the outer surface. As the sulfonation fraction f increases, the ionic, center block is increasingly segregated from the hydrophobic regions. In the 1:1 mixture of cyclohexane and heptane both the flexible and end blocks are swollen while the center ionic block is collasped for f>0, while for f=0 all blocks are swollen. In both implicit poor solvents the pentablock is collapsed into a nearly spherical shape for all f. The sodium counterions are dispersed widely throughout the simulation cell for both water and ε =77.73 whereas for ε =1.0 the counterions are largely condensed on the collapsed pentablock.

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TYPE Journal Article YEAR 2015
OSTI

Recent Progress and Future Potential of Magnetized Liner Inertial Fusion (MagLIF)

Sandia journal manuscript; Not yet accepted for publication

Slutz, Stephen A.; Gomez, Matthew R.; Sefkow, Adam B.; Sinars, Daniel; Hahn, Kelly; Hansen, Stephanie B.; Harding, Eric H.; Knapp, P.F.; Schmit, Paul; Jennings, Christopher A.; Awe, Thomas J.; Herrmann, M.C.; Hess, Mark H.; Johns, Owen; Lamppa, Derek C.; Martin, Matthew R.; Mcbride, Ryan; Geissel, Matthias; Rovang, Dean C.; Chandler, Gordon A.; Cooper, Gary; Cuneo, Michael E.; Harvey-Thompson, Adam J.; Peterson, K.J.; Porter, John L.; Robertson, G.K.; Rochau, G.A.; Ruiz, Carlos L.; Savage, Mark E.; Smith, Ian C.; Stygar, William A.; Vesey, Roger A.

The standard approaches to inertial confinement fusion (ICF) rely on implosion velocities greater than 300 km/s and spherical convergence to achieve the high fuel temperatures (T > 4 keV) and areal densities (ρr > 0.3 g/cm2) required for ignition1. Such high velocities are achieved by heating the outside surface of a spherical capsuleeither directly with a large number of laser beams (Direct Drive) or with x-rays generated within a hohlraum (Indirect Drive). A much more energetically efficient approach is to use the magnetic pressure generated by a pulsed power machine to directly drive an implosion. In this approach 5-10% of the stored energy can be converted to the implosion of a metal tube generally referred to as a “liner”. However, the implosion velocity is not very high 70-100 km/s and the convergence is cylindrical (rather than spherical) making it more difficult to achieve the high temperatures and areal densities needed for ignition.

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TYPE Journal Article YEAR 2015
OSTI

Better Incident Response with SCOT

Sandia journal manuscript; Not yet accepted for publication

Bruner, Todd

SCOT is an incident response management system and knowledge base designed for incident responders by incident responders. SCOT increases the effectiveness of the team without adding undue burdens. Focused on reducing the friction between analysts and their tools, SCOT enables analysts to document and share their research and response efforts in near real time. Automatically identifying indicators and correlating those indicators, SCOT helps analysts discover and respond to advanced threats.

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TYPE Journal Article YEAR 2015
OSTI

Confirming the Strength of Residential Roof Structures for Solar Installations

Sandia journal manuscript; Not yet accepted for publication

Dwyer, Stephen F.

Researchers at the U.S. Department of Energy’s Sandia National Laboratories conducted a first-ofits- kind study to help dispel misperceptions that many existing rooftops cannot carry the actual load created by rooftop solar photovoltaic (PV) installations. Test data on rooftop structure load capacity wasn’t previously available to the industry, and research to collect such data was made costly by the need to test each scaled structure to the point of failure. The Energy Department funded this study to provide scientific data to the industry that can decrease uncertainty, help eliminate misperceptions, and ultimately alleviate extraneous solar PV permitting costs.

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TYPE Journal Article YEAR 2015
OSTI

Computational redesign reveals allosteric mutation hotspots of organophosphate hydrolase that enhance organophosphate hydrolysis

Sandia journal manuscript; Not yet accepted for publication

Jacob, Reed B.; Ding, Feng; Ye, Dongmei Y.; Ackerman, Eric; Dokholyan, Nikolay V.

Organophosphates are widely used for peaceful (agriculture) and military purposes (chemical warfare agents). The extraordinary toxicity of organophosphates and the risk of deployment, make it critical to develop means for their rapid and efficient deactivation. Organophosphate hydrolase (OPH) already plays an important role in organophosphate remediation, but is insufficient for therapeutic or prophylactic purposes primarily due to low substrate affinity. Current efforts focus on directly modifying the active site to differentiate substrate specificity and increase catalytic activity. Here, we present a novel strategy for enhancing the general catalytic efficiency of OPH through computational redesign of the residues that are allosterically coupled to the active site and validated our design by mutagenesis. Specifically, we identify five such hot-spot residues for allosteric regulation and assay these mutants for hydrolysis activity against paraoxon, a chemical-weapons simulant. A high percentage of the predicted mutants exhibit enhanced activity over wild-type (kcat =16.63 s-1), such as T199I/T54I (899.5 s-1) and C227V/T199I/T54I (848 s-1), while the Km remains relatively unchanged in our high-throughput cell-free expression system. Further computational studies of protein dynamics reveal four distinct distal regions coupled to the active site that display significant changes in conformation dynamics upon these identified mutations. These results validate a computational design method that is both efficient and easily adapted as a general procedure for enzymatic enhancement.

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TYPE Journal Article YEAR 2015
OSTI

Building detection in SAR imagery

Steinbach, Ryan M.

Current techniques for building detection in Synthetic Aperture Radar (SAR) imagery can be computationally expensive and/or enforce stringent requirements for data acquisition. I present two techniques that are effective and efficient at determining an approximate building location. This approximate location can be used to extract a portion of the SAR image to then perform a more robust detection. The proposed techniques assume that for the desired image, bright lines and shadows, SAR artifact effects, are approximately labeled. These labels are enhanced and utilized to locate buildings, only if the related bright lines and shadows can be grouped. In order to find which of the bright lines and shadows are related, all of the bright lines are connected to all of the shadows. This allows the problem to be solved from a connected graph viewpoint, where the nodes are the bright lines and shadows and the arcs are the connections between bright lines and shadows. For the first technique, constraints based on angle of depression and the relationship between connected bright lines and shadows are applied to remove unrelated arcs. The second technique calculates weights for the connections and then performs a series of increasingly relaxed hard and soft thresholds. This results in groups of various levels on their validity. Once the related bright lines and shadows are grouped, their locations are combined to provide an approximate building location. Experimental results demonstrate the outcome of the two techniques. The two techniques are compared and discussed.

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TYPE Thesis or Dissertation YEAR 2015
OSTI

Galerkin v. discrete-optimal projection in nonlinear model reduction

Sandia journal manuscript; Not yet accepted for publication

Carlberg, Kevin T.; Barone, Matthew F.; Antil, Harbir

Discrete-optimal model-reduction techniques such as the Gauss{Newton with Approximated Tensors (GNAT) method have shown promise, as they have generated stable, accurate solutions for large-scale turbulent, compressible ow problems where standard Galerkin techniques have failed. However, there has been limited comparative analysis of the two approaches. This is due in part to difficulties arising from the fact that Galerkin techniques perform projection at the time-continuous level, while discrete-optimal techniques do so at the time-discrete level. This work provides a detailed theoretical and experimental comparison of the two techniques for two common classes of time integrators: linear multistep schemes and Runge{Kutta schemes. We present a number of new ndings, including conditions under which the discrete-optimal ROM has a time-continuous representation, conditions under which the two techniques are equivalent, and time-discrete error bounds for the two approaches. Perhaps most surprisingly, we demonstrate both theoretically and experimentally that decreasing the time step does not necessarily decrease the error for the discrete-optimal ROM; instead, the time step should be `matched' to the spectral content of the reduced basis. In numerical experiments carried out on a turbulent compressible- ow problem with over one million unknowns, we show that increasing the time step to an intermediate value decreases both the error and the simulation time of the discrete-optimal reduced-order model by an order of magnitude.

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TYPE Journal Article YEAR 2015
OSTI

Benchmarking Adiabatic Quantum Optimization for Complex Network Analysis

Parekh, Ojas D.; Wendt, Jeremy; Shulenburger, Luke N.; Landahl, Andrew J.; Moussa, J.E.; Aidun, John B.

We lay the foundation for a benchmarking methodology for assessing current and future quantum computers. We pose and begin addressing fundamental questions about how to fairly compare computational devices at vastly different stages of technological maturity. We critically evaluate and offer our own contributions to current quantum benchmarking efforts, in particular those involving adiabatic quantum computation and the Adiabatic Quantum Optimizers produced by D-Wave Systems, Inc. We find that the performance of D-Wave's Adiabatic Quantum Optimizers scales roughly on par with classical approaches for some hard combinatorial optimization problems; however, architectural limitations of D-Wave devices present a significant hurdle in evaluating real-world applications. In addition to identifying and isolating such limitations, we develop algorithmic tools for circumventing these limitations on future D-Wave devices, assuming they continue to grow and mature at an exponential rate for the next several years.

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TYPE SAND Report YEAR 2015
DOIOSTI
Results 48601–48800 of 99,299
Results 48601–48800 of 99,299