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At least 1,225 records · Page 68

Scoping, Tailoring, and Abstraction Refinement in the Hazard Assessment Process

Hazard assessment is an engineering activity that produces insight into which states of thing being engineered might be hazardous. In aviation contexts, it is often performed for certification credit at both the aircraft and system levels during the early design phase of the system’s lifecycle. However, novel aircraft paradigms such as urban air mobility (UAM) operations might either violate assumptions on which traditional aviation hazard assessment is based or simply possess attributes that would make other approaches more effective. In this paper, we define the key concepts underpinning hazard assessment and identify the limitations and assumptions inherent in hazard analysis. We analyze popular techniques to show how they embody these key concepts. We identify ways in which hazard assessment may be scoped and tailored to an application. And, using worked examples, we discuss how, where, and why such tailoring might be needed, especially in novel contexts.

Aviation Safety↗

Computational Investigations of Trichoderma Reesei Cel7A Suggest New Routes for Enzyme Activity Improvements [Abstract Only]

The Trichoderma reesei Family 7 cellulase (Cel7A) is a key industrial enzyme in the production of biofuels from lignocellulosic biomass. It is a multi-modular enzyme with a Family 1 carbohydrate-binding module, a flexible O-glycosylated linker, and a large catalytic domain. We have used simulation to elucidate new functions for the 3 sub-domains, which suggests new routes to increase the activity of this central enzyme. These findings include new roles for glycosylation, which we have shown can be used to tune the binding affinity. We have also examined the structures of the catalytically-active complex of Cel7A and its non-processive counterpart, Cel7B, engaged on cellulose, which suggests allosteric mechanisms involved in chain binding when these cellulases are complexed on cellulose. Our computational results also suggest that product inhibition varies significantly between Cel7A and Cel7B, and we offer a molecular-level explanation for this observation. Finally, we discuss simulations of the absolute and relative binding free energy of cellulose ligands and various mutations along the CD tunnel, which will affect processivity and the ability of Cel7A (and related enzymes) to digest cellulose. These results highlight new considerations in protein engineering for processive and non-processive cellulases for production of lignocellulosic biofuels.

09 BIOMASS FUELS↗

RHENIUM SOLUBILITY IN BOROSILICATE NUCLEAR WASTE GLASS IMPLICATIONS FOR THE PROCESSING AND IMMOBILIZATION OF TECHNETIUM-99 (AND SUPPORTING INFORMATION WITH GRAPHICAL ABSTRACT)

The immobilization of 99Tc in a suitable host matrix has proved a challenging task for researchers in the nuclear waste community around the world. At the Hanford site in Washington State in the U.S., the total amount of 99Tc in low-activity waste (LAW) is {approx} 1,300 kg and the current strategy is to immobilize the 99Tc in borosilicate glass with vitrification. In this context, the present article reports on the solubility and retention of rhenium, a nonradioactive surrogate for 99Tc, in a LAW sodium borosilicate glass. Due to the radioactive nature of technetium, rhenium was chosen as a simulant because of previously established similarities in ionic radii and other chemical aspects. The glasses containing target Re concentrations varying from 0 to10,000 ppm by mass were synthesized in vacuum-sealed quartz ampoules to minimize the loss of Re by volatilization during melting at 1000 DC. The rhenium was found to be present predominantly as Re7 + in all the glasses as observed by X-ray absorption near-edge structure (XANES). The solubility of Re in borosilicate glasses was determined to be {approx}3,000 ppm (by mass) using inductively coupled plasma-optical emission spectroscopy (ICP-OES). At higher rhenium concentrations, some additional material was retained in the glasses in the form of alkali perrhenate crystalline inclusions detected by X-ray diffraction (XRD) and laser ablation-ICP mass spectrometry (LA-ICP-MS). Assuming justifiably substantial similarities between Re7 + and Tc 7+ behavior in this glass system, these results implied that the processing and immobilization of 99Tc from radioactive wastes should not be limited by the solubility of 99Tc in borosilicate LAW glasses.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

Waste Treatment And Immobilization Plant U. S. Department Of Energy Office Of River Protection Submerged Bed Scrubber Condensate Disposition Project - Abstract # 13460

The Hanford Waste Treatment and Immobilization Plant (WTP) will generate an off-gas treatment system secondary liquid waste stream [submerged bed scrubber (SBS) condensate], which is currently planned for recycle back to the WTP Low Activity Waste (LAW) melter. This SBS condensate waste stream is high in Tc-99, which is not efficiently captured in the vitrified glass matrix. A pre-conceptual engineering study was prepared in fiscal year 2012 to evaluate alternate flow paths for melter off-gas secondary liquid waste generated by the WTP LAW facility. This study evaluated alternatives for direct off-site disposal of this SBS without pre-treatment, which mitigates potential issues associated with recycling.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

Book of Extended Abstracts IWCE 2014

It is well known that Cu plays an important role in CdTe solar cell performance as a dopant. In this work, a finitedifference method is developed and used to simulate Cu diffusion in CdTe solar cells. In the simulations, which are done on a twodimensional (2D) domain, the CdTe is assumed to be polycrystalline, with the individual grains separated by grain boundaries. When used to fit experimental Cu concentration data, bulk and grain boundary diffusion coefficients and activation energies for CdTe can be extracted. In the past, diffusion coefficients have been typically obtained by fitting data to simple functional forms of limited validity. By doing full simulations, the simplifying assumptions used in those analytical models are avoided and diffusion parameters can thus be determined more accurately.

14 SOLAR ENERGY↗

Book of Extended Abstracts IWCE 2014

In this work, we report on developing 1D reaction-diffusion solver to understand the kinetics of p-type doping formation in CdTe absorbers and to shine some light on underlying causes of metastabilities observed in CdTe PV devices. Evolution of intrinsic and Cu-related defects in CdTe solar cell has been studied in time-space domain self-consistently with free carrier transport and Poisson equation. Resulting device performance was simulated as a function of Cu diffusion anneal time showing pronounced effect the evolution of associated acceptor and donor states can cause on device characteristics. Although 1D simulation has intrinsic limitations when applied to poly-crystalline films, the results suggest strong potential of the approach in better understanding of the performance and metastabilities of CdTe photovoltaic device.

14 SOLAR ENERGY↗

An Innovative Carbonate Fuel Cell Matrix, Abstract #188

The electrolyte matrix in direct carbonate fuel cell (DFC) is a microporous ceramic structure sandwiched between the electrodes to isolate the fuel from the oxidant, store electrolyte and facilitate ionic transport. FCE has advanced DFC electrolyte matrix over the years and demonstrated that the matrix meets the requirements for greater than 5 year life based on accelerated tests and field stack operations. However, development of advanced designs and materials that can further increase the performance and extend cell life will enable accelerated MCFC deployment. This paper will report the progress on the development of an unique and innovative matrix design that offers numerous benefits to the carbonate fuel cell performance and durability. In addition, this paper will also review parameters that affect matrix material stability and approaches to extend cell life.

08 HYDROGEN↗

Effect of oxidation state and ionic strength on sorption of actinides (Th, U, Np, Am) to geologic media [Abstract and References Only]

The degree of conservatism in the estimated sorption partition coefficients (K d s) used in a performance assessment model is being evaluated based on a complementary batch and column method. The main focus of this work is to investigate the role of ionic strength, solution chemistry, and oxidation state (III-VI) in actinide sorption to dolomite rock. Based on redox conditions and solution chemistry expected at the WIPP, possible actinide species include Pu(III), Pu(IV), U(IV), U(VI), Np(IV), Np(V), Am(III), and Th(IV).

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗

Demo Abstract: Toward Data-driven Demand-Response Optimization in a Campus Microgrid

We describe and demonstrate a prototype software architecture to support data-driven demand response optimization (DR) in the USC campus microgrid, as part of the Los Angeles Smart Grid Demonstration Project. The architecture includes a semantic information repository that integrates diverse data sources to support DR, demand forecasting using scalable machine-learned models, and detection of load curtailment opportunities by matching complex event patterns.

Amam, Saima↗

Thermomechanical Modeling of Sintered Silver - A Fracture Mechanics-based Approach: Extended Abstract: Preprint

Sintered silver has proven to be a promising candidate for use as a die-attach and substrate-attach material in automotive power electronics components. It holds promise of greater reliability than lead-based and lead-free solders, especially at higher temperatures (less than 200 degrees Celcius). Accurate predictive lifetime models of sintered silver need to be developed and its failure mechanisms thoroughly characterized before it can be deployed as a die-attach or substrate-attach material in wide-bandgap device-based packages. We present a finite element method (FEM) modeling methodology that can offer greater accuracy in predicting the failure of sintered silver under accelerated thermal cycling. A fracture mechanics-based approach is adopted in the FEM model, and J-integral/thermal cycle values are computed. In this paper, we outline the procedures for obtaining the J-integral/thermal cycle values in a computational model and report on the possible advantage of using these values as modeling parameters in a predictive lifetime model.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗