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A many-electron tight binding method for the analysis of quantum dot systems

Journal of Applied Physics

Nielsen, Erik N.; Rahman, Rajib; Muller, Richard P.

We present a method which computes many-electron energies and eigenfunctions by a full configuration interaction, which uses a basis of atomistic tight-binding wave functions. This approach captures electron correlation as well as atomistic effects, and is well suited to solid state quantum dot systems containing few electrons, where valley physics and disorder contribute significantly to device behavior. Results are reported for a two-electron silicon double quantum dot as an example. © 2012 American Institute of Physics.

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TYPE Journal Article YEAR 2012
OSTIScopus

Thermoelectric energy harvesting from diurnal heat flow in the upper soil layer

Energy Conversion and Management

Whalen, Scott A.; Dykhuizen, Ronald C.

We built and tested a subterranean thermoelectric power source that converts diurnal heat flow through the upper soil layer into electricity. This paper describes the operation, design, and performance of the device. Key features of the power source include the use of bismuth-telluride thermopiles optimized for small ΔT and aerogel insulation to minimize thermal losses. The device weighs 0.24 kg and was designed with a flat form factor measuring 12 × 12 × 1.7 cm to facilitate modularity, packing, and assembly into larger arrays. One full year of field testing was performed between June 2009 and May 2010 in Albuquerque, New Mexico where the device generated an average power output of 1.1 mW. The season with the highest performance was spring (March-May) while the season of lowest performance was winter (November-January). During May 2010, the device generated an average power of 1.5 mW and a peak power of 9.8 mW at 9.3 V. Ten years of continuous operation at 1.1 mW would yield an energy density and specific energy of 1384 W h/L and 1430 W h/kg respectively, which is competitive with chemical batteries and is orders of magnitude greater than published subterranean and ambient thermoelectric harvesters. Numerical simulations show that performance is sensitive to the thermal properties of the soil and environmental conditions. This class of energy harvester may provide an option for supplemental power, or possibly primary power, for low power remote sensing applications. © 2012 Elsevier Ltd. All rights reserved.

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TYPE Journal Article YEAR 2012
DOIOSTIScopus

Multiparameter spectral representation of noise-induced competence in bacillus subtilis

IEEE/ACM Transactions on Computational Biology and Bioinformatics

Sargsyan, Khachik; Safta, Cosmin; Debusschere, Bert; Najm, Habib N.

In this work, the problem of representing a stochastic forward model output with respect to a large number of input parameters is considered. The methodology is applied to a stochastic reaction network of competence dynamics in Bacillus subtilis bacterium. In particular, the dependence of the competence state on rate constants of underlying reactions is investigated. We base our methodology on Polynomial Chaos (PC) spectral expansions that allow effective propagation of input parameter uncertainties to outputs of interest. Given a number of forward model training runs at sampled input parameter values, the PC modes are estimated using a Bayesian framework. As an outcome, these PC modes are described with posterior probability distributions. The resulting expansion can be regarded as an uncertain response function and can further be used as a computationally inexpensive surrogate instead of the original reaction model for subsequent analyses such as calibration or optimization studies. Furthermore, the methodology is enhanced with a classification-based mixture PC formulation that overcomes the difficulties associated with representing potentially nonsmooth input-output relationships. Finally, the global sensitivity analysis based on the multiparameter spectral representation of an observable of interest provides biological insight and reveals the most important reactions and their couplings for the competence dynamics. © 2013 IEEE.

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TYPE Journal Article YEAR 2012
ScopusOSTIDOI

Titanium tritide radioisotope heat source development: Palladium-coated titanium hydriding kinetics and tritium loading tests

Energy Conversion and Management

Shugard, Andrew D.; Van Blarigan, Peter

For applications requiring 5-20 mW electrical power for 10-20 years, tritium-based radioisotope thermoelectric generators may be an alternative to Pu-238 based devices. Tritium can be stored compactly on a titanium bed. However, one of the main challenges then becomes loading the heat source at temperatures compatible with existing bismuth telluride thermoelectric module technology (<300 °C). We find that a 180 nm palladium coating enables titanium to be loaded with hydrogen isotopes without the typical 400-500 °C vacuum activation step. Further, we observe that the hydriding kinetics of Pd coated and vacuum activated Ti are similar; both of which can be described by the Mintz-Bloch adherent film model, where the rate of hydrogen absorption is controlled by diffusion through an adherent metal-hydride layer. Finally, we design a prototype heat source vessel and demonstrate that it can be loaded completely, at temperatures below 300 °C, in less than 10 h. © 2012 Elsevier Ltd. All rights reserved.

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TYPE SAND Report YEAR 2012
DOIOSTIScopus

Use of a SPAR-H bayesian network for predicting human error probabilities with missing observations

11th International Probabilistic Safety Assessment and Management Conference and the Annual European Safety and Reliability Conference 2012, PSAM11 ESREL 2012

Groth, Katrina M.; Swiler, Laura P.

Many of the Performance Shaping Factors (PSFs) used in Human Reliability Analysis (HRA) methods are not directly measurable or observable. Methods like SPAR-H require the analyst to assign values for all of the PSFs, regardless of the PSF observability; this introduces subjectivity into the human error probability (HEP) calculation. One method to reduce the subjectivity of HRA estimates is to formally incorporate information about the probability of the PSFs into the methodology for calculating the HEP. This can be accomplished by encoding prior information in a Bayesian Network (BN) and updating the network using available observations. We translated an existing HRA methodology, SPAR-H, into a Bayesian Network to demonstrate the usefulness of the BN framework. We focus on the ability to incorporate prior information about PSF probabilities into the HRA process. This paper discusses how we produced the model by combining information from two sources, and how the BN model can be used to estimate HEPs despite missing observations. Use of the prior information allows HRA analysts to use partial information to estimate HEPs, and to rely on the prior information (from data or cognitive literature) when they are unable to gather information about the state of a particular PSF. The SPAR-H BN model is a starting point for future research activities to create a more robust HRA BN model using data from multiple sources.

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TYPE Conference YEAR 2012
OSTIScopus

Multiparameter spectral representation of noise-induced competence in bacillus subtilis

IEEE/ACM Transactions on Computational Biology and Bioinformatics

Sargsyan, Khachik; Safta, Cosmin; Debusschere, Bert; Najm, Habib N.

In this work, the problem of representing a stochastic forward model output with respect to a large number of input parameters is considered. The methodology is applied to a stochastic reaction network of competence dynamics in Bacillus subtilis bacterium. In particular, the dependence of the competence state on rate constants of underlying reactions is investigated. We base our methodology on Polynomial Chaos (PC) spectral expansions that allow effective propagation of input parameter uncertainties to outputs of interest. Given a number of forward model training runs at sampled input parameter values, the PC modes are estimated using a Bayesian framework. As an outcome, these PC modes are described with posterior probability distributions. The resulting expansion can be regarded as an uncertain response function and can further be used as a computationally inexpensive surrogate instead of the original reaction model for subsequent analyses such as calibration or optimization studies. Furthermore, the methodology is enhanced with a classification-based mixture PC formulation that overcomes the difficulties associated with representing potentially nonsmooth input-output relationships. Finally, the global sensitivity analysis based on the multiparameter spectral representation of an observable of interest provides biological insight and reveals the most important reactions and their couplings for the competence dynamics. © 2013 IEEE.

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TYPE Journal Article YEAR 2012
DOIOSTIScopus

Investigation of molten/oxidized aluminum powder deposition on stainless steel 304

American Society of Mechanical Engineers, Fluids Engineering Division (Publication) FEDSM

Sanchez, Tomas M.; Donaldson, Burl; Gill, Walter

Accidents involving solid propellants containing aluminum can be difficult to model due to the additional heat transfer from molten aluminum or aluminum combustion and impingement/deposition of oxide on target objects. A series of tests has been carried out using a commercially available oxy-acetylene torch and powder feeder to investigate the effects of molten/oxidized aluminum on stainless steel 304 substrates. SEM and EDS have been used to determine diffusion/interaction of aluminum with the stainless steel and characterize the constituents of the resulting interfacial layers. These techniques indicated that at the test conditions, aluminum was undetectably oxidized before it deposited on the substrate surface. However, temperature data from thermocouples attached to backside of each substrate detected an increased heat flux to the substrate when aluminum is introduced into the flame spray. Results also indicate that the boundary layers of the aluminum and stainless steel were well defined implying that little diffusion or solution of the aluminum with the stainless steel occurred. Copyright © 2012 by ASME.

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TYPE Conference YEAR 2012
ScopusOSTI
Results 60401–60500 of 99,299
Results 60401–60500 of 99,299