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Reuter, Matthew G

Publications and source records attributed to Reuter, Matthew G.

6 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Solving PDEs in Irregular Geometries with Multiresolution Methods I: Embedded Dirichlet Boundary Conditions

In this work, we develop and analyze a formalism for solving boundary value problems in arbitrarily-shaped domains using the MADNESS (multiresolution adaptive numerical environment for scientific simulation) package for adaptive computation with multiresolution algorithms. We begin by implementing a previously-reported diffuse domain approximation for embedding the domain of interest into a larger domain (Li et al., 2009 [1]). Numerical and analytical tests both demonstrate that this approximation yields non-physical solutions with zero first and second derivatives at the boundary. This excessive smoothness leads to large numerical cancellation and confounds the dynamically-adaptive, multiresolution algorithms inside MADNESS. We thus generalize the diffuse domain approximation, producing a formalism that demonstrates first-order convergence in both near- and far-field errors. We finally apply our formalism to an electrostatics problem from nanoscience with characteristic length scales ranging from 0.0001 to 300 nm.

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2012

Signatures of Cooperative Effects and Transport Mechanisms in Conductance Histograms

We present a computational investigation into the lineshapes of peaks in conductance histograms, finding that they possess high information content. In particular, the histogram peak associated with conduction through a single molecule elucidates the electron transport mechanism and is generally well-described by beta distributions. A statistical analysis of the peak corresponding to conduction through two molecules reveals the presence of cooperative effects between the molecules and also provides insight into the underlying conduction channels. This work provides tools for extracting additional interpretations from experimental statistical data, helping us better understand electron transport processes.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2012

Model for Adsorption of Ligands to Colloidal Quantum Dots with Concentration-Dependent Surface Structure

A study of the adsorption equilibrium of solution-phase CdS quantum dots (QDs) and acid-derivatized viologen ligands (N-[1-heptyl],N'-[3-carboxypropyl]-4,4'-bipyridinium dihexafluorophosphate, V{sup 2+}) reveals that the structure of the surfaces of the QDs depends on their concentration. This adsorption equilibrium is monitored through quenching of the photoluminescence of the QDs by V{sup 2+} upon photoinduced electron transfer. When modeled with a simple Langmuir isotherm, the equilibrium constant for QD-V{sup 2+} adsorption, K{sub a}, increases from 6.7 x 10{sup 5} to 8.6 x 10{sup 6} M{sup -1} upon decreasing the absolute concentration of the QDs from 1.4 x 10{sup 6} to 5.1 x 10{sup 8} M. The apparent increase in K{sub a} upon dilution results from an increase in the mean number of available adsorption sites per QD from 1.1 (for [QD] = 1.4 x 10{sup 6} M) to 37 (for [QD] = 5.1 x 10{sup 8} M) through desorption of native ligands from the surfaces of the QDs and through disaggregation of soluble QD clusters. A new model based on the Langmuir isotherm that treats both the number of adsorbed ligands per QD and the number of available binding sites per QD as binomially distributed quantities is described. This model yields a concentration-independent value for K{sub a} of 8.7 x 10{sup 5} M{sup -1} for the QD-V{sup 2+} system and provides a convenient means for quantitative analysis of QD-ligand adsorption in the presence of competing surface processes.

77 NANOSCIENCE AND NANOTECHNOLOGY↗