Events

Past Events

November 11-17 2011 Denver, Colorado
2011 ASME International Mechanical Engineering Congress and Exposition


Graduate papers to be presented:”Extension of an Empirical Mismatch Model to Predict Phonon Transmissivity at Complex Interfaces” Nam Q. Le, John C. Duda, Timothy S. English, Christopher H. Baker, Pamela M. Norris, Patrick E. HopkinsA new empirical model is shown to predict phonon transmissivity in excellent agreement with results from molecular dynamics simulations using wave packets across epitaxial interfaces, at a fraction of the computational cost. That formulation is then used as input to a mesoscopic particle model to predict the phonon transmissivity across multilayered structures with little computational expense. This approach yields quantitative agreement with a previous model based on the results of molecular dynamics simulations. Therefore the approach is extended to gain insight into the effects of atomic mass and alloyed materials on transmissivity in multilayered structures.“Lattice Mismatch Model for Predicting Frequency-Dependent Phonon Transmissivity Across Interfaces Between Dissimilar Materials,” John Duda.
“Role Of Bonding Strength And Interface Structure On Thermal Transport,” Justin L. Smoyer, Timothy S. English, Pamela M. NorrisTraditional theories of phonon thermal transport have assumed bulk properties in material systems, i.e. dispersion and density of states, in the calculation of transport properties. Little attention has been paid to the role of the interface and the deviation of phonon properties due to the superposition of material systems. In this work we illuminate the role of bonding and the strength of the bonding environment near an interface in determining phononic properties and phononic thermal transport. Through simulations explored using molecular dynamics, we show that phononic thermal transport across an interface is not independent of the interface structure properties and cannot be calculated considering the bulk properties of the constituent materials alone. Additionally, we perform wave packet simulations at 0K to isolate the effects of phonon occupation on phonon scattering at interfaces. Finally, for relevant interfaces, we demonstrate that the thermal efficiency of interfacial thermal transport is strongly correlated to the phononic properties within the interface region and discuss how these formulations would affect future consideration and modeling of phononic interfacial transport.“Role of Dispersion and Density of States on Phonon-phonon Scattering,” Timothy S. English, Justin L. Smoyer, Pamela M. NorrisIn this work, we consider the wide use of phonon dispersion relations and density of states as deterministic factors governing phonon-phonon scattering processes, both in the bulk of materials, and at interfaces. While phonon dispersion and density of states are widely accepted as the unique ‘fingerprint’ of phonon properties in a crystal, we re-evaluate the role of these two factors in determining both elastic and in-elastic as well as normal and Umklapp phonon-phonon scattering processes. Through a thought experiment subsequently explored via molecular dynamics simulations, we show that phonon-phonon scattering at interfaces cannot be uniquely or deterministically described using phonon dispersion and density of states alone, despite the consideration of selection rules which conserve energy and maintain wave vector mappings allowed by the reciprocal lattice. We propose that the premise of detailed balance along with its application in models such as the Diffuse Mismatch Model, where phonon dispersion and density of states are the source of all phonon properties in a crystal, provide necessary but insufficient information to accurately determine phonon scattering. Our results provide evidence to support this conclusion by systematically demonstrating the breakdown of detailed balance in the simplest case of an ideal, epitaxial, and perfectly crystalline interface.Our hypothesis concerning the non-deterministic role of dispersion relations and density of states with regard to phonon scattering is explored with occupied phonon dispersion relations and density of states calculated directly from molecular dynamics simulations at finite temperatures and pressures where no assumptions about either scattering (elastic or inelastic) or the harmonic nature of interactions (harmonic, quasi-harmonic, or anharmonic effects) are made; the effects of each are intrinsically included through the atomic velocity autocorrelation function and estimation of the dynamical matrix of the crystal using the fluctuation dissipation theorem. Additionally, we use harmonic lattice dynamics to calculate dispersion relations for comparison to those extracted from molecular dynamics simulations. For many relevant interface scenarios, we demonstrate that in order to rigorously predict interfacial transport, it is not most important to consider the phonon dispersion relations and density of states of the materials from which phonons emerge and are destined (i.e., bulk properties), but the strength of scattering mechanisms and variations in local inter-atomic interactions experienced in between.

ASME-JSME 2011 Thermal Engineering Joint Conference will be held in Honolulu, Hawaii

March 13th-17th, Honolulu, Hawaii

AJTEC 2011 — 8th ASME/JSME Thermal Engineering Joint Conference

Papers  presented:

John DudaRole of Chemical Ordering on Phononic Transport in Binary Alloys
Timothy EnglishModeling Grain Boundary Scattering and Thermal Conductivity of Polysilicon Using an Effective Medium Approach
Patrick HopkinsContributions of Anharmonic Phonon Interactions to Thermal Boundary Conductance
Christopher SaltonstallAssessment of Vibrational Coupling at Solid-Sam Junctions
Justin SmoyerThermal Boundary Conductance Between Thin Metal Films and Graphite Substrates


University of Virginia in Charlottesville, site of ONR 2010 MURI Review Conference

 

ONR 2010 MURI Review Conference was held September 7th & 8th

Professor Pamela Norris hosted a review in Charlottesville, Virginia of the Multidisciplinary University Research Initiative (MURI) Program. Attendees included the Department of Defense awarding offices: the Army Research Office (ARO), Office of Naval Research (ONR) and the Air Force Office of Scientific Research (AFOSR), as well as faculty, research scientists, and students from university team members from Arizona State, the University of California at Berkeley, the University of Illinois, and Rensselaer Polytechnic University, and the University of Virginia.

 November 12th-18th 2011

ASME International Mechanical Engineering Congress & Exposition
Christina Haden presented the paper “Deposition of Polypyrrole onto a Novel Polymer Electrode for use in a Biomimetic Artificial Excitable Cell Membrane” at the ASME International Mechanical Engineering Congress & Exposition in Vancouver, Canada, November 12-18th.

November 5th 2011
Phonon Transport Across Interfaces and Within Nanostructures
John Duda conducted a seminar at the Mechanical Engineering Department at Villanova University in Villanova, Pennsylvania, November 5, 2011.

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