Browsing by Subject "shape"

Now showing 1 - 4 of 4

Au@Pt Dendrimer Encapsulated Nanoparticles As Model Electrocatalysts for Comparison of Experiment and Theory
(2012-01) Yancey, David F.; Zhang, Liang; Crooks, Richard M.; Henkelman, Graeme; Yancey, David F.; Zhang, Liang; Crooks, Richard M.; Henkelman, Graeme
In this paper we report the electrochemical synthesis of core@shell dendrimer-encapsulated nanoparticles (DENs) consisting of cores containing 147 Au atoms (Au-147) and Pt shells having similar to 54 or similar to 102 atoms (Au-147@Pt-n (n = 54 or 102)). The significance of this work arises from the correlation of the experimentally determined structural and electrocatalytic properties of these particles with density functional theory (DFT) calculations. Specifically, we describe an experimental and theoretical study of Pb underpotential deposition (UPD) on Au-147 DENs, the structure of both Au-147@Pb-n and Au-147@Pt-n DENs, and the activity of these DENs for the oxygen reduction reaction (ORR). DFT calculations show that Pb binding is stronger on the (100) facets of Au as compared to (111), and the calculated deposition and stripping potentials are consistent with those measured experimentally. Galvanic exchange is used to replace the surface Pb atoms with Pt, and a surface distortion is found for Au-147@Pt-n particles using molecular dynamics simulations in which the Pt-covered (100) facets shear into (111) diamond structures. DFT calculations of oxygen binding show that the distorted surfaces are the most active for the ORR, and that their activity is similar regardless of the Pt coverage. These calculations are consistent with rotating ring-disk voltammetry measurements.
Determination of a Shape and Size Independent Material Modulus for Honeycomb Structures in Additive Manufacturing
(University of Texas at Austin, 2017) Le, Thao; Bhate, Dhruv; Parsey, John M.; Hsu, Keng H.
Most prior work on modeling cellular structures either assumes a continuum model or homogenizes “effective” cell behavior. The challenge with the former is that bulk properties do not always represent behavior at the scale of the cellular member, while homogenization results in models that are shape specific and offer little insight into practical design matters like transitions between shapes, partial cells or skin junction effects. This paper demonstrates the strong dependence of measured properties on the size of the honeycomb specimen used for experimental purposes and develops a methodology to extract a material modulus in the presence of this dependence for three different honeycomb shapes. The results in this paper show that the extracted modulus for each shape converges as the number of cells in the specimen increases and further, that the converging values of the material moduli derived from the three shapes are within 10% of each other.
Letter to W. Bock from H.B. Stenzel on 1945-06-12
(1945-06-12) Stenzel, Henryk B.
The Shape Of Ethics: Kantian Moral Agency Under Reason Holism
(2018) Barrish, Elijah
I explore the possibility of Kantian moral particularism, a moral system that would include reason holism on the one hand and the Categorical Imperative on the other.