Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session D5: Catalysis and Complexity: Ken Hass Memorial |
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Sponsoring Units: FIAP Chair: Willes Weber, Caltech Room: Baltimore Convention Center 309 |
Monday, March 13, 2006 2:30PM - 3:06PM |
D5.00001: Environmental Catalysis from First Principles Invited Speaker: Innovation in environmental catalysis---catalysis related to sustainable production and consumption of energy and materials---is one of the most pressing societal needs of the day. Fuel cells, fuel reforming, hydrogen generation, emissions control, and many other processes all rely on effective catalysts to facilitate the transformation of chemicals into more desirable forms. Historically these heterogeneous catalysts, most often consisting of active transition metal particles dispersed on a high surface area support, have advanced in a largely evolutionary fashion. Today, the increasing demands for more capable catalysts have dovetailed with a revolution in experimental and computational techniques available for preparing and studying these materials at the nanoscale to create the potential for unprecedented advances in catalyst research and discovery. Three central questions have emerged in nanoscale environmental catalysis: First, how does the structure and catalytic function of transition metal catalysts evolve as particles decrease in size from the micro to the nanoscale? Second, how do these particles interact and communicate with supports, and what are the effects on structure and catalytic function? Third, how does the particle/support system respond to realistic and dynamic reaction environments? Density functional theory (DFT) simulations provide a means to interrogate these questions independently and have proved a powerful complement to experiment in the investigation and development of nanocatalysis. In this talk we will review recent progress in studying these questions using DFT methods, with a particular emphasis on the connection between oxidation environment, catalyst composition, and activity for CO and NO oxidation with Pt and Ru catalysts. [Preview Abstract] |
Monday, March 13, 2006 3:06PM - 3:42PM |
D5.00002: Density functional calculations in the automotive industry: Catalyst supports and hydrogen storage materials Invited Speaker: In my talk, I will describe some uses of density functional theory (DFT) calculations in the research laboratory at Ford, and particularly highlight work that was inspired by, or performed in collaboration with Ken Hass. I begin with a discussion of past work on $\gamma $-Al$_{2}$O$_{3}$ catalyst support materials, but also discuss the current main focus of our group's activities: hydrogen storage materials. Catalyst Supports: In current three-way automotive catalysts, precious metals are often supported by the phase of aluminum oxide known as $\gamma $-Al$_{2}$O$_{3}$. Despite the ubiquitous nature of this oxide in current automobile catalysts, and a considerable amount of effort expended to understand this material, many questions about the phase stability and even crystal structure of $\gamma $-Al$_{2}$O$_{3}$ remain. DFT calculations have made significant progress in unraveling these unanswered questions, allowing one to construct realistic models of the supported catalysts materials. Hydrogen Storage Materials: One of the major bottlenecks to the widespread use of hydrogen-fueled vehicles is the~ability to store sufficient energy on-board to enable vehicle attributes acceptable to customers.~ I will give a general introduction to the topic of hydrogen storage, and a broad survey of the various classes of hydrogen storage technologies, and point out some pros and cons associated with each class. Currently known technologies have insufficient usable energy densities, and I will describe how DFT calculations are aiding the search for improved high density storage materials. [Preview Abstract] |
Monday, March 13, 2006 3:42PM - 4:18PM |
D5.00003: From Condensed Matter Theory to Complex Biological Structures Invited Speaker: Condensed matter theory has given us many successful examples of the combination of analytic theory and numerical modeling in treating microscale and nanoscale physical phenomena. The methods of condensed-matter theory are increasingly being applied to biological problems. We will describe recent work modeling the growth of actin networks in biological cells. Actin, an abundant intracellular protein, polymerizes into semiflexible filaments which are important for many processes, including cell motion and shape changes. The growth of the filaments is regulated by intracellular proteins that can, for example, cap the growing ends of filaments, cause new branches to grow on existing filaments, or sever filaments. These activities generate a dynamic actin filament network at the cell edge. The filaments' growth can generate forces large enough to move the cell and change its shape. The talk will describe Brownian-dynamics simulations of the growth of single filaments against an obstacle, and stochastic-growth modeling of the growth of the actin network. The single-filament growth simulations show that even filaments attached to an obstacle can grow and push it forward, at rates comparable to free-filament growth rates. This result is consistent with experimental observations of filament-obstacle attachments. The network-growth simulations use a minimal stochastic growth model including capping, branching, and severing. Simulation studies of this model yield a network structure quite similar to that seen by electron microscopy. Surprisingly, the growth velocity of the network is almost independent of the opposing force. Analytic theory shows that this effect is due to the autocatalytic nature of the branching route to filament generation. Studies of the polymerization dynamics of this model reveal a ``branching explosion'' in which large clusters of branched filaments form at short times, but the filaments are nearly unbranched at long times. [Preview Abstract] |
Monday, March 13, 2006 4:18PM - 4:54PM |
D5.00004: The Physics of Traffic Invited Speaker: Congestion in freeway traffic is an example of self-organization in the language of complexity theory. Nonequilibrium, first-order phase transitions from free flow cause complex spatiotemporal patterns. Two distinct phases of congestion are observed in empirical traffic data--wide moving jams and synchronous flow. Wide moving jams are characterized by stopped or slowly moving vehicles within the jammed region, which widens and moves upstream at 15-20 km/h. Above a critical density of vehicles, a sudden decrease in the velocity of a lead vehicle can initiate a transition from metastable states to this phase. Human behaviors, especially delayed reactions, are implicated in the formation of jams. The synchronous flow phase results from a bottleneck such as an on-ramp. Thus, in contrast to a jam, the downstream front is pinned at a fixed location. The name of the phase comes from the equilibration (or synchronization) of speed and flow rate across all lanes caused by frequent vehicle lane changes. Synchronous flow occurs when the mainline flow and the rate of merging from an on-ramp are sufficiently large. Large-scale simulations using car-following models reproduce the physical phenomena occurring in traffic and suggest methods to improve flow and mediate congestion. [Preview Abstract] |
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