Events at Physics

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Events on Friday, February 18th, 2011

High Energy Seminar
New Spectacles for Spectacular Discoveries
Time: 11:00 am
Place: 4274 Chamberlin Hall
Speaker: Prof. Daniel Ferenc, University of California Davis
Abstract: IceCube and SuperKamiokande are huge, but we need significantly larger experiments in the future.Who will make the PMTs, how, and when? Who will pay for them? It is high time to introduce a new technology. I will describe ABALONE, a vacuum photosensor concept that is simplified to the bones, and mass-producible at a low cost.
Host: Teresa Montaruli
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Physics Department Colloquium
Fay Ajzenberg-Selove Colloquium
Regular and Irregular Polyhedra in Multi-Component Crystalline Shells
Time: 4:00 pm
Place: 2241 Chamberlin Hall (coffee at 3:30 pm)
Speaker: Monica Olvera de la Cruz, Northwestern University, Department of Materials Science and Engineering
Abstract: The captivating charm of uniform convex polyhedra such as Platonic and Archimedean solids has beguiled scientist, philosophers, and artists for millenia. In our modern era, it is incorporated in the revolutionary Descartes' geometrization of nature, and still reflects the common practice of introducing esthetic elements in physical sciences. While mathematicians have rigorously captured the "morphological essence" of such highly regular polytopes by classifying and formalizing their symmetries and isometries, the search of such structures in the realm of nature has been rather elusive. Icosahedral shapes, among all Platonic polyhedrals, have been identified in molecular elastic shells such as large viral shells or fullerenes. We demonstrate that other geometries, including some Archimedean polyhedrals, arise spontaneously in shells formed by more than one component. We study the buckling of an elastic shell with two coexisting elastic components, at different relative concentrations. By using theoretical arguments and numerical simulations we find various polyhedra and n-gonal hosohedra shapes. Our work explains the principles to design various hallow polyhedra and the existence of the regular and irregular polyhedra shells recently observed in organelles. Our analysis suggests that these polyhedral shapes are ubiquitous in cellular shells and in closed elastic membranes made of various proteins. We provide experimental evidence of the spontaneous buckling phenomena in shells made of mixtures of cationic and anionic amphiphiles, where electrostatics drives their co-assembly, and orders the assembly into faceted ionic structures.
Host: Gilbert
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