SUNMONTUEWEDTHUFRISAT
Conferences, Lectures, & Seminars
Events for December
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Overall Electromagnetic Properties of Multifunctional Composites
Wed, Dec 05, 2007 @ 03:30 PM - 04:30 PM
Aerospace and Mechanical Engineering
Conferences, Lectures, & Seminars
Alireza V. Amirkhizi Postdoctoral FellowCenter of Excellence for Advanced Materials Department of Mechanical and Aerospace EngineeringUniversity of California at San Diego La Jolla, CA 92093 Abstract:Composite materials are used for their excellent structural performance. Load-bearing properties are traditionally the only aspects for which a composite structure is designed. Recent technological advances have made it possible to reach beyond this limited view. Inspired by biological systems, we seek to develop engineering materials that exhibit multiple functionalities in addition to providing structural integrity. I will present my research on embedding periodic arrays of scattering elements within composites to modify and tune their overall electromagnetic properties. A number of techniques for numerical and analytical modeling of the periodic media are discussed. Based on these methods we have designed and fabricated composites with tuned electromagnetic properties. Examples include fiber-reinforced polymer composites with embedded arrays of straight wires or coils. In both cases, the overall dielectric constant of the medium is reduced and can even be rendered negative within microwave frequencies. The coil medium can exhibit chiral response. Solutions for eliminating this behavior as well as a method for calculation of the bianisotropic material parameters are presented. One can achieve similar modification of the overall properties at higher frequencies by reducing the length scale. For example, we demonstrated that a polymer film with embedded nano-strips of gold can demonstrate negative dielectric constant in infrared regime. An example of a structural composite is fabricated and tested for which the magnetic permeability is altered and even turned negative. Finally, a general method for homogenization of the electromagnetic properties of periodic media based on the microstructure is presented.
Location: Stauffer Science Lecture Hall, Rm 102
Audiences: Everyone Is Invited
Contact: April Mundy
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Lessons on Structure from the Structure of Viruses
Fri, Dec 07, 2007 @ 03:30 PM - 04:30 PM
Aerospace and Mechanical Engineering
Conferences, Lectures, & Seminars
RICHARD D. JAMES Russell J. Penrose ProfessorandDistinguished McKnight University ProfessorUniversity of MinnesotaMinneapolis, MN 55455 Abstract:
As the most primitive organisms, occupying the gray area between the living and nonliving, viruses are the least complex biological system. One can begin to think about them in a quantitative way, while still being at some level faithful to biochemical processes. We make some observations about their structure, formalizing in mathematical terms some rules-of-construction discovered by Watson and Crick and Caspar and Klug. We call the resulting structures objective structures. It is then seen that objective structures include many of the most important structures studied in science today: carbon nanotubes, the capsids, necks, tails and other parts of many viruses, the cilia of some bacteria, DNA octahedra, buckyballs, actin and collagen and many other common proteins, and numerous atomic-scale rods, springs and wires now being synthesized. Objective structures also have an intriguing relation to the crystalline and noncrystalline structures adopted by elements in the Periodic Table. The rules defining them relate to the basic invariance group of quantum mechanics. We develop a methodology for computing such structures. Some of the nonperiodic structures revealed by the formulas exhibit beautifully subtle relations of symmetry. This common mathematical structure paves the way toward many interesting calculations for such structures: the likelihood of unusual electromagnetic and other collective properties, simplified schemes for exact molecular dynamics of such structures, phase transformations between them, defects and failure, new x-ray methods of determination of structure not relying on crystallization, and their growth by self-assembly.
Location: Stauffer Science Lecture Hall, Rm 102
Audiences: Everyone Is Invited
Contact: April Mundy