TcSUH
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Bi-Weekly Seminar
Does DNA act as it's own sunscreen?
by: Prof. Eric Bittner
Date: Friday July 07, 2006
Time: 12:00 pm – 1:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
DNA is a surprisingly robust molecular system in spite of its rather large UV absorption cross-section in the 310-290 nm range. Part of this robustness comes from DNA's ability to rapidly dissipate the electronic photoexcitation energy into heat, thus preventing to some extent photochemical processes that can lead to mutation. One of the key questions is whether or not this dissipation is due to base-pairing and hydrogen transfer in localized excited states or if it is due to base-stacking effects. In this talk, I shall give an overview of our two-band lattice model for the excited states of DNA double helices. Our theoretical calculations corroborates recent ultrafast experimental results that indicate that base-stacking dictates the fate of an excitation in A-T DNA. Moreover, our work suggest that in AT DNA, excitonic dynamics along the A chain is dramatically different than along the T chain. Finally, we speculate that these processes may have played a crucial role in the evolutionary selection of DNA.
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Bi-Weekly Seminar
Interface - A Key Role to Functional Thin Film Epitaxy
Date: Friday March 03, 2006
Time: 12:00 pm – 1:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
Driven in parallel by technological needs and basic sciences and engineering's inquisitiveness, there has been an explosion in the development of new materials over the last decades, especially in the nanoscale regime. Interface, an unforgettable topic, has attracted more and more attention in the functional materials research and active device fabrication. It plays a key role in controlling the physical properties of advanced materials and result in the discovery of various new phenomena with an excellent opportunity for developing new materials for active nanostructures and their engineered nanosystems. We have focused on the systematic investigation of interface effects on highly epitaxial functional oxide thin films and have achieved many excellent results. For instance, we have achieved an extremely high dielectric tenability of 80% from highly epitaxial ferroelectric Mn:(Ba,Sr)TiO3 thin films, strong anisotropic phenomena in highly epitaxial (Pb,Sr)TiO3, a new record of giant magnetoresistance ratio of 1010 from artificial domain structural epitaxial (La,Ca)MnO3 thin films, the interface-controlled oxide nanorod/ribbon highly epitaxial thin films, and many other results. A series of models were developed to understand these interface phenomena. Details will be presented in the talk.
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Bi-Weekly Seminar
Novel Bioelectric Phenomena in Cellular Organelles
Date: Friday February 03, 2006
Time: 12:00 pm – 1:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
We have been investigating unusual bioelectric phenomena using novel, generally noninvasive, sensors. Recent topics of interest include: (1) studies of harmonic response of active membrane pumps (P-type ATPases), which we have observed in budding yeast cells using superconducting quantum interference devices (SQUIDs); (2) nonlinear harmonics, in response to sinusoidal electric fields, produced by electron transport chain complexes and a molecular turbine, known as ATP synthase, in mitochondria; (3) similar studies of light-activated harmonics, which we have recently discovered in chloroplasts; and (4) studies of the dielectric and conducting properties of cytoskeletal proteins, such as tubulin heterodimers, which self-assemble to form microtubules.
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Bi-Weekly Seminar
MOD Development of Coated Conductors at TcSUH
by: Prof. Kamel Salama
Date: Friday December 02, 2005
Time: 1:00 pm – 2:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
Currently, first-generation high temperature superconducting (HTS) wires/tapes are commercially available for practical applications. However, second-generation HTS wires/tapes (coated conductors) exhibit the capability of carrying a larger current operating at higher temperatures and stronger magnetic fields. Development of the second generation will accelerate the applications of HTS products into the marketplace. Highlights of our research on YBCO coated conductors at TcSUH include results on textured substrates, metal-organic deposition (MOD) buffer layers and YBCO films. The sharpest cube textured non-ferromagnetic Ni-9at%W alloy substrates were successfully achieved for the first time using the powder metallurgy process and give promise for coated conductors with reduced AC losses. Also, new MOD buffer layers have been developed to simplify coated conductor architectures, leading to a lower cost/performance ratio. In addition, chemically doped MOD YBCO films with enhanced critical current density (Jc) were developed and Jc exceeding 5 MA/cm2 at 77 K was obtained. Finally, we will present results of electric-mechanical properties of SuperPower IBAD coated conductors as part of the collaboration between TcSUH and SuperPower.
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Bi-Weekly Seminar
Magnetoelectric Effects, Spin Frustration, and Ferroelectricity in Multiferroic Manganites
by: Bernd Lorenz
Date: Friday November 18, 2005
Time: 1:00 pm – 2:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
The interaction between electric and magnetic fields in matter and/or between dielectric and magnetic orders is one of the fundamental problems in condensed matter physics. The magnetoelectric effect that allows the control of magnetic (dielectric) properties by electric (magnetic) fields is of principal physical interest and it bears the potential for the development of a new type of magnetoelectric memory. The topic has attracted renewed interest quite recently with the discovery of the coexistence of ferroelectricity and magnetic orders in multiferroic rare earth manganites. We discuss the complex physical properties of multiferroic RMnO3 and RMn2O5 (R=rare earth, Y) and show that magnetic frustration as well as strong spin-lattice coupling are the origin of a wealth of interesting phenomena such as incommensurate magnetic orders, frustration-induced ferroelectricity, magnetic field control of ferroelectric polarization, etc. The interactions between the Mn spins, the rare earth magnetic moments, and the ferroelectric polarization in these compounds give rise to an unprecedented phase complexity, e.g. as observed in hexagonal HoMnO3. In orthorhombic RMn2O5, our high-resolution thermal expansion measurements provide unambiguous proof that the ferroelectric transitions are accompanied by strong structural anomalies resulting in anisotropic lattice strain along the principal crystallographic directions.
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