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Bi-Weekly Seminar

Mesoscopic Modeling of Biomolecules

 Margaret S. Cheung

by: Margaret S. Cheung

Date: Friday June 13, 2008

Time: 12:00 pm – 1:00 pm

Location: Houston Science Center – Building 593 — Room 102

Overview

Reconstruction algorithms from coarse-grained models to fine-grained (all-atomistic) models of biomolecules are essential in implementing multi-scale simulations. We developed an innovative algorithm for reconstruction that results in high precision all-atom structures (SCAAL). Our method is validated by the computation of structural differences in reconstructed conformations and Protein Data Bank structures for 67 proteins. Significant improvements are observed while we consider a special relevance between the side chain and the backbone of a protein into our modeling method.

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Colloquium

IBAD-Textured Coated Conductors

by: Dr. Vladimir Matias

Date: Wednesday May 28, 2008

Time: 11:00 am – 12:00 pm

Location: Houston Science Center – Building 593 — Room 102

Overview

Second generation high temperature superconducting (HTS) wire, also known as coated conductor, holds great promise, thanks to its relatively low cost and high superconducting critical currents, to enable a number of superconducting power applications. In this talk we review some of the progress on ion-beam assisted deposition (IBAD) textured coated conductors. At Los Alamos National Laboratory we have developed processes for continuous texturing of MgO on metal tapes, buffer layer depositions, and HTS deposition by laser ablation and reactive coevaporation. IBAD-MgO texturing is the enabling process for these coated conductors. It is an extremely fast process but requires smooth surfaces over long lengths, which is achieved in our laboratory by electropolishing or sol-gel planarization of metal alloy tapes. The research to date has demonstrated that IBAD-MgO texture can develop in less than one second. Under optimized processing conditions the in-plane mosaic spread FWHM for the MgO layer is less than 5° and less than 2° out-of-plane. In the YBCO layer the texture improves further to less than 2° in-plane and 1° out-of-plane. At this level of grain alignment critical currents in HTS are no longer limited by the grain boundaries. Critical currents for YBCO layers deposited on the IBAD-MgO templates have been steadily increasing over the last 10 years, and have been demonstrated to exceed 600 A/cm-width. An important remaining issue for coated conductors is the decrease of Jc with thickness of the HTS layer. We discuss methods of addressing this issue as well as other key outstanding challenges.

This work is funded by the Department of Energy Office of Electricity Delivery & Energy Reliability.

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Special Seminar

Supercurrents Through a Ferromagnet, Josephson π- Junctions as Superconducting Phase Inverters

by: Dr. V. V. Ryazanov

Date: Thursday May 22, 2008

Time: 12:00 pm – 1:00 pm

Location: Houston Science Center – Building 593 — Room 102

Overview

It was predicted by Larkin and Ovchinnikov and by Fulde and Ferrel that superconducting pairing can occur when the electron momenta at the Fermi energy are different for the two electron spin directions, for instance as the result of an exchange field in magnetic superconductors. The resulting 'LOFF'-state is qualitatively different from the zero-momentum state: it is spatially inhomogeneous and the order parameter contains nodes where the phase changes by π. The LOFF state was never observed in bulk material, but we present experimental evidence that it can be induced in a weak ferromagnet (F) sandwiched between two superconductors (S). Such an SFS junction can yield a phase shift of π between the superconducting banks. The phase change of the superconducting order parameter in the ferromagnet arises as a response of the Cooper pair, which consists of two electrons of opposite spin and momentum, to the energy difference between two spin directions in the ferromagnet. This shift manifests itself in reentrant superconducting behavior of the critical supercurrent temperature dependence, Ic(T), of the Josephson SFS junction as well as in half-period shift of Ic(H)-dependence of a triangular SFS junction array at point of a transition of the junctions from a "0-" to a "π"- state. The π-state offers fundamentally new ways for studying the coexistence of superconductivity and magnetism and may also be important for superconducting electronics, in particular in quantum computing: several schemes for the realization of the necessary qubits (quantum two level systems) rely on the use of phase shifts of π in a superconducting network.

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Student Symposium

35th Semiannual Student Symposium and Family BBQ

by: TcSUH Administration

Date: Friday May 16, 2008

Time: 1:00 pm – 7:00 pm

Location: Houston Science Center – Building 593 — Room 102

Overview

The Student Symposium will begin at 1:00 p.m. with a series of 15-minute presentations representing novel work by undergraduate and graduate students from each laboratory. A Symposium Program, including the schedule and abstracts for each presentation, will be provided at the door. The Family BBQ will follow the symposium from 5:00 – 7:00 p.m. There will lots of food, drinks, and games. Sign up for darts, croquet, and horseshoe teams by contacting:

Physics: Omar Lozano (x38264 or lozanogo@yahoo.com.mx)Chemistry: Carmen Reznik (x35949 or creznik@uh.edu)Engineering: Mina Hanna (x34081 or Mina.Hanna@mail.uh.edu)

There will be bountiful prizes and a first place team plaque that will be placed in the TcSUH case on the 2nd floor.

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Joint Seminar

An X-ray Vision of Structure-Function Relationships in Organic Electronics and Biointerfaces

Dr. Bert  Nickel

by: Dr. Bert Nickel

Date: Thursday May 08, 2008

Time: 4:00 pm – 5:00 pm

Location: Houston Science Center – Building 593 — Room 102

Overview

Organic molecules exhibit remarkable self-assembly properties which allow them to form highly organized thin film structures. A prominent example for such ultrathin films are lipid bilayers, which represent the structural backbone of cell membranes. Lipid bilayers can be deposited on various substrates ranging from optical resonators to semiconducting layers, permitting the addition of bioselectivity to such devices. I discuss how synchrotron x-ray based techniques can be used to access the structure of such hybrid systems. Another example to be discussed is molecular thin films for organic electronics. Here, I discuss how to determine details of the molecular arrangement, as well as the nature of structural defects, and how they relate to electronic device characteristics such as trap densities.

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