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Bi-Weekly Seminar

Quench Propagation Analysis in MgB2 Superconducting Magnets

by: Matteo Alessandrini

Date: Friday August 17, 2007

Time: 12:00 pm – 1:00 pm

Location: Houston Science Center – Building 593 — Room 102

Overview

Reliability and durability of high temperature superconducting magnets depends on our knowledge of their behavior during a quench. Simulation of quench propagation and voltage growth along composite MgB2 superconducting wires are presented by taking into account sharing current and temperature dependence of heat capacity, thermal conductivity and resistivity. A description will be given of our recently developed testing facility for quench propagation studies in MgB2 superconducting magnets. Finally some of the latest results on large bore solenoids will be presented and discussed.

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Bi-Weekly Seminar

Single Molecule Studies of Disease-Related Biological Processes

 Christy  Landes

by: Christy Landes

Date: Friday August 03, 2007

Time: 12:00 pm – 1:00 pm

Location: Houston Science Center – Building 593 — Room 102

Overview

Biological processes are often heterogeneous. Single molecule spectroscopy allows us to distinguish between multiple pathways in disease progression or drug/pathogen interactions. Thus, it is possible to identify, for example, which steps are most amenable to drug therapy. The experimental technique is especially powerful when combined with simulations in which we model processes such as protein-nucleic acid binding. I will discuss the recent progress in our group using single molecule fluorescence resonance energy transfer (SMFRET) and fluorescence correlation spectroscopy (FCS) to study retroviral chaperone steps and model macular degeneration inhibitor

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Bi-Weekly Seminar

Optical and Electronic Properties of Zn4Sb3 Thermoelectrics

Dr. Alexander P. Lytvynchuk

by: Dr. Alexander P. Lytvynchuk

Date: Friday July 20, 2007

Time: 12:00 pm – 1:00 pm

Location: Houston Science Center – Building 593 — Room 102

Overview

We will report on an experimental study of optical and electronic properties of Zn4Sb3, an excellent thermoelectric material, across the structural ß-α transition using optical techniques. The phase transition from highly disordered high temperature ß phase into low symmetry ordered &alpha phase is shown to be accompanied by an increase of thermoelectric power and electrical conductivity, and also significant rise in the free charge carrier density. Concomitant with these electronic changes is an unexpected increase in the carrier scattering rate, which exhibits features of localization.

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Bi-Weekly Seminar

Electromagnetic Probes of Enzymatic Activity in Live Organisms

Prof. John H. Miller

by: Prof. John H. Miller

Date: Friday May 25, 2007

Time: 12:00 pm – 1:00 pm

Location: Houston Science Center – Building 593 — Room 102

Overview

We report on measurements of the harmonics generated by live cells, mitochondria, photosynthetic organelles, and whole organisms in response to sinusoidal electric fields. The frequency and amplitude dependence of the induced harmonics correlate with physiological processes occurring in various enzyme complexes. The motion of charged residues and ions leads to a nonsinusoidal response to an applied sinusoidal field, leading to the generation of harmonics. For example, H+-ATPase, a proton pump that plays an important role in yeast (S. cerevisiae) generates harmonics that are affected by suitable inhibitors or substrates, such as vanadate or glucose. A high-Tc SQUID is used to measure its response at low frequencies (< 1 kHz). At higher frequencies the field capacitively couples through the plasma membrane and probes complexes within internal organelles. Some features in the frequency-dependent harmonics produced by whole cells appear to correlate with those seen in isolated mitochondria, which can be increased by adding substrates that activate the electron transport chain, or suppressed by inhibitors such as rotenone or antimycin A. Finally, both the linear and harmonic responses of whole leaves and thylakoid membrane (chloroplast) suspensions, responsible for photosynthesis in plants, are strongly affected by the presence or absence of light.

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Bi-Weekly Seminar

Some New Insights on the Chemistry of Intermetallics and Metal-Rich Phases

Prof. Arnold Mejia Guloy

by: Prof. Arnold Mejia Guloy

Date: Friday April 13, 2007

Time: 12:00 pm – 1:00 pm

Location: Houston Science Center – Building 593 — Room 102

Overview

Polar intermetallic phases formed between transition and post-transition metals with one or more of the electropositive alkali, alkaline-earth, and rare-earth metals exhibit a rich variety of complex structures. More importantly, the smooth transition of electronic properties from semiconducting intermetallics to classical metallic compounds along the Zintl border provides a fertile area to search for materials with novel electronic properties. This also offers unique opportunities in investigating structure-bonding-property relationships among materials at the border between metals and nonmetals. We have used the Zintl concept in rationalizing the synthesis, stoichiometry, and chemical bonding of novel ternary and quaternary “electron-poor” Zintl phases that exhibit unusual π-bonding. Recently, our exploratory work near the Zintl border has also resulted in a number of novel polar intermetallic structures. These compounds and other newly discovered polar intermetallics add new insight to the structural and chemical bonding peculiarities of Zintl phases and the less polar intermetallics. In addition, results of exploratory forays into the yet unexplored chemical reactivity of Zintl phases will be presented. The mild reduction and oxidation of the “salt-like” intermetallics provides a novel route to new materials with interesting properties and structures.

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