TcSUH
Warning: Undefined variable $events_postname in /home1/tcsuh570/public_html/events_select2.php on line 105
Special Seminar
Chemistry and Physics of Intermetallic Clathrates and Skutterudite-like Compounds
by: Dr. Yuri Grin
Date: Tuesday February 26, 2008
Time: 11:00 am – 12:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
Crystal structures of intermetallic clathrates and skutterudite derivatives are formed by the 3D host frameworks with the differently sized filled or non-filled cages. Beside a variety of physical behaviours these compounds attracted the worldwide attention, e.g., as promising thermoelectric materials. Chemical bonding in clathrates and skutterudites is one of the key questions for the creation of the new materials of these classes. While the bonding in intermetallic clathrates may be sufficiently described by the Zintl concept with some modifications, the presence of transition metals in the filled skutterudites does not allow the straight forward description with simple electron counting. A more general description is possible with the new quantum chemical toolbox for bonding analysis in real space - electron localizability indicator [1]. Understanding of the chemical bonding allows to concept new preparation routes for synthesis of new representatives of this materials family. Especially, the (partial) control of the cage filling is achievable on this way [2]. This allows to prepare ‘empty’ clathrates, e.g., new modification of germanium [3]. Two new groups of filled skutterudites were successfully prepared. The iron-antimonides of the alkali metals NaFe4Sb12, KFe4Sb12 [4] and TlFe4Sb12 [5] represent the electron-poorest members of this family and reveal a wide spectrum of electronic properties. The novel family of REPt4Sb12 compounds shows i.e., superconductivity at relatively high temperatures [6]. [1] A. Leithe-Jasper et al. Phys. Rev. B. 2004 70 214418. [2] B. Bo?hme et al. J. Am. CHem. Soc. 2007 129 5348. [3] A. M. Guloy et al. Nature 2006 443 320-323. [4] W. Schnelle et al. 2008 submitted. [5] A. Leithe-Jasper et al. Phys. Rev. B. 2008 in press. [6] R. Gumeniuk et al. Phys. Rev. Lett. 2008 100 017002.
Download: Event PDF
Back to TcSUH News & Events
Special Seminar
Magnetic Resonance Imaging: an Evolving Clinical Imaging Tool
by: Prof. Raja Muthupillai
Date: Friday February 22, 2008
Time: 12:00 pm – 1:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
This lecture will focus on the various mechanisms through which contrast could be generated in Magnetic Resonance Images (MRI), and the clinical applications of MR. Among diagnostic imaging modalities, MRI is arguably the most versatile. Magnetic resonance imaging allows non-invasive evaluation of an array of tissue properties in vivo, e.g., tissue magnetic-resonance relaxation (anatomic imaging), metabolite distribution within tissue (spectroscopy), tissue micro-structure (diffusion), tissue micro-vascular flow (perfusion), tissue velocity, etc. This versatility has resulted in widespread use of MRI as a diagnostic imaging tool to assess pathology in patients. Recent technological advances have made it possible to use MR not just as diagnostic imaging modality, but also to use in conjunction with interventional, therapeutic procedures, e.g., MR guided focused ultrasound, and other MR guided interventions.
Download: Event PDF
Back to TcSUH News & Events
Special Seminar
Nanoscale Torque Measurements of F1 ATP-Synthase
Date: Monday January 07, 2008
Time: 3:00 pm – 4:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
What is the efficiency of a biological molecular motor? The enzyme F1 ATP-synthase is a rotary motor/ generator found in a huge variety of organisms (plants, animals, and bacteria). Being a major player in cellular respiration, F1 has evolved to optimize efficiency. However, a thermodynamic measurement of F1?s efficiency has been difficult to obtain due to the 10 nanometer size of F1. To address this, we have constructed a new type of magnetic torque manipulator, involving the binding of specially designed nanoscale magnetic rods to glass surface anchored F1. By controlling the external magnetic field and observing the rod?s rotation via optical microscopy, kBT scale torque can be both applied and measured. Attaining this required overcoming non-trivial obstacles such as reducing thermal fluctuations of the rod magnetization, non-specific surface interactions, focus drift, and background magnetic field effects. Both mechanical energy production (ATP hydrolysis) and consumption (ATP synthesis) will be discussed.
Download: Event PDF
Back to TcSUH News & Events
Special Seminar
Exploring Exotic Superfluidity of Polarized Ultracold Fermions in Optical Lattices
by: Prof. Yan Chen
Date: Friday January 04, 2008
Time: 12:00 pm – 1:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
Enormous interest has been paid to ultracold Fermi gases due to the interplay between Cooper pairing and strong correlations. Beautiful experiments on the superfluidity have been performed in these systems with unequal spin populations. Arrestingly, it was found that the superfluid paired core is surrounded by a shell of normal unpaired fermions while the density distribution of the difference of the two components becomes bimodal. Here we explore theoretically the novel superfluidity of harmonically- trapped polarized ultracold fermionic atoms in a two-dimensional optical lattice by solving the Bogoliubov-de Gennes equations. The pairing amplitude is found to oscillate along the radial direction at low particle density and along the angular direction at high density. The former is able to account for the existing experimental observations, while the latter predicts a new kind of Fulde-Ferrell-Larkin- Ovchinnikov states, which can be tested in experiments.
Download: Event PDF
Back to TcSUH News & Events
Special Seminar
Enhanced ferroelectricity in doped niobium clusters
by: Prof. Ramiro Moro
Date: Friday January 04, 2008
Time: 3:00 pm – 4:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
In September of 2002 we observed a surprising effect in free niobium clusters: some of them acquired an electric dipole moment at low temperature. It is a surprising phenomenon because metallic particles are supposed to screen electric fields and because electronic transitions in small particles usually have very high transition temperatures, but the most surprising characteristic of the effect is that it seems to be related with superconductivity: It happens in the same metals, with similar transition temperatures, it is affected by magnetic dopants and it is enhanced for particles with even number of electrons (suggesting pairing).
It was already suggested in 1992 [Friedel, 1992] that a weakly interacting lattice of superconducting nanoparticles or clusters could yield a very high temperature superconductor. That work was prompted by the superconductivity seen in doped fullerenes, but the idea can be extended further. Recently there has been a discovery of superconductivity in a gallium cluster compound [Bakharev, 2006] which could be the first realization of Friedel?s proposal. Moreover there is recent theoretical work done by V.Z. Kresin and Ovchinnikov [Ovchinnikov, 2005] that suggest that small particles of certain metals could have an enhanced Tc due to shell effects.
Barring an incredible coincidence, Nb clusters are indeed superconducting, but its superconductivity is manifested as ferroelectricity. And some alloys, like gold-doped niobium have transition temperatures at more than 300K!
Download: Event PDF
Back to TcSUH News & Events