TcSUH
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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!
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Special Seminar
Technology Needs for Future Human Space Missions
by: Dr. Kumar Krishen
Date: Wednesday November 07, 2007
Time: 12:00 pm – 1:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
A discussion of the need for technology development for the human exploration and development of space will be presented. Human exploration and development of space is aimed at opening the space frontier by exploring, using, and enabling the development of space and expanding the human experience into the far reaches of space. This includes increasing human knowledge of nature's processes using the space environment, exploring and settling the solar system, achieving routine space travel, and enriching life on Earth through people living and working in space. NASA's Mars Pathfinder and the International Space Station provide extensive experience, research and technology (R&T), and infrastructure for other envisioned programs in support of human exploration and development of space.
In the past decade, the Clementine and the Lunar Prospector missions have provided valuable remotely sensed data of the Moon. In addition, NASA has studied the development of a lunar habitat and human mission to Mars as possible missions. These missions face common challenges of travel to these planets and for survival of humans on the surface of planets. With the human Mars mission being the first to such a distant planet, advanced technologies will be required to enable the mission and to provide cost effective and safer approaches.
The R&T areas considered important for a human mission to Mars include advanced human support, renewable resources and utilization of planetary resources, space transportation, automation and robotics, space power, information processing and communications systems, sensors, and instruments. NASA is actively providing the technology developed for the space applications to industry, universities, and other organizations for research, education and commercialization purposes. Strategies for this technology transfer will also be presented.
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Special Seminar
Superconducting Magnets in Space
by: Dr. Stephen M. Harrison
Date: Tuesday October 23, 2007
Time: 11:00 am – 12:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
A brief introduction to Scientific Cryomagnetics Company will be given, followed by a review of some of the earlier attempts to use superconducting magnets in space. Our present and past projects will be shown emphasizing design, construction and cryogenics of some of the superconducting magnets built (or still under fabrication) by our company for space applications: Alpha Magnetic Spectrometer (AMS), Variable Specific Impulse Magnetoplasma Rocket (VASIMR), and X-Ray Evolving Universe Spectroscopy (XEUS). Future possibilities for applied superconductivity in space will be presented, with project overviews and possibility to discuss details during and after the seminar.
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Special Seminar
New Properties in Old Materials: Doped Layered Dichalcogenides
by: Prof. Emilia Morosan
Date: Monday October 22, 2007
Time: 4:00 pm – 5:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
Transition metal dichalcogenides MX2 (M is transition metal, X = S, Se, or Te) have long been known and explored. Due to their reduced dimensionality, such compounds sometimes display charge density wave (CDW) transitions, which are periodic modulations of the conduction electron density. In addition, the CDW state is believed to compete with a superconducting state (SC), both the CDW and the SC representing collective electron states induced by Fermi surface instabilities. Upon doping with various complexes, the transition metal dichalcogenides often reveal dramatic changes of their physical properties. I will discuss the effects of transition metal intercalation on the properties of two layered chalcogenide materials, TiSe2 and TaS2. Although TiSe2 is one of the first known CDW-bearing materials, the nature of its CDW transition remains controversial. Recently the interest in TiSe2 has been renewed by our discovery of the new superconducting state SC that emerges upon Cu doping. Thus CuxTiSe2 provides the first example of a system in which controlled chemical doping can be used to study the competition between the CDW and SC. I will also discuss experiments on FexTaS2 aimed at studying the sharp switching of the magnetization that we recently observed in this compound for x = 1/4. For this particular Fe content, FexTaS2 orders ferromagnetically below 160 K and displays very sharp hysteresis loops in the ordered state for H||c. This is indicative of a very rapid switch of the magnetization direction, and the time dependence of this magnetization switch reveals unexpected time dependence.
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Special Seminar
Current State of the MgB2 Superconductor and Devices Development at Columbus Superconductors
by: Dr. Giovanni Grasso
Date: Tuesday May 29, 2007
Time: 11:00 am – 12:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
Six years is a limited amount of time to bring a new material to a successful level of development. However, this is indeed happening for MgB2, as recently proven by a number of impressive news items coming from industries and institutions working on it. The capability of MgB2 wires and tapes to carry large currents at intermediate temperatures between those of liquid helium and liquid nitrogen has been recently demonstrated by the realization of a full scale prototype of an open MRI fully working system. Such a system contains many innovative features, such as the cryogenic-free operation and the innovative magnet design that reduces claustrophobia issues, as well as the use of as much as 18 Km of multifilamentary conductor. In this talk, the further progress of MgB2 wire development will be discussed, with the aim of drawing a realistic picture of the future impact of MgB2 on many superconducting devices.
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