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Distinguished Lecture Series

Atoms and Ions Near Carbon Nanostructures

by: Prof. Jene Golovchenko

Date: Thursday April 29, 2010

Time: 4:00 pm – 6:00 pm

Location: Houston Science Center – Building 593 — Room 102

Overview

I will present recent results revealing new aspects of the interaction of atoms and ions with carbon nano-structures. Two examples of new research directions are discussed. In the first, laser cooled neutral atoms are launched towards the sidewalls of a highly charged, freestanding, carbon nanotube. A long range interaction causes the atoms to spiral towards the nanotube, as if attracted to an atomic scale "black hole". As an atom approaches the surface of the nanotube an outer electron tunnels into the tube leaving an ion behind that can be readily detected. Experimental results reveal many nano-scale and atomic scale processes at work. Application include high spatial resolution and extremely sensitive detectors of neutral atoms. The second topic involves the use of an atomically thin graphene layer as a "trans-electrode" for ions in aqueous solution. I will show electrical properties of a graphene sheet that is mounted in a fluidic cell so one side of the sheet serves as an electrochemical anode and the other a cathode. The structure shows a very low trans-ionic conductivity at low voltage bias. Embedding a small nanopore in a membrane dramatically increases the trans-ionic conductivity and allows the insulating thickness of the graphene to be determined. Sub nanometer insulating thicknesses are observed which remarkably withstand hundred of millivolts of applied voltage bias. Applications to molecular and chemical sensing are discussed.

Distinguished Lecture Series

Past, Present and Future of the ICTP Trieste

Dr. Fernando  Quevedo

by: Dr. Fernando Quevedo

Date: Friday April 02, 2010

Time: 4:00 pm – 6:00 pm

Location: Houston Science Center – Building 593 — Room 102

Overview

The Abdus Salam International Center for Theoretical Physics is the pre-eminent center for scientifc collaboration and training between developed and developing countries. For more four decades the ICTP has trained thousands of students and scientists from developing countries, promoting the development of science and technology in their countries of origin and establishing long-lasting connections among scientists from different parts of the world. Dr. Quevedo will give an overview of the ICTP and some of its plans for the future, including possible ICTP-USA Centers.

Distinguished Lecture Series

“Why Our Proteins Have to Die So We Shall Live”

Dr. Aaron  Ciechanover

by: Dr. Aaron Ciechanover

Date: Thursday February 11, 2010

Time: 4:00 pm – 6:00 pm

Location: Houston Science Center – Building 593 — Room 102

Overview

Between the sixties and eighties, most life scientists focused their attention on studies of nucleic acids and the translation of the information coded by DNA. Protein degradation was a neglected area, considered to be a non-specific, dead-end process. While it was known that proteins do turn over, the large extent and high specificity of the process - whereby distinct proteins have half-lives that range from a few minutes to several days - was not appreciated. The discovery of the lysosome by Christian de Duve did not significantly change this view, as it was clear that this organelle is involved mostly in the degradation of extracellular proteins, and their proteases cannot be substrate-specific. The discovery of the complex cascade of the ubiquitin pathway revolutionized the field. It is clear now that degradation of cellular proteins is a highly complex, temporally controlled, and tightly regulated process that plays major roles in a variety of basic pathways during cell life and death, and in health and disease. With the multitude of substrates targeted, and the myriad processes involved, it is not surprising that aberrations in the pathway are implicated in the pathogenesis of many diseases, certain malignancies and neurodegeneration among them. Degradation of a protein via the ubiquitin/proteasome pathway involves two successive steps: (a) conjugation of multiple ubiquitin moieties to the substrate, and (b) degradation of the tagged protein by the downstream 26S proteasome complex. Despite intensive research, the unknown still exceeds what we currently know on intracellular protein degradation, and major key questions remain unsolved. Among these are the modes of specific and timed recognition for the degradation of the many substrates, and the mechanisms that underlie aberrations in the system that lead to pathogenesis of diseases.

Distinguished Lecture Series

Are all HTS Josephson Junctions the Same?

Dr. Cathy  Foley

by: Dr. Cathy Foley

Date: Wednesday July 16, 2008

Time: 12:00 pm – 1:00 pm

Location: Houston Science Center – Building 593 — Room 102

Overview

Josephson junctions are the basis of all active superconducting electronics. Since the discovery of high temperature superconducting (HTS) materials and YBCO, in particular, a number of different methods of junction fabrication have been devised on a range of different substrates; grain boundary step-edges, bi-epitaxial, bi-crystal and ramp junctions are common examples. The properties of these junctions vary with differences in the range of critical currents and normal resistance that are achievable, their response to magnetic fields and the amount of s-or d-wave phase shifting across the junction. Superconducting electronic applications are broad ranging including SQUIDs for magnetometry, gradiometry, macroscopic quantum state formation for quantum computer qubits, and microwave and terahertz resonators and detectors. However the requirements of the Josephson junction for each of these applications are quite different. This paper will review four different Josephson junction types and what their properties are by considering the impact of the junction morphology and the substrate material on their demonstrated characteristics. We will report on various devices fabricated at CSIRO and use some data from the literature. We will show that these different junctions have different s- and d-wave contributions as well as other properties that make different junctions more appropriate for each specific application in superconducting electronics.

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Distinguished Lecture Series

The Role of Vortices in Limiting Tc in Cuprate Superconductors

Prof. N. P. Ong

by: Prof. N. P. Ong

Date: Friday April 18, 2008

Time: 4:00 pm – 6:00 pm

Location: Houston Science Center – Building 593 — Room 102

Overview

Superconductivity in the copper oxides occurs at temperatures much higher than in all other metals. There is growing evidence that the Cooper pairs actually survive to even higher temperatures. I will discuss Nernst and torque magnetometry experiments which suggest the scenario that, above Tc in the cuprates, long-range phase stiffness is destroyed, rather than the gap order parameter. In the Nernst experiment, the vortex current produced by a temperature gradient generates a Josephson E-field perpendicular to the applied field H. A large Nernst signal eN persisting to a high onset temperature ~130 K is observed in nearly all cuprate families. Extensive Nernst experiments in the cuprates LSCO, Bi 2201, and 2212 yield a 3D phase diagram (x, T, H) in fields up to 45 T. This picture has been confirmed by recent torque magnetometry experiments. In a tilted H, local planar supercurrents associated with vortices above Tc produce a torque that deflects a cantilever. The inferred diamagnetism provides thermodynamic evidence for the vortex liquid picture suggested by the Nernst effect. Recent high-temperature STM experiments providing direct test of these ideas will also be described.

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