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Bi-Weekly Seminar

Bioconjugation onto Silicon Surfaces

 Chengzhi  Cai

by: Chengzhi Cai

Date: Friday June 27, 2008

Time: 12:00 pm – 1:00 pm

Location: Houston Science Center – Building 593 — Room 102

Overview

We have recently prepared robust monolayers on silicon or silicon carbide surfaces by surface hydrosilylation. We have demonstrated that these monolayers are the most protein-resistant and stable monolayers reported to date. We have also developed a method for nanopatterning on the above monolayers with 10 nm resolution, and introduced handles on the monolayers for bioconjugation. Meanwhile, we are developing "click" reaction based methods for efficient bioconjugation onto surfaces and nanoparticles. We have used the method to functionalize silicon and silicon carbide surfaces with carbohydrates. The research is relevant to the development of efficient silicon-neuron interfaces.

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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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Bi-Weekly Seminar

The Newly-Discovered Fe-Based Layered High Temperature Superconductors

Dr. Ching Wu Chu

by: Dr. Ching Wu Chu

Date: Friday April 11, 2008

Time: 12:00 pm – 1:00 pm

Location: Houston Science Center – Building 593 — Room 102

Overview

Built upon insight gained from cuprate high temperature superconductors and work on the equiatomic quarternary rare-earth transition metal oxypnictide superconductors, ROTP with R = rare-earth, O = oxygen, T = transition metal, and P = pnictogen over the last few years, Hideo Hosona's group in the Tokyo Institute of Technology reported in late February of this year that they achieved superconductivity with a Tc of 26 K in F-doped LaOFeAs. The report has generated great excitement. Last week, three groups in China achieved a Tc = 41 K in F-doped CeOFeAs, a Tc = 43K in F-doped SmOFeAs, and a Tc = 50 K in F-doped PrOFeAs, respectively. Tens of papers flooded the scientific community in a very short period of time, due to the possible scientific implications on high temperature superconductivity and the intriguing physics involved. In this talk, I will present experimental results from our group on some of these compounds at TcSUH and discuss the similarities and differences between the cuprate and pnictide superconductors, after briefly presenting the history on and summarizing the present status of the study on superconducting ROTP.

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Bi-Weekly Seminar

Electronic Mechanism of Two-Dimensional D-Wave Superconductivity

Prof. W. P. Su

by: Prof. W. P. Su

Date: Friday March 28, 2008

Time: 12:00 pm – 1:00 pm

Location: Houston Science Center – Building 593 — Room 102

Overview

Motivated by high-temperature superconductors, it is useful to discuss a BCS-like effective Hamiltonian for a two-dimensional d-wave superconductor independent of the origin of the pairing potential and to explore the consequences of such a model. A particular aspect of this model which has so far not received adequate attention is the intrinsic instability of the charge carriers towards phase separation. Such an instability can lead to phenomenologies strikingly similar to those observed in the cuprates including inhomogeneous superconductivity and the ‘pseudogap’ phase diagram. This raises the issue of how much of the cuprate phenomenology is independent of the origin of the pairing potential. In the case of the s-wave superconductors, it is well-known that most of the properties of the superconductors can be explained by an effective Hamiltonian which contains an attractive pairing potential which might or might not be mediated by phonons.

As an example of electronic mechanism for d-wave pairing, we have studied a model inspired by an idea proposed by W. A. Little in the sixties. In this model, a charge moving in a conduction plane can induce charge polarization in polarizable molecules surrounding the conduction plane. This polarization can in turn attract a second charge carrier thus establishing an effective attractive interaction between two carriers. For certain choice of parameters, the model does seem to exhibit d-wave superconductivity. Interestingly, the model also seem to exhibit phase separation.

For the cuprates, a more likely origin of the pairing force is probably interlayer polarization. Theoretical as well as experimental arguments will be presented to support this speculation.

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Bi-Weekly Seminar

X-ray Scattering Studies of Semiconductor Nanoclusters in Zeolites

 Milinda  Abeykoon

by: Milinda Abeykoon

Date: Friday February 29, 2008

Time: 12:00 pm – 1:00 pm

Location: Houston Science Center – Building 593 — Room 102

Overview

When electrons and holes in a semiconductor are confined to ultra-small regions of space (typically 1-25 nm), the optical and electronic properties of the semiconductor become strongly size-dependent. Such structures are called quantum dots, nanowires or nanoclusters, depending upon their shape and dimensionality. These nanostructures are of great interest for a variety of potential electronic, photochemical and nonlinear optical applications and are necessary for an analysis of the transition from molecular to bulk semiconductor properties.

This talk will discuss the structure of HgSe and Se semiconductor nanoclusters synthesized in both Nd-Y (spherical pore) and LTL (tubular pore) zeolites. The molecular structures of these systems were modeled by performing the Rietveld refinement on X-ray Bragg data. A remarkable feature in our X-ray diffraction patterns, continuous diffuse scattering under the Bragg peaks, will also be discussed along with our PDF (Pair Distribution Function) data. We use the results of optical studies to complement our X-ray structural work.

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