Conferences, Lectures, & Seminars
Events for September
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Material Science Seminar
Fri, Sep 01, 2006 @ 02:30 PM - 04:00 PM
Mork Family Department of Chemical Engineering and Materials Science
Conferences, Lectures, & Seminars
Daniel R. MerrillDirector of Applications Engineering
Alfred E. Mann Foundation for Scientific ResearchSanta Clarita, CA 91355 Increased Electrode Impedance as a Mechanism of Recording Instability Abstract The mechanisms underlying performance degradation of chronically implanted silicon microelectrode arrays in the central nervous system (CNS) remain unclear. One proposed mechanism is increased electrical impedance due to the foreign body reaction at the electrode-brain tissue interface. In this seminar I will first discuss some of the technical issues of impedance measurement including procedural issues that are often poorly understood and implemented. Next I will present experimental work directed towards understanding the failure mechanisms of chronically implanted devices. Several components of the foreign body response were evaluated to determine whether their presence correlates with increased electrical impedance that may be a factor in loss of device performance. Iridium oxide microelectrode recording arrays were electrically characterized in vitro in the presence of saline, culture media with 10% fetal bovine serum (FBS), and coated with various CNS cell types isolated from young Sprague-Dawley rats. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were performed using a three-electrode system. Microelectrodes coated with various cell types known to participate in the foreign body response caused a significant increase in impedance immediately after seeding on the order of 50%, and this value remained constant or gradually increased for up to several weeks. These findings indicate that the attachment of various molecular and cellular species likely contribute to increases in electrical impedance following implantation in brain tissue, but do not appear sufficient to hinder recording performance. These data further suggest that designers may consider incorporation of adherent cells on implanted microelectrodes to promote integration, improve tissue response or deliver therapeutic agents to adjacent tissue. I will lastly present preliminary results of in vivo impedance measurements using a novel tool for characterizing temporal changes at the electrode-brain tissue interface. September 1st, 20062:30-3:50 PM(Refreshments will be served at 2:15 PM)SLH 102**All first year materials science majors are required to attend**Location: John Stauffer Science Lecture Hall (SLH) - 102
Audiences: Everyone Is Invited
Contact: Petra Pearce
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Material Science Seminar
Fri, Sep 08, 2006 @ 02:30 PM - 04:00 PM
Mork Family Department of Chemical Engineering and Materials Science
Conferences, Lectures, & Seminars
From Electrons To Finite Elements: A Concurrent Multiscale Approach For Metalsby
Gang LuDepartment of Physics, California State University, Northridge, CA 91330-8268In this talk, I will discuss how multiscale modeling can be applied to study (1) Hydrogen
enhanced local plasticity in Al, which is crucial to understanding of H embrittlement of
metals. The atomic and electronic mechanism for enhanced dislocation mobility is
explored; (2) Ductile fracture in Al under mode I loading. The atomistic mechanisms of
dislocation nucleation from the crack tip, and crack propagation are investigated. The
electronic states at the crack tip during the fracture process are examined in detail.
Multiscale modeling of material properties has emerged as one of the grand challenges in
materials science and engineering. Multiscale modeling is necessary because the
macroscopic properties of materials are largely determined by the microscopic processes,
taken place particularly at lattice defects. A typical example is the mechanical response of
metals to external loads, which is characterized as ductile or brittle at the macroscopic
scale, depending on the ability of the material to absorb the load by plastic deformations.
This response can be drastically altered by the presence of impurities and their influence
on bonding between the atoms in crucial regions like the crack tip and dislocation core.
The delocalized nature of electronic states in a metal makes the description of such
effects particularly challenging. We have recently developed a multiscale modeling
approach that concurrently couples quantum mechanical calculations for electrons, to
empirical atomistic simulations for classical atoms, and to continuum mechanical
modeling for finite elements, in a unified description [1]. In specific, the electronic
structure calculations are performed with the plane-wave pseudopotential method based
on the density-functional theory (DFT), the classical atomistic simulations with the
embedded-atom method (EAM), and the continuum modeling with the Cauchy-Born rule
in the local Quasicontinuum (QC) formulation [2]. The multiscale method is
implemented in the context of the QC framework with the additional capability to include
DFT calculations for a selection of non-local QC atoms. A novel coupling scheme has
been developed to combine the DFT and EAM calculations [3] in a seamless fashion to
deal with non-local QC atoms.
Reference:
[1] G. Lu, E.B. Tadmor, and E. Kaxiras, Phys. Rev. B 73, 024108 (2006).
[2] E.B. Tadmor, M. Ortiz, and R. Phillips, Philos. Mag. A 73, 1529 (1996).
[3] N. Choly, G. Lu, W. E and E. Kaxiras, Phys. Rev. B 71, 094101 (2005).Refreshments served at 2:15All MASC first-year students are required to attendLocation: John Stauffer Science Lecture Hall (SLH) - 102
Audiences: Everyone Is Invited
Contact: Petra Pearce
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Lyman L. Handy Colloquium
Thu, Sep 14, 2006 @ 12:45 PM - 02:00 PM
Mork Family Department of Chemical Engineering and Materials Science
Conferences, Lectures, & Seminars
"Opportunities and Challenges in Nanostructured Materials"Professor Jagdish (Jay) Narayan
Department of Materials Science and Engineering
North Carolina State University
Raleigh, NC ABSTRACT
This talk addresses some of the fundamental issues and critical advantages in reducing the grain size/ feature size to the nanoscale regime. We find that as the grain size or feature size is reduced, there is a critical size below which the defect content can be frozen or reduced virtually to zero. This critical size for most defects in materials falls in the nanoscale regime. Thus, nanostructured materials offer a unique opportunity to realize the property of a perfect material. However, with this opportunity comes a great challenge in terms of engineering a large fraction of atoms near the surfaces/interfaces. Another challenge is to self-assemble nanounits with desired structure and orientation with respect to the matrix. This often requires thin film epitaxy across the misfit scale with lattice misfit ranging from about 1% to 50%. Using a new paradigm of domain matching epitaxy (DME), we are able to deal with thin film epitaxy across the misfit scale within the continuum ground state energy description of the strained system. The DME framework is based upon matching of integral multiples of lattice planes, where there is one dislocation in each domain corresponding to missing (compressive strain) or extra (tensile strain) half plane. According to the DME paradigm, 2.0% and 25% misfits correspond to 49/50 and 3/4 planar matching, respectively. The misfit in between the integral multiples of planes is accommodated by the principle of domain variation. The limiting factors in DME are associated with matching of interface interatomic potentials, lattice relaxation, overlapping of dislocation cores and bending of lattice planes. For large misfit systems, strain free energy often dominates over chemical free energy. We focus on integration of systems based on III-nitrides, II-oxides, and perovskites.Thursday, September 14, 2006
12:45 p.m.
OHE 122
Refreshments will be served after the seminar in the HED Lobby
The Scientific Community is cordially invited.
Location: Olin Hall of Engineering (OHE) - 122
Audiences: Everyone Is Invited
Contact: Petra Pearce
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Material Science Seminar
Fri, Sep 15, 2006 @ 02:30 PM - 04:00 PM
Mork Family Department of Chemical Engineering and Materials Science
Conferences, Lectures, & Seminars
Dr Matthew Halsall,
School of Electrical and Electronic Engineering,
The University of Manchester,
UK.Visible and Infrared spectroscopy of nitride quantum wells and dotsABSTRACTThe speaker will describe some his recent research concerning the optical properties of semiconductor quantum wells and dots based on the wide gap Al/Ga/In nitride materials. Indium rich InGaN quantum dots have been grown on GaN by MOVPE and studied by AFM. The dots occur at low surface densities, are typically 20-30nm in diameter and 5nm in height, and they also have tendency to occur in closely spaced pairs. Macro and micro photoluminescence studies of these dots show emission due to the dots in the 2.5-2.9eV region of the spectrum and the presence of sharp spectral lines demonstrates the 1D nature of their electronic energy levels. The dot PL linewidth also show the effects of spectral diffusion due to the charging of defect levels in the underlying "wetting layer". The use of Schottky junctions to deplete the impurity levels and reduce this linewidth is discussed. After depletion in this way, the power dependent PL of individual dots reveals a complex energy spectrum dominated by the internal fields present in these wurtzite systems. Finally some recent results on near/mid infrared intersuband structures grown in the AlGaN/GaN system will be presented. These include first mid-infrared Quantum well infrared photoresponse in the 2-5micron region of the spectrum from a device fabricated in this system.September 15th, 2006
2:30-3:50 PM
(Refreshments will be served at 2:15 PM)
SLH 102**All first year materials science majors are required to attend**
Location: John Stauffer Science Lecture Hall (SLH) - 102
Audiences: Everyone Is Invited
Contact: Petra Pearce
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Material Science Seminar
Fri, Sep 22, 2006 @ 02:30 PM - 04:00 PM
Mork Family Department of Chemical Engineering and Materials Science
Conferences, Lectures, & Seminars
Ng Lam (Argonne National Lab)
Location: John Stauffer Science Lecture Hall (SLH) - 102
Audiences: Everyone Is Invited
Contact: Petra Pearce
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Chemical Engineering and Materials Science Seminar
Thu, Sep 28, 2006 @ 02:30 PM - 04:00 PM
Mork Family Department of Chemical Engineering and Materials Science
Conferences, Lectures, & Seminars
Ultrafast Biological Dynamics at Atomic Scale Dongping ZhongDepartments of Physics, Chemistry and Biochemistry,
Programs of Biophysics, Chemical Physics and Biochemistry,
The Ohio State University, 191 West Woodruff Avenue, Columbus, OH 43210, USAProtein dynamics is a complex process and the current challenge is to break down its complexity into elementary processes which act on different time scales and length scales. We integrate femtosecond spectroscopy, molecular biology techniques, and computational simulations to study functional evolution in real time and thus elucidate the complex dynamics with unprecedented detail. Here, two important biological systems, protein surface hydration and light-driven DNA repair, will be reported. With femtosecond temporal and single-residue spatial resolution, we mapped out the global water motion in the hydration layer using intrinsic tryptophan residue to scan the protein surface with site-directed mutagenesis. The results reveal the ultrafast nature of surface hydration dynamics and provide a molecular basis for protein conformational flexibility, an essential determinant of protein function. For DNA repair, we followed the entire functional evolution through femtosecond synchronization. We resolved a series of ultrafast processes including active-site solvation, energy transfer, and electron tunneling. These results elucidate the crucial role of ultrafast dynamics in control of biological function efficiency and lay bare the molecular mechanism of DNA repair at atomic scale.
Location: John Stauffer Science Lecture Hall (SLH) - 102
Audiences: Everyone Is Invited
Contact: Petra Pearce