Friday, May 30, 2008
Johannes Lehman, Associate Professor
Crop and Soil Sciences
"TBA"
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CHESS Special Journal Club
Monday,
April 14, 2008 -
2:00pm, Wilson Commons
Dr. Joel Parriott, Program Examiner
Office of Management and Budget
Executive Office of the President
"Sausage Making and the Federal Science Budget Process: Implications for Universities"
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Friday, March 28, 2008
Roy Clarke,
Professor of Physics
University of Michigan
"Emergent Phenomena at Epitaxial Interfaces: A Structural View"
Recent discoveries at the film-substrate interface in epitaxial oxide heterostructures such as LaAlO3-SrTiO3 have opened the lid on a wealth of "emergent" correlated electron phenomena. Examples include: novel metal-insulator behavior, interfacial superconductivity, and the onset of "colossal" magnetoresistance. Structural insights provided by direct x-ray phasing methods are essential to understanding the physics of these systems [PRL 99, 155502 (2007)].
Roy Clarke is a Professor of Applied Physics at the University of Michigan, Ann Arbor. He is a Fellow of the American Physical Society and is active in the Materials Research Society and the American Vacuum Society. His research spans a broad range of topics in epitaxial thin films, most recently in the behavior of interfaces in nanoscale magnetic and ferroelectric thin films. Much of this work bears on technological applications and the company he co-founded, k-Space Associates, serves the need for in-situ real-time metrology in semiconductor device production.
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Friday, March 21, 2008
Jocelyn Rose, Associate Professor
Director of the Cornell Initiative
Dept. of Plant Biology
"Proteomics Based Discovery of New Plant Cell Wall Localized Enzymes"
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Friday,
February 29, 2008
George Flynn, Team Leader, Chemical
Analysis NASA Stardust Science Team, Professor of Physics
Astrochemistry, SUNY Plattsburgh
"STARDUST: The Mission and the Critical Role of X-ray Chemical Analysis"
NASA's Stardust spacecraft collected dust in low-density silica aerogel during its passage through the dust coma of Comet 81P/Wild 2 in January 2004. The aerogel capture cells, containing hundreds of Wild 2 particles, were recovered on January 15, 2006.
A compact, single grain captured in low-density aerogel produces an entry damage track several hundred times the diameter of the particle, with an intact particle at the end of the track. Initial inspection of the Wild 2 samples indicated that, as expected, the comet dust was very weak. Most particles broke up on collection, depositing material all along the entry track.
X-Ray Microprobes, with their ability to penetrate into the interior of the aerogel, permitted the distribution of all but the lightest elements (Z < sulfur) to be mapped over the entire entry track. Seven groups of investigators using six synchrotrons on four continents contributed to the preliminary chemical characterization of the Wild 2 samples, determining the element distributions in 23 tracks.
The X-Ray Microprobe analyses demonstrated that the compositions of the terminal particles, which were generally dominated by mineral grains (olivine, pyroxene, or Fe-sulfide) were quite different from the composition of the finer-grained material deposited along the entry track. Thus, the composition of the incident particle could not be determined simply by extracting a terminal grain and analyzing it with conventional laboratory instruments, such as an electron microprobe. X-Ray Microprobes provided the critical analytical capability to characterize the material distributed along the entry tracks.
The average elemental composition of the 23 particles agrees well with the composition of the CI carbonaceous meteorites, which are believed to represent the initial composition of the Solar System for the non-volatile elements. However, several moderately volatile minor elements (Cu, Zn, Ga, and Ge) were found to be enriched over the CI meteorite composition, suggesting the outer region of the Solar Nebula, where comets such as Wild 2 are believed to have formed, may have contained higher concentrations of these elements than the inner region of the Solar Nebula, where the meteorites formed.
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Friday, February 22, 2008
Rui Peng Li, Visiting Scientist
CHESS, Cornell University
"Overview of National Synchrotron Radiation Laboratory (NSRL), China and a Capillary Test"
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CHESS/ERL Special Journal Club
Wednesday,
February 20, 2008 -
3:00pm, 380 Wilson Lab
Roger Falcone, Professor of Physics
and co-director of the Cal Teach Program - UC Berkely
Director, Advanced Light Source at LBNL
"A Proposed Soft X-ray FEL Facility"
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Friday, February 8, 2008
J.C. Séamus Davis, Professor
Physics, Cornell University
"Visualizing Complex Electronic Structure with Spectroscopic Imaging STM" (pdf)
Professor Davis will describe the development of spectroscopic imaging STM and review examples of how long-unsolved physics problems can be addressed with this exciting technique.
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NOTE: Talk will begin at 2:30pm
Friday, February 1, 2008
Andrew
Smith, Associate Professor
Dept. of Biology, Ithaca College
"Gluing with an Iron Fist: how small snails turn gels into strong adhesives"
Gastropod molluscs such as snails and slugs secrete glues that create strong, temporary adhesion. These glues are dilute gels, containing over 95% water, yet the animals can be extraordinarily difficult to detach by hand. Furthermore, they can adhere to a wide variety of surfaces, whether dry or wet. Because of the novel characteristics of these glues, there is good potential for biomimetic applications. Recent work has shown that the glues are structurally similar to the lubricating gels the animals normally use for locomotion except for a few key changes. The primary change is the addition of specific proteins that have been labeled "glue proteins". Such glue proteins have been identified in four different species. The glue proteins have been isolated and they stiffen gels non-specifically. The major questions we are currently addressing focus on the structure of the proteins and how they trigger gel stiffening. A striking feature of the glues is the presence of iron bound tightly to the glue proteins. In addition, substantial quantities of other transition metals are present. Removing or binding these metals with a strong chelator blocks the ability of the glue proteins to function in several different assays. Comparisons of how tightly the metals are bound to the gel, and their separate effects on glue activation suggest that iron may play a central role. These observations suggest several possible mechanisms by which the glue proteins may act.
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NOTE: Talk will begin at 2:45pm
Friday, January 25, 2008
Lara Estroff, Assistant Professor
Dept. of Materials Science and Engineering
Cornell University
"Formation and Characterization of Polymer-Reinforced Porous Single Crystals"
In this work, we characterize the internal structure of calcite crystals grown in an agarose hydrogel and show that the gel-grown calcite crystals, like biogenic calcite crystals, incorporate the organic matrix. The gel fibers are uniformly distributed within the crystals, without changing the regular rhombohedral morphology of calcite crystals. Etching of the gel-grown crystals with distilled water reveals an interpenetrating network of gel fibers and crystalline material. TEM examination of microtomed slices shows directly the porous internal structures of the crystals. Both electron-back scattered diffraction (EBSD) and selected area electron diffraction (SAED) demonstrate that the structures are single crystals of calcite.
I will also discuss the mechanism of gel incorporation during crystal growth. The effects of gel concentration, gel strength, and the concentration of calcium ions on the amount of incorporated gel were investigated by SEM and TGA. The results show that: 1) The amount of incorporated agarose increases roughly linearly with increasing gel concentration; 2) Crystals grown in a weaker gel (agarose IX) do not incorporate the organic matrix; 3) The amount of incorporated agarose initially increases and then reaches a constant value with increasing concentration of calcium ions. Based on these results, we propose the following mechanism: The gel network causes the growing crystals to incorporate the gel fibers by blocking mass transport to the growth fronts. Counter to this force, the crystallization pressure acts on the gel fibers to push them away. If the gel network is weak, the fibers will be pushed away by the pressure, while if the gel network is strong, the pressure will expand the gel network and the growing crystals will incorporate the fibers. The degree of expansion of the network decreases with increasing supersaturation (calcium concentration). This work provides an in vitro platform to study the biomineralization of calcite and a potential approach to fabricate single crystals coupled with large internal surface areas.
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Friday, January 11, 2008
Mark Dumont, Associate Professor
Dept. of
Biochemistry and Biophysics
University of Rochester Medical Center
"Improving Expression, Purification, and Crystallization of Eukaryotic Transmembrane Proteins for Structure Determination"
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CANCELED
Friday, January 4, 2008
Jocelyn Rose, Associate Professor
Director of the Cornell Institute for Sustainable Bioenergy Crops
Dept. of Plant Biology
"Proteomics Based Discovery of New Plant Cell Wall Localized Enzymes"
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