DAY 1: Sunday, June 27
Located at the confluence of three major rivers, the Ottawa, the Gatineau and the Rideau, the city of Ottawa is the capital of Canada. This week, it is also the venue of the 2010 American Conference on Neutron Scattering, being held at the historic Fairmont Château Laurier hotel. The conference opened Saturday evening with a reception. Two tutorials were held on Saturday as well. An opening plenary session was held Sunday morning with six speakers. Several technical sessions were held during the day, while the first poster session in conjunction with the exhibit was held in the evening.
The major event of the day was the plenary session in the morning that included six major talks. Conference chair Simon Billinge (Columbia University) opened the session and the conference by welcoming all attendees. He also thanked the various organizers responsible for bringing this conference to fruition. Bruce Gaulin (McMaster University) who is current president of the Neutron Scattering Society of America welcomed overseas visitors to Canada and Ottawa, and recommended attendees spend some time outside of the conference exploring Ottawa.
Fifty Years of Neutron Scattering in Canada - William J. Buyers
William Buyers of the Canadian Neutron Beam Centre at Chalk River, Ontario, is a well known name in neutron science. It was fitting that Buyers was the first plenary speaker of this conference being held in Canada. In his talk, he overviewed developments in neutron scattering from a Canadian perspective subtitling his talk, from Brockhouse to the 21st century. Bertram N. Brockhouse of course won the 1994 Nobel Prize in Physics "for the development of neutron spectroscopy" along with Clifford Shull. Buyers is originally from Scotland, and came to Canada over 50 years ago. Starting with some of his early work in neutron science, he described specific examples of seminal work done in Canada in this field. He covered cobalt oxide spin waves, perovskite antiferromagnets, quantum He-4 fluid, and solitons in one-dimensional antiferromagnets. He also described some recent very interesting work including residual stress determination in engineering materials (formed into a commercial entity), polarized neutron beam science, and the orientation of cholesterol molecules in a bio-membrane. Buyers concluded by mentioning the export of talented neutron science researchers to institutions outside Canada including to Oxford, NIST, MIT, Berkeley, and Oak Ridge showing Canada's ability to consistently produce scientific leaders.
Tackling our Energy Challenges in a New Era of Science - Linda Horton
Linda Horton is Director of the Materials Sciences and Engineering Division of the Office of Basic Energy Sciences (BES) within the U.S. Department of Energy (DOE). In her plenary talk, Horton described opportunities for funding of neutron scattering through the DOE. The energy needs of the world continue to grow at a torrid pace, particularly in Asia. Along with this is the alarming rise in CO2 levels in the atmosphere accompanied by ice loss in the polar regions. Clearly breakthoughs are needed in various energy areas to be able to supply the energy for such gowth, and to do this in a manner that does not disrupt the current environmental balance, which is already tilting in a negative direction. The DOE is involved in various ways in promoting research on critical energy-related areas, and Horton overviewed these in her talk. She described strategic planning efforts within BES. In particular, DOE invests in science to achieve transformational discoveries, she said. Horton indicated that neutron scattering plays an important role in several research directions supported by the DOE and BES. In addition to core research support, BES also has funded Energy Frontier Research Centers and Energy Innovation Hubs. Further information on all of these topics as well as much more is available on the BES website at http://www.sc.doe.gov/bes/BES.html.
Neutron Scattering and Energy - Thomas Mason
Thomas Mason is Director of the Oak Ridge National Laboratory in Oak Ridge, Tennessee, in the United States. He is also originally Canadian and was involved in neutron research. He was deeply involved in the construction phase of the Spallation Neutron Source at Oak Ridge. Mason presented the plenary lecture on neutron scattering as a crucial tool for scientific breakthroughs in developing advanced energy technologies. The starting point of his talk was world energy consumption, which is expected to increase significantly by 49% from 2007-2035. He emphasized that economic and population growth results in increasing energy demand. Another important point is that human activity is affecting global climate and the concentration of CO2 is progressively increasing in the atmosphere, as also mentioned by the previous speaker.
The main questions to ask are (1) where we are going to get the energy, and (2) what we are going to do to resolve the problem of climate change? It is clear that a new set of transformational discoveries and disruptive technologies are needed involving efficient use of energy and new alternative sources. In this respect, the essential “green” energy technologies include nuclear power, wind, solar, biofuels, and electrically-driven vehicles. Mason also emphasized that materials form a crucial proportion of the energy equation.
His main focus was on today’s neutron facilities which provide capabilities for understanding of structure-dynamics-function relationships of materials leading to the development of clean and sustainable energy technologies. The talk highlighted the use of neutron scattering to explore biomaterials, superconductors, and other engineering energy-related systems. One of the examples Thomas mentioned was developing high-temperature long-lasting materials based on nickel alloys for high-strength and light-weight vehicles. Another example is the investigation of bio-based fuel systems for sustainable energy based on cellulose digestion. One more recent study performed with neutrons focused on the design of next generation batteries with dramatically improved capacities and long life-times.
Magnetic Superconductors: The Perfect Playground for Neutron Scattering - Jeffrey Lynn
Jeffrey Lynn (NIST) in his talk described the development of superconductors over nearly a century, the connections to magnetism and how neutron scattering plays a crucial role in understanding the connection between the two. He started with a history of superconductors and Cooper pairs recognized to be the mechanism for superconductivity in the original systems. Magnetic impurities disrupt spin pairing and were recongnized to be detrimental. However, exceptions to this were found including magnetic sublattices with long range magnetic order and ferromagnets. He discussed the use of small angle neutron scattering to elucidate some of the properties of these materials. Lynn then described cuprate superconductors with high Tc values discovered in the mid-1980s. In these, the parent 'systems' are Mott-Hubbard antiferromagnetic insulators with very strong two-dimensional magnetic interactions. These strong exchange interactions survive into the superconducting state yielding highly correlated electrons that participate directly in the superconducting pairing. Finally, Lynn discussed the new iron-based superconductors first discovered in 2008 that are attracting tremendous current attention. Neutron scattering has been used to investigate all of these systems.
Lynn summarized his talk by suggesting that magnetic superconductors have a rich history going from "should not have magnetic spins in the lattice" to "must have magnetic spins in the lattice" for high Tc. For cuprate superconductors, the Cu spin dynamics provide the needed high energy scale. In these materials, the magnetic resonance is directly tied to the superconducting state for both hole and electron-doped cuprates. Finally, iron-based superconductors exhibit a similar phase diagram as the cuprates. The 'parent' systems exhibit a ubiquitous structural transition below which long range antiferromagnetism is seen. The role of spin fluctuations in the superconducting pair is clear. Lynn suggested that our understanding of this new family of superconductors is better than for the cuprates thanks to neutron scattering, and this might yield the key to a full understanding of both classes of high Tc superconductors.
Neutron Imaging: The Vision Superman should have had - Muhammad Arif
There have been tremedous strides made over the last two decades in neutron imaging, that is, using thermal and cold neutrons to image materials that can reveal startling details that cannot be imaged by other techniques. Muhammad Arif of NIST presented various examples of images formed using neutrons in his talk in the plenary session. Currently, a range of imaging techniques including neutron tomography, phase contrast imaging and energy selective imaging are available. Neutrons in particular are very effective for probing low atomic number materials, which are difficult to image using X-rays. Images are captured using high efficiency neutron detectors yielding spatial resolutions of ten micrometers. Arif then presented various examples of using neutron imaging for useful applications.
Polymer electrode membranes are used in current fuel cells. Arif described how neutron scattering can be used to image the flow of water within channels in the fuel cell. In addition, water distribution within a membrane could also be imaged. Another example was hydrogen storage beds used to store hydrogen for use in vehicles. Neutron imaging was used in real-time to measure H-uptake and the distribution along the length of the storage bed. The H-distribution could also be measured in 3-D to study effects of temperature gradients and bed construction. Another example was Li-batteries wherein both Li and H are energy carriers. Neutron scattering was used to image Li and H-ion transport bottlenecks. Neutron tomography was also used to investigate the growth patterns of ancient (2 billion years old) microbes using buried organic inclusions, using the hydrogenous component. Another fascinating example was imaging the complete 3-D structure of the lung of a rat. Phase contrast imaging has various applications. In a forensic application, phase contrast neutron imaging was used to image the serial number on a car that had been machined out. The number could still be imaged using neutrons. In another study, polarized neutrons were used to image phase transitions in a magnetic system, a PdNi crystal at different temperatures. Clearly, neutron imaging will find a host of useful applications and continue to see rapid growth.
Tau Protein Directed Assembly in Neuronal Systems - Cyrus R. Safinya
Understanding interactions of supramolecular assemblies of biological molecules gives important information on structure-function relationships in biological systems and leads to the development of nanoscale functional biomolecular materials. Cyrus Safinya (University of California at Santa Barbara) focused his plenary talk on the elucidation of directed assembly of Tau proteins in neurological systems. Nerve cells provide a rich variety of bundles and networks of interacting neurofilaments, microtubulus, and filamentous actin. In this respect, Tau is an unstructured but fully functional protein which plays a critical role in the nervous system in stabilizing mature neurons and in the outgrowth of axons in developing neurons.
In his talk, Safinya addressed several important questions targeted at understanding microtubule interactions and functions in vivo. Some of these involved the effects of Tau proteins on microtubule assembly, the role of counter-ions in bundling, and the significance of bundles in the maintenance of axons in mature neurons. The study is crucial for exploring Tau-induced bundling in axonogenesis and in understanding how unnatural interactions between tau and microtubules lead to neurodegeneration (including Alzheimer’s Disease).
Safinya emphasized that a fundamental understanding of interactions between cell cytoskeletal proteins and their associated molecules can be obtained by combining state-of-the-art techniques such as reciprocal space and real space data resulting from X-ray diffraction and scattering, light-microscopy differential-interference-contrast and three-dimensional confocal imaging, and electron microscopy experiments. He demonstrated that synchrotron small angle X-ray scattering (SAXS) and electron microcopy were capable to probe non-crystalline structures of Tau-directed filament assemblies in neurons; while small angle neutron scattering (SANS) is an ideal tool to directly examine the structural nature of distinct Tau domains on the microtubule surface.
Symposium C: Soft Condensed Matter
Dynamic studies of gel network morphology under flow
Hydrogels as crosslinked polymers networks are very attractive for biomedical applications as they are soft, bio-mimetic, and tissue-friendly. Congqi Yan, a graduate student from the University of Delaware, presented a mechanically robust hydrogel which was prepared by crosslinking of peptides. Remarkably, the peptide was bio-compatible and possessed self-healing properties. She demonstrated that hydrogels were highly responsive to mechanical shear under flow. However, the shear-thin gel solution was restored into a solid stiff gel after stress was removed. A rheometric study was performed to investigate the restoration of gel rigidity with various shear stresses applied. SANS and SAXS were used to investigate the dynamic gel morphology under various flow conditions. This remarkable self-healing capability suggests that the gels are excellent candidates for tissue regeneration, since they can recover after syringe injection.
Symposium E: Chemistry & Materials
Controlling Zeolite Beta Nucleation and Growth
Zeolites are a class of crystalline microporous aluminasilicate materials. Their unique 3-D porous structure along with high thermal stability are very attractive for applications in ion-exchange, catalysis, and separation. One outstanding problem is understanding the nucleation mechanism of zeolites which would afford rational design of the high-performance materials. Nathan Hould, a graduate student from the University of Delaware, focused his work on investigating the fundamental aspects of the beta nucleation process and compared the results with the classical nucleation theory. He found that the presence of sodium ions in Al-containing precursor solutions is important to control the density of the zeolite particles. On the other hand, Al controls particle aggregation as it slows down nucleation at low Al concentrations. More importantly, he was able to probe the transition from amorphous to crystalline zeolite by applying neutron scattering.
Symposium F: Condensed Matter Physics
Polarized Neutron Scattering Studies of Multiferroic Ni3V2O8 in an Electric Field
Ivelisse M. Cabrera of Johns Hopkins University presented a study on using polarized neutrons to investigate multiferroic domains in Ni3V2O8 (NVO), a system that is both magnetic and ferroelectric. Polarized neutron scattering can reveal details on complex magnetic structures. In the present work, polarized neutrons along with electric polarization measurements yielded direct electric control of multiferroic domains in NVO, as suggested by control of cycloidal domains. The study revealed that magnetic and ferroelectric domains coincided in NVO at low temperatures. This suggests that magnetic domains can be controlled by an external electric field. Polarized neutrons provided a quantitative measure of the population of cycloidal domains as a function of the electric field. Interestingly, an unusual memory effect was observed in the multiferroic phase of NVO, where a previously electrically-polarized sample "remembered" its polarization direction on leaving and re-entering the multiferroic phase in the absence of a field. The underlying reasons for this memory effect are still not clear and will be the subject of future investigations according to the speaker.
Scanning the Conference
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