Colloquium Spring 2009
The Spitzer Space Telescope: Reionization to Exoplanets
Dr Michael Werner
The Spitzer Space Telescope, launched in August 2003, has dramatically advanced the state of the art for infrared space observatories. Spitzer's three instruments, equipped with modern detector arrays for both imaging and spectroscopy, are returning stunning images and fascinating spectra of objects far too faint to have been seen in the infrared up until now. The large data bases produced by Spitzer have provided important new insights on questions ranging from the edge of the observable Universe to our local neighborhood within the Milky Way, while clever observers have used Spitzer to make pioneering studies of extrasolar planets. This talk will review the technical foundations of the mission, provide an overview of the rich scientific return from Spitzer, and look forward to the Spitzer Warm Mission which will commence later this year when the liquid helium supply is exhausted.
Martin Luther King, Jr. Birthday, University Holiday
Opening up the black box called 'Physical Review Letters'
Dr Deniz van Heijnsbergen
Institute for Molecules and Materials, Managing Director, Radboud University Nijmegen
What happens once you've submitted a manuscript to Physical Review Letters? How are referees chosen for your paper? What factors play a role when the editor makes a decision on the disposition of your paper? How does the editorial office work? How is PRL performing in the new millennium? How is your university and country performing in the last few years? What is PHYSICS? And what other turbulent developments are there in the world of publishing scientific material? These and other questions will be discussed in a presentation about facts, style, statistics, history, referees, authors and 'hot' papers, which will hopefully culminate in a lively debate about the imminent changes in the landscape of scientific publishing.
Spintronic Materials - Half Metals with Simple Structures, Si-based Quantum Structures and MnxSi1-x
Professor Ching Fong
We explain first why half metals are ideal materials for spintronic devices, in particular, the key property relevant to the magnetoresistance, and the reasons for the search for half metals with simple structures. We then present (1) a few half metals with simple structures and the basic interactions determining the half metallicity; (2) a Si based digital ferromagnetic heterostructure and the effects of the defects on its half metallic properties, and (3) the magnetic moment in MnxSi1-x with x < 0.2%. Finally, the prospects of all these half metals and the dilute alloys for spintronic applications will be commented on.
Explore Information Resources and Services at USC
Norah B Xiao
Science and Engineering Library, USC
The presentation will give an overview of USC Libraries information resources and services available to users in Physics and Astronomy. Everyone is using the library in his research and study. Do you realize your liberal borrowing privilege at USC Libraries? How about all new resources provided by USC Libraries, and their new added-in features? Did you find all you need at USC Libraries? Have you ever talked to your subject librarian for your research, teaching and/or study needs at USC Library is neither a physical cage, nor a dull study place. It is a place where your imagination gets entertained and cultivated.
Presidents' Day, University Holiday
Functional Magnetic Resonance Imaging and Its Applications in Understanding the Neural Mechanisms of Attention
Professor Zhong-Lin Lu
William M. Keck Chair in Cognitive Neuroscience, Psychology, Biomedical Engineering & Neuroscience Graduate Program, USC
Functional Magnetic Resonance Imaging (fMRI) has become an important tool in studying the neural basis of human behavior. In the first part of the talk, I will briefly introduce the physical principles underlying Magnetic Resonance Imaging (MRI), the physiological basis of functional Magnetic Resonance Imaging (fMRI), and the basic experimental paradigms and data analysis techniques in fMRI, with highlights of the challenges and needs for developing novel data analysis and modeling techniques in brain imaging research. In the second part of the talk, I will talk about applications of fMRI in understanding the neural mechanisms of attention. Attention solves the problem of information overload by selecting some information for further processing, or by managing resources applied to several sources of information simultaneously. Sensory physiologists and psychologists have recognized the importance of attention on human performance for more than 100 years. In recent years, cognitive and neural mechanisms of attention have become one of the central focuses in cognitive science. Using external noise analysis in psychophysics and a theoretical framework based on the perceptual template model (Lu & Dosher, VR'1998; Lu & Dosher, Psych Review'2008), we conclude that covert spatial attention operates via two independent mechanisms: (1) excluding external noise/distrators in the target region, and (2) enhancing stimulus in the target location. In two recent studies (Li et al, PNAS'2008; Lu et al, under revision), we investigated neural mechanisms of covert attention by studying the blood oxygenation level dependent (BOLD) contrast response functions in retinotopically defined early visual areas. Previous fMRI studies have found increased BOLD responses to attended spatial regions. We found that covert attention reduced the BOLD response to external noise by about 50% in early visual areas, while at the same time increased the contrast gain and dynamic range of the BOLD response. Identification of the distinct mechanisms of attention may lead to future investigations of the status of these distinct mechanisms in various mental health conditions that have been associated with abnormalities in deployment of attention, with strong implications for remediation strategies.
Sunlight-Driven Hydrogen Formation By Membrane-Supported Photoelectrochemical Water Splitting
Prof Nathan S. Lewis
Division of Chemistry and Chemical Engineering, California Institure of Technology
We are developing an artificial photosynthetic system that will only utilize sunlight and water as the inputs and will produce hydrogen and oxygen as the outputs. We are taking a modular, parallel development approach in which the three distinct primary components-the photoanode, the photocathode, and the product-separating but ion-conducting membrane-are fabricated and optimized separately before assembly into a complete water-splitting system. The design principles incorporate two separate, photosensitive semiconductor/liquid junctions that will collectively generate the 1.7-1.9 V at open circuit necessary to support both the oxidation of H2O (or OH-) and the reduction of H+ (or H2O). The photoanode and photocathode will consist of rod-like semiconductor components, with attached heterogeneous multi-electron transfer catalysts, which are needed to drive the oxidation or reduction reactions at low overpotentials. The high aspect-ratio semiconductor rod electrode architecture allows for the use of low cost, earth abundant materials without sacrificing energy conversion efficiency due to the orthogonalization of light absorption and charge-carrier collection. Additionally, the high surface-area design of the rod-based semiconductor array electrode inherently lowers the flux of charge carriers over the rod array surface relative to the projected geometric surface of the photoelectrode, thus lowering the photocurrent density at the solid/liquid junction and thereby relaxing the demands on the activity (and cost) of any electrocatalysts. A flexible composite polymer film will allow for electron and ion conduction between the photoanode and photocathode while simultaneously preventing mixing of the gaseous products. Separate polymeric materials will be used to make electrical contact between the anode and cathode, and also to provide structural support. Interspersed patches of an ion conducting polymer will maintain charge balance between the two half-cells. The modularity of the system design approach allows each piece to be independently modified, tested, and improved, as future advances in semiconductor, polymeric, and catalytic materials are made. Hence, this work will demonstrate a feasible and functional prototype and blueprint for an artificial photosynthetic system, composed of only inexpensive, earth-abundant materials, that is simultaneously efficient, durable, manufacturably scalable, and readily upgradeable.
Frustrated, degenerate, and decaying: the Bright Side of Life of quantum spins
Prof Sasha Chernyshev
Physics, UC Irvine
I will present some evidence that despite some seemingly negative connotation of the words, the life of frustrated quantum magnets is very bright and interesting. This is true, even more so, for their spin excitations. In this talk I will introduce these systems and discuss the complex behavior they exhibit.
No abstract provided.
Examining Cell-to-Cell Variation in Intracellular Biochemical Response in Live Cells under Controlled Stress: A New Paradigm
Dr Siyuan Lu
Nanostructure Materials and Devices Laboratory, Department of Physics and Ophthalmology, USC
Biological cells are amazingly complex and delicate machinery whose phenotype response (motility, proliferation, death, etc.) to external stresses is governed by complex signaling networks typically involving dozens of known or unknown biochemical processes. Although the stochastic nature of these processes and their inter-dependence on the level and spatial distribution of the signaling molecules ensures cell-to-cell variation, relying upon the average behavior of cell populations is the norm. We, however, take the view that the cells that fall in the tails of the distribution are, by virtue of being extreme, central to understanding resistance or susceptibility to external stress causing disease. Consequently, we have developed a real-time imaging system which simultaneously tracks, via time-multiplexing, multiple cellular processes in all individual cells in a statistically significant population. Using this unique imaging system, we are examining cellular processes related to mechanical stress induced neuronal cell apoptosis (programmed cell death). The experiments reveal for the first time the simultaneous temporal evolution of apoptotic markers, cell morphology, and a significant cell-to-cell variation. Such studies open the pathway to the development of quantitative database necessary to develop a new framework of mathematical models of stress induced cellular response that account for the observed cell-to-cell variation. Work carried out with Jae Kyoo Lee and Anupam Madhukar.
The Biotic-Abiotic Interface at the Nanoscale
Professor Anupam Madhukar
Departments of Physics, Biomed. Eng., Chem. Eng. & Mat. Sc.,, USC
Occurrence of the interface between living and non-living entities is common place but examination of the variety of interfacial phenomena at the nanoscale arising in the context of human health (implants, drug delivery, etc.) and environment (pollution) remain surprisingly under explored. In part this is because addressing the issues involved requires well-integrated highly inter- and multi-disciplinary research efforts. In this talk I will provide a glimpse of some opportunities, including a new paradigm for addressing biological and medical issues: engineered abiotic functionally-active nanosystems (FANs) designed for direct intervention with cells in-vivo with the objective of probing, manipulating, and endowing new cell function.
Novel Materials for Next Generation Spintronics and Nanoelectronics
Prof Stuart Wolf
University of Virginia Institute for Nanoscale and Quantum Scientific and Technological Advanced Research
In this talk I will describe our efforts to develop a toolkit of new materials for use in novel spintronic memory and logic devices. There is a worldwide effort to develop a new magnetic non-volatile random access memory based on spin torque transfer switching called STT-RAM and we are developing new materials to provide unique new capabilities for this memory. In addition we are working on several novel ideas for logic switches including both spintronic and phase change materials. I will describe these efforts and indicate how they compare with current state of the art CMOS.
Laboratory astrochemistry: A powerful tool to understand the origin of organic molecules in the interstellar medium, comets and meteorites
Dr Michel Nuevo
NASA Ames Research Center
During the last decade, astrochemistry laboratory simulations have shown that complex organic molecules, among which compounds of astrobiological interest such as amino acids, can be formed under astrophysical conditions from the vacuum UV irradiation of ice mixtures containing simple species such as H2O, CO, CO2, CH3OH, and NH3.1-3 However, the presence of amino acids in the interstellar medium (ISM) has not been confirmed yet, the detection of glycine being still under debate.4,5 But they are present in abundance in meteorites,6-8 indicating that biomolecules and/or their precursors can be formed under extraterrestrial conditions, although the meteoritic distribution is somewhat different from what is observed in the laboratory simulations. Nucleobases, the building blocks of DNA and RNA, have also been detected in meteorites,9,10 broadening the variety of complex organic molecules that can be formed in space environments, but like amino acids, nucleobases and other N-heterocycles have not been observed in the ISM.11,12 After a review of the formation of amino acids under interstellar-like conditions in laboratory simulations, from the UV irradiation of ices at low temperature, I will present recent studies of the formation of nucleobase derivatives from the UV irradiation of pyrimidine (C4H4N2) mixed in H2O- and/or NH3-rich ices. Pyrimidine is the carbonaceous backbone for 3 biological nucleobases (cytosine, thymine and uracil) as well as other compounds. The first results show that pyrimidine mixed in ices and subjected to UV photons leads to the formation of hydroxy/keto- (-OH/=O), amino- (NH2), and methyl- (CH3) pyrimidine derivatives. These products include the nucleobase uracil,13 and possibly other species of astrobiological interest. References: 1. M. P. Bernstein et al., Nature 416, 401 (2002). 2. G. M. Muñoz Caro et al., Nature 416, 403 (2002). 3. Nuevo, M. et al., Orig. Life Evol. Biosph., 38, 37 (2008). 4. Kuan, Y.-J. et al., Astrophys. J., 593, 848 (2003). 5. Snyder, L. E. et al., Astrophys. J., 619, 914 (2005). 6. Engel, M. H. and Macko, S. A., Nature, 389, 265 (1997). 7. Cronin, J. R. and Pizzarello, S., Science, 275, 951 (1997). 8. Cronin, J. R. and Pizzarello, S., Adv. Space Res., 23, 293 (1999). 9. van der Velden, W. and Schwartz, A., Geochim. Cosmochim. Acta, 41, 961 (1977). 10. Stocks, P. and Schwartz, A., Nature, 282, 709 (1979). 11. Kuan, Y.-J. et al., Monthly Not. R. Astron. Soc., 345, 650 (2003). 12. Charnley, S. B. et al., Adv. Space Res., 36, 137 (2005). 13. Nuevo, M. et al., submitted to Astrobiology.
The Central Bulge of the Galaxy: New Surveys and New Results
Prof Mike Rich
The central bulge of the galaxy is the nearest example of an old, metal rich, spheroid population-roughly half the stars in the local Universe live in such populations. Application of Galactic Archeology is enabling us to derive the age and the history of star formation of the bulge with unprecedented precision. Galactic Archeology involves measuring direct ages of stars, but additional age constraints come from abundances of elements in the oldest stars. We are also well along in a survey of the velocities of bulge stars; this project is revealing that the bulge as a whole is a dynamical system that is best understood as a rotating, football-shaped, coherent structure, that formed from a massive disk. However, there are problems with this scenario, posing a challenge for observers and theorists.
Observational constraints on the dense plasma of the solar interior
Department of Physics and Astronomy, USC
Helioseismology has become a very successful diagnosis of the equation of state. Although the gas in the solar interior is only weakly coupled and weakly degenerate, the great observational accuracy of the helioseismological measurements puts strong constraints on the nonideal part of the equation of state. For solar and stellar modeling, a high-quality equation of state is crucial. But the inverse is also true: the astrophysical data (helioseismic today, asteroseismic tomorrow) can put constraints on the physical formalisms, thus making the Sun and the stars laboratories for plasma physics. I will review mainly plasma physics issues, but in passing also mention other breakthroughs in solar physics, such as with neutrinos.
Sensing and Imaging using Surface-Enhanced Raman Spectroscopy
Professor Martin Moskovits
SERS was discovered over 30 years ago and has remained an active and vibrant research area. Its potential as a highly sensitive sensing strategy was recognized early on. However, early SERS systems and SERS substrates showed poor reproducibility and reliability. Recent advances in nanofabrication technologies and in plasmonics have led to new strategies with significantly increased likelihood of success as ultra-sensitive chemical and biological sensor technologies and imaging agents based on SERS. Examples of progress along these lines will be illustrated. Speaker Brief Biography Martin Moskovits, was Bruce and Susan Worster Dean of Science until 2007 and is currently Professor of Physical Chemistry at UC Santa Barbara. He was educated at the University of Toronto (BSc Physics and Chemistry, 1965, Ph.D. Chemical Physics, 1971). After receiving his BSc he co-founded OHM Distributors and Manufacturers Ltd. an electronics manufacturing company which was sold in 1968. From 1970-72 he worked at Alcan Research and Development and returned to the University of Toronto attaining the rank of Professor of Chemistry in 1982. From 1993-1999 he was Chair of the Department of Chemistry. He is a Fellow of the Canadian Institute for Advanced Research and was founding Director of its Nanoelectronics Program. Professor Moskovits has authored or co-authored ca 250 technical papers, edited or co-edited 4 books and holds 15 patents. Over 80 graduate students and postdocs completed their studies under his supervision. Professor Moskovits' research interests include surface-enhanced Raman and plasmonics, metal and semiconductor clusters, nanowires and nanotubes, catalysis and chemical and biological sensor development, fabrication in nanotemplates and other aspects of nanoscience and technology, especially nano-optics and nanoelectronics. Professor Moskovits is a Fellow of the American Association for the Advancement of Science, Fellow of the Optical society of America and of the Royal Society of Canada. He spent 1986-87 at UC, Berkeley as Guggenheim Fellow. He is member of the Advisory Board of the National Institute for Nanotechnology, Edmonton, and vice Chair of the US Department of Energy Basic Energy Sciences Advisory Committee.