Physics Colloquia - 2011

Friday, 9 December 2011, 3:00 PM. Physics 135 (Cookies 2:45 PM)

Phantoms at the OPERA: Faster-than-Light Neutrinos (!?) and the Negation of Cause and Effect

Professor Thomas J. Weiler, Dept. of Physics and Astronomy, Vanderbilt University

Einstein's relation between space and time is challenged by the results of an ongoing neutrino-detection experiment named OPERA, at the Gran Sasso Laboratory in Italy. Remarkably, OPERA claims (arXiv:1109.4897) a space-like separation between neutrino production at CERN in Geneva, Switzerland, and the subsequent detection at Gran Sasso, 732 km downstream. The logical inference from this result is that the neutrinos travel super-luminally, i.e. faster than light. If this experimental result is reproduced by other experiments, then profound alterations to our understanding of cause and effect will result.

After a brief overview of the OPERA paper, I will discuss the meaning of the result in the context of relativity, and then comment on some models proposed to accommodate the result. My is conclusion is that the data is most probably wrong due to some subtle, presently unknown systematic error; otherwise we are forced to consider baroque models such as sterile neutrinos propagating in extra dimensions. Finally, time permitting, I will briefly mention two bizarre possibilities for the Large Hadron Collider (LHC) experiments at CERN: (i) a space-time metric which allows for the secondary interaction events of particles to "pre-appear" before the particles are produced; and (ii) a latticized version of space that effectively loses dimension(s) as the energy increases.

Friday, 2 December 2011, 3:00 PM. Physics 135 (Cookies 2:45 PM)

White Dwarf Binaries, Mergers, and Explosions

Professor Marten van Kerkwijk, Dept. of Astronomy & Astrophysics, University of Toronto

Stars in binaries often have much more exciting lives, deaths, and afterlives than single ones. I will review the especially varied possibilities involving white dwarfs, which include revival and total annihilation. The latter leads to so-called type Ia supernova explosions, for which empirical calibrations of the their luminosities have allowed the measurement of the acceleration of the expansion of the Universe. The standard theoretical picture, in which unstable fusion is ignited in white dwarfs that approach or are made to exceed the largest possible (Chandrasekhar) mass, has a number of problems.

I will discuss these problems and will show that they would be resolved if instead, as I will propose, the ignition occurs more generally when two carbon-oxygen white dwarfs merge.

Friday, 18 November 2011, 3:00 PM. Physics 135 (Cookies 2:45 PM)

Looking for Stability: Hydrogen on the O-polar ZnO Surface

Sara E. Chamberlin, University of Wisconsin-Milwaukee

Every solid substance interacts with its environment via its surface. Additionally, the properties of the outermost few atomic layers often differ from those found in the bulk of a material. The fundamental goal of surface science is to understand these altered physical properties and reveal the chemistry occurring at such surfaces. By doing so, we can gain important insights into new material properties required to advance devices such as computer chips, solar cells, catalytic converters, and video displays.

Zinc Oxide (ZnO) has recently gained much interest as a promising transparent conducting material for the next generation of photovoltaics. Due to its crystalline structure, however, some ZnO surfaces have a net charge and dipole moment perpendicular to the surface. These ideal, so-called "polar" surfaces, are highly unstable, so the surface must respond in a way that minimizes the energy.

In this colloquium I will discuss recent work, both experimental and theoretical, to investigate the stabilization mechanism of the oxygen terminated polar ZnO surface. Low Energy Electron Diffraction (LEED) has been employed to investigate the atomic surface structure using a novel, low current system which has been specially designed for studying sensitive surfaces. In addition, Density Function Theory (DFT) analysis has been used to aid in interpreting the structural findings. The results support a fractional, disordered coverage of hydrogen adsorbed on the surface.

Friday, 11 November 2011, 3:00 PM. Physics 135 (Cookies 2:45 PM)

Secular Chaos: Formation of Hot Jupiters and the Organization of Planetary Systems

Dr. Yoram Lithwick, Assistant Professor, Dept. of Physics & Astronomy, Northwestern University

In a planetary system with well-spaced planets, there is a nonlinear instability that can lead to chaotic behaviour. One of the planets can gradually become unstable, in which case its orbit becomes highly eccentric. This "secular chaos" is known to be responsible for the eventual destabilization of Mercury in our own Solar System.

Here I focus on systems with multiple giant planets. I show that after an extended period of eccentricity diffusion, the inner planet's pericentre can approach the star to within a few stellar radii. Strong tidal interactions with the star then pull the planet inward, creating a hot Jupiter. In contrast to other proposed channels for the production of hot Jupiters, such a scenario (which I term "secular migration") explains a range of observations: the pile-up of hot Jupiters at 3-day orbital periods, the fact that hot Jupiters are in general less massive then other RV planets, that they may have misaligned inclinations with respect to stellar spin, and that they have a few easily detectable companions (but may have giant companions in distant orbits). I will also show that if an unstable planet escapes the influence of the other planets, the remaining planetary system becomes increasingly stable. This may explain the stable architecture of observed systems.

Friday, 4 November 2011, 3:00 PM. Physics 135 (Cookies 2:45 PM)

Multi-messenger Observations of Neutron Rich Matter

Prof. Charles J. Horowitz, Director, Nuclear Theory Center, Dept. of Physics, Indiana University

Neutron rich matter is central to many fundamental questions in nuclear physics and astrophysics. Moreover, this material is being studied with an extraordinary variety of new tools such as the Facility for Rare Isotope Beams (FRIB) and the laser Interferometer Gravitational Wave Observatory (LIGO). We describe the Lead Radius Experiment (PREX) that uses parity violating electron scattering to measure the neutron radius of a 208Pb nucleus. This has important implications for neutron stars and their crusts. We discuss X-ray observations of neutron star radii.

These also have important implications for neutron rich matter. Gravitational waves (GW) open a new window on neutron rich matter. They come from sources such as neutron star mergers, rotating neutron star mountains, and collective r-mode oscillations. Using large-scale molecular dynamics simulations, we find neutron star crust to be very strong. It can support mountains on rotating neutron stars large enough to generate gravitational waves.

Friday, 28 October 2011, 3:00 PM. Physics 135 (Cookies 2:45 PM)

Half-Metals: In Search of 100% Spin Polarized Materials

Dr. Vlado Lazarov, Senior Research Fellow, Dept. of Physics, The University of York

Spintronics is a new, emerging field that utilizes the electron spin in addition to its charge to create novel devices combining logic, data storage and sensor applications. One of the main challenges in the field is to find / create half-metals (i.e. 100% spin polarized materials at the Fermi level).

In this talk, I will present our current work on the Fe3O4 and Co-based Heuslers alloys. These are predicted half-metal materials of large technological importance due to their high Curie temperature and good epitaxial match to technologically important oxide semiconductors. The control of the spin polarization in these materials, as well as their exploitation in real devices, will be discussed and presented.

Friday, 21 October 2011, 3:00 PM. Physics 135 (Cookies 2:45 PM)

Proteins in Motion: Probing Structural Disorder and Dynamics by Single-Molecule Fluorescence

Dr. Claudiu Gradinaru, Associate Professor of Physics, Dept. of Chemical & Physical Sciences, University of Toronto - Mississauga

Intrinsically disordered proteins (IDPs) lack stable globular tertiary folded structure under physiological conditions. Roughly 65% of the signaling and 75% of the human cancer-associated proteins are predicted to have significant disordered regions, thus implying a role for disorder in mediating regulatory protein interactions in complex biological processes. The question emerges of whether specific recognition can occur despite conformational disorder or whether disordered protein states may even provide advantages in recognition over well-folded proteins. With the ability to directly detect molecular processes without the loss of information due to ensemble averaging, and the capacity to resolve complex structural distributions and dynamics in a straightforward manner, the use of single-molecule fluorescence (SMF) spectroscopy in the study of IDPs can provide important new insights into the conformational properties of the disordered ensemble and how these features are altered by binding to cellular partners.

In my talk, I will explain how SMF techniques such as Förster Resonance Transfer (FRET) and Fluorescence Correlation Spectroscopy (FCS) are currently employed in my lab to investigate two such proteins, the cyclin inhibitor Sic1 from yeast and the SH3 domain of the Drosophila adaptor Drk.

Friday, 14 October 2011, 3:00 PM. Physics 135 (Cookies 2:45 PM)

Solving Einstein's Equations for Binary Black Hole Spacetimes

Dr. Lee Lindblom, Senior Research Scientist, Theoretical Astrophysics, CALTECH

This talk will give an overview of the methods now being used to perform numerical simulations of binary black hole spacetimes. The discussion will include brief descriptions of some interesting theoretical challenges that were overcome to make these simulations possible, brief descriptions of some of the most interesting physical results to date, and a brief discussion of challenges that still remain.

Friday, 7 October 2011, 3:00 PM. Physics 135 (Cookies 2:45 PM)

Can Quasars Quench Star Formation?

Dr. Christy Tremonti, Assistant Professor, Dept. of Astronomy, UW-Madison

Since quasars were first recognized as cosmological sources their relation to galaxies has been a puzzle. We now know that quasars are powered by accretion of gas onto supermassive black holes at the centers of massive galaxies. What continues to elude our understanding is the impact that quasars have on their host galaxies. Recent numerical simulations suggest that quasars can drive powerful gas outflows that ultimately bring about an end to star formation and black hole activity.

I will discuss observations designed to directly test this hypothesis. Because gas outflows are challenging to observe in the presence of a bright quasar, our study focuses on a sample of galaxies that are a few 100 million years past the peak of their star formation and black hole activity. In these 'post-starburst' galaxies we find evidence for outflowing cool gas with velocities upwards of 1000 km/s. We consider the energetics of the gas and argue that quasars play a significant role in removing gas from galaxies and quenching star formation.

Friday, 30 September 2011, 3:00 PM. Physics 135 (Cookies 2:45 PM)

Development of Next Generation of Optical Bio-imaging Devices

Miniature Imaging Systems and Multi-Dimensional Imaging Modalities

Dr. Tomasz Thaczyk, Asst. Professor of Bioengineering and Electrical Engineering, Rice University

Optical Microscopy is one of the most important experimental tools in biology. This presentation will provide an overview of the next generation of optical-biomedical devices which leverage advances in optical micro-fabrication and detector technology. Using these approaches, it is possible to reduce the size and cost of imaging systems without compromising optical performance and to integrate new multidimensional imaging modalities. I will discuss my group efforts to develop integrated miniature diagnostic systems and novel acquisition and processing tools for new multidimensional imaging modalities. Traditional imaging usually yields an intensity distribution across the object, I(x,y). In many biological applications, it is important to also capture spectral information at each point in the image, i.e., one can obtain I(x,y,λ) data. This spectral information can provide crucial insight about bio-chemical processes occurring in the individual cells or tissue by allowing for multiplexed imaging that follows multiple molecules and their interactions. State-of-the-art systems (like commercial confocal spectral imaging instruments) often use sequential scanning to build images point by point (or line by line). The spectrum is resolved using line of photo-multiplier tubes or CCD cameras. Scanning approach however limits temporal resolution and often leads to photobleaching. To follow molecular events with finer temporal and spectral resolution decrease photobleaching effects my lab has developed fully parallel imaging approach which can acquire an entire I(x,y,λ) data set in a single, brief snapshot. The system called Image Mapping reorganizes images on a large format CCD/CMOS and allows efficient and fast, spacial-spectral acquisition without scanning. We have already validated system in multiple applications (cell signaling, diffused imaging, endoscopy etc.). In addition this concept is being further extended to detection of multiple molecular probes (10+) or expanded to other imaging dimensions (for example depth, polarization etc.).

Friday, 16 September 2011, 3:00 PM. Physics 135 (Cookies 2:45 PM)

Protein-Protein Interactions and Gap Junction Coupling in Neuroendocrine Secretion

Dr. David W. Piston, Professor - Biophysics and Physics, Director - Keck Free-Electron Laser Center, Vanderbilt University

Our research centers on the real-time examination of basic molecular mechanisms underlying the function of a model multicellular system, the islet of Langerhans. The islet is the functional unit responsible for glucose-stimulated insulin secretion from beta-cells and glucose inhibition of glucagon secretion from alpha-cells. To study these cells we have utilized the Green Fluorescent Protein (GFP), and developed a novel "lock-in" detection scheme of photoswitchable probes to greatly improve imaging sensitivity - down to the single molecule level. We have used Förster resonance energy transfer (FRET), combined with multiple-colored fluorescent proteins, to quantitatively measure protein interactions along the signaling pathways involved in insulin secretion from islet beta-cells. We have also applied the imaging of GFP and other probes to imaging of intact tissues and live animals. Our model system, the pancreatic islet, exhibits synchronous behavior of membrane action potentials, Ca2+ oscillations, and pulsatile insulin secretion across all beta-cells in the islet, but we have only a rudimentary understanding of the basic multicellular mechanisms that lead to these synchronous behaviors.

Using quantitative imaging methods and novel microfluidic devices, we have measured the role of gap junction coupling between cells in the islet, and how this coupling interacts with the membrane action potential changes of individual cells. These data can be compared with mathematical models of this multicellular system, which can yield a true quantitative understanding of the molecular mechanisms involved.

Friday, 26 August 2011, 3:00 PM. Physics 135 (Cookies 2:45 PM)

Black Holes in String Theory

Dr. Satoshi Nawata, Tata Institute of Fundamental Research (Mumbai, India)

The pioneering work of Bekenstein and Hawking in the 70's produced a universal area law for black hole entropy valid in the infinite size limit. One of the important successes of string theory is that one can obtain a statistical understanding of the thermodynamic entropy of certain supersymmetric black holes in terms of microscopic counting. The entropy of black holes supplies us with very useful quantitative information about the fundamental degrees of freedom of quantum gravity. In recent years, there have been tremendous developments in understanding the entropy and other thermodynamic properties of black holes within string theory, going well beyond the thermodynamic limit.

It has now become possible to begin exploring finite size effects in perturbation theory in inverse size and even nonperturbatively, with highly nontrivial agreements between thermodynamics and statistical mechanics.

This talk will pedagogically describe some of this progress in our understanding of the quantum structure of black holes for general audience.

Monday, 1 August 2011, 3:00 PM. Physics 135 (Cookies 2:45 PM)

Rotating and Binary Relativistic Stars With Magnetic Field

Charalampos Markakis, University of Wisconsin-Milwaukee

We develop a geometrical treatment of general relativistic magnetohydrodynamics for perfectly conducting fluids in Einstein-Maxwell-Euler spacetimes. The theory is applied to describe a neutron star that is rotating or is orbiting a black hole or another neutron star. Under the hypotheses of stationarity and axisymmetry, we obtain the equations governing magntohydrodynamic equilibria of rotating neutron stars with poloidal, toroidal or mixed magnetic fields. Under the hypothesis of an approximate helical symmetry, we obtain the first law of thermodynamics governing magnetized equilibria of double neutron star or black hole - neutron star systems in close circular orbits.

In addition, in an attempt to provide a better theoretical understanding of the methods used to construct models of isolated rotating stars and corotating or irrotational binaries and their unexplained convergence properties, we analytically examine the behavior of different iterative schemes near a static solution. We find the spectrum of the linearized iteration operator and show for self-consistent field methods that iterative instability corresponds to unstable modes of this operator. On the other hand, the success of iteratively stable methods is shown to be due to (quasi-)nilpotency of this operator.

Monday, 25 July 2011, 3:00 PM. Physics 135 (Cookies 2:45 PM)

Extreme-mass-ratio Inspirals in a Modified Radiation Gauge

Abhay G. Shah, University of Wisconsin-Milwaukee

The gravitational radiation emitted from the inspiral of a solar mass black hole into a supermassive black hole is an important target for the space-based antenna, LISA. To produce accurate theoretical templates that can extract the physical features of the source from the radiation observed, one has to take into account the effect of gravitational self-force. Due to this large mass ratio one can approximate the smaller black hole as a point particle orbiting the larger black hole. As this particle falls into the central galactic black hole, it interacts with its own smooth gravitational field. The resulting correction to its orbit leads to a correction in the radiation emitted. The field arising from the point-particle approximation must be renormalized by subtracting a singular field that does not contribute to the self-force.

Earlier work uses a gauge where one has to solve a set of coupled partial differential equations. Instead of doing that, we use a radiation gauge where we solve a single separable differential equation whose solution gives us the required perturbation fields when acted upon by suitable operators.

In this talk, we outline the method to compute gravitational self-force for generic orbits in Kerr spacetime. We use this method to compute gauge-invariant quantities and self-force for a particle in circular orbit around a Schwarzschild black hole where a successful comparison is done with other groups. We later use it to compute the gauge invariant quantity for a particle in circular orbit around a Kerr black hole.

Friday, 12 May 2011, 3:00 PM. Physics 135 (Cookies 2:45 PM)

The Odd Orbital Orientations of Exoplanets

Dr. Josh Winn, MIT

In the Solar system, the planets follow orbits that are aligned with the Sun's equatorial plane to within about 7 degrees. What about planets around other stars? Recently we have measured the orbital orientations (relative to their parent stars' equators) of about 30 exoplanets, using a technique first theorized in the 19th century.

Many systems have good alignment, as in the Solar system -- but there are also many surprises. I will discuss these results and their implications for theories of planet formation and migration.

Friday, 29 April 2011, 3:00 PM. Physics 135 (Cookies 2:45 PM)

A new cluster phase in polyelectrolyte decorated colloids: Interesting phenomenology and possible biotechnological applications

Dr. Federico Bordi, Sapienza University, Rome

Different charged colloidal particles have been shown to be able to self-assemble, when mixed in an aqueous solvent with oppositely charged linear polyelectrolytes. Under proper conditions they form long-lived finite-size mesoscopic aggregates, whose size depends on the polyelectrolyte/particle charge ratio in a rather unexpected way. The mechanism underlying the formation of this cluster phase is still controversial, however the interesting phenomenology shown by these systems seems to have a high potential for biotechnological applications, particularly when the primary colloidal particles are bio-compatible lipid vesicles.

This talk will discuss a phenomenological model of the aggregation and possible applications of these systems as multi-compartment vectors for the simultaneous intra-cellular delivery of different pharmacologically active substances.

Friday, 15 April 2011, 3:00 PM. Physics 135 (Cookies 2:45 PM)

Sundance Plesiosaurs: Jurassic marine reptile discoveries from the Bighorn Basin, Wyoming

Dr. F. Robin O’Keefe, Marshall University

Plesiosaurs are familiar marine reptiles from the Mesozoic Era, characterized by their long necks and the unique adaptation of all four limbs as hydrofoils. However, our current knowledge of Jurassic plesiosaurs is hobbled by a lack of fossils from outside the Oxford Clay deposits of England. Recent field work in the Sundance Formation (Upper Jurassic, Oxfordian) in the Bighorn Basin, Wyoming, has resulted in the collection of significant new fossils of two plesiosaur taxa. During preparation of this skeleton, remains of another, smaller ichthyosaur skeleton was found within the body cavity. The close association of the ichthyosaur with a plesiosaur thorax, as well as other evidence, suggests the ichthyosaur may be stomach contents. This find is the first discovery of possible predation by plesiosaurs on neonatal ichthyosaurs.

The second partial skeleton is referable to the Tatenectes laramiensis, and is the most complete and best preserved example of the taxon found to date, comprising a complete dorsal vertebral series, many ribs and gastralia, and a complete pelvic girdle. We hypothesize that these features were adaptations for increased near-surface stability, perhaps allowing access to shallow, inshore environments in the sediment-choked Sundance Seaway.

Friday, 1 April 2011, 3:00 PM. Physics 135 (Cookies 2:45 PM)

The Factory and the Beehive: Stellar Rotations at 600 Myr

Marcel Agueros, Columbia University

In a classic 1972 paper, Andrew Skumanich showed that stellar rotation decreases over time --- as does chromospheric activity, a proxy for magnetic field strength. This relationship between age, rotation, and activity has been a cornerstone of stellar evolution work for over 40 years. However, rotation periods are scarce for stars with ages greater than 500 Myr, complicating the calibration of an age-rotation-activity relation that can be applied to field stars. The Columbia/Cornell/Caltech Palomar Transient Factory (CCCP) survey of open clusters is an effort to systematically map stellar rotation in open clusters. I will present the first CCCP results for Praesepe, a rich, nearby, 600 Myr open cluster.

Friday, 11 March 2011, 3:00 PM. Physics 135 (Cookies 2:45 PM)

Journey to the Core of a Neutron Star

Ed Brown, Michigan State University

Neutron stars are composed of the densest observable matter in nature and occupy the intellectual frontier between gravitational physics, astrophysics, and nuclear physics. Within the next decade, current and planned nuclear experiments, X-ray observations, and, perhaps, gravity wave observations of neutron stars will be exploring the nature of dense matter from complimentary approaches. Many observed neutron stars accrete hydrogen- and helium-rich matter from a companion. During the slow compression to nuclear density, the accreted matter is transmuted from being proton-rich to being proton-poor. These reactions affect many observable phenomena -- from energetic explosions on the neutron star's surface, to the recently detected thermal relaxation of the surface layers -- that in turn inform us about the nature of the deep interior of the neutron star.

In this talk, I shall describe the journey of matter that is accreted onto a neutron star and describe what we can learn about the physics of the dense matter of the neutron star's crust and core by observing phenomena powered by nuclear physics on the neutron star's surface.

Friday, 4 March 2011, 3:00 PM. Physics 135 (Cookies 2:45 PM)

Gravity, the Quantum, and the Observable Universe

Ivan Agullo, Penn State

Historically, gravity was the first interaction to be understood and formulated mathematically. In contrast, three hundred years later, a complete understanding of this interaction remains elusive, and its relation with quantum theory is considered as one of the biggest puzzles in theoretical physics. This problem can be rooted in the weakness of gravity as compared to other interactions, which produces an important lack of experimental guidance. The observation of the universe may change this situation. The mechanism of inflation predicts that the inhomogeneities that we observe in the cosmic microwave background and in the distribution of galaxies were generated in the early universe when the effects of gravity and quantum mechanics were both important.

In this talk, I review those questions, and describe how the astonishing improvement in the precision of the observations of the universe made in recent years (and those expected in the near future), opens a promising window to obtain detailed observational information about physical processes where the relationship between gravity and quantum mechanics plays a major role. 

Friday, 25 February 2011, 3:00 PM. Engelmann 105 (Cookies 2:45 PM)

Never Say Diagonal of the Covariance Matrix: 6 Things Scientists Can Learn From Science Journalists

Maggie Koerth-Baker, Freelance Science Journalist and Science Editor

When you talk about your research, do you feel like you're talking to yourself? Have you ever accidentally left a lay person more confused than they were before they met you? Does your left eye go twitchy every time a journalist calls? Communicating science is scary. Fortunately, the same lessons that turn cringe-worthy journalism into smart science reporting can help you do a better job of communicating your own work--whether directly to the public, or to journalists themselves. Don't freak out. Don't give up. Instead, come to this presentation.

Friday, 11 February 2011, 3:00 PM. Physics 135 (Cookies 2:45 PM)

Long-Range Climate Forecasts Using Data Clustering and Information Theory

Dimitris Giannakis, New York University

Even though forecasting the weather beyond about two weeks is not possible, certain climate processes (involving, e.g., the large-scale circulation in the Earth's oceans) are predictable up to a decade in advance. These so-called climate regimes can influence regions as large as the West Coast of North America over several years, and therefore developing models to predict them is a problem of wide practical impact. An additional central issue is to quantify objectively the errors and biases that are invariably associated with these models.

In this talk, we discuss methods based on data clustering and information theory to build and assess probabilistic models for long-range regime forecasts. With reference to a simple ocean simulation mimicking the Gulf Stream in the Atlantic (or the Kuroshio Current in the North Pacific), we demonstrate that details of the initial state are not needed in order to make skillful long-range predictions, provided that an appropriate coarse-grained partitioning of the set of possible initial conditions is employed. Here, that partitioning is constructed empirically using running-average coarse graining and K-means clustering of observed data, and optimized by means of relative-entropy measures. We apply the same tools in a related formalism for quantifying errors in imperfect climate models. Together, these techniques provide a framework for measuring predictive skill and model error in a manner that is invariant under general transformations of the prediction observables.

Friday, 4 February 2011, 3:00 PM. Physics 135 (Cookies 2:45 PM)

Discovery of the Porosome: The Universal Secretory Machinery in Cells

Bhanu P. Jena, Wayne State University School of Medicine and NanoBioScience Institute

“Porosomes,” discovered in early 1996, are supramolecular, lipoprotein structures at the cell plasma membrane, where membrane-bound secretory vesicles transiently dock and fuse to release intravesicular contents to the outside during cell secretion. The porosome opening to the outside, range in size from 150 nm in diameter in acinar cells of the exocrine pancreas and in neuroendocrine cells, to 12 nm in neurons and astrocytes, which dilates during cell secretion, returning to its resting size following completion of the process. In the past decade, the composition of the porosome, its structure and dynamics at nm resolution and in real time, and its functional reconstitution into artificial lipid membrane, have been elucidated.

In this lecture, the discovery of the porosome, its structure, function, isolation, chemistry, and reconstitution, the molecular mechanism of SNARE-induced secretory vesicle fusion at the porosome base, and how this new information provides a paradigm shift in our understanding of cell secretion, will be discussed.

Monday, 10 January 2011, 3:00 PM. Physics 135 (Cookies 2:45 PM)

Hyperspectral Spontaneous and Nonlinear Raman Imaging for Biomedical Applications

Rajan Arora, University of Wisconsin-Milwaukee

Chemical imaging has greatly revolutionized our ability to study complex chemical processes occurring in the microscopic world with unprecedented details and thus, has had tremendous applications in several disciplines including chemistry, medicine and pharmacy, food science and agriculture, and biology. However, traditional chemical imaging techniques either rely on contrast-enhancing agents or are limited by a poor signal quality, a lack of chemical specificity, and sensitivity. As a part of my dissertation work, I will describe non-invasive, vibrational spectroscopic imaging techniques that can address the limitations of current clinical diagnostic procedures and has the potential to provide real time chemically specific information.

Vibrational spectroscopic imaging, in particular, Raman Scattering and Coherent Anti-stokes Raman Scattering (CARS)-based imaging techniques are successfully applied on various complex biological systems for detecting microcalcifications in a cancerous tissue, screening of protein crystals, distinguishing omega-3 fatty acid from omega-6 fatty acid, and detecting bacterial endospores responsible for anthrax. I will also present some of the results from experiments based on flow cytometry and scattering. 

The second part of my talk will mainly focus on details of how spectroscopic techniques are used in conjunction with statistical tools such as phase retrieval algorithm, principal component analysis, and cluster analysis, to arrive at more conclusive results. In these studies, the collected results show the combined potential of spectroscopic imaging and statistical tools to study some of the key challenges in biology and medical science. This combined approach will one day replace traditional diagnostic procedures and will open doors to a number of potential clinical applications.