Colloquia Archive: 2003

Monday February 03, 2003, 3:00pm

Dr. Vladislav Toronov, University of Illinois, Urbana-Champaign
Near-infrared imaging of the brain function
Location: Physics 152

Principles of optical spectroscopy and imaging of biological tissues. Non-invasive optical measurements of functional cerebral hemodynamics and neuronal activity. Studies of the underlying physiology of fMRI signals using near-infrared spectroscopy. Biophysical modeling of functional cerebral hemodynamics from near-infrared data.

Thursday February 06, 2003, 3:00pm

Dr. Armin Kargol, University of Tulane
The nonequilibrium response study of voltage-gated ion channels
Location: Physics 152

Voltage-gated ion channel proteins play a crucial role in many cellular processes, such as electrical excitability of neurons and muscle (e.g. cardiac) cells. The study of their functional properties is one of the major, most active research areas in biophysics. One of the goals is to develop kinetic models based on electrophysiological measurements. They are used to summarize both the gating properties and the responses to pharmacological agents. In my lab we develop a new electrophysiological technique called the nonequilibrium response spectroscopy (NRS), which involves application of large amplitude fluctuating voltages across a cell membrane via the voltage clamp. The gating response to such fluctuating fields is sensitive to features of the kinetics that are difficult or impossible to adequately resolve by means of traditional relaxation transient methods. Our study is aimed at developing a systematic approach to the NRS protocol design, testing on selected ion channels, as well as application to new ion channels with a goal of developing more reliable models of their gating and pharmacological properties. The project is an example of applying modern physical concepts (fluctuation-induced phenomena) to biological research. I will present current results including proposed NRS protocols and their design algorithms. The methods have been tested on two types of voltage-gated ion channels: the Shaker K+ channel and the human cardiac Na+ channel. I will show that new information is gained by applying NRS technique to well-studied cases and that the method is effective in testing various kinetic models for channel kinetics.

Monday February 10, 2003, 3:00pm

Dr. Valery Milner, Queens College, CUNY
Atoms in Optical Potentials: Billiards, Disordered Media, and Maxwell's Demon
Location: Physics 152

Motion of atoms inside optical structures, created by light, has become the subject of active research due to the recent achievements in laser cooling of dilute gases down to nano-Kelvin temperatures. Enormous flexibility of controlling an optical potential, e.g. its strength and its temporal and spatial distribution, opens new ways of studying many effects of solid state physics and nonlinear dynamics in a much cleaner optical environment, beyond the widely used optical lattice configuration. As an example, I will first present the proof-of-principle experiments on optical billiards, where we play pool with neutral atoms, sending them to bounce between the walls created by laser beams. Understanding the dynamics of these, rather simple, chaotic billiards may now be followed by the studies of more complicated systems, such as combined optical billiards or optical potentials with disorder. These and other directions of research will be discussed.

Friday February 28, 2003, 3:00pm

Prasenjit Guptasarma, University of Wisconsin-Milwaukee
The many faces of Superconductivity and Magnetism
Location: Physics 152

Friday March 7, 2003, 3:00pm

Michael Reddy, University of Wisconsin-Milwaukee
The Smallpox Vaccine
Location: Physics 152

Friday March 14, 2003, 3:00pm

Michelle Goetz, University of Wisconsin-Milwaukee
Electron Microscopy Studies of Mn doped GaN films
Location: Physics 152

GaN wide band gap semiconductors have been greatly studied for their optical properties that are suitable for blue lasers. More recently their magnetic properties are acquiring a growing fascination as transition metal doped GaN semiconductors, which exhibit ferromagnetism. Mn is one of the most promising dopants, despite its low solubility in GaN. This study uses Molecular Beam Epitaxy (MBE) to grow GaN films with delta Mn doping as well as multilayer Mn doping. High Resolution Transmission Electron Microscopy (HRTEM) images of cross sectional samples were recorded with a Hitachi H9000 NAR microscope. The images were analyzed with Digital Micrograph 3.3 to measure lattice spacings using digital diffractograms calculated by Fast Fourrier Transforms. Histograms of the experimental data were plotted to compare the GaN phases forming under the two Mn doping conditions. Interesting results surfaced when comparing the two different growths. Lattice structures in the pre- and post-doping layers of both films fit the hexagonal 2H-wurtzite structure in the [11-20] zone. However, the cubic zinc blende GaN phase in the [110] zone was only present in the multilayer Mn doped film with variable thickness. Furthermore, the differences in thickness appear to correlate with the presence of local defects. Both films have edge, mixed, and screw dislocations, as well as stacking faults and inversion domain boundaries, whose densities are drastically reduced within and beyond the doping regions. The implications of this analysis form a beginning path towards further research of various Mn doped films.

Friday March 21, 2003, 3:00pm

Zeeshan Habeeb, University of Wisconsin-Milwaukee
Location: Physics 152

Friday April 11, 2003, 3:00pm

Lian Li, University of Wisconsin-Milwaukee
Spintronics: Play with the Spin of an Electron
Location: Physics 152

Friday April 18, 2003, 3:00pm

Cherryl Whitson, Thomas More High School
Teaching Physics at the High School level
Location: Physics 152

Helping high school seniors absorb, translate, comprehend, apply, and appreciate the field of physics is my goal as a physics teacher. Accomplishing this goal within the framework of time allowance, student ability, teaching methodology, and content material is the subject of this presentation. The students themselves have a large impact on the success of the teaching/learning continuum. High school seniors display a wide range of intellectual ability, mathematical acumen, emotional stability, self-discipline, and attention span. It is the range that is more challenging than the actual level of any particular student. Time management is another important consideration. There are 180 school days, and the students are in each class 45 minutes each day. This does not, however, accurately reflect available instructional time; special schedules (early dismissal for meetings or conferences), student extracurricular (sports competition, theater arts), student absenteeism (chronic), and time of year (fall vs winter vs spring) are all factors defining the actual quantity and quality of instructional time. Within the considerations of time and student character, some actual physics content is explored. Physics entails a thought process that is not generally familiar to students, and considerable time is spent at the beginning of the year shepparding the students into a logical, problem-solving state of mind. Linear motion, velocity, and acceleration are treated with a two-pronged approach: graphical analysis and problem solving with equations. Forces, vectors, circular motion, centripetal motion, gravitational interactions, and energy studies complete the first semester. The field of wave phenomena (sound, light, refraction, reflection, diffraction) is studied during the third quarter. The year is completed with the electricity basics: electric force, electric fields, power, household circuitry, and series/parallel circuits.

Friday April 25, 2003, 3:00pm

Dr. Marvin Schofield, Brookhaven National Laboratory
Electron Holography of Charge at High Tc Semiconductor Boundaries
Location: Physics 152

Grain-boundaries in high-temperature superconductors represent the major factor limiting high current applications. Various mechanisms have been proposed to understand and improve the grain-boundary transport properties. The recently discovered increase of the intergranular critical current density by substitution of Y3+ by Ca2+ in YBa2Cu3O7-x suggests that grain-boundary charging and bending of the electronic band structure may be responsible for the suppression of superconductivity. The long-standing difficulty in resolving the mechanism of suppressed critical current density is the ability to directly measure crucial quantities such as electrostatic potential and charge density at the grain-boundary interface. I will present recent results of electron holography experiments carried out on grain boundaries in 20% Ca-doped and Ca-free YBa2Cu3O7-x thin films. The experiments allow us to directly measure the electrostatic potential and charge distribution at the grain-boundary interfaces. Our measurements indicate, unexpectedly, a negatively charged grain-boundary where, in the words of one of my collaborators, “…we have completely new physics.” I will discuss the implications of our measurements for suppressed superconductivity, and give an overview of the rich physics involved.

Friday, May 2, 2003, 3:00pm

Zeeshan Habeeb (Undergrad Student), University of Wisconsin-Milwaukee
Introduction to Surface Science and its Experimental Techniques
Location: Physics 152

Surface science, as its name suggests, seeks to explore the physical, chemical and material properties of surfaces. It is upon the surface of an object where all chemical reactions and physical interactions occur in heterogeneous and homogeneous environments. Of particular interest are the surfaces of catalysts, semiconductors and the effects of corrosion on metal fixtures, all of which are a study primarily of heterogeneous environments. Although the field of surface science has been in existence for the last two hundred years, technological advances as recent as the 1960's has allowed rapid advances in this field. The progress of vacuum technology as well as the improved sensitivity and diversity of probes and detectors has lead to about 60 different surface analytical techniques that are currently being used.

Friday, May 9, 2003, 3:00pm

Mariallessandra Papa, Max Planck Institut f. Gravitationsphysik
Setting upper limits on the strength of periodic gravitational waves using the first science data from the GEO 600 and LIGO detectors
Location: Physics 152

I will present the procedures that have been employed to place upper limits on the strength of periodic gravitational waves from the pulsar PSRJ1939+2134, using data from four gravitational wave detectors during their first science run. This talk is given on behalf of the LSC (Ligo Scientific Collaboration), the LIGO and GEO projects.

Friday, May 16, 2003, 3:00pm

Prof. Solomon Saltiel, University of Sofia, Bulgaria
Manipulation of Polarization Properties of Laser Light with Cascaded Nonlinear Optical Processes
Location: Physics 152

rect and cascaded nonlinear-optical processes: – classification of nonlinear optical cascaded processes – some important applications of nonlinear-optical cascaded processes: generation of new waves; change of parameters of laser light; mode locking. 2. Nonlinear generation of orthogonal polarization component via cascaded quadratic processes: – experiment in BBO. 3. Strong nonlinear polarization rotation and efficient generation of orthogonal polarization component via cascaded cubic processes experiment in BaF2 and YVO4; theoretical description; possible applications.

Monday, June 9, 2003, 3:00pm

Prof. Robert Caldwell, Dartmouth College
Gravitational Clustering in Cosmology
Location: Physics 152

Understanding the origin and evolution of the clustering pattern of galaxies is one of the most important goals of cosmology. Since galaxies and clusters appear to be dominated by dark matter, we have a more basic goal of understanding how dark matter behaves in gravity. In this talk I will present some analytic models of gravitational clustering and collapse, and I'll show how a little theory goes a long way. Certainly, nothing works better than computer experiments for testing our understanding of gravitational many-body physics, and for detailed comparison with observation. But after running a few computer experiments, I'll show how we can learn something new about clustering dark matter, and save us some time and effort in the future.

Monday, July 28, 2003, 3:00pm

Antonius Tsokaros, University of Wisconsin-Milwaukee
Problems Related to Gravitational Wave from Binary Black Holes
Location: Physics 152

Friday September 19, 2003, 3:00pm

Dr. Dave Keavney, Advanced Photon Source, Argonne National Laboratory
Induced magnetic moments and the local Mn environment in the ferromagnetic semiconductor (GaMn)As
Location: Physics 152

Friday September 26, 2003, 3:00pm

John Friedman, University of Wisconsin-Milwaukee
Gravitational collapse, black holes, and the dawn of gravitational-wave astronomy
Location: Physics 152

Wednesday October 15, 2003, 3:00pm

Philip Batson, T.J. Watson Research Center, IBM
Obtaining Semiconductor Device Limits Using Atomic Resolution Electron Energy Loss Spectroscopy
Location: Physics 152

Pushing electronic device structures to sub-nanometer sizes will require understanding the behavior of heterogeneous materials at several levels of detail. For instance, over distances well characterized as bulk-like, quantities such as conductivity, mobility, breakdown, leakage, dielectric constant, dopant concentration, and thickness have well known practical definitions useful to device design. When the scale of a device reaches the nanometer level, none of these quantities are well behaved. For instance, the conductivity in 10 nm sized Al spheres is sharply reduced by non-specular scattering of conduction electrons at the surface of the particle.[1] Investigation of 2-10 nm sized Si spheres has shown that the crystalline bandstructure is lost in structures smaller than about 2-3 nm in size. [2] When SiO2 gate layers are made thinner than about 1 nm their insulating ability is lost because the correct bandgap cannot be obtained with incomplete Si-O4 structural coordination. [3] These issues are made more complicated by the fact that even the measurement physics is not well understood at the nm-length scale. For instance, in Si, bandstructure-related EELS features become indistinct in thin regions, but on a length scale that is much too large to be caused by quantum confinement of the carrier electrons.[4] In spite of this, progress has been made in understanding how to obtain the chemistry and electronic structure of very small regions near interfaces and defects.[5, 6] But it is very clear, that further progress requires more accurate EELS experiments using more precise electron probes. Therefore, aberration correctors [7] and electron monochromators [8] are being added to electron microscope EELS machines to take the spatial resolution to below 1 Angstrom and the energy resolution to below 100 meV. These new capabilities will allow much more detailed investigation of sub-nm regions of device structures. At first, many new questions will arise about how to interpret EELS scattering using a very small probe which excites only a small part of a semiconductor unit cell. Does the concept of bandstructure mean anything in that case? Or does it make more sense to speak about molecular orbitals? Since the small electron beam must be characterized by a coherent sum over many plane waves, does this affect the outcome of the scattering? The idea that EELS results may depend on coherent sums over initial and final electron states gave rise to the introduction of the mixed dynamical form factor to treat surface plasmon scattering in confined shapes.[9] Using an extension of this idea, it has been demonstrated that the local symmetry of excitations within a unit cell can be probed, using carefully selected channeling conditions.[10] Now that a sub-Angstrom sized probe has been achieved, it may be possible to excite similar excitations directly. What is clear here is that exciting new areas of investigation are likely to appear as the new instrumental capabilities are explored.

Thursday October 16, 2003, 3:00pm

Professor David Hafemeister, California Polytechnic State University
Physics of Societal Issues: Calculations on Climate and Energy
Location: Physics 152

Part 1: The Energy Situation in 2003 The conclusions of the APS-POPA energy study of 1996 are still relevant today, and they will be briefly discussed in terms of recent trends. Cars, refrigerators and houses have greatly improved, but yet energy use continues to climb. The best news on the supply side is the Combined Cycle Gas Turbine. The talk will use basic models to do the following: King Hubbert's model for petroleum resources will be extended to include economics. Combined cycle gas turbine efficiency will be shown to be about 60%. The cost-of conserved energy and life-cycle costs will be used to examine some conservation measures. Part 2: Basic Climate Change Calculations Using global consumption rate of fossil fuels, the carbon dioxide level will be projected into the middle of this century. Working backwards in time, the carbon dioxide level is estimated at the beginning of the industrial revolution. Using a multi-layered box model the temperature rise at the surface of Earth and Venus are estimated under a wide variety of circumstances. It is believed that doubling carbon dioxide increases Earth's cloudiness, but it is not known exactly what the additional cloud cover will do to the surface temperature of the Earth. We vary some of the cloud parameters to discuss the effects of high clouds vs. low clouds. Early results from the ocean thermal tomography experiments are roughly analyzed in terms of a solar-thermal coupling to the oceans. The Kyoto-Bonn caps will be examined.

Friday October 17, 2003, 3:00pm

Dr. Donna Chen, University of South Carolina
Studies of the Growth and Reactivity of Oxide-Supported Metal Nanoparticles as Models for Heterogeneous Catalysts
Location: Physics 152

Metal particles supported on oxide surfaces serve as excellent model systems for developing a better understanding of commercial heterogeneous catalysts. We have investigated the growth of Cu and Ni nanoparticles on a TiO2(110) surface by scanning tunneling microscopy (STM) under ultrahigh vacuum conditions (P<1×10-10 Torr). In order to study potential particle size-dependent surface chemistry, we have developed a protocol for depositing metal particles with uniform size distributions. Narrow size distributions can be achieved when the rate of diffusion on the surface is slow compared to the deposition flux rate. Temperature programmed desorption studies of methanol reaction on oxidized Cu nanoparticles showed that methanol oxidation was not sensitive to the size of the particles; formaldehyde and water were the major desorption products observed for particles 30'-80' in diameter. However, STM experiments indicate that there is a major change in the morphology of the Cu particles during oxidation. The formation of Cu-O bonds appears to weaken the Cu-Cu bond, allowing two-dimensional Cu clusters to form on the surface at the expense of the existing three-dimensional clusters. This effect has also been observed for Ni particles, but the rate of particle dissociation is slower even though Ni is more easily oxidized than Cu.

Friday October 24, 2003, 3:00pm

Professor Paul M. Voyles, University of Wisconsin-Madison
Atomic-Scale Imaging of Individual Dopant Atoms and Deactivating Nanoclusters in Highly n-type Si
Location: Physics 152

As silicon-based transistors in integrated circuits grow smaller, the concentration of charge carriers generated by the introduction of impurity dopant atoms must steadily increase. Current technology, however, is rapidly approaching the limit at which introducing additional dopant atoms ceases to generate additional charge carriers because the dopants form electrically inactive nanoclusters. Using annular dark-field scanning transmission electron microscopy, we report the direct, atomic-resolution observation of individual Sb dopant atoms in crystalline Si, and we identify the Sb clusters responsible for the saturation of charge carriers. The size, structure, and distribution of these clusters are determined with a Sb-atom detection efficiency of almost 100%. This is the first time individual atoms still bonded inside their crystalline host environment have been unambiguously resolved. Although single heavy atoms on surfaces or supporting films have been visualized previously, our technique is able to view the individual dopant atoms and clusters as they exist within actual devices.

Tuesday November 12, 2003, 3:00pm

Vladislav Shscheslevsky, University of Wisconsin-Milwaukee
Probing Biochemical Processes with Ultrafast Nonlinear Optics
Location: Physics 152

Nonlinear optical microscopy, utilizing third-harmonic generation is one of the emerging techniques for noninvasive microscopic imaging of biological structures. The talk begins with an introduction to ultrafast solid-state laser sources and nonlinear optics. From that point, the colloquium will focus on a novel technique developed in the laboratory for nonlinear optical material characterization and the study of the effects obtained from different environmental conditions. The speaker will provide evidence that the third harmonic can be very sensitive to the structure of the biological objects. In particular, a transformation of collagen in solution is observed for the first time using third harmonic generation. Lastly, there will also be a presentation of the findings on the ultimate limits of the third harmonic to detect micro- and nanoscopic features inside living cells and find that structures as small as 20-30 nm can be detected using the current level of technology.

Friday November 14, 2003, 3:00pm

Prof. John Zasadzinski, IIT Chicago and Argonne National Laboratory
Probing the Pairing Mechanism of High Tc Superconductors
Location: Physics 152

Tunneling spectra of the BSCCO-2212 cuprate superconductor are highly reproducible, revealing a d-wave energy gap and higher bias dip/hump features. It is shown that the dip/hump features are consistent with structures expected from strong-coupling, self- energy effects, similar to the phonon structures found in conventional superconductors. Eliashberg analysis of the dip/hump features leads to a single- peak boson spectrum centered at 36.5 meV which self- consistently generates the measured energy gap. Doping dependent studies link this boson spectrum to the spin excitations measured in neutron scattering.

Tuesday November 18, 2003, 3:00pm

Dr. Emil Mottola, U.S. Department of Energy, Los Alamos National Laboratory
Dark Energy and Condensate Stars: A Quantum Alternative to Classical Black Holes
Location: Physics 152

The difficulties in reconciling general relativity with quantum theory are nowhere better illustrated than in two quite macroscopic effects: the very small but non-zero vacuum dark energy apparently pervading our universe, causing its expansion to accelerate; and the complete gravitational collapse of a dying star to a black hole singularity, which gives rise to a quantum `information paradox.' After reviewing both the theoretical and observational status of these problems, I propose that vacuum energy may be viewed as a kind of gravitational Bose-Einstein condensate or GBEC. This idea of a quantum BEC phase transition in gravity leads immediately to the possibility of a non-singular endpoint of gravitational collapse, a GBEC `star.' Like a black hole a collapsed object of this kind would be cold and dark, but unlike a classical black hole a GBEC star has no singularities, no event horizons, is thermodynamically stable to further collapse and has no information paradox.

Wednesday November 19, 2003, 7:00pm

Professor Emeritus Dale Snider, University of Wisconsin-Milwaukee
Celestial Mechanics Done the Old Way; a' la Kepler
Location: Physics 135

Celestial Mechanics Done the Old Way; a' la Kepler, or From Newton to Planetary Motion through Kepler's Three Laws and Kepler's Equation:
Kepler used his Three Laws to make an ephemeris (a table of the planets' positions as a function of time) for many years into the future. He did this by using what we now call Kepler's Equation (which, however, can't be solved in closed form). With it (and a table of the elements of the planetary orbits from an almanac, i.e. the initial conditions) you can make your own computer program that will show the motion of the planets. Such a program will be shown. Kepler's derivation of Kepler's Equation will be presented and explained. The derivation of Kepler's Laws, from Newton's Laws, will also be discussed. Dale Snider is a Prof. Emeritus at UWM where he taught physics and astronomy and has studied theoretical physics for over 30 years. Before that he earned his Ph.D. in Particle Physics at UCSD and was a Post Doc at Lawrence Berkley Lab. This colloquium is jointly sponsored by the UWM Physics Department and the Physics Club of Milwaukee.