Physics Colloquia - 2004

Friday January 30, 2004, 3:00pm

Professor Sumit R. Das, University of Kentucky
Black Holes, Holograms and Matrices
Location: Physics 152

The holographic principle states that a consistent quantum theory of gravity is equivalent to a theory without gravity in one less dimension. We will review how progress in understanding of black holes in string theory have led to concrete realizations of this principle and have shed new light on the quark confinement problem.

Thursday February 05, 2004, 3:00pm

Dr. Hans Robinson, University of California, Los Angeles
Avalanche free single photon detection
Location: Physics 152

In commercial single photon detectors, such as the avalanche photo diode (APD) and photo multiplier tube (PMT), the gain mechanism consists of a multi-step 'avalanche', in which a single photo-induced charge generates several other charges, each of which in turn generates several charges, etc., until a macroscopic current pulse is created. In this talk, I will present an alternative gain mechanism, where the electrostatic field from a trapped photo-charge induces a detectable change in the environment, for instance by changing the conductivity of a nearby device such as a quantum point contact or a single electron transistor. In this case, the gain mechanism consists of a single photo-charge influencing the passage of a very large number of other charges. Three experimental results will be presented as examples, using first an optical technique for detecting the charges, then electrical measurements of trapped photo-holes and photo-electrons respectively. While this detection scheme will not replace conventional detectors, it has a possible application in quantum communication, as the detector in principle can be designed to preserve the quantum state of the absorbed photon, including any entanglement with distant particles. I will discuss how this property can be used to perform quantum cryptography over long distances -- establishing an intrinsically secure communications channel between distant parties.

Friday February 6, 2003, 3:00pm

Professor J.M. Zuo, University of Illinois, Urbana-Champaign
TBA
Location: Physics 152
TBA

Wednesday February 11, 2004, 3:00pm

Dr. Han Htoon, Los Alamos National Laboratory
Photoluminescence of Individual Carbon Nanotubes: A Glimpse into the Wonders of the One-Dimensional World
Location: Physics 152

Single-walled carbon nanotubes are one-dimensional marcromolecular systems with unique properties. Depending on the chirality of their atomic structure, they can be excellent metals or semiconductors with a band-gap that is inversely proportional to their diameter. Semiconducting nanotubes have enormous potential for future carbon-based optoelectronic applications. A detailed study of their photoluminescence properties is essential to fully evaluate this potential. In addition, this line of studies could also reveal interesting quantum mechanical phenomena of the one-dimensional system. In this talk, I will first review the fundamental science of carbon nanotubes and then present our studies on the photoluminescence of semiconducting nanotubes. We perform single-nanotube, low-temperature photoluminescence studies to probe intrinsic electronic properties without the effects of ensemble inhomogenities and thermal broadening. Our spectra reveal many interesting features including atomically sharp spectral lines of 1-D excitons (electron-hole pair bounded tightly by the enhanced Coloumb interaction of 1-D system) and asymmetrically broadened spectral lines, which we interpret as evidence of an important many-body effect known as Fermi-edge singularity.

Monday February 16, 2004, 3:00pm

Dr. John Miao, Stanford Linear Accelerator Center, Stanford University
3D Diffraction Microscopy and Its Applications in Nanoscience and Structural Biology
Location: Physics 152

When a coherent diffraction pattern is sampled at a spacing sufficiently finer than the Bragg peak frequency (i.e. the inverse of the sample size), the phase information is in principle embedded inside the diffraction pattern, and can be directly retrieved by using an iterative process. In combination of this oversampling phasing method with either coherent X-rays or electrons, a novel form of diffraction microscopy has recently been developed to image nanostructured materials and biological samples. In this talk, I will present the principle of the oversampling method, discuss the first experimental demonstration of this microscope, and illustrate some applications in nanoscience and biology.

Friday February 20, 2004, 3:00pm

Professor Arun Bansil, Northeastern University
Alice in the Wonderland of Novel Materials: Cuprates, Manganites and Quantum Dots
Location: Physics 152

Novel materials with all the wonderful opportunities they offer for understanding a wide range of exotic effects have become a central theme of current research in condensed matter physics. This talk presents a selection from our recent results concerning cuprates, manganites and quantum dots. In connection with the cuprate superconductors, we show how the Fermi surface evolves with electron doping in Nd_{2-x}Ce_xCuO_{4-delta} as the Mott pseudogap collapses, in the light of recent high resolution ARPES experiments and related mean field Hartree-Fock and self consistent renormalization computations within the framework of the one-band t-t'-t''-U Hubbard model Hamiltonian. We also discuss how the ARPES matrix element via its selectivity properties can be exploited to focus on interesting physics in the cuprates (e.g. the issue of coherence effects and bilayer splitting in Bi2212). In connection with quantum dots, we discuss an exactly solvable model Hamiltonian for describing the interacting electron gas in a quantum dot. Results for a spherical square well confining potential are presented. The ground state is found to exhibit striking oscillations in spin polarization with dot radius at a fixed electron density. These oscillations are shown to induce characteristic signatures in the momentum density of the electron gas, providing a novel route for direct experimental observation of the dot magnetization via spectroscopies sensitive to the electron momentum density. Finally, we comment on recent magnetic inelastic x-ray scattering measurements on La$_{1.2}$Sr$_{1.8}$Mn$_{2}$O$_{7}$ and show how the shapes of the spectra for various directions of the momentum transfer vector contain signatures of specific magnetic orbitals.

Friday February 27, 2004, 3:00pm

Professor Saul Teukolsky, Cornell University
TBA (General Relativity/Cosmology)
Location: Physics 152

TBA

Monday March 01, 2004, 3:00pm

Dr. Valerica Raicu, University of Toronto, CANADA
Studies of biological tissues, cells, macromolecules, and bio-molecular aggregates by using linear and nonlinear electrical and optical spectroscopic methods
Location: Physics 152

The end of the twentieth century witnessed rapid developments in technology, which facilitated the study of a variety of biological systems ranging from organs, tissues and cells down to the molecular make-up of the cell and cellular organelles. Of particular interest in recent years are the physico-chemical processes through which the genome (i.e., an organism's entire DNA sequence) expresses information that enables cells to carry out the full repertoire of biological functions, processes which involve both the genome and its protein complement, or the proteome. Physics plays a special role in this science-wide endeavor by offering the grounds both for understanding the cellular and molecular processes fundamental to life, and for developing the tools necessary for their study. I will begin this talk with a brief overview of our work on the dielectric spectroscopical properties of biological cells and tissues, with particular reference to the dielectric signature of the fractal (self-similar) organization of cells into supracellular aggregates or tissues. This will be followed by an introduction to our recent studies of protein dynamics in vitro, and of protein-protein interactions in living cells through the use of linear and nonlinear spectroscopic and microscopic techniques, such as fluorescence microscopy, pump-probe, and transient grating spectroscopy. I will expand on our contributions to F'rster Resonance Energy Transfer (FRET) theory and methodology (relying on spectrally resolved fluorescence imaging and genetically engineered fluorescent tags) for studies of protein-protein interactions in living cells. We anticipate that use of this type of techniques for in vivo studies will play an important role in the emerging proteomics revolution in life sciences.

Friday March 05, 2004, 3:00pm

Associate Professor Gay B. Stewart, University of Arkansas, Fayetteville
Intro Courses that Entice Majors and Improve Student Performance
Location: Physics 152

University of Arkansas is part of the Physics Teacher Education Coalition (PhysTEC), an APS/AAPT/AIP program. PhysTEC provides dramatic improvement of science preparation of teachers, developing programs to work at a range of institutions. Features of our undergraduate program already in place that benefit all students that led to our selection for this program, and in-progress curricular revisions will be discussed. As an example, we began with introductory calculus-based electromagnetism and optics, UPII. Our goal was to improve the level of student learning, confidence, and enjoyment of science, while maintaining the resource level common to large institutions. The program is successful. Confidence is up, particularly women end the course as confident as men, with strong correlation between confidence and performance. Students who successfully complete UPII go on to earn a SMET degree. This is the majority, as we make it hard not to learn the material. Students given a 50-minute closed-book test from a 1990 class (ave=53.8%) finished in 35 minutes with an average of 69.2%. They outperformed previous classes where the concepts had been specifically addressed by 18% on multiple-choice questions. Students have a higher retention to degree than university average. Graduation rates tripled concurrent with our first UPII students graduating and continues to increase. Our method involves leading the student from concrete hands-on examples to conceptual understanding through group discussion. Experimental results provide verification. Concepts are related to familiar phenomena. Students are taught to reason in a structured manner about both conceptual and quantitative problems. Cooperative learning, found to improve retention of female and minority students, is emphasized. The increased number of majors impacts almost every aspect of the department.

Friday March 12, 2004, 3:00pm

Professor Rajat Bhaduri, McMaster University
Bosons in a trap : Ground State Number Fluctuations and Statistical
Location: Physics 152

Taking the example of trapped bosons at ultra low temperatures, the concept of micro- and macro-states would be reviewed, with special emphasis on the Microcanonical Ensemble. It will be shown that under some circumstances, anomalous results are obtained from the canonical and the grandcanonical calculations. The talk will be an introductory one, with emphasis on the basic physics, and some number theoretical application.

Friday March 19, 2004, 3:00pm

Professor Ruth Howes, Marquette University
The Changing Landscape of Undergraduate Physics (why some programs thrive and others don't)
Location: Physics 152

The National Task Force on Undergraduate Physics was convened by APS,AAPT and AIP to study the steep decline in the number of physics majors that occurred during the 1990s. This year, the Task Force has conducted project SPIN-UP (Strategic Programs for Innovations in Undergraduate Physics) to investigate why some departments are thriving while others are losing majors. With support from the ExxonMobil Foundation, we have conducted site visits to 21 'thriving' departments and have worked with the AIP statistics program to survey the 562 departments that grant undergraduate degrees in physics. The results of the study have identified key ingredients in thriving departments and essential elements needed to make changes that respond to the changing environments in which physics departments find themselves.

Friday April 09, 2004, 3:00pm

Vlado Lazarov, University of Wisconsin-Milwaukee
Polar Oxide Interfaces: Atomic and Electronic Structure
Location: Physics 152

The instability of polar surfaces is closely related to that of polar interfaces, resulting from the apparent presence of an electric dipole moment in the repeat unit parallel to the surface/interface. Studies of polar semiconductor interfaces, based on classical electrostatic models, exclude the existence of atomically abrupt polar semiconductor interfaces in order to avoid the huge dipole fields that would otherwise arise at the interface, and consequently produce interface charge accumulation. In this classical model, atomically abrupt polar oxide interfaces are even less likely, since ionicity in oxides is more pronounced. Thus the question of polar oxide interface stability remains open for both experiment and theory. I will present Electron Microscopy and Density Functional Theory study of how the interface polarity affects the atomic and electronic structure of interfaces, using Fe3O4(111)/MgO(111) polar oxide interface as a model system. The substrate polarity cancellation appears to be a driving force that determines the structure of the polar Fe3O4(111) film and atomic structure of the Fe3O4(111)/MgO(111) polar oxide interface. The results of our study suggest that surface polarity could be used as an additional growth parameter in creating novel material structures.

Monday May 03, 2004, 3:00pm

Kevin King, Ph.D., University of Wisconsin-Milwaukee
Parallel Imaging in MRI
Location: Physics 152

Parallel imaging is a new development in magnetic resonance imaging that allows faster scanning using multiple receive coils. In MRI, data acquisition speed is frequently the limiting factor in diagnostic image quality. Early advances in MR techniques focused on shortening scan time by improving hardware, especially gradient amplifiers, and developing more efficient data acquisition schemes. As modern scanners have reached cost limits and physiological limits allowed for gradient switching, and as acquisition efficiency has become fully developed, other methods like parallel imaging, have emerged to reduce scan time. In parallel imaging, scan time is decreased by reducing the number of gradient encoding steps required to make an image. The spatial distribution of the receive coil magnetic field is used to compensate the missing spatial encoding information. This scan time reduction enables shorter patient breath holds, greater spatial resolution, better temporal resolution, and opens up new applications that would not have been possible because of prohibitive scan time.

Friday May 07, 2004, 3:00pm

Professor Vinayak P. Dravid, Northwestern University, Evanston, IL
Teaching 'Old' Materials 'New' Tricks: Site-Specific Nanopatterning of Functional Inorganics
Location: Physics 152

Our recent research efforts at Northwestern University are geared towards designing intricate architecture of functional nanostructures, as well as using them as building blocks for device systems for sensing, diagnostics and therapeutics. Embedded in this scheme are several nanopatterning approaches, some are based on the original invention of Dip-Pen Nanolithography (DPN) developed at Northwestern. The original DPN approach is modified to pattern, at the nanoscale, templates for inorganic and organic-inorganic complexes of arbitrary shape/size on arbitrary substrates, thus extending the efficacy and elegance of DPN. Subsequently, several direct methods (e.g. nano-fountain-pen) in conjunction with sol-based precursors have been developed for site- and shape-specific patterning of functional inorganics at nanoscale, thus circumventing the two-step template-based approach. The talk will outline modified DPN and sol-based precursor 'inks' as an enabling approach to pattern and characterize magnetic, electronic, chemical- and optical active nanostructures at the nanoscale. Success is already evident for magnetic oxides, inorganic mesoporous structures, ferroelectrics and optically-active nanostructures. The real need for characterizing structure/crystallography, 3-D morphology, local chemistry and conformation of such nanopatterns, as well as unambiguous measurement of their local properties, will be emphasized. The prospects for patterning at single-molecule resolution, especially for bioactive molecules, both by themselves and as templates for inorganics, will also be discussed. It will be argued that functional nanostructures go beyond the 'hype', and present challenging yet exciting opportunities for synthesis-structure-architecture-form-function-performance relationships, especially in hybrid organic-inorganic systems.

Monday May 10, 2004, 2:00pm

Professor Laura Mersini, Dept of Physics & Astronomy/University of North Carolina at Chapel Hill
Too Many Cosmic Coincidences and New Physics
Location: Physics 453

Please attend this Relativity and Cosmology seminar on the work of one of our recent Ph.D. graduates.

Friday May 14, 2004, 3:00pm

William Komp, University of Wisconsin-Milwaukee
Vacuum Metamorphosis and Recent Experimental Data
Location: Physics 152

In 1998, the Supernova Cosmology Project and High-Z Research Team independently published supernovae experimental data that appeared to indicate a late-time accelerated epoch of the Universe's evolution. One of the most important questions in cosmology today is: What is the source of this acceleration? This source has been given the label of dark energy. In this colloquium, I will review the standard cold dark matter model of cosmology assuming an early inflation and show that this late-time acceleration requires at least some extension of this standard model. I will present two extensions of this model which incorporate modifications of the classical Einstein- Hilbert action, the Cosmological Constant Cold Dark Matter (Lambda-CDM) model and Vacuum Cold Dark Matter (VCDM) model of Leonard Parker and Alpan Raval. From a historical perspective, the Lambda-CDM model appears as a good first guess for dark energy. Originally proposed by Einstein to obtain a static universe, this model supposes that there is a non-zero cosmological constant (Lambda). One alternative model is the VCDM model of Parker and Raval, which supposes that there is a low mass quantized scalar field which produces a vacuum energy density. This vacuum energy dominates over the classical sources of energy (non-relativistic matter and radiation) when the energy scale is of order 10-29g/cm3. I will present the results of fitting these models to very recent experimental data to obtain reasonable parameter estimates. Next, I will use these parameters to compute and compare the model dependent quantities for the Lambda-CDM and VCDM models and will show that the present data is not able to distinguish between the two models although they have very different models of dark energy. Thus, at present there is insufficient information to distinguish the nature of dark energy.

Monday May 17, 2004, 3:00pm

Qun Shen, Ph.D., Cornell University
From Phase-Sensitive Diffraction to Coherent Imaging Applications
Location: Physics 152

There have been significant advances in recent years in x-ray imaging of semiconductor and biological materials using highly brilliant x-ray sources and state-of-the-art phasing algorithms. These advances are gradually changing the landscape of x-ray science and allowing x-ray structural science to move from mostly crystal-based to nonperiodic materials. In this talk, I will first review a phase-sensitive x-ray diffraction method for crystalline-based structural determination, and then will discuss the prospects of future applications in phasing structures of nonperiodic materials with highly coherent x-rays. The discussion will mostly cover three areas in biological and biomedical science: medical imaging, cellular imaging, and molecular imaging, with different emphases on image contrast and spatial resolution in each of these emerging fields of x-ray imaging science.

Friday June 18, 2004, 3:00pm

Professor K.N.Pathak, Panjab University, Chandigarh
Two-Dimensional Coulomb Fluids
Location: Physics 152

Two-dimensional coulomb systems will be mentioned and some aspect of dynamics of electrons confined to a plane with neutralizing background will be discussed due to their varied applications. In particular, a simple theoretical model calculation for the density correlation function and velocity auto correlation function will be presented with some emphasis on collective excitations of the systems. The result will be compared with molecular dynamics data. Finally, the effect of magnetic fields on collective dynamics of electrons will be mentioned.

Friday July 09, 2004, 3:00pm

Damien Cho, University of Wisconsin-Milwaukee
Can quantum geometry save the world?
Location: Physics 152

According to some unified field theories we live in the universe with more than 3 spatial dimensions that are compactified in a very tiny region. The compact dimensions are, however, typically unstable to either collapse or expand. My talk will address the question whether quantum geometry will remove the instability. (thus, save the world) A large portion of my talk will be on an (alleged) self-contained introduction to many related concepts appropriate to non-experts. Then, I will provide some results on a toy model.

Friday August 13, 2004, 3:00pm

Xiaofeng Hu, University of Wisconsin-Milwaukee
Vibrational Spectroscopy at Surfaces: Long Range Coadsorbate Interactions And Water Adsorption on High Tc Superconductor
Location: Physics 152

Infrared Spectroscopy is a powerful technique to determine the chemical nature of substrates and adsorbates. Its fast data collection makes it suitable for in-situ studies. It can provide direct information on the nature of the bonding and energy transfer between the adsorbate and the substrate, and between the coadsorbates. The infrared study of CO on pre-sulfided Cu(100), combined with Auger Electron Spectroscopy (AES) and Thermal Desorption Mass Spectrometry (TDMS), reveals that S modifies the local density of states, and affects the C-O bonding strength through the metal. The strengthening of the CO stretch is attributed to a reduction in back-donated electrons from the metal into the 2'*-MO of CO. As S coverage increases, S reduces available adsorption sites for CO, isolating CO adsorbates from each other and reducing CO intermolecular dipole-dipole coupling. For a low S coverage, where dipole-dipole coupling is still dominant, a Coherent Potential Approximation (CPA) treatment of dipole-dipole coupling by Persson and Ryberg is used to estimate the spatial extent (reffective) of S and CO through-metal interactions. reffective is found to be between 6 & 7°. Temperature dependent infrared study of water adsorption on the surface normal to the ab-plane of a Bi2212 single crystal reveals that water adsorbs molecularly. The main absorption bands occur between 3200-3500 cm-1 and are assigned to the OH stretching and the overtone of OH bending. The appearance of this band at low exposures suggests the formation of hydrogen-bonded clusters. This absorption feature is similar for 85K and 120K, and is slightly modified at 140K due to the slight structure change in the amorphous ice. At 150K, a well defined absorption feature indicates the crystalization of the water clusters.

Friday September 10, 2004, 3:00pm

Duncan Brown, University of Wisconsin-Milwaukee
Searching for Gravitational Waves from Binary Black Hole MACHOs
Location: Physics 152

The search for gravitational radiation from binary inspirals with LIGO is well underway. One possible source is of gravitational radiation is low mass binary systems in the halo of dark matter surrounding the Milky Way. Observations of gravitational microlensing events of stars in the Large Magellanic Cloud suggest that some fraction of the dark matter in the halo may be in the form of Massive Compact Astrophysical Objects (MACHOs). It has been proposed that low mass black holes formed in the early universe may be a component of the MACHO population; some fraction of these black hole MACHOs will be in binary systems and detectable by LIGO. Data from the second science run is currently being analyzed by the Inspiral Working Group of the LSC. I will present the methods that we have used in the binary black hole MACHO search and the preliminary results obtained from ``playground'' data.

Friday October 15, 2004, 1:00pm

See abstract for speaker schedule, UWM Chemistry
Keulks Lectures
Location: Chemistry 180

Agenda/Schedule for October 15, 2004 11:30 a.m. - 1:00 p.m. Poster session for graduate students and postdoctorals in the Physics, Engineering and Chemistry/Biochemistry Departments Outside Chem 180 1:00 p.m. Welcome by Chancellor Carlos Santiago Chem 180 1:15 p.m. "Dr. Keulks as a Mentor" by Dr. David Krenzke, Advanced Refining Technologies Chicago, IL Chem 180 1:30 p.m. Professor Alain Kaloyeros, Executive Director of Albany NanoTech University of Albany, Albany, NY Chem 180 2:30 p.m. Professor J. Fraser Stoddart, Fred Kavli Chair in NanoSystems Sciences Director of the California NanoSystems Institute UCLA, Los Angeles, CA Chem 180 3:30 p.m. Professor Ivan Petrov, Director of Center for Microanalysis of Materials Frederick Seitz Materials Research Laboratory University of Illinois-Urbana Champaign, Urbana, IL Chem 180 4:30 p.m. Closing Remarks by Dr. Dale Jaffe Interim Dean of the Graduate School, on George's Contribution to Scholarship, Research, and Graduate Education at UW-Milwaukee Chem 180 5:00 p.m. - 7:30 p.m. Social Hour for attendees, friends and colleagues of George Keulks UW-Milwaukee Helene Zelazo Center 2419 East Kenwood Blvd.

Friday October 22, 2004, 3:00pm

Professor Valerica Raicu, University of Wisconsin-Milwaukee
Joint Undergraduate Seminar/Physics Colloquium: Developing Photonic Tools for the Post-Genomic Revolution
Location: Physics 147

Studies of the physical and chemical processes through which DNA expresses information that enable biological cells to support and perpetuate life have been central to the genomic research revolution. Complete understanding of life processes, however, requires the study not only of the DNA sequence (the genome), but also of the protein complement (the proteome), which is part of the complex machinery that expresses the gene-encoded information into real biochemical products, namely, proteins and protein aggregates (complexes) with specific biological functions. Such studies are just beginning to emerge; however, they have huge implications for life sciences and will likely trigger a preoteomic revolution. Physics can play a central role in this endeavor, by providing the foundations for understanding molecular interactions involved in formation of protein complexes in living cells, and by developing the tools for mapping the spatial disposition of proteins and protein complexes inside the cell and for determining the identity and number of the proteins forming specific complexes. This talk will provide an elementary introduction to (a) the physical methods used in such studies, (b) our recent contributions to the field, and (c) our present efforts for developing photonic tools for three-dimensional imaging of the proteome distribution and interactions in single living cells. The long-term goal of this research is to refine the techniques so that they can be used to acquire movies presenting the birth, life, and death of the proteome in living cells.

Friday November 05, 2004, 3:00pm

Professor Dilano Saldin, University of Wisconsin-Milwaukee
Entropy, Information, and Crystal Revelations
Location: Physics 147

The concept of entropy first arose out of an effort to understand the behavior of heat engines during the industrial revolution of the 19th century. The scientific concept of information was a product of communication revolution of the 20th century. The two concepts are intimately related. Indeed, Shannon's definition of information is almost identical in mathematical form to the statistical definition of entropy in thermodynamics. We will discuss the relationship between ideas in the two fields, and illustrate the usefulness of the entropy concept for the practical problem of making optimal deductions from incomplete data. The three-dimensional arrangements of atoms is the key to understanding the properties of materials. The vast majority of such atomic-scale structures are determined by the analysis of the scattering of radiation of wavelengths of the order of typical interatomic spacings. Essential to this analysis is an estimation of the unmeasured phases of the scattered radiation. We will show in this talk how the entropy concept may be exploited to obtain the best guesses of these phases from available data, thus suggesting an approach to the solution of the inverse scattering problem in this field. This allows the efficient determination of the atomic-scale structures of materials ranging from proteins to those that will form the basis of future nanotechnology.

Friday November 12, 2004, 3:00pm

Professor Guillaume Gervais, National High Magnetic Field Laboratory-Florida State University
NMR in Flatland, and With Too Few Spins
Location: Physics 147

In this talk, I will briefly review the transport properties of the two-dimensional electron gas (2DEG) confined at semiconductor interfaces, and in particular in the so-called fractional quantum Hall regime. I will then describe how we can perform unorthodox magnetic resonance on the 2DEG by means of resistively detected NMR so that we can obtain the nucleus' point-of-view of two-dimensional electrons (flatland). I will show evidence from NMR relaxation experiments for the formation of a lattice of spin topological textures, i.e. a Skyrmion crystal, and describe further experiments aimed at elucidating non-abelian quantum statistics that might occur in flatland.

Friday, November 19, 2004, 3:00pm

Professor Sharon Morsink, University of Alberta, CANADA
Neutron Stars as Laboratories for Relativity
Location: Physics 135

Neutron stars are tiny stars with ultra-strong magnetic and gravitational fields and densities larger than nuclear. Their small size and large average densities allow them to spin at very rapid rates, with surface velocities that are a large fraction of the speed of light. The very large gravitational fields and relativistic rotation rates make it necessary to use Einstein's theory of general relativity to describe these stars. As a result, neutron stars have great potential to act as "laboratories" for strong field relativistic effects. In this talk, I will review some of the interesting effects that may be observed by X-ray satellites and gravitational wave detectors and discuss the prospects for constraining the unknown nuclear equation of state describing these dense stars.

Tuesday, November 23, 2004, 3:00pm

Professor Rangarajan, I.I.T. Madras
Probing Clustered States in Magnetoresistive Manganites
Location: Physics 135

The physics of 'giant' magnetoresistance has been responsible for breakthroughs in spin-based storage technologies over the last ~20 years, giving us computer hard drives with high-speed access to giga-sized memory(*). More recently, a fascinating class of 'collosal' magnetoresistive manganite-based materials has attracted the attention of the condensed matter community. These materials are characterized by a correlation among lattice, spin, charge and orbital degrees of freedom. The primary consequence of such interplay is the presence of intrinsic inhomogeneities in the form of nanoscale-clustered states. Such clustered states are common to other materials such as high-temperature superconducting cuprates or dilute magnetic semiconductors, and has emerged as a new conceptual framework for studying condensed matter physics. In this talk, I will review properties of such clustered states using experimental probes sensitive to different degrees of freedom. In particular, I will present our results on single crystals and polycrystals of Nd1-xSrxMnO3 using zero-field spin-echo 55Mn nuclear magnetic resonance (NMR), electron spin resonance (ESR) and polarized Raman scattering (in collaboration with S. Angappane and M. Pattabiraman).

Friday, December 3, 2004, 3:00pm

Professor Dale Snider, University of Wisconsin-Milwaukee
Kepler Orbits in Quantum Mechanics?
Location: Physics 135

The 1/r potential is special. In classical mechanics it is called the Kepler problem and produces the famous elliptical orbits. In Q.M. it is called the Coulomb problem and produces the hydrogen-atom wave functions. Many introductory texts have pictures of these wave functions, and they don't look anything like ellipses. But isn't Q.M. suppose to give the classical results in the proper limit? This paradox will be resolved in this lecture.

Friday, December 10, 2004, 3:00pm

Nic Langlois & Amanda Alstad, University of Wisconsin-Milwaukee
Undergraduate Student Seminars
Location: Physics 147

Nic Langlois
An Introduction to Quantum Entanglement
3:00 PM
Quantum Entanglement has recently become a pop-physics topic with references to it in articles regarding both Quantum Computing and Quantum Teleportation. Both of these fields are looking towards the phenomenon of Entanglement for a way to achieve real world results. As such an understanding of Entanglement is necessary for anyone interested in these field. This talk will cover the basic concepts presented originally in the Einstein, Podolsky and Rosen's paper on the subject, and a look at the more recent Greenberger, Horne, Shimony and Zeilinger paper "Bell's Theorem without inequalities"; as both are important pieces of our understanding of Quantum Entanglement.

Amanda Alstad
Determining Standard Reduction Potential of Enzyme Mediators Involved in the Nitrogen Cycle
3:30 PM
The Nitrogen cycle is critically supported by bacteria, which aid the process of nitrification (eg. oxidizing ammonia). Understanding these processes is important to our understanding and design of wastewater treatment. In this talk, I will review the Nitrogen cycle, bacterial function in Nitrification and other relevant topics. I will also describe some of the work I have been doing with the Pacheco group at UWM.

Friday, December 17, 2004, 3:00pm

Professor G. Mukhopadhyay, I.I.T. Bombay
Optical Absorption by Nano Particles
Location: Physics 135

Optical absorption from small particles has a very wide applications, for example, paint industry, environmental study, weather forecasting, study of instellar dust, etc. In this talk, an outline on what one knows about the absorptive properties of nano sized particles of ellipsoidal shape will be discussed. Very often, one is interested in coated small particles, whose absorptive poperties can be different because of the coating. It is also of interest to study the effect of anisotropy in the dielectric function of the coating, which can occur naturally especially when the coating is very thin. This is interesting, because of its similarity with biological cells, and will be discussed in the end.