Physics Colloquia – Spring 2007

 (Fridays 2:00 PM. PS 227)

Titles link to the abstracts.
Date Speaker Title
Jan 19
 Warner Miller (FAU)
Jan 26
 Shane Walker (UCSD)
Feb 2
 A. De Rujula (CERN)
Feb 9
 G. J. Mathews (U. Notre Dame)
Feb 16
 Steve Drasco (JPL + Caltech)
Feb 23
 Jorge Pullin (LSU)
Mar 2
 Clyde R. Burnett (Emeritus FAU)
Mar 16
 Stefan Vetter (FAU)
Mar 23
 Diandra Leslie-Pelecky (UNL)
Thursday Mar 29
 Ivan I. Smalyukh (UIUC)
Mar 30
 Aniket Bhattacharya (UCF)
Monday Apr 2
 Nikoleta Theodoropoulou (MSU)
Apr 6
 Khalid Eid (PSU)
Apr 20
 Stanimir Bonev (Dalhousie Univ.)
Apr 27
 Lilia Woods (USF)
     

 

Colloquium Abstracts

Hybrid Spacetimes: An Introduction to Gravitation on Lattice Geometries
Warner Miller (FAU), Jan 19
The speaker will present a novel introduction to the lattice representation of gravitation introduced in 1960 by Tullio Regge. This geometric and coordinate-free approach to general relativity is commonly referred to as Regge Calculus. He will discuss the importance of the Voronoi and Delaunay lattices in Regge Calculus, and offer a fresh geometric interpretation of this 40 year-old theory. The Voronoi and Delaunay lattices are dual to one another and are ubiquitous in almost every facet of nature. These dual tesselations are unavoidable in Regge Calculus. He will show how this new interpretation may solve problems of current interest in classical and quantum gravity.
 
Acoustic imaging in the shallow ocean
Shane Walker (UCSD), Jan 26
During the cold war, oceanographic research was dominated by a preoccupation with locating nuclear-capable submarines in the deep ocean. More recently, conflicts between coastal nations, both military and social, have precipitated renewed emphasis on research in the shallow ocean environment spanning the continental shelf. In contrast to the deep ocean which is dominated by refractive processes, acoustic propagation in shallow water environments is dominated by interactions with the air/water and water/sediment interfaces. Similar to a wide range of fields such as nondestructive testing, medical ultrasonics, multi-channel communications, seismic processing, adaptive optics, and radio astronomy, shallow water acoustics problems involve propagating waves that carry information to the boundaries of a minimally accessible, poorly known, complex, noisy medium where they are detected. Extracting a signal from noise can be complicated, especially along a coastline filled with marine life, shipping lanes, undersea waves, shelves, and fronts that scatter sound. However, the rapid proliferation of computational technologies has opened the door to a wide range of new acoustic-based environmental diagnostics that have generated advances in target detection, communications, sea-floor mapping, mine location, tomography, and ocean biology. The speaker will provide an overview of the field of shallow ocean acoustics and discuss a few of the proven methods for imaging in the shallow ocean.
 
From the very large to the very small and back - Video lecture
A. De Rujula (CERN), Feb 2
Dr. De Rujula, head of the Theory Division at CERN, gives a concise summary of some of the important topics in theoretical physics covered in the CERN Physics Summer School conducted in 2006. These range from astrophysics to particle physics and end with a discussion of the cosmic microwave background.
 
A Journey to the Center of the Galaxy: A Giant Black Hole, Lost Matter; and Exploding Stars
G. J. Mathews (University of Notre Dame), Feb 9
Although hidden from view for centuries, many new images of the mysterious center of the Galaxy have been revealed recently. In this talk we will unveil these various views of the galactic center and the giant black hole which resides there. Within this region one can see a microcosm of stellar births and disruption as material plunges unavoidably toward the horizon of the black hole. We will explore the usefulness of this region as a test bed of the theory of relativity and explore the astrophysics of the strong gravitational field and stellar density in this region.
 
Gravity wave capture events as tools for physics and astronomy
Steve Drasco (JPL + Caltech), Feb 16
Gravity wave detectors are expected to observe the capture of compact objects by much more massive host black holes. I will describe how these observations will be conducted and discuss their potential as tools for physicists and astronomers. The most anticipated class of these events is the capture of star-sized compact objects by massive black holes in galactic nuclei. These are relatively low-frequency events (around 1 to 10 mHz) and can be both found and monitored for years by future space-based gravity wave detectors. At higher frequencies (above 10 Hz) earth based detectors can search for the capture of objects by intermediate mass black holes that might reside in globular clusters. Both classes of these capture events become observable when the captured object is within a few multiples of the black hole's horizon radius, and when it moves relative to the larger one at nearly light-speed. Though highly relativistic, the events can be accurately modeled with a perturbative formalism, introduced in the 1970's, that exploits the mass-ratio as a natural small parameter. Observing the detailed predictions of this formalism with gravity wave detectors would validate our understanding of black hole physics. Specific tests include the motion of test particles over thousands of orbital cycles, the interaction of radiation and the horizon, and possibly an explicit map of the spacetime geometry's multipole structure. These observations would also open a new window for astronomers as a survey tool for galactic nuclei and the black holes that reside within them, and as a constraint on the existence of intermediate mass black holes.
 
Quantum mechanics with real clocks, decoherence and the black hole information puzzle
Jorge Pullin (LSU), Feb 23
When one formulates quantum mechanics in terms of real clocks, one gets a formulation that differs from the traditional Schroedinger one. In particular pure states evolve into mixed states. We will estimate what is the minimum size of this effect and argue that it is large enough to render the black hole information puzzle unobservable and it also places a fundamental limit on the top speed of a quantum computer.
 
The Atmospheric Science of Global Warming
Clyde R. Burnett, (Professor Emeritus, FAU), Mar 2
There will be an initial presentation of a review of Atmospheric Structure, Black Body Radiation, and the Greenhouse Effect. Following this, there will be a discussion of the history and behavior of the various greenhouse gases. A summary will be presented of the evidence of global warming and model predictions in the Intergovernmental Panel on Climate Change report of 2 February 2007, followed by discussion of mitigation possibilities.
 
Using Phage Display to Develop RAGE Antagonists
Stefan Vetter (FAU), Mar 16
The Receptor for Advanced Glycation Endproducts (RAGE) is a cell surface receptor recognizing several classes of ligands, including protein damaged by glycation and S100 protein. Activation of RAGE by these ligands promotes vascular inflammation, leading to heart disease, stroke and kidney damage. We are interested in the biophysical characterization of the RAGE - ligand interaction and the discovery of ligand specific RAGE antagonists. Since the structure of RAGE remains elusive, we use a shotgun approach to screen large phage display libraries of antibodies and peptides for RAGE ligands. The lecture will introduce RAGE as a potential drug target involved in vascular diseases associated with diabetes, explain the principles of phage display technology and summarize our current research here at FAU in the Department of Chemistry and Biochemistry.
 
Biomedical Applications of Magnetic Nanomaterials
Diandra Leslie-Pelecky (UNL), Mar 23
Nanoscale materials offer unprecedented opportunities to investigate and interact with biological systems. Magnetic nanomaterials are especially interesting due to the potential for locating materials inside the body using an external magnetic field. Magnetically targeting chemotherapy drugs, for example, could decrease the systemic effects that make cancer treatment so debilitating. Biomedical applications, however, impose constraints. Magnetic targeting requires large magnetic moments, but also that materials be biocompatible, and stable in air and aqueous environments. Size and surface characteristics (e.g. charge, chemical functionality) must be controlled to regulate how the nanomaterials circulate within the body and interact with different types of cells. After a general overview of the challenges and opportunities for physical scientists interested in applying their expertise to biomedical challenges, I will describe our work developing multifunctional magnetic nanoparticle fluids. These materials are capable of delivering multiple hydrophobic anti-cancer drugs to specific locations, as well as enhancing magnetic resonance imaging of the affected area. In this formulation, the drugs partition in the hydrophobic portion of a double-layer surfactant, which improves drug loading and release, while the outer layer of the surfactant improves the circulation time in the body. I will then describe our use of inert-gas condensation into liquids to produce increased magnetic moment nanoparticles that will improve the magnetic targeting capability, and our efforts to understand the mechanisms by which surfactants change magnetic properties.
 
Ordered structures and patterns of biopolymers and bacteria
Ivan I. Smalyukh (University of Illinois), Mar 29, THURSDAY, 3:30-4:30, BS 303
Locally ordered molecular structures are common for membranes, cytoskeleton proteins, amino acids, and viruses. They form not only /in vitro/ but even /in vivo/, ranging from self-organized states of collagen in cornea to nematic-like actin and myosin organization in muscle fibers, and to ordered molecular structures in spermatozoa. The knowledge of physical mechanisms behind these partially ordered states has a potential to impinge broadly on understanding their biological function. In this lecture, I will discuss the liquid crystalline phases and pattern formation in the concentrated DNA, when the extended molecular chains can trace out zigzags and form the periodic ordered structures. I will then show that even the live biological cells (such as /Pseudomonas aeruginosa/) can be orientationally ordered when placed into the matrices of biopolymers. Both experimental observations are modeled considering the elastic properties of the liquid crystalline states of the concentrated DNA biopolymers. These studies shed light on the role played by the bacterial shape and extracellular biopolymers in important biological processes, such as cell-to-cell signaling and biofilm formation. Moreover, the controlled alignment has potential applications in nanotechnology and biotechnology.
 
DNA translocation through protein and synthetic nano pores
Aniket Bhattacharya (UCF), Mar 30
DNA translocation through narrow protein channels is recognized as an important process in biology. Recently it has attracted lot of attention in the biophysical community following several experiments on DNA translocation through protein nano-pores, and more recently, through synthetic silicon nano-pores. A fundamental understanding is needed for various biological processes, e.g., entry and exit of a DNA in and out of a cell, efficient separation methods for macromolecules, and, possibly fast DNA sequencing. In this talk I will be presenting results for the DNA translocation using a coarse-grained model for an idealized DNA as well as the pore. I will consider several scenarios for the DNA translocation. First, I will show scaling of translocation time of a homopolymer as it escapes from the trans side to the cis} side of an idealized thin membrane. Then I will consider DNA dynamics subject to a driving force inside the pore. Next, I will consider heteropolymer threading through a nano-pore. Specifically we will consider both highly ordered and completely random sequences of the chain and relate specific sequences to the distribution of the translocation time and the residence time inside the pore. These studies also will include effects due to different environment on either side of the pore, specific DNA-pore interactions located at selective sites, etc. I will discuss relevance of these simulation results to recent experiments and theoretical models.
 
Magnetic Semiconductors and Spin-Transfer Torques in Magnetic Nanopillars
Nikoleta Theodoropoulou (MSU), Apr 2, MONDAY, 2:00-3:00, BU 112
Spintronics is the field of physics that explores the creation, detection and manipulation of the electron spin. I will present two different approaches to Spintronics. The first approach is focused on the study and investigation of semiconductors that are doped with magnetic elements, while the second concentrates on spin transport studies in metallic/magnetic multilayer structures. I will present evidence that Zn1?xMnxO thin films, grown by reactive magnetron sputtering without external carrier doping, are ferromagnetic at temperatures significantly above 300 K. The onset of the ferromagnetic behavior is controlled by the detailed growth conditions and the magnetic properties strongly depend on the Mn concentration. In well-characterized, single-phase films, the magnetic moment is 4.8?B/Mn at 350 K, one of highest moments yet reported for any Mn doped magnetic semiconductor. Anomalous Hall effect shows that the charge carriers are spin-polarized electrons and participate in the observed ferromagnetic behavior. Zn1?xMnxO appears to be a promising candidate as a magnetic semiconductor and for use in spin based electronic applications of the future. The second approach is by investigating the spin transport in alternating metallic and magnetic layers. The Giant Magnetoresistance (GMR) effect that has been successfully implemented in technology is such an example. The inverse of the GMR effect is the effect of the spin-transfer torque. It can be demonstrated in a magnetic nanopillar where a spin-polarized current flowing through a ferromagnetic layer exerts a torque on its magnetization. I investigate the effect of the normal layer on the switching characteristics of magnetic nanopillars in the case of ballistic(Cu) and diffusive transport (Cu(Ge5%)) by comparing the magnetization switching currents (_IS) in Py/Cu and Py/Cu(Ge5%) nanopillars and relating them to the calculated spin-transfer torques. Spin-transfer torques can also lead to microwave-frequency dynamics and I will present very recent data of such high-frequency excitations on Py/Cu nanopillars.
 
Experiments in Spintronics and Nanomagnetism
Khalid Eid (PSU), Apr 6
The field of magnetism has seen revolutionary advances in the past two decades. The discovery of giant magnetoresistance, current-driven magnetization switching, and ferromagnetic semiconductors gave birth to the field of spintronics; that is the devices and materials that utilize both the spin and electronic charge of electrons (or holes) for more functionalities. Those developments in magnetism were fueled mainly by advances in materials and nanotechnology. The new era of nanotechnology made it feasible to envision and realize (among other things) current driven magnetization switching, domain wall manipulation and single molecule magnets studies. I will talk about some experiments in nano-spintronics that I conducted at Penn State. They include electric-current manipulation of magnetization, exchange bias, and nanoengineering of Curie temperature in the new ferromagnetic semiconductor GaMnAs. I will also talk briefly about a modern experiment that attempts to use a nano-bridge SQUID to study spin dynamics in single molecule magnets.
 
Astromagnetism - studies of magnetized stars and accreting gas flows around black holes
Shin Yoshida (FAU)
Magnetic field is ubiquitous in the Universe and there are many astrophysical phenomena in which it may play crucial parts. Advances of powerful numerical codes of magnetohydrodynamics (MHD) as well as availability of huge computer resources have helped a lot for us to understand physics of these objects, though quite a significant basic questions, related to the origin, stability and evolution of these field, still remain to be investigated. We have been interested in modeling structures and evolutions of magnetic fields in astrophysical objects that are coupled to hydrodynamics and gravity. In this talk I would like to present some results from two projects on astromagnetism which I have been currently working on. The first is the structure and stability of rotating magnetized stars. Our interest here is modeling such stars as Ap stars, magnetized white dwarfs and neutron stars. The second study is on magnetized accretion disks/tori around black holes. These types of system may be at the central engine of gamma-ray bursts. We are investigating black hole-magnetized torus systems by performing general relativistic MHD simulations as well as by using perturbative approach for their stability.
 
Unexpected complexity in elemental materials under pressure
Stanimir Bonev (Dalhousie University), Apr 20
When materials are compressed, increased electron-electron and electron-ion interactions can give rise to dramatic and often counterintuitive electronic and structural changes. Pressures higher than 400 GPa are now accessible in the laboratory, but techniques for high-pressure experiments at elevated temperatures are relatively recent and measurements remain difficult. The physics and chemistry of many materials over such diverse conditions are poorly known. I will discuss recent theoretical work, which predicts unusual phase transitions in elemental solids and liquids at high pressure and temperature. Dense hydrogen is found to have anomalous melting behavior, indicating the existence of a low-temperature liquid metallic state. Such a state is expected to have exotic quantum properties. Alkali liquids are predicted to undergo liquid transitions characterized by a symmetry breaking in their local order. These changes are remarkable in that they are contrary to the intuitive expectations for the role of temperature and pressure. They are driven by a pseudogap opening in the electronic density of states; the first observation of a pseudogap in a liquid metal. The trends in the theoretical findings establish a relationship between high-temperature liquid transitions and low-temperature crystalline phases.
 
Tailoring carbon nanotube properties through chemistry, mechanics and optics
Lilia M. Woods (USF), Apr 27, BU 105
Carbon nanotubes are quasi-one dimensional structures obtained by rolling single or multiple graphite sheets. Depending on the way of rolling, semiconducting or metallic ones can be synthesized. The unique electronic, mechanical, thermal, and optical properties of these nanostructures have made possible for various applications such as sensors, building blocks in nano-electronics, biocompatible agents, functionalized elements and more. This seminar will focus on presenting additional ways to modify nanotube properties indicating new potential applications and devices of these nanostructures. Theoretical models will be presented to explore the chemistry, mechanics and optics of single wall carbon nanotubes. Both, density functional and tight-binding methods, are used to analyze the adsorption of organic molecules and DNA, mechanical defects and deformations, and optical excitations of carbon nanotubes.