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Department of Physics and Astronomy
Seminars/Colloquia, Spring 2008

Unless noted otherwise, Tuesday Colloquia are at 4:00 pm
with refreshments served 15 minutes before each colloquium.

Scheduling for additional seminars will vary.

Abstracts of Talks

Roger Waxler Department of Physics and Astronomy University of Mississippi Sound Propagation in the Nocturnal Boundary Layer On clear nights, as the ground cools, a temperature inversion forms in the lowest hundred meters or so of the atmosphere. The winds in the inversion tend to be light and turbulence levels tend to be low. Above the temperature inversion one generally finds a stiff wind known as the nocturnal jet. The temperature inversion and the nocturnal jet form a duct in which sound propagates efficiently to distances of many kilometers. Despite the intrinsic variability of the atmosphere we have found that sound fields in a typical nocturnal duct have a robust observable deterministic structure. Our long-term goal is to exploit this structure to obtain a direct relation between meteorological conditions and the acoustic signal received at long ranges from a source. The theoretical and experimental progress we've made to date towards this goal will be presented.

Alakabha Datta Department of Physics and Astronomy University of Mississippi Hunting for New Physics After a brief introduction to the aim of Particle Physics I will describe the Standard Model of Particle Physics (SM). I will discuss the Higgs mass problem and the Flavor Puzzles of the Standard Model. These problems of the SM suggest that beyond the SM physics and new particles should appear at a scale of a TeV. This new physics and new particles are very likely to be observed soon at the Tevatron in Fermilab or the Large Hadron Collider(LHC) at CERN. I will discuss various new physics models that are candidates for beyond the SM physics and how present and future measurements will help us find the mathematical structure of the new physics.

Sheng Meng Department of Physics Harvard University Biomolecule-materials Interactions at the Nanoscale: Atomistic Structure, Electronic Properties, and Energy Applications Understanding the interaction of biomolecules with a variety of traditional or novel solid-state materials, not only plays important roles in recognizing many natural processes such as denaturation, adhesion, and cell apoptosis, but also proves to be essential in advancing modern technologies including biosensing, catalysis, DNA diagnosis, drug delivery, and renewable energy. However, the underlying mechanism of the biomolecule-materials interaction at the microscopic level is still by and large challenging. With the help of computer modeling, we are able to investigate the very molecular details of the bio-materials interface structure, bonding, electronic and optical properties, and dynamic processes that lead to desired functions; as well as to make new predictions. The resulting spectroscopic data can be directly compared with experiments. In this talk, I will mainly cover three such examples that are currently under intensive discussion: i) water/solid surface interaction and a molecular picture of hydrophilicity at surfaces; ii) DNA interaction with carbon nanotube and ultrafast DNA sequencing; iii) melanin, flavonoids and their application to renewable energy.

Gregory Harry Kavli Institute for Astrophysics & Space Research Massachusetts Institute of Technology Einstein's Dual Legacy: Thermal Noise and Gravitational Waves Two ideas originating with Albert Einstein, thermal noise and gravitational waves, are coming together to create the new field of gravitational astronomy. I will present the status of current gravitational wave searches and present results from the LIGO detectors. I will then describe what is keeping LIGO from directly detecting these waves and illustrate the role that thermal noise has in limiting sensitivity. Finally, I will show what progress is being made in reducing thermal noise and what prospects there are for significant increases in sensitivity in next generation gravitational wave antennas.

Eric Schnetter Center for Computation & Technology Louisiana State University Modeling Black Hole Binary Mergers Binary black hole systems and their merger are one of the most important sources of gravitational radiation, which is expected to be soon detected by experiments like LIGO, GEO600, or LISA. About two years ago it became possible to simulate these systems numerically with high accuracy. As these simulations requires very expensive numerical calculations, it is of advantage to derive accurate analytic approximations describing the merger process from such full numerical calculations. I give an overview over some properties of binary black hole systems, our numerical simulation methods, and some recent results on analytic approximations to predicting the final state of black hole binary mergers.

David Mandrus Department of Physics and Astronomy University of Tennessee — Knoxville & Oak Ridge National Laboratory Charge Ordering materials: The Good, the Bad, and the Ugly Charge ordering phenomena are ubiquitous in correlated electron systems, but despite its conceptual simplicity charge ordering in real materials is poorly understood. In this talk I will first review the concepts and history of charge ordering, beginning with Verwey and Wigner in the 1930s. I will then discuss some new charge ordering materials, Fe2OBO3 and LuFe2O4. Fe2OBO3 is an excellent model system, displaying nearly ideal ionic charge order. LuFe2O4, on the other hand, is a poor model system, but nevertheless displays rich physics, including the appearance of ferroelectricity as a result of charge ordering. These new materials will be compared with the prototypical material Fe3O4 (magnetite), which is still poorly understood despite nearly 70 years of study.

Yaroslav Koshka Dept. of Electrical & Computer Engineering Mississippi State University Wide Bandgap Semiconductor Research at Mississippi State University Wide bandgap semiconductor materials are extremely important for high-power and high-frequency applications. Silicon carbide (SiC) and diamond are two semiconductors that offer particularly strong promise also for high-temperature and high-radiation-tolerant applications. While diodes and transistors made of monocrystalline diamond are still in the research stage, certain types of SiC devices are already commercially available today. SiC research at Mississippi State University (MSU) evolved from the basic materials science (SiC materials growth and characterization) to design and processing of SiC devices. One of the highlights of these activities was the founding in 2000 of an MSU spin-off small business SemiSouth Laboratories, Inc dedicated to commercialization of SiC high-power rectifiers and transistors for military, aerospace, and commercial applications. A brief overview of the current status of modern SiC technologies will be given. A few selected projects targeting investigation of electrically and optically active defects in SiC as well as development of novel techniques for epitaxial growth of monocrystalline SiC films will be briefly covered. A particular attention will be given to (1) an unusual behavior of hydrogen in SiC and (2) to development of epitaxial growth techniques for SiC at record-low temperatures.

Ken Bader Department of Physics and Astronomy University of Mississippi Characterization of High Q Spherical Resonators This talk describes the vibrational dynamics of a spherical acoustical resonator system used in the study of acoustic cavitation phenomena in liquids as part of an effort to scale up the energy density of collapse of transient cavitation. The system consists of a stainless steel shell (10" OD and 0.5"thick) filled with degassed water that exhibits several high Q (>10 000) modes in the 20-40 kHz range, and which is driven by an external horn-type transducer. This talk will focus on the characterization of the vibrational spectrum of the resonator as well as the radial variations of the pressure fields in the liquid internal to the shell. The vibrations of the shell surface are monitored using an attached ultrasonic transducer as well as a laser Doppler vibrometer. The internal pressure fields of the sphere are mapped using needle type hydrophones. The vibrational spectrum will be compared with theoretical predictions for moderately thick shell resonators developed by Mehl (JASA 78(2), 1985, pp. 782-788) Carl Jensen Department of Physics and Astronomy University of Mississippi Simulating Thermoacoustics in Random Fibrous Materials Computational fluid dynamics is being used to investigate the thermoacoustic properties of stack materials with irregular pore geometries. Available models for stack materials with irregular geometries (such as wools and foams) are based empirically on parameters of the material that must be acoustically measured. A direct simulation of the thermohydrodynamic acoustic flow using a thermal lattice Boltzmann method provides a model of the acoustics from the base parameters of the material's make-up and provides insight into the mechanisms affecting that behavior. A particular focus is being placed on fibrous stack materials because their simple geometry is less challenging to replicate on a computer.

A. F. Bose (Fermilab) and P. A. Petit-Leptaine (CERN) Joint Fermilab-LHC Press Conference on the Federal Lawsuit to Stop the Large Hadron Collider A screening of the film “BLACK HOLE” will take place tomorrow at 4:00 PM in lieu of the colloquium. It will be followed by a brief discussion of the physics by Dr. Cavaglia. It will also be preceded by a short investigative report entitled: “Separated at Birth, Famous Scientists and Their Long Lost Twins.” The event was precipitated by the striking coincidence of that April Fools was so closely preceded by the following announcement of a lawsuit against CERN to shut down the Large Hadron Collider: On March 21th 2008, a federal lawsuit seeking to stop the activities of the Large Hadron Collider has been filed in a Hawaii court. The plaintiffs, Walter F. Wagner and Luis Sancho, argued that the “LHC could accidentally create strange new particles that would instantly transform any matter they touched, engulfing the Earth, or, even worse, make a rapidly expanding black hole that could consume the entire planet.” As a consequence of this lawsuit, the Fourth Federal District Court of Hawaii has ordered on March 26th the “immediate suspension of all activities related to the commissioning of the Large Hadron Collider”. This injunction has devastating effects on Fermilab and CERN, and threatens to shut down the entire LHC project indefinitely. Dr. A. F. Bose (Fermilab) and Dr. P. A. Petit-Leptaine (CERN) will host an online press conference to discuss its implications on the near and long-term future of CERN. The press conference will be broadcasted through EVO. (The above article has been slightly modified. The original article about the Lawsuit can be found at: Fox News) Also see the Los Angeles Times Story.

Greg Landsberg Department of Physics Brown University Searches for New Physics with Early LHC Data The Large Hadron Collider (LHC) at CERN is going to start operating later this year. This machine is an order of magnitude more powerful than the existing accelerators and has potential of fascinating discoveries almost overnight. In this colloquium I'll discuss the status of the machine and general-purpose particle detectors preparing to do physics at the LHC: ATLAS and CMS. Using CMS as example, I'll discuss prospects and strategies for searches for new physics with early LHC date, with the focus on Supersymmetry and models with extra dimensions, including an exciting possibility of finding mini-black holes at the LHC.

Myungkee Sung Department of Physics and Astronomy Louisiana State University Gravitational Wave Detection in the LIGO Experiment The LIGO detectors are designed to search for gravitational waves from astrophysical systems. The LIGO interferometers achieved the designed sensitivity in a recently completed science run, and the next phase of the experiment is being prepared currently. The LIGO experiment can detect gravitational waves in the near future and open a door to new physics. In this presentation, I will describe the LIGO experiment and data analyses in general terms, including some discussion on data calibration, hardware injection and other analysis tools. I will also discuss the prospects of the LIGO experiment and the field of gravitational wave detection physics, which is still evolving rapidly.

Rahmat Department of Physics University of Oregon τ Physics at BABAR Most of us think of BABAR as an experiment only at a B-factory. However it is also an experiment at a τ factory. The present BABAR τ data sample has around 800 million τ decays. In this talk I will present some recent results from τ Physics at BABAR on several topics including searches for lepton number violation and studies of multi-hadronic τ decays.

William Komp Department of Physics and Astronomy Western Kentucky University Constraining Dark Energy Models It has been 10 years since the startling discovery from observations of type-Ia supernovae (SN) that the Universe is presently in a late-time accelerating phase to its evolution. In the intervening years, the data set of SN observations has increase by an order of magnitude. Spacebased searches (Goods and Essence) have brought over 20 observations with very low uncertainties. Given projected observations with Several Beyond Einstein projects, SN might be able to distinguish between cosmological models. At the sametime, our information about the Cosmic Microwave Background Radiation (CMB) has grown signficantly with the observations of the Wilkinson Microwave Anisotropy Probe (WMAP). We know possess knowledge not just of the temperature anisotropy but also but the polarization of this light in the early Universe. Combined these two sets of observations are providing very tight constraints on perspective cosmological models. However as of yet, there is no direct model on model comparisons. In this talk, I will give an update of the Vacuum Cold Dark Matter (VCDM) model using the WMAP 3yr data and the Goods SN data. I will provide a model comparison based on likelihood countours resulting from fitting to the SN and CMB data sets for two models. I will outline a presently ongoing project to do a direct model comparison and some preliminary trends using several generations of SN data using a spline test function.

Emanuele Berti Division of Physics, Mathematics & Astronomy Caltech and the Jet Propulsion Laboratory Gravitational Wave Astronomy Analysis of data from the Earth-based gravitational-wave detector LIGO is ongoing while the instruments are being upgraded. The space-based detector LISA, expected to fly within the next decade, will observe massive black holes out to large redshifts, allowing us to study their mass and spin evolution, to check whether they have the properties predicted by Einstein's general relativity, and to set bounds on alternative theories of gravity. I will review the status of our numerical and analytical understanding of gravitational-wave sources, and I will argue that recent theoretical results are already interesting for astrophysics and fundamental physics. Numerical calculations of the recoil velocities and spins resulting from black hole mergers shed light on hierarchical galaxy formation scenarios and on the cosmological evolution of black hole spins. Simulations of ultrarelativistic black hole collisions are improving our understanding of strong-field gravity, and they could be relevant for estimates of the energy loss if mini-black hole production occurs at the Large Hadron Collider.