Seminars:Fall 2009


Department of Physics and Astronomy

George Mason University, Fairfax, VA 22030

Location: Room 134, Innovation Hall

Day and Time: Friday, 11:30am-12:30pm (unless otherwise indicated)


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Driving Directions to GMU

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Visitor parking decks


Sept. 11: Dr. Sergey Polyakov, Optical Technology Division, NIST

A Tale of Two Correlated Photons

Manipulation of correlated photons is an enabling technology that helps the advancement of a range of problems in contemporary optics from precision sensing and metrology to quantum information. I present our latest efforts to develop and improve single-photon-based tools and methods that rely on our ability to generate, manipulate and detect pairs of correlated photons. These include better single-photon detectors that allow improved counting rates; better single-photon sources that are more efficient; improved quantum-enabled measurements that yield better accuracy and long anticipated quantum memory for entanglement storage.


Sept. 25: Dr. Evgenya Shkolnik, Carnegie Fellow, Department of Terrestrial Magnetism Carnegie Institution of Washington, http://www.dtm.ciw.edu/shkolnik

Star-Planet Interactions: A Probe of Extrasolar Planetary Magnetic Fields

Much effort has been invested in recent years, both observationally and theoretically, to understand the interacting processes taking place in planetary systems consisting of a hot Jupiter orbiting its star within 10 stellar radii. Several independent studies have converged on the same scenario: that a short-period planet can induce activity on the photosphere and upper atmosphere of its host star. The growing body of evidence for such magnetic star-planet interactions includes a diverse array of photometric, spectroscopic and spectropolarimetric studies. The nature of which is modeled to be strongly affected by both the stellar and planetary magnetic fields, possibly influencing the magnetic activity of both bodies, as well as affecting irradiation and non-thermal and dynamical processes. Studying such star-planet interactions (SPI) aids our understanding of the formation, migration and evolution of hot Jupiters, and improves SPI's potential as a probe of extrasolar planetary magnetic fields..



Joint seminar, Department of Physics & Astronomy, Department of Chemistry & Biochemistry

Tuesday, Sept 29. 4:30pm, location: Johnson Center, 3rd floor, Rm. F

Professor Igor Sokolov, Department of Physics, Clarkson University, Potsdam, NY

On the Cross of Nano and Bio with Atomic Force Microscopy

Atomic Force Microscopy (AFM) is one of the major tools responsible for the emergence of what is called Nanoscience and Nanotechnology nowadays. We observe now a tremendous proliferation of AFM applications in the fields of soft condensed matter, materials science, chemistry, bioengineering, nanotechnology, etc. AFM has a particular advantage in dealing with biological objects, soft condensed matter in general, where ability to study objects in their natural environment is paramount. In this talk I will briefly overview the basic principles of the AFM work, and show a spectrum of unique applications of this technique in biological and soft condensed matter physics. Particular emphasis will be done on the use of AFM beyond simple imaging, on quantitative analysis. Such analysis is important because of typically high complexity of the systems of study, and therefore, difficulty in recognizing potential artifacts. I will describe the variety of research has been done in my laboratory, from single molecules to the study of small creatures, like beetles. Specifically, I will describe the study of conformational changes of single biomolecules (lactose/galactose receptors, ELISA immunosensors), mechanics of human epithelial cells (aging and cancerous versus normal cells), and the development of "nano-physiology" of insects.


Oct.9: Dr. Vladimir Airapetian, GMU/NASA/GSFC

Hot and Violent Mega Aurorae in Extrasolar Giant Planets

Hot extrasolar giant planets are subject to strong stellar radiative and particles fluxes. While effects of extreme UV radiative (EUV) heating on EGP atmospheres has become a research area of increased study, the fundamental physical processes of wind-magnetosphere interactions in these systems remain poorly understood. Models show EUV emission can heat their upper layers to tens of thousands of Kelvins and cause thermal escape of hydrogen plasma from them, but this modeling neglects a pathway for energy injection due to wind-magnetosphere interaction that constitutes more than half of the total energy budget. We show that once the effects of particles fluxes due to wind-magnetosphere interaction are included in the overall atmosphere models, they introduce a qualitative new class of atmospheric phenomena, mega aurorae, represented by highly dynamic, fast and hot atmospheric outflows from polar regions of EGPs. Our model predicts spectral signatures from evaporating EGPs which is strikingly different than what is currently believed to be visible. Based on our model predictions, we suggest an observational technique to detect and characterize EGPs using HST/COS, IRAC/Spitzer Space Telescope, and ground-based telescopes.


Oct.23: Dr. Frank Narducci, Navy Air System, Patuxent River, MD

Progress towards an atom interferometer gradient magnetometer

At the heart of many state of the art sensors lies an atom interferometer. These devices have demonstrated outstanding sensitivities. However, this is not true for the field of magnetometers. In this talk, I explore the workings of an atom interferometer designed to measure magnetic fields and show that, to first order, the interferometer is NOT sensitive to magnetic fields BUT is sensitive to magnetic field gradients. This makes an atom interferometer an INHERENTLY gradient device, useful for Naval applications. I then will discuss some of the building blocks we have had to develop to construct such a device, which is underway.


Nov. 6, Dr. Bernard Peyaud, CEA/Saclay, DSM/IRFU

"Experimental studies of Ke4 and K3π decays from the NA48/2 experiment"

The NA48/2 experiment at the CERN SPS has collected about 1.2x106 Ke4 (K±→π+π-e±ν) decays in 2003 and 2004. The analysis of these unprecedented samples has been used for a precise measurement of the Ke4 decay parameters. This includes the measurement of the phase shift δππ as a function of the ππ invariant mass which in turn gives access to the ππ scattering lengths a00 and a02. The measurement of δππ is model independent and can be confronted with predictions made in the framework of Chiral Perturbation Theory. The same experiment has also collected a very large amount of K±→π0π0π± decays which is another precise tool for extracting a00 and a02 and for testing different theoretical models.



Nov. 13, Dr. Bob Ehrlich, Department of Physics and Astronomy, GMU

Renewable Energy at Mason and Around the Nation: Lessons Learned by One Faculty Member New to the Field.

I present an overview of renewable energy, the imperative to transition to greater reliance on it, and the state of renewable energy educational programs around the nation, and at Mason. In a parallel thread, I discuss why faculty & students should consider getting more involved in renewable energy. Students apparently need no such encouragement, but 99% of four-year schools have been slow to move into this area (apart from an occasional course or two), despite evidence of strong student interest & strong job prospects. I consider various reasons for this reluctance and I also discuss one recent effort (http://rev-up.org) begun during the past year to tunnel through a significant barrier facing faculty new to the field. More details...[http://mason.gmu.edu/~rehrlich/FPS_article.htm ]


Nov. 20, Dr. Christine Chen, Space Telescope Science Institute

Debris Disks in the Era of Terrestrial Planet Formation

The terrestrial planets in our Solar System are believed to have formed via a multi-stage process that included the conglomeration of sub-micron sized interstellar dust particles into kilometer-sized parent bodies, the growth of pluto-size planetary embryos from collisions of kilometer-sized parent bodies, and the accretion of the patina from giant collisions between planetary embryos. The Spitzer Space Telescope has enabled photometric surveys of mid- and far-infrared excess around stars in nearby young associations that constrain models for the formation of pluto-sized objects, and spectroscopic characterization of the circumstellar material that suggests that giant collisions may be occuring in some systems. In this talk, I will outline the properties of young debris disks in which terrestrial planets may be forming, compare MIPS photometric observations of stars in the 5-20 Myr old Scorpius-Centaurus OB Association to the evolution predicted by self-stirred disk models, and discuss possible diagnostics for giant collisions in young Solar Systems. I will also describe outstanding questions about solar system evolution that can not be addressed with Spitzer and will require future ground- and space-based instruments.


Dec. 4, Dr. Tom Duxbury, Department of Physics and Astronomy, GMU

STARDUST: Bringing Cosmic History to Earth

NASA launched the STARDUST mission in 1999 whose main goal was to return samples from a comet for detailed studies on Earth. Comets that live on the outer edge of our solar system are believed to be remnants of the original dust, ice and gas that formed our solar system and have remained unchanged for 4.5 billion years. Comets are believed to have brought water and the chemical building blocks needed for life on earth. We are comprised of this material, star dust. On its historic 7 year journey, STARDUST traveled 3 billion km on its 3 orbits about the sun, flew by the asteroid Annefrank and the comet Wild 2 where it collected the cometary dust prior to returning to earth in 2006. This was the first planetary sample return mission launched since the Apollo missions to the moon more than 25 years earlier. It was the last of NASA's "faster, cheaper, better" Discovery missions that stayed within budget and exceeded all expectations. The earth return and sample recovery were spectacular with the particle analyses now underway for the next few decades. Prof. Duxbury was the Project Manager and Recovery Commander of the mission.

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