Department of Physics

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Colloquia & Seminars, Fall 2009

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Astrophysical Masers: A tool to uncover the mysteries of massive star formation

Speaker: Professor Esteban Araya
Date: September 25, 2009 (Friday)
Time: 4 p.m.
Room: 205 Currens Hall

Abstract
Massive stars are fundamental in all aspects of astronomy, from the synthesis of heavy elements to the injection of turbulence into the interstellar medium. However, the formation of massive stars remains poorly understood. A number of probes have been used to study the process of massive star formation, among them, astrophysical masers. I will review some of the main results derived from the study of masers in massive star forming regions. In particular, I will summarize the research on formaldehyde masers, which are one of the few maser species that are exclusively associated with massive star formation. The discovery of periodic formaldehyde maser flares, correlated variability with methanol masers, and the implications of these findings on massive star formation will be discussed.

About the speaker:
Professor Esteban Araya is a new faculty member of the physics department at WIU. His research focuses on the study of massive star formation and the interstellar medium. He carries out observations at radio frequencies with some of the most sophisticated radio telescopes.

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Introduction to shock wave physics of condensed matter

Speaker: Dr. Jerry W. Forbes
Date: October 9, 2009 (Friday)
Time: 4 p.m.
Room: 205 Currens Hall

Abstract
An overview on the contribution of shock wave physics to understanding condensed matter behavior at high pressures will be presented. One-dimensional (1-D) strain conditions will be discussed including the conservation of mass, momentum, and energy for plane 1-D shocks. The generic P-V-T surface of a material is shown to illustrate the relative relationship between isotherms, isentropes, and shock Hugoniot adiabats. Use of a gas gun to obtain the 1-D strain conditions will be presented with a slide show of the gun operation. Two diagnostics will be briefly described for measuring pressure and mass particle motion with sub-microsecond temporal resolution.

About the speaker:
Dr. Jerry W. Forbes is a Senior Research Physicist at Energetics Technology, LaPlata, MD and a Visiting Professor in Mechanical Engineering Department at University of Maryland. Dr. Forbes’ main research is in the study of material response to rapid energy disposition, in particular shock wave loading of inert and energetic materials. Dr. Forbes is a former student of the Department of Physics, WIU.

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The Art and Science of Soap Bubbles and Soap Films

Speaker: Professor Fred Behroozi
Date: October 16, 2009 (Friday)
Time: 4 p.m.
Room: 205 Currens Hall

Abstract
Soap bubbles fascinate and delight us all. Nowadays we associate soap bubbles with fun and laughter, young children at play, and carefree summer days. But this was not always so. Soap bubbles became popular in the 17th century paintings and prints primarily as a metaphor to convey the impermanence and fragility of life. In this talk, we will first view soap bubbles through the work of several 17th and 18th century painters with particular attention to the work of the French painter Jean Simeon Chardin (1699-1779). Chardin was first to use soap bubbles to convey a sense of play and wonder. Next we will discuss a little of the chemistry, physics, and mathematics associated with soap bubbles. Along the way we will demonstrate and discuss several fascinating physical phenomena (light scattering, interference colors, bubble mechanics, and minimal surfaces) using soap bubbles and soap films.

About the speaker:
Professor Fred Behroozi is a professor of physics at The University of Northern Iowa. His research focuses on the use of a miniature laser interferometer to study the properties of solid and fluid surfaces at the nanometer scale.

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Induced Anisotropies in a Ferromagnet Exchange - Coupled to a Polycrystalline Antiferromagnet

Speaker: Dr. Jyotirmoy Saha
Date: October 23, 2009 (Friday)
Time: 4 p.m.
Room: 205 Currens Hall

Abstract
When a ferromagnet (FM) is coupled to an antiferromagnet (AF), the magnetocrystalline anisotropy of the AF induces various forms of anisotropies in the FM mediated by uncompensated spins at the AF-FM interface. The two basic yet cardinal experimental outcomes that quantify these anisotropies are: 1) Hysteresis loops (HLs) yielding exchange bias (HE) and enhanced coercivity and 2) ferromagnetic resonance (FMR) plots yielding the resonant frequency (fR) of the FM. A crucial point of distinction is that HE yields a measure of the induced unidirectional anisotropy (UA) as the FM switches between the two magnetic states whereas fR is a measure of the ground state UA field induced in the FM. To draw system independent (general) conclusions on these two classes of UA, a realistic model is presented that can produce HLs and FMR response independently based on inputs from material characteristics and avoids the use of adjustable parameters. The time evolution of the FM magnetization is established by solving the Landau-Lifshitz-Gilbert equation for each FM degree of freedom. The energetics of each AF grain is considered within the framework of a uniform rotation model and its time evolution is evaluated by its barrier switching capability under thermal excitations. Two technologically relevant systems are investigated: 1) Co35Fe65/Ni50Mn50; 2) Ni80Fe20/Ni50Mn50 and the results are compared with those obtained from experiments. A novel mechanism is presented that outlines the induction of UA in an otherwise isotropic FM/AF system just by the mere application of the first field point in the hysteresis loop evaluation.

About the speaker:
Dr. Jyotirmoy Saha is a theoretical physicist studying magnetism in the broad area of condensed matter physics. He is a graduate from the University of Minnesota, Twin Cities and he did his post-doctoral research at the Commissariat à l’Énergie Atomique (CEA), Grenoble, France. Dr. Saha uses computational methods to study the properties of magnetic alloys.