Physics Seminar

 physics seminar1

Physics Seminars will nominally be scheduled for Tuesdays at 2:30 pm in Optics Building Room 234. Coffee and cookies will be available 15 minutes prior to the start of each seminar.

Schedule

Upcoming Seminars

  

Tuesday, August 26, 2014

Optics Building 234, 2:30PM

A Journey of Burst Adventures

Dr. Binbin Zhang (CSPAR/UAH)

Abstract: In this talk I will review our current understanding of Gamma-Ray Bursts (GRBs), including their prompt emission and  mulit-wavelength observations. The talk will take you to  several milestones in the history of GRB research, along which I will discuss several difficult but fun topics such as GRB  radius, compositions, dissipation, radiation mechanisms, diversities and classifications.

Presnetation


Tuesday, September 2, 2014

Optics Building 234, 2:30PM

Physical Random Number Generation Using Chaos

Dr. Ned Corron (U.S. Army RDECOM)

Abstract: Chaos is a type of dynamics generated by deterministic systems that exhibit random, unpredictable behavior. The capability to generate randomness from a deterministic process is, to say the least, counterintuitive.   However, in terms of Shannon's information theory, a chaotic oscillator is an information source characterized by positive entropy when observed with finite precision. As such, chaotic dynamics offers a physical source of randomness that can be exploited for technological application. In this talk, we will explore the nature of chaos as an information source, including how determinism can yield random behavior, and consider recent reports of very fast physical random number generation using laser chaos.
 

 

Tuesday, September 9, 2014

Optics Building 234, 2:30PM

Detecting WHIM filaments with UV and X-ray spectroscopy - The sightline towards PKS2155-304

Prof. Max Bonamente (Physics/UAH)       

Abstract: Much of the universe's baryons are located in a diffuse warm-hot intergalactic medium (WHIM), and not in collapsed structures such as galaxies or stars. The diffuse nature and their temperature (T=10^5-10^7 K) make them challenging to observe. A useful probe of these baryons is absorption spectroscopy, which uses a bright background source to detect the WHIM in absorption. We use FUSE and HST spectroscopy to measure a number of absorption lines towards a bright quasar, PKS2155-304. These absorption lines match the prediction of WHIM structures based on the distribution of galaxies from the two-degree-field (2dF) galaxy redshift survey. We show that WHIM structures can be identified efficiently from optical galaxy surveys, and their hydrogen content estimated accurately using results from numerical simulations.                             

Presentation


Wednesday, September 17, 2014 (attention for the date)

Optics Building 234, 2:30PM

The Search for Black Holes in Globular Clusters

Prof. Jimmy Irwin (UA Tuscaloosa)

Abstract: The existence of both stellar- and intermediate-mass black holes within globular clusters has been the subject of intense debate for decades. The rich globular cluster populations of nearby elliptical galaxies provide much more fertile hunting grounds over the meager globular cluster population of the Milky Way to search for accreting black holes emitting near their Eddington limit. Extreme X-ray variability of >1e39 ergs/s sources provide the best means of identifying such black holes. I will present the current evidence for black hole existing within globular clusters, and discuss the possibility that intermediate-mass (100-10,000 dolar mass) black holes reside at the centers of globular clusters much like supermassive black holes reside at the centers of galaxies.

Presentation


Tuesday, September 23, 2014 (cancelled)

Optics Building 234, 2:30PM 

Magnetic Reconnection: Anomalous resistivity a myth or reality affecting reconnection!

Prof. Nagendra Singh (ECE/UAH)

Abstract: Anomalous resistivity has been a controversial topic for affecting magnetic reconnection in laboratory, space and astrophysical plasmas. If one takes the meaning of anomalous resistivity in a broad physical sense of the loss of momentum from the current carrying particles (electrons and/or ions) in the reconnection diffusion region, the effective resistivity is absolute reality. This effective resistivity supports the reconnection (inductive) electric field. On the other hand, if one defines anomalous resistivity in a limited sense as that arising from instabilities generated by current-driven instabilities, then the application of this resistivity is limited to reconnection in electron current sheets when they thin down to a half width of the order of a few electron skin depths. Such anomalous resistivity plays a role in the onset of the reconnection. Since onset requires a reduction in current at the location of the onset, anomalous resitivity helps reduce the current and thus breaks the magnetic field lines, which subsequently rejoin affecting the reconnection. Once the reconnection has occurred, then the anomalous resistivity has no role any more, it is the effective resistivity due to the transport of the current carriers out of the diffusion region takes the role of resistivity. This effective resitivity does not dissipate power locally into heat; it transports momentum/energy out of the diffusion region.

   We will discuss these issues along with analytical calculations and/or 3D PIC numerical simulations of reconnection onset preceded by the generation of anomalous resistivity involving current-driven ion modes and their modulational collapse into filamentary structures of electric field and density cavities.

   We will briefly visit the often used generalized Ohm’s low in explaining reconnection, mainly to point out that the various terms in the law do not ‘generate’ electric fields. Instead, they merely support the reconnection (induction) electric field. It is similar idea as in an electrical circuit driven by a voltage source; the source generates the voltage and the passive elements (resistor) merely support the part of the voltage drop.

 


Tuesday, September 30, 2014

Optics Building 234, 2:30PM

Exciting physics with merging galaxy clusters

Dr. Reinout van Weeren (Harvard/CfA)

Abstract: Merging galaxy clusters are excellent laboratories to study particle acceleration in dilute cosmic plasmas, to explore the nature of dark matter, and to investigate galaxy cluster growth. In a few dozen merging galaxy clusters diffuse extended radio emission has been found, implying the presence of relativistic particles and magnetic fields in the intracluster medium. A major question is how these particles are accelerated up to such extreme energies. In this talk I will present X-ray and radio observations of merging clusters which provide new insights about the acceleration mechanism.  I will also show the latest results from the new revolutionary low-frequency telescope LOFAR, allowing observations of diffuse cluster emission with unprecedented resolution and sensitivity.  Finally, I will highlight ongoing work to constrain the properties of dark matter with merging clusters.

Presentation

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Tuesday, October 7, 2014

Optics Building 234, 2:30P

Optical/Digital Doomsday Navigation

Prof. Don Gregory and Mr. John Jasper (Physics/UAH)

In most EOTWAWKI (End Of The World As We Know It) event scenarios, it is assumed that access to the GPS satellite system will be limited or nonexistent. An updated “navigation by the stars” technique will be presented which is based on a classic Fourier optics idea covered in any course on the subject. The digital implementation of this analog optical technique utilizes a stand-alone (no internet) high-end PC equipped with a programmable gaming board and is capable of accurately aiding global navigation of any type, especially spacecraft. It has recently been used on a NASA/MSFC X-ray balloon flight to successfully monitor telescope alignment. The demonstration of this technology during the seminar will be interactive with attendees being allowed to convince themselves the technique really works.

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Tuesday, October 14, 2014

Optics Building 234, 2:30PM

Testing optical surfaces

Dr. Patrick Readon (Center for Applied Optics/UAH)

Testing optical surfaces for errors employs relatively straightforward instrumentation and methods.  However, for even the most simple surfaces, getting absolute measurements becomes quite complex.  This talk discusses optical testing methods, for simple rotationally symmetric spherical surfaces, and the modifications surfaces that must be employes to extract useful data on more complicated aspheres, off--axis aspheres, and general free-form surfaces.  Some specific examples will be given, include recent efforts in testing near-cylindrical surfaces.

Presentation

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Tuesday, October 21, 2014

Optics Building 234, 2:30PM

Cherenkov Telescope Array: Adventures in ground-based gamma-ray astronomy

Dr. Valerie Connaughton (CSPAR/UAH)

Ground-based Very High Energy (VHE) gamma-ray astronomy has moved from the fringes of the barely possible to become a vibrant field that explores the most energetic phenomena in the universe. VHE science is at the crossroads of physics and astronomy and draws from a diverse community of scientists interested in subjects from the origin of cosmic rays to the nature of dark matter through black hole formation and the invariance of the speed of light. I will review the history of ground-based gamma-ray astronomy from its lonely days in the wilderness of the Sonoran desert to the ambitious plan of a worldwide consortium dedicated to building the Cherenkov Telescope Array (CTA).

Presentation

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Tuesday, October 28, 2014

Optics Building 234, 2:30PM

The Phase Rule and Chemical Equilibrium near the Critical Point of Solution

Prof. James Baird (Chemistry/UAH)

We will show how the principle of critical point universality, which is thought to apply to all critical phenomena, can be applied to understand chemical equilibria in binary liquid mixtures with a critical point of solution.

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Tuesday, November 4, 2014

Optics Building 234, 2:30PM

Novel Stimuli-Responsive Shape Memory Polymers for Smart Nanooptics

Prof. Peng Jiang (Chemical Engineering/University of Florida)

Photonic crystals may hold the key to continued progress towards all-optical integrated circuits and quantum information processing. Shape memory polymers (SMPs), which can memorize and recover their permanent shapes upon application of an external stimulus (e.g., heat and light), provide a unique opportunity to achieve smart, reconfigurable photonic crystals with bistable states. Unfortunately, most of the currently available SMPs are thermoresponsive and they suffer from slow response speed and heat-demanding programming and recovery steps. Although pressure is an easily adjustable process variable like temperature, pressure-responsive SMPs are largely unexplored. By integrating scientific principles drawn from two disparate fields that do not typically intersect - the fast-growing photonic crystal and SMP technologies, we have recently developed a new type of SMP that enables unusual "cold" programming and instantaneous shape recovery triggered by applying an external pressure or exposing to an organic vapor (e.g., acetone) at ambient conditions. This unique integration has not only led to the discovery of the new pressure- and vapor-responsive SMPs, it also provides a simple and sensitive optical technique for investigating the intriguing shape memory effects at nanoscale. Simultaneously, stimuli-responsive SMPs can empower smart and reconfigurable nanooptical devices and thus can significantly broaden the fabrication and application scopes of current photonic crystal technology. The applications of these novel SMPs in a wide spectrum of fields ranging from smart nanooptical devices (e.g., tunable antireflection coatings) to chromogenic pressure and vapor sensors to new biometric and anti-counterfeiting materials will also be demonstrated. Improved fundamental understanding of capillary pressure-induced macropore collapse, as well as capillary condensation of vapors in complex hierarchical porous networks which is a topic that has received little examination, will also be presented.

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Tuesday, November 11, 2014

Optics Building 234, 2:30PM

Genus Topology of Large-Scale Structure in the Cosmic Microwave
Background:  Overview and Recent Results from BICEP2

Dr. Wesley Colley (CMSA/UAH)

I will provide an overview of using genus topology to characterize large-scale structure in the Universe, and a brief overview of science  from the cosmic microwave background.  I will then discuss our group's  work on topology from the WMAP data, and our very recent work on the  BICEP2 data, the latter of which appears to confirm, at least partially,  the discovery of a gravity wave signature in the CMB.

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Tuesday, November 25, 2014

Optics Building 234, 2:30PM

Prof. John Fix (Physics/UAH)

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Tuesday, December 2, 2014

Optics Building 234, 2:30PM

Supermassive black hole binaries

Prof. Tamara Bogdanovic (CRA/Georgia Tech)