Events at Physics |
Events During the Week of February 19th through February 26th, 2012
Sunday, February 19th, 2012
- Wonders of Physics
- Physics of the Wisconsin Idea
- Time: 1:00 pm
- Place: 2103 Chamberlin
- Abstract: The twenty-ninth annual presentation of The Wonders of Physics with Professor Clint Sprott and colleagues will show some of the many ways physics has benefited society. This fun-filled educational presentation is suitable for people of all ages.
- Wonders of Physics
- Physics of the Wisconsin Idea
- Time: 4:00 pm
- Place: 2103 Chamberlin
- Abstract: The twenty-ninth annual presentation of The Wonders of Physics with Professor Clint Sprott and colleagues will show some of the many ways physics has benefited society. This fun-filled educational presentation is suitable for people of all ages.
Monday, February 20th, 2012
- NPAC (Nuclear/Particle/Astro/Cosmo) Forum
- High-Energy Astrophysics with the High Altitude Water Cherenkov Experiment
- Time: 11:00 am
- Place: 5280 Chamberlin Hall
- Speaker: John Pretz, Los Alamos National Lab
- Abstract: The High Altitude Water Cherenkov (HAWC) experiment, under construction at Sierra Negra, Mexico, consists of a 22500 square meter area of water tanks instrumented with light-sensitive photo-multiplier tubes. The experiment detects energetic secondary particles reaching the ground when a high-energy cosmic ray or gamma ray interacts in the atmosphere above the experiment. High-energy gamma ray astronomy provides a probe of some of the most gravitationally and electromagnetically extreme regions in the universe, from neutron stars and supernova remnants to active galactic nuclei and gamma-ray bursts. High-energy gamma ray are also key to understanding the origin of galactic cosmic radiation. I will describe the design of the HAWC instrument, scheduled to be completed in 2014, and discuss the motivation and scientific return the experiment will bring.
- Host: Halzen
- Plasma Physics (Physics/ECE/NE 922) Seminar
- Impulsive Fast Reconnection via Flux Rope Dynamics
- Time: 12:00 pm
- Place: 2241 Chamberlin
- Speaker: Hantao Ji, Princeton Plasma Physics Laboratory
- Abstract: Magnetic reconnection, the efficient release of magnetic energy by topological rearrangement of field lines, is one of the most important and fundamental plasma processes in space, solar and more distant astrophysical plasmas. The modern collisionless models predict that ions exhaust through a thick, ion-scale layer while mobile electrons leave through a thin, electron-scale layer, allowing for efficient release of magnetic energy. While ion layers have been frequently detected in space and studied in detail in the laboratory, the dissipation on the electron scales near the X-line remains largely unknown. The discrepancies [1-3] between the measured thickness of the electron diffusion layer in MRX and best available 2D kinetic simulations suggest that the electron scale dissipation must be 3D in nature. In this talk, the most recent experimental results from MRX and their comparisons with 3D kinetic simulations will be discussed. It is found that impulsive fast reconnection is caused by a disruption of the current channel localized in 3D space, associated with a burst of electromagnetic fluctuations. There exists substantial evidence that these impulsive behaviors are caused by 3D flux rope dynamics [4]. Looking into the future, a new theme of multiple X-line reconnection in a phase diagram [5] possibly provides solutions for fast reconnection in large space and astrophysical systems and for efficient particle acceleration often observed there. Scientific opportunities for a next generation laboratory experiment based on MRX to study magnetic reconnection in such regimes directly relevant to space and astrophysical plasmas will be described.<br>
<br>
[1] H. Ji et al., GRL 35, L13106 (2008).<br>
[2] S. Dorfman et al., PoP 15, 102107 (2008).<br>
[3] V. Roytershteyn et al. PoP 17, 055706 (2010).<br>
[4] S. Dorfman, Ph. D. Thesis (2011); to be submitted to PRL (2012).<br>
[5] H. Ji and W. Daughton, PoP 18, 111207 (2011).<br>
- Host: Cary Forest
- Condensed Matter Theory Group Seminar
- Topology of Quantum Discord
- Time: 4:30 pm
- Place: 5310 Chamberlin
- Speaker: Nga Nguyen, UW-Madison
- Abstract: Quantum discord is arguably a more sensitive measure of quantum correlations than quantum entanglement, and may be able to serve as a resource for quantum computation. All quantum correlations are subject to destruction by external noise. The route by which this destruction takes place depends on the shape of the hypersurface of zero discord in the space of generalized Bloch vectors. In the case of 2 qubits, we show that, except at the origin, this hypersurface is a 9-dimensional manifold with boundary embedded in a 15-dimensional background space. This is done by computing the tangent vectors explicitly and verifying that there are no self-intersections. We discuss the implications for the time evolution of discord in physical models, which contrasts sharply with the evolution of entanglement.
- Host: Perkins
Tuesday, February 21st, 2012
- Chaos & Complex Systems Seminar
- Evolution of intelligence
- Time: 12:05 pm
- Place: 4274 Chamberlin
- Speaker: David Krakauer, Director, Wisconsin Institute for Discovery
- Abstract: In this lecture I shall survey key ideas from the history of mathematics, physics, computation, and biology that have extraordinarily converged on very similar explanations for adaptive or selective behavior. This convergence presents itself in the form of a universal structure in all models describing adaptive search in high dimensional state spaces. I shall describe how intelligent mechanisms, to include nervous systems, evolved to overcome a fundamental limit to the velocity of evolutionary adaptation.
- Host: Sprott
- Theory Seminar (High Energy/Cosmology)
- W+jj: collider physics on the wild frontier
- Time: 4:00 pm
- Place: 5280 Chamberlin Hall
- Speaker: Adam Martin, Fermilab
- Abstract: As data flows in from the LHC, unexpected signals are inevitable. The key question will be: are these 'surprise' signals new physics or do they point to a mis-modeling/misunderstanding of standard model physics? To disentangle the possibilities requires crosstalk between experiment, QCD/Monte Carlo, phenomenology and model building. The W+jj excess observed by CDF last year gave us an example of this process at work. I will elaborate on the efforts to explain this excess -- which remains unresolved -- in the standard model and beyond, and what we should look for at the LHC
Wednesday, February 22nd, 2012
- Department Meeting
- Time: 12:15 pm
- Place: 5310 Chamberlin Hall
Thursday, February 23rd, 2012
- R. G. Herb Condensed Matter Seminar
- Seeing and Sculpting Nematic Liquid Crystal Textures with the Thom construction
- Time: 10:00 am
- Place: 5310 Chamberlin
- Speaker: Bryan Chen, University of Pennsylvania
- Abstract: Nematic liquid crystals are the foundation for modern display technology and also exhibit topological defects that can readily be seen under a microscope. Recently, experimentalists have been able to create and control more and more interesting defect textures, including controllably knotted defect lines around colloids (Ljubljana) and the "toron", a pair of hedgehogs bound together with a ring of double-twist between them (CU Boulder). I will discuss recent work with Gareth Alexander (Warwick) applying the Thom construction from algebraic topology which allows us to visualize 3 dimensional molecular orientation fields as certain colored surfaces in the sample. These surfaces turn out to be a generalization to 3 dimensions of the dark brushes seen in Schlieren textures of two-dimensional samples of nematics. Manipulations of these surfaces correspond to deformations of the nematic orientation fields, giving a hands-on way to classify liquid crystal textures which is also easily computable from data and robust to noise.
- Host: Coppersmith
- Plasma Physics (Physics/ECE/NE 922) Seminar
- Studying Fast Magnetic Reconnection with Laboratory Plasmas
- Time: 12:00 pm
- Place: 4274 Chamberlin
- Speaker: William Fox, University of New Hampshire
- Abstract: Magnetic reconnection is a ubiquitous plasma process which controls the dynamics of magnetic fields a number of plasma systems, allowing the release of magnetic energy which powers solar flares and magnetospheric substorms, and also which allows instabilities in magnetized fusion devices to quickly transport plasma out of the core of the device. In this talk I will discuss two sets of experiments studying magnetic reconnection in laboratory plasmas. First, I will discuss the Versatile Toroidal Facility (VTF) experiment at MIT, a basic laboratory experiment which studies magnetic reconnection in the regime of a strong toroidal "guide" field, and specifically my work studying current-driven instabilities driven by reconnection events. In the second set of experiments, I will discuss my recent work to understand magnetic reconnection experiments conducted on inertial-fusion-class laser-facilities. This is a novel regime for magnetic reconnection study, characterized by extremely high magnetic fields, high plasma beta and strong, super-Alfvenic plasma inflow. Work to-date with particle-in-cell simulations has identified two key ingredients for explaining the fast observed rates of reconnection: two-fluid reconnection mediated by collisionless effects (the Hall current and electron pressure tensor), and strong flux-pileup of the inflowing magnetic field. I will close with a discussion of our new proposals for upcoming laser-driven reconnection experiments using this new platform.
- Host: Cary Forest
- Astronomy Colloquium
- Star Formation, gas loss, and the molecular gas in simulations of evolving galaxies
- Time: 3:30 pm - 5:00 pm
- Place: 4421 Sterling Hall
- Speaker: Charlotte Christensen, University of Arizona
- Abstract: The physics of the interstellar media (ISM) affects both the location of star formation and the efficiency of supernova feedback by changing the properties of the star forming gas. In most previous galaxy formation simulations, though, the cold, molecular phase of the ISM has been neglected. In this talk, I present a method for integrating the non-equilibrium molecular hydrogen (H2) abundance throughout a simulation, including such processes as dissociation by Lyman-Werner radiation, shielding of molecular gas, and H2-based star formation. I apply this model to high-resolution cosmological simulations of galaxies ranging from 10^9 to 10^12 solar masses and compare it to simulations with different ISM models. I find that the inclusion of H2 results in galaxies with clumpier ISMs and more dispersed star formation. The increased clumpiness of the gas leads to greater efficiency of supernova at removing of low-angular momentum material from the galaxy. The result is spiral galaxies with smaller bulges and more realistic rotation curve. I discuss how the these interaction between the ISM structure, star formation, and supernova feedback result in changes to the mass distribution and compare the formation histories of galaxies of different masses.
- Host: Alyson Brooks
- NPAC (Nuclear/Particle/Astro/Cosmo) Forum
- The Pierre Auger Observatory: the highest energy frontier
- Time: 4:00 pm
- Place: 4274 Chamberlin Hall
- Speaker: Ines Valino Rielo, University of Santiago de Compostela
- Abstract: A century after the discovery of cosmic rays, the nature and origin of the highest energy particles in the Universe, the Ultra-High Energy Cosmic Rays (UHECR), remain enigmatic. Thanks to experiments dedicated to probing the extreme end of the energy spectrum, exciting progress is being made in solving these puzzles.The Pierre Auger Observatory is currently the World`s largest detector for UHECR. The goal is to measure the cosmic ray energy spectrum, arrival directions, and the properties of the extensive air showers induced by the UHECRs in the atmosphere with the objective of unveiling cosmic ray elemental composition, origins and propagation effects. The observatory has now collected more data than all previous experiments combined, and employs multiple detection (hybrid) detection techniques allowing for a large exposure and excellent control of systematic uncertainties. The original design, optimized for the energy range from 1018 eV to the end of the spectrum, has recently been enhanced to cover energies down to almost 1017 eV, allowing us to view additional interesting features of the spectrum. I will give an overview of the latest results with a focus on the current status of the search for ultra-high energy neutrinos and photons and the promising prospect to use cosmic rays to study hadronic interactions at energies beyond the reach of the LHC.
- Host: Halzen
Friday, February 24th, 2012
- Special NOON Astronomy Talk
- The early Evolution of the Milky Way Satellite Galaxies
- Time: 12:00 pm - 1:10 pm
- Place: 4421 Sterling Hall
- Speaker: Professor Gerhard Hensler, Institute of Astronomy, University of Vienna
- Abstract: The dwarf spheroidal galaxies (dSphs) around the Milky Way (MWG)
belong to the most poorly understood class of astronomical objects
and serve as the most challenging targets of astrophysical researchfor various reasons:
At first, in LCDM cosmology a huge number of subhalos are expected
to surround massive galaxies what is contrasted by the observed number of satellite galaxies around the MWG. In addition, it is debated whether the recently detected ultra-faint dSphs can account for this mismatch.
Secondly, the still at present observable accretion of satellite galaxies by the MWG should have led to the built-up of the Galactic halo and left behind kinematic and chemical witnesses by their stars. Besides that these expected signatures and similarities between halo stars and existing dSphs are not observed, also their spatial distribution and number pose serious questions to our understanding of satellite-galaxy
evolution. To solve these problems numerical simulations from cosmological to galactic scales and semi-analytical galaxy models have been undertaken by numerous authors which will be highlighted, but also critically reviewed here.
New comprehensive approaches will be presented and their results compared with observations. - Host: Professor Emeritus Ed Churchwell
- Theory Seminar (High Energy/Cosmology)
- Title to be announced
- Time: 2:00 pm - 3:00 pm
- Place: 5280 Chamberlin Hall
- Speaker: JiJi Fan, Princeton University
- Physics Department Colloquium
- FT-IR spectrochemical imaging: Design and applications with Focal Plane Array and multiple beam synchrotron radiation source
- Time: 3:30 pm
- Place: 2241 Chamberlin Hall (coffee at 4:30 pm)
- Speaker: Carol Hirschmugl, UW-Milwaukee
- Abstract: * This work has been done with support from NSF (MRI-DMR-0619759 and CHE-1112433) and the Synchrotron Radiation Center, which is also supported by NSF (DMR-0537588) and UW-Milwaukee and UW-Madison.
FT-IR spectrochemical imaging, which combines the chemical specificity of mid-infrared spectroscopy with spatial specificity, is an important demonstration of label-free molecular imaging. Mid-infrared optical frequencies are resonant with the vibrational frequencies of functional groups, thus an absorption spectrum is a "molecular fingerprint" of the material at every pixel. Each spectrum can be correlated with known material properties to extract chemical information. Synchrotron based FT-IR spectrochemical imaging, as recently implemented at the Synchrotron Radiation Center in Stoughton, WI, demonstrates the new capability to achieve diffraction limited chemical imaging across the entire mid-infrared region, simultaneously, with high signal to noise ratio.
IRENI (Infrared Environmental Imaging) extracts a large swath of radiation (320 hor. x 25 vert. mrads2) to homogeneously illuminate a commercial IR microscope equipped with an infrared Focal Plane Array (FPA) detector. Wide field images are collected. IRENI rapidly generates high quality, high spatial resolution data. The relevant advantages (spatial oversampling, speed, sensitivity and signal to noise ratio) will be presented and demonstrated using examples from a variety of disciplines, including formalin fixed and flash frozen tissue samples, live cells, fixed cells, paint cross sections, polymer fibers and novel nano-materials will be presented.
M.J. Nasse, et al. "High resolution Fourier-transform infrared chemical imaging with multiple synchrotron beams", Nature Methods, 8, (2011) 413-416
E.C. Mattson, et al. "Evidence of Nanocrystalline Semiconducting Graphene Monoxide During Thermal Reduction of Graphene Oxide in Vacuum," ACS Nano 5, pp 9710-9717
M.Z. Kastyak-Ibrahim, et al. "Biochemical label-free tissue imaging with subcellular -resolution synchrotron FTIR with Focal Plane Array Detector," NeuroImage 60, (2012) 376-383.
- Host: Himpsel