This Week at Physics

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Events During the Week of February 12th through February 19th, 2012

Sunday, February 12th, 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.
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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.
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Monday, February 13th, 2012

Plasma Physics (Physics/ECE/NE 922) Seminar
Complex Plasma - A Potential Field for Interdisciplinary Research Using Laboratory and Space Experiments
Time: 12:05 pm
Place: 2241 Chamberlin
Speaker: Dr. Uwe Kokopka, Max Planck Institute for Extraterrestrial Physics, Garching
Abstract: Dust particles, embedded in a plasma, are getting charged due to a variety of mechanisms like electron-/ion- bombardment or secondary electron emission. At low densities the dust in the plasma can be treated as an impurity that mainly probes the background plasma without significantly altering it. At higher densities a change from dust in plasma to a "dusty plasma" takes place. The dust species begin to alter the overall behavior of the other plasma components, and vice versa, so that the dust has to be treated as an integral component. Both situations can be frequently observed in astrophysical and plasma processing environments. At sufficient high dust densities, the dynamics of the whole system eventually become dominated by the dust species, since most of the inertia in the system is bound to it. In this situation the charged dust particles are often treated similarly to a one-component system of directly interacting charged particles that are "somehow" screened by the background plasma. Due to the high particle mass, the time and spatial scales of the dynamics are shifted towards macroscopic scales. Typically, very fast plasma dynamics such as waves, diffusion, or gyro motion of particles can then be observed simply with the naked eye. This so-called "complex plasma", named in analogy to complex fluids (e.g. colloidal particles in a liquid suspension), also shows strongly coupled phenomena like crystallization that are least expected to be present in a plasma environment. All of this is visible on the fundamental, "atomic" scale of single (dust) particles for the systems that can consist of just a few or up-to billions of particles. This makes complex plasmas a very attractive research field which heavily supports and strongly benefits from interdisciplinary research efforts. The high mass of the dust particles that shifts the dynamics towards macroscopic scales has a drawback however. In a typical laboratory complex plasma setup the dust sediments, forming compressed layers close to the lower sheath boundaries where the weight of the particles is compensated by the effect of the sheath/pre-sheath electric field. Only small/light particles (~ 1 um) can easily fill the bulk of the plasma. Alternatively, experiments in u-gravity must be performed. Since the discovery in 1994 of the crystalline state of a complex plasma, the "plasma crystal", by my colleague H. Thomas, I have studied a variety of topics related to complex plasmas. I have looked at fundamental themes like single particle interaction, instabilities and the role of a magnetic fields in a complex plasmas. Additionally, I studied interdisciplinary topics such as crystallization and flow dynamics. Some experiments were aimed at applications for dust removal, or dust growth, that have relevance to plasma processing and fusion. Experiments on dust coagulation and runaway growth provided unintended yet significant results regarding the astrophysical question of planet formation. The presentation contains an introduction to fundamental complex plasma research. I will discuss the charging and "somehow" screening of microparticles in a plasma environment as well as the role of gravity. Examples of laboratory and u-gravity experiments will be shown, demonstrating the interdisciplinary potential of complex plasmas research. Also two experimental setups that I have designed and built to perform the shown experiments will be introduced: a unique high magnetic field plasma facility and a flexible plasma device, the "PlasmaLab", that is foreseen to be operated as part of a future experiment aboard the international space station (ISS).
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Condensed Matter Theory Group Seminar
Magnetic penetration depth of iron-pnictides in case of coexistence between superconducting and spin-density wave orders
Time: 4:30 pm
Place: 5310 Chamberlin
Speaker: Dushko Kuzmanovski, UW-Madison
Abstract: We obtain an analytic expression for the response function of a superconductor to an external vector potential in the London limit. We work within the framework of a two-band model with both intra- and interband pairings leading to superconducting (SC) and spin-density wave (SDW) orders, and assume that the mean-field approach is valid. For definiteness, we assume a homogeneous s+- SC order parameter, and a commensurate SDW order parameter. We numerically solve the relevant coupled self-consistency conditions in the zero-temperature limit for the two order parameters, and use those solutions to calculate the London penetration depth dependence on doping, modeled by a doping-dependent anisotropic band-splitting. This would serve as a preliminary guide into future investigation of possible features in the temperature dependence of the London penetration depth, found in recent experiments.
Host: Perkins
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Tuesday, February 14th, 2012

Chaos & Complex Systems Seminar
Energy harvesting for mobile electronics
Time: 12:05 pm
Place: 4274 Chamberlin
Speaker: Ashley Taylor, UW Department of Mechanical Engineering
Abstract: Energy harvesting is a very old idea arguably going back to the invention of the windmill, sail, and waterwheel. More recently efforts have been focused on ways to convert environmental energy into electrical power. Many types of energy harvesters exist covering a very broad range of applications from large scale power generators to portable power sources for mobile devices and sensors. The harvesting of environmental mechanical energy is particularly promising for portable applications by using such high-power sources as human locomotion, but currently its use is substantially limited by low power output of energy converters. Existing methods of mechanical-to-electrical energy conversion such as electromagnetic, piezoelectric, or electrostatic are not well suited for effective direct coupling to the majority of high-power environmental mechanical energy sources suitable for portable applications, thus their energy output remains in the microwatt to hundreds of milliwatt range. However with the rapid growth of mobile devices the demand for power sources producing watts or tens of watts has acutely increased. To bridge this gap we have developed a radically new mechanical-to-electrical energy conversion method which is based on reverse electrowetting aEuro&quot; a novel microfluidic phenomenon. Energy generation is achieved through the interaction of arrays of moving microscopic liquid droplets with a novel multilayer thin film. We believe that this approach has a number of significant advantages over existing mechanical energy harvesting technologies.
Host: Sprott
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"Physics Today" Undergrad Colloquium (Physics 301)
X-ray Astronomy
Time: 1:20 pm
Place: 2223 Chamberlin
Speaker: Dan McCammon, University of Wisconsin Department of Physics
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Ghosts in the ice - Searching for the Universe's most elusive particles at the South Pole
Time: 4:00 pm
Place: 4274 Chamberlin Hall
Speaker: Darren Grant, University of Alberta
Abstract: In one of the planet's most extreme environments, South Pole Station Antarctica, scientists have instrumented more than a cubic kilometer of ice to construct the world's largest neutrino detector to date: the IceCube Neutrino Observatory. Given its enormous size, IceCube is designed to detect the highest energy neutrinos predicted to be produced in the most violent astrophysical processes. The milestone deployment of the last of the observatory's 86 strings of optical detectors, in December 2010, included the completion of two noteworthy additions to the original design: a low-energy neutrino extension (DeepCore) and a prototype direct-detection dark matter detector (DM-Ice). These new detectors establish the first steps towards a precision particle astrophysics program in the Antarctic. The early results from this emerging and potentially game-changing program will be discussed. Also included will be the initial expectations of future detector upgrades in the ice towards large-scale direct detection dark matter searches and multi-megaton neutrino detectors with very low, O(10 MeV), energy thresholds.
Host: Halzen
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Wednesday, February 15th, 2012

NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Hunting for Dark Matter in Antarctica
Time: 11:00 am
Place: 5280 Chamberlin Hall
Speaker: Carsten Rott, Ohio State University
Abstract: Despite overwhelming evidence that it composes the vast majority of the mass in the Universe, dark matter's particle properties literally remain in the dark. Identifying the mysterious nature of dark matter is one of today's most pressing scientific problems and is being sought for using colliders, direct-detection experiments, and powerful indirect techniques. With the completion of the gigaton-scale IceCube neutrino telescope a new era in astro-particle physics has begun.

IceCube exploits the excellent optical properties of the ice beneath the South Pole to detect neutrinos through the Cherenkov light emission of secondary particles produced by neutrino interactions. Its unprecedented size will finally allow us to address long standing questions such as the sources of cosmic rays and unknown properties of neutrinos. IceCube further provides a novel discovery potential for dark matter through striking neutrino signatures that may further shed light on its fundamental particle properties and its distribution in the Milky Way. I will discuss our recent results on the search for dark matter and new ways to achieve greater sensitivity. I will conclude by discussing ideas towards a new low-energy threshold multi-megaton ice Cherenkov array (MICA). Such a detector would provide exciting possibilities for the study of neutrino properties, supernova burst neutrinos, Galactic neutrino sources, and dark matter.

Host: Halzen
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Thursday, February 16th, 2012

Astronomy Colloquium
Through a Glass Darkly: Galaxy Clusters and Strong Lensing
Time: 3:30 pm
Place: 4421 Sterling Hall
Speaker: Michael Gladders, University of Chicago
Abstract: A detailed and statistically robust visual inspection of the SDSS DR7 imaging footprint, and similarly the entire RCS-2 cluster catalog, has produced hundreds of candidate cluster-scale strong lensing systems, over a volume of approximately 9 Gpc^3 out to a redshifts beyond z=1. An extensive multi-wavelength multi-telescope follow-up program has confirmed the lensing interpretation of several hundred of these lensing candidates, providing a dramatic increase the total number of known lenses from all previous samples. The resulting samples probe strong lensing from group mass scales all the way to the most massive clusters, covering two orders of magnitude in mass. These lenses inform our understanding of massive dark matter halos through studies both of the statistics of the source images and lenses, and detailed lensing studies of individual systems. The highly magnified images of the lensed sources also provide a unique view into star formation in the early universe, probing spatial and mass scales otherwise not accessible with current telescopes.

Host: Christy Tremonti
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Friday, February 17th, 2012

Physics Department Colloquium
Plasma Techniques Used to Trap Antihydrogen[1]
Time: 3:30 pm
Place: 2241 Chamberlin Hall (coffee at 4:30 pm)
Speaker: Joel Fajans, University of California, Berkeley
Abstract:

Recently, the ALPHA collaboration at CERN trapped antihydrogen atoms.[2] To date, over three hundred antiatoms have been confined, some for as long as 1000s.[3] This was the first time that anti-atoms had ever been trapped. The ultimate goal of the ALPHA collaboration is to test CPT invariance by comparing the spectra of hydrogen and antihydrogen, and to measure the gravitational attraction between matter and antimatter. Such studies might resolve the baryogenesis problem: why is there very little antimatter in the Universe? The ALPHA experiment brought together techniques from many different fields of physics, but the crucial breakthroughs were in plasma physics. The essential problem is this: How does one combine two Malmberg-Penning trapped plasmas, one made from antiprotons, and the other positrons, which have opposite electrostatic potentials of nearly one volt, in such a manner that the antiprotons traverse the positrons with kinetic energies of less than 40μeV, this latter being the depth of the superimposed neutral antihydrogen trap? The plasma techniques ALPHA developed to accomplish this include:

  • Minimizing the effects of the neutral trap multipole fields on the positron and antiproton plasma confinement.
  • Compressing antiprotons down to less than 0.5mm.
  • Using autoresonance to inject antiprotons into the positrons with very little excess energy.
  • Evaporative cooling of the electrons and antiprotons to record low temperatures.
  • Development of charge, radial profile, temperature, and antiproton loss location diagnostics.
  • Careful and lengthy manipulations to finesse the plasmas into the best states for optimal antihydrogen production and trapping.

  • The plasma techniques necessary to trap antihydrogen will be reviewed in this talk.


    [1] This work was supported by DOE and NSF, and is reported on behalf of the ALPHA collaboration.
    [2] Trapped antihydrogen, Nature, 468, 673, 2010.
    [3] Confinement of antihydrogen for 1000 seconds, Nature Physics, 7, 558, 2011.

    Host: Forest
    Poster: http://www.physics.wisc.edu/twap/posters/2012/2350.pdf
    Video: http://www.physics.wisc.edu/vod/2012/02/17.html
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    Saturday, February 18th, 2012

    Physics Fair
    The 5th Annual Physics Fair
    Time: 11:00 am
    Place: Chamberlin Hall
    Abstract: This event is an open house for the University of Wisconsin - Madison Department of Physics.
    Host: Michael Randall
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    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.
    Add this event to your calendar

    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.
    Add this event to your calendar

    Wonders of Physics
    Physics of the Wisconsin Idea
    Time: 7:00 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.
    Add this event to your calendar

    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.
    Add this event to your calendar

    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.
    Add this event to your calendar

    "This Week at Physics" poster: http://www.physics.wisc.edu/twap/posters/2012/2012-02-13.pdf

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