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"In the Footsteps of the Master..."
John S. Gianforte, Blue Sky Observatory
January 26, 2009
DeMeritt Hall, Room 240
Coffee: 3:40 pm - Physics Common
Talk: 4:00 - 5:00 PM
Abstract
In my lecture I will discuss the connections between the discoveries and accomplishments of Galileo and modern astronomy and how they fit into the International Year of Astronomy (IYA) that we are celebrating all through this year. In August of last year, my wife and I traveled to Italy to research the life and accomplishments of Galileo for ourselves. Some of the highlights of that memorable trip will be included in the lecture. I will also touch upon the important role that public outreach plays in society and how it benefits all branches of astronomical research. Galileo understood this very well!
The Interstellar Boundary Explorer (IBEX) --
Taking its first Image of the Heliospheric Boundary
Prof. Eberhard Moebius, University of New Hampshire
Feb 16, 2009
DeMeritt Hall, Room 240
Coffee: 3:40 pm - Physics Common
Talk: 4:00 - 5:00 PM
Abstract
The solar wind carves out a large void - the heliosphere - into the surrounding interstellar plasma. On October 19, 2008, the Interstellar Boundary Explorer (IBEX) has been launched, which carries two highly sensitive Energetic Neutral Atom (ENA) cameras that will take the first global images of the heliosphere’s interaction with the surrounding interstellar medium, hence opening another window on astrophysics. Because the Sun moves relative to the local interstellar cloud at ≈26 km/s, an interstellar wind of neutral gas blows through our solar system, thus forming a point source on the ENA image. In spite of the large size of the heliosphere we can probe this flow for He and O near Earth. At a distance of about 100 AU the solar wind slows down to subsonic speed through interaction with the interstellar gas, thus forming the termination shock. Here ions are accelerated efficiently, preferably those created from inflowing interstellar gas and then picked up by the solar wind. Through charge exchange with interstellar gas atoms these accelerated ions form a diffuse source of ENAs. These neutrals - if released towards the Earth – arrive on straight trajectories, carrying information about the energy spectra and spatial distribution of the energetic ions at the termination shock. From both, the interstellar flow through the inner heliosphere and the image of the termination shock ENAs, we expect complementary insight into the exciting observations that the two Voyagers have returned from their recent passage through termination shock, i.e. a distinct asymmetry of the heliosphere and the fact that, contrary to theoretical predictions, the source of anomalous cosmic rays has not yet been found at the termination shock. Currently, the IBEX payload is operational and takes its first full-sky image.
A Guided Tour of Heliospheric Waves, Shocks and Energetic Particles
Prof. Marty Lee, University of New Hampshire
Feb 23, 2009
DeMeritt Hall, Room 240
Coffee: 3:40 pm - Physics Common
Talk: 4:00 - 5:00 PM
Abstract:
This colloquium will be a guided tour through the heliosphere featuring hydromagnetic waves, shocks, and energetic particle populations, their observed behavior from the Sun to the solar wind termination shock, and the theoretical concepts that have been developed to describe them. The tour will include, for example, stops at Earth's bow shock, the shocks bounding corotating interaction regions in the solar wind, the solar wind termination shock, the space environment around comets, the mass and momentum loading of the solar wind through its interaction with the interstellar gas, the theory of diffusive shock acceleration, and the process of stochastic acceleration. The lecture will end with a list of outstanding puzzles concerning energetic particle transport and shock structure for which we seek solutions as we complete Voyagers' exploration of the outer heliosphere, interpret the energetic neutral atom intensities being measured by IBEX, and start to explore the inner neighborhood of the Sun.
Title: Polarized neutron scattering and the development of polarized Helium-3 based neutron spin filters at the Oak Ridge National Laboratory
Dr. Hal (Wai-Tung) Lee, Spallation Neutron Source
March 9, 2009
DeMeritt Hall, Room 240
Coffee: 3:40 pm - Physics Common
Talk: 4:00 - 5:00 PM
Abstract:
Neutron beams with the neutron kinetic energy in the "thermal" and "cold" range have been used in studying physics phenomena and material science for many years. When a beam of neutrons impinges on a sample, the interaction of the neutrons with the nuclei in the sample results in the scattering of the neutron beam. By measuring the angular distribution of the scattered neutrons, we can study the material properties of the sample down to the atomic scale. The neutron also has a magnetic moment and can interact with the magnetic field generated by the atomic moment. Impinging a polarized neutron beam on a sample gives us great details of the magnetic properties of the sample material. The Oak Ridge National Laboratory recently completed the construction of a new facility dedicated to neutron scattering work, the Spallation Neutron Source, and is now bringing instruments on line. Polarized neutrons will be an integral part of the facility. To provide the capability for using polarized neutrons, we have also been developing the techniques of using polarized Helium-3 based neutron polarizers and polarization analyzers. In this talk, polarized neutron scattering will be introduced together with some examples illustrating its uses, followed by an overview of the polarized 3He neutron spin filter development efforts at our laboratory.
Learning about a Torched Planet : Insights into the Ion Composition and Plasma Environment of Planet Mercury from MESSENGER
Prof. Thomas Zurbuchen, University of Michigan
March 30, 2009
DeMeritt Hall, Room 240
Coffee: 3:40 pm - Physics Common
Talk: 4:00 - 5:00 PMysics Common
Talk: 4:00 - 5:00 PM
Abstract:
MESSENGER has provided the first measurements of the composition and dynamic properties of ions near Mercury. Here, we focus on observations made with the Fast Imaging Plasma Spectrometer (FIPS), the plasma sensor of the Energetic Particle and Plasma Spectrometer (EPPS) instrument, during MESSENGER's first two flybys of Mercury. This instrument has a near-hemispheric instantaneous field of view and provided plasma and compositional parameters for particles from 50 eV to 20 keV per charge throughout the first MESSENGER flyby on January 14, 2008, as it is expected to do as well during the second flyby on October 6, 2008. We first discuss the global distribution of plasma in Mercury's environment. We then report compositional measurements and spatial distributions of heavy ions, with mass up to Fe, originating from Mercury. We particularly focus on the distribution of Na and water-group ions. Finally, we discuss doubly charged ions and the implications of these results for our understanding of the intensive solar wind interaction with Mercury's surface.
Heating of the Solar Corona and its Loops
Dr. James A. Klimchuk, NASA Goddard Space Flight Center
April 6, 2009
DeMeritt Hall, Room 240
Coffee: 3:40 pm - Physics Common
Talk: 4:00 - 5:00 PM
Abstract:
At several million degrees, the solar corona is more than two orders of magnitude hotter than the underlying solar surface. The reason for these extreme conditions has been a puzzle for decades and is considered one of the fundamental problems in astrophysics. Much of the coronal plasma is organized by the magnetic field into arch-like structures called loops. Recent observational and theoretical advances have led to great progress in understanding the nature of these loops. In particular, we now believe they are bundles of unresolved magnetic strands that are heated by storms of impulsive energy bursts called nanoflares. Turbulent convection at the solar surface shuffles the footpoints of the strands and causes them to become tangled. A nanoflare occurs when the magnetic stresses reach a critical threshold, probably by way of a mechanism called the secondary instability. I will describe our current state of knowledge concerning the corona, its loops, and how they are heated.
Antimatter plasmas and antihydrogen production and trapping
Prof. Joel Fajans, University of California, Berkeley
April 20, 2009
DeMeritt Hall, Room 240
Coffee: 3:40 pm - Physics Common
Talk: 4:00 - 5:00 PM
Abstract:
Experiments whose ultimate goal is to test CPT have been producing slow, but untrapped, antihydrogen at CERN since 2002. Trapping antihydrogen, the current goal of these experiments, is much more difficult than merely synthesizing it. The primary problem is cooling the antiprotons by fourteen orders of magnitude from their energy at creation. The first ten orders are relatively easy; we (the ALPHA collaboration) are now struggling with the last four. The scale size is set by the potentials of the antimatter plasmas in which the antiatoms are synthesized. In this talk, I will discuss some of the techniques we are developing to control the synthesis process.
Holographic Superfluidity and Superconductivity
Prof. Christopher Herzog, Princeton University
May 4, 2009
DeMeritt Hall, Room 240
Coffee: 3:40 pm - Physics Common
Talk: 4:00 - 5:00 PM
Abstract:
Gauge/gravity duality, a concept which emerged from string theory, holds promise for revealing the secrets of certain strongly interacting real world condensed matter systems. Historically, string theorists presented their subject as a promising framework for a quantum theory of gravity. More recently, the AdS/CFT correspondence and gauge/gravity dualities have emerged as powerful tools for using what we already know about gravity to investigate the properties of strongly interacting field theories. In this colloquium, I will survey recent developments where black holes are used to calculate the thermodynamic and transport properties of quantum critical systems, superconductors, superfluids, and fermions at unitarity.
Student Senior Thesis Presentations
May 11, 2009
DeMeritt Hall, Room 240
Coffee: 3:40 pm - Physics Common
Talks: 3:00 - 5:00 PM
Sam MeehanCharacterization of the Charge Sharing Effect in Silicon Vertex Tracker Detectors for Use in CLAS12
Sam Meehan
The energy upgrade of the electron accelerator at Jefferson Lab from 6GeV to 12GeV will allow phenomena to be studied in an entirely new energy regime. For the CLAS12 collaboration in Hall B, this means studying the quark and gluon structure of the nucleon in a more complete manner. This requires that the upgraded spectrometer system, including the silicon vertex trackers (SVT) used for path reconstruction, have high spatial resolution. Using a Monte Carlo simulation, I have studied an effect called charge sharing, which affects detector precision, within the SVTs with respect to the separation of the detector microstrips to show that the current design works sufficiently well. Furthermore, by studying the variation of charge sharing with respect to incident particle angle, I have shown that the incident angle has a significant influence on the detector response and must be characterized experimentally.
Morgan O'Neill Precision pointing in the sky for IBEX interstellar flow observations - Use of the moon with the IBEX-Lo star sensor
Morgan E O'Neill et al.
The Interstellar Boundary Explorer (IBEX) is in Earth orbit and imaging Energetic Neutral Atoms (ENAs) from the heliospheric boundary and beyond. A star sensor provides precision pointing information for the IBEX sensors. The known coordinates of stars, planets and the moon act as direction pointers for the satellite’s position. The moon poses a unique problem because of its highly variable shape and distance from the satellite. The moon’s barycenter can be found by modeling the star sensor’s response to a range of moon phases. The correction can be accurately applied to the moon signal from flight data.
Ryan GoslinDead Layer Energy corrections with the High Energy Telescope on the Ulysses Spacecraft
Ryan Goslin
In order to calculate the energy of a particle traveling through a detector we have to consider energy loss that might occur in the inactive regions, this is because when Li drifted Si detectors are created there is a small layer that is left behind that will be "dead". Energy loss in these regions are small at nearly one percent, but a better estimate to correct for this energy loss in order to find more precise results is desirable. The Ulysses High Energy Telescope uses six Li drifted silicon detectors to calculate the energy for a particle that travels through it. If we consider particles that are relativistic they should travel entirely through and deposit nearly an equal amount of energy in each of the six detectors since the energy loss is minimal. Using this we can establish 5 equations between the 6 detectors which reduces the 6 unknowns to 1 free parameter. These dead layers make over 17 years of elemental charge calculations one percent more accurate and is very useful for researching solar energetic particles.
George ClarkAnalysis of the Diffuse Background Components towards Efficient Use of the IBEX-lo Star Sensor for the Interstellar Flow Direction Determination
George Clark
A key objective of the Interstellar Boundary Explorer (IBEX) mission is to compare the interstellar oxygen flow to the helium flow through the solar system. This comparison requires an accurate determination of the incoming energetic neutral atoms (ENAs) of the interstellar gas flow to the background stars. The magnitude range of stars that can be used for the direction determination is greatly affected by diffuse background sources including the Milky Way and the zodiacal light. Using detailed background models for subtraction increases the usable dynamic range. A preliminary background model of the sky was created assuming one color band, but analysis of Milky Way photometry maps show it is necessary to include all color bands to increase the angular resolution of the star sensor.
Austin P Purves
Constraints on the Spectral Index from Multi-Field Slow-Roll Inflation
Austin P Purves
Cosmological inflation describes a period of exponential expansion driven by the presence of a scalar field in the early universe. Inflation solves several problems of the big bang description of the universe sans inflation, including the horizon problem, and the flatness problem. Slow-roll inflation is a widely studied class of inflation models that makes certain assumptions about the potential in which the scalar field moves. These models yield predictions consistent with observed properties of the CMB (measured by WMAP). We consider slow-roll inflation with multiple scalar fields present during inflation, and evaluate predictions made by such a multi-field inflation model.
Jeffrey TesseinSolar Wind Turbulence: A Study of Corotating Interaction Regions at 1 AU
Jeffrey Tessein
I have taken 5 CIR events from the solar minimum years 2007 and 2008 to analyze their turbulence parameters and compared them to non-CIR turbulence from solar maximum years. The CIR turbulence differs from the ambient turbulence because it is effectively a point source and the hope is to find evidence of turbulent energy emanating from the interface. This should present some nonhomogeneities not seen by non-CIR turbulence. We find that there are some differences with the CIR turbulence, but for the most part the CIR turbulence has the same results as past turbulence studies.
Robert HoltNumerical Analysis of Flutter with Aircraft Wing Model in Subsonic Air Flow
Robert Holt
An analytical and a numerical model of flutter (a violent, often destructive vibration) in aircraft wings of high aspect ratio are discussed. Asymptotics are applied to the analytical model to produce distinct eigenvalue branches of a dynamics generating operator. This new model is analyzed numerically in order to be able to change different parameters of the system. We find coalescent eigenvalues at specific combinations of generalized parameters which indicate an unstable system.
Muon Ionization Cooling: an R&D project for the Neutrino Factory
Dr. Ulisse Bravar, University of New Hampshire
September 18, 2008
DeMeritt Hall, Room 112 (Note special place and time)
Coffee: 3:40 pm - Physics Common
Talk: 4:00 - 5:00 PM
Abstract
Observations of the solar neutrino deficit and the atmospheric neutrino anomaly mark a major milestone in the history of neutrino physics, confirming the presence of neutrino oscillations. Several still open questions on the nature of these particles will be answered by forthcoming experiments. Amongst them, unparalleled results are expected from the Neutrino Factory, a new concept for producing neutrino beams of unprecedented quality in terms of luminosity, flavor composition and precision of the beam parameters. These beams will enable the exploration of otherwise inaccessible domains in neutrino oscillation physics by exploiting baselines of planetary dimensions. An essential ingredient in the engineering design of the Neutrino Factory is a muon cooling channel, a component where the emittance of a muon beam, used by the factory as the source of neutrinos, is reduced by orders of magnitude within the short lifetime of a muon. While straightforward in principle, muon cooling has never been demonstrated in practice and the Neutrino Factory cooling channel presents formidable engineering challenges. The /International Muon Ionization Cooling Experiment/ (MICE) is a proof-of-concept design, aimed at demonstrating the viability of muon ionization cooling and the feasibility of a cooling channel with the desired performance for the first time. MICE will reduce the 6D emittance of muon beams over a range of beam momenta from 140 to 240 MeV/c over a 5.5 m long channel with various magnetic field configurations and measure that reduction. The muon beam will be extracted from pions produced at a dedicated beamline at the ISIS source at Rutherford Appleton Laboratory in the UK. The MICE beamline is presently in the final stages of commissioning. Measurements will begin in early 2009 with first results becoming available later during the year. I will discuss the motivation and design of the Neutrino Factory and describe in detail the MICE project, including its current status, future schedule and expectations
Advancing the Study of High-Energy Galactic Binaries with the Next Generation of Gamma-Ray Instrumentation
Dr. Peter F. Bloser, Space Science Center, University of New Hampshire
September 22, 2008
DeMeritt Hall, Room 240
Coffee: 3:40 pm - Physics Common
Talk: 4:00 - 5:00 PM
Abstract
The medium-energy gamma-ray energy band, roughly 0.5 - 50 MeV, is home to a rich variety of high-energy astrophysical phenomena. One process in particular, the non-thermal acceleration of charged particles to very high energies, is ubiquitous throughout the universe, from the centers of distant galaxies to the Earth's magnetosphere. One example of particle acceleration that is especially ripe for exploration and discovery with a new generation of sensitive space-borne gamma-ray instrumentation occurs in high-energy binary systems in the Galaxy.
Galactic binaries containing black holes or neutron stars have long been known to be bright sources of thermal X-rays from their accretion disks, but a few have also exhibited non-thermal spectra extending to 1 MeV and beyond. A handful have now been detected at TeV energies as well, proving that highly relativistic particle acceleration is taking place. Medium-energy observations are needed to form a complete picture. Most of these systems are relatively faint and highly time-variable, and so require sensitive, wide-field observations to study. The medium-energy gamma-ray band, however, is a notoriously difficult energy range in which to perform sensitive observations, due to complex photon interactions and high backgrounds. The recent availability of advanced scintillator materials, most notably lanthanum bromide (LaBr3:Ce), and new scintillation light readout devices, such as silicon photomultipliers (SiPMs), offers a promising path to realizing powerful new gamma-ray instrumentation. New scintillators such as LaBr3:Ce offer an energy resolution that is competitive with that of semiconductor detectors, while retaining the many advantages of scintillators: simple and reliable implementation, high stopping power, large volumes, room temperature operation, and very fast timing. I will describe an exciting application of advanced scintillator technology currently under development: a fast scintillator-based Compton telescope which will survey the MeV sky with ten times the sensitivity of COMPTEL.
This instrument would allow comprehensive studies of energetic particle acceleration in the universe, both in relatively new sources, such as Galactic binary systems, and in unprecedented detail in known sources, such as pulsars, active galactic nuclei, and solar flares.
Magnetospheric Substorms: Controversies About the Majestic Light
Jimmy Raeder, University of New Hampshire
October 20, 2008
DeMeritt Hall, Room 240
Coffee: 3:40 pm - Physics Common
Talk: 4:00 - 5:00 PM
Abstract
Substorms were first identified (and incorrectly named, they are for the most part not sub-storms) as a coherent auroral phenomenon by Shin Akasofu in the early 1960's. We now know that substorms encompass most of the magnetosphere-ionosphere system.
A substorm growth phase, during which energy from the solar wind is stored in the magnetotail, is followed by an abrupt energy release that powers the aurora. That is where the consensus ends. What exactly controls and triggers this energy release and how it powers the aurora to the tune of ~1TW is still hotly debated. NASA's THEMIS mission is the first mission dedicated to solve some of the mysteries. The mission, 5 satellites launched in 2007, is now about half through its prime phase. Although the data solidify some models the final word is certainly not yet spoken. It has become clear already that the data may still be too sparse to be unambiguous and that extensive numerical modeling will be needed to make substantial progress. In this presentation I will outline the current substorm controversies, introduce the THEMIS mission, and present latest results both from THEMIS data analysis and from modeling studies.
"The Phoenix Mission to Mars -- NASA's innovative explorer of liquids and biohability on the red planet"
Prof. Suzanne Young, NASA/Tufts University
October 27, 2008
DeMeritt Hall, Room 240
Coffee: 3:40 pm - Physics Common
Talk: 4:00 - 5:00 PM
Abstract: TBA
CEPS Frontier Lecture Series: The Unreasonable Effectiveness of Physics in Mathematics
Prof. Arthur Jaffe, Harvard University
November 3, 2008
DeMeritt Hall, Room 112 (large lecture hall)
Coffee: 3:40 pm - Physics Common
Talk: 4:00 - 5:00 PM
Abstract
During much of the 20th century Mathematics has been the language of Physics. Now we see this situation turned on its head, with Physics playing the role of lighthouse for Mathematics. The title is a play on the title of a famous paper by E. Wigner, which serves as our starting point.
The Invisible Solar System: Magnetic Fields and Magnetized Plasmas
Prof. Margaret Galland Kivelson, UCLA
November 10, 2008
DeMeritt Hall, Room 112
Coffee: 3:40 pm - Physics Common
Talk: 4:00 - 5:00 PM
Abstract
The Sun, whose gravitational force binds the planets and other bodies of the solar system to it, is also the source of the solar wind, a magnetized plasma that fills the surrounding volume out to distances beyond 1 AU (the distance between the Earth and the Sun). The interaction of the solar wind with the solid bodies in orbit around it produces a diverse set of responses, some significant at Earth and others more important elsewhere. This talk will describe briefly how the regions near planets, moons, and comets are modified by the solar wind interaction. Active research based on data being acquired by carefully designed spacecraft missions at Earth and other planets is addressing questions related to the temporal variation of the interactions, some of which will be discussed.
Lattice QCD for Nuclear Physics
Prof. Silas Beane, University of New Hampshire
November 17, 2008
DeMeritt Hall, Room 240
Coffee: 3:40 pm - Physics Common
Talk: 4:00 - 5:00 PM
Abstract: TBA
The Role of Ionospheric Ions in the Magnetosphere
Lynn Kistler, University of New Hampshire
November 24, 2008
DeMeritt Hall, Room 240
Coffee: 3:40 pm - Physics Common
Talk: 4:00 - 5:00 PM
Abstract: TBA
Space Physics
John Dorelli, University of New Hampshire
December 1, 2008
DeMeritt Hall, Room 240
Coffee: 3:40 pm - Physics Common
Talk: 4:00 - 5:00 PM
Abstract: TBA
"When going underground, remember the sunscreen..."
(What the sun has told us about neutrinos, and vice-versa.)
Joe Formaggio, MIT
December 8, 2008
DeMeritt Hall, Room 240
Coffee: 3:40 pm - Physics Common
Talk: 4:00 - 5:00 PM
Abstract
The properties of neutrinos have been eluding scientists for over four decades. Making use of massive experiments buried deep underneath the Earth’s surface, experimentalists have shed light on the nature of this elusive particle by providing overwhelming evidence that neutrinos from the sun undergo oscillations –the quantum mechanical process by which a neutrino of one type spontaneously changes into another due to its mass. The talk will review the journey taken by physicists to learn about neutrinos and provide an outlook on how future experimental endeavors hope to reveal even more about neutrinos and neutrino mass.
"Senior Thesis Presentations."
UNH Physics Seniors.
May 5, 2008
Presentations: 4:00-5:00 PM
Abstract
Presentations will be 10 minutes with about 5 minutes for questions.
"Bubble Wrap For Bullets (and Bubbles): Draping of the Magnetic Fields of Galaxy Clusters"
Dr. Jonathan Dursi, Canadian Institute for Theoretical Astrophysics, University of Toronto
February 4, 2008
S145 Kingsbury, Coffee: 3:40 PM,
Talk: 4:00-5:00 PM
Abstract
Clusters of galaxies are the largest bound objects in the Universe, and most of their normal matter exists in the form of extremely hot, diffuse, gas. High-resolution X-ray observations have revealed cavities with sharp edges in temperature, density, and metallicity in this gas. Their presence poses a puzzle since these features are not expected to be hydrodynamically stable, or to remain sharp in the presence of diffusion. The mergers of galaxy clusters can be the most energetic events in the Universe, and even 'minor' mergers are very dynamic events, which eventually lead to the stripping and dissolution of the smaller core. However, where this occurs is important -- it helps determine the thermal and compositional history of the evolution of the cluster (and thus its component galaxies). However, with large 3D adaptive-mesh MHD simulations, and smaller more focused 2D simulations, we show how a moving core or bubble in even a very weakly magnetized plasma necessarily sweeps up enough magnetic field to build up a dynamically important sheath around the object; the layer's strength is set by a competition between 'plowing up' of field and field lines slipping around the core, and to first order depends only on the ram pressure seen by the moving object.
"Simulations of Type Ia Supernovae and Buoyancy-Driven Turbulent Nuclear Combustion"
Dr. Robert Fisher, Department of Astronomy and Astrophysics, University of Chicago
February 11, 2008
S145 Kingsbury, Coffee: 3:40 PM,
Talk: 4:00-5:00 PM
Abstract
In recent years, advances in computational science have led to fundamental insights into physical processes, particularly under extreme conditions of temperature and density. These advances have placed computation alongside theory and experiment as one of the foundational pillars of the physical sciences. In this colloquium, I will discuss one of the best examples of physical insight gleaned from computation -- full-star simulations of Type Ia supernovae. I will introduce Type Ia supernovae as astronomical events, highlighting their importance as standard candles and their use in the determination of cosmological parameters, including the equation of state of dark energy. I will present recent, exciting, fully three-dimensional simulations of Type Ia supernovae which have -- for the first time -- self-consistently detonated. I will then conclude with current simulations which we are now undertaking on a new generation of petascale supercomputers which will improve our understanding of buoyancy-driven turbulent nuclear burning -- one of the key fundamental physical processes which must be modeled in full-star Ia simulations.
Magnetic reconnection and turbulent transport in astrophysical and laboratory plasmas
Dr. Paolo Ricci, Ecole Polytechnique Federale de Lausanne, Switzerland
February 14, 2008
MUB Theater I, Coffee: 3:40 PM,
Talk: 4:00-5:00 PM
Abstract
Magnetic reconnection and turbulence-driven plasma transport are phenomena of fundamental importance in nearly all plasma systems, including the Earth's magnetosphere, the solar corona, the interstellar medium, molecular clouds, accretion disks, and laboratory fusion experiments. Magnetic reconnection allows a plasma to rapidly convert magnetic energy into high speed flows and thermal energy. Solar flares are a stunning example of this phenomenon, in which stored magnetic energy approaching a billion megatons is released in a matter of minutes. In magnetic fusion devices, turbulence driven by small-scale instabilities leads to a transport of density and heat from the hot dense core of the machine to its periphery, making confinement of the plasma a challenging endeavor. Despite the vital importance of these phenomena to our understanding of a wide range of plasma systems, basic physics questions still remain: Can magnetic reconnection really account for the observed explosively fast release of magnetic energy? Can turbulent transport in a magnetically confined plasma be reduced to levels compatible with fusion energy production? This talk will address my ongoing investigations of these topics and the hope for future progress.
Singularities in fluids and plasmas: Drivers of fast reconnection and turbulence
Prof. Kai Germaschewski, College of Staten Island, City University of New York
February 18, 2008
S145 Kingsbury, Coffee: 3:40 PM,
Talk: 4:00-5:00 PM
Abstract
Computer simulations have become a new tool in physics and other sciences that supplement the theoretical and experimental approaches. I will present two examples where numerical simulations have enabled major progress. In both of these examples, computer simulations using Adaptive Mesh Refinement have enabled the study of singularities that may lie beyond the capability of experimental diagnostics, and yet are crucial in developing a fundamental understanding of the underlying physics. The question whether finite-time-singularities develop from smooth initial conditions in the Navier-Stokes and Euler equations is one of the important open problems in fluid dynamics and also of importance for understanding turbulence in fluids. I will show high-resolution numerical work investigating the occurrence of a finite time singularity in a high-symmetry initial condition introduced by Kida. Plasmas are also amenable to a fluid description, using the equations of magnetohydrodynamics (MHD), or two-fluid equations that recognize the distinct identity of electrons and ions. Magnetic reconnection is a process which allows magnetic field lines in plasmas to change topology, releasing magnetic energy. In experiments on earth as well as in plasmas in space, the observed reconnection events are typically bursty and impulsive, i.e. intrinsically nonlinear. Computer simulations are an important tool to gain a better understanding of these phenomena, and show that is essential to go beyond the MHD model to include two-fluid effects in order to reproduce the behavior observed in reality.
Kinetic Turbulence in Space and Astrophysical Plasmas
Dr. Gregory Howes, Department of Astronomy, University of California, Berkeley
February 21, 2008
MUB Theater I, Coffee: 3:40 PM,
Talk: 4:00-5:00 PM
Abstract
Plasma is a ubiquitous form of matter in the universe and is nearly always found to be magnetized and turbulent. One must understand this behavior to interpret a large body of astronomical observations. Examples include turbulence in the interstellar medium, which is stirred by violent events like supernova explosions; turbulence in accretion flows around stars and compact objects; and turbulence in the solar wind streaming outward from our Sun. Although the dynamics at large scales is well-described by fluid theory, for scales smaller than the collisional mean free path, the dynamics must be described instead by kinetic theory. Because the energy of the turbulent motions is converted into heat at these small scales, important macroscopic properties are determined by microscopic physics. To advance our understanding of kinetic turbulence requires a concerted effort of analytical modeling, nonlinear kinetic simulation, and analysis of observational data. I will present the first-of-a-kind nonlinear simulations of near-Earth solar wind turbulence; the numerical approach is based on gyrokinetic theory, a reduced kinetic theory of magnetized, low-frequency plasma turbulence applicable to many space and astrophysical plasmas. The energy spectra computed from the simulations show good qualitative agreement with satellite observations in the solar wind, and the entire shape of the numerical spectra are well reproduced by a simple analytical model of kinetic turbulence. These results support the view that the observed break in the magnetic-energy spectrum in the solar wind corresponds to a transition to kinetic-Alfven-wave turbulence, not to the onset of ion cyclotron damping. This study demonstrates that such kinetic simulations of plasma turbulence may be undertaken with some confidence, using existing computational resources, and may guide the journey into the rich yet largely unexplored terrain of kinetic turbulence in space and astrophysical plasmas.
When Magnetized Winds Collide: Probing the Interaction of the Solar System with the Interstellar Medium
Prof. Merav Opher, Department of Physics and Astronomy, George Mason University
February 25, 2008
S145 Kingsbury, Coffee: 3:40 PM,
Talk: 4:00-5:00 PM
Abstract
Magnetic effects are ubiquitous and known to be crucial in space and astrophysical media; these media are excellent plasma laboratories and provide observational data that add valuable constraints to theoretical models. Modern computational techniques such as magnetohydrodynamic (MHD) and kinetic modeling are currently used to explore several fundamental plasma effects such as turbulence, reconnection, shocks etc. It is essential in a strong guided physical approach to use computer simulations in order to obtain novel information on critical research questions. In this talk I will discuss one example of how sophisticated computational work allied with detailed observational data can be guided towards resolving important physical questions. The twin Voyager spacecraft, both approximately 100 AU from the Sun, are providing us with an unexpected view of how stars interact with their surrounding media. For the first time we are able to make in situ measurements of particles and fields at the boundaries of the solar system. Voyager 1 crossed the termination shock in December 2004, and is now in the heliosheath, and in August 2007 Voyager 2 also crossed the shock. Recently, combining radio emission and energetic particle streaming measurements from Voyager 1 and 2 with extensive state-of-the art 3D MHD modeling, we were able to constrain the direction of the local interstellar magnetic field. As a result of the interstellar magnetic field, we have shown that the solar system is asymmetric, being pushed towards the Sun in the southern hemisphere. I will also review our previous work that showed that Kelvin-Helmholtz instabilities and turbulence exist near the current sheets. These effects will be able to be sampled by the Voyager observations in the heliosheath, providing direct testing of the theories and simulations we have developed. I will discuss these results, future work plans and their implications for the local interstellar magnetic turbulence.
In Search of Pentaquarks
Dr. Hovanes Egiyan, UNH Nuclear Physics Group.
March 10, 2008
S145 Kingsbury, Coffee: 3:40 PM,
Talk: 4:00-5:00 PM
Probing Hot Deconfined QCD Matter with Jets at the Relativistic Heavy Ion Collider
Dr. Anne Sickles, Brookhaven National Laboratory
March 24, 2008
S145 Kingsbury, Coffee: 3:40 PM,
Talk: 4:00-5:00 PM
Abstract
The Relativistic Heavy Ion Collider at Brookhaven is a unique tool to study deconfined QCD matter, the strongly interacting quark gluon plasma, at extremely high energy density. In the first years of RHIC operation it was established that a new form of matter, incompatible with ordinary hadronic degrees of freedom, was formed in Au+Au collisions. With recent high luminosity data sets, the RHIC experiments have exploited high momentum transfer quark and gluon scattering--jet production, which can only happen during early stage of the collision before formation of a quark gluon plasma, as calibrated probes of the produced matter. One, two and three particle observables have been used to extract propertiesof the matter including: information on plasma constitutents, it's responseto the propagation of fast quarks and gluons, and it's interaction with heavy charm and bottom quarks. Quantitative extraction of these effects is allowed by comparison of heavy ion results with p+p measurements of the same observables in the same detectors. I will present recent results from both heavy ion and p+p collisions and discuss their impact on our understanding of the hot deconfined matter and directions for future measurements.
"The Spin Structure of the Nucleon"
Dr. Carl Slifer, UVA Institute of Nuclear and Particle Physics.
March 26, 2008
S145 Kingsbury, Coffee: 3:40 PM,
Talk: 4:00-5:00 PM
Abstract
Much of our knowledge of the spin structure of the proton and neutron comes from polarized electron scattering. This experimental program has revealed that quarks, which are fundamental constituents of the nucleon, only carry a small fraction of its total spin. In recent years, we have developed a deeper understanding into how the nucleon spin arises from the intrinsic properties of the quarks and their orbital angular momentum, along with the role played by the 'glue' that holds the nucleon together. Insight into this topic has been gained by testing fundamental sum rule predictions. Some of these, such as the Bjorken sum rule, provide direct tests of Quantum Chromodynamics (QCD), while others such as the GDH, or the Burkhardt-Cottingham sum rule allow us to test some of the underlying assumptions inherent in QCD. In this talk, we'll give an overview of the experimental Spin Structure program with emphasis on recent results from Jefferson Laboratory and perspectives for future experiments
"Discovering neutrino properties: a low energy nuclear physics perspective"
Dr. Henninh Back, North Carolina State University
March 31, 2008
S145 Kingsbury, Coffee: 3:40 PM,
Talk: 4:00-5:00 PM
Abstract
It has been more than 75 years since the neutrino was first postulated and more than 50 years since it was first detected. In that time the neutrino has been reluctant to give up its secrets. Although large strides have been made in neutrino physics over the past decade, basic fundamental properties such as the value of the neutrino mass are still not known. The neutrino has also been useful as a messenger for other physics, such as confirming that solar energy production is a nuclear process. The low energy nuclear physics community has had a major role in pursuing neutrino properties and for using the neutrino as a tool for other physics. In this talk I will tell the story of the neutrino, what we currently know about them, and where the future may take us.
"RHIC discoveries; the perfect liquid and new phases of QCD matter"
Dr. Paul Sorensen, Brookhaven National Laboratory.
April 2, 2008
S145 Kingsbury, Coffee: 3:40 PM,
Talk: 4:00-5:00 PM
Abstract
Collisions at the relativistic heavy ion collider (RHIC) at Brookhaven National Laboratory lead to energy densities large enough to create new forms of matter with quark and gluon degrees of freedom. Data collected with RHIC detectors indicate that the geometry of the initial overlap region is reflected in correlations of the produced particles. The correlations can be explained by the expansion of a liquid like matter with nearly zero viscosity. In this talk, I'll discuss these conclusions and future efforts to map out other regions of the QCD phase diagram.
"The shape of the nucleon."
Dr. Nikos Sparveris, MIT
April 14, 2008
S145 Kingsbury, Coffee: 3:40 PM,
Talk: 4:00-5:00 PM
Abstract
Nucleon is the smallest stable building block in nature and thus its role in nuclear physics is fundamental. The exploration of the shape of the nucleon has been the subject of intense scientific activity in recent years. Revealing the shape of the nucleon will provide access to its structure and properties. Results from nuclear physics experiments held at the MIT Bates Linear Accelerator Center and at the MAMI Microtron indicate that the shape of the nucleon deviates from spherical symmetry and have provided access to the reaction mechanisms that lead to the deformation. The Bates and MAMI experimental programs, their results and the most recent theoretical developments will be presented. The plans for a new series of experiments that are scheduled to take place at the Thomas Jefferson National Accelerator Facility will also be discussed.
A short history of solar and celestial high-energy observations
Dr. Gerald Share of U. Maryland, Naval Research Lab.
May 4, 2007 4pm
TBA
Dr. Ted Einstein of Univ. of Maryland
April 30, 2007 4pm
(Host: Karsten Pohl)
The Neutron, the Big Bang, and the "Left-Handed" Universe.
Dr. Geoff Greene of U. of Tennessee, Oak Ridge Nat. Lab.
April 23, 2007 4pm
(Host: John Calarco)
Abstract
Measurements of the properties of the free neutron shed light on a number of interesting problems including Big Bang nucleosynthesis, the origin of parity violation, and the cosmic matter -antimatter asymmetry. Of particular interest are the measurement of parameters that describe the decay of the free neutron and the search for a possible neutron electric dipole moment. An overview of these issues will be given along with a discussion of the program of research planned at the newly operational Spallation Neutron Source at Oak Ridge National Laboratory.
Electrical manipulation of single spins in semiconductors
Dr. Jian-Ming Tang of Univ. of Iowa
April 16, 2007 1pm
(Host: Jim Connell )
Abstract
The ability to control and monitor single spins in a solid-state environment provides a new pathway to study the fundamental physics of magnetism in solids. In this talk I will present our studies of the spin-spin interactions between two magnetic atoms in a semiconductor. These interactions are unusual and long-ranged because they are mediated through the charge carriers loosely bound to the magnetic atoms. The highly extended carrier wavefunction is susceptible to external perturbation. I will describe our predictions that single spins associated with individual magnetic atoms can be controlled using electric or strain fields. From a technological point of view an all-electrical spin manipulation scheme is highly desirable for building high-density spin-based electronic devices or scalable quantum computers. I will discuss our joint efforts with experimental groups to probe the local electronic structure near a magnetic atom (Mn) substituted into a semiconductor (GaAs) using scanning tunneling microscopy. Our predictions of the strong spatial anisotropy of the charge carrier bound to the magnetic atom, and the anisotropic magnetic interaction between two magnetic atoms have been verified by these measurements. These results improve our understanding of ferromagnetism in semiconductors, and suggest new approaches for building atomic quantum spin systems in a solid.
Elusive Massless Particles and Condensed Matter Physics.
Dr. Ivan Sergienko of Oak Ridge National Lab.
April 12, 2007 1pm
Abstract
Magnetic reconnection is the process by which magnetic field flux in plasmas is annihilated and the released energy is converted to plasma kinetic energy. It is now recognized as a universal process that occurs in space plasmas around the Sun, the Earth, and magnetized astrophysical objects as well as within laboratory plasma confinement devices, such as future fusion reactors. Forty years ago, it was generally believed to be impossible; today, the observational evidence is overwhelming that it occurs universally. No one knows how it works, although there are lots of opinions. As the highest priority for heliophysical research for both the National Academy of Sciences and the NASA Science plan, NASA has undertaken the Magnetospheric MultiScale (MMS) mission to resolve the mysteries of reconnection. This talk will describe the dilemma of reconnection in space plasmas and how MMS is designed to answer them.
Who Needs Space Weather Forecasts?
Terry Onsager of NOAA, Space Environment Center
April 9, 2007 4pm
Abstract
Space weather disturbances occur due to a complex chain of interactions involving the sun, the solar wind, the magnetosphere, the ionosphere, and the upper atmosphere. This presentation will summarize the different aspects of space weather and the commercial and government activities that are affected, including impacts on commercial airline communication, GPS navigation accuracy, satellite failures, and electric power generation and transmission. An important challenge for solar-terrestrial physics research is to advance our understanding of the Sun-Earth system and to develop models that give timely and accurate predictions of space weather that result in benefits to society. For this to occur, the information provided by these models must be directly usable and must enable decisions to be made that have positive economic consequences. The current overlap between emerging scientific capabilities and space weather needs will also be discussed.
TBA
Dr. Predrag Nikolić of Harvard
February 28, 2008 4pm
Abstract
Charge Transport Characteristics
of Molecular Devices
Dr. Emil Prodan of Princeton, Center for Complex Materials
February 26, 2007 4pm
Abstract
Charge transport across molecules and nano-structures is a subject of great interest these days. Understanding, predicting and controlling this physical process can revolutionize the electronic devices. Charge transport, however, is one of the most challenging problems in physics since it involves out-of-equilibrium, open, interacting many- body systems. Better and better measurements of the transport characteristics and the gradual down-scaling of the devices to the molecular level, where the quantum effects are important and measurable, lead to re-consideration of several fundamental issues, like what is really measured and how to interpret such experiments? What is conductance and how can it be rigorously defined? Does the conductance depend on how electrons are injected in the device?
The current, most successful theoretical approaches involve Time Dependent Density Functional Theory (TDFT) at different levels of approximation. In the first part of my talk, I will discuss my efforts of going beyond TDFT and give a rigorous definition and formally exact expression of the two-terminal conductance based on the new and promising approach of Time Dependent Current-Density Functional Theory. This answers some of the above questions.
For long molecular chains, I was able to analytically manipulate the above formal expression to a point where one can explicitly see which properties of the chain and contacts directly influence the two- terminal conductance. For insulating chains, for example, I found the well known exponential decay behavior of the conductance with the chain's length, but, in addition, I obtained an explicit expression for the amplitudes of the exponentially decaying factors. These will be discussed in the second part of my talk, which will also include explicit numerical examples.
In the third part of the talk I will discuss how these new results enhance our understanding of several experiments, such as those on transport characteristics of alkyl chains self-assembled on silicon substrates (in both thermionic and tunneling regimes) or those on tunneling magneto-resistance.
Acknowledgments: This work is in collaboration with Prof. Roberto Car. Some of the analytical tools used in the project were derived during my previous postdoc with Prof. Walter Kohn. On the computational side, I am also strongly interacting with Prof. Leeor Kronik. On the experimental side, I am collaborating with Prof. Antoine Kahn and Prof. David Cahen.
Phase fluctuations and charge ordering in two-dimensional superfluids
Anton Burkov of Harvard, Condensed Matter Theory Group
February 19, 2007 4pm
Abstract
In this talk I will discuss the interplay between charge ordering and superfluidity in two-dimensional superfluids. Understanding the physics of two-dimensional superfluids and superconductors with low superfluid density is an important problem in modern condensed matter theory. This physics is at play in a wide variety of experimental systems: high-temperature superconductors, thin amorphous superconducting films, excitonic superfluids in quantum Hall bilayers, and many others. I will discuss a theory of charge ordering in two-dimensional superfluids, which is based on the idea that quantum mechanics of low-energy vortex excitations of the superfluid determines the "most natural" charge ordered states, proximate to it. I will discuss the situations in which this theory may be relevant and illustrate this with numerical simulations of specific models of charge ordering.
"Discovering the nanoworld", NOTE: Colloquium is on Thursday 1pm.
Francesca Baletto of DMSE-MIT
February 15, 2007 4pm>
Abstract
The emergence and spectacularly rapid evolution of the field of atomic and molecular nanoparticles are among the most exciting developments in the recent history of materials science. The pursuit of nanoscience and nanotechnology is to understand, control, and manipulate ob jects of a few nanometer size (say 1-100 nm). The structure is one of the most fundamental properties of a cluster and plays an important role to understand all aspects of its chemical and physical behavior. Here, I present an overview of the structural properties of nanoclusters, with the aim of defining 'magicity' in the nanoworld, showing the interplay of energetic, thermodynamic and kinetic factors in building up the structures. Several examples have shown that this interplay is crucial, and that a satisfactory explanation of the experimental outcomes is very often impossible on the basis of energetic considerations alone. This can have deep consequences on the very important issue of controlling the shapes of the produced nanoclusters, which is of relevant technological importance.
Orbital magnetization in periodic solids
Timo Thonhauser of MIT, Physics
February 12, 2007 4pm
Abstract
A complete description of magnetism in solids requires not only the spin degrees of freedom, but also the ''orbital magnetization.'' Despite the recent surge of interest in magnetic materials, it is quite surprising that the theory of orbital magnetization has remained in a condition similar to that of the polarization before the early 1990s, when the problem of computing finite polarization changes was solved [R.D. King-Smith and D. Vanderbilt, Phys. Rev. B 47, 1651 (1993)]. The essential difficulty, that the matrix elements of the position operator "r" are not well-defined in the Bloch representation, could be overcome by reformulating the problem in the Wannier representation. In order to derive an analogous theory for the orbital magnetization, we again work in the Wannier representation and assume a periodic insulator with broken time-reversal symmetry and vanishing magnetic field. We show that a naive replacement of the dipole operator "r" by the circulation operator "r x v" in the expectation value of a bulk Wannier function gives only one contribution to the magnetization, i.e., the magnetization associated with the internal circulation of bulk-like Wannier functions. The missing contribution arises from net currents carried by the Wannier functions at the boundary of the sample. We prove that both contributions can be expressed as bulk properties in terms of Bloch functions in a gauge-invariant way [T. Thonhauser, Davide Ceresoli, David Vanderbilt, and R. Resta, Phys. Rev. Lett. 95, 137205 (2005)].
James Drake of University of Maryland
2006-12-04
(Host: Amitava Bhattacharjee )
Magnetic Fields at the Large Cosmic Scales
Steven Cowley of UCLA
2006-11-27
Magnetic Reconnection and the Magnetospheric MultiScale Mission
Roy Torbert
2006-11-20
Abstract:
Magnetic reconnection is the process by which magnetic field flux in plasmas is annihilated and the released energy is converted to plasma kinetic energy. It is now recognized as a universal process that occurs in space plasmas around the Sun, the Earth, and magnetized astrophysical objects as well as within laboratory plasma confinement devices, such as future fusion reactors. Forty years ago, it was generally believed to be impossible; today, the observational evidence is overwhelming that it occurs universally. No one knows how it works, although there are lots of opinions. As the highest priority for heliophysical research for both the National Academy of Sciences and the NASA Science plan, NASA has undertaken the Magnetospheric MultiScale (MMS) mission to resolve the mysteries of reconnection. This talk will describe the dilemma of reconnection in space plasmas and how MMS is designed to answer them.
Hyperpolarized Xenon and Functional Lung Imaging
Bill Hersman of UNH
2006-11-13
Jeff Yepez
2006-11-06
Recent Results from the Spitzer Sapce Telescope: A New View of the Infrared Universe
Giovanni Fazio of Harvard
2006-10-23
(Host: Edward Chupp )
Scott Thomas of Rutgers
2006-10-16
(Host: Per Berglund )
Problem Solving and the Use of Math in Physics Courses
Joe Redish of UMD
2006-10-02
(Host: Dawn Meredith )
Abstract:
Mathematics is an essential element of physics problem solving, but as professionals, we often fail to appreciate exactly what we are doing with it. Math may be the language of science, but math-in-physics is a distinct dialect of that language that requires both more subtlety and more skills than are typically taught in math courses. Research with students in classes ranging from algebra-based physics to graduate quantum mechanics indicates that (1) we sometimes don't appreciate the skills students need to solve the problems we assign, and (2) students' problems are sometimes with their expectations about what they are supposed to be doing rather than with their math skills. Implications for instruction will be discussed.
The Earth's Plasma Sheet
Dick Kaufmann
2006-09-25
Viscous Energy Dissipation by Flux Pile-Up Merging in the Solar Corona
Yuri Litvinenko of UNH
2006-09-18
Abstract:
Magnetic field annihilation in resistive viscous incompressible plasmas is analyzed. Anisotropic viscous transport is modeled by the dominant terms in the Braginskii viscous stress tensor. An analytical solution for steady-state magnetic merging, driven by vortical plasma flows in two dimensions, is derived. Resistive and viscous energy dissipation rates are calculated. It is shown that, except in the limiting case of zero vorticity, viscous heating can significantly exceed Joule heating at the merging site. The results strongly suggest that viscous dissipation can provide a significant fraction of the total energy release in solar flares, which may have far-reaching implications for flare models.
Recent Developments in Astronomical Gamma-Ray Polarimetry
Mark McConnell
2006-09-11
Nathaniel Fisch of Princeton
to be determined
(Host: Amitava Bhattacharjee )
The Future of Gravity
James Hartle of University of California, Santa Barbara
2006-05-08
(Host: Per Berglund )
Abstract:
Of the four fundamental forces, gravity has been studied the longest, yet gravitational physics is one of the most rapidly developing areas of science today. This talk will give a broad brush survey of the past achievements and future prospects of general relativistic gravitational physics. Gravity is a two frontier science being important on both the very largest and smallest length scales considered in contemporary physics. Recent advances and future prospects will be surveyed in precision tests of general relativity, gravitational waves, black holes, and cosmology. The aim will be an overview of a subject that is becoming increasingly integrated with experiment and other branches of physics.
The strong nuclear force on a space-time lattice
Silas Beane of UNH
2006-04-24
Abstract:
I will discuss recent work which uses large computers in conjunction with effective quantum field theories to compute properties of hadrons (like the proton) and simple nuclear systems (like the deuteron) directly from Quantum Chromo-dynamics (QCD), the underlying theory of the strong nuclear force.
Ultra-sensitive Atomic Magnetometers
Michael Romalis of Princeton
2006-04-17
(Host: Bill Hersman )
Abstract:
IElectron spins in alkali-metal atoms can be easily polarized with lasers and caused to precess around a magnetic field. The frequency of their precession is directly proportional to the strength of the magnetic field and can be used for accurate magnetometery. With recently developed techniques for suppressing various sources of spin relaxation such atomic magnetometers have reached unprecedented sensitivity, surpassing even SQUID magnetometers operating in liquid helium. I will discuss the physics of atomic magnetic field sensors and several applications explored in our group, including detection of nuclear magnetic resonance and magnetic fields generated by the brain. In other applications of atomic magnetometers it is often desirable to cancel magnetic field noise while retaining sensitivity to other sources of spin precession. For such applications we developed a co-magnetometer consisting of noble gas and alkali-metal spins occupying the same volume. Using spin-exchange interaction between the two spin ensembles one can arrange for an effective cancellation of magnetic field drifts. Such co-magnetometer can serve as a sensitive gyroscope, measuring spin precession due to microradian level rotation of the apparatus. The co-magnetometer is also utilized for tests of fundamental symmetries, in particular, search for a violation of Local Lorentz invariance manifested by spin coupling to a background field, as recently predicted in some theories of quantum gravity.
Dynamics and Excitations in Time-Dependent Density Functional Theory: Successes and Challenges
Neepa Maitra of Hunter College
2006-04-10
(Host: James Harper )
Abstract:
Density functional theory (DFT) is recognized as a powerful alternative to traditional wavefunction methods for studying the properties of atoms, molecules, clusters, solids, and biomolecules. Its extension to electron dynamics in time-dependent fields (TDDFT) has become increasingly popular for calculating excitation spectra, frequency-dependent (hyper)polarizabilities, magneto-optical response, van der Waals coefficients, and, most recently, molecular electronics. The promise to describe electron correlation in strong-field phenomena, including high-harmonic generation, above-threshold ionization, and electronic quantum control theory, is only beginning to be tapped; the non-perturbative regime is where TDDFT is the only feasible scheme, as wavefunction methods for even a few electrons are prohibitively expensive. Although in principle exact, the functionals of TDDFT must in practice be approximated. There is intense activity concerning functional development, and when and why the usual approximations fail. In this talk, I begin with an introduction to DFT and TDDFT, and then present current challenges for the theory, with some partial solutions: including quantum control, double excitations and long-range charge transfer.
Professor Maitra's background:
BSc (Hons) from University of Otago in New Zealand, 1993. Came to Harvard University for PhD (with Frank Knox fellowship). Studied semiclassical methods and quantum chaos under Rick Heller there, with my thesis title "Topics in Semiclassics: Non-Classical Phenomena in Integrable and Non-Integrable Systems". Graduated in 1998. Postdoc'ed in Bill Miller's chemical physics group at Berkeley for a year before joining Kieron Burke's density functional theory group at Rutgers as a postdoc. Joined Hunter CUNY as assistant professor in January 2004, where I conduct research in time-dependent density functional theory for excitations and dynamics of atoms, molecules, and systems of chemical interest. External Grants: ACS PRF (2004-2006), NSF Career (2006-2011).
Probing Fundamental Physics with Ultracold Neutrons: Following the Bouncing Ball
Albert R. Young of NCSU
2006-04-03
(Host: Bill Hersman )
Abstract:
Ultracold neutrons (UCN) are neutrons with energies below about 400 neV that can be stored in material bottles for hundreds of seconds and poured or guided into a variety of experiments. The goal of the UCNA experiment is to improve our knowledge of the angular correlation between the emitted electron and the initial spin of the neutron in beta-decay (the beta-asymmetry) using ultracold neutrons. The precision of this correlation defines the current limits to which fundamental electroweak data can be extracted from neutron decay and also the limits which can be placed on new physics from neutron decay. In the process of developing their experimental approach, the UCNA collaboration developed the first functioning solid deuterium superthermal source of UCN coupled to a spallation target, initiated a unique program to develop new technnology to transport UCN and to understand the systematics of UCN depolarization, initiated the first detailed studies of the backscattering of electrons in the energy range of beta-decay, and developed new technology for low energy proton detection. The experiment is now fully constructed and is in the process of commissioning. The motivation and status of this experiment will be reviewed, and recent results of its research and development program presented.
The properties of matter a micro-second after the Big Bang: RHIC tells all
< Raju Venugopalan of Brookhaven
2006-03-27
(Host: Silas Beane )
Abstract:
Ultrarelativistic nuclear collisions at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory create the hottest and densest matter on earth - comparable to those existing 0.000001 seconds after the Big Bang. We review the remarkable and unexpected results from RHIC and what they may tell us about the properties of this matter.
Helium Isotopes in the Solar wind and in the Interstellar Gas
Constraints for Solar and Galactic Evolution Models
Peter Bochsler
2006-02-20
(Host: Eberhard Möbius )
Abstract:
With the foil experiments, which were deployed on the Moon during the Apollo missions, and with several in-situ experiments we have been measuring the helium isotopic composition of the solar wind. More recently, we have also been able to successfully use the foil collection technique onboard the Mir space station to measure the isotopic composition of helium in the local interstellar medium (ISM). 4He in the Sun and in the ISM is mostly a remnant from the cosmological big bang, and some 4He has also been recycled into the ISM from stars during galactic evolution. 3He originates partly from cosmological D and 3He. Furthermore, it is built up in low-mass stars (such as the Sun) at the fringes of their nuclear burning zones. The solar wind helium isotopic composition can be used to infer the isotopic composition of the outer convective zone of the Sun. The low solar 3He abundance proves that the Sun never was never mixed after ignition of nuclear reactions, and it can also be used as a reference for the local galactic composition at the time of the formation of the solar system, 4.6 Gy ago. The composition of the contemporary ISM indicates, whether low-mass stars have altered the interstellar gas during the last 4.6 Gy of galactic evolution. I will present our results in the context of recent galactic models.
John Dorelli of UNH, EOS Space Science Center
2006-01-30
(Host: Bill Hersman )