Physics Department Colloquium Schedule
From PhysicsWiki
Refreshments at 3:30pm and lecture at 4:00pm in Meyer Hall Room 220 Meyer Hall is at the northeast corner of 16th and Illinois Streets in Golden. For more information, call (303)273-3830
Tuesday, September 1, 2009
Timothy Sweitzer
Assistant Director, Environmental Health and Safety, CSM
“EHS Safety & Waste Generator Training”
Abstract: MANDATORY safety training for faculty, staff, postdocs, continuing grad students, and undergraduates working in laboratories. NOTE: This is refresher training only - new students must take the full training.
Tuesday, September 8, 2009
Petra Heuntemeyer
Michigan Technical University
“TeV Gamma Rays, the Origin of Cosmic Rays, and the HAWC Experiment”
Abstract: Many theorists think that TeV gamma rays are the best candidates to probe the sites of highest energy particle production and acceleration, and that studying them will bring us closer to the answer of the 100 year old question of the origin of cosmic rays. In particular, TeV gamma rays traveling to us – undeflected by Galactic magnetic fields - from locations of the most extreme astrophysical objects, such as for example supernova remnant shocks, are believed to be produced by cosmic rays accelerated in these sources. Many aspects of the production and acceleration processes are still unclear. Discovering and collecting as much information as possible about TeV gamma-ray objects and finding general classes of TeV sources will help us understand cosmic particle acceleration and production mechanism better. The Milagro observatory, a pioneering water Cherenkov detector near Los Alamos, has demonstrated that a detector with a wide field of view (2sr) and nearly 100% duty cycle can discover new sources of TeV gamma rays and that it can map the diffuse gamma-ray emission from our Galaxy. However, e.g. in the case of diffuse gamma-ray emission there is a significant discrepancy between data and model predictions based on cosmic-ray measurements at Earth and simulations of cosmic-ray propagation in space. An experiment that will help to resolve inconsistencies in our understanding of the Universe such as the one above will be the High Altitude Water Cherenkov (HAWC) detector, which is being built on the Sierra Negra plateau in Mexico. In my talk I will give an overview of the physics motivation for building the HAWC observatory, showcase some of the most important discoveries of its predecessor Milagro, and describe the new water Cherenkov detector design of HAWC.
Tuesday, September 15, 2009
Alan Bristow
JILA, University of Colorado & National Institute of Standards and Technology/ Adjunct Instructor Colorado School of Mines
“THE JILA-MONSTR : shedding a new light on ultrafast phenomena in semiconductors”
Abstract: Coherent light-matter interactions in semiconductors are essential to future communications and optoelectronics technologies. Semiconductors and their nanostructures provide a link between light and electrons. They are also a good test bed for fundamental research into quantum electronic and many-body physics. Coherent spectroscopy is a vital tool for unraveling complex light-matter interactions. Known quantum electronic interactions can then be coherently controlled with a tailored light-field. Two-dimensional Fourier-transform spectroscopy is used to find the "interaction fingerprint" of excitons and biexcitons in low-temperature GaAs quantum wells. Two-dimensional spectroscopy unambiguously separates and isolates the various contributions of the coherent response. Phase-resolved spectra provide critical information resolving issues that have hitherto been hard to determine using other spectroscopic techniques.
Tuesday, September 22, 2009
Dinesh Loomba
University of New Mexico
“Shedding Light on Dark Matter”
Abstract: We are now in the era of precision cosmology, where we know the age of the Universe, the geometry of space, the total energy density and what types of energy and matter contribute to it. Measurements suggest that ordinary matter, composed of protons and neutrons, is a mere 15% of the gravitational mass in the Universe. The rest is dark, and so far we infer its existence only gravitationally. The goal of detecting and identifying dark matter is arguably the most important problem in 21st century cosmology.
We will review some of the observational evidence and theoretical motivations for dark matter. Finally, we will describe an experimental effort underway at UNM and its collaborating institutions, which has the unique ability to detect one of the most important signatures necessary for the discovery of dark matter.
Tuesday, September 29, 2009
Segev BenZvi
University of Wisconsin
“The Search for Astrophysical Neutrinos with the IceCube Experiment”
Abstract: The IceCube Neutrino Observatory, currently under construction at the South Pole, is designed to detect high-energy neutrinos from astrophysical sources. When it is fully deployed in 2011, the detector will comprise 4800 optical modules embedded inside a cubic kilometer of clear ice, located one mile below the surface of the Antarctic ice sheet. By recording particles from air showers and from neutrino interactions inside the ice, the detector is sensitive to charged cosmic rays and neutrinos with energies between 100 GeV and 100 PeV. This energy range includes the neutrinos we expect to see from extragalactic particle accelerators such as Gamma Ray Bursts and Active Galactic Nuclei. In this talk, we will describe the configuration, deployment status, and sensitivity of the IceCube detector. We will also review preliminary results from IceCube, including a search for neutrino point sources, a measurement of the energy spectrum of atmospheric neutrinos, and a surprising (and unexplained) observation of a large-scale anisotropy in TeV cosmic rays.
Tuesday, October 6, 2009
Jack Surek
National Institute of Standards and Technology, Boulder, CO
“Electron Paramagnetic Resonance to Measure Electrostatic Potential at Probes in Solution”
Abstract: Paramagnetic metal complexes were selected as relaxation agents fornitroxide spin probes, these probes being organic ring moleculessynthesized to sterically protect an unpaired electron spin. This stable unpaired organic electron has a spin-lattice relaxation time around 1 microsecond and is the basis for probing local molecular environments(distance, orientation, motion and in this case accessibility) in most biochemical electron paramagnetic resonance (EPR) spectroscopy experiments. I will present the considerations for metal complex selection, calibration of a set of complexes that carry different charge states and spectroscopic measurement when probe and agent are combined in solution. The method can achieve 1 mV accuracy and is based on Heisenberg spin exchange, where the EPR excited spin state on the unpaired organic electron transfers to the unpaired electron on the metal complex upon collision. Based on this underlying physics, the electrostatic potential at the spin probe nitroxyl oxygen surface causes a measurable change in half saturation power for sets of progressive saturation (applying successively higher applied microwave fields in the sample) spectra acquired with relaxation agents carrying different charge states. These half-saturation powers can be combined to form a Nernst potential measurement. The motivation for this work has been to detect long distance (several nanometer) electrostatic energy transmission through critical pathways in the myosin crossbridge, a motor protein that undergoes a reversible conformational as a result of adenosine triphosphate (ATP) hydrolysis during muscle contraction. Spectral saturation is measured differently between freely tumbling spin probes and those that are reacted to larger molecules such as myosin and I will describe these extremes using the Bloch equation for magnetic resonance absorption. Measurements with a probe reacted to the Cys707 location on the rabbit skeletal myosin cross bridge indicate a cyclic change in electrostatic potential as evidence of electrostatic energy transmission along the peptide backbone of the underlying SH1 helix. This and the adjacent relay helix are pathways already identified from snapshots of hydrolysis structures, mutational studies and mechanical modeling as critical to ATP hydrolysis energy transmission to the myosin lever arm. A reversible conformational change at the lever arm is established as the essential conformational change that causes muscle contraction.
Tuesday, October 13, 2009
Steve Jefferts
NIST- Time and Frequency Division
"Atomic Clocks and the Limits of Accuracy"
Abstract: In the SI system of units a second is defined as 9,192,631,770 cycles (exactly) of the ground state hyperfine transition frequency of an unperturbed cesium atom at rest on the reference geoid of the earth. Primary frequency standards ( a particular breed of atomic clock) such as NIST-F1 in Boulder attempt to realize this definition with the highest possible fidelity. Atomic clocks have progressed steadily from fractional inaccuracies of
fifty years ago to the best microwave clocks (NIST-F1) giving inaccuracies at the
level, with optical clocks promising even more phenomenal performance at the 10 − 17 level and beyond. This level of performance requires an excruciating attention to detail when attempting to correct for frequency biases. For example, an uncertainty of 1 meter in the altitude of the device with respect to a fictitious reference geoid (about mean sea level) causes a frequency uncertainty of more than
while an uncertainty in the temperature of the radiation field to which the atom is exposed of 1K yields frequency shifts of several times this much. In this talk we will discuss some history of these devices, the current state of the art in laser-cooled microwave clocks and some fundamental limits to their attainable accuracy (we are almost there!) We will briefly examine some of the current uses of this level of accuracy Finally we examine the new optical clocks, which share many features with the current best microwave atomic clocks but with the promise of much higher accuracy.
Tuesday, October 27, 2009
Silke Ospelkaus
JILA, University of Colorado
“Ultracold Polar Molecules”
Abstract: Polar molecules - molecules exhibiting a permanent electric dipole moment - have bright perspectives as systems with long-range and anisotropic interaction. These interactions have been the basis for numerous exciting theoretical proposals ranging from ultra-cold chemistry, precision measurements and quantum phase transitions to novel systems for quantum control with external magnetic and electric fields. I will present our recent work on the creation and characterization of a near-quantum degenerate gas of absolute ground-state polar 40K87Rb molecules.
Tuesday, November 3, 2009
Edward Hartouni
Lawrence Livermore National Laboratory
“Particle Physics and Nuclear Physics Applied to Homeland Security Challenges”
Abstract: During the last decade the need to resolve a number of longstanding challenges to homeland security have become a high priority for the national and international scene. A number of R&D institutions have been addressing these challenges using the intellectual resources from a number of basic science fields. I will describe some of the challenges to national security and describe proposed solutions which are innovative applications from the fields of particle and nuclear physics being pursued by LLNL and collaborators.
Tuesday, November 10, 2009
Alice Bean
University of Kansas
“Particle Physics at the Large Hadron Collider”
Abstract: The CMS detector is one of two large all purpose detectors which will record collisions at the Large Hadron Collider starting in the Fall of 2009. The collider will provide at least a factor of three in the energy available for collisions which will allow scientists to search for new kinds of matter. The talk will describe the physics goals and context as well as the status of the collider and experiments.
Tuesday, November 17, 2009
Richard Mu
Fisk University
“Nanostructures for Enhanced Photon Energy Conversion and Nano-PV Program at Fisk University”
Abstract: This presentation begins with the discussion of the challenges and limitations of materials for all polymer-based PV devices. The power conversion efficiency around 5% can be routinely realized but no further significant improvement and breakthrough has been made over the past years. Most limiting factors include low photocurrent due to high recombination rates and low carrier mobilities, low optical absorption cross section, and narrow photon absorption spectral region. There have been no effective ways to address these critical issues from all polymer materials alone. In this research, a device structure with an active layer consisting of ZnO nanowire (NWs), quantum dots (QDs), and semiconducting polymers is employed. In order to demonstrate the potential impact of the device, efforts have been made in several fronts: 1) growth of vertically-oriented ZnO NWs on conducting ITO electrodes; 2) investigation of pulsed electron-beam deposition (PED) as a practical and effective technique to produce QDs and to functionalize ZnO NWs; 3) comparative studies of new hybrid nanocomposite device structures with all polymeric devices. In addition, a recent work in the area of surface plasmon – exciton and doped rare earth ions interactions will be presented. The major goal of this effort is to understand the physics of energy conversion and transfer as well as their enhancement effects through characterization of the kinetics and dynamics of interactions between single-particle excitations in a wide bandgap semiconductor (ZnO), or doped rare earth ions in glasses and a collective excitation (plasmon) in a metal at nanometer length scales and on various relaxation time scales. The presentation will be concluded with a brief introduction about Fisk University, Physics Department and Nano-PV program.
Tuesday, November 24, 2009
Cheng Chin
James Franck Institute and Department of Physics, the University of Chicago
“Having your cake and seeing it too-In Situ Observation of Mott Insulating Domains of Ultracold Atoms in Optical Lattices”
Abstract: The observation of the superfluid to Mott insulator phase transition of ultracold atoms in optical lattices provides the first tangible example of a quantum phase transition (one that occurs even at zero temperature) in an ultracold atomic gas. In this talk I will report spatially resolved, in-situ imaging of a two-dimensional ultracold atomic gas as it crosses the superfluid to Mott insulator transition, providing direct access to individual characteristics of the insulating, superfluid, and normal phases. We present results for the local compressibility in all phases, observing a strong suppression in the insulator domain and suppressed density fluctuations for the Mott insulator, in accordance with the fluctuation–dissipation theorem. These methods enable a complete characterization of multiple phases in a strongly correlated Bose gas, and of the interplay between quantum dynamics and fluctuations in the quantum critical regime.
Tuesday, December 1, 2009
Ed Cecil
Department of Physics, Colorado School of Mines
"Development of a Lost Alpha Particle Detector for High-Yield d-t Tokamak Fusion Plasmas"
Abstract: For a number of years we have been working on a new concept in charge particle spectrometry which will operate in very harsh radiation environments. One application of this concept is to measure lost or unconfined alpha particles from the d-t reaction which is the fundamental energy producing reaction in the first generation fusion reactors, both magnetically or inertially confined. This confinement is crucial to an ignited fusion plasma. Prototypes of this detector concept have operated on the Tokamak Fusion Test Reactor (TFTR) at the Princeton Plasma Physics Lab, the Joint European Torus(JET) at Culham Laboratories near Oxford, U.K. and are under consideration as a lost alpha diagnostic for the International Tokamak Experimental Reactor(ITER)at Cadarache Laboratory in France. Recent significant progress in understanding the sensitivity of the concept using the device currently installed at JET will be discussed.
Tuesday, December 8, 2009
Graduate Students
Colorado School of Mines, Department of Physics
Abstract: This is an opportunity to learn about some of the research projects of graduate students in the physics program. The students will give a ten-minute, APS-style presentation on their thesis research.
Refreshments at 3:30pm and lecture at 4:00pm in Meyer Hall Room 220 Meyer Hall is at the northeast corner of 16th and Illinois Streets in Golden. For more information, call (303)273-3830
