Xe| Graduate Student Seminar Series, 2003-2004 |
XeNuclear Magnetic Resonance (NMR) normally requires relatively large samples for adequate signal-to-noise. NMR spectroscopists often go to great lengths to achieve signal enhancements of only. However, sensitivity can be greatly improved in some materials by transferring nuclear polarization from hyperpolarized
C by Hartmann-Hahn polarization transfer and low-field thermal mixing.
Aircraft manufacturing companies are increasingly using composite materials in the construction of airplanes and helicopters. Carbon fiber/epoxy mixes are light and strong. Boeing uses these materials in helicopter rotor blades, parts for the Harrier fighter jet and 777 passenger jet, and other applications. Boeing contracted with our research group to determine if NMR could be used to detect unwanted water that had leeched into rotor blades, and to detect thermal damage in airplane materials. Boeing also loaned us their one-sided NMR rig (a "Bruker Minispec Mouse") to do some of these experiments. I will give a brief NMR overview, and discuss our experiments and results. I will also mention some interesting aspects of doing physics for industrial applications instead of pure research.
We adapted and used for different purposes, in an electricity and magnetism course for K-8 school teachers in fall 2003, three research-based tests. The course is designed to accomplish conceptual change toward accepted scientific conceptions. Our results support that using the research-based tests to identify alternative conceptions is a promising way to use the knowledge of alternative conceptions in professional development. Comparing the teachers' conceptions to accepted scientific conceptions in discussions of test results with teachers encourages them to try to understand the scientific conceptions and to make them their own.
Heart architecture is very complex. The predominant myocardial fiber orientation changes by about 120 degrees from the outer (epicardial) to the inner (endocardial) wall. Ultrasonic properties, such as velocity, attenuation and back scatter coefficients, are anisotropic (and therefore are different when insonifying along compared to across fibers, for example). Currently our lab (the Laboratory For Ultrasonics) performs measurements of those properties on "fresh" (as opposed to formalin preserved) lamb and cow hearts. The Kramer-Kronig relationships adapted for ultrasound represent a link between velocity and attenuation. While both quantities are of physical interest, in certain situations, one might be more readily measurable than another. I am going to talk about phase spectroscopy in ultrasound and show results of phase velocity measurements compared with Kramer-Kronig predictions based on measurements of attenuation. I will also identify problems in the determination of phase difference and show how to eliminate phase sheet ambiguity using the Kramer-Kronig relationships adapted for ultrasound.
Of the 52 elemental solids known to be superconducting, 23 enter this state only if compressed to sufficiently high pressures. The latest confirmed member of this group is the alkali metal Lithium. Recently our group measured the dependence of the superconducting transition temperature (Tc) on nearly hydrostatic pressure to 670,000 atm. We also measured Tc as a function of applied dc magnetic field. In this talk I will explain why superconductivity in Lithium represents 'new physics'. I will provide an overview of the diamond anvil cell (DAC) technology that we use to obtain extremely high static pressures and I will present the results of our experiments on Lithium to date. Finally I will discuss the experiments that I am currently performing as well as future prospects for this line of research.
There is lots of observational evidence that the radio emissions from the jets of Active Galactic Nuclei(AGN) is of synchrotron origin. A number of radio jets have been observed in the optical and X-Ray regimes. For many of those sources, it is possible to extrapolate the power law derived from the synchrotron radiation model to account for the optical and even X-Ray emission. However, this simple extrapolation does not explain the X-Ray emission of some jets, such as 3C 273. In this talk, A new jet toy model will be introduced to explain the radiations of many radio jets. We used 3C 273's jet data to try out the toy model, because the source has been observed exhaustively and detailed radio, optical and X-Ray data are available.
This is an ongoing project with Prof. Henric at WUSTL and D.E. Harris at Smithsonian Astrophysical Observatory.
Humans and other animals generally perceive motion independently of the cues that define the moving object. To understand the underlying mechanisms of this generalization of stimulus attributes, we have examined the cellular properties of avian wide-field tectal neurons that are sensitive to a variety of moving stimuli but not to static stationary stimuli. This in vitro study showed phasic signal transfer at the retinotectal synapse and binary dendritic responses to synaptic inputs that interact in a mutually exclusive manner in the postsynaptic tectal neuron. A model of the tectal circuitry predicts that these two cellular properties mediate sensitivity to a wide range of dynamic spatiotemporal stimuli, including moving stimuli, but not to static stationary stimuli in a tectal neuron. The computation that is independent of stimulus detail is initiated by tectal neurons and is completed by rotundal neurons that integrate outputs from multiple tectal neurons in a directionally selective manner.
Cardiologists need some way of looking at the heart and trying to decide how healthy it is. Doctors do a reasonable job trying to differentiate pathology, but they rarely have the physical basis for any of their work. Physicists can fill in this gaping hole. I'll try to describe what its like working at *gasp!* the medical campus, and hopefully give you a feel of how we use the ideas we learn in physics, and how they can be applied to the heart. A quiz may be given in the talk, and of course I will demand absolute attention and that you retain everything I say so I don't ever have to repeat any information in a future grad seminar. ...or at least that you enjoy your snacks and beverages.
While lacking the long-range translationally periodic order of a crystalline solids, liquids contain a significant amount of short-range order (SRO), which discriminates from crystals and gases. Unlike crystals, however, no method exists to directly observe local structure (short range order) of liquid. To understand the local structure of liquid is important to determine its chemical and physical properties. One of remarkable phenomena of liquid is undercooling, that is, liquid can be retained below its melting temperature for a long time without crystallization. The short range order of liquid is related to undercooling phenomenon. Frank in 1952 hypothesized icosahedral short-range order for the local structure of liquid metals. However, there is no direct evidence to support the hypothesis. Recently our group proved the hypothesis over 50 years unsolved problem, by new technique, combination of electrostatic levitation and high-energy synchrotron x-ray. In this talk, I will introduce concepts of nucleation, undercooling and local structure of liquid, and show results of undercooling experiment and synchrotron x-ray scattering experiment giving relation of local structure of liquid and nucleation barrier (undercooling phenomena).
The study of the physics of ultrasound in materials which are inherently anisotropic is a primary area of interest in the Laboratory for Ultrasonics. The heart has always been an interesting medium forthe study of anisotropy because of its special fiber structure. This lab has a substantial investment in the study of anisotropy in the heart. In this talk, I will start with an introduction to our lab and the ultrasonic measurement techniques used in our lab. Then I will share with you the work I am doing now on the heart. Also I will show you some results of this study on the anisotropy of the attenuation and the anisotropy of the velocity.
Quantum Chromodynamics (QCD) is the presently accepted theory of the strong interactions. When describing processes at low energies, however, perturbation theory is not applicable, as the effective coupling constant becomes far too large. With the help of Buffy Summers, I will discuss putting QCD on a discrete spacetime lattice, focusing on the various difficulties when discretizing a Quantum Field Theory as well as technical limitations when performing calculations. I will finish up by showing some current results for various projects that show both the usefulness and the success of Lattice QCD.
I will give an overview of the post-Newtonain approximation using a method that was developed by our group known as the direct integration of the relaxed Einstein equations (DIRE). Using DIRE I will go into some detail of the 3PN equations of motion, which I am currently working on, specifically why completing the calculation via DIRE is important even though it has been done by other groups using other methods.
The Trans-Iron Galactic Element Recorder has recently finished another successful long-duration balloon campaign from McMurdo Station, Antarctica. How the TIGER instrument works will be described and fantastic pictures of the campaign will be shown. There will also be a bit on life in Antarctica. This presentation will be shown in flashy PowerPoint™, Office XP™.
A novel in-situ method to fabricate lateral patterns in thin films is presented. Using various physical vapor deposition (PVD) techniques, numerous materials, such as Ag, Co and TiOx were deposited onto Si single crystal substrates. Simultaneous with deposition, the substrate was irradiated with a two-beam laser interference intensity distribution. This high power laser interference creates temperature gradient from the constructive zones to destructive zones. This temperature gradient results in the anisotropic diffusion of materials, as a result of which the topology of the thin films is modified. We find that the resulting thin film topology under irradiation mimics the fringe pattern, i.e. the film has a periodic thickness modulation. In comparison, films deposited without the interference follow the typical random cluster distribution. This simple in-situ lateral thickness modulation process is promising as an economical and simple nanostructured film fabrication technique.
Some of the most interesting topics in modern astronomy involve objects of incredible mass and energy. To study such phenomena requires the use of Einstein's Theory of General Relativity. Unfortunately, the equations of GR are so complex and non-linear that we can derive full solutions for only the simplest of examples. For some problems we can use the analytic techniques of Post-Newtonian Approximation, but for the rest we must rely on computational models of Einstein's equations. In particular, investigations on the collisions of black holes and neutron stars, and the gravitational wave emitted will aid us in understanding results from LIGO and observations in X-ray and Gamma-ray astronomy. This talk will provide a (very) brief background in General Relativity, with specifics on the formation of Neutron Star, Black Holes and Gravitational Waves. Then I will discuss the development of CACTUS, a collaborative software development of computation general relativistic astrophysics, and the on-going work to develop a more efficient code with Adaptive Mesh Refinement.
I'll discuss the theory and practice of Chemical Vapor Deposition (CVD) asit applies to the manufacture of Hydrogenated Amorphous Silicon (a-Si:H). Amorphous Silicon has applications in photovoltaics, detectors, and thin-film transistors.
My recent analysis of observations of the Galactic Center with the Whipple Gamma Ray Observatory seems to indicate some TeV emission from that region. If real, such emission could be an indication that our galaxy has more in common with Active Galactic Nuclei (AGNs) than previously expected. Alternately, the emission could be caused by more exotic sources such as the annihilation of weakly-interacting Dark Matter particles. In this talk, I will present an overview of TeV gamma-ray emission mechanisms, present the latest data, and discuss the steps we are taking to understand what is happening at the center of our own galaxy.
Quantizing the familiar non-relativistic Schroedinger field of a single particle moving in a binding potential bridges the conceptual gaps between non-relativistic quantum mechanics and quantum field theory. This approach not only illuminates the physical interpretation of field quantization without the complications introduced by incorporating special relativity, but also suggests the axioms of field quantization in a natural, elegant way.
Beginning with a review of time evolution in the Heisenberg picture and a recollection of the relevant results from classical field theory, we will inquire of the physical content of some pedagogically popular quantum field theories. We will then show how the equivalence of the quantized Schroedinger theory with the classical field theory of the many-particle Schroedinger equation facilitates the interpretation of quantum field theory. If time permits, we will explicitly indicate how field eigenstates furnish the connection between canonical and functional integral quantization.
There are 1,000,000 Americans that have been diagnosed with congestive heart failure (CHF). Among these patients, more than 50% have normal systolic function (ejection fraction (EF) > 50%). This is especially evident in elderly individuals. These Patients are categorized as diastolic heart failure (DHF). Research has shown that DHF will ultimately lead to systolic heart failure. However, there is continued controversy surrounding the definition of diastolic dysfunction and the diagnostic criteria for DHF. As a result, clinical therapeutic trials have been slow to develop and difficult to design. This talk will deal with how the heart works, more specifically systolic and diastolic function. Moreover, I will discuss my research project on interpreting diastolic function from a mechanical point of view, and the resultant frequency-based analysis on diastolic function.
My detectors are cheaper and they are just as good as the more expensive kind. Furthermore, Kris is bad at bzflag. In my talk, I'll introduce you to why we want to use CZT detectors in X-Ray astrophysics and try to explain how they work. Then, I'll present some results that are to be presented at the 13th International Workshop on Room-Temperature Semiconductor X- and Gamma-ray Detectors.
In this work, I analyzed the results of three research-based tests/surveys, adapted and used for different purposes, in an astronomy course for K-8 school teachers in spring, 2003. To enhance our consistency of the assessment and the instruction, I used Bloom's taxonomy to review all the test items and our course objectives for the astronomy course. Then I analyzed tests we are using in the electricity and magnet course we are teaching this semester (EDU6001). Our results support that using the research-based tests/surveys to identify alternative conceptions is an efficient way to use the knowledge of alternative conceptions in professional development. The results also support our point of view that a combination of using different researched-based tests and trying scientific ways of analyzing those tests will help our teachers to understand science and enhance their awareness of self-assessment. Finally I will raise questions as how to transfer similar tools back into teachers' classrooms and how to assess inquiry based courses.
Shortly after discovering fire humans invented clubs to beat each other over the heads with. One person who was beat particularly savagely saw stars and hence the science of astrophysics was born. X-ray astrophysics is the study of high energy systems in the universe. Recently the deployment of the Chandra and XMM Newton observatories has brought X-ray astrophysics into the 21st century (even though they were deployed in the 20th century) with there excellent angular as well as energy resolution. The X-ray universe is a rich collage of interesting thingys. Some of the more interesting X-ray producers are the interacting galaxy clusters, blazars (like quasars but they blaze) neutron stars, pulsar wind nebula and cold fronts (cold only in the X-ray sense ~ 10M Kelvin). We shall also be talking more specifically about my wonderful work on the merging cluster A 115, and Mrk 421, a blazar with style. Come one come all enjoy free food and drinks while listening to one of my historic one beer seminar.
With VERITAS, the Very Energetic Radiation Imaging Telesope Array System, the third generation of atmospheric Cherenkov telescopes are coming online. This talk will cover some of the basic science questions that can be answered with gamma-ray astronomy, an overview of extensive air showers, and the atmospheric Cherenkov effect. A description of the inner workings of VERITAS, focusing on the parts made here at Washington University, will also be discussed.
Oscillating systems such as finite strings or membranes have preferred harmonic states of motion. They are called normal modes and the oscillation frequencies form a discrete set of real numbers. In the framework of general relativity, the oscillations of relativistic stars and black holes produce gravitational waves which carry energy away from the systems. The oscillations are damped and the frequencies become complex ("quasi-normal"). In this talk, we will discuss some recent discoveries related to the quasi-normal modes (QNM) of compact objects: ranging from the so-called r-mode instability of rotating neutron stars to how the QNM of black holes may shed some light on quantum gravity. [Remark: No background on general relativity is required]
I will report on work done with the Cosmic Ray Isotope Spectrometer (CRIS), the Trans-Iron Galactic Element Recorder (TIGER), and on Galactic Cosmic Rays (GCRs) in general, thereby attempting to cram all of the exciting things that the Laboratory for Experimental Astrophysics (LEXAS) do here into one talk. You will sit and relax, sipping the beverage of your choice, munching on something yellowish, and contemplating the excessive use of silly acronyms. You may feel free to laugh during this lecture. As a bonus, there will be pictures from Antarctica.
The only non-perturbative method to solve a quantum field theory is to formulate it on a discrete spacetime lattice. In a lattice simulation of QCD (the theory of strong nuclear interactions), one must use unphysical (heavy) values of quark masses with present-day technology. Then, one must extrapolate from the unphysical quark masses to the physical values using Chiral Perturbation Theory (cPT). After an introduction to the lattice and continuum cPT, I will discuss the modification of cPT to incorporate staggered fermions used in lattice simulations and show preliminary results for meson masses and decay constants.
