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Program Information

Travel Information

2008

Previous Summers

Research Projects

REU Application

1. Dr. Qiuhong He
   qiuhong@mrctr.upmc.edu
   412-647-9726
   
   Radiology
   
   Students working with Dr. He have assisted in the development of magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) for medical and biological research.
   
   
   
2. Professor Joe Boudreau
   
   Elementary Particle Physics
   
   I work on two major world–class experiments in experimental particle physics. The first is the CDF Experiment at Fermilab. The second is the ATLAS experiment at CERN. CERN is the French acronym for "The European Center for Particle Physics," which is located in Geneva, Switzerland.
   
   
   
3. Professor Vittorio Paolone
   
   Elementary Particle Physics
   
   Professor Paolone works in the field of particle physics. Particle physics is the study of the fundamental constituents of matter and how they interact. Through the use of particle accelerators we probe smaller and smaller distance scales (<10^-18 meters!) and try to untangle the fabric of space. Since the universe was once a small, hot and therefore energetic place we also recreate early phases of the universe soon after its birth. The universe looks like it does today because these fundamental particles interact in very specific ways.
   Specifically Professor Paolone studies the properties of neutrinos. Neutrinos are one of the most prevalent particles that exist in the universe and therefore their behavior influences its structure. He is presently working on the properties of the tau neutrino and trying to untangle the masses of all the neutrinos. In addition Prof. Paolone is involved in an experiment at CERN(ATLAS) that will exploit the next generation particle accelerator to probe the structure of the universe to even smaller distance scales. Particle physicists are expecting to observe new phenomena with this machine including a zoo of new particles, a better understanding of gravity and maybe even signatures of extra dimensions!
   
   
   
4. Professor Vladimir Savinov
   
   Elementary Particle Physics
   
   Professor Savinov works on supersymmetry and extra dimensions, Strong interaction dynamics, Computational physics, Electronics for energy measurements and New data analysis techniques.
   
   
   
5. Professor John Hillier
   
   Astrophysics
   
   My principal area of research involves the development and application of numerical modeling to interpret the spectra of the most massive and luminous stars. Due to their high luminosities massive stars shed a significant fraction of their mass during their lifetime. As a consequence material that has undergone nuclear processing is exposed at the stellar surface. Through spectroscopic analyses we can learn about the composition of this material, and hence gain insights into nuclear processes, convection, and stellar evolution, and consequently into the evolution of our galaxy. The research utilizes many different scientific fields including numerical modeling, radiative transfer, radiation–hydrodynamics, polarization, and atomic physics.
   
   To model the spectrum produced by a star we need to determine the density and temperature structure of the star's atmosphere. These depend on the opacity which is a measure of the resistance of the gas to the flow of radiation. In many stars the opacity can be simply determined from local quantities — the composition of the gas, its density, and its temperature. In such a case we can use local thermodynamic equilibrium (LTE) to fully specify the ionization state of the gas, and the populations in excited states of atoms and ions. However hot stars have an intense radiation field, and this radiation affects the gas. Because the radiation propagates through the atmosphere it couples together regions of different temperature. As a consequence the state of the gas is not in LTE (i.e., non–LTE), and we have to determine the ionization state of the gas, and the populations of excited levels, from first principles (i.e., we solve the equations that describe how individual atomic levels are populated and depopulated). This problem is nontrivial and requires iteration. The state of the gas is determined by the radiation field which itself is determined by the populations. Some elements, such as iron, have thousands of lines which impede the flow of radiation through the atmosphere. This is referred to as line blanketing
   
   To perform my research I have developed a large radiative transfer code, CMFGEN, which is now used by many different investigators. CMFGEN allows non–LTE line blanketed model atmospheres to be constructed and used for detailed spectroscopic analyses. It has been used to study O stars and their descendents — Luminous Blue Variables and Wolf–Rayet Stars.
   
   In collaboration with Luc Dessart (University of Arizona) CMFGEN is currently being used to model Type II SN. The debris of supernovae explosions can be utilized to study their nuclear evolution. We can also use supernovae studies to place constraints on hydrodynamical models — there is still considerable uncertainty in hydrodynamical models of supernovae explosions. Further, supernovae can be used to measure distances. Measuring distances in astrophysics is always difficult — supernovae have advantages since they are very bright and hence can be seen to large distances. We are exploring the accuracy of a distance measuring technique called the expanding photosphere method. This method does not make any assumption about supernovae being standard candles — rather it relies on the expansion of the supernovae to determine distances. In principle the technique is straightforward — in practice there are uncertainties because of radiation transfer effects which we are addressing using CMFGEN.
   
   
   
6. Professor Arthur Kosowsky
   
   Astrophysics and Cosmology
   
   My research so far has centered on cosmology and related issues of theoretical physics. I have done extensive work on the theory of the cosmic microwave background radiation and the ways in which it constrains our models of the universe. Current microwave observations, combined with optical observations of the large–scale galaxy distribution, cosmic abundances of light elements, and the supernova–1a Hubble diagram, combine to give tight constraints on the properties of the universe. The resulting "standard model" fits most observations well, but is troubling theoretically: our best guess says that only 5 percent of the universe's energy density is in the form of ordinary matter, 25 percent is made of as–yet undetected dark matter (which does not interact either via the strong or electromagnetic forces), and the remaining 70 percent is in an even stranger "dark energy", evenly distributed in space and having a negative effective pressure. Theorists have a number of good candidates for the dark matter particles, which are currently being pursued by many experimental groups, including the high energy experiment group at Pitt. Current ideas as to the nature of dark energy are all highly speculative.
   
   I am interested in a variety of techniques to test our model of cosmology; these include further observations of the temperature and polarization fluctuations in the microwave background radiation, gravitational lensing, dynamics of galaxies and clusters of galaxies, and the large–scale distribution of galaxies in the universe. I am also interested in possible alternatives to the standard cosmological model, and observational tests which can distinguish particular alternatives from the standard cosmology. As an example, the "dark energy" may actually be telling us that the usual equations describing the expansion of the universe, based on general relativity, are not valid; in other words, we could be observing not the result of a mysterious form of energy density but rather the breakdown of our basic theory of gravitation.
   
   On the observational side, I am a member of the Atacama Cosmology Telescope (ACT) project, which is building a custom–designed 6–meter microwave telescope with superconducting bolometric detectors to observe the microwave sky from the Atacama Desert in the Chilean Andes (see http://www.hep.upenn.edu/act/). ACT will produce microwave maps with arcminute angular resolution and micro–Kelvin temperature sensitivity, in three frequency bands. One result of these observations will be the detection of thousands of galaxy clusters via their thermal distortion of the microwave radiation (the Sunyaev–Zeldovich effect), and another aspect of the project is optical follow–up observations of these newly detected galaxy clusters, using telescopes in Chile and also the new Southern African Large Telescope (see http://www.salt.ac.za).
   
   
   
7. Professor Sandhya Rao
   
   Astrophysics
   
   My current area of research involves studying the evolution of galaxies as traced by QSO absorption lines. Specifically, I am studying the properties of low–redshift damped Lyman alpha(DLA) systems. DLA systems contain the bulk of the observable neutral gas in the Universe and are, therefore, important probes of galaxy formation and evolution. The hydrogen Lyman alpha line falls in the ultraviolet region of the electromagnetic spectrum for redshifts z <1.65. Consequently, space based observatories, like the Hubble Space Telescope(HST), are required to discover them in QSO spectra. Since this redshift interval covers the most recent ~70% of the age of the Universe, it is particularly important that low–redshift examples of DLA systems be discovered so that evolutionary links between the high–redshift DLA absorbers found in optical surveys and nearby galaxies can be studied. My research over the past few years has involved surveys of QSO spectra with HST and follow–up observations with Chandra (the X–ray observatory) as well as several ground–based observatories. Telescopes such as the WIYN, the 4m, and the MDM on Kitt Peak in Arizona, as well as the IRTF on Mauna Kea in Hawaii, the NTT in Chile, and the WHT in La Palma are being used to study the properties of the newly–discovered low–redshift DLA systems.
   
   
   
8. Professor David Turnshek
   
   Astrophysics
   
   Most of Turnshek's work has been devoted to the study of Quasi–Stellar Objects (QSOs) and the use of them as probes of galaxies and the intergalactic medium. QSOs (often called quasars) are widely believed to be the active nucleus of galaxies, with the active nuclei powered by a supermassive (one million to one billion solar masses) black hole surrounded by an accretion disk. A large amount of Turnshek`s effort has gone toward the study of Broad Absorption Line (BAL) QSOs, which eject matter at high velocity, often near one–tenth the speed of light. Turnshek's BAL QSO studies include multi–wavelength observations (x–ray, UV, optical, IR, radio), ionization and abundance investigations, and the derivation of covering factor and geometry constraints. His numerical modelling in this area involves photoionization and radiative transfer calculations. Other work in the area of QSO research includes the general problem of the interpretation of QSO emission–line spectra, the study of QSO host galaxies, and observation and interpretation of quiescent brightness variations in QSOs. He has also worked on various classes of intervening QSO absorption–line systems. One line of such research involves investigations of the evolution and properties of damped Lyman–Alpha systems. The damped systems in QSO spectra are the result of absorption of background QSO light by large amounts of neutral hydrogen gas in foreground galaxies and proto–galaxies. The damped systems contain the bulk of the neutral gas mass in the Universe. Neutral gas is a necessary requirement for the eventual formation of molecular clouds and the conversion of gas into stars. Turnshek's current work in this area emphasizes the determination of the statistical properties of the damped Lyman–Alpha systems at low redshift, which are poorly known, and the use of these results to constrain the galaxy formation process. Some of Turnshek's other lines of research involve placing observational constraints on the size–scales of intervening absorbers, as well as the use of gravitational lenses to study QSOs, intervening foreground gas the gravitational potentials of the lenses. Most of Turnshek's efforts have involved making observations with either the Hubble Space Telescope or large ground–based telescopes.
   
   
   
9. Professor Xiao-Lun Wu
   
   Condensed Matter and Biophysics
   
   My research interest is in nonlinear dynamics and biophysics. In the nonlinear dynamic studies, I am focusing on fluid turbulence in freely suspended liquid films that behave as a two dimensional (2D) fluid. 2D turbulence shares many important attributes of 3D turbulence, such as nonlinearity and stochasticity. However, 2D turbulence is unique in that the energy flux is reversed resulting in a greater tendency for the formation of large coherent structures or vortices. The study, aside from its intrinsic physical interest, is beneficial for understanding a variety of natural phenomena such as formations of cyclonic/anticyclonic eddies. In the biophysics studies, we are investigating population dynamics using bacteria and phages as model systems and using novel optical techniques to study vesicle dynamics in synapses of hippocampal neurons.
   
   
   
10. Professor Albert Heberle
    
    Solid State Physics
    
    Research Interests:
    Femtosecond Optics and Lasers
    Femtosecond Dynamics in Solids
    Coherent Quantum Control
    Ultrafast Optoelectronics
    
    
    
11. Professor Jeremy Levy
    
    Solid State Physics, Quantum Information
    
    My research interests are primarily based upon exploring novel phenomena in solid state systems, in order to provide the physical foundation for future technologies. Areas of interest include physical systems capable of quantum information processing and quantum computation, the study of ferroelectric domain dynamics using optical probes, ferroelectrically nanostructured semiconductors, formation of Ge/Si quantum dots by "directed self–assembly", and development of novel optical and scanning probe techniques including near–field optical microscopy. I am the director of the DARPA sponsored Center for Oxide–Semiconductor Materials for Quantum Computation (COSMQC).
    
    
    
12. Professor David Snoke
    
    Solid State Physics
    
    Bose–Einstein Condensation of Excitons in Two and Three Dimensions
    
    Bose–Einstein condensation is one of the most fascinating phase transitions in physics. When an ensemble of bosons is cooled to below a critical temperature, a macroscopic number of them will be attracted to occupy a single quantum state. This phenomenon, known as "spontaneous symmetry breaking," leads to super fluidity, superconductivity, and other fascinating effects.
    
    Excitons are bosons and can undergo Bose condensation under certain conditions. Since excitons are created by photons and can convert into photons, an exciton condensate essentially corresponds to coherent transport of optical energy. But because excitons have an effective mass, they move much more slowly than photons and have much shorter wavelength.
    
    We create excitons in semiconductor samples at liquid helium temperatures via an intense, picosecond laser pulse and then examine the evolution of their momentum distribution and spatial distribution by detecting the light they emit, either via a time–gated CCD camera with 5 ns resolution, time–correlated photon counting with 40 ps resolution, or a streak camera with 5 ps resolution.
    
    We collect the excitons in traps inside a semiconductor in two different ways. First, a trap can be made in three dimensions by applying an in homogeneous stress to a bulk crystal of Cu2O. Excitons are attracted to the region of a shear stress maximum. When an intense laser pulse illuminates the region, excitons are created in the trap and remain there. A second method works in a two–dimensional system, namely, excitons in GaAs or InGaAs quantum wells. When an electric field is applied perpendicular to the plane of the wells, the excitons become polarized and move in response to a gradient in the electric field. We also can stretch the 2D sample slightly to create a hydrostatic expansion. Excitons are attracted to a region in the crystal which is expanded.
    
    Several claims of Bose condensation of excitons have been made in the past ten years, but there is still debate. By taking images of the excitons as they collect in a trap, we hope to provide definitive evidence of this novel effect.
    
    Nonlinear Optics in Semiconductor Nanostructures
    
    In electronics, the transistor plays an essential role as a switch by which one electrical signal turns another electrical signal on and off. Can we do the same thing with light beams? If we could make an "optical transistor" by which one light beam switches another one, we could make an optical computer in which all signals were carried by light instead of electrical signals. This would revolutionize technology in the way the electronic transistor did 50 years ago.
    
    One way to do this is with nonlinear optics. In "linear" optics, the absorption and reflection coefficients of a medium are not dependent on the light intensity. In nonlinear optics, these coefficients can depend on the intensity, polarization, and wavelength of light. Therefore one can devise many schemes in which the presence of one light beam affects the transmission of another.
    
    Besides optical–optical interactions, two other important effects are electro–optics and magneto–optics, in which an electric field or a magnetic field causes a shift of the optical properties of a material. These effects can be used for optical communications and memory devices.
    
    Our interest is in the system of "coupled quantum wells." In this system, two very thin layers of semiconductor (about 6 nm, that is, 6 billionths of a meter) lie side by side. When electric field is applied to the sample, negative charges accumulate in one layer (or "well") and positive charges accumulate in the other one. There is a thin barrier in between the two layers, and quantum mechanics allows charge to "tunnel" from one layer to the other without hopping over the barrier; as if passing magically through a wall.
    
    The optical properties of this system depend sensitively on all kinds of things. We see large shifts of the luminescence wavelength with laser intensity, with electric field, and with magnetic field, in addition to shifts due to stress and temperature. We can control these shifts and use them to modulate the light signals.
    
    
    
13. Dr. Russell Clark
    
    Physics Education
    
    Dr. Clark is interested in helping students to use laboratory experiments in learning the fundamental principles of physics. Physics is best described by the language of math, but it is easy for a student to become disconnected from reality when dealing solely with equations. Lab experiments help students to see the true physical meaning of the equations they derive and use in their lecture courses. The challenge for an instructor is to create robust experiments that are easy to perform and at the same time lead the students to think about the physics involved.
    
    
    
14. Professor Chandralekha Singh
    
    Physics Education
    
    The goal of my research is to identify sources of student difficulties in learning physics both at the introductory and advanced levels, and to design, implement, and assess curricula/pedagogies that may significantly reduce these difficulties. The objective is to enable students at all levels to develop critical thinking skills, and to become good problem solvers and independent learners.
    
    Below are examples of investigations in both the introductory and advanced courses we are pursuing:
    
    
    
    • Difficulties in learning Quantum Mechanics and tutorial development: We have been investigating the difficulties that advanced undergraduate students have in learning quantum physics by designing surveys and interviewing individual students. We find that the difficulties and misconceptions displayed by advanced students are largely independent of their background, teaching style, and textbook similar to those documented for introductory physics. We are currently developing and evaluating tutorials for helping students learn various topics in advanced quantum mechanics.
    
    
    • Introductory level topics: We have been investigating the difficulties that introductory students have with energy and momentum concepts, symmetry and Gauss's law, magnetism, and rotational and rolling motion concept. We have developed and administered free–response and multiple–choice questions and conducted interviews with individual students using think–aloud protocol to understand their difficulties. We have developed tutorials to help students learn superposition, symmetry, and Gauss's law.
    
    
    • Cognitive issues in learning physics: We are interested in researching the connection between student difficulties in learning physics and models of cognition. For example, we want to understand how physical intuition develops and how the problem solving strategies of individuals at different levels of expertise in physics shows similarities and differences when physical intuition fails. We are also investigating how expertise develops in the context of learning physics.
    
    
    • Teaching effective problem solving: We are currently investigating the extent to which students can be taught effective problem solving heuristics. We are developing video–tutorials that help students learn effective problem solving strategies using concrete examples in an interactive environment. The tutorials are designed to provide scaffolding support and help students view the problem solving process as an opportunity for knowledge and skill acquisition rather than a "plug and chug" chore. Preliminary evaluations are encouraging.
    
    
    
    
    
    
15. Special Projects.
    
    In some cases, we are able to find special projects for well-defined student interests not discussed above. Past examples have included propagation of signals in optical wave guides, and projects related to biophysics, among others. Such accommodation cannot be guaranteed but sometimes can be arranged. Students interested in developing such a special project, are asked to check this option and include a brief description or proposal.