UC Davis Physics Department
June 15 to August 22, 2008
Research Project Areas:
- Condensed Matter Experiment
- Condensed Matter Theory
- Biological Physics
- Complex Systems and Computational Physics
- Nuclear Physics Experiment
- High Energy Theory
- Cosmology
The following descriptions should give a sense of the subject areas of our projects. Bear in mind that in many cases summer projects are in an ongoing research area, and the exact project will depend on how much progress is made during the schoolyear. A few of these projects may not, in the end, be offered in summer 2008, depending on applicants' interests and faculty travel schedules.
Project Descriptions
Condensed Matter Experiment
Rena Zieve
1. Quantum criticality: The most familiar phase transitions, such as water freezing, occur as a function of temperature. Other parameters, including applied pressure or magnetic field, can also induce transitions. When a compound has a pressure- or field-driven phase transition at zero temperature, also known as a quantum critical point, its behavior near the transition becomes dominated by quantum rather than thermal fluctuations. The resulting unusual behavior may be important in understanding systems from high-temperature superconductivity to magnetism in coupled two-dimensional electron gases. Our group uses uniaxial pressure to tune materials near quantum criticality. We both map out phase diagrams and study quantitatively how resistivity, susceptibility, and heat capacity evolve near a critical point. A student would learn a variety of lab skills: cutting, polishing and mounting samples; handling liquid cryogens, leak checking; winding magnet coils; and evaporating thin-film heaters. He or she would also work closely with a graduate student in running the pressure experiments on a dilution refrigerator, at temperatures well below 1K.
2. Granular materials: This project will investigate shape effects in a relatively controlled way, using ball bearings welded together to construct more complex shapes. A pile of these grains, when tilted past an angle of stability, undergoes an avalanche with rapid flow of particles, much like sand in an hourglass. The angle of stability depends on the shapes of the individual particles that make up the pile. The current goal is to mix particles of two different shapes to illuminate how the avalanche begins. The lab's equipment includes several setups for shaking or rotating granular samples, and digital still and video cameras interfaced to a personal computer. The apparatus is straightforward to operate; the challenge lies in finding meaningful patterns within the huge amount of available detail. The student will be responsible for taking and analyzing data.
Condensed Matter Theory
Summer projects in Condensed Matter Theory are likely to be jointly supervised
by two of the following faculty members.
Warren Pickett
Our group's research focuses on the microscopic description of the behavior of electrons in solids and in nanoparticles, with special attention to the origin of magnetism in condensed systems, and to extending our understanding of the mechanisms of superconductivity. The summer project will be computational. The student will run existing codes and write, debug, and implement new algorithms to extend the analysis of the output of much larger programs. In addition to becoming familiar with scientific programming techniques and practices, the student will begin to learn basic principles of solid state physics and materials behavior. Computation will be done primarily on the group's computer cluster.
Sergey Savrasov
The project is on calculating electronic structure of various materials and building material research databases. The prototype of the database and the software for the electronic structure calculation is available at http://www.physics.ucdavis.edu/~mindlab. A student would learn how to use the Windows-based material research software to calculate several properties of real materials (including optical properties, resistivity, and superconducting or magnetic behavior) from their known crystal structures. The calculation results would then be prepared in html format with graphics and explanation and added to the materials database available on the Web.
Richard Scalettar
My research group uses classical and quantum monte carlo methods to study systems of interacting electrons. Of particular interest are the phase transitions which occur between magnetically ordered and disordered states, and between insulators and metals.
Some programming experience in either C or fortran is necessary for these projects, though the experience need not be extensive. Knowledge of quantum mechanics and statistical mechanics is desirable, but will also be developed in the course of the project. Indeed, the student will spend some initial time, whose length would depend on his/her background, becoming familiar with the computational approach: classical monte carlo and perhaps quantum monte carlo, and also the basic physics of the problem. Besides working directly under my supervision, the REU student will have the opportunity to work with members of my research group, which currently consists of one postdoctoral researcher, two graduate students, and two undergraduates.Biological Physics
Daniel Cox
Professor Cox applies ideas from condensed matter theory to biologically important systems. For example, one ongoing project studies how metal ions bind to proteins and whether attached ions affect how the protein folds. The particular proteins are those relevant for mad cow disease and Alzheimer's. The binding sites are identified and modeled. The models can be compared to experimental data by calculating the resulting binding energies with density functional theory code. The REU student would carry out these calculations using existing density functional theory computer programs. The programs are straightforward to master, and an important part of the research is making good choices about what subsystems of complex problems to model.
Xiangdong Zhu
The student will use special robots to fabricate microarrays of tens or thousands of biologically significant molecules on functionalized glass slides, and then use novel optical scanning microscopes to detect and analyze how selected proteins react with the surface-bound molecules ("targets"). The special optical microscopes are based on detection of minute changes in optical reflection when a protein reacts with some of the targets. The student may also help with instrumentation, improving the microscopes' sensitivity or developing additional capabilities. The project will introduce a physics-oriented undergraduate to some of the issues significant for life sciences that can be addressed in a condensed matter physics laboratory.
Complex Systems and Computational Physics
Jim Crutchfield
Dr. Crutchfield investigates the structures and patterns that emerge in complex systems. Topics include nonlinear dynamics, quantum computation and dynamics, interacting multiagent systems, distributed robotics, and evolution (both as optimization, as pursued in computer science, and as a model of emergent biological organization). A main thrust is programming that automatically discovers emergent structures and builds filters to identify similar patterns. An REU student will work on developing a particular numerical simulation, and if theoretically inclined can also participate in more rigorous mathematical work. The student will become familiar with mathematical concepts from statistical mechanics, dynamical systems, information theory, and the theory of computation. Only minimal prior programming background is needed for a successful experience, but enjoyment of computational work is key.Nuclear Physics Experiment
Manuel Calderon and Daniel Cebra
Relativistic heavy-ion collisions at the highest achievable energies are pursued by the Nuclear Group at UC Davis. The goal is to study the properties of the strong nuclear force, the force responsible to bind protons and neutrons in atomic nuclei. In particular, at the highest energies, a nucleus-nucleus collision produces highly excited matter that should consist not of protons or neutrons, but rather of quarks and gluons (the fundamental particles of the strong nuclear force). These collisions produce thousands of particles, and individual groups focus on studying one or two particular signals. Our group is interested in identifying particles made up of heavy quark-antiquark pairs through their decays in the detector. The project will involve simulating the decay of such particles, studying the detector response to the decay particles in order to find the best way to identify them among the large background of the other collision products. Required background includes special relativity and computer programming in C or Fortran.
High Energy Physics
Steve Carlip
The goal of reconciling quantum mechanics and general relativity is fundamental to theoretical physics, but in the 70 years since the first papers on this subject, we have not yet succeeded in finding a complete, consistent quantum theory of gravity. In the past five years, though, interesting progress has been made in a new discrete approximation to quantum gravity, ``causal Lorentzian triangulation." This approach approximates curved spacetime by a collection of flat building blocks, much as a curved geodesic dome is constructed from flat triangles. Dr. Carlip and a graduate student are setting up a computer code to evaluate quantum amplitudes in this approximation (by approximating a Feynman path integral). They will initially look at the model of gravity in two spatial dimensions, a simplified setting in which other approaches to quantum gravity are better understood. The REU student will help adapt the code to spaces of different topologies, a crucial test for comparing to existing results. The student will also work on adding a variety of physical tests, such as superimposing a diffusion process to explore the effective dimension of the quantum spacetime. For this project, a student must have substantial programming and mathematics background. Applicants should not list this project as their only interest on the application form!Hsin-Chia Cheng
Dr. Cheng will direct a student in analyzing simulated LHC events. When the Large Hadron Collider (LHC) in Geneva, Switzerland, starts taking data in 2008 at the highest energies ever probed in an accelerator, we expect that signals for new physics beyond the Standard Model should quickly appear. Once new physics signal events are discovered, it's important to reconstruct their kinematics and figure out what new physics gives rise to these signals. In preparing for this, one needs to test various methods using simulated LHC data sets. It will provide a good starting point for students to learn collider phenomenology. The REU student will learn to run data analysis tools on simulated LHC data sets, and to compare results with predictions for different models. Required background includes special relativity and computer programming, at a minimum C or Fortran and Mathematica.Cosmology
Pat Boeshaar
Dr. Boeshaar will supervise a student in using a combination of CCD detectors, interference or broad band filters, a Fabry-Perot etalon, and self-guiding spectrograph on 12- and 14-inch telescopes, and will also introduce the student to IRAF software. Possible topics include examining the time dependent structure of the chromosphere of the sun, interpreting the color-magnitude diagrams of stellar clusters, calibrating stellar populations from galaxy photometry, or calculating binary stellar masses from their radial velocity profiles. The REU student will learn to characterize the digital detector, remove background noise, and calculate the effect of atmospheric extinction. This hands-on project will help the student fully comprehend the data acquisition and analysis, and will be excellent preparation for further astronomy research.Matt Richter
Dr. Richter works with a small team that builds and operates mid-infrared spectrographs, which are used for a wide variety of science projects with collaborations from around the world. Because time on large telescopes is precious, substantial effort is made to maintain and improve performance. The REU student will be involved in the efforts to make observing more efficient, for example by developing tools to improve quicklook data analysis software. The work would require the student to become familiar with the tools already used, develop and debug new code, and integrate the final product with the existing package.Tony Tyson
1. Deep Lens Survey: Five regions of the sky have been observed in detail with sensitive CCD cameras on large wide-field telescopes for the past seven years. The chosen regions have been studied at different wavelengths as well. The long timescale of the observations allows "deep" images that include objects that are very distant, and hence very faint. Altogether, the database for the measurements contains a great deal of information on mass distribution in the universe and on objects such as supernovae and moving objects in the solar system with signals that changed over the course of the data acquisition. A student on the project would work on analyzing the data collected from the survey to search for some of these objects.
2. Large Synoptic Survey Telescope: A proposed large ground-based telescope, the LSST, will survey the sky nightly, recording a vast number of images with 15-second exposure times. The fast exposure will allow the telescope to track transient phenomena such as supernovae or near-Earth asteroids, while the 8.4-meter diameter will mean that even such brief data collection periods will yield usable information. The LSST will be an important tool for exploring the most exciting problems in cosmology, including the nature of dark matter and dark energy. A summer student will help prepare for the telescope by running computer simulations on its expected performance. A student with a good knowledge of electronics could join a lab project for testing novel CCD imagers.
David Wittman
Clusters of galaxies are the largest bound structures in the universe and can be seen to great distances. Their mass distribution as a function of redshift is a good diagnostic of cosmological parameters, and they are interesting astrophysical laboratories in their own right. (Physical processes happening inside the cluster include infalling galaxies being stripped of mass, and X-ray emission from a hot intracluster medium.) However, an image of the sky is only two-dimensional and does not trivially reveal where the galaxies are truly clustered in three dimensions. The goal of the project is to assemble a catalog of galaxy clusters in the Deep Lens Survey which is as complete and pure as possible. The student will not have to start from scratch as various cluster-finding codes exist, but he/she will have to think about the pros and cons of the different codes, run them on both real and simulated data to determine things like the rate of false positives, and likely tweak the codes to produce good results on this particular dataset.