(last updated on March 3, 2005)
Paul Bach with Corbin Covault
Stability Testing of GPS Units Used for the Pierre Auger Project
When high energy cosmic rays strike the Earth's atmosphere, they trigger a shower of particles detectable on the ground. Detecting these showers is the focus of the Auger Observatory, 1600 detectors being built in 3000 square kilometers of Argentina. A shower nearly simultaneously triggers several detectors spread over a large distance and the slight differences in arrival time at each detector indicate the direction of the shower's origin. The arrival times are determined by using Global Positioning System signals; CWRU has been responsible for testing this GPS equipment. Although this equipment has been tested in the lab to Auger standards, there is a question of the equipment's long term stability and behavior in the field. It would be useful to characterize likely failure modes of the GPS equipment that Auger may encounter by stressing receivers in the lab to failure and investigating the field performance of installed receivers at the observatory.
Brandon Bachler with Dan Akerib and Kathy Kash
Fabrication and Characterization of Superconducting Films for Dark Matter Particle Detectors
The Cryogenic Dark Matter Search (CDMS) experiment uses particle detectors that, when operated at temperatures near 10-20 mK, can measure both an ionization signal and a phonon signal from a particle interaction. The transition-edge sensors used in the phonon detection are made with superconducting films fabricated through the deposition of amorphous Al, W, and Si, followed by various etching, photolithographic, and annealing techniques. Our goal is to explore characterization and testing techniques of the films, as well as to investigate preparation techniques to improve their quality – specifically uniformity and range of T c . Cryogenic measurements and room temperature measurements will be made using a variety of techniques, including x-ray crystallography and surface resistivity measurements.
Paul Fey with Glenn Starkman
Statistical Isotropy of Low-D CMB
If the cosmic microwave background sky is statistically isotropic, then a two point angular correlation function of the temperature can be expressed solely as a function of the angular separation between any two points ( C(theta) ). C-sub l is the power of the l th multipole of T, i.e. the average square magnitude of the coefficients of fixed m in a spherical harmonic decomposition. With statistical isotropy, C(theta) can be expressed as a sum over the C-sub l multiplied by the Legendre polynomials of cos(theta).
However, for very low l (large theta) there are results that suggest that statistical isotropy might not be true. The goal of this project would be to examine the effects that violating statistical isotropy has on C(theta) and C-sub l .
Michael Helle with Arnold Dahm
Anisotropic Diffusion of Isotopic Impurities in HCP Helium
4 He crystallizes at low temperature and pressure into an hcp lattice. Vacancies in the 4 He lattice propagate along the basal and transverse planes of the crystal as waves in straight lines. 3 He impurities can diffuse in the crystal by tunneling into these delocalized vacancies. It is the spins of a dilute concentration of 3 He that is used to measure the diffusion of vacancies. Prior attempts to measure the diffusion coefficients and their temperature dependence have yielded results that vary significantly. NMR techniques will be used to measure these diffusion coefficients. This will be accomplished by placing the crystal in a gradient coil and saturating a given slice of spins with a large rf pulse. This will create a one to one ratio between spins up and spins down making the NMR signal vanish. As 3 He atoms diffuse into/out of the slice the signal will recover, allowing the measurement of the diffusion coefficient in a direction normal to the field gradient. The diffusion rate will be measured along three orthogonal field gradients to determine whether 3 He diffuses anisotropically in an attempt to explain the discrepancy between previous results.
Chiumun Michelle Hui with Corbin Covault and Glenn Starkman
Simulations for the X-Ray Occulting Steerable Satellite (XOSS)
The angular resolution of current x-ray telescopes is 0.5 arcseconds at best, but the x-ray diffraction limit for a 1-meter aperture is about 3 milli -arcseconds. To achieve a higher angular resolution, the XOSS project proposes a large occulting satellite to be used in combination with existing or planned telescopes. Previous research by Steve Rodney has tested various occultation mask patterns and found that one-dimensional series of slits arranged as uniformly redundant arrays is most efficient to reconstruct 2D x-ray images. To demonstrate that lab work can be duplicated in the space environment, the configuration of the detector, mask, and source will be set up so that its scaling is comparable to that of Constellation-X, a x-ray telescope expected to launch by the end of the decade. Different signal-to-background ratios will be investigated to determine the effectiveness of the reconstruction technique when being used in actual observations.
Sarah Lehrian with Robert Brown
Continuing the Battle to Find a Cure for Post-Exam Syndrome
There has been preliminary research^1 into the question of increasing the learning value associated with student examinations. Initial results considered the degree to which students benefit from revisiting, correcting, and analyzing their examination effort, before progressing with new material. The analysis step refers to the requirement that the students explain the thought processes behind any originally incorrect answer. The benefits were assessed by use of follow-up exams, but suffered from difficulties in choosing appropriate questions and format for such exams. (For example, questions that are too hard or too easy may mask significant differences in understanding.) In this senior project, we will investigate the possibility of constructing more useful follow-up tests, and we will consider their value in assessing other learning methods. We will attempt to find guidelines for instructors who wish to pursue some of these methods.
1. See M. Finnerty, 2004 CWRU Senior Thesis for a discussion.
Adam Light with Kathy Kash
Laser Trapping and Cooling of Neutral Atoms
Laser trapping and cooling is a cutting edge research tool that has made possible the work of several recent Nobel laureates, including the production of Bose-Einstein condensates by Carl E. Wieman and Eric A. Cornell in 1995. In a trapping system, gas atoms absorb laser light from a particular direction and emit photons in a random direction, resulting in a net momentum transfer in the direction of the incoming laser beam. Because atoms of different velocities interact with monochromatic light at slightly different frequencies (Doppler effect), trapping lasers can be set to stimulate a transition only in slower atoms whose trajectory is opposite the direction of the laser beam. In addition to this velocity selection, a position-dependent interaction can be provided by using a non-uniform magnetic field to Zeeman-shift the energy levels of the atoms at the hyperfine level as a function of distance from the trapping center. According to selection rules for angular momentum, the polarizations of the trapping lasers can be adjusted to interact in these hyperfine transitions only with those atoms whose trajectory is pointed outward from the trapping center. With a simple magneto-optical trap, up to 10 7 atoms at micro-kelvin temperatures can be confined to a ~4 cm 3 volume for several seconds. Construction of a magneto-optical laser trapping and cooling system for use in the CWRU teaching laboratories will be completed and the system characterized. A suite of possible experiments for use in the senior lab, including measurements of temperature and emission spectra and demonstration of the quantization of angular momentum, will be explored.
Marisa Quattrone with Robert J. Maciunas, MD, (Univ. Hosp.) (2nd semester of project in Fall 2004)
Nonrigid Registration Algorithm for Warping Intraoperative MR Scans to Preoperative MR Scan for Optimal Surgical Navigation
Selected neurosurgical patients will have markers filled with Vitamin E placed on their heads to appear on an MRI scan of their brains. The BrainLab Navigation System will be used to register and match these markers on the MRI scan to the actual spatial area of the head at the beginning of the surgical procedure. Intraoperative MRI images will be taken and then several different algorithms will be used to warp the pre- and intraoperative images. This method of nonrigid registration will be very useful in ensuring optimal surgical navigation, making these procedures more accurate and less invasive.
Christian Perez with Arnold Dahm (project started January 2005 )
Quantum Computation: From Electron to Qubit
The characterization of electron states for quantum computing with electrons on liquid He requires several proprietary components. Two of those are a low-T, low noise microwave bolometer and submicron electrode array for electron localization and control of the confinement potential. This project will investigate the feasibility of constructing an InSb hot electron bolometer from commercial materials using standard fabrication technologies. If possible, several prototypes will be constructed and tested. The electrode array (or pad) design, field calculations, signal analysis, and fabrication process is the main goal. Once these are implemented, proof of principle tests and single qubit gate operations will be attempted.
Nicholai Salovich with Daniel Scherson (Dept. of Chemistry)
Toward a Mesoscopic Description of Ion Channels and Nerve Conduction in Biological Membranes
Nerve impulses in the brain and muscle propagate through the depolarization of specific cellular membranes. Depolarization occurs when a stimulus of some sort triggers the opening of ion channels embedded in the membrane. The change in local potential due to the newly opened ion channel can then trigger the opening of yet more ion channels which in a cascading effect can cause a large propagating current pulse. Ion channels then spontaneously close and the membrane undergoes repolarization prior to another triggering.
Current models of this phenomenon approach the problem through an equivalent circuit representation and cable theory. This work will directly model current propagation through excitable tissue in a mesoscopic fashion. This approach differs from macroscopic and microscopic treatments because it regards ion channels as structureless but discrete elements that respond to differences in the local electrostatic potential, while also treating the membrane and the surrounding electrolyte as a continuous media.
Ravi Shekhar with Corbin Covault
Design and Testing of a Solid State Tertiary Detector Element and Amplification Scheme for the Pierre Auger Project
With the southern hemisphere Auger array nearing completion, it is now time to shift attention to the design of northern hemisphere array. In addition to the particle and fluorescence detectors, an additional detector is being considered. This tertiary detector would detect Cherenkov light from extremely high energy (10^18 eV and up) cosmic rays. It needs to be highly reliable and able to operate continuously for approximately twenty years without human intervention. Because of such stringent requirements, Solid State Silicon or Germanium photodetectors seem like the most likely candidate. But the sensor itself is not enough. In the case of a Silicon photodiode, the signal from an actual Cherenkov event is on the order of tens of picoamps. The noise background is usually on the order of nanoamps. It will take an exceptionally well designed filter in order to amplify the signal and cut through the noise. Various types of photodetectors will be explored and once a candidate is chosen, an amplification scheme will be designed. To this effect, testing will be done with a UV laser that simulates a Cherenkov spectrum, and possibly with computer simulations.
Matt Smith with Robert Brown
RF Challenges in High-Field MRI
Using the interaction of nuclear magnetic moments with applied magnetic fields, MRI (magnetic resonance imaging) represents the ability to capture powerful images of anatomical structures. To investigate dynamic processes, such as brain functioning, a more dynamic imaging method, fMRI (functional MRI), can be used that takes advantage of the magnetic susceptibility properties of human tissue. Improvement of the resolution of fMR images is expected in the cutting-edge implementation of higher-strength magnetic fields (and, from resonance matching, higher radiofrequencies to be used in the RF coil part of the MRI system). At higher frequencies, RF coil transmission and detection must be effective with shorter dielectric wavelengths inside the imaged body. This study explores the challenges of designing new RF hardware (using state-of-the art methods of computational electromagnetism) in the light of the new physics regime encountered in the interaction of high frequencies with biological tissue.
Justin Thrall with Dr. Christian Zorman (Electrical Engineering)
Evaluation of MEMS-based Micromechanical Resonators
Research into the use MEMS technology in harsh environments has shown that current silicon-based MEMS devices are not as strong as desired. Silicon carbide based structures may have the strength to survive where ordinary silicon MEMS cannot. The quality factor and Young's modulus of SiC-based resonators will be explored, as compared to Si-based resonators. Additionally, the behavior of the modulus and the quality factor will be investigated over temperatures ranging from room temperature to those in excess of 600 °C. These resonators will then be tested in different environments and their feasibility in sensor applications for harsh environments will be explored.
Brian Tinker with Tanmay Vachaspati
Particle Propagation in Astrophysical Magnetic Fields
The influence of large scale astrophysical magnetic fields on cosmic ray propagation may aid in understanding the observed cosmic ray energy spectrum and arrival direction distribution. After learning some magnetohydrodynamics (MHD), and studying earlier work on cosmic ray propagation in randomly distributed magnetic fields, I will simulate this process. A magnetic helicity (handedness) will be added to the simulation, and its effect on the propagation of cosmic rays will be studied. I will also consider the propagation of particle spin in a randomly magnetized plasma.
Alyx Treat with Robert Brown
Once Again, With Feeling: Repetition Methods in Physics Instruction
We examine three newer methods of Physics education, all of which rely on the idea of repetition of concepts. Spiral Physics and Overview Case Study Physics (OCS) both start out with simple qualitative overviews of the subject, and build up to more quantitative mathematical concepts. Spiral Physics increases the complexity of the topics in small chunks, whereas OCS is designed to break the more qualitative learning into the first half of a semester, and the quantitative learning into the second half of the semester. Both systems make use of alternative types of questions and testing, with an emphasis on qualitative questions.
Another repetition method is currently being taught to Physics 123 students. It uses the idea of teaching the topics repeatedly and with increasing complexity, but without sacrificing the math early on. In addition, it stresses the whole spectrum of the subject in each round of repetition. A comparison of last year's 123-class performance (which was taught using the more traditional method) with that of this semester will be made. An investigation of longer-term retention will also be attempted, which would give additional information on the value of the new teaching method. The test scores may also be compared to previous studies done on the Spiral and OCS. Proposed interviews with students currently in the Physics 123 class could also give information on how the students feel about the new method and how they think it compares to other Physics classes they have had.