 oklahoma state universitydepartment of physics |
| oklahoma state university department of physics |
Henry Bradshear (The University of Oklahoma, Physics Major)
Advisor: Prof. Gordon Emslie (Physics)
Polarization of high energy solar flare radiation
Abstract: Observations made by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) of the X4.8 Flare of July 23, 2002 provided data on the polarization of high energy X-rays. We have attempted to develop a model that can recreate the photon polarization cross-section curves for solar flare events. If successful this model could provide predictions of polarization cross-sections for future solar flare events that can be checked against recorded data. We discuss the details of this model, how it compares with earlier work in the field and analyze its accuracy when evaluated at various angles and photon energies.
Christine G. Co (Oklahoma State University, Electrical and Computer Engineering Major)
Advisor: Prof. Alan Cheville (ECEN)
Increasing Terahertz Pulse Intensity Using an Array of Optically Matched Single Mode Fiber
Abstract: The emission strength of a Terahertz (THz) strip line transmitter is limited by the damage threshold of the metallized structure due to the applied electrical bias and incident optical intensity. A way to increase THz output strength without damaging the stripline structures is to excite two transmission lines simultaneously below damage threshold conditions to generate a stronger pulse. This approach requires the use of more than one single mode fiber to deliver optical pulses. With the use of multiple fibers, precisely matched optical delay lines are required for the femtosecond laser excitation pulses. An Ericsson FSU 925 Fusion Splicer was used to create a differential stretch to match the fiber lengths with sub-millimeter level of accuracy. A fiber array in combination with an imaging lens must also be used in order to generate focused laser pulses that will generate a terahertz signal. The purpose of this study is to develop a method using a pair of optically matched single mode fiber in combination with a fiber array and imaging lens to increase terahertz pulse intensity.
Robert Cockrell (Tulane University, Physics Major)
Advisor: Prof. Bret Flanders (Physics)
Construction of a dielectrophoretically assembled model of a field effect transistor
Abstract: Constructing inexpensive and easily reproducible and fabricated electronic nanostructures is a goal at the forefront of research in nanoscience. Using a dielectrophoretic process, ultra thin nanowires were constructed from gold nanorods and nanoparticles. From these nanowires, a prototype for a nano- Field Effect Transistor (FET) was fabricated. An FET is commonly used to amplify weak signals. In an FET, the current flows along the channel. The channel is bounded by the source and the drain. The channel’s electrical properties can be easily varied by applying excess voltage to the gate. The FET’s conductivity is regulated by the voltage applied to the channel. Design of a functional nanoFET would be a large step forward for constructing complex nano-circuits.
Jessica Conry (Henderson State University, Physics Major)
Advisor: Prof. Nicholas Materer (Chemistry)
Determination of ClO2 Optical Parameters and Development of a Spectrophotometric Sensor for ClO2 Gas
Abstract: ClO2 is of interest because of it’s capability to kill biological hazards such as mold. The need to detect the amount of ClO2 after disinfection is reason to construct a low cost sensor for ClO2. Concentrations of ClO2(g) and aqueous solutions is determined by titration and correlated with UV-visible absorption measurements. A maximum absorption is observed at 359 nm, and the cross section at this wavelength is determined to be 4.79x10-18cm2, which agreed with previous observations. Using Henry’s law, solutions of known concentration of gas is made. The absorption of ClO2 gas is successfully analyzed and concentrations are determined as low as 100 ppm (~4x10-6 M). A prototype sensor is being designed and calibrated using the previously determined standards.
Elijah Dale (Oklahoma State University, Physics Major)
Advisors: Prof. Albert Rosenberger and Prof. Donna Bandy (Phsyics)
Mark Dickins (The University of Texas at Austin, Physics Major)
Advisor: Prof. Aihua Xie (Physics)
Finite-Difference methods for calculations of the Navier-Stokes and convection-diffusion equations modeling a diffusional micromixer
Abstract: The low-Reynolds flow in a diffusional micromixer on a silicon chip can be modeled with finite-difference methods for the Navier-Stokes and convection-diffusion equations. The primary purpose here is to numerically solve the convection-diffusion equations to determine the diffusion time and distance for application to analyzing kinetics of proteins during chemically triggered reactions. In current experiments protein unfolding is analyzed as an acid buffer mixes with the proteins. Our mixing channel (10um x 100um x 1-10mm) is compromised of 5 alternating buffer-protein layers of non-uniform width (1.25um, 2.5um, 2.5um, 2.5um, 1.25um) but with equal inflow rates of buffer and proteins. To conserve volume-flux of each layer the layers must change widths to match the expected flow as the calculated parabolic velocity profile in the narrow dimension develops. A ratio less than one of the length of the narrow dimension to the larger transverse dimension sets up the plug velocity profile in the larger transverse dimension. As this ratio gets closer to one the needed plug profile is lost and a parabolic profile forms. The beam size (50um) also determines the minimum width of this larger dimension, as the beam needs to be focused on the constant velocity section of the plug. This avoids distortion due to slower fluid speed near the walls. We show that the interesting diffusion calculations are about the separate problems of diffusion of proteins into the buffer and diffusion of the buffer into the proteins. The much slower diffusion of the proteins allows us to retain accuracy as the proteins will not approach the slow moving fluid at the walls, and not become distorted due to the band broadening of Taylor dispersion, which is more dramatic at the walls. However the diffusion of the buffer into the protein occurs roughly 10 times faster than the protein diffusion, allowing almost complete diffusion near 1-1.35mm of the start of the mixing channel, with a maximum fluid velocity of 1m/s and z-averaged fluid velocity two thirds of vmax. This corresponds to a diffusion time of 1-1.35ms near the center of the channel. This is in agreement with estimated experimentally observed diffusion.
Ben Dvorak (Oklahoma State University, Mechanical and Aerospace Engineering Major)
Advisor: Prof. Demirkan Coker (MAE)
Experimental observations of localized deformation and stress fields due to frictional sliding in PMMA specimens
Abstract: Recent experimental observations of frictional sliding between two polymethylmethacrylate (PMMA) specimens subject to quasi-static compressive loading are presented. Frictional sliding between two deforming solids is a basic problem of mechanics that surfaces in a variety of subjects such as machinery contact interaction, material tool cutting, fiber pullout within reinforced composites and even in the study of earthquake dynamics. This type of sliding has a direct link to earthquake science whereas the basic cause of earthquakes is the sliding occurring between plates of the earth’s crust. The discussed experiments were performed on PMMA as it has brittle characteristics analogous to the rocks located in tectonic plates. This paper outlines previous studies of PMMA-PMMA friction and also gives an introduction to the unique experimental setup created for this study. The specimens in the experiment are subjected to compressive displacement controlled loading in order to induce sliding along a diagonal plane. The stress fields and localized deformation were visualized in real time using the interferometric technique of coherent gradient sensing along with high-speed photography. The images produced in the study show the classical stress fields and stick-slip motion shown in previous studies. The load-displacement curves concur with the high-speed image conclusion that stick-slip motion was present. The overall goal of this experiment is to provide an introduction to the original setup and optical techniques and how they were implemented in the analysis of frictional sliding.
Garrett Hardesty (Oklahoma State University, Physics Major)
Advisor:
Prof. Girish Agarwal (Physics)
A Numerical Treatment of Dispersion Throughout a Prism
Abstract: There are numerous effects to be considered when numerically simulating the output of a pulse traversing the interior of a right triangular prism, specifically of fused silica, being transmitted through two interfaces and internally reflected once. Nearly all of these are a function of frequency due most often to the fact that the index of refraction is frequency dependent. Amplitude losses arise at both transmitting interfaces, given by the Fresnel equations. As the light is internally reflected, either a loss or phase shift arises, depending on whether the incident angle is less than or greater than the critical angle, respectively. The incident and transmitted angles must also be propagated through the prism to be employed in the Fresnel equations and the determination of the internal path length, and are frequency dependent through Snell's equation. Phase velocity is another varying quantity, and together with the path length yields the relatively large phase shift due simply to crossing the medium. In order to apply this behavior to a given signal, its Fourier transform must be taken so that these effects can be multiplied to a succession of monochromatic signals, forming a modified frequency distribution. The inverse transform of this distribution then yields the output signal. One motive of this simulation is to verify numerically that the Wigner time delay occurring from total internal reflection will arise solely from the Fresnel reflection coefficients, and particular attention is paid to this aspect.
Lesley Hess (Oklahoma State University, Electrical and Computer Engineering Major)
Advisor:
Prof. Alan Cheville (ECEN)
Barbara Johnson (Oklahoma State University, Electrical and Computer Engineering Major)
Advisor: Prof. Joel Martin (Physics)
Radiation Effects in Cu-doped Lithium Tetraborate Glass
Abstract: Lithium tetraborate (Li2B4O7) glass doped with different concentrations of copper were studied, specifically 0.03wt%, 0.015wt%, and undoped samples. The glasses were made by melting Li2B4O7-CuO mixtures in a platinum crucible and controlled cooling; the melt was cooled by 100°C every fifteen minutes. The resulting material was optically clear with some occlusions. Radiation analysis was performed on the different samples to discover if lithium tetraborate (LTB) doped with copper is a viable material for use as a dosimeter. Radiation affected the spectra of all glass samples but did not significantly affect the sample of undoped LTB crystal studied. Each glass was also temperature annealed after exposure to radiation; temperatures above 200°C restored the samples to the original spectra.
Andy Lau (Oklahoma Babtist University, Physics Major)
Advisor: Prof. John Mintmire (Physics)
Parallel Programming and Molecular Dynamics Simulation
Abstract: Molecular dynamics simulations can successfully model molecules in three-space, and from these models energies and forces can be calculated. However, a run on a machine could take a considerable amount of time, depending on the efficiency of the code and performance of the machine. A solution for more runs and less time is the use of a cluster and parallelizing the code. In this project I created a parallelized program for molecular dynamics simulation that would compute energies, forces, and the increase in performance versus the non-parallelized program. There have been many books and tutorials for such a procedure, this paper is an informal introduction to parallel programming.
Timothy Lindstrom (Northpark University, Physics Major)
Advisor: Prof. Eduardo Yukihara (Physics)
A continued study in the precision of Al2O3:C dosimeters for radiation dosimetry using the Optically Stimulated Luminescence (OSL) technique with thin 1mm x 1mm dosimeters and powder
Abstract: Optically Stimulated Luminescence (OSL) dosimetry using thin aluminum oxide (Al2O3:C) dosimeters has been shown to be an efficient and precise method of measuring absorbed doses of radiation. Recent experiments have shown high reproducibility rates (uncertainty of 0.69%) and dose response accuracy in 7mm diameter dosimeters. In this project, attention was focused on the affects of dosimeter accuracy and reproducibility when the size of the dosimeters was limited to 1mm x 1mm thin squares and Al2O3:C powder. The use of smaller dosimeters such as these may be desirable for medical applications such as radiotherapy in the case of higher precision dose mapping on a 2D or even 3D scale. Preliminary irradiations were carried out in the laboratory with a 90Sr/90Y source, followed by clinical irradiations using a linear accelerator. All dosimeter signals were normalized with respect to a reference dose to avoid dealing with changes in dosimeter mass and sensitivity. The uncertainty in a single measurement from a sample of dosimeters that received the same dose in the laboratory was 0.36% in 1mm x 1mm dosimeters and 0.40% in powder. Clinical reproducibility tests with a linear accelerator yielded uncertainties of 1.9% in 1mm x 1mm dosimeters and 2.8% in powder. Dose response tests with a linear accelerator that ranged from 0.06 Gy to 1.995 Gy were also performed on 1mm x 1mm dosimeters. The uncertainty from these results was <5.0% in all cases. Finally, a clinical test was also performed on a 2-dimensional square matrix of dosimeters in which the dose delivered to the matrix was varied and the results were observed to determine the potential accuracy of 2D dose mapping using very small dosimeters. In all cases the measured dose from the dosimeters was less than 10% difference from the expected dose. These tests showed that there is a potential for using very small dosimeters for dose mapping and quality assurance programs; however we believe that more precise and accurate results could be achieved in experiments using more sensitive methodology and equipment to account for the apparent sensitivity of dosimeters of this size.
Drew Spain (Baker University, Math and Communications Major)
Advisor: Prof. James Wicksted (Physics)
Raman Spectroscopy of Lead-Bismuth-Gallium Glasses
Abstract: Lead-Bismuth-Gallium glasses have been investigated using Raman Spectroscopy to better understand their structure and network. Totaling five in all, the glasses are unique as the amount of lead is increased from 0% to 62% while the amount of bismuth is simultaneously decreased from 62% to 0%. Peaks are observed at five corresponding bands: 130 cm-1, 200 cm-1, 400 cm-1, 500 cm-1, and 650 cm-1, respectively. Fitting software has been utilized to identify the peak wavenumber and its significance. Past studies have indicated that the 130 cm cm-1 band corresponds to the stretching vibration of Pb-O and Bi-O bonds. An increase in the peak wavenumber of the 130 cm-1 band has been observed and suggests a higher covalency of the Pb-O bond as compared to the Bi-O bond. Additionally, the peak becomes narrower as the amount of lead is increased which is consistent with prior research suggesting more uniformity in Pb-O bond lengths. The higher wavenumber peaks of 550 cm-1 and 650 cm-1 previously identified correspond to the occurrence of bending vibration in the Ga-O-Ga bond and the stretching vibration involving non-bridging oxygens within GaO4 tetrahedra. An analysis of the intensity ratio I(650)/I(550)of the two bands has been performed showing a decrease as the lead content is increased while bismuth content is decreased. As a result, it has been concluded that Pb2+ acts as a stronger network former in the structure of the glass than Bi3+.
Pete Thompson (Oklahoma State University, Physics Major)
Advisor: Prof. Gil Summy (Physics)
Electromagnetic microwave frequency emission to induce hyperfine state transitions and superposition of trapped Rubidium-87 atoms
Abstract: In an existing experiment it has been found advantageous to provide a method for switching between and creating a superposition of the F1 and F2 hyperfine states of trapped Rubidium-87 atoms. This transition and superposition can be induced with a specific electromagnetic pulse. The duration and the power of the pulse will dictate whether a complete state change or a superposition occurs. Both the F1 and F2 hyperfine states lie within the 5s1/2 ground state and are thus very stable, because of this stability, the lifetime of the F2 state is very long. The lifetime of the state, according to the Heisenberg uncertainty principle, varies inversely with allowed variation and instability of the frequency inducing this state change, thus a very precise and stable electromagnetic frequency must be used to induce this change. In the case of Rb87 atoms, this frequency is 6.80GHz. Using a Phase Locked Oscillator externally referenced from a crystal oscillator and combined with a variable sine wave from a function generator used for switching and minor adjustments of the frequency, an electric signal will be generated which will then be sent into a waveguide in order to convert the electric signal into an electromagnetic microwave signal at the desired frequency.
Oklahoma State University, Department of Physics, 145 Physical Sciences, Stillwater, OK 74078-3072