Browsing by Subject "School of Physics and Astronomy"
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Item 3D Maps of the Supernova Remnant Cassiopeia A(2010-04-21) Olmschenk, GregWe studied the supernova remnant Cassiopeia A using NASA’s Spitzer Space Telescope. A supernova remnant is the debris of a supernova – the explosive death of a star in one of the most energetic events in the universe. Studying the supernova remnant gives us insight into the exotic physics of the explosion itself as well as the physics of the material affected by the powerful shock waves. We are especially interested in particle acceleration – the acceleration of particles to near the speed of light by magnetic fields in the shock waves. One eventual goal of our work is to create 3-dimensional density and temperature maps of the supernova debris. This will allow us to compare the debris before and after encountering a shock wave and potentially detect, for the first time, the energy lost to accelerated particles at this type of shock wave.Item Characterization of Variant Phase Transitions in Smectic-C* Liquid Crystals by Computer Simulation(2009-04-08) Martin, StephenRecent experiments have identified a smooth transition from smectic-C*[alpha1] to smectic-C*[alpha2] in mixtures of some liquid crystalline compounds. However, phenomenological theories implementing only short-range interactions have predicted the intervention of smectic-C*[FI2] in this transition. Using a parameterized free-energy model, this smooth transition in smectic-C*[alpha] is rationalized by variation of three interaction parameters independently in a computer simulation. A phase diagram characterizing the results of our simulation is presented.Item Detecting Bose-Einstein Condensation in Liquid Helium-4(2009-04-08) Svenkeson, Adam J.Purpose: To search for Bose-Einstein characteristics in liquid helium-4. Background: Theory has predicted that helium will form a Bose-Einstein condensate when cooled to a low temperature, but experimental evidence is fragmentary. There is an ongoing experiment, directed by Prof. J. Woods Halley of the Physics Department, seeking to witness Bose-Einstein characteristics by analyzing the transmission of particles through a disk of liquid helium-4. During 2008 I wrote a LabView program to create the beam of pulses sent at the disk of helium by evaporation of superfluid on the tip of an optical fiber or heater, and record the bolometer response to the transmitted particles.Item Detecting Helium Vapor Pulses in Low Temperature Transmission Experiments(2010-09-13) Maunu, TylerBose-Einstein condensation, originally predicted in 1924 by S. Bose and A. Einstein, refers to a quantum configuration at low temperatures in which a large portion (the condensate fraction) of particles collapse into the ground state. Figure 1 shows the phenomena in Rb-87, a less complicated system that superfluid 4He, but the first experimental evidence of BEC . A superfluid is described as a phase of matter with zero viscosity, infinite conductivity, quantized vortices, and zero entropy. It is also characterized by the Cooper pairing of atoms and not electrons. It is generally accepted that superfluidity exhibited in Helium-4 is a consequence of composite boson exhibiting behavior that is associated with Bose-Einstein condensation. It has been proposed that experiments observing the transmission characteristics of a slab of Helium-4 superfluid that is subjected to a pulse of Helium-4 vapor. Figure 3 shows the set-up of our experimental cell. In the current experiment, we use a fiber optic cable to heat a slab of Helium-4 superfluid, which results in a pulse of vapor. This pulse of vapor is then allowed to impinge on the bottom of a slab of suspended Helium-4 atoms. The resultant atomic flux is then observed on a series of superconducting bolometers, which allow us to see the energy levels of transmitted Helium-4 atoms. Bolometers are essential for the detection system in this experiment because they are designed to function at the low temperatures needed to carry out this experiment, and allow for detection speeds on the order of 1 μs. Our experiment aims at pinning down Helium-4 superfluid as a Bose-Einstein condensate by observing the transmission characteristics of a Helium-4 superfluid slab. The purpose of my research was to understand and test the detection system being used to measure these transmission characteristics.Item Developing Software for the TURBO Telescope Prototype(2020) Wieber, MeredithItem Electrical Detection of Electron Spin Resonance in Fe/n-GaAs(2010-04-21) Brecht, TeresaA magnetic field applied to a collection of spins splits up and down spins into two distinct energy states. Application of an additional transverse field at a resonant frequency drives transitions between these states in a phenomenon known as electron spin resonance (ESR). Here, detection of ESR is attempted in a system of spins in n-GaAs. While ESR in GaAs has been detected optically in the past, here purely electrical injection and detection is attempted with a three-terminal measurement device. The ESR spin signal in this system is modeled with a computer simulation. Two ESR measurement schemes are developed and attempted. The schemes employ a data taking procedure which significantly reduces the effects of nuclear spin accumulation. A coil mounted on the device is able to successfully drive nuclear magnetic resonance (NMR) but does not produce a large enough radiofrequency (RF) field to induce measureable ESR.Item EPR Analysis of Myosin Structural Dynamics(2009-10-07) Harris, RobertThe structural dynamics of myosin during muscle contraction can be discerned in situ through site directed spin labeling of myosin and electron paramagnetic resonance (EPR) spectroscopy. To achieve in situ measurements, spin labeled myosin regulatory light chain (RLC) is exchanged for endogenous RLC in rabbit psoas fiber bundles. In order to ensure the structural integrity of exchanged muscle fibers, functional measurements must be done before and after exchange. After verifying function after RLC exchange, we can use EPR to measure the orientational dynamics of the RLC in a variety of states during muscle contraction.Item Fermi Acceleration Model of Particles in Centaurus A’s Inner Lobes(2020) Thomson, AaronA first order Fermi acceleration model is built to investigate non-thermal synchrotron and inverse-Compton infrared radiation from the inner lobes of nearby radio galaxy Centaurus A. The model’s predicted spectra are consistent with observation. However, the model is founded on assumptions and estimations that do not allow conclusive verdicts. Estimations of the local intracluster medium density, pressure, and temperature support the model’s validity because they agree with estimates of previous research.Item Fiber Optic Feedthrough Design For Use In Cryogenic Dilution Refrigeration Systems(2012-04-18) Maunu, TylerBose-Einstein condensation is a fundamental state of dilute gases of bosons. It was originally predicted in 1924 by S. Bose and A. Einstein, and it refers to a quantum configuration at low temperatures in which a large portion (the condensate fraction) of particles collapse into the ground state. As can be seen in Figure 1, Rb-87 has been shown to exhibit the properties of Bose-Einstein condensation at low temperatures. Our experiment focuses on studying superfluid Helium-4. A superfluid is a phase of matter with zero viscosity, infinite conductivity, and other unusual properties. It is generally accepted that the superfluid properties of supercooled Helium-4 is caused by the composite boson exhibiting behavior associated with Bose-Einstein condensation, but it has not yet been conclusively proven. The goal of our experiment is to analyze the transmission characteristics of a slab of Helium-4 superfluid. These transmission characteristics could hopefully be used to offer some evidence of Bose-Einstein condensation in superfluid Helium-4. To accomplish this task, we used a dilution refrigeration system to cool our experimental cell down to extremely low temperatures. Inside the cell, we use a laser pulse in a fiber optic cable to produce a pulse of atoms at the bottom of the slab of Helium-4. These atoms are then transmitted through the slab and shot out the other side. The transmitted atoms are then detected on a series of superconducting bolometers. With bolometers, we are able to accurately and quickly determine energy levels of the transmitted atoms when they strike the surface of each bolometer. The purpose of my research focused on the design of our internal vacuum can and cell. The aspect of the design that needed modifying was the optical fiber feed through, which can be seen in Figure 3. These feedthroughs are essential in transferring laser pulses from an external source into the experimental cell. The feedthroughs must be leak proof in order to allow the dilution refrigeration system to run smoothly as well as to maintain accuracy within the experimental cell.Item Frequency Response of a Magnetostrictive Ferromagnet-Polymer Composite(2020) Alaei, Sauviz; Dahlberg, E. DanItem Graphene Point Junctions: A Potential Platform for Achieving Valley Polarization(2024-08-31) Tavakley, Jack; Ren, Wei; Davydov, Konstantin; Wang, KeItem Heat Diffusion from an Optical Source in a Low-Temperature Experiment(2009-04-08) Berntson, BjornMy research involves the study of heat diffusion in an optical cable that will be used as a heat source in a low-temperature experiment. The system of study consists of a fiber optical cable coated by a film of liquid helium. This system is cooled to near absolute zero, where quantum mechanical properties of the system are studied by using a laser to send short pulses of light through the cable to evaporate pulses of helium vapor. Doing so requires an optical source. To characterize the vapor pulses, it may be important to consider the flow of thermal energy back into the fiber as well as into the liquid helium film. The system can be modeled by a partial differential equation known as the heat equation. Solving the heat equation with respect to the optical source affects the overall experiment. To solve the equation, I use the FORTRAN programming language along with analytical methods whenever feasible.Item Kinetics of Polybutadiene-poly(ethyleneoxide) Micelles in an Ionic Liquid(2009-04-08) Santiago, JessicaAmphiphilic block copolymers can form micellar structures when dissolved in a selective solvent, which are of interest in a range of applications. Once in solution, a dynamic steady state is established; however, in some cases the incompatibility between block and solvent prevents the realization of equilibrium, forming kinetically frozen aggregates. The expectation is that sufficient thermal energy may allow the locked-in micelle system to relax into a more stable conformation. In this experiment, polybutadiene-poly(ethylene oxide) (PB-PEO) micelles were prepared in the ionic liquid 1-butyl-3-methyl imidazolium bis(trifluoromethylsulfonyl) imide [BMI][TFSI] via direct dissolution and cosolvent-aided dissolution using dichloromethane. Measurements of the hydrodynamic radii conducted by dynamic light scattering revealed the formation of micelles with drastically different average sizes in each preparation procedure. The thermally stable environment provided by [BMI][TFSI] then permitted the annealing of both samples at relatively high temperatures. The micelles formed by direct dissolution significantly decreased in size and width of distribution, in contrast to the cosolvent-produced micelles, which retained their smaller size and low polydispersity. Interestingly, the aggregates prepared by the two protocols yielded different micelle sizes even after thermal relaxation, suggesting the formation of a metastable morphology. These findings illustrate the strong path-dependence of micelle formation and relaxation.Item Lateral Shower Shape of Photons in the Electromagnetic Calorimeter at BES-III(2010-04-21) Reeves, KatherineBES-III is an electron-positron detector in Beijing, China. I analyzed the lateral shower shape of photons in the electromagnetic calorimeter. My study showed how simulated data correlate with real data. I studied the differences for various energy photons, differences based on locations of where the shower originated, and the effects of how material in front of the calorimeter effects these shower measurements.Item Low Background Measurements of Radioisotope Contamination via Gamma Spectroscopy(2012-04-18) Epland, MatthewAstronomical observations have shown that most of the universe is made up of dark matter and dark energy rather than the normal matter and energy we observe every day. The Cryogenic Dark Matter Search, CDMS, is working to detect dark matter particles with very pure, super-cooled germanium crystals. In order to be sensitive enough to discover weakly interacting dark matter the germanium detectors must be well shielded by placing them deep underground and surrounding them with lead in addition to many other means. In this research project the low level contamination of materials used in the construction of current and planned detector assemblies was measured in order to reduce the background of future CDMS detectors. The isotopes investigated included U-238, Th-232, K-40, Co-60 and Cs-137. The contamination measurements were done via gamma spectroscopy in a low background detector, named Gopher, located in the Soudan mine. A selection of the analyzed samples are presented here, as well as the results of a shielding upgrade to Gopher that improved its measurement capabilities considerably. The results obtained in Gopher are very important to improving the CDMS experiment in the future and it's new shield design can be used in upgrading similar detectors elsewhere.Item Measurement of Diamagnetism in Water(2010-04-21) Chen, ZijunDiamagnetic materials create magnetic fields that opposes an externally applied magnetic field. Water is a diamagnetic material. However, the interaction is extremely weak, and visually noticeable effects can only be obtained using powerful superconducting magnets. In the past, demonstrations of diamagnetism in water using more accessible permanent magnets have been qualitative. The goal of the experiment was to quantify the diamagnetic effect of a permanent magnet on water using techniques accessible at a high school or introductory college physics level.Item Measurement of Viscosity of Cellular Mediums Using Brownian Motion(2011-04-13) Morris, JonathanThe viscosity of an artificial biological medium developed in Vincent Noireaux’s laboratory based on cytoplasm extracted from cells will be determined. These measurements will allow for comparison of the viscosity of the artificial medium used for in vitro protein expression with that of real cytoplasm used in cells. Using an optical microscope, the displacement after thirty seconds time interval of a one micrometer latex bead in the medium. The displacement measurements form a distribution. The root mean square of the displacement is the square root of 2Dt, where D is the diffusion coefficient and t is the time. From the diffusion coefficient, using the Stokes-Einstein equation, D = KbT/(6*pi*nu*a), where Kb is Boltzmann's constant, a is the radius of the bead, and nu gives the viscosity of the medium. The viscosity of water will be determined as a baseline and validation of the procedure, before measuring the viscosity of the medium.Item Non-collinear Spin Characterization of Platinum Catalyst Clusters from Computer Simulations(2010-04-21) Maunu, Ryan E.Catalysts are central to many present and future technologies used in pollution control and energy conservation. The chemical mechanisms of such catalysts however remains largely unknown. A fundamental understanding of these catalytic mechanisms is imperative for optimization of their use in such technologies as in fuel cells of future cars. The Halley research group has developed a self consistent tight-binding (SCTB) code that has been shown calculate band structures, lattice coefficients, and cohesive energies of platinum catalyst clusters consistent with the most accurate and widely used first-principles simulation package, the Vienna Ab-initio Simulation Package (VASP). The ability to calculate spin structures has recently been added to the SCTB code, and its results must be must be verified against VASP calculations before further development can be made to the SCTB code. In the future, the SCTB code will allow simulated catalytic reactions to be studied on a larger scale that is allowed by first principles calculations. This research has studied the collinear and non-collinear spin structure of 13 atom platinum clusters, as calculated from first principles simulations using VASP.Item Optimization of the Crystal Growth Process for the High-Temperature Superconductor HgBa2 CuO4+8(2012-04-18) Dorow, ChelseyHgBa2 CuO4+8(Hg1201)is of critical importance in the study of high-temperature superconductivity as it possesses one of the highest Tc values and is considered a model compound with a relatively simple structure. Research on Hg1201, particularly in the area of neutron scattering, has been limited by the demanding crystal growth procedure. Neutron scattering has proven to be a useful tool as neutrons interact magnetically with crystals, allowing for the detection of magnetic excitations; magnetic properties in different phases of high-Tc materials are thought to be linked to the mechanism for superconductivity. Preparing a sample suitable for neutron scattering involves an intensive growth effort, as the weak nature of the neutron scattering cross section requires large, high-‐quality crystal samples. The growth process of Hg1201 was optimized, resulting in several crystal samples to be measured with neutron scattering.