Browsing by Subject "Physics"

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An Analytical Solution to Nonlinear Flow Response of Soft Hair Beds
(2020-05) Vural, Zerrin
Beds of passive, hair-like fibers can be found in many biological systems, including inside ourselves. Intestines, tongues, and blood vessels contain these types of surfaces, making us ‘hairy’ on the inside. A coupled elastoviscous problem arises when hairy surfaces are sub- jected to shear-driven Stokes flows. The hairs deform in response to fluid flows, and in turn, hair deformation affect fluid stresses. The the- oretical model that accounts for the large-deformation flow response of a biomimetic model system of elastomer hair beds is known. However, the solution to the differo-integral equation governing the behavior of a bed of hairs immersed in fluid is difficult to uncover. Here we show a method to find the analytic solution to this equation of equilibrium. The time-independent equation of motion describing the bending of the hairs can be found by extending the pendulum problem for large angles to the case of bed hairs subject to Stokes flows. We consider the Hamiltonian formalism, analyze phase portraits, and utilize elliptic integrals to reduce the problem to a numerical problem. By these methods we find a solution that characterizes the hairs’ shape by giving the angle with respect to the surface normal at any distance along the hair. Since it was found that biological hairy surfaces reduce fluid drag, angled hairs may be used in the design of integrated microfluidic components, such as diodes and pumps. Thus our solution would be useful to manufacture these devices.
The application of visualization methods to educational data sets with inspiration from statistical and fluid mechanics
(2014-05) Bendinelli, Anthony James; Marder, Michael P., 1960-
This dissertation focuses on the development of visualization methods that enable us to examine longitudinal data in a unique way. We take inspiration from statistical and fluid mechanics to represent our data as a "flow" through time. Our visualizations represent vector fields (or flow plots), streamlines, and trajectories, and they are constructed in a similar manner to how one might analyze the aggregate motion of particles in a fluid. However, the subject of our research extends beyond ordinary fluid mechanics. We will use our visualizations to examine statewide standardized test scores in Texas from 2003 to 2011. The nature of the data makes it a perfect match for our methodology, since students' test scores tend to change over time in a semi-deterministic but nonlinear manner. Furthermore, our methods represent a departure from the standard ways of analyzing educational data. By visualizing the changes in students' test scores over a nine-year period, we discovered that our flow plots were changing with the eventual graduating class of 2012. The change in our visualizations was caused by an educational policy known as the Student Success Initiative, or SSI. The policy forced students to pass their standardized tests in 5th and 8th grade, or risk being held back a grade. To help with this process, students who initially failed were given extra instruction and additional opportunities to take the test. SSI was implemented in such a way that it would affect the class of 2012 and beyond, although we did not know of the program's existence until our plots had been developed. SSI had a successful impact on the educational career of Texas students; a far greater percentage of students were able to pass the 5th and 8th grade standardized tests after SSI was implemented. The striking feature of SSI, however, is that it also significantly improved test scores in 6th, 7th, 9th, and 10th grade. Despite its success at improving test scores over many years and grades, the program was eventually defunded. This was partially due to an inability to construct a lengthy longitudinal analysis of the program's influence. Our methodology would have conclusively shown the effectiveness of the SSI policy. Despite the defunding of the SSI, I am confident our methodology can be extended to illustrate changes in other data systems. These systems may or may not be related to education; our code and techniques are designed to be as universal as possible. We will explore several extensions to other data sets at the end of this dissertation.
Characterization of photomultiplier DOM for Cherenkov detectors
(2015-12) Knipper, Chelsea Jaclyn; Lang, Karol, 1955-; Ritchie, Jack
Several qualities of the IceCube Digital Optical Module (DOM) are characterized for use in the CHIPS neutrino detection project through tests of charge linearity, uniformity, gain, and Cherenkov radiation. The charge is linear in transmittance with a chi^2/ndf of 2.42. The DOM shows a radial decrease in sensitivity with a slight angular asymmetry. A nominal gain of 10^7 is reached near 1400 HV. These tests are found to largely agree with IceCube reults. The measured Cherenkov spectrum of light created inside the DOM is compared with an analytical estimate of the upper limit for photoelectrons produced at the cathode, and experimental results are found to be 62% lower than the estimated limit.
Cold plasma dispersion surfaces
(Journal of Plasma Physics, 1979) Oakes , M. E.; Michie, R. B.; Tsui, K. H.; Copeland, J. E.
A culture of dissonance : Wassily Kandinsky, atonality, and abstraction
(2014-05) Boland, Lynn; Henderson, Linda Dalrymple, 1948-
A Culture of Dissonance: Wassily Kandinsky, Atonality, and Abstraction by Lynn Edward Boland, Ph.D. Supervisor: Linda D. Henderson Wassily Kandinsky's interest in music as a source for abstraction in painting has often been noted in the scholarship on his art. However, no studies have sufficiently explained how the artist employed musical strategies, especially as he was developing his abstract style in the first decade of the twentieth century. Kandinsky's looked primarily to Arnold Schoenberg's new musical idioms and theories, and he was deeply inspired by highly dissonant music, but his ideas were set within a much broader context that further suggested and encouraged the expressive and transformative power of dissonance. By the late nineteenth century, extended passages of dissonance were common in musical compositions. At the same time, the concept of dissonance as a positive force was suggested in a wide range of late nineteenth-century literature, including the writings of Friedrich [should be this spelling throughout] Nietzsche, occult authors, popular texts on physics and experimental psychology, as well as within music and art theory. Close readings of Kandinsky's theoretical texts and selected works of art provide insights into how he might have understood and employed these concepts in his formation of an abstract style. Kandinsky's paintings Impression III (Concert) of 1911 and Composition VII of 1913 are the primary artistic foci of this study, along with his book Concerning the Spiritual in Art and the anthology Der Blaue Reiter, which he co-edited. This dissertation will seek to restore the concept of musical dissonance and its application in the visual arts to its historical context for Kandinsky. This will facilitate more informed formal analyses of Schoenberg's music and Kandinsky's paintings, which, in turn, suggest strategies of atonal musical composition applied to abstract painting. Additionally, this dissertation will establish an artistic context of visual dissonance that goes beyond Kandinsky, including artistic movements in France and Russia, allowing additional comparisons and a consideration of the larger impact of these ideas.
Development of variable temperature NMR force microscopy : proton spin relaxation measurements in ammonium sulfate
(2012-08) Manzanera Esteve, Isaac Vicente, 1977-; Markert, John T.; de Lozanne, Alejandro; Li, Xiaoqin; Yao, Zhen; Goodenough, John
Nuclear magnetic resonance force microscopy (NMRFM) of a micron size sample of ammonium sulfate was performed by measuring the cantilever deflection produced by coupling the magnetic force to a mechanical cantilever at its resonance frequency. Spin-lattice and spin-spin relaxation measurements were obtained with our newly developed NMRFM probe. A system with more advanced positioning, acquisition and analysis has been fabricated. A new device in which a semi-automatic system performs nanoposition control, spin manipulation, dynamical measurements, and data analysis has been demonstrated to be successful. The new system has proven to be an improvement with respect to other versions of NMRFM probes, thanks to its versatility for pulse sequence designs, faster data acquisition, and automatic analysis of the information. This thesis presents an explanation of the theoretical details of nuclear magnetic resonance force microscopy, and experiments are described in which dynamical measurements of proton spin interactions are obtained. Finally, relaxation time e ffects of the observed force signal are considered in detail. A novel spin manipulation technique which is being implemented for future measurements is described in detail, and magnet con figurations for larger magnetic field gradients and consequently larger signal-to-noise ratio, are also described.
The effect of laser contrast and target thickness on laser-plasma interactions at the Texas Petawatt
(2014-12) Meadows, Alexander Ross; Hegelich, Bjorn Manuel
A two-year experimental campaign is described during which diamond-like carbon and plastic targets with thicknesses from 20 nanometers to 15 micrometers were irradiated by the Texas Petawatt Laser. Target composition and thickness were varied to modify the specifics of the laser-matter interaction. Plasma mirrors were selectively implemented to affect the contrast of the laser system and provide additional control of the physical processes under investigation. A number of particle diagnostics were implemented to measure the distribution of laser accelerated ions and electrons. In addition, optical diagnostics were fielded to measure the intensity profile of the laser and measure the density of the target pre-plasma. The results of these experiments suggest that the Texas Petawatt laser pulse has pre-pulse and pedestal features with intensities at least 10⁻⁸ of the main pulse. Micronscale targets were able to survive these features and maintain a relatively sharp density gradient until the arrival of the main laser pulse, allowing for ion acceleration. Electron spectra measured in this configuration show an average temperature of 10 MeV, with no v angular dependence out to at least 60 degrees. By contrast, interferometric plasma density measurements and a lack of any observable ion acceleration suggest that nanoscale targets were destroyed well before the main pulse. In this case, the peak of the laser pulse interacted with a cloud of plasma between 10⁻³ and 10⁻² of critical density. The contrast improvement offered by the implementation of plasma mirrors was seen to increase the maximum energy of laser accelerated protons from targets thicker than 1 micrometer. In addition, the plasma mirrors allowed nanoscale targets to survive pre-pulse and pedestal features and support the production of ion beams. Proton spectra show that ions were accelerated to greater maximum energies from nanoscale targets than from more traditional micron-scale targets. This effect can be attributed to a reduction in the target pre-plasma scale length upon the introduction of plasma mirrors. These results indicate that the manipulation of target properties and laser contrast can significantly affect the interaction between an ultrahigh intensity laser and a target.
Exploration of models of dark matter and portals to new physics
(2023-12) Desai, Niral; Kilic, Can; Caceres, Elena; Onyisi, Peter; Boylan-Kolchin, Mike
Although the Standard Model of particle physics has seen tremendous experimental success, there remain still unanswered questions. One such question is the nature of dark matter, which has been only observed through its gravitational effects and yet comprises about 80% of all matter in the Universe. Many models have been proposed to solve the dark matter problem and other open questions, although they can face severe experimental constraints, especially from data from particle colliders. The paradigm of probing new physics through portals, which are gauge-neutral Standard Model operators, alleviates many of these constraints. In this dissertation I explore the phenomenology of three different models of new physics. The first model proposes a setup of lepton-flavored dark matter in a 5-dimensional setup in which lepton flavor violating processes are naturally suppressed. The second model proposes that dark matter is a composite state emerging from a rich strongly-coupled beyond-Standard Model sector which also contains states coupling to neutrinos, such that the dark matter communicates to the Standard Model via a neutrino portal. In the third model, we propose a strongly-coupled beyond-Standard Model sector which interacts with the Standard Model through both a neutrino portal and a Higgs portal, resulting in collider signatures which are nontrivially different from those of either type of portal separately.
Explosive evolution of near-threshold kinetic instabilities
(2017-08) Sanz Orozco, David; Berk, H. L.; Breizman, Boris N.; Morrison, Philip J; Waelbroeck, Francois L; Gamba, Irene M
In the past, studies of waves close to marginal stability have revealed a rich variety of behavior in different physical contexts. One of the possible outcomes is an explosive growth of the mode amplitude, which forms the core of this thesis. This outcome has been predicted in both the fluid mechanics and the plasma literature. While we make some comments regarding the fluids context, in this work we focus on the near-threshold waves that are excited in kinetic systems (such as plasmas). With a few exceptions, the explosive behavior is found to asymptote to an attractor that depends on a system parameter that we shall discuss. When the mode amplitude is sufficiently large, the explosive growth loses physical meaning, and here we explore the transition between the weakly-nonlinear regime where the explosive description holds, and the strongly-nonlinear phase where the mode amplitude saturates. By investigating the phase space dynamics associated with the kinetic response, we find a link between a local flattening, or folding, of the particle distribution function and the breakdown of the explosive description. Since the explosive growth sets the stage for long-term frequency chirping modes, it is hoped that the present work can be of relevance for the prediction of the variety of chirping modes that have been observed in many experimental situations. These modes are expected to have a very significant effect on the confinement properties of fusion plasmas.
The Faculty Member: Peter Onyisi
(2015-01) Airhart, Marc
First-principles studies of perovskite thin films and heterostructures
(2015-08) Fredrickson, Kurt David; Demkov, Alexander A.; Chelikowsky, James R; Ekerdt, John G; Fiete, Gregory A; MacDonald, Allan H
The growth of oxides on semiconductors is of great interest for electronics applications; however, the effects of film growth, atomic adsorption, and strain can have fundamental effects on the properties of the oxides in question. In this dissertation, we use density functional theory to calculate the properties of SrTiO₃ and BaTiO₃, and discover the effects of the environment on the electronic and atomic properties of these systems. We examine the effects of H adsorption on the SrTiO₃ and BaTiO₃(001) surfaces, and discover the coverage-dependent onset and retreat of metallic surface states. We calculate the effect of Pt film growth on BaTiO₃, and study the effects on the polarization of BaTiO₃ for different Pt/BaTiO₃ interfaces. We study how strain and interfacial chemistry affect the ferroelectricity of BaTiO₃/Ge and BaTiO₃/SrTiO₃/Ge heterostructures. We also discuss the development of two-dimensional conducting states created in BaTiO₃/SrTiO₃ heterostructures.
Frequency response characteristics of fluid-immersed hairbeds
(2022) Freeman, Naiesa
A high-intensity cold atom source
(2012-08) Borysow, Michael; Heinzen, Daniel J.; Fink, Manfred; Keto, John; Sitz, Greg; Varghese, Philip L.
Presented in this thesis is the design and characterization of a new, high-flux source of cold atoms based on continuous, post-nozzle injection of lithium atoms into a cryogenic, supersonic helium jet. To date, experiments have been performed with lithium injection fractions up to [approximately equal to]10⁻⁶, where fluorescence spectroscopy reveals successful capture and thermalization of lithium atoms within the helium jet. The observed lithium beam copropagates with the helium jet and has a temperature of less than 10 mK, a brightness of 1.1x10¹⁹ m⁻² s⁻¹ sr⁻¹, and a brilliance of 3.1x10²⁰ m⁻² s⁻¹ sr⁻¹. Lithium atoms contained within a solid angle of [approximately equal to]0.018 sr are good candidates for future magnetic extraction. This results in a potentially capturable lithium flux of 1.1x10¹² s⁻¹, comparable to the existing record for a cold atomic beam. Also presented is preliminary data showing lithium fluorescence nearly 1 m downstream, demonstrating that the cold lithium beam can be successfully extracted from the seeding region. Numerical simulations reproduce capture efficiency to within 50%, suggesting that the process is well understood. We believe that successful seeding may be possible at a fraction up to 10⁻⁴. Seeding at this rate could produce an atomic beam with a flux as high as 1.3x10¹⁴ s⁻¹ at a phase-space density up to 1.6x10⁻⁷, corresponding to brightness and brilliance of order 10²² m⁻² s⁻¹ sr⁻¹ and 10²⁴ m⁻² s⁻¹ sr⁻¹ , respectively. If this novel cooling method performs as well at higher incident lithium flux, it could serve as a pump source and pave the way to the realization of the first truly continuous atom laser.
High-sensitivity tracking of optically trapped particles in gases and liquids : observation of Brownian motion in velocity space
(2014-08) Kheifets, Simon; Raizen, Mark G.
The thermal velocity fluctuations of microscopic particles mediate the transition from microscopic statistical mechanics to macroscopic long-time diffusion. Prior to this work, detection methods lacked the sensitivity necessary to resolve motion at the length and time scales at which thermal velocity fluctuations occur. This dissertation details two experiments which resulted in velocity measurement of the thermal motion of dielectric microspheres suspended by an optical trap in gases and liquids. First, optical tweezers were used to trap glass microspheres in air over a wide range of pressures and a detection system was developed to track the trapped microspheres' trajectories with MHz bandwidth and <100 fm/rt(Hz) position sensitivity. Low-noise trajectory measurements allowed for observation of fluctuations in the instantaneous velocity of a trapped particle with a signal to noise ratio (SNR) of 26 dB, and provided direct verification of the equipartition theorem and of the Maxwell-Boltzmann velocity distribution for a single Brownian particle. Next, the detection technology was further optimized and used to track optically trapped silica and barium titanate glass microspheres in water and acetone with >50 MHz bandwidth and <3 fm/rt(Hz) sensitivity. Brownian motion in a liquid is influenced by hydrodynamic, time-retarded coupling between the particle and the fluid flow its motion generates. Our measurements allowed for instantaneous velocity measurement with an SNR of up to 16 dB and confirmed the Maxwell Boltzmann distribution for Brownian motion in a liquid. The measurements also revealed several unusual features predicted for Brownian motion in the regime of hydrodynamic coupling, including faster-than-exponential decay of the velocity autocorrelation function, correlation of the thermal force and non-zero cross-correlation between the particle's velocity and the thermal force preceding it.
Higher precision mass measurement via the boundary of many-body phase space
(2013-12) White, Craig Ian; Kilic, Can
We introduce a new method of mass measurement for particles in decay chains. The method relies upon performing a likelihood analysis on the phase space of the decay in its full dimensionality in a Lorentz-invariant formulation. This method is applicable for any decay chain, but we demonstrate it specifically in the case of a four-body final state decay in which one of the final particles is invisible. We directly compare our method to the edge and endpoint method and show that our new method can achieve higher precision with limited statistics.
Laboratory Detection of Two New C5H2 Isomers
(The Astrophysical Journal, 1998-12-20) Gottlieb, C.A.; McCarthy, M.C.; Gordon, Vernita D.; Chakan, J. M.; Apponi, A.J.; Thaddeus, P.
Two new isomers of the C5H2 molecule have been detected in the laboratory, and their microwave spectra have been characterized to high accuracy. Both are good candidates for radio astronomical detection. Like the two isomers previously detected in the laboratory, both are closed-shell carbenes, and both are extremely polar and fairly stable. The first, calculated to lie 0.73 eV above isomer 1, the C5H2 ring-chain ground state, has a bent carbon chain backbone with single, double, and triple bonds; the second, calculated to lie only 0.19 eV higher in energy, is a new type of ring chain formed by adding a pair of doubly bonded carbon atoms to the top of the C3H2 ring, which is one of the most abundant interstellar molecules. Subject headings: ISM: molecules—line: identification—molecular data—molecular processes— radio lines: ISM
Low-temperature magnetic force microscopy with a simple design: analyzing the magnetic domains of a simple hard disk drive
(2024-05) Vit, Jeffrey Orlando ; de Lozanne, Alejandro L.; John Markert; Incorvia , Jean Anne; Tsoi, Maxim
The first part of this dissertation introduces the theoretical background for the Magnetic Force Microscope (MFM) and the theoretical basis for magnetic domains. The second part will address issues we have come across on previous designs and how our newer design overcomes these issues. Along with the construction of our low temperature magnetic force microscope (LT-MFM) and its operation. The third part focuses on the LT-MFM experimental investigation on a simple memory storage disk. Scanning probe microscopy (SPM) was first developed to study various electronic properties of different materials, such as imaging high T [subscript c] superconductors. Soon after, the SPM grew and expanded in terms of techniques and properties that could be imaged. For example, some variations of the SPM family have developed into powerful techniques to characterize magnetic features or even studying nonlinear effects in living samples. These being the MFM and Second-Harmonic imaging microscopy (SHIM). The former, and for the focus of this dissertation, was widely used for imaging surface magnetic properties from hundreds of micrometers down to the nanometer scale. With our new LT-MFM, we studied two hard disk drives (HDD) and have concluded that their magnetic domain structure closely matches with other former studies on similar HDD samples. In addition, with its simple design and open architecture, our homebuilt LT-MFM has proved, once again, that a low cost and efficient microscope can be built with minimal loss to its magnetic domain resolution.
Mapping the nanoplasma regime using harmonics
(2017-12) Korzekwa, Richard Clement; Downer, Michael Coffin; Breizman, Boris; Ditmire, Todd; Fink, Manfred; Varghese, Philip
Laser-irradiated microclusters exhibit a range of useful and scienti cally-relevant phenomena, including e cient absorption, harmonic generation, and anomalous dispersion. These properties make them useful for applications such as particle accelaration, nuclear fusion, and phase-matching for UV and X-ray sources. The generation of third harmonic light by intense illumination of pre-heated expanding clusters can be used as a way of mapping the nanoplasma regime, characterized by partial removal of the ionized cluster's electron core. We present measurements of this harmonic generation, showing a drop in expansion-related enhancement between probe intensity I[subscript pr] = 1.5 x 10¹⁶ W/cm² and I[subscript pr] = 1.0 x 10¹⁸ W/cm², where the harmonic generation vanishes. This is consistent with our model of cluster ionization, expansion, and polarizability, which we also use to estimate the cluster size distribution.
Novel tools for ultrafast spectroscopy
(2011-12) Jarvis, Thomas William; Li, Elaine; Fink, Manfred; Keto, John; Lim, Sang-Hyun; Shih, Chih-Kang; Sitz, Greg
Exciton dynamics in semiconductor nanostructures are dominated by the effects of many-body physics. The application of coherent spectroscopic tools, such as two-dimensional Fourier transform spectroscopy (2dFTS), to the study of these systems can reveal signatures of these effects, and in combination with sophisticated theoretical modeling, can lead to more complete understanding of the behaviour of these systems. 2dFTS has previously been applied to the study of GaAs quantum well samples. In this thesis, we outline a precis of the technique before describing our own experiments using 2dFTS in a partially collinear geometry. This geometry has previously been used to study chemical systems, but we believe these experiments to be the first such performed on semiconductor samples. We extend this technique to a reflection mode 2dFTS experiment, which we believe to be the first such measurement. In order to extend the techniques of coherent spectroscopy to structured systems, we construct an experimental apparatus that permits us to control the beam geometry used to perform four-wave mixing reflection measurements. To isolate extremely weak signals from intense background fields, we extend a conventional lock-in detection scheme to one that treats the optical fields exciting the sample on an unequal footing. To the best of our knowledge, these measurements represent a novel spectroscopic tool that has not previously been described.
Prescribed versus enacted curriculum : analyzing authentic assessments through performance tasks
(2014-12) Ekeoba, Jacqueline Njideka; Allen, David T.
As the requirements for completion of a high school diploma and the standards set locally and nationally take shifts towards more rigorous coverage of science, technology, engineering and mathematics (STEM), and applicability to the work place, public school curricula must evolve. This report focuses on an urban school district in Texas in the midst of transitioning towards using (i) assessments based on use of STEM principles in “authentic” applications and (ii) product-based evaluations dubbed performance tasks. Physics instructors within the district provided their experiences in the implementation process as well as their views on the authenticity of the tasks they are urged to use. The information from the physics teachers was used as the basis for identifying areas for professional training needed to support instructors in the use of authentic assessments, whether prescribed or instructor-developed.