Browsing by Subject "physics"

Now showing 1 - 20 of 36

Book Review of Discovering Relativity for Yourself by Sam Lilley
(Library Journal, 1981-07-01) Sandy, John H.
Conjuring Time Crystals
(The Texas Scientist, 2018) The Texas Scientist
Defying Gravity
(The Texas Scientist, 2016) Airhart, Marc
Effect of CSLM imaging rate on biofilms of P. aeruginosa and S. aureus
(2015-05) Du, Reginald; Gordon, Vernita
Biofilms are sessile communities of bacteria that can be found in an wide range of environments. Their inhabitants are phenotypically distinct from plank- tonic bacteria and are capable of forming complex, three-dimensional structures. Biofilms are studied using confocal scanning laser microscopy, or CSLM. This technique uses lasers and Novel Fluorescent Proteins (NFPs) to measure growth and structure formation of single- and multi-species biofilms in situ in three dimensions. We investigate the effects of slow and fast rates of image acquisition on mono- and co-cultures of biofilm forming bacteria: Pseudomonas aeruginosa and Staphylococcus aureus. After calculating growth rates and lag times, we find that fast scanning rates reduce the growth rate of P. aeruginosa in co-culture. Additionally, co-culture speeds up P. aeruginosa growth relative to monoculture when imaged at a slow rate, and fast scanning reverts co-culture growth to monoculture-like behavior. Additionally, a significant lag time is observed for P. aeruginosa grown in co-culture. The observed influence of confocal imaging rate on population dynamics should be considered in future studies to ensure accurate measurement of bacterial phenomena.
Energy Microfiche Collection
(1984) Sandy, John H.
Fueled by Physics
(The Texas Scientist, 2017) The Texas Scientist
Numerical Boltzmann Equation Solutions for Secretly Asymmetric Dark Matter Scenarios
(2017-05) Dessert, Christopher; Kilic, Can
The Standard Model (SM) of particle physics was completed as we know it today in 1967, but experimental confirmation had to wait until 2012 when the Large Hadron Collider (LHC) announced the discovery of the Higgs boson. In the meantime many particle theorists have been searching for physics Beyond the Standard Model (BSM), one part of which is the search for a particle physics explanation of dark matter. One potential explanation is asymmetric dark matter (ADM), in which the initial amount of dark matter and antidark matter in the universe is unequal. What makes our model, one of several ADM models, special is that there are three flavors, or types, of dark matter and even though the initial amounts are unequal in each flavor, the total amount of dark matter is equal to that of antidark matter. The three flavors interact in various ways. These interactions serve to change the flavor of the dark matter particles or annihilate them altogether. One important interaction is the decay of the heavier flavors into lighter flavors, and after a long time only the light flavor will remain. In this case there will appear to only be one flavor of dark matter with equal amounts of dark matter and antidark matter. For this reason, the model is named "Secretly Asymmetric Dark Matter (SADM)." The results presented in this thesis are a direct followup to this work. We would like to understand if the model could be a realistic theory for dark matter. To do so, we use the interactions to write down a set of equations, known as Boltzmann equations, that model the density of the dark matter in the early universe as it expands and see if the results match experimental measurements today. The interactions are complicated and the resulting equations are impossible to solve by hand. I have written a program in Mathematica 11 that will solve them numerically.
Of Blind Men and an Elephant: The Schism of Physics and Philosophy and Non-Empirical Validation
(2020) Young, Daniel F.; Juhl, Cory F.
Great revolutions in the study of nature in the past century have brought forth an onslaught of philosophical complications to the clarity of the classical perspective to which natural science was espoused prior to the twentieth century. The objective, intuitive principles by which we determined the reality of the world were beset by the ontological implications that flowed out of quantum mechanics and relativistic law. Wary of philosophical problems, a great number of the physical sciences lodge themselves in the comfort of empirical dogmatism as its only means of progression. But in light of the success of quantum systems, the ambiguity that buds must be taken into greater consideration. This paper discusses the background, development, objections, and interpretations of quantum mechanics and concurrent ontological premises to argue that such a philosophical tenet is inherent to nature, and, as such, is capable of producing results and predictions consistent with its physical and mathematical counterparts. To do so, the properties of measurement and the premises of causality are treated in terms of their physical terminology and foundations. The frameworks of Carroll, Everett, Heisenberg, Popper, and others analyze established interpretations and abstractions of quantum mechanics; its ties to the metaphysical and ontological descriptions of an existing entity are explored by means of the contrived spacetime allegory, which in principle determines the parameters that bound real systems. It is evident that ontological accounts for physical phenomena are not only viable and admissible but are necessary as our ability to describe the universe surpasses our ability to test and quantify these descriptions. These realizations allow us to better understand our world and move beyond empirical data when it is technologically unattainable, enabling us to build on statistical bases and approach the structure of realism through its essence of ambiguity.
On the structure of collisionless magneto-plasma shock waves at super-critical Alfven-Mach numbers
(Journal of Plasma Physics, 1969) Woods, L. C.
One Photon at a Time
(The Texas Scientist, 2020) The Texas Scientist
Pablo Laguna, Ph.D., ’87 & Deirdre Shoemaker, Ph.D., ’99
(The Texas Scientist, 2021) The Texas Scientist
Photonic topological insulators: Building topological states of matter
(2013-05) Berdanier, William; Shvets, Gennady
The discovery of topological insulators -- materials which are conventional insulators in the bulk but support dissipationless, "topologically protected" edge states -- has revolutionized condensed matter physics in recent years. Indeed, topological insulators have been of interest to physicists as much for their unique physics as for their plethora of potential applications, which run the gamut from nano-scale electronic circuits to the realization of Majorana fermions and large-scale quantum computers. However, the main drawback of topological insulators is that they are currently difficult to produce experimentally, and only a handful of materials supporting the topological insulator state are known. The Shvets group recently proposed an analogue of the topological insulator state in photonic crystals. In contrast to the topological insulator state in conventional materials, in which we must simply take what nature gives us, in photonics we can literally build a topological insulator. In order for this photonic topological insulator state to occur, non-zero bianisotropy is introduced. Bianisotropy simply adds another coupling $\chi$ to the constitutive relations for the crystal: $\v{D} = \hat\epsilon \cdot \v{E} + \hat\chi \cdot \v{H}$, $\v{B} = \hat{\chi}^\dagger \cdot \v{E}+\hat\mu \cdot \v{H}$. A photonic crystal composed of a hexagonal lattice of rods has a Dirac point crossing in its band structure at the K-point, and in the presence of a non-zero bianisotropy, this Dirac point becomes gapped, supporting topologically protected edge states. This thesis seeks to extend the photonic topological insulator model originally proposed by Shvets et. al. by adding another important term from photonics, a so-called "magneto-optic" (MO) term. This term is produced by applying an external magnetic field to the crystal, which is interesting theoretically because magnetic-fields are not time-reversal symmetric. Thus this research has a twofold purpose: (1) to determine the effects of another important photonic property on the photonic topological insulator structure and potentially exploit those effects in novel applications, thereby \emph{building} topologically insulating structures, and (2) to investigate the role of time-reversal symmetry breaking in topological insulators via photonic crystals. For the photonic topological insulator structure, I derive an effective Dirac Hamiltonian that describes the two bands of the Dirac crossing. I show that this Hamiltonian, when no MO term is present, is identical to the famous Kane-Mele Hamiltonian that introduced the topological insulator state in conventional materials. Here, bianisotropy plays the role of spin-orbit coupling, with the states $\Psi^+=E_z + H_z$ and $\Psi^-= E_z - H_z$ playing the roles of spin-up and spin-down, respectively. I demonstrate that these states are immune to disorder -- a consequence of their topological protection -- by calculating the Chern numbers of the edge states, calculating their band diagrams, and by launching these states in simulations and showing that they propagate one-way through various obstacles with no backscattering. I also calculate the new terms added by the time-reversal-symmetry-breaking MO term and calculate analytically what becomes of the system's eigenstates. As well, a weak form of Maxwell's equations is derived for use in finite-element-method simulations in COMSOL, then implemented for band-structure calculations. I find that MO adds a second mass term to the Dirac Hamiltonian which has no natural analogue in conventional topological insulators, as this mass term is not time-reversal invariant. The system's eigenstates are shown to be an admixture of spin-up and spin-down, which I refer to as $\Phi^+$ and $\Phi^-$, which become $\Psi^+$ and $\Psi^-$ in the limit of bianisotropy being much stronger than MO and become just $E_z$ and $H_z$ (TE and TM modes) in the limit of MO being much stronger than bianisotropy. MO's effect on the band structure is shown to be that it splits the gap caused by bianisotropy alone, dividing it into two gaps, one larger than the other. As the magnitude of the MO term increases, one of the gaps becomes smaller indefinitely while the other grows, a consistent result with previous literature in photonics which predicts that the MO term alone only opens \emph{one} gap (only TM waves are affected by the MO term). Several types of interfaces are explored in order to investigate the edge states in the presence of MO and bianisotropy. Remarkably, it is found that if the ratio of the MO term and the bianisotropy is kept constant across two interfacing photonic crystals, then the edge states survive. More remarkable still, they retain their topological protection, demonstrated via propagating $\Phi^\pm$ through disordered interfaces. This result is truly unexpected, as the topological protection of the edge states of topological insulators is fundamentally dependent on the system being time-reversal invariant.
Physics: Selected Reference Sources for Instruction and Research
(1980) Sandy, John H.
Plasma Channels And Laser Pulse Tailoring For Gev Laser-Plasma Accelerators
(2002-12) Downer, M.C.; Chiu, C.; Fomyts'kyi, M.; Gaul, E.W.; Grigsby, F.; Matlis, N.H.; Shim, B.; Smith, P.J.; Zgadzaj, R.; Downer, M.C.; Chiu, C.; Fomyts’kyi, M.; Gaul, E.W.; Grigsby, F.; Matlis, N.H.; Shim, B.; Smith, P.J.; Zgadzaj, R.
We have demonstrated distortion-free guiding of I TW pulses at near relativistic intensity (0.2 x 10(18) W/cm(2)) over 60 Rayleigh lengths at 20 Hz repetition rate in a preformed helium plasma channel. As steps toward efficient channeled Laser Wakefield Acceleration up to the dephasing limit, we have upgraded our laser system from I to 4 TW, adapted femtosecond interferometric diagnostics to probe plasma density fluctuations inside the channel, and developed detailed strategies for managing ionization distortions at the channel entrance and exit at the upgraded intensity. We also report simulations, and preliminary experiments, that explore a strategy for Raman-seeding laser pulses to coherently control both unchanneled and channeled LWFA in order to lower the laser energy threshold and increase the repetition rate of election pickup and acceleration.
Pyramid Probe
(The Texas Scientist, 2016) The Texas Scientist
Relationships Between Selected Physical Parameters and Cost Responses for the Deep-Well Disposal of Aqueous Industrial Wastes
(University of Texas at Austin, 1968-08) Moseley, J.C. II; Malina, J.F.
Resolving Multiple Gravitational Wave Sources in Pulsar Timing Array Data
(2022-09-29) Mohanty, Soumya D.; Qian, Yi-Qian; Wang, Yan
Timing the arrival of radio pulses from an array of rapidly spinning neutron stars (Pulsars) is a promising method for detecting gravitational waves (GWs) in the ultra-low frequency regime (10!" Hz to 10!# Hz), primarily from supermassive (billion solar mass and above) black hole binaries . It is expected that next-generation radio telescopes, namely, the Five-Hundred-Meter Aperture Spherical Radio Telescope (FAST) and the Square Kilometer Array (SKA), will grow the number of well-timed pulsars to 𝑂(10$). This will result in greater distance reach for GW sources, uncovering multiple resolvable GW sources in addition to an unresolved population. The multisource resolution problem for PTAs poses a unique set of data analysis challenges such as nonuniformly sampled data, a large number of so-called pulsar phase parameters that arise from the inaccurately measured distances to the pulsars, and poor separation of signals in the Fourier domain due to a small number of cycles in the observed waveforms. We are developing an end-to-end software pipeline for addressing these challenges. The core idea is the iterative subtraction of individually estimated GW sources from the data. However, multiple stages of refinement are needed improve the sample of identified sources, including a novel approach that mitigates spurious sources by cross-checking the outputs from two semi-independent refinement steps. The performance of the current version of the pipeline was quantified on simulated data from PTAs containing 10% and 10$ pulsars, leading to state-of-the-art results in all cases. For example, the fraction of sources found by the method that correspond to true sources in the simulated data exceeds 78% and 93% for a large-scale (with 10$ pulsars and 200 sources) and a midscale (with 10% pulsars and 100 sources) PTA, respectively. The pipeline is currently implemented as a mix of Matlab and parallelized C-code running on TACC resources.
Science Study Break - "2012"
(2010-09-14) Kopp, Sacha
Science Study Break - Feynman
(2011-09-30) Ottaviani, Jim
Signal Processing Compact Binary Coalescence Gravitational Wave Data from the Advanced LIGO Detectors
(2017-12) Bogat, Sophia E.; Matzner, Richard
Abstract or description: This thesis explores the complex signal processing tools and techniques used to perform gravitational wave astronomy. The first ever direct observation of spatial strain caused by a gravitational wave was achieved by the Laser Interferometer Gravitational-Wave Observatory (LIGO) on September 14th, 2015, nearly 100 years after Albert Einstein predicted their existence. Because the amplitude of the strain is so small (on the order of 10-21), it must be measured by a 4 kilometer long interferometer equipped with extremely advanced thermal and seismic vibration isolation systems. Furthermore, the data must undergo significant processing in the form of whitening, matched filtering, and bandpass filtering. We present a detailed study of the steps undergone to identify and validate potential gravitational wavesignals using the LIGO-designed PyCBC software framework for the observation of compact binary coalescence.