Columnar jointing is a fracture pattern, best known from locations such as the Giant's Causeway, or Fingal's Cave, in which cracks self-organize into a nearly hexagonal arrangement, leaving behind an ordered colonnade. In this thesis observations of columnar jointing are reported from both a controlled laboratory setting, and in cooled lava flows. Experiments were performed in slurries of corn starch and water, which form columnar joints when dried. This drying process is examined in detail, and it is shown how desiccation leads to the propagation of a sharp shrinkage front. In general, but with some significant exceptions, the size of columnar joints is inversely dependent on the speed of this shrinkage front during their formation. The exceptions, which include sudden jumps in column scale, show that hysteresis is also important in choosing the column scale. Novel observations of the 3D structure of joints in starch show that columnar joints do not settle down to a perfect hexagonal pattern, but rather mature into a continuously evolving dynamic pattern. This pattern is scale invariant, and the same statistical distribution of column shapes applies equally to joints in both starch and lava. Field work was performed to study columnar jointing in the basalts of the Columbia River Basalt Group and the island of Staffa, and the more heterogeneous lava flows of Southwestern British Columbia. The widths of columns and the heights of striae (chisel-like markings that record details of cooling) were examined in detail, and these length scales are shown to be inversely proportional to each other. An additional length scale, that of wavy columns, is also first reported here. Based on these measurements, empirical advective-diffusive models are developed to describe the transport of water in a drying starch-cake, and the transport of heat in a cooling lava flow. These models have only a single scaling parameter, the Péclet number, which relates the fracture front velocity times the column size to the (thermal or hydraulic) diffusivity. In both cases, the formation of columnar joints occurs at a Péclet number of about 0.2. This model explains the hundred-fold differences in scale between columnar joints in starches and lavas, and can be used as a tool for the interpretation of joint patterns in the field.

Master of Science / Department of Physics / Robert Szoszkiewicz / Nanoscale modifications of polymer surfaces by scratching them with sharp tips with curvature radii of tens of nanometers and at variable temperatures are expected to provide wealth of information characterizing wear response of these polymers. Such studies are important in the light of understanding the nanoscale behavior of matter for future applications in advanced polymer coatings. This thesis describes how Atomic Force Microscopy (AFM) and hot-tip AFM (HT-AFM) methods were used to characterize thermal and mechanical properties of a 30 nm thick film of poly(styrene-block-ethylene oxide), PS-b-PEO, and modify its lamellar surface patterns. Additionally, it is revealed how contact AFM and HT-AFM methods can efficiently characterize the wear response of two popular polymer surfaces, poly(methyl methacrylate), PMMA, and polystyrene, PS. The AFM and HT-AFM studies on PS-b-PEO copolymer were aimed at producing spatial alignment of respective PS and PEO parts. Instead, however, surface ripples were obtained. These measurements are explained using mode I crack propagation model and stick-and-slip behavior of an AFM tip. In addition, HT-AFM studies allowed extraction of several thermo-physical properties of a PS-b-PEO film at local volumes containing about 30 attograms of a polymer. These thermo-physical quantities are: PEO melting enthalpy of, 111 ± 88 J g[superscript]-1, PS-b-PEO local specific heat of 3.6 ± 2.7 J g[superscript]-1K[superscript]-1, and molecular free energy of Helmholtz of 10[superscript]-20 J nm[superscript]-2 for the PEO within PS-b-PEO. Utilizing a spiral scan pattern at constant angular speed and at various temperatures at the AFM tip-polymer interfaces, the wear response of PS and PMMA polymers was characterized. Cross-sections along the obtained spiral wear patterns provided plots of polymer corrugation as a function of scanning speed. From these studies it was found that the corrugation of the modified polymer surface decays exponentially with linear velocity of the scanning tip.

Master of Science / Department of Physics / Carlos Trallero / Over the past four decades, the single-electron ionization of atoms has been a subject of great interest within the ultra-fast community. While contemporary atomic ionization models tend to agree well with experiment across a wide range of intensities (10[superscript]13-10[superscript]15 W/cm[superscript]2), analogous models for the ionization of molecules are currently lacking in accuracy. The deficiencies present in molecular ionization models constitute a formidable barrier for experimentalists, who wish to model the single-electron ionization dynamics of molecules in intense laser fields. The primary motivation for the work presented in this thesis is to provide a comprehensive data set which can be used to improve existing models for the strong-field ionization of molecules. Our approach is to simultaneously measure the singly-charged ion yield of a diatomic molecule paired with a noble gas atom, both having commensurate ionization potentials. These measurements are taken as a function of the laser intensity, typically spanning two orders of magnitude (10[superscript]13-10[superscript]15 W/cm[superscript]2). By taking the ratio of the molecular to atomic yields as a function of laser intensity, it is possible to "cancel out" systematic errors which are common to both species, e.g. from laser instability, or temperature fluctuations. This technique is very powerful in our ionization studies, as it alludes to the distinct mechanisms leading to the ionization of both molecular and atomic species at the same intensity which are not a function of the experimental conditions. By using the accurate treatments of atomic ionization in tandem with existing molecular ionization models as a benchmark, we can use our experimental ratios to modify existing molecular ionization theories. We hope that the data procured in this thesis will be used in the development of more accurate treatments describing the strong-field ionization of molecules.

Doctor of Philosophy / Department of Physics / Glenn Horton-Smith / Double Chooz is a reactor neutrino experiment which has shown evidence of electron anti-neutrino disappearance at 1 km distance. It has been able to exclude the no-oscillation hypothesis at 99.8% CL (2.9ς) with only one detector. From a rate plus spectral shape analysis, the value of sin²2θ₁₃ was found to be 0.109±0.030(stat) ± 0.025(syst). Correlated events mimicking an anti-neutrino event are one of the most important backgrounds for a reactor neutrino experiment like Double Chooz which measured the neutrino mixing angle θ₁₃. Cosmic muons passing through the rock surrounding the detector produce fast neutrons which give rise to correlated events through proton recoil followed by a neutron capture. Muons stopping around the chimney region subsequently decay into Michel electrons also contributing to the correlated background. Measurement of the shape and rate of this background is very important for the precise measurement of θ₁₃. Experimental techniques to estimate of the shape and rate of this background in the Double Chooz far detector are presented in this thesis.

Doctor of Philosophy / Department of Physics / Bret N. Flanders / Directed electrochemical nanowire assembly (DENA) is a method for fabricating nano-structured materials via electrochemical dendritic solidification. This thesis presents two new applications of nano-structured materials that are fabricated via the DENA methodology: cellular force sensors to probe adhesive sites on living cells and single-crystalline metallic dendrites as surface coating materials. Fast migrating cells like D. discoideum, leukocytes, and breast cancer cells migrate by attachment and detachment of discrete adhesive contacts, known as actin foci, to the substrate where the cell transmits traction forces. Despite their importance in migration, the physics by which actin foci bind and release substrates is poorly understood. This gap is largely due to the compositional complexity of actin foci in living cells and to a lack of technique for directly probing these sub-cellular structures. Recent theoretical work predicts these adhesive structures to depend on the density of adhesion receptors in the contact sites, the receptor-substrate potential, and cell-medium surface tension. This thesis describes the fabrication of sub-microscopic force sensors composed of poly(3,4-ethylene dioxythiophene) fibers that can interface directly with sub-cellular targets such as actin foci. The spring constants of these fibers are in the range of 0.07-430 nN m-1. These fibers were used to characterize the strength and lifetime of adhesion between the single adhesive contacts of D. discoideum cells and the fibers, finding an average force of 3.1 ± 2.7 nN and lifetime of 23.4 ± 18.5 s. This capability is significant because direct measurement of these properties will be necessary to measure the cell-medium surface tension and to characterize the receptor-substrate potential in the next (future) stage of this project. The fabrication of smart materials that are capable of the high dynamic range structural reconfiguration would lead to their use to confer hydrophobic, lipophobic, and anti-corrosive character to substrates in a regenerative manner. As a step towards this goal, we have extended the DENA method to enable repetitive growth and dissolution of metallic dendrites to substrates. The experimental parameters that control this process are the frequency and duty cycle of the alternating voltage signal that initiates the dendritic growth.

Doctor of Philosophy / Department of Physics / Dean A. Zollman / This research presents an investigation of how students dynamically construct knowledge in a new situation. In particular, this work focuses on the contexts of light and optics, and examines the dynamic construction of an understanding of wavefront aberrometry. The study began with clinical interviews designed to elicit students’ prior knowledge about light, basic optics, and vision; the data were analyzed phenomenographically to obtain student models of understanding and examine the possible model variations. The results indicate that students have a significant number of resources in this subject area, though some are incomplete or less useful than others. In subsequent phases, many learning and teaching interviews were conducted to design and test scaffolding procedures that could be of use to students as they constructed their understanding of the given phenomenon. Throughout this work, student responses were analyzed in terms of the resources that were being used through the knowledge construction process. Finally, a modified analysis method is presented and utilized for quantifying what types of concepts students use while constructing their understanding, and how they are able to link varying types of concepts together. Significant implications extend beyond the single context of wavefront aberrometry. Each distinct analysis technique provides further insight to the ways in which students learn across contexts and the ways in which we can scaffold their learning to improve curriculum and instruction.

Master of Science / Department of Physics / Brian R. Washburn / Rare-earth doped optical fibers can be used to make optical amplifiers in the near infrared with large optical gain in an all fiber based system. Indeed, erbium doped fibers made gain possible within the 1532 to 1560 nm band which makes long span fiber optical communication systems a possibility. Erbium doped fibers have also been used to make narrow linewidth or mode-locked lasers. Other rare-earth doped fibers can be used for amplifiers in other near-infrared spectral regions. Recently, fiber amplifier technology has been pushed to produce watt level outputs for high power applications such as laser machining. These high power amplifiers make new experiments in ultrafast fiber optics a possibility. This report reviews the current literature on Watt-class continuous wave erbium doped amplifiers and discussed our attempt to develop a high power Yb/Er amplifier. After the design of the cladding pump in 1999, the world’s first single mode fiber laser with a power greater than 100 Watts of the continuous wave light was introduced. After 2002 there was a huge spike in the output powers (up to 2 kW) of lasers based on rare-earth doped fibers. Our own work involved developing a 10 W amplifier at 1532 nm and 1560 nm. A high power amplifier was made by seeding a dual-clad Yb/Er co-doped fiber pumped at 925 nm using a lower power erbium doped fiber amplifier. We will discuss the design and construction of the amplifier, including the technical difficulties for making such an amplifier.

Doctor of Philosophy / Department of Curriculum and Instruction / Dean A. Zollman / The work described here represents an effort to design, construct, and test an interactive online multimedia learning environment that can provide physics instruction to students in their homes. The system was designed with one-on-one human tutoring in mind as the mode of instruction. The system uses an original combination of a video-based tutor that incorporates natural language processing video-centered lessons and additional illustrative multimedia. Our Synthetic Interview (SI) tutor provides pre-recorded video answers from expert physics instructors in response to students’ typed natural language questions. Our lessons cover Newton’s laws and provide a context for the tutoring interaction to occur, connect physics ideas to real-world behavior of mechanical systems, and allow for quantitative testing of physics. Additional multimedia can be used to supplement the SI tutors’ explanations and illustrate the physics of interest. The system is targeted at students of algebra-based and concept-based physics at the college and high school level. The system logs queries to the SI tutor, responses to lesson questions and several other interactions with the system, tagging those interactions with a username and timestamp. We have provided several groups of students with access to our system under several different conditions ranging from the controlled conditions of our interview facility to the naturalistic conditions of use at home. In total nearly two-hundred students have accessed the system. To gain insight into the ways students might use the system and understand the utility of its various components we analyzed qualitative interview data collected with 22 algebra-based physics students who worked with our system in our interview facility. We also performed a descriptive analysis of data from the system’s log of user interactions. Finally we explored the use of machine learning to explore the possibility of using automated assessment to augment the interactive capabilities of the system as well as to identify productive and unproductive use patterns. This work establishes a proof-of-concept level demonstration of the feasibility of deploying this type of system. The impact of this work and the possibility of future research efforts are discussed in the context of Internet technologies that are changing rapidly.

When the tensor product of two irreducible representations contains multiple copies of some of its irreducible constituents, there is a problem of choosing specific copies: resolving the multiplicity. This is typically accomplished by some ad hoc method chosen primarily for convenience in labelling and calculations. This thesis addresses the possibility of making choices according to other criteria. One possible criterion is to choose copies for which the Clebsch-Gordan coefficients have a simple form. A method fulfilling this is introduced for the tensor product of three irreps of $su(2)$. This method is then extended to the tensor product of two irreps of $su(3)$. In both cases the method is shown to construct a full nested sequence of basis independent highest weight subspaces. Another possible criterion is to make choices which are intrinsic, independent of all choices of bases. This is investigated in the final part of the thesis with a basis independent method that applies to the tensor product of finite dimensional irreps of any semisimple Lie algebra over $\mathbb{C}$.

Episodic weak stratification is a persistent and important feature of the epilimnion of Lake Opeongo. Field studies were conducted in Lake Opeongo in 2009 and 2010 to assess the effect of the epilimnetic weak thermal stratification on turbulent mixing and ecological processes. Near surface thermoclines (as defined by dT/dz > 0.2 ̊C m-1 between 1 m and 2 m) occur approximately 20 % of the time and correspond to periods of high values of gradient Richardson number (Rig). Extended periods of near surface stratification (> 1 hr), account for more than 80% of the stratified period. We compare these findings with previous observations from the Experimental Lakes Area and discuss the biological implications of near surface thermoclines. The persistent weak temperature stratification that characterizes the entire epilimnion of Lake Opeongo, acts to reduce the magnitude of turbulent mixing. During these stratified periods, the values of Rig, increase, with a corresponding decrease in the rates of dissipation of turbulent kinetic energy, (ε ), the turbulence activity parameter, I = ε/νN2, and vertical eddy diffusivity (Kz). Mixing during cold fronts occur over time scales of minutes to hours, which work to erode diurnal thermoclines. The direct implications of weak stratification on aquatic organisms are also assessed. The presence of weak stratification also allows for the existence of internal waves within the epilimnion. A key observation in this thesis is the relationship between enhanced small-scale spatial variability in zooplankton distribution and the presence of internal waves in the weakly stratified epilimnion. To quantify this physical-biological coupling, we compare variance of isotherm displacement and gradient Richardson number (Rig) with small-scale spatial distributions of zooplankton. For smaller size ranges of zooplankton (284-450 μm), we find that spatial variability is statistically greatest for the highest values of variability of isotherm displacement. As vertical velocities estimated from wave characteristics are faster than swimming speeds of small zooplankton, these organisms become passively advected by the internal waves leading to increased spatial variability.