The history of diffraction theory, exact frequency domain solutions and selected past time domain solutions are briefly reviewed. Exact time domain solutions for scattering of plane, cylindrical and spherical acoustic waves by a half plane are derived by inverse Fourier transforming the frequency domain integral solutions. The solutions consist of two diffraction terms, a reflected term and a direct term. The diffracting edge induces step function discontinuities in the direct and reflected terms at two shadow boundaries. At each boundary, the associated diffraction term reaches a maximum amplitude of half the geometrical optics term and has a signum function discontinuity, so that the total field remains continuous. A physical interpretation is developed in terms of Huygen's principle near the diffracting edge. Solutions for practical point source configurations are evaluated by numerically convolving the impulse diffraction responses with a wavelet. The numerical problems presented by convolution with a singular, truncated operator are solved by analytically derived correction techniques, which are favourably compared to those used by earlier authors. The diffraction solution collapses into a compact discretized formulation. The half plane is shown to be a limiting form of wedge solutions, which can thus be computed using similar algorithms. Two zero offset sections are produced and compared to approximate Kirchhoff integral solutions. The exact diffraction hyperbola is noticeably non-symmetric, with higher amplitudes on the reflector side of the edge. Near the apex of the hyperbola the Kirchhoff solution is nearly equivalent to the exact diffraction term symmetric in amplitude about the reflection shadow boundary but fails to describe the other, low amplitude, term equivalent to half the response of a line scatterer. The differences are more noticeable on the flanks of the hyperbola, where the two terms are comparable in amplitude, and at shallow depths, due to an aperture effect. Increasing either the depth of the edge or the angle of the seismic line to the normal to the edge results in a flatter diffraction hyperbola showing little amplitude variation with moveout. As the seismic line becomes parallel to the edge the diffraction curve becomes flat and is indistinguishable from a reflection event. At great depth diffraction events may be mistaken for reflection events as well. Examples of CDP and CSP gathers, when compared to the Common Offset (CO) gathers, demonstrate that CO gathers are optimal for diffraction processing. Also, since the diffraction moveout and reflection moveout curves differ widely except for depth points near the edge, normal moveout stacking will distort the diffractions and diffraction stacking is essential to retain diffraction information. Strips of varying width are modelled by superposition of half planes to demonstrate resolution effects and show that the limit of a strip is a line scatterer. A dipping strip and an offset half plane model are produced and added for later comparison with wedge solutions. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Administrators have an impact on teacher peer observations in their schools. The purpose of this research was to explore administrators' perceptions of and strategies for supporting peer observation practices among K–5 teachers at their schools. The two research questions were: What are Virginia elementary school administrators' perceptions of supporting teacher peer observation practices in their schools? What strategies do these administrators use or recommend for supporting teacher peer observation practices in elementary schools? The study employed a basic qualitative design using demographic surveys and one-on-one semi-structured interviews. Inductive and deductive codes were assigned to interview data for analysis. Deductive codes were developed based on the research questions and literature reviewed. In addition, organic coding was used to capture emerging ideas. Findings were that administrators perceived teacher peer observations to be beneficial PD in their schools, assumed various roles and responsibilities to support teacher peer observations, found time, coverage, and negative teacher mindsets to be barriers to success, and had thoughts on expanding and refining teacher peer observation practices at their schools. Other findings were strategies for building culture, involving teachers in the development of teacher peer observation initiatives, collecting and reflecting on peer observations, and resourcefully addressing logistical barriers. Implications included the development of peer observation teams, collaborating with administrators from other schools to share ideas and strategies, and intentionally incorporating teacher peer observation practices into school strategic plans and master schedule considerations. The findings and implications may be of interest to elementary administrators in their efforts to support and improve the practice of teacher peer observations in their schools, as well as leadership directors and central office staff who strive to support principals. / Doctor of Education / Administrators have an impact on teacher peer observations in their schools. The purpose of this research was to explore administrators' perceptions of and strategies for supporting peer observation practices among K–5 teachers at their schools. The two research questions were: What are Virginia elementary school administrators' perceptions of supporting teacher peer observation practices in their schools? What strategies do these administrators use or recommend for supporting teacher peer observation practices in elementary schools? The study employed a basic qualitative design using demographic surveys and one-on-one semi-structured interviews. Findings were that administrators perceived teacher peer observations to be beneficial PD in their schools, assumed various roles and responsibilities to support teacher peer observations, found time, coverage, and negative teacher mindsets to be barriers to success, and had thoughts on expanding and refining teacher peer observation practices at their schools. Other findings were strategies for building culture, involving teachers in the development of teacher peer observation initiatives, collecting and reflecting on peer observations, and resourcefully addressing logistical barriers. The findings and implications may be of interest to elementary administrators who want to support and sustain the practice of teacher peer observations in their schools, as well as leadership directors and central office staff who strive to support principals.

Call number: LD2668 .T4 1964 H75 / Master of Science

Modern cosmological theory is based on the Friedmann-Robertson-Walker (FRW) metric. Often written in terms of co-moving coordinates, this well-known solution to Einstein's equations owes its elegant and highly practical formulation to the Cosmological principal and Weyl's postulate, upon which it is founded. But there is physics behind such symmetries, and not all of it has yet been recognized. In this paper, we derive the FRW metric coefficients from the general form of the spherically-symmetric line element, and demonstrate that, because the co-moving frame also happens to be in free fall, the symmetries in FRW are valid only for a medium with zero active mass. In other words, the spacetime of a perfect fluid in cosmology may be correctly written as FRW only when its equation-of-state is $\rho+3p=0$, in terms of the {\it total} pressure $p$ and {\it total} energy density $\rho$. There is now compelling observational support for this conclusion, including the Alcock-Paczy\'nski test, which shows that only an FRW cosmology with zero active mass is consistent with the latest model-independent Baryon Acoustic Oscillation data.

The design of BOLTS (Broad Area Lightning Telescope Sensor) is presented. This sensor will provide full-time (day/night) coverage of the continental U.S. from a geosynchronous orbit. The average ground resolution will be 8 km and the system will be able to detect ≃ 10⁷ watt strokes during nighttime and ≃ 4 x 10⁷ watt strokes during daytime with a probability of detection of 0.9. We present the system's requirements and projected performance, together with the design rationale. Contrast enhancement is achieved using a narrow band interference filter deposited on a curved surface inside the F/2.5, 101.7 mm optical system. Deposition of the interference layers on the curved surface reduce the passband wandering caused by off-axis bundles. The focal plane constitutes an 800 x 800 element virtual phase CCD array with a multiple outputs option. The central 800 x 400 elements are used for imaging while the outer 2x (800 x 200) elements serve as buffer memory for one frame storage. An additional 2x (800 x 200) array serves for storing a second frame. Signal detection is achieved via a frame-to-frame subtraction algorithm that is hardware implemented immediately following the CCD arrays. An integration time of 5 msec is used, which stems from SNR optimization requirements and from the fact that lightning strokes occur randomly in time and space. The data obtained after frame-to-frame subtraction is subjected to a threshold test and the resulting positive events are digitized and stored in an on-board digital memory using 48 bits/event. Each record contains intensity information over a dynamic range of 4000, location information and time of occurrence information. A prototype instrument built to perform measurements from aboard a U-2 plane is described. The purpose of this instrument is to refine some of the lightning data used in defining the system's parameters. A short discussion about the changes required to expand the design to either a global coverage instrument or a high resolution, smaller field instrument is presented.

Intermediate-degree g-modes (those with angular order ℓ ≈ 30) were first observed in the late 1970's by Hill and Caudell (1979). However, it wasn't until 1986 that a preliminary survey was made of the 1979 differential radius observations (see Bos 1982) and a set of 4 multiplets exhibiting mode-locking was classified by Hill (1986). These multiplets with angular order ℓ ≈ 30 and eigenfrequencies of ≈350 μHz were used as a starting point for the comprehensive analysis discussed in this work. This comprehensive study culminated in the classification of a set of 20 intermediate-degree g-mode multiplets containing over 600 normal modes of oscillation. Each of these multiplets was found to contain mode-coupled sections. Of more importance, however, are the internal properties of the Sun that can be inferred from this large body of classified modes. In this work two significant consequences will be discussed. Because these modes of oscillation are localized within the inner 50% of the Sun by radius and because of their large temperature eigenfunctions implied by the observed phase-locking, these modes of oscillation provide a modification of the effective temperature profile defined for a given process in the Sun. One of these processes is the ⁸B neutrino production. The second consequence of these observations is a predicted periodic modulation of the neutrino production rates. The existence of a large set of mode-coupled gravity modes will lead to a low-frequency modulation of neutrino production rates which may account for the observed periodicity in the ⁸B neutrino production (see Haubold and Gerth 1985). The prediction of this periodicity in the neutrino production rates is unique among all the competing theories that resolve the solar neutrino paradox and is testable by the new generation of solar neutrino detectors.

This work analyzes data taken in 1979 using a modification of the solar detector at SCLERA (Santa Catalina Laboratory for Experimental Relativity) designed to enhance spatial properties of the previously observed solar oscillations. Unlike previous solar observations taken at SCLERA, where the data consisted of single solar diameter measurements, the 1979 data consisted of six recorded limb profiles. This has important ramifications for the amount of signal present in the data which was generated by the terrestrial atmosphere, for the origin of the observed solar oscillations in fluctuations of the solar limb darkening function, and, most importantly, for the spatial symmetry properties of the observed solar eigenfunctions. The data consisted of 18 days of observations averaging ten hours per day and covering a total of 41 days. A linked Fourier transform of all 18 days was done for signal generated from each limb profile, and combinations of these six Fourier transforms made to increase sensitivity to symmetric or antisymmetric properties of the observed solar eigenmodes. The following results were found: 1. The observed oscillations are manifestations of fluctuations in the solar limb darkening function. 2. Terrestrial atmospheric contributions to the observed signal are negligible; thus, the sun constitutes the only possible source of the signal. 3. Given a resolution element of 1/(41 days) or 0.28 μHz, the solar oscillations observed represent individual solar eigenstates. 4. The spatial properties of the eigenstates are consistent with their interpretation in terms of spherical harmonics defined with respect to the observed solar rotational axis. 5. The eigenstates are temporally coherent for > 2 days and, in selected samples, for > 41 days. 6. The observed spacing of groups of eigenmodes is shown to be indicative of solar rotational effects; this spacing implies that the core of the sun is rotating approximately six times faster than the observed surface rotational velocity.

The magnetic rotator model has long been the favored explanation for coherent photometric modulations in the DQ Herculis class of cataclysmic variables. However, to date, all evidence supporting this model has been of the indirect variety. Unlike their synchronously rotating cousins, the AM Herculis objects, DQ Herculis stars have not yet been discovered to emit polarized radiation. Therefore, in light of this crucial lack, the evidence used to place these objects in the magnetic cataclysmic variable category has been strictly circumstantial, based primarily on the coherence of the photometric periodicities. In this work, time-resolved spectroscopy of four long-period DQ Herculis stars is performed. In addition, two of the same objects are observed with a new, sensitive circular polarimeter. Chapters II and III describe these observations and the results of each. To summarize, coherent variations in the wavelength of emission lines were found with the spectroscopic observations. A model is put forth, explaining this phenomenon as being due to varying illumination from a bright spot on the primary. This, of course, adds strength to the magnetic rotator model. Secondly, circular polarization was definitely found in one object studied, and possibly in a second. Therefore, for the first time, there is direct evidence of the magnetic nature of these binaries. In Chapter IV, the model of the rotating bright spot illuminating the disk is explored in further detail, including modeling with a minicomputer. Afterward, a problem brought out by the low polarization coupled with large amplitude photometric variations and a cool spectrum is investigated, namely, is it possible to produce large amounts of cyclotron radiation without producing large amounts of circular polarization? The results tend to show that, for a large emitting area, the answer is yes. Chapter V is a summary of the rest of the work.

model-derived wind gusts determined by each method are then compared to wind reports from the Storm Prediction Centerâ s severe storm reports archive and reports from observing stations. Model-derived wind gusts are then compared to the observed wind gusts for varying times of day and observed wind gust ranges. Wind gust frequency plots are examined for each wind method to determine accuracy and to characterize any patterns. The T1 method was the most accurate overall for this study, but was shown to be less sensitive to varying atmospheric conditions. The T2 method was the least accurate of the three methods during all situations. The WINDEX method performed well in most situations and was nearly as accurate as the T1 method, while WINDEX also proved to be the most sensitive of the three to varying mesoscale conditions.

Luminous quasars at z > 5.6 can be studied in detail with the current generation of telescopes and provide us with unique information on the first gigayear of the universe. Thus far, these studies have been statistically limited by the number of quasars known at these redshifts. Such quasars are rare, and therefore, wide-field surveys are required to identify them, and multiwavelength data are required to separate them efficiently from their main contaminants, the far more numerous cool dwarfs. In this paper, we update and extend the selection for the z similar to 6 quasars presented in Banados et al. (2014) using the Pan- STARRS1 (PS1) survey. We present the PS1 distant quasar sample, which currently consists of 124 quasars in the redshift range 5.6 less than or similar to z less than or similar to 6.7 that satisfy our selection criteria. Of these quasars, 77 have been discovered with PS1, and 63 of them are newly identified in this paper. We present the composite spectra of the PS1 distant quasar sample. This sample spans a factor of similar to 20 in luminosity and shows a variety of emission line properties. The number of quasars at z > 5.6 presented in this work almost doubles the previously known quasars at these redshifts, marking a transition phase from studies of individual sources to statistical studies of the high-redshift quasar population, which was impossible with earlier, smaller samples.