Thesis (M.S.)--University of Wisconsin--Madison, 1968. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

This thesis describes the investigation carried out on the propagation of radio pulses of frequency 4.73 Mc/s between Grahamstown and Durban. The thesis is divided into two sections - A and B. Section A consists of two chapters. The introductory chapter gives a brief account of how the existence of the ionosphere came to be known. Then follows a description of the different layers of ionization and a review of the theories that have been propounded on the formation of these layers. Chapter 2 deals with the apparatus which includes the transmitter in Grahamstown and the receiving apparatus in Durban. The receiving apparatus comprises: i) a superheterodyne receiver whose gain was high (between 130 and 140 dbs); (ii) a time delay calibrator which could measure time differences of 100 μsec fairly accurately; (iii) a 310 A Tektronix oscilloscope; (iv) a continuously running 35 mm recording camera. Section B is made up of three chapters and is concerned with the actual analysis of the data recorded. The theory of propagation of radio waves in the ionosphere is discussed in Chapter 3. The effects of the magnetic field are neglected since it is found that the error introduced would not make the results unacceptable. Chapter 4 contains the analysis of the data recorded. One summer day and one winter day are discussed in detail in order to obtain the pattern of the diurnal variations for both summer and winter. Some interesting phenomena are also dealt with. An attempt to do ray tracing was successful and the paths followed by a Pedersen and a lower ray from Grahamstown to Durban have been drawn. New topics for further research are discussed in Chapter 5. There are two appendices. Appendix I gives the time delays of all the pulses recorded and their possible identifications. An overall picture of the propagation via the various layers throughout the day (both for summer and for winter is presented in Appendix II.

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Degree of Master of Science by research only: A dissertation submitted to the faculty of science, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Master of Science. Department of Physics Faculty of Science University of the Witwatersrand January 4, 2016 / Quasi-simultaneous observations of a flaring blazar source at multiple frequencies, offer an unprecedented view of the region surrounding a supermassive black hole during a large energy outburst. Blazars are active galaxies that host a super massive black hole releasing large amounts of energy through narrow jets of highly relativistic plasma located along the polar axes. Within these jets, electrons and protons move at relativistic speeds creating interactions that generate radio waves and gamma-rays that travel down the jet towards the observer. Based on the angle of inclination of the source towards the observer ( < 20◦), we can study relativistically boosted emission to peer into regions where high-energy particles (gamma-rays) are thought to be generated. Using high cadence monitoring campaigns, both the slow and fast variations in the source flux can be traced in detail revealing spatial and temporal information about the source state and activity. In this dissertation I studied the physics behind the variable behavior of the bright blazar PKS 1424-418, also known as J1427-4206. PKS 1424-418 is a Southern Hemisphere blazar that recently underwent a number of flaring events detected by FERMI-LAT. The study was specifically concerned with the behavior of PKS 1424-418 during the outburst/flaring events that occurred between 19 October 2012 and 9 October 2013. PKS 1424-418’s daily gamma-ray flux reached an average of 1.4 ± 0.2 x 10−6 ph cm−2 s−1 for E > 100 MeV, triggering radio follow up observations with the Hartebeesthoek Radio Astronomy Observatory 26 m radio telescope at 2.3-GHz, 4.8-GHz, 8.4-GHz and 12.2-GHz frequencies. The objective was to examine the nature of the relationship between the high-energy gamma rays detected by FERMI-LAT and the low-energy radio waves detected by the Hart26m radio telescope. In the study we investigated the relationship between the two energy regimes using Discrete cross-correlation functions to estimate the time-lags between two corresponding frequencies. We also studied the spectral index variation to establish the source behavior over the observing period at multiple epochs. A Lomb-Scargle periodicity search was also performed to investigate whether some periodic modulation was present in the gamma-ray data as it varied quite dramatically on shorter time-scales. Observations in gamma-rays and radio frequencies were done using the All-Sky mode and drift scan technique respectively at the different frequencies. Results indicated the existence of a strong correlation between the gamma-ray and radio data, with the gamma rays leading the radio. With each gamma-ray flaring event the radio spectra indicated some spectral hardening and the possibility of an 86 day gamma-ray period in the shorter term flares was also established in the study. This study however only shows the large scale relationship between time-series over the entire observing period. On smaller scales, each gamma-ray and radio flare is unique and as such requires individual analysis for each respective component. to successfully achieve this, more data is needed to confirm the individual radio flaring periods. Observations at VLBI scales are extremely useful in this kind of work and instrumental in studying the source structure behavior during flaring and will form part of the future work planned for studying blazar source variability.

Scalability is a challenging yet key aspect required for large scale quantum computing and simulation using ions trapped in radio-frequency (rf) Paul traps. In this thesis 171Yb+ ions are used to demonstrate a magnetic field insensitive qubit which has a measured coherence time of 1.5 s, making it an ideal candidate to use for storing quantum information. A magnetic field sensitive qubit is also characterised which can be used for the implementation of multi-qubit gates using a potentially very scalable scheme based on microwaves in conjunction with a static magnetic field gradient instead of using lasers. However, the measured coherence time is limited by magnetic field fluctuations and will prohibit high fidelity gate operations from being performed. To address this issue, the preparation of a dressed-state qubit using a microwave based stimulated rapid adiabatic passage (STIRAP) pulse sequence will be presented. This qubit is protected against the noisy environment making it less sensitive to magnetic field fluctuations. The lifetime of this qubit is measured to demonstrate its suitability for storing quantum information. A powerful method for manipulating the dressed-state qubit will be presented and is used to measure a coherence time of the qubit of 500 ms which is two orders of magnitude longer compared to the magnetic field sensitive qubit. It will also be shown that our method allows for the implementation of arbitrary rotations of the dressed-state qubit on the Bloch sphere using only a single rf field. This substantially simplifies the experimental setup for single and multi-qubit gates. Furthermore, this thesis will present a experimental setup capable of successfully operating microfabricated surface ion traps. This setup is then used to operate and characterise the first two-dimensional (2D) lattice of ion traps on a microchip. A unique feature of the microfabrication technique used for this device is the extremely large voltage that can be applied which allows long ion lifetimes along with large secular frequencies to be measured, demonstrating the robustness of this device. Rudimentary shuttling between neighbouring lattice sites will be shown which could be used as part of a efficient scheme to load a large lattice of ions. One of the many applications of a 2D lattice of ions lies in the field of quantum simulations where many-body systems such as quantum magnetism, high temperature superconductivity, the fractional quantum hall effect and synthetic gauge fields can be simulated. It will be shown how making only minor modifications to the microchip the ion-ion separation can be reduced sufficiently to offer an exciting platform for the successful implementation of 2D quantum simulations. A theoretical investigation on the optimal 2D ion trap lattice geometry will also be presented with the aim to maximise the ratio of ion-ion coupling strength to decoherence from motional heating of the ions and to laser induced off-resonant coupling.

G. Bekefi, Sanborn C. Brown. / Reprinted from American journal of physics, v. 29, no. 7, 404-428, July, 1961. "February 14, 1961"--Cover. / Includes bibliographical references. / Army Signal Corps Contract DA36-039-sc-78108. Dept. of the Army Task 3-99-20-001 and Project 3-99-00-000.

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