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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
191

Parameter estimation in small extensive air showers /

Chow, Chi-kin. January 1993 (has links)
Thesis (M. Phil.)--University of Hong Kong, 1994. / Includes bibliographical references (leaves 115-117).
192

The evolution of neutron star magnetic fields /

Zhang, Chengmin. January 2000 (has links)
Thesis (Ph. D.)--University of Hong Kong, 2000. / Includes bibliographical references (leaves [83]-90).
193

Application of random field models to the analysis of the cosmic microwave background /

Jewell, Jeffrey B. January 2000 (has links)
Thesis (Ph. D.)--University of Chicago, Dept. of Astronomy and Astrophysics, August 2000. / Includes bibliographical references. Also available on the Internet.
194

Far-infrared polarization by absorption in the molecular cloud sagittarius B2 /

Dowell, Charles Darren. January 1997 (has links)
Thesis (Ph. D.)--University of Chicago, Dept. of Astronomy and Astrophysics, June 1997. / Includes bibliographical references. Also available on the Internet.
195

Nucleosynthesis and s-process element formation in giant stars : a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Astronomy in the University of Canterbury /

Wylie, Elizabeth C. January 2006 (has links)
Thesis (Ph. D.)--University of Canterbury, 2006. / Typescript (photocopy). Includes bibliographical references (p. 195-204). Also available via the World Wide Web.
196

The effect of dust and gas energetics on the clustered star formation process

Urban, Andrea, January 1900 (has links)
Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.
197

Cosmology with Planck : an all-sky temperature and polarisation analysis

Crowe, Christopher Michael January 2013 (has links)
Cosmology is now a precision science. The temperature anisotropies in the cosmic microwave background (CMB) have been exquisitely mapped by many experiments over the last decade. The Planck satellite was launched in 2009, observed the sky in temperature and polarisation, and released the nominal mission temperature data to the public in 2013. Planck has shed new light on CMB polarisation anisotropies and the polarisation signal from our own galaxy, and knowledge of the galactic emission forms a central part of this analysis presented in this thesis. I first introduce the background cosmology and review what we know about CMB temperature and polarisation anisotropies, including their mathematical formulation and representation on the sphere. I review our knowledge of the origin of galactic polarised foregrounds, particularly electron synchrotron and thermal dust emission. I then describe the generation of polarised CMB maps from an input cosmological model, and the generation of CMB polarised foregrounds using a variety of methods to create full-sky maps of the microwave sky at the Planck observing frequencies between 30 and 353 GHz. I develop a parametric fitting maximum-likelihood polarised component separation routine with correlated foreground parameters to extract the CMB and associated foregrounds to a high precision, and show that my method can reliably recover a primordial B-mode polarisation signal at r = 0.1 at multiple map resolutions. I then test the sky model against the full mission Planck data to examine how accurately the foregrounds are simulated, and find that along the galactic plane the simulations are accurate, but at high latitudes the agreement worsens. I also compare the polarisation morphology to that seen in the WMAP data and find a tension between Planck and WMAP. I present an analysis of the dx8 polarisation data in terms of polarised amplitudes and orientations, and investigate a variety of foreground separation routines to get a feel for the reliability of the data. Significant systematic issues are found and I conclude that in their current state, the polarisation data are not reliable enough for precise cosmology. Finally I develop a Fisher matrix analysis of the temperature power spectrum using the full mission covariance matrix to explore the parameter space around a CosmoMC simulation, and extract the principal components for different models. I use this to explore a strange oscillation in the power spectrum and conclude that it is a statistical fluke, a conclusion confirmed in a recent data release. I close by offering extensions to the work and a look into the future of the field.
198

The divine warrior and cosmic catastrophe : the impact of the Sibylline Oracles on interpretation of Mark 13:24-25

McBay, Susannah E. January 2017 (has links)
The meaning of cosmic catastrophe language (CCL) in Mark 13:24-25 is widely contested: both in regards to what type of language is used and to what event it refers, namely the fall of temple at Jerusalem in 70CE or the Parousia of Christ. Recent contributions from Marcus, Shively and Angel have identified the mythological background behind the language, but still interpret this mythology in different ways. In this thesis I elucidate the tradition behind CCL, specifically that of the Jewish Divine Warrior Tradition (DWT), to assess further its development in the Second Temple period and inform interpretations of Mark 13:24-25. Using a historical-critical, criterion-based approach, I demonstrate that the DWT is used in thirteen texts in the Sibylline Oracles and that this use expresses divine opinion and judgement upon political entities and spiritual powers that oppose God and his heavenly host. I also show that the DWT in Sib. Or. 3-5 incorporates elements from Stoic cosmological imagery, which was separated from the Stoic doctrine of ἐκπύρωσις with the advent and rise of Roman Stoicism. The result of this has various implications for navigating the interpretations of Mark 13:24-27 and I conclude that the cosmic catastrophe of vv.24-25 is best understood as describing the cosmic upheaval and demise of spiritual powers that relate to the temple and its leaders at the coming of the Divine Warrior.
199

A Comparison of Cosmological Parameters Determined from CMB Temperature Power Spectra from the South Pole Telescope and the Planck Satellite

Aylor, K., Hou, Z., Knox, L., Story, K. T., Benson, B. A., Bleem, L. E., Carlstrom, J. E., Chang, C. L., Cho, H-M., Chown, R., Crawford, T. M., Crites, A. T., Haan, T. de, Dobbs, M. A., Everett, W. B., George, E. M., Halverson, N. W., Harrington, N. L., Holder, G. P., Holzapfel, W. L., Hrubes, J. D., Keisler, R., Lee, A. T., Leitch, E. M., Luong-Van, D., Marrone, D. P., McMahon, J. J., Meyer, S. S., Millea, M., Mocanu, L. M., Mohr, J. J., Natoli, T., Omori, Y., Padin, S., Pryke, C., Reichardt, C. L., Ruhl, J. E., Sayre, J. T., Schaffer, K. K., Shirokoff, E., Staniszewski, Z., Stark, A. A., Vanderlinde, K., Vieira, J. D., Williamson, R. 21 November 2017 (has links)
The Planck cosmic microwave background temperature data are best fit with a Lambda CDM model that mildly contradicts constraints from other cosmological probes. The South Pole Telescope (SPT) 2540 deg(2) SPT-SZ survey offers measurements on sub-degree angular scales (multipoles 650 <= l <= 2500) with sufficient precision to use as an independent check of the Planck data. Here we build on the recent joint analysis of the SPT-SZ and Planck data in Hou et al. by comparing Lambda CDM parameter estimates using the temperature power spectrum from both data sets in the SPT-SZ survey region. We also restrict the multipole range used in parameter fitting to focus on modes measured well by both SPT and Planck, thereby greatly reducing sample variance as a driver of parameter differences and creating a stringent test for systematic errors. We find no evidence of systematic errors from these tests. When we expand the maximum multipole of SPT data used, we see low-significance shifts in the angular scale of the sound horizon and the physical baryon and cold dark matter densities, with a resulting trend to higher Hubble constant. When we compare SPT and Planck data on the SPT-SZ sky patch to Planck full-sky data but keep the multipole range restricted, we find differences in the parameters n(s) and A(s)e(-2 tau). We perform further checks, investigating instrumental effects and modeling assumptions, and we find no evidence that the effects investigated are responsible for any of the parameter shifts. Taken together, these tests reveal no evidence for systematic errors in SPT or Planck data in the overlapping sky coverage and multipole range and at most weak evidence for a breakdown of Lambda CDM or systematic errors influencing either the Planck data outside the SPT-SZ survey area or the SPT data at l > 2000.
200

The study of cosmological radio backgrounds with the Sunyaev-Zel'dovich effect

Emritte, Mohammad Shehzad January 2017 (has links)
A thesis submitted to the Faculty of Science, University of Witwatersrand, in the ful lment of the requirements for the degree of Doctor of Philosophy Johannesburg, South Africa, 2017. / According to the standard model of cosmology, the Universe has evolved from a thermal bath of elementary particles and photons towards one comprising of collapsed structures such as stars, galaxies and clusters of galaxies. The Cosmic Microwave Background (CMB) spectrum and its angular anisotropy across the sky contain information on the physical processes, matter distribution and evolution of the Universe across cosmic time. Primordial spectral distortions of the CMB and its anisotropy can be studied through the inverse comptonization process occuring in cosmic structures, known as the Sunyaev-Zel'dovich e ect (SZE). This present study demonstrates how the SZE can be used to obtain information on the 21 cm background produced between the Dark Ages (DA) and the Epoch of Reionization (EoR), on Non-Planckian (NP) modi cations of the CMB due to plasma frequency at the recombination epoch, and on the anisotropy of the CMB at cluster locations, through the study of the polarization of the SZE. To these aims, a full relativistic approach is employed, that allows us to calculate the spectra of the SZE and its polarization component with high precision, and allows to calculate it for any kind of electron population (thermal or nonthermal plasma), and for an input spectrum that can deviate from the standard black-body spectrum. The SZE-21cm, which is the comptonized spectrum of the modi ed CMB due to physical processes occuring during the DA and the EoR, is calculated for four models of the 21-cm background. A full spectral analysis of the signal is performed and the importance of relativistic e ects are highlighted. The results demonstrate that relativistic e ects are nonzero over the entire frequency spectrum and hence cannot be ignored, particularly for hot clusters. It is found that the amplitude of the SZE-21cm signal is of the order of Jy and is within the reach of the SKA instrument. Clusters with high temperature and optical depth are optimal targets to search for the SZE-21cm signal. The SKA can measure the signal in the frequency interval 75-90 MHz for clusters with temperature higher than 5 keV. Discerning the SZE-21cm from the standard SZE can be achieved using the SKA depending on the 21-cm background model for temperatures > 10 keV. Using CMB spectral data at both low and high frequencies, upper limits (206, 346 and 418 MHz at 1, 2, 3 con dence level) are placed on NP e ects associated with a non-zero plasma frequency at the recombination epoch. The SZENP is derived for a CMB spectrum modi ed due to plasma e ects using these upperlimits and a unique spectral feature is obtained. A peak occures at the plasma frequency in the SZENP independent of cluster parameters and the possibility of measuring the plasma frequency with the SKA and eVLA is shown. Plasma e ects are also investigated on the spectrum of the cosmological 21-cm background and it is found that such an e ect is important to consider when recovering the history of the Universe during these epochs. Polarization is a natural outcome of inverse Compton (IC) scattering and the anisotropy of the CMB plays a big role in the production of polarization in Comptonization process. The SZE polarization associated with the anisotropy of the CMB is derived in the full relativistic regime for any general electron distribution. The spectral shapes of the Stokes parameters induced by the IC scattering of the multipoles of the CMB for thermal and non-thermal electrons are derived, focusing mainly on the quadrupole and octupole which provide the largest possible detectable signals in cosmic structures. Our results demonstrate the implication of relativistic e ects, which become important for high temperature or non-thermal cluster environments. When relativistic e ects are accounted for, all the multipoles of the CMB are involved in the production of polarization. The octupole induced polarization spectrum reveals the existence of a cross-over frequency which is dependent on cluster parameters such as temperature, minimum momentum and spectral index. The possibilities to disentangle the quadrupole spectrum from the octupole one are discussed, which would allow the measurments of these multipoles at cluster locations. The generality of our approach allows us to calculate the SZE polarization spectra of the Bullet cluster using multifrequency SZE data in intensity and compare the results with the sensitivities of the SKA, ALMA, Millimetron and CORE++ instruments. Although the e ects that we studied here are small, however, they are still within the detection limits of the SKA, due to its very high sensitivity. Therefore, the SKA will play a big role in the study of cosmological radio backgrounds by providing high precision SZE data. / LG2018

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