Applications of in situ cosmogenic nuclides to problems in Quaternary geology require increasingly accurate and precise knowledge of nuclide production rates. Production rates depend on the terrestrial cosmic-ray intensity, which is a function of the elevation and geomagnetic coordinates of a sample site and the geomagnetic field intensity. The main goal of this dissertation is to improve the accuracy of cosmogenic dating by providing better constraints on the spatial variability of production rates.In this dissertation I develop a new scaling model that incorporates the best available cosmic-ray data into a framework that better describes the effects of elevation and geomagnetic shielding on production rates. This model is based on extensive measurements of energetic nucleon fluxes from neutron monitor surveys and on more limited data from low-energy neutron surveys. A major finding of this work is that neutron monitors yield scaling factors different from unshielded proportional counters. To verify that the difference is real I conducted an airborne survey of low-energy neutron fluxes at Hawaii (19.7° N 155.5° W) to compare with a nearby benchmark neutron monitor survey. Our data confirm that the attenuation length is energy dependent and suggest that the scaling factor for energetic nucleons is 10% higher between sea level and 4000 m than for low-energy neutrons at this location. An altitude profile of cosmogenic 36Cl production from lava flows on Mauna Kea, Hawaii, support the use of neutron flux measurements to scale production rates but these data do not have enough precision to confirm or reject the hypothesis of energy-dependent scaling factors.

No description available.

In the present study we aim to further our understanding of charged particle transport in a magnetized medium. To this end, we perform direct numerical simulations of particle transport in a turbulent magnetic field. From the particle trajectories we calculate diffusion and drift coefficients. In contrast to previous numerical simulations of this nature, we also consider a background magnetic field that contains a gradient perpendicular to the magnetic field direction. By using a non-uniform background magnetic field, we can investigate the simultaneous large scale drift due to the gradient in the background magnetic field and the diffusion due to the turbulence which is superimposed on this background magnetic field. Upon comparison with the simulated diffusion coefficients, the newly proposed weakly non-linear theory (WNLT) of Shalchi et al. (2004b) seems to be the most appropriate theory for the simultaneous description of parallel and perpendicular diffusion over a wide range of fluctuation amplitude and particle rigidity. As for the effect of large scale drift on perpendicular diffusion, we find that under conditions of small amplitude turbulence and/ or high particle rigidity the transport perpendicular to the background field can exhibit super-diffusive behaviour. Diffusive behaviour seems to be recovered for the cases when the turbulence amplitude is sufficiently large and/ or the particle rigidity is sufficiently small. We furthermore find that both the drift coefficient and the drift speed are reduced from their weak scattering counterparts in the presence of scattering, with the reduction becoming more pronounced with increasing turbulence amplitude. For the drift coefficient in particular, the reduction from its weak scattering counterpart behaves differently for the cases in which the background magnetic field is either uniform or non-uniform. For the former case the reduction is predominantly at small rigidities, while for the latter case the reduction is predominantly at large rigidities. The latter result might be of significance for heliospheric modulation models in which the background magnetic field is highly non-uniform. Finally, we use a two-dimensional steadystate cosmic ray modulation model to see how our improved understanding of the underlying transport processes influences the overall cosmic ray modulation in the heliosphere. We conclude that in the absence of a theory which connects large scale drift with small scale diffusion, any statements about the inadequacy of a two-dimensional steady-state modulation model might be premature. / Thesis (Ph.D. (Physics))--North-West University, Potchefstroom Campus, 2006.

In this thesis we examine the theoretical origin and statistical features of the Cosmic Microwave Background radiation. We particularly focus on the CMB power spectra and cosmological parameter estimation from QUaD CMB experiment data in order to derive implications for the concordance cosmological model. In chapter 4 we present a detailed parameter estimation analysis of the combined polarization and temperature power spectra from the second and third season observations of the QUaD experiment. QUaD has for the first time detected multiple acoustic peaks in the polarization spectrum, allowing meaningful parameter analyses from the polarization data alone. In a standard 6-parameter ACDM parameter estimation analysis we find the QUaD TT power spectrum to be in very good agreement with previous results. However, the QUaD polarization data shows some tension with ACDM model. The origin of this 1−2σ tension remains unclear, and may point to new physics, residual systematics or simple random chance. Combining polarization and temperature data we find an acceptable fit, and show that our results are dominated by the polarization signal. We combine QUaD with the five-year data from the WMAP satellite and the SDSS Luminous Red Galaxies 4th data release power spectrum, and extend our analysis to constrain the tensor-to-scalar ratio and the primordial isocurvature perturbations. Our analysis sets a benchmark for future polarization experiments. In chapter 5 we outline and test a new semi-analytical approach for the estimation of the pseudo- temperature and polarization CMB power spectra for experiments with incomplete sky coverage. We propose a method for constructing the mode-mode coupling matrices which connect the temperature and polarization pseudo-Cℓ’s to the unbiased all-sky bandpowers in the flat sky approximation. We apply this method to the apodization masks of the QUaD CMB experiment and we show that the true underlying bandpowers can be reconstructed from the simulated QUaD-like pseudo-Cℓ’s to high precision. We further investigate the possibility of extending the proposed analytical flat sky approach to the exact calculation of the PCL covariance matrices over a large range of multipoles and we find that the numerical calculation is extremely computationally expensive. The flat sky pseudo-Cℓ and covariances methods presented in this chapter are still work in progress and require more testing.

We detect the kinematic Sunyaev-Zel'dovich (kSZ) effect with a statistical significance of 4.2 sigma by combining a cluster catalogue derived from the first year data of the Dark Energy Survey with cosmic microwave background temperature maps from the South Pole Telescope Sunyaev-Zel'dovich Survey. This measurement is performed with a differential statistic that isolates the pairwise kSZ signal, providing the first detection of the large-scale, pairwise motion of clusters using redshifts derived from photometric data. By fitting the pairwise kSZ signal to a theoretical template, we measure the average central optical depth of the cluster sample, (tau) over bar (e) = (3.75 +/- 0.89) x 10(-3). We compare the extracted signal to realistic simulations and find good agreement with respect to the signal to noise, the constraint on (tau) over bar (e), and the corresponding gas fraction. High-precision measurements of the pairwise kSZ signal with future data will be able to place constraints on the baryonic physics of galaxy clusters, and could be used to probe gravity on scales greater than or similar to 100 Mpc.

This thesis presents theoretical work on the propagation of ultra high energy cosmic rays, from their source to Earth. The different energy loss processes, resulting from cosmic ray interactions with the radiation fields, are addressed. The subsequent uncertainties in the energy loss rates and the effect produced on the arriving cosmic ray spectrum are highlighted. The question of the composition of ultra high energy cosmic rays remains unresolved, with the range of possibilities leading to quite different results in both the secondary fluxes of particles produced through cosmic ray energy loss interactions en route, and the arriving cosmic ray spectra at Earth. A large range of nuclear species are considered in this work, spanning the range of physically motivated nuclear types ejected from the cosmic ray source. The treatment of cosmic ray propagation is usually handled through Monte Carlo simulations due to the stochastic nature of some of the particle physics processes relevant. In this work, an analytic treatment for cosmic ray nuclei propagation is developed. The development of this method providing a deeper understanding of the main components relevant to cosmic ray nuclei propagation, and through its application, a clear insight into the contributing particle physics aspects of the Monte Carlo simulation. A flux of secondary neutrinos, produced as a consequence of cosmic ray energy loss through pion production during propagation, is also expected to be observed at Earth. This spectrum, however, is dependent on several loosely constrained factors such as the radiation field in the infrared region and cosmic ray composition. The range of possible neutrino fluxes obtainable with such uncertainties are discussed in this work. High energy cosmic ray interactions with the radiation fields present within the source may also occur, leading to cosmic ray energy loss before the cosmic ray has even managed to escape. The secondary spectra produced are investigated through the consideration of three candidate sources. A relationship between the degree of photo-disintegration in the source region and the neutrino flux produced through p γ interactions is found.

In this thesis, I present the results of a new search for, and study of, luminous galaxies in the first billion years of cosmic time. This work is primarily based on a new selection of bright (L≫L*) Lyman-break galaxies (LBGs) at z ≅6 and z≅7 in the UltraVISTA first and second data releases (DR1, DR2) and the UKIDSS (UKIRT Infrared Deep Survey) UDS DR10 (Ultra Deep Survey). The UltraVISTA survey provides deep Y, J,H andKs near-imaging over 1.5 deg² of the Cosmic Evolution Survey (COSMOS) field and the UKIDSS UDS provides J,H and K band data overlapping with the Subaru XMM-Newton Deep Survey (SXDS), with both fields also containing deep optical and mid-infrared imaging essential for the clean detection of z > 5 galaxies. The fields combined provide an unprecedented 1.65 deg² of deep multiwavelength data with which to securely select LBGs using a photometric redshift fitting technique, which can additionally remove probable low-redshift galaxy interlopers and galactic dwarf stars that can contaminate ground-based samples. At z ≅7, the DR1 of the UltraVISTA survey was used to select a sample of ten high-redshift galaxy candidates, which extended to a 5σ limiting magnitude of Y + J ~ 25 (AB magnitude, 2-arcsec diameter circular aperture) over 1 deg². A stack of the four most robust objects from the sample indicated that they were massive (M*≅5 × 109M ʘ), had blue rest-frame UV slopes (β ≅−2.0±0.2) and were highly star-forming (SFR ≅25–50Mʘ yr−1) when compared to previous, fainter, samples of galaxies at z = 7. The number counts of z≅7 galaxies selected within the UltraVISTA DR1 survey was higher than that expected from extrapolations of the rest-frame UltraViolet (UV) luminosity function (LF) from fainter data, a result that was strongly confirmed with an improved search for z ≅7 galaxies using the UltraVISTA DR2 imaging and the UDS field. A total of 34 galaxies at 6.5 < z < 7.5 were found in the combined fields, which included the previously identified robust galaxies from the DR1 imaging. This expanded sample allowed the first determination of the rest-frame UV LF in the range −23.0 < MUV < −21.5 at z ≅7, and the results reveal a power-law decline to bright magnitudes in contrast to the commonly assumed exponentially declining Schechter function extrapolated from fainter data. The excess of galaxies observed at bright magnitudes cannot be accounted for by gravitational lensing or by significant contamination of the sample by Active Galactic Nuclei (AGN) . The observed LF is well described by a double power law, which at the bright end follows the form of the underlying dark matter halo mass function, suggesting that the physical mechanism that inhibits star formation activity in massive galaxies (e.g. AGN feedback or some other form of ‘mass quenching’) has yet become efficient at z ≅7. The deeper imaging data confirm that the z ≅7 LBGs show blue rest-frame UV slopes (median β = −2.0) and are massive (up to M*≅1010M ʘ). Furthermore, an analysis of the ground-based imaging shows that the majority are resolved consistent with larger sizes (r1/2 ≅1–1.5 kpc) than displayed by less massive galaxies. Finally, a new search for z ≅6 galaxies within the UltraVISTA and UDS datasets was undertaken, resulting in a sample of 266 LBGs (−22.7 < MUV < −20.5) galaxies with which to investigate the rest-frame UV LF. The potential contamination by galactic brown dwarfs was investigated quantitatively using a simple model of the Galaxy, showing that the expected contamination rate of the sample was < 3 per cent, and that the stars can be effectively removed by fitting standard stellar spectra to the observed photometry. The galaxy surface density in the UltraVISTA/COSMOS field exceeds that in the UDS/SXDS by a factor of ≅1.4, indicating strong cosmic variance between the two fields. The number counts of galaxies we find are a factor of 2 lower than predicted by the recent LF determination by Bouwens et al., and the derived rest-frame UV LF at z ≅6 revealed that an under dense UDS field can account for some of the observed differences between previous analyses. An evolution in the characteristic magnitude between z ≅5 and z≅7 of ∆M*~ 0.5 was found in contrast to other smaller area surveys, and a double power law was shown to equally well describe the LF at z = 6 as compared to the commonly assumed Schechter function. The bright-end of the LF at z ≅6 tentatively shows a steeper decline than found at z ≅7, which could indicate the onset of mass quenching of the most massive galaxies or the rise of dust obscuration. Comparison with the predictions of the latest theoretical models and simulations of galaxies reveals that most models require substantial (A1500 ~ 1.5–2) average dust extinction at the bright end to reproduce the shape of the galaxy UV LF at z ≅7.

Cosmic rays at energies 10^18 eV and above are known as Ultra High Energy Cosmic Rays (UHECR). UHECR are charged particles that are accelerated by the biggest accelerators in our universe. Candidate accelerators generating these UHECR are super novas, black holes and neutron stars. But where and what these intergalactic accelerators is at large still unknown. One of the experiments in the forefront of research in this eld is JEM-EUSO, a planed space based telescope for detecting UHECR particles as they enter Earth's atmosphere. Made possible by the advances in photon detectors and light weighted Fresnel lenses. A ground based path nder experiment was carried out in 2015 called EUSO-TA to test the optics and photomultiplier technologies. When the UHECR enters the atmosphere it collides with the atoms generating a number of secondary particles which in turn interacts with other atoms in the atmosphere generating a cascade of secondary particles. These trails are known as Extensive Air Showers (EAS). Mostly electrons are generated and in turn they excites the nitrogen atoms in the atmosphere which generate a isotropic characteristic uorescence light. The JEM-EUSO telescope is designed to detect and measure the photon ux. From the photon ux it will be able to estimate the energy of the initial UHECR. JEM-EUSO will cover the largest area of EAS search and increase statistics of UHECR data. This thesis describes the method and development of algorithms made for EAS analysis and detection based on EUSO-TA data. A simulation of EUSO-TA focal surface was developed, simulating background, stars and EAS. The algorithms developed involves a background subtracting lter, line detection using Hough transform and a neural network for decision making. The Hough transform is used in computer vision and is a method used to detect lines in the pictures. It successfully identi ed both simulated and captured UHECR incoming direction with small errors. Neural network are a machine learning method used classi cation and regression problems. With the use of know example data simulated or real captured data a neural network can without explicit programing it, adjust its parameters to t the data. Based on method called supervised learning. The algorithms was programed in Python and using ROOT software to build the neural network. The resulting algorithm was able to successfully detect simulated data. Test on the EUSO-TA captured data shows a promising result but has to be developed and tested further.

Neste trabalho, cujo objetivo foi fornecer subsídios que permitam estabelecer um sistema de dosimetria para as tripulações de aeronaves que operam no território nacional, foi desenvolvida uma técnica para realizar medições do equivalente de dose ambiente em aeronaves. Foi testado um detector ativo, para uso embarcado em aeronaves, avaliando-se sua adequação a este tipo específico de medição, assim como sua suscetibilidade às interferências magnética e eletromagnética. O equipamento foi calibrado em campos metrologicamente rastreados e foi verificado em um campo especial do laboratório europeu CERN, que reproduz com grande proximidade o espectro de partículas existentes em altitudes de voo de aeronaves, sendo a seguir testado em diversos ensaios em voo, em uma aeronave da Força Aérea Brasileira. Os resultados foram avaliados e comparados com aqueles obtidos por diversos programas computacionais de estimativa de dose oriunda de radiação cósmica, com respeito à sua adequação para uso na região da América do Sul e foi selecionado o programa CARI-6 para avaliar as doses efetivas médias estimadas a que estão sujeitas as tripulações que operam nesta região. Foi efetuada uma avaliação estatística da distribuição de doses efetivas das tripulações dos voos que operam na região da América do Sul e Caribe e concluiu-se que grande parte destas tripulações estão sujeitas a doses efetivas anuais que ultrapassam o limite estabelecido para membros do público. Adicionalmente, foi proposto um dosímetro passivo preliminar, baseado em detectores termoluminescentes, e foram ainda estabelecidas colaborações internacionais com grupos de pesquisa do Reino Unido e da Itália, para a realização de medições conjuntas do equivalente de dose ambiente em aeronaves. / The objective of this work is the establishment of a dosimetric system for the aircrew in the domestic territory. A technique to perform measurements of ambient dose equivalent in aircrafts was developed. An active detector was evaluated for onboard aircraft use, testing its adequacy to this specific type of measurement as well as its susceptibility to the magnetic and electromagnetic interferences. The equipment was calibrated in standard radiation beams and in a special field of the European Laboratory CERN, that reproduces with great proximity the real spectrum in aircraft flight altitudes; it was also tested in several flights, in an Brazilian Air Force\'s aircraft. The results were evaluated and compared with those obtained from several computational programs for cosmic radiation estimatives, with respect to its adequacy for use in the South American region. The program CARI-6 was selected to evaluate the estimated averaged effective doses for the aircrew who operate in this region. A statistical distribution of aircrew effective doses in South America and Caribe was made, and the results show that a great part of this aircrew members are subjected to annual effective doses that exceed the dose limits for the members of the public. Additionally, a preliminary passive dosemeter, based in thermoluminescent detectors, was proposed; international collaborations with United Kingdom and Italy were established for joint measurements of the ambient equivalent doses in aircrafts.

Lau, King = 普朗克衛星測量對純量-張量比例的規範 / 劉荊. / Thesis M.Phil. Chinese University of Hong Kong 2013. / Includes bibliographical references (leaves 83-89). / Abstracts also in Chinese. / Title from PDF title page (viewed on 15, September, 2016). / Lau, King = Pulangke wei xing ce liang dui chun liang-zhang liang bi li de gui fan / Liu Jing.