37 research outputs found

    Improvements In Interferometric Data Modeling For The New Era Of Radio Cosmology

    Get PDF
    The redshifted 21 cm line promises to provide a wealth of information about the evolution of our universe but remains as yet undetected. The general theme of this thesis is developing increasingly realistic models of the raw data we collect from a radio telescope. This is important because at the end of the day extracting the cosmological signal from the data will be accomplished by achieving a level of understanding of all the possible alternative sources that might mimic the cosmological signal, to a degree that we can confidently reject those alternatives as causes of our detection. The work presented in this thesis has been done in the context of working on the HERA experiment which aims to make the first measurements of spatial fluctuations in the emission from neutral hydrogen. In this thesis I emphasized aspects of the visibility function that are important for efficient and realistic visibility simulations including full account of polarization effects, in particular using a harmonic parameterization of the integrand. I assessed the effect of potential ionospheric attenuation on the suppression of polarization contamination in 21 cm power spectrum measurements using visibility simulations based on historical ionospheric plasma density data. I showed how we can use closed-form calculations of the cross-frequency angular power spectrum on the sky to generate simple mock cosmological signal simulations that are useful for validating data analysis methods. I showed how the window functions associated with a 21 cm power spectrum estimate can be approximated by simple forms that are much cheaper to evaluate than the general definition. Finally, I produced a new Southern Sky Model that combines the best available diffuse radio emission surveys that cover HERA\u27s field of view and observing bandwidth with a point source catalog without double counting flux

    Recent Advances in Wireless Communications and Networks

    Get PDF
    This book focuses on the current hottest issues from the lowest layers to the upper layers of wireless communication networks and provides "real-time" research progress on these issues. The authors have made every effort to systematically organize the information on these topics to make it easily accessible to readers of any level. This book also maintains the balance between current research results and their theoretical support. In this book, a variety of novel techniques in wireless communications and networks are investigated. The authors attempt to present these topics in detail. Insightful and reader-friendly descriptions are presented to nourish readers of any level, from practicing and knowledgeable communication engineers to beginning or professional researchers. All interested readers can easily find noteworthy materials in much greater detail than in previous publications and in the references cited in these chapters

    Developing Parameter Constraints for Radar-based SWE Retrievals

    Get PDF
    Terrestrial snow is an important freshwater reservoir with significant influence on the climate and energy balance. It exhibits natural spatiotemporal variability which has been enhanced by climate change, thus it is important to monitor on a large scale. Active microwave, or radar remote sensing has shown frequency-dependent promise in this regard, however, interpretation remains a challenge. The aim of this thesis was to develop constraints for radar based SWE retrievals which characterize and limit uncertainty with a focus on the underlying physical processes, snowpack stratigraphy, the influence of vegetation, and effects of background scattering. The University of Waterloo Scatterometer (UWScat) was used to make measurements at 9.6 and 17.2 GHz of snow and bare ground in a series of field-based campaigns in Maryhill and Englehart, ON, Grand Mesa, CO (NASA SnowEx campaign, year 1), and Trail Valley Creek, NT. Additional measurements from Tobermory, ON, and Churchill, MB (Canadian Snow and Ice Experiment) were included. The Microwave Emission Model for Layered Snowpacks, Version 3, adapted for backscattering (MEMLS3&a) was used to explore snowpack parameterization and SWE retrieval and the Freeman-Durden three component decomposition (FD3c) was used to leverage the polarimetric response. Physical processes in the snow accumulation environment demonstrated influence on regional snowpack parameterization and constraints in a SWE retrieval context with a single-layer snowpack parameterization for Maryhill, ON and a two-layer snowpack parameterization for Englehart, ON resulting in a retrieval RMSE of 21.9 mm SWE and 24.6 mm SWE, respectively. Use of in situ snow depths improved RMSE to 12.0 mm SWE and 10.9 mm SWE, while accounting for soil scattering effects further improved RMSE by up to 6.3 mm SWE. At sites with vegetation and ice lenses, RMSE improved from 60.4 mm SWE to 21.1 mm SWE when in situ snow depths were used. These results compare favorably with the common accuracy requirement of RMSE ≤ 30 mm and underscore the importance of understanding the driving physical processes in a snow accumulation environment and the utility of their regional manifestation in a SWE retrieval context. A relationship between wind slab thickness and the double-bounce component of the FD3c in a tundra snowpack was introduced for incidence angles ≥ 46° and wind slab thickness ≥ 19 cm. Estimates of wind slab thickness and SWE resulted in an RMSE of 6.0 cm and 5.5 mm, respectively. The increased double-bounce scattering was associated with path length increase within a growing wind slab layer. Signal attenuation in a sub-canopy SWE retrieval was also explored. The volume scattering component of the FD3c yielded similar performance to forest fraction in the retrieval with several distinct advantages including a real-time description of forest condition, accounting for canopy geometry without ancillary information, and providing coincident information on forest canopy in remote locations. Overall, this work demonstrated how physical processes can manifest regional outcomes, it quantified effects of natural inclusions and background scattering on SWE retrievals, it provided a means to constrain wind slab thickness in a tundra environment, and it improved characterization of coniferous forest in a sub-canopy SWE retrieval context. Future work should focus on identifying ice and vegetation conditions prior to SWE retrieval, testing the spatiotemporal validity of the methods developed herein, and finally, improving the integration of snowpack attenuation within retrieval efforts

    New Fundamental Technologies in Data Mining

    Get PDF
    The progress of data mining technology and large public popularity establish a need for a comprehensive text on the subject. The series of books entitled by "Data Mining" address the need by presenting in-depth description of novel mining algorithms and many useful applications. In addition to understanding each section deeply, the two books present useful hints and strategies to solving problems in the following chapters. The contributing authors have highlighted many future research directions that will foster multi-disciplinary collaborations and hence will lead to significant development in the field of data mining

    Wave propagation: laser propagation and quantum transport

    Get PDF
    2021 Spring.Includes bibliographical references.This dissertation consists of two independent projects, where wave propagation is the common theme. The first project considers modeling the propagation of laser light through the atmosphere using an approximation procedure we call the variational scaling law (VSL). We begin by introducing the Helmholtz equation and the paraxial approximation to the Helmholtz equation, which is the starting point of the VSL. The approximation method is derived by pairing the variational formulation of the paraxial Helmholtz equation with a generalized Gaussian ansatz which depends on the laser beam parameters. The VSL is a system of stochastic ODEs that describe the evolution of the Gaussian beam parameters. We will conclude with a numerical comparison between the variational scaling law and the paraxial Helmholtz equation. Through exploring numerical examples for increasing strengths of atmospheric turbulence, we show the VSL provides, at least, an order-one approximation to the paraxial Helmholtz equation. The second project focuses on quantum transport by numerically studying the quantum Liouville equation (QLE) equipped with the BGK-collision operator. The collision operator is a relaxation-type operator which locally relaxes the solution towards a local quantum equilibrium. This equilibrium operator is nonlinear and is obtained by solving a moment problem under a local density constraint using the quantum entropy minimization principle introduced by Degond and Ringhofer in \cite{degondringhofer}. A Strang splitting scheme is defined for the QLE in which the collision and transport of particles is treated separately. It is proved that the numerical scheme is well-defined and convergent in-time. The splitting scheme for the QLE is applied in a numerical study of electron transport in different collision regimes by comparing the QLE with the ballistic Liouville equation and the quantum drift-diffusion model. The quantum drift-diffusion model is an example of a quantum diffusion model which is derived from the QLE through a diffusive limit. Finally, it is numerically verified that the QLE converges to the solution to the quantum drift-diffusion equation in the long-time limit

    Polarimetric Synthetic Aperture Radar, Principles and Application

    Get PDF
    Demonstrates the benefits of the usage of fully polarimetric synthetic aperture radar data in applications of Earth remote sensing, with educational and development purposes. Includes numerous up-to-date examples with real data from spaceborne platforms and possibility to use a software to support lecture practicals. Reviews theoretical principles in an intuitive way for each application topic. Covers in depth five application domains (forests, agriculture, cryosphere, urban, and oceans), with reference also to hazard monitorin

    New Physics and New Technologies in Next-Generation Neutrino Experiments.

    Get PDF
    PhD ThesisWe are living a pivotal moment for neutrino physics. A new generation of experiments is about to begin and will extend our understanding of neutrinos. Very large scale experiments, like Hyper-Kamiokande, will collect unprecedented statistics and will constrain oscillation parameters to high precision: the CP violation phase, the octant of 23, and the mass hierarchy are likely to be determined. Many are the experimental difficulties behind a successful megaton water Cherenkov detector, but improvements in photodetection technologies luckily allow such an ambitious project. One of the most important challenges is to keep systematical uncertainties under control, so as they do not dominate over statistical errors. Assessing the impact of the systematics on the overall sensitivity of the experiment is a fundamental requirement to the final success of Hyper-Kamiokande. Thanks to powerful accelerator facilities, future long baseline experiments, such as DUNE, will also explore the intensity frontier of neutrino physics and study rare phenomena. Numerous extension to the Standard Model (SM) and alternative theories have been introduced to explain neutrino masses and mixings. These new scenarios often predict new physics, the signature of which is accessible to next-generation experiments. An interesting example comes from lowscale see-saw models, which consider GeV-scale neutral leptons coupled to SM particles with suppressed mixing angles. The near detector system of DUNE is an ideal place for searches of these particles, thanks to high exposure that compensate small event rates. Current neutrino experiments have also joined this new venture; Super-Kamiokande has been extensively refurbished in view of a new phase, starting in early 2020, in which the detector will turn into a supernova observatory. This is achieved by doping the water of Super-Kamiokande with gadolinium, in order to increase the efficiency of neutron tagging up to 90 %. The use of gadolinium is a novel technique which will be adopted by many existing and planned experiments. The benefits of improved neutron tagging are not limited just to supernova neutrinos, but to a plethora of other studies, such as reactor and atmospheric neutrinos or proton decay. In this thesis, all of the topics above are addressed. After a review of SM neutrino physics in Chapter 1, the gadolinium-loaded water Cherenkov technique is discussed in Chapter 2 with particular focus on Super-Kamiokande. A new technique to monitor gadolinium concentration in water using UV spectroscopy and an improved method for neutron calibration using a californium source are presented. Chapter 3 deals with CP violation in neutrino oscillation and the potential of Hyper-Kamiokande to constraining oscillation parameters. The methodology used to asses the experimental sensitivity is described in detail. First estimations are shown with the full systematic model and some of its variations are also taken into account. In Chapter 4 a possible Standard Model extension to explain neutrino masses is considered, and the phenomenology of such models is extensively studied in the context of a beam dump experiment. The prospect of the DUNE’s near detector to searches of heavy neutral lepton decays is then evaluated in Chapter 5. It is found that the DUNE ND is capable of extending current limits on these searches, reaching regions of the parameter space extremely interesting from a theoretical point of view

    Geometric descriptions for the polarization for nonparaxial optical fields: a tutorial

    Full text link
    This article provides an overview of the local description of polarization for nonparaxial fields, for which all Cartesian components of the vector field are significant. The polarization of light at each point is characterized by a 3×33\times3 polarization matrix, as opposed to the 2×22\times2 matrix used in the study of polarization for paraxial light. For nonparaxial light, concepts like the degree of polarization, the Stokes parameters and the Poincar\'e sphere have generalizations that are either not unique or not trivial. This work aims to clarify some of these discrepancies and provide a framework that highlights the similarities and differences with the description for the paraxial regimes. Particular emphasis is placed on geometric interpretations.Comment: 38 pages, 9 figure

    Applications

    Get PDF
    corecore