PRISM :: Browsing by Author "Hobill, David W."

Browsing by Author "Hobill, David W."

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Open Access
Application of 1-D Inverse Scattering to Inversion of Laboratory Seismic Data and Distributed Acoustic Sensing Data
(2020-09-02) Izadi, Hormoz; Innanen, Kristopher A.; Karchewski, Brandon; Hobill, David W.; Trad, Daniel O.
The Born series provides a framework for constructing a connection between Earth model parameters and a wavefield characterised by perturbation about a known reference wavefield. The inverse scattering series provides a linear and a nonlinear expression for approximating Earth’s model parameters. Based on our results, the linear expression provides an accurate approximation of the 1-D depth varying velocity profile. However, with increasing contrast, one has to utilise the nonlinear expression for increased accuracy. In seismic inversion, a major problem relates to the bandlimited nature of recorded seismic data, limiting the inversion for absolute amplitudes. Numerical results on a 1-D synthetic model demonstrate the capacity of the algorithm to recover low frequency information, critical for accurate inversion. By extending the application of projection onto convex sets (POCS) to 1-D physical modelling data, we obtain an accurate reconstruction of the dataset. Inversion of the data demonstrates the advantage of nonlinear inverse scattering in approximating a relatively accurate velocity profile. In comparison, the linear scattering expression fails to provide a reasonable estimate of reflectors beyond the first interface. One of the areas of growing interest in the field of exploration geophysics is the application of optical fibre sensing technology. Recent studies suggest the advantage of this technique in providing a greater range of applicability in comparison to traditional methods. Among various Optical time-domain reflectometer (OTDR) arrangements, the intensity based measurement is generally limited by the nonlinear response of a signal to external disturbances such as strain. This has served as a motivation in the second half of this thesis to frame the problem as a 1-D scattering problem, in an attempt to apply the Born series to recover information related to variations in external measurements such as strain. Our attempts to utilise the Born series fails to provide an accurate estimation of changes in location of scattering points. This is primarily due to the complexity of the model and interference of backscattered optical pulse within the fibre. Continued research could potentially provide a framework for a robust detection of external perturbation based on variation in intensity.
Open Access
Assessment of r-process sensitivity studies and metrics
(2020-09-04) Osakwe, Carlton-James U.; Ouyed, Rachid; Hobill, David W.; Cully, Christopher M.; Heyne, Belinda
Understanding the r-process is essential to understanding the early Universe. Sensitivity studies are important to developing this understanding, but they are hindered by discrepancies in how their results are reported. The fundamentals of the r-process and sensitivity studies are described. These discrepancies are explored in detail. We primarily discuss the way sensitivity is quantified and the normalization of results. The need for consistent results is asserted, and the issues with inconsistent results are made evident. The discrepancies themselves suggest various future avenues of study. We conclude with several recommendations for consistent reporting of sensitivity studies.
Open Access
Black holes and radiative fields in general relativity
(1999) Webster, Paul S.; Hobill, David W.
Open Access
Classical charged particle radiation orthogonal magnetic and electric fields
(1974) Hobill, David W.; Bland, Clifford J.
Open Access
A Complex Systems Study of Social Hierarchies and Jurisprudence
(2019-11) Hickey, Joseph; Davidsen, Jörn; Campbell, Lyndsay M.; Redner, Sidney; Feder, David L.; Hobill, David W.; Yau, Andrew W.
Humanity's understanding of complex societal phenomena is still in its infancy, and there is much to discover about the organizing principles governing social life on Earth. How do societal structures such as social hierarchies form, and under what conditions do these structures remain stable versus become unstable and collapse? What is the structure of the jurisprudence that regulates modern human societies and how does it evolve in time? In this thesis, I apply quantitative analysis and modeling approaches from physics and network science to investigate these questions. In Part I, I develop simple models of the formation and stability of social hierarchies and compare their results to interaction data from animal societies and proxy data from human societies. The models are based on pairwise interactions between randomly-selected individuals that result in exchanges of societal "status." Following many interactions, a distribution of status forms, the shape of which ranges from egalitarian (many individuals with near average status) to very unequal (many low status individuals and a few high status individuals), depending on the model parameters. An Arrhenius relationship between a characteristic time controlling the evolution of the status distribution and the model parameters quantifies "long-lived" status distributions which appear to be stable in time, but in fact are not. In Part II, I analyze citation networks of court decisions (judgments) in the areas of family, bankruptcy, and defamation law, using unique datasets covering all levels of the Canadian court hierarchy (trial, appellate, and Supreme Court of Canada). In each network, judgments are "nodes" and judges' citations of past decisions are directed "links" between nodes. Despite the legal differences between the three areas of law, many large-scale network properties are similar. However, one can use refined network tools (clustering methods) to draw out differences in the datasets and interpret them in relation to legal developments (landmark judgments and important legislation) in the specific areas of law. This leads to an in-depth examination of the influence of landmark judgments and statutory changes on the explosion in family litigation that occurred in Canada in the 1990s.
Open Access
Differentiating Diffuse Aurora
(2019-12) Grono, Eric M.; Donovan, Eric; Behjat, Laleh; Norman, Ann-Lise; Hobill, David W.; Liemohn, Michael W.
Pulsating aurora is a pervasive early morning auroral display. Perhaps because of the awkward viewing hours, it received comparatively little attention in past years and is often discussed as if it is just one phenomenon. However, pulsating aurora can be differentiated into at least three types based on the extent of their pulsation and structuring (Grono and Donovan, 2018). Amorphous pulsating aurora (APA) is characterized by extensive pulsation and a lack of persistent structuring. In contrast, patchy pulsating aurora (PPA) and patchy aurora (PA) features can persist for tens of minutes and follow ionospheric convection (Grono et al., 2017). While PPA structures pulsate over much of their area, PA is mostly non-pulsating. The most common pulsating aurora is APA, which is nearly ubiquitous during the early morning and can appear earlier than PPA and PA (Grono and Donovan, 2019b). Pulsating auroras do not occur poleward of the proton aurora, only within or equatorward of it (Grono and Donovan, 2019a). PPA and PA appear predominantly equatorward of the boundary between stably trapped protons and those scattered by tight magnetic field curvature. This suggests that the processes responsible for the patchiness of PPA and PA are constrained to the mostly dipolar inner magnetosphere. Nishimura et al. (2010) demonstrated that there can be a nearly one-to-one correspondence between plasma wave power and auroral brightness. Consequently, auroral brightness should be able to act as a proxy for wave power, and wave structuring should indicate which type of pulsating aurora a spacecraft is observing. PA should be associated with unmodulated plasma waves persisting for the length of time it takes for a spacecraft to transit the source region of a patch. The location of such wave structuring coincides with where PA occurs (Grono and Donovan, 2019c). Sunrise prevents optical observations of the aurora from continuing past dawn, making it difficult to assess how long pulsating aurora can persist for. However, these plasma wave observations indicate that the processes responsible for PA and PPA structuring may continue into the afternoon.
Open Access
Evolutionary Algorithm for Adaptive Quantum-Channel Control
(2019-01-23) Palittapongarnpim, Pantita; Sanders, Barry C.; Wiseman, Howard M.; Simon, Ch; Hobill, David W.; Denzinger, Jörg
The key to successful implementations of quantum technologies is quantum control, whose aim is to steer quantum dynamics such that the desired outcome is achieved. Quantum control techniques rely on models of the quantum dynamics to generate control policies that attain the control targets. In a practical situation, the dynamic model may not match the dynamic in the implementation, and this mismatch can lead to reduced performance or even a failed control procedure. Data-driven control has been proposed as an alternative to model-based control design. In this approach, measurement outcomes from the system are used to generate a policy, which enables robust control without the need for a noise model. The potential for data-driven quantum control has been demonstrated in the problem of quantum-enhanced adaptive phase estimation. However, the performance and robustness of data-driven policies have never been compared with performance and robustness of model-based control techniques. In this thesis, we aim to determine the advantages and disadvantages of model-based and data-driven policy generation using a simulated quantum-enhanced adaptive phase estimation as an example of a quantum control task. In the process, we explore the connection between an adaptive quantum-enhanced metrological procedure to a decision-making process, which is an alternative model of the dynamic during the control task. We also devise a robust search algorithm based on an evolutionary algorithm that is ignorant of the properties of the phase noise but is still able to deliver quantum-enhanced precision. We then compare the performances of feedback control policies designed using Bayesian inference, which is a model-based technique, to policies generated using this robust evolutionary algorithm on their performance in both noisy and noiseless interferometers. We also assess the resources used in generating and implementing a control policy and use the complexities of the time and space costs as parts of selecting a practical control procedure.
Open Access
Framework for Learning and Control in the Classical and Quantum Domains
(2024-06-20) Vedaie, Seyed Shakib; Sanders, Barry C.; Hobill, David W.; Oblak, Daniel; Far, Behrouz H.; Haljan, Paul C.
Control and learning are essential to technological advancement, both in the classical and quantum domains, yet their interrelationship is insufficiently clear in the literature, especially between classical and quantum definitions of control and learning. In this thesis, we aim to construct a framework that formally relates learning and control, both classical and quantum, to each other, with this formalism showing how learning can aid control. We formulate new versions of quantum learning and control that essentially quantise classical learning and control, respectively. Furthermore, our framework helps identify interesting unsolved problems in the nexus of classical and quantum control and learning and helps choose tools to solve problems. Our unification of these fields relies on diagrammatically representing the state of knowledge, which elegantly summarises existing knowledge and exposes knowledge gaps. As use cases, we cast the well-studied problem of adaptive quantum-enhanced interferometric phase estimation as a supervised learning problem for devising feasible control policies and develop effective quantum control for two-qubit gate design with trapped ions. Informed by the knowledge that the plant, i.e.~ion trap, is a channel, we develop a comprehensive model of controlled open-system dynamics described by a quantum master equation and validate our model based on empirical data gathered from a control system for preparing Bell states. We then employ global optimisation to design pulse sequences for achieving a robust, rapid two-qubit gate for a chain of seven trapped $^{171}$Yb$^{+}$ ions by optimising over numerically integrated quantum master equation solutions. We further explore the nexus of classical and quantum learning through hybrid classical-quantum learning algorithms. We introduce the ``analogue-quantum kitchen sinks'' algorithm, a quantum extension of the classical "random kitchen sinks," which employs an analogue-quantum computer for mapping data features into new features in a non-linear manner. A classical algorithm can then perform machine learning tasks using the new features. We show the effectiveness of our algorithm for performing binary classification on both a synthetic and a real-world data set through computer simulation of a quantum annealer's operation.
Open Access
Ice Nucleation: Sulfate and Its Influence in Arctic and Rural and Urban NW Continental Precipitation
(2019-08-20) Derksen, Mark; Norman, Ann-Lise; Else, Brent G. T.; Hobill, David W.; Wieser, Michael E.
With the growth of urban centers and decline of natural ecosystems, the increasing presence of aerosol particles has the potential to have major impacts on climate. This study assessed the ice nucleation characteristics of anthropogenic and organic/biogenic sulfate sources in precipitation samples from the Arctic, Kananaskis (rural continental), and Calgary (Urban continental). Samples were analyzed using droplet freezing technique, isotopic analysis, and anion/cation measurements. Comparisons between deposition-based precipitation sampler and passive fog/rain sampler yielded no significant differences in ice nucleation characteristics. Arctic fog samples had distinct ice nucleating particle characteristics compared to rain and dry deposition samples. A 32% increase in the influence of biogenic matter was apparent in 2016 Arctic samples relative to 2014 samples. The influence of a continental biogenic and/or organic material was apparent in the ice nucleating characteristics of both rural and urban continental samples. Snow samples exhibited the greatest biogenic influence, followed by rain samples, and then dry deposition samples.
Open Access
Identifying Zinc Inputs to Heard and McDonald Islands Region using Zinc Concentrations and Isotopic Compositions
(2020-08-24) Mohamed, Fwziah Ali Abdalali; Wieser, Michael E.; Yang, Lu; Hobill, David W.; Yau, Andrew W.; Mayer, Bernhard
Zinc (Zn) availability in the ocean is thought to have the potential to impact the health and the biomass of phytoplankton communities in the ocean. The application of Zn isotopic composition is an effective approach to understand sources and environmental receptors of Zn in the ocean. An important challenge; however, is to measure the Zn isotopic composition reliably because of the limited range in Zn isotopic composition and the low amount of Zn found in the ocean. Zinc is a micronutrient that has received much attention due to its role in the biology of marine phytoplankton. Ocean surface water Zn concentrations are in the low nanomolar range, potentially limiting the growth of some phytoplankton species. Identifying and assessing Zn sources in the ocean can provide insights into the significance and the influence of Zn availability on phytoplankton growth. This thesis research project entails the development of a reliable method to explore the Zn sources in the vicinity of Heard and McDonald Islands, an Australian territory, in the Southern Ocean. The region of Heard and McDonald Islands, two of the most active volcanic islands in the world, is one of the regions in the Southern Ocean where large phytoplankton blooms are produced annually. This raises the possibility that the islands’ hydrothermal activity is releasing large amounts of trace elements including Zn to the water column thereby enhancing the biological productivity in the region. The development of the analytical method included a careful consideration of all factors that may affect Zn measurements, including Zn laboratory blanks introduced during the sample handling and preparation, isobaric interferences from the sample matrix, and the data reduction technique. Zinc concentrations and isotopic compositions were measured in seawater, suspended particles, sediments, and rock samples collected during the Heard Earth Ocean Biosphere Interactions (HEOBI) voyage in January and February of 2016 led by the Institute for Marine and Antarctic Studies (IMAS) at the University of Tasmania, Australia. Zinc concentrations and isotope amount ratio data indicated that; a possible Zn hydrothermal component may have been influencing the waters near McDonald Island and at a couple of stations in the waters surrounding Heard Island. A more definitive indication of possible Zn hydrothermal sources in the waters surrounding Heard and McDonald Islands could be possible if additional data including Zn excess and the concentration of mantle helium become available.
Open Access
The Large-Scale Structure of Magnetic Fields Associated with Filamentary Molecular Clouds
(2019-01-22) Tahani, Mehrnoosh; Plume, René; Brown, Jo Anne C.; Houde, Martin; Hobill, David W.; Knudsen, David J.; Behjat, Laleh
Magnetic fields pervade the interstellar medium and are believed to be important in the star formation process. However, probing magnetic fields in these star-forming regions is challenging. I propose and demonstrate a new method, using Faraday rotation measurements, to probe the direction and magnitude of the magnetic field along the line-of-sight in and around filamentary molecular clouds that are forming stars. Using my method, which utilises rotation measure data from the literature, a chemical evolution code, and extinction maps to estimate electron column density, I determine the magnetic field in four nearby molecular clouds: Orion A, Orion B, Perseus, and California. I find that my method produces results in agreement with the limited number of available Zeeman measurements. Using the magnetic field results from this new method, I find that the line-of-sight magnetic field on either side of the California and Orion A filaments has opposing magnetic field directions. Three theoretical magnetic field morphologies can explain this change of direction across filaments: toroidal, helical, and bow morphologies. I investigate these three models by combining my results with those of Planck observations to determine the 3D magnetic field structure in Orion A. I find that of the three possible morphologies, toroidal is the least probable whereas the bow morphology is the most natural. To investigate these morphologies further, I use magnetohydrodynamics simulations to simulate filamentary molecular clouds and their magnetic field evolution. I use different initial parameters to see if the magnetic field lines can become twisted around a rotating filament, potentially forming helical fields. I find that helical fields are not easily generated in these scenarios.
Open Access
Magnitude correlations and criticality in a self-similar model of seismicity
(2019-03-25) Zambrano Moreno, Andres Felipe; Davidsen, Jörn; Hobill, David W.; Jackel, Brian J.; Dettmer, Jan; Simon, Ch M.
We present an analysis of the statistical relation between subsequent magnitudes for a previously proposed self-similar aftershock rates model of seismicity whose main distinguishing feature arises as a consequence of the dependency of the rates on the magnitude difference between trigger-triggered events. By means of a particular statistical measure we studied the level of magnitude correlations among time-ordered subsequent events for various magnitude thresholds under specific types of time conditioning, explained their provenance through the model and found that the type of null model chosen in the analysis plays a pivotal role in the type of observed correlations. With particular time conditioning between subsequent events, we also analyzed and compared a model catalog to data from Southern California (SC), and found that model and real-world catalogues are consistent with each other within our statistical measure. When comparing a culled SC and the corresponding culled model catalogue under a specific type of time conditioning and magnitude thresholds, correlations do not significantly deviate from zero for the model but are present in the subset SC catalogue; these observed correlations in the SC catalogue we attributed to a process where a fraction of events are missed in the seismic recordings. The former was substantiated when we looked at the culled SC catalog for higher magnitude thresholds and saw no significant correlations, although the amount of data for this already shortened catalog is relatively low. By creating synthetic catalogues between 2 − 26 times the culled model catalogue, we estimated the length of a catalogue needed to begin to observe magnitude correlations at 3σ to be ∼ 15 times the current culled model catalogue ( ∼ 150 years worth of data) while the existence of magnitude correlations can be used in earthquake forecasting, only the time variations in the frequency-magnitude distribution might lead to a significant improvement in forecasting. We also studied the criticality of the self-similar model from the perspective of finite size effects through the introduction of an upper magnitude cut-off in the analysis and established that the model lies in the sub-critical regime for the SC parameters.
Open Access
Neuronal avalanche dynamics and criticality in neuronal cultures
(2018-12-27) Yaghoubi, Mohammad Hassan; Davidsen, Jörn; Hobill, David W.; Simon, Ch. H.; Sotero Díaz, Roberto C.
The brain is often thought to be organized in a way that it optimizes its information processing and storage capabilities, supported by studies indicating that neuronal networks self-organize to a critical state. This is characterized by the emergence of scale-free statistics in neuronal avalanches close to those predicted by mean-field theory, suggesting that neuronal avalanches propagate in a tree-like network. Here, we use optical imaging techniques to study neuronal avalanches in different preparation of neuronal cultures and different dynamical regimes. We present an experimental case study where the avalanche statistics is significantly different from mean-field, suggesting that feed-back loops play a leading role in propagation of neuronal avalanches. Another phenomenon is that cortical and hippocampal neurons alternate between high and low activity regimes (up and down states) characterized by distinct firing rates. In contrast with previous theoretical works, our experimental findings suggest both states exhibit scale-free behavior with different intrinsic time scales.
Open Access
Numerical simulations of bianchi IX cosmologies
(2006) Guo, Wanwen; Hobill, David W.
Open Access
Planar Structures in the Solar Wind and Their Effect on the Magnetosphere
(2019-09-18) Cameron, Taylor Grant; Jackel, Brian J.; Brown, Jo C.; Cully, Christopher M.; Hobill, David W.; Knudsen, David J.; Ridley, Aaron J.
This thesis is comprised of three studies which all concern implications of planar structuring in the solar wind. The first study presents a statistical comparison of various methods of determining solar wind phase front orientation for use in time-shifting solar wind data from the first Earth-Sun Lagrange point (L1) to the bowshock. It is found that the well known constrained minimum variance (MVAB-0) method is the best performing method for determining phase front orientation. The second study investigates using a 1.5 dimensional magnetohydrodynamic (MHD) numerical model oriented along the average phase front orientation as an alternative to time-shifting. The model is found to perform better than traditional time-shifting during times of sudden solar wind velocity changes. The third and final study investigates the effects of solar wind phase front orientation on magnetospheric activity using information theory. It is found that phase fronts oriented in the average Parker spiral orientation during times when the interplanetary magnetic field points northward (IMF Bz > 0) are more geoeffective than would otherwise be expected.
Open Access
Power and Certifiability of Quantum Computing for Open Systems
(2022-11-21) Karuvade, Salini; Sanders, Barry C.; Gour, Gilad; Hobill, David W.; Scheidler, Renate; Croke, Sarah
Although a quantum computer is commonly modelled as a closed physical system, in practice the computer inevitably interacts with its environment and other systems. The aim of this thesis is to ascertain the advantages offered by controlled open-system phenomena and the limitations placed by unwanted system-environment interactions on quantum computation. This thesis is divided into two parts. The first part aims to ascertain whether a changing Hilbert-space inner product (IP), which is a controlled open-system phenomenon, enhances the power of quantum computers. The uniqueness of the IP associated to a quantum system has come under scrutiny following the advent of PT-symmetric quantum mechanics. A changing IP is valuable for quantum information processing applications; however, perfunctory use of this change can lead to counterfactual conclusions. In the first part of this thesis, we develop an operational framework for a changing IP, which is fully consistent with quantum mechanics. Next, to determine the utility of this change for computation, we construct a model of computation that uses IP changing operations along with unitary gates. We prove that the new model is equivalent to the quantum circuit model in terms of computational power. We also simulate the changing IP of a single qubit on Aspen-11 qubit and qutrit processors, and certify the quality of simulations. This experiment lays the foundation for simulating non-Hermitian dynamics on quantum computers. The second part of this thesis focuses on the effect of photon losses on certifiability of boson computers. Although improving the programmability of a boson computer is necessary for the demonstration of quantum advantage, it comes with the added challenge of increased photon losses. We develop a validation protocol that certifies the output of a lossy boson computer against an adversary with limited interferometer programmability. We also analyze the resource cost for validation with respect to two models of photon losses and show that validation becomes infeasible if each interferometer mode of the computer loses photons with a fixed probability. This work highlights the importance of accurately characterizing and suppressing photon losses in near-term boson computers.
Open Access
Properties of exact analytic models for neutron stars
(2009) Raghoonundun, Ambrish M.; Hobill, David W.
Open Access
Pulse timings for binary black hole-pulsar systems
(1998) Gomez, Julio D.; Hobill, David W.
Open Access
Quantum Phase Characterization via Entanglement Scaling in Fermionic Quantum Wires
(2019-10-08) Cameron, Alexander Carlo; Feder, David L.; Hobill, David W.; Gour, Gilad
Quantum entanglement is studied in the context of its use as a probe of quantum phases within fermionic non-interacting quantum wires. In particular, we consider the uniform lattice, as well as the Su-Schreiffer-Heeger (SSH) model, and use the bipartite entropy of entanglement to characterize their quantum phases. In 1D, it has been shown analytically that the von Neumann entropy defined for a subsystem $\mathcal{H}_A \subset \mathcal{H}_A\otimes\mathcal{H}_B$ takes distinct forms dependent on the whether or not the state is thermodynamically gapped. It is also known that entanglement can be used to identify topological phases of a quantum system, such as the symmetry protected phase found in the SSH model. These results are confirmed numerically, and some common techniques for the calculation of bipartite entanglement are compared according to their aptitude for simulating larger and more complicated systems.
Open Access
Study of the decay of Zr-96 by isotope geochemistry and Penning trap mass spectrometry
(2018-04-30) Mayer, Adam John; Thompson, Robert Ian; Wieser, Michael E.; Dilling, Jens; Sharma, Kumar; Nair, Rajeev Sasidharan; Hobill, David W.
Double-beta ( ßß) decay measurements are a class of nuclear studies with the objective of detecting a neutrinoless decay process. 96Zr is of particular interest as a ßß decay candidate as it has one of the shortest ßß-decay half-lives and largest Q-values. In addition, it is also unstable against the fourfold unique-forbidden single ß decay, decaying via 96Zr->96Nb which then immediately decays to 96Mo. These properties thus designate 96Zr as a unique system to test nuclear theory. Prior to the work outlined in this thesis, two published measurements of the 96Zr half-life yielded quite different results. A geochemical measurement of the decay in ancient zircon samples resulted in a value of T(1/2)=0.94(32)x10^19 a. Conversely, a direct count rate measurement found the ßß-decay half-life to be T( 1/2,ßß)=2.35(21)x10^19 a. The geochemical measurement of the 96Zr half-life does not discriminate between the two decay channels and thus, in conjunction with ßß-decay count-rate data, could provide a way to measure the single-beta decay rate. The aim of this project was to study this system through a series of experiments combining nuclear physics and geochemical techniques. First, the single and double-ß decay Q-values were measured using the JYFLTRAP mass spectrometer. This measurement significantly improved the Q-value uncertainties over previous measurements, refining the underlying nuclear theory to improve understanding of the single-ß decay path of 96Zr->96Nb. A study of the geochemical measurement was then performed. Zircon can remain a closed system over its lifetime and is especially suitable for this investigation due to its high Zr content and low Mo content. A novel method for the separation of molybdenum from zirconium was developed to enable the detection of the small amount of accumulated decay product as an excess compared to the natural Mo isotopic composition. The 96Mo isotopic anomaly in a 2.68 Ga zircon sample was determined to be 107(40) ppm, which translates to a 96Zr half-life of (1.8(+0.7/-0.4))x10^19 a. With the 2νßß partial decay half-life known to be 2.35(21)x10^19 a, a lower limit for the single ß decay half-life was set at T(1/2,ß)=3.5x10^19 a.