Dynamics of Metastable Magnetic Skyrmions

Skyrmions, vortex-like objects composed of magnetic moments, have seen a recent surge of research interest due to their unique transport and topological properties. With an ever-increasing demand for more efficient memory and computation, skyrmionic devices have been conceived as an ultra-low power, high density data storage solution. While they are found in a range of materials, in this thesis we will primarily be concerned with skyrmions found in bulk chiral magnets. In such systems, skyrmions are typically only at equilibrium in a small range of temperature and applied magnetic field. However, they can exist in a metastable state over a much wider range of the magnetic phase diagram, formed by cooling the system under an applied magnetic field. Metastable skyrmions therefore have technological application by enabling the existence of skyrmions at room temperature and zero applied magnetic field. However, they also posses a finite, temperature-dependent lifetime, which places limitations on the stability of metastable skyrmions, and also restricts the population remaining after the cooling process. This lifetime is realised in nanoscopic mechanisms which are governed by topological defects, known as Bloch points. Due to the locality of these structures, the development of real-space imaging techniques are vital for gaining true understanding of skyrmion formation and annihilation. In this thesis, the dynamics of metastable skyrmions are thoroughly investigated through the use of magnetometry, and a range of neutron and x-ray scattering techniques. The effect of chemical substitution, or doping, on the magnetic phase transitions in Zn-doped Cu$_2$OSeO$_3$ is explored, and found to introduce pinning effects which dramatically increases the lifetime of metastable skyrmions. Furthermore, by adapting x-ray imaging methods for cryogenic sample environments, the first real-space observation of the vertical, tube-like, structure of skyrmions is demonstrated. The results open the door to a variety of experiments capable of further investigation into the dynamics of the skyrmion spin texture

Pre-fabrication for providing biocapacity to support vaccine manufacturing

The industry landscape is evolving rapidly and requires new and innovative approaches for more rapidly addressing the growing global demand for drug products as well as the challenges of unpredictability and inflexibility that have historically burdened the industry. Over the past two years, the industry’s herculean response to the COVID-19 pandemic has proven that with the proper focus, investment, science, and manufacturing technologies, these historic challenges can be overcome as well as establishing new benchmarks for how the industry can perform in the future to ensure availability of drug products and therapies to the global patient base Prefabricated modular construction of cleanrooms, utilities, and facility structures, is an innovative approach to building new manufacturing facilities that the industry has benefited from and is currently being utilised in critical COVID related projects. Prefabricated and modular facilities have been utilized in many industries such as food, chemical, and consumer products in the past, and have started to see significant adoption within the pharma and biopharma industries over the past ten years. This has largely been driven by the need to reduce project timelines, improve capability and flexibility, and minimize the risks associated with traditional construction for manufacturing facilities. It has helped as well to make Biopharma manufacturing more accessible to emerging regions, where in the past biomanufacturing was too complex to establish. Please click Download on the upper right corner to see the full abstract

Comparison of acoustic travel-time measurement of solar meridional circulation from SDO/HMI and SOHO/MDI

Time-distance helioseismology is one of the primary tools for studying the solar meridional circulation. However, travel-time measurements of the subsurface meridional flow suffer from a variety of systematic errors, such as a center-to-limb variation and an offset due to the P-angle uncertainty of solar images. Here we apply the time-distance technique to contemporaneous medium-degree Dopplergrams produced by SOHO/MDI and SDO/HMI to obtain the travel-time difference caused by meridional circulation throughout the solar convection zone. The P-angle offset in MDI images is measured by cross-correlating MDI and HMI images. The travel-time measurements in the south-north and east-west directions are averaged over the same observation period for the two data sets and then compared to examine the consistency of MDI and HMI travel times after correcting the systematic errors. The offsets in the south-north travel-time difference from MDI data induced by the P-angle error gradually diminish with increasing travel distance. However, these offsets become noisy for travel distances corresponding to waves that reach the base of the convection zone. This suggests that a careful treatment of the P-angle problem is required when studying a deep meridional flow. After correcting the P-angle and the removal of the center-to-limb effect, the travel-time measurements from MDI and HMI are consistent within the error bars for meridional circulation covering the entire convection zone. The fluctuations observed in both data sets are highly correlated and thus indicate their solar origin rather than an instrumental origin. Although our results demonstrate that the ad hoc correction is capable of reducing the wide discrepancy in the travel-time measurements from MDI and HMI, we cannot exclude the possibility that there exist other systematic effects acting on the two data sets in the same way.Comment: accepted for publication in A&

Does ‘Scientists believe…’ imply ‘All scientists believe...’? Individual differences in the interpretation of generic news headlines

Media headlines reporting scientific research frequently include generic phrases such as “Scientists believe x” or “Experts think y”. These phrases capture attention and succinctly communicate science to the public. However, by generically attributing beliefs to ‘Scientists’, ‘Experts’ or ‘Researchers’ the degree of scientific consensus must be inferred by the reader or listener (do all scientists believe x, most scientists, or just a few?). Our data revealed that decontextualized generic phrases such as “Scientists say…” imply consensus among a majority of relevant experts (53.8% in Study 1 and 60.7-61.8% in Study 2). There was little variation in the degree of consensus implied by different generic phrases, but wide variation between different participants. These ratings of decontextualized phrases will inevitably be labile and prone to change with the addition of context, but under controlled conditions people interpret generic consensus statements in very different ways. We tested the novel hypothesis that individual differences in consensus estimates occur because generic phrases encourage an intuitive overgeneralization (e.g., Scientists believe = All scientists believe) that some people revise downwards on reflection (e.g., Scientists believe = Some scientists believe). Two pre-registered studies failed to support this hypothesis. There was no significant relationship between reflective thinking and consensus estimates (Study 1) and enforced reflection did not cause estimates to be revised downwards (Study 2). Those reporting scientific research should be aware that generically attributing beliefs to ‘Scientists’ or ‘Researchers’ is ambiguous and inappropriate when there is no clear consensus among relevant experts

Human Reliability Analysis using a Human Factors Hazard Model

Human Reliability Analysis (HRA) has found application within a diverse set of engineering domains, but the methods used to apply HRA are often complicated, time-consuming, costly to apply, specific to particular (i.e., nuclear) applications, and are not suitable for direct comparison amongst themselves. This paper proposes a Human Factors Hazard Model (HFHM), which builds an HRA method from the tools of Fault Tree Analysis (FTA), Event Tree Analysis (ETA), and a novel model of considering serial Human Error Probability (HEP) more relevant to psychomotor-intensive industrial and commercial applications such as manufacturing, teleoperation, and vehicle operation. The HEP approach uses Performance Shaping Factors (PSFs) relevant to human behavior, as well as specific characteristics unique to a system architecture and its corresponding operational behavior. The HFHM tool is intended to establish a common analysis approach, to simplify and automate the modeling of the likelihood of a mishap due to a human-system interaction during a hazard event. The HFHM is executed commercial software tools (MS Excel and SysML) such that trade and sensitivity studies can be conducted and iterated automatically. The results generated by the HFHM can be used to guide risk assessment, safety requirements generation and management, design options, and safety controls within the system design architecting process. Verification and evaluation of the HFHM through simulation and subject matter expert evaluation illustrate the value of the HFHM as a tool for HRA and system safety analysis in a set of key industrial applications

Solar meridional circulation from twenty-one years of SOHO/MDI and SDO/HMI observations: Helioseismic travel times and forward modeling in the ray approximation

The south-north travel-time differences are measured by applying time-distance helioseismology to the MDI and HMI medium-degree Dopplergrams covering May 1996-April 2017. Our data analysis corrects for several sources of systematic effects: P-angle error, surface magnetic field effects, and center-to-limb variations. An interpretation of the travel-time measurements is obtained using a forward-modeling approach in the ray approximation. The travel-time differences are similar in the southern hemisphere for cycles 23 and 24. However, they differ in the northern hemisphere between cycles 23 and 24. Except for cycle 24's northern hemisphere, the measurements favor a single-cell meridional circulation model where the poleward flows persist down to $\sim$0.8 $R_\odot$, accompanied by local inflows toward the activity belts in the near-surface layers. Cycle 24's northern hemisphere is anomalous: travel-time differences are significantly smaller when travel distances are greater than 20$^\circ$. This asymmetry between northern and southern hemispheres during cycle 24 was not present in previous measurements (e.g., Rajaguru & Antia 2015), which assumed a different P-angle error correction where south-north travel-time differences are shifted to zero at the equator for all travel distances. In our measurements, the travel-time differences at the equator are zero for travel distances less than $\sim$30$^\circ$, but they do not vanish for larger travel distances. This equatorial offset for large travel distances need not be interpreted as a deep cross-equator flow; it could be due to the presence of asymmetrical local flows at the surface near the end points of the acoustic ray paths.Comment: accepted for publication in A&

Snow in the Tropics

Snow in the Tropics offers the first comprehensive history of the independent reefer operators, companies that are dedicated to transport refrigerated products by ship, from the early 20th century to the present. Readership: All interested in maritime history, particularly those with an interest in the modern history of the shipping industry