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Vision-based shared control for intuitive robotic teleoperation
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MEC-assisted integrated sensing, communication, and control for autonomous vehicles towards intelligent transportation system
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Optical skyrmions and polarizations of highly focused structured light
Get PDFStructured light refers to the controlled tailoring of light fields, encompassing customized attributes such as intensity, phase, and polarization. The study of structured light is motivated by its broad applications, including optical tweezers for trapping and manipulating microscopic particles, multiplexed optical communication, advanced imaging techniques like super resolution microscopy, and quantum information processing. Additionally, structured light offers unique properties such as orbital angular momentum (OAM), which allows information encoding in the twisted phase of light, and spatially varying polarization patterns, which facilitate precise control over light-matter interactions.
In this thesis, we investigate various topics related to structured light, including the Faraday effect in strongly focused fields, optical skyrmions, and a two-sphere method for analyzing 3D polarization fields generated by strong focusing. We demonstrate that, for structured light, magneto-optical interactions, specifically the well-known Faraday effect, exhibit a more intricate pattern, which we term the secondary Faraday effect. This effect, arising from the same mechanism as the linear Faraday effect, becomes significant in a strong focusing system, where it reaches a magnitude comparable to the linear effect.
We also introduce skyrmionic beams, a class of structured light that has attracted significant research attention. Building on existing methods for calculating skyrmion numbers, we propose a novel approach that explicitly links these numbers to their topological definitions. Furthermore, we identify that skyrmions and bimerons—configurations involving two distinct regions of opposite topological charge—are topologically equivalent by generalizing the definition of their parameters. Emphasis is placed on the geometrical interpretations, which lead to an extended definition of singularities.
Throughout the thesis, we are particularly interested in highly focused systems, where additional spatial dimensions play a crucial role compared to paraxial optics. To investigate this, we introduce a two-sphere method to comprehensively describe general 3D polarization fields and apply it to a focused, hence non-paraxial skyrmion beam, as an example
Hybrid wireless power transfer system for sensor applications in harsh environments
Get PDFWireless Power Transfer (WPT) is a promising solution to eliminate the dependence of low-power devices on batteries and cables. WPT technologies, including electric field coupling (EC-WPT), magnetic field coupling (MC-WPT), radio frequency (RF-WPT), laser (L-WPT), and ultrasound (U-WPT), each have inherent limitations. EC-WPT, MC-WPT, and U-WPT are restricted to short distances, L-WPT is limited by precise alignment, while metal, water and biological tissues are harsh transmission environment for RF-WPT. These constraints make powering devices in harsh environments, such as underwater, underground, within metal enclosures, distributed over long distances, ormobile, a significant challenge. Traditional battery-based, wired and independent WPT solutions are often impractical due to high maintenance costs, accessibility issues, and size limitations.
This study proposes a hybrid wireless power transmission system integrating RF-WPT and U-WPT to establish a dual-path energy transfer framework in air and metallic environments. The RF link enables long-range and omnidirectional energy transmission, while the ultrasonic link supports power safe penetration through metal, water, and biological tissues. However, integrating these two technologies is challenging due to their fundamentally different transmission mechanisms, necessitating distinct circuit architectures and components. This work develops a combined radio frequency and ultrasonic wireless power transfer (CRFU-WPT) architecture, analyses the link loss between RF and ultrasonic transmission, and establishes a power budgeting model for various application scenarios. An experimental validation demonstrates the system’s capability to power a low-power Bluetooth sensor through a 10 mm metal plate with 0 dBm input, achieving a conversion circuit efficiency of 39.7%
A damage plastic approach for modelling strain hardening cementitious composites
Get PDFStrain hardening cementitious composites or engineered cementitious composites exhibit significantly larger strains at maximum tensile stress than ordinary fibre reinforced concrete. The performance of strain hardening cementitious composites relies on the fibre/matrix properties at the micro-scale. A micro-mechanics based constitutive model for fibre reinforced strain hardening cementitious composites for finite element simulations of structural components is required.
Steel reinforced strain hardening cementitious composites potentially could be used as a composite material of structural component to improve ductility and load capacity. However, the failure process of steel reinforced strain hardening cementitious composite is not well understood because of the complex interaction of two scales of reinforcement involving crack patterns with spacings at multiple scales.
In this research, it is aimed to establish the link of micro-mechanics to structural component by incorporating a micro-mechanics based fibre bridging stress crack opening law into a macroscopic damage-plasticity approach, which is called CDPM2F. The model is implemented in the open-source finite element program OOFEM. The model produces mesh-insensitive results and its response agrees well with experimental results for failure in tension, shear and compression reported in the literature.
The response of specimens made of cementitious composites with a single reinforcement bar embedded in its centre is also investigated. The modelling reproduces well the experimental results which shows that the use of strain hardening matrix can lead to reduced overall ductility. By means of post-processing of the results, it is shown that this reduction of ductility is strongly dependent on the interplay between the ultimate matrix stress and ultimate steel stress
The utility of right ventricular speckle tracking echocardiography strain analysis in the Intensive Care Unit and perioperative period
Get PDFRight ventricular (RV) function is highly important, but underappreciated, in the intensive care unit (ICU) and the perioperative period. Right ventricular dysfunction (RVD) has been shown to be common in ICU and it is associated with poor outcomes in patients with sepsis and acute respiratory distress syndrome (ARDS). The prevalence and impact of RVD in patients in the perioperative period is less well understood. Global assessment of RV function is challenging, with conventional RV echocardiography parameters often only assessing localised function, and perform poorly compared with gold standard methods such as cardiovascular magnetic resonance imaging. RV speckle tracking echocardiography (STE) is a novel parameter thought to overcome some of these limitations. This thesis aims to assess the utility of RV-STE in ICU and the perioperative period.
The fundamentals of RV anatomy and function are firstly described in Chapter 1. This includes a discussion about invasive and non-invasive methods for assessing RV function. The conventional echocardiography parameters are described, with which RV-STE is compared.
The principles underlying RV-STE are described in Chapter 2. Consensus guidelines recommend the use of peak RV free wall longitudinal strain (RVFWLS), and this is the primary measure of RV-STE assessed in this work. Reference ranges and the effects of different strain software are described.
A framework for utility is defined in Chapter 3, forming the basis for assessment of RVFWLS utility. Utility is assessed by three domains: feasibility, reproducibility, and validity. Feasibility is defined as the percentage of echocardiography studies of adequate image quality for RVFWLS analysis. Validity is explored via three subtypes; concurrent (comparing RVFWLS to a gold standard), predictive, and construct validity (hypothesis testing where expected relationships between variables and RV function are analysed using RVFWLS as a surrogate for RV function).
To establish the current body of work investigating the utility of RVFWLS, a literature review is presented (Chapter 4). This review is divided into two parts, examining ICU and the perioperative period separately. Meta-analysis identified that RVFWLS feasibility in ICU is improved by prospective study design whereas increasing proportions of patients receiving mechanical ventilation reduces feasibility. In the perioperative group, preoperative echocardiography scans had better feasibility than postoperative. Reproducibility of RV-STE was high in both ICU and perioperative groups. In ICU patients, predictive validity was demonstrated with regards the association between RVFWLS and short-term mortality in patients with sepsis and coronavirus disease 2019 (COVID-19). Concurrent and construct validity was less well investigated in these groups.
The COVID-RV study (Chapter 5) investigated the utility of RVFWLS in patients with COVID-19 requiring invasive mechanical ventilation. Patients underwent echocardiography post-intubation. High RVFWLS feasibility was identified, with excellent reproducibility. Abnormal RVFWLS was found in 28.7% of patients, and was independently associated with 30-day and one-year mortality. Abnormal RVFWLS was also associated with raised cardiac biomarkers and raised ventilatory driving pressures, implicating myocardial injury and injurious mechanical ventilation in the manifestation of RVD. These findings support the predictive and construct validity of RVFWLS in this setting.
The RV exercise study was undertaken (Chapter 6) to assess RVFWLS as a measure of dynamic RV function when undertaking exercise stress echocardiography (termed right ventricular contractile reserve: RVCR) in a perioperative group undergoing lung resection. Postoperative exertional symptoms are common in this group and this study aimed to investigate if impaired RVCR contributes to these symptoms. Results showed that exercise stress echocardiography was tolerable to patients, and RVFWLS feasibility and reproducibility were again high. There was no improvement in RVFWLS when patients underwent exercise pre- or postoperatively, however RVFWLS-rate was shown to increase pre-operatively when exercising and this relationship was lost postoperatively. This suggests that RVFWLS-rate may be the better measure for identifying RVCR, and that RVCR is impaired in patients following lung resection.
This thesis provides a comprehensive assessment supporting the utility of RV-STE in ICU and the perioperative period. The utility of RV-STE in the perioperative setting will be further investigated by the “IMPRoVE study”, set up by the author and his supervisors. This study aims, for the first time, to investigate the prevalence of perioperative RVD across a range of surgical specialties, and elucidate the mechanisms and impact of perioperative RVD on patient outcomes using RVFWLS as the primary measure of RV function
Quantum interactions of atoms with designed environments
Get PDFThe theory of quantum electrodynamics (QED) describes the intricacies of atom-light interactions with great accuracy, however, viewing a system via fully-microscopic lens can in certain instances be counter-productive. For example, we can consider a quantum system (containing atoms) which encounters a macroscopic surface (made of astronomical number of atoms). It is then advantageous to describe such a system utilising a modified framework, called macroscopic QED. Given a large enough distance between a test atom and a surface, we can abstract away the constituent atoms of the object replacing it with an emergent entity, a familiar classical surface described by its electric permittivity.
This thesis explores the relationship between structures and physical observables, considering the notion that a macroscopic surface influences the nature of the electromagnetic field. We examine both classical and quantum properties of fields and atoms, utilising two distinct approaches to geometry design. First, we employ and adapt a reverse-engineering protocol, wherein structures are discovered algorithmically without input from a human designer. This is particularly beneficial in systems where no discernible intuitive design can be formulated, resulting in purpose-driven structures with superior performance, often featuring the appearance of seemingly-random characteristics. Second, we investigate conventional structures whose stationary effects on atoms (electrostatic potentials) are known analytically from antenna design. We apply these to novel scenarios in the quantum realm, measuring the impact on atomic properties, both for intrinsic interest and applications in sensing
Writing (bitter)sweetness: queer ecologies of the sugar plantation in Caribbean literature
Get PDFThis dissertation takes the works of four queer and lesbian diasporic Caribbean writers to investigate what a queer ecological analysis of Caribbean literature may engender in an age of climate change. Bringing scholarship from queer ecology and Geography to bear on a decolonial and ecofeminist literary analysis, the following investigation takes interdisciplinarity at its fore to reflect the tentacular and interwoven nature of our ecological age and its layers of sedimented histories. It draws on the Haitian creative practice of rasanblaj by which pieces of fabric are brought together to present a complex whole. As a central point in this tapestry, the sugar plantation is used as both metaphor and landscape through which to ask what it means for queer writers to address and reclaim this bittersweetness, building on the work of Omise’eke Natasha Tinsley with ecological and geographical scholarship. Tracing this sugar from the Caribbean, across oceans, and to diasporic cities in the Global North through storytelling, it investigates what it means to write bittersweetness in all its entanglements
If war is the answer, what is the question? A genealogy of ideas in the Greek Just War tradition
Get PDFJust War theories are shaped by distinct cultures, collective mentalities, and historical developments. However, the existing International Relations literature on Just Wars has not effectively integrated the role of ideas in how actions acquire meaning and legitimacy. Even within the literature on the Just War tradition, there has been a predominant focus on the evolution of Roman ‘Ciceronian’ concepts through the Western medieval system, which became ingrained in Western thought as part of the collective mentalities and experiences of recent centuries.
My study tried to address this gap by examining the genealogy of the Greek Just War tradition. The central question of my research is: how did the concept of Just War develop within Greek thought from antiquity to the establishment of an independent Greek state in the 19th century, and can we trace a distinct (Greek) Just War tradition shaped by unique collective experiences, norms, and ideas? References to the Greeks are not ethnological; they refer to the Mediterranean culture centred on the Greek language, concepts, and way of life, which leads to a precise analysis on ideas and practices that construct Just War mentalities. My study demonstrated that the origins of Western Just War traditions can be traced back to Ancient Greek thought and examined how these ideas contributed to the Greco-Roman and Christian synthesis. I explored how Christianity, alongside factors such as geopolitical circumstances, interactions with other cultures, and pre-existing ideas and norms, shaped Eastern Roman practices and created a distinct normative environment, i.e., a different Just War tradition. This environment influenced the evolution of Modern Greek thought, particularly among the Greek diaspora, during the Greek War of Independence, and in the social constructions that legitimised armed conflict as a core element of Greek identity and future Greek security discourses on various domains.
Analysing Just War traditions as part of the evolution of ideas across different cultures is both methodologically and ontologically significant. Such an approach enables a deeper understanding of how communities justify warfare, how ideas give meaning to action, and ultimately challenges the positivist view prevalent in modern International Relations, which often treats war merely as a strategic manoeuvre in the game of international politics, rather than as a reflection of diverse cultures. In a globalised interdependent world, the understanding of how warfare is an extension of different communities’ mentality and how ideas legitimise practice is crucial for any aim to improve security discourses, multilateral strategy, and crisis management
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