13,104 research outputs found

    Breaking boundaries:Charge density waves, quantum measurement, and black holes in theoretical physics

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    This thesis, titled “Breaking Boundaries” is a journey through three topics united by the theme of boundaries in physics. First, the journey begins with an investigation into charge density waves (CDWs) and their nearly commensurate phase, focusing on the materials 2H-TaSe2 and 1T-TaS2. An extensive treatment of Ginzburg-Landau theory is covered with an extension into truly two-dimensional systems. This extension is used to study spiral patches of commensurate charge density waves observed in experiment. The research leads to a novel perspective on CDW behaviour with the existence of a spiral CDW phase in a range of materials. Secondly, transitioning to the quantum realm, the thesis addresses the quantum measurement problem, emphasizing the constraints any valid theory must possess. It critiques existing models, demonstrates the non-linearity of objective collapse theories, and proposes a minimal model that bridges quantum mechanics and classical physics. Thirdly, the thesis delves into black holes and specifically the phenomena of thermal radiation due to a horizon. First, we explore analogue models that mimic the thermal spectrum near a black hole horizon, to pave the way to experimental realization. Then we focus on the region far away from a black hole horizon and challenge the notion of remnant radiation at this position. With a theoretical toy model, we study the regime and find a non-evaporating black hole. This questions the validity of standard Hawking radiation calculations.In conclusion, the thesis navigates through the boundaries of material behaviours, the quantum-classical divide, and the enigmatic nature of black holes. It highlights the blurring and breaking of boundaries in physics, offering new perspectives and promising avenues for future discoveries

    Precision Surface Processing and Software Modelling Using Shear-Thickening Polishing Slurries

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    Mid-spatial frequency surface error is a known manufacturing defect for aspherical and freeform precision surfaces. These surface ripples decrease imaging contrast and system signal-to-noise ratio. Existing sub-aperture polishing techniques are limited in their abilities to smooth mid-spatial frequency errors. Shear-thickening slurries have been hypothesised to reduce mid-spatial frequency errors on precision optical surfaces by increasing the viscosity at the tool-part interface. Currently, controlling the generation and mitigating existing mid-spatial frequency surface errors for aspherical and freeform surfaces requires extensive setup and the experience of seasoned workers. This thesis reports on the experimental trials of shear-thickening polishing slurries on glass surfaces. By incorporating shear-thickening slurries with the precessed bonnet technology, the aim is to enhance the ability of the precessions technology in mitigating mid-spatial frequency errors. The findings could facilitate a more streamlined manufacturing chain for precision optics for the versatile precessions technology from form correction and texture improvement, to MSF mitigation, without needing to rely on other polishing technologies. Such improvement on the existing bonnet polishing would provide a vital steppingstone towards building a fully autonomous manufacturing cell in a market of continual economic growth. The experiments in this thesis analysed the capabilities of two shear-thickening slurry systems: (1) polyethylene glycol with silica nanoparticle suspension, and (2) water and cornstarch suspension. Both slurry systems demonstrated the ability at mitigating existing surface ripples. Looking at power spectral density graphs, polyethylene glycol slurries reduced the power of the mid-spatial frequencies by ~50% and cornstarch suspension slurries by 60-90%. Experiments of a novel polishing approach are also reported in this thesis to rotate a precessed bonnet at a predetermined working distance above the workpiece surface. The rapidly rotating tool draws in the shear-thickening slurry through the gap to stiffen the fluid for polishing. This technique demonstrated material removal capabilities using cornstarch suspension slurries at a working distance of 1.0-1.5mm. The volumetric removal rate from this process is ~5% of that of contact bonnet polishing, so this aligns more as a finishing process. This polishing technique was given the term rheological bonnet finishing. The rheological properties of cornstarch suspension slurries were tested using a rheometer and modelled through CFD simulation. Using the empirical rheological data, polishing simulations of the rheological bonnet finishing process were modelled in Ansys to analyse the effects of various input parameters such as working distance, tool headspeed, precess angle, and slurry viscosity

    Optimization of Beyond 5G Network Slicing for Smart City Applications

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    Transitioning from the current fifth-generation (5G) wireless technology, the advent of beyond 5G (B5G) signifies a pivotal stride toward sixth generation (6G) communication technology. B5G, at its essence, harnesses end-to-end (E2E) network slicing (NS) technology, enabling the simultaneous accommodation of multiple logical networks with distinct performance requirements on a shared physical infrastructure. At the forefront of this implementation lies the critical process of network slice design, a phase central to the realization of efficient smart city networks. This thesis assumes a key role in the network slicing life cycle, emphasizing the analysis and formulation of optimal procedures for configuring, customizing, and allocating E2E network slices. The focus extends to catering to the unique demands of smart city applications, encompassing critical areas such as emergency response, smart buildings, and video surveillance. By addressing the intricacies of network slice design, the study navigates through the complexities of tailoring slices to meet specific application needs, thereby contributing to the seamless integration of diverse services within the smart city framework. Addressing the core challenge of NS, which involves the allocation of virtual networks on the physical topology with optimal resource allocation, the thesis introduces a dual integer linear programming (ILP) optimization problem. This problem is formulated to jointly minimize the embedding cost and latency. However, given the NP-hard nature of this ILP, finding an efficient alternative becomes a significant hurdle. In response, this thesis introduces a novel heuristic approach the matroid-based modified greedy breadth-first search (MGBFS) algorithm. This pioneering algorithm leverages matroid properties to navigate the process of virtual network embedding and resource allocation. By introducing this novel heuristic approach, the research aims to provide near-optimal solutions, overcoming the computational complexities associated with the dual integer linear programming problem. The proposed MGBFS algorithm not only addresses the connectivity, cost, and latency constraints but also outperforms the benchmark model delivering solutions remarkably close to optimal. This innovative approach represents a substantial advancement in the optimization of smart city applications, promising heightened connectivity, efficiency, and resource utilization within the evolving landscape of B5G-enabled communication technology

    Hydration water and ionic aggregation in aqueous solutions of imidazolium-based protic ionic liquids

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    Water molecules, present as additive or as contaminant of Protic Ionic Liquids (PILs), can compete for the hydrogen bond sites leading to important modifications of the local order of these liquids and to the modulation of their physical–chemical properties. In this work, aqueous solutions of a set of N-methylimidazolium-based PILs [MIM][X] (X = NO3-- , TfO-- , HSO4-- , and Cl-- ) were investigated by deep UV Resonance Raman (UVRR) spectroscopy in the water-rich domain where ionic aggregates and bulk-like water coexist. A differential method was used to analyze the OH stretching profile to extract the so-called solute-correlated (SC) spectrum, which is particular informative of the hydration features of the PILs. Moreover, specific bands of the cation, sensitive to the hydrogen bonding, were comparatively investigated. The progressive evolution from solvent-separated ion pairs (SIP) and/or solvent-shared ion pairs (SSIP) to contact ion pairs (CIP) and/or larger ionic aggregates can be monitored as a function of the hydration level, in the water-rich domain. Our approach showed that, in the highly diluted regime, the hydration environment around the [MIM] cation does not depend on the type of anion. Moreover, [MIM][NO3] and [MIM][TfO] showed cation-water (ionic) H-bonds at the NH site stronger than the cation–anion (double-ionic) ones. The analysis of SC Raman spectra points out the formation of cation–anion Hbonds (through the CH ring groups), stronger than cation-water ones, upon PILs concentration increase, especially evident in the case of [MIM][Cl]. The H-bond strength between the anion and hydration water is found to decrease following the order: [Cl] ~ [HSO4] > [NO3] > [TfO]. Chloride ions tend to perturb a larger number of water molecules than the other anions. The number of perturbed water molecules decreases at increasing PIL concentration, showing a larger dependence for [MIM][Cl], consistently with its larger propensity to form ionic aggregates. The unique response of [MIM][Cl] to hydration found by analyzing SC-UVRR data is related to the synergy of different factors such as the anion reduced size (higher charge density), spherical symmetry, and high H-bond basicity

    Proceedings of the 10th International congress on architectural technology (ICAT 2024): architectural technology transformation.

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    The profession of architectural technology is influential in the transformation of the built environment regionally, nationally, and internationally. The congress provides a platform for industry, educators, researchers, and the next generation of built environment students and professionals to showcase where their influence is transforming the built environment through novel ideas, businesses, leadership, innovation, digital transformation, research and development, and sustainable forward-thinking technological and construction assembly design

    Azo dye polyelectrolyte multilayer films reversibly re-soluble with visible light

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    Polymeric multilayer films were prepared using a layer-by-layer (LBL) technique on glass surfaces, by repeated and sequential dipping into dilute aqueous solutions of various combinations of water-soluble polyanions (polyacrylic acid (PAA)), polycations (polyallylamine hydrochloride (PAH) or chitosan (CS)), with bi-functional water-soluble cationic azo dyes bismark brown R bismarck brown red or bismark brown Y (BBY), or anionic azo dyes allura red (ALR) or amaranth (AMA), as ionic cross-linkers. The electrostatically-assembled ionically-paired films showed good long-term stability to dissolution, with no re-solubility in water. However, upon exposure to low power visible light under running water, the films photo-disassembled back to their water-soluble constituent components, via structural photo-isomerization of the azo ionic crosslinkers. The relative rate of the disassembly (RRD) of the films was established using UV-Vis spectroscopy, demonstrating that these assemblies can in principle represent fully recyclable, environmentally structurally degradable materials triggered by exposure to sunlight, with full recovery of starting components. A density functional theory treatment of the allura red azo dye rationalizes the geometrical isomerization mechanism of the photo-disassembly and provides insight into the energetics of the optically-induced structural changes that trigger the disassembly and recovery

    The development of liquid crystal lasers for application in fluorescence microscopy

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    Lasers can be found in many areas of optical medical imaging and their properties have enabled the rapid advancement of many imaging techniques and modalities. Their narrow linewidth, relative brightness and coherence are advantageous in obtaining high quality images of biological samples. This is particularly beneficial in fluorescence microscopy. However, commercial imaging systems depend on the combination of multiple independent laser sources or use tuneable sources, both of which are expensive and have large footprints. This thesis demonstrates the use of liquid crystal (LC) laser technology, a compact and portable alternative, as an exciting candidate to provide a tailorable light source for fluorescence microscopy. Firstly, to improve the laser performance parameters such that high power and high specification lasers could be realised; device fabrication improvements were presented. Studies exploring the effect of alignment layer rubbing depth and the device cell gap spacing on laser performance were conducted. The results were the first of their kind and produced advances in fabrication that were critical to repeatedly realising stable, single-mode LC laser outputs with sufficient power to conduct microscopy. These investigations also aided with the realisation of laser diode pumping of LC lasers. Secondly, the identification of optimum dye concentrations for single and multi-dye systems were used to optimise the LC laser mixtures for optimal performance. These investigations resulted in novel results relating to the gain media in LC laser systems. Collectively, these advancements yielded lasers of extremely low threshold, comparable to the lowest reported thresholds in the literature. A portable LC laser system was integrated into a microscope and used to perform fluorescence microscopy. Successful two-colour imaging and multi-wavelength switching ability of LC lasers were exhibited for the first time. The wavelength selectivity of LC lasers was shown to allow lower incident average powers to be used for comparable image quality. Lastly, wavelength selectivity enabled the LC laser fluorescence microscope to achieve high enough sensitivity to conduct quantitative fluorescence measurements. The development of LC lasers and their suitability to fluorescence microscopy demonstrated in this thesis is hoped to push towards the realisation of commercialisation and application for the technology
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