9,318 research outputs found

    Undergraduate Catalog of Studies, 2023-2024

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    Numerical Simulations of Cavitating Bubbles in Elastic and Viscoelastic Materials for Biomedical Applications

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    The interactions of cavitating bubbles with elastic and viscoelastic materials play a central role in many biomedical applications. This thesis makes use of numerical modeling and data-driven approaches to characterize soft biomaterials at high strain rates via observation of bubble dynamics, and to model burst-wave lithotripsy, a focused ultrasound therapy to break kidney stones. In the first part of the thesis, a data assimilation framework is developed for cavitation rheometry, a technique that uses bubble dynamics to characterize soft, viscoelastic materials at high strain-rates. This framework aims to determine material properties that best fit observed cavitating bubble dynamics. We propose ensemble-based data assimilation methods to solve this inverse problem. This approach is validated with surrogate data generated by adding random noise to simulated bubble radius time histories, and we show that we can confidently and efficiently estimate parameters of interest within 5% given an iterative Kalman smoother approach and an ensemble- based 4D-Var hybrid technique. The developed framework is applied to experimental data in three distinct settings, with varying bubble nucleation methods, cavitation media, and using different material constitutive models. We demonstrate that the mechanical properties of gels used in each experiment can be estimated quickly and accurately despite experimental inconsistencies, model error, and noisy data. The framework is used to further our understanding of the underlying physics and identify limitations of our bubble dynamics model for violent bubble collapse. In the second part of the thesis, we simulate burst-wave lithotripsy (BWL), a non- invasive treatment for kidney stones that relies on repeated short bursts of focused ultrasound. Numerical approaches to study BWL require simulation of acoustic waves interacting with solid stones as well as bubble clouds which can nucleate ahead of the stone. We implement and validate a hypoelastic material model, which, with the addition of a continuum damage model and calibration of a spherically- focused transducer array, enables us to determine how effective various treatment strategies are with arbitrary stones. We present a preliminary investigation of the bubble dynamics occurring during treatment, and their impact on damage to the stone. Finally, we propose a strategy to reduce shielding by collapsing bubbles ahead of the stone via introduction of a secondary, low-frequency ultrasound pulse during treatment.</p

    Exploring the utilisation of natural biosorbents for effective methylene blue removal

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    This paper presents a comprehensive analysis of the adsorbent capacity of five distinctly different biosorbents derived from untreated biomasses. The optimal adsorption capacity of seaweed (Laminaria digitata), horse chestnut husk, hazelnut husk, rapeseed residue, and whitewood to remove methylene blue (MB) dye was assessed by analysing the effects of particle size, pH, temperature, and initial dye concentrations. Furthermore, the adsorption kinetics, isotherms, and adsorption thermodynamics were investigated. The results showed that relatively high MB adsorption capacity was achieved by Laminaria digitata (~180 mg/g), in addition to a reasonable MB adsorption capacity of horse chestnut husk (~130 mg/g), hazelnut husk (~110 mg/g), and rapeseed residue (~80 mg/g). However, whitewood provides a relatively low adsorption capacity of below 20 mg/g. The best fit with experimental results regardless of biosorbent type was a pseudo-second-order kinetic model with the lowest mean absolute percentage error (Δ, MAPE 0.99). Although the pseudo-second-order kinetic model is often associated with chemisorption, the low enthalpy values (<29.30 kJ/mol) typically suggest that the adsorption process is more characteristic of physisorption, which involves weaker van der Waals forces rather than the stronger covalent bonds of chemisorption. This proposed a multi-step adsorption process involving both physisorption and chemisorption. The adsorption isotherm of Langmuir showed superior fitting results for Laminaria digitata and hazelnut husk. In contrast, rapeseed residue and horse chestnut husk fit better with the Freundlich adsorption isotherm. The Langmuir adsorption isotherms showed a maximum adsorption capacity of ~500 mg/g for Laminaria digitata, followed by horse chestnut husk (~137 mg/g), hazelnut husk (~120 mg/g), and rapeseed residue (~85 mg/g). The Gibbs free energy was negative for Laminaria digitata < horse chestnut husk < hazelnut husk < 0, which suggests that the removal of MB is thermodynamically favourable, as the adsorption process occurs spontaneously. The results of the study indicate that MB dye removal using untreated biomasses has the potential to be a low-cost valorisation option in the holistic whole life cycle valorisation pathway for Laminaria digitata, horse chestnut husk, and hazelnut husk

    Non-Equilibrium Quantum Dynamics in a Disordered Ising Magnet

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    The quantum two-level system, or “qubit,” is a simple platform that nonetheless displays fundamentally non-trivial quantum behavior. The rare-earth magnet LiHoF₄ is a natural physical representation of a system of coupled qubits. With its uncommonly high crystal anisotropy, LiHoF₄ can be mapped to the problem of the Ising model in a transverse field. However, while this Ising approximation can quantitatively predict much of the equilibrium behavior, quantum corrections, originating from off-diagonal terms in the dipolar interaction that generate quantum fluctuations, are crucial in driving non-equilibrium dynamics when subject to an external drive. Furthermore, quenched disorder can be introduced through chemical substitution, which, through the dipolar interaction, generates spatially random pinning fields, as well as internal transverse fields, which drive quantum fluctuations. Noise measurements on the disordered ferromagnet LiHo0.65Y0.35F4 show critical behavior, whose statistics are driven from the underlying pinning distribution, while measurements on LiHo0.40Y0.60F4 display non-critical behavior that can only be attributed to quantum co-tunneling processes. This is the first demonstration of crackling noise in a ferromagnet in the purely quantum regime. Furthermore, pump-probe susceptibility measurements on the decoupled cluster glass show the system being driven out of equilibrium with astonishingly weak drives, due to resonant transitions arising from off-diagonal dipolar terms σiz σjx. Non-linear sample response is observable in inelastic Raman scattering measurements, and these spin clusters also exhibit asymmetric Fano resonances with high Q-factors of ~10⁔. Quantum interference effects can be tuned to fully decouple one of the dressed states from the others, rendering the sample transparent to the drive. This is analogous to optical systems that display electromagnetically-induced transparency, but at 100 Hz frequencies

    Force-Chain Finder: A software tool for the recursive detection of force-chains in granular materials via minor principal stress

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    Force transmission in granular media occurs through an inhomogeneous network of inter-particle contacts referred to as force-chains. A thorough understanding of the structure of these chains is indispensable for a better comprehension of the macroscopic signatures they generate. This paper introduces Force-Chain Finder (FCF), an open-source software tool designed for detecting force-chains in granular materials. Leveraging the stress tensor computed for each particle based on its interactions with neighboring particles, the tool effectively identifies the magnitude and direction of the most compressive principal stress. Through a recursive traversal of particles and their neighbours, force-chains are robustly detected based on the alignment of the principal stress directions, which is decided by a parameter α (an angle in radians). The software provides a comprehensive suite of post-processing features, including the exportation of results in different formats, enabling detailed analysis of specific regions and dynamic phenomena. Additionally, the software facilitates the computation of statistical measures pertaining to chain size and population. By streamlining the identification and characterization of force-chains within discrete element method (DEM) simulations, this tool significantly enhances the efficiency and accuracy of force-chain analysis. Thus, the software promotes deeper insights into the behaviour of granular materials by enabling researchers to effortlessly detect and analyse force-chains

    Fluid effects in model granular flows

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    Pore fluid plays a crucial role in many granular flows, especially those in geophysical settings. However, the transition in behaviour between dry flows and fully saturated flows and the underlying physics that relate to this are poorly understood. In this paper, we report the results of small-scale flume experiments using monodisperse granular particles with varying water content and volume in which the basal pore pressure, total pressure, flow height and velocity profile were measured at a section. We compare the results with theoretical profiles for granular flow and with flow regimes based on dimensional analysis. The runout and the centre of mass were also calculated from the deposit surface profiles. As the initial water content by mass was increased from zero to around 10%, we first observed a drop in mobility by approximately 50%, as surface tension caused cohesive behaviour due to matric suction. As the water content was further increased up to 45%, the mobility also increased dramatically, with increased flow velocity up to 50%, increased runout distance up to 240% and reduced travel angle by up to 10° compared to the dry case. These effects can be directly related to the basal pore pressure, with both negative pressures and positive pore pressures being measured relative to atmospheric during the unsteady flow. We find that the initial flow volume plays a role in the development of relative pore pressure, such that, at a fixed relative water content, larger flows exhibit greater positive pore pressures, greater velocities and greater relative runout distances. This aligns with many other granular experiments and field observations. Our findings suggest that the fundamental role of the pore fluid is to reduce frictional contact forces between grains thus increasing flow velocity and bulk mobility. While this can occur by the development of excess pore pressure, it can also occur where the positive pore pressure is not in excess of hydrostatic, as shown here, since buoyancy and lubrication alone will reduce frictional forces

    Stabilization of metal and metalloids from contaminated soils using magnesia-based tundish deskulling waste from continuous steel casting

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    This study presents a groundbreaking exploration into the potential use of refractory tundish deskulling waste (TUN), a magnesium oxide-based by-product from continuous steel casting, as a stabilizing agent for remediating metal and metalloids contaminated soils. Up-flow column horizontal percolation tests were conducted to measure the concentrations of metals and metalloids, pH, and electrical conductivity (EC) in the leachates of two different combinations of contaminated soil and stabilizer (95-5 wt% and 90-10 wt%). The effectiveness of TUN as a soil-stabilizing agent for contaminated soils with metals and metalloids was evaluated by comparing its leachates with those obtained from a sample of a well-established low-grade magnesium oxide (LG-MgO) by-product, which underwent the same testing procedure. The findings revealed a significant correlation between the mobility of the examined metals and metalloids, and the water-soluble or acid phase of the contaminated soil, primarily governed by precipitation-solution reactions. While the stabilizing impact on non-pH-dependent metals, particularly redox-sensitive oxyanions, was less pronounced, both MgO-based stabilizers exhibited a favourable influence on soil pH-dependent metals and metalloids. They achieved this by establishing an optimal pH range of approximately 9.0-10.5, wherein the solubility of metal (hydr)oxides is minimized. Notably, metals like Zn and Cu, which have high leaching potential, experienced a remarkable reduction in leaching - Zn by over 99% and Cu by around 97% - regardless of the stabilizer content. In a broader context, this research champions the principles of the circular economy by offering a technical remedy for treating soils contaminated with pH-dependent metals and metalloids. The proposed solution harnesses industrial waste - currently relegated to landfills - as a resource, aligning with sustainable practices and environmental responsibility

    ‘When is a hotspot a good nanospot’:review of analytical and hotspot-dominated surface enhanced Raman spectroscopy nanoplatforms

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    Substrate development in surface-enhanced Raman spectroscopy (SERS) continues to attract research interest. In order to determine performance metrics, researchers in foundational SERS studies use a variety of experimental means to characterize the nature of substrates. However, often this process would appear to be performed indiscriminately without consideration for the physical scale of the enhancement phenomena. Herein, we differentiate between SERS substrates whose primary enhancing structures are on the hundreds of nanometer scale (analytical SERS nanosubstrates) and those whose main mechanism derives from nanometric-sized gaps (hot-spot dominated SERS substrates), assessing the utility of various characterization methods for each substrate class. In this context, characterization approaches in white-light spectroscopy, electron beam methods, and scanning probe spectroscopies are reviewed. Tip-enhanced Raman spectroscopy, wavelength-scanned SERS studies, and the impact of surface hydrophobicity are also discussed. Conclusions are thus drawn on the applicability of each characterization technique regarding amenability for SERS experiments that have features at different length scales. For instance, while white light spectroscopy can provide an indication of the plasmon resonances associated with 10 s–100 s nm-scale structures, it may not reveal information about finer surface texturing on the true nm-scale, critical for SERS’ sensitivity, and in need of investigation via scanning probe techniques

    Energy assessment of advanced and switchable windows for less energy-hungry buildings in the UK

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    This is the final version. Available on open access from Elsevier via the DOI in this recordData availability: Data will be made available on request.Globally, greenhouse gas emissions from the operational phase of buildings are significantly contributing towards climate change. Global and national efforts, through the Sustainable Development Goals and the UK's 2050 targets, aim to reduce these emissions with net zero energy buildings (NZEBs). A building's glazing plays a significant role in overall building energy consumption due to their traditionally ‘leaky’ nature. This study utilises experimental data from test cells and the International Glazing Database to evaluate the performance of advanced and smart/switchable windows on an existing low energy building (LEB) situated in north Wales, UK, as a step towards making the modelled building a NZEB. A number of glazing constructions were considered in this work; advanced window – vacuum, aerogel, vacuum-aerogel and smart window – PDLC, PDLC-aerogel and PDLC-vacuum, in their fixed and switching states. Results revealed that PDLC-vacuum offered the greatest reduction in building energy, yielding a theoretical U-value of 0.810–0.831 W/m2K and a G-value of 0.257–0.455. Despite its successes, it was notably susceptible to window orientation and window-to-wall ratio. Vacuum and aerogel glazing both offered similar energy savings, with the latter prone to overheating, stressing cooling loads. These advanced windows offered differing daylighting potential with vacuum able to meet 78% of useful daylight illuminance compared to aerogel's 60%. Given the prioritisation trilemma between heating, lighting and cooling needs of a building, PDLC-vacuum presents the best step towards a NZEB. As such, further efforts should concentrate on the development of a PDLC-vacuum window, maintaining smart window functionality and achieving low U-value for cold climates

    Non-invasive and non-intrusive diagnostic techniques for gas-solid fluidized beds – A review

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    Gas-solid fluidized-bed systems offer great advantages in terms of chemical reaction efficiency and temperature control where other chemical reactor designs fall short. For this reason, they have been widely employed in a range of industrial application where these properties are essential. Nonetheless, the knowledge of such systems and the corresponding design choices, in most cases, rely on a heuristic expertise gained over the years rather than on a deep physical understanding of the phenomena taking place in fluidized beds. This is a huge limiting factor when it comes to the design, the scale-up and the optimization of such complex units. Fortunately, a wide array of diagnostic techniques has enabled researchers to strive in this direction, and, among these, non-invasive and non-intrusive diagnostic techniques stand out thanks to their innate feature of not affecting the flow field, while also avoiding direct contact with the medium under study. This work offers an overview of the non-invasive and non-intrusive diagnostic techniques most commonly applied to fluidized-bed systems, highlighting their capabilities in terms of the quantities they can measure, as well as advantages and limitations of each of them. The latest developments and the likely future trends are also presented. Neither of these methodologies represents a best option on all fronts. The goal of this work is rather to highlight what each technique has to offer and what application are they better suited for
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