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Modelling Heat Exchangers with Embedded Phase Change Materials for Aircraft
No full textThe growing thermal load in aircraft design poses challenges for the development of thermal management systems (TMS) for future generation aircraft. Current systems are often oversized to manage highly transient thermal loads encountered during flight. Phase change material (PCM)-based heat exchangers offer a promising alternative by mitigating temperature fluctuations, which could lead to an overall system size reduction. PCM are materials that absorb and release thermal energy during phase transitions, typically between solid and liquid states, at nearly constant temperatures. However, existing PCM heat exchanger designs, primarily developed for building applications, require significant geometric modifications to meet the aerospace industry's stringent requirements for high thermal loads and rapid melting cycles. In this work, the integration of PCM in compact heat exchanger is studied on the basis of a plate-fin heat exchanger.
To establish a foundational understanding of PCM melting behaviour and develop an accurate modelling framework, a study of a shell-and-tube heat exchanger from the literature was recreated. Initial two dimensional simulations demonstrated overpredictions in PCM melting due to neglected temperature variations within the fluid channel. This was addressed by incorporating a conjugate heat transfer model, which coupled the PCM and fluid domains. An additional three-dimensional model further highlighted the complex dynamics of axial and lateral convection plumes, emphasizing the need for detailed modelling in future designs. These validations provided critical insights into PCM melting and informed the development of subsequent models.
The melting behaviour of PCM within plate-fin heat exchangers, which are commonly used in thermal management systems, was investigated by using numerical simulations across various extended surface configurations and operating conditions. The incorporation of fins on both the fluid and PCM sides demonstrated significant improvements in the thermal performance, leading to enhanced heat transfer and increased PCM melting efficiency, when compared to the simple rectangular geometries that are commonly found in the literature.
An effectiveness-NTU model was developed based on these findings, providing reliable performance estimates at a fraction of the computational cost of full Computational Fluid Dynamics (CFD) simulations. The model results were compared to the CFD simulations under aerospace-relevant conditions, achieving good agreement for rectangular cavities and capturing the melting dynamics of finned PCM layers. Its flexibility allows for rapid adjustments to design parameters, making it a practical tool for sizing and optimizing compact heat exchangers. This work advances the understanding and modelling of PCM-based heat exchangers, offering a foundation for efficient, lightweight thermal management solutions tailored to high-performance aircraft applications
Understanding the interactions of Aurora A kinase and its intrinsically disordered binding partners
No full textAurora A kinase (AurA) is a serine/threonine kinase essential for mitosis. AurA is
frequently overexpressed in cancers and is implicated in cancer-associated cellular
phenotypes such as centrosome amplification, aneuploidy, and mitotic checkpoint
override, making it a promising therapeutic target. Localisation and activation of
AurA depends on its binding partners, each associated with one of its various
functions, though few have been studied in detail. This work has focused on,
GADD45α and hnRNPK, two less well characterised interactions of AurA.
Growth Arrest and DNA Damage alpha protein (GADD45α) has been reported to
inhibit AurA kinase activity but the molecular basis remains unclear. In this work,
each GADD45 paralogue has been shown to interact with AurA and activate
autophosphorylation, contrary to previous observations. The binding interface
involves the C-terminus of GADD45α and in AurA, the TACC3 pocket on the N-
lobe and an adjacent putative α-helix.
Heterogenous nuclear ribonucleoprotein K (hnRNPK) is a substrate of AurA, and
their interaction is implicated in driving MYC transcription and promoting cancer cell
migration. In this work, hnRNPK has been shown to activate AurA kinase activity.
The interaction involves the TPX2 pocket on the N-lobe of AurA and an intrinsically
disordered region of hnRNPK that includes key residues Phe339 and Trp345. A
model of the complex is presented that is consistent with experimental data.
Previously characterised AurA binding partners are IDRs which fold upon binding to
AurA. Using TPX2 and AurA as a model, this project investigates the dynamics and
structural basis of folding-upon-binding in IDRs. Single α-helical domains were
fused to the C-terminus of the AurA-binding region of TPX2 to preform the α-helix
that otherwise folds upon binding to AurA. These modified constructs activate the
kinase and preliminary results suggest that their affinity for AurA is enhanced due to
an energetically more favourable interaction
Application of polydimethylsiloxane as a coating for the fouling mitigation of calcium carbonate
No full textFouling prevention is a key issue that is constantly a concern for many industries. From geothermal power generation to pharmaceutical production to marine transportation, fouling results in losses in process efficiencies, equipment breakdown and increased operational costs. There have been many different methods used to tackle the problem of fouling with varying levels of success.
This report centres on the use of a polydimethylsiloxane (PDMS) coating to mitigate calcium carbonate (CaCO3) formation. CaCO3 was the foulant chosen for this investigation as it is one of the most common in industrial processes that utilise freshwater or seawater. PDMS is an elastomer that is a combination of a silicone oil and a curing agent. PDMS was chosen as it is an elastomer that can have its mechanical properties altered through the curing ratio of the silicone oil to curing agent. Increase in curing ratio results in less crosslinks and therefore results in change in material stiffness. Therefore, samples of PDMS at different curing ratios were investigated to determine the effect of material stiffness on fouling. The range of ratio used initially was from 5:1 to 50:1, however, through material characterisation, this scope was narrowed to 10:1 to 30:1. The effect of curing ratios on material and surface properties were characterised.
To understand how the PDMS samples performed, bulk precipitation and surface scaling experiments were carried out. Bulk scale precipitation was observed using a traditional bulk jar test with high saturation ratio (SR) brine solution. Using a high SR, would significantly reduce the induction time in which crystals would form in the bulk and therefore drive towards crystal precipitation rather than surface crystallisation. SEM images were taken to analyse the surfaces. PDMS surfaces at curing ratio 10:1 in these tests had the lowest surface coverage despite having the larger crystal structures. Curing ratios of 20:1, 25:1 and 30:1 displayed similar results with low average crystal area and high surface coverage.
Surface scaling was investigated by using a visualisation cell and using a low SR brine solution. By using a low SR, the driving mechanism for crystal formation onto the surfaces was surface crystallisation. Images were taken at intervals and by using image analysis software, the surfaces were analysed. An increase in curing ratio resulted in an increase in average crystal count, decrease in average crystal area and an increase in average area coverage. PDMS of curing ratios 10:1, 15:1 and 20:1 all produced low results with average area coverage <5%. PDMS of curing ratio 30:1 performed poorly with an average area coverage of 20.6%. Understanding how crystals form onto the PDMS surfaces would help determine the feasibility of PDMS as an antifouling surface and how the surfaces can be optimised through curing ratio
Tracking and Tracing Complex DNA Structures and DNA-Protein Interactions Implicated in Aging and Disease
No full textWhile the genetic code of DNA is undeniably fundamental for cellular development, proliferation and function, the significance of DNA structure has largely been overlooked. DNA structure is intrinsically linked to function, influencing processes such as DNA packaging into chromatin, unwinding of the double helix, protein binding and formation of alternative structures. All of which are critical for accurate DNA replication and gene expression, which can be implicated in human diseases.
Atomic Force Microscopy was used as a single-molecule imaging technique to probe the structure of complex DNA molecules, including knots and catenanes. With nanometre resolution, we have established a technique to observe which DNA strand is over-passing and which strand is under-passing, thereby explicitly determining the topology of DNA. The analysis of AFM images can be challenging due to high volume data sets. Therefore, an automated pipeline was developed to accurately classify the topology of these molecules.
Using this technique to observe changes to DNA structure, we looked at DNA-protein interaction. The Shelterin complex caps and protects telomeres from DNA damage proteins. When looking at the binding of Shelterin to telomeric repeat sequences, novel intra- and intermolecular bridging mechanisms were observed, mediated by the TRFH domain of TRF2. This mechanism provides insight into the protective roles of the Shelterin complex at telomeres.
Telomeres also form various alternative structures in the cell. They consist of the G-rich DNA repeat sequence TTAGGGn, prone to forming G-quadruplex structures (G4s). However, little is known about the formation of these structures in double-stranded telomeric DNA. Using AFM, the formation of G4s in double-stranded telomeric DNA was detected after physiological heating and the addition of potassium ions. On the addition of lithium ions, these structures appear to collapse. This information provides valuable insight into G4 formation and protection at telomeres
Behavioural Economics and Individual Taxpayer Compliance: Empirical Evidence from Two Field Experiments in Indonesia
No full textThis thesis investigates taxpayers' compliance behaviour in response to various nudges
from the tax authority by providing empirical evidence from two large-scale randomised
controlled trials in an emerging economy. This thesis includes two empirical chapters that
address distinct but related issues.
The first empirical chapter investigated the effectiveness of behaviourally informed
letters and the standard Surat Tagihan Pajak – STP (tax penalty bill) on tax penalty
payment compliance through a randomised experiment with over 10,000 individual
taxpayers. Participants received deterrence, information, simplification, or no letters. The
simplification nudge significantly improved compliance, while the deterrence nudge was
less effective, particularly in less-developed regions where taxpayers perceived a higher
likelihood of detection. In contrast, the information letter did not significantly promote
timely tax penalty payments. Despite mentioning penalties for late submissions, an
extended analysis of the potential spillover effect on annual tax returns revealed that the
interventions did not induce increased compliance among taxpayers in their annual tax
return filing. The study recommends that policymakers integrate well-designed nudges
into their systems, considering taxpayers' backgrounds and leveraging insights from
psychology and linguistics to create more effective and accessible forms.
The second empirical chapter analyses the monthly income tax payment behaviour of
over 41,000 self-employed taxpayers who received WhatsApp reminders prior to their
due dates. Taxpayers were assigned to either the early, close, combined, deadline, or a
control group, with no reminders. The results indicate that all reminders enhance tax
compliance, with single reminders sent near the deadline being the most cost-efficient
option, despite yielding a less marginal impact than multiple reminders. The intervention
is more efficacious for taxpayers in more developed regions (e.g., Java) and those who
filed tax returns electronically, underscoring the importance of tax and digital literacy.
We observed no sustained effects beyond the duration of the intervention. This suggests
single reminders may not be sufficient to induce lasting changes in taxpayer behaviour.
The findings of this chapter have several significant implications. Tax authorities should
consider the message content by integrating behavioural economics into the design and
select the most optimal timing and frequency. Utilising personalised digital messaging
can be an efficient choice of communication with taxpayers. Sending messages through
the tax authorities' official accounts is essential to maintain credibility.
The findings have significant implications for behavioural economists, social
scientists, policymakers, and tax authorities. Despite its limitations, it warrants further
research to enhance existing knowledge. Ultimately, this thesis advances tax compliance
nudges in developing countries, building on behavioural economics, public finance, and
development economics
Design of high temperature, 800V, 40kW, Silicon Carbide based, full scale inverter demonstrator for aerospace applications
No full textThis thesis focusses on the design of a loss optimized, Silicon Carbide (SiC) based, 800V, multi kilowatt three phase inverter prototype for aerospace application, targeted for high temperature ambient conditions. Given the multiple design constraints such as spatial envelope, mass and efficiency optimization, this research addresses multiple topics that influence the objective. It begins with the overall loss modelling of the inverter, analysis of 2 – level inverter architecture (implementing multiple devices in parallel) to optimize efficiency at high temperatures, impact of paralleling multiple SiC MOSFETs on efficiency, etc.
It then proceeds with analytical modelling of SiC MOSFET switching characteristics with the aim to improve the accuracy of estimation as compared to the existing models. Specifically, the impact of drain to source voltage, junction temperature and load parasitic elements on the switching dynamics is modelled to enhance the accuracy. It is ensured that this modelling methodology relies only on the information provided in the datasheet of the device, which eliminates the need for additional tests to improve the accuracy of loss estimation and thereby saves time and cost. The proposed modelling strategy is verified experimentally by building a suitable double pulse test bench setup.
Further, the key aspects of suitable component selection and placement, PCB layout strategies that suits the temperature requirement, total mass and efficiency targets are delved into. The commutation loop parasitic inductance that impacts the turn off voltage overshoot and thereby the choice of gate resistance that directly impacts the overall efficiency of the inverter is optimized. Suitable placement of multilayer copper planes under the DC link capacitors, in the PCB is analyzed using ANSYS Q3D tool to address the same. Also, the choice of placement of paralleled SiC MOSFETs that gives a tradeoff between either minimizing the commutation loop inductance or minimizing the asymmetry in current sharing between paralleled devices is analyzed. Critical elements of high voltage, high power rated PCB design, such as switching node copper placement, isolation of high voltage and low voltage copper areas and the components that form the boundary between them are discussed. Since SiC MOSFET have lower junction capacitances, they can be switched at high speeds to optimize efficiency. This results in high rate of change in voltages, more so when the design is rated for 800V. The design of gate driver circuitry that can carry out the same, while ensuring minimal cross coupling between power and signal areas of the layout is presented. The full scale prototype is validated extensively at multiple DC link voltages from 400V to 800V and at across a wide range of load upto 30 kW. The impact of load and DC link on efficiency is experimentally recorded. Furthermore, the impact of paralleling of SiC MOSFETs on overall converter efficiency and junction temperature are experimentally observed through temperature logging and power analyzer measurements. To further analyze the variation of the inverter’s efficiency with load and DC link, a MATLAB – Simulink based simulation, that takes into account the device’s switching and conduction losses, based on manufacturer datasheet information, is built. The simulation result exhibited a decent match with the experimental results and also helped deep dive into the distribution of semiconductor losses and their variation with operating conditions. Simulation study is further used to compare the SiC MOSFETs with similar figure of merits but with different chip areas. This helped bring out the load ranges where each device choice would result in maximum efficiency. To improve the accuracy of
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the Simulink based model that estimates the inverter’s efficiency, the switching loss look up tables are replaced with the switching loss estimated using the accurate analytical models developed and discussed in the previous chapters of this thesis. This resulted in improved accuracy of efficiency estimates.
The experimental device current waveforms captured during the exhaustive validation of the full scale prototype, revealed the asymmetric sharing of currents between paralleled SiC MOSFETs. An in – depth analysis of the PCB layout, based on ANSYS Q3D attributed this asymmetry to the difference in source parasitic inductances of the paralleled MOSFETs. To further optimize the design that mitigates this issue significantly, a novel, multilayer copper layout strategy that takes advantage of flux cancellation between copper planes carrying currents in opposite directions is proposed, analyzed in ANSYS Q3D and experimentally validated. The proposed methodology was found to have improved the current sharing both in the dynamic and static regions of the drain current
Wireless Surgical Capsule Robots for the Gastrointestinal Tract: Towards small scale therapeutic functions without on-board computation
Get PDFCapsule robots provide an alternative route of entry to the gastrointestinal tract with minimal discomfort to patients. There are many examples of therapeutic capsules, but a gap exists in their capability in carrying out complex surgical functions such as manipulation in a suitable capsule size. There are two major factors for that limit the size of capsules; small scale actuators and on-board computation and communication required to control them. Controlling soft actuation wirelessly with an on-board pneumatic source of pressure could help with miniaturisation of efficient small scale actuators due to their scalability. An untethered robotic capsule that can provide volumetric expansion using a chemical reaction without on-board electronic components was designed along with a theoretical model for predicting the inflation behaviour. The expansion is based on the reaction between chemicals that are safe for ingestion, operated with thermal input provided by alternating magnetic fields from outside the body. Additionally, a new amplifier design that can deliver power to simple receiver circuits in parallel was presented. This allows the control of a wireless capsule that can use the electrical power for applications such as heating a target location, powering small motors bidirectionally and turn on LEDs without the use of a microcontroller. The design was tested for up to 6 addressable components, and an analysis on the limitations of this approach has been carried out. An example design of a capsule robot capable of anchoring itself to the intestinal tissues, use its manipulator arm to target a specific location and heat the location to patch wounds, or destroy pathogens or cancer cells was presented. Together, the wireless soft actuator and the wireless powering method should benefit further miniaturisation of therapeutic capsule robots capable of more complex in-vivo surgical functionality
Investigating the assembly and egress of arenaviruses
Get PDFThere are around 70 segmented RNA viruses contained within the Arenaviridae family, and multiple members are associated with fatal haemorrhagic fevers, including Lassa and Junín viruses. Established LCMV strains are biosafety level (BSL) 2 pathogens, and can model for these serious pathogens since fatality is only common within immunocompromised populations. Here, the project details three aims which collectively investigate the later stages of arenavirus multiplication. Firstly, an siRNA library, which targeted cellular trafficking components, identified coat protein 1 (COPI) coatomer and adapter protein 4 (AP-4) complexes as important during LCMV infection. Immunofluorescence (IF) was performed for cells infected with an infectious recombinant LCMV harbouring a FLAG tag within GP-1, which identified close co-localisation of COPA, AP4E1 and viral proteins. Additionally, the inhibitor Brefeldin A (BFA) was applied to LCMV infection, which suggests that COPI and AP-4 complexes are critical for efficient virion production.
Secondly, it was noted during live-cell imaging that cells initially infected with LCMV result in infection of neighbouring cells, with discrete foci formed. IF analysis revealed LCMV structural proteins co-localise within cell-cell connections resembling tunnelling nanotubes (TNT-like). Fluorescent in situ hybridisation was applied and identified that TNT-like connections also contain genomic sense RNA. Strikingly, blocking the extracellular route of infection (post initial entry) through application of a potent neutralising antibody did not abolish progression of LCMV infection, and thus implied intracellular connections could account for around half of infection events.
Finally, we investigated the phosphorylation of LCMV NP during infection. We noted that CK-869 caused an increased post-translational modification of NP. Through investigations, we reveal that S343 is phosphorylated, and we established infectious NP phospho-ablantant (S343A) and phospho-mimetic (S343E) mutants. Here, we identified that S343 phosphorylation of NP is not a viral-dependent process, and acts in an anti-viral manner within the mouse macrophage RAW264.7 cell line. Mechanistically, we suggest that phosphorylation of NP may trigger lysosomal degradation, reporting co-localisation of NP and LAMP-1 during S343E infected cultures. Additionally, we reveal that S343 NP phosphorylation is LCMV strain specific, which may contribute to difference in pathogenicity.
Taken together, these results increase our knowledge surrounding the later stages of arenavirus multiplication, which may contribute to the development of effective preventatives or therapeutics
Combining Shape and Electrostatics in a Spectral Geometry Alignment-Free Three-Dimensional Molecular Descriptor
No full textModelling Enzyme-Driven pH Control and Dynamic Behaviour in Compartmentalised Enzymatic Networks
No full textThis thesis uses numerical simulations based on ordinary differential equations to investigate enzymatic pH control within lipid vesicles. These membrane-bound compartments are widely used in synthetic cell research and offer controllable environments with potential applications in drug delivery, synthetic biology, and dynamic materials. Despite their widespread use, the mechanistic behaviour and interactions of encapsulated enzyme networks present outstanding questions, limiting the interpretation of experimental trends and the design of predictable systems. Chapters 1-3 establish the context of this work, reviewing relevant literature, developing the modelling framework, and presenting baseline models of urease-driven pH modulation that underpin subsequent analyses. Chapter 4 demonstrates a tunable urease–glucose oxidase oscillator that operates within physiological pH ranges and remains dampened but functional when confined to vesicles, offering a design roadmap for synthetic biological timers. Chapter 5 moves to more realistic systems and examines the influence of membrane transport and electrochemical gradients on feedback mechanisms, uncovering counterintuitive effects of membrane thickness and identifying conditions where ionic transport and membrane potential shape system behaviour. Chapter 6 explores applications in metabolite-responsive drug release, demonstrating how enzymatic pH modulation can be used to pre-program the timing and extent of vesicle release and identifying regimes where chemical control dominates over passive dissolution or diffusion. Collectively, the studies establish general principles linking enzyme kinetics, transport, and compartmentalisation, highlighting the power of mechanistic modelling to guide the design and experimental implementation of dynamic chemical networks in compartmentalised system
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