University of Birmingham
University of Birmingham Research Archive, E-theses RepositoryNot a member yet
11811 research outputs found
Sort by
Unravelling the electronic and magnetic properties of quantum materials: from metal-organic frameworks to frustrated magnets
Get PDFQuantum materials are expected to be the future of technology, with emerging IT relying on new materials capable of switchable and stimuli-responsive behaviour. Quantum mechanics governs the physical nature of all materials, able to describe how atoms and electrons behave and interact. At the macroscopic level, quantum effects are not normally visible and the system can be approximated by a classical description, however, in quantum materials, these effects remain noticeable and manifest over a large range of energy and length scales. This work presents a density-functional theory (DFT) study on two promising quantum materials: and , candidate structures to host the S=2 Haldane phase and the quantum spin liquid phase respectively. This research also aims at the discovery of new quantum materials via structure prediction of .
DFT struggles to account for the strong electron correlations found in quantum materials and, therefore, a Hubbard U correction is needed. Such an approach has been first applied to study the low-dimensional metal-organic magnet . DFT+U (U = 3 eV) geometry optimisation results found the presence of a Jahn-Teller distortion, confirming a oxidation state with crystal field splitting resulting in S = 2. Band-structure and density of states calculations showed a band gap of 1.2 eV. Despite approaching the quasi-one-dimensional antiferromagnet limit with a magnetic exchange ratio / = 8.4, the Haldane phase was not confirmed by experimental collaborators, most likely suppressed by superexchange interactions or single ion anisotropy.
Another focus of this work is the investigation of the quantum spin liquid candidate barlowite . Despite barlowite having an adequately small spin of S= to be a quantum spin liquid, such a quantum phase was not found, although non-collinear DFT calculations confirmed the frustrated magnetic nature of the system. Structural disorder is present in the system; DFT+U (U = 5 eV) geometry optimisations relaxed the system in the and space groups. Band-structure calculations found a band gap of 0.56 eV, and a similar insulating nature was found for analogues containing different halides, namely claringbullite and iodide .
Building on the techniques fine tuned in modelling the systems presented above, a search for novel quantum materials was carried out starting from in which Cr was exchanged with a series of transition metals (V, Fe, Co, Ni) to create new systems, discover trends and test for their properties. Furthermore, the search was expanded to include a different organic ligand, pyridazine. The novel structure was discovered by carrying out structure searching by means of the Wyckoff Alignment of Molecules (WAM) technique. Magnetic exchange results show that this material is quasi-one-dimensional, with / = 16.9. This is a promising result, suggesting that the DFT tested requirements to host the S = 2 Haldane phase are met and this structure is ready to be physically synthesised and experimentally proven
An interpretive phenomenological analysis of the experiences of Deaf and Hard of Hearing teachers
No full textThis study was an interpretive phenomenological analysis of the experiences of d/Deaf and Hard of Hearing teachers and Teachers of Deaf Children and Young People who were currently or had recently been working in UK schools. Four teachers were interviewed; two used spoken English and two interviews were facilitated by a British Sign Language interpreter. Interviewees discussed their experience of deafness, their experiences as a teacher, what barriers they may have faced and what things helped them to be successful. Perceptions of deafness were influenced by the people around them and for some, the school environment was a challenging place. Communicating with the children could be difficult when spoken language was used, and hearing colleagues were respectful in some settings but described as impatient in others. All teachers described deriving job satisfaction from their relationships with the children and being a part of their achievements. The leadership and culture of the school could act as either a barrier or a facilitator; where there was d/Deaf representation throughout the leadership teams, the culture of the school was more inclusive for d/Deaf people. Where leaders did not take the teachers’ concerns seriously, this led to the teachers leaving their posts. Implications for d/Deaf teachers include being aware of their rights and what environmental adjustments are considered ‘reasonable’ for school staff. Hearing colleagues and school leaders can help by practicing deaf awareness and ensuring that d/Deaf teachers are part of the decision-making processes that will affect them. For educational psychologists, this research provides perspectives on some of the cultural, linguistic, and social barriers that can affect d/Deaf people working alongside hearing colleagues, as well as facilitating and supportive factors. The majority of d/Deaf children are currently educated in mainstream environments and may have limited access to sign language or d/Deaf role models; educational psychologists can support these settings to address challenges early and provide an accessible environment
The concept of the state in contemporary Islamic thought: Abdullah Al-Nafisi as a case study
No full textThe concept of the state, and what is meant by it, has been widely discussed by many thinkers of the East and the West recently, especially after the events of 9/11 and the emergence of al-Qaeda and then ISIS, as well as the events of the Arab Spring and the arrival of political Islamic movements in power, such as in Tunisia and Egypt. Numerous statements about the classification of the state have arisen. Among those intellectuals who have dealt with the concept of the state in contemporary Islamic thought is the thinker Abdullah al-Nafisi, who is one of the most controversial personalities in contemporary Islamic thought, regarded by many observers as a mysterious figure, and even described by some as volatile and unstable. This ambiguity in his personality has caused many who study political and religious change in the Gulf to feel confused by al-Nafisi’s affiliations, trends, and methodology in relation to many contemporary issues, among them his concept of the state in Islam.
This study seeks to answer several questions about al-Nafisi, including: How significant is al-Nafisi in the development of contemporary Islamic thought? What are his thoughts about the relationship between the state and religion? What lessons can be learned from al-Nafisi’s doctrine, and how can it be adapted to enhance Islamic political systems worldwide?
Through the study of his thought, this thesis suggests that al-Nafisi illustrates ongoing changes in contemporary Islamic thought in many contemporary issues, such as the concepts of democracy and secularism, as well as Islamism. This study also argues that al-Nafisi provides a window into contemporary Islamic political thought about democratization, state secularisation, and political pluralism, in the Middle East generally and in the Arab Gulf region in particular
«Le Clézio L’Africain»? The role and place of Africa and Africans in Désert, Onitsha, Gens des Nuages and L’Africain
Get PDFThe French author Le Clézio has garnered widespread acclaim for his postcolonial literary works, which are deeply rooted in his African heritage and extensive travels. His writings serve as a medium through which he articulates his unique Africanist perspective. In addition to inquiring into his African identity, Le Clézio's oeuvre explores a myriad of themes including childhood memories, personal journeys and reflections, family histories, and the influential role of photography in shaping one's perception of reality. These thematic threads constitute essential components of our scholarly inquiry, which seeks to illuminate the complex interplay between Le Clézio's African identity and the profound influence of Africa on his literary creations. This study aims to dissect Le Clézio's intricate relationship with Africa and this continent's pivotal role in his artistic endeavours. Central to our examination is the interrogation of how the author acquired his profound knowledge of Africa, probing whether this deep understanding stems solely from his African lineage or whether external factors have also contributed to shaping his perspective. By synthesizing the insights of various scholars who have meticulously scrutinized the works of this Nobel Laureate, we are shedding light on the multifaceted dimensions of Africa in Le Clézio's literary tapestry.
While existing scholarly discourse provides a substantial foundation for our investigation, a wealth of untapped fields remains waiting to be explored, particularly concerning the nuanced interplay between colonial legacies and postcolonial narratives in Le Clézio's writings. Le Clézio's literary corpus serves as a rich repository of material for our analysis, with works such as Désert, Gens des Nuages, Onitsha, and L’Africain offering poignant vignettes that encapsulate the author's profound engagement with Africa. Through a meticulous examination of these texts, our research attempts to unravel the intricate web of themes, motifs, and narratives that underscore Le Clézio's portrayal of Africa, thereby contributing to a deeper understanding of this continent's profound impact on his literary imagination
Synthesis, design and fabrication of microwave filters and multiplexers
Get PDFThis thesis presents new synthesis processes for filters and multiplexers. It also demonstrates novel implementation of microwave filters using Selective Laser Melting (SLM) and Micro Laser-Sintering (MLS) based 3-D printing technologies. The thesis contains six projects.
The first project proposes a synthesis and design approach for filters with multiple transmission zeros generated using dual/multiple dangling nodes. It starts with the synthesis of the general characteristic polynomials. An analytical method is proposed to derive the coupling matrix from the polynomials. Two third-order-two-zero bandpass filters (BPFs) are used to demonstrate the synthesis and design procedure. Two third-order-four-zero BPFs are then designed and prototyped using two pairs of mixed E/H-plane dual dangling nodes. The fabrication is enabled by 3D printing technology. Excellent agreement between the measurement and the design substantially verifies the synthesis and design approach and demonstrates the capability of the additive manufacture technology.
The second project presents an iterative method to achieve a strong initial coupling matrix for triggering the subsequent matrix optimization of diplexers/multiplexers with all-resonator topologies. The method is based on the synthesis of a single channel filter in consideration of the estimated loading effect of other channels. The synthesis starts with the characteristic polynomials of each channel filter, obtaining corresponding input admittance, and extracting the equivalent circuit model. Seven examples are used to demonstrate the synthesis process and validate the proposed technique. For most topologies, the iterative method converges after less than 20 iterations. The proposed method provides good initial values of the coupling matrix which can substantially reduce the optimization time to seconds, even for complicated topologies.
The third project demonstrates a narrowband third-order filter at 9 GHz with two transmission zeros generated using the non-resonating node (NRN) method. The filter is fabricated out of aluminium-copper alloy (A20X) using selective laser melting (SLM) technology. Without tuning, the measurements show promising results, but with a resonator detuning. Micro X-Ray CT imaging is performed to investigate the imperfection in the manufacture. Dimension measurement of the structure show the level of dimension offset and some evidence of excessive shrinkage from the small iris structures.
The fourth project presents a fifth-order BPF for communication satellite feed systems, fabricated using 3D-printing with Titanium alloy Ti-6Al-4V or Ti64. Taking advantage of the alloy's high strength-to-weight ratio, the filter is printed with a wall thickness of only 1 mm and a weight of 40 g. Ti64 also has a much lower coefficient of thermal expansion (CTE) than aluminium. The filter was designed with modified rectangular cavity resonators with rounded corners, enabling monolithic printing of the structure in a lying-down position without any internal supports. The coupling irises are moved to one side of the filter to facilitate polishing and silver coating. The measured response of the as-printed filter showed a minimum insertion loss of 2.7 dB and a frequency shift of about 140 MHz. After silver plating, the insertion loss was significantly reduced to a minimum of 0.55 dB. The challenge with plating on the Ti64 filter is discussed.
The fifth project presents an irregular-hexagonal resonator geometry for additively manufactured microwave filters. This geometry allows closely packed resonators to form very compact filters of various topologies fulfilling transfer functions with transmission zeros. It also minimizes the overhangs and allows vertical printing along the direction of the input/output ports, without any internal support structure and with a much-reduced profile. The characteristics of the resonator and the trade-off between compactness and quality factor is analysed. Three BPFs are demonstrated. Two of them are designed with NRN topologies with fractional bandwidths of 5% and 1%, respectively, using the step-tuning technique. All three filters are fabricated using SLM technique. The performance of the fabricated filters is compared with the EM simulation. Very good agreement is achieved for all three filters. The effectiveness of tuning is also demonstrated. The resonator structure offers high printability and high level of modularity and flexibility in the design.
Finally, in the sixth project, an E-band bandpass (81 – 86 GHz) filter has been demonstrated to show the effectiveness of surface treatments and a new electrochemical polishing technique, in particular, on the metal 3D-printed millimeter-wave waveguide device. The third-order filter is designed using a modified hexagonal resonator, a compact and self-supportive structure, and two samples have been printed monolithically using a high-precision micro-laser-sintering (MLS) technology out of stainless-steel. The effects of polishing and gold coating have been investigated. The coating improves the insertion loss by ~1 dB whereas the polishing step further reduces the loss by ~0.3 dB. This results in a very low insertion loss of only 0.14 dB for one of the two samples. This correlates with the 50% reduction in the surface roughness after polishing. The demonstrated end-to-end manufacture and surface treatment process shows great promise in addressing the surface quality issues with metal 3D printing for millimeter-wave devices
Investigation into the grinding performance and surface integrity of advanced aerospace superalloys in creep feed grinding
Get PDFTitanium alloys exhibit exceptional mechanical properties, including high rigidity, favourable strength-to-weight ratio, and excellent resistance to corrosion. Such features have resulted in their widespread application across several industries, more particularly in aerospace and automotive. The increased demand for enhanced burn resistance coupled with low weight has led to the development of more advanced titanium alloys such as gamma titanium aluminide intermetallic (γ-TiAl) and burn-resistant titanium alloy (BuRTi), which are considered potential alternative materials for nickel-based superalloys in aerospace components such as compressors and turbine blades or vanes. However, machining these materials poses significant challenges to the industry in part due to their inherent features, for instance, low thermal conductivity, strong chemical reactivity, and the ability to maintain their tensile strengths at elevated temperatures. The process of grinding plays a crucial role in the manufacturing of mechanical components with high surface quality and dimensional accuracy, and compared to other machining processes, grinding has consistently exhibited improved surface quality when utilised for cutting titanium alloys. In comparison to conventional grinding, creep feed grinding achieves more efficiently in terms of stock removal rate while maintaining good surface finish and tolerances (from ±8µm to ±80µm).
The available information in the literature regarding creep feed grinding of the thermo-mechanically produced duplex latest generation gamma titanium aluminide (Ti-45Al-8Nb-0.2C), the patent burn-resistant titanium alloy (Ti-25V-15Cr-2Al-0.2C) and the alpha/beta titanium alloy (Ti-6Al-4V) is scarce and only involving limited investigated machining/grinding conditions. In addition, the existing literature on creep feed grinding of γ-TiAl (Ti–45Al–8Nb–0.2C) lacks information regarding the temperature and residual stresses that are produced during the machining operation, with extremely limited information given for burn-resistant titanium (Ti-25V-15Cr-2Al-0.2C). Moreover, the majority of published work to date has primarily focused on the evaluation of the two-dimensional average surface roughness parameter (Ra), and no details on extreme or three-dimensional surface roughness parameters were reported (Rt, Rz, Sa, St and Sz).
Following an extensive literature review on titanium alloy development, grinding fundamentals, surface integrity, experimental design, and grinding of relevant titanium alloys, the thesis details the findings from three main phases of experimental work. The first focused on creep feed grinding of gamma titanium aluminide intermetallic alloy (Ti–45Al–8Nb–0.2C wt%), whilst the second phase provided an assessment of creep feed grinding for burn resistant titanium alloy (Ti-25V-15Cr-2Al-0.2C) and compared its grindability to γ-TiAl material. The last phase is pertinent to creep feed grinding of alpha/beta titanium alloy (Ti-6Al-4V) with benchmarking against the two previously investigated materials. Results provided in each phase/material covered information for both conventional and super-abrasive wheels. Full factorial experimental designs were utilised in each phase to investigate the impact of various operational parameters (wheel speed, depth of cut and feed rate) and their corresponding levels (20 and 30m/s, 0.3 and 1mm, and 150 and 300mm/min) on performance output measures, including the G-ratio, grinding forces, grinding power, specific energy, grinding temperature, and workpiece surface roughness. Furthermore, an assessment of the surface integrity of the machined samples is provided, which encompasses the evaluation of the produced workpiece surface, microstructure, microhardness and residual stresses.
The experimental findings demonstrate that γ-TiAl showed more favourable outcomes when compared to BuRTi and Ti-6Al-4V. This was evident from the lower values observed including, 3 times lower wheel wear, ~40% lower grinding forces and power, reduced temperature at the majority of tests and ~50% lower surface roughness. BuRTi and Ti-6Al-4V materials exhibited a moderate degree of similarity in terms of their grinding performance at lower rates of material removal. At increased depths of cuts, the former showed reduced wheel wear (~27µm compared to ~50µm), ~30% lower grinding forces and ~30-40% lower surface roughness. However, these were accompanied by the occurrence of surface burn and crack formation. In terms of grinding temperature, surface integrity, and generated residual stresses, the diamond wheel exhibited superior performance compared to the SiC wheel across all materials that were examined. The results indicate that a significant rise in the G-ratio was only evident in γ-TiAl subjected to diamond wheel machining, while no such improvement was observed in BuRTi and Ti-6Al-4V. Tensile residual stresses were predominantly present on γ-TiAl and BuRTi surfaces ground with a SiC wheel under extreme operating conditions and accompanied with fractures, burn marks, and softening layers on machined surfaces. Compressive residual stresses, on the other hand, were restricted to surfaces free of burn and microstructural deformation, particularly in samples cut with diamond wheels.
The current work provides new insights into the generated temperature, residual stresses and 3D surface roughness parameters during creep feed grinding of the thermo-mechanically produced duplex alloy γ-TiAl (Ti–45Al–8Nb–0.2C), the patent burn-resistant titanium alloy (Ti-25V-15Cr-2Al-0.2C) as well as for alpha/beta titanium alloy (Ti-6Al-4V). The findings presented in this thesis demonstrate strong correlations between the output measures pertaining to surface integrity and the generated temperature, 3D surface roughness parameters, and induced residual stress results. These aspects are missing in published literature for investigated materials. The machinability data presented here are extremely useful for future work in understanding the analysis of the performance of grinding processes for titanium alloys including modelling activities
Development of protective coatings for metallic bipolar plates for PEM fuel cell applications
Get PDFPolymer electrolyte membrane fuel cells have the potential to progress the worlds energy cycle toward a greener future. PEM fuel cells have the potential to power data centres, drones, auxiliary power units on planes, heavy and light duty vehicles but are still hindered by high costs and low hydrogen supply. For PEM fuel cells to become a mainstream power source, the price of stacks needs to be reduced. In addition, some applications require improvements in the gravimetric power density currently produced by systems.
Metallic bipolar plates have become the standard for modern fuel cell systems but plates often require expensive coatings. For this reason cheaper alternatives to PVD coating were investigated for stainless steel plates. Polyaniline/TiN - TiN bilayer coatings were investigated due to the simple equipment needed for coating and the low cost raw materials. Contact resistance was reduced by increasing TiN surface layer loading. This also improved the corrosion resistance of the sample. The optimised coating however failed to meet DoE contact resistance targets.
Reducing PVD coating thickness is another method to reduce coating costs. PVD coatings have already been shown to achieve DoE contact resistance targets. To increase gravimetric power density the mass of bipolar plates needs to be reduced. Aluminium was selected as the density is 40% that of stainless steel. Aluminium however readily corrodes in simulated fuel cell conditions, the metal is also covered in an insulating oxide layer which would lead to unacceptable contact resistance values. For this reason the substrate must be coated. In this work, TiN, TiC, CrC and TiAu, PVD coatings were applied to 99.0% pure aluminium and TiC, CrC and TiAu coatings to Alloy Al6082 substrates. All coated samples, except the TiC 99.0% coated sample, possessed excellent contact resistance values that far exceed DoE targets. However all the samples displayed typical aluminium corrosion phenomena. The corrosion resistance of materials was probed by means of linear sweep voltammetry and chronoamperometry, with ICPOES, EDX and SEM analysis characterisation techniques utilised to investigate the corrosion solutions and the samples.
Further investigations on the feasibility of aluminium bipolar plates were carried out by means of in situ degradation testing. In situ degradation was carried out by a duty cycle whereby the voltage was cycled between 0.9 V and 0.6 V. Polarisation curves and impedance spectroscopy measurements were carried out at the start of tests and every 12 hours to assess the performance degradation. The TiAu coating displayed superior performance to the graphitic bipolar plate at beginning of life but degraded through the test. Further work is required to achieve durability requirements. However PVD coated aluminium bipolar plates show promise in increasing the volumetric power density of PEM fuel cells
Exploring the roles of UPF1 in mRNA generation
No full textThe RNA helicase UPF1 is predominantly studied in relation to the cytoplasmic pathways of nonsense-mediated mRNA decay (NMD). However, this investigation focused on its potential nu- clear functionalities, building on recent evidence showing it associates with nascent transcripts. A combination of experimental and bioinformatic approaches were performed in parallel, using two different types of Drosophila cells. Firstly, RNAseq datasets were generated to assess changes in pre-mRNA splicing patterns in UPF1-depleted cells. Several mRNAs appear to be alternatively processed in both S2 and salivary gland cells. This effect is most apparent at riboso- mal protein and translation–related genes where there is increased usage of intronic splice sites, leading to the production of putative NMD-sensitive mRNA isoforms. It is currently understood that such mRNA isoforms are at low levels in wild-type cells because they are destroyed by NMD in the cytoplasm. However, this study shows that switches in splicing patterns are appar- ent in nuclear RNA, chromatin associated RNA and more prominent in newly synthesised RNA relative to steady-state levels. This switching phenotype is not generally seen in UPF2 and UPF3 knockdowns, implying UPF1 specificity. Analyses of chromatin immunoprecipitation of UPF1, show it associates strongly at ribosomal protein gene loci. Additionally, abnormalities in RNA polymerase II (Pol II) loading are apparent at the transcription start sites of these genes during UPF1 depletion. Kinetics of mRNA synthesis and decay were also examined by 4SU metabolic labelling and T>C base recoding. These data indicate that the transcriptomic changes observed in UPF1-depleted cells cannot be explained by an increase in RNA stability, as NMD predicts. Instead, depleting UPF1 leads to increased RNA synthesis rates of putative NMD candidates, a phenotype which is also observed in some instances during UPF2 depletion. Furthermore, Pol II appears to be hyperphosphorylated at these loci. Part of this increase in mRNA production is likely the consequence of the upregulation of positive regulators of gene expression. However, given that UPF1 binds strongly to their nascent RNA, it is conceivable that, UPF1 plays a direct role in transcription and RNA processing. Overall, this research indicates a role for UPF1 in the pre-mRNA splicing of ribosomal protein genes and the transcriptional regulation of canonical "NMD targets"
Design and construction of atomic comagnetometers
Get PDFThis thesis presents an in depth look into the design and construction of a series of new co-magnetometry experiments. Work to design a high performance magnetic shield that minimises magnetic shield noise whilst maintaining a larger internal volume is detailed. A high-performance magnetic coil assembly that optimally fits within a cylindrical environment is designed and implemented. Preliminary work to characterise one of the co-magnetometry systems utilising novel high pressure 87Rb - 21Ne atomic vapour cells is conducted. This presented possible multiple Lar-mor precession resonances within the vapour cell, representing new physics. The creation of separated regions within the vapour cell due to high diffusion times is hypothesised and offered for further investigation
A critical posthuman geography of digital youth mental health
Get PDFThis thesis explores young people’s experiences of using digital technologies designed to support mental health and wellbeing, such as smartphone apps, chatbots and digital platforms. It critically examines the digital youth mental healthcare assemblage in the context of urgent unmet needs, long waiting lists and the turn towards digital mental healthcare in England. It draws on qualitative data from 40 interviews and two focus groups with three groups of participants: young people (aged 16 to 25) who use digital technologies for their mental health and wellbeing, practitioners who work within youth mental health and emotional wellbeing services, researchers and developers of digital mental health. Firstly, this thesis enquires into the logics and practices of digital mental health using a broadly posthuman geographical conceptual framework and assemblage theory. Secondly, the thesis addresses how digital mental health technologies, services and interventions are changing the ways young people know, engage and intervene in their own mental health and wellbeing. Literatures on digitally mediated experience and psychoanalytic geographies support this endeavour.
Across three empirical chapters, the thesis examines how digital technologies change mental health support, therapy and relationships. I explore young people’s experiences of digital mental health and examine how certain components of therapeutic relationships are primed for automation. I show how mental health and wellbeing apps mediate young people’s experiences of using them, temporally, through cues to ‘check in’. This shapes reflective capacities and can have unintentional effects, such as repetitive introspection. Reflection is generated as part of an associated milieu of data, practices and logics with recursive functions. I use assemblage as a method to identify material and discursive components, relations and forces that assemble digital youth mental healthcare. Secondly, I use assemblage to analyse relations of dependency between components and how capitalism and psychopower organises the arrangement. Overall, this thesis contributes to contemporary understandings of digital therapeutic relations and gives insight into the status of digital youth mental healthcare in England and beyond. In doing so, it advances a critical posthumanist geography that takes seriously the material capacities of digital technologies, without losing sight of the humanness of the concept of the psyche and therapeutic relations, or the production of these by technoscientific capitalism
Data sources:
Access Repository Dashboard
Do you manage Open Research Online? Become a CORE Member to access insider analytics, issue reports and manage access to outputs from your repository in the CORE Repository Dashboard! 👇