Engineering & Physical Sciences

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1,1ʹ-Bis(ortho-carborane) : ruthenium chelates, phosphines and tether derivatives
(Engineering and Physical Sciences, 2017-03) Riley, Laura E.; Welch, Professor Alan J.
Chapter one provides a brief exposition on the history and importance of boron and carboranes and introduces 1,1ʹ-bis(o-carborane). It also provides literature examples of 1,1ʹ-bis(o-carborane) chelates, 1,1ʹ-bis(o-carboranyl)phosphines and tethered 1,1ʹ-bis(o carboranes). Chapter two discusses the reaction between dilithiated 1,1ʹ-bis(o-carborane) and di halogenated ruthenium compounds to afford several new compounds of the formula [Ru(κ2/3-2,2ʹ(3ʹ)-{1-(1ʹ-1ʹ,2ʹ-closo-C2B10H10)-1,2-closo-C2B10H10})(L)]. The first compound prepared, whereby L = p-cymene, reacts with either PPh3 or dppe and shows unusual displacement of the p-cymene ligand and a change in the bonding mode of 1,1ʹ bis(o-carborane). The fully saturated (MeCN or CO) derivatives of these compounds are also synthesised and studied, some of which are excellent examples of illustrating the structural trans effect. The initial {Ru(p-cymene)} was tested as a catalyst and displayed good Lewis acid catalytic activity of a Diels-Alder cycloaddition. Chapter three explores two carboranylphosphines [µ-2,2ʹ-PR-{1-(1ʹ-1ʹ,2ʹ-closo C2B10H10)-1,2-closo-C2B10H10}], where R = Et or Ph. Two-dimensional NMR spectroscopy and DFT calculations are used to explain an unusual lack of observed 2JPH coupling in the 1H NMR spectrum of the ethyl derivative. Their subsequent reactions with {AuCl} and {Se} are also discussed as they provide a route to identifying the steric bulk and electronic properties of these carboranylphosphines. Chapter four discusses one new tethered 1,1ʹ-bis(o-carborane) and its comparison with non-carborane analogues. A known tethered carborane is also synthesised and its single decapitation and metalation with {Ru(p-cymene)} explored producing the desired 12 vertex ruthenacarborane/12-vertex carborane but also an unusual 13-vertex diruthenacarborane/12-vertex carborane. Chapter five gives all the synthetic and analytical details for the compounds discussed. Appendix one provides crystallographic tables and appendix two provides all the crystallographic information on a CD. Appendix three includes copies of all published work related to this thesis (to date).
1/f noise in mercury cadmium telluride semiconductor diodes
(Heriot-Watt University, 2005) Haigh, Mary K
2-μm wavelength thin slab amplifiers and lasers
(Heriot-Watt University, 2021-09) Morris, Daniel; Esser, Professor Daniel
Abstract currently unavailable. Please refer to PDF. Restricted access until 15.12.2025.
2D photonic crystals to enhance up-conversion emission for silicon photovoltaics
(Heriot-Watt University, 2016-01) Morton, Jonathan Andrew Scott
This thesis investigates the application of 2D photonic crystals to enhance the emission of up-conversion layers to improve the efficiency of silicon photovoltaics. Two up-conversion material compositions are of particular interest in this work: erbium doped titanium dioxide (TiO2:Er) and erbium doped yttrium fluoride (YF3:Er). The 2D photonic crystals under investigation are composed of TiO2:Er and air; and YF3:Er and silicon. These nano-structures are investigated using both simulation and experimental methods. Further work in this thesis analyses the properties of the highly conductive polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) for use as a transparent electrode and thin film electrically conductive adhesive for the application of silicon photovoltaics. The design and geometrical parameters for the 2D photonic crystals were optimised through simulations (plane wave expansion and finite-difference time-domain), before the structures were experimentally fabricated and optically characterised. The novel analysis of the refractive index of the prepared up-conversion materials using ellipsometry was a key step in the design of the photonic crystal structures. A maximum photoluminescence enhancement of 3.79 times was observed for the 980 nm emission profile, however this could not be successfully attributed to a photonic crystal effect. The optical, mechanical and electronic properties of PEDOT:PSS were characterised for thin film samples, using novel ellipsometry analysis.
3-D spatial field and force distributions in axial field machines using a computed tomography method
(Heriot-Watt University, 1990) Gair, Sinclair
3D biofabrication of cell-laden alginate hydrogel structures
(Heriot-Watt University, 2017-06) Tabriz, Atabak Ghanizadeh; Shu, Professor Will
Biofabrication has been receiving a great deal of attention in tissue engineering and regenerative medicine either by manual or automated processes. Different automated biofabrication techniques have been used to produce cell-laden alginate hydrogel structures, especially bioprinting approaches. , These approaches have been limited to 2D or simple 3D structures, however. In this thesis, a new extrusion-based bioprinting technique and a new simple, manual 3D biofabrication method are presented to culture cells in 3D. These methods do not rely on any complex fabrication methods. The bioprinting technique was developed to produce more complex alginate hydrogel structures. This was achieved by dividing the alginate hydrogel cross-linking process into 3 stages: primary calcium ion cross-linking for printability of the gel, secondary calcium cross-linking for rigidity of the alginate hydrogel immediately after printing and tertiary barium ion cross-linking for the long-term stability of the alginate hydrogel in the culture medium. Simple 3D structures including tubes were first printed to ensure the feasibility of the bioprinting technique. Complex 3D structures, such as branched vascular structures, were subsequently printed successfully. The static stiffness of the alginate hydrogel after printing was 20.18 ± 1.62 kPa which was rigid enough to sustain the integrity of the complex 3D alginate hydrogel structure during the printing. The addition of 60 mM barium chloride was found to significantly extend the stability of the cross-linked alginate hydrogel from 3 days to beyond 11 days without compromising the cellular viability. The results based on cell bioprinting suggested that the viability of U87-MG cells was 92.94 ± 0.91 % immediately after bioprinting. Cell viability was maintained above 88 ± 4.3 % in the alginate hydrogel over a period of 11 days. On the other hand, the manual biofabrication approach developed in this thesis enabled the fabrication of scalable 3D cell-laden hydrogel structures easily, without complex machinery. The technique could be carried out using only apparatus available in a typical cell biology laboratory. The fabrication method would involve micro coating cell-laden hydrogels covering the surface of a metal bar by dipping into cross-linking reagent CaCl2 or BaCl2, to form hollow tubular structures. This method could be used to form single- or multi-layered tubular structures. This fabrication method has incorporated the use alginate hydrogel as the primary biomaterial and secondary biomaterial could be added depending on the desired application. The feasibility of this method has been demonstrated by showing the cell survival rate and normal responsiveness of cells within these tubular structures using mouse dermal embryonic fibroblast cells and human embryonic kidney 293 cells containing a tetracycline responsive red fluorescence protein (tHEK cells). By adjusting the fabrication protocol, complex hollow alginate hydrogel structures could be generated.
3D bioprinting of multilineage human glioblastoma models
(Heriot-Watt University, 2018-02) Hermida, Miguel Angel; Leslie, Professor Nick
In the last decade, the importance of three-dimensional cultures has been highlighted as a way to support the correct physiological and pathological behaviour of cell cultures. Many cells behave differently when grown in a 2D environment compared with a 3D matrix and this can result in a different sensitivity to drugs. Especially relevant in cancer is that many forms of interaction and communication between different cell types can either promote or repress cell proliferation and survival. In order to overcome the difficulty of studying cancer cells in a relevant microenvironment, new methods capable of generating 3D multicellular systems need to be implemented. Ideally, these methods have to allow a relatively fast and cheap way of generating different 3D constructs with minimal effects on cells caused by the preparation methods themselves. Spatial organization and automation of these processes would be highly desirable. The approach described in this thesis is based on a 3D printing strategy using the common biocompatible hydrogel, alginate, modified to promote cell attachment. Results show that the printing process can be performed without reduced cell viability; that cells proliferate within the gel and form more complex structures. The results here presented show that glioma stem cells (GSC) can be 3D printed and provide a response to drug treatment that resembles more closely the in vivo situation. Co-culture drug treatments in the 3D printed models showed that the presence of monocytes can increase the sensitivity of the glioma cell line U87MG, while the GSC line G7 showed no difference when co-cultured with microglia. The GSC lines seem to retain pluripotency better in the 3D system than in 2D cultures. Performing co-culture 3D printed studies, a differential kinase activity was observed, showing that macrophage-like cells can increase the activity of ERK, JNK, PKA and p38 only in the printed system. The 3D printing strategy here presented shows potential for biological applications, and the results obtained testing drugs and using biosensors to analyse real-time single-cell signalling changes indicate that the strategy can be a useful tool in cancer research.
3D direct-write photonics for optical transceivers
(Heriot-Watt University, 2021-07) Mitchell, Paul; Kar, Professor Ajoy
Abstract unavailable. Please refer to PDF. Previously restricted until 22/02/2024. Restricted access extended until 28/02/2027.
3D printing of electrically conductive soft multi-material composites for strain and pressure sensors
(Heriot-Watt University, 2021-05) Alsharari, Meshari Mubarak Awadh; Shu, Professor Will
3D printing on flexible microelectronics design and manufacturing is an emerging and burgeoning field. However, the existing platforms cannot meet the requirements for processing complex 3D flexible electronic circuit models. This project aims to establish a full-scale framework for 3D printing and its applications. The combination of stretchable polymers with conductive carbon-based fillers has attracted attention in the multifunctional sensing materials field. Upon dynamic loading, these polymer composites exhibit piezoresistive behaviour that can be utilised for strain and tactile pressuresensing applications. This project investigates the piezoresistive behaviour of stretchable thermoplastic conductive polymers and their strain and pressure-sensing capabilities. Modification of the conductive composites has led to the development of fully 3D printed strain sensors. A 3D printer with a dual material extrusion system was employed to fabricate the conductive composites embedded in a stretchable elastomer substrate to create highly sensitive and linear strain sensors. Pre-straining of the 3D printed strain sensors caused crack formations; higher pre-straining values resulted in higher sensitivity. The sensors’ sensitivity reached a gauge factor (GF) value of 163. Highly sensitive and tuneable pressure sensors were also realised by utilising multi-material 3D printing techniques. Combining conductive flexible polymers and scaffold materials allowed the fabrication of novel pressure sensors with enhanced compressibility and a wide sensing range. The physical properties of the materials were tested, and the electromechanical properties of the 3D printed sensors were investigated. Characterisation through scanning electron microscopy (SEM) and optical microscopic imaging was conducted throughout this research. The 3D printed strain and pressure sensors demonstrated cyclic behaviour with linear, repeatable, and reproducible responses suggesting great potential for many applications.
3D reconstruction and motion estimation using forward looking sonar
(Heriot-Watt University, 2013-10) Assalih, Hassan; Petillot, Professor Yvan
Autonomous Underwater Vehicles (AUVs) are increasingly used in different domains including archaeology, oil and gas industry, coral reef monitoring, harbour’s security, and mine countermeasure missions. As electromagnetic signals do not penetrate underwater environment, GPS signals cannot be used for AUV navigation, and optical cameras have very short range underwater which limits their use in most underwater environments. Motion estimation for AUVs is a critical requirement for successful vehicle recovery and meaningful data collection. Classical inertial sensors, usually used for AUV motion estimation, suffer from large drift error. On the other hand, accurate inertial sensors are very expensive which limits their deployment to costly AUVs. Furthermore, acoustic positioning systems (APS) used for AUV navigation require costly installation and calibration. Moreover, they have poor performance in terms of the inferred resolution. Underwater 3D imaging is another challenge in AUV industry as 3D information is increasingly demanded to accomplish different AUV missions. Different systems have been proposed for underwater 3D imaging, such as planar-array sonar and T-configured 3D sonar. While the former features good resolution in general, it is very expensive and requires huge computational power, the later is cheaper implementation but requires long time for full 3D scan even in short ranges. In this thesis, we aim to tackle AUV motion estimation and underwater 3D imaging by proposing relatively affordable methodologies and study different parameters affecting their performance. We introduce a new motion estimation framework for AUVs which relies on the successive acoustic images to infer AUV ego-motion. Also, we propose an Acoustic Stereo Imaging (ASI) system for underwater 3D reconstruction based on forward looking sonars; the proposed system features cheaper implementation than planar array sonars and solves the delay problem in T configured 3D sonars.
3D reconstruction and object recognition from 2D SONAR data
(Engineering and Physical Sciences, 2018-08) Guerneve, Thomas; Petillot, Professor Yvan; Subr, Doctor Kartic
Accurate and meaningful representations of the environment are required for autonomy in underwater applications. Thanks to favourable propagation properties in water, acoustic sensors are commonly preferred to video cameras and lasers but do not provide direct 3D information. This thesis addresses the 3D reconstruction of underwater scenes from 2D imaging SONAR data as well as the recognition of objects of interest in the reconstructed scene. We present two 3D reconstruction methods and two model-based object recognition methods. We evaluate our algorithms on multiple scenarios including data gathered by an AUV. We show the ability to reconstruct underwater environments at centimetre-level accuracy using 2D SONARs of any aperture. We demonstrate the recognition of structures of interest on a medium-sized oil-ﬁeld type environment providing accurate yet low memory footprint semantic world models. We conclude that accurate 3D semantic representations of partially-structured marine environments can be obtained from commonly embedded 2D SONARs, enabling online world modelling, relocalisation and model-based applications.
A) Aspects of the chemistry of sydnones. B) Thermolysis and photolysis of compounds containing an o-nitroaryl substituent
(Heriot-Watt University, 1971) Goudie, Robert Sinclair
The accuracy of hydrodynamic force prediction for offshore structures and Morison's equation
(Heriot-Watt University, 1996) Naghipour, Morteza
Acidic complexes on the surface of carbon: a selective neutralization study with bases of different strengths
(Heriot-Watt University, 1979) Khan, Mohammad Arsala
Acoustic emission analysis for quality assessment of thermally sprayed coatings
(Heriot-Watt University, 2009-11) Faisal, Nadimul Haque; Reuben, Professor Robert L.; Ahmed, Doctor Rehan; Steel, Professor John Iain A.
This study describes a new approach to the quality assessment of thermally sprayed carbide and ceramic coatings produced by High Velocity Oxy-Fuel (HVOF) and Air Plasma Spray (APS) processes. The aim of the work was to develop an experimental methodology based on Acoustic Emission (AE) monitoring of a dead-weight Vickers indentation to assess the degree of cracking and hence the toughness of the coating. AE monitoring was also applied to an industrial process as a contribution to the possibility of quality assessment during the deposition process. AE data were acquired during indentation tests on samples of coating of nominal thickness 250-325 μm at a variety of indentation loads ranging from 49 to 490 N. Measurements were carried out on six different thick-film coatings (as-sprayed HVOFJP5000/ JetKote WC-12%Co, HIPed HVOF-JetKote WC-12%Co, as-sprayed HVOFJP5000 WC-10%Co-4%Cr, conventional powder APS-Metco/9MB Al2O3 and fine powder HVOF-theta gun Al2O3) and also on soft and hard metallic samples and metals. The raw AE signals were analysed along with force and displacement history and the total surface crack length around the indent determined. Also, a selection of the indents was sectioned in order to make some observations on the sub-surface damage. The results show characteristic AE time evolutions during indentation for tough metals, hard metals, and carbide and ceramic coatings. Within each category, AE can be used as a suitable surrogate for crack length measurement for assessing coating quality. Finally, a preliminary observation on AE monitoring during HVOF (JP5000) WC- 10%Co-4%Cr thermal spraying was made. It was found that AE is sensitive to individual particle landings during thermal spraying and therefore can, in principle, be used to monitor the spray process.
Acoustic emission detection by fibre optic interferometry
(Heriot-Watt University, 1994) Carolan, Thomas Andrew
Acoustic emission monitoring of pipes; combining finite element simulation and experiment for advanced source location and identification
(Heriot-Watt University, 2019-05) Abolle-Okoyeagu, Chika Judith; Reuben, Professor Robert; Chen, Doctor Yuhang
Impact is a common source of damage in pipes and pipeline systems, detecting the location and nature of damage is vital for reliability and safety of these systems. This work sets out to assess the capacity of Acoustic Emission (AE) to monitor pipes and pipelines for externally applied mechanical damage. AE is a non-destructive testing and monitoring technique that relies on the propagation of elastic (stress) waves generated by impulsive events such as particle impingement, cracking or fluid flow. These waves are recorded at one or more sensors mounted on the surface of the object to be monitored. The key scientific question was to determine the extent to which the structure of a non-impulsive event could be reconstructed using sensors located on the external surface of a pipe. The aim was to combine Finite Element simulations with a series of experiments in order that the relationship between the generating event (source) and the resulting stress-time history at a given point on the surface could be elucidated. Experiments and simulations were carried out with impulsive sources (pencil-lead breaks) and dropped objects, the latter being used to represent a non-impulsive event with a reproducible structure lasting around one second. The AE resulting from these sources was recorded over a period of around 2 seconds for both experiments and simulations. Two test objects, a solid cylindrical steel block of diameter 307mm and length 166mm and various lengths of pipe of diameter 100mm and wall thickness 10mm were used, the former to provide a relatively simple and well-studied platform to examine a number of essential principles. The work on the solid cylinder first validated the simulation of the stress wave from an impulsive source and identified the main modes present, by comparing with analytical solutions. Then it was possible to identify the part of the experimental time series record at a given sensor which is uncontaminated by reflections from the edges and surfaces of the cylinder. The dropped object measurements on the solid cylinder provided clear records of the first and subsequent impacts as the dropped steel balls recoiled and returned back to the surface. There was a clear relationship between the measured AE energy and the estimated incident energy of the dropped objects at a range of timescales irrespective of contamination by reflections. The work on the pipe sections formed the main series of systematic experiments. First it was established that an unloading time in the simulations of around 10-8 seconds gave a reasonable representation of the frequency structure of experimentally observed stress waves. It was also observed from both experiments and simulations that a low amplitude wave travelling at around 5500ms-1 was the first to arrive at any surface sensor. The structure thereafter was complex, probably involving reflections from the inner wall of the cylinder and geometric interference as the wave spreads around the circumference of the pipe. The key finding of this aspect of the work is that the AE line structure of an impulsive source can be reproduced by simulation for short times, for longer times, the damping associated with reflections would require to be measured and introduced into the simulations in order to fully represent the real practical simulation. The degree of damping is important in making a cumulative assessment of multiple impulsive sources. The dropped objects on the pipe confirmed that a mechanical disturbance which is extended in time can be identified from its energy-time imprint carried on the stress wave. The analysis was carried out at three different timescales; short (initial interactions free of reflections), medium (first contact including recoil) and long (involving several bounces). Generally, for medium and short timescales, the AE energy varied with drop height and mass consistently with existing models for balls on plate. For multiple bounces, the behaviour was more erratic probably due to the imprecise control of ball contact point. The simulations of AE worked well at medium and long timescales, providing an idealised framework unto which could be added effects of restitution and damping. At the short timescale, the twin challenges of time and spatial resolution meant that a solution could not be obtained within the limitations of the computing power available. It is generally concluded that AE monitoring can be used to identify the nature of a mechanical disturbance on the surface of a pipe. Suggestions for future work include improvements to the simulations to include attenuation and to better simulate the dynamics of mechanical interactions at the surface, and extensions to the experiments to cover the effect of internal and external pipe environment and the use of mechanical sources which involve actual pipe damage.
Acoustic emission monitoring of propulsion systems : a laboratory study on a small gas turbine
(Heriot-Watt University, 2010-11) Nashed, Mohamad Shadi; Reuben, Professor Robert L.; Steel, Professor John A.
The motivation of the work is to investigate a new, non-intrusive condition monitoring system for gas turbines with capabilities for earlier identification of any changes and the possibility of locating the source of the faults. This thesis documents experimental research conducted on a laboratory-scale gas turbine to assess the monitoring capabilities of Acoustic Emission (AE). In particular it focuses on understanding the AE behaviour of gas turbines under various normal and faulty running conditions. A series of tests was performed with the turbine running normally, either idling or with load. Two abnormal running configurations were also instrumented in which the impeller was either prevented from rotation or removed entirely. With the help of demodulated resonance analysis and an ANN it was possible to identify two types of AE; a background broadband source which is associated with gas flow and flow resistance, and a set of spectral frequency peaks which are associated with reverberation in the exhaust and coupling between the alternator and the turbine. A second series of experiments was carried out with an impeller which had been damaged by removal of the tips of some of the blades (two damaged blades and four damaged blades). The results show the potential capability of AE to identify gas turbine blade faults. The AE records showed two obvious indicators of blade faults, the first being that the energy in the AE signals becomes much higher and is distinctly periodic at higher speeds, and the second being the appearance of particular pulse patterns which can be characterized in the demodulated frequency domain.
Acoustic emission propagation through bone tissue with focus on a jaw bone surrogate model
(Heriot-Watt University, 2024-04) Boron, Gabriel; Wolfram, Doctor Uwe; Reuben, Professor Robert
Implants are used to improve quality of life, for example, dental implants can resolve negative effects of tooth loss, however current techniques for monitoring dental implants have limitations. An Acoustic Emission Finite Element framework could reduce limitations, whilst adding more capabilities. To realise this, simulations of AE propagation through an implant-less system are needed. Therefore the aim of this study was to simulate AE propagation through bone tissue. To that end, a material model for bone was developed and implemented into FE, in-conjunction with µCT-image-based 3D rib models created from fifteen rib samples used in the AE experiments. These experiments were then sim ulated in FE – ten of the samples were used to identify viscoelastic parameter β for the material model. The remaining five were used to validate the simulations of AE propa gation through bone. The material model was verified against theory, and the viscoelastic parameter, β, was identified to range from 0.0648 to 0.22 for the ten samples, with no clear correlation with bone sample properties. The material model was validated with three out of the five samples used for validation. Simulation of AE propagation through bone can be accomplished, thus there is potential for development of an AE FE implant monitoring framework.
Acoustic Source Localisation in constrained environments
(Heriot-Watt University, 2020-02) Vargas Vargas, Elizabeth; Brown, Doctor Keith Edgar; Subr, Doctor Kartic
Acoustic Source Localisation (ASL) is a problem with real-world applications across multiple domains, from smart assistants to acoustic detection and tracking. And yet, despite the level of attention in recent years, a technique for rapid and robust ASL remains elusive – not least in the constrained environments in which such techniques are most likely to be deployed. In this work, we seek to address some of these current limitations by presenting improvements to the ASL method for three commonly encountered constraints: the number and configuration of sensors; the limited signal sampling potentially available; and the nature and volume of training data required to accurately estimate Direction of Arrival (DOA) when deploying a particular supervised machine learning technique. In regard to the number and configuration of sensors, we find that accuracy can be maintained at state-of-the-art levels, Steered Response Power (SRP), while reducing computation sixfold, based on direct optimisation of well known ASL formulations. Moreover, we find that the circular microphone configuration is the least desirable as it yields the highest localisation error. In regard to signal sampling, we demonstrate that the computer vision inspired algorithm presented in this work, which extracts selected keypoints from the signal spectrogram, and uses them to select signal samples, outperforms an audio fingerprinting baseline while maintaining a compression ratio of 40:1. In regard to the training data employed in machine learning ASL techniques, we show that the use of music training data yields an improvement of 19% against a noise data baseline while maintaining accuracy using only 25% of the training data, while training with speech as opposed to noise improves DOA estimation by an average of 17%, outperforming the Generalised Cross-Correlation technique by 125% in scenarios in which the test and training acoustic environments are matched.