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Dissipative engineering of cold atoms in optical lattices
Get PDFStrathclyde theses - ask staff. Thesis no. : T15134Cold atom systems in optical lattices provide a promising platform for a wide variety of applications, ranging from quantum simulation to quantum metrology, due to their extremely high tunability and the ability to derive microscopic models under well-controlled approximations that allows us to model them. The proper characterization of those systems requires, in many scenarios, taking into account that they are subject to some dissipation sources, as dissipation can drastically modify the behaviour of the known phases of matter or even generate new ones.In this thesis, we investigate several important examples of dissipative many-body dynamics. The first one relates to the use of engineered coupling to the environment,both coherent and dissipative, to robustly create spin-symmetric fermionic states.This scheme, which combines a Raman transfer between Bloch bands and sympathetic cooling with a reservoir gas, prepares entangled states that exhibit quantum enhanced precision for metrology. In the second topic we explore, we focus on the study of one-dimensional spinless fermions and hard-core bosons. We observe how dissipation induces differences in local observables that are identical in the closed system. The third topic that we include in this thesis focuses on characterizing the role of dissipation, specifically particle loss and dephasing, in the long-time behaviour of many-body localized systems. We analyze under which conditions dissipation leads to thermalization in the localized phase.In all these projects, we make use of tensor network techniques to tackle the open system dynamics combining matrix product states and matrix product operator approaches, in both cases, exploiting symmetries in the system to optimize the numerical performance.All in all, the application of open system ideas to the study of quantum many-body problems provides not only an improved description of the realistic scenario but also can give access novel tools to engineer cold atomic systems in regimes that are not accessible for closed systems.Cold atom systems in optical lattices provide a promising platform for a wide variety of applications, ranging from quantum simulation to quantum metrology, due to their extremely high tunability and the ability to derive microscopic models under well-controlled approximations that allows us to model them. The proper characterization of those systems requires, in many scenarios, taking into account that they are subject to some dissipation sources, as dissipation can drastically modify the behaviour of the known phases of matter or even generate new ones.In this thesis, we investigate several important examples of dissipative many-body dynamics. The first one relates to the use of engineered coupling to the environment,both coherent and dissipative, to robustly create spin-symmetric fermionic states.This scheme, which combines a Raman transfer between Bloch bands and sympathetic cooling with a reservoir gas, prepares entangled states that exhibit quantum enhanced precision for metrology. In the second topic we explore, we focus on the study of one-dimensional spinless fermions and hard-core bosons. We observe how dissipation induces differences in local observables that are identical in the closed system. The third topic that we include in this thesis focuses on characterizing the role of dissipation, specifically particle loss and dephasing, in the long-time behaviour of many-body localized systems. We analyze under which conditions dissipation leads to thermalization in the localized phase.In all these projects, we make use of tensor network techniques to tackle the open system dynamics combining matrix product states and matrix product operator approaches, in both cases, exploiting symmetries in the system to optimize the numerical performance.All in all, the application of open system ideas to the study of quantum many-body problems provides not only an improved description of the realistic scenario but also can give access novel tools to engineer cold atomic systems in regimes that are not accessible for closed systems
New optical techniques and hardware for studying live cell dynamics
Get PDFThis thesis was previously held under moratorium from 12/02/2019 to 21/05/2021.Fluorescence optical microscopy has become an integral technique in the life sciences and has opened the door to investigating live biological specimens non-invasively at sub-cellular spatial resolutions with high specificity and temporal resolutions. One of the limiting factors of optical microscopy is that the spatial resolution is dictated by the diffraction limit of light.;This work shows the first use of LEDs to carry out widefield axial super-resolution standing wave microscopy with high temporal resolution. The technique was used to image red blood cell membrane dynamics in real time with no increase in photobleaching or toxicity rates compared to standard widefield imaging. This work also presents 3D computational reconstructions of the data allowing for easier visualisation and the possibility of carrying out further quantitative analysis.;Following on from Chapter 2, is an investigation into the development and application of multi-wavelength standing wave microscopy on live specimens in both emission and excitation modalities. These techniques are henceforth referred to in this thesis as TartanSW. This investigation found that using multiple excitation wavelengths allowed for a reduction in the nodal contribution of the images resulting in obtaining 32.3 % more spatial information about the structure of the specimen. It is also shown that by taking the difference images between each excitation channel the standing wave antinodal planes could be reduced in thickness enabling axial resolutions on the order of 55 nm when imaging live cell experiments.;The multi-emission technique was shown that it could be applied to be applied to imaging biological specimens using both widefield and confocal microscopy. However, the widefield data was not in line with the expected theoretical structure. There is the possibility of using plane ordering though to infer the directionality of a specimen structure and extract height maps though further work to develop computational tools to enable this will have to be implemented.;Finally, this thesis describes the work carried out making use of a new high-brightness 340 nm LED to develop a fast switching 340/380 nm illuminator and demonstrate its application for ratiometric Fura-2 Ca2+ imaging of live cell specimens with sub-5 nM precision that supports full frame video-rate temporal resolutions.Fluorescence optical microscopy has become an integral technique in the life sciences and has opened the door to investigating live biological specimens non-invasively at sub-cellular spatial resolutions with high specificity and temporal resolutions. One of the limiting factors of optical microscopy is that the spatial resolution is dictated by the diffraction limit of light.;This work shows the first use of LEDs to carry out widefield axial super-resolution standing wave microscopy with high temporal resolution. The technique was used to image red blood cell membrane dynamics in real time with no increase in photobleaching or toxicity rates compared to standard widefield imaging. This work also presents 3D computational reconstructions of the data allowing for easier visualisation and the possibility of carrying out further quantitative analysis.;Following on from Chapter 2, is an investigation into the development and application of multi-wavelength standing wave microscopy on live specimens in both emission and excitation modalities. These techniques are henceforth referred to in this thesis as TartanSW. This investigation found that using multiple excitation wavelengths allowed for a reduction in the nodal contribution of the images resulting in obtaining 32.3 % more spatial information about the structure of the specimen. It is also shown that by taking the difference images between each excitation channel the standing wave antinodal planes could be reduced in thickness enabling axial resolutions on the order of 55 nm when imaging live cell experiments.;The multi-emission technique was shown that it could be applied to be applied to imaging biological specimens using both widefield and confocal microscopy. However, the widefield data was not in line with the expected theoretical structure. There is the possibility of using plane ordering though to infer the directionality of a specimen structure and extract height maps though further work to develop computational tools to enable this will have to be implemented.;Finally, this thesis describes the work carried out making use of a new high-brightness 340 nm LED to develop a fast switching 340/380 nm illuminator and demonstrate its application for ratiometric Fura-2 Ca2+ imaging of live cell specimens with sub-5 nM precision that supports full frame video-rate temporal resolutions
Structural investigations with high pressure techniques and multicomponent systems
Get PDFThis thesis illustrates the use of high pressure crystallography techniques for the discovery and investigation of solid-state forms and probes the relationship between molecular structure and compression of both single and multicomponent systems. As well as investigating a data-driven approach to directing experimental co-crystallisation attempts.;Single crystal X-ray diffraction techniques are a highlight in all areas of this study, as well as computational approaches which were used in the evaluation of the interactions of small molecule systems. Data-mining of the Cambridge Structural Database made the comparison of the compression studies richer.;The pharmaceutical co-crystal, indomethacin and saccharin was analysed with respect to increasing pressure. The system is an example of a homomolecular synthon co-crystal allowing investigation of the component dimers free of strong interaction with surrounding molecules. The ambient pressure structure remains stable but investigation showed that the saccharin dimer sits in a pocket made by indomethacin allowing the dimer to lie further apart than in the pure compound.;To follow, a structural compression study of the single component saccharin using synchrotron radiation lead to the structural characterisation of the first new polymorph of saccharin. The hydrogen bonding pattern of the new phase remains consistent however Pixel calculations revealed that the biggest difference in packing arises due to the reduction of an interlayer distance.;To further explore multicomponent systems, two stoichiometric ratios of benzoic acid and isonicotinamide (2:1 & 1:1) were investigated. The rate of compression in these systems are almost identical despite the different molecular packing in each of the stoichiometric ratios. Through the investigation of materials in these initial chapters, the rate of compression in particular supramolecular synthons, e.g. amide-dimers, is demonstrated to be consistent despite the difference in the molecular make-up of the materials under study and their packing arrangements.;Lastly, a data-driven approach was applied in directing the discovery of a new solid-state entity. Following previous failed attempts, machine learning was employed to direct experimental co-crystallisations which led to a new co-crystal of Artemisinin and 1-Napthol. Pixel calculations revealed that the largest contribution to crystal stabilisation comes from dispersion energy and enabled the identification of dominant intermolecular interactions in the crystal structures.This thesis illustrates the use of high pressure crystallography techniques for the discovery and investigation of solid-state forms and probes the relationship between molecular structure and compression of both single and multicomponent systems. As well as investigating a data-driven approach to directing experimental co-crystallisation attempts.;Single crystal X-ray diffraction techniques are a highlight in all areas of this study, as well as computational approaches which were used in the evaluation of the interactions of small molecule systems. Data-mining of the Cambridge Structural Database made the comparison of the compression studies richer.;The pharmaceutical co-crystal, indomethacin and saccharin was analysed with respect to increasing pressure. The system is an example of a homomolecular synthon co-crystal allowing investigation of the component dimers free of strong interaction with surrounding molecules. The ambient pressure structure remains stable but investigation showed that the saccharin dimer sits in a pocket made by indomethacin allowing the dimer to lie further apart than in the pure compound.;To follow, a structural compression study of the single component saccharin using synchrotron radiation lead to the structural characterisation of the first new polymorph of saccharin. The hydrogen bonding pattern of the new phase remains consistent however Pixel calculations revealed that the biggest difference in packing arises due to the reduction of an interlayer distance.;To further explore multicomponent systems, two stoichiometric ratios of benzoic acid and isonicotinamide (2:1 & 1:1) were investigated. The rate of compression in these systems are almost identical despite the different molecular packing in each of the stoichiometric ratios. Through the investigation of materials in these initial chapters, the rate of compression in particular supramolecular synthons, e.g. amide-dimers, is demonstrated to be consistent despite the difference in the molecular make-up of the materials under study and their packing arrangements.;Lastly, a data-driven approach was applied in directing the discovery of a new solid-state entity. Following previous failed attempts, machine learning was employed to direct experimental co-crystallisations which led to a new co-crystal of Artemisinin and 1-Napthol. Pixel calculations revealed that the largest contribution to crystal stabilisation comes from dispersion energy and enabled the identification of dominant intermolecular interactions in the crystal structures
Conceptions of milk (and 'milking') in seventeenth-century England
No full textThis thesis examines perceptions of milk in the seventeenth century in two unique ways. Firstly, it considers milk the substance from a posthumanist standpoint that studies the perceived links between both human and animal lactation. Secondly, it examines how 'milk' was conceived of as semen and 'milking' as its ejaculation, relating this to how masculinity was both lauded and threatened in the seventeenth century.;This thesis pursues how animals and humans were believed to be interconnected through their milk, particularly focussing upon how motherhood was thought to be a trait that all lactating females shared. It then discusses how these views were endangered in the same century, reflected through an alteration of language that indicated an ongoing separation of terms and concepts that were once applied to both humans and animals.;The remainder of this thesis is given over to an analysis of sexual 'milk' and 'milking', particularly in the works of William Shakespeare, as well as Thomas Middleton and Ben Jonson. It relates this to both male and female lactation, focussing upon how seminal 'milk' and its ejaculation reflected superior and anxious notions of masculinity. Thus, it will argue that conceptions of femininity and animality cannot be escaped when discussing milk.This thesis examines perceptions of milk in the seventeenth century in two unique ways. Firstly, it considers milk the substance from a posthumanist standpoint that studies the perceived links between both human and animal lactation. Secondly, it examines how 'milk' was conceived of as semen and 'milking' as its ejaculation, relating this to how masculinity was both lauded and threatened in the seventeenth century.;This thesis pursues how animals and humans were believed to be interconnected through their milk, particularly focussing upon how motherhood was thought to be a trait that all lactating females shared. It then discusses how these views were endangered in the same century, reflected through an alteration of language that indicated an ongoing separation of terms and concepts that were once applied to both humans and animals.;The remainder of this thesis is given over to an analysis of sexual 'milk' and 'milking', particularly in the works of William Shakespeare, as well as Thomas Middleton and Ben Jonson. It relates this to both male and female lactation, focussing upon how seminal 'milk' and its ejaculation reflected superior and anxious notions of masculinity. Thus, it will argue that conceptions of femininity and animality cannot be escaped when discussing milk
Bioactive surfaces for improved coronary stent performance
Get PDFThis thesis was previously held under moratorium from 4th June 2018 until 4th June 2023Drug eluting stents (DES) are widely used to treat coronary heart disease. Although current DES generally perform well, restenosis and delayed endothelium healing still remains an issue following stent implantations. Research efforts are now focused on the development of stent coatings that address these limitations. Amongst many different materials currently being investigated as stent coatings, conducting polymers, such as polypyrrole (PPy) have particular promise. Drug-containing polypyrrole coatings can be deposited onto metal surfaces through electropolymerisation, a process that may be superior to the spray coating techniques commonly used by stent manufacturers. However, the full potential of this approach for use in stent coatings remains to be determined. An anti-inflammatory agent, Salicylate (Sa) was incorporated into PPy coatings by electropolymerisation in the present study and four key aspects of the coatings were characterised. Firstly, the surface morphology and topography of the polypyrrole/salicylate (PPy/Sa)coatings were examined using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). These methods were optimised through an initial investigation into surface topography of a limited number of existing bare metal stents (BMS) and DES. The surface roughness (RMS) ranged from 14 ± 11 nm (GazelleTM, scan size 5µm) to 182 ± 37 nm (Yukon®, scan size 5µm) with similarities noted between the DES. The surfaces roughness values of the PPy/Sa coatings were found to be within this range of roughness values.Secondly, the release of Sa from the PPy/Sa coatings was examined. Coatings produced by either galvanostatic or potentiostatic electropolymerisation were immersed in phosphate buffered saline and the release of salicylate monitored over time using UV-spectroscopy. Both polymerisation methods released a similar total mass of drug (~12 µg), with the release period ranging from 1 day for potentiostatic coatings to 3 days for galvanostatic coatings. Thirdly, the biocompatibility of the coatings was analysed by live/dead staining and LDHassay, showing porcine endothelial cells to successfully grow on both PPy/Sa coating types. Finally, the antioxidative activity of the coatings was investigated using a DPPH assay. The coatings were found to possess antioxidative activity for a period of 24 hours, an effect which was independent of salicylate release. This represents a potentially beneficial action that has not previously been demonstrated within a stent coating. By virtue of their controllable drug release properties and a novel anti-oxidant mechanism, polypyrrole surfaces warrant further development as a potential stent coating.Drug eluting stents (DES) are widely used to treat coronary heart disease. Although current DES generally perform well, restenosis and delayed endothelium healing still remains an issue following stent implantations. Research efforts are now focused on the development of stent coatings that address these limitations. Amongst many different materials currently being investigated as stent coatings, conducting polymers, such as polypyrrole (PPy) have particular promise. Drug-containing polypyrrole coatings can be deposited onto metal surfaces through electropolymerisation, a process that may be superior to the spray coating techniques commonly used by stent manufacturers. However, the full potential of this approach for use in stent coatings remains to be determined. An anti-inflammatory agent, Salicylate (Sa) was incorporated into PPy coatings by electropolymerisation in the present study and four key aspects of the coatings were characterised. Firstly, the surface morphology and topography of the polypyrrole/salicylate (PPy/Sa)coatings were examined using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). These methods were optimised through an initial investigation into surface topography of a limited number of existing bare metal stents (BMS) and DES. The surface roughness (RMS) ranged from 14 ± 11 nm (GazelleTM, scan size 5µm) to 182 ± 37 nm (Yukon®, scan size 5µm) with similarities noted between the DES. The surfaces roughness values of the PPy/Sa coatings were found to be within this range of roughness values.Secondly, the release of Sa from the PPy/Sa coatings was examined. Coatings produced by either galvanostatic or potentiostatic electropolymerisation were immersed in phosphate buffered saline and the release of salicylate monitored over time using UV-spectroscopy. Both polymerisation methods released a similar total mass of drug (~12 µg), with the release period ranging from 1 day for potentiostatic coatings to 3 days for galvanostatic coatings. Thirdly, the biocompatibility of the coatings was analysed by live/dead staining and LDHassay, showing porcine endothelial cells to successfully grow on both PPy/Sa coating types. Finally, the antioxidative activity of the coatings was investigated using a DPPH assay. The coatings were found to possess antioxidative activity for a period of 24 hours, an effect which was independent of salicylate release. This represents a potentially beneficial action that has not previously been demonstrated within a stent coating. By virtue of their controllable drug release properties and a novel anti-oxidant mechanism, polypyrrole surfaces warrant further development as a potential stent coating
IT apprenticeships in Scotland : good quality or same old problems?
No full textThis thesis will explore and examine the quality of modern apprenticeships within the IT sector. Presently, there is limited existing literature regarding apprenticeship quality in Scotland, and no academic research into the IT sector specifically. There is an ongoing change to the Scottish labour market as employers embrace digitalisation and evolving technologies. This research seeks to add to wider apprenticeship literature around the overall quality of apprenticeships and the factors that contribute towards this. From this literature, Fuller and Unwin's (2003)expansive/restrictive continuum and three specially selected elements of job quality were established as the conceptual framework. Utilising a single case study approach, data was collected from nine semi structured interviews with key apprenticeship stakeholders and two focus groups with ten apprentices. The data was gathered to address the research aim of 'exploring the quality of IT apprenticeships to assess if they can be considered 'good' quality apprenticeships or suffer from the criticisms linked to modern apprenticeships in 'non-traditional 'industries'. The research findings demonstrate the complex and subjective nature of apprenticeship quality. They also highlight various issues which affect apprenticeship quality both positively and negatively.This thesis will explore and examine the quality of modern apprenticeships within the IT sector. Presently, there is limited existing literature regarding apprenticeship quality in Scotland, and no academic research into the IT sector specifically. There is an ongoing change to the Scottish labour market as employers embrace digitalisation and evolving technologies. This research seeks to add to wider apprenticeship literature around the overall quality of apprenticeships and the factors that contribute towards this. From this literature, Fuller and Unwin's (2003)expansive/restrictive continuum and three specially selected elements of job quality were established as the conceptual framework. Utilising a single case study approach, data was collected from nine semi structured interviews with key apprenticeship stakeholders and two focus groups with ten apprentices. The data was gathered to address the research aim of 'exploring the quality of IT apprenticeships to assess if they can be considered 'good' quality apprenticeships or suffer from the criticisms linked to modern apprenticeships in 'non-traditional 'industries'. The research findings demonstrate the complex and subjective nature of apprenticeship quality. They also highlight various issues which affect apprenticeship quality both positively and negatively
Structure-property relationships and salt selection for functional organic materials
Get PDFEleven salt forms of salicylic acid were prepared, all of which contained strontium or calcium as counterions with nine of the eleven samples containing a mix of both metals which occupied the same crystallographic site. Ten of these forms were successfully characterised by single crystal diffraction, these shared the formula [Ca(1-x)Srx(C7H5O3)2(OH2)2] with x having the following values: 0, 0.041, 0.083, 0.165, 0.306, 0.529, 0.632, 0.789, 0.835 and 1.;The calcium to strontium ratios of each sample was also measured using atomic absorption spectroscopy and reported. The aqueous solubility of each sample was also measured. Systematic changes to structure and to solubility with changing metal ratio are reported.;Thirteen previously unpublished organic complexes of 4-nitrophenol (NPOH or 4-nitrophenolate NPO) were prepared and had their crystal structures elucidated.;These were: 1S2R-(+)-methylephedrine-NPO, 2-amino-3-pyridinecarboxaldehyde -NPOH, 4-acetylpyridine-NPOH, 2-aminobenzylamine-NPO, dimethylpiperidine-NPO(H2O), dipropylenetriamine-NPO, 1S2R-(+)-ephedrine-NPO(MeCN)2, ethanolamine-NPO, n-methylpyrollidine-NPO-NPOH, Rhodamine B-NPOH(MeCN)2 ,tris-2-amino-ethylenetriamine-NPO(H2O)2, isopropylamine-NPO(H2O) and 1,4-diaminobutane-NPO.;These 13 structures were compared to 50 structures containing NPOH or NPO found on the Cambridge Structural Database (CSD).;Hydrogen bonding and other intermolecular interactions were studied extensively in an attempt to find common interactions which could be linked to the apparent tendency for 4-nitrophenol materials to crystallise in non-centrosymmetric space groups. This included a study of packing analysis and graph set notations. Two separate isostructural groups of cocrystal of salt structures were found to share packing similarities. Potential links between non-centrosymmetric packing and hydrogen bonding, chemical type and pKa values are evaluated.Eleven salt forms of salicylic acid were prepared, all of which contained strontium or calcium as counterions with nine of the eleven samples containing a mix of both metals which occupied the same crystallographic site. Ten of these forms were successfully characterised by single crystal diffraction, these shared the formula [Ca(1-x)Srx(C7H5O3)2(OH2)2] with x having the following values: 0, 0.041, 0.083, 0.165, 0.306, 0.529, 0.632, 0.789, 0.835 and 1.;The calcium to strontium ratios of each sample was also measured using atomic absorption spectroscopy and reported. The aqueous solubility of each sample was also measured. Systematic changes to structure and to solubility with changing metal ratio are reported.;Thirteen previously unpublished organic complexes of 4-nitrophenol (NPOH or 4-nitrophenolate NPO) were prepared and had their crystal structures elucidated.;These were: 1S2R-(+)-methylephedrine-NPO, 2-amino-3-pyridinecarboxaldehyde -NPOH, 4-acetylpyridine-NPOH, 2-aminobenzylamine-NPO, dimethylpiperidine-NPO(H2O), dipropylenetriamine-NPO, 1S2R-(+)-ephedrine-NPO(MeCN)2, ethanolamine-NPO, n-methylpyrollidine-NPO-NPOH, Rhodamine B-NPOH(MeCN)2 ,tris-2-amino-ethylenetriamine-NPO(H2O)2, isopropylamine-NPO(H2O) and 1,4-diaminobutane-NPO.;These 13 structures were compared to 50 structures containing NPOH or NPO found on the Cambridge Structural Database (CSD).;Hydrogen bonding and other intermolecular interactions were studied extensively in an attempt to find common interactions which could be linked to the apparent tendency for 4-nitrophenol materials to crystallise in non-centrosymmetric space groups. This included a study of packing analysis and graph set notations. Two separate isostructural groups of cocrystal of salt structures were found to share packing similarities. Potential links between non-centrosymmetric packing and hydrogen bonding, chemical type and pKa values are evaluated
Electrostatic precipitation of fine airborne particles and biological decontamination : efficiency and energy consumption tendencies
Get PDFParticulate matter poses serious health problems to human beings. Electrostatic precipitation, which utilises high voltage energised plasma, has been proved to be one of the most effective and efficient method to solve the problems caused by particulate matter. However, there are issues of the electrostatic precipitation which have been noticed. One of the most critical issues of the electrostatic precipitation is the efficiency. There are two meanings of the efficiency, which are particulate matter precipitation efficiency and energy using efficiency.;There are reports that the electrostatic precipitation in certain cases is with low particulate matter precipitation efficiency and high energy consumption. Therefore, the first objective of this thesis is to solve the problems of low efficiency and high energy consumption. The first solution is to design and develop a novel system with unique topology, which is the hypodermic needle-mesh system in this thesis. The second solution is to make suggestions on the electrostatic precipitation system which has already been widely used (coaxial topology).;The two suggestions are the increase of electrostatic precipitation stage and the increase humidity of the inner environment. Both solutions have been compared with typical state-of-the-art researches and both solutions have been proven to be with high precipitation efficiency and with low energy consumption.;In addition to the electrostatic precipitation effect by plasma, the effect of biological decontamination by plasma has also been investigated. A biological decontamination system has been designed and developed. The objective of the research is not only to control particulate matter, but also to decontaminate pathogenic microbes.;Finally, a model which is able to simulate particle dynamics in electrostatic precipitators and calculate particle collection efficiency has been designed. The model has considered the parameters which are neglected by classical approaches and is more accurate. The particle dynamics characteristics and the particle collection efficiency influenced by the dynamics can be used to make suggestions to the electrostatic precipitators in practice.Particulate matter poses serious health problems to human beings. Electrostatic precipitation, which utilises high voltage energised plasma, has been proved to be one of the most effective and efficient method to solve the problems caused by particulate matter. However, there are issues of the electrostatic precipitation which have been noticed. One of the most critical issues of the electrostatic precipitation is the efficiency. There are two meanings of the efficiency, which are particulate matter precipitation efficiency and energy using efficiency.;There are reports that the electrostatic precipitation in certain cases is with low particulate matter precipitation efficiency and high energy consumption. Therefore, the first objective of this thesis is to solve the problems of low efficiency and high energy consumption. The first solution is to design and develop a novel system with unique topology, which is the hypodermic needle-mesh system in this thesis. The second solution is to make suggestions on the electrostatic precipitation system which has already been widely used (coaxial topology).;The two suggestions are the increase of electrostatic precipitation stage and the increase humidity of the inner environment. Both solutions have been compared with typical state-of-the-art researches and both solutions have been proven to be with high precipitation efficiency and with low energy consumption.;In addition to the electrostatic precipitation effect by plasma, the effect of biological decontamination by plasma has also been investigated. A biological decontamination system has been designed and developed. The objective of the research is not only to control particulate matter, but also to decontaminate pathogenic microbes.;Finally, a model which is able to simulate particle dynamics in electrostatic precipitators and calculate particle collection efficiency has been designed. The model has considered the parameters which are neglected by classical approaches and is more accurate. The particle dynamics characteristics and the particle collection efficiency influenced by the dynamics can be used to make suggestions to the electrostatic precipitators in practice
Numerical Optimisation of low alloy steel friction stir welding
Get PDFThe development of advanced joining processes such as friction stir welding (FSW) is necessary to maintain manufacturing competitiveness in any industrial nation. Substantial research that has been carried out on FSW of aluminium alloys has demonstrated considerable benefits; this has led to greater interest in FSW of steel and other high melting temperature alloys. In this context, numerical modelling can provide cost-effective development of steel FSW. This thesis is focussed on a three dimensional thermomechanical simulation of FSW in Abaqus/Explicit, featuring low alloy steel with previously generated experimental temperature dependant properties. Unlike any previous numerical research in which either the workpiece is assumed as a highly viscous body or the tool is modelled as a moving heating source, the Coupled Eulerian Lagrangian approach has been innovatively applied to model the FSW process on steel. All stages of FSW (plunge, dwell and traverse) have been modelled for slow and fast process parameters and their results compared with previous experimental work on the same grade of steel. Various numerical results, such as temperature distribution, plastic strain, reaction forces, material flow and flash generation, were analysed for both models. In each model, the weld shape and weld surface flash were found to be in exceptionally close alignment with previous experimental results.To optimise the FSW process and reduce the forces on the tool, laser assisted FSW (LAFSW) on steel has been numerically developed and analysed as a viable process amendment. LAFSW increased the traverse speed from 500 mm/min to 1500 mm/min, significantly higher than conventional steel FSW. The application of laser assistance with a distance of 20 mm from the rotating tool reduced the reaction forces on the tool probe tip up to 55% as compared to standard FSW during the plunge stage.The development of advanced joining processes such as friction stir welding (FSW) is necessary to maintain manufacturing competitiveness in any industrial nation. Substantial research that has been carried out on FSW of aluminium alloys has demonstrated considerable benefits; this has led to greater interest in FSW of steel and other high melting temperature alloys. In this context, numerical modelling can provide cost-effective development of steel FSW. This thesis is focussed on a three dimensional thermomechanical simulation of FSW in Abaqus/Explicit, featuring low alloy steel with previously generated experimental temperature dependant properties. Unlike any previous numerical research in which either the workpiece is assumed as a highly viscous body or the tool is modelled as a moving heating source, the Coupled Eulerian Lagrangian approach has been innovatively applied to model the FSW process on steel. All stages of FSW (plunge, dwell and traverse) have been modelled for slow and fast process parameters and their results compared with previous experimental work on the same grade of steel. Various numerical results, such as temperature distribution, plastic strain, reaction forces, material flow and flash generation, were analysed for both models. In each model, the weld shape and weld surface flash were found to be in exceptionally close alignment with previous experimental results.To optimise the FSW process and reduce the forces on the tool, laser assisted FSW (LAFSW) on steel has been numerically developed and analysed as a viable process amendment. LAFSW increased the traverse speed from 500 mm/min to 1500 mm/min, significantly higher than conventional steel FSW. The application of laser assistance with a distance of 20 mm from the rotating tool reduced the reaction forces on the tool probe tip up to 55% as compared to standard FSW during the plunge stage
Survival risk and liquidity risk involving hedge fund
No full textThe purpose of this thesis is to examine the predictability of hedge fund performance by using survival risk and liquidity risk analyses. Institutional investors are interested in long-run investments in the hedge fund industry and the high liquidation rate in the hedge fund industry brings significant risk to their investors. This research not only estimates the relationship between hedge fund characteristics and failure risk, but also examines the relationship between hedge fund survival risk, liquidity risk and their relative performance. This thesis is relevant to both researchers and practitioners in exploring a tangible analysis of hedge fund performance.;The sample of this study derives from the TASS database from January 1984 to July 2014. The sampling time period covers the Asian crisis in 1997, the Russian crisis in 1998, the collapse of the sub-prime mortgage crisis in the US in 2007 and the subsequent credit crunch. The original database contains 14,031 hedge funds for this period, of which 6,505 are live funds and 7,526 are liquidated funds. The first empirical chapter estimates the predictability of hedge fund performance by use of a semi-parametric procedure.;The results suggest that hedge fund monthly returns are predictable with proper identification of fund failure. The identification of fund failure can extract funds that are liquidated because of poor performance. The empirical evidence suggests that fund failure risk has strong explanatory power regarding hedge fund performance;The second empirical chapter estimates the predictability of hedge fund performance by using investor-induced liquidity. It suggests that hedge fund liquidity risk derived from investors is an important factor of hedge fund performance analysis. The result also confirms that investor-induced liquidity in the more recent past has more explanatory power regarding its post-performance. Moreover, incubation bias could influence the predictability of hedge fund performance significantly. The result from fund performance shows that the fire sale problem was more significant in the recent financial crisis period but not significant in a normal period.;The last empirical chapter investigates the predictability of hedge fund performance by using a combined prediction model. The result indicates that a model combining survival risk and liquidity risk exhibits more detail and performs better than using a prediction model with a single dimension. The result also indicates that incubation bias influences the predictability of hedge fund performance. Moreover, more recent data influences the predictability of hedge fund performance more significantly.;On the other hand, long distance past data can provide a more significant result in estimation of covariates by using the Cox proportional hazard model. It is helpful to investigate the interactions between the risk of hedge fund characteristics and their performance practically.The purpose of this thesis is to examine the predictability of hedge fund performance by using survival risk and liquidity risk analyses. Institutional investors are interested in long-run investments in the hedge fund industry and the high liquidation rate in the hedge fund industry brings significant risk to their investors. This research not only estimates the relationship between hedge fund characteristics and failure risk, but also examines the relationship between hedge fund survival risk, liquidity risk and their relative performance. This thesis is relevant to both researchers and practitioners in exploring a tangible analysis of hedge fund performance.;The sample of this study derives from the TASS database from January 1984 to July 2014. The sampling time period covers the Asian crisis in 1997, the Russian crisis in 1998, the collapse of the sub-prime mortgage crisis in the US in 2007 and the subsequent credit crunch. The original database contains 14,031 hedge funds for this period, of which 6,505 are live funds and 7,526 are liquidated funds. The first empirical chapter estimates the predictability of hedge fund performance by use of a semi-parametric procedure.;The results suggest that hedge fund monthly returns are predictable with proper identification of fund failure. The identification of fund failure can extract funds that are liquidated because of poor performance. The empirical evidence suggests that fund failure risk has strong explanatory power regarding hedge fund performance;The second empirical chapter estimates the predictability of hedge fund performance by using investor-induced liquidity. It suggests that hedge fund liquidity risk derived from investors is an important factor of hedge fund performance analysis. The result also confirms that investor-induced liquidity in the more recent past has more explanatory power regarding its post-performance. Moreover, incubation bias could influence the predictability of hedge fund performance significantly. The result from fund performance shows that the fire sale problem was more significant in the recent financial crisis period but not significant in a normal period.;The last empirical chapter investigates the predictability of hedge fund performance by using a combined prediction model. The result indicates that a model combining survival risk and liquidity risk exhibits more detail and performs better than using a prediction model with a single dimension. The result also indicates that incubation bias influences the predictability of hedge fund performance. Moreover, more recent data influences the predictability of hedge fund performance more significantly.;On the other hand, long distance past data can provide a more significant result in estimation of covariates by using the Cox proportional hazard model. It is helpful to investigate the interactions between the risk of hedge fund characteristics and their performance practically
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