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Generation, acceleration and measurement of attosecond electron beams from laser-plasma accelerators
No full textStrathclyde theses - ask staff. Thesis no. : T14888Accelerator-based light sources are extremely useful machines for investigating matter on a microscopic level, yet their capability for time-resolved research is limited by the femtosecond-scale duration of their radiation pulses. Attosecond beams could enhance these capacities enabling the measurement of most outer shell electron dynamics in molecular and atomic systems. However,one of the main challenges in this direction remains the generation of attosecond-scale electron bunches which can be used for ultrashort radiation generation or as probes themselves.The research presented in this thesis tackles this issue from two angles. First, mechanisms for ultrashort electron beam generation and acceleration in laser wakefield accelerators - as promising,compact accelerator systems - are investigated through particle-in-cell simulations. Bothan optimised electron plasma injector, using upramp-assisted self-injection, and an external injection setup with the plasma stage as an energy booster to a conventionally accelerated beam are capable of providing electron bunches of few hundred attoseconds duration. The externally injected beams are found to be limited in duration, but preserve well the initial high beam quality for energies up to gigaelectronvolts, while in self-injection high beam currents and ultrashort duration can be achieved, yet at some cost to beam quality and stability. As a second research branch, longitudinal beam profile diagnostics with sub-femtosecond resolution are examined as possible means for measuring such ultrashort electron beams. A first proof-of-principle experiment of a novel streaking device is presented and compared with measurements with anX-band radiofrequency deflecting cavity. Additional computational and theoretical studies provide insights into the possibilities and challenges to apply this new diagnostic technique to sub-femtosecond electron beams from conventional and novel accelerators.Accelerator-based light sources are extremely useful machines for investigating matter on a microscopic level, yet their capability for time-resolved research is limited by the femtosecond-scale duration of their radiation pulses. Attosecond beams could enhance these capacities enabling the measurement of most outer shell electron dynamics in molecular and atomic systems. However,one of the main challenges in this direction remains the generation of attosecond-scale electron bunches which can be used for ultrashort radiation generation or as probes themselves.The research presented in this thesis tackles this issue from two angles. First, mechanisms for ultrashort electron beam generation and acceleration in laser wakefield accelerators - as promising,compact accelerator systems - are investigated through particle-in-cell simulations. Bothan optimised electron plasma injector, using upramp-assisted self-injection, and an external injection setup with the plasma stage as an energy booster to a conventionally accelerated beam are capable of providing electron bunches of few hundred attoseconds duration. The externally injected beams are found to be limited in duration, but preserve well the initial high beam quality for energies up to gigaelectronvolts, while in self-injection high beam currents and ultrashort duration can be achieved, yet at some cost to beam quality and stability. As a second research branch, longitudinal beam profile diagnostics with sub-femtosecond resolution are examined as possible means for measuring such ultrashort electron beams. A first proof-of-principle experiment of a novel streaking device is presented and compared with measurements with anX-band radiofrequency deflecting cavity. Additional computational and theoretical studies provide insights into the possibilities and challenges to apply this new diagnostic technique to sub-femtosecond electron beams from conventional and novel accelerators
Study of escaping electron dynamics and applications from high-power laser-plasma interactions
Get PDFIn recent years, high intensity laser-matter interactions (> 1018 W/cm2) have been shown to produce bright, compact sources of many different particles. These include x-rays, neutrons, protons and electrons, which can be used in applications such as x-ray and electron radiography. The potential use of these sources for industrial applications is promising. However, the scalability and tuning of the sources needs to be understood at a fundamental level. This thesis reports on three aspects of the development and application of these sources; the first two discuss applications of laser-plasma interactions. Firstly, the generation, characterisation and tunability of high-energy x-rays (= 200 keV) produced by the hot-electrons generated inside a solid target for the application of x-ray radiography. The characterisation of the x-ray source is conducted using a novel scintillator based absorption spectrometer. This source of x-rays was then used to radiograph a high density test object. Secondly, a novel technique of x-ray backscatter is investigated numerically and demonstrated experimentally for the first time on a laser facility. This uses the high energy electrons generated via wakefield acceleration to probe deeper into materials than traditional backscatter techniques. Finally, an investigation is reported examining the fundamental dynamics of electrons escaping from solid targets under different irradiation conditions. Experimentally, the number of escaping electrons was shown to maximise for certain laser illumination conditions; this was also explored using PIC simulations. The new results discussed in these three sections produce important new understanding of laser-driven x-ray generation and its application to penetrative probing and imaging for possible future industrial applications as well as the understanding of escaping electron dynamics.In recent years, high intensity laser-matter interactions (> 1018 W/cm2) have been shown to produce bright, compact sources of many different particles. These include x-rays, neutrons, protons and electrons, which can be used in applications such as x-ray and electron radiography. The potential use of these sources for industrial applications is promising. However, the scalability and tuning of the sources needs to be understood at a fundamental level. This thesis reports on three aspects of the development and application of these sources; the first two discuss applications of laser-plasma interactions. Firstly, the generation, characterisation and tunability of high-energy x-rays (= 200 keV) produced by the hot-electrons generated inside a solid target for the application of x-ray radiography. The characterisation of the x-ray source is conducted using a novel scintillator based absorption spectrometer. This source of x-rays was then used to radiograph a high density test object. Secondly, a novel technique of x-ray backscatter is investigated numerically and demonstrated experimentally for the first time on a laser facility. This uses the high energy electrons generated via wakefield acceleration to probe deeper into materials than traditional backscatter techniques. Finally, an investigation is reported examining the fundamental dynamics of electrons escaping from solid targets under different irradiation conditions. Experimentally, the number of escaping electrons was shown to maximise for certain laser illumination conditions; this was also explored using PIC simulations. The new results discussed in these three sections produce important new understanding of laser-driven x-ray generation and its application to penetrative probing and imaging for possible future industrial applications as well as the understanding of escaping electron dynamics
A phenomenon of the critical factors of accounting information system (AIS) effectiveness
Get PDFThe complexity of the Government's environment provides greater challenges in making the AIS effective. Prior studies have reported many and inconsistent determinants of system effectiveness, as well as its measurement. This study intends to fill the gaps by understanding the phenomenon of the critical factors of AIS effectiveness for an on-going and stable system. This includes exploring the critical factors of AIS effectiveness and examining the factors that significantly influence the phenomenon. In addition, the condition of the identified factors is investigated based on perceived importance versus perceived performance. The effectiveness of AIS in this study is viewed from the perspective of user satisfaction. This study was conducted using multiple methods (qualitative and quantitative). The qualitative method includes group discussions, observation and semi-structured interviews. The qualitative findings were used to develop a survey questionnaire for the quantitative study on a larger scale.This study contributes to the literature by presenting a comprehensive measure of AIS effectiveness using a user satisfaction approach. In addition, the results emphasise the AIS main components that are crucial for the achievement of an effective system, which are user commitment, technology support function and teamwork. Furthermore, this study is different to earlier studies in that its findings uncover additional factors that are antecedents for the critical factors of AIS effectiveness. Moreover, the perceived importance-performance gap shows the benefit of the assessment in providing a strategic direction for management. Overall,this study has shed light on the investigated phenomenon by offering: a comprehensive measure of AIS effectiveness; the factors important in achieving an effective system; and further action to be taken by the management and the system's users on each of those factors. Thus, in addition to academic literature contributions,practitioners will also derive benefits from the findings of this study.The complexity of the Government's environment provides greater challenges in making the AIS effective. Prior studies have reported many and inconsistent determinants of system effectiveness, as well as its measurement. This study intends to fill the gaps by understanding the phenomenon of the critical factors of AIS effectiveness for an on-going and stable system. This includes exploring the critical factors of AIS effectiveness and examining the factors that significantly influence the phenomenon. In addition, the condition of the identified factors is investigated based on perceived importance versus perceived performance. The effectiveness of AIS in this study is viewed from the perspective of user satisfaction. This study was conducted using multiple methods (qualitative and quantitative). The qualitative method includes group discussions, observation and semi-structured interviews. The qualitative findings were used to develop a survey questionnaire for the quantitative study on a larger scale.This study contributes to the literature by presenting a comprehensive measure of AIS effectiveness using a user satisfaction approach. In addition, the results emphasise the AIS main components that are crucial for the achievement of an effective system, which are user commitment, technology support function and teamwork. Furthermore, this study is different to earlier studies in that its findings uncover additional factors that are antecedents for the critical factors of AIS effectiveness. Moreover, the perceived importance-performance gap shows the benefit of the assessment in providing a strategic direction for management. Overall,this study has shed light on the investigated phenomenon by offering: a comprehensive measure of AIS effectiveness; the factors important in achieving an effective system; and further action to be taken by the management and the system's users on each of those factors. Thus, in addition to academic literature contributions,practitioners will also derive benefits from the findings of this study
The influence of assistant grade nurses on the clinical development of student mental health nurses : a phenomenological study
Get PDFThere has been increased professional, public and press focus in recent years over what are perceived to be deficiencies within healthcare delivery in the UK. Government commissioned reports have highlighted suggested limitations within the attributes and preparation of nursing staff as contributing to this and have recommended integration between nurse education and the role of the nursing assistant as a remedy.;This has been done without any significant investigation of the existing interrelationship between these staff groups, a relationship that is presently considered under-researched, and which has been largely excluded from any significant investigation or recognition. As the small number of related studies available have largely focused on students training for the adult and older adult fields of nursing, so there is even less known about the contact nursing assistants have with student mental health nurses and the impact of this relationship on the students' clinical development.;To explore this phenomenon, a study was undertaken to investigate how individuals from each of the groups most closely involved with student mental health nurse clinical development; mentors, nursing assistants and the students themselves, understand how nursing assistants contribute to student nurse training within the clinical setting. This study involved an initial review of the literature relevant to this subject, a review that shaped a subsequent mixed methods study underpinned by a phenomenological ontology. Data was collected via the use of diaries and individual interviews and analysed using Interpretative Phenomenological Analysis.;Analysis of completed diaries and transcribed interviews from the nine participants identified three superordinate themes that provided recognition of key involvement of nursing assistants in the clinical development of student mental health nurses during practice placements. The nursing assistants were seen to provide guidance around complex and significant skills and interventions, and often provided this at crucial times within the students training.There has been increased professional, public and press focus in recent years over what are perceived to be deficiencies within healthcare delivery in the UK. Government commissioned reports have highlighted suggested limitations within the attributes and preparation of nursing staff as contributing to this and have recommended integration between nurse education and the role of the nursing assistant as a remedy.;This has been done without any significant investigation of the existing interrelationship between these staff groups, a relationship that is presently considered under-researched, and which has been largely excluded from any significant investigation or recognition. As the small number of related studies available have largely focused on students training for the adult and older adult fields of nursing, so there is even less known about the contact nursing assistants have with student mental health nurses and the impact of this relationship on the students' clinical development.;To explore this phenomenon, a study was undertaken to investigate how individuals from each of the groups most closely involved with student mental health nurse clinical development; mentors, nursing assistants and the students themselves, understand how nursing assistants contribute to student nurse training within the clinical setting. This study involved an initial review of the literature relevant to this subject, a review that shaped a subsequent mixed methods study underpinned by a phenomenological ontology. Data was collected via the use of diaries and individual interviews and analysed using Interpretative Phenomenological Analysis.;Analysis of completed diaries and transcribed interviews from the nine participants identified three superordinate themes that provided recognition of key involvement of nursing assistants in the clinical development of student mental health nurses during practice placements. The nursing assistants were seen to provide guidance around complex and significant skills and interventions, and often provided this at crucial times within the students training
Robotic-assisted 3D printing for bone defect reconstruction
No full textReconstruction of bone defects has always been a challenging task for the surgeons over the years. The expected goals of this kind of reconstructive surgery are not only to restore bone function but also to maintain the appearance of the human body. One of the methods to repair the defected bone is to reconstruct the missing or defective parts with artificial standard sized bone implants. In the traditional surgery, this kind of bone implants are adjusted to the requirement of most surgical procedures and are suitable for many of the patients, but might not be for all the patients. In addition, the traditional surgery might affect patient's skin by leaving visible scars, because the bone implants need to be surgically placed into the patient's body. The outcome of this kind of operation may be improved by using robot-assisted 3D printing technologies. To demonstrate the capability of robotic-assisted 3D printing for bone defect reconstruction, this MRes study has been conducted through several steps. Firstly, a 3D laser scanner was used to obtain 3D imaging data of the required site of the bone model. Secondly, with the use of 3D post-processing software, a 3D printable STL file was generated. Finally, as the last steps, the required parts were printed directly on the defected site of the original bone model by the robot-assisted 3D printer using PLA filaments. This study also provides the first academic research on the reconstruction of the bone defect by using the robotic-assisted 3D printer. This newest method links the advantages of the 3D printing in the reconstruction of bone defect with the flexibility of robotic arms to perform surgery.Reconstruction of bone defects has always been a challenging task for the surgeons over the years. The expected goals of this kind of reconstructive surgery are not only to restore bone function but also to maintain the appearance of the human body. One of the methods to repair the defected bone is to reconstruct the missing or defective parts with artificial standard sized bone implants. In the traditional surgery, this kind of bone implants are adjusted to the requirement of most surgical procedures and are suitable for many of the patients, but might not be for all the patients. In addition, the traditional surgery might affect patient's skin by leaving visible scars, because the bone implants need to be surgically placed into the patient's body. The outcome of this kind of operation may be improved by using robot-assisted 3D printing technologies. To demonstrate the capability of robotic-assisted 3D printing for bone defect reconstruction, this MRes study has been conducted through several steps. Firstly, a 3D laser scanner was used to obtain 3D imaging data of the required site of the bone model. Secondly, with the use of 3D post-processing software, a 3D printable STL file was generated. Finally, as the last steps, the required parts were printed directly on the defected site of the original bone model by the robot-assisted 3D printer using PLA filaments. This study also provides the first academic research on the reconstruction of the bone defect by using the robotic-assisted 3D printer. This newest method links the advantages of the 3D printing in the reconstruction of bone defect with the flexibility of robotic arms to perform surgery
The audiovisual translation and audience reception of satire : Extras, a case study
Get PDFIn recent years, the number of studies of the audiovisual translation (AVT) of humour and its audience reception have increased (e.g. Fuentes Luque, 2000; Chiaro, 2004, 2007; Schauffler, 2012 etc.). However, no previous studies of the audience reception of AVT have looked at specific types of humour such as satire. A more detailed look into the textual and discoursal properties of satire (Simpson, 2003) reveal that satire is significantly different from other types of humorous discourses and thus, its translation should be studied separately in order to gain insight into the translation issues that might be specific to this type of discourse. Moreover, Mason (2009: 55) notes that enquiries into reader response would be useful for translation studies. Audience reception experiments should aim at seeking evidence of inferences drawn by actual users of a text and its translation as a means to support and correct the analyst's findings. In light of these observations, this study investigates the audiovisual translation and audience reception of satirical discourse. In order to fulfil this aim, and as a case study, the British television programme (Extras, 2005, BBC Two) and its dubbed version in Spanish for Spain are analysed in the light of Simpson's (2003) model of satirical discourse. This comparative analysis is followed by an audience reception test which has been carried out in order to elicit responses from British and Spanish participants regarding their interpretations of both source and target texts. The results of the study show that recurrent aspects of satirical discourse such as culture-specific items, intertextuality and taboo topics etc. often prevent the successful 'uptake' of satirical discourse amongst the target viewers. The study also proves that the use of audience response tests is useful in order to elicit viewers' responses to elements of satirical discourse and their translations.In recent years, the number of studies of the audiovisual translation (AVT) of humour and its audience reception have increased (e.g. Fuentes Luque, 2000; Chiaro, 2004, 2007; Schauffler, 2012 etc.). However, no previous studies of the audience reception of AVT have looked at specific types of humour such as satire. A more detailed look into the textual and discoursal properties of satire (Simpson, 2003) reveal that satire is significantly different from other types of humorous discourses and thus, its translation should be studied separately in order to gain insight into the translation issues that might be specific to this type of discourse. Moreover, Mason (2009: 55) notes that enquiries into reader response would be useful for translation studies. Audience reception experiments should aim at seeking evidence of inferences drawn by actual users of a text and its translation as a means to support and correct the analyst's findings. In light of these observations, this study investigates the audiovisual translation and audience reception of satirical discourse. In order to fulfil this aim, and as a case study, the British television programme (Extras, 2005, BBC Two) and its dubbed version in Spanish for Spain are analysed in the light of Simpson's (2003) model of satirical discourse. This comparative analysis is followed by an audience reception test which has been carried out in order to elicit responses from British and Spanish participants regarding their interpretations of both source and target texts. The results of the study show that recurrent aspects of satirical discourse such as culture-specific items, intertextuality and taboo topics etc. often prevent the successful 'uptake' of satirical discourse amongst the target viewers. The study also proves that the use of audience response tests is useful in order to elicit viewers' responses to elements of satirical discourse and their translations
Design, microfabrication and characterisation of Photonic Integrated Circuits
No full textThis doctoral dissertation deals with the design, fabrication and characterization of state-of-the-art Photonic Integrated Circuits (PICs) for non-linear applications. Silicon PICs is a technology mainly used for application in telecommunications and quantum optics. The strong third order non-linearity of silicon makes it also attractive for non-linear PIC design. In FWM applications, SOI technology can be used not only for non-linear generation but also to fabricate photonic filters to remove the residual pump. This thesis deals with three requirements for the realisation of on-chip FWM optical devices, the dual polarisation rejection of the pump on-chip and the integration and stabilisation of the FWM source and optical filter. In this work two of the most used SOI photonic integrated filters, ring resonators and Bragg gratings, are presented. These devices present two different solutions for high extinction({acute}{89}{88} 60 dB) dual polarisation filtering. An integrated structure of non-linear source and filter is presented. The device used for non-linear generation is then monolithically integrated with a novel ring resonators cascade filter technology. FWM experiments were carried out obtaining an on chip pump high dual polarisation extinction of 62 dB with a low insertion loss for the propagating signal and idler of only 1.8 dB.The realisation of a microprocessor feedback loop stabilisation system integrated with SOI non-linear structures is also demonstrated. The system is based on a local thermal heater element on-chip used to stabilise the PICs against thermal refractive index variations. Using this method, a silicon {cedil}{9D}{9C}{8B}-phase shifted grating with a cavity Q-factor of 40k is demonstrated to operate over an ambient temperature detuning range of 40 oC and injection wavelength range of 1.5 nm, nearly 3 orders of magnitude greater than the resonant cavity line width. The last part of this work is dedicated to the description of a custom made laser photolitography system for rapid prototyping of PIC designs, a tool designed to overcome the costs of the typical lithography systems and drastically decrease the time required for multiple micro-fabrications. The hardware and the software created for this tool are presented together with the first results on the fabrication of SU-8 Photoresist (SU {acute}{88}{92} 8) on Silicon Dioxide (SiO2) waveguides, bends, Mach Zehnder interferometers and ring resonators.This doctoral dissertation deals with the design, fabrication and characterization of state-of-the-art Photonic Integrated Circuits (PICs) for non-linear applications. Silicon PICs is a technology mainly used for application in telecommunications and quantum optics. The strong third order non-linearity of silicon makes it also attractive for non-linear PIC design. In FWM applications, SOI technology can be used not only for non-linear generation but also to fabricate photonic filters to remove the residual pump. This thesis deals with three requirements for the realisation of on-chip FWM optical devices, the dual polarisation rejection of the pump on-chip and the integration and stabilisation of the FWM source and optical filter. In this work two of the most used SOI photonic integrated filters, ring resonators and Bragg gratings, are presented. These devices present two different solutions for high extinction({acute}{89}{88} 60 dB) dual polarisation filtering. An integrated structure of non-linear source and filter is presented. The device used for non-linear generation is then monolithically integrated with a novel ring resonators cascade filter technology. FWM experiments were carried out obtaining an on chip pump high dual polarisation extinction of 62 dB with a low insertion loss for the propagating signal and idler of only 1.8 dB.The realisation of a microprocessor feedback loop stabilisation system integrated with SOI non-linear structures is also demonstrated. The system is based on a local thermal heater element on-chip used to stabilise the PICs against thermal refractive index variations. Using this method, a silicon {cedil}{9D}{9C}{8B}-phase shifted grating with a cavity Q-factor of 40k is demonstrated to operate over an ambient temperature detuning range of 40 oC and injection wavelength range of 1.5 nm, nearly 3 orders of magnitude greater than the resonant cavity line width. The last part of this work is dedicated to the description of a custom made laser photolitography system for rapid prototyping of PIC designs, a tool designed to overcome the costs of the typical lithography systems and drastically decrease the time required for multiple micro-fabrications. The hardware and the software created for this tool are presented together with the first results on the fabrication of SU-8 Photoresist (SU {acute}{88}{92} 8) on Silicon Dioxide (SiO2) waveguides, bends, Mach Zehnder interferometers and ring resonators
The classical simulation of noisy quantum computers : a polyhedral approach
Get PDFIn this thesis we explored the consequences of considering generalised non-quantum notions of entanglement in the classical simulation of noisy quantum computers where the available measurements are restricted. Such noise rates serve as upper bounds to fault tolerance thresholds. These measurement restrictions come about either through imperfection, and/or by design to some limited set. By considering sets of operators that return positive measurement outcome probabilities for the restricted measurements, one can construct new single particle state spaces containing quantum and non-quantum operators. These state spaces can then be used with a modified version of Harrow and Nielsen's classical simulation algorithm to efficiently simulate noisy quantum computers that are incapable of generating generalised entanglement with respect to the new state spaces. Through this approach we developed alternative methods of classical simulation, strongly connected to the study of non-local correlations, in that we constructed noisy quantum computers capable of performing non-Clifford operations and could generate some forms of multiparty quantum entanglement, but were classical in that they could be efficiently classically simulated and could not generate non-local statistics. We focused on magic state quantum computers (that are limited to only Pauli measurements), with ideal local gates, but noisy control-Pauli Z gates, and calculated the noise needed to ensure the control-Z gates became incapable of generating generalised entanglment for a variety of noise models and state space choice, with the aim of finding an optimal single particle state space requiring the least noise to remove the generalised entanglement. The state spaces were required to always return valid measurement probabilities, this meant they also had had to have octahedral symmetry to ensure local gates did not take states outside the state space. While we able to find to the optimal choice for highly imperfect measurements, were we unable to find the optimal in all cases. Our best candidate state space required less joint depolarising noise at [approximately equal to] 56% in comparison to noise levels of [approximately equal to] 67% required if the algorithm used quantum notions of separability. This suggests that generalised entanglement may offer more insight than quantum entanglement when discussing the power of Clifford operation based quantum computers.In this thesis we explored the consequences of considering generalised non-quantum notions of entanglement in the classical simulation of noisy quantum computers where the available measurements are restricted. Such noise rates serve as upper bounds to fault tolerance thresholds. These measurement restrictions come about either through imperfection, and/or by design to some limited set. By considering sets of operators that return positive measurement outcome probabilities for the restricted measurements, one can construct new single particle state spaces containing quantum and non-quantum operators. These state spaces can then be used with a modified version of Harrow and Nielsen's classical simulation algorithm to efficiently simulate noisy quantum computers that are incapable of generating generalised entanglement with respect to the new state spaces. Through this approach we developed alternative methods of classical simulation, strongly connected to the study of non-local correlations, in that we constructed noisy quantum computers capable of performing non-Clifford operations and could generate some forms of multiparty quantum entanglement, but were classical in that they could be efficiently classically simulated and could not generate non-local statistics. We focused on magic state quantum computers (that are limited to only Pauli measurements), with ideal local gates, but noisy control-Pauli Z gates, and calculated the noise needed to ensure the control-Z gates became incapable of generating generalised entanglment for a variety of noise models and state space choice, with the aim of finding an optimal single particle state space requiring the least noise to remove the generalised entanglement. The state spaces were required to always return valid measurement probabilities, this meant they also had had to have octahedral symmetry to ensure local gates did not take states outside the state space. While we able to find to the optimal choice for highly imperfect measurements, were we unable to find the optimal in all cases. Our best candidate state space required less joint depolarising noise at [approximately equal to] 56% in comparison to noise levels of [approximately equal to] 67% required if the algorithm used quantum notions of separability. This suggests that generalised entanglement may offer more insight than quantum entanglement when discussing the power of Clifford operation based quantum computers
Raman spectroscopic techniques for the detection of malaria parasite infection
Get PDFRaman spectroscopy and its analogues, surface enhanced (resonance) Raman scattering (SERS and SERRS) have been widely applied in malaria research to target early diagnosis of malaria infection in blood or plasma samples primarily via the identification of the infection specific biomarker hemozoin. However, the capability of Raman spectroscopy to contribute to tackling other areas of malaria research is not as thoroughly investigated. In this work two such areas were studied. The first looked to utilise Raman spectroscopy to differentiate malaria parasite infected tissue from non-infected and the second investigated coupling portable Raman with malaria diagnostic tests to improve detection levels.Research commenced by investigating the potential of Raman spectroscopy to detect tissue burden within malaria infected samples. Sequestration of parasite infected red blood cells in the vascular endothelium is associated with features of severe malaria pathology such as cerebral malaria. Currently, there is difficulty in assessing the presence of parasites sequestered within tissue during the progression of the infection, with many reported studies carried out post-mortem. Raman imaging coupled with chemometric analysis showed very clear separation of malaria infected mice spleen sections from non-infected, with an associated increase in concentration of heme-based Raman vibrations within the infected data set. An in-vivo mouse study also highlighted the ability of Raman spectroscopy to gain biological information from whole organs. These results demonstrated that Raman spectroscopy can be used to easily discriminate the subtle changes in tissue burden upon malarial infection within tissue sections.Finally, the coupling of rapid diagnostic tests with a handheld portable Raman spectrometer for the detection of HRP-II malaria biomarker via SERRS was investigated. By applying a 3D-microfluidic paper-based device in a sandwich assay format, SERRS detection gave a theoretical LoD of 1.68 ng/mL HRP-II which converted to ~22 parasites/μL (~0.00044 % parasitemia). This detection limit of infection density was lower than what is typically capable of a technician analysing a blood smear by light microscopy (~100 parasites/μL, 0.002 % parasitemia), which is a current gold standard detection method. The results displayed the advantages of high sensitivity and specificity gained from SERRS and as it was conducted on a portable Ramanspectrometer it has the potential to be implemented as a point-of-care method. This coupling could be applied to enhance the detection capabilities of the already widely applied rapid diagnostic tests. The possibility of being able to reliably detect lower density parasitemia with this SERRS-3D-μPAD could also allow positive malaria identification in asymptomatic individuals.Raman spectroscopy and its analogues, surface enhanced (resonance) Raman scattering (SERS and SERRS) have been widely applied in malaria research to target early diagnosis of malaria infection in blood or plasma samples primarily via the identification of the infection specific biomarker hemozoin. However, the capability of Raman spectroscopy to contribute to tackling other areas of malaria research is not as thoroughly investigated. In this work two such areas were studied. The first looked to utilise Raman spectroscopy to differentiate malaria parasite infected tissue from non-infected and the second investigated coupling portable Raman with malaria diagnostic tests to improve detection levels.Research commenced by investigating the potential of Raman spectroscopy to detect tissue burden within malaria infected samples. Sequestration of parasite infected red blood cells in the vascular endothelium is associated with features of severe malaria pathology such as cerebral malaria. Currently, there is difficulty in assessing the presence of parasites sequestered within tissue during the progression of the infection, with many reported studies carried out post-mortem. Raman imaging coupled with chemometric analysis showed very clear separation of malaria infected mice spleen sections from non-infected, with an associated increase in concentration of heme-based Raman vibrations within the infected data set. An in-vivo mouse study also highlighted the ability of Raman spectroscopy to gain biological information from whole organs. These results demonstrated that Raman spectroscopy can be used to easily discriminate the subtle changes in tissue burden upon malarial infection within tissue sections.Finally, the coupling of rapid diagnostic tests with a handheld portable Raman spectrometer for the detection of HRP-II malaria biomarker via SERRS was investigated. By applying a 3D-microfluidic paper-based device in a sandwich assay format, SERRS detection gave a theoretical LoD of 1.68 ng/mL HRP-II which converted to ~22 parasites/μL (~0.00044 % parasitemia). This detection limit of infection density was lower than what is typically capable of a technician analysing a blood smear by light microscopy (~100 parasites/μL, 0.002 % parasitemia), which is a current gold standard detection method. The results displayed the advantages of high sensitivity and specificity gained from SERRS and as it was conducted on a portable Ramanspectrometer it has the potential to be implemented as a point-of-care method. This coupling could be applied to enhance the detection capabilities of the already widely applied rapid diagnostic tests. The possibility of being able to reliably detect lower density parasitemia with this SERRS-3D-μPAD could also allow positive malaria identification in asymptomatic individuals
Effect of incremental equal channel angular pressing (I-ECAP) on the microstructural characteristics and mechanical behaviour of commercially pure titanium
Get PDFOwing to its high specific strength, low density, outstanding corrosion resistance and excellent bio-compatibility titanium and its alloys are a material of choice in many aerospace, military, chemical and biomedical applications. Ti-6Al-4V is the most widely used alloy for medical device applications such as in total replacement implants, where higher strength characteristics are generally a requirement. However, research has suggested that alloying elements such as aluminium and vanadium present in that alloy can be toxic in the long term and are therefore undesirable for full bio-integration. Commercially pure titanium (CP-Ti) has superior biocompatibility but it lacks the strength required for most load bearing implants. One viable solution is to abandon the use of alloying elements and to improve the mechanical strength and performance of CP-Ti by nano-structuring or grain refinement.;Severe plastic deformation (SPD) is an established method for introducing extreme grain refinement in metals. The technique imparts high plastic strain to the material without significantly changing the sample dimensions and is capable of achieving ultrafine grain (UFG) structure in metals. UFG materials are characterized by an average grain size of <1 μm and with mostly high angle grain boundaries. These materials exhibit exceptional improvements in strength, superplastic behaviour and in case for titanium, improved corrosion resistance and enhanced biocompatibility. Among the various available SPD methods, equal channel angular pressing (ECAP) is the most widely used method for obtaining bulk UFG materials. However, ECAP (in its classical form) suffers from low productivity and is not a practical option for commercialization.;Therefore, lately the interest is in the development of continuous SPD techniques, capable of processing very long or continuous billets for use in commercial applications. Incremental ECAP (I-ECAP) developed at the University of Strathclyde, offers such possibility. This promising technique has a strong potential of obtaining the much-needed high strength CP-Ti for biomedical implants on an industrial scale. The aim of the present research work is to investigate the feasibility of the I-ECAP process in improving the mechanical performance of CP-Ti by refining its grain structure.;However, before processing CP-Ti on the I-ECAP experimental rig, it was necessary to eliminate the some existing limitations of the rig and improve the overall process efficiency. Major upgrades and enhancements were implemented as part of the present work. These include: automation of material feeding system, elevated temperature capability, press controller upgrade, data acquisition and process control during experiments. Moreover, finite element analysis was performed to optimize the tooling geometry by studying the billet deformation behaviour and subsequently new I-ECAP dies were designed and manufactured suitable for processing CP-Ti billets.;Using the considerably improved I-ECAP experimental facility, CP-Ti billets were subjected to multiple passes of the I-ECAP process at elevated temperatures. To investigate the effect of different levels of induced shear strain per pass, billets were processed using two separate dies with channel intersection angles of 120 and 90°. Microstructural evolution and textural development in the material was tracked and examined using high-resolution electron backscatter diffraction (EBSD) technique. Twinning and continuous dynamic recrystallization (CDRX) have been observed to act as a grain refinement mechanism during subsequent passes of I-ECAP. Analysis of the microstructure shows that UFG structure was successfully obtained with mostly high angle grain boundaries (HAGB) in the processed billets using the two dies.;Room temperature tensile tests carried out before and after processing show significant increase in strength with some loss in ductility in the processed material. The yield strength and ultimate tensile strength (UTS) of the material after I-ECAP processing using the die angle of 120° was increased by 81% and 25%, respectively. The material processed using the die angle of 90° exhibits an even higher increase in yield strength and UTS i.e. 118% and 33%, respectively.;Compression tests conducted at different strain rates at room temperature show increase in strength with a three stage hardening behaviour, though the severely deformed UFG material suffers a loss in its strain hardening ability. Detailed microhardness measurements also show the increase in hardness after processing with a reasonable level of homogeneity. Finally, workability characteristics of UFG titanium is determined by compression testing at room and warm temperature conditions (400 to 600 °C). The work has successfully demonstrated that I-ECAP process is effective in improving the mechanical performance of titanium and has a potential for commercialization.Owing to its high specific strength, low density, outstanding corrosion resistance and excellent bio-compatibility titanium and its alloys are a material of choice in many aerospace, military, chemical and biomedical applications. Ti-6Al-4V is the most widely used alloy for medical device applications such as in total replacement implants, where higher strength characteristics are generally a requirement. However, research has suggested that alloying elements such as aluminium and vanadium present in that alloy can be toxic in the long term and are therefore undesirable for full bio-integration. Commercially pure titanium (CP-Ti) has superior biocompatibility but it lacks the strength required for most load bearing implants. One viable solution is to abandon the use of alloying elements and to improve the mechanical strength and performance of CP-Ti by nano-structuring or grain refinement.;Severe plastic deformation (SPD) is an established method for introducing extreme grain refinement in metals. The technique imparts high plastic strain to the material without significantly changing the sample dimensions and is capable of achieving ultrafine grain (UFG) structure in metals. UFG materials are characterized by an average grain size of <1 μm and with mostly high angle grain boundaries. These materials exhibit exceptional improvements in strength, superplastic behaviour and in case for titanium, improved corrosion resistance and enhanced biocompatibility. Among the various available SPD methods, equal channel angular pressing (ECAP) is the most widely used method for obtaining bulk UFG materials. However, ECAP (in its classical form) suffers from low productivity and is not a practical option for commercialization.;Therefore, lately the interest is in the development of continuous SPD techniques, capable of processing very long or continuous billets for use in commercial applications. Incremental ECAP (I-ECAP) developed at the University of Strathclyde, offers such possibility. This promising technique has a strong potential of obtaining the much-needed high strength CP-Ti for biomedical implants on an industrial scale. The aim of the present research work is to investigate the feasibility of the I-ECAP process in improving the mechanical performance of CP-Ti by refining its grain structure.;However, before processing CP-Ti on the I-ECAP experimental rig, it was necessary to eliminate the some existing limitations of the rig and improve the overall process efficiency. Major upgrades and enhancements were implemented as part of the present work. These include: automation of material feeding system, elevated temperature capability, press controller upgrade, data acquisition and process control during experiments. Moreover, finite element analysis was performed to optimize the tooling geometry by studying the billet deformation behaviour and subsequently new I-ECAP dies were designed and manufactured suitable for processing CP-Ti billets.;Using the considerably improved I-ECAP experimental facility, CP-Ti billets were subjected to multiple passes of the I-ECAP process at elevated temperatures. To investigate the effect of different levels of induced shear strain per pass, billets were processed using two separate dies with channel intersection angles of 120 and 90°. Microstructural evolution and textural development in the material was tracked and examined using high-resolution electron backscatter diffraction (EBSD) technique. Twinning and continuous dynamic recrystallization (CDRX) have been observed to act as a grain refinement mechanism during subsequent passes of I-ECAP. Analysis of the microstructure shows that UFG structure was successfully obtained with mostly high angle grain boundaries (HAGB) in the processed billets using the two dies.;Room temperature tensile tests carried out before and after processing show significant increase in strength with some loss in ductility in the processed material. The yield strength and ultimate tensile strength (UTS) of the material after I-ECAP processing using the die angle of 120° was increased by 81% and 25%, respectively. The material processed using the die angle of 90° exhibits an even higher increase in yield strength and UTS i.e. 118% and 33%, respectively.;Compression tests conducted at different strain rates at room temperature show increase in strength with a three stage hardening behaviour, though the severely deformed UFG material suffers a loss in its strain hardening ability. Detailed microhardness measurements also show the increase in hardness after processing with a reasonable level of homogeneity. Finally, workability characteristics of UFG titanium is determined by compression testing at room and warm temperature conditions (400 to 600 °C). The work has successfully demonstrated that I-ECAP process is effective in improving the mechanical performance of titanium and has a potential for commercialization
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