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Surface Modification of PDMS Films through the Addition of Amphiphiles & Oils
Get PDFThere is a great deal of industrial interest in surfactant/polymer systems. In the case of fouling-release coatings, there is a desire to better understand the surface modification of coatings through the restructuring or migration of amphiphilic additives. This thesis is focussed on characterisation of model coatings consisting of a poly(dimethylsiloxane) network and one of a variety of nonionic surfactants to improve understanding of the factors affecting their accumulation at polymer interfaces, and the properties they impart on the coating. This is with the intention to feed into predictive models, capable of shifting industrial formulation away from current “brute force” methods.
Concentration profiling techniques did not reveal an excess of surfactant at the air-PDMS surface. However, adsorbed surfactant was detected at the water-PDMS interface, demonstrating a seemingly reversible accumulation of surfactant. Such accumulation yielded hydrophilised PDMS surfaces, driven by a reduction in the interfacial energy.
The phase behaviour also plays a role in the surface modification behaviour. Using members of the polyethylene glycol monododecyl ether (CE) surfactant series, a positive correlation between the measured hydrophilisation profile and the incompatibility in PDMS was found. However, such rapid hydrophilisation behaviour was not observed for the incompatible commercial fluorosurfactant Fluorolink E10-H, showing that the chemistry of the hydrophobic moiety is vital in dictating the surface behaviour. This difference between the fluorosurfactant and the oxyethylene alkyl ethers in PDMS may be due to the disintegration of surfactant self-assemblies in the latter systems. The importance of phase behaviour was further suggested by PDMS doped with tetraethylene glycol monododecyl ether (CE) being affected by the inclusion of alkane oils to the system, whereas Fluorolink E10-H-doped films showed no such behaviour.
This work has shown that it is possible to mimic many aspects of of the complex behaviour of surface-active materials in silicone resin, using simple, well-defined surfactants
The Temptation of Eve in Proba's Cento Vergilianus and Milton's Paradise Lost
Get PDFRe-narrations of biblical texts have a long and complex history. In this thesis I shall seek to answer two of the questions posed by the re-narration of biblical narratives. Firstly, I shall address the issue of why Christians have felt it necessary to re-write biblical narratives. I shall then turn my attention to the more interesting issue of how these texts could be, and indeed were, received as authoritative after the closing of the biblical canon. I shall begin by providing an overview of the scholarship so far. The second chapter will then address issues of terminology, genre, and methodology. Chapter three contains the first of my case studies, an analysis of the temptation of Eve in Proba's Cento Vergilianus. This is followed in chapter four by an investigation of the concepts of authorship and scriptural authority in late antiquity, the importance of an apostolic connection for a work's authority, the development of an authorial apostolic succession, and how this led to Proba's text being received as a form of subordinate scripture. Chapter five presents my second case study, Milton's Paradise Lost and is in turn followed by chapter six, which plots the history of literary interpretation as an inspired prophetic activity from its origins in the Jewish literature of the Second Temple period, through the Early Church's authorial apostolic succession, to the re-appropriation of prophetic identity by Protestant Reformers in the fifteenth and sixteenth centuries. Finally, I offer a brief conclusion in which I draw together the various means by which biblical epics have enabled authors to compose scriptural texts after the closing of the biblical canon in order to demonstrate the continuing existence of scripture beyond the Bible, and to call for a re-evaluation of the definition of 'scripture' as a result of these findings
Optimizing Weights And Biases in MLP Using Whale Optimization Algorithm
Get PDFArtificial Neural Networks are intelligent and non-parametric mathematical models inspired by the human nervous system. They have been widely studied and applied for classification, pattern recognition and forecasting problems. The main challenge of training an Artificial Neural network is its learning process, the nonlinear nature and the unknown best set of main controlling parameters (weights and biases). When the Artificial Neural Networks are trained using the conventional training algorithm, they get caught in the local optima stagnation and slow convergence speed; this makes the stochastic optimization algorithm a definitive alternative to alleviate the drawbacks. This thesis proposes an algorithm based on the recently proposed Whale Optimization Algorithm(WOA). The algorithm has proven to solve a wide range of optimization problems and outperform existing algorithms. The successful implementation of this algorithm motivated our attempts to benchmark its performance in training feed-forward neural networks. We have taken a set of 20 datasets with different difficulty levels and tested the proposed WOA-MLP based trainer. Further, the results are verified by comparing WOA-MLP with the back propagation algorithms and six evolutionary techniques. The results have proved that the proposed trainer can outperform the current algorithms on the majority of datasets in terms of local optima avoidance and convergence speed
Synthesis of two-dimensional structures based on exfoliation of tungsten disulphide and thin film fabrication using different deposition methods
Get PDFLayered crystalline solids possess chemical bonds that are generally covalent and
in-plane but have weak van derWaals bonds perpendicular to the plane. They can
be readily exfoliated into quasi two-dimensional nanosheets with a thickness of
less than one nanometer, providing a simple and scalable route for the production
of two-dimensional solids. Among two-dimensional materials, transition metal
dichalcogenides (TMDs), with structural formula MX2 (where M is a transition
metal and X a chalcogen) have attracted much interest for their unique properties
such as high carrier mobility and change of the energy band structure due
to physical changes and optoelectronic properties arising from their quasi two dimensional structure. In this work, we aim to find alternative approaches for
fabrication using less environmentally harmful solvents. We use liquid phase processing of bulk layered crystals to produce suspensions of a single layer and few layer of tungsten disulfide, WS2, with water and Triton X-100 as a non-ionic surfactant. After that, we investigated the exfoliated WS2 in low boiling point solvents including isopropanol (IPA), ethanol (EtOH), methanol (MeOH), and acetonitrile (ACN) to successfully find a few layers of WS2. The sample preparation procedure can be broken in two main parts: 1) high shear mixing and 2) centrifugation. The centrifuge process aims to separate the thicker material that has not been fully exfoliated from the WS2 dispersions, stabilized in water. We found that the recycling of previously exfoliated powder gives excellent suspension stability without reaggregation for long periods of more than 8 months, compared to the original powder that was exfoliated for the first time. When we recycle the powder, we are effectively removing small surface contaminants on the flakes from the original powder, and they are not present in the recycled powder. Removing these contaminants produces more stable solutions. We find the dispersed concentration increases with increasing speed of the mixer while the optimum stable dispersions are obtained at shear speeds of 8000 rpm. Dispersions were characterized by absorption spectroscopy, Raman spectroscopy, Scanning Electron Microscopy (SEM), and Transmission electron microscopy (TEM). The concentration of the material, fabricated with optimum shear rates of 5 × 104 s−1, has been determined using optical absorption, giving a WS2 concentration of 0.025 mg/ml. In addition, multiple deposition processes including drop casting, vacuum oven, spin coating, and dip coatingwith non-polar solventwere utilised to investigate the optimal dispersion for nanosheets on the substrate, and determine the best procedure for the fabrication of stable films of WS2 nanosheets
Reproducibility of Statistical Inference Based on Randomised Response Data
Get PDFReproducibility of an experiment’s conclusion is an important topic in a variety of
fields, including social studies. This thesis presents a theory of reproducibility of statistical
inference based on randomised response data. First, reproducibility of statistical hypothesis
tests based on randomised response data is studied. This thesis presents statistical inference
for reproducibility of the outcome of a hypothesis test based on data resulting from
different randomised response techniques (RRT). Secondly, a new method for quantifying
reproducibility of statistical estimates is introduced. Finally, this method is applied to derive
reproducibility of estimates of population characteristics based on randomised response
data.
The quantification of reproducibility uses nonparametric predictive inference (NPI),
which is suitable for reproducibility when considering this as a prediction problem. NPI uses
only few model assumptions and results in lower and upper reproducibility probabilities.
We compared different randomised response methods. The results of this thesis open up the
possibility of pre-selecting a randomised response method with higher reproducibility and
also indicate the relationship between variance and reproducibility with the same privacy
level. We find that less variability in the reported responses of RRT methods leads to higher
reproducibility of statistical hypothesis tests based on RRT data with the same privacy
degree.
Therefore, for RRT methods using binary responses, reproducibility of hypothesis tests
based on the forced method is greater than reproducibility of hypothesis tests based on the Greenberg method. For RRT methods using real-valued responses, reproducibility of
estimates is greater for data collected from the Greenberg method than the reproducibility
of estimates for data collected from the optional multiplicative method and the Eichhorn
and Hayre method
An investigation into the effects of prenatal flavour exposure through maternal diet on fetal and infant behaviours
Get PDFThe research presented in this thesis is an examination of the effects of prenatal flavour exposure on fetal and infant behaviours. Throughout pregnancy, a fetus is exposed to a range of flavours in the amniotic fluid which contains maternal dietary aromas. There is a body of research investigating the effects of prenatal flavour exposure on infant behaviours, however, direct investigation of fetal reactions has to date been lacking. To address this, Chapter 3 examined the fetal facial reactions, via 4D ultrasound scans, to prenatally exposed flavours, namely kale and carrot. The findings indicate the first direct evidence of fetal facial reactions to flavours in the amniotic fluid. Chapter 4 is a systematic review and meta-analysis that indicated that this prenatal flavour experience provides continuous chemosensory information from prenatal to the first year of postnatal life. Chapter 5 indicated that neonates at around one month of age “prefer” the odour of flavours they experienced in the last three weeks of pregnancy. Additionally, a longitudinal analysis that was reported in Chapter 5 shows that fetal reactions to flavours can be modified by repeated exposure in utero, resulting in increased preferences for the exposed flavour irrespective of the type of flavour. This PhD thesis makes an important and novel contribution to the research literature by providing a window into the chemosensory world of the human fetus and showing a potential way to shape postnatal food preferences
Exploring the Structure of Scattering Amplitudes in Quantum Field Theory: Scattering Equations, On-Shell Diagrams and Ambitwistor String Models in Gauge Theory and Gravity
Get PDFIn this thesis I analyse the structure of scattering amplitudes in super-symmetric gauge and gravitational theories in four dimensional spacetime, starting with a detailed review of background material accessible to a non-expert. I then analyse the 4D scattering equations, developing the theory of how they can be used to express scattering amplitudes at tree level. I go on to explain how the equations can be solved numerically using a Monte Carlo algorithm, and introduce my Mathematica package treeamps4dJAF which performs these calculations. Next I analyse the relation between the 4D scattering equations and on-shell diagrams in N = 4 super Yang-Mills, which provides a new perspective on the tree level amplitudes of the theory. I apply a similar analysis to N = 8 supergravity, developing the theory of on-shell diagrams to derive new Grassmannian integral formulae for the amplitudes of the theory. In both theories I derive a new worldsheet expression for the 4 point one loop amplitude supported on 4D scattering equations. Finally I use 4D ambitwistor string theory to analyse scattering amplitudes in N = 4 conformal supergravity, deriving new worldsheet formulae for both plane wave and non-plane wave amplitudes supported on 4D scattering equations. I introduce a new prescription to calculate the derivatives of on-shell variables with respect to momenta, and I use this to show that certain non-plane wave amplitudes can be calculated as momentum derivatives of amplitudes with plane wave states
What do polyglots know about learning languages? Assessing the beliefs and perceptions of polyglots vis-à-vis language learning
Get PDFThere is an apparent dichotomy between the maligned fortunes of national language programs and the increasing stories of success shared at international polyglot gatherings. As enrolment in foreign language programs in several countries continues to decline and commissioned bodies are tasked with finding ways to improve language learning outcomes, the polyglot community continues to thrive and proclaim to have solutions to the woes voiced by individuals and governments alike. Despite this, there remains a dearth of research on polyglots and their beliefs regarding language acquisition. This research aims to fill this void by investigating the beliefs and perceptions of polyglots vis-à-vis language learning. The study focused on essential characteristics of a successful language learner, important considerations for successful language acquisition, and the benefits of technology for language acquisition.
This study used a mixed methods design to ascertain polyglots’ beliefs and perceptions. A questionnaire utilising a five-point Likert scale was administered to 513 polyglots from 71 countries, and a quantitative analysis of their responses was conducted. This was followed by a qualitative document analysis of 13 polyglots’ documents in order to elaborate on the initial findings from the questionnaire. Directed content analysis was conducted manually on the polyglots’ documents and underlying themes which emerged from the documents were reported.
The results indicated that the polyglots were divided on whether successful language learners are born with an aptitude for language learning. Nevertheless, they held that anyone can learn a second language. Characteristics of passion and effort were deemed pertinent, as well as the motivation of the learner. The findings also highlighted the polyglots’ belief that language education in schools is in need of reform. The way languages are taught and the way tests are used were scrutinised. Several benefits of the use of technology for language learning, such as increased resources and enhanced intercultural competence, also emerged from the study. The study concludes with some recommendations for language learners, language instructors, and course administrators, as well as some suggestions for future research
Music and Addiction The development of Music Addiction Scale (MAS)
Get PDFStudies have reported cases of addictive dependency on musical behaviours. Although these investigated specific musical behaviours patterns, no instrument has been designed for a generic assessment of addictive music dependency. This study aims to develop a new instrument for assessing the addictiveness of generic engagement with music. This instrument, called Music Addiction Scale (MAS), is a comprehensive measurement instrument for detecting potential addictiveness and high engagement of generic engagement with music. Twenty-eight items in the MAS were adapted based on the literature and an online survey conducted with a sample with a range of cultural and national backgrounds. The structure of the MAS was investigated through exploratory factor analyses (EFA) and correlations between factors and
other variables. The original MAS was revised to 20 items based on the results of these analyses. The trimmed MAS has ten items each for the addictive core criteria and engagement core criteria. Cronbach’s alpha for the MAS was 0.93, and the concurrent of the addictive core criteria and the engagement core criteria was supported by loading scores to the factor structure and
correlation scores to the addictive and high engagement phenomena. The MAS is a promising measurement instrument for assessing addictive dependency based on generic musical habits
STRUCTURAL INVESTIGATIONS INTO CELL WALL BIOMASS IN THE ULVA SEAWEED GENUS
Get PDFClimate change is a notorious and serious problem that needs to be attended with no delays. Mitigation of fossil fuel emissions are mandatory to reduce the production of green-house gases, however, as population increases, the global energy demand increases as well, with fossil fuels acting as the main energy source, globally. Worldwide, different strategies towards the development of sustainable societies applying circular economy principles and decarbonization of the industrial infrastructures are among the most important goals to achieve for the coming years. The use of biomass to accomplish such goals by producing bio-derived commodities and biofuels have gained track on the last two decades. One important source of biomass that has been highly studied in the recent years is the one coming from the aquatic feedstock called macro algae, which is normally used for food and cosmetic applications. However, the application of the macro algae to produce the so-called third generation biofuels or other chemical commodities, although having some drawbacks, seem to lead to promising results for the coming years with more and more mature technologies for such tasks. Belonging to the genus Ulva, the sea lettuce, a group of green algae have been identified as a potential candidate to be used to produce bio-derived products. In this work, through a literature review, the effects of the use of carbon and oil worldwide were appraised, as well as some of the most studied alternatives to mitigate the negative effects caused to the environment using fossil fuels. The possible use of macro algae as a promising candidate to produce bio-derived products was also highlighted. Using an Ulva sp. collected from the coast at county Durham, qualitative analysis of the cellulose and ulvan biochemical fractions were obtained. Through Fourier-Transformed Infrared Spectroscopy, the possible existence of acetylated cellulose in algae was explored. Mass-spectrometry analysis was performed to clarify the obtained results from the Fourier-Transformed Infrared analysis and finally, Thin-Layer chromatography analysis was performed to assess whether the presence of the endotransglycosylase enzymes could catalyze the linking between wall polysaccharides from the sample and some oligosaccharides. In this work, a better understanding of the composition from the Ulva sp. collected from Durham coast was gained, developing a foundation for more in-depth focused research of ulvan biomass as a resource to produce high quality biofuels in the coming future
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