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Toward Efficient Organic Photovoltaics: From Formulation and Novel Materials to Device Architectures
Get PDFOrganic photovoltaic (OPV) offer unique advantages such as molecular engineering, flexibility and roll-to-roll manufacturing that can significantly reduce production costs. However, their efficiencies still lag behind inorganic PVs. It has been demonstrated that morphology control and recombination mechanisms play a key role in the efficiency. In this way, methods to enhance the performance by enabling morphology tuneability to further optimise OPVs are needed. To this end, this thesis introduces three novel approaches that can be utilised to improve the efficiency in OPVs.
In the first part of this work, a formulation approach is investigated by examining OPVs in which the morphology is optimised by ternary blends. Particularly, donor polymers P3HT, PTB7 and fullerene acceptors PC71BM and ICBA were systematically characterised. It is shown that different combinations of ternary blends outperformed binary controls. Results demonstrated that depending on the donor material used, the molecular intermixing of the constituents was different, yielding varied impacts on the performance and thus determining whether ternary blends offer a benefit or not.
The second approach reviewed consisted in the study of charge transport in novel materials, specifically non-fullerenes (NFA), hybrid fullerenes and fullerenes. For the first time, electron mobility was probed, which can be a limiting factor of the efficiency. It was demonstrated that NFA realised higher electron mobilities (closer to benchmark PCBM) in contrast to hybrid fullerenes, which yielded low mobilities. It was shown that the synthetic approach utilised to fabricate these compounds and its resulting morphology had a profound impact in their capability to mediate electron transport.
For the third method, device architectures were simulated in the form of multi junction OPVs termed as tandems. In such devices, a current matching between photoactive layers is generally required to maximise the performance. Through advanced modelling, it was shown that devices with unbalanced current matching are dominated by recombination losses of charges in the layer doing most of the absorption. It was demonstrated that changing the transport properties of the layer performing least of the absorption could assist alleviating these losses. It is also shown that different illumination conditions can further reduce the performance in tandem OPVs and that one can mitigate these reductions by suitable materials selection
Energy saving technologies and optimisation of energy use for decarbonised iron and steel industry
Get PDFThe iron and steel industry relies significantly on fossil energy use and is one of the largest energy consumers and carbon emitters in the manufacturing sector. Simultaneously, a huge amount of waste heat is directly discharged into the environment during steel production processes. Conservation of energy and energy-efficient improvement should be a holistic target for iron and steel industry. There is a need to investigate and analyse potential effects of application i.e., a number of primary and secondary energy saving and decarbonisation technologies to the basic energy performance and CO2 emissions profile of iron and steel industry. A 4.7Mt annual steel capacity iron and steel plant in the UK is selected as a case study.
By carrying out a comprehensive literature review of current primary and secondary energy saving and decarbonisation technologies, suitable technologies are categorised based on their purpose of utilisation and installation positions. It is found that fuel substitution technologies and waste heat recovery technologies have wide application prospects in iron and steel industry. To further investigate effects of these technologies on the UK integrated steelwork, a comprehensive model of iron and steel production processes is built by using the software Aspen Plus. The model is fully validated and is used to examine the specific energy consumption and direct CO2 emissions. Energy consumption and CO2 emissions of whole production chain to produce a ton of crude steel are 17.5 GJ and 1.06 t. Waste heat from hot coke and gas cooling could cover 40% of electricity consumed in the plant if coking process has the maximum coke capacity.
To implement primary energy saving and decarbonisation technologies, the performance of blast furnace is optimised first by substituting coke with bio-reducers based on the proposed model. Three biomass substitutions are considered to reduce coke rate and CO2 emissions of ironmaking process. Results show that coke demand of per ton of hot metal and CO2 emissions of the ironmaking process are improved by replacing partial coke with biomass. An optimal coke replacement is operated with 200 kg bio-oil and 222 kg coke when producing one ton of product. The reaction involving bio-syngas has the most potential to reduce CO2 emissions.
To find a sustainable way to capture CO2 and recover waste heat onsite, a model of adopting organic Rankine cycle with amine-based CO2 capture in ironmaking process is introduced. In comparison with different reducing agents injected into BF, bio-oil has the most advantage to improve energy consumption of CO2 capture system. CO2 emissions from total sites can be maximumly reduced by 69% through the method of CO2 capture with waste heat recovery technologies. The combination of various decarbonised technologies creates great opportunity to reduce CO2 emissions.
A mass-thermal network of iron and steel industry is finally built up, where primary and secondary energy saving technologies are implemented to optimise energy use and reduce CO2 emissions. The general guideline i.e., 5-step method is summarised to optimise the mass-thermal network. Exergy analysis is used to evaluate overall network after applications of energy saving and decarbonisation technologies. Injection of biomass-based syngas can maximumly increase the exergy efficiency of ironmaking process. Sinter and BOF steelmaking processes are related with mass ratio of hot metal. Optimisation insights of energy use and decarbonisation for steelwork are revealed based on exergy efficiency and destruction results
Turkish Foreign Policy towards Iran since the Arab Uprisings (December 2010 to July 2018): A Neoclassical Realist Account
Get PDFWith the outbreak of the Arab Uprisings across the Middle East and North Africa at the end of 2010, regional and global state actors, including Turkey and Iran, sought to shape and manage these political and social phenomena in alignment with their regional interests and objectives. Although Turkey’s foreign policy towards Iran was initially tense, it later became more manageable due to specific unit-level factors. In this context, the Arab Uprisings offer the historical context by which to assess how Turkish Foreign Policy (TFP) towards Iran was shaped and conducted. This thesis explores the rationale behind TFP towards Iran since the Arab Uprisings by asking two central questions:
1. To what extent did structural forces shape the formulation of Turkish foreign policy towards Iran following the Arab Uprisings, from December 2010–July 2018?
2. How did unit-level (domestic) factors interact with structural imperatives in shaping Turkish foreign policy towards Iran following the Arab Uprisings, from December 2010–July 2018?
Consequently, the thesis uses the perception and domestic security and economic considerations of the AKP elites as intervening variables to clarify the cause-effect relationship between systemic changes and the relative power position of Turkey (as independent variables) to examine the TFP towards Iran (the dependent variable) in the short to medium term. In this regard, NCR provides a useful theoretical framework for the intervening variables to explain the causal link between independent and dependent variables. Schweller’s balance of interest theory also helps explain Turkey’s alliance choice with Iran, considering Turkey’s economic and security considerations. This study contributes to a deeper understanding of TFP and TFP towards Iran in particular by establishing a conceptual framework through the use of NCR while also providing fresh insights concerning the key variables connected to foreign relations and domestic politics in TFP towards Iran. In short, the empirical goal of this work is to provide an innovative contribution to the study of TFP from a theory-driven standpoint. As a result, this thesis provides a solid foundation for scholars to build on and use NCR in future research that explores the actions of state actors facing seismic regional shifts and new security challenges
EU Corporate Tax Harmonisation
Get PDFSeveral problems arise from each Member State having their own corporate tax system and they have received increased publicity due to LuxLeaks and other scandals increasing the awareness of these problems. However, not all Member States want to change the status quo. The purpose of this thesis is therefore to establish what progress in the short and long term should look like in respect of tackling the problems which arise from the coexistence of 27 different corporate tax systems. To achieve this, the problems which arise due to the lack of harmonisation are identified and used as a framework for subsequent analysis of the different forms of harmonisation. Both the four freedoms case law and the State aid controls are analysed respectively. These two forms of negative harmonisation are assessed because positive harmonisation or integration would only be necessary if it would prove more effective at tackling the problems.
Positive harmonisation is assessed to ascertain whether it would provide a better response than negative harmonisation. This thesis demonstrates that the more effective a measure is likely to be, the less likely it is that a measure will gain the necessary support to be implemented. The unanimity requirement means that the Member States who benefit from the current differences between corporate tax systems by competing for FDI can veto corporate tax proposals that may be beneficial for the majority of Member States. As such, while in theory, positive harmonisation would provide the best solution, the most effective positive harmonisation measures are unlikely to be implemented. This thesis, therefore, illustrates that future progress at tackling the problems identified in Chapter One will only take place through negative harmonisation
Reindeer ecology in a changing Arctic: Snow, vegetation, and traditional ecological knowledge
Get PDFThe cumulative effects of anthropogenic development on reindeer (Rangifer tarandus, L.), and how these impacts interact with a changing climate, remain largely unknown. To fill this knowledge gap, this thesis begins by examining how presence and winter accessibility of reindeer forage is affected by silviculture in boreal forests of northern Sweden, as stands progress from clear-cut to mature forests. Original surveys show that the abundance of various lichen species generally increases with stand age, highlighting the roles of competition, grazing pressure and disturbance in this process. Snow depth is consistently shallower in old stands, and the number of ice layers in the snow column increases throughout winter, affecting the ability of reindeer to dig to ground-lying lichens. Overall, there is upto 61 % lower availability of forage in clear-cut sites compared to old stands, showing that changes in forest structure have notable impacts on reindeer grazing.
Next the effects of multiple forms of land-use, individually and cumulatively, on reindeer are examined. A model is created which considers the impact of silviculture, roads, mines, hydropower stations, settlements and four climate scenarios, on reindeer populations over 50 years. All scenarios saw a loss of 54-100 % of reindeer, and only 25 % resulted in economically sustainable herd sizes for reindeer herders. Climate had the greatest impact on reindeer survival within the model. The results highlight that current and many projected future scenarios of land development create an unsustainable environment for reindeer and herders.
Alongside natural science methodologies, the role of history, politics and economics in the lives of Indigenous Sámi herders are explored, arguing that to gain a fuller understanding of reindeer ecology in a changing system, it is essential to consider both the biological and human context surrounding them. The processes of trying to carry out research using both scientific and traditional ecological knowledges are discussed, providing suggestions for others undertaking interdisciplinary work in this field
Photohadronic emission of VHE gamma rays in blazars and the CTA neutrino target of opportunity program
Get PDFBlazars are an extremely luminous and highly variable type of AGN, which possess a relativistic jet with a small viewing angle towards the observer. Recent results, such as the 3-sigma spatial and temporal coincidence of TXS~0506+056 with the IceCube neutrino alert IC-170922A, have motivated an ongoing discussion of how these astrophysical sources can produce high-energy neutrinos during a flaring state and which scenario can successfully describe the observed gamma-ray behaviour.
In this thesis, the possibility of a hadronic contribution to the very high energy (VHE) gamma-ray emission of blazars, as well as the possible detection of neutrino events, are explored by considering photohadronic interactions in a lepto-hadronic scenario. The model is applied to fit the flaring period of Markarian 421 in 2010, for which a dedicated analysis of Fermi-LAT data from the source was performed in the MeV range (100 MeV - 1 GeV). The fit results were compared with two leptonic models using the Akaike Information Criterion (AIC) test. In all cases, the photohadronic model was favoured as a better fit description in comparison to the one-zone leptonic model.
The photohadronic model was also applied to the blazar 4FGL J0658.6+0636, which was found within the 90% localisation region of the IceCube neutrino alert IC-201114A. By analysing 12.3-years of Fermi-LAT data, the periods in which the blazar was detected significantly were identified and studied. For one of these periods, it was found that the photohadronic flaring model results are consistent with the observed gamma-ray behaviour of 4FGL J0658.6+0636 and the IC-201114A is discussed under the photohadronic scenario. These results show the potential of a photohadronic contribution to a lepto-hadronic origin of gamma-ray flux of blazars.
The final part of this thesis describes the neutrino and gamma-ray simulations performed for the Neutrino Target of Opportunity (NToO) program for the Cherenkov Telescope Array (CTA). The detection probability with CTA of the gamma-ray flux associated with the simulated IceCube hot-spots for steady neutrino source populations is investigated, and the performance of the CTA Omega configuration array is analysed to predict the potential science reach of the NToO program
Pastoral Care on Remand and the Role of the Prison Chaplain
Get PDFHow do prisoners experience life on remand in England, and how do prison chaplains offer them pastoral care in this setting?
This thesis explores the question of how prison chaplains deliver pastoral care in a remand prison, and how this care is received and experienced by prisoners. With my own experience as a remand prison chaplain as a catalyst, I engage with literature around practical theological approaches to exploring prison experience, criminological studies of remand, and prison chaplaincy.
Using a grounded theory methodology, I explore the challenges of being on remand and the role of prison chaplains in meeting the needs of remandees, as well as chaplains’ own understandings of their vocation and ministry. Chaplains and prisoners were interviewed at three Local prisons in the North of England, and the major themes from these interviews explored thematically and theologically.
I discuss issues of trust building and the precarious nature of the prisoner-chaplain relationship, and the core theme of liminality in the role of the chaplain and the experience of the remand prisoner. Liminality is explored as a key theme linking the limbo-like nature of remand life, the challenges of navigating the prison environment, and the status of the chaplain on the thresholds of prison life and ministry.
The liminality of the chaplain is considered as a positive characteristic that enables a flexible ministry in a remand context. This leads to a theological analysis of remand chaplaincy through the lens of Walter Brueggemann’s concepts of the disorientation of lament and the notion of prophetic imagination. Remand chaplaincy is explored through the lens of a ministry of presence as ‘being with’ in conversation with the work of Samuel Wells.
The thesis concludes with new understandings of remand chaplaincy in light of the liminality of the role and of the remand prisoner, and considers the challenges of the practical and theological aspects of providing pastoral care in this complex context
Why is colour special? Understanding the differences between red and blue quasars
Get PDFThe majority of quasars have very blue ultraviolet-optical colours due to the unobscured view of the accretion disc. However, recent work has uncovered a significant population of quasars with much redder colours ("red quasars") which are prime candidates for a transitional phase in the evolution of quasars. In this thesis, I build on the work from Klindt et al. (2019), who discovered fundamental differences in the 1.4 GHz radio properties of a sample of Sloan Digital Sky Survey (SDSS) optically selected red quasars, compared to typical blue quasars, adding weight to this evolutionary paradigm. I aim to further investigate these differences, using higher spatial resolution and deeper radio data, and utilise optical-near-infrared spectroscopy in order to understand the physical origin of the red colours and mechanisms driving the radio emission in red quasars.
Firstly, I investigate the radio properties of red quasars across a broad range of frequencies (0.144-3GHz) and sensitivities (~20-750Jy/bm at 1.4GHz). I build on the results from Klindt et al. (2019), finding that SDSS-selected red quasars display enhanced radio emission compared to typical blue quasars, which peaks around the radio-quiet threshold across all of the radio datasets utilised, but at a higher statistical significance than previous studies (Chapters 3 and 4). Using the high spatial resolution of VLA Stripe 82, I find that this enhanced radio emission is compact/unresolved at ~16 kpc (host-galaxy) scales (at z~1.5). Utilising the radio-far-infrared correlation, I show that the origin of this radio emission is likely due to AGN processes, rather than star formation (Chapter 3).
To explore the origin of the red colours and the enhanced radio emission in red quasars, I utilise ultraviolet-near-infrared VLT/X-shooter medium resolution spectroscopy of 40 red and blue quasars (Chapter 5). From fitting a dust-reddened control composite to the spectra, I find that the majority of red quasars are indeed red due to the line-of-sight dust, also consistent with the larger Balmer decrements calculated for the red quasars. Only one Fermi-detected red quasar cannot be fit well by any dust extinction curve, and is instead likely to be synchrotron dominated. Fitting a simple thin accretion disc model to both the red and blue quasars, I identify no significant differences in the accretion properties, suggesting that this is not driving the enhanced radio emission. Finally, by fitting the [OIII]5007 and CIV emission lines, I explore the incidence of outflows in the red and blue quasars. I detect outflows in both the red and blue quasars, but do not find any evidence to suggest outflows are more powerful or prevalent in the red quasar sample.
Extending this work to more obscured systems, I present the first eight months of our program within the Dark Energy Spectroscopic Instrument (DESI), which selects dust-reddened quasars predominantly based on their mid-infrared colours (Chapter 6). So far, 3038 candidates have been observed. From visual inspection of their spectra, I find that 74% of the high quality objects are quasars, consistent with the main DESI quasar survey. Defining red quasars based on their optical colour, and “Extremely Red Quasars” (ERQs) based on their optical–mid-infrared colour, I discover that 76% and 38% of the quasars in our sample are red quasars and ERQs, respectively. From fitting dust extinction curves, I find that my sample doubles the number of quasars with an mags, compared to the nominally selected quasars. Exploring the 144MHz radio properties, I identify a striking relationship between the line-of-sight dust extinction towards a quasar and the radio detection fraction, that is not driven by redshift or luminosity effects.
Overall, my thesis demonstrates an intrinsic connection between opacity and the production of radio emission in quasars. Future work will help to uncover the physical mechanisms behind the enhanced radio emission in dusty quasars
The clustering properties of the reddest galaxies with UKIDSS-DXS
Get PDFDeep, photometric near-infrared surveys are the most effective ways to select massive galaxies at redshift , where their characteristic spectral features are observed at wavelengths longer than optical surveys are designed to measure.
In this Thesis, we present and study the clustering properties of such galaxies using the UKIDSS-DXS near-infrared survey.
Firstly we produce deep, uniform mosaics for the of and band imaging, which reach depths of ( for point sources), and produce galaxy catalogues which we match with deep optical surveys.
We demonstrate that these catalogues have reliable photometry (by way of comparison with 2MASS), we are able to efficiently remove foreground galactic stars, and that we produce the expected number counts galaxies.
These catalogues will be made available at some point in the near future.
From these catalogues we select Extremely Red Objects (EROs), Distant Red Galaxies (DRGs) and s, all of which aim to exploit the strong break which is present in the oldest stellar populations.
The combination of area and depth provided by DXS allows us to probe the large scale structure of the universe to tens of megaparsecs at .
We demonstrate using the small area of -band DXS coverage that selection of EROs is still effective with similar criteria in and , although do not suggest any new criteria different to those already existing in literature.
We measure the angular two point correlation of the EROs and passive selection of galaxies.
We show that these selections of galaxies exhibit significantly stronger clustering on the smallest scales than what is often assumed by the clustering studies of main sequence galaxies, indicating that these galaxies are residing in the most massive dark matter haloes.
Further, we demonstrate that there is a strong break in the correlation function in these selections of galaxies.
The correlation length we measure when considering the small scale (intra-halo) clustering alone is roughly constant for across the range of magnitudes DXS detects EROs, to .
Given that the halo mass of will be determined by the largest mass galaxy, we interpret this (in a qualitative sense) to mean that the dark matter host halo mass of the most massive EROs is roughly constant over the redshift range DXS measures EROs ().
A comparison of the angular correlation function for passive and star-forming galaxies (for three magnitude cuts where we have sufficient number counts) indicates that the passive galaxies are indeed much more strongly clustered than the star-forming: evidence of environmental quenching.
We present -band luminosity functions of our galaxy catalogues, and the ERO selection for .
We observe that the faint end slope of the ERO luminosity function is much steeper than those of the full galaxy catalogues, confirming that the ERO criteria selects galaxies that are amongst the most luminous in this redshift range.
Finally, we measure the galaxy stellar mass function of the full sample of galaxies, and of restframe selected passive galaxies over the range .
We compute the integrated stellar mass density of the full galaxy sample, and our values match well with those in the literature.
By computing the galaxy stellar mass density of the passive galaxy sample, and the contribution of the very massive end, we observe that the stellar mass density in the most massive passive galaxies is increasing faster than the stellar mass density of the passive galaxies as a whole, an observation which agrees with previous studies.
Given that the galaxy stellar mass function of passive galaxies is well-described by a single Schechter function, which implies a single mechanism of galaxy quenching, we rule out a significant amount of dry mergers at the massive end, and instead postulate that this tentatively suggests that the mass quenching efficiency of the most massive galaxies is lower at later times.
UKIDSS-DXS represents only a fraction of the vast datasets that the upcoming generation of instruments and surveys such as \textit{Rubin}-LSST, \textit{Euclid} and \textit{Roman} will produce, and this work is a precursor to investigations which use these surveys
Mapping above- and below-ground carbon stocks in the Sundarbans mangrove forest, Bangladesh
Get PDFThe study estimated ecosystem carbon stocks in the Bangladesh Sundarbans using field inventory data with species-specific allometric models, carbon fractions and remote sensing data. The plot level ecosystem carbon stocks were interpolated with regression kriging using a forest-type map developed from Sentinel-2 MSI satellite imagery and GEDI-based canopy height data in Google Earth Engine (GEE) platform. Error propagation from the field measurement and allometric models was estimated and interpolated. The study highlighted that both the above-ground carbon (AGC) and soil organic carbon (SOC) were significantly higher in the oligohaline zone, followed by the mesohaline and polyhaline zone. Multiple regression results indicated that soil salinity, organic C: N and tree diameter were the best predictor for the variability of the SOC in the Sundarbans. To understand how individual species affects biomass estimates in mangrove forests, five species-specific and four genus-specific allometric models were developed. At the individual tree level, the generic allometric models overestimated AGB from 22% to 167% compared to the species-specific models. At the plot level, mean AGB significantly differed in all generic models compared to the species-specific models. Using measured species wood density (WD) in the allometric model showed 4.5% to 9.7% less biomass than WD from a published database. When using plot top height and plot average height rather than measured individual tree height, the AGB was overestimated and underestimated by 19.5% and 8.3%, respectively. The total 1 m SOC in the Sundarbans was 21.37 Teragram (Tg) and the total AGC stocks comprised 23.91 Tg. On the other hand, the total ecosystem carbon (TEC) stocks were 62.70 Tg, which is comparatively lower than most mangrove forests in the world. The study demonstrated a methodology that could be used as an IPCC (Intergovernmental Panel on Climate Change) Tier 3 approach for estimating TEC stocks in the Bangladesh Sundarbans and also to monitor TEC stocks in mangroves and other tropical forests. The study also emphasised the importance of spatial conservation planning to safeguard the carbon-rich zones in the Bangladesh Sundarbans from anthropogenic tourism and development activities to support climate change adaptation and mitigation strategies
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