A kinetic and spectroscopic analysis of distance-dependent singlet fission in TIPS-pentacene

Singlet exciton fission (SF) is a process with the potential to extend the maximum theoretical efficiency of solar cells from 34% to 46%. By generating two triplet excitons from one singlet exciton, the process effectively splits the energy of a high-energy photon in two, reducing efficiency loss by thermal relaxation. While the process has a strong theoretical grounding, the mechanistic details of SF and practicalities of implementation in photovoltaic devices are insufficiently understood to exploit its full potential. In this thesis the effect of intermolecular distance on SF is studied by embedding 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) in an amorphous polymer matrix in the form of aqueous nanoparticle dispersions. By varying the mass ratio of TIPS-pentacene to the host polymer, the average intermolecular separation between TIPS-pentacene molecules is varied systematically from approximately 1 to 5 nm, resulting in a range of SF quantum yields. We study this system using both steady-state and ultrafast time-resolved spectroscopic techniques, and fit the results to a kinetic model to decipher the observed behaviour. The quantum yield of SF is shown to decrease with intermolecular separation, which is explained by diffusion-limited SF and an increase in loss pathways through exciton trap sites. We additionally identify an intermediate species in the SF process, and show that a significant proportion of this species decays non-radiatively without dissociating to form separated triplets, revealing another major loss pathway that has important implications for future research and applications.Thesis (M.Phil.) -- University of Adelaide, School of Physical Sciences, 201

OrganiZational communication and organiSational communication: Binaries and the fragments of a field

In this paper, I employ personal narrative to help cast light on connections and tensions between organiZational communication research, as produced in the United States, and organiSational communication research, as produced in Aotearoa New Zealand. I address the issue by highlighting three sets of differences between these bodies of research: canonical, institutional and theoretical. I then unpack how these differences are apparent in my own university before sketching out three ways in which we might productively use such tensions to achieve radical engagement, and critique disciplinary others, identities, and locations

Microbially Induced Calcite Precipitation (MICP) to mitigate contact erosion in earth embankment dams and levees

Internal erosion of water retaining structures (such as earth embankment dams, levees and dykes) is a major geotechnical problem. Contact erosion is a specific type of internal erosion that occurs at the interface between fine and coarse soils, for instance along the downstream edge of the core-filter interface, and can lead to earth dam failure due to internal erosion. Although in new dams this may be avoided by fulfilling the filter criteria or with the construction of barriers, retrofitting older structures often entails significant design and construction costs due to the uncertainties surrounding their materials and behaviour. In this context, microbially induced calcite precipitation (MICP), a bacteria-induced bio-mineralisation process capable of binding soil particles in situ, provides a cost-effective alternative for contact erosion control. However, it is necessary to establish a solid understanding of how biogenic cementation occurs at the interface between fine and coarse sands and its influence on the erosion and hydro-mechanical characteristics.The author would like to acknowledge Mr Chris Knight for the production of the EFA device and EPSRC for funding this studentship as part of the Centre for Doctoral Training in Future Infrastructure and Built Environment (EP/L016095/1)

The production of quick scoping reviews and rapid evidence assessments: a how to guide

This document contains a brief overview of the different Evidence Reviews (ER) but is written primarily for those intending to commission and/or produce an ER in the form of Quick Scoping Reviews (QSR) or Rapid Evidence Assessments (REA), that lie between literature reviews and SRs in terms of rigour of assessment. These have been found to be well suited to meet the evidence challenges most frequently faced by the authors in meeting policy and practice evidence requirements

Flume study on the effects of microbial induced calcium carbonate precipitation (MICP) on the erosional behaviour of fine sand

Tangential flow-induced interface erosion poses a major threat to a wide variety of engineering structures, such as earth-filled embankment dams, and oil- and gas-producing wells. This study explores the applicability of microbial induced calcium carbonate (CaCO3) precipitation (MICP) by way of the ureolytic soil bacterium Sporosarcina pasteurii as a method for enhancing the surface erosion resistance of fine sand. Specimens were treated with cementation solution concentrations between 0·02 and 0·1 M, and the erosional behaviour examined in a flume under surface-parallel flow and increasing shear stress. Photographs, cumulative height eroded-time series and erosion rates were obtained as a function of specimen height, MICP treatment formulation and calcium carbonate content. Results showed that while untreated specimens eroded primarily in particulate and mass form, MICP-treated specimens were characterised by a block erosion mechanism. Further, erodibility was found to depend on the calcium carbonate content and the cementation solution concentration. To understand this, a systematic study of the calcium carbonate crystal sizes and distributions was undertaken through X-ray computed tomography. Fundamentally, the effectiveness of MICP for erosion control was found to be dominated both by the precipitated calcium carbonate content and microstructural features, with higher contents and larger crystals yielding lower erodibility values. Additionally, crystal growth mechanisms varied depending on the cementation solution concentration.</p

Strong Light-Matter Coupling Facilitated Charge Carrier Transport in Cavity Organic Solar Cells

Strong light-matter coupling has shown great potential for modifying the electro-optical properties of semiconducting materials in recent years. In the strong coupling regime, excitons and cavity photons form new states named exciton-polaritons, with their properties a hybrid of each constituent. Herein, we report strong coupling observed in solution-processed donor:acceptor bulk-heterojunction organic solar cells (OSCs) evidenced by the observed Rabi splitting of ~300 meV and the effects of strong coupling on OSC operations. Combining the transient photovoltage decay measurement and nanosecond transient absorption spectroscopy, our results reveal that the effective charge carrier lifetimes are longer in cavity devices, attributed to the reduced bimolecular recombination. It is also found that access to CT state(s) of higher energy is enabled in cavity devices. This study demonstrates that strong coupling can effectively modify the device- and photo-physics in OSCs and opens a new pathway for engineering more efficient OSCs

Approximation Algorithms for Quantum Max-dd-Cut

We initiate the algorithmic study of the Quantum Max-$d$-Cut problem, a quantum generalization of the well-known Max-$d$-Cut problem. The Quantum Max-$d$-Cut problem involves finding a quantum state that maximizes the expected energy associated with the projector onto the antisymmetric subspace of two, $d$-dimensional qudits over all local interactions. Equivalently, this problem is physically motivated by the $SU(d)$-Heisenberg model, a spin glass model that generalized the well-known Heisenberg model over qudits. We develop a polynomial-time randomized approximation algorithm that finds product-state solutions of mixed states with bounded purity that achieve non-trivial performance guarantees. Moreover, we prove the tightness of our analysis by presenting an algorithmic gap instance for Quantum Max-d-Cut problem with $d \geq 3$.Comment: 42 page

Prevalence of liver fluke (Fasciola hepatica) in wild Red Deer (Cervus elaphus): coproantigen ELISA is a practicable alternative to faecal egg counting for surveillance in remote populations

Red deer (Cervus elaphus) are hosts of liver fluke (Fasciola hepatica); yet, prevalence is rarely quantified in wild populations. Testing fresh samples from remote regions by faecal examination (FE) can be logistically challenging; hence, we appraise frozen storage and the use of a coproantigen ELISA (cELISA) for F. hepatica surveillance. We also present cELISA surveillance data for red deer from the Highlands of Scotland. Diagnoses in faecal samples (207 frozen, 146 fresh) were compared using a cELISA and by FE. For each storage method (frozen or fresh), agreement between the two diagnostics was estimated at individual and population levels, where population prevalence was stratified into cohorts (e.g., by sampling location). To approximate sensitivity and specificity, 65 post-slaughter whole liver examinations were used as a reference. At the individual level, FE and cELISA diagnoses agreed moderately (κfrozen = 0.46; κfresh = 0.51), a likely reflection of their underlying principles. At the population level, FE and cELISA cohort prevalence correlated strongly (Pearson’s R = 0.89, p &lt; 0.0001), reflecting good agreement on relative differences between cohort prevalence. In frozen samples, prevalence by cELISA exceeded FE overall (42.8% vs. 25.8%) and in 9/12 cohorts, alluding to differences in sensitivity; though, in fresh samples, no significant difference was found. In 959 deer tested by cELISA across the Scottish Highlands, infection prevalence ranged from 9.6% to 53% by sampling location. We highlight two key advantages of cELISA over FE: i) the ability to store samples long term (frozen) without apparent loss in diagnostic power; and ii) reduced labour and the ability to process large batches. Further evaluation of cELISA sensitivity in red deer, where a range of fluke burdens can be obtained, is desirable. In the interim, the cELISA is a practicable diagnostic for F. hepatica surveillance in red deer, and its application here has revealed considerable geographic, temporal, sex and age related differences in F. hepatica prevalence in wild Scottish Highland red deer

The use of residual dipolar coupling for conformational analysis of structurally related natural products

The authors would like to acknowledge the EPSRC for funding.Determining the conformational preferences of molecules in solution remains a considerable challenge. Recently, the use of residual dipolar coupling (RDC) analysis has emerged as a key method to address this. Whilst to date the majority of the applications have focused on biomolecules including proteins and DNA, the use of RDCs for studying small molecules is gaining popularity. Having said that, the method continues to develop and here we describe an early case study of the quantification of conformer populations in small molecules using RDC analysis. Having been inspired to study conformational preferences by unexpected differences in the NMR spectra and the reactivity of related natural products, we showed that the use of more established techniques was unsatisfactory in explaining the experimental observations. The use of RDCs provided an improved understanding which, following use of methods to quantify conformer populations using RDCs, culminated in a rationalisation of the contrasting diastereoselectivities observed in a ketone reduction reactionPostprintPeer reviewe