Probing the formation of polarons in organic semiconductors and their optoelectronic properties

Solution processable organic semiconducting polymers show favourable properties for applications in low-cost printed electronics, which offer unique capabilities and low-cost alternatives to conventional devices. The performance of devices is critically dependent on the formation and transport of charges in the organic semiconducting material. Electron-phonon coupling in conjugated polymers leads to a structural deformation when it becomes charged (so called ‘polaron’). Polaron formation has profound implications on the transport of charge carriers in conjugated polymers. In this work we develop a powerful structural probe that allows direct observation of polaron formation in situ using electrochemical resonant Raman spectroscopy (ERRS). We were able to elucidate the fundamental relationships between polaron formation and chemical composition/structure, polymer conformation and optoelectronic properties for a range of conjugated polymers. First, for the model semiconducting polymer, poly(3-hexyl)thiophene (P3HT) we find that molecular order plays a significant role in determining conformational changes induced during hole polaron formation. Our study provides direct spectroscopic evidence for a lower degree of lattice reorganisation in crystalline (and therefore more planarised) polymers than in conformationally disordered polymers. This observation is consistent with higher charge carrier mobility and better device performance commonly found in crystalline polymer materials. Blending P3HT with PCBM (a model solar cell system) disturbs polymer crystallinity and reduces the density of polarons that can form, whilst post-deposition thermal annealing partly restores this lost capacity for charge. Second, donor-acceptor type copolymers are an important class of materials, which display superior optoelectronic properties compared to homopolymers such as P3HT. We consider a series of copolymers that incorporate fused rings and acceptor units into the P3HT backbone and how their chemical design affects polaron formation. We find that fused thienothiophene units in poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT) results in a large lattice reorganisation during polaron formation. By incorporating diketopyrrolopyrrole (DPP) units in poly[2,5-(2-octyldodecyl)-3,6-diketopyrrolopyrrole-alt-5,5-(2,5-di(thien-2-yl)thieno [3,2-b]thiophene) (DPPT-TT) the lattice reorganisation can be completely reduced owing to the highly planar conformation of the polymer backbone. This contributes to the high hole mobility commonly reported for DPP based polymers. We investigate another planar donor-acceptor copolymer, indacenodithiophene–benzothiadiazole (IDTBT), but with much stronger D-A strength. We find this copolymer displaying much stronger D-A strength results in a redistribution of π-electron density which generates polarons with a relatively higher lattice reorganisation. The IDTBT shows the photo-generation of free charges in neat films; which is not observed for the other polymers studied here. Furthermore, we demonstrate that the degree of lattice reorganisation governs the polymers stability to electrochemical oxidative stress. The DPPT-TT displaying the lowest degree of lattice reorganisation shows the highest stability to electrochemically induced oxidative stress of all the polymers studied here. Our results are highly relevant to improve performance and operational stability in optoelectronic devices, in which charges are injected/ extracted and transported. Finally, we investigate the effect of a small molecule additive, DBSA, on polaron formation in conjugated polymers. For the case of P3HT we directly probe structural changes in the polymer when DBSA is added to the electrolyte. We find adding DBSA enhances the electrochemical doping effect of the electrolyte by lowering the onset of oxidation and allowing the generation of a higher polaron density. We employ DBSA by adding it to the gating electrolyte in an organic electrochemical transistor (OECT) to improve the device performance for a range of p-type polymers, including P3HT, PBTTT and DPPT-TT. This study demonstrates the application of DBSA for low-power accumulation mode OECTs, and opens the possibility to utilise otherwise unsuitable polymers, with deep HOMO levels, in OECT devices for biosensing applications.Open Acces

Doctor of Pharmacy

dissertationIn July 1979, in accordance with the Joint Commission on Accreditation of Hospitals (JCAH) standards, the Pharmacy and Therapeutics Committee approved a policy for reporting adverse drug reactions (ADRs) occurring within the 370-bed University of Utah Hospital. This policy was intended "to provide a mechanism to accurately and completely report adverse drug reactions which are suspected within the hospital." It required the health care provider initially suspecting the adverse drug reaction to complete an Adverse Drug Reaction Experience Reports Form (FDA Form #1639). These report forms were to be available at each inpatient unit out outpatient clinic. A follow-up was then conducted on each of these reports. The results were to be sent to the Food and Drug Administration and a copy kept on file within the Drug Information Center. The objectives of this study study were: 1.) To assess the general compliance rate of a more accessible reporting system; 2.) To determine whether the format of a short versus a long form is more acceptable to physicians; 3.) To compare the incidence of reported adverse drug reactions using a reporting form to the incidence of adverse drug reactions reported in the medical record, and; 4.) To compare the incidence of adverse drug reactions with the new system versus the incidence for the prior system

The “External” Shears In Strong Lens Models

The distribution of mass in galaxy-scale strong gravitational lenses is often modelled as an elliptical power law plus ‘external shear’, which notionally accounts for line-of-sight galaxies and cosmic shear. We argue that it does not, using three lines of evidence from the analysis of 54 galaxy-scale strong lenses: (i) strong lensing external shears do not correlate with weak lensing; (ii) the measured shear magnitudes in strong lenses (which are field galaxies) are too large (exceeding 0.05) for their environment and; (iii) the external shear position angle preferentially aligns or anti-aligns with the mass model position angle, indicating an internal origin. We argue the measured strong lensing shears are therefore systematically accounting for missing complexity in the canonical elliptical power-law mass model. If we can introduce this complexity into our lens models, this will further lensing studies of galaxy formation, dark matter and Cosmology

Learning to Select SAT Encodings for Pseudo-Boolean and Linear Integer Constraints

Many constraint satisfaction and optimisation problems can be solved effectively by encoding them as instances of the Boolean Satisfiability problem (SAT). However, even the simplest types of constraints have many encodings in the literature with widely varying performance, and the problem of selecting suitable encodings for a given problem instance is not trivial. We explore the problem of selecting encodings for pseudo-Boolean and linear constraints using a supervised machine learning approach. We show that it is possible to select encodings effectively using a standard set of features for constraint problems; however we obtain better performance with a new set of features specifically designed for the pseudo-Boolean and linear constraints. In fact, we achieve good results when selecting encodings for unseen problem classes. Our results compare favourably to AutoFolio when using the same feature set. We discuss the relative importance of instance features to the task of selecting the best encodings, and compare several variations of the machine learning method.Comment: 24 pages, 10 figures, submitted to Constraints Journal (Springer

Influence of a home-based exercise intervention on human health indices in individuals with chronic spinal cord injury (HOMEX-SCI):study protocol for a randomized controlled trial

BACKGROUND: Spinal cord injury (SCI) creates a complex pathology that can lead to an increase in sedentary behaviours and deleterious changes in body composition. Consequently, individuals with SCI are at increased risk of developing cardiovascular disease and type-2 diabetes mellitus. While the role of physical activity on the reduction of chronic disease risk is well documented in non-disabled individuals the evidence is less conclusive for persons with SCI. The aim of this methodological paper is to outline the design of a study that will assess the role of a home-based exercise intervention on biomarkers of metabolic and cardiovascular health in persons with SCI: the HOMEX-SCI study. METHODS/DESIGN: Eligible participants will be inactive (physical activity level ≤1.60) individuals, with a chronic (more than 1 year) spinal cord lesion between the second thoracic and the fifth lumbar vertebrae, and aged between 18 and 65 years. Following baseline laboratory testing and lifestyle monitoring, participants will be randomly allocated to a control (CON) group or a 6-week home-based exercise intervention (INT) group. The INT consists of 45 minutes of moderate-intensity (60–65 % peak oxygen uptake) arm-crank exercise four times per week. Participants assigned to the CON group will be asked to maintain their normal lifestyle. The main outcomes of this study (biomarkers of metabolic and cardiovascular health) are obtained from venous blood samples, collected in the fasted and postprandial state. Eight other measurement categories will be assessed: (1) body composition, (2) physical activity, (3) energy intake, (4) measures of health and wellbeing, (5) resting metabolic rate, heart rate and blood pressure, (6) aerobic capacity, (7) immune function, and (8) adipose tissue gene expression. DISCUSSION: This study will explore the feasibility of home-based moderate-intensity exercise and ascertain its impact on metabolic and cardiovascular health in comparison to a lifestyle maintenance CON group. Findings from this study may help to inform new evidence-based physical activity guidelines and also help to elucidate the physiological mechanisms whereby exercise might exert beneficial effects in persons with chronic SCI. The results will also act as a scientific platform for further intervention studies in other diverse and at-risk populations. TRIAL REGISTRATION: International Standard Randomised Controlled Trial Number: ISRCTN57096451. Registered on 11 July 2014

Using Prediction to Improve Patient Flow in a Health Care Delivery Chain

Often, in a health care delivery chain, lack of coordination has been detrimental to timely, high quality care. This paper focuses on the two steps of the hospital health care delivery chain, an emergency department and a hospital’s inpatient units. Past research into this chain has suggested that early prediction of patient need for admission can be used to better align flow between the two departments. This chain and the nature of prediction in health care delivery are discussed as well as a how prediction may be useful in this context. Finally tools for making admission predictions are tested and their possible implications are explored. The results of this exploration show that both expert opinion and a Naïve Bayesian statistical approach have predictive value in this context

A single bout of upper-body exercise has no effect on postprandial metabolism in persons with chronic paraplegia

PURPOSE: The acute effects of a single bout of upper-body exercise on postprandial metabolism in persons with spinal cord injury are currently not well understood. The primary aim of this study was to evaluate the effects of a single bout of upper-body high-intensity interval exercise (HIIE) and moderate-intensity continuous exercise (MICE) in comparison with a no-exercise control (REST) condition on postprandial metabolic responses in persons with chronic paraplegia. METHODS: Ten participants (eight males, two females; age, 49 ± 10 yr; time since injury, 22 ± 13 yr) with chronic paraplegia took part in a randomized crossover study, consisting of three trials: HIIE (8 × 60 s at 70% peak power output [PPEAK]), MICE (25 min at 45% PPEAK), and REST, at least 3 d apart. Exercise was performed in the fasted state, and participants consumed a mixed-macronutrient liquid meal 1-h postexercise. Venous blood and expired gas samples were collected at regular intervals for 6-h postmeal consumption. RESULTS: There were no significant differences in postprandial incremental area under the curve for triglycerides (P = 0.59) or glucose (P = 0.56) between conditions. Insulin incremental area under the curve tended to be lower after MICE (135 ± 85 nmol·L-1 per 360 min) compared with REST (162 ± 93 nmol·L-1 per 360 min), but this did not reach statistical significance (P = 0.06, d = 0.30). Participants reported a greater fondness (P = 0.04) and preference for HIIE over MICE. CONCLUSIONS: After an overnight fast, a single bout of upper-body exercise before eating has no effect on postprandial metabolism in persons with chronic paraplegia, irrespective of exercise intensity. This suggests that alternative exercise strategies may be required to stimulate postprandial substrate oxidation for this population.</p

AutoLens: automated modeling of a strong lens's light, mass and source

The intricate analysis of a strong gravitational lens is a complex and computationally demanding problem, requiring the lensed source galaxy's extended light profile to be reconstructed simultaneously with non-linear modeling of the lens galaxy's mass and light. When successful, this analysis gives unrivaled insight into dark matter, cosmology and the most distant Universe. However, such studies remain resigned to small samples, simply due to how long this involved analysis takes. To address this, this thesis presents AutoLens, the first automated framework for comprehensive modeling of a strong gravitational lens's light, mass and source. Reconstruction of the lensed source galaxy uses an adaptive pixel-grid, which is derived in a completely stochastic manner such that a unique pixelization is used for every source reconstruction. This removes biases inherent to pixelized methods associated with the discrete nature of the source-plane. Light profile fitting of the lens galaxy is fully integrated into AutoLens, making it the first method to successfully unify modeling of the lens's light, mass and source into one coherent framework. This allows the method to advocate decomposed mass modeling, which treats separately the lens galaxy's light and dark matter. AutoLens is therefore capable of addressing a diverse range of unique science cases, most notably its ability to determine the central density of a lens galaxy's dark matter halo. These features are incorporated into a fully-automated pipeline, such that the analysis requires no input from the user after an initial setup. This pipeline is tested using a suite of simulated strong lens images which span a variety of source morphologies, lens profiles and lensing geometries. Following the completion of AutoLens's development, the method is ready to analyze the hundreds of archival images of strong gravitational lenses that have been amassed over the past decade, and which are still yet to receive a comprehensive lens analysis. With of order one hundred thousand lenses set to be discovered in the next decade, AutoLens's automated philosophy will be paramount to making analysis of the incoming strong lens samples feasible