Muon spin relaxation as a probe of electron spin relaxation in organic semiconductors

PhDThe purpose of this thesis is to study the electron spin relaxation (eSR) in small organic molecular semiconductors using the muon spin relaxation (MuSR) technique. One of the inherent problems in utilising the spin degree of freedom is the lack of understanding of the fundamental mechanisms behind spin relaxation. Two interactions have been proposed as the dominant mechanisms behind the spin relaxation, the Hyper ne interaction (HFI) and the Spin Orbit (SO) interaction. There remains much debate over the models for these interactions and their exact role, a contention that drives the work carried out in this thesis. The MuSR technique is utilised providing a novel molecular scale probe sensitive to relaxation rates in the range of 0.01-10 MHz. The Avoided Level crossing (ALC) MuSR application is useful in accessing the spin relaxation information. Temperature dependent ALC-MuSR measurements are performed for a selection of functionalised acenes and Quinolate molecules. Transverse eld MuSR measurements are also taken to determine the Hyper ne coupling constants present. DFT and semi-empirical computational methods are employed to determine theoretical values for the isotropic and anisotropic terms and the suitability of these methods was discussed. It is concluded that an intra-molecular eSR is present in all small organic molecular semiconductors. The mechanism behind this eSR was found not to be the HFI but in fact the SO interaction. It is also determined that the eSR is coupling to the vibrations in the molecule and a possible theory based on the curvature of the molecule from the vibrational modes inducing an enhanced SO coupling is proposed, which results in the eSR. The nal part of this thesis looks at the future experiments that have been initiated or can be conducted to further the understanding of spin relaxation and determine the role of a vibrationally enhanced SO coupling

Effect of a differentiated service delivery model on virological failure in adolescents with HIV in Zimbabwe (Zvandiri): a cluster-randomised controlled trial.

BACKGROUND: Adolescents living with HIV face challenges to their wellbeing and antiretroviral therapy adherence and have poor treatment outcomes. We aimed to evaluate a peer-led differentiated service delivery intervention on HIV clinical and psychosocial outcomes among adolescents with HIV in Zimbabwe. METHODS: 16 public primary care facilities (clusters) in two rural districts in Zimbabwe (Bindura and Shamva) were randomly assigned (1:1) to provide enhanced HIV care support (the Zvandiri intervention group) or standard HIV care (the control group) to adolescents (aged 13-19 years) with HIV. Eligible clinics had at least 20 adolescents in pre-ART or ART registers and were geographically separated by at least 10 km to minimise contamination. Adolescents were eligible for inclusion if they were living with HIV, registered for HIV care at one of the trial clinics, and either starting or already on ART. Exclusion criteria were being too physically unwell to attend clinic (bedridden), psychotic, or unable to give informed assent or consent. Adolescents with HIV at all clinics received adherence support through adult counsellors. At intervention clinics, adolescents with HIV were assigned a community adolescent treatment supporter, attended a monthly support group, and received text messages, calls, home visits, and clinic-based counselling. Implementation intensity was differentiated according to each adolescent's HIV vulnerability, which was reassessed every 3 months. Caregivers were invited to a support group. The primary outcome was the proportion of adolescents who had died or had a viral load of at least 1000 copies per μL after 96 weeks. In-depth qualitative data were collected and analysed thematically. The trial is registered with Pan African Clinical Trial Registry, number PACTR201609001767322. FINDINGS: Between Aug 15, 2016, and March 31, 2017, 500 adolescents with HIV were enrolled, of whom four were excluded after group assignment owing to testing HIV negative. Of the remaining 496 adolescents, 212 were recruited at Zvandiri intervention sites and 284 at control sites. At enrolment, the median age was 15 years (IQR 14-17), 52% of adolescents were female, 81% were orphans, and 47% had a viral load of at least 1000 copies per μL. 479 (97%) had primary outcome data at endline, including 28 who died. At 96 weeks, 52 (25%) of 209 adolescents in the Zvandiri intervention group and 97 (36%) of 270 adolescents in the control group had an HIV viral load of at least 1000 copies per μL or had died (adjusted prevalence ratio 0·58, 95% CI 0·36-0·94; p=0·03). Qualitative data suggested that the multiple intervention components acted synergistically to improve the relational context in which adolescents with HIV live, supporting their improved adherence. No adverse events were judged to be related to study procedures. Severe adverse events were 28 deaths (17 in the Zvandiri intervention group, 11 in the control group) and 57 admissions to hospital (20 in the Zvandiri intervention group, 37 in the control group). INTERPRETATION: Peer-supported community-based differentiated service delivery can substantially improve HIV virological suppression in adolescents with HIV and should be scaled up to reduce their high rates of morbidity and mortality. FUNDING: Positive Action for Adolescents Program, ViiV Healthcare

Scaling up peer-led community-based differentiated support for adolescents living with HIV: keeping the needs of youth peer supporters in mind to sustain success.

INTRODUCTION: Low rates of viral suppression among adolescents living with HIV (ALHIV) indicate that more effective support is urgently required at scale. The provision of peer support has generated considerable enthusiasm because it has the potential to ameliorate the complex social and relational challenges which underpin suboptimal adherence. Little is known about the impact on young peer supporters themselves, which is the focus of this paper. METHODS: We present qualitative findings from the Zvandiri trial investigating the impact of a peer support intervention on the viral load for beneficiaries (ALHIV, aged 13 to 19 years) in Zimbabwe. The Zvandiri peer supporters aged 18 to 24 years, known as community adolescent treatment supporters (CATS), are themselves living with HIV. Individual in-depth interviews were conducted in late 2018 with 17 CATS exploring their experiences of delivering peer support and their own support needs. Interviews were analysed iteratively using thematic analysis. RESULTS: The CATS reported that being peer supporters improved their own adherence behaviour and contributed to an improved sense of self-worth. The social connections between the CATS were a source of comfort and enabled them to develop skills to manage the challenging aspects of their work. Two substantial challenges were identified. First, their work may reveal their HIV status. Second, managing the emotional labour of this caring work; given how commonly the complexity of the beneficiaries' needs mirrored the circumstances of their own difficult lives. Both challenges were ameliorated by the support the CATS provided to each other and ongoing supervision from the adult mentor. There was variation in whether they felt their roles were appropriately valued through the remuneration they received and within the health system. There was a consensus that their experience meant that they would graduate from being a CATS with transferable skills that could enhance their employability. CONCLUSIONS: Their experiences illustrate the advantages and opportunities of being a CATS. To minimize potential harms, it is vital to ensure that they feel valued in their role, which can be demonstrated by the provision of appropriate remuneration, recognition and respect, and that there is continued investment in ongoing support through ongoing training and mentoring

Little perpetrators, witness-bearers and the young and the brave: towards a post-transitional aesthetics

The aesthetic choices characterizing work produced during the transition to democracy have been well documented. We are currently well into the second decade after the 1994 election - what then of the period referred to as the 'second transition'? Have trends consolidated, hardened, shifted, or have new 'post-transitional' trends emerged? What can be expected of the future 'born free' generation of writers and readers, since terms such as restlessness, dissonance and disjuncture are frequently used to describe the experience of constitutional democracy as it co-exists with the emerging new apartheid of poverty? Furthermore, what value is there in identifying post-transitional aesthetic trends?DHE

Peeling off effects in vertically aligned Fe3C filled carbon nanotubes films grown by pyrolysis of ferrocene

We report the observation of an unusual self-peeling effect which allows the synthesis of free standing vertically aligned carbon nanotube films filled with large quantities of Fe3C and small quantities of ?-Fe crystals. We demonstrate that this effect depends on the interplay of three main factors: (1) the physical interactions between the chosen substrate surface and grown carbon nanotubes (CNTs), which is fixed by the composition of the used substrate (111 SiO2/Si or quartz), (2) the CNT-CNT Van der Waals interactions, and (3) the differential thermal contraction between the grown CNT film and the used substrate, which is fixed by the cooling rate differences between the grown film and the used quartz or Si/SiO2 substrates. The width and stability of these films are then further increased to cm-scale by addition of small quantities of toluene to the ferrocene precursor

Peeling off effects in vertically aligned Fe3C filled carbon nanotubes films grown by pyrolysis of ferrocene

We report the observation of an unusual self-peeling effect which allows the synthesis of free standing vertically aligned carbon nanotube films filled with large quantities of Fe3C and small quantities of ?-Fe crystals. We demonstrate that this effect depends on the interplay of three main factors: (1) the physical interactions between the chosen substrate surface and grown carbon nanotubes (CNTs), which is fixed by the composition of the used substrate (111 SiO2/Si or quartz), (2) the CNT-CNT Van der Waals interactions, and (3) the differential thermal contraction between the grown CNT film and the used substrate, which is fixed by the cooling rate differences between the grown film and the used quartz or Si/SiO2 substrates. The width and stability of these films are then further increased to cm-scale by addition of small quantities of toluene to the ferrocene precursor

Muon spin relaxation study of spin dynamics in poly(triarylamine)

Organic semiconductors (OSCs) have been of great interest over the last couple of decades owing to their mechanic flexibility, ease of processing, high tuneability and availability. One area of OSCs that is of growing interest is polymers as they possess many of the desirable properties, in particular print processing and tunability of electronic properties, necessary for application in devices such as organic solar cells and the spin valves being engineered for hard disks and logic devices. Much focus has been given in recent years to the areas of research including the electron and hole dynamics, transport mechanisms and spin relaxation in OSCs in order to utilise them in novel organic devices. In this paper the µSR technique is applied to carry out an in depth study of the electron dynamics and spin relaxation in the commonly used Poly(triarylamine) polymer (PTAA). It is shown that the electron wavefunction can be considered localised to the aromatic rings providing a strong hyperfine coupling interaction with the muon. In addition the presence of an electron spin relaxation (eSR) is demonstratated that resembles that previously reported in the small organic molecule series

Participant engagement with a UK community-based preschool childhood obesity prevention programme: : a focused ethnography study

Background Children’s centres in the UK provide a setting for public health programmes; offering support to families living in the most disadvantaged areas where obesity prevalence is at its highest. Health, Exercise and Nutrition in the Really Young (HENRY) is an eight-week obesity prevention programme currently delivered in children’s centres across the UK. However, low participant engagement in some local authorities threatens its potential reach and impact. This study aimed to explore the factors influencing participant engagement with HENRY to describe where local intervention may support engagement efforts. Method A focused ethnography study was undertaken in five children’s centres delivering HENRY across the UK. One hundred and ninety hours of field observations, 22 interviews with staff (commissioners, HENRY co-ordinators, managers and facilitators) and six focus groups (36 parents), took place over five consecutive days in each centre. The Consolidated Framework for Implementation Research (CFIR) was used to guide the observations and analysis of the data. Results Three overarching themes described the factors influencing participant engagement with HENRY: local authority decision making around children’s centre programmes; children’s centre implementation of HENRY; and the participant experience of HENRY. The results indicate that factors influencing participant engagement with public health programmes begin at the commissioning body level, influencing children’s centre implementation and subsequently the experience of participants. Local authority funding priorities and constraints influence availability of places and who these places are offered to, with funding often targeted towards those deemed most at need. This was perceived to have a detrimental effect on participant experience of the programme. Conclusion In summary, participant engagement is affected by multiple factors, working at different levels of the children’s centre and local authority hierarchy, most of which are at play even before participants decide whether or not they choose to enrol and maintain attendance. For programmes to achieve their optimal reach and impact, factors at the commissioning and local implementation level need to be addressed prior to addressing participant facing issues

Averting biodiversity collapse in tropical forest protected areas

The rapid disruption of tropical forests probably imperils global biodiversity more than any other contemporary phenomenon¹⁻³. With deforestation advancing quickly, protected areas are increasingly becoming final refuges for threatened species and natural ecosystem processes. However, many protected areas in the tropics are themselves vulnerable to human encroachment and other environmental stresses⁴⁻⁹. As pressures mount, it is vital to know whether existing reserves can sustain their biodiversity. A critical constraint in addressing this question has been that data describing a broad array of biodiversity groups have been unavailable for a sufficiently large and representative sample of reserves. Here we present a uniquely comprehensive data set on changes over the past 20 to 30 years in 31 functional groups of species and 21 potential drivers of environmental change, for 60 protected areas stratified across the world’s major tropical regions. Our analysis reveals great variation in reserve ‘health’: about half of all reserves have been effective or performed passably, but the rest are experiencing an erosion of biodiversity that is often alarmingly widespread taxonomically and functionally. Habitat disruption, hunting and forest-product exploitation were the strongest predictors of declining reserve health. Crucially, environmental changes immediately outside reserves seemed nearly as important as those inside in determining their ecological fate, with changes inside reserves strongly mirroring those occurring around them. These findings suggest that tropical protected areas are often intimately linked ecologically to their surrounding habitats, and that a failure to stem broad-scale loss and degradation of such habitats could sharply increase the likelihood of serious biodiversity declines.Keywords: Ecology, Environmental scienc