Flat-top temperature tuning response in periodically-poled nonlinear crystals

Second harmonic generation via periodically-poled nonlinear materials offers an efficient means of generating high-quality visible light that would be otherwise unattainable with traditional laser sources. While this technology has the potential for implementation in many mass-industrial applications, temperature stability requirements of 0.1 deg.C can make packaging with a pump source problematic. Using our high fidelity poling technique we have achieved precise placement of poled domains in Lithium Niobate based on the resulting mathematical models. These initial devices provide more than 4 deg.C flat-top temperature stability, albeit with a corresponding loss in operational efficiency. Our aim is to implement improved designs in magnesium-doped Lithium Niobate for packaging with near-room temperature diode-based pump sources, as could be applied towards RGB TV and projector applications

Stochastic Models for Replication Origin Spacings in Eukaryotic DNA Replication

We consider eukaryotic DNA replication and in particular the role of replication origins in this process. We focus on origins which are `active' - that is, trigger themselves in the process before being read by the replication forks of other origins. We initially consider the spacings of these active replication origins in comparison to certain probability distributions of spacings taken from random matrix theory. We see how the spacings between neighbouring eigenvalues from certain collections of random matrices has some potential for modelling the spacing between active origins. This suitability can be further augmented with the use of uniform thinning which acts as a continuous deformation between correlated eigenvalue spacings and exponential (Poissonian) spacings. We model the process as a modified 2D Poisson process with an added exclusion rule to identify active points based on their position on the chromosome and trigger time relative to other origins. We see how this can be reduced to a stochastic geometry problem and show analytically that two active origins are unlikely to be close together, regardless of how many non-active points are between them. In particular, we see how these active origins repel linearly. We then see how data from various DNA datasets match with simulations from our model. We see that whilst there is variety in the DNA data, comparing the data with the model provides insight into the replication origin distribution of various organisms.Comment: 18 pages, 26 figure

Establishing the requirements to support improved adoption of alternate technologies for the long-haul road freight decarbonisation

The UK has a target of achieving net-zero carbon emissions by 2050, which will require the decarbonisation of road transport. However, in the long-haul road freight segment, the optimal pathway to achieving net-zero is uncertain. This review paper explores and evaluates existing approaches to building decarbonisation pathways for heavy goods vehicles (HGVs). The search and review methodology, utilising the frameworks SALSA, PRISMA, and PESTEL, found gaps in three main aspects of pathway building. While a number of the studies considered vehicle or energy systems, a few took a broader system-level view. The parameters used for measuring the utility of the alternate technology required to achieve net-zero were not comprehensive. Further, the pathways lacked a socio-technical approach. The findings from the research have been used to provide insights and a conceptual framework that can be used for building a comprehensive model for improving technology adoption for the HGV decarbonisation pathway

Chemical and device degradation in PCPDTBT: PCBM solar cells using XPS and ToF-SIMS

Analysis of the degradation routes for PCPDTBT-based solar cells under illumination and in the presence of air have been conducted using a combination of X-ray Photoelectron Spectroscopy (XPS), Time-Of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) and solar cell device data. After ageing, XPS studies show that PCPDTBT appears as an oxygen-containing polymer, with data indicating that a break-up in the aromatic rings, formation of sulphates at the thiophene ring, chain scission in the polymer backbone and also loss of side chains. XPS studies on active layers blends of PCPDTBT and PCBM also show significant changes in the vertical composition during ageing, with increased enrichment of PCPDTBT observed at the top surface and that the use of a processing additive (ODT) has a negative impact on the morphological stability. TOF-SIMS has been used to study electrode degradation during ageing experiments leads to migration of indium and tin ions into the active layer in non-inverted devices, but is eliminated for inverted devices.RAEng and EC financial support and Prof TJ Lewis (Bangor) for technical suppor

Biogeography of cephalopods in the Southern Ocean using habitat suitability prediction models

Our understanding of how environmental change in the Southern Ocean will affect marine diversity, habitats and distribution remain limited. The habitats and distributions of Southern Ocean cephalopods are generally poorly understood, and yet such knowledge is necessary for research and conservation management purposes, as well as for assessing the potential impacts of environmental change. We used net-catch data to develop habitat suitability models for 15 of the most common cephalopods in the Southern Ocean. Using modeled habitat suitability, we assessed favorable areas for each species and examined the relationships between species distribution and environmental parameters. The results compared favorably with the known ecology of these species and with spatial patterns from diet studies of squid predators. The individual habitat suitability models were overlaid to generate a “hotspot” index of species richness, which showed higher numbers of squid species associated with various fronts of the Antarctic circumpolar current. Finally, we reviewed the overall distribution of these species and their importance in the diet of Southern Ocean predators. There is a need for further studies to explore the potential impacts of future climate change on Southern Ocean squid

Alternative selection of processing additives to enhance the lifetime of OPVs

The use of processing additives is known to accelerate the degradation of Organic Photovoltaics (OPVs) and therefore, this paper studies the impact of selecting alternative processing additives for PCPDTBT:PC71BM solar cells in order to improve the stability. The use of naphthalene-based processing additives has been undertaken, which is shown to reduce the initial power conversion efficiency by 23%-42%, primarily due to a decrease in the short-circuit current density, but also fill factor. However, the stability is greatly enhanced by using such additives, with the long term stability (T50%) enhanced by a factor of four. The results show that there is a trade-off between initial performance and stability to consider when selecting the initial process additives. XPS studies have provided some insight into the decreased degradation and show that using 1-chloronaphthalene (ClN) leads to reduced morphology changes and reduced oxidation of the thiophene-ring within the PCPDTBT backbone.HW would like to thank Bangor University for his 125 scholarship enabling his PhD study. JK would like to thank Sêr Cymru national research network in Advanced Engineering and Materials and the Newton Research Collaboration Programme scheme through the Royal Academy for Engineerin