Small molecule tandem organic photovoltaic cells incorporating an α-NPD optical spacer layer

We report an improvement in power conversion efficiency in a small molecule tandem organic photovoltaic (OPV) device by the optimisation of current balancing of the sub-cells using an optical spacer layer. A co-deposited layer of N,N’-bis(1-naphthyl)-N,N′-diphenyl-1,1’-biphenyl-4,4’-diamine (α-NPD) and molybdenum oxide was used as the optical spacer layer and provided a highly transparent and conductive layer. Optical simulations showed the addition of the optical spacer in a boron subphthalocyanine (SubPc)/C60 based tandem OPV device increased the SubPc absorption in the front sub-cell and resulted in current balancing through the device. Fabricated tandem OPV devices showed similar trends, with the power conversion efficiency increasing from 2.3% to 4.2% with the addition of an optimised optical spacer thickness. External quantum efficiency and total absorption efficiency measurements back up the optical model data which attribute the increased performance to improved SubPc absorption in the front sub-cell, balancing the photocurrents of the two sub-cells

Successful Termination in Timed CSP

In previous work the authors investigated the inconsistencies of how successful termination was modelled in Hoare, Brookes and Roscoe's original CSP. This led to the definition of a variant of CSP, called CSPt. CSPt presents a solution to these problems by means of adding a termination axiom to the original process axioms. In this paper we investigate how successful process termination is modelled in Reed and Roscoe's Timed CSP, which is the temporal version of Hoare's original untimed CSP. We discuss the issues that need to be considered when selecting termination axioms for Timed CSP, based on our experiences in defining CSPt. The outcome of this investigation and discussion is a collection of candidate successful termination axioms that could be added to the existing Timed CSP models, leading to an improved treatment of successful termination within the Timed CSP framework. We outline how these termination axioms would be added to the family of semantic models for Timed CSP. Finally, we outline what further work needs to be done once these new models for Timed CSP have been defined. For example, it would then be possible to define timed versions of the new more flexible parallel operators introduced in CSPt

Specifying and Analysing Networks of Processes in CSPt (or In Search of Associativity)

In proposing theories of how we should design and specify networks of processes it is necessary to show that the semantics of any language we use to write down the intended behaviours of a system has several qualities. First in that the meaning of what is written on the page reflects the intention of the designer; second that there are no unexpected behaviours that might arise in a specified system that are hidden from the unsuspecting specifier; and third that the intention for the design of the behaviour of a network of processes can be communicated clearly and intuitively to others. In order to achieve this we have developed a variant of CSP, called CSPt, designed to solve the problems of termination of parallel processes present in the original formulation of CSP. In CSPt we introduced three parallel operators, each with a different kind of termination semantics, which we call synchronous, asynchronous and race. These operators provide specifiers with an expressive and flexible tool kit to define the intended behaviour of a system in such a way that unexpected or unwanted behaviours are guaranteed not to take place. In this paper we extend out analysis of CSPt and introduce the notion of an alphabet diagram that illustrates the different categories of events that can arise in the parallel composition of processes. These alphabet diagrams are then used to analyse networks of three processes in parallel with the aim of identifying sufficient constraints to ensure associativity of their parallel composition. Having achieved this we then proceed to prove associativity laws for the three parallel operators of CSPt. Next, we illustrate how to design and construct a network of three processes that satisfy the associativity law, using the associativity theorem and alphabet diagrams. Finally, we outline how this could be achieved for more general networks of processes

Recent advances in understanding the effects of climate change on coral reefs

Climate change is one of the greatest threats to the persistence of coral reefs. Sustained and ongoing increases in ocean temperatures and acidification are altering the structure and function of reefs globally. Here, we summarise recent advances in our understanding of the effects of climate change on scleractinian corals and reef fish. Although there is considerable among-species variability in responses to increasing temperature and seawater chemistry, changing temperature regimes are likely to have the greatest influence on the structure of coral and fish assemblages, at least over short–medium timeframes. Recent evidence of increases in coral bleaching thresholds, local genetic adaptation and inheritance of heat tolerance suggest that coral populations may have some capacity to respond to warming, although the extent to which these changes can keep pace with changing environmental conditions is unknown. For coral reef fishes, current evidence indicates increasing seawater temperature will be a major determinant of future assemblages, through both habitat degradation and direct effects on physiology and behaviour. The effects of climate change are, however, being compounded by a range of anthropogenic disturbances, which may undermine the capacity of coral reef organisms to acclimate and/or adapt to specific changes in environmental conditions

Artificial intelligence for safe assisted driving based on user head movements in robotic wheelchairs

Wheelchairs users don’t always have the ability to control a powered wheelchair using a normal joystick due to factors that restrict the use of their arms and hands. For a certain number of these individuals, which still retain mobility of their head, alternative methods have been devised, such as chin-joysticks, head switches or sip-and-puff control. Such solutions can be bulky, cumbersome, unintuitive or simply uncomfortable and taxing for the user. This work presents an alternative head-based drive-control system for wheelchair users