Open Access compliance and financial report to RCUK 2015-16

This report provides information in support of Northumbria University’s compliance with the third year of RCUK’s Open Access policy within the context of the University’s wider work to support Open Access (OA) as part of its mission to create and apply knowledge for the benefit of individuals and the economy through ground-breaking research. The data underlying this report is available on Figshare: https://dx.doi.org/10.6084/m9.figshare.3859023.v

Complex beam profiles for laser annealing of thin-film CdTe photovoltaics

Within the family of thin-film photovoltaics (PV), cadmium telluride (CdTe) has the fastest growing market share due to its high efficiencies and low cost. However, as with other PV technologies, the energy required to manufacture the panels is excessive, encompassing high environmental impact and manufacturing energy payback times of the order of 2-3 years. As part of the manufacturing process, the panels are annealed at temperatures of approximately 400°C for 30 minutes, which is inherently inefficient. Laser heating has previously been investigated as an alternative process for thin film annealing, due to its advantages with regard to its ability to localise heat treatment, anneal selectively and its short processing time. In this investigation, results focussing on improvements to the laser-based annealing process, designed to mitigate panel damage by excessive thermal gradients, are presented. Simulations of various laser beam profiles are created in COMSOL and used to demonstrate the benefit of laser beam shaping for thin film annealing processes. An enabling technology for this, the holographic optical element (HOE), is then used to experimentally demonstrate the redistribution of laser beam energy into an optimal profile for annealing, eliminating thermal concentrations

Optimising Resources to Develop a Strategic Approach to Open Access - final report

Our Open Access (OA) Pathfinder, a collaboration between the University of Northumbria and the University of Sunderland, aimed to develop and share tools and best practice to enable HEIs with limited external resources to effectively and creatively respond to the challenges and opportunities presented by OA. To achieve this we identified four discrete project objectives and a methodology which emphasised engagement locally and with the other HEI’s that comprised the wider programme. Importantly, the wider context of this focus was our recognition of the global movement towards open research and an impact agenda which demonstrates and rewards value for money from public investment. Subsequently, throughout our project activity we aimed to explore and develop extensible models, policies and procedures which go beyond OA compliance to engage with and shape these wider debates. Throughout the programme we disseminated our preliminary findings and ongoing thinking via our project blog (http://oapathfinder.wordpress.com) as well as fora including conferences and workshops. By the end of the two year programme, our project had successfully delivered against the four objectives and in so doing demonstrated tangible impact. Crucially, for each aspect of our project further work is needed to refine and develop solutions and practice to meet the challenges and opportunities presented by OA. We believe that against a background of a rapidly evolving policy and funding landscape JISC are uniquely positioned to facilitate a community of practice to play a pivotal role in making this happen

A 'design for energy minimization' approach to reduce energy consumption during the manufacturing phase

The combustion of fossil fuels for energy generation has contributed considerably to the effects of climate change. In order to reduce fossil fuel consumption, designers are increasingly seeking to reduce the energy consumption of products over their life cycle. To achieve a significant reduction in energy consumption, it is essential that energy considerations are incorporated within the design phase of a product, since the majority a product's environmental impact is determined during this phase. This work proposes a new ‘Design for Energy Minimization’ (DfEM) approach, which is intended to provide increased transparency with respect to the energy consumed during manufacture in order to help inform design decisions. An energy simulation model based on this approach is then presented to aid designers during the design phase. The application of this novel design tool is demonstrated in two cases: That of a simple product (designed by a single Original Equipment Manufacturer (OEM) through a centralized approach); and a complex product (designed by a number of designers within a supply chain using a distributed approach). The subsequent benefits to energy minimization are then discussed and conclusions drawn

Annealing of thin-film cadmium telluride photovoltaics using holographically controlled laser processing

CdTe-based thin film solar cells currently represent one of the fastest growing PV technologies, with a superior combination of efficiency, energy payback time and lifecycle environmental impact. However, the current post-deposition annealing treatment is still an energy intensive step of the manufacturing process. A novel method is presented for annealing of CdTe using a high-power diode laser (35 W, 808 nm) for thermal post-processing, combined with holographic optical elements (HOE’s) for laser beam heat flow control. The advantage of a laser for annealing lies in its ability to selectively heat only the surface of the CdTe solar cell; improving energy efficiency, process speed and energy resilience. Heat transfer simulations were used to predict the effects of different laser irradiance profiles on the annealing process thermal cycle influence the experimental design and predict optimal laser irradiance profiles. Variations in power and process speed on as-deposited and MgCl2-treated close-space sublimated (CSS) CdTe samples have been performed. The results were characterised using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Optical properties were analysed with a spectrophotometer and ellipsometric spectroscopy (SE). The laser annealing treatment was found to be effective in promoting Chlorine diffusion and improving the optical and morphological properties of CdTe thin film device

Use of laser beam diffraction for non-invasive characterisation of CdTe thin film growth structure

Characterisation of Cadmium Telluride (CdTe) thin films commonly requires the use of invasive techniques for the identification of their structural growth and the detection of defects which occur during the deposition process. Structural growth and the presence of defects can affect the performance of the final device. A non-invasive inspection system for CdTe films has been developed to identify the structural properties of this material, comparing two different deposition techniques, Close Space Sublimation (CSS) and Magnetron Sputtering (MS). The proposed system utilises a 1 μm diode laser which passes through the CdTe layer, originating detectable diffraction patterns, which are characterised using image processing techniques and assessed using a neural network-based cognitive decision-making support system. Results are found to be consistent with the conventional microscopic techniques (SEM and TEM) used to analyse morphological and structural properties of thin-film CdTe solar cells

Laser annealing of thin film CdTe solar cells using a 808 nm diode laser

© 2017 IEEE. We report on the effect of a new laser annealing treatment for thin film CdTe solar cells using a 808 nm diode laser. As-deposited, laser annealed and MgCl2treated/laser annealed CdTe thin films have been analysed. One part of the work has been focused on understanding the efficacy of the activation treatment by laser annealing. The results show partial chlorine diffusion and associated partial re-crystallisation of the absorber. The second part of this work has been focused on the effect of the treatment on the chemical composition of the CdTe surface. It has been found that the process also contributes to the formation of a Te-rich layer on the surface of the CdTe absorber, which may provide a useful process to produce a back contact. This paper reveals the effect of the laser treatment on the microstructural properties of the CdTe absorber material. The microstructure has been analysed using STEM/EDX, HRTEM and XRD. Further work is required to optimise the process but it has the potential to provide much greater control than current activation methods and also to provide a Te back contact suitable for CdTe solar cells

Closing The Brief Case: A Rare Case of Invasive Amebiasis Requiring Emergency Subtotal Colectomy in an HIV-Positive Man.

In April 2017, a 56-year-old HIV-positive man was transferred from another institution to our regional infectious disease unit having presented with 2 weeks of profuse, watery diarrhea accompanied by intermittent, fresh bleeding of the rectum. Symptoms had started during a 2-month vacation to Indonesia, Vietnam, and Malaysia. While on vacation, he stayed in hotels in urban areas, had no rural travel, and drank only bottled water. He reported that he was not a man who has sex with men (MSM) and preferred to discuss his further sexual history confidentially with the genitourinary medicine team. Two months prior to admission, his CD4 count was 194 cells/mm3, and while taking an antiretroviral therapy regimen consisting of tenofovir, emtricitabine, and nevirapine, his HIV RNA had been undetectable in his plasma for 3 years

An Efficient Coding Hypothesis Links Sparsity and Selectivity of Neural Responses

To what extent are sensory responses in the brain compatible with first-order principles? The efficient coding hypothesis projects that neurons use as few spikes as possible to faithfully represent natural stimuli. However, many sparsely firing neurons in higher brain areas seem to violate this hypothesis in that they respond more to familiar stimuli than to nonfamiliar stimuli. We reconcile this discrepancy by showing that efficient sensory responses give rise to stimulus selectivity that depends on the stimulus-independent firing threshold and the balance between excitatory and inhibitory inputs. We construct a cost function that enforces minimal firing rates in model neurons by linearly punishing suprathreshold synaptic currents. By contrast, subthreshold currents are punished quadratically, which allows us to optimally reconstruct sensory inputs from elicited responses. We train synaptic currents on many renditions of a particular bird's own song (BOS) and few renditions of conspecific birds' songs (CONs). During training, model neurons develop a response selectivity with complex dependence on the firing threshold. At low thresholds, they fire densely and prefer CON and the reverse BOS (REV) over BOS. However, at high thresholds or when hyperpolarized, they fire sparsely and prefer BOS over REV and over CON. Based on this selectivity reversal, our model suggests that preference for a highly familiar stimulus corresponds to a high-threshold or strong-inhibition regime of an efficient coding strategy. Our findings apply to songbird mirror neurons, and in general, they suggest that the brain may be endowed with simple mechanisms to rapidly change selectivity of neural responses to focus sensory processing on either familiar or nonfamiliar stimuli. In summary, we find support for the efficient coding hypothesis and provide new insights into the interplay between the sparsity and selectivity of neural responses