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The UK is currently approaching a critical point in the fight against climate change. To achieve carbon neutral by 2050, it is crucial that the way in which buildings are heated are reviewed to determine the most suitable solution. The UK government has acknowledged that district heating (also referred to as heat networks) forms an important part of their plan for future sustainability in heating homes as well as improving energy costs. At present, there are five generations of district heating with distinctive improvements between each. However, research shows a lack of progression with only minor improvements to efficiencies and carbon emissions in the past two decades. Therefore, this paper aimed to review the key technologies and design principles of the low-impact network which shall be implemented into future networks to ensure sustainability and carbon neutral. Furthermore, data were utilised from UK government's ‘Heat Network Project Pipeline’ documents which cover a wide range of projects supported through the development stage by the UK Heat Network Delivery Unit. A statistical analysis was also undertaken to identify popular heat source technologies currently being implemented into the UK networks. Information such as technologies, size and costs were analysed to establish the intercorrelations, which may influence the type of technologies being selected. The results show that 56% of total networks contained Combined Heat and Power (CHP) as a primary heat source, of which over 40% were gas fired CHP, displaying the current dominance of the technology. Overall, it is evident in the UK that, the new networks have been improved from previous generations with a high concentration of renewable energy technologies and heat recovery methods being used. However, there is still a high reliance on natural gas, which does not fulfil the characteristics of a low-impact heating network.

We utilize optical pump – THz probe spectroscopy to estimate electron mobility in strained GaAs/(In,Al)As core/shell nanowires. Our results demonstrate that strain-induced reduction of the effective electron mass leads to a remarkable increase of the mobility. The data analysis indicates an important role of the inhomogeneous plasmon broadening that may affect THz spectra of dense ensembles of nanowires.

Optical pump – THz probe spectroscopy has been established as a tool for contactless probing of electronic transport in semiconductor nanowires (NWs) [1]. Particularly in III-V NWs, scattering rates of charge carriers, as well as their plasmonic resonances for typical doping levels, are located in the THz range. The analysis of the optical conductivity spectra using the localized surface plasmon model provides an estimation of the carrier density and the mobility. Here, we employ THz spectroscopy to study electron mobility in the strained GaAs core of GaAs/InAlAs core/shell nanowires. Owing to the lattice mismatch between the core and the shell in these NWs, the bandgap energy in the strained GaAs core exhibits a reduction by up to 40% [2]. Our results demonstrate that this effect is accompanied by a notable increase in the electron mobility by 30-50% with respect to a bulk GaAs [3]. We discuss the role of various scattering mechanisms and their dependence on strain and temperature. In addition to the homogeneous plasmon broadening caused by the carrier scattering, we also observe an inhomogeneous broadening in dense ensembles of NWs as illustrated in Fig. 1(a). Our modelling demonstrates that such broadening stems from the plasmonic interaction between neighboring NWs leading to the shift of the plasmon frequency as shown in Fig. 1(b). This effect has to be considered in the analysis of THz response of NWs since it may result in a significant underestimation of the mobility values.

Novel transistor concepts based on semiconductor nanowires promise high performance, lower energy consumption and better integrability in various platforms in nanoscale dimensions. Concerning the intrinsic transport properties of electrons in nanowires, relatively high mobility values that approach those in bulk crystals have been obtained only in core/shell heterostructures, where electrons are confined inside the core and, thus, their scattering on the nanowire surface is suppressed. Here, we demonstrate that the large strain in core/shell nanowires with significant lattice-mismatch between the core and the shell can affect the effective mass and the scattering of electrons in a way that boosts their mobility to higher levels compared to results obtained by any other means. Specifically, we use GaAs/InAlAs core/shell nanowires with a lattice mismatch in the range of 3%, grown on Si substrates by molecular beam epitaxy. Overgrown with an 80-nm-thick shell, the 22-nm-thick core is hydrostatically tensile-strained as found by both Raman scattering and photoluminescence measurements [1, 2]. The transport properties and dynamics of electrons were probed at room temperature by optical-pump THz-probe spectroscopy, which is an established contactless method that circumvents challenges in the fabrication of electrical contacts on nanowires. We found that the mobility of electrons inside the strained GaAs core undergoes a remarkable enhancement despite the small core thickness, becoming 30 – 50 % higher than in unstrained GaAs/AlGaAs nanowires or bulk GaAs [2]. Our studies are extended to modulation-doped GaAs/InAlAs nanowires and the results will be presented. The reported strain-induced mobility enhancement is of major importance for the realization of transistors with high speed and low power consumption, having the potential to trigger major advancements in high-performance nanowire electronic devices monolithically integrated in Si platforms. [1] L. Balaghi, G. Bussone

Optical pump – Terahertz (THz) probe (OPTP) spectroscopy has proven efficacy for contactless probing of electronic transport in semiconductor NWs [1]. Particularly in III-V NWs, scattering rates of charge carriers, as well as their plasmonic resonances for typical doping levels, are located in the THz range. The analysis of the optical conductivity spectra using the localized surface plasmon model allows estimating the carrier lifetime and the carrier mobility. Here, OPTP spectroscopy is employed to study two unique phenomena in GaAs/(In,Al,Ga)As core/shell nanowires. First, it is demonstrated that the mobility of electrons in the hydrostaticallystrained GaAs core (owing to the lattice mismatch between the core and the shell [2]) exceeds the mobility in bulk GaAs by 30-50% [3]. The role of the various scattering mechanisms is analyzed as a function of strain and temperature. Depending on the density of NWs in the probed sample, some of them can form bundles or touch each other, leading to an inhomogeneous broadening of the plasmon resonance. We discuss the role of this effect and its impact on the estimation of carrier mobility [3, 4]. Second, we demonstrate a strong THz nonlinearity using single-cycle intense THz pulses with peak electric fields reaching up to 0.6 MV/cm. With the increase of the driving THz field, we observe a systematic redshift of the plasmon frequency, accompanied by a gradual suppression of the spectral weight. Remarkably, the spectral weight does not remain proportional to the square of the plasmon frequency when the driving electric field exceeds 0.4 MV/cm, indicating an onset of a spatially inhomogeneous carrier distribution across the NW. The observed behavior can be ascribed to nonlinear effects caused by the scattering of electrons from the Gamma- to L-valley occurring in the high electric field regime. However, in contrast to bulk semiconductors, this effect initially sets in at hot spots of the NW, where the local electric field is enha

Images semantic segmentation on moulds is presented to achieve automatic and continuous defect detection during injection moulding (IM) processing. Generally, a vital prerequisite of training a robust segmentation neural network is to build a suitable dataset, which requires a large amount of image data with plentiful mould colours, different illumination conditions and specific defect labels. The approach requires long data preparation to collect a sufficient dataset, which could meet the needs of online defect detection during injection moulding. To address robust dataset development, the present work uses 3D CAD modelling software to fabricate defects and colours on moulds, creating an augmented dataset mixed with virtual data and real-process data. In this investigation, moulds printed by vat photopolymerization is used as object for which both mould pictures during injection moulding process and virtual mould pictures from 3D modelling software are collected. Mixed datasets with different proportion of virtual images are labelled and fed into the segmentation neural network. The experimental work shows that the proposed method provides a reliable augmentation on the dataset for subsequent IM semantic segmentation framework.

Tropospheric ozone is an air pollutant that substantially harms vegetation and is also strongly dependent on various vegetation-mediated processes. The interdependence between ozone and vegetation may constitute feedback mechanisms that can alter ozone concentration itself but have not been considered in most studies to date. In this study we examine the importance of dynamic coupling between surface ozone and leaf area index (LAI) in shaping ozone air quality and vegetation. We first implement an empirical scheme for ozone damage on vegetation in the Community Land Model (CLM) and simulate the steady-state responses of LAI to long-term exposure to a range of prescribed ozone levels (from 0 to 100 ppb). We find that most plant functional types suffer a substantial decline in LAI as ozone level increases. Based on the CLM-simulated results, we develop and implement in the GEOS-Chem chemical transport model a parameterization that computes fractional changes in monthly LAI as a function of local mean ozone levels. By forcing LAI to respond to ozone concentrations on a monthly timescale, the model simulates ozone-LAI coupling dynamically via biogeochemical processes including biogenic volatile organic compound (VOC) emissions and dry deposition, without the complication from meteorological changes. We find that ozone-induced damage on LAI can lead to changes in ozone concentrations by-1.8 to +3 ppb in boreal summer, with a corresponding ozone feedback factor of-0.1 to +0.6 that represents an overall self-amplifying effect from ozone-LAI coupling. Substantially higher simulated ozone due to strong positive feedbacks is found in most tropical forests, mainly due to the ozone-induced reductions in LAI and dry deposition velocity, whereas reduced isoprene emission plays a lesser role in these low-NOx environments. In high-NOx regions such as the eastern US, Europe, and China, however, the feedback effect is much weaker and even negative in some regions, reflecting the comp