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Van der Waals heterostructures form a massive interdisciplinary research field, fueled by the rich material science opportunities presented by layer assembly of artificial solids with controlled composition, order and relative rotation of adjacent atomic planes. Here we use atomic resolution transmission electron microscopy and multiscale modeling to show that the lattice of MoS$_2$ and WS$_2$ bilayers twisted to a small angle, $\theta

Being a flexible wide band gap semiconductor, hexagonal boron nitride (h-BN) has great potential for technological applications like efficient deep ultraviolet light sources, building block for two-dimensional heterostructures and room temperature single photon emitters in the ultraviolet and visible spectral range. To enable such applications, it is mandatory to reach a better understanding of the electronic and optical properties of h-BN and the impact of various structural defects. Despite the large efforts in the last years, aspects such as the electronic band gap value, the exciton binding energy and the effect of point defects remained elusive, particularly when considering a single monolayer. Here, we directly measured the density of states of a single monolayer of h-BN epitaxially grown on highly oriented pyrolytic graphite, by performing low temperature scanning tunneling microscopy (STM) and spectroscopy (STS). The observed h-BN electronic band gap on defect-free regions is $(6.8\pm0.2)$ eV. Using optical spectroscopy to obtain the h-BN optical band gap, the exciton binding energy is determined as being of $(0.7\pm0.2)$ eV. In addition, the locally excited cathodoluminescence and photoluminescence show complex spectra that are typically associated to intragap states related to carbon defects. Moreover, in some regions of the monolayer h-BN we identify, using STM, point defects which have intragap electronic levels around 2.0 eV below the Fermi level., 50 Pages, 8 Figures, 100+ references

Hexagonal boron nitride is a large band-gap insulating material which complements the electronic and optical properties of graphene and the transition metal dichalcogenides. However, the intrinsic optical properties of monolayer boron nitride remain largely unexplored. In particular, the theoretically expected crossover to a direct-gap in the limit of the single monolayer is presently not confirmed experimentally. Here, in contrast to the technique of exfoliating few-layer 2D hexagonal boron nitride, we exploit the scalable approach of high-temperature molecular beam epitaxy to grow high-quality monolayer boron nitride on graphite substrates. We combine deep-ultraviolet photoluminescence and reflectance spectroscopy with atomic force microscopy to reveal the presence of a direct gap of energy 6.1 eV in the single atomic layers, thus confirming a crossover to direct gap in the monolayer limit., Insulating hexagonal boron nitride (hBN) is theoretically expected to undergo a crossover to a direct bandgap in the monolayer limit. Here, the authors perform optical spectroscopy measurements on atomically thin epitaxial hBN providing indications of the presence of a direct gap of energy 6.1 eV in the single atomic layer.

Integration of graphene and hexagonal boron nitride (hBN) into lateral heterostructures has drawn focus due to the ability to broadly engineer the material properties. Hybrid monolayers with tuneable bandgaps have been reported, while the interface itself possesses unique electronic and magnetic qualities. Herein, we demonstrate lateral heteroepitaxial growth of graphene and hBN by sequential growth using high-temperature molecular beam epitaxy (MBE) on highly oriented pyrolytic graphite (HOPG). We find, using scanning probe microscopy, that graphene growth nucleates at hBN step edges and grows across the surface to form nanoribbons with a controlled width that is highly uniform across the surface. The graphene nanoribbons grow conformally from the armchair edges of hexagonal hBN islands forming multiply connected regions with the growth front alternating from armchair to zigzag in regions nucleated close to the vertices of hexagonal hBN islands. Images with lattice resolution confirm a lateral epitaxial alignment between the hBN and graphene nanoribbons, while the presence of a moiré pattern within the ribbons indicates that some strain relief occurs at the lateral heterojunction. These results demonstrate that high temperature MBE is a viable route towards integrating graphene and hBN in lateral heterostructures.

We show that ordered monolayers of organic molecules stabilized by hydrogen bonding on the surface of exfoliated few-layer hexagonal boron nitride (hBN) flakes may be incorporated into van der Waals heterostructures with integral few-layer graphene contacts forming a molecular/two-dimensional hybrid tunneling diode. Electrons can tunnel through the hBN/molecular barrier under an applied voltage VSD, and we observe molecular electroluminescence from an excited singlet state with an emitted photon energy hν > eVSD, indicating upconversion by energies up to ∼1 eV. We show that tunneling electrons excite embedded molecules into singlet states in a two-step process via an intermediate triplet state through inelastic scattering and also observe direct emission from the triplet state. These heterostructures provide a solid-state device in which spin-triplet states, which cannot be generated by optical transitions, can be controllably excited and provide a new route to investigate the physics, chemistry, and quantum spin-based applications of triplet generation, emission, and molecular photon upconversion.

An Accurate forecast of PV output power is essential to optimize the relationship between energy supply and demand. However, it is a challenging task due to the intermittent nature of solar PV output and the effect of number of meteorological variables on it. In this paper, a multivariate neural network (NN) ensemble forecast framework is proposed. First multiple neural predictors are trained with input data from meteorological variables and then accurate predictors are combined with a Bayesian model averaging (BMA) technique. To identify the best performing framework, three different NN ensemble networks are created, namely feedforward neural network (FNN), Elman backpropagation network (ELM) and cascade-forward backpropagation (NewCF) network and trained with three different training techniques. The real time recorded solar PV data along with meteorological variables of the University of Queensland’s solar facility from 2014 to 2015 is used. To validate the forecast framework, one day ahead (24 h) forecasts are selected for different seasons. The results show that the proposed ensemble framework substantially improves the forecast accuracy of PV power output as compared benchmark methods, particularly for short term forecasting horizons.

Residential buildings in Kuwait account for almost 60% of the country's national electrical power generated, considerably greater than all other sectors or building types. This paper identifies key drivers of energy use in Kuwaiti villas based on a survey of 250 households undertaken throughout the six districts of Kuwait. The survey consists of a cross-sectional interviewer-administered questionnaire designed to gather detailed information about building physical characteristics, occupants’ socio-demographic background and energy-use behaviours. Survey data is analysed using both statistical descriptive methods and multiple linear regression analysis to identify key determinants of energy consumption in a sample of Kuwaiti villas. Analysis indicates that an occupant driven cooling behaviour (air-conditioning thermostat temperature set points) is the major driver of energy use, followed by the number of rooms and the number of occupants. Together, such drivers significantly explain 32% of the variability in energy consumption Survey findings provide descriptive information about Kuwaiti households and insights into the key drivers of energy use to better inform further research and policy interventions in this field.

Lattice-matched graphene on hexagonal boron nitride is expected to lead to the formation of a band-gap but requires the formation of highly strained material and has not hitherto been realised. We demonstrate that aligned, lattice-matched graphene can be grown by molecular beam epitaxy using substrate temperatures in the range 1600-1710 °C and co-exists with a topologically-modified moiré pattern, and with regions of strained graphene which have giant moiré periods up to ~80 nm. Raman spectra reveal narrow red-shifted peaks due to isotropic strain, while the giant moiré patterns result in complex splitting of Raman peaks due to strain variations across the moiré unit cell. The lattice-matched graphene has a lower conductance than both the Frenkel-Kontorova-type domain walls, and also the topological defects where they terminate. We relate these results to theoretical models of band-gap formation in graphene/boron nitride heterostructures.

In light of current climate change projections in recent years, there has been an increasing interest in the assessment of indoor overheating in domestic environments in previously heating-dominated climates. This paper presents a monitoring study of overheating in 122 London dwellings during the summers of 2009 and 2010. Dry Bulb Temperature and Relative Humidity in the main living and sleeping area were monitored at 10 min intervals. The ASHRAE Standard 55 adaptive thermal comfort method was applied, which uses outdoor temperature to derive the optimum indoor comfort temperature. It was found that 29% of all living rooms and 31% of all bedrooms monitored during 2009 had more than 1% of summertime occupied hours outside the comfort zone recommended by the standard to achieve 90% acceptability. In 2010, 37% of monitored living rooms and 49% of monitored bedrooms had more than 1% of summertime occupied hours outside this comfort zone. The findings of this study indicate that London dwellings face a significant risk of overheating under the current climate. Occupant exposure to excess indoor temperatures is likely to be exacerbated in the future if climate change adaptation strategies are not incorporated in Building Regulations, building design and retrofit.

The regular packing of atoms, molecules and nanoparticles provides the basis for the understanding of structural order within condensed phases of matter. Typically the constituent particles are considered to be rigid with a fixed shape. Here we show, through a combined experimental and numerical study of the adsorption of cyclic porphyrin polymers, nanorings, on a graphite surface, that flexible molecules can exhibit a rich and complex packing behaviour. Depending on the number of porphyrin sub-units within the nanoring we observe either a highly ordered hexagonal phase or frustrated packing driven by directional interactions which for some arrangements is combined with the internal deformation of the cyclic polymer. Frustration and deformation occur in arrays of polymers with ten sub-units since close packing and co-alignment of neighbouring groups cannot be simultaneously realised for nanorings with this internal symmetry., The packing of spheres, disks and other simple shapes into arrays on surfaces is relevant to many problems across the physical sciences. Here the authors study the influence of flexibility and reduced symmetry on the packing of porphyrin nanorings which are deposited from solution onto a graphite surface.

In this work we present our recent results on the high-temperature plasma-assisted molecular beam epitaxy (PA-MBE) of hBN monolayers with atomically controlled thicknesses for 2D applications and on the growth of significantly thicker hBN layers for potential DUV applications. We also report our recent results on the high-temperature PA-MBE growth of hBN layers using a high-efficiency RF plasma source with high active nitrogen fluxes. Our results demonstrate that PA-MBE growth on highly oriented pyrolytic graphite (HOPG) substrates at temperatures ~1390°C can achieve mono- and few-layer thick hBN with a control of the hBN coverage and atomically flat hBN surfaces which is essential for 2D applications of hBN layers. The hBN monolayer coverage can be reproducible controlled by the PA-MBE growth temperature, time and B:N flux ratios. Significantly thicker hBN layers have been achieved at higher B:N flux ratios. We observed a gradual increase of the hBN thickness by decreasing the growth temperature from 1390°C to 1080°C. However, by decreasing the MBE growth temperature below 1250°C, we observe a rapid degradation of the optical properties of hBN layers. Therefore, high-temperature PA-MBE, above 1250°C, is a viable approach for the growth of high-quality hBN layers for 2D and DUV applications.

Professionals engaged in the design of new or retrofit of existing school buildings currently struggle to find comprehensive guidelines for achieving healthy and energy-efficient school environments. Recently, two major and independent research projects aimed at improving indoor environmental quality and energy performance of school buildings in Europe have been completed: SINPHONIE and School of the Future. Their guidelines reflect the distinct priorities and limited scope of each project. This paper compares for the first time and, as far as possible, synthesizes these outputs to facilitate their use in practice and research. Overall, SINPHONIE is most useful in addressing indoor environmental quality of schools in terms of the physical, chemical and microbiological stressors that impact and potentially affect human health. It aims to influence the future development of policy and regulations. By contrast, School of the Future presents a broader design-oriented approach based on best practice in four European countries. For the most part they complement each other in their recommendations; however, this review highlights several areas that require further clarification and research including links between indoor environmental quality and cognitive performance, the consequent appropriate level for the designed ventilation rate, and the role of adaptive thermal comfort in schools.

Real-space images of polymers with sub-molecular resolution could provide valuable insights into the relationship between morphology and functionality of polymer optoelectronic devices, but their acquisition is problematic due to perceived limitations in atomic force microscopy (AFM). We show that individual thiophene units and the lattice of semicrystalline spin-coated films of polythiophenes (PTs) may be resolved using AFM under ambient conditions through the low-amplitude (≤ 1 nm) excitation of higher eigenmodes of a cantilever. PT strands are adsorbed on hexagonal boron nitride near-parallel to the surface in islands with lateral dimensions ~10 nm. On the surface of a spin-coated PT thin film, in which the thiophene groups are perpendicular to the interface, we resolve terminal CH3-groups in a square arrangement with a lattice constant 0.55 nm from which we can identify abrupt boundaries and also regions with more slowly varying disorder, which allow comparison with proposed models of PT domains., Semiconducting polymers are widely used in optoelectronic devices, in which their microstructure informs function. Here, the authors are able to resolve the molecular and sub-molecular ordering of polythiophene strands and thin films using atomic force microscopy, a significant step towards correlating polymer structure with device performance.

Monolayer hexagonal boron nitride (hBN) tunnel barriers investigated using conductive atomic force microscopy reveal moiré patterns in the spatial maps of their tunnel conductance consistent with the formation of a moiré superlattice between the hBN and an underlying highly ordered pyrolytic graphite (HOPG) substrate. This variation is attributed to a periodc modulation of the local density of states and occurs for both exfoliated hBN barriers and epitaxially grown layers. The epitaxial barriers also exhibit enhanced conductance at localized subnanometer regions which are attributed to exposure of the substrate to a nitrogen plasma source during the high temperature growth process. Our results show clearly a spatial periodicity of tunnel current due to the formation of a moiré superlattice and we argue that this can provide a mechanism for elastic scattering of charge carriers for similar interfaces embedded in graphene/hBN resonant tunnel diodes.

The aim of this paper is to investigate whether keeping indoor thermal conditions and carbon dioxide (CO2) levels within the current guideline values can provide a healthy and comfortable school environment. The study was organised as a longitudinal investigation over an academic year using a cohort of 376 students aged 9 to 11 (response rate: 87%) attending 15 classrooms in five London primary schools. The prevalence of asthmatic symptoms and asthma attacks was significantly higher among children attending urban schools (10.2%) than suburban schools (1.5%), and was significantly related to exposure to higher nitrogen dioxide (NO2) concentrations (odds ratio: 1.11, 95% confidence interval: 1.00–1.19). Self-reported dermal, mucosal, respiratory and general symptoms were 18.5%, 60.7%, 28.2% and 43.6% respectively in the heating season, and decreased in the non-heating season. Infiltration rates were negatively associated with prevalence and incidence of all sick building syndrome symptoms. Exposure to traffic-related pollutants, such NO2, ozone (O3) and tetrachloroethylene (T4CE), associated with mucosal symptoms, also increased dissatisfaction with indoor air quality (IAQ) and, therefore, perceived IAQ might be a first indication of exposure. Among targeted microbial counts, only Trichoderma viride remained significant predictors of satisfaction with IAQ even at low concentrations. The study provides evidence that simultaneous provision for limiting indoor CO2 levels and thermal conditions below current guidelines (e.g. below 1000 ppm and 26℃ or 22℃ depending on season) may improve perceived IAQ. This paper stresses the need to go beyond current regulations to investigate concentrations of specific pollutants to ensure a healthy school environment, and closes with a section on the practical implications on the UK policy and the building design industry. Practical application: The findings highlight the role and responsibility of stakeholders, from regulators to designers and school authorities, to account for the external environment and take the steps needed to ensure that schools provide a healthy indoor environment for their students. The recommendations focus on the need to decrease outdoor pollution levels in the school vicinity, thus improving health of the students and reducing the prevalence of respiratory illness. Building designers and engineers shall adopt an integrated approach for the simultaneous provision of adequate thermal conditions and IAQ in classrooms.

Supporting the development of a strong evidence base on which to improve the energy performance of buildings requires having access to research from different ‘levels’ of data. This includes high-level studies to carefully constructed representative samples, exploratory and investigative studies. As sensors and data collection becomes more widely applied within buildings (and the broader built environment) a clear articulation of the potential benefits and risks of data access is needed to avoid unintended consequences and regressive positions to data access. The objective of this work is to identify and discuss the co-benefits of energy and built environment data and the mechanisms needed to enable them. We outline a number of potential benefits and limitations of making energy and buildings data more widely available. Access to and linking/ matching together data can provide numerous benefits, including: research benefits, education and training, academic benefits, funder benefits, policy benefits, among others. However, there are also concerns of making data accessible including: privacy, management of access and communication protocols, commercial sensitivity, intellectual property, and archiving and legacy repository. The mechanisms needed to support data access should include requirements from funders for long-term data management and sharing, funding available for data archaeology, journal requirements for publication, government support and evaluation requests, and industry interest in capturing wider benefits from proprietary data.

We demonstrate direct epitaxial growth of high-quality hexagonal boron nitride (hBN) layers on graphite using high-temperature plasma-assisted molecular beam epitaxy. Atomic force microscopy reveals mono- and few-layer island growth, while conducting atomic force microscopy shows that the grown hBN has a resistance which increases exponentially with the number of layers, and has electrical properties comparable to exfoliated hBN. X-ray photoelectron spectroscopy, Raman microscopy and spectroscopic ellipsometry measurements on hBN confirm the formation of sp2-bonded hBN and a band gap of 5.9 ± 0.1 eV with no chemical intermixing with graphite. We also observe hexagonal moiré patterns with a period of 15 nm, consistent with the alignment of the hBN lattice and the graphite substrate.

The assumed U-values of solid walls represent a significant source of uncertainty when estimating the energy performance of dwellings. The typical U-value for UK solid walls used for stock-level energy demand estimates and energy certification is 2.1 Wm−2 K−1. A re-analysis (based on 40 brick solid walls and 18 stone walls) using a lumped thermal mass and inverse parameter estimation technique gives a mean value of 1.3 ± 0.4 Wm−2 K−1 for both solid wall types. Among the many implications for policy, this suggests that standard UK solid-wall U-values may be inappropriate for energy certification or for evaluating the investment economics of solid-wall insulation. For stock-level energy modelling, changing the assumed U-value for solid walls reduces the estimated mean annual space heating demand by 16%, and causes a proportion of the stock to change Energy Performance Certification (EPC) band. The analysis shows that the diversity of energy use in domestic buildings may be as much influenced by heterogeneit...

The overall aim of the study is to provide empirical evidence on indoor pollution levels to assist the formation of indoor air quality (IAQ) benchmarking of school buildings under operational conditions. This article is the second part of the study and aims to quantify seasonal variation of chemical and microbial levels in London schools. Passive diffusive sampling was employed for radon, NO2, and O3 measurements. Fungal and bacterial groups and allergens were sampled with suction-based methods in settled dust and endotoxin levels were sampled in dust collected with natural deposition. Biological contaminants were analysed with molecular, cultivation-independent methods. The strong temporal and spatial variability of outdoor NO2 levels affected indoor levels and is therefore an important consideration when selecting sites for new school buildings. There is a need to further clarify on the effect of finishing, such as wall-to-wall carpeting, which may act as a significant reservoir of irritants and allerge...

This study aims to assess the adequacy of current guidelines, framed around thermal comfort, estimated ventilation rates, and CO2 levels, for the provision of indoor air quality (IAQ) in school classrooms. It draws on detailed monitoring data from a sample of 18 classrooms from 6 London schools. Overheating during the non-heating season was identified in eight south-, south-east-, and east-facing classrooms in two Victorian and two contemporary schools. Four classrooms in these contemporary schools also failed to keep average indoor CO2 levels below 1500 ppm in the non-heating season. During the heating season, eight classrooms exceeded the daily average indoor CO2 levels. Mean indoor particulate matter (PM)10 and PM2.5 levels recorded in all classrooms in both seasons were higher than 20 and 10 μg/m3, respectively, indicating that school exposure during an academic year may exceed annual recommended WHO [2006. Air Quality Guidelines: Global Update 2005: Particulate Matter, Ozone, Nitrogen Dioxide, and Su...

This paper compares energy and ventilation performance, and levels of pollutants in six school classrooms and associates them to asthmatic and Sick Building Syndrome (SBS) symptoms and the perceived indoor air quality (IAQ) of students. Self-reported data on subjective perception of air quality and health responses were gathered with a standardised questionnaire completed by 151 school children (Response Rate (RR):86%) attending two schools in the Greater London Area: a contemporary suburban low carbon school building and an urban, high thermal mass school built in the 19th century. Temperature, particulate matter (PM), nitrogen dioxide (NO2), ozone (O3), and volatile organic compounds (VOCs) concentrations were monitored in three classrooms and one outdoor site in each school for 5 consecutive days during the heating seasons. Biological parameters were determined in settled dust and analysed with molecular methods. Overall, asthma prevalence in the school environment was associated with exposure to higher NO2 levels (odds ratio (OR): 1.1, 95% confidence interval (CI): 1.0–1.2). Exposure to PM in all classrooms was high and was associated with increased mucosal symptoms (OR: 1.4, 95% CI: 1.1–1.9) and eczema (OR: 1.3, 95% CI: 1.0–1.6) prevalence. Higher indoor CO2 levels were associated with general symptoms (OR: 1.1, 95% CI: 1.0–1.2). Increased dissatisfaction with IAQ was associated with higher temperatures and exposure to higher NO2, CO2, fungal, cat allergens, and VOC levels (limonene and formaldehyde). Direct access to the playground without buffer zone and user behavioural patterns may affect energy consumption. Findings suggest that increased ventilation rates may mitigate overheating, alleviate SBS symptoms, and improve satisfaction with IAQ.

Little detailed evidence has previously been available regarding the uptake rate or prevalence of energy efficiency interventions among specific household groups. This study uses the Home Energy Efficiency Database (HEED) to investigate both the combination of measures that have been installed, and in which dwellings, according to key neighbourhood socio-demographic variables, including income and tenure. Analysis of 2000–07 data indicates that approximately 40% (9.3 million) dwellings in England had approximately 23.7 million efficiency measures installed, with an average of 2.5 measures per dwelling. Building fabric-related measures were the most frequent (e.g. cavity wall insulation, loft insulation and glazing) with an average of 2.1 million installed each year. Dwellings with the highest number of fabric interventions (the top 20%) were more likely to be found in areas with low income, with more owner-occupied dwellings, experiencing lower winter temperatures, having a lower proportion of flats, and ...

Heating patterns and temperatures are among the most important determinants of English home energy use. Consequently, building stock models, widely used for informing UK energy policy, are highly sensitive to the assumptions they make on how occupants heat their homes. This study examined heating patterns in English living rooms and compared them to model assumptions. A time-series of winter spot temperature measurements was translated into statements of the heating system being on or off during weekdays and weekend days, and the heating demand temperature estimated. The analysis showed that weekdays and weekend days are far more similar than commonly assumed. Contrary to model assumptions, homes were frequently heated outside assumed heating hours and not all homes were heated at the same time or followed the same pattern. The estimated demand temperature was about 20.6 °C, and the average temperature during heating periods was about 19.5 °C, both lower than the commonly assumed 21 °C used in models. Significantly, variability between homes in demand temperature and hours of heating was substantial. The results indicate the need to revisit some assumptions made in building stock models, and to take account of variability between homes when aiming at predicting space heating demand for an individual home.

Objective This study examines the extent that temperatures in English living rooms correspond to standard assumptions made in established UK building stock models. Methods Spot temperature measurements taken every 45 min over 92 winter days in 248 homes in England were analyzed and compared to the assumed thermostat setting of 21 °C inside and outside the assumed heating periods. Results Homes on average displayed lower internal temperatures during assumed heating periods and significantly shorter durations of heating to 21 °C than common models assume, with about 20% of homes never reaching the assumed demand temperature of 21 °C. Data showed a difference of only about 45 min in the duration of temperatures at or above the demand temperature for weekdays and weekends, contrary to the assumed difference of 7 h. Variability between homes was large. Conclusion These findings suggest that currently used standard assumptions of heating demand and heating duration do not accurately reflect the living room temperatures of dwellings in England. Practice implications Standard assumptions might have to be revised, in particular regarding the weekday–weekend differentiation. The prediction of internal temperature for a given home contains potential large error when using standard assumptions.

The UK Government has unveiled an ambitious retrofit programme that seeks significant improvement to the energy efficiency of the housing stock. High quality data on the energy efficiency of buildings and their related energy demand is critical to supporting and targeting investment in energy efficiency. Using existing home improvement programmes over the past 15 years, the UK Government has brought together data on energy efficiency retrofits in approximately 13 million homes into the Homes Energy Efficiency Database (HEED), along with annual metered gas and electricity use for the period of 2004–2007.This paper describes the HEED sample and assesses its representativeness in terms of dwelling characteristics, the energy demand of different energy performance levels using linked gas and electricity meter data, along with an analysis of the impact retrofit measures has on energy demand. Energy savings are shown to be associated with the installation of loft and cavity insulation, and glazing and boiler replacement. The analysis illustrates this source of ‘in-action’ data can be used to provide empirical estimates of impacts of energy efficiency retrofit on energy demand and provides a source of empirical data from which to support the development of national housing energy efficiency retrofit policies.

The call for action to transform the built environment and address the threats of climate change has been clearly made. However, to support the development, implementation and on-going evaluation of energy demand policy, a strong evidence base is needed to identify associations and establish underlying causes behind outcomes and variations in end-use energy demand within the population. A new approach to end-use energy demand research is presented which is founded on the interdisciplinary health sciences research framework of epidemiology, along with the establishment of a research centre. A case is made that through an ‘energy epidemiology’ approach a strong, population-level, empirically based research foundation can be advanced. Energy epidemiology is a whole-system approach that focuses on empirical research and provides a methodological framework for building physicists, engineers, sociologists and economists to engage in interdisciplinary work. The adaptation of the epidemiological approach to end-u...

We demonstrate direct epitaxial growth of high-quality hexagonal boron nitride (hBN) layers on graphite using high-temperature plasma-assisted molecular beam epitaxy. Atomic force microscopy reveals mono- and few-layer island growth, while conducting atomic force microscopy shows that the grown hBN has a resistance which increases exponentially with the number of layers, and has electrical properties comparable to exfoliated hBN. X-ray photoelectron spectroscopy, Raman microscopy and spectroscopic ellipsometry measurements on hBN confirm the formation of sp2-bonded hBN and a band gap of 5.9 ± 0.1 eV with no chemical intermixing with graphite. We also observe hexagonal moiré patterns with a period of 15 nm, consistent with the alignment of the hBN lattice and the graphite substrate.

The increasing interest in indoor environmental quality of educational buildings has been underpinned by the rising incidence of asthma and respiratory disease among children, who spend a substantial amount of their lives on the school premises. The susceptibility of children to respiratory disease compared with adults has led to the formulation of regulatory frameworks for the school environment, which specifies maximum CO2 concentrations and minimum airflow rates. This article reviews the evidence that school buildings provide a healthy and satisfactory indoor environment for the occupants. It summarized air pollution levels reported from indoor air quality (IAQ) monitoring surveys and evidence linking school exposure with health responses from the occupants. In addition, environmental and behavioural factors affecting pollution levels in school buildings were examined. The analysis has highlighted the degraded IAQ in some schools that often exceed WHO guidelines, while health impacts of school exposure...

In 2007 Building Research & Information published a special issue on the challenges posed by climate change for the building stock. Its focus was well-timed in addressing technical strategies and g...

A lack of empirical data for residential indoor temperature has important implications for policy-makers in terms of energy performance objectives and the use of energy demand models for the building stock. This study investigates winter indoor temperatures, relative humidity and vapour pressure excess in 2009-2010 across various types and ages of buildings using half-hourly monitoring of 96 dwellings representative of residential buildings in Belgrade, including those with district heating (DH) with no direct occupant control in which heating is charged on a floor area basis. The average daily living room temperature of 22.8 degrees C (95%CI: 21.9-22.7) in DH dwellings was 2.3 degrees C higher than those with other heating types, including individual central heating (ICH) and non-central heating (non-CH), daily bedroom temperature of 22.3 degrees C (95%CI: 21.9-22.7) was 3.0 degrees C higher. Evening living room and night bedroom temperatures in ICH dwellings were 22% and 37% of the time respectively below 18 degrees C, and 10% and 27% of the time respectively in non-CH dwellings. The high degree of overheating in DH dwellings indicates the considerable potential to reduce energy consumption, if user controls and heating bills reflected household consumption were introduced. (C) 2012 Elsevier B.V. All rights reserved.

The UK government has ambitious goals to reduce national carbon dioxide (CO2) emissions and has targeted the new and existing built stock with measures to improve building performance and provide more local and centralized renewable energy. New dwellings are proposed to be ‘net-zero carbon’ by 2016, which includes proposals to offset CO2 by integrating new and existing development. To what extent can new zero-carbon communities be more readily achieved through increasing the integration between new and existing domestic developments? A methodology is presented for determining the ratio of on-site renewable energy supply to energy demand for a series of densities using a simplified model. Options that increase the proportion of existing dwellings served by a new development to balance further energy demands are presented. The practical opportunities and constraints are considered for integrating new and existing domestic development to achieve net-zero carbon. Meeting net-zero on-site annual energy require...

The growth and properties of hexagonal boron nitride (hBN) have recently attracted much attention due to applications in graphene-based monolayer thick 2D-structures and at the same time as a wide band gap material for deep-ultraviolet device (DUV) applications. We present our results on the high-temperature plasma-assisted molecular beam epitaxy (PA-MBE) of hBN monolayers on highly oriented pyrolytic graphite (HOPG) substrates. Our results demonstrate that PA-MBE growth at temperatures ~1390 oC can achieve mono- and few-layer thick hBN with a control of the hBN coverage and atomically flat hBN surfaces which is essential for 2D applications of hBN layers. The hBN monolayer coverage can be reproducible controlled by the PA-MBE growth temperature, time and B:N flux ratios. Significantly thicker hBN layers have been achieved at higher B:N flux ratios. We observed a gradual increase of the hBN thickness from 40 to 70 nm by decreasing the growth temperature from 1390 oC to 1080 oC.\ud However, by decreasing the MBE growth temperature below 1250 oC, we observe a rapid degradation of the optical properties of hBN layers. Therefore, high-temperature PA-MBE, above 1250 oC, is a viable approach for the growth of high-quality hBN layers for 2D and DUV applications.

To measure change in energy demand, a follow-up study was conducted in 2005–2007 of 36 ‘low-energy’ UK dwellings that were originally monitored for hourly energy consumption between 1989 and 1991. All results were compared under standardized daily external winter conditions of 5°C. Overall, no significant evidence of change over 15–17 years was found in average gas consumption (67 kWh/day, with a 95% confidence interval (CI) = 55, 79) and average electricity usage (14 kWh/day; 95% CI = 11, 18). Dwellings were then classified into low, middle, and high groups according to energy usage in 1990. Gas usage of the high group at follow-up was 107 kWh/day (95% CI = 89, 125) in 2005–2007, and was consistent with increased floor space, but electricity consumption increased by 72% to 24 kWh/day (95% CI = 18, 30). The high group comprised dwellings that were both larger originally than in the other groups and they were more likely to have been extended. These results are broadly consistent with national statistics t...

From publicly available data, two simple models are developed to help identify the trajectory of total delivered energy to UK households and provide benchmarks for the UK domestic sector. Both models can help to inform policy-makers and the public whether delivered energy in the domestic sector is on track and whether the reductions correspond with the expected impact of a more efficient domestic sector. The annual delivered energy, price, and temperature (ADEPT) model uses multiple linear regression to fit consumption data since 1970 (R 2 = 0.76). Findings indicate that with typical recent heating season temperatures of 7°C and at 2005 energy prices, average household delivered energy is estimated at 21.7 MWh (95% confidence interval = 20.8, 22.6). For every 1°C increase in heating season temperature, average household delivered energy drops by approximately 1 MWh/year. Energy price elasticity is estimated at –0.2, so that a 50% rise in energy prices corresponds to an approximate 10% decline in energy de...

A follow-up study was undertaken of 15 'low-energy' dwellings in Milton Keynes, UK, that were originally monitored for temperature and energy consumption from 1989 to 1991. These measurements were repeated in 2005-2006, with the results compared with the baseline using standardised daily external conditions of 5 degrees C. The 2005-2006 study found mean temperatures of 19.8 degrees C (95% confidence interval: 19.7-20.5) for living rooms and 19.3 degrees C (CI: 19.6-20. 1) for main bedrooms. Weak evidence was found for a 10% increase in gas consumption over 15 years to 87 kWh/day (95%CI: 77-96) and overall electricity usage rose by 30% to 15 kWh/day (CI: 13.6-16.5). Dwellings were classified into three groups of low, middle, and high-energy users in 1990. In 2005-2006, this high group consumed more energy than the other two groups combined and accounted for most increases in energy use; their gas usage rose by 20% to 130 kWh/day (110-150), electricity by 75% to 28 kWh/day (CI: 25.331.2), and had 50% higher energy intensity at 172 Wh/m(2) (CI: 150-195). On average the high group comprised dwellings that were larger, had been extended, and whose occupants had higher incomes than the two other groups. The results suggest that research for the development of energy policy, including building regulations, should focus both on how energy is currently used and on households where the largest future increases are likely to occur. (C) 2007 Elsevier B.V. All rights reserved.

Rings of chlorophyll molecules harvest sunlight remarkably efficiently during photosynthesis in purple bacteria. The key to their efficiency lies in their highly delocalized excited states that allow for ultrafast energy migration. Here we show that a family of synthetic nanorings mimic the ultrafast energy transfer and delocalization observed in nature. π-Conjugated nanorings with diameters of up to 10 nm, consisting of up to 24 porphyrin units, are found to exhibit excitation delocalization within the first 200 fs of light absorption. Transitions from the first singlet excited state of the circular nanorings are dipole-forbidden as a result of symmetry constraints, but these selection rules can be lifted through static and dynamic distortions of the rings. The increase in the radiative emission rate in the larger nanorings correlates with an increase in static disorder expected from Monte Carlo simulations. For highly symmetric rings, the radiative rate is found to increase with increasing temperature. Although this type of thermally activated superradiance has been theoretically predicted in circular chromophore arrays, it has not previously been observed in any natural or synthetic systems. As expected, the activation energy for emission increases when a nanoring is fixed in a circular conformation by coordination to a radial template. These nanorings offer extended chromophores with high excitation delocalization that is remarkably stable against thermally induced disorder. Such findings open new opportunities for exploring coherence effects in nanometer molecular rings and for implementing these biomimetic light-harvesters in man-made devices. This journal is

Detailed domestic stock energy models can be used to help formulate optimum energy reduction strategies. However, there will always be considerable uncertainty related to their predictions due to the complexity of the housing stock and the many assumptions required to implement the models. This paper presents a simple Monte Carlo (MC) model that can be easily extended and/or transformed in relation to data available for investigating and quantifying uncertainties in both the housing stock models predictions and scenario assumptions. While 90% of the MC model predictions fell within a range which is +/- 19% the mean value, 50% of them were within +/- 8% of the mean. The findings suggest that the uncertainties associated with the model predictions and scenario assumptions need to be acknowledged fully and - where possible - quantified as even fairly small variability in the influential variables may result in rather large uncertainty in the aggregated models prediction.

This paper presents the development and evaluation of the Belgrade Domestic Energy Model (BEDEM) for predicting the energy consumption and carbon dioxide (CO2) emissions of the existing housing stock. The distribution of energy use in relation to the end use is estimated as: space heating, 71%; light and appliances, 15%; water heating, 9%; and cooking 5%, while the distribution of CO2 emissions is space heating, 59%; light and appliances, 22%; water heating, 13%; and cooking 6%. Local sensitivity analysis is carried out for dwellings of different type and year built, and the largest normalized sensitivity coefficients were calculated for parameters which almost exclusively influence space heating energy consumption in housing. For all input parameters under investigation, the effects of the input uncertainty were linear for a moderate range of input change (Delta x=+/- 10%) and superposable for a small range of input change (Delta x=+/- 1%). However, the non-linear and non-additive properties of some input parameters over the wider range hinder the development of a simple but reliable model for estimating energy and CO2 reductions. The findings show that the uncertainty in the stock models predictions can be large and more work is needed in the area of the predictive uncertainty of stock models. (C) 2013 Elsevier B.V. All rights reserved.

The recent extremely hot summers in Europe have seen a rapidly expanding market in mechanical cooling in dwellings, especially in big cities. Along with urban climate factors, a number of behavioral factors are further contributing to a significant rise in cooling demand across the EU including countries with a more moderate climate, such as the UK. This chapter investigates environmental and behavioral factors affecting residential air conditioning use in two large EU cities with different climates – Athens and London. This scoping study analyses carbon and health implications of increasing cooling demand, and identifies important physical attributes and occupants’ behavioral patterns that affect air conditioning use, as well as, typical operational temperatures and schedules. The high satisfaction with domestic air conditioning units highlighted in both studies suggests that in the foreseeable future with changing climate the UK may experience a similar increase in market penetration of domestic air conditioning as has occurred in Greece over the last 20 years. This might have a major impact on the summer electricity load and domestic sector carbon emissions in the UK, which already accounts for almost 30% of the UK building stock emission.

Two different SURMOF films have been grown on a transparent conducting surface for spectro-electrochemical characterisation of radical species., The application of metal–organic framework (MOF) materials in electrochemical and electrochromic devices remains rare. One of the main reasons for this is the inability to readily access their detailed electrochemistry. The inherent insolubility of these materials does not allow interrogation by traditional solution-based electrochemical or spectroscopic methods. In this study, we report a straightforward alternative approach to the spectroelectrochemical study of MOFs. We have used two systems as exemplars in this study, MFM-186 and MFM-180. The method involves chemical modification of a working electrode to attach MOF materials without using corrosive reagents such as inorganic acids or bases which otherwise could limit their application in device development. MFM-186 demonstrates the formation of a stable radical species [MFM-186]˙+ on electrochemical oxidation, and this has been characterised by electrochemical, spectroelectrochemical and EPR spectroscopic techniques coupled to DFT analysis.