Symmetry-break in Voronoi tessellations

We analyse in a common framework the properties of the Voronoi tessellations resulting from regular 2D and 3D crystals and those of tessellations generated by Poisson distributions of points, thus joining on symmetry breaking processes and the approach to uniform random distributions of seeds. We perturb crystalline structures in 2D and 3D with a spatial Gaussian noise whose adimensional strength is α and analyse the statistical properties of the cells of the resulting Voronoi tessellations using an ensemble approach. In 2D we consider triangular, square and hexagonal regular lattices, resulting into hexagonal, square and triangular tessellations, respectively. In 3D we consider the simple cubic (SC), body-centred cubic (BCC), and face-centred cubic (FCC) crystals, whose corresponding Voronoi cells are the cube, the truncated octahedron, and the rhombic dodecahedron, respectively. In 2D, for all values α>0, hexagons constitute the most common class of cells. Noise destroys the triangular and square tessellations, which are structurally unstable, as their topological properties are discontinuous in α=0. On the contrary, the honeycomb hexagonal tessellation is topologically stable and, experimentally, all Voronoi cells are hexagonal for small but finite noise with α0.5), memory of the specific initial unperturbed state is lost, because the statistical properties of the three perturbed regular tessellations are indistinguishable. When α>2, results converge to those of Poisson-Voronoi tessellations. In 2D, while the isoperimetric ratio increases with noise for the perturbed hexagonal tessellation, for the perturbed triangular and square tessellations it is optimised for specific value of noise intensity. The same applies in 3D, where noise degrades the isoperimetric ratio for perturbed FCC and BCC lattices, whereas the opposite holds for perturbed SCC lattices. This allows for formulating a weaker form of the Kelvin conjecture. By analysing jointly the statistical properties of the area and of the volume of the cells, we discover that also the cells shape heavily fluctuates when noise is introduced in the system. In 2D, the geometrical properties of n-sided cells change with α until the Poisson-Voronoi limit is reached for α>2; in this limit the Desch law for perimeters is shown to be not valid and a square root dependence on n is established, which agrees with exact asymptotic results. Anomalous scaling relations are observed between the perimeter and the area in the 2D and between the areas and the volumes of the cells in 3D: except for the hexagonal (2D) and FCC structure (3D), this applies also for infinitesimal noise. In the Poisson-Voronoi limit, the anomalous exponent is about 0.17 in both the 2D and 3D case. A positive anomaly in the scaling indicates that large cells preferentially feature large isoperimetric quotients. As the number of faces is strongly correlated with the sphericity (cells with more faces are bulkier), in 3D it is shown that the anomalous scaling is heavily reduced when we perform power law fits separately on cells with a specific number of faces

Meeting the challenge of zero carbon homes : a multi-disciplinary review of the literature and assessment of key barriers and enablers

Within the built environment sector, there is an increasing pressure on professionals to consider the impact of development upon the environment. These pressures are rooted in sustainability, and particularly climate change. But what is meant by sustainability? It is a term whose meaning is often discussed, the most common definition taken from the Bruntland report as “sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs” (World Commission on Environment and Development, 1987). In the built environment, the sustainability issues within the environment, social and economic spheres are often expressed through design considerations of energy, water and waste. Given the Stern Report’s economic and political case for action with respect to climate change (Stern, 2006) and the IPCC’s Fourth Assessment Report’s confirmation of the urgency of the climate change issue and it’s root causes (IPCC, 2007), the need for action to mitigate the effects of climate change is currently high on the political agenda. Excess in carbon dioxide concentrations over the natural level have been attributed to anthropogenic sources, most particularly the burning of carbon-based fossil fuels. Over 40% of Europe’s energy and 40% of Europe’s carbon dioxide emissions arise from use of energy in buildings. Energy use in buildings is primarily for space heating, water heating, lighting and appliance use. Professionals in the built environment can therefore play a significant role in meeting targets for mitigating the effects of climate change. The UK Government recently published the Code for Sustainable Homes (DCLG, 2006). Within this is the objective of development of zero carbon domestic new build dwellings by 2016. It is the domestic zero carbon homes agenda which is the focus of this report. The report is the culmination of a research project, funded by Northumbria University, and conducted from February 2008 to July 2008, involving researchers from the Sustainable Cities Research Institute (within the School of the Built Environment) and academics, also from within the School. The aim of the project was to examine, in a systematic and holistic way, the critical issues, drivers and barriers to building and adapting houses to meet zero carbon targets. The project involved a wide range of subject specialisms within the built environment and took a multi-disciplinary approach. Practitioner contribution was enabled through a workshop. The focus of this work was to review the academic literature on the built environment sector and its capabilities to meet zero carbon housing targets. It was not possible to undertake a detailed review of energy efficiency or micro-generation technologies, the focus of the research was instead in four focussed areas: policy, behaviour, supply chain and technology.What follows is the key findings of the review work undertaken. Chapter One presents the findings of the policy and regulation review. In Chapter Two the review of behavioural aspects of energy use in buildings is presented. Chapter Three presents the findings of the review of supply chain issues. Chapter Four presents the findings of the technology review, which focuses on phase change materials. A summary of the key barriers and enablers, and areas for future research work, concludes this report in Chapter Five. Research is always a work in progress, and therefore comments on this document are most welcome, as are offers of collaboration towards solutions. The School of the Built Environment at Northumbria University strives to embed its research in practical applications and solutions to the need for a low carbon economy

Effect of curing conditions and harvesting stage of maturity on Ethiopian onion bulb drying properties

The study was conducted to investigate the impact of curing conditions and harvesting stageson the drying quality of onion bulbs. The onion bulbs (Bombay Red cultivar) were harvested at three harvesting stages (early, optimum, and late maturity) and cured at three different temperatures (30, 40 and 50 oC) and relative humidity (30, 50 and 70%). The results revealed that curing temperature, RH, and maturity stage had significant effects on all measuredattributesexcept total soluble solids

Micro-encapsulated phase change material (MPCM) slurries: characterization and building applications

© 2017 Micro-encapsulated Phase Change Material (MPCM) slurries, acting as the heat transfer fluids or thermal storage mediums, have gained applications in various building thermal energy systems, significantly enhancing their energy efficiency and operational performance. This paper presents a review of research on MPCM slurries and their building applications. The research collects information on the currently available MPCM particles and shells, studies of the physical, structural and thermal stability, and rheological properties of MPCM slurries, and identification/determination of the critical parameters and dimensionless numbers relating to the MPCM slurries’ heat transfer. The research suggests possible approaches for enhancing the heat transfer between a MPCM slurry and its surroundings, while several controversial phenomena and potential causes were also investigated. Furthermore, the research presents mathematical correlations established between different thermal and physical parameters relating to the MPCM slurries, and introduces a number of practical applications of the MPCM slurries in building thermal energy systems. Based on such extensive review and analyses, the research will help in identifying the current status, potential problems in existence, and future directions in research, development and practical application of MPCM slurries. It will also promote the development and application of cost-effective and energy-efficient PCM materials and thus contribute to achieving the UK and international targets in energy saving and carbon emission reductions in the building sector and beyond

climatology

Energy and momentum deposition from planetary-scale Rossby waves as well as from small-scale gravity waves (GWs) largely control stratospheric dynamics. Interactions between these different wave types, however, complicate the quantification of their individual contribution to the overall dynamical state of the middle atmosphere. In state-of-the-art general circulation models (GCMs), the majority of the GW spectrum cannot be resolved and therefore has to be parameterised. This is commonly implemented in two discrete schemes, one for GWs that originate from flow over orographic obstacles and one for all other kinds of GWs (non-orographic GWs). In this study, we attempt to gain a deeper understanding of the interactions of resolved with parameterised wave driving and of their influence on the stratospheric zonal winds and on the Brewer–Dobson circulation (BDC). For this, we set up a GCM time slice experiment with two sensitivity simulations: one without orographic GWs and one without non-orographic GWs. Our findings include an acceleration of the polar vortices, which has historically been one of the main reasons for including explicit GW parameterisations in GCMs. Further, we find inter-hemispheric differences in BDC changes when omitting GWs that can be explained by wave compensation and amplification effects. These are partly evoked through local changes in the refractive properties of the atmosphere caused by the omitted GW drag and a thereby increased planetary wave propagation. However, non-local effects on the flow can act to suppress vertical wave fluxes into the stratosphere for a very strong polar vortex. Moreover, we study mean age of stratospheric air to investigate the impact of missing GWs on tracer transport. On the basis of this analysis, we suggest that the larger ratio of planetary waves to GWs leads to enhanced horizontal mixing, which can have a large impact on stratospheric tracer distributions

Outdoor test cells for building envelope experimental characterisation - A literature review

partially_open4siThe present work has been partially developed within the framework of IEA EBC Annex 58In the past decades the construction sector experienced the diffusion of a wide variety of complex building envelope components and passive elements and strategies, characterized by a dynamic response to the climatic parameters. Many of these components have been claimed to contribute to reducing building energy use and improving occupants’ comfort. These kind of envelope elements need nevertheless to be tested under laboratory and real dynamic weather conditions in order to characterise, and possibly to model, their behaviour and their effectiveness both in terms of energy saving and indoor environmental quality. Both indoor laboratories and outdoor test cells have been developed in order to tackle the challenging issue of experimentally characterising innovative envelope elements. However, not always the experimental methodologies are fully and explicitly described in the available literature, and they are rarely compared to other types of experimental procedures. The aim of the present paper is to describe and review recent state of the art technologies for outdoor test cells. The paper starts with a short introduction on potentialities and limitations of outdoor facilities with respect to indoor laboratories and real buildings field tests, and it continues with a detailed classification and description of the most relevant outdoor test cells developed in recent years.openCattarin, Giulio; Causone, Francesco; Kindinis, Andrea; Pagliano, LorenzoCattarin, Giulio; Causone, Francesco; Kindinis, Andrea; Pagliano, Lorenz