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The paper compares the results of two studies of salt damage at the Wakefield Tower, Tower of London. The first, in 1993, was based on semi-quantitative salt analysis and hygroscopicity measurements. The second was based on quantitative analysis and a thermodynamic model, ECOS. Both studies aimed to predict environmental conditions that would minimise salt damage to the interior stonework. Their predictions are markedly different, and this paper examines the reasons for the differences. It is shown that hygroscopicity alone is not a reliable indicator of crystallisation from mixed salt solutions. [ABSTRACT FROM AUTHOR]

This paper describes the collaborative process of building a simulation model in order to understand patient waiting times in an accident and emergency department. The purpose is to explore the issues that arise when involving clients, in this case health care professionals, in the process of model building. The study background and a detailed account of the modelling process are presented. The focus of the paper is on some general themes that can be discovered running through the process. These offer some tentative insights into client involvement in system dynamics modelling, in particular its application in health care. Given this study's first promising results, further collaborative studies are encouraged. [ABSTRACT FROM AUTHOR]

Positioning using the Global Positioning System (GPS) is unreliable in dense urban areas with tall buildings and/or narrow streets, known as ‘urban canyons’. This is because the buildings block, reflect or diffract the signals from many of the satellites. This paper investigates the use of 3-Dimensional (3-D) building models to predict satellite visibility. To predict Global Navigation Satellite System (GNSS) performance using 3-D building models, a simulation has been developed. A few optimized methods to improve the efficiency of the simulation for real-time purposes were implemented. Diffraction effects of satellite signals were considered to improve accuracy. The simulation is validated using real-world GPS and GLObal NAvigation Satellite System (GLONASS) observations.The performance of current and future GNSS in urban canyons is then assessed by simulation using an architectural city model of London with decimetre-level accuracy. GNSS availability, integrity and precision is evaluated over pedestrian and vehicle routes within city canyons using different combinations of GNSS constellations. The results show that using GPS and GLONASS together cannot guarantee 24-hour reliable positioning in urban canyons. However, with the addition of Galileo and Compass, currently under construction, reliable GNSS performance can be obtained at most, but not all, of the locations in the test scenarios. The modelling also demonstrates that GNSS availability is poorer for pedestrians than for vehicles and verifies that cross-street positioning errors are typically larger than along-street due to the geometrical constraints imposed by the buildings. For many applications, this modelling technique could also be used to predict the best route through a city at a given time, or the best time to perform GNSS positioning at a given location. [ABSTRACT FROM AUTHOR]

Abstract: London is expected to experience more frequent periods of intense rainfall and tidal surges, leading to an increase in the risk of flooding. Damp and flooded dwellings can support microbial growth, including mould, bacteria, and protozoa, as well as persistence of flood-borne microorganisms. The amount of time flooded dwellings remain damp will depend on the duration and height of the flood, the contents of the flood water, the drying conditions, and the building construction, leading to particular properties and property types being prone to lingering damp and human pathogen growth or persistence. The impact of flooding on buildings can be simulated using Heat Air and Moisture (HAM) models of varying complexity in order to understand how water can be absorbed and dry out of the building structure. This paper describes the simulation of the drying of building archetypes representative of the English building stock using the EnergyPlus based tool ‘UCL-HAMT’ in order to determine the drying rates of different abandoned structures flooded to different heights and during different seasons. The results are mapped out using GIS in order to estimate the spatial risk across London in terms of comparative flood vulnerability, as well as for specific flood events. Areas of South and East London were found to be particularly vulnerable to long-term microbial exposure following major flood events. [Copyright &y& Elsevier]

Abstract: This paper presents a meanline model to predict the performance parameters of a turbocharger turbine under steady state conditions. The turbine was developed at Imperial College and the design was based on a commercial nozzleless unit that was modified into a variable geometry single-entry turbine. The wide range of tests data from the Imperial College Turbocharger Group dynamometer enabled the evaluation of the model in the areas of the turbine map where currently no previous comparison had been made in the literature. This facility is designed to allow testing over a wide range of velocity ratios (0.3–1.1) previously unavailable with conventional test stands. The nozzleless turbine model was validated against experimental results spanning an equivalent speed range of 27.9 and 53.8rev/s√K while for the nozzled case the model was validated against one single speed (43.0rev/s√K) and three different vane angle settings (40°, 60° and 70°). The results of the model simulation showed that the performance can be predicted with excellent accuracy for different turbine speeds and vane angles. Based on the model prediction, a breakdown aerodynamic loss was performed. [Copyright &y& Elsevier]

Abstract: This paper investigates pedestrian exposure to traffic emissions at the Marylebone Road–Gloucester Place intersection in central London, taking a particular interest in the peak exposures occurring within minutes. The approach is based on the large eddy simulation modelling methodology, which enables high spatial resolution of air movements and pollutant concentrations to be achieved at relatively moderate computational cost. The results show the complexity of the air flows in the vicinity of the intersection at pedestrian height and the large variability of peak exposures due to the turbulent air flows. [Copyright &y& Elsevier]

Abstract: This study investigates Box–Jenkins (BJ), autoregressive with external inputs (ARX), autoregressive moving average with external inputs (ARMAX) and output error (OE) models to identify the thermal behaviour of an office positioned in a modern commercial building in London. These models can all be potentially used for improving the performance of the thermal environment control system. External and internal climate data, recorded over the summer, autumn and winter seasons, were used to build and validate the models. The paper demonstrates the potential of using linear parametric models to predict room temperature and relative humidity for different time scales (30min or 2h ahead). The prediction performance is evaluated using the criteria of goodness of fit, coefficient of determination, mean absolute error and mean squared error between predicted model output and real measurements. The results demonstrate that all models provide reasonably good predictions but the BJ model outperforms the ARMAX and ARX models. [Copyright &y& Elsevier]

Abstract: X-ray phase contrast imaging solves the basic problem of conventional X-ray imaging, i.e. low image contrast arising from small absorption differences. For years X-ray phase contrast imaging was thought to be restricted to synchrotron radiation facilities, but a new approach was recently developed at UCL which makes synchrotron-like phase effects achievable with conventional sources, by introducing two separate sets of appropriately designed coded-apertures at either side of the imaged object. Although most proposed applications of X-ray phase contrast imaging are focused on medical aspects, substantial advantages can be gained in other fields, including security inspections. In this case the system has to be based around higher X-ray energies, which has an impact on the system design. This paper describes such a design. A previously developed and experimentally validated simulation program was used to estimate the image contrast that can be expected from a range of details of interest in security inspections imaged under various conditions, including beam spectrum, detector characteristics, coded-aperture design, source-to-sample and sample-to-detector distances, etc.—while taking into account the interplay between these different parameters. The conditions providing maximum image contrast were chosen and used in the ultimate system design. [Copyright &y& Elsevier]

The parameterization of surface heat-flux variability in urban areas relies on adequate representation of surface characteristics. Given the horizontal resolutions (e.g. $$\approx $$0.1-1 km) currently used in numerical weather prediction (NWP) models, properties of the urban surface (e.g. vegetated/built surfaces, street-canyon geometries) often have large spatial variability. Here, a new approach based on Urban Zones to characterize Energy partitioning (UZE) is tested within a NWP model (Weather Research and Forecasting model; WRF v3.2.1) for Greater London. The urban land-surface scheme is the Noah/Single-Layer Urban Canopy Model (SLUCM). Detailed surface information (horizontal resolution 1 km) in central London shows that the UZE offers better characterization of surface properties and their variability compared to default WRF-SLUCM input parameters. In situ observations of the surface energy fluxes and near-surface meteorological variables are used to select the radiation and turbulence parameterization schemes and to evaluate the land-surface scheme and choice of surface parameters. For radiative fluxes, improved performance (e.g. $$>$$25 W m $$^{-2}$$ root-mean-square error reduction for the net radiation) is attained with UZE parameters compared to the WRF v3.2.1 default for all three methods from the simplest to the most detailed. The UZE-based spatial fluxes reproduce a priori expectations of greater energy storage and less evaporation in the dense city centre compared to the residential surroundings. Problems in Noah/SLUCM partitioning of energy between the daytime turbulent fluxes are identified with the overestimation of the turbulent sensible heat and underestimation of the turbulent latent heat fluxes. [ABSTRACT FROM AUTHOR]

The traditional approach to measuring segregation is based upon descriptive, non-model-based indices. A recently proposed alternative is multilevel modeling. The authors further develop the argument for a multilevel modeling approach by first describing and expanding upon its notable advantages, which include an ability to model segregation at a number of scales simultaneously. The authors then propose a major extension to this approach by introducing a simple simulation method that allows traditional descriptive indices to be reformulated within a modeling framework. The multilevel approach and the simulation method are illustrated with an application that models recent social segregation among schools in London, UK. [ABSTRACT FROM AUTHOR]

The aim of the study is to devise a new reliable dynamic route guidance approach by integrating the A* algorithm, the concept of reliability and an existing route guidance method into a single package. A new purpose-developed software tool, the Imperial College Navigation Software (ICNavS), is presented, so as to implement and demonstrate the new approach on a real road network, using simulated data. A summary of the background of the program is given, followed by a procedure developed in order to model the features of real road networks as well as missing data. Then, a simulation experiment on a part of West London's road network is carried out and the results are presented. [ABSTRACT FROM AUTHOR]