Condensation risk: comparison of steady-state and transient methods

Accurate assessment of both surface and interstitial condensation risk is important not only to reduce the damaging effect of moisture within the structure of buildings, but also to provide a healthy environment free from mould growth. The current British Standard (BS EN ISO 13788: 2002) contains an assessment procedure based on the assumption of a steady-state heat flow through the building envelope, neglecting the transient nature of the problem. This paper compares and evaluates numerical results of the condensation risk calculation under both steady-state and transient conditions using the existing numerical codes. Significant differences are apparent between the predictions of the simple (steady-state) and complex (transient) methods for all construction details modelled

The effect of stellar-mass black holes on the structural evolution of massive star clusters

We present the results of realistic N-body modelling of massive star clusters in the Magellanic Clouds, aimed at investigating a dynamical origin for the radius-age trend observed in these systems. We find that stellar-mass black holes, formed in the supernova explosions of the most massive cluster stars, can constitute a dynamically important population. If a significant number of black holes are retained (here we assume complete retention), these objects rapidly form a dense core where interactions are common, resulting in the scattering of black holes into the cluster halo, and the ejection of black holes from the cluster. These two processes heat the stellar component, resulting in prolonged core expansion of a magnitude matching the observations. Significant core evolution is also observed in Magellanic Cloud clusters at early times. We find that this does not result from the action of black holes, but can be reproduced by the effects of mass-loss due to rapid stellar evolution in a primordially mass segregated cluster.Comment: Accepted for publication in MNRAS Letters; 2 figures, 1 tabl

SCUBA imaging of NGC 7331 dust ring

We present observations of the spiral galaxy NGC 7331 using the Sub-millimetre Common User Bolometer Array (SCUBA) on the James Clark Maxwell Telescope. We have detected a dust ring of 45 arcsec radius (3.3 kpc) at wavelengths of 450 and 850-micron. The dust ring is in good correspondence with other observations of the ring in the mid-infrared (MIR), CO and radio-continuum, suggesting that the observed dust is associated with the molecular gas and star formation. A B-K colour map shows an analogous ring structure with an asymmetry about the major axis, consistent with the extinction being produced by a dust ring. The derived temperature of the dust lies between 16 and 31 K and the gas-to-dust ratio between 150 and 570, depending on the assumed dust emission efficiency index (beta=1.5 or 2.).Comment: 5 pages, 6 figures, to be published in MNRA

The central molecular gas structure in LINERs with low luminosity AGN: evidence for gradual disappearance of the torus

We present observations of the molecular gas in the nuclear environment of three prototypical low luminosity AGN (LLAGN), based on VLT/SINFONI AO-assisted integral-field spectroscopy of H2 1-0 S(1) emission at angular resolutions of ~0.17". On scales of 50-150 pc the spatial distribution and kinematics of the molecular gas are consistent with a rotating thin disk, where the ratio of rotation (V) to dispersion (sigma) exceeds unity. However, in the central 50 pc, the observations reveal a geometrically and optically thick structure of molecular gas (V/sigma10^{23} cm^{-2}) that is likely to be associated with the outer extent of any smaller scale obscuring structure. In contrast to Seyfert galaxies, the molecular gas in LLAGN has a V/sigma<1 over an area that is ~9 times smaller and column densities that are in average ~3 times smaller. We interpret these results as evidence for a gradual disappearance of the nuclear obscuring structure. While a disk wind may not be able to maintain a thick rotating structure at these luminosities, inflow of material into the nuclear region could provide sufficient energy to sustain it. In this context, LLAGN may represent the final phase of accretion in current theories of torus evolution. While the inflow rate is considerable during the Seyfert phase, it is slowly decreasing, and the collisional disk is gradually transitioning to become geometrically thin. Furthermore, the nuclear region of these LLAGN is dominated by intermediate-age/old stellar populations (with little or no on-going star formation), consistent with a late stage of evolution.Comment: 15 pages, including 4 figures and 1 table, Accepted for publication in ApJ Letter

Condensation risk – impact of improvements to Part L and robust details on Part C Final report: BD2414

This report summarises the main findings of the project ‘Impacts of Improvements to Part L and Robust Construction Details (RCD) on Part C’. The work consisted of a fieldwork element, undertaken by Leeds Metropolitan University and a modelling element carried out by University College London. Details of the work programme are contained in Appendix 1. The fieldwork consisted of the analysis of design material and site surveys from 16 housing developments constructed to Part L 2002 and adopting the Robust Construction Detail route to compliance. The modelling element of the project sought to identify the extent to which the ‘as built’ details give rise to a significantly increased condensation risk as compared to the relevant ‘standard’ robust construction details, as defined in the guidance. In addition to assessing ‘as built’ performance, the modelling phase of the project has investigated the suitability of the relevant calculation methods used to assess the risk of surface and interstitial condensation and mould growth. This report draws together the important conclusions from the project which has previously been presented in several very detailed interim reports and also for the first time presents the results of a workshop where these results were discussed to obtain industry feedback. The overall conclusions, future work and dissemination plans are also presented

An evaluation of the hygrothermal performance of 'standard' and 'as built' construction details using steadystate and transient modelling

Accurate assessment of both surface and interstitial condensation risk at the design stage of buildings is of great importance - not just to minimise the damaging effects moisture can cause to building envelopes, but also to contribute to the provision of adequate indoor air quality. Guidance certainly does exist with regards to limiting thermal bridging in order to prevent condensation occurring on new constructions. However, a recent study has provided clear evidence that the reality, both in translating the available guidance into a specific design and in construction on site is often rather different from the 'ideal'. This paper reports on that study and compares and evaluates the hygrothermal performance of construction details for different phases during the building life cycle. The results of both the surface and interstitial condensation risk simulations under both steady-state and transient conditions are presented and discussed. Significant differences in the hygrothermal performance of 'standard' and 'as built' construction details are observed

The Low Surface Brightness Extent of the Fornax Cluster

We have used a large format CCD camera to survey the nearby Fornax cluster and its immediate environment for low luminosity low surface brightness galaxies. Recent observations indicate that these are the most dark matter dominated galaxies known and so they are likely to be a good tracer of the dark matter in clusters. We have identified large numbers of these galaxies consistent with a steep faint end slope of the luminosity function (alpha~ -2) down to MB ~ -12. These galaxies contribute almost the same amount to the total cluster light as the brighter galaxies and they have a spatial extent that is some four times larger. They satisfy two of the important predictions of N-body hierarchical simulations of structure formation using dark halos. The luminosity (mass ?) function is steep and the mass distribution is more extended than that defined by the brighter galaxies. We also find a large concentration of low surface brightness galaxies around the nearby galaxy NGC1291.Comment: 16 pages, 6 figure