A Statistical Semi-Empirical Model: Satellite galaxies in Groups and Clusters

We present STEEL a STatistical sEmi-Empirical modeL designed to probe the distribution of satellite galaxies in groups and clusters. Our fast statistical methodology relies on tracing the abundances of central and satellite haloes via their mass functions at all cosmic epochs with virtually no limitation on cosmic volume and mass resolution. From mean halo accretion histories and subhalo mass functions the satellite mass function is progressively built in time via abundance matching techniques constrained by number densities of centrals in the local Universe. By enforcing dynamical merging timescales as predicted by high-resolution N-body simulations, we obtain satellite distributions as a function of stellar mass and halo mass consistent with current data. We show that stellar stripping, star formation, and quenching play all a secondary role in setting the number densities of massive satellites above $M_*\gtrsim 3\times 10^{10}\, M_{\odot}$. We further show that observed star formation rates used in our empirical model over predict low-mass satellites below $M_*\lesssim 3\times 10^{10}\, M_{\odot}$, whereas, star formation rates derived from a continuity equation approach yield the correct abundances similar to previous results for centrals.Comment: 21 pages, 17 Figures. MNRAS, in pres

The significant effects of stellar mass estimation on galaxy pair fractions

There exist discrepancies in measurements of the number and evolution of galaxy pairs. The pair fraction appears to be sensitive to both the criteria used to select pair fraction and the methods used to analyze survey data. This paper explores the connection between stellar mass estimation and the pair fraction of galaxies making use of STEEL, the Statistical sEmi-Emprical modeL. Previous results have found the pair fraction is sensitive to choices made when selecting what qualifies as a pair, for example luminosity or stellar mass selections. We find that different estimations of stellar mass such as photometric choice mass-to-light ratio or IMF that effect the stellar mass function also significantly affect the derived galaxy pair fraction. By making use of the galaxy halo connection we investigate these systematic affects on the pair fraction. We constrain the galaxy halo connection using the stellar-mass-halo-mass relationship for two observed stellar mass functions, and the Illustris TNG stellar mass function. Furthermore, we also create a suite of toy models where the stellar-mass-halo-mass relationship is manually changed. For each stellar-mass-halo-mass relation the pair fraction, and its evolution, are generated. We find that enhancements to the number density of high mass galaxies cause steepening of the stellar-mass-halo mass relation, resulting in a reduction of the pair fraction. We argue this is a considerable cause of bias that must be accounted for when comparing pair fractions.Comment: Submitted to MNRAS 29-Nov-201

Steady-state large-eddy simulations of convective and stable urban Boundary layers

A comprehensive investigation is carried out to establish best practice guidelines for the modelling of statistically steady-state non-neutral urban boundary layers (UBL) using large-eddy simulation (LES). These steady-state simulations enable targeted studies under realistic non-neutral conditions without the complications associated with the inherently transient nature of the UBL. An extensive set of simulations of convective and stable conditions is carried out to determine which simplifications, volumetric forcings, and boundary conditions can be applied to replicate the mean and turbulent (variance and covariance) statistics of this intrinsically transient problem most faithfully. In addition, a new method is introduced in which a transient simulation can be ‘frozen’ into a steady state. It is found that non-neutral simulations have different requirements to their neutral counterparts. In convective conditions, capping the boundary-layer height h with the top of the modelled domain to h/5 and h/10 (which is common practice in neutral simulations) reduces the turbulent kinetic energy by as much as 61% and 44%, respectively. Consistent with the literature, we find that domain heights lz≥5|L| are necessary to reproduce the convective-boundary-layer dynamics, where L is the Obukhov length. In stably stratified situations, the use of a uniform momentum forcing systematically underestimates the mechanical generation of turbulence over the urban canopy layer, and therefore leads to misrepresentations of both the inner- and outer-layer dynamics. The new ‘frozen-transient’ method that is able to maintain a prescribed flow state (including entrainment at the boundary-layer top) is shown to work well in both stable and convective conditions. Guidelines are provided for future studies of the capped and uncapped convective and stable UBL

Environmental education in public schools.

Massachusetts Institute of Technology. Dept. of Architecture. Thesis. 1971. B.Arch.Text within red line borders.B.Arch

How trees affect urban air quality: It depends on the source

Large-eddy simulation (LES) is used to systematically analyse the impacts of trees on air quality in idealised street canyons. The LES tree model includes radiation, transpiration, drag and deposition effects. The superposition of background concentrations and local emissions is used to construct realistic urban scenarios for fine particulate matter (PM2.5) and nitrogen oxides (NOx). Both neutral and convective atmospheric conditions are considered to assess the importance of buoyancy effects and the role of tree shading and transpiration. Tree impact on local air quality is shown to be driven by the balance between the rate at which they actively remove pollutants from the air (deposition) and the way in which they alter the transport of pollutants within and out of the street canyon (dispersion). For pollutant species or street types where the concentration field is dominated by background levels (such as PM2.5), deposition will generally dominate and thus local air quality will improve. For pollutants and street types where local emission sources dominate (e.g. NOx on a busy road), the dispersion effects of trees become more prominent and can lead to elevated concentrations where mixing or exchange is significantly inhibited. Mixing in the convective simulation is more vigorous than in the neutral simulation which results in substantial differences in in-canyon flow fields and exchange velocities, highlighting the importance of incorporating thermal effects when studying urban trees. Increased residency times, and thus deposition, under neutral conditions suggest that trees can have amplified effects under conditions conducive of poor air quality. For the cases considered, trees largely act to improve air quality with the exception of localised hotspots. The competing effects of trees — specifically deposition versus altered exchange with the atmosphere — are also incorporated in a simple integral model that predicts whether or not the air quality will improve. The model matches well with LES predictions for both PM2.5 and NOx and can serve as a simple tool for urban design purposes

uDALES: large-eddy-simulation software for urban flow, dispersion, and microclimate modelling

With continuing urbanization, challenges associated with the urban environment such as air quality, heat islands, pedestrian thermal comfort, and wind loads on tall buildings, are increasingly relevant. Our ability to realistically capture processes such as the transport of heat, moisture, momentum and pollutants, and those of radiative transfer in urban environments is key to understanding and facing these challenges (Oke et al., 2017). The turbulent nature of the urban flow field and the inherent heterogeneity and wide range of scales associated with the urban environment result in a complex modelling problem. Large-eddy simulation (LES) is an approach to turbulence modelling used in computational fluid dynamics to simulate turbulent flows over a wide range of spatial and temporal scales. LES is one of the most promising tools to model the interactions typical of urban areas due to its ability to resolve the urban flow field at resolutions of O(1 m, 0.1 s), over spatial domains of O(100 m), and time periods of O(10 h). Although there are many scalable LES models for atmospheric flows, to our knowledge, only few are capable of explicitly representing buildings and of modelling the full range of urban processes (e.g. PALM-4U Resler et al. (2017); Maronga et al. (2020); or OpenFoam Weller et al. (1998))

The Halls Creek Way of Residential Child Care: Protecting Children is Everyone's Business

This paper describes the collaboration between an Aboriginal community and Western Australia's (WA) Department for Child Protection (DCP) in designing and operating a residential child care facility in a predominantly Aboriginal community. Research literature has established that the effective operation of child protection systems in remote Aboriginal communities requires practitioners and policy-makers to have awareness of local and extra-local cultural, historical and contemporary social factors in nurturing children. This ethnographic case study describes how a newspaper campaign heightened public and professional awareness of child abuse in the town of Halls Creek, in WA's Kimberley region. With its largely Aboriginal population, Halls Creek lacked the infrastructure to accommodate an inflow of regional people. Homelessness, neglect and poverty were widespread. Within a broader government and local response, DCP joined with community leaders to plan out of home care for children. Detailed are the importance and complexities of negotiating between universal standardised models of care and local input. Strategies for building positive relationships with children's family while strengthening both parenting capacity and community acceptance, and use of the facility are identified. Key to success was the development of a collaborative ‘third-space’ for threading together local and professional child protection knowledge

The State of Global Air Quality Funding 2022

The only global snapshot of clean air funding from donor governments and philanthropic foundations. This report highlights funding trends and gaps in 2015-2021, as well as recommendations for smarter investment for people and planet.99% of the world's population breathes air that exceeds World Health Organization air quality guidelines. Cleaning the air is a massive opportunity to improve public health and climate change. Because air pollution and climate change are mainly caused by burning fossil fuels, these problems can be tackled together. By addressing these issues in isolation, funders and policymakers drastically overlook the potential of clean air to realise multiple health, social and sustainable economic benefits.Our fourth annual report is the only global snapshot of projects funded by international development funders and philanthropic foundations to tackle air pollution. We identify gaps in funding, and opportunities for strategic investment and collaboration for systemic change.?As the world prepares for COP27 in Egypt, we call for more joined up policies and funding to address air pollution, climate change and unsustainable economic growth simultaneously. This report provides recommendations for decision makers, policy makers and philanthropic foundations

Galaxy sizes and the galaxy-halo connection - I: the remarkable tightness of the size distributions

The mass and structural assembly of galaxies is a matter of intense debate. Current theoretical models predict the existence of a linear relationship between galaxy size (Re) and the host dark matter halo virial radius (Rh). By making use of semi-empirical models compared to the size distributions of central galaxies from the Sloan Digital Sky Survey, we provide robust constraints on the normalization and scatter of the Re - Rh relation. We explore the parameter space of models in which the Re - Rh relation is mediated by either the spin parameter or the concentration of the host halo, or a simple constant the nature of which is in principle unknown. We find that the data require extremely tight relations for both early-type and late-type galaxies (ETGs,LTGs), especially for more massive galaxies. These constraints challenge models based solely on angular momentum conservation, which predict significantly wider distributions of galaxy sizes and no trend with stellar mass, if taken at face value. We discuss physically-motivated alterations to the original models that bring the predictions into better agreement with the data. We argue that the measured tight size distributions of SDSS disk galaxies can be reproduced by semi-empirical models in which the Re - Rh connection is mediated by the stellar specific angular momenta jstar. We find that current cosmological models of galaxy formation broadly agree with our constraints for LTGs, and justify the strong link between Re and jstar that we propose, however the tightness of the Re - Rh relation found in such ab-initio theoretical models for ETGs is in tension with our semi-empirical findings

On the continuous and discontinuous precipitation of the L12 phase in Cu-Ni-Al alloys

L12 precipitate hardened Cu-Ni-Al alloys offer high strength, corrosion resistance and anti-biofouling properties, making them useful in marine engineering applications. Optimisation of their mechanical properties requires a full understanding of their complex precipitate nucleation and coarsening mechanisms. In this work, the microstructural characteristics and hardness of three Cu-Ni-Al alloys with compositions of Cu(95-x)NixAl5 (x = 5, 15, 25 at%) were investigated in the homogenised state and following heat treatments at 700˚C for 1, 10, 100 and 1000 hours. L12 precipitates were observed in the alloys containing ≥ 15 at% Ni. In these alloys, the L12 phase was found to precipitate via both continuous and discontinuous routes following all exposures at 700˚C. The coarsening behaviours of the continuous and discontinuous L12 distributions were characterised and correlated to measurements of hardness and lattice misfit. The alloys containing 15 and 25 at% Ni exhibited peak hardness after 1 h at 700˚C, which corresponded to average particle diameters of 30 nm, respectively. These results were rationalised through calculations of the change in the critical resolved shear stress associated with the transition from weakly to strongly coupled superpartial dislocations. The discontinuous reaction was observed to be led by L12 phase formation, which extended into the neighbouring grain, ahead of the reorientation front of the matrix