Streams Going Notts: The tidal debris finder comparison project

While various codes exist to systematically and robustly find haloes and subhaloes in cosmological simulations (Knebe et al., 2011, Onions et al., 2012), this is the first work to introduce and rigorously test codes that find tidal debris (streams and other unbound substructure) in fully cosmological simulations of structure formation. We use one tracking and three non-tracking codes to identify substructure (bound and unbound) in a Milky Way type simulation from the Aquarius suite (Springel et al., 2008) and post-process their output with a common pipeline to determine the properties of these substructures in a uniform way. By using output from a fully cosmological simulation, we also take a step beyond previous studies of tidal debris that have used simple toy models. We find that both tracking and non-tracking codes agree well on the identification of subhaloes and more importantly, the {\em unbound tidal features} associated with them. The distributions of basic properties of the total substructure distribution (mass, velocity dispersion, position) are recovered with a scatter of $\sim20$. Using the tracking code as our reference, we show that the non-tracking codes identify complex tidal debris with purities of $\sim40$. Analysing the results of the substructure finders, we find that the general distribution of {\em substructures} differ significantly from the distribution of bound {\em subhaloes}. Most importantly, both bound and unbound {\em substructures} together constitute $\sim18$ of the host halo mass, which is a factor of $\sim2$ higher than the fraction in self-bound {\em subhaloes}. However, this result is restricted by the remaining challenge to cleanly define when an unbound structure has become part of the host halo. Nevertheless, the more general substructure distribution provides a more complete picture of a halo's accretion history.Comment: 19 pages, 12 figures, accepted for publication in MNRA

Printmaking communities at the edge of chaos

© 2024 The Authors. Published by University of the West of England. This is an open access article available under a Creative Commons licence. The published version can be accessed at the following link on the publisher’s website: https://doi.org/10.54632/524.IMPJ4The theme for the conference, ‘The Printmakers Voice’, and the notion of a ‘Post-pandemic Voice’, has prompted reflection upon the previously taken-for-granted social and material aspects of printmaking now brought into sharp focus. Utilising ideas from complexity theory and alternative geographies within this paper we consider how the printmaking community we are part of has evolved and how the printmaker's voice and the post-pandemic voice meet. Printmaking is an integral part of the BA (Hons) Fine Art course at the Wolverhampton School of Art. With introductory workshops in the first year, developing into an advanced ‘experimental printmaking and photography’ workshop in the second year. In 2016-17 a ‘Print Club’ developed out of this formal teaching and learning space into weekly sessions on Wednesday evenings. The Club brings together students and staff across a range of courses (not solely fine art) who have a specific interest in pursuing printmaking. There are no set agendas, and print club members work alongside each other on their projects in a supportive environment. Some regulars come each week and those who drop in. Some are trying to realise a project and those who want to sit and chat. Recognising the impacts of space and place on social cohesion and voice, we borrow from feminist geographer Doreen Massey, who stated that ‘space is a product of inter-relations between people and place’[i], in which different trajectories co-exist and are always under construction. Collective moments of social interaction orbit around printing presses, spaces of multiplicity embedded within material practices. [i] Massey, D. (2005) For Space. (London: Sage Publishing).Published onlin

Mind The Gap: Developing Contexts for Practice

Special Edition on Transforming Assessment in Higher EducationAn investigation into the development of patchwork texts as a model for enabling students to make progressive links between theory and practice on a BA (Hons) Fine Art course and how this model of delivery might support a more holistic assessment of contextual knowledge in which learning takes place and ‘makes sense over time’ and in relation to a range of experiences

Power, Pathological Worldviews, and the Strengths Perspective in Social Work

This article takes up Blundo’s (2001) assertion in this journal that in order to practice from the strengths perspective, social workers need to alter their “frames.” Expanding on this assertion, we specify a particular frame that requires change: a pathological worldview. Examining the strengths perspective with regard to a Foucauldian analysis of power, we argue that to thoroughly implement the strengths perspective, we need to consider the dividing practices that allow us to maintain power and that reflect a pathological worldview. This article provides considerations for social work practice that will be of interest to practicing social workers and social work educators interested in continuing to develop their strengths-based practice

Sussing merger trees: the Merger Trees Comparison Project

Merger trees follow the growth and merger of dark-matter haloes over cosmic history. As well as giving important insights into the growth of cosmic structure in their own right, they provide an essential backbone to semi-analytic models of galaxy formation. This paper is the first in a series to arise from the Sussing Merger Trees Workshop in which 10 different tree-building algorithms were applied to the same set of halo catalogues and their results compared. Although many of these codes were similar in nature, all algorithms produced distinct results. Our main conclusions are that a useful merger-tree code should possess the following features: (i) the use of particle IDs to match haloes between snapshots; (ii) the ability to skip at least one, and preferably more, snapshots in order to recover subhaloes that are temporarily lost during merging; (iii) the ability to cope with (and ideally smooth out) large, temporary fluctuations in halo mass. Finally, to enable different groups to communicate effectively, we defined a common terminology that we used when discussing merger trees and we encourage others to adopt the same language. We also specified a minimal output format to record the results

Sussing merger trees: a proposed merger tree data format

We propose a common terminology for use in describing both temporal merger trees and spatial structure trees for dark-matter halos. We specify a unified data format in HDF5 and provide example I/O routines in C, FORTRAN and PYTHON

Apparent bypass of negative selection in CD8+ tumours in CD2-myc transgenic mice.

A role for antigen stimulation in lymphoid neoplasia has been postulated and is supported by indirect evidence that suggests that the interaction of antigen with both T cells and B cells may constitute an epigenetic event that can contribute to tumour induction or tumour progression. Using myc-bearing transgenic mice that develop mainly clonal T-cell lymphomas we have investigated the possibility that endogenous antigen-mediated clonal deletion might be overridden in tumorigenesis. CD2-myc transgenic mice were backcrossed on to a CBA/Ca background to ensure Mtv-mediated deletion of V beta 11-expressing T cells in the resultant offspring. Lymphomas arising from these mice were subsequently screened for V beta 11 expression. There was a clear correlation between the age at which mice developed neoplasia and the tumour phenotype. Mice with CD4- CD8+ tumours succumbed to thymic lymphoma at a significantly younger age than mice developing CD4+ CD8+ tumours. A small number of tumours consisted of the 'forbidden' V beta 11 phenotype, showing that cells vulnerable to transformation could escape negative selection. The majority of the V beta 11-positive tumours were CD4- CD8+ and were only observed in mice showing clinical evidence of tumour development at a relatively young age. The phenotype of these cells and the age at which tumours arose suggests that T cells escaping tolerance may be susceptible to transformation

Sussing merger trees: the influence of the halo finder

Merger tree codes are routinely used to follow the growth and merger of dark matter haloes in simulations of cosmic structure formation. Whereas in Srisawat et. al. we compared the trees built using a wide variety of such codes, here we study the influence of the underlying halo catalogue upon the resulting trees. We observe that the specifics of halo finding itself greatly influences the constructed merger trees. We find that the choices made to define the halo mass are of prime importance. For instance, amongst many potential options different finders select self-bound objects or spherical regions of defined overdensity, decide whether or not to include substructures within the mass returned and vary in their initial particle selection. The impact of these decisions is seen in tree length (the period of time a particularly halo can be traced back through the simulation), branching ratio (essentially the merger rate of subhaloes) and mass evolution. We therefore conclude that the choice of the underlying halo finder is more relevant to the process of building merger trees than the tree builder itself. We also report on some built-in features of specific merger tree codes that (sometimes) help to improve the quality of the merger trees produced