Probing the Low Surface Brightness Dwarf Galaxy Population of the Virgo Cluster

We have used public data from the Next Generation Virgo Survey (NGVS) to investigate the dwarf galaxy population of the Virgo cluster beyond what has previously been discovered. We initially mask and smooth the data, and then use the object detection algorithm Sextractor to make our initial dwarf galaxy selection. All candidates are then visually inspected to remove artefacts and duplicates. We derive Sextractor parameters to best select low surface brightness galaxies using g band central surface brightness values of 22.5 to 26.0 mag sq arc sec and exponential scale lengths of 3.0 - 10.0 arc sec to identify 443 cluster dwarf galaxies - 303 of which are new detections. These new detections have a surface density that decreases with radius from the cluster centre. We also apply our selection algorithm to 'background', non-cluster, fields and find zero detections. In combination, this leads us to believe that we have isolated a cluster dwarf galaxy population. The range of objects we are able to detect is limited because smaller scale sized galaxies are confused with the background, while larger galaxies are split into numerous smaller objects by the detection algorithm. Using data from previous surveys combined with our data, we find a faint end slope to the luminosity function of -1.35+/-0.03, which does not significantly differ to what has previously been found for the Virgo cluster, but is a little steeper than the slope for field galaxies. There is no evidence for a faint end slope steep enough to correspond with galaxy formation models, unless those models invoke either strong feedback processes or use warm dark matter.Comment: Accepted for publication in MNRA

UNICEF IWASH Project, Northern Region, Ghana : an adapted training manual for groundwater development

This report is an adapted training manual, with specific best practice recommendations for groundwater development practitioners working in the Northern Region, Ghana. It is designed to be used in conjunction with the existing comprehensive training manual ‘Developing Groundwater: a guide to rural water supply’ by MacDonald, Davies, Calow and Chilton (2005). The additional guidelines provided in this supplementary report are specific to the Northern Region of Ghana, and have been informed by a review of groundwater development in the region which BGS carried out on behalf of UNICEF in 2010-2011. The Northern Region is a difficult area in which to find and develop groundwater resources. For this reason, more resources – time and money – need to be focussed on careful borehole siting and development in order to maximise success. This includes detailed desk and field reconnaissance surveys; the effective use and interpretation of geophysical siting methods; collection of good quality data during drilling and test pumping; rigorous recording and management of data; and effective interpretation, sharing and use of hydrogeological information by all groundwater development practitioners. This report, and the associated manual ‘Developing Groundwater’, provide practical help for carrying out these activities effectively. The authors gratefully acknowledge those persons who contributed to the formation of these guidelines, who include: UNICEF Ghana – Othniel Habila, Kabuka Banda and David Ede Community Water and Sanitation Agency (CWSA), Ghana – John Aduakye Canadian International Development Agency (CIDA) – Hydrogeological Assessment Project (HAP) – James Racicot All participants at the UNICEF/BGS workshop and training programme held in Tamale, Northern Region, from 7 to 18 February 2011

Public ubiquitous computing systems:lessons from the e-campus display deployments

In this paper we reflect on our experiences of deploying ubiquitous computing systems in public spaces and present a series of lessons that we feel will be of benefit to researchers planning similar public deployments. We focus on experiences gained from building and deploying three experimental public display systems as part of the e-campus pro ject. However, we believe the lessons are likely to be generally applicable to many different types of public ubicomp deployment

Electron-electron interactions in antidot-based Aharonov-Bohm interferometers

We present a microscopic picture of quantum transport in quantum antidots in the quantum Hall regime taking electron interactions into account. We discuss the edge state structure, energy level evolution, charge quantization and linear-response conductance as the magnetic field or gate voltage is varied. Particular attention is given to the conductance oscillations due to Aharonov-Bohm interference and their unexpected periodicity. To explain the latter we propose the mechanisms of scattering by point defects and Coulomb blockade tunneling. They are supported by self-consistent calculations in the Hartree approximation, which indicate pinning and correlation of the single-particle states at the Fermi energy as well as charge oscillation when antidot-bound states depopulate. We have also found interesting phenomena of anti-resonance reflection of the Fano type.Comment: 12 pages, 8 figure

Attack of the Flying Snakes : Formation of Isolated HI Clouds By Fragmentation of Long Streams

The existence of long (> 100 kpc) HI streams and small (< 20 kpc) free-floating HI clouds is well-known. While the formation of the streams has been investigated extensively, and the isolated clouds are often purported to be interaction debris, little research has been done on the formation of optically dark HI clouds that are not part of a larger stream. One possibility is that such features result from the fragmentation of more extended streams, while another idea is that they are primordial, optically dark galaxies. We test the validity of the fragmentation scenario (via harassment) using numerical simulations. In order to compare our numerical models with observations, we present catalogues of both the known long HI streams (42 objects) and free-floating HI clouds suggested as dark galaxy candidates (51 objects). In particular, we investigate whether it is possible to form compact features with high velocity widths (> 100 km/s), similar to observed clouds which are otherwise intriguing dark galaxy candidates. We find that producing such features is possible but extremely unlikely, occurring no more than 0.2% of the time in our simulations. In contrast, we find that genuine dark galaxies could be extremely stable to harassment and remain detectable even after 5 Gyr in the cluster environment (with the important caveat that our simulations only explore harassment and do not yet include the intracluster medium, heating and cooling, or star formation). We also discuss the possibility that such objects could be the progenitors of recently discovered ultra diffuse galaxies.Comment: 46 pages, 27 figures, accepted for publication in MNRA

A review of recent determinations of the composition and surface pressure of the atmos- phere of mars

Recent determinations of composition and surface pressure of Mars atmospher

Dynamical trapping and relaxation of scalar gravitational fields

We present a framework for nonlinearly coupled scalar-tensor theory of gravity to address both inflation and core-collapse supernova problems. The unified approach is based on a novel dynamical trapping and relaxation of scalar gravity in highly energetic regimes. The new model provides a viable alternative mechanism of inflation free from various issues known to affect previous proposals. Furthermore, it could be related to observable violent astronomical events, specifically by releasing a significant amount of additional gravitational energy during core-collapse supernovae. A recent experiment at CERN relevant for testing this new model is briefly outlined.Comment: 4 pages; version to appear in PL

The salting of brick-work

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