27,348 research outputs found
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
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
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
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
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
Prediction of the bottomonium D-wave spectrum from full lattice QCD
We calculate the full spectrum of D-wave states in the Upsilon system in
lattice QCD for the first time, using an improved version of NonRelativistic
QCD on coarse and fine "second generation" gluon field configurations from the
MILC collaboration that include the effect of up, down, strange and charm
quarks in the sea. Taking the 2S-1S splitting to set the lattice spacing, we
determine the ^3D_2 - 1S splitting to 2.3%, and find agreement with experiment.
Our prediction of the fine structure relative to the ^3D_2 gives the ^3D_3 at
10.181(5) GeV and the ^3D_1 at 10.147(6) GeV. We also discuss the overlap of
^3D_1 operators with ^3S_1 states.Comment: 4 pages, 5 figure
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
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