5,681 research outputs found
The most massive galaxies in clusters are already fully grown at
By constructing scaling relations for galaxies in the massive cluster
MACSJ0717.5 at and comparing with those of Coma, we model the
luminosity evolution of the stellar populations and the structural evolution of
the galaxies. We calculate magnitudes, surface brightnesses and effective radii
using HST/ACS images and velocity dispersions using Gemini/GMOS spectra, and
present a catalogue of our measurements for 17 galaxies. We also generate
photometric catalogues for galaxies from the HST imaging. With
these, we construct the colour-magnitude relation, the fundamental plane, the
mass-to-light versus mass relation, the mass-size relation and the
mass-velocity dispersion relation for both clusters. We present a new, coherent
way of modelling these scaling relations simultaneously using a simple physical
model in order to infer the evolution in luminosity, size and velocity
dispersion as a function of redshift, and show that the data can be fully
accounted for with this model. We find that (a) the evolution in size and
velocity dispersion undergone by these galaxies between and is mild, with and , and (b) the stellar populations are old, Gyr,
with a Gyr dispersion in age, and are consistent with evolving purely
passively since with . The implication is that these galaxies formed their stars early and
subsequently grew dissipationlessly so as to have their mass already in place
by , and suggests a dominant role for dry mergers, which may have
accelerated the growth in these high-density cluster environments.Comment: 20 pages; accepted for publication in MNRA
Development and use of an extensometer for determining the mechanical compliance of crack toughness test specimens
Extensometer for determining mechanical compliance of crack toughness test specimen
Electrical charging of ash in Icelandic volcanic plumes
The existence of volcanic lightning and alteration of the atmospheric
potential gradient in the vicinity of near-vent volcanic plumes provides strong
evidence for the charging of volcanic ash. More subtle electrical effects are
also visible in balloon soundings of distal volcanic plumes. Near the vent,
some proposed charging mechanisms are fractoemission, triboelectrification, and
the so-called "dirty thunderstorm" mechanism, which is where ash and convective
clouds interact electrically to enhance charging. Distant from the vent, a
self-charging mechanism, probably triboelectrification, has been suggested to
explain the sustained low levels of charge observed on a distal plume. Recent
research by Houghton et al. (2013) linked the self-charging of volcanic ash to
the properties of the particle size distribution, observing that a highly
polydisperse ash distribution would charge more effectively than a monodisperse
one. Natural radioactivity in some volcanic ash could also contribute to
self-charging of volcanic plumes. Here we present laboratory measurements of
particle size distributions, triboelectrification and radioactivity in ash
samples from the Gr\'{i}msv\"{o}tn and Eyjafjallaj\"{o}kull volcanic eruptions
in 2011 and 2010 respectively, and discuss the implications of our findings.Comment: XV Conference on Atmospheric Electricity, 15-20 June 2014, Norman,
Oklahoma, US
Why the Universe Started from a Low Entropy State
We show that the inclusion of backreaction of massive long wavelengths
imposes dynamical constraints on the allowed phase space of initial conditions
for inflation, which results in a superselection rule for the initial
conditions. Only high energy inflation is stable against collapse due to the
gravitational instability of massive perturbations. We present arguments to the
effect that the initial conditions problem {\it cannot} be meaningfully
addressed by thermostatistics as far as the gravitational degrees of freedom
are concerned. Rather, the choice of the initial conditions for the universe in
the phase space and the emergence of an arrow of time have to be treated as a
dynamic selection.Comment: 12 pages, 2 figs. Final version; agrees with accepted version in
Phys. Rev.
Young people and organised outdoor activities: a study of opportunities in national parks
This thesis examines young people's opportunities to participate in organised outdoor
activities. It is set within a context of changing leisure interests, a growth in private
sector leisure provision, and increasing emphasis on consumer choice. It argues that
whilst, in principle, there is widespread support for young people's participation in
outdoor activities, in practice, opportunities are becoming increasingly limited. The
study aims to examine the nature of outdoor facilities, to determine their use by
young people, to identify changes occurring within the outdoor sector, and to
consider the changes in relation to young people's access to the outdoors.
The empirical research focuses~ on outdoor activity centres, in acknowledgement that
the residential experience offered by such centres can contribute to the social and
personal development of young people. It also focuses on the National Parks of
England and Wales. These areas possess a wealth of natural resources suitable for a
wide range of outdoor activities and, collectively, contain the highest number of
outdoor centres in the UK. A combination of quantitative and qualitative methods of
data collection, including a questionnaire survey of outdoor centres, interviews with
centre operators, and a review of National Park policies, has been used to build up a
picture of centre operations, visitor profiles, and the nature of outdoor programmes.
The study findings suggest that a number of factors influence young people's
opportunities to participate in outdoor activities. These include centre ownership,
safety and educational reforms, planning and environmental policies, and young
people's leisure behaviour. Recent years have seen a significant growth in privately
owned centres and an associated rise in skills-based activities and non-sporting
special interest holidays. These programmes have been largely directed at the adult
market. There are few indications that this pattern is about to change. Regulation of
the outdoor industry, including safety licensing, has put increasing pressures on
under-resourced centres and has led to readjustments in centre operations and in the
profile of visitor groups. Young people's opportunities to take part in adventurous
activities, as a result of safety licensing, have diminished. Educational reforms have
further dictated the direction of outdoor courses. Since the late 1980s, there has been
a marked increase in primary school visits to outdoor centres and in field studies,
whilst secondary schools visits and involvement in physical pursuits have continued to
decline. Centre diversification has led to an overall reduction in the number of places
available for young people. Planning and environmental policies have shaped the
pattern of centre development. The emphasis on environmental protection in the
National Parks has led to constraints on outdoor provision although policies, across
Parks, vary. Changes in young people's lifestyles have also begun to impact upon the
content of outdoor courses, such as the demand for more varied programmes and less
traditional activities. Sporting and recreational organisations can, by addressing
factors of motivation, play. a significant role in increasing levels of participation.
Given the dynamics of the outdoor industry, the relative importance of these factors
is difficult to determine, although the provisions of the Education Reform Act 1988
have induced some of the most radical and widespread changes within the outdoor
sector in recent years.
In trying to encourage and assist young people to take up outdoor opportunities, the
outdoor community faces a number of difficulties. These include a lack of cohesion
and .. poor image, increasing commercialisation, and the effects of changing leisure
interests. The thesis recommends greater collaboration within the community,
possibly through a new organisation, to represent a wider range of interests and to act
as a more effective lobbying mechanism. It also recommends a strengthening of the
links between the outdoor sector and the key players involved in facilitating outdoor
opportunities. Finally, it advises organisations to take heed of newly emerging
Government statements on out-of-school learning. These may offer viable
alternatives to help safeguard young people's opportunities to participate in outdoor
activities
Improving health behaviours and outcomes: An intervention to support engagement in physical activity
The purpose of this case study is to offer reflections on the personal experiences, processes of behavioural change; and subsequent outcomes of designing and implementing a collaborative exercise psychology intervention. The intervention, based on Bandura’s (1977) Self Efficacy Theory and using self-efficacy related behaviour change techniques (Michie et al., 2015), aimed to provide families affected by health inequalities with opportunities to enhance their understanding of health and make positive behavioural changes. This case is based around one female client aged 48 years of age who took part in the project with her ten-year-old daughter. Pre- intervention the client was engaging in minimal levels of weekly physical activity and reported poor self-rated mental well-being. Through improvements in self-efficacy, achieved through opportunities on the project, the client was able to make notable improvements to her physical activity levels leading to significant weight loss and improvements in mental well-being. From the practitioners’ perspective, reflection on areas for future work within the field of exercise psychology, particularly guidance on developing effective client-practitioner relationships with ‘hard-to-reach’ individuals and groups is warranted. More consideration for the suitability of the PA guidelines for individuals with poor physical and mental health is also required
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