1,290 research outputs found
Properties of simulated Milky Way-mass galaxies in loose group and field environments
We test the validity of comparing simulated field disk galaxies with the
empirical properties of systems situated within environments more comparable to
loose groups, including the Milky Way's Local Group. Cosmological simulations
of Milky Way-mass galaxies have been realised in two different environment
samples: in the field and in environments with similar properties to the Local
Group. Apart from the environments of the galaxies, the samples are kept as
homogeneous as possible with equivalent ranges in last major merger time, halo
mass and halo spin. Comparison of these two samples allow for systematic
differences in the simulations to be identified. Metallicity gradients, disk
scale lengths, colours, magnitudes and age-velocity dispersion relations are
studied for each galaxy in the suite and the strength of the link between these
and environment of the galaxies is studied. The bulge-to-disk ratio of the
galaxies show that these galaxies are less spheroid dominated than many other
simulated galaxies in literature with the majority of both samples being disk
dominated. We find that secular evolution and mergers dominate the spread of
morphologies and metallicity gradients with no visible differences between the
two environment samples. In contrast with this consistency in the two samples
there is tentative evidence for a systematic difference in the velocity
dispersion-age relations of galaxies in the different environments. Loose group
galaxies appear to have more discrete steps in their velocity dispersion-age
relations. We conclude that at the current resolution of cosmological galaxy
simulations field environment galaxies are sufficiently similar to those in
loose groups to be acceptable proxies for comparison with the Milky Way
provided that a similar assembly history is considered.Comment: 16 pages, 11 figures, abstract abridged for arXiv. Accepted for
publication in Astronomy & Astrophysic
Being on the Juvenile Dermatomyositis Rollercoaster: a qualitative study
Objectives: Juvenile Dermatomyositis is a rare, potentially life-threatening condition with no known cure. There is no published literature capturinghow children and young people feel about their condition, from their perspective. This study was therefore unique in that it asked children and young people what is it like to live with Juvenile Dermatomyositis.
Methods: Data wereobtained from fifteen young people with Juvenile Dermatomyositis, between eightand nineteen years of age from one Paediatric Rheumatology department using audio-recordedinterpretive phenomenology interviews. Data were analyzed phenomenologically, using a process that derives narratives from transcripts resulting in a collective composite of participants shared experiences, called a‘phenomenon’.
Results:The overarching metaphor of a rollercoaster captures the phenomenon of living withJuvenile Dermatomyositisas a young person, with the ups and downs at different time points clearly described by those interviewed. The five themes plotted on the rollercoaster, began with confusion; followed by feeling different, being sick, steroidal and scared from the medications; uncertainty; and then ended with acceptance of the disease over time.
Conclusion: Young people were able to talk about their experiences about having Juvenile Dermatomyositis. Our findings will aid clinicians in their practice by gaining a deeper understanding of what daily life is like and highlighting ways to enhance psychosocial functioning. Hopefully, this study and any further resulting studies,will raise understanding of Juvenile Dermatomyositis worldwide and will encourage health care professionals to better assess psychosocial needs in the future
A unified approach to combinatorial key predistribution schemes for sensor networks
There have been numerous recent proposals for key predistribution schemes for wireless sensor networks based on various types of combinatorial structures such as designs and codes. Many of these schemes have very similar properties and are analysed in a similar manner. We seek to provide a unified framework to study these kinds of schemes. To do so, we define a new, general class of designs, termed “partially balanced t-designs”, that is sufficiently general that it encompasses almost all of the designs that have been proposed for combinatorial key predistribution schemes. However, this new class of designs still has sufficient structure that we are able to derive general formulas for the metrics of the resulting key predistribution schemes. These metrics can be evaluated for a particular scheme simply by substituting appropriate parameters of the underlying combinatorial structure into our general formulas. We also compare various classes of schemes based on different designs, and point out that some existing proposed schemes are in fact identical, even though their descriptions may seem different. We believe that our general framework should facilitate the analysis of proposals for combinatorial key predistribution schemes and their comparison with existing schemes, and also allow researchers to easily evaluate which scheme or schemes present the best combination of performance metrics for a given application scenario
Sustaining Urban Forests in Post-Industrial Cities: Place Attachment, Ecology, and Stewardship Potential
People value urban green spaces for enjoying nature and socializing with friends, family, and other park users. However, overgrown urban forests without clear access points can be perceived as dark, dangerous, and wild places. As many cities experience reduced budgets, they struggle to maintain green spaces established in more prosperous times. We conducted a descriptive analysis of how constrained parks budgets and subsequent city decisions about maintenance are associated with patterns of forest use, place attachment, and social capital and their impacts on the potential for stewardship of forested parks. We selected Springfield, Massachusetts for our study because it is typical of former industrial cities with highly constrained budgets. We used both qualitative and quantitative analyses of field observations and interviews with park users and nearby residents. We found that access to forests and park use were the strongest predictors of place attachment, and that on-site services, access, and maintenance level were the strongest predictors of use rather than surrounding socioeconomic conditions. Users valued the ecology of the sites, even while park managers highlighted invasive plants as a major maintenance issue. Even though many sites had low levels of use, there remains a strong sense of ownership, community, and safety. Taken together, there is a great deal of untapped stewardship potential in the city, with few organized avenues for users and residents to engage in stewardship. The findings support the hypothesized ‘virtuous circle’ whereby higher levels of maintenance and access beget greater use and attachment, which motivates stewardship. Alternatively, the more neglected forested parks become, the less use they will have, and the more unknown and unloved they will become. In high use sites, some outreach may be all that is needed to move into the ‘virtuous circle,’ while greater interventions will be needed in low use sites with no facilities, and these sites are the ones at greatest risk. Since the long-term sustainability of urban forests requires that local residents appreciate, use, and steward them, Springfield and other post-industrial cities need to find creative models for supporting greater involvement of residents in park stewardship while recognizing these residents frequently inhabit communities under stress
Breathing in Low Mass Galaxies: A Study of Episodic Star Formation
We simulate the collapse of isolated dwarf galaxies using SPH + N-Body
simulations including a physically motivated description of the effects of
supernova feedback. As the gas collapses and stars form, the supernova feedback
disrupts enough gas to temporarily quench star formation. The gas flows outward
into a hot halo, where it cools until star formation can continue once more and
the cycle repeats. The star formation histories of isolated Local Group dwarf
galaxies exhibit similar episodic bursts of star formation. We examine the mass
dependence of the stellar velocity dispersions and find that they are no less
than half the velocity of the halos measured at the virial radius.Comment: 5 pages, 3 figures, accepted ApJ. Full resolution figures and movies
available at http://hpcc.astro.washington.edu/feedbac
The National Teaching Repository − Sharing effective interventions: Learning from each other so that we can continue to enhance and improve what we do
The National Teaching Repository (NTR) is a widely
recognised Open Educational Resource (OER) that has
made a significant impact on the global higher education
community. Recently, the UNESCO Secretariat invited the
NTR team to present reports on the repository’s reach and
impact (Wooff and Irving-Bell, 2022), which has prompted
this article. In it, we provide an overview of the NTR’s
origins, values, and vision, and we also extend an invitation
for you to join us in this exciting initiative
High accuracy power spectra including baryonic physics in dynamical Dark Energy models
The next generation mass probes will obtain information on non--linear power
spectra P(k,z) and their evolution, allowing us to investigate the nature of
Dark Energy. To exploit such data we need high precision simulations, extending
at least up to scales of k 10 h/Mpc, where the effects of baryons can no longer
be neglected.
In this paper, we present a series of large scale hydrodynamical simulations
for LCDM and dynamical Dark Energy (dDE) models, in which the equation of state
parameter is z-dependent. The simulations include gas cooling, star formation
and Supernovae feedback. They closely approximate the observed star formation
rate and the observationally derived star/Dark Matter mass ratio in collapsed
systems. Baryon dynamics cause spectral shifts exceeding 1% at k > 2-3 h/Mpc
compared to pure n-body simulations in the LCDM simulations. This agrees with
previous studies, although we find a smaller effect (~50%) on the power
spectrum amplitude at higher k's. dDE exhibits similar behavior, even though
the dDE simulations produce ~20% less stars than the analogous LCDM
cosmologies. Finally, we show that the technique introduced in Casarini et al.
to obtain spectra for any cosmology from constant-w models at any
redshift still holds when gas physics is taken into account. While this
relieves the need to explore the entire functional space of dark energy state
equations, we illustrate a severe risk that future data analysis could lead to
misinterpretation of the DE state equation.Comment: 12 pages, 13 figures, minor changes to match the accepted version,
MNRAS in pres
The stellar metallicity distribution of disc galaxies and bulges in cosmological simulations
By means of high-resolution cosmological hydrodynamical simulations of Milky
Way-like disc galaxies, we conduct an analysis of the associated stellar
metallicity distribution functions (MDFs). After undertaking a kinematic
decomposition of each simulation into spheroid and disc sub-components, we
compare the predicted MDFs to those observed in the solar neighbourhood and the
Galactic bulge. The effects of the star formation density threshold are visible
in the star formation histories, which show a modulation in their behaviour
driven by the threshold. The derived MDFs show median metallicities lower by
0.2-0.3 dex than the MDF observed locally in the disc and in the Galactic
bulge. Possible reasons for this apparent discrepancy include the use of low
stellar yields and/or centrally-concentrated star formation. The dispersions
are larger than the one of the observed MDF; this could be due to simulated
discs being kinematically hotter relative to the Milky Way. The fraction of low
metallicity stars is largely overestimated, visible from the more negatively
skewed MDF with respect to the observational sample. For our fiducial Milky Way
analog, we study the metallicity distribution of the stars born "in situ"
relative to those formed via accretion (from disrupted satellites), and
demonstrate that this low-metallicity tail to the MDF is populated primarily by
accreted stars. Enhanced supernova and stellar radiation energy feedback to the
surrounding interstellar media of these pre-disrupted satellites is suggested
as an important regulator of the MDF skewness.Comment: 20 pages, 14 figures, MNRAS, accepte
High precision spectra at large redshift for dynamical DE cosmologies
The next generation mass probes will investigate DE nature by measuring
non-linear power spectra at various z, and comparing them with high precision
simulations. Producing a complete set of them, taking into account baryon
physics and for any DE state equation w(z), would really be numerically
expensive. Regularities reducing such duty are essential. This paper presents
further n-body tests of a relation we found, linking models with DE state
parameter w(z) to const.-w models, and also tests the relation in hydro
simulations.Comment: PASCOS 2010, the 16th International Symposium on Particles, Strings
and Cosmology, Valencia (Spain), July 19th - 23rd, 201
- …