144 research outputs found
Accurate Realizations of the Ionized Gas in Galaxy Clusters: Calibrating Feedback
Using the full, three-dimensional potential of galaxy cluster halos (drawn
from an N-body simulation of the current, most favored cosmology), the
distribution of the X-ray emitting gas is found by assuming a polytropic
equation of state and hydrostatic equilibrium, with constraints from
conservation of energy and pressure balance at the cluster boundary. The
resulting properties of the gas for these simulated redshift zero clusters (the
temperature distribution, mass-temperature and luminosity-temperature
relations, and the gas fraction) are compared with observations in the X-ray of
nearby clusters. The observed properties are reproduced only under the
assumption that substantial energy injection from non-gravitational sources has
occurred. Our model does not specify the source, but star formation and AGN may
be capable of providing this energy, which amounts to 3 to 5 x10^{-5} of the
rest mass in stars (assuming ten percent of the gas initially in the cluster
forms stars). With the method described here it is possible to generate
realistic X-ray and Sunyaev-Zel'dovich cluster maps and catalogs from N-body
simulations, with the distributions of internal halo properties (and their
trends with mass, location, and time) taken into account.Comment: Matches ApJ published version; 30 pages, 7 figure
Non-Gaussian Scatter in Cluster Scaling Relations
We investigate the impact of non-Gaussian scatter in the cluster
mass-observable scaling relation on the mass and redshift distribution of
clusters detected by wide area surveys. We parameterize non-Gaussian scatter by
incorporating the third and forth moments (skewness and kurtosis) into the
distribution P(Mobs|M). We demonstrate that for low scatter mass proxies the
higher order moments do not significantly affect the observed cluster mass and
redshift distributions. However, for high scatter mass indicators it is
necessary for the survey limiting mass threshold to be less than 10^14 h^-1
Msol to prevent the skewness from having a significant impact on the observed
number counts, particularly at high redshift. We also show that an unknown
level of non-Gaussianity in the scatter is equivalent to an additional
uncertainty on the variance in P(Mobs|M) and thus may limit the constraints
that can be placed on the dark energy equation of state parameter w.
Furthermore, positive skewness flattens the mass function at the high mass end,
and so one must also account for skewness in P(Mobs|M) when using the shape of
the mass function to constrain cluster scaling-relations.Comment: 6 Pages, 3 Figures, to be submitted to ApJ Letter
The Impact of Halo Properties, Energy Feedback and Projection Effects on the Mass-SZ Flux Relation
We present a detailed analysis of the intrinsic scatter in the integrated SZ
effect - cluster mass (Y-M) relation, using semi-analytic and simulated cluster
samples. Specifically, we investigate the impact on the Y-M relation of energy
feedback, variations in the host halo concentration and substructure
populations, and projection effects due to unresolved clusters along the line
of sight (the SZ background). Furthermore, we investigate at what radius (or
overdensity) one should measure the integrated SZE and define cluster mass so
as to achieve the tightest possible scaling. We find that the measure of Y with
the least scatter is always obtained within a smaller radius than that at which
the mass is defined; e.g. for M_{200} (M_{500}) the scatter is least for
Y_{500} (Y_{1100}). The inclusion of energy feedback in the gas model
significantly increases the intrinsic scatter in the Y-M relation due to larger
variations in the gas mass fraction compared to models without feedback. We
also find that variations in halo concentration for clusters of a given mass
may partly explain why the integrated SZE provides a better mass proxy than the
central decrement. Substructure is found to account for approximately 20% of
the observed scatter in the Y-M relation. Above M_{200} = 2x10^{14} h^{-1}
msun, the SZ background does not significantly effect cluster mass
measurements; below this mass, variations in the background signal reduce the
optimal angular radius within which one should measure Y to achieve the
tightest scaling with M_{200}.Comment: 12 pages, 6 figures, to be submitted to Ap
Impact of Cluster Physics on the Sunyaev-Zel'dovich Power Spectrum
We use an analytic model to investigate the theoretical uncertainty on the
thermal Sunyaev-Zel'dovich (SZ) power spectrum due to astrophysical
uncertainties in the thermal structure of the intracluster medium. Our model
accounts for star formation and energy feedback (from supernovae and active
galactic nuclei) as well as radially dependent non-thermal pressure support due
to random gas motions, the latter calibrated by recent hydrodynamical
simulations. We compare the model against X-ray observations of low redshift
clusters, finding excellent agreement with observed pressure profiles. Varying
the levels of feedback and non-thermal pressure support can significantly
change both the amplitude and shape of the thermal SZ power spectrum.
Increasing the feedback suppresses power at small angular scales, shifting the
peak of the power spectrum to lower ell. On the other hand, increasing the
non-thermal pressure support has the opposite effect, significantly reducing
power at large angular scales. In general, including non-thermal pressure at
the level measured in simulations has a large effect on the power spectrum,
reducing the amplitude by 50% at angular scales of a few arcminutes compared to
a model without a non-thermal component. Our results demonstrate that
measurements of the shape of the power spectrum can reveal useful information
on important physical processes in groups and clusters, especially at
high-redshift where there exists little observational data. Comparing with the
recent South Pole Telescope measurements of the small-scale cosmic microwave
background power spectrum, we find our model reduces the tension between the
values of sigma_8 measured from the SZ power spectrum and from cluster
abundances.Comment: 15 Pages, 9 Figures, updated to match version accepted by Ap
Statistics of Physical Properties of Dark Matter Clusters
We have identified over 2000 well resolved cluster halos, and also their
associated bound subhalos, from the output of a 1024^3 particle cosmological
N-body simulation (of box size 320 h^-1 Mpc and softening length 3.2 h^-1 kpc).
This has allowed us to measure halo quantities in a statistically meaningful
way, and for the first time analyse their distribution for a large and well
resolved sample. We characterize each halo in terms of its morphology,
concentration, spin, circular velocity and the fraction of their mass in
substructure. We also identify those halos that have not yet reached a state of
dynamical equilibrium using the virial theorem with an additional correction to
account for the surface pressure at the boundary. These amount to 3.4% of our
initial sample. For the virialized halos, we find a median of 5.6% of halo mass
is contained within substructure, with the distribution ranging between no
identified subhalos to 65%. The fraction of mass in substructure increases with
halo mass with logarithmic slope of 0.44 +- 0.06. Halos tend to have a prolate
morphology, becoming more so with increasing mass. Subhalos have a greater
orbital angular momentum per unit mass than their host halo. Furthermore, their
orbital angular momentum is typically well aligned with that of their host.
Overall, we find that dimensionless properties of dark matter halos do depend
on their mass, thereby demonstrating a lack of self-similarity.Comment: Updated to match version published in ApJ, includes longer discussion
of the virialisation criterium, 4 figures from original version deemed not
essential to the main results and conclusions removed, uses emulate ap
Sharpening the Precision of the Sunyaev-Zel'dovich Power Spectrum
Using both halo model calculations and a large sample of simulated SZ maps,
we demonstrate that high-mass clusters add significant non-Gaussian variance to
measurements of the SZ power spectrum amplitude. The difficulty in correctly
accounting theoretically for the contribution of these objects to the
uncertainty in C_l leads to a reduced sensitivity to \sigma_8. We show that a
simple solution is to mask out the brightest clusters in the map before
measuring the power spectrum. We demonstrate that fairly conservative masking
can reduce the variance and Gaussianize the statistics significantly, thus
increasing the sensitivity to cosmological parameters. Choosing which objects
to mask is non-trivial; we found that using a fixed sky density produced a
well-defined and well-behaved estimate that can easily be applied to real maps.
For example, masking the 10 (90) brightest clusters in a 100 deg^2 SZ map will
improve the sensitivity to C_l by a factor of two at l = 1000 (2000) and 1.5 at
l = 2000 (4000). We show that even in the presence of astrophysical foregrounds
(primary CMB and point sources) and instrument noise, one can increase the
precision on measurements of \sigma_8 by masking up to 0.9 clusters/deg^2.Comment: 11 pages, 8 figures, submitted to Ap
Posthumous Medical Data Donation: The Case for a Legal Framework
This article explores the options for establishing a legal framework for posthumous medical data donation (PMDD). This concept has not been discussed in legal scholarship to date at all. The paper is, therefore, a first legal study of PMDD, aiming to address the gap and shed light on the most significant legal issues that could affect this concept. The paper starts by looking at the protection of the deceasedâs health records and medical data, finding that this protection in law is more extensive than the general protection of the deceasedâs personal data, or the protection of post-mortem privacy as a concept. The paper then investigates key issues around ownership and succession of personal data, including medical and health-related data, and how these could affect PMDD and its legal framework. The author then goes on to explore some parallels with organ donation to determine whether there are some lessons to be learned from this comparable regulatory framework. The paper concludes with the discussion around the need for a Code for posthumous medical data donation developed by the Digital Ethics Lab at the Oxford Internet Institute, and a more formal regime that would enable and facilitate this practice. Here, the author proposes key law reforms in the area of data protection and governance related to PMDD. These reforms would include amendments to the general data protection ideally, to ensure harmonisation and consistency across the EU, as well as between the general and sector-specific data protection laws and policies. These changes would contribute to legal and regulatory clarity and would help implement this important and valuable practice, which aims to facilitate research and advances in medical treatments and care
The mechanisms and processes of connection: developing a causal chain model capturing impacts of receiving recorded mental health recovery narratives.
BACKGROUND: Mental health recovery narratives are a core component of recovery-oriented interventions such as peer support and anti-stigma campaigns. A substantial number of recorded recovery narratives are now publicly available online in different modalities and in published books. Whilst the benefits of telling one's story have been investigated, much less is known about how recorded narratives of differing modalities impact on recipients. A previous qualitative study identified connection to the narrator and/or to events in the narrative to be a core mechanism of change. The factors that influence how individuals connect with a recorded narrative are unknown. The aim of the current study was to characterise the immediate effects of receiving recovery narratives presented in a range of modalities (text, video and audio), by establishing the mechanisms of connection and the processes by which connection leads to outcomes. METHOD: A study involving 40 mental health service users in England was conducted. Participants were presented with up to 10 randomly-selected recovery narratives and were interviewed on the immediate impact of each narrative. Thematic analysis was used to identify the mechanisms of connection and how connection leads to outcome. RESULTS: Receiving a recovery narrative led participants to reflect upon their own experiences or those of others, which then led to connection through three mechanisms: comparing oneself with the narrative and narrator; learning about other's experiences; and experiencing empathy. These mechanisms led to outcomes through three processes: the identification of change (through attending to narrative structure); the interpretation of change (through attending to narrative content); and the internalisation of interpretations. CONCLUSIONS: This is the first study to identify mechanisms and processes of connection with recorded recovery narratives. The empirically-based causal chain model developed in this study describes the immediate effects on recipients. This model can inform selection of narratives for use in interventions, and be used to support peer support workers in recounting their own recovery narratives in ways which are maximally beneficial to others
Regulators of G protein Signaling (RGS) proteins (version 2019.4) in the IUPHAR/BPS Guide to Pharmacology Database
Regulators of G protein signalling (RGS) proteins display a common RGS domain that interacts with the GTP-bound Gα subunits of heterotrimeric G proteins, enhancing GTP hydrolysis by stabilising the transition state [29, 419, 418], leading to a termination of GPCR signalling. Interactions through protein:protein interactions of many RGS proteins have been identified for targets other than heteromeric G proteins. Sequence analysis of the 20 RGS proteins suggests four families of RGS: RZ, R4, R7 and R12 families. Many of these proteins have been identified to have effects other than through targetting G proteins. Included here is RGS4 for which a number of pharmacological inhibitors have been described
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