525 research outputs found
A summative report on the qualitative evaluation on the eleven remodelling social work pilots 2008-11
Modelling circumstellar discs with 3D radiation hydrodynamics
We present results from combining a grid-based radiative transfer code with a
Smoothed Particle Hydrodynamics code to produce a flexible system for modelling
radiation hydrodynamics. We use a benchmark model of a circumstellar disc to
determine a robust method for constructing a gridded density distribution from
SPH particles. The benchmark disc is then used to determine the accuracy of the
radiative transfer results. We find that the SED and the temperature
distribution within the disc are sensitive to the representation of the disc
inner edge, which depends critically on both the grid and SPH resolution. The
code is then used to model a circumstellar disc around a T-Tauri star. As the
disc adjusts towards equilibrium vertical motions in the disc are induced
resulting in scale height enhancements which intercept radiation from the
central star. Vertical transport of radiation enables these perturbations to
influence the mid-plane temperature of the disc. The vertical motions decay
over time and the disc ultimately reaches a state of simultaneous hydrostatic
and radiative equilibrium.Comment: MNRAS accepted; 15 pages; 17 figures, 4 in colou
Smoothed Particle Hydrodynamics and Magnetohydrodynamics
This paper presents an overview and introduction to Smoothed Particle
Hydrodynamics and Magnetohydrodynamics in theory and in practice. Firstly, we
give a basic grounding in the fundamentals of SPH, showing how the equations of
motion and energy can be self-consistently derived from the density estimate.
We then show how to interpret these equations using the basic SPH interpolation
formulae and highlight the subtle difference in approach between SPH and other
particle methods. In doing so, we also critique several `urban myths' regarding
SPH, in particular the idea that one can simply increase the `neighbour number'
more slowly than the total number of particles in order to obtain convergence.
We also discuss the origin of numerical instabilities such as the pairing and
tensile instabilities. Finally, we give practical advice on how to resolve
three of the main issues with SPMHD: removing the tensile instability,
formulating dissipative terms for MHD shocks and enforcing the divergence
constraint on the particles, and we give the current status of developments in
this area. Accompanying the paper is the first public release of the NDSPMHD
SPH code, a 1, 2 and 3 dimensional code designed as a testbed for SPH/SPMHD
algorithms that can be used to test many of the ideas and used to run all of
the numerical examples contained in the paper.Comment: 44 pages, 14 figures, accepted to special edition of J. Comp. Phys.
on "Computational Plasma Physics". The ndspmhd code is available for download
from http://users.monash.edu.au/~dprice/ndspmhd
The challenges and affordances of online participatory workshops in the context of young people's everyday climate crisis activism: insights from facilitators
Participatory workshops can provide an equitable way of working with diverse communities to co-produce new knowledge and understanding in the context of young peopleâs everyday climate crisis activism. Drawing on data from interviews with seven facilitators, we consider the specific affordances and challenges provided by participatory workshops that are held online with groups including young people and teachers. We highlight that the online format can provide a powerful methodological tool for co-production, community building and developing constructive intergenerational dialogue. Although online workshops can include diverse voices, barriers and challenges remain when seeking to reduce the persistent under-representation of some groups
On the rate of convergence of the Hamiltonian particle-mesh method
The Hamiltonian Particle-Mesh (HPM) method is a particle-in-cell method for compressible fluid flow with Hamiltonian structure. We present a numer- ical short-time study of the rate of convergence of HPM in terms of its three main governing parameters. We find that the rate of convergence is much better than the best available theoretical estimates. Our results indicate that HPM performs best when the number of particles is on the order of the number of grid cells, the HPM global smoothing kernel has fast decay in Fourier space, and the HPM local interpolation kernel is a cubic spline
The acute oncologist's role in managing patients with cancer and other co-morbidities
Background: An Acute Oncology Service (AOS) is paramount to providing timely and improved pathways
of care for patients who are admitted to hospital with cancer-related problems or suspected cancer. Objective:
To establish an AOS pilot study to decide how best to implement such a service locally. Methods: The AOS,
which included collaboration between the oncology and palliative care teams at the Northern General Hospital
in Sheffi eld, UK, ensured that the majority of oncology patients in the region received timely assessment
by an oncologist if they became acutely unwell as a result of their cancer or its treatment. The AOS consisted
of a thrice-weekly ward round, and daily telephone advice service. Results: We report on patient data during
the fi rst 12 months of the pilot study. Delivery of the AOS enhanced communication between the services
and provided inter-professional education and support, resulting in earlier oncological team involvement in the
management of patients with cancer admitted under other teams, as well as provision of advice to patients and
their caregivers and families. Provision of the AOS shortened the mean length of hospital stay by 6 days. Two
case studies are presented to illustrate the typical challenges faced when managing these patients. Conclusions:
Establishment of the AOS enabled effective collaboration between the oncology and other clinical teams to
provide a rapid and streamlined referral pathway of patients to the AOS. Locally, this process has been supported
by the development of acute oncology protocols, which are now in use across the local cancer network
A method for reconstructing the variance of a 3D physical field from 2D observations: Application to turbulence in the ISM
We introduce and test an expression for calculating the variance of a
physical field in three dimensions using only information contained in the
two-dimensional projection of the field. The method is general but assumes
statistical isotropy. To test the method we apply it to numerical simulations
of hydrodynamic and magnetohydrodynamic turbulence in molecular clouds, and
demonstrate that it can recover the 3D normalised density variance with ~10%
accuracy if the assumption of isotropy is valid. We show that the assumption of
isotropy breaks down at low sonic Mach number if the turbulence is
sub-Alfvenic. Theoretical predictions suggest that the 3D density variance
should increase proportionally to the square of the Mach number of the
turbulence. Application of our method will allow this prediction to be tested
observationally and therefore constrain a large body of analytic models of star
formation that rely on it.Comment: 8 pages, 9 figures, accepted for publication in MNRA
rpSPH: a novel Smoothed Particle Hydrodynamics Algorithm
We suggest a novel discretisation of the momentum equation for Smoothed
Particle Hydrodynamics (SPH) and show that it significantly improves the
accuracy of the obtained solutions. Our new formulation which we refer to as
relative pressure SPH, rpSPH, evaluates the pressure force in respect to the
local pressure. It respects Newtons first law of motion and applies forces to
particles only when there is a net force acting upon them. This is in contrast
to standard SPH which explicitly uses Newtons third law of motion continuously
applying equal but opposite forces between particles. rpSPH does not show the
unphysical particle noise, the clumping or banding instability, unphysical
surface tension, and unphysical scattering of different mass particles found
for standard SPH. At the same time it uses fewer computational operations. and
only changes a single line in existing SPH codes. We demonstrate its
performance on isobaric uniform density distributions, uniform density shearing
flows, the Kelvin-Helmholtz and Rayleigh-Taylor instabilities, the Sod shock
tube, the Sedov-Taylor blast wave and a cosmological integration of the Santa
Barbara galaxy cluster formation test. rpSPH is an improvement these cases. The
improvements come at the cost of giving up exact momentum conservation of the
scheme. Consequently one can also obtain unphysical solutions particularly at
low resolutions.Comment: 17 pages, 13 figures. Final version. Including section of how to
break i
Hydrodynamic capabilities of an SPH code incorporating an artificial conductivity term with a gravity-based signal velocity
This paper investigates the hydrodynamic performances of an SPH code
incorporating an artificial heat conductivity term in which the adopted signal
velocity is applicable when gravity is present. In accordance with previous
findings it is shown that the performances of SPH to describe the development
of Kelvin-Helmholtz instabilities depend strongly on the consistency of the
initial condition set-up and on the leading error in the momentum equation due
to incomplete kernel sampling. An error and stability analysis shows that the
quartic B-spline kernel (M_5) possesses very good stability properties and we
propose its use with a large neighbor number, between ~50 (2D) to ~ 100 (3D),
to improve convergence in simulation results without being affected by the
so-called clumping instability. SPH simulations of the blob test show that in
the regime of strong supersonic flows an appropriate limiting condition, which
depends on the Prandtl number, must be imposed on the artificial conductivity
SPH coefficients in order to avoid an unphysical amount of heat diffusion.
Results from hydrodynamic simulations that include self-gravity show profiles
of hydrodynamic variables that are in much better agreement with those produced
using mesh-based codes. In particular, the final levels of core entropies in
cosmological simulations of galaxy clusters are consistent with those found
using AMR codes. Finally, results of the Rayleigh-Taylor instability test
demonstrate that in the regime of very subsonic flows the code has still
several difficulties in the treatment of hydrodynamic instabilities. These
problems being intrinsically due to the way in which in standard SPH gradients
are calculated and not to the implementation of the artificial conductivity
term.Comment: 26 pages, 15 figures, accepted for publication in A&
Kelvin-Helmholtz instabilities with Godunov SPH
Numerical simulations for the non-linear development of Kelvin-Helmholtz
instability in two different density layers have been performed with the
particle-based method (Godunov SPH) developed by Inutsuka (2002). The Godunov
SPH can describe the Kelvin-Helmholtz instability even with a high density
contrast, while the standard SPH shows the absence of the instability across a
density gradient (Agertz et al. 2007). The interaction of a dense blob with a
hot ambient medium has been performed also. The Godunov SPH describes the
formation and evolution of the fingers due to the combinations of
Rayleigh-Taylor, Richtmyer-Meshkov, and Kelvin-Helmholtz instabilities. The
blob test result coincides well with the results of the grid-based codes. An
inaccurate handling of a density gradient in the standard SPH has been pointed
out as the direct reason of the absence of the instabilities. An unphysical
force happens at the density gradient even in a pressure equilibrium, and
repulses particles from the initial density discontinuity. Therefore, the
initial perturbation damps, and a gap forms at the discontinuity. The
unphysical force has been studied in terms of the consistency of a numerical
scheme. Contrary to the standard SPH, the momentum equation of the Godunov SPH
doesnt use the particle approximation, and has been derived from the kernel
convolution or a new Lagrangian function. The new Lagrangian function used in
the Godunov SPH is more analogous to the real Lagrangian function for
continuum. The momentum equation of the Godunov SPH has much better linear
consistency, so the unphysical force is greatly reduced compared to the
standard SPH in a high density contrast.Comment: 11 pages, 7 figures, Accepted for publication in MNRA
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