1,692 research outputs found
Shingle 2.0: generalising self-consistent and automated domain discretisation for multi-scale geophysical models
The approaches taken to describe and develop spatial discretisations of the
domains required for geophysical simulation models are commonly ad hoc, model
or application specific and under-documented. This is particularly acute for
simulation models that are flexible in their use of multi-scale, anisotropic,
fully unstructured meshes where a relatively large number of heterogeneous
parameters are required to constrain their full description. As a consequence,
it can be difficult to reproduce simulations, ensure a provenance in model data
handling and initialisation, and a challenge to conduct model intercomparisons
rigorously. This paper takes a novel approach to spatial discretisation,
considering it much like a numerical simulation model problem of its own. It
introduces a generalised, extensible, self-documenting approach to carefully
describe, and necessarily fully, the constraints over the heterogeneous
parameter space that determine how a domain is spatially discretised. This
additionally provides a method to accurately record these constraints, using
high-level natural language based abstractions, that enables full accounts of
provenance, sharing and distribution. Together with this description, a
generalised consistent approach to unstructured mesh generation for geophysical
models is developed, that is automated, robust and repeatable, quick-to-draft,
rigorously verified and consistent to the source data throughout. This
interprets the description above to execute a self-consistent spatial
discretisation process, which is automatically validated to expected discrete
characteristics and metrics.Comment: 18 pages, 10 figures, 1 table. Submitted for publication and under
revie
Hyperparathyroidism with presumed sellar-parasellar brown tumour based on imaging findings
Brown tumours are an end-stage complication of hyperparathyroidism. They are relatively rare today, due to earlier diagnosis and prompt treatment of hyperparathyroidism.1 Common locations are the mandible, pelvis, ribs and long bones of the axial skeleton.2 The skull base is an extremely rare site and, for obvious reasons, it is difficult to confirm the diagnosis in the absence of other lesions. In the face of a solitary lesion, a histological diagnosis of a ‘giant-cell tumour’ of benign nature should only be made once hyperparathyroidism has been actively excluded. Brown tumours, solid aneurysmal bone cysts, giant-cell reparative granuloma and giant cell tumour can all appear identical both macroand microscopically
Subgrid scale modelling of transport processes.
Consideration of stabilisation techniques is essential in the development of physical models if
they are to faithfully represent processes over a wide range of scales. Careful application of
these techniques can significantly increase
flexibility of models, allowing the computational
meshes used to discretise the underlying partial differential equations to become highly nonuniform
and anisotropic, for example. This
exibility enables a model to capture a wider
range of phenomena and thus reduce the number of parameterisations required, bringing a
physically more realistic solution.
The next generation of
fluid
flow and radiation transport models employ unstructured
meshes and anisotropic adaptive methods to gain a greater degree of
flexibility. However
these can introduce erroneous artefacts into the solution when, for example, a process becomes
unresolvable due to an adaptive mesh change or advection into a coarser region of mesh in
the domain. The suppression of these effects, caused by spatial and temporal variations in
mesh size, is one of the key roles stabilisation can play.
This thesis introduces new explicit and implicit stabilisation methods that have been
developed for application in
fluid and radiation transport modelling. With a focus on
a consistent residual-free approach, two new frameworks for the development of implicit
methods are presented. The first generates a family of higher-order Petrov-Galerkin methods,
and the example developed is compared to standard schemes such as streamline upwind
Petrov-Galerkin and Galerkin least squares in accurate modelling of tracer transport. The
dissipation generated by this method forms the basis for a new explicit fourth-order subfilter
scale eddy viscosity model for large eddy simulation. Dissipation focused more sharply on
unresolved scales is shown to give improved results over standard turbulence models. The
second, the inner element method, is derived from subgrid scale modelling concepts and,
like the variational multiscale method and bubble enrichment techniques, explicitly aims to
capture the important under-resolved fine scale information. It brings key advantages to
the solution of the Navier-Stokes equations including the use of usually unstable velocity-pressure
element pairs, a fully consistent mass matrix without the increase in degrees of
freedom associated with discontinuous Galerkin methods and also avoids pressure filtering.
All of which act to increase the
flexibility and accuracy of a model.
Supporting results are presented from an application of the methods to a wide range
of problems, from simple one-dimensional examples to tracer and momentum transport in
simulations such as the idealised Stommel gyre, the lid-driven cavity, lock-exchange, gravity
current and backward-facing step. Significant accuracy improvements are demonstrated
in challenging radiation transport benchmarks, such as advection across void regions, the scattering Maynard problem and demanding source-absorption cases. Evolution of a free
surface is also investigated in the sloshing tank, transport of an equatorial Rossby soliton,
wave propagation on an aquaplanet and tidal simulation of the Mediterranean Sea and global
ocean.
In combination with adaptive methods, stabilising techniques are key to the development
of next generation models. In particular these ideas are critical in achieving the aim of
extending models, such as the Imperial College Ocean Model, to the global scale
Does current UK research address priorities in palliative and end-of-life care?
The Palliative and end of life care Priority Setting Partnership uncovered 83 unanswered research questions. Florence Todd Fordham, Bridget Candy, Stevie McMillan and Sabine Best show that, as current UK research starts to address some of these questions, UK open grant data have the potential to encourage collaboratio
Mutual Fund Management and Fund Performance
This study examines management characteristics, including education and experience, as determinants of mutual fund performance. Managers with graduate degrees did not perform differently from managers without graduate degrees. However, graduates of top 20 MBA programs outperformed MBAs from business schools not on the top 50 Wall Street Journal list. Manager’s tenure was positively related to performance
An Enhanced Nonlinear Critical Gradient for Electron Turbulent Transport due to Reversed Magnetic Shear
The first nonlinear gyrokinetic simulations of electron internal transport
barriers (e-ITBs) in the National Spherical Torus Experiment show that reversed
magnetic shear can suppress thermal transport by increasing the nonlinear
critical gradient for electron-temperature-gradient-driven turbulence to three
times its linear critical value. An interesting feature of this turbulence is
nonlinearly driven off-midplane radial streamers. This work reinforces the
experimental observation that magnetic shear is likely an effective way of
triggering and sustaining e-ITBs in magnetic fusion devices.Comment: 4 pages, 5 figure
An Enhanced Nonlinear Critical Gradient for Electron Turbulent Transport due to Reversed Magnetic Shear
The first nonlinear gyrokinetic simulations of electron internal transport
barriers (e-ITBs) in the National Spherical Torus Experiment show that reversed
magnetic shear can suppress thermal transport by increasing the nonlinear
critical gradient for electron-temperature-gradient-driven turbulence to three
times its linear critical value. An interesting feature of this turbulence is
nonlinearly driven off-midplane radial streamers. This work reinforces the
experimental observation that magnetic shear is likely an effective way of
triggering and sustaining e-ITBs in magnetic fusion devices.Comment: 4 pages, 5 figure
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