1,903 research outputs found
The pear-shaped fate of an ice melting front
A fluid-structure interaction problem with the melting of water around a
heated horizontal circular cylinder is analysed with numerical simulations.
Dynamic meshing was used for evolving the flow domain in time as the melting
front extended radially outward from the cylinder; a node shuffle algorithm was
used to retain mesh quality across the significant mesh deformation. We
simulated one case above the density inversion point of water and one case
below, yielding pear-shaped melting fronts due to thermal plumes either rising
or falling from the cylinder, respectively. Results were compared with previous
experimental studies and the melting front profiles matched reasonably well and
melting rates were in agreement. We confirm that natural convection plays a
significant role in the transport of energy as the melt zone increases, and
needs to be considered for accurately modelling phase change under these
conditions.Comment: Accepted for the 12th International Conference on CFD in Oil & Gas,
Metallurgical and Process Industries. SINTEF, Trondheim, Norway. May 30th -
June 1st, 201
A frequency-independent boundary element method for scattering by two-dimensional screens and apertures
We propose and analyse a hybrid numerical-asymptotic boundary element method for time-harmonic scattering of an incident plane wave by an arbitrary collinear array of sound-soft two-dimensional screens. Our method uses an approximation space enriched with oscillatory basis functions, chosen to capture the high frequency asymptotics of the solution. Our numerical results suggest that fi�xed accuracy can be achieved at arbitrarily high frequencies with a frequency-independent computational cost. Our analysis does not capture this observed behaviour completely, but we provide a rigorous frequency-explicit error analysis which proves that the method converges exponentially as the number of degrees of freedom increases, and that to achieve any desired accuracy it is sufficient to increase in proportion to the square of the logarithm of the frequency as the frequency increases (standard boundary element methods require to increase at least linearly with frequency to retain accuracy). We also show how our method can be applied to the complementary "breakwater" problem of propagation through an aperture in an infinite sound-hard screen
A Separate Higgs?
We investigate the possibility of a multi-Higgs doublet model where the
lightest neutral Higgs boson () decouples from the fermion sector. We are
partially motivated by the four events with
\,GeV recently observed by the L3 collaboration,
which could be a signal for .
Collider signatures for the additional physical Higgs bosons present in such
models are discussed.Comment: 8 pages (plus 2 figures, available by request), latex,
ANL-HEP-PR-92-10
Physical degrees of freedom in stabilized brane world models
We consider brane world models with interbrane separation stabilized by the
Goldberger-Wise scalar field. For arbitrary background, or vacuum
configurations of the gravitational and scalar fields in such models, we
construct the second variation Lagrangian, study its gauge invariance, find the
corresponding equations of motion and decouple them in a suitable gauge. We
also derive an effective four-dimensional Lagrangian for such models, which
describes the massless graviton, a tower of massive gravitons and a tower of
massive scalars. It is shown that for a special choice of the background
solution the masses of the graviton excitations may be of the order of a few
TeV, the radion mass of the order of 100 GeV, the inverse size of the extra
dimension being tens of GeV. In this case the coupling of the radion to matter
on the negative tension brane is approximately the same as in the unstabilized
model with the same values of the fundamental five-dimensional energy scale and
the interbrane distance.Comment: 17 pages, LaTeX, corrected typos, amended the normalization constants
of the scalar modes and their coupling constants to matte
Modelling ripple morphodynamics driven by colloidal deposition
Fluid dynamics between a particle-laden flow and an evolving boundary are
found in various contexts. We numerically simulated the morphodynamics of
silica particle deposition from flowing water within geothermal heat exchangers
using the arbitrary Lagrangian-Eulerian method. The silica particles were of
colloidal size, with submicron diameters, which were primarily transported
through the water via Brownian motion. First, we validated the Euler-Euler
approach for modelling the transport and deposition of these colloidal
particles within a fluid by comparing our simulation results with existing
experiments of colloidal polystyrene deposition. Then we combined this
multiphase model with a dynamic mesh model to track the gradually accumulated
silica along the pipe walls of a heat exchanger. Surface roughness was modelled
by prescribing sinusoidally-shaped protrusions on the wall boundary. The silica
bed height grew quickest at the peaks of the ripples and the spacing between
the protrusions remained relatively constant. The rough surface experienced a
20 % reduction in silica deposition when compared to a smooth surface. We also
discuss the challenges of mesh deforming simulations with an emphasis on the
mesh quality as the geometry changes over time
Discovering hidden sectors with mono-photon Z' searches
In many theories of physics beyond the Standard Model, from extra dimensions
to Hidden Valleys and models of dark matter, Z' bosons mediate between Standard
Model particles and hidden sector states. We study the feasibility of observing
such hidden states through an invisibly decaying Z' at the LHC. We focus on the
process pp -> \gamma Z' -> \gamma X X*, where X is any neutral, (quasi-) stable
particle, whether a Standard Model (SM) neutrino or a new state. This
complements a previous study using pp -> Z Z' -> l+ l- X X*. Only the Z' mass
and two effective charges are needed to describe this process. If the Z' decays
invisibly only to Standard Model neutrinos, then these charges are predicted by
observation of the Z' through the Drell-Yan process, allowing discrimination
between Z' decays to SM neutrinos and invisible decays to new states. We
carefully discuss all backgrounds and systematic errors that affect this
search. We find that hidden sector decays of a 1 TeV Z' can be observed at 5
sigma significance with 50 fb^{-1} at the LHC. Observation of a 1.5 TeV state
requires super-LHC statistics of 1 ab^{-1}. Control of the systematic errors,
in particular the parton distribution function uncertainty of the dominant Z
\gamma background, is crucial to maximize the LHC searchComment: 13 pages, 4 figure
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