502 research outputs found
Thermomechanical surface instability at the origin of surface fissure patterns on heated circular MDF samples
When a flat sample of medium density fibreboard (MDF) is exposed to radiant
heat in an inert atmosphere, primary crack patterns suddenly start to appear
over the entire surface before pyrolysis and any charring occurs. Contrary to
common belief that crack formation is due to drying and shrinkage, it was
demonstrated for square samples that this results from thermomechanical
instability.
In the present paper, new experimental data are presented for circular
samples of the same MDF material. The sample was exposed to radiant heating at
20 or 50 kW/m2, and completely different crack patterns with independent
Eigenmodes were observed at the two heat fluxes. We show that the two patterns
can be reproduced with a full 3-D thermomechanical surface instability model of
a hot layer adhered to an elastic colder foundation in an axisymmetric domain.
Analytical and numerical solutions of a simplified 2-D formulation of the same
problem provide excellent qualitative agreement between observed and calculated
patterns.
Previous data for square samples together with the results reported in the
present paper for circular samples confirm the validity of the model for
qualitative predictions, and indicate that further refinements can be made to
improve its quantitative predictive capability.Comment: 9 pages, 13 figures. New title and abstract, added experimental and
simulation details and figures, conclusions unchanged. Matches the version
published in Fire And Material
Anti-inflammatory interventions and biomarker identification in Peritoneal Dialysis
Beelen, R.H.J. [Promotor]Wee, P.M. ter [Promotor]Vervloet, M.G. [Copromotor]Ittersum, F.J. van [Copromotor
Cosmological evolution of scalar fields and gravitino dark matter in gauge mediation at low reheating temperatures
We consider the dynamics of the supersymmetry-breaking scalar field and the
production of dark matter gravitinos via its decay in a gauge-mediated
supersymmetry breaking model with metastable vacuum. We find that the scalar
field amplitude and gravitino density are extremely sensitive to the parameters
of the hidden sector. For the case of an O'Raifeartaigh sector, we show that
the observed dark matter density can be explained by gravitinos even for low
reheating temperatures T_{R} < 10 GeV. Such low reheating temperatures may be
implied by detection of the NLSP at the LHC if its thermal freeze-out density
is in conflict with BBN.Comment: 11 pages RevTex. Extended discussion and minor corrections,
conclusions unaltered. Version to be published in JCA
Non-perturbative production of matter and rapid thermalization after MSSM inflation
A {\it gauge invariant} combination of LLe {\it sleptons} within the Minimal
Supersymmetric Standard Model is one of the few inflaton candidates that can
naturally explain population of the observable sector and creation of matter
after inflation. After the end of inflation, the inflaton oscillates coherently
about the minimum of its potential, which is a point of {\it enhanced gauged
symmetry}. This results in bursts of non-perturbative production of the
gauge/gaugino and (s)lepton quanta. The subsequent decay of these quanta is
very fast and leads to an extremely efficient transfer of the inflaton energy
to (s)quarks via {\it instant} preheating. Around 20% of the inflaton energy
density is drained during every inflaton oscillation. However, all of the
Standard Model degrees of freedom (and their supersymmetric partners) {\it do
not} thermalize immediately, since the large inflaton vacuum expectation value
breaks the electroweak symmetry. After about 100 oscillations -- albeit within
one Hubble time -- the amplitude of inflaton oscillations becomes sufficiently
small, and all of the degrees of freedom will thermalize. This provides by far
the most efficient reheating of the universe with the observed degrees of
freedom.Comment: 13 pages, 3 figures. Comments and references added to match the final
version accepted for publication in Phys. Rev.
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