2,054 research outputs found
Spectral analysis of the biharmonic operator subject to Neumann boundary conditions on dumbbell domains
We consider the biharmonic operator subject to homogeneous boundary
conditions of Neumann type on a planar dumbbell domain which consists of two
disjoint domains connected by a thin channel. We analyse the spectral behaviour
of the operator, characterizing the limit of the eigenvalues and of the
eigenprojections as the thickness of the channel goes to zero. In applications
to linear elasticity, the fourth order operator under consideration is related
to the deformation of a free elastic plate, a part of which shrinks to a
segment. In contrast to what happens with the classical second order case, it
turns out that the limiting equation is here distorted by a strange factor
depending on a parameter which plays the role of the Poisson coefficient of the
represented plate.Comment: To appear in "Integral Equations and Operator Theory
Domain Dependence of Elliptic Operators in Divergence Form
Domain Dependence of Elliptic Operators in Divergence For
On the flow separation mechanism in the inverse Leidenfrost regime
The inverse Leidenfrost regime occurs when a heated object in relative motion
with a liquid is surrounded by a stable vapour layer, drastically reducing the
hydrodynamic drag at large Reynolds numbers due to a delayed separation of the
flow. To elucidate the physical mechanisms that control separation, here we
report a numerical study of the boundary-layer equations describing the
liquid-vapour flow around a solid sphere whose surface temperature is above the
Leidenfrost point. Our analysis reveals that the dynamics of the thin layer of
vaporised liquid controls the downstream evolution of the flow, which cannot be
properly described substituting the vapour layer by an effective slip length.
In particular, the dominant mechanism responsible for the separation of the
flow is the onset of vapour recirculation caused by the adverse pressure
gradient in the rearward half of the sphere, leading to an explosive growth of
the vapour-layer thickness due to the accumulation of vapour mass. Buoyancy
forces are shown to have an important effect on the onset of recirculation, and
thus on the separation angle. Our results compare favourably with previous
experiments.Comment: 17 pages, 5 figures, revised version submitted to J Fluid Mec
Comparison of hydrochar fractionation and composition in batch and continuous hydrothermal liquefaction
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Atmospheric-Pressure Non-thermal Plasma-JET effects on PS and PE surfaces
https://www.scopus.com/inward/record.url?eid=2-s2.0-84938125206&partnerID=40&md5=c2325a28f944e7e3e20b601b8d9a73efThe Atmospheric-Pressure Non-Thermal Plasma (APNTP) has become a topic of a great interest for a wide spectrum of applications in different industry branches, including the surface of treatment processes. In this work we evaluate the effect of an argon APNTP exposure to determine changes suffered by a polystyrene (PS) and polyethylene (PE) polymer surface through RAMAN spectroscopy and SEM. It was determined that the hydrophilic change in energetic terms, i.e. surface activation in the PS and PE polymers is addition of oxygen by surface activation when the samples with jet plasma are exposed with the inert argon gas. It was possible to characterize the hydrophilic shift based on the change in intensity of the spectra. © Published under licence by IOP Publishing Ltd.Ad Astra Rocket Company,Instituto Tecnologico de Costa Rica,International Atomic Energy Agency (IAEA),Universidad Nacional de Costa Ric
Coarsening Kinetics of Complex Macromolecular Architectures in Bad Solvent
This study reports a general scenario for the out-of-equilibrium features of collapsing polymeric architectures. We use molecular dynamics simulations to characterize the coarsening kinetics, in bad solvent, for several macromolecular systems with an increasing degree of structural complexity. In particular, we focus on: flexible and semiflexible polymer chains, star polymers with 3 and 12 arms, and microgels with both ordered and disordered networks. Starting from a powerful analogy with critical phenomena, we construct a density field representation that removes fast fluctuations and provides a consistent characterization of the domain growth. Our results indicate that the coarsening kinetics presents a scaling behaviour that is independent of the solvent quality parameter, in analogy to the time–temperature superposition principle. Interestingly, the domain growth in time follows a power-law behaviour that is approximately independent of the architecture for all the flexible systems; while it is steeper for the semiflexible chains. Nevertheless, the fractal nature of the dense regions emerging during the collapse exhibits the same scaling behaviour for all the macromolecules. This suggests that the faster growing length scale in the semiflexible chains originates just from a faster mass diffusion along the chain contour, induced by the local stiffness. The decay of the dynamic correlations displays scaling behavior with the growing length scale of the system, which is a characteristic signature in coarsening phenomena.This research was funded by projects PGC2018-094548-B-I00 (MCIU/AEI/FEDER, UE) and IT-1175-19 (GV, Spain
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