396 research outputs found
Energy transport and fluctuations in small conductors
The Landauer-B\"uttiker formalism provides a simple and insightful way for
investigating many phenomena in mesoscopic physics. By this approach we derive
general formulas for the energy properties and apply them to the basic setups.
Of particular interest are the noise properties. We show that energy current
fluctuations can be induced by zero-point fluctuations and we discuss the
implications of this result.Comment: Revised and corrected versio
Simulation of capillary infiltration into packing structures by the Lattice-Boltzmann method for the optimization of ceramic materials
In this work we want to simulate with the Lattice-Boltzmann method in 2D the
capillary infiltration into porous structures obtained from the packing of
particles. The experimental problem motivating our work is the densification of
carbon preforms by reactive melt infiltration. The aim is to determine
optimization principles for the manufacturing of high-performance ceramics.
Simulations are performed for packings with varying structural properties. Our
analysis suggests that the observed slow infiltrations can be ascribed to
interface dynamics. Pinning represents the primary factor retarding fluid
penetration. The mechanism responsible for this phenomenon is analyzed in
detail. When surface growth is allowed, it is found that the phenomenon of
pinning becomes stronger. Systems trying to reproduce typical experimental
conditions are also investigated. It turns out that the standard for accurate
simulations is challenging. The primary obstacle to overcome for enhanced
accuracy seems to be the over-occurrence of pinning
Coarse-graining MARTINI model for molecular-dynamics simulations of the wetting properties of graphitic surfaces with non-ionic, long-chain and T-shaped surfactants
We report on a molecular dynamics investigation of the wetting properties of
graphitic surfaces by various solutions at concentrations 1-8 wt% of
commercially available non-ionic surfactants with long hydrophilic chains,
linear or T-shaped. These are surfactants of length up to 160 [\AA]. It turns
out that molecular dynamics simulations of such systems ask for a number of
solvent particles that can be reached without seriously compromising
computational efficiency only by employing a coarse-grained model. The MARTINI
force field with polarizable water offers a framework particularly suited for
the parameterization of our systems. In general, its advantages over other
coarse-grained models are the possibility to explore faster long time scales
and the wider range of applicability. Although the accuracy is sometimes put
under question, the results for the wetting properties by pure water are in
good agreement with those for the corresponding atomistic systems and
theoretical predictions. On the other hand, the bulk properties of various
aqueous surfactant solutions indicate that the micellar formation process is
too strong. For this reason, a typical experimental configuration is better
approached by preparing the droplets with the surfactants arranged in the
initial state in the vicinity of contact line. Cross-comparisons are possible
and illuminating, but equilibrium contanct angles as obtained from simulations
overestimate the experimental results. Nevertheless, our findings can provide
guidelines for the preliminary assessment and screening of surfactants. [See
pdf file for full abstract]Comment: Revised version. Publication: http://dx.doi.org/10.1063/1.4747827.
Material: https://sites.google.com/site/material4sim
Surface growth for molten silicon infiltration into carbon millimeter-sized channels: Lattice-Boltzmann simulations, experiments and models
The process of liquid silicon infiltration is investigated for channels with
radii from to [mm] drilled in compact carbon preforms. The
advantage of this setup is that the study of the phenomenon results to be
simplified. For comparison purposes, attempts are made in order to work out a
framework for evaluating the accuracy of simulations. The approach relies on
dimensionless numbers involving the properties of the surface reaction. It
turns out that complex hydrodynamic behavior derived from second Newton law can
be made consistent with Lattice-Boltzmann simulations. The experiments give
clear evidence that the growth of silicon carbide proceeds in two different
stages and basic mechanisms are highlighted. Lattice-Boltzmann simulations
prove to be an effective tool for the description of the growing phase. Namely,
essential experimental constraints can be implemented. As a result, the
existing models are useful to gain more insight on the process of reactive
infiltration into porous media in the first stage of penetration, i.e. up to
pore closure because of surface growth. A way allowing to implement the
resistance from chemical reaction in Darcy law is also proposed
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