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Asymptotic analysis of evaporating droplets
This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.We consider the evaporation dynamics of a two-dimensional, partially-wetting sessile droplet of a
volatile liquid in its pure vapour, which is supported on a smooth horizontal superheated substrate. Assuming
that the liquid properties remain unchanged, we utilise a one-sided lubrication-type model for the evolution of
the droplet thickness, which accounts for the effects of evaporation, capillarity, slip and the kinetic resistance
to evaporation. We follow an asymptotic approach, which yields a set of coupled evolution equations for
the droplet radius and area, estimating analytically the evaporation-modified apparent angle when evaporation
effects are weak. The validity of our matching procedure is verified by numerical experiments, obtaining also
an estimate for the evaporation time
Asymptotic theory for a Leidenfrost drop on a liquid pool
Droplets can be levitated by their own vapour when placed onto a superheated
plate (the Leidenfrost effect). It is less known that the Leidenfrost effect
can likewise be observed over a liquid pool (superheated with respect to the
drop), which is the study case here. Emphasis is placed on an asymptotic
analysis in the limit of small evaporation numbers, which proves to be a
realistic one indeed for not so small drops. The global shapes are found to
resemble "superhydrophobic drops" that follow from the equilibrium between
capillarity and gravity. However, the morphology of the thin vapour layer
between the drop and the pool is very different from that of classical
Leidenfrost drops over a flat rigid substrate, and exhibits different scaling
laws. We determine analytical expressions for the vapour thickness as a
function of temperature and material properties, which are confirmed by
numerical solutions. Surprisingly, we show that deformability of the pool
suppresses the chimney instability of Leidenfrost drops
Pattern formation without heating in an evaporative convection experiment
We present an evaporation experiment in a single fluid layer. When latent
heat associated to the evaporation is large enough, the heat flow through the
free surface of the layer generates temperature gradients that can destabilize
the conductive motionless state giving rise to convective cellular structures
without any external heating. The sequence of convective patterns obtained here
without heating, is similar to that obtained in B\'enard-Marangoni convection.
This work present the sequence of spatial bifurcations as a function of the
layer depth. The transition between square to hexagonal pattern, known from
non-evaporative experiments, is obtained here with a similar change in
wavelength.Comment: Submitted to Europhysics Letter
Penta-hepta defect chaos in a model for rotating hexagonal convection
In a model for rotating non-Boussinesq convection with mean flow we identify
a regime of spatio-temporal chaos that is based on a hexagonal planform and is
sustained by the {\it induced nucleation} of dislocations by penta-hepta
defects. The probability distribution function for the number of defects
deviates substantially from the usually observed Poisson-type distribution. It
implies strong correlations between the defects inthe form of density-dependent
creation and annihilation rates of defects. We extract these rates from the
distribution function and also directly from the defect dynamics.Comment: 4 pages, 5 figures, submitted to PR
Large amplitude dynamics of micro/nanomechanical resonators actuated with electrostatic pulses
International audienceIn the field of resonant NEMS design, it is a common misconception that large-amplitude motion, and thus large signal-to-noise ratio, can only be achieved at the risk of oscillator instability. In the present paper, we show that very simple closed-loop control schemes can be used to achieve stable largeamplitude motion of a resonant structure, even when jump resonance (caused by electrostatic softening or Duffing hardening) is present in its frequency response. We focus on the case of a resonant accelerometer sensing cell, consisting in a nonlinear clamped-clamped beam with electrostatic actuation and detection, maintained in an oscillation state with pulses of electrostatic force that are delivered whenever the detected signal (the position of the beam) crosses zero. We show that the proposed feedback scheme ensures the stability of the motion of the beam much beyond the critical Duffing amplitude and that, if the parameters of the beam are correctly chosen, one can achieve almost full-gap travel range without incurring electrostatic pull-in. These results are illustrated and validated with transient simulations of the nonlinear closed-loop system
A clock network of distributed ADPLLs using an asymmetric comparison strategy
International audienceIn this paper, we describe an architecture of a distributed ADPLL (All Digital Phase Lock Loop) network based on bang-bang phase detectors that are interconnected asymmetrically. It allows an automatic selection between two operating modes (uni- and bidirectional) to avoid mode-locking phenomenon, to accelerate the network convergence and to improve the robustness to possible network failures in comparison to simple unidirectional mode
Tensor Product and Permutation Branes on the Torus
We consider B-type D-branes in the Gepner model consisting of two minimal
models at k=2. This Gepner model is mirror to a torus theory. We establish the
dictionary identifying the B-type D-branes of the Gepner model with A-type
Neumann and Dirichlet branes on the torus.Comment: 26 page
Charge Distributions in Metallic Alloys: a Charge Excess Functional theory approach
Charge Distributions in Metallic Alloys: a Charge Excess Functional theory
approachComment: 13 pages, 5 figure
First-principles study of ternary fcc solution phases from special quasirandom structures
In the present work, ternary Special Quasirandom Structures (SQSs) for a fcc
solid solution phase are generated at different compositions,
and , ,
whose correlation functions are satisfactorily close to those of a random fcc
solution. The generated SQSs are used to calculate the mixing enthalpy of the
fcc phase in the Ca-Sr-Yb system. It is observed that first-principles
calculations of all the binary and ternary SQSs in the Ca-Sr-Yb system exhibit
very small local relaxation. It is concluded that the fcc ternary SQSs can
provide valuable information about the mixing behavior of the fcc ternary solid
solution phase. The SQSs presented in this work can be widely used to study the
behavior of ternary fcc solid solutions.Comment: 20 pages, 7 figure
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