190 research outputs found
Binding potentials for vapour nanobubbles on surfaces using density functional theory
We calculate density profiles of a simple model fluid in contact with a
planar surface using density functional theory (DFT), in particular for the
case where there is a vapour layer intruding between the wall and the bulk
liquid. We apply the method of Hughes et al. [J. Chem. Phys. 142, 074702
(2015)] to calculate the density profiles for varying (specified) amounts of
the vapour adsorbed at the wall. This is equivalent to varying the thickness
of the vapour at the surface. From the resulting sequence of density
profiles we calculate the thermodynamic grand potential as is varied and
thereby determine the binding potential as a function of . The binding
potential obtained via this coarse-graining approach allows us to determine the
disjoining pressure in the film and also to predict the shape of vapour
nano-bubbles on the surface. Our microscopic DFT based approach captures
information from length scales much smaller than some commonly used models in
continuum mechanics.Comment: 15 pages, 15 figure
On the moving contact line singularity: Asymptotics of a diffuse-interface model
The behaviour of a solid-liquid-gas system near the three-phase contact line
is considered using a diffuse-interface model with no-slip at the solid and
where the fluid phase is specified by a continuous density field. Relaxation of
the classical approach of a sharp liquid-gas interface and careful examination
of the asymptotic behaviour as the contact line is approached is shown to
resolve the stress and pressure singularities associated with the moving
contact line problem. Various features of the model are scrutinised, alongside
extensions to incorporate slip, finite-time relaxation of the chemical
potential, or a precursor film at the wall.Comment: 14 pages, 3 figure
The contact line behaviour of solid-liquid-gas diffuse-interface models
A solid-liquid-gas moving contact line is considered through a
diffuse-interface model with the classical boundary condition of no-slip at the
solid surface. Examination of the asymptotic behaviour as the contact line is
approached shows that the relaxation of the classical model of a sharp
liquid-gas interface, whilst retaining the no-slip condition, resolves the
stress and pressure singularities associated with the moving contact line
problem while the fluid velocity is well defined (not multi-valued). The moving
contact line behaviour is analysed for a general problem relevant for any
density dependent dynamic viscosity and volume viscosity, and for general
microscopic contact angle and double well free-energy forms. Away from the
contact line, analysis of the diffuse-interface model shows that the
Navier--Stokes equations and classical interfacial boundary conditions are
obtained at leading order in the sharp-interface limit, justifying the creeping
flow problem imposed in an intermediate region in the seminal work of Seppecher
[Int. J. Eng. Sci. 34, 977--992 (1996)]. Corrections to Seppecher's work are
given, as an incorrect solution form was originally used.Comment: 33 pages, 3 figure
A comparison of slip, disjoining pressure, and interface formation models for contact line motion through asymptotic analysis of thin two-dimensional droplet spreading
The motion of a contact line is examined, and comparisons drawn, for a
variety of models proposed in the literature. Pressure and stress behaviours at
the contact line are examined in the prototype system of quasistatic spreading
of a thin two-dimensional droplet on a planar substrate. The models analysed
include three disjoining pressure models based on van der Waals interactions, a
model introduced for polar fluids, and a liquid-gas diffuse-interface model;
Navier-slip and two non-linear slip models are investigated, with three
microscopic contact angle boundary conditions imposed (two of these contact
angle conditions having a contact line velocity dependence); and the interface
formation model is also considered. In certain parameter regimes it is shown
that all of the models predict the same quasistatic droplet spreading
behaviour.Comment: 29 pages, 3 figures, J. Eng. Math. 201
Slip or not slip? A methodical examination of the interface formation model using two-dimensional droplet spreading on a horizontal planar substrate as a prototype system
We consider the spreading of a thin two-dimensional droplet on a planar
substrate as a prototype system to compare the contemporary model for contact
line motion based on interface formation of Shikhmurzaev [Int. J. Multiphas.
Flow 19, 589 (1993)], to the more commonly used continuum fluid dynamical
equations augmented with the Navier-slip condition. Considering quasistatic
droplet evolution and using the method of matched asymptotics, we find that the
evolution of the droplet radius using the interface formation model reduces to
an equivalent expression for a slip model, where the prescribed microscopic
dynamic contact angle has a velocity dependent correction to its static value.
This result is found for both the original interface formation model
formulation and for a more recent version, where mass transfer from bulk to
surface layers is accounted for through the boundary conditions. Various
features of the model, such as the pressure behaviour and rolling motion at the
contact line, and their relevance, are also considered in the prototype system
we adopt.Comment: 45 pages, 18 figure
Fluid structure in the immediate vicinity of an equilibrium three-phase contact line and assessment of disjoining pressure models using density functional theory
We examine the nanoscale behavior of an equilibrium three-phase contact line
in the presence of long-ranged intermolecular forces by employing a statistical
mechanics of fluids approach, namely density functional theory (DFT) together
with fundamental measure theory (FMT). This enables us to evaluate the
predictive quality of effective Hamiltonian models in the vicinity of the
contact line. In particular, we compare the results for mean field effective
Hamiltonians with disjoining pressures defined through (I) the adsorption
isotherm for a planar liquid film, and (II) the normal force balance at the
contact line. We find that the height profile obtained using (I) shows good
agreement with the adsorption film thickness of the DFT-FMT equilibrium density
profile in terms of maximal curvature and the behavior at large film heights.
In contrast, we observe that while the height profile obtained by using (II)
satisfies basic sum rules, it shows little agreement with the adsorption film
thickness of the DFT results. The results are verified for contact angles of
20, 40 and 60 degrees
The vicinity of an equilibrium three-phase contact line using density functional theory: Density profiles normal to the fluid interface
The paper by Nold et al. [Phys. Fluids 26 (7), 072001 (2014)] examined density profiles and the micro-scale structure of an equilibrium three-phase (liquid–vapour–solid) contact line in the immediate vicinity of the wall using elements from the statistical mechanics of classical fluids, namely density-functional theory. The present research note, building on the above work, further contributes to our understanding of the nanoscale structure of a contact line by quantifying the strong dependence of the liquid–vapour density profile on the normal distance to the interface, when compared to the dependence on the vertical distance to the substrate. A recent study by Benet et al. [J. Phys. Chem. C 118 (38), 22079 (2014)] has shown that this could explain the emergence of a film-height-dependent surface tension close to the wall, with implications for the Frumkin–Derjaguin theory
Entamoeba histolytica Phagocytosis of Human Erythrocytes Involves PATMK, a Member of the Transmembrane Kinase Family
Entamoeba histolytica is the cause of amebic colitis and liver abscess. This parasite induces apoptosis in host cells and utilizes exposed ligands such as phosphatidylserine to ingest the apoptotic corpses and invade deeper into host tissue. The purpose of this work was to identify amebic proteins involved in the recognition and ingestion of dead cells. A member of the transmembrane kinase family, phagosome-associated TMK96 (PATMK), was identified in a proteomic screen for early phagosomal proteins. Anti-peptide affinity-purified antibody produced against PATMK demonstrated that it was a type I integral membrane protein that was expressed on the trophozoite surface, and that co-localized with human erythrocytes at the site of contact. The role of PATMK in erythrophagocytosis in vitro was demonstrated by: (i) incubation of ameba with anti-PATMK antibodies; (ii) PATMK mRNA knock-down using a novel shRNA expression system; and (iii) expression of a carboxy-truncation of PATMK (PATMKΔ932). Expression of the carboxy-truncation of PATMKΔ932 also caused a specific reduction in the ability of E. histolytica to establish infection in the intestinal model of amebiasis, however these amebae retained the ability to cause hepatic abscesses when directly injected in the liver. In conclusion, PATMK was identified as a member of the TMK family that participates in erythrophagocytosis and is uniquely required for intestinal infection
Low power radiometric partial discharge sensor using composite transistor-reset integrator
The measurement of partial discharge provides a means of monitoring insulation health in high-voltage equipment. Traditional partial discharge measurements require separate installation for each item of plant to physically connect sensors with specific items. Wireless measurement methods provide an attractive and scalable alternative. Existing wireless monitoring technologies which use time-difference-of-arrival of a partial discharge signal at multiple, spatially separated, sensors place high demands on power consumption and cost due to a requirement for rapid sampling. A recently proposed partial discharge monitoring system using a wireless sensor network and measuring received signal strength only, has potential cost and scalability advantages. An incoherent wireless sensor incorporating a transistor-reset integrator has been developed that reduces the measurement bandwidth of the PD events and alleviates the need for high-speed sampling. It is based on composite amplifier techniques to reduce the power requirements by a factor of approximately four without compromising precision. The accuracy of the proposed sensor is compared to that obtained using a high-speed digital sampling oscilloscope. Received energies were measured over a 10 m distance in 1 m increments and produced an error within 1 dB beyond 4 m and 3.2 dB at shorter distances, resulting in a measurement accuracy within 1 m
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