8,743 research outputs found
Interfacial Structural Changes and Singularities in Non-Planar Geometries
We consider phase coexistence and criticality in a thin-film Ising magnet
with opposing surface fields and non-planar (corrugated) walls. We show that
the loss of translational invariance has a strong and unexpected non-linear
influence on the interface structure and phase diagram. We identify 4
non-thermodynamic singularities where there is a qualitative change in the
interface shape. In addition, we establish that at the finite-size critical
point, the singularity in the interface shape is characterized by two distint
critical exponents in contrast to the planar case (which is characterised by
one). Similar effects should be observed for prewetting at a corrugated
substrate. Analogy is made with the behaviour of a non-linear forced oscillator
showing chaotic dynamics.Comment: 13 pages, 3 figure
Correlation function algebra for inhomogeneous fluids
We consider variational (density functional) models of fluids confined in
parallel-plate geometries (with walls situated in the planes z=0 and z=L
respectively) and focus on the structure of the pair correlation function
G(r_1,r_2). We show that for local variational models there exist two
non-trivial identities relating both the transverse Fourier transform G(z_\mu,
z_\nu;q) and the zeroth moment G_0(z_\mu,z_\nu) at different positions z_1, z_2
and z_3. These relations form an algebra which severely restricts the possible
form of the function G_0(z_\mu,z_\nu). For the common situations in which the
equilibrium one-body (magnetization/number density) profile m_0(z) exhibits an
odd or even reflection symmetry in the z=L/2 plane the algebra simplifies
considerably and is used to relate the correlation function to the finite-size
excess free-energy \gamma(L). We rederive non-trivial scaling expressions for
the finite-size contribution to the free-energy at bulk criticality and for
systems where large scale interfacial fluctuations are present. Extensions to
non-planar geometries are also considered.Comment: 15 pages, RevTex, 4 eps figures. To appear in J.Phys.Condens.Matte
Coupled Fluctuations near Critical Wetting
Recent work on the complete wetting transition has emphasized the role played
by the coupling of fluctuations of the order parameter at the wall and at the
depinning fluid interface. Extending this approach to the wetting transition
itself we predict a novel crossover effect associated with the decoupling of
fluctuations as the temperature is lowered towards the transition temperature
T_W. Using this we are able to reanalyse recent Monte-Carlo simulation studies
and extract a value \omega(T_W)=0.8 at T_W=0.9T_C in very good agreement with
long standing theoretical predictions.Comment: 4 pages, LaTex, 1 postscript figur
New electrocatalysts for hydrogen-oxygen fuel cells
Platinum-silver, palladium-gold, and platinum-gold alloys serve as oxygen reduction catalysts in high-current-density cells. Catalysts were tested on polytetrafluoroethylene-bonded cathodes and a hydrogen anode at an operating cell temperature of 80 degrees C
SPIRAL Phase A: A Prototype Integral Field Spectrograph for the AAT
We present details of a prototype fiber feed for use on the Anglo-Australian
Telescope (AAT) that uses a dedicated fiber-fed medium/high resolution (R >
10000) visible-band spectrograph to give integral field spectroscopy (IFS) of
an extended object. A focal reducer couples light from the telescope to the
close-packed lenslet array and fiber feed, allowing the spectrograph be used on
other telescopes with the change of a single lens. By considering the
properties of the fibers in the design of the spectrograph, an efficient design
can be realised, and we present the first scientific results of a prototype
spectrograph using a fiber feed with 37 spatial elements, namely the detection
of Lithium confirming a brown dwarf candidate and IFS of the supernova remnant
SN1987A.Comment: 41 pages, 15 figures, 3 tables; accepted by PAS
3D wedge filling and 2D random-bond wetting
Fluids adsorbed in 3D wedges are shown to exhibit two types of continuous
interfacial unbinding corresponding to critical and tricritical filling
respectively. Analytic solution of an effective interfacial model based on the
transfer-matrix formalism allows us to obtain the asymptotic probability
distribution functions for the interfacial height when criticality and
tricriticality are approached. Generalised random walk arguments show that, for
systems with short-ranged forces, the critical singularities at these
transitions are related to 2D complete and critical wetting with random bond
disorder respectively.Comment: 7 pages, 3 figures, accepted for publication in Europhysics Letter
Development of uniform and predictable battery materials for nickel cadmium aerospace cells Quarterly report, 8 Aug. - 7 Nov. 1968
Sintering of carbonyl nickel powders for nickel cadmium batteries fabricatio
Derivation of a Non-Local Interfacial Hamiltonian for Short-Ranged Wetting II: General Diagrammatic Structure
In our first paper, we showed how a non-local effective Hamiltionian for
short-ranged wetting may be derived from an underlying Landau-Ginzburg-Wilson
model. Here, we combine the Green's function method with standard perturbation
theory to determine the general diagrammatic form of the binding potential
functional beyond the double-parabola approximation for the
Landau-Ginzburg-Wilson bulk potential. The main influence of cubic and quartic
interactions is simply to alter the coefficients of the double parabola-like
zig-zag diagrams and also to introduce curvature and tube-interaction
corrections (also represented diagrammatically), which are of minor importance.
Non-locality generates effective long-ranged many-body interfacial interactions
due to the reflection of tube-like fluctuations from the wall. Alternative wall
boundary conditions (with a surface field and enhancement) and the diagrammatic
description of tricritical wetting are also discussed.Comment: (14 pages, 2 figures) Submitted J. Phys. Condens. Matte
Non-locality and short-range wetting phenomena
We propose a non-local interfacial model for 3D short-range wetting at planar
and non-planar walls. The model is characterized by a binding potential
\emph{functional} depending only on the bulk Ornstein-Zernike correlation
function, which arises from different classes of tube-like fluctuations that
connect the interface and the substrate. The theory provides a physical
explanation for the origin of the effective position-dependent stiffness and
binding potential in approximate local theories, and also obeys the necessary
classical wedge covariance relationship between wetting and wedge filling.
Renormalization group and computer simulation studies reveal the strong
non-perturbative influence of non-locality at critical wetting, throwing light
on long-standing theoretical problems regarding the order of the phase
transition.Comment: 4 pages, 2 figures, accepted for publication in Phys. Rev. Let
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