2,663 research outputs found
Role of inertia in two-dimensional deformation and breakup of a droplet
We investigate by Lattice Boltzmann methods the effect of inertia on the
deformation and break-up of a two-dimensional fluid droplet surrounded by fluid
of equal viscosity (in a confined geometry) whose shear rate is increased very
slowly. We give evidence that in two dimensions inertia is {\em necessary} for
break-up, so that at zero Reynolds number the droplet deforms indefinitely
without breaking. We identify two different routes to breakup via two-lobed and
three-lobed structures respectively, and give evidence for a sharp transition
between these routes as parameters are varied.Comment: 4 pages, 4 figure
Sulphur isotope geochemistry of black shale-hosted antimony mineralization, Arnsberg, northern Rhenish Massif, Germany
Vein-type and bedding-concordant mesothermal (180ā410 Ā°C) stibniteāsulphosalt mineralization at Arnsberg, NE Rhenish Massif, Germany, is hosted by Carboniferous pyrite-rich black shales and siliceous limestones. A detailed sulphur isotope study of the stibniteāsulphosalt mineralization and pyrite from a variety of regional host-rock lithologies has been carried out using an in situ laser combustion technique. The 34S values of stibnite of various textural types are distinctly negative and lie in a narrow range between -23.9 and -17.1 (mean -20.1). In contrast, regional sedimentaryādiagenetic pyrites display a large variation of their 34S values between -45.4 and +9.3. There is little evidence for significant modification of the hydrothermal fluid during deposition and the S isotope signatures suggest that the sulphur of the stibnite mineralization was not locally derived. The 34S values of pyrite in Givetian shales display a significantly narrower range of -28.2 to -7.5 and their mean composition (-17.1) is close to the 34S values of the Arnsberg stibnite deposits. Considering the temperature-dependent isotopic fractionation between stibnite and reduced sulfur species, the 34S values of the mineralizing fluid (-16.8; 200 Ā°C) and the Givetian rock source are essentially identical. Therefore, we propose a model of leaching and isotopic homogenization of sulphur from the Middle Devonian shales and a subsequent northward migration of these fluids. The fluids were trapped in permeability-controlled positions within anticlinal zones, where fluid cooling induced deposition of stibnite and sulphosalts
Scale invariance in coarsening of binary and ternary fluids
Phase separation in binary and ternary fluids is studied using a two
dimensional Lattice Gas Automata. The lengths, given by the the first zero
crossing point of the correlation function and the total interface length is
shown to exhibit power law dependence on time. In binary mixtures, our data
clearly indicate the existence of a regime having more than one length scale
where the coarsening process proceeds through the rupture and reassociation of
domains. In ternary fluids; in the case of symmetric mixtures there exists a
regime with a single length scale having dynamic exponent 1/2, while in
asymmetric mixtures our data establish the break down of scale invariance.Comment: 20 pages, 13 figure
Comparison of Fuzzy Integral-Fuzzy Measure based Ensemble Algorithms with the State-of-the-art Ensemble Algorithms
The Fuzzy Integral (FI) is a non-linear aggregation operator which enables the fusion of information from multiple sources in respect to a Fuzzy Measure (FM) which captures the worth of both the individual sources and all their possible combinations. Based on the expected potential of non-linear aggregation offered by the FI, its application to decision-level fusion in ensemble classifiers, i.e. to fuse multiple classifiers outputs towards one superior decision level output, has recently been explored. A key example of such a FI-FM ensemble classification method is the Decision-level Fuzzy Integral Multiple Kernel Learning (DeFIMKL) algorithm, which aggregates the outputs of kernel based classifiers through the use of the Choquet FI with respect to a FM learned through a regularised quadratic programming approach. While the approach has been validated against a number of classifiers based on multiple kernel learning, it has thus far not been compared to the state-of-the-art in ensemble classification. Thus, this paper puts forward a detailed comparison of FI-FM based ensemble methods, specifically the DeFIMKL algorithm, with state-of-the art ensemble methods including Adaboost, Bagging, Random Forest and Majority Voting over 20 public datasets from the UCI machine learning repository. The results on the selected datasets suggest that the FI based ensemble classifier performs both well and efficiently, indicating that it is a viable alternative when selecting ensemble classifiers and indicating that the non-linear fusion of decision level outputs offered by the FI provides expected potential and warrants further study
The d'-Dibaryon in the Nonrelativistic Quark Model
The narrow peak recently found in various pionic double charge exchange (DCX)
cross sections can be explained by the assumption of a universal resonance at
2065 MeV, called d'. We calculate the mass of a six-quark system with J^P=0^-,
T=0 quantum numbers employing a cluster model and a shell model basis to
diagonalize the nonrelativistic quark model Hamiltonian.Comment: 7 pages, Latex, 2 figures, invited talk at 6th Int. Symp. on Mesons
and Nucleons 1995, Blaubeuren, Germany, 10-14 July 1995, to be published in
pi-N Newsletter
Pionic Decay of a Possible d'-Dibaryon
The pionic decay of a possible d'-dibaryon in the process d' --> pi + N + N
is studied in the microscopic quark shell model and with a single-quark
transition operator describing the transition q --> pi + q'. For the d' with
quantum numbers J^P=0^-, T=0, we employ a six-quark shell-model wave function
with a spatial s^5p [51]_X-configuration with N=1 harmonic oscillator quanta.
It is shown that the pionic decay width depends strongly on the mass and size
of the d'. In the case that the calculated d' mass is close to the experimental
one a small pionic decay width of 0.04 MeV is obtained. This is an order of
magnitude smaller than the experimentally suggested value of 0.5 MeV. Two
possibilities to improve the calculated width are suggested. The effect of the
nonstatic correction term in the transition operator and the influence of the
form factor at the decay vertex on the decay width are also discussed.Comment: Latex, 15 pages, 1 postscript figure, accepted for publication in
Nucl. Phys.
Theory of Phase Ordering Kinetics
The theory of phase ordering dynamics -- the growth of order through domain
coarsening when a system is quenched from the homogeneous phase into a
broken-symmetry phase -- is reviewed, with the emphasis on recent developments.
Interest will focus on the scaling regime that develops at long times after the
quench. How can one determine the growth laws that describe the time-dependence
of characteristic length scales, and what can be said about the form of the
associated scaling functions? Particular attention will be paid to systems
described by more complicated order parameters than the simple scalars usually
considered, e.g. vector and tensor fields. The latter are needed, for example,
to describe phase ordering in nematic liquid crystals, on which there have been
a number of recent experiments. The study of topological defects (domain walls,
vortices, strings, monopoles) provides a unifying framework for discussing
coarsening in these different systems.Comment: To appear in Advances in Physics. 85 pages, latex, no figures. For a
hard copy with figures, email [email protected]
The Effect of Shear on Phase-Ordering Dynamics with Order-Parameter-Dependent Mobility: The Large-n Limit
The effect of shear on the ordering-kinetics of a conserved order-parameter
system with O(n) symmetry and order-parameter-dependent mobility
\Gamma({\vec\phi}) \propto (1- {\vec\phi} ^2/n)^\alpha is studied analytically
within the large-n limit. In the late stage, the structure factor becomes
anisotropic and exhibits multiscaling behavior with characteristic length
scales (t^{2\alpha+5}/\ln t)^{1/2(\alpha+2)} in the flow direction and (t/\ln
t)^{1/2(\alpha+2)} in directions perpendicular to the flow. As in the \alpha=0
case, the structure factor in the shear-flow plane has two parallel ridges.Comment: 6 pages, 2 figure
Multicomponent flow on curved surfaces: A vielbein lattice Boltzmann approach
We develop and implement a novel finite difference lattice Boltzmann scheme to study multicomponent flows on curved surfaces, coupling the continuity and Navier-Stokes equations with the Cahn-Hilliard equation to track the evolution of the binary fluid interfaces. The standard lattice Boltzmann method relies on regular Cartesian grids, which makes it generally unsuitable to study flow problems on curved surfaces. To alleviate this limitation, we use a vielbein formalism to write down the Boltzmann equation on an arbitrary geometry, and solve the evolution of the fluid distribution functions using a finite difference method. Focussing on the torus geometry as an example of a curved surface, we demonstrate drift motions of fluid droplets and stripes embedded on the surface of such geometries. Interestingly, they migrate in opposite directions: fluid droplets to the outer side while fluid stripes to the inner side of the torus. For the latter we demonstrate that the global minimum configuration is unique for small stripe widths, but it becomes bistable for large stripe widths. Our simulations are also in agreement with analytical predictions for the Laplace pressure of the fluid stripes, and their damped oscillatory motion as they approach equilibrium configurations, capturing the corresponding decay timescale and oscillation frequency. Finally, we simulate the coarsening dynamics of phase separating binary fluids in the hydrodynamics and diffusive regimes for tori of various shapes, and compare the results against those for a flat two-dimensional surface. Our finite difference lattice Boltzmann scheme can be extended to other surfaces and coupled to other dynamical equations, opening up a vast range of applications involving complex flows on curved geometries
Exchange Currents in Photoproduction of Baryon Resonances
We calculate photoexcitation amplitudes for several nucleon and delta
resonances. We use a chiral quark model including two-body exchange currents.
The two-body currents give important contributions. For the delta (1232) and
the D13 (1520) we observe that the individual exchange current contributions
considerably cancel each other while in the case of the Roper resonance and the
S11 (1535) we get a reinforcement of the two-body amplitudes. In comparison
with present experimental data, we obtain both for the S11 (1535) and for the
Roper resonance an improvement with respect to the impulse approximation.Comment: 9 pages, 1 figur
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