5,228 research outputs found
How bees and foams respond to curved confinement:Level set boundary representations in the Surface Evolver
We investigate the equilibrium properties of a single area-minimising bubble trapped between two narrowly-separated parallel curved plates. We begin with the simple case of a bubble trapped between concentric spherical plates. We develop a model that shows that the surface tension energy of the bubble is lower when confined between spherical plates as compared to a bubble trapped between flat plates. We confirm our findings by comparing against Surface Evolver simulations. Next, we derive a simple model for a bubble between arbitrarily curved parallel plates. The energy is found to be higher when the local Gaussian curvature of the plates is negative and lower when the curvature is positive. To check the validity of the model we consider a bubble trapped between concentric tori. In the toroidal case we find that the sensitivity of the bubble's energy to the local curvature acts as a geometric potential capable of driving bubbles from regions with negative to positive curvature
Laboratory rearing of the squid Loligo pealei to the juvenile stage: growth comparisons with fishery data
The Birth of a Galaxy - III. Propelling reionisation with the faintest galaxies
Starlight from galaxies plays a pivotal role throughout the process of cosmic
reionisation. We present the statistics of dwarf galaxy properties at z > 7 in
haloes with masses up to 10^9 solar masses, using a cosmological radiation
hydrodynamics simulation that follows their buildup starting with their
Population III progenitors. We find that metal-enriched star formation is not
restricted to atomic cooling ( K) haloes, but can occur
in haloes down to masses ~10^6 solar masses, especially in neutral regions.
Even though these smallest galaxies only host up to 10^4 solar masses of stars,
they provide nearly 30 per cent of the ionising photon budget. We find that the
galaxy luminosity function flattens above M_UV ~ -12 with a number density that
is unchanged at z < 10. The fraction of ionising radiation escaping into the
intergalactic medium is inversely dependent on halo mass, decreasing from 50 to
5 per cent in the mass range . Using our galaxy
statistics in a semi-analytic reionisation model, we find a Thomson scattering
optical depth consistent with the latest Planck results, while still being
consistent with the UV emissivity constraints provided by Ly forest
observations at z = 4-6.Comment: 21 pages, 15 figures, 4 tables. Accepted in MNRA
Senior Leonard Hayes Wins National Piano Competition
Lawrence Universityâs Leonard Hayes, a senior from Dallas, Texas, won the recent Young Artistsâ Division of the 2011 Tourgee Debose National Piano Competition conducted at Southern University in Baton Rouge, La.
This was Hayesâ second first-place showing in the competition having previously won the Tourgee Deboseâs sophomore division in 2009.
Hayes received a first-place prize of $1,000 for his winning performance of Beethovenâs âPiano Sonata Op. 90,â Cesar Franckâs âPoco Allegro and Fugueâ and two movements from George Walkerâs âPiano Sonata No. 2.â
A third-place finisher in the 2010 National Association of Negro Musiciansâ Piano Scholarship competition, Hayes studies in the piano studio of Catherine Kautsky
Minkowski Tensors of Anisotropic Spatial Structure
This article describes the theoretical foundation of and explicit algorithms
for a novel approach to morphology and anisotropy analysis of complex spatial
structure using tensor-valued Minkowski functionals, the so-called Minkowski
tensors. Minkowski tensors are generalisations of the well-known scalar
Minkowski functionals and are explicitly sensitive to anisotropic aspects of
morphology, relevant for example for elastic moduli or permeability of
microstructured materials. Here we derive explicit linear-time algorithms to
compute these tensorial measures for three-dimensional shapes. These apply to
representations of any object that can be represented by a triangulation of its
bounding surface; their application is illustrated for the polyhedral Voronoi
cellular complexes of jammed sphere configurations, and for triangulations of a
biopolymer fibre network obtained by confocal microscopy. The article further
bridges the substantial notational and conceptual gap between the different but
equivalent approaches to scalar or tensorial Minkowski functionals in
mathematics and in physics, hence making the mathematical measure theoretic
method more readily accessible for future application in the physical sciences
Local Anisotropy of Fluids using Minkowski Tensors
Statistics of the free volume available to individual particles have
previously been studied for simple and complex fluids, granular matter,
amorphous solids, and structural glasses. Minkowski tensors provide a set of
shape measures that are based on strong mathematical theorems and easily
computed for polygonal and polyhedral bodies such as free volume cells (Voronoi
cells). They characterize the local structure beyond the two-point correlation
function and are suitable to define indices of
local anisotropy. Here, we analyze the statistics of Minkowski tensors for
configurations of simple liquid models, including the ideal gas (Poisson point
process), the hard disks and hard spheres ensemble, and the Lennard-Jones
fluid. We show that Minkowski tensors provide a robust characterization of
local anisotropy, which ranges from for vapor
phases to for ordered solids. We find that for fluids,
local anisotropy decreases monotonously with increasing free volume and
randomness of particle positions. Furthermore, the local anisotropy indices
are sensitive to structural transitions in these simple
fluids, as has been previously shown in granular systems for the transition
from loose to jammed bead packs
Minkowski tensors and local structure metrics: Amorphous and crystalline sphere packings
A Family of Maximum Margin Criterion for Adaptive Learning
In recent years, pattern analysis plays an important role in data mining and
recognition, and many variants have been proposed to handle complicated
scenarios. In the literature, it has been quite familiar with high
dimensionality of data samples, but either such characteristics or large data
have become usual sense in real-world applications. In this work, an improved
maximum margin criterion (MMC) method is introduced firstly. With the new
definition of MMC, several variants of MMC, including random MMC, layered MMC,
2D^2 MMC, are designed to make adaptive learning applicable. Particularly, the
MMC network is developed to learn deep features of images in light of simple
deep networks. Experimental results on a diversity of data sets demonstrate the
discriminant ability of proposed MMC methods are compenent to be adopted in
complicated application scenarios.Comment: 14 page
Minkowski tensors and local structure metrics: Amorphous and crystalline sphere packings
Robust and sensitive tools to characterise local structure are essential for investigations of granular or particulate matter. Often local structure metrics derived from the bond network are used for this purpose, in particular Steinhardt's bond-orientational order parameters ql . Here we discuss an alternative method, based on the robust characterisation of the shape of the particles' Voronoi cells, by Minkowski tensors and derived anisotropy measures. We have successfully applied these metrics to quantify structural changes and the onset of crystallisation in random sphere packs. Here we specifically discuss the expectation values of these metrics for simple crystalline unimodal packings of spheres, consisting of single spheres on the points of a Bravais lattice. These data provide an important reference for the discussion of anisotropy values of disordered structures that are typically of relevance in granular systems. This analysis demonstrates that, at least for sufficiently high packing fractions above Ï > 0.61, crystalline sphere packs exist whose Voronoi cells are more anisotropic with respect to a volumetric moment tensor than the average value of Voronoi cell anisotropy in random sphere packs
Fire analysis of steel frames with the use of artificial neural networks
The paper presents an alternative approach to the modelling of the mechanical behaviour of steel frame material when exposed to the high temperatures expected in fires. Based on a series of stress-strain curves obtained experimentally for various temperature levels, an artificial neural network (ANN) is employed in the material modelling of steel. Geometrically and materially, a non-linear analysis of plane frame structures subjected to fire is performed by FEM. The numerical results of a simply supported beam are compared with our measurements, and show a good agreement, although the temperature-displacement curves exhibit rather irregular shapes. It can be concluded that ANN is an efficient tool for modelling the material properties of steel frames in fire engineering design studies. (c) 2007 Elsevier Ltd. All rights reserved
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