5,237 research outputs found
Conformal Mapping on Rough Boundaries I: Applications to harmonic problems
The aim of this study is to analyze the properties of harmonic fields in the
vicinity of rough boundaries where either a constant potential or a zero flux
is imposed, while a constant field is prescribed at an infinite distance from
this boundary. We introduce a conformal mapping technique that is tailored to
this problem in two dimensions. An efficient algorithm is introduced to compute
the conformal map for arbitrarily chosen boundaries. Harmonic fields can then
simply be read from the conformal map. We discuss applications to "equivalent"
smooth interfaces. We study the correlations between the topography and the
field at the surface. Finally we apply the conformal map to the computation of
inhomogeneous harmonic fields such as the derivation of Green function for
localized flux on the surface of a rough boundary
Signature Sequence of Intersection Curve of Two Quadrics for Exact Morphological Classification
We present an efficient method for classifying the morphology of the
intersection curve of two quadrics (QSIC) in PR3, 3D real projective space;
here, the term morphology is used in a broad sense to mean the shape,
topological, and algebraic properties of a QSIC, including singularity,
reducibility, the number of connected components, and the degree of each
irreducible component, etc. There are in total 35 different QSIC morphologies
with non-degenerate quadric pencils. For each of these 35 QSIC morphologies,
through a detailed study of the eigenvalue curve and the index function jump we
establish a characterizing algebraic condition expressed in terms of the Segre
characteristics and the signature sequence of a quadric pencil. We show how to
compute a signature sequence with rational arithmetic so as to determine the
morphology of the intersection curve of any two given quadrics. Two immediate
applications of our results are the robust topological classification of QSIC
in computing B-rep surface representation in solid modeling and the derivation
of algebraic conditions for collision detection of quadric primitives
On Weingarten transformations of hyperbolic nets
Weingarten transformations which, by definition, preserve the asymptotic
lines on smooth surfaces have been studied extensively in classical
differential geometry and also play an important role in connection with the
modern geometric theory of integrable systems. Their natural discrete analogues
have been investigated in great detail in the area of (integrable) discrete
differential geometry and can be traced back at least to the early 1950s. Here,
we propose a canonical analogue of (discrete) Weingarten transformations for
hyperbolic nets, that is, C^1-surfaces which constitute hybrids of smooth and
discrete surfaces "parametrized" in terms of asymptotic coordinates. We prove
the existence of Weingarten pairs and analyse their geometric and algebraic
properties.Comment: 41 pages, 30 figure
Fast directional continuous spherical wavelet transform algorithms
We describe the construction of a spherical wavelet analysis through the
inverse stereographic projection of the Euclidean planar wavelet framework,
introduced originally by Antoine and Vandergheynst and developed further by
Wiaux et al. Fast algorithms for performing the directional continuous wavelet
analysis on the unit sphere are presented. The fast directional algorithm,
based on the fast spherical convolution algorithm developed by Wandelt and
Gorski, provides a saving of O(sqrt(Npix)) over a direct quadrature
implementation for Npix pixels on the sphere, and allows one to perform a
directional spherical wavelet analysis of a 10^6 pixel map on a personal
computer.Comment: 10 pages, 3 figures, replaced to match version accepted by IEEE
Trans. Sig. Pro
Morphological analysis of stylolites for paleostress estimation in limestones surrounding the Andra Underground Research Laboratory site
We develop and test a methodology to infer paleostress from the morphology of
stylolites within borehole cores. This non-destructive method is based on the
analysis of the stylolite trace along the outer cylindrical surface of the
cores. It relies on an automatic digitization of high-resolution photographs
and on the spatial Fourier spectrum analysis of the stylolite traces. We test
and show, on both synthetic and natural examples, that the information from
this outer cylindrical surface is equivalent to the one obtained from the
destructive planar sections traditionally used. The assessment of paleostress
from the stylolite morphology analysis is made using a recent theoretical
model, which links the morphological properties to the physical processes
acting during stylolite evolution. This model shows that two scaling regimes
are to be expected for the stylolite height power spectrum, separated by a
cross-over length that depends on the magnitude of the paleostress during
formation. We develop a non linear fit method to automatically extract the
cross-over lengths from the digitized stylolite profiles. Results on cores from
boreholes drilled in the surroundings of the Andra Underground Research
Laboratory located at Bure, France, show that different groups of sedimentary
stylolites can be distinguished, and correspond to different estimated vertical
paleostress values. For the Oxfordian formation, one group of stylolites
indicate a paleostress of around 10 MPa, while another group yields 15 MPa. For
the Dogger formation, two stylolites indicate a paleostress of around 10 MPa,
while others appear to have stopped growing at paleostresses between 30 and 22
MPa, starting at an erosion phase that initiated in the late Cretaceous and
continues today. This method has a high potential for further applications on
reservoirs or other geological contexts where stylolites are present.Comment: International Journal of Rock Mechanics and Mining Sciences (2013)
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