16,789 research outputs found
From 3D Point Clouds to Pose-Normalised Depth Maps
We consider the problem of generating either pairwise-aligned or pose-normalised depth maps from noisy 3D point clouds in a relatively unrestricted poses. Our system is deployed in a 3D face alignment application and consists of the following four stages: (i) data filtering, (ii) nose tip identification and sub-vertex localisation, (iii) computation of the (relative) face orientation, (iv) generation of either a pose aligned or a pose normalised depth map. We generate an implicit radial basis function (RBF) model of the facial surface and this is employed within all four stages of the process. For example, in stage (ii), construction of novel invariant features is based on sampling this RBF over a set of concentric spheres to give a spherically-sampled RBF (SSR) shape histogram. In stage (iii), a second novel descriptor, called an isoradius contour curvature signal, is defined, which allows rotational alignment to be determined using a simple process of 1D correlation. We test our system on both the University of York (UoY) 3D face dataset and the Face Recognition Grand Challenge (FRGC) 3D data. For the more challenging UoY data, our SSR descriptors significantly outperform three variants of spin images, successfully identifying nose vertices at a rate of 99.6%. Nose localisation performance on the higher quality FRGC data, which has only small pose variations, is 99.9%. Our best system successfully normalises the pose of 3D faces at rates of 99.1% (UoY data) and 99.6% (FRGC data)
Energy conserving schemes for the simulation of musical instrument contact dynamics
Collisions are an innate part of the function of many musical instruments.
Due to the nonlinear nature of contact forces, special care has to be taken in
the construction of numerical schemes for simulation and sound synthesis.
Finite difference schemes and other time-stepping algorithms used for musical
instrument modelling purposes are normally arrived at by discretising a
Newtonian description of the system. However because impact forces are
non-analytic functions of the phase space variables, algorithm stability can
rarely be established this way. This paper presents a systematic approach to
deriving energy conserving schemes for frictionless impact modelling. The
proposed numerical formulations follow from discretising Hamilton's equations
of motion, generally leading to an implicit system of nonlinear equations that
can be solved with Newton's method. The approach is first outlined for point
mass collisions and then extended to distributed settings, such as vibrating
strings and beams colliding with rigid obstacles. Stability and other relevant
properties of the proposed approach are discussed and further demonstrated with
simulation examples. The methodology is exemplified through a case study on
tanpura string vibration, with the results confirming the main findings of
previous studies on the role of the bridge in sound generation with this type
of string instrument
Phenomenological modeling of strain hardening, phase transformation and damage effects of trip-steels
In this study, the constitutive modeling of loading state dependent strain hardening and martensite evolution of high alloyed TRIP-steels are addressed, which are experimentally observed comparing uni-axial tension and compression test results. Furthermore, a damage mechanics extension of the model is proposed, which is based on the continuum damage mechanics framework. An implicit gradient based enrichment method is applied to realize a non-local damage formulation. For the implementation into the commercial FEM-software ABAQUS, the analogy between the additional Helmholtztype equation of implicit gradient enrichment and the already built-in heat conduction equation is used. Finally, the developed model is fitted to experimental data and cell model calculations. A convergence study using the non-local extension is discussed
On Role Logic
We present role logic, a notation for describing properties of relational
structures in shape analysis, databases, and knowledge bases. We construct role
logic using the ideas of de Bruijn's notation for lambda calculus, an encoding
of first-order logic in lambda calculus, and a simple rule for implicit
arguments of unary and binary predicates. The unrestricted version of role
logic has the expressive power of first-order logic with transitive closure.
Using a syntactic restriction on role logic formulas, we identify a natural
fragment RL^2 of role logic. We show that the RL^2 fragment has the same
expressive power as two-variable logic with counting C^2 and is therefore
decidable. We present a translation of an imperative language into the
decidable fragment RL^2, which allows compositional verification of programs
that manipulate relational structures. In addition, we show how RL^2 encodes
boolean shape analysis constraints and an expressive description logic.Comment: 20 pages. Our later SAS 2004 result builds on this wor
Fast PRISM: Branch and Bound Hough Transform for Object Class Detection
This paper addresses the task of efficient object class detection by means of the Hough transform. This approach has been made popular by the Implicit Shape Model (ISM) and has been adopted many times. Although ISM exhibits robust detection performance, its probabilistic formulation is unsatisfactory. The PRincipled Implicit Shape Model (PRISM) overcomes these problems by interpreting Hough voting as a dual implementation of linear sliding-window detection. It thereby gives a sound justification to the voting procedure and imposes minimal constraints. We demonstrate PRISM's flexibility by two complementary implementations: a generatively trained Gaussian Mixture Model as well as a discriminatively trained histogram approach. Both systems achieve state-of-the-art performance. Detections are found by gradient-based or branch and bound search, respectively. The latter greatly benefits from PRISM's feature-centric view. It thereby avoids the unfavourable memory trade-off and any on-line pre-processing of the original Efficient Subwindow Search (ESS). Moreover, our approach takes account of the features' scale value while ESS does not. Finally, we show how to avoid soft-matching and spatial pyramid descriptors during detection without losing their positive effect. This makes algorithms simpler and faster. Both are possible if the object model is properly regularised and we discuss a modification of SVMs which allows for doing s
Linear and non-linear dynamic analyses of sandwich panels with face sheet-tocore debonding
А survey of recent developments in the dynamic analysis of sandwich panels with face sheet-to-core
debonding is presented. The finite element method within the ABAQUSTM code is utilized. The emphasis
is directed to the procedures used to elaborate linear and non-linear models and to predict dynamic response
of the sandwich panels. Recently developed models are presented, which can be applied for structural
health monitoring algorithms of real-scale sandwich panels. First, various popular theories of intact
sandwich panels are briefly mentioned and a model is proposed to effectively analyse the modal dynamics
of debonded and damaged (due to impact) sandwich panels. The influence of debonding size, form and
location, and number of such damage on the modal characteristics of sandwich panels are shown. For
nonlinear analysis, models based on implicit and explicit time integration schemes are presented and dynamic
response gained with those models are discussed. Finally, questions related to debonding progression
at the face sheet-core interface when dynamic loading continues with time are briefly highlighted
Active skeleton for bacteria modeling
The investigation of spatio-temporal dynamics of bacterial cells and their
molecular components requires automated image analysis tools to track cell
shape properties and molecular component locations inside the cells. In the
study of bacteria aging, the molecular components of interest are protein
aggregates accumulated near bacteria boundaries. This particular location makes
very ambiguous the correspondence between aggregates and cells, since computing
accurately bacteria boundaries in phase-contrast time-lapse imaging is a
challenging task. This paper proposes an active skeleton formulation for
bacteria modeling which provides several advantages: an easy computation of
shape properties (perimeter, length, thickness, orientation), an improved
boundary accuracy in noisy images, and a natural bacteria-centered coordinate
system that permits the intrinsic location of molecular components inside the
cell. Starting from an initial skeleton estimate, the medial axis of the
bacterium is obtained by minimizing an energy function which incorporates
bacteria shape constraints. Experimental results on biological images and
comparative evaluation of the performances validate the proposed approach for
modeling cigar-shaped bacteria like Escherichia coli. The Image-J plugin of the
proposed method can be found online at http://fluobactracker.inrialpes.fr.Comment: Published in Computer Methods in Biomechanics and Biomedical
Engineering: Imaging and Visualizationto appear i
- …