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34
Realtime subspace integration for St. VenantKirchhoff deformable models
 ACM Transactions on Graphics
, 2005
"... In this paper, we present an approach for fast subspace integration of reducedcoordinate nonlinear deformable models that is suitable for interactive applications in computer graphics and haptics. Our approach exploits dimensional model reduction to build reducedcoordinate deformable models for ob ..."
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Cited by 85 (13 self)
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In this paper, we present an approach for fast subspace integration of reducedcoordinate nonlinear deformable models that is suitable for interactive applications in computer graphics and haptics. Our approach exploits dimensional model reduction to build reducedcoordinate deformable models for objects with complex geometry. We exploit the fact that model reduction on large deformation models with linear materials (as commonly used in graphics) result in internal force models that are simply cubic polynomials in reduced coordinates. Coefficients of these polynomials can be precomputed, for efficient runtime evaluation. This allows simulation of nonlinear dynamics using fast implicit Newmark subspace integrators, with subspace integration costs independent of geometric complexity. We present two useful approaches for generating lowdimensional subspace bases: modal derivatives and an interactive sketching technique. Massscaled principal component analysis (massPCA) is suggested for dimensionality reduction. Finally, several examples are given from computer animation to illustrate high performance, including forcefeedback haptic rendering of a complicated object undergoing large deformations.
Needle insertion modelling and simulation
 In IEEE Trans. on Rob. and Aut., Special issue on medical robotics
"... Abstract—A methodology for estimating the force distribution that occurs along a needle shaft during insertion is described. An experimental system for measuring planar tissue phantom deformation during needle insertions has been developed and is presented. A twodimensional linear elastostatic ma ..."
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Cited by 56 (3 self)
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Abstract—A methodology for estimating the force distribution that occurs along a needle shaft during insertion is described. An experimental system for measuring planar tissue phantom deformation during needle insertions has been developed and is presented. A twodimensional linear elastostatic material model, discretised using the finite element method, is used to derive contact force information that is not directly measurable. This approach provides a method for quantifying the needle forces and soft tissue deformations that occur during general needle trajectories in multiple dimensions. The needle force distribution is used for graphical and haptic realtime simulations of needle insertion. Since the force displacement relationship is required only along the needle, a condensation technique is shown to achieve very fast interactive simulations. Stiffness matrix changes corresponding to changes in boundary conditions and material coordinate frames are performed using lowrank matrix updates. Index Terms—Haptics, needle insertion model, percutaneous intervention, planning, simulation, tissue model, training. I.
Constructing PhysicsBased Facial Models of Individuals
 In Proc. Graphics Interface ’93
, 1993
"... This paper develops a highly automated approach to constructing realistic, working models of human heads for use in animation. These physicsbased models are anatomically accurate and may be made to conform closely to specific individuals. We begin by scanning a person with a laser sensor which circ ..."
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Cited by 36 (3 self)
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This paper develops a highly automated approach to constructing realistic, working models of human heads for use in animation. These physicsbased models are anatomically accurate and may be made to conform closely to specific individuals. We begin by scanning a person with a laser sensor which circles around the head, acquiring detailed range and reflectance information. Next, an automatic conformation algorithm adapts a triangulated face mesh of predetermined topological structure to these data. The generic mesh, which is reusable with different individuals, reduces the range data to an efficient, polygonal approximation of the facial geometry and supports a highresolution texture mapping of the skin reflectivity. The conformed polygonal mesh forms the epidermal layer of a new, physicsbased model of facial tissue. An automatic algorithm constructs the multilayer synthetic skin and estimates an underlying rigid "skull" substructure with a jointed jaw. Finally, the algorithm inserts synthetic muscles into the deepest layer of the facial tissue. These contractile actuators, which emulate the primary muscles of facial expression, generate forces that deform the synthetic tissue into meaningful expressions. To increase realism, we include constraints to emulate tissue incompressibility and to enable the tissue to slide over the skull substructure without penetrating into it. The resulting animate models appear significantly more realistic than our previous physicsbased facial models. Keywords: PhysicsBased Facial Modeling, Facial Animation, Cylindrical Facial Scanning, FeatureBased Facial Adaptation, Texture Mapping, Discrete Deformable Models. 1
Interactive simulation of surgical needle insertion and steering
 in ACM SIGGRAPH
, 2009
"... We present algorithms for simulating and visualizing the insertion and steering of needles through deformable tissues for surgical training and planning. Needle insertion is an essential component of many clinical procedures such as biopsies, injections, neurosurgery, and brachytherapy cancer treatm ..."
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Cited by 17 (6 self)
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We present algorithms for simulating and visualizing the insertion and steering of needles through deformable tissues for surgical training and planning. Needle insertion is an essential component of many clinical procedures such as biopsies, injections, neurosurgery, and brachytherapy cancer treatment. The success of these procedures depends on accurate guidance of the needle tip to a clinical target while avoiding vital tissues. Needle insertion deforms body tissues, making accurate placement difficult. Our interactive needle insertion simulator models the coupling between a steerable needle and deformable tissue. We introduce (1) a novel algorithm for local remeshing that quickly enforces the conformity of a tetrahedral mesh to a curvilinear needle path, enabling accurate computation of contact forces, (2) an efficient method for coupling a 3D finite element simulation with a 1D inextensible rod with stickslip friction, and (3) optimizations that reduce the computation time for physically based simulations. We can realistically and interactively simulate needle insertion into a prostate mesh of 13,375 tetrahedra and 2,763 vertices at a 25 Hz frame rate on an 8core 3.0 GHz Intel Xeon PC. The simulation models prostate brachytherapy with needles of varying stiffness, steering needles around obstacles, and supports motion planning for robotic needle insertion. We evaluate the accuracy of the simulation by comparing against realworld experiments in which flexible, steerable needles were inserted into gel tissue phantoms.
Constitutive Modeling of NanotubeReinforced Polymer Composite Systems
, 2001
"... In this study, a technique has been proposed for developing constitutive models for polymer composite systems reinforced with singlewalled carbon nanotubes (SWNT). Since the polymer molecules are on the same size scale as the nanotubes, the interaction at the polymer/nanotube interface is highly de ..."
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Cited by 16 (2 self)
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In this study, a technique has been proposed for developing constitutive models for polymer composite systems reinforced with singlewalled carbon nanotubes (SWNT). Since the polymer molecules are on the same size scale as the nanotubes, the interaction at the polymer/nanotube interface is highly dependent on the local molecular structure and bonding. At these small length scales, the lattice structures of the nanotube and polymer chains cannot be considered continuous, and the bulk mechanical properties of the SWNT/polymer composites can no longer be determined through traditional micromechanical approaches that are formulated using continuum mechanics. It is proposed herein that the nanotube, the local polymer near the nanotube, and the nanotube/polymer interface can be modeled as an effective continuum fiber using an equivalentcontinuum modeling method. The effective fiber retains the local molecular structure and bonding information and serves as a means for incorporating micromechanical analyses for the prediction of bulk mechanical properties of SWNT/polymer composites with various nanotube sizes and orientations. As an example, the proposed approach is used for the constitutive modeling of two SWNT/polyethylene composite systems, one with continuous and aligned SWNT and the other with discontinuous and randomly aligned nanotubes.
Myocardial Motion and Function Assessment Using 4D Images
, 1994
"... This paper describes efforts aimed at more objectively and accurately quantifying the local, regional and global function of the left ventricle (LV) of the heart from fourdimensional (4D) image data. Using our shapebased image analysis methods, pointwise myocardial motion vector fields between ..."
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Cited by 13 (1 self)
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This paper describes efforts aimed at more objectively and accurately quantifying the local, regional and global function of the left ventricle (LV) of the heart from fourdimensional (4D) image data. Using our shapebased image analysis methods, pointwise myocardial motion vector fields between successive image frames through the entire cardiac cycle will be computed. Quantitative LV motion, thickening, and strain measurements will then be established from the point correspondence maps. In the paper, we will also briefly describe an in vivo experimental model which uses implanted imagingopaque markers to validate the results of our image analysis methods. Finally, initial experimental results using image sequences from two different modalities will be presented. 1 Introduction Ischemic heart disease is a major clinical issue. Myocardial injury from ischemic heart disease is often regional, and it is the fundamental goal of many forms of cardiac imaging and image analysis method...
The nonlinear sieve problem and applications to thin films
, 2004
"... We consider variational problems defined on domains ‘weakly’ connected through a separation hyperplane (‘sieve plane’) by an εperiodically distributed ‘contact zone’. We study the asymptotic behaviour as ε tends to 0 of integral functionals in such domains in the nonlinear and vectorvalued case, s ..."
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Cited by 4 (1 self)
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We consider variational problems defined on domains ‘weakly’ connected through a separation hyperplane (‘sieve plane’) by an εperiodically distributed ‘contact zone’. We study the asymptotic behaviour as ε tends to 0 of integral functionals in such domains in the nonlinear and vectorvalued case, showing that the asymptotic memory of the sieve is described by a nonlinear ‘capacitarytype’ formula. In particular we treat the case when the integral energies on both sides of the sieve plane satisfy different growth conditions. We also study the case of thin films, with flat profile and thickness ε, connected by the same sieve plane.
Modeling simulation and planning of needle motion in soft tissues
, 2003
"... Precise needle placement is required for the success of a wide variety of percutaneous interventions in medicine. Insertions into soft tissues can be difficult to learn and to perform, due to tissue deformation, needle deflection and limited visual feedback. Little quantitative information is known ..."
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Cited by 4 (0 self)
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Precise needle placement is required for the success of a wide variety of percutaneous interventions in medicine. Insertions into soft tissues can be difficult to learn and to perform, due to tissue deformation, needle deflection and limited visual feedback. Little quantitative information is known about the interaction between needles and soft tissues during puncture, and no effective physicallybased training, planning and guidance systems exist for such procedures. This work aims to characterise needletissue interaction by measuring contact forces and deformations that are applied during insertions into soft tissue phantoms. A new methodology for estimating the forces that occur along the needle shaft during insertion is described. The approach is based on physical experiments, as well as on linear elastic phantom models that are discretised by traditional Finite Element Methods. Shaft force distributions are derived from insertions into homogeneous and simple layered inhomogeneous tissue phantoms at several driving velocities, and are applied as boundary conditions to tissue models for physicallybased simulations of needle insertion trajectories. A largestrain elastic needle model is coupled to the tissue models to account for needle deflection and bending during simulated insertion. Since
Animating Fracture
 Communications of the ACM
, 2000
"... objects tend to have many degrees of freedom, making keyframing or motion capture difficult. Moreover, while passive objects are often essential to the plot of an animation and to its appearance or mood, they are not characters and do not require the same control over the subtle details of t ..."
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Cited by 4 (0 self)
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objects tend to have many degrees of freedom, making keyframing or motion capture difficult. Moreover, while passive objects are often essential to the plot of an animation and to its appearance or mood, they are not characters and do not require the same control over the subtle details of their motion. Therefore, simulations in which motion is These fracture patterns propagate arbitrarily in 3D solid objects as they break, crack, or tear realistically. a a a a COMMUNICA 0 SOF THE A MJuly2000/Vo 43, No 769 Animating Frac ture controlled only by initial conditions, physical equations, and material parameters are often sufficient to produce appealing animations of passive objects. The computer graphics literature includes many examples of passive systems modeled with simulation. For example, computational fluid dynamics models have been used to animate splashing water, rising smoke, and explosions in the air. Foot