919090
Fast penetration depth estimation using rasterization hardware and hierarchical refinement
We present a novel and fast algorithm to estimate penetration depth (PD) between two polyhedral models. Given two overlapping polyhedra, it computes the minimal translational distance to separate them using a combination of discretized computations and hierarchical refinement. The algorithm computes pair-wise Minkowski sums of decomposed convex pieces, performs closest point query using rasterization hardware, and refines the estimated PD by incremental walking. It uses bounding volume hierarchies, model simplification, and culling algorithms to further accelerate the computation and refines the estimated PD in a hierarchical manner. We highlight its performance on complex models.
9041268
Modeling ice dynamics as a thin-film Stefan problem
Large, 3D ice formations such as icicles exhibit a high degree of geometric and optical complexity. Modeling these features by hand can be a daunting task, so we present a novel physically-based algorithm for simulating this phenomenon. Solidification is usually posed as a so-called 'Stefan problem', but the problem in its classic form is inappropriate for simulating the ice typically found in a winter scene. We instead use the 'thin-film' variant of the Stefan problem to derive velocity equations for a level set simulation. However, due to the scales involved in the problem, even an adaptive grid level set solver is still insufficient to track the tip of an icicle. Therefore, we derive an analytical solution for the icicle tip and use it to correct the level set simulation. The results appear to be in agreement with experimental data. We also present a physically-based technique for modeling ripples along the ice surface that alleviates the need to explicitly track small-scale geometry. To our knowledge, our approach is the most complete model available, and produces complex visual phenomena that no previous method has been able to capture.
6243696
Geometry-driven physical interaction between avatars and virtual environments
We present an interactive technique on virtual contact handling for avatars in virtual environments using geometry-driven physics. If a contact has occurred between an articulated avatar and a virtual environment, the global penetration depth and contact points are estimated based on a fast local penetration depth computation for decomposed convex pieces. The penetration depth and contact information are then used to resolve overlap between the avatar and the virtual environment. If applicable, joint angles for an articulated body are computed using an inverse kinematics approach based on cyclic coordinate descent. Resulting dynamic response with friction is modeled with impulse-based dynamics under the Coulomb friction law. We demonstrate the algorithm on a modestly complex virtual environment. The resulting system is able to maintain an interactive frame rate of 30–60 Hz. Copyright © 2004 John Wiley & Sons, Ltd.
7639620
Stable and responsive six-degree-of-freedom haptic manipulation using implicit integration
In this paper we present a novel approach for simulating the rigid body dynamics of a haptically manipulated object using implicit integration. Our formulation requires the linearization of contact and manipulation forces, and it provides higher stability and responsiveness than previous methods. The linearization of contact forces, coupled with fast, perceptually based collision detection algorithms, enables us to perform highly stable and responsive 6-degree-of-freedom haptic rendering of complex polygonal models.
8273317
A video-based rendering acceleration algorithm for interactive walkthroughs
We present a new approach for faster rendering of large synthetic environments using video-based representations. We decompose the large environment into cells and pre-compute video based impostors using MPEG compression to represent sets of objects that are far from each cell. At runtime, we decode the MPEG streams and use rendering algorithms that provide nearly constant-time random access to any frame. The resulting system has been implemented and used for an interactive walkthrough of a model of a house with 260,000 polygons and realistic lighting and textures. It is able to render this model at 16 frames per second (an eightfold improvement over simpler algorithms) on average on a Pentium II PC with an off-the-shelf graphics card.
7169150
A versatile interactive 3D brush model
We present a flexible modeling approach capable of realistically simulating many varieties of brushes commonly used in painting. Our geometric model of brush heads is a combination of subdivision surfaces and hundreds of individual bristles represented by thin polygonal strips. We exploit bristle-to-bristle coherence, simulating only a fraction of the bristles and using interpolation for the remainder. Our dynamic model incorporates realistic physically-based deformation, including anisotropic friction, brush plasticity, and tip spreading. We use an energy minimization framework with a novel geometric representation of the brush head to generate a wider variety of brushes. Finally, we have developed an improved haptic model that provides realistic force feedback, directly related to the results of the brush dynamic simulation. Using this model, we are able to simulate a wide range of brush styles and create an excellent variety of strokes such as the crisp, curvy strokes of Western decorative painting, or rough scratchy strokes like certain Oriental calligraphy. We have also developed an exporter for a popular free 3D modeling package that makes it easier for non-programmers to create any desired style of brush, real or fanciful.
24905908
Constant Weight Codes for Correcting Symmetric Errors and Detecting Unidirectional Errors
Proposes two classes of constant weight codes, which can be used for correcting t symmetric errors and simultaneously detecting all unidirectional errors. Codes in the first class are in quasi-systematic form and codes in the second class are in systematic form. Since each codeword of codes in both classes can be divided into a data part and a parity check part, the proposed codes have the merit of easily mapping messages into codewords. >
35226732
Linear-time algorithms for computing the reliability of bipartite and (#<=2) star distributed computing systems
Abstract Let S =( V , F ) denote a distributed computing system with star topology, where V is the set of nodes of S and F is the set of files distributed in V . The problem of computing the reliability of S has been shown to be #P-complete. Therefore, all known exact algorithms for this problem have exponential time complexity. This study presents two linear-time algorithms to compute the reliability of two restricted subclasses of S . The first algorithm runs in O(| F |) when the file distribution is limited to being bipartite and non-separable. The second algorithm runs in O(| V |), when each file is allocated to at most two distinct nodes and each node contains at most two distinct records. If the failure and working probabilities of every node are identical, then the computation can be accelerated to O(log(| V |)) time by means of the Fibonacci number and the Lucas number. Scope and purpose The star topology has become increasingly popular in distributed computing systems as it offers higher reliability, lower installation cost, and more flexibility than other topologies. The computation of the reliability of star distributed computing systems is shown to be #P-complete. Therefore, computing the reliability of such a system is intractable. This article presents two fast linear-time algorithms to compute the reliability of two restricted subclasses of star distributed computing systems.
16198203
On Semantics of Reactive Rule-Based Systems
In this paper we address special issues which arise when the rule-based programming paradigm is emlployed in development of reactive real-time systems. We begin by presenting a rule-based language which has emerged while developing intelligent cruise control systems. We describe a naive operational semantics based on an an implemented inference engine, and explain why the semantics is not appropriate in safety-critical real-time contexts. We then deene a number of correct-ness criteria ensuring termination, consistency and determinism, based on a formal declarative semantics. However, the declarative semantics is non-constructive. In order to be able to build an implementation satisfying the correctness criteria, two alternative approaches are proposed. Both approaches build upon static checks of a rule-based program. In the rst approach some correctness criteria are met by accepting only stratiied programs after the static checks. In the second approach we accept programs which are correct with respect to a constructive semantics. For both approaches we present the analysis methods and soundness results with respect to the desired declarative semantics. Abstract In this paper we address special issues which arise when the rule-based programming paradigm is emlployed in development of reactive real-time systems. We begin by presenting a rule-based language which has emerged while developing intelligent cruise control systems. We describe a naive operational semantics based on an an implemented inference engine, and explain why the semantics is not appropriate in safety-critical real-time contexts. We then deene a number of correct-ness criteria ensuring termination, consistency and determinism, based on a formal declarative semantics. However, the declarative semantics is non-constructive. In order to be able to build an implementation satisfying the correctness criteria, two alternative approaches are proposed. Both approaches build upon static checks of a rule-based program. In the rst approach some correctness criteria are met by accepting only stratiied programs after the static checks. In the second approach we accept programs which are correct with respect to a constructive semantics. For both approaches we present the analysis methods and soundness results with respect to the desired declarative semantics.
28156768
A VLSI implementation of the blowfish encryption/decryption algorithm
We propose an efficient hardware architecture for the Blowfish algorithm [1]. The speed is up to 4 bit/clock, which is 9 times faster than a Pentium. By applying operator-rescheduling method, the critical path delay is improved by 21.7%. We have successfully implemented it using Compass cell library targeted at a 0.6 μm TSMC SPTM CMOS process. The die size is 5.7x6.1 mm and the maximum frequency is 50MHz.
205481590
Fast and simple algorithms to count the number of vertex covers in an interval graph
This study provides the following fast and simple algorithms for an interval graph: (1) an algorithm for counting the number of vertex covers, and (2) an algorithm for counting the number of minimal vertex covers.