Browsing by Type "conference proceedings and papers preprints"
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ItemAutomatic Construction of Coarse, High-Quality Tetrahedralizations that Enclose and Approximate Surfaces for Animation(ACM, 2013-11-06) Stuart, David A.; Levine, Joshua A.; Jones, Ben; Bargteil, Adam W.Embedding high-resolution surface geometry in coarse control meshes is a standard approach to achieving high-quality computer animation at low computational expense. In this paper we present an effective, automatic method for generating such control meshes. The resulting high-quality, tetrahedral meshes enclose and approximate an input surface mesh, avoiding extrapolation artifacts and ensuring that the resulting coarse volumetric meshes are adequate collision proxies. Our approach comprises three steps: we begin with a tetrahedral mesh built from the body-centered cubic lattice that tessellates the bounding box of the input surface; we then perform a sculpting phase that carefully removes elements from the lattice; and finally a variational vertex adjustment phase iteratively adjusts vertex positions to more closely approximate the surface geometry. Our approach provides explicit trade-offs between mesh quality, resolution, and surface approximation. Our experiments demonstrate the technique can be used to build high-quality meshes appropriate for simulations within games. ItemChatbot Application on Cryptocurrency(IEEE, 2019-07-11) Xie, Qitao; Zhang, Qingquan; Tan, Dayuan; Zhu, Ting; Xiao, Shen; Li, Beibei; Sun, Lei; Yi, Ping; Wang, JunyuMany chatbots have been developed that provide a multitude of services through a wide range of methods. A chatbot is a brand-new conversational agent in the highspeed changing technology world. With the advance of Artificial Intelligence and machine learning, chatbots are becoming more and more popular. A chatbot is the extension of human interface mediums such as the phone and social platforms. Similarly, Cryptocurrency is a new extension of digital or virtual currency designed to work as a medium of exchange. In the current digital exchanging world, investors and interested parties are eager to know more information about, and the capabilites of, this new type of currency. One of the potential paths to retrieve the info automatically and quickly is through a chatbot. We explored the open source python library, Chatterbot, to apply Itchat API (a WeChat interface) with the aim of building a robot chatting application, I&C Chat, on the topic of cryptocurrency. First, we collected question and answer pairs datasets from Quora websites. Furthermore, we also created API calls to query the real time quote for the top 25 cryptocurrencies. Then we used the collected data to train our chatbot and implemented a logic adapter to receive the price quote of cryptocurrencies based on the incoming question. The Itchat API method will return the best matched answer to the asking party automatically. The response time of different questions has been investigated. The results imply that this application is quite useful, feasible and beneficial to the digital currency world. ItemDeveloping and Delivering Hands-On Information Assurance Exercises: Experiences with the Cyber Defense Lab at UMBC(IEEE, 2005-06-10) Sherman, Alan T.; Roberts, Brian O.; Byrd, William E.; Baker, Matthew R.; Simmons, JohnIn summer 2003, we developed four new hands-on information assurance educational exercises for use in the UMBC undergraduate and graduate curricula. Exercise topics comprise buffer overflow attacks, vulnerability scanning, password security and policy, and flaws in the Wired Equivalent Privacy (WEP) protocol. During each exercise, each student carries out structured activities using a laptop from a mobile cart that can be rolled into any classroom. These dedicated, isolated machines permit a student to make mistakes safely, even while acting as the system administrator, without adversely affecting any other user. Each exercise is organized in a modular fashion to facilitate varied use for different courses, levels, and available time. Our experiences delivering these exercises show that practical hands-on activities motivate students and enhance learning. In this paper we describe our exercises and share lessons learned, including the importance of careful planning, ethical considerations, the rapid obsolescence of tools, and the difficulty of including exercises in already busy courses. ItemDynamic Sprites(ACM, 2013-11-06) Jones, Ben; Popovic, Jovan; McCann, James; Li, Wilmot; Bargteil, AdamTraditional methods for creating dynamic objects and characters from static drawings involve careful tweaking of animation curves and/or simulation parameters. Sprite sheets offer a more drawing-centric solution, but they do not encode timing information or the logic that determines how objects should transition between poses and cannot generalize outside the given drawings. We present an approach for creating dynamic sprites that leverages sprite sheets while addressing these limitations. In our system, artists create a drawing, deform it to specify a small number of example poses, and indicate which poses can be interpolated. To make the object move, we design a procedural simulation to navigate the pose manifold in response to external or user-controlled forces. Powerful artistic control is achieved by allowing the artist to specify both the pose manifold and how it is navigated, while physics is leveraged to provide timing and generality. We used our method to create sprites with a range of different dynamic properties. ItemEnhancements to Model-reduced Fluid Simulation(ACM, 2013-11-06) Gerszewski, Dan; Kavan, Ladislav; Sloan, Peter-Pike; Bargteil, Adam W.We present several enhancements to model-reduced fluid simulation that allow improved simulation bases and two-way solid-fluid coupling. Specifically, we present a basis enrichment scheme that allows us to combine data driven or artistically derived bases with more general analytic bases derived from Laplacian Eigenfunctions. We handle two-way solid-fluid coupling in a time-splitting fashion—we alternately timestep the fluid and rigid body simulators, while taking into account the effects of the fluid on the rigid bodies and vice versa. We employ the vortex panel method to handle solid-fluid coupling and use dynamic pressure to compute the effect of the fluid on rigid bodies. ItemFluid Simulation on Unstructured Quadrilateral Surface MeshesBhattacharya, Haimasree; Levine, Joshua A.; Bargteil, Adam W.In this paper, we present a method for fluid simulation on unstructured quadrilateral surface meshes. We solve the Navier-Stokes equations by performing the traditional steps of fluid simulation, semi-Lagrangian advection and pressure projection, directly on the surface. We include level-set based front-tracking for visualizing “liquids,” while we use densities to visualize “smoke.” We demonstrate our method on a variety of meshes and create an assortment of visual effects ItemKiloGrams: Very Large N-Grams for Malware Classification(2019-08-01) Raff, Edward; Fleming, William; Zak, Richard; Anderson, Hyrum; Finlayson, Bill; Nicholas, Charles; McLean, MarkN-grams have been a common tool for information retrieval and machine learning applications for decades. In nearly all previous works, only a few values of n are tested, with n>6 being exceedingly rare. Larger values of n are not tested due to computational burden or the fear of overfitting. In this work, we present a method to find the top-k most frequent n-grams that is 60× faster for small n, and can tackle large n≥1024. Despite the unprecedented size of n considered, we show how these features still have predictive ability for malware classification tasks. More important, large n-grams provide benefits in producing features that are interpretable by malware analysis, and can be used to create general purpose signatures compatible with industry standard tools like Yara. Furthermore, the counts of common n-grams in a file may be added as features to publicly available human-engineered features that rival efficacy of professionally-developed features when used to train gradient-boosted decision tree models on the EMBER dataset. ItemA Level-set Method for Skinning Animated Particle Data(ACM, 2011-08-07) Bhatacharya, Haimasree; Gao, Yue; Bargteil, AdamIn this paper, we present a straightforward, easy to implement method for particle skinning—generating surfaces from animated particle data. We cast the problem in terms of constrained optimization and solve the optimization using a level-set approach. The optimization seeks to minimize the thin-plate energy of the surface, while staying between surfaces defined by the union of spheres centered at the particles. Our approach skins each frame independently while preserving the temporal coherence of the underlying particle animation. Thus, it is well-suited for environments where particle skinning is treated as a post-process, with each frame generated in parallel. We demonstrate our method on data generated by a variety of fluid simulation techniques and simple particle systems ItemModeling phase noise in high-power photodetectors(IEEE, 2019-08-22) Mahabadi, Seyed Ehsan Jamali; Carruthers, Thomas F.; Menyuk, Curtis R.We describe the simulation model that we use to calculate the impulse response and phase noise in a modified unitraveling carrier (MUTC) photodetector using the drift-diffusion equations while avoiding computationally expensive Monte Carlo simulations. ItemMultiphase flow of immiscible fluids on unstructured moving meshes(ACM, 2013-07-03) Misztal, M. K.; Erleben, K.; Bargteil, A.; Fursund, J.; Christensen, B. Bunch; Bærentzen, J. A.; Bridson, R.In this paper, we present a method for animating multiphase flow of immiscible fluids using unstructured moving meshes. Our underlying discretization is an unstructured tetrahedral mesh, the deformable simplicial complex (DSC), that moves with the flow in a Lagrangian manner. Mesh optimization operations improve element quality and avoid element inversion. In the context of multiphase flow, we guarantee that every element is occupied by a single fluid and, consequently, the interface between fluids is represented by a set of faces in the simplicial complex. This approach ensures that the underlying discretization matches the physics and avoids the additional book-keeping required in grid-based methods where multiple fluids may occupy the same cell. Our Lagrangian approach naturally leads us to adopt a finite element approach to simulation, in contrast to the finite volume approaches adopted by a majority of fluid simulation techniques that use tetrahedral meshes. We characterize fluid simulation as an optimization problem allowing for full coupling of the pressure and velocity fields and the incorporation of a second-order surface energy. We introduce a preconditioner based on the diagonal Schur complement and solve our optimization on the GPU. We provide the results of parameter studies as well as a performance analysis of our method. ItemA Peridynamic Perspective on Spring-Mass Fracture(ACM, 2014-07-21) Levine, J. A.; Bargteil, A. W.; Corsi, C.; Tessendorf, J.; Geist, R.The application of spring-mass systems to the animation of brittle fracture is revisited. The motivation arises from the recent popularity of peridynamics in the computational physics community. Peridynamic systems can be regarded as spring-mass systems with two specific properties. First, spring forces are based on a simple strain metric, thereby decoupling spring stiffness from spring length. Second, masses are connected using a distance-based criterion. The relatively large radius of influence typically leads to a few hundred springs for every mass point. Spring-mass systems with these properties are shown to be simple to implement, trivially parallelized, and well-suited to animating brittle fracture. ItemA Point-based Method for Animating Elastoplastic Solids(ACM, 2009-08-01) Gerszewski, Dan; Bhattacharya, Haimasree; Bargteil, Adam W.In this paper we describe a point-based approach for animating elastoplastic materials. Our primary contribution is a simple method for computing the deformation gradient for each particle in the simulation. The deformation gradient is computed for each particle by finding the affine transformation that best approximates the motion of neighboring particles over a single timestep. These transformations are then composed to compute the total deformation gradient that describes the deformation around a particle over the course of the simulation. Given the deformation gradient we can apply arbitrary constitutive models and compute the resulting elastic forces. Our method has two primary advantages: we do not store or compare to an initial rest configuration and we work directly with the deformation gradient. The first advantage avoids poor numerical conditioning and the second naturally leads to a multiplicative model of deformation appropriate for finite deformations. We demonstrate our approach on a number of examples that exhibit a wide range of material behaviors. ItemA Point-based Method for Animating Incompressible Flow(ACM, 2009-08-01) Sin, Funshing; Bargteil, Adam W.; Hodgins, Jessica K.In this paper, we present a point-based method for animating incompressible flow. The advection term is handled by moving the sample points through the flow in a Lagrangian fashion. However, unlike most previous approaches, the pressure term is handled by performing a projection onto a divergence-free field. To perform the pressure projection, we compute a Voronoi diagram with the sample points as input. Borrowing from Finite Volume Methods, we then invoke the divergence theorem and ensure that each Voronoi cell is divergence free. To handle complex boundary conditions, Voronoi cells are clipped against obstacle boundaries and free surfaces. The method is stable, flexible and combines many of the desirable features of point-based and grid-based methods. We demonstrate our approach on several examples of splashing and streaming liquid and swirling smoke. ItemPunchscan: Introduction and System Definition of a High-Integrity Election System(2006-05) Fisher, Kevin; Carback, Richard; Sherman, Alan T.Punchscan is a unique hybrid paper/electronic voting system concept. As a receipt-based system, Punchscan provides high voter privacy and election integrity, yet it does not rely on the complex and fragile electronic voting machines found in many current implementations. In this paper, we define the Punchscan system and voting protocol, including the people, objects and events involved and the ways they interact. We also trace the flow of data throughout the election process. This definition will aid those implementing the Punchscan system, but also lays a foundation for critical analysis and discussion within the voting research community. ItemQuantifying Network Denial of Service: A Location Service Case Study(Springer, Berlin, Heidelberg, 2001-10-24) Chen, Yan; Bargteil, Adam; Bindel, David; Katz, Randy H.; Kubiatowicz, JohnNetwork Denial of Service (DoS) attacks are increasing in frequency, severity and sophistication, making it desirable to measure the resilience of systems to DoS attacks. In this paper, we propose a simulation-based methodology and apply it to attacks on object location services such as DNS. Our results allow us to contrast the DoS resilience of three distinct architectures for object location. ItemStrain limiting for clustered shape matching(ACM, 2014-11-06) Bargteil, Adam W.; Jones, BenIn this paper, we advocate explicit symplectic Euler integration and strain limiting in a shape matching simulation framework. The resulting approach resembles not only previous work on shape matching and strain limiting, but also the recently popular position-based dynamics. However, unlike this previous work, our approach reduces to explicit integration under small strains, but remains stable in the presence of non-linearities.