[{"related_material":{"record":[{"id":"452","relation":"later_version","status":"public"}]},"acknowledgement":"This project was supported in part by the ERC Starting Grant iModel (StG-2012-306877). Emily Whiting is supported by the ETH Zurich / Marie Curie COFUND Postdoctoral Fellowship.","doi":"10.1145/2601097.2601157","article_processing_charge":"No","quality_controlled":"1","abstract":[{"lang":"eng","text":"Spinning tops and yo-yos have long fascinated cultures around the world with their unexpected, graceful motions that seemingly elude gravity. We present an algorithm to generate designs for spinning objects by optimizing rotational dynamics properties. As input, the user provides a solid 3D model and a desired axis of rotation. Our approach then modifies the mass distribution such that the principal directions of the moment of inertia align with the target rotation frame. We augment the model by creating voids inside its volume, with interior fill represented by an adaptive multi-resolution vox-elization. The discrete voxel fill values are optimized using a continuous, nonlinear formulation. Further, we optimize for rotational stability by maximizing the dominant principal moment. We extend our technique to incorporate deformation and multiple materials for cases where internal voids alone are insufficient. Our method is well-suited for a variety of 3D printed models, ranging from characters to abstract shapes. We demonstrate tops and yo-yos that spin surprisingly stably despite their asymmetric appearance. "}],"article_type":"original","publication":"ACM Transactions on Graphics","scopus_import":"1","publisher":"ACM","fulldoi":"https://doi.org/10.1145/2601097.2601157","type":"journal_article","extern":"1","article_number":"96","volume":33,"publication_status":"published","oa_version":"None","status":"public","citation":{"mla":"Bächer, Moritz, et al. “Spin-It: Optimizing Moment of Inertia for Spinnable Objects.” <i>ACM Transactions on Graphics</i>, vol. 33, no. 4, 96, ACM, 2014, doi:<a href=\"https://doi.org/10.1145/2601097.2601157\">10.1145/2601097.2601157</a>.","short":"M. Bächer, E. Whiting, B. Bickel, O. Sorkine Hornung, ACM Transactions on Graphics 33 (2014).","apa":"Bächer, M., Whiting, E., Bickel, B., &#38; Sorkine Hornung, O. (2014). Spin-It: Optimizing moment of inertia for spinnable objects. <i>ACM Transactions on Graphics</i>. ACM. <a href=\"https://doi.org/10.1145/2601097.2601157\">https://doi.org/10.1145/2601097.2601157</a>","ama":"Bächer M, Whiting E, Bickel B, Sorkine Hornung O. Spin-It: Optimizing moment of inertia for spinnable objects. <i>ACM Transactions on Graphics</i>. 2014;33(4). doi:<a href=\"https://doi.org/10.1145/2601097.2601157\">10.1145/2601097.2601157</a>","ieee":"M. Bächer, E. Whiting, B. Bickel, and O. Sorkine Hornung, “Spin-It: Optimizing moment of inertia for spinnable objects,” <i>ACM Transactions on Graphics</i>, vol. 33, no. 4. ACM, 2014.","ista":"Bächer M, Whiting E, Bickel B, Sorkine Hornung O. 2014. Spin-It: Optimizing moment of inertia for spinnable objects. ACM Transactions on Graphics. 33(4), 96.","chicago":"Bächer, Moritz, Emily Whiting, Bernd Bickel, and Olga Sorkine Hornung. “Spin-It: Optimizing Moment of Inertia for Spinnable Objects.” <i>ACM Transactions on Graphics</i>. ACM, 2014. <a href=\"https://doi.org/10.1145/2601097.2601157\">https://doi.org/10.1145/2601097.2601157</a>."},"date_created":"2018-12-11T11:55:35Z","year":"2014","month":"07","author":[{"last_name":"Bächer","first_name":"Moritz","full_name":"Bächer, Moritz"},{"full_name":"Whiting, Emily","first_name":"Emily","last_name":"Whiting"},{"first_name":"Bernd","id":"49876194-F248-11E8-B48F-1D18A9856A87","last_name":"Bickel","full_name":"Bickel, Bernd","orcid":"0000-0001-6511-9385"},{"full_name":"Sorkine Hornung, Olga","first_name":"Olga","last_name":"Sorkine Hornung"}],"publication_identifier":{"eissn":["1557-7368"],"issn":["0730-0301"]},"intvolume":"        33","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","date_published":"2014-07-01T00:00:00Z","date_updated":"2025-08-05T14:20:24Z","publist_id":"4958","title":"Spin-It: Optimizing moment of inertia for spinnable objects","day":"01","issue":"4","_id":"2080","language":[{"iso":"eng"}]},{"status":"public","doi":"10.1145/1899404.1899405","citation":{"short":"A.M. Bronstein, M.M. Bronstein, L.J. Guibas, M. Ovsjanikov, ACM Transactions on Graphics 30 (2011) 1–20.","apa":"Bronstein, A. M., Bronstein, M. M., Guibas, L. J., &#38; Ovsjanikov, M. (2011). Shape google: Geometric words and expressions for invariant shape retrieval. <i>ACM Transactions on Graphics</i>. Association for Computing Machinery. <a href=\"https://doi.org/10.1145/1899404.1899405\">https://doi.org/10.1145/1899404.1899405</a>","ama":"Bronstein AM, Bronstein MM, Guibas LJ, Ovsjanikov M. Shape google: Geometric words and expressions for invariant shape retrieval. <i>ACM Transactions on Graphics</i>. 2011;30(1):1-20. doi:<a href=\"https://doi.org/10.1145/1899404.1899405\">10.1145/1899404.1899405</a>","mla":"Bronstein, Alex M., et al. “Shape Google: Geometric Words and Expressions for Invariant Shape Retrieval.” <i>ACM Transactions on Graphics</i>, vol. 30, no. 1, Association for Computing Machinery, 2011, pp. 1–20, doi:<a href=\"https://doi.org/10.1145/1899404.1899405\">10.1145/1899404.1899405</a>.","ieee":"A. M. Bronstein, M. M. Bronstein, L. J. Guibas, and M. Ovsjanikov, “Shape google: Geometric words and expressions for invariant shape retrieval,” <i>ACM Transactions on Graphics</i>, vol. 30, no. 1. Association for Computing Machinery, pp. 1–20, 2011.","ista":"Bronstein AM, Bronstein MM, Guibas LJ, Ovsjanikov M. 2011. Shape google: Geometric words and expressions for invariant shape retrieval. ACM Transactions on Graphics. 30(1), 1–20.","chicago":"Bronstein, Alex M., Michael M. Bronstein, Leonidas J. Guibas, and Maks Ovsjanikov. “Shape Google: Geometric Words and Expressions for Invariant Shape Retrieval.” <i>ACM Transactions on Graphics</i>. Association for Computing Machinery, 2011. <a href=\"https://doi.org/10.1145/1899404.1899405\">https://doi.org/10.1145/1899404.1899405</a>."},"date_created":"2024-10-15T11:20:55Z","year":"2011","article_processing_charge":"No","month":"01","quality_controlled":"1","author":[{"last_name":"Bronstein","id":"58f3726e-7cba-11ef-ad8b-e6e8cb3904e6","first_name":"Alexander","orcid":"0000-0001-9699-8730","full_name":"Bronstein, Alexander"},{"last_name":"Bronstein","first_name":"Michael M.","full_name":"Bronstein, Michael M."},{"first_name":"Leonidas J.","last_name":"Guibas","full_name":"Guibas, Leonidas J."},{"last_name":"Ovsjanikov","first_name":"Maks","full_name":"Ovsjanikov, Maks"}],"abstract":[{"lang":"eng","text":"The computer vision and pattern recognition communities have recently witnessed a surge of feature-based methods in object recognition and image retrieval applications. These methods allow representing images as collections of “visual words” and treat them using text search approaches following the “bag of features” paradigm. In this article, we explore analogous approaches in the 3D world applied to the problem of nonrigid shape retrieval in large databases. Using multiscale diffusion heat kernels as “geometric words,” we construct compact and informative shape descriptors by means of the “bag of features” approach. We also show that considering pairs of “geometric words” (“geometric expressions”) allows creating spatially sensitive bags of features with better discriminative power. Finally, adopting metric learning approaches, we show that shapes can be efficiently represented as binary codes. Our approach achieves state-of-the-art results on the SHREC 2010 large-scale shape retrieval benchmark."}],"publication":"ACM Transactions on Graphics","scopus_import":"1","intvolume":"        30","publication_identifier":{"issn":["0730-0301"],"eissn":["1557-7368"]},"publisher":"Association for Computing Machinery","fulldoi":"https://doi.org/10.1145/1899404.1899405","type":"journal_article","extern":"1","user_id":"3E5EF7F0-F248-11E8-B48F-1D18A9856A87","date_updated":"2024-12-18T14:59:43Z","date_published":"2011-01-01T00:00:00Z","page":"1-20","title":"Shape google: Geometric words and expressions for invariant shape retrieval","volume":30,"publication_status":"published","day":"01","issue":"1","oa_version":"None","_id":"18433","language":[{"iso":"eng"}]},{"article_processing_charge":"No","publication":"ACM Transactions on Graphics","abstract":[{"text":"We introduce a method for efficiently animating a wide range of deformable materials. We combine a high resolution surface mesh with a tetrahedral finite element simulator that makes use of frequent re-meshing. This combination allows for fast and detailed simulations of complex elastic and plastic behavior. We significantly expand the range of physical parameters that can be simulated with a single technique, and the results are free from common artifacts such as volume-loss, smoothing, popping, and the absence of thin features like strands and sheets. Our decision to couple a high resolution surface with low-resolution physics leads to efficient simulation and detailed surface features, and our approach to creating the tetrahedral mesh leads to an order-of-magnitude speedup over previous techniques in the time spent re-meshing. We compute masses, collisions, and surface tension forces on the scale of the fine mesh, which helps avoid visual artifacts due to the differing mesh resolutions. The result is a method that can simulate a large array of different material behaviors with high resolution features in a short amount of time.","lang":"eng"}],"article_type":"original","doi":"10.1145/1360612.1360646","volume":27,"oa_version":"None","publication_status":"published","publisher":"ACM","main_file_link":[{"url":"http://www.cc.gatech.edu/~turk/my_papers/fast_goop_2008.pdf"}],"extern":"1","type":"journal_article","fulldoi":"https://doi.org/10.1145/1360612.1360646","month":"08","author":[{"full_name":"Wojtan, Christopher J","orcid":"0000-0001-6646-5546","first_name":"Christopher J","last_name":"Wojtan","id":"3C61F1D2-F248-11E8-B48F-1D18A9856A87"},{"last_name":"Turk","first_name":"Greg","full_name":"Turk, Greg"}],"status":"public","OA_type":"closed access","year":"2008","date_created":"2018-12-11T12:05:01Z","citation":{"ieee":"C. Wojtan and G. Turk, “Fast viscoelastic behavior with thin features,” <i>ACM Transactions on Graphics</i>, vol. 27, no. 3. ACM, 2008.","ista":"Wojtan C, Turk G. 2008. Fast viscoelastic behavior with thin features. ACM Transactions on Graphics. 27(3).","chicago":"Wojtan, Chris, and Greg Turk. “Fast Viscoelastic Behavior with Thin Features.” <i>ACM Transactions on Graphics</i>. ACM, 2008. <a href=\"https://doi.org/10.1145/1360612.1360646\">https://doi.org/10.1145/1360612.1360646</a>.","mla":"Wojtan, Chris, and Greg Turk. “Fast Viscoelastic Behavior with Thin Features.” <i>ACM Transactions on Graphics</i>, vol. 27, no. 3, ACM, 2008, doi:<a href=\"https://doi.org/10.1145/1360612.1360646\">10.1145/1360612.1360646</a>.","apa":"Wojtan, C., &#38; Turk, G. (2008). Fast viscoelastic behavior with thin features. <i>ACM Transactions on Graphics</i>. ACM. <a href=\"https://doi.org/10.1145/1360612.1360646\">https://doi.org/10.1145/1360612.1360646</a>","short":"C. Wojtan, G. Turk, ACM Transactions on Graphics 27 (2008).","ama":"Wojtan C, Turk G. Fast viscoelastic behavior with thin features. <i>ACM Transactions on Graphics</i>. 2008;27(3). doi:<a href=\"https://doi.org/10.1145/1360612.1360646\">10.1145/1360612.1360646</a>"},"title":"Fast viscoelastic behavior with thin features","publist_id":"2467","_id":"3760","language":[{"iso":"eng"}],"issue":"3","day":"01","publication_identifier":{"issn":["0730-0301"],"eissn":["1557-7368"]},"intvolume":"        27","date_updated":"2026-06-10T10:33:19Z","date_published":"2008-08-01T00:00:00Z","user_id":"317138e5-6ab7-11ef-aa6d-ffef3953e345"},{"language":[{"iso":"eng"}],"_id":"18431","day":"01","publication_status":"published","oa_version":"None","issue":"4","article_number":"104","title":"Parallel algorithms for approximation of distance maps on parametric surfaces","volume":27,"date_published":"2008-10-01T00:00:00Z","user_id":"3E5EF7F0-F248-11E8-B48F-1D18A9856A87","date_updated":"2024-12-18T14:46:45Z","fulldoi":"https://doi.org/10.1145/1409625.1409626","extern":"1","type":"journal_article","publisher":"Association for Computing Machinery","intvolume":"        27","publication_identifier":{"issn":["0730-0301"],"eissn":["1557-7368"]},"scopus_import":"1","publication":"ACM Transactions on Graphics","abstract":[{"lang":"eng","text":"We present an efficient O(n) numerical algorithm for first-order approximation of geodesic distances on geometry images, where n is the number of points on the surface. The structure of our algorithm allows efficient implementation on parallel architectures. Two implementations on a SIMD processor and on a GPU are discussed. Numerical results demonstrate up to four orders of magnitude improvement in execution time compared to the state-of-the-art algorithms."}],"author":[{"full_name":"Weber, Ofir","first_name":"Ofir","last_name":"Weber"},{"last_name":"Devir","first_name":"Yohai S.","full_name":"Devir, Yohai S."},{"first_name":"Alexander","id":"58f3726e-7cba-11ef-ad8b-e6e8cb3904e6","last_name":"Bronstein","orcid":"0000-0001-9699-8730","full_name":"Bronstein, Alexander"},{"last_name":"Bronstein","first_name":"Michael M.","full_name":"Bronstein, Michael M."},{"first_name":"Ron","last_name":"Kimmel","full_name":"Kimmel, Ron"}],"quality_controlled":"1","month":"10","article_processing_charge":"No","date_created":"2024-10-15T11:20:55Z","doi":"10.1145/1409625.1409626","citation":{"ista":"Weber O, Devir YS, Bronstein AM, Bronstein MM, Kimmel R. 2008. Parallel algorithms for approximation of distance maps on parametric surfaces. ACM Transactions on Graphics. 27(4), 104.","chicago":"Weber, Ofir, Yohai S. Devir, Alex M. Bronstein, Michael M. Bronstein, and Ron Kimmel. “Parallel Algorithms for Approximation of Distance Maps on Parametric Surfaces.” <i>ACM Transactions on Graphics</i>. Association for Computing Machinery, 2008. <a href=\"https://doi.org/10.1145/1409625.1409626\">https://doi.org/10.1145/1409625.1409626</a>.","ieee":"O. Weber, Y. S. Devir, A. M. Bronstein, M. M. Bronstein, and R. Kimmel, “Parallel algorithms for approximation of distance maps on parametric surfaces,” <i>ACM Transactions on Graphics</i>, vol. 27, no. 4. Association for Computing Machinery, 2008.","ama":"Weber O, Devir YS, Bronstein AM, Bronstein MM, Kimmel R. Parallel algorithms for approximation of distance maps on parametric surfaces. <i>ACM Transactions on Graphics</i>. 2008;27(4). doi:<a href=\"https://doi.org/10.1145/1409625.1409626\">10.1145/1409625.1409626</a>","short":"O. Weber, Y.S. Devir, A.M. Bronstein, M.M. Bronstein, R. Kimmel, ACM Transactions on Graphics 27 (2008).","apa":"Weber, O., Devir, Y. S., Bronstein, A. M., Bronstein, M. M., &#38; Kimmel, R. (2008). Parallel algorithms for approximation of distance maps on parametric surfaces. <i>ACM Transactions on Graphics</i>. Association for Computing Machinery. <a href=\"https://doi.org/10.1145/1409625.1409626\">https://doi.org/10.1145/1409625.1409626</a>","mla":"Weber, Ofir, et al. “Parallel Algorithms for Approximation of Distance Maps on Parametric Surfaces.” <i>ACM Transactions on Graphics</i>, vol. 27, no. 4, 104, Association for Computing Machinery, 2008, doi:<a href=\"https://doi.org/10.1145/1409625.1409626\">10.1145/1409625.1409626</a>."},"year":"2008","status":"public"},{"doi":"10.1145/1015706.1015720","article_processing_charge":"No","abstract":[{"lang":"eng","text":"The problem of efficient, interactive foreground/background segmentation in still images is of great practical importance in image editing. Classical image segmentation tools use either texture (colour) information, e.g. Magic Wand, or edge (contrast) information, e.g. Intelligent Scissors. Recently, an approach based on optimization by graph-cut has been developed which successfully combines both types of information. In this paper we extend the graph-cut approach in three respects. First, we have developed a more powerful, iterative version of the optimisation. Secondly, the power of the iterative algorithm is used to simplify substantially the user interaction needed for a given quality of result. Thirdly, a robust algorithm for &quot;border matting&quot; has been developed to estimate simultaneously the alpha-matte around an object boundary and the colours of foreground pixels. We show that for moderately difficult examples the proposed method outperforms competitive tools."}],"publisher":"ACM","main_file_link":[{"url":"http://research.microsoft.com/pubs/67890/siggraph04-grabcut.pdf"}],"fulldoi":"https://doi.org/10.1145/1015706.1015720","extern":"1","type":"conference","page":"309 - 314","volume":23,"publication_status":"published","oa_version":"None","status":"public","citation":{"ista":"Rother C, Kolmogorov V, Blake A. 2004. &#38;quot;GrabCut&#38;quot; - Interactive foreground extraction using iterated graph cuts . SIGGRAPH: Special Interest Group on Computer Graphics and Interactive Techniques vol. 23, 309–314.","chicago":"Rother, Carsten, Vladimir Kolmogorov, and Andrew Blake. “&#38;quot;GrabCut&#38;quot; - Interactive Foreground Extraction Using Iterated Graph Cuts ,” 23:309–14. ACM, 2004. <a href=\"https://doi.org/10.1145/1015706.1015720\">https://doi.org/10.1145/1015706.1015720</a>.","ieee":"C. Rother, V. Kolmogorov, and A. Blake, “&#38;quot;GrabCut&#38;quot; - Interactive foreground extraction using iterated graph cuts ,” presented at the SIGGRAPH: Special Interest Group on Computer Graphics and Interactive Techniques, 2004, vol. 23, no. 3, pp. 309–314.","mla":"Rother, Carsten, et al. <i>&#38;quot;GrabCut&#38;quot; - Interactive Foreground Extraction Using Iterated Graph Cuts </i>. Vol. 23, no. 3, ACM, 2004, pp. 309–14, doi:<a href=\"https://doi.org/10.1145/1015706.1015720\">10.1145/1015706.1015720</a>.","ama":"Rother C, Kolmogorov V, Blake A. &#38;quot;GrabCut&#38;quot; - Interactive foreground extraction using iterated graph cuts . In: Vol 23. ACM; 2004:309-314. doi:<a href=\"https://doi.org/10.1145/1015706.1015720\">10.1145/1015706.1015720</a>","short":"C. Rother, V. Kolmogorov, A. Blake, in:, ACM, 2004, pp. 309–314.","apa":"Rother, C., Kolmogorov, V., &#38; Blake, A. (2004). &#38;quot;GrabCut&#38;quot; - Interactive foreground extraction using iterated graph cuts  (Vol. 23, pp. 309–314). Presented at the SIGGRAPH: Special Interest Group on Computer Graphics and Interactive Techniques, ACM. <a href=\"https://doi.org/10.1145/1015706.1015720\">https://doi.org/10.1145/1015706.1015720</a>"},"date_created":"2018-12-11T12:01:51Z","year":"2004","OA_type":"gold","month":"08","conference":{"name":"SIGGRAPH: Special Interest Group on Computer Graphics and Interactive Techniques"},"author":[{"full_name":"Rother, Carsten","last_name":"Rother","first_name":"Carsten"},{"full_name":"Kolmogorov, Vladimir","first_name":"Vladimir","id":"3D50B0BA-F248-11E8-B48F-1D18A9856A87","last_name":"Kolmogorov"},{"full_name":"Blake, Andrew","first_name":"Andrew","last_name":"Blake"}],"OA_place":"publisher","intvolume":"        23","publication_identifier":{"issn":["0730-0301"],"eissn":["1557-7368"]},"user_id":"317138e5-6ab7-11ef-aa6d-ffef3953e345","date_published":"2004-08-01T00:00:00Z","date_updated":"2026-09-11T12:16:13Z","title":"&quot;GrabCut&quot; - Interactive foreground extraction using iterated graph cuts ","publist_id":"3505","language":[{"iso":"eng"}],"_id":"3179","day":"01","issue":"3"},{"day":"01","issue":"1","language":[{"iso":"eng"}],"_id":"4063","publist_id":"2058","title":"Simulation of simplicity: A technique to cope with degenerate cases in geometric algorithms","date_updated":"2022-02-22T14:58:39Z","date_published":"1990-01-01T00:00:00Z","user_id":"ea97e931-d5af-11eb-85d4-e6957dddbf17","intvolume":"         9","publication_identifier":{"eissn":["1557-7368"],"issn":["0730-0301"]},"author":[{"id":"3FB178DA-F248-11E8-B48F-1D18A9856A87","last_name":"Edelsbrunner","first_name":"Herbert","orcid":"0000-0002-9823-6833","full_name":"Edelsbrunner, Herbert"},{"first_name":"Ernst","last_name":"Mücke","full_name":"Mücke, Ernst"}],"month":"01","citation":{"ama":"Edelsbrunner H, Mücke E. Simulation of simplicity: A technique to cope with degenerate cases in geometric algorithms. <i>ACM Transactions on Graphics</i>. 1990;9(1):66-104. doi:<a href=\"https://doi.org/10.1145/77635.77639\">10.1145/77635.77639</a>","short":"H. Edelsbrunner, E. Mücke, ACM Transactions on Graphics 9 (1990) 66–104.","apa":"Edelsbrunner, H., &#38; Mücke, E. (1990). Simulation of simplicity: A technique to cope with degenerate cases in geometric algorithms. <i>ACM Transactions on Graphics</i>. ACM. <a href=\"https://doi.org/10.1145/77635.77639\">https://doi.org/10.1145/77635.77639</a>","mla":"Edelsbrunner, Herbert, and Ernst Mücke. “Simulation of Simplicity: A Technique to Cope with Degenerate Cases in Geometric Algorithms.” <i>ACM Transactions on Graphics</i>, vol. 9, no. 1, ACM, 1990, pp. 66–104, doi:<a href=\"https://doi.org/10.1145/77635.77639\">10.1145/77635.77639</a>.","chicago":"Edelsbrunner, Herbert, and Ernst Mücke. “Simulation of Simplicity: A Technique to Cope with Degenerate Cases in Geometric Algorithms.” <i>ACM Transactions on Graphics</i>. ACM, 1990. <a href=\"https://doi.org/10.1145/77635.77639\">https://doi.org/10.1145/77635.77639</a>.","ista":"Edelsbrunner H, Mücke E. 1990. Simulation of simplicity: A technique to cope with degenerate cases in geometric algorithms. ACM Transactions on Graphics. 9(1), 66–104.","ieee":"H. Edelsbrunner and E. Mücke, “Simulation of simplicity: A technique to cope with degenerate cases in geometric algorithms,” <i>ACM Transactions on Graphics</i>, vol. 9, no. 1. ACM, pp. 66–104, 1990."},"date_created":"2018-12-11T12:06:43Z","year":"1990","status":"public","publication_status":"published","oa_version":"None","page":"66 - 104","volume":9,"fulldoi":"https://doi.org/10.1145/77635.77639","type":"journal_article","extern":"1","scopus_import":"1","main_file_link":[{"url":"https://dl.acm.org/doi/10.1145/77635.77639"}],"publisher":"ACM","article_type":"original","abstract":[{"text":"This paper describes a general-purpose programming technique, called Simulation of Simplicity, that can be used to cope with degenerate input data for geometric algorithms. It relieves the programmer from the task of providing a consistent treatment for every single special case that can occur. The programs that use the technique tend to be considerably smaller and more robust than those that do not use it. We believe that this technique will become a standard tool in writing geometric software.","lang":"eng"}],"publication":"ACM Transactions on Graphics","article_processing_charge":"No","quality_controlled":"1","acknowledgement":"Research of both authors was supported by Amoco Foundation Faculty Development grant CS 1-6-44862. It was partially carried out while both authors were with the Institutes for Information Processing at the Technical University of Graz, Austria. The first author also acknowledges support by the National Science Foundation under grant CCR-8714565. ","doi":"10.1145/77635.77639"}]