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96
Disco: Running commodity operating systems on scalable multiprocessors
 ACM Transactions on Computer Systems
, 1997
"... In this paper we examine the problem of extending modern operating systems to run efficiently on largescale shared memory multiprocessors without a large implementation effort. Our approach brings back an idea popular in the 1970s, virtual machine monitors. We use virtual machines to run multiple c ..."
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Cited by 251 (9 self)
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In this paper we examine the problem of extending modern operating systems to run efficiently on largescale shared memory multiprocessors without a large implementation effort. Our approach brings back an idea popular in the 1970s, virtual machine monitors. We use virtual machines to run multiple commodity operating systems on a scalable multiprocessor. This solution addresses many of the challenges facing the system software for these machines. We demonstrate our approach with a prototype called Disco that can run multiple copies of Silicon Graphics ’ IRIX operating system on a multiprocessor. Our experience shows that the overheads of the monitor are small and that the approach provides scalability as well as the ability to deal with the nonuniform memory access time of these systems. To reduce the memory overheads associated with running multiple operating systems, we have developed techniques where the virtual machines transparently share major data structures such as the program code and the file system buffer cache. We use the distributed system support of modern operating systems to export a partial single system image to the users. The overall solution achieves most of the benefits of operating systems customized for scalable multiprocessors yet it can be achieved with a significantly smaller implementation effort. 1
Weighted finitestate transducers in speech recognition
 COMPUTER SPEECH & LANGUAGE
, 2002
"... We survey the use of weighted finitestate transducers (WFSTs) in speech recognition. We show that WFSTs provide a common and natural representation for hidden Markov models (HMMs), contextdependency, pronunciation dictionaries, grammars, and alternative recognition outputs. Furthermore, general tr ..."
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Cited by 199 (5 self)
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We survey the use of weighted finitestate transducers (WFSTs) in speech recognition. We show that WFSTs provide a common and natural representation for hidden Markov models (HMMs), contextdependency, pronunciation dictionaries, grammars, and alternative recognition outputs. Furthermore, general transducer operations combine these representations flexibly and efficiently. Weighted determinization and minimization algorithms optimize their time and space requirements, and a weight pushing algorithm distributes the weights along the paths of a weighted transducer optimally for speech recognition. As an example, we describe a North American Business News (NAB) recognition system built using these techniques that combines the HMMs, full crossword triphones, a lexicon of 40 000 words, and a large trigram grammar into a single weighted transducer that is only somewhat larger than the trigram word grammar and that runs NAB in realtime on a very simple decoder. In another example, we show that the same techniques can be used to optimize lattices for secondpass recognition. In a third example, we show how general automata operations can be used to assemble lattices from different recognizers to improve recognition performance.
Statistical syntaxdirected translation with extended domain of locality
 In Proc. AMTA 2006
, 2006
"... A syntaxdirected translator first parses the sourcelanguage input into a parsetree, and then recursively converts the tree into a string in the targetlanguage. We model this conversion by an extended treetostring transducer that have multilevel trees on the sourceside, which gives our system m ..."
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Cited by 122 (14 self)
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A syntaxdirected translator first parses the sourcelanguage input into a parsetree, and then recursively converts the tree into a string in the targetlanguage. We model this conversion by an extended treetostring transducer that have multilevel trees on the sourceside, which gives our system more expressive power and flexibility. We also define a direct probability model and use a lineartime dynamic programming algorithm to search for the best derivation. The model is then extended to the general loglinear framework in order to rescore with other features like ngram language models. We devise a simpleyeteffective algorithm to generate nonduplicate kbest translations for ngram rescoring. Initial experimental results on EnglishtoChinese translation are presented. 1
ApproximatelyStrategyproof and Tractable MultiUnit Auctions
, 2004
"... We present an approximatelyefficient and approximatelystrategyproof auction mechanism for a singlegood multiunit allocation problem. The bidding language allows marginaldecreasing piecewise constant curves and quantitybased side constraints. We develop a fully polynomialtime approximation sch ..."
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Cited by 63 (12 self)
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We present an approximatelyefficient and approximatelystrategyproof auction mechanism for a singlegood multiunit allocation problem. The bidding language allows marginaldecreasing piecewise constant curves and quantitybased side constraints. We develop a fully polynomialtime approximation scheme for the multiunit allocation problem, which computes a approximation in worstcase time , given bids each with a constant number of pieces. We integrate this approximation scheme within a VickreyClarke Groves mechanism and compute payments for an asymptotic cost of ! . The maximal possible gain from manipulation to a bidder in the combined scheme is bounded by 429416716 " is the total surplus in the efficient outcome.
The pitfalls of verifying floatingpoint computations
 ACM Transactions on programming languages and systems
"... Current critical systems often use a lot of floatingpoint computations, and thus the testing or static analysis of programs containing floatingpoint operators has become a priority. However, correctly defining the semantics of common implementations of floatingpoint is tricky, because semantics ma ..."
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Cited by 56 (3 self)
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Current critical systems often use a lot of floatingpoint computations, and thus the testing or static analysis of programs containing floatingpoint operators has become a priority. However, correctly defining the semantics of common implementations of floatingpoint is tricky, because semantics may change according to many factors beyond sourcecode level, such as choices made by compilers. We here give concrete examples of problems that can appear and solutions for implementing in analysis software. 1
Radix Sort For Vector Multiprocessors
 In Proceedings Supercomputing '91
, 1991
"... We have designed a radix sort algorithm for vector multiprocessors and have implemented the algorithm on the CRAY YMP. On one processor of the YMP, our sort is over 5 times faster on large sorting problems than the optimized library sort provided by CRAY Research. On eight processors we achieve a ..."
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Cited by 50 (6 self)
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We have designed a radix sort algorithm for vector multiprocessors and have implemented the algorithm on the CRAY YMP. On one processor of the YMP, our sort is over 5 times faster on large sorting problems than the optimized library sort provided by CRAY Research. On eight processors we achieve an additional speedup of almost 5, yielding a routine over 25 times faster than the library sort. Using this multiprocessor version, we can sort at a rate of 15 million 64bit keys per second. Our sorting algorithm is adapted from a dataparallel algorithm previously designed for a highly parallel Single Instruction Multiple Data (SIMD) computer, the Connection Machine CM2. To develop our version we introduce three general techniques for mapping dataparallel algorithms ontovector multiprocessors. These techniques allow us to fully vectorize and parallelize the algorithm. The paper also derives equations that model the performance of our algorithm on the YMP. These equations are then used t...
APPROXIMATING THE MINIMUM EQUIVALENT DIGRAPH
, 1995
"... The minimum equivalent graph (MEG) problem is as follows: given a directed graph, find a smallest subset of the edges that maintains all teachability relations between nodes. This problem is NPhard; this paper gives an approximation algorithm achieving a performance guarantee of about 1.64 in poly ..."
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Cited by 43 (2 self)
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The minimum equivalent graph (MEG) problem is as follows: given a directed graph, find a smallest subset of the edges that maintains all teachability relations between nodes. This problem is NPhard; this paper gives an approximation algorithm achieving a performance guarantee of about 1.64 in polynomial time. The algorithm achieves a performance guarantee of 1.75 in the time required for transitive closure. The heart of the MEG problem is the minimum strongly connected spanning subgraph (SCSS) problemthe MEG problem restricted to strongly connected digraphs. For the minimum SCSS problem, the paper gives apractical, nearly lineartime implementation achieving a performance guarantee of 1.75. The algorithm and its analysis are based on the simple idea of contracting long cycles. The analysis applies directly to2EXCHANCE, a general "local improvement" algorithm, showing that its performance guarantee is 1.75.
A perceptiondriven autonomous urban vehicle
 Journal of Field Robotics
, 2008
"... This paper describes the architecture and implementation of an autonomous passenger vehicle designed to navigate using locally perceived information in preference to potentially inaccurate or incomplete map data. The vehicle architecture was designed to handle the original DARPA Urban Challenge requ ..."
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Cited by 41 (10 self)
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This paper describes the architecture and implementation of an autonomous passenger vehicle designed to navigate using locally perceived information in preference to potentially inaccurate or incomplete map data. The vehicle architecture was designed to handle the original DARPA Urban Challenge requirements of perceiving and navigating a road network with segments defined by sparse waypoints. The vehicle implementation includes many heterogeneous sensors with significant communications and computation bandwidth to capture and process highresolution, highrate sensor data. The output of the comprehensive environmental sensing subsystem is fed into a kinodynamic motion planning algorithm to generate all vehicleFigure 1: Talos in action at the National Qualifying Event. motion. The requirements of driving in lanes, threepoint turns, parking, and maneuvering through obstacle fields are all generated with a unified planner. A key aspect of the planner is its use of closedloop simulation in a Rapidlyexploring Randomized Trees (RRT) algorithm, which can randomly explore the space while efficiently generating smooth trajectories in a dynamic and uncertain environment.
AprilTag: A robust and flexible visual fiducial system
 In Proceedings of the IEEE International Conference on Robotics and Automation
"... Abstract — While the use of naturallyoccurring features is a central focus of machine perception, artificial features (fiducials) play an important role in creating controllable experiments, ground truthing, and in simplifying the development of systems where perception is not the central objective ..."
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Cited by 39 (4 self)
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Abstract — While the use of naturallyoccurring features is a central focus of machine perception, artificial features (fiducials) play an important role in creating controllable experiments, ground truthing, and in simplifying the development of systems where perception is not the central objective. We describe a new visual fiducial system that uses a 2D bar code style “tag”, allowing full 6 DOF localization of features from a single image. Our system improves upon previous systems, incorporating a fast and robust line detection system, a stronger digital coding system, and greater robustness to occlusion, warping, and lens distortion. While similar in concept to the ARTag system, our method is fully open and the algorithms are documented in detail. I.
Optimal Energy Aware Clustering in Sensor Networks
, 2002
"... Sensor networks is among the fastest growing technologies that have the potential of changing our lives drastically. These collaborative, dynamic and distributed computing and communicating systems will be self organizing. They will have capabilities of distributing a task among themselves for effic ..."
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Cited by 38 (1 self)
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Sensor networks is among the fastest growing technologies that have the potential of changing our lives drastically. These collaborative, dynamic and distributed computing and communicating systems will be self organizing. They will have capabilities of distributing a task among themselves for efficient computation. There are many challenges in implementation of such systems: energy dissipation and clustering being one of them. In order to maintain a certain degree of service quality and a reasonable system lifetime, energy needs to be optimized at every stage of system operation. Sensor node clustering is another very important optimization problem. Nodes that are clustered together will easily be able to communicate with each other. Considering energy as an optimization parameter while clustering is imperative. In this paper we study the theoretical aspects of the clustering problem in sensor networks with application to energy optimization. We illustrate an optimal algorithm for clustering the sensor nodes such that each cluster (which has a master) is balanced and the total distance between sensor nodes and master nodes is minimized. Balancing the clusters is needed for evenly distributing the load on all master nodes. Minimizing the total distance helps in reducing the communication overhead and hence the energy dissipation. This problem (which we call balanced kclustering) is modeled as a mincost flow problem which can be solved optimally using existing techniques.