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29th Annual acm symposium on applied computing, SAC 2014

作者： Wang, Mingyang Hu, Yiming Department of Electrical Engineering and Computing Systems University of Cincinnati Cincinnati OH 45221 United States

ISBN: (纸本)9781450324694

Although the many benefits delivered by Solid State Disks (SSDs), they also pose some unique and serious challenges to I/O and file system designers. Unlike HDDs and other memory devices, SSDs cannot perform in-place updates. A block has to be erased before it can be re-written. Moreover, the costs of different SSD operations are highly asymmetric. A write operation in an SSD is an order of magnitude slower than a read operation, and an erase operation is in turn an order of magnitude slower than a write. Moreover, a block can endure only a limited number of erasures before it wears out. Most SSDs employ a log-structured Flash-Translation-Layer (FTL) to solve the not-in-place update problem. The unique operations of the FTLs, together with the asymmetric overheads of different operations, imply that many traditional solutions optimized for HDDs do not work well for SSDs. For example, sequential writes that are not perfectly aligned to the flash block boundary, may reduce performance and increase wearing overhead. In this paper, we proposed a novel I/O scheduler which is based on fine-grained access patterns in a per-process per-stream manner. These patterns are used to guide a set of novel scheduling policies, including pre-alignment, inner-padding, write merging, merging-and-splitting, to improve the write performance of SSDs that adopt log-structured FTLs. Simulation results show that these policies can improve write performance by up to 60%. Moreover, the schemes reduce SSD erasure cycle by up to 64%, which is directly translated to a major improvement on the lifespan of SSDs. Copyright 2014 acm.

关键词： Merging

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Finding targets with the nearest favor neighbor and farthest disfavor neighbor by a skyline query 14

Finding targets with the nearest favor neighbor and farthest...

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29th Annual acm symposium on applied computing, SAC 2014

作者： Lin, Yi-Wen Wang, En Tzu Chiang, Chieh-Feng Chen, Arbee L.P. Department of Computer Science National Tsing Hua University Hsinchu Taiwan Cloud Computing Center for Mobile Application Industrial Technology Research Institute Hsinchu Taiwan Department of Computer Science National Chengchi University Taipei Taiwan

ISBN: (纸本)9781450324694

Finding the nearest neighbors and finding the farthest neighbors are fundamental problems in spatial databases. Consider two sets of data points in a two-dimensional data space, which represent a set of favor locations F, such as libraries and schools, and a set of disfavor locations D, such as dumps and gambling houses. Given another set of data points C in this space as houses for rent, one who needs to rent a house may need a recommendation which takes into account the favor and disfavor locations. To solve this problem, a new two-dimensional data space is employed, in which dimension X describes the distance from a data point c in C to its nearest neighbor in D and dimension Y describes the distance from c to its farthest neighbor in F. Notice that the larger value is preferred in dimension X while the smaller value is preferred in dimension Y. Following the above dominance rule, the recommendation for the house renting can be achieved by a skyline query. A naïve method to processing this query is 1) to find the nearest neighbor from D and the farthest neighbor from F for each data point in C and then 2) to construct a new two-dimensional data space based on the results from 1) and to apply any of the existing skyline algorithms to get the answer. In this paper, based on the quad-tree index, we propose an efficient algorithm to answer this query by combining the above two steps. A series of experiments with synthetic data and real data are performed to evaluate this approach and the experiment results demonstrate the efficiency of the approach. Copyright 2014 acm.

关键词： Location

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Distributed Approximation Algorithms for Weighted Shortest Paths 14

Distributed Approximation Algorithms for Weighted Shortest P...

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46th Annual acm symposium on Theory of computing (STOC)

作者： Nanongkai, Danupon Brown Univ ICERM Providence RI 02912 USA Nanyang Technol Univ Singapore 637371 Singapore

ISBN: (纸本)9781450327107

A distributed network is modeled by a graph having n nodes (processors) and diameter D. We study the time complexity of approximating weighted (undirected) shortest paths on distributed networks with a O(log n) bandwidth restriction on edges (the standard synchronous CONGEST model). The question whether approximation algorithms help speed up the shortest paths and distance computation (more precisely distance computation) was raised since at least 2004 by Elkin (SIGACT News 2004). The unweighted case of this problem is well-understood while its weighted counterpart is fundamental problem in the area of distributed approximation algorithms and remains widely open. We present new algorithms for computing both single-source shortest paths (SSSP) and all-pairs shortest paths (APSP) in the weighted case. Our main result is an algorithm for SSS P. Previous results are the classic O(n)-time Bellman-Ford algorithm and an O(n(1/2+1/2k) +D)-time (8k inverted right perpendicularlog (k +1)inverted left perpendicular - 1)-approximation algorithm, for any integer k >= 1, which follows from the result of Lenzen and Patt-Shamir (STOC 2013). (Note that Lenzen and Patt-Shamir in fact solve a harder problem, and we use O(.) to hide the O(poly log n) term.) We present an O(n(1/2)D(1/4) D) time (1 + o(1))-approximation algorithm for SSS P. This algorithm is sublinear-time as long as D is sublinear, thus yielding a sublinear-time algorithm with almost optimal solution. When D is small, our running time matches the lower bound of Omega(n(1/2) D) by Das Sarma et al. (SICOMP 2012), which holds even when D = Theta(log n), up to a poly log n factor. As a by-product of our technique, we obtain a simple O(n)-time (1-1 o(1))-approximation algorithm for APSP, improving the previous a(n)-time O(1)-approximation algorithm following from the results of Lenzen and Patt-Shamir. We also prove a matching lower bound. Our techniques also yield an O(n(1/2)) time algorithm on fully-connected networks, whic

关键词： distributed computing graph algorithms single-source shortest paths all-pairs shortest paths time complexity CONGEST model lower bounds

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computing stimulation voltage in a bipolar electrode configuration to avoid side effects during deep brain stimulation

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SENSORS AND ACTUATORS A-PHYSICAL 2015年 233卷 9-14页

作者： Chuang, Wei-Yi Chao, Paul C. -P. Chen, Shin-Yuan Tsai, Sheng-Tzung Young, Kuu-Young Ting, Ta-Wei Natl Chiao Tung Univ Dept Elect Engn Hsinchu Taiwan Buddhist Tzu Chi Gen Hosp Dept Neurosurg Hualien Taiwan Tzu Chi Univ Dept Med Hualien Taiwan Yuanpei Univ Dept Biomed Engn Hsinchu Taiwan

Deep brain stimulation (DBS) in the subthalamic nucleus (STN) has been applied for advanced Parkinson's disease (PD). In clinical practices, monopolar configuration is often utilized based on clinical efficiency. Meanwhile, the volume of tissue activated (VTA) by DBS is estimated for controlling and/or limiting the stimulated region. However, side effects like dyskinesia and tremor were accompanied during stimulation. Most studies had found that bipolar stimulation is an alternative approach for side effects avoidance. The goal of this paper is to develop a quantified relationship of stimulation voltage from monopolar to bipolar configuration to improve neural stimulation. In this paper, an electromagnetic finite element model is first built for a patient-specific physiological brain model, which is established by magnetic resonance imaging (MRI) data. The model is then used for finite element analysis (PEA) to estimate VTA with varied electrode voltage in monopolar and bipolar configurations. With the goals to avoid side effects and achieve symptoms suppression, the stimulation voltage of bipolar configuration is successfully computerized based on the electromagnetic PEA simulations. Experiments are conducted successfully to validate simulation results. (C) 2015 Elsevier B.V. All rights reserved.

关键词： Deep brain stimulation (DBS) Volume of tissue activated (VTA) Side effects Stimulation configuration Magnetic resonance imaging (MRI) Finite element analysis (FEA)

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28th Annual acm symposium on applied computing, SAC 2013

28th Annual ACM Symposium on Applied Computing, SAC 2013

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28th Annual acm symposium on applied computing, SAC 2013

ISBN: (纸本)9781450316569

The proceedings contain 328 papers. The topics discussed include: spatial interpolation: an analytical comparison between kriging and RBF networks;faster construction of ball-partitioning-based metric access methods;a multiple feature vector framework for forest species recognition;towards skeleton biometric identification using the Microsoft kinect sensor;convexity local contour sequences for gesture recognition;an evolutionary spline fitting algorithm for identifying filamentous cyanobacteria;gesture unit segmentation using support vector machines: segmenting gestures from rest positions;a data reduction and organization approach for efficient image annotation;an intelligent building that listens to your needs;a collective robotic architecture in search and rescue scenarios;performance based task assignment in multi-robot patrolling;and towards a domain specific modeling language for agent-based models in land use science.

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On efficient algorithms for computing parametric local cohomology classes associated with semi-quasihomogeneous singularities and standard bases 14

On efficient algorithms for computing parametric local cohom...

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2014 39th International symposium on Symbolic and Algebraic Computation, ISSAC 2014

作者： Nabeshima, Katsusuke Tajima, Shinichi Institute of Socio-Arts and Sciences University of Tokushima 1-1 Minamijosanjima Tokushima Japan Graduate School of Pure and Applied Sciences University of Tsukuba 1-1-1 Tennoudai Tsukuba Japan

ISBN: (纸本)9781450325011

A new algorithm is given for computing parametric local cohomology classes associated with semi-quasihomogeneous singularities. The essential point of the proposed algorithm involves Poincaré polynomials and weighted degrees. The proposed algorithm gives a suitable decomposition of the parameter space depending on the structure of the parametric local cohomology classes. As an application, an algorithm for computing parametric standard bases of zerodimensional ideals, is given. These algorithms work for nonparametric cases, too. Copyright 2014 acm.

关键词： Topology

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Extracting logical structure and identifying stragglers in parallel execution traces 14

Extracting logical structure and identifying stragglers in p...

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2014 19th acm SIGPLAN symposium on Principles and Practice of Parallel Programming, PPoPP 2014

作者： Isaacs, Katherine E. Gamblin, Todd Bhatele, Abhinav Bremer, Peer-Timo Schulz, Martin Hamann, Bernd Department of Computer Science University of California Davis United States Center for Applied Scientific Computing Lawrence Livermore National Laboratory United States

ISBN: (纸本)9781450326568

We introduce a new approach to automatically extract an idealized logical structure from a parallel execution trace. We use this structure to define intuitive metrics such as the lateness of a process involved in a parallel execution. By analyzing and illustrating traces in terms of logical steps, we leverage a developer's understanding of the happened-before relations in a parallel program. This technique can uncover dependency chains, elucidate communication patterns, and highlight sources and propagation of delays, all of which may be obscured in a traditional trace visualization.

关键词： Visualization

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Can Quantum Communication Speed Up Distributed Computation? 14

Can Quantum Communication Speed Up Distributed Computation?

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acm symposium on Principles of Distributed computing (PODC)

作者： Elkin, Michael Klauck, Hartmut Nanongkai, Danupon Pandurangan, Gopal Ben Gurion Univ Negev Dept Comp Sci Beer Sheva Israel Nanyang Technol Univ Singapore Singapore Ctr Quantum Technol Singapore Singapore Univ Vienna Fac Comp Sci Vienna Austria Brown Univ Providence RI 02912 USA

ISBN: (纸本)9781450329446

The focus of this paper is on quantum distributed computation, where we investigate whether quantum communication can help in speeding up distributed network algorithms. Our main result is that for certain fundamental network problems such as minimum spanning tree, minimum cut, and shortest paths, quantum communication does not help in substantially speeding up distributed algorithms for these problems compared to the classical setting. In order to obtain this result, we extend the technique of Das Sarma et al. [SICOMP 2012] to obtain a uniform approach to prove non-trivial lower bounds for quantum distributed algorithms for several graph optimization (both exact and approximate versions) as well as verification problems, some of which are new even in the classical setting, e.g. tight randomized lower bounds for Hamiltonian cycle and spanning tree verification, answering an open problem of Das Sarma et al., and a lower bound in terms of the weight aspect ratio, matching the upper bounds of Elkin [STOC 2004]. Our approach introduces the Server model and Quantum Simulation Theorem which together provide a connection between distributed algorithms and communication complexity. The Server model is the standard twoparty communication complexity model augmented with additional power;yet, most of the hardness in the two-party model is carried over to this new model. The Quantum Simulation Theorem carries this hardness further to quantum distributed computing. Our techniques, except the proof of the hardness in the Server model, require very little knowledge in quantum computing, and this can help overcoming a usual impediment in proving bounds on quantum distributed algorithms. In particular, if one can prove a lower bound for distributed algorithms for a certain problem using the technique of Das Sarma et al., it is likely that such lower bound can be extended to the quantum setting using tools provided in this paper and without the need of knowledge in quantum computing.

关键词： distributed computing graph algorithms quantum communication time complexity lower bound CONGEST model

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A cubic algorithm for computing gaussian volume

A cubic algorithm for computing gaussian volume

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25th Annual acm-SIAM symposium on Discrete Algorithms, SODA 2014

作者： Cousins, Ben Vempala, Santosh Georgia Tech United States

ISBN: (纸本)9781611973389

We present randomized algorithms for sampling the standard Gaussian distribution restricted to a convex set and for estimating the Gaussian measure of a convex set, in the general membership oracle model. The complexity of the integration algorithm is 0*(n3) while the complexity of the sampling algorithm is 0*(n3) for the first sample and 0*(n2) for every subsequent sample. These bounds improve on the corresponding state-of-the-art by a factor of n. Our improvement comes from several aspects: better isoperimetry, smoother annealing, avoiding transformation to isotropic position and the use of the "speedy walk" in the analysis. Copyright © 2014 by the Society for Industrial and applied Mathematics.

关键词： Gaussian distribution

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Approximating local homology from samples

Approximating local homology from samples

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25th Annual acm-SIAM symposium on Discrete Algorithms, SODA 2014

作者： Skraba, Primoz Wang, Bei Možef Stefan Institute Slovenia Scientific Computing and Imaging Institute University of Utah United States

ISBN: (纸本)9781611973389

Recently, multi-scale notions of local homology (a variant of persistent homology) have been used to study the local structure of spaces around a given point from a point cloud sample. Current reconstruction guarantees rely on constructing embedded complexes which become difficult to construct in higher dimensions. We show that the persistence diagrams used for estimating local homology can be approximated using families of Vietoris-Rips complexes, whose simpler construction are robust in any dimension. To the best of our knowledge, our results, for the first time make applications based on local homology, such as stratification learning, feasible in high dimensions. Copyright © 2014 by the Society for Industrial and applied Mathematics.

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