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Improving the scalability of data center networks with trafficaware virtual machine placement
 in Proc. of INFOCOM’10
, 2010
"... Abstract—The scalability of modern data centers has become a practical concern and has attracted significant attention in recent years. In contrast to existing solutions that require changes in the network architecture and the routing protocols, this paper proposes using trafficaware virtual machin ..."
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Cited by 83 (2 self)
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Abstract—The scalability of modern data centers has become a practical concern and has attracted significant attention in recent years. In contrast to existing solutions that require changes in the network architecture and the routing protocols, this paper proposes using trafficaware virtual machine (VM) placement to improve the network scalability. By optimizing the placement of VMs on host machines, traffic patterns among VMs can be better aligned with the communication distance between them, e.g. VMs with large mutual bandwidth usage are assigned to host machines in close proximity. We formulate the VM placement as an optimization problem and prove its hardness. We design a twotier approximate algorithm that efficiently solves the VM placement problem for very large problem sizes. Given the significant difference in the traffic patterns seen in current data centers and the structural differences of the recently proposed data center architectures, we further conduct a comparative analysis on the impact of the traffic patterns and the network architectures on the potential performance gain of trafficaware VM placement. We use traffic traces collected from production data centers to evaluate our proposed VM placement algorithm, and we show a significant performance improvement compared to existing generic methods that do not take advantage of traffic patterns and data center network characteristics. I.
A linear nongaussian acyclic model for causal discovery
 J. Machine Learning Research
, 2006
"... In recent years, several methods have been proposed for the discovery of causal structure from nonexperimental data. Such methods make various assumptions on the data generating process to facilitate its identification from purely observational data. Continuing this line of research, we show how to ..."
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Cited by 74 (24 self)
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In recent years, several methods have been proposed for the discovery of causal structure from nonexperimental data. Such methods make various assumptions on the data generating process to facilitate its identification from purely observational data. Continuing this line of research, we show how to discover the complete causal structure of continuousvalued data, under the assumptions that (a) the data generating process is linear, (b) there are no unobserved confounders, and (c) disturbance variables have nonGaussian distributions of nonzero variances. The solution relies on the use of the statistical method known as independent component analysis, and does not require any prespecified timeordering of the variables. We provide a complete Matlab package for performing this LiNGAM analysis (short for Linear NonGaussian Acyclic Model), and demonstrate the effectiveness of the method using artificially generated data and realworld data.
InformationTheoretic Control of Multiple Sensor Platforms
, 2002
"... Ben Grocholsky Doctor of Philosophy The University of Sydney March 2002 InformationTheoretic Control of This thesis is concerned with the development of a consistent, informationtheoretic basis for understanding of coordination and cooperation decentralised multisensor multiplatform systems. Au ..."
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Cited by 69 (5 self)
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Ben Grocholsky Doctor of Philosophy The University of Sydney March 2002 InformationTheoretic Control of This thesis is concerned with the development of a consistent, informationtheoretic basis for understanding of coordination and cooperation decentralised multisensor multiplatform systems. Autonomous systems composed of multiple sensors and multiple platforms potentially have significant importance in applications such as defence, search and rescue, mining or intelligent manufacturing. However, the e#ective use of multiple autonomous systems requires that an understanding be developed of the mechanisms of coordination and cooperation between component systems in pursuit of a common goal. A fundamental, quantitative, understanding of coordination and cooperation between decentralised autonomous systems is the main goal of this thesis.
Frequency Assignment Problems
 HANDBOOK OF COMBINATORIAL OPTIMIZATION
, 1999
"... The ever growing number of wireless communications systems deployed around the globe have made the optimal assignment of a limited radio frequency spectrum a problem of primary importance. At issue are planning models for permanent spectrum allocation, licensing, regulation, and network design. Furt ..."
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Cited by 38 (3 self)
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The ever growing number of wireless communications systems deployed around the globe have made the optimal assignment of a limited radio frequency spectrum a problem of primary importance. At issue are planning models for permanent spectrum allocation, licensing, regulation, and network design. Further at issue are online algorithms for dynamically assigning frequencies to users within an established network. Applications include aeronautical mobile, land mobile, maritime mobile, broadcast, land fixed (pointto point), and satellite systems. This paper surveys research conducted by theoreticians, engineers, and computer scientists regarding the frequency assignment problem (FAP) in all of its guises. The paper begins by defining some of the more common types of FAPs. It continues with a discussion on measures of optimality relating to the use of spectrum, models of interference, and mathematical representations of the many FAPs, both in graph theoretic terms, and as mathematical pro...
Tracking and coordination of multiple agents using sensor networks: system design, algorithms and experiments
"... This paper considers the problem of pursuit evasion games (PEGs), where a group of pursuers is required to chase and capture a group of evaders in minimum time with the aid of a sensor network. We assume that a sensor network is previously deployed and provides global observability of the surveilla ..."
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Cited by 37 (13 self)
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This paper considers the problem of pursuit evasion games (PEGs), where a group of pursuers is required to chase and capture a group of evaders in minimum time with the aid of a sensor network. We assume that a sensor network is previously deployed and provides global observability of the surveillance region, allowing an optimal pursuit policy. While sensor networks provide global observability, they cannot provide high quality measurements in a timely manner due to packet losses, communication delays, and false detections. This has been the main challenge in developing a realtime control system using sensor networks. We address this challenge by developing a realtime hierarchical control system which decouples the estimation of evader states from the control of pursuers via multiple layers of data fusion. While a sensor network generates noisy, inconsistent, and bursty measurements, the multiple layers of data fusion convert them into consistent and high quality measurements and forward them to the controllers of pursuers in a timely manner. For this control system, three new algorithms are developed: multisensor fusion, multitarget tracking and multiagent coordination algorithms. The multisensor fusion algorithm converts correlated sensor measurements into position estimates, the multitarget tracking algorithm tracks an unknown number of targets, and the multiagent coordination algorithm coordinates pursuers to capture all evaders in minimum time using a robust minimumtime feedback controller. The combined system is evaluated in simulation and tested in a sensor network deployment. To our knowledge, this paper presents the first demonstration of multitarget tracking using a sensor network without relying on classification.
Swarm Coordination for Pursuit Evasion Games Using Sensor Networks
 Proc. Int’l Conf. Robotics and Automation
, 2005
"... Abstract — In this work we consider the problem of pursuit evasion games (PEGs) where a group of pursuers is required to detect, chase and capture a group of evaders with the aid of a sensor network in minimum time. Differently from standards PEGs where the environment and the location of evaders is ..."
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Cited by 34 (4 self)
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Abstract — In this work we consider the problem of pursuit evasion games (PEGs) where a group of pursuers is required to detect, chase and capture a group of evaders with the aid of a sensor network in minimum time. Differently from standards PEGs where the environment and the location of evaders is unknown and a probabilistic map is built based on the pursuer onboard sensors, here we consider a scenario where a sensor network, previously deployed in the region of concern, can detect the presence of moving vehicles and can relay this information to the pursuers. Here we propose a general framework for the design of a hierarchical control architecture that exploit the advantages of a sensor networks by combining both centralized and decentralized realtime control algorithms. We also propose a coordination scheme for the pursuers to minimize the timetocapture of all evaders. In particular, we focus on PEGs with sensor networks orbiting in space for artificial space debris detection and removal. Index Terms — Sensor networks, pursuit evasion games, vehicle coordination, space vehicles, space debris over the area of interest. This constraint makes designing a cooperative pursuit algorithm harder because lack of complete observability only allows for suboptimal pursuit policies. See Figure 1(left). Furthermore, a smart evaders makes the mapbuilding process dynamic since their location changes over time. The maplearning phase is, by itself, timeconsuming and computationally intensive even for simple twodimensional rectilinear environments [5]. Moreover, inaccurate sensors complicate this process and a probabilistic approach is often required [21]. I.
Director, Anthropometry and Biomechanics Laboratory. Responsible for human performance, anthropometry, and biomechanics in the research areas relating to manned spaceflight. Duties included directing the technical activities of professional laboratory sta
 Biometrika
, 2006
"... An important problem in shape analysis is to match configurations of points in space filtering out some geometrical transformation. In this paper we introduce hierarchical models for such tasks, in which the points in the configurations are either unlabelled, or have at most a partial labelling cons ..."
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Cited by 27 (11 self)
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An important problem in shape analysis is to match configurations of points in space filtering out some geometrical transformation. In this paper we introduce hierarchical models for such tasks, in which the points in the configurations are either unlabelled, or have at most a partial labelling constraining the matching, and in which some points may only appear in one of the configurations. We derive procedures for simultaneous inference about the matching and the transformation, using a Bayesian approach. Our model is based on a Poisson process for hidden true point locations; this leads to considerable mathematical simplification and efficiency of implementation. We find a novel use for classical distributions from directional statistics in a conditionally conjugate specification for the case where the geometrical transformation includes an unknown rotation. Throughout, we focus on the case of affine or rigid motion transformations. Under a broad parametric family of loss functions, an optimal Bayesian point estimate of the matching matrix can be constructed, that depends only on a single parameter of the family. Our methods are illustrated by two applications from bioinformatics. The first problem is of matching protein gels in two dimensions, and the second consists of aligning active sites of proteins in three dimensions. In the latter case, we also use information related to the grouping of the amino acids. We discuss some open problems and suggest directions for future work.
Periodic Patterns of Actin Turnover in Lamellipodia and Lamellae of Migrating Epithelial Cells Analyzed by Quantitative Fluorescent Speckle Microscopy
, 2005
"... ABSTRACT We measured actin turnover in lamellipodia and lamellae of migrating cells, using quantitative Fluorescent Speckle Microscopy. Lamellae disassembled at low rates from the front to the back. However, the dominant feature in their turnover was a spatially random pattern of periodic polymeriza ..."
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Cited by 12 (1 self)
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ABSTRACT We measured actin turnover in lamellipodia and lamellae of migrating cells, using quantitative Fluorescent Speckle Microscopy. Lamellae disassembled at low rates from the front to the back. However, the dominant feature in their turnover was a spatially random pattern of periodic polymerization and depolymerization moving with the retrograde flow. Power spectra contained frequencies between 0.5 and 1 cycle/min. The spectra remained unchanged when applying Latrunculin A and Jasplakinolide in low doses, except that additional frequencies occurred beyond 1 cycle/min. Whereas Latrunculin did not change the rate of mean disassembly, Jasplakinolide halted it completely, indicating that the steady state and the dynamics of actin turnover are differentially affected by pharmacological agents. Lamellipodia assembled in recurring bursts at the leading edge and disassembled;2.5 mm behind. Events of polymerization correlated spatially and temporally with transient formation of Arp2/3 clusters. In lamellae, Arp2/3 accumulation and polymerization correlated only spatially, suggesting an Arp2/3independent mechanism for filament nucleation. To acquire these data we had to enhance the resolution of quantitative Fluorescent Speckle Microscopy to the submicron level. Several algorithmic advances in speckle image processing are described enabling the analysis of kinetic and kinematic activities of polymer networks at the level of single speckles.
Coordination and Control of Multiple Spacecraft Using Convex Optimization Techniques
, 2002
"... Formation flying of multiple spacecraft is an enabling technology for many future space science missions. These future missions will,for example, use the highly coordinated, distr#pWkfl ar#p y of vehicles for ear#V mapping inter#(jWp.fl(jj and synthetic aper#icp r#r#ic This thesis pr#V ents coor#Vk ..."
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Cited by 9 (1 self)
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Formation flying of multiple spacecraft is an enabling technology for many future space science missions. These future missions will,for example, use the highly coordinated, distr#pWkfl ar#p y of vehicles for ear#V mapping inter#(jWp.fl(jj and synthetic aper#icp r#r#ic This thesis pr#V ents coor#VkVzzp. and contr#p algor#zVp. designed for a fleet of spacecr# ft. These algor ithms a r# embedded in ahier# r chical fleet ar chitectur # that includes a highlevel coor#V(jjVp for the fleet maneuver# used to for#k r#r# ize,or r##,pWVzW thefor#w)Wzp configur#.flW) and lowlevel contr#VzVw togener#wk and implement the individual contr#V inputs for each vehicle. The tr# jector# and contr#W pr#Ww(zj a r# posed aslinear pr#ar#jp.V) (LP) optimizations to solvefor the minimum fuel maneuver#e The combinedr esult of the highlevel coor#jkwjp.V and lowlevel contr# ller# is a ver# flexible optimization fr amewor k that can be used o#line to analyze aspects of a mission design and inr ealtime as par# of an onb oar# autonomousfor#nomou flying contr#p system. This thesis also investigates sever# cr#zw ical issues associated with the implementation of this for# ation flying appr#WV h. In par#VWkkp.V modifications to the LP algor#jzp. a r#pr# ented to: includer#lud tness tosensor noise, includeactuator constr#r# ts, ensur# that the optimization solutions ar# always feasible, andr educe the LP solution times. Fur#(k(Wp.W( the dynamicsfor the contr#W pr#WV(w ar# analyzed inter#j of two key issues: 1) what dynamics model should be used to specify the desir# d state to maintain a passive aper#ep ; and 2) what dynamics model should be used in the LP tor#pflVVww t the motion about this state. Sever#W linear#.WW models of ther elative dynamics a r# consider#W in this analysis, includi...
Local Search Heuristics for the Multidimensional Assignment Problem
 OF LECTURE NOTES COMP. SCI
, 2009
"... The Multidimensional Assignment Problem (MAP) (abbreviated sAP in the case of s dimensions) is an extension of the wellknown assignment problem. The most studied case of MAP is 3AP, though the problems with larger values of s also have a large number of applications. We consider several known nei ..."
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Cited by 8 (4 self)
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The Multidimensional Assignment Problem (MAP) (abbreviated sAP in the case of s dimensions) is an extension of the wellknown assignment problem. The most studied case of MAP is 3AP, though the problems with larger values of s also have a large number of applications. We consider several known neighborhoods, generalize them and propose some new ones. The heuristics are evaluated both theoretically and experimentally and dominating algorithms are selected. We also demonstrate a combination of two neighborhoods may yield a heuristics which is superior to both of its components.