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Articles 1381 - 1410 of 1828

Full-Text Articles in Engineering

Limit Crossing For Decision Problems, Sharlee Climer, Weixiong Zhang Jan 2006

Limit Crossing For Decision Problems, Sharlee Climer, Weixiong Zhang

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Limit crossing is a methodology in which modified versions of a problem are solved and compared, yielding useful information about the original problem. Pruning rules that are used to exclude portions of search trees are excellent examples of the limit-crossing technique. In our previous work, we examined limit crossing for optimization problems. In this paper, we extend this methodology to decision problems. We demonstrate the use of limit crossing in our design of a tool for identifying K-SAT backbones. This tool is guaranteed to identify all of the backbone variables by solving at most n+1 formulae, where n is the …

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A Proposed Architecture For The Geni Backbone Platform, Jonathan Turner Jan 2006

A Proposed Architecture For The Geni Backbone Platform, Jonathan Turner

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The GENI Project (Global Environment for Network Innovation) is a major NSF-sponsored initiative that seeks to create a national research facility to enable experimental deployment of innovative new network architectures on a sufficient scale to enable realistic evaluation. One key component of the GENI system will be the GENI Backbone Platform (GBP) that provides the resources needed to allow multiple experimental networks to co-exist within the shared GENI infrastructure. This report reviews the objectives for the GBP, reviews the key issues that affect its design and develops a detailed reference architecture in order to provide a concrete example for how …

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The Real Effect Of Warm-Cool Colors, Reynold J. Bailey, Cindy M, Grimm, Chris Davoli Jan 2006

The Real Effect Of Warm-Cool Colors, Reynold J. Bailey, Cindy M, Grimm, Chris Davoli

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The phenomenon of warmer colors appearing nearer in depth to viewers than cooler colors has been studied extensively by psychologists and other vision researchers. The vast majority of these studies have asked human observers to view physically equidistant, colored stimuli and compare them for relative depth. However, in most cases, the stimuli presented were rather simple: straight colored lines, uniform color patches, point light sources, or symmetrical objects with uniform shading. Additionally, the colors used were typically highly saturated. Although such stimuli are useful in isolating and studying depth cues in certain contexts, they leave open the question of whether …

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Tuple Space Coordination Across Space & Time, Gruia-Catalin Roman, Radu Handorean, Chenyang Lu Jan 2006

Tuple Space Coordination Across Space & Time, Gruia-Catalin Roman, Radu Handorean, Chenyang Lu

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CAST is a coordination model designed to support interactions among agents executing on hosts that make up a mobile ad hoc network (MANET). From an application programmer’s point of view, CAST makes it possible for operations to be executed at arbitrary locations in space, at prescribed times which may be in the future, and on remote hosts even when no end-to-end connected route exists between the initiator and target(s) of the operation. To accomplish this, CAST assumes that each host moves in space in accordance with a motion profile which is accurate but which at any given time extends into …

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Fair Efficiency, Or Low Average Delay Without Starvation, Christoph Jechlitschek, Sergey Gorinksky Jan 2006

Fair Efficiency, Or Low Average Delay Without Starvation, Christoph Jechlitschek, Sergey Gorinksky

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Elastic applications are primarily interested in minimal delay achievable for their messages under current network load. In this paper, we investigate how to transmit such messages over a bottleneck link efficiently and fairly.

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Virtualizing Network Processors, Ben Wun, Jonathan Turner, Patrick Crowley Jan 2006

Virtualizing Network Processors, Ben Wun, Jonathan Turner, Patrick Crowley

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This paper considers the problem of virtualizing the resources of a network processor (NP) in order to allow multiple third-parties to execute their own virtual router software on a single physical router at the same time. Our broad interest is in designing such a router capable of supporting virtual networking. We discuss the issues and challenges involved in this virtualization, and then describe specific techniques for virtualizing both the control and data-plane processors on NPs. For Intel IXP NPs in particular, we present a dynamic, macro-based technique for virtualization that allows multiple virtual routers to run on multiple data plane …

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An Improved Analysis For A Greedy Remote-Clique Algorithm Using Factor-Revealing Lps, Benjamin E. Birnbaum, Kenneth J. Goldman Jan 2006

An Improved Analysis For A Greedy Remote-Clique Algorithm Using Factor-Revealing Lps, Benjamin E. Birnbaum, Kenneth J. Goldman

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Given a complete graph with nonnegative edge weights satisfying the triangle inequality and a positive integer p, the remote-clique problem is to find a subset of p vertices having a maximum-weight induced subgraph. A simple greedy algorithm for the problem has been shown to have an approximation ratio of 4, but a tight example has not been provided. In this paper, we use the technique of factor revealing linear programs to prove that this algorithm actually achieves an approximation ratio of 2, matching the best-known ratio for the problem. The greedy algorithm's running time of O(pn) makes it the fastest …

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Agilla: A Mobile Agent Middleware For Sensor Networks, Chien-Liang Fok, Gruia-Catalin Roman, Chenyang Lu Jan 2006

Agilla: A Mobile Agent Middleware For Sensor Networks, Chien-Liang Fok, Gruia-Catalin Roman, Chenyang Lu

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Agilla is a mobile agent middleware for sensor networks. Mobile agents are special processes that can migrate across sensors. They increase network flexibility by enabling active in-network reprogramming. Neighbor lists and tuple spaces are used for agent coordination. Agilla was originally implemented on Mica2 motes, but has been ported to other platforms. Its Mica2 implementation consumes 41.6KB of code and 3.59KB of data memory. Agents can move five hops in less than 1.1s with over 92% success. Agilla was used to develop multiple applications related to fire detection and tracking, cargo container monitoring, and robot navigation.

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Feature Detection Using Curvature Maps And The Min-Cut/Max-Flow Graph Cut Algorithm, Timothy Gatzke, Cindy Grimm Jan 2006

Feature Detection Using Curvature Maps And The Min-Cut/Max-Flow Graph Cut Algorithm, Timothy Gatzke, Cindy Grimm

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Automatic detection of features in three-dimensional objects is a critical part of shape matching tasks such as object registration and recognition. Previous approaches to local surface matching have either focused on man-made objects, where features are generally well-defined, or required some type of user interaction to select features. Manual selection of corresponding features and subjective determination of the difference between objects are time consuming processes requiring a high level of expertise. Curvature is a useful property of a surface, but curvature calculation on a discrete mesh is often noisy and not always accurate. However, the em Curvature Map, which represents …

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Distributed Utilization Control For Real-Time Clusters With Load Balancing, Yong Fu, Hongan Wang, Chenyang Lu, Ramu S. Chandra Jan 2006

Distributed Utilization Control For Real-Time Clusters With Load Balancing, Yong Fu, Hongan Wang, Chenyang Lu, Ramu S. Chandra

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Recent years have seen rapid growth of online services that rely on large-scale server clusters to handle high volume of requests. Such clusters must adaptively control the CPU utilizations of many processors in order to maintain desired soft real-time performance and prevent system overload in face of unpredictable workloads. This paper presents DUC-LB, a novel distributed utilization control algorithm for cluster-based soft real-time applications. Compared to earlier works on utilization control, a distinguishing feature of DUC-LB is its capability to handle system dynamics caused by load balancing, which is a common and essential component of most clusters today. Simulation results …

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Mobiwork: Mobile Workflow For Manets, Gregory Hackmann, Rohan Sen, Mart Haitjema, Gruia-Catalin Roman, Gill Jan 2006

Mobiwork: Mobile Workflow For Manets, Gregory Hackmann, Rohan Sen, Mart Haitjema, Gruia-Catalin Roman, Gill

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The workflow model is well suited for scenarios where many entities work collaboratively towards a common goal, and is used widely today to model complex business processes. However, the fundamental workflow model is very powerful and can be applied to a wider variety of application domains. This paper represents an initial investigation into the possibility of using workflows to model collaboration in an ad hoc mobile environment. Moving to a mobile setting introduces many challenges as the mobility of the participants in a workflow imposes constraints on allocation of workflow tasks, coordination among participants, and marshaling of results. We present …

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Efficient Mapping Of Virtual Networks Onto A Shared Substrate, Jing Lu, Jonathan Turner Jan 2006

Efficient Mapping Of Virtual Networks Onto A Shared Substrate, Jing Lu, Jonathan Turner

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Virtualization has been proposed as a vehicle for overcoming the growing problem of internet ossification [1]. This paper studies the problem of mapping diverse virtual networks onto a common physical substrate. In particular, we develop a method for mapping a virtual network onto a substrate network in a cost-efficient way, while allocating sufficient capacity to virtual network links to ensure that the virtual network can handle any traffic pattern allowed by a general set of traffic constraints. Our approach attempts to find the best topology in a family of backbone-star topologies, in which a subset of nodes constitute the backbone, …

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Adaptive Embedded Roadmaps For Sensor Networks, Gazihan Alankus, Nuzhet Atay, Chenyang Lu, Burchan Bayazit Jan 2006

Adaptive Embedded Roadmaps For Sensor Networks, Gazihan Alankus, Nuzhet Atay, Chenyang Lu, Burchan Bayazit

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In this paper, we propose a new approach to wireless sensor network assisted navigation while avoiding moving dangers. Our approach relies on an embedded roadmap in the sensor network that always contains safe paths. The roadmap is adaptive, i.e., it adapts its topology to changing dangers. The mobile robots in the environment uses the roadmap to reach their destinations. We evaluated the performance of embedded roadmap both in simulations using realistic conditions and with real hardware. Our results show that the proposed navigation algorithm is better suited for sensor networks than traditional navigation field based algorithms. Our observations suggest that …

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Control Of Decoherence In Open Quantum Systems, Narayan Ganesan Jan 2006

Control Of Decoherence In Open Quantum Systems, Narayan Ganesan

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No abstract provided.

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Knuth-Bendix Completion With Modern Termination Checking, Master's Thesis, August 2006, Ian Wehrman Jan 2006

Knuth-Bendix Completion With Modern Termination Checking, Master's Thesis, August 2006, Ian Wehrman

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Knuth-Bendix completion is a technique for equational automated theorem proving based on term rewriting. This classic procedure is parametrized by an equational theory and a (well-founded) reduction order used at runtime to ensure termination of intermediate rewriting systems. Any reduction order can be used in principle, but modern completion tools typically implement only a few classes of such orders (e.g., recursive path orders and polynomial orders). Consequently, the theories for which completion can possibly succeed are limited to those compatible with an instance of an implemented class of orders. Finding and specifying a compatible order, even among a small number …

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Sliver: A Bpel Workflow Process Execution Engine For Mobile Devices, Gregory Hackmann, Mart Haitjema, Christopher Gill, Catalin-Gruia Roman Jan 2006

Sliver: A Bpel Workflow Process Execution Engine For Mobile Devices, Gregory Hackmann, Mart Haitjema, Christopher Gill, Catalin-Gruia Roman

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The Business Process Execution Language (BPEL) has become the dominant means for expressing traditional business processes as workflows. The widespread deployment of mobile devices like PDAs and mobile phones has created a vast computational and communication resource for these workflows to exploit. However, BPEL so far has been deployed only on relatively heavyweight server platforms such as Apache Tomcat, leaving the potential created by these lower-end devices untapped. This paper presents Sliver, a BPEL workflow process execution engine that supports a wide variety of devices ranging from mobile phones to desktop PCs. We discuss the design decisions that allow Sliver …

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Reusable Models For Timing And Liveness Analysis Of Middleware For Distributed Real-Time And Embedded Systems, Venkita Subramonian, Christopher Gill, Cesar Sanchez, Henny Sipma Jan 2006

Reusable Models For Timing And Liveness Analysis Of Middleware For Distributed Real-Time And Embedded Systems, Venkita Subramonian, Christopher Gill, Cesar Sanchez, Henny Sipma

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Distributed real-time and embedded (DRE) systems have stringent constraints on timeliness and other properties whose assurance is crucial to correct system behavior. Formal tools and techniques play a key role in verifying and validating system properties. However, many DRE systems are built using middleware frameworks that have grown increasingly complex to address the diverse requirements of a wide range of applications. How to apply formal tools and techniques effectively to these systems, given the range of middleware configuration options available, is therefore an important research problem. This paper makes three contributions to research on formal verification and validation of middleware-based …

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Multimodal Congestion Control For Low Stable-State Queuing, Maxim Podlesny, Sergey Gorinsky Jan 2006

Multimodal Congestion Control For Low Stable-State Queuing, Maxim Podlesny, Sergey Gorinsky

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To discover an efficient fair sending rate for a flow, Transmission Control Protocol (TCP) saturates the bottleneck link and its buffer until the router discards a packet. Such TCP-caused queuing is detrimental for interactive and other delay-sensitive applications. In this paper, we present Multimodal Control Protocol (MCP) which strives to maintain low queues and avoid congestion losses at network links. The multimodal MCP engages routers and hosts in limited explicit communication. A distinguishing property of MCP is stable transmission after converging to efficient fair states. To ensure convergence to fairness, MCP incorporates an innovative mechanism that enables a flow to …

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Dynamic Resource Management In A Static Network Operating System, Kevin Klues, Vlado Handziski, David Culler, David Gay, Phillip Levis Levis, Chenyang Lu, Adam Wolisz Jan 2006

Dynamic Resource Management In A Static Network Operating System, Kevin Klues, Vlado Handziski, David Culler, David Gay, Phillip Levis Levis, Chenyang Lu, Adam Wolisz

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We present novel approaches to managing three key resources in an event-driven sensornet OS: memory, energy, and peripherals. We describe the factors that necessitate using these new approaches rather than existing ones. A combination of static allocation and compile-time virtualization isolates resources from one another, while dynamic management provides the flexibility and sharing needed to minimize worst-case overheads. We evaluate the effectiveness and efficiency of these management policies in comparison to those of TinyOS 1.x, SOS, MOS, and Contiki. We show that by making memory, energy, and peripherals first-class abstractions, an OS can quickly, efficiently, and accurately adjust itself to …

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Link Layer Support For Unified Radio Power Management In Wireless Sensor Networks, Kevin Klues, Guoliang Xing, Chenyang Lu Jan 2006

Link Layer Support For Unified Radio Power Management In Wireless Sensor Networks, Kevin Klues, Guoliang Xing, Chenyang Lu

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Radio power management is of paramount concern in wireless sensor networks that must achieve long lifetimes on scarce amounts of energy. While a multitude of power management protocols have been proposed in the past, the lack of system support for flexibly integrating them with a diverse set of applications and network platforms has made them difficult to use. Instead of proposing yet another power management protocol, this paper focuses on providing link layer support towards realizing a Unified Power Management Architecture (UPMA) for flexible radio power management in wireless sensor networks. In contrast to the monolithic approaches adopted by existing …

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Cian: A Language And Middleware For Collaboration In Ad Hoc Networks, Rohan Sen, Gruia-Catalin Roman, Andrew Frank Jan 2006

Cian: A Language And Middleware For Collaboration In Ad Hoc Networks, Rohan Sen, Gruia-Catalin Roman, Andrew Frank

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Designing software that supports collaboration among multiple users in mobile ad hoc networks is challenging due to the dynamic network topology and inherent unpredictability of the environment. However, as we increasingly migrate to using mobile computing platforms, there is a pertinent need for software that can support a wide range of collaborative activities anywhere and at any time without relying on any external infrastructure. In this paper, we adopt the workflow model to represent the structure of an activity that involves multiple tasks being performed in a structured, collaborative fashion by multiple users. Using the workflow model as a base, …

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Virtualization For A Network Processor Runtime System, Brandon Heller, Jonathan Turner, John Dehart, Patrick Crowley Jan 2006

Virtualization For A Network Processor Runtime System, Brandon Heller, Jonathan Turner, John Dehart, Patrick Crowley

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The continuing ossification of the Internet is slowing the pace of network innovation. Network diversification presents one solution to this problem, by virtualizing the network at multiple layers. Diversified networks consist of a shared physical substrate, virtual routers (metarouters), and virtual links (metalinks). Virtualizing routers enables smooth and incremental upgrades to new network services. Our current priority for a diversified router prototype is to enable reserved slices of the network for researchers to perform repeatable, high-speed network experiments. General-purpose processors have well established techniques for virtualization, but do not scale efficiently to multi-gigabit speeds. To achieve these speeds, we employ …

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Auto-Pipe And The X Language: A Toolset And Language For The Simulation, Analysis, And Synthesis Of Heterogeneous Pipelined Architectures, Master's Thesis, August 2006, Eric J. Tyson Jan 2006

Auto-Pipe And The X Language: A Toolset And Language For The Simulation, Analysis, And Synthesis Of Heterogeneous Pipelined Architectures, Master's Thesis, August 2006, Eric J. Tyson

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Pipelining an algorithmis a popularmethod of increasing the performance of many computation-intensive applications. Often, one wants to form pipelines composed mostly of commonly used simple building blocks such as DSP components, simple math operations, encryption, or pattern matching stages. Additionally, one may desire to map these processing tasks to different computational resources based on their relative performance attributes (e.g., DSP operations on an FPGA). Auto-Pipe is composed of the X Language, a flexible interface language that aids the description of complex dataflow topologies (including pipelines); X-Com, a compiler for the X Language; X-Sim, a tool for modeling pipelined architectures based …

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Real-Time Memory Management: Life And Times, Andrew Borg, Andy Wellings, Christopher Gill, Ron K. Cytron Jan 2006

Real-Time Memory Management: Life And Times, Andrew Borg, Andy Wellings, Christopher Gill, Ron K. Cytron

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As high integrity real-time systems become increasingly large and complex, forcing a static model of memory usage becomes untenable. The challenge is to provide a dynamic memory model that guarantees tight and bounded time and space requirements without overburdening the developer with memory concerns. This paper provides an analysis of memory management approaches in order to characterise the tradeoffs across three semantic domains: space, time and a characterisation of memory usage information such as the lifetime of objects. A unified approach to distinguishing the merits of each memory model highlights the relationship across these three domains, thereby identifying the class …

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Supporting Collaborative Behavior In Manets Using Workflows, Rohan Sen, Gregory Hackmann, Mart Haitjema, Gruia-Catalin Roman, Gill Jan 2006

Supporting Collaborative Behavior In Manets Using Workflows, Rohan Sen, Gregory Hackmann, Mart Haitjema, Gruia-Catalin Roman, Gill

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Groupware activities provide a powerful representation for many collaborative tasks. Today, the technologies that support typical groupware applications often assume a stable wired network infrastructure. The potential for collaboration in scenarios that lack this fixed infrastructure remains largely untapped. Such scenarios include activities on construction sites, wilderness exploration, disaster recovery, and rapid intervention teams. Communication in these scenarios can be supported using wireless ad hoc networks, an emerging technology whose full potential is yet to be understood and realized. In this paper, we consider the fundamental technical issues that need to be addressed in order to introduce groupware concepts into …

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Three Dimensional Panoramic Fast Flourescence Imaging Of Cardiac Arryhtymias In The Rabbit Heart, Fujian Qu, Vladimir P. Nikolski, Cindy Grimm, Igor R. Efimov Jan 2006

Three Dimensional Panoramic Fast Flourescence Imaging Of Cardiac Arryhtymias In The Rabbit Heart, Fujian Qu, Vladimir P. Nikolski, Cindy Grimm, Igor R. Efimov

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Cardiac high spatio-temporal optical mapping provides a unique opportunity to investigate the dynamics of propagating waves of excitation during ventricular arrhythmia and defibrillation. However, studies using single camera imaging systems are hampered by the inability to monitor electrical activity from the entire surface of the heart. We have developed a three dimensional panoramic imaging system which allows high-resolution and high-dynamic-range optical mapping from the entire surface of the heart. Rabbit hearts (n=4) were Langendorff perfused and imaged by the system during sinus rhythm, epicardial pacing, and arrhythmias. The reconstructed 3D electrical activity provides us with a powerful tool to investigate …

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Discovering Weak Community Structures In Large Biological Networks , Jianhua Ruan, Weixiong Zhang Jan 2006

Discovering Weak Community Structures In Large Biological Networks , Jianhua Ruan, Weixiong Zhang

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Identifying intrinsic structures in large networks is a fundamental problem in many fields, such as biology, engineering and social sciences. Motivated by biology applications, in this paper we are concerned with identifying community structures, which are densely connected sub-graphs, in large biological networks. We address several critical issues for finding community structures. First, biological networks directly constructed from experimental data often contain spurious edges and may also miss genuine connections. As a result, community structures in biological networks are often weak. We introduce simple operations to capture local neighborhood structures for identifying weak communities. Second, we consider the issue of …

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Automatic Application-Specific Customization Of Softcore Processor Microarchitecture, Masters Thesis, May 2006, Shobana Padmanabhan Jan 2006

Automatic Application-Specific Customization Of Softcore Processor Microarchitecture, Masters Thesis, May 2006, Shobana Padmanabhan

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Applications for constrained embedded systems are subject to strict runtime and resource utilization bounds. With soft core processors, application developers can customize the processor for their application, constrained by available hardware resources but aimed at high application performance. The more reconfigurable the processor is, the more options the application developers will have for customization and hence increased potential for improving application performance. However, such customization entails developing in-depth familiarity with all the parameters, in order to configure them effectively. This is typically infeasible, given the tight time-to-market pressure on the developers. Alternatively, developers could explore all possible configurations, but being …

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Manifold Learning For Natural Image Sets, Doctoral Dissertation August 2006, Richard Souvenir Jan 2006

Manifold Learning For Natural Image Sets, Doctoral Dissertation August 2006, Richard Souvenir

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The field of manifold learning provides powerful tools for parameterizing high-dimensional data points with a small number of parameters when this data lies on or near some manifold. Images can be thought of as points in some high-dimensional image space where each coordinate represents the intensity value of a single pixel. These manifold learning techniques have been successfully applied to simple image sets, such as handwriting data and a statue in a tightly controlled environment. However, they fail in the case of natural image sets, even those that only vary due to a single degree of freedom, such as a …

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Design Issues Of Reserved Delivery Subnetworks, Doctoral Dissertation, May 2006, Ruibiao Qiu Jan 2006

Design Issues Of Reserved Delivery Subnetworks, Doctoral Dissertation, May 2006, Ruibiao Qiu

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The lack of per-flow bandwidth reservation in today's Internet limits the quality of service that an information service provider can provide. This dissertation introduces the reserved delivery subnetwork (RDS), a mechanism that provides consistent quality of service by implementing aggregate bandwidth reservation. A number of design and deployment issues of RDSs are studied. First, the configuration problem of a single-server RDS is formulated as a minimum concave cost network flow problem, which properly reflects the economy of bandwidth aggregation, but is also an NP-hard problem. To make the RDS configuration problem tractable, an efficient approximation heuristic, largest demands first (LDF), …

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