50 research outputs found

    Sketchmate: A Computer-Aided Sketching and Simulation Tool for Teaching Graph Algorithms

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    In this dissertation, we developed and tested a sketching, visualization, and simulation tool called Sketchmate for demonstrating graph algorithms commonly taught in undergraduate computer science courses. For this research, we chose to focus on shortest path and network flow algorithms. Two versions of this tool have been implemented: 1) an instructor tool that supports computer-aided manual simulations of algorithms that augment traditional whiteboard presentations, allowing lectures to be more dynamic and interactive, and 2) a student tool that supports computer-aided manual practice of algorithms that enables students to work through homework problems more quickly while providing detailed incremental feedback about their performance and about how to solve a problem when they get stuck. Previous algorithm simulation systems have essentially forced instructors to narrate an algorithm as though they were describing an automated set of slides. In contrast, our tool allows instructors to manually manipulate attributes of a graph as they demonstrate an algorithm. A set of experiments was conducted using the tools. The results for the student tool showed that there was no statistically significant difference in test score improvement between Sketchmate and paper and pencil students, although they did show that Sketchmate students scored roughly one letter grade higher than paper and pencil students. Based on survey data, the students preferred using the tool to using paper and pencil. The results of the experiment involving the instructor tool showed that although there was no statistically significant difference in learning between Sketchmate and the whiteboard, both the instructor and the students preferred a Sketchmate lecture to a whiteboard lecture

    Une approche générique pour l'automatisation des expériences sur les réseaux informatiques

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    This thesis proposes a generic approach to automate network experiments for scenarios involving any networking technology on any type of network evaluation platform. The proposed approach is based on abstracting the experiment life cycle of the evaluation platforms into generic steps from which a generic experiment model and experimentation primitives are derived. A generic experimentation architecture is proposed, composed of an experiment model, a programmable experiment interface and an orchestration algorithm that can be adapted to network simulators, emulators and testbeds alike. The feasibility of the approach is demonstrated through the implementation of a framework capable of automating experiments using any combination of these platforms. Three main aspects of the framework are evaluated: its extensibility to support any type of platform, its efficiency to orchestrate experiments and its flexibility to support diverse use cases including education, platform management and experimentation with multiple platforms. The results show that the proposed approach can be used to efficiently automate experimentation on diverse platforms for a wide range of scenarios.Cette thĂšse propose une approche gĂ©nĂ©rique pour automatiser des expĂ©riences sur des rĂ©seaux quelle que soit la technologie utilisĂ©e ou le type de plate-forme d'Ă©valuation. L'approche proposĂ©e est basĂ©e sur l'abstraction du cycle de vie de l'expĂ©rience en Ă©tapes gĂ©nĂ©riques Ă  partir desquelles un modĂšle d'expĂ©rience et des primitives d'expĂ©rimentation sont dĂ©rivĂ©s. Une architecture gĂ©nĂ©rique d'expĂ©rimentation est proposĂ©e, composĂ©e d'un modĂšle d'expĂ©rience gĂ©nĂ©rique, d'une interface pour programmer des expĂ©riences et d'un algorithme d'orchestration qui peux ĂȘtre adaptĂ© aux simulateurs, Ă©mulateurs et bancs d'essai de rĂ©seaux. La faisabilitĂ© de cette approche est dĂ©montrĂ©e par la mise en Ɠuvre d'un framework capable d'automatiser des expĂ©riences sur toute combinaison de ces plateformes. Trois aspects principaux du framework sont Ă©valuĂ©s : son extensibilitĂ© pour s'adapter Ă  tout type de plate-forme, son efficacitĂ© pour orchestrer des expĂ©riences et sa flexibilitĂ© pour permettre des cas d'utilisation divers, y compris l'enseignement, la gestion des plate-formes et l'expĂ©rimentation avec des plates-formes multiples. Les rĂ©sultats montrent que l'approche proposĂ©e peut ĂȘtre utilisĂ©e pour automatiser efficacement l'expĂ©rimentation sur les plates-formes d'Ă©valuation hĂ©tĂ©rogĂšnes et pour un Ă©ventail de scĂ©narios variĂ©s

    Accelerating the simulation of wireless cellular systems

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    The simulation of comprehensive models for cellular wireless systems poses a computational burden of great proportions. When a sub-model for transmitter power level control is included in the simulation, a continuous process in discrete-time is introduced, requiring traditional execution to advance in small, regular time-steps. to accelerate these simulations, we propose the use of interval jumping, a novel technique which allows time to progress in adaptive, irregularly-sized jumps in time. The foundations for this mechanism are laid out in the light of the simulation of a complex simulation model which includes teletraffic, radio propagation, channel allocation, transmitter power control, and user mobility. We demonstrate the performance of this method through the use of sequential and parallel simulation.;Approaching the problem of accelerating the simulation of wireless systems from a different angle, we also identify a second important performance bottleneck. Calculations for interference computation, which may be carried out hundreds of times for each second of simulated time, require the evaluation of O(N2) interactions, for a system with N transmitter/receiver pairs. In order to provide a computationally cheaper and more scalable alternative to these operations, we study the applicability of an N-body algorithm, which brings time complexity down to O(N log N)

    Error minimising gradients for improving cerebellar model articulation controller performance

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    In motion control applications where the desired trajectory velocity exceeds an actuator’s maximum velocity limitations, large position errors will occur between the desired and actual trajectory responses. In these situations standard control approaches cannot predict the output saturation of the actuator and thus the associated error summation cannot be minimised.An adaptive feedforward control solution such as the Cerebellar Model Articulation Controller (CMAC) is able to provide an inherent level of prediction for these situations, moving the system output in the direction of the excessive desired velocity before actuator saturation occurs. However the pre-empting level of a CMAC is not adaptive, and thus the optimal point in time to start moving the system output in the direction of the excessive desired velocity remains unsolved. While the CMAC can adaptively minimise an actuator’s position error, the minimisation of the summation of error over time created by the divergence of the desired and actual trajectory responses requires an additional adaptive level of control.This thesis presents an improved method of training CMACs to minimise the summation of error over time created when the desired trajectory velocity exceeds the actuator’s maximum velocity limitations. This improved method called the Error Minimising Gradient Controller (EMGC) is able to adaptively modify a CMAC’s training signal so that the CMAC will start to move the output of the system in the direction of the excessive desired velocity with an optimised pre-empting level.The EMGC was originally created to minimise the loss of linguistic information conveyed through an actuated series of concatenated hand sign gestures reproducing deafblind sign language. The EMGC concept however is able to be implemented on any system where the error summation associated with excessive desired velocities needs to be minimised, with the EMGC producing an improved output approximation over using a CMAC alone.In this thesis, the EMGC was tested and benchmarked against a feedforward / feedback combined controller using a CMAC and PID controller. The EMGC was tested on an air-muscle actuator for a variety of situations comprising of a position discontinuity in a continuous desired trajectory. Tested situations included various discontinuity magnitudes together with varying approach and departure gradient profiles.Testing demonstrated that the addition of an EMGC can reduce a situation’s error summation magnitude if the base CMAC controller has not already provided a prior enough pre-empting output in the direction of the situation. The addition of an EMGC to a CMAC produces an improved approximation of reproduced motion trajectories, not only minimising position error for a single sampling instance, but also over time for periodic signals

    Configuration Management of Distributed Systems over Unreliable and Hostile Networks

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    Economic incentives of large criminal profits and the threat of legal consequences have pushed criminals to continuously improve their malware, especially command and control channels. This thesis applied concepts from successful malware command and control to explore the survivability and resilience of benign configuration management systems. This work expands on existing stage models of malware life cycle to contribute a new model for identifying malware concepts applicable to benign configuration management. The Hidden Master architecture is a contribution to master-agent network communication. In the Hidden Master architecture, communication between master and agent is asynchronous and can operate trough intermediate nodes. This protects the master secret key, which gives full control of all computers participating in configuration management. Multiple improvements to idempotent configuration were proposed, including the definition of the minimal base resource dependency model, simplified resource revalidation and the use of imperative general purpose language for defining idempotent configuration. Following the constructive research approach, the improvements to configuration management were designed into two prototypes. This allowed validation in laboratory testing, in two case studies and in expert interviews. In laboratory testing, the Hidden Master prototype was more resilient than leading configuration management tools in high load and low memory conditions, and against packet loss and corruption. Only the research prototype was adaptable to a network without stable topology due to the asynchronous nature of the Hidden Master architecture. The main case study used the research prototype in a complex environment to deploy a multi-room, authenticated audiovisual system for a client of an organization deploying the configuration. The case studies indicated that imperative general purpose language can be used for idempotent configuration in real life, for defining new configurations in unexpected situations using the base resources, and abstracting those using standard language features; and that such a system seems easy to learn. Potential business benefits were identified and evaluated using individual semistructured expert interviews. Respondents agreed that the models and the Hidden Master architecture could reduce costs and risks, improve developer productivity and allow faster time-to-market. Protection of master secret keys and the reduced need for incident response were seen as key drivers for improved security. Low-cost geographic scaling and leveraging file serving capabilities of commodity servers were seen to improve scaling and resiliency. Respondents identified jurisdictional legal limitations to encryption and requirements for cloud operator auditing as factors potentially limiting the full use of some concepts

    An aesthetic for sustainable interactions in product-service systems?

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    Copyright @ 2012 Greenleaf PublishingEco-efficient Product-Service System (PSS) innovations represent a promising approach to sustainability. However the application of this concept is still very limited because its implementation and diffusion is hindered by several barriers (cultural, corporate and regulative ones). The paper investigates the barriers that affect the attractiveness and acceptation of eco-efficient PSS alternatives, and opens the debate on the aesthetic of eco-efficient PSS, and the way in which aesthetic could enhance some specific inner qualities of this kinds of innovations. Integrating insights from semiotics, the paper outlines some first research hypothesis on how the aesthetic elements of an eco-efficient PSS could facilitate user attraction, acceptation and satisfaction

    The 1995 Goddard Conference on Space Applications of Artificial Intelligence and Emerging Information Technologies

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    This publication comprises the papers presented at the 1995 Goddard Conference on Space Applications of Artificial Intelligence and Emerging Information Technologies held at the NASA/Goddard Space Flight Center, Greenbelt, Maryland, on May 9-11, 1995. The purpose of this annual conference is to provide a forum in which current research and development directed at space applications of artificial intelligence can be presented and discussed
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