School of Engineering Sciences and Technology

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  • Item
    Thermodynamic behavior of a model covalent material described by the environment-dependent interatomic potential
    ( 2002-08-01) Keblinski, P. ; Bazant, M. Z. ; Dash, R. K. ; Treacy, M. M.
    Using molecular-dynamics simulations we study the thermodynamic behavior of a single-component covalent material described by the recently proposed environment-dependent interatomic potential (EDIP). The parametrization of EDIP for silicon exhibits a range of unusual properties typically found in more complex materials, such as the existence of two structurally distinct disordered phases, a density increase upon melting of the low-temperature amorphous phase, and negative thermal-expansion coefficients for both the crystal (at high temperatures) and the amorphous phase (at all temperatures). Structural differences between the two disordered phases also lead to a first-order transition between them, which suggests the existence of a second critical point, as is believed to exist for amorphous forms of frozen water. For EDIP-Si, however, the unusual behavior is associated not only with the open nature of tetrahedral bonding but also with a competition between fourfold (covalent) and fivefold (metallic) coordination. The unusual behavior of the model and its unique ability to simulate the liquid/amorphous transition on molecular-dynamics time, scales make it a suitable prototype for fundamental studies of anomalous thermodynamics in disordered systems.
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    Water hyacinth char addition in iron ore pellet: An exploratory study
    ( 2003-01-01) Gupta, R. C. ; Gautam, J. P. ; Mohan, Sunil
    The utilization of water hyacinth as an additive in the preparation of iron ore pellets was investigated. The prepared pellets, fired for particular time and temperature, were tested via cold crushing strength (CCS) examination. The water hyacinth char was found to strengthen the crushing behavior of pellets during heating, and hence its use as a potential additive was recommended.
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    The Effect of Additives and Reductants on the Strength of Reduced Iron Ore Pellet
    ( 2003-01-01) Gupta, R. C. ; Gautam, J. P.
    The higher strength of directly reduced iron (DRI) in pellet form is useful in handling, storing and charging from height without breakage. The DRI pellets commonly exhibit 60 kg cold crushing strength. In this work the effect of reduction temperature, sintering time, quantity/quality of additives and manner of reduction by solid reductant has been studied. The reduced pellet strength could be increased by improving metallic bonds by offering higher reduction temperature (max, 1 250°C) and subsequent sintering. The strength was found to increase by adding slag forming constituents e.g. bentonite. The strength of reductant mixed reduced pellet was observed to be affected by the nature of reductant. The reductant with low bulk density and lower carbon content provided higher voidage rendering lower strength. The cold crushing strength (CCS) of reduced pellets observed in this study ranged from 5 to 200 kg exhibiting ductile to brittle behaviour during deformation.
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    Testing techniques for mechanical characterization of nanostructured materials
    ( 2003-01-01) Koch, Carl C. ; Scattergood, Ronald O. ; Murty, K. Linga ; Guduru, Ramesh K. ; Trichy, Gopinath ; Rajulapati, Koteswararao V.
    Testing methods are reviewed that can be applied to the small sample sizes which result from many of the processing routes for preparation of nanocrystalline materials. These include the measurement of elastic properties on small samples; hardness, with emphasis on nanoindentation methods; the miniaturized disk bend test (MDBT); the automated ball indentation test (ABI); the shear punch test; and the use of subsize compression and tensile samples.
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    A quantitative measure of medium-range order in amorphous materials from transmission electron micrographs
    ( 2003-08-13) Dash, R. K. ; Voyles, P. M. ; Gibson, J. M. ; Treacy, M. M.J. ; Keblinski, P.
    We propose an extension to the technique of fluctuation electron microscopy that quantitatively measures a medium-range order correlation length in amorphous materials. In both simulated images from computer-generated paracrystalline amorphous silicon models and experimental images of amorphous silicon, we find that the spatial autocorrelation function of dark-field transmission electron micrographs of amorphous materials exhibits a simple exponential decay. The decay length measures a nanometre-scale structural correlation length in the sample, although it also depends on the microscope resolution. We also propose a new interpretation of the fluctuation microscopy image variance in terms of fluctuations in local atomic pair distribution functions.
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    Computational-Mechanism Design: A Call to Arms
    ( 2003-11-01) Dash, Rajdeep K. ; Jennings, Nicholas R. ; Parkes, David C.
    The field of computational-mechanism design (CMD), which applies economic principles to computer systems design is discussed. CMD has an important role to play in developing complex distributed systems comprising multiple ineracting agents. The latest subfield of distributed-computational-mechanism design (DMD) is an emerging field of interest as it is a better match with the computational multiagent systems (MAS) model. A distributed mechanism transfers the computational burden from a central node in the mechanism to the agents.
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    A risk-based bidding strategy for continuous double auctions
    ( 2004-01-01) Vytelingum, Perukrishnen ; Dash, Rajdeep K. ; David, Esther ; Jennings, Nicholas R.
    We develop a novel bidding strategy that software agents can use to buy and sell goods in Continuous Double Auctions (CDAs). Our strategy involves the agent forming a bid or ask by assessing the degree of risk involved and making a prediction about the competitive equilibrium that is likely to be reached in the marketplace. We benchmark our strategy against two of the most common strategies for CDAs, namely the Zero-Intelligence and the Zero- Intelligence Plus strategies, and we show that our agents outperform these benchmarks. Specifically, our agents win in 100% of the simulations against the ZI agents and, on average, 75% of the games against the ZIP agents.
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    Trust-based mechanism design
    ( 2004-09-27) Dash, Rajdeep K. ; Ramchurn, Sarvapali D. ; Jennings, Nicholas R.
    We define trust-based mechanism design as an augmentation of traditional mechanism design in which agents take into account the degree of trust that they have in their counterparts when determining their allocations. To this end, we develop an efficient, individually rational, and incentive compatible mechanism based on trust. This mechanism is embedded in a task allocation scenario in which the trust in an agent is derived from the reported performance success of that agent by all the other agents in the system. We also empirically study the evolution of our mechanism when iterated and show that, in the long run, it always chooses the most successful and cheapest agents to fulfill an allocation and chooses better allocations than other comparable models when faced with biased reporting.
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    Unifying learning in games and graphical models
    ( 2005-01-01) Rezek, I. ; Roberts, S. J. ; Rogers, A. ; Dash, R. K. ; Jennings, N.
    The ever increasing use of intelligent multi-agent systems poses increasing demands upon them. One of these is the ability to reason consistently under uncertainty. This, in turn, is the dominant characteristic of probabilistic learning in graphical models which, however, lack a natural decentralised formulation. The ideal would, therefore, be a unifying framework which is able to combine the strengths of both multi-agent and probabilistic inference In this paper we present a unified interpretation of the inference mechanisms in games and graphical models. In particular, we view fictitious play as a method of optimising the Kullback-Leibler distance between current mixed strategies and optimal mixed strategies at Nash equilibrium. In reverse, probabilistic inference in the variational mean-field framework can be viewed as fictitious game play to learn the best strategies which explain a probabilistic graphical model. © 2005 IEEE.
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    Variable focal length microlens by low voltage Electrowetting on Dielectric (EWOD) actuation
    ( 2005-01-01) Dash, Raj K. ; Borca-Tasciuc, Theodorian
    This work presents a design and proposed microfabrication steps for a two-liquid variable focal length capillary microlens. The capillary lens is actuated by electrowetting on dielectric effect. The microlens is made from a dielectric liquid whereas a conducting liquid serves as one of the electrodes for the actuation. The dependence of the microlens focal length on the properties of the dielectric materials is investigated using a model for electrowetting on dielectric effect. The model indicates that low voltage actuation ( < 20V) is possible by adjusting the dielectric layer thickness. The effect of the microlens size on the focal length is presented. The advantages of a two-liquid capillary microlens are briefly discussed. Copyright © 2005 by ASME.
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    Constrained bandwidth allocation in multi-sensor information fusion: A mechanism design approach
    ( 2005-01-01) Dash, R. K. ; Rogers, A. ; Jennings, N. R. ; Reece, S. ; Roberts, S.
    Sensor networks are increasingly seen as a solution for a large number of environmental, security and military monitoring tasks. Typically, in these networks, noisy data from a number of local sensors is fused to reduce the uncertainty in the global picture. A central issue in this information fusion is the decision of what data should be shared between sensors, in order to maximise the global gain in information, when the bandwidth of the communication network is limited. In this paper, we study the problem from a selfish agent perspective. We show how the uncertainty in the measurement of an event can be cast as a utility function derived from the Kalman filter. We then use the tools of mechanism design to engineer an incentive-compatible mechanism that allows rational selfish agents to individually maximise their own utility, whilst ensuring that the overall utility of the system is also maximised. We apply the mechanism to multi-sensor target detection and consider the complexity of finding an efficient solution with broadcast communication protocols. © 2005 IEEE.
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    Engineering distributed protocols for multi-agent interactions using game theory
    ( 2005-12-01) Dash, Rajdeep K.
    This thesis considers engineering both protocols and strategies in multi-agent systems comprised of selfish, rational autonomous agents. Mechanisms dealing with failures as well as aspects of decentralisation are designed and applied to a multi-sensor network scenario. A model for designing strategies is also proposed and a risk-based strategy for a continuous double auctions designed. Copyright 2005 ACM.
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    A mechanism for multiple goods and interdependent valuations
    ( 2005-12-01) Dash, Rajdeep K. ; Rogers, Alex ; Jennings, Nicholas R.
    This paper reports on the design of an auction mechanism for allocating multiple goods when the buyers have interdependent valuations. We cast the problem as a multi-agent system consisting of selfish, rational agents and develop an auction mechanism which is efficient, incentive compatible and individually rational. We first discuss the necessary assumptions that any mechanism developed for this scenario should satisfy so as to achieve the aforementioned properties. We then present our mechanism and show how it is a generalisation of the Vickrey-Clarke-Groves mechanism. © Springer-Verlag Berlin Heidelberg 2005.
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    Trusted kernel-based coalition formation
    ( 2005-12-01) Blankenburg, Bastian ; Dash, Rajdeep K. ; Ramchurn, Sarvapali D. ; Klusch, Matthias ; Jennings, Nicholas R.
    We define Trusted Kernel-based Coalition Formation as a novel extension to the traditional kernel-based coalition formation process which ensures agents choose the most reliable coalition partners and are guaranteed to obtain the payment they deserve. To this end, we develop an encryption-based communication protocol and a payment scheme which ensure that agents cannot manipulate the mechanism to their own benefit. Moreover, we integrate a generic trust model in the coalition formation process that permits the selection of the most reliable agents over repeated coalition games. We empirically evaluate our mechanism when iterated and show that, in the long run, it always chooses the coalition structure that has the maximum expected value and determines the payoffs that match their level of reliability. Copyright 2005 ACM.
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    Trading strategies for markets: A design framework and its application
    ( 2006-01-01) Vytelingum, P. ; Dash, R. K. ; He, M. ; Sykulski, A. ; Jennings, N. R.
    In this paper, we present a novel multi-layered framework for designing strategies for trading agents. The objective of this work is to provide a framework that will assist strategy designers with the different aspects involved in designing a strategy. At present, such strategies are typically designed in an ad-hoc and intuitive manner with little regard for discerning best practice or attaining reusability in the design process, Given this, our aim is to put such developments on a more systematic engineering footing. After we describe our framework, we then go on to illustrate how it can be used to design strategies for a particular type of market mechanism (namely the Continuous Double Auction), and how it was used to design a novel strategy for the Travel Game of the International Trading Agent Competition. © Springer-Verlag Berlin Heidelberg 2006.
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    Initial growth of nanocrystalline diamond/ Β-SiC composite films: A competitive deposition process
    ( 2006-02-24) Srikanth, Vadali V.S.S. ; Tan, M. H. ; Jiang, X.
    Although nanocrystalline diamond/ Β-SiC composite gradient interlayers have been successfully deposited in dealing with the problem of diamond thin-film adhesion to metallic substrates, initial growth process of the two components has not been described, so far. In this letter, we propose that the deposition of composite interlayer is possible because of a selective growth process of diamond and Β-SiC phases. There is a competition between the diamond and the Β-SiC crystallites to occupy the spaces available on the substrate. The space competition is during the initial nucleation period of the process and also during film growth, leading to the formation of the nanocrystalline composite. The secondary nucleation of Β-SiC on the existing diamond surfaces depends on the flux of incoming Β-SiC forming gas species. This provides us with a possibility to control phase structure and composition of the composite film by adjusting the tetramethyl silane flow rate. © 2006 American Institute of Physics.
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    Effect of Pb on the mechanical properties of nanocrystalline Al
    ( 2006-07-01) Rajulapati, Koteswararao V. ; Scattergood, Ronald O. ; Murty, Korukonda L. ; Duscher, Gerd ; Koch, Carl C.
    Nanocrystalline (nc) Al-Pb two phase mixtures of different Pb concentrations were made by two different routes using high energy ball milling. The microhardness measurements show a softening in nc Al-Pb composites with the increase in Pb content, contradicting the previous results reported in the literature. We conclude that interaction of Pb atoms with nanocrystalline Al grain boundaries is responsible for the softening of the nc Al matrix observed in the current study. © 2006 Acta Materialia Inc.
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    Overlapping coalition formation for efficient data fusion in multi-sensor networks
    ( 2006-11-13) Dang, Viet Dung ; Dash, Rajdeep K. ; Rogers, Alex ; Jennings, Nicholas R.
    This paper develops new algorithms for coalition formation within multi-sensor networks tasked with performing wide-area surveillance. Specifically, we cast this application as an instance of coalition formation, with overlapping coalitions. We show that within this application area sub-additive coalition valuations are typical, and we thus use this structural property of the problem to derive two novel algorithms (an approximate greedy one that operates in polynomial time and has a calculated bound to the optimum, and an optimal branch-and-bound one) to find the optimal coalition structure in this instance. We empirically evaluate the performance of these algorithms within a generic model of a multi-sensor network performing wide area surveillance. These results show that the polynomial algorithm typically generated solutions much closer to the optimal than the theoretical bound, and prove the effectiveness of our pruning procedure. Copyright © 2006, American Association for Artificial Intelligence (www.aaai.org). All rights reserved.
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    Competing sellers in online markets: Reserve prices, shill bidding, and auction fees
    ( 2006-12-01) Gerding, Enrico H. ; Rogers, Alex ; Dash, Rajdeep K. ; Jennings, Nicholas R.
    In this paper, we consider competition between sellers offering similar items in concurrent online auctions, where each seller must set its individual auction parameters (such as the reserve price) in such a way as to attract buyers. We show that there exists a pure Nash equilibrium in the case of two sellers with asymmetric production costs. In addition, we show that, rather than setting a reserve price, a seller can further improve its utility by shill bidding (i.e., pretending to be a buyer in order to bid in its own auction). But, using an evolutionary simulation, we show that this shill bidding introduces inefficiences within the market. However, we then go on to show that these inefficiences can be reduced when the mediating auction institution uses appropriate auction fees that deter sellers from submitting shill bids. Copyright 2006 ACM.
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    Computational mechanism design for multi-sensor information fusion
    ( 2006-12-01) Rogers, A. ; Dash, R. K. ; Jennings, N. R. ; Reece, S. ; Roberts, S.
    Conventional information fusion architectures are challenged by developments in sensor networks that allow individually-owned (and thereby selfish) sensors to interact and share data. Given this, we advocate the use of tools and techniques from computational mechanism design, a field at the intersection of computer science, game theory and economics, to address the challenges posed by these networks. These techniques allow us to engineer networks with desirable system-wide properties, in which sensors are represented as selfish rational agents, each attempting to fulfill their own individuals goals. In this paper, we present the work of the Argus II DARP project (http://www.robots.ox.ac.uk/~argus/) and we demonstrate the application of mechanism design within a real world information fusion sensor network scenario. Copyright 2006 ACM.