Mechanical Engineering - Research Publications

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    A UNIFYING FRAMEWORK FOR ANALYSIS AND DESIGN OF EXTREMUM SEEKING CONTROLLERS
    Nesic, D ; Tan, Y ; Manzie, C ; Mohammadi, A ; Moase, W (IEEE, 2012-01-01)
    We summarize a unifying design approach to continuous-time extremum seeking that was recently reported by the authors. This approach is based on a feedback control paradigm that was to the best of our knowledge explicitly summarized for the first time in this form in our recent work. This paradigm covers some existing extremum seeking schemes, provides a direct link to off-line optimization and can be used as a unifying framework for design of novel extremum seeking schemes. Moreover, we show that other extremum seeking problem formulations can be interpreted using this unifying viewpoint. We believe that this unifying view will be invaluable to systematically design and analyze extremum seeking controllers in various settings.
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    On a Shubert Algorithm-Based Global Extremum Seeking Scheme
    Nesic, D ; Nguyen, T ; Tan, Y ; Manzie, C (IEEE, 2012)
    This paper adapts the so-called Shubert algorithm for Extremum Seeking Control (ESC) to seek the global extremum (in presence of local extrema) of general dynamic plants. Different from derivative based methods that are widely used in ESC, the Shubert algorithm is a good representative of sampling optimization methods. With knowledge of the Lipschitz constant of an unknown static mapping, this deterministic algorithm seeks the global extremum. By introducing “waiting time” the proposed Shubert algorithm-based global extremum seeking guarantees the semi-global practical convergence (in the initial states) to the global extremum if compact sets of inputs are considered. Several numerical examples demonstrate how proposed method may be successfully deployed.
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    Multidimensional global extremum seeking via the DIRECT method
    Khong, SZ ; Manzie, C ; Nesic, D ; Tan, Y (IEEE, 2012-01-01)
    This paper adapts the DIRECT method with a modified termination criterion for global extremum seeking control of multivariable dynamical plants - DIRECT is a sampling type global optimisation method for Lipschitz-continuous functions defined over compact multidimensional domains. Finite-time semi-global practical convergence is established based on a deadbeat sampled-data control law, whose sampling period is a parameter which determines the region and accuracy of convergence. A crucial part of the development is dedicated to a robustness analysis of the DIRECT method against bounded additive perturbations on the objective function. A numerical example of global extremum seeking in the presence of local extrema based on DIRECT is presented at the end.
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    Extremum seeking methods for online optimization of spark advance in alternative fueled engines
    Mohammadi, A ; Manzie, C ; Nešić, D (Elsevier, 2012-01-01)
    Alternative fueled engines offer greater challenges for engine control courtesy of uncertain fuel composition. This make optimal tuning of input parameters like spark advance extremely difficult in most existing ECU architectures. This paper proposes the use of greybox extremum seeking techniques to provide real-time optimization of the spark advance in alternative fueled engines. The ability and flexibility of the proposed framework is demonstrated through simulation examples. The approaches demonstrated may be extended to other engine inputs requiring online optimization.
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    Curvature-constrained directional-cost paths in the plane
    Chang, AJ ; Brazil, M ; Rubinstein, JH ; Thomas, DA (SPRINGER, 2012-08)
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    Gradient-Constrained Minimum Networks. III. Fixed Topology
    Brazil, M ; Rubinstein, JH ; Thomas, DA ; Weng, JF ; Wormald, N (SPRINGER/PLENUM PUBLISHERS, 2012-10)
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    Towards Reconciling the Large-Scale Structure of Turbulent Boundary Layers in the Atmosphere and Laboratory
    Hutchins, N ; Chauhan, K ; Marusic, I ; Monty, J ; Klewicki, J (SPRINGER, 2012-11)
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    Physical therapies for Achilles tendinopathy: systematic review and meta-analysis
    Sussmilch-Leitch, SP ; Collins, NJ ; Bialocerkowski, AE ; Warden, SJ ; Crossley, KM (BMC, 2012-07-02)
    BACKGROUND: Achilles tendinopathy (AT) is a common condition, causing considerable morbidity in athletes and non-athletes alike. Conservative or physical therapies are accepted as first-line management of AT; however, despite a growing volume of research, there remains a lack of high quality studies evaluating their efficacy. Previous systematic reviews provide preliminary evidence for non-surgical interventions for AT, but lack key quality components as outlined in the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) Statement. The aim of this study was to conduct a systematic review and meta-analysis (where possible) of the evidence for physical therapies for AT management. METHODS: A comprehensive strategy was used to search 11 electronic databases from inception to September 2011. Search terms included Achilles, tendinopathy, pain, physical therapies, electrotherapy and exercise (English language full-text publications, human studies). Reference lists of eligible papers were hand-searched. Randomised controlled trials (RCTs) were included if they evaluated at least one non-pharmacological, non-surgical intervention for AT using at least one outcome of pain and/or function. Two independent reviewers screened 2852 search results, identifying 23 suitable studies, and assessed methodological quality and risk of bias using a modified PEDro scale. Effect size calculation and meta-analyses were based on fixed and random effects models respectively. RESULTS: Methodological quality ranged from 2 to 12 (/14). Four studies were excluded due to high risk of bias, leaving 19 studies, the majority of which evaluated midportion AT. Effect sizes from individual RCTs support the use of eccentric exercise. Meta-analyses identified significant effects favouring the addition of laser therapy to eccentric exercise at 12 weeks (pain VAS: standardised mean difference -0.59, 95% confidence interval -1.11 to -0.07), as well as no differences in effect between eccentric exercise and shock wave therapy at 16 weeks (VISA-A:-0.55,-2.21 to 1.11). Pooled data did not support the addition of night splints to eccentric exercise at 12 weeks (VISA-A:-0.35,-1.44 to 0.74). Limited evidence from an individual RCT suggests microcurrent therapy to be an effective intervention. CONCLUSIONS: Practitioners can consider eccentric exercise as an initial intervention for AT, with the addition of laser therapy as appropriate. Shock wave therapy may represent an effective alternative. High-quality RCTs following CONSORT guidelines are required to further evaluate the efficacy of physical therapies and determine optimal clinical pathways for AT.
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    Graphite flake self-retraction response based on potential seeking
    Ng, TW ; Lau, CY ; Bernados-Chamagne, E ; Liu, JZ ; Sheridan, J ; Tan, N (SPRINGER, 2012-03-09)
    The high elastic modulus and interlayer strengths of graphite flakes make them a durable solid superlubricant. Apart from this, they have configurable electrical properties, exhibit quantum Hall effects, and possess a myriad of useful photonic properties. The self-retraction behavior of graphite flakes can have significant impact on the creation of ordered stacks for various applications because any accidental or intentional displacement of the top flake over the stacks below may result in a misalignment of the carbon-carbon atomic arrangement which, in turn, can have influence over the electrical and photonic properties. It has also been revealed that there was a tendency of the displaced microflake to fail at times to return to its original starting position and orientation. Here, we elucidate this behavior by considering the influence of the interlayer potential forces based on minimal potential energy seeking. The maps of the parameters interrogated here provide the ability for precautions to be undertaken. They also potentially permit the creation of an array of microflake stacks in which the metastable states permit different information to be encoded by virtue of the differentiated photonic or electrical characteristics readable from each array site.
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    Unsupervised discovery of microbial population structure within metagenomes using nucleotide base composition
    Saeed, I ; Tang, S-L ; Halgamuge, SK (OXFORD UNIV PRESS, 2012-03)
    An approach to infer the unknown microbial population structure within a metagenome is to cluster nucleotide sequences based on common patterns in base composition, otherwise referred to as binning. When functional roles are assigned to the identified populations, a deeper understanding of microbial communities can be attained, more so than gene-centric approaches that explore overall functionality. In this study, we propose an unsupervised, model-based binning method with two clustering tiers, which uses a novel transformation of the oligonucleotide frequency-derived error gradient and GC content to generate coarse groups at the first tier of clustering; and tetranucleotide frequency to refine these groups at the secondary clustering tier. The proposed method has a demonstrated improvement over PhyloPythia, S-GSOM, TACOA and TaxSOM on all three benchmarks that were used for evaluation in this study. The proposed method is then applied to a pyrosequenced metagenomic library of mud volcano sediment sampled in southwestern Taiwan, with the inferred population structure validated against complementary sequencing of 16S ribosomal RNA marker genes. Finally, the proposed method was further validated against four publicly available metagenomes, including a highly complex Antarctic whale-fall bone sample, which was previously assumed to be too complex for binning prior to functional analysis.