Mechanical Engineering - Research Publications
Permanent URI for this collection
Search Results
1 - 10 of 27
-
ItemOnline optimization of spark advance in alternative fueled engines using extremum seeking control(Elsevier, 2014-08-01)Alternative fueled engines offer greater challenges for engine control courtesy of uncertain fuel composition. This makes optimal tuning of input parameters like spark advance extremely difficult in most existing ECU architectures. This paper proposes the use of grey-box extremum seeking techniques to provide real-time optimization of the spark advance in alternative fueled engines. Since practical implementation of grey-box extremum seeking methods is typically done using digital technology, this paper takes advantage of emulation design methods to port the existing continuous-time grey-box extremum seeking methods to discrete-time frameworks. The ability and flexibility of the proposed discrete-time framework is demonstrated through simulations and in practical situation using a natural gas fueled engine.
-
ItemMulti-agent source seeking via discrete-time extremum seeking control(PERGAMON-ELSEVIER SCIENCE LTD, 2014-09)Recent developments in extremum seeking theory have established a general framework for the methodology, although the specific implementations, particularly in the context of multi-agent systems, have not been demonstrated. In this work, a group of sensor-enabled vehicles is used in the context of the extremum seeking problem using both local and global optimisation algorithms to locate the extremum of an unknown scalar field distribution. For the former, the extremum seeker exploits estimates of gradients of the field from local dithering sensor measurements collected by the mobile agents. It is assumed that a distributed coordination which ensures uniform asymptotic stability with respect to a prescribed formation of the agents is employed. An inherent advantage of the frameworks is that a broad range of nonlinear programming algorithms can be combined with a wide class of cooperative control laws to perform extreme source seeking. Semi-global practical asymptotically stable convergence to local extrema is established in the presence of field sampling noise. Subsequently, global extremum seeking with multiple agents is investigated and shown to give rise to robust practical convergence whose speed can be improved via computational parallelism. Nonconvex field distributions with local extrema can be accommodated within this global framework.
-
Item
-
ItemEuclidean Steiner trees optimal with respect to swapping 4-point subtrees(SPRINGER HEIDELBERG, 2014-04)
-
Item
-
ItemOn the history of the Euclidean Steiner tree problem(SPRINGER, 2014-05)
-
ItemCoexistence of Reward and Unsupervised Learning During the Operant Conditioning of Neural Firing Rates(PUBLIC LIBRARY SCIENCE, 2014-01-27)A fundamental goal of neuroscience is to understand how cognitive processes, such as operant conditioning, are performed by the brain. Typical and well studied examples of operant conditioning, in which the firing rates of individual cortical neurons in monkeys are increased using rewards, provide an opportunity for insight into this. Studies of reward-modulated spike-timing-dependent plasticity (RSTDP), and of other models such as R-max, have reproduced this learning behavior, but they have assumed that no unsupervised learning is present (i.e., no learning occurs without, or independent of, rewards). We show that these models cannot elicit firing rate reinforcement while exhibiting both reward learning and ongoing, stable unsupervised learning. To fix this issue, we propose a new RSTDP model of synaptic plasticity based upon the observed effects that dopamine has on long-term potentiation and depression (LTP and LTD). We show, both analytically and through simulations, that our new model can exhibit unsupervised learning and lead to firing rate reinforcement. This requires that the strengthening of LTP by the reward signal is greater than the strengthening of LTD and that the reinforced neuron exhibits irregular firing. We show the robustness of our findings to spike-timing correlations, to the synaptic weight dependence that is assumed, and to changes in the mean reward. We also consider our model in the differential reinforcement of two nearby neurons. Our model aligns more strongly with experimental studies than previous models and makes testable predictions for future experiments.
-
ItemDynamic foot function as a risk factor for lower limb overuse injury: a systematic review(BioMed Central, 2014)BACKGROUND:Dynamic foot function is considered a risk factor for lower limb overuse injuries including Achilles tendinopathy, shin pain, patellofemoral pain and stress fractures. However, no single source has systematically appraised and summarised the literature to evaluate this proposed relationship. The aim of this systematic review was to investigate dynamic foot function as a risk factor for lower limb overuse injury.METHODS:A systematic search was performed using Medline, CINAHL, Embase and SportDiscus in April 2014 to identify prospective cohort studies that utilised dynamic methods of foot assessment. Included studies underwent methodological quality appraisal by two independent reviewers using an adapted version of the Epidemiological Appraisal Instrument (EAI). Effects were expressed as standardised mean differences (SMD) for continuous scaled data, and risk ratios (RR) for nominal scaled data.RESULTS:Twelve studies were included (total n=3,773; EAI 0.44 to 1.20 out of 2.00, representing low to moderate quality). There was limited to very limited evidence for forefoot, midfoot and rearfoot plantar loading variables (SMD 0.47 to 0.85) and rearfoot kinematic variables (RR 2.67 to 3.43) as risk factors for patellofemoral pain; and plantar loading variables (forefoot, midfoot, rearfoot) as risk factors for Achilles tendinopathy (SMD 0.81 to 1.08). While there were significant findings from individual studies for plantar loading variables (SMD 0.3 to 0.84) and rearfoot kinematic variables (SMD 0.29 to 0.62) as risk factors for ’non-specific lower limb overuse injuries’, these were often conflicting regarding different anatomical regions of the foot. Findings from three studies indicated no evidence that dynamic foot function is a risk factor for iliotibial band syndrome or lower limb stress fractures.CONCLUSION:This systematic review identified very limited evidence that dynamic foot function during walking and running is a risk factor for patellofemoral pain, Achilles tendinopathy, and non-specific lower limb overuse injuries. It is unclear whether these risk factors can be identified clinically (without sophisticated equipment), or modified to prevent or manage these injuries. Future prospective cohort studies should address methodological limitations, avoid grouping different lower limb overuse injuries, and explore clinically meaningful representations of dynamic foot function.
-
ItemPerformance Analysis of a Semiactive Suspension System with Particle Swarm Optimization and Fuzzy Logic Control(HINDAWI LTD, 2014)This paper uses a quarter model of an automobile having passive and semiactive suspension systems to develop a scheme for an optimal suspension controller. Semi-active suspension is preferred over passive and active suspensions with regard to optimum performance within the constraints of weight and operational cost. A fuzzy logic controller is incorporated into the semi-active suspension system. It is able to handle nonlinearities through the use of heuristic rules. Particle swarm optimization (PSO) is applied to determine the optimal gain parameters for the fuzzy logic controller, while maintaining within the normalized ranges of the controller inputs and output. The performance of resulting optimized system is compared with different systems that use various control algorithms, including a conventional passive system, choice options of feedback signals, and damping coefficient limits. Also, the optimized semi-active suspension system is evaluated for its performance in relation to variation in payload. Furthermore, the systems are compared with respect to the attributes of road handling and ride comfort. In all the simulation studies it is found that the optimized fuzzy logic controller surpasses the other types of control.
-
ItemInterfacial nanodroplets guided construction of hierarchical Au, Au-Pt, and Au-Pd particles as excellent catalysts(NATURE PORTFOLIO, 2014-05-06)Interfacial nanodroplets were grafted to the surfaces of self-sacrificed template particles in a galvanic reaction system to assist the construction of 3D Au porous structures. The interfacial nanodroplets were formed via direct adsorption of surfactant-free emulsions onto the particle surfaces. The interfacial nanodroplets discretely distributed at the template particle surfaces and served as soft templates to guide the formation of porous Au structures. The self-variation of footprint sizes of interfacial nanodroplets during Au growth gave rise to a hierarchical pore size distribution of the obtained Au porous particles. This strategy could be easily extended to synthesize bimetal porous particles such as Au-Pt and Au-Pd. The obtained porous Au, Au-Pt, and Au-Pd particles showed excellent catalytic activity in catalytic reduction of 4-nitrophenol.