Learning to Race through Coordinate Descent Bayesian Optimisation

In the automation of many kinds of processes, the observable outcome can often be described as the combined effect of an entire sequence of actions, or controls, applied throughout its execution. In these cases, strategies to optimise control policies for individual stages of the process might not be applicable, and instead the whole policy might have to be optimised at once. On the other hand, the cost to evaluate the policy's performance might also be high, being desirable that a solution can be found with as few interactions as possible with the real system. We consider the problem of optimising control policies to allow a robot to complete a given race track within a minimum amount of time. We assume that the robot has no prior information about the track or its own dynamical model, just an initial valid driving example. Localisation is only applied to monitor the robot and to provide an indication of its position along the track's centre axis. We propose a method for finding a policy that minimises the time per lap while keeping the vehicle on the track using a Bayesian optimisation (BO) approach over a reproducing kernel Hilbert space. We apply an algorithm to search more efficiently over high-dimensional policy-parameter spaces with BO, by iterating over each dimension individually, in a sequential coordinate descent-like scheme. Experiments demonstrate the performance of the algorithm against other methods in a simulated car racing environment.Comment: Accepted as conference paper for the 2018 IEEE International Conference on Robotics and Automation (ICRA

Anomalous diffusion: A basic mechanism for the evolution of inhomogeneous systems

In this article we review classical and recent results in anomalous diffusion and provide mechanisms useful for the study of the fundamentals of certain processes, mainly in condensed matter physics, chemistry and biology. Emphasis will be given to some methods applied in the analysis and characterization of diffusive regimes through the memory function, the mixing condition (or irreversibility), and ergodicity. Those methods can be used in the study of small-scale systems, ranging in size from single-molecule to particle clusters and including among others polymers, proteins, ion channels and biological cells, whose diffusive properties have received much attention lately.Comment: Review article, 20 pages, 7 figures. arXiv admin note: text overlap with arXiv:cond-mat/0201446 by other author

On the effect of contraction ratio in viscoelastic flow through abrupt contractions

A numerical study of the creeping flow of a PTT fluid through planar sudden contractions was carried out to quantify the effect of contraction ratio upon the flow characteristics (streamlines and size and intensity of recirculation vortices). The relevant governing equations were solved with a finite volume method embodying a new high-resolution scheme (Alves et al. [Int. J. Numer. Meth. Fluids 41 (2003) 47]) for the discretisation of convection terms, which is here explained and shown to yield improved accuracy and robustness. The results of the simulations, in terms of streamline patterns, give further evidence for a lip-vortex enhancement mechanism and are in remarkable agreement with flow visualization photographs from the literature. In addition, the results show that the variation of flow features in the vicinity of the re-entrant corner, such as lip vortex size and streamlines, are dominated by downstream quantities and scale with the common definition for the Deborah number in this flow, while flow characteristics in the salient corner region scale with that Deborah number divided by the contraction ratio

Viscoelastic flow in a 3D square/square contraction: Visualizations and simulations.

The inertialess three-dimensional (3D) flow of viscoelastic shear-thinning fluids in a 4:1 sudden square-square contraction was investigated experimentally and numerically and compared with the flow of inelastic fluids. Whereas for a Newtonian fluid the vortex length remains unchanged at low Reynolds numbers, with the non-Newtonian fluid there is a large increase in vortex length with fluid elasticity leading to unstable periodic flow at higher flow rates. In the steady flow regime the vortices are 3D and fluid particles enter the vortex at the middle plane, rotate towards its eye, drift sideways to the corner-plane vortex, rotate to its periphery, and exit to the downstream duct. Such dynamic process is reverse of that observed and predicted with Newtonian fluids. Numerical predictions using a multimode Phan-Thien–Tanner viscoelastic model are found to match the visualizations accurately and in particular are able to replicate the observed flow reversal. The effect of fluid rheology on flow reversal, vortex enhancement, and entry pressure drop is investigated in detail

Identifying the centrality levels of futsal players : a network approach

The aim of this study it was verify the differences of prominence levels between tactical positions in futsal (indoor football). For that reason, it was performed an analysis of variance between competitive levels and tactical positions for the centrality metrics computed by using network analysis. Forty-six futsal players from different competitive levels (U12, U14, U16 and Amateurs) it were analysed during three official futsal matches. Results revealed no differences in centrality metrics between competitive levels (p = 1.00; = 0.001; very small effect size) had no significant statistical differences in the centrality metrics. Nevertheless, tactical position (p = 0.001; = 0.593; moderate effect size) had significant main effects on the centrality metrics. Centrality metrics revealed that defenders are the most prominent players in to receive the ball. By the other hand, defenders and wings are the positions with greater centralities in to pass the ball for the teammates.info:eu-repo/semantics/publishedVersio

Learning and Aging Related Changes in Intrinsic Neuronal Excitability

A goal of many laboratories that study aging is to find a key cellular change(s) that can be manipulated and restored to a young-like state, and thus, reverse the age-related cognitive deficits. We have chosen to focus our efforts on the alteration of intrinsic excitability (as reflected by the postburst afterhyperpolarization, AHP) during the learning process in hippocampal pyramidal neurons. We have consistently found that the postburst AHP is significantly reduced in hippocampal pyramidal neurons from young adults that have successfully learned a hippocampus-dependent task. In the context of aging, the baseline intrinsic excitability of hippocampal neurons is decreased and therefore cognitive learning is impaired. In aging animals that are able to learn, neuron changes in excitability similar to those seen in young neurons during learning occur. Our challenge, then, is to understand how and why excitability changes occur in neurons from aging brains and cause age-associated learning impairments. After understanding the changes, we should be able to formulate strategies for reversing them, thus making old neurons function more as they did when they were young. Such a reversal should rescue the age-related cognitive deficits

Assessment of interactions at children playgrounds using network measures : an exploratory study based on graph theory

This study has used network measures to classify the children interactions in playground. The variance of network processes between genders was tested. Five girls and boys (n = 10; 4.6 0.6 years old) were observed. Statistical procedures has revealed significant differences between genders in IDC (p = 0.027; ES = 0.476; moderate effect) and BC (p = 0.011; ES = 0.576; moderate effect). Results revealed a greater cooperation process between boys.info:eu-repo/semantics/publishedVersio

Who is the prominent tactical position in rink-hockey? : a network approach based on centrality metrics

The aim of this study was to verify the prominence levels of rink-hockey players in different competitive levels. For that reason, it was analysed the variance of network centrality metrics between competitive levels and tactical positions. Fifty-four rink-hockey players from five different levels (U12, U14, U16, U18 and Elite) were analysed during three official matches. The results did not found statistical differences in centrality levels of players between competitive levels (p-value = 1.00; partial eta square = 0.001; very small effect size). Nevertheless, tactical position (p-value = 0.001; partial eta square = 0.534; moderate effect size) had significant main effects on the centrality metrics. In this study it was found that defender and forward are the positions that most receive balls from the teammates. In other hand, the forward is the position that most passes performed until the U16 and in older levels the defender assumes the centrality in passes performed.info:eu-repo/semantics/publishedVersio

Network measures and digraph theory applied to soccer analysis : midfielder is the key player in youth teams

Graph and digraph theories have been used to test the relationships between teammates and the network properties of team sports. Nevertheless, no studies in young soccer teams have been found, as far we know. Therefore, the objective of the study was to apply network measures to identify centrality levels of young soccer players during official matches and analyse the variance between tactical positions and tactical line-ups. Seventy young soccer players from under-10 competitive level were observed during 10 matches. Significant statistical differences were found between players’ positions in IDC (p = 0.001; ES = 0.090; minimum effect); ODC (p = 0.001; ES = 0.156; minimum effect); and BC (p = 0.001; ES = 0.110; minimum effect) variables. No significant statistical differences were found between 1-3-2-1 and 1-2-3-1 line-ups for %IDC (p = 0.113; ES = 0.056; minimum effect), %ODC (p = 0.126; ES = 0.048; minimum effect) and %BC (p = 0.204; ES = 0.035; minimum effect). This study found that midfielder is the key position on the field, being a linkage player to attacking building.info:eu-repo/semantics/publishedVersio