Dynamical system learning using extreme learning machines with safety and stability guarantees

This article presents a continuous dynamical system model learning methodology that can be used to generate reference trajectories for the autonomous systems to follow, such that these trajectories are invariant to a given closed set and uniformly ultimately bounded with respect to an equilibrium point inside the closed set. The autonomous system dynamics are approximated using extreme learning machines (ELM), the parameters of which are learned subject to the safety constraints expressed using a reciprocal barrier function, and the stability constraints derived using a Lyapunov analysis in the presence of the ELM reconstruction error. This formulation leads to solving a constrained quadratic program (QP) that includes a finite number of decision variables with an infinite number of constraints. Theorems are developed to relax the QP with infinite number of constraints to a QP with a finite number of constraints which can be practically implemented using a QP solver. In addition, an active sampling methodology is developed that further reduced the number of required constraints for the QP by only evaluating the constraints at a smaller subset of points. The proposed method is validated using a motion reproduction task on a seven degree-of-freedom Baxter robot, where the task space position and velocity dynamics are learned using the presented methodology.     

Numerical simulation of 2-D laminar flow subjected to the Lorentz force effect in a channel with backward-facing step

This paper presents the numerical solutions of a two-dimensional laminar flow over a backward-facing step in the presence of the Lorentz body force. The Navier-Stokes equations in a vorticity-stream function formulation are numerically solved using a uniform grid mesh of 2001 × 51 points. A second-order central difference approximation is used for spatial derivatives. The solutions progress in time with a fourth-order Runge-Kutta method. The unsteady backward-facing step flow solution is computed for Reynolds numbers 100 to 800. The size and genesis of the recirculating regions are dramatically affected by applying the Lorentz force. The results demonstrate that using an appropriate configuration for applying the Lorentz force can make it an essential tool for controlling the flow in channels with a backward-facing step.     

Wind tunnel study and numerical simulation of dust particle resuspension from indoor surfaces in turbulent flows

Particle resuspension from flooring is an important source of air pollution in the indoor environment. In this work, resuspension of monolayer, polydisperse, irregularly shaped dust particles from various types of floorings was studied via a series of wind tunnel experiments. The range of free-stream velocity needed for resuspension of dust particles was evaluated as a function of particle size and material of particles and surfaces. In addition, a Monte Carlo simulation for predicting the resuspension of dust particles was developed. The resuspension model took into account the effects of particle irregularity, particle surface roughness, and flow characteristics. The dust particle resuspension from different floorings for several particle sizes was evaluated. The model predictions for resuspension fractions were compared with the experimental data and good agreement was observed. The study provided information on the role of airflow velocity on irregular dust particle resuspension from common floorings.     

Blur invariants: A novel representation in the wavelet domain

Blur invariants in the wavelet domain are proposed for the first time in this paper. Wavelet domain blur invariants take advantage of several benefits that this domain provides, i.e. different alternatives for wavelet function and analysis in different scales. It is not required to model the blur system in order to extract the invariants. It will be shown how the space domain blur invariants are a special case of the proposed invariants. It will also be explained how the proposed invariants would not have the null space that their special case in the spatial domain have which limits their discriminative power. The performance of these invariants will be demonstrated through experiments, and compared to its counterpart which is defined in the spatial domain.     

Eco‐friendly,acrylic resin‐modified potassium silicate as water‐based vehicle for anticorrosive zinc‐rich primers

Potassium silicate binder of zinc‐rich coating was modified by adding water‐based acrylic resin. Several series of coatings containing 5, 10, and 15 wt % of acrylic and acrylic/styrene binders were added to potassium silicate. The coatings were applied on steel and the corrosion resistance of coatings was evaluated by conventional methods such as electrochemical impedance spectroscopy, corrosion potential, salt spray, and scanning electron microscopy. The results indicated that the modification of silicate binder with acrylic and acrylic/styrene led to shortening the curing time, improved corrosion protection, better dispersion of zinc particles, and enhanced salt spray resistance of resultant coatings. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40370.     

Oxytetracycline nanosensor based on poly-ortho-aminophenol/multi-walled carbon nanotubes composite film

Poly-ortho-aminophenol (PoAP) and multi-walled carbon nanotubes (MWCNTs) were deposited on the platinum electrode using cyclic voltammetry technique to form the Pt/PoAP/MWCNTs nanosensor for the electrochemical determination of oxytetracycline as analyte. This electrochemical nanosensor with good uniformity and high surface area was prepared in the presence of an ionic surfactant (sodium dodecyl sulfate) as electrolyte to suspend carbon nanotubes within the PoAP and improve the stability and electroactivity of the composite film. The surface morphology of the prepared nanosensor was characterized by scanning electron microscopy and showed a three-dimensional network structure. The influence of several parameters such as number of potential cycles, scan rate and pH of the solution on the electrochemical response of the resultant electrode was investigated. The prepared electrode functioned as a selective recognition element for oxytetracycline determination. It showed excellent electrochemical response to oxytetracycline at low oxidative potential in buffer solution of pH 2.0, with good stability and sensitivity. Under the optimal experimental conditions, the electrochemical response of the sensor was linear with respect to the concentration of oxytetracycline in a dynamic range of 0.2 μM–0.25 mM. The detection limit of the fabricated nanosensor was calculated as 0.10 μM (signal/noise = 3). This sensor was used successfully for the oxytetracycline determination in real samples with recoveries of 96.9–103.5 %.     

Numerical evaluation of a granular column reinforced by geosynthetics using encasement and laminated disks

Structures built on soft strata may experience substantial settlement, large lateral deformation of the soft layer and global or local instability. Granular columns reinforced by geosynthetic materials reduce settlement and increase the bearing capacity of the composite ground. Reinforcement is more common in the form of geosynthetic encasement, but laminated disks can also be used. This paper compares these two forms of reinforcement by means of unit cell finite element analyses. Numerical results were initially validated using field and experimental data, and parametric studies were subsequently performed. The parametric studies varied the geosynthetic interval and the geosynthetic tensile stiffness of the laminated disks as well as the length of the reinforced column. The analyses showed that in both modes; encasement and laminated disks; the geosynthetic increases the vertical stress mobilized on the reinforced column and reduces settlement on soft soil. It was also observed that in order to achieve the same performance as with encased column, the optimum interval between laminated disks is dependent on the stiffness of the geosynthetics and the column reinforced length.     

Free vibration analysis of functionally graded plates with multiple circular and non-circular cutouts

Cutouts are inevitable in structures due to practical consideration.In order to investigate the free vibration of functionally graded plates with multiple circular and non-circular cutouts,finite eleme...     

Assessment of mean and fluctuating velocity and temperature of CuO/water nanofluid in a horizontal channel: Large eddy simulation

Abstract

A comprehensive investigation applying the large eddy simulation approach to turbulent forced convection of CuO/water nanofluid flowing through a horizontal channel is carried out. Dealing with the sub-grid scale stress tensor and heat flux vector, the wall-adopting local eddy-viscosity model is employed. The periodic boundary condition is imposed to the streamwise and spanwise directions, while the no-slip and constant heat flux are applied to the walls. The results indicate that adding nanoparticles into the base fluid increases the dimensionless mean velocity and fluctuations of velocity and temperature. This increment is more evident for turbulent Reynolds stress and turbulent heat flux in the streamwise direction than the other directions. Therefore, higher energy is transferred between nanofluid layers which results in a higher amount of heat transfer than the pure water. It is also observed that the nanoparticles enhance the turbulence energy at all frequencies, and the decay in the fluctuations occurs at the higher wavenumbers.