Friction compensation of double inverted pendulum on a cart using locally linear neuro-fuzzy model

Double inverted pendulum on a cart (DIPC) is a highly nonlinear system. Due to its complex dynamics, it is widely used as a test-bed plant for the verification of newly designed controllers. In DIPC, two pendulums are kept upward by linear movements of cart. Because of this linear motions and frequent switching of velocity directions, another nonlinearity caused by friction becomes dominant around the equilibrium point. Friction introduces limit cycles to the system and results in a poor steady-state response. To eliminate these negative effects, the locally linear neuro-fuzzy (LLNF) approach is used to build an inverse model for friction compensation. This model is compared with multilayer perceptron network in order to demonstrate the better performance of LLNF. To stabilize DIPC, a common optimal controller is used, and despite its limited performance, experimental results show that the application of inverse modeling for friction compensation improves the steady-state response outstandingly.     

Inverse optimality in the class of Hopfield neural networks with input nonlinearity

This paper presents the chaos suppression problem in the class of Hopfield neural networks (HNNs) with input nonlinearity using inverse optimality approach. Using the inverse optimality technique and based on Lyapunov stability theory, a stabilizing control law, which is optimal with respect to meaningful cost functional, is determined to achieve global asymptotically stability in the closed-loop system. Numerical simulation is performed on a four-dimensional hyper-chaotic HNN to demonstrate the effectiveness of the proposed method.     

Performance of glass fiber reinforced polymer bars under elevated temperatures

This paper investigates the residual tensile properties of newly developed glass fiber reinforced polymer (GFRP) bars after being subjected to elevated temperatures for different periods. A total of 120 GFRP specimens were tested in this study. Half of the samples were covered with concrete while the other half were bare bars. The specimens were subjected to three different controlled temperatures (100, 200 and 300 °C) for three different periods (1, 2, and 3 h). Test results showed that almost no losses were observed in the tensile modulus after all exposure periods and temperatures. Losses in the tensile strength, proportional to the level of temperature and exposure period, were recorded. The bars with concrete cover showed higher residual tensile strength compared to their counterparts without coating. The concrete cover was more effective at the lowest temperature level (100 °C) and at the shortest time period (1 h). Scanning Electronic Microscopy (SEM) technique was also used to investigate the effect of elevated temperature on the degradation mechanism of the GFRP bars. The results showed that increasing the temperature level affected the resin matrix surrounding the glass fibers and consequently affected the bond between the fibers and the matrix.     

Numerical simulation of solvent and water assisted electrical heating of oil sands including aquathermolysis and thermal cracking reactions

Simulations of bitumen recovery using solvent‐ and water‐assisted electrical heating of oil sands are presented to evaluate the process and to study gas generation. Aquathermolysis and thermal cracking and dissolution of acid‐gases in water are included. Steam‐assisted gravity drainage (SAGD) is also simulated for comparison. Results show that gas generation negatively impacts SAGD. However, in electrical heating dissolution of gases into solvent weakens their negative impact. Results indicate that SAGD generates a larger gas volume than electrical heating. In both processes, methane is found to be the major species in the produced gas and H₂S concentration can reach high values. While the effect of acid–gas solubility in water on oil recovery is not evident its effect on generated gas volume is significant. Simulation results demonstrate that electrical heating is more energy efficient than SAGD. These results find application in design of experiments and pilot and field‐scale implementation of the process. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4243–4258, 2017     

Large‐scale fading behavior for a cellular network with uniform spatial distribution

Large‐scale fading (LSF) between interacting nodes is a fundamental element in radio communications, responsible for weakening the propagation, and thus worsening the service quality. Given the importance of channel‐losses in general, and the inevitability of random spatial geometry in real‐life wireless networks, it was then natural to merge these two paradigms together in order to obtain an improved stochastical model for the LSF indicator. Therefore, in exact closed‐form notation, we generically derived the LSF distribution between a prepositioned reference base‐station and an arbitrary node for a multi‐cellular random network model. In fact, we provided an explicit and definitive formulation that considered at once: the lattice profile, the users' random geometry, the effect of the far‐field phenomenon, the path‐loss behavior, and the stochastic impact of channel scatters. The veracity and accuracy of the theoretical analysis were also confirmed through Monte Carlo simulations.     

Determining the Main Factors in Declining the Urmia Lake Level by Using System Dynamics Modeling

Urmia Lake in Iran is the second largest saline lake in the world. This ecosystem is the home for different species. Due to various socio-economical and ecological criteria, Urmia Lake has important role in the Northwestern part of the country but it has faced many problems in recent years. Because of droughts, overuse of surface water resources and dam constructions, water level has decreased in such a way that one quarter of the lake has changed to saline area in the last 10 years. The purpose of this research is to determine the main factors which reduce the lake’s water level. To this end, a simulation model, based on system dynamics method, is developed for the Urmia Lake basin to estimate the lake’s level. After successful verification of the model, results show that (among the proposed factors) changes in inflows due to the climate change and overuse of surface water resources is the main factor for 65% of the effect, constructing four dams is responsible for 25% of the problem, and less precipitation on lake has 10% effect on decreasing the lake’s level in the recent years. In the future, the model also can be used by managers as a decision support system to find the effects of building new dams or other infrastructures.     

Nodular structure of isotactic polypropylene crystallizes from the melt

This article highlights the melt crystallization behavior of different grades of isotactic polypropylene (iPP) using a hot‐stage polarizing optical microscopy. iPP samples were heated up at a heating rate of 10°C/min passing the melting temperature and then kept for 3 min at a temperature range of 175–200°C before they cooled rapidly at 40°C/min to crystallize isothermally at a range of 130–145°C. It has been found that the temperature at which the samples were kept has a strong effect on the crystallization mode; for samples heated up and kept at temperatures below 190°C, the crystallization started with thin and long rods or nodules, which grew in the circumferential direction only while their lengths remain unchanged as the time passed. The shape of the nodules can be straight, circular, branched, or entangled, and they can grow parallel to each other or they can be crossed or in a random way. This phenomenon disappeared completely for samples melted and kept at temperatures above 195°C. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Cyanoethylation of Hydroxyethyl Cellulose: Preparation and Characterization

Commercial hydroxyethyl cellulose (HEC) was cyanoethylated with acrylonitrile in nonaqueous medium in the presence of sodium hydroxide under a variety of conditions. Variables studied included the amount of acrylonitrile and the reaction temperature. The reaction was proved by NMR and its extent was measured by determining the nitrogen content. The physical properties of the obtained derivatives—i.e., the electric properties and the apparent viscosity at various rates of shear—were investigated. It was found that the extent of reaction was increased by increasing the amount of acrylonitrile as well as the reaction temperature. The products were water soluble and their apparent viscosity increased with increasing nitrogen content. The same holds true for the dielectric constant and dielectric loss.     

Characterization of stabilized porous magnetite core–shell nanogel composites based on crosslinked acrylamide/sodium acrylate copolymers

Stabilized and dispersed superparamagnetic porous nanogels based on sodium acrylate (AA‐Na) and acrylamide (AM) in a surfactant‐free aqueous system were synthesized via solution polymerization at room temperature. The formation of magnetite nanoparticles was confirmed and their properties characterized using Fourier transform infrared spectroscopy. Extensive characterization of the magnetic polymer particles using transmission electron microscopy (TEM), dynamic light scattering and zeta potential measurements revealed that Fe₃O₄ nanoparticles were incorporated into the shells of poly(AM/AA‐Na). The average particle size was 5–8 nm as determined from TEM. AM/AA‐Na nanoparticles with a diameter of about 11 nm were effectively assembled onto the negatively charged surface of the as‐synthesized Fe₃O₄ nanoparticles via electrostatic interaction. Crosslinked magnetite nanocomposites were prepared by in situ development of surface‐modified magnetite nanoparticles in an AM/AA‐Na hydrogel. Scanning electron microscopy was used to study the surface morphology of the prepared composites. The morphology, phase composition and crystallinity of the prepared nanocomposites were characterized. Atomic force microscopy and argon adsorption–desorption measurements of Fe₃O₄.AM/AA indicated that the architecture of the polymer network can be a hollow porous sphere or a solid phase, depending on the AA‐Na content. © 2013 Society of Chemical Industry