Remarks on the relationship between stability and internal stability of nonlinear systems

In this paper, we investigate the relationship between stability and internal stability of nonlinear systems. It is shown that under certain conditions, stability implies attractivity of the equilibrium and that local stability with finite gain implies local asymptotic stability of the origin. Copyright © 2012 John Wiley & Sons, Ltd.     

Selective Deep Catalytic Cracking Process of Hydrocarbon Feedstocks for the Production of Light Olefins: II. Cooperative Effect of Thermal Cracking and Catalytic Reactions Observed in a 1-Zone Reactor

Hybrid catalysts comprising a chromium-based cocatalyst and a silica-rich ZSM-5 zeolite, when doped with lithium, showed quite a high on-stream stability even at a relatively high reaction temperature (735 °C). The cooperative effect of the thermal cracking and the catalytic reactions, and the interactions between the two catalyst components of the hybrid catalyst, resulted in maximum production of light olefins when the hybrid catalyst contained 40 wt% of zeolite. The main chemical links between the thermal cracking (TC) and the catalytic reactions were the conversions of diolefins and large olefins, the latter being produced by the TC and the active sites of the chromium-bearing cocatalyst, respectively.     

Development of MgAl2O4 spinel coating on graphite surface to improve its water-wettability and oxidation resistance

Low water-wettability and oxidation resistance of graphite have limited its application in carbon containing refractory castables. The aims of this study are the improvement of water-wettability and the oxidation resistance of natural flaky graphite by applying an oxide coating on its surface. To develop the coating, magnesium aluminate spinel sol was formulated via a citrate–nitrate route and graphite powder was then added to the sol. The mixture was heat treated in appropriate temperature and atmosphere to get the polycrystalline MgAl₂O₄ coating on graphite particles surface. The microstructure of coating was studied by X-ray diffractometer, SEM and TEM. The water-wettability was evaluated by measuring the water drop contact angle and plotting the zeta potential vs. pH. The results showed the development of a stable nanocrystalline MgAl₂O₄ spinel coating which improved the water-wettability and oxidation resistance of graphite significantly. Also, characterization of the coating is explained with emphasis on its application importance.     

Preparation of sulfuric acid ([3-(3-silicapropyl)sulfanyl]propyl)ester: A new and recyclable catalyst for the formylation and acetylation of alcohols under heterogeneous conditions

We describe a simple and efficient procedure for the preparation of sulfuric acid ([3-(3-silicapropyl)sulfanyl]propyl)ester (3) by the reaction of 3-(thio(propy-3-yl)silica)-propanol (2) and chlorosulfonic acid in chloroform. 3-(Thio(propy-3-yl)silica)-propanol was prepared by the reaction of 3-mercaptopropylsilica (MPS) with 3-chloropropanol in refluxing toluene. This solid sulfuric acid ([3-(3-silicapropyl)sulfanyl]propyl)ester is employed as a new catalyst for the formylation of alcohols with ethyl formate under mild and heterogeneous conditions at room temperature with good to excellent yields. Also, 3 can catalyze the acetylation of various alcohols by the reaction of alcohols with ethyl acetate under reflux conditions or with acetic anhydride at room temperature.     

A flexible algorithm for fault diagnosis in a centrifugal pump with corrupted data and noise based on ANN and support vector machine with hyper-parameters optimization

Fault detection and diagnosis have an effective role for the safe operation and long life of systems. Condition monitoring is an appropriate way of the maintenance technique that is applicable in the fault diagnosis of rotating machinery faults. A unique flexible algorithm is proposed for classifying the condition of centrifugal pump based on support vector machine hyper-parameters optimization and artificial neural networks (ANNs) which are composed of eight distinct steps. Artificial neural networks (ANNs), support vector classification with genetic algorithm (SVC-GA) and support vector classification with particle swarm optimization (SVC-PSO) algorithm have been considered in a flexible algorithm to perform accurate classification in the manufacturing area. SVC-GA, SVC-PSO and ANN have been used together due to their importance and capabilities in classifying domain. Also, the superiority of the proposed hybrid algorithm (SVC with GA and PSO) is shown by comparing its results with SVC performance. Two types of faults through six features, flow, temperature, suction pressure, discharge pressure, velocity, and vibration, have been classified with proposed integrated algorithm. To test the robustness of the efficiency results of the proposed method, the ability of proposed flexible algorithm in dealing with noisy and corrupted data is analyzed.     

Synthesis and characterization of nanocrystalline MgAl2O4 spinel via sucrose process

Nanocrystalline MgAl₂O₄ spinel powder was synthesized using metal nitrates and a polymer matrix precursor composed of sucrose and polyvinyl alcohol (PVA). The precursor and the calcined powders were characterized by simultaneous thermal analysis (STA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). According to XRD results, the inceptive formation temperature of spinel via this technique was between 600 and 700 °C. The calcined powder at 800 °C for 2 h has faced shaped morphology and its crystallite size is in the range of 8-12 nm. Further studies also showed that the amount of polymeric matrix to metal ions has significant influence on the crystallite size of synthesized magnesium aluminate spinel powder.     

Behavior of semi‐rigid connections and semi‐rigid frames

Semi‐rigid connections are widely used in different countries. These connections are usually used in semi‐rigid frames with bracing system. Considering the frequent use of these connections, studying their behavior as an individual connection or as a frame with a semi‐rigid connection is of great importance. In this paper, moment–rotation behavior of bolted angle connection as a usual semi‐rigid connection is studied, and the affecting factors on there are investigated. Finite element connection models are developed. These models are verified by comparing the results of finite element analyses with the results of experimental test, and the verified models are used to investigate the behavior of the connections. The behavior of semi‐rigid frame with bolted angle connection is then studied conducting time‐history analyses. The results show that the increase in shear stiffness of angle bolted connections significantly decreases the lateral drift and increase the frame stability against lateral loading. Copyright © 2012 John Wiley & Sons, Ltd.     

Rotational capacity of castellated steel beams

This paper numerically studies the behavior of castellated beams with two simply supported ends under moment gradient loading and investigates the effect of beam and braced lengths on rotational capacity of castellated beams. To assure the ability of numerical models in predicting the complex behavior (especially at the location of opening) as well as the failure modes, numerical models of two experimentally tested specimens are developed. Comparison of force–displacement curves and failure modes shows that neglecting the boundary condition of the specimens, the numerical method can properly predict the behavior of castellated beams. All geometrical properties of the beams are the same as the study parameters so that the finite element model of the corresponding plain‐webbed beams can be easily created by filling the web openings in castellated beams. The accuracy of finite element models of plain‐webbed beams is evaluated by comparing the moment–rotation behavior with that of numerical models developed by other researchers. Rotational capacity of castellated beams derived from numerical models is compared with that of the corresponding I‐shaped plain‐webbed steel beams, and it is observed that in the case of short beams, web openings reduce energy absorption and plastic moment capacity of the beams compared with that of long ones. Copyright © 2012 John Wiley & Sons, Ltd.     

Simultaneous H2/H∞ optimal control The state feedback case

A simultaneous H₂/H_∞ control problem is considered. This problem seeks to minimize the H₂ norm of a closed-loop transfer matrix while simultaneously satisfying a prescribed H_∞ norm bound on some other closed-loop transfer matrix by utilizing dynamic state feedback controllers. Such a problem was formulated earlier by Rotea and Khargonekar (Automatica, 27, 307–316, 1991) who considered only so called regular problems. Here, for a class of singular problems, necessary and sufficient conditions are established so that the posed simultaneous H₂/H_∞ problem is solvable by using state feedback controllers. The class of singular problems considered have a left invertible transfer function matrix from the control input to the controlled output which is used for the H₂ norm performance measure. This class of problems subsumes the class of regular problems.