Backstepping-based Lyapunov redesign control of hysteretic single degree-of-freedom structural systems

This paper considers the problem of active control design for a hysteretic single-degree-of-freedom (SDOF) structural system which is exposed to an earthquake excitation. First, backstepping-based control is used to design a controller for the structural system neglecting the effect of the earthquake disturbance. Then, Lyapunov redesign is utilized to design a robust controller for the system in the presence of the earthquake excitation. The hysteretic part of the structural system is modeled by the well-known Bouc–Wen equation, and this equation is directly utilized in the controller design. The controller is proposed for two cases: (a) when the parameters of the structure and the Bouc–Wen model are known, and (b) when these parameters are uncertain. A Lyapunov function is introduced for the closed-loop system, which guarantees the stability of the system equilibrium point. Since the controllers use the nominal and/or minimum and maximum values of the system parameters, the proposed methods are model based. Numerical evaluations are conducted to show the effectiveness of the proposed method. Seven different earthquakes are considered as the external excitations. Simulation results show that the displacement, velocity, and acceleration responses of the controlled structure are reduced significantly compared to the uncontrolled structure.     

Real solutions of the direct geometrico-static problem of under-constrained cable-driven parallel robots with 3 cables: a numerical investigation

This paper addresses the direct geometrico-static problem of under-constrained cable-driven parallel robots with 3 cables. The task at hand consists in finding all equilibrium configurations of the end-effector when the cable lengths are assigned. This problem is known to admit 156 solutions in the complex field, but the upper bound on the number of real solutions is as yet an open issue. Finding this bound is the objective of the paper. For this purpose, three numerical approaches are developed, namely a continuation procedure adapted from an algorithm originally proposed by Dietmaier and two evolutionary techniques based on a genetic algorithm and particle swarm optimization. In all cases, a number of sets of robot parameters for which the direct geometrico-static problem provides at the most 54 real configurations is found. The coherence of the obtained results leads to conjecture that the achieved bound is tight. However, formal proof is yet to be discovered.     

Kinetic Study of the Electro-Catalytic Oxidation of Hydrazine on Cobalt Hydroxide Modified Glassy Carbon Electrode

Electrocatalytic oxidation of hydrazine was investigated on a cobalt hydroxide modified glassy carbon (CHM-GC) electrode in alkaline solution. The process of oxidation involved and its kinetics were established by using cyclic voltammetry, chronoamperometry techniques as well as steady state polarization measurements. In cyclic voltammetry (CV) studies, in the presence of hydrazine the peak current increase of the oxidation of cobalt hydroxide is followed by a decrease in the corresponding cathodic current. This indicates that hydrazine is oxidized on the redox mediator that is immobilized on the electrode surface via an electrocatalytic mechanism. A mechanism based on the electrochemical generation of Co(IV) active sites and their subsequent consumption by the hydrazine in question was also investigated.     

A novel ternary GO@SiO2‐HPW nanocomposite as an efficient heterogeneous catalyst for the synthesis of benzazoles in aqueous media

A new solid acid catalyst, consisting of 12‐phosphotungstic heteropoly acid (HPW) supported on graphene oxide/silica nanocomposite (GO@SiO₂), has been developed via immobilizing HPW onto an amine‐functionalized GO/SiO₂ surface through coordination interaction (GO@SiO₂‐HPW). The GO@SiO₂‐HPW nanocomposite was characterized by Fourier transform infrared (FT‐IR) spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and powder X‐ray diffraction (XRD). The prepared nanocomposite could be dispersed homogeneously in water and further used as a heterogeneous, reusable, and efficient catalyst for the synthesis of benzimidazoles and benzothiazoles by the reaction of 1,2‐phenelynediamine or 2‐aminothiophenol with different aldehydes.     

Stress and strain effects on the electronic structure and optical properties of ScN monolayer

Based on the density functional theory, electronic and optical properties of a monolayer scandium nitride structure have been studied under different strain conditions. Our results indicate that both biaxial compressive and tensile strain effects lead to change the band gap of this structure with different rates. Also, optical absorption spectrum peaks experience an obvious red and blue shifts with the exerting of tensile and compressive strains, respectively. Our results express that ScN monolayer can be the promising candidate for the future nano-base electrical and optical devices.     

Selective cloud point extraction and preconcentration of trace amounts of silver as a dithizone complex prior to flame atomic absorption spectrometric determination

Dithizone (diphenylthiocarbazone) was used as a complexing agent in cloud point extraction for the first time and applied for selective preconcentration of trace amounts of silver. The analyte in the initial aqueous solution was acidified with sulfuric acid (pH<1) and Triton X-114 was added as a surfactant. After phase separation, based on the cloud point separation of the mixture, the surfactant rich phase was diluted with tetrahydrofuran (THF) and the analyte determined in the enriched solution by flame atomic absorption spectrometry. After optimization of the complexation and extraction conditions, a preconcentration factor of 43 was obtained for only 10 ml of sample. The analytical curve was linear in the range of 3-200 ng ml⁻¹ and the limit of detection was 0.56 ng ml⁻¹. The proposed method was applied to the determination of silver in water samples.     

A facile synthesis of oxazolo[3,2-a][1,10]phenanthrolines via a new multicomponent reaction

The synthesis of N-cyclohexyl-10-(2-fluorophenyl)-8aH-oxazolo[3,2-a][1,10]phenanthroline and N-(2,6-dimethylphenyl)-10-(2-fluorophenyl)-8aH-oxazolo[3,2-a][1,10]phenanthroline by reaction of 2-fluorobenzaldehyde, phenanthroline and cyclohexyl or 2,6-dimethylphenyl isocyanide is reported.     

Variational approaches to impulsive elastic beam equations of Kirchhoff type

In this paper, we study the existence of multiple solutions for impulsive fourth-order differential equations of Kirchhoff type. Using a variational method and some critical points theorems, we obtain some new criteria for guaranteeing that impulsive fourth-order differential equations of Kirchhoff type have three and infinitely many solutions. Some recent results are extended and improved. Some examples are presented to demonstrate the applications of our main results.     

Study of complexation of phenylaza-15-crwon-5, 4-nitrobenzo- 15-crown-5, and benzo-15-crown-5 with Ag+, Tl+ and Pb2+ ions in methanol by competitive potentiometry

The complexation reaction of phenylaza-15-crwon-5, 4- nitrobenzo- 15-crown-5, and benzo-15-crown-5 with Ag⁺, Tl⁺ and Pb²⁺ ions in methanol solution have been studied by a competitive potentiometric method. The Ag⁺/Ag electrode used both as an indicator and reference electrode in a concentration cell. The emf of cell monitored as the crown ethers concentration varies through the titration. The stoichiometry and stability constants of resulting complexes have been evaluated by MINIQUAD. The stoichiometry for all resulting complexes was 1:1. The stability of these metal ions with derivatives of 15-crown-5 are in order phenylaza-15-crown-5 > Benzo-15-crown-5 > 4-nitrobenzo-15-crown-5, and for the each used crown ethers are as Pb²⁺ > Ag⁺ > Tl⁺. The effect of the substituted group on the stability of resulting complexes was considered. The obtained results are novel and interesting.     

A Novel Synthetic Method and Potential Application of a Sulfanilic Acid-Based Surfactant

A novel synthetic method was developed to prepare a difunctional surfactant using sulfanilic acid and dodecyl bromide. In the first step, sulfanilic acid was protected by acetic anhydride. Then, Friedel–Crafts alkylation of the synthesized acetanilide with dodecyl bromide was performed in the presence of aluminum chloride. The protecting group (amide) was removed easily by acid hydrolysis. The formation of surfactant was confirmed with Fourier transform infrared and proton nuclear magnetic resonance spectroscopy. The demulsification property of this surfactant was studied using brine-fuel oil emulsion, and its result was compared with a commercially available demulsifier. The results showed that 52% of water was separated from emulsion at room temperature, but at elevated temperature 98% of water was separated from brine-fuel oil emulsion.