Simultaneous Kinetic‐Spectrophotometric Determination of Hydrazine and its Derivatives by Partial Least Squares and Principle Component Regression Methods

Simultaneous kinetic‐spectrophotometric determination of a ternary mixture of hydrazine (HZ) and its derivatives by principal component regression (PCR) and partial least squares (PLS) calibration is described. The methods were based on the difference observed in the reduction rate of iron(III) with HZ, thiosemicarbazide (TSCZ) and phenylhydrazine (PHZ) in the presence of 2,2′‐bipyridine (Bpy). The colored complex of [Fe(Bpy)₃]²⁺ was formed in sodium dodecyl sulfate (SDS) as micellar media, and then monitored at 520 nm. The results showed that simultaneous determination of HZ, TSCZ and PHZ could be performed in their concentration ranges of 1.0–70.0, 0.2–6.0 and 0.1–10.0 μg mL^?1, respectively. The root mean squares errors of prediction (RMSEP) of HZ, TSCZ and PHZ were 0.719, 0.164 and 0.105 (for PLS) 0.788, 0.166 and 0.993 (for PCR), respectively. Both methods (PCR and PLS) were validated using a set of synthetic sample mixtures and then applied for simultaneous determination of HZ, TSCZ and PHZ in water samples.     

Methylated Azopyridine as a New Electron Transfer Mediator for the Electrocatalytic Oxidation of NADH

Carbon ionic liquid electrode (CILE) has been modified with a new synthesized mediator i.e. N,N′‐dimethyl‐4,4′‐azopyridinium hexafluorophosphate (MAZPHP) via sol process and the electron transfer mediating characteristics of this mediator has been evaluated. 4,4′‐Azopyridine (AZP) did not show any electrocatalytic activity toward the selected probe, NADH, while its synthesized methylated derivative, MAZPHP, is a very efficient mediator for the electrocatalytic NADH oxidation. Cyclic voltammetry of MAZPHP/Sol/CILE exhibited a pair of reversible peaks corresponding to incorporated mediator with a formal potential of about 221 mV vs. Ag/AgCl. MAZPHP/Sol/CILE is free from fouling effects by the oxidation products of NADH which generally give hindrance to amperometric detection of NADH. Using amperometric technique, NADH can be determined in the range of 1.0×10^?5 M to 1.4×10^?3 M with a detection limit of 2.0×10^?6 M.     

Retraction algorithms for solving variational inequalities,pseudomonotone equilibrium problems,and fixed-point problems in Banach spaces

In this paper, using sunny generalized nonexpansive retractions which are different from the metric projection and generalized metric projection in Banach spaces, we present new extragradient and line search algorithms for finding the solution of a J-variational inequality whose constraint set is the common elements of the set of fixed points of a family of generalized nonexpansive mappings and the set of solutions of a pseudomonotone J-equilibrium problem for a J -α-inverse-strongly monotone operator in a Banach space. To prove strong convergence of generated iterates in the extragradient method, we introduce a ? _?-Lipschitz-type condition and assume that the equilibrium bifunction satisfies this condition. This condition is unnecessary when the line search method is used instead of the extragradient method. Using FMINCON optimization toolbox in MATLAB, we give some numerical examples and compare them with several existence results in literature to illustrate the usability of our results.     

Simultaneous kinetic determination of sulfite and sulfide using artificial neural networks

Artificial neural networks (ANNs) are proposed for the determination of sulfite and sulfide simultaneously. The method is based on the reaction between Brilliant Green (BG) as a colored reagent and sulfite and/or sulfide in buffered solution (pH 7.0) and monitoring the changes of absorbance at maximum wavelength of 628 nm. Experimental conditions such as pH, reagents concentrations, and temperature were optimized and training the network was performed using principal components (PCs) of the original data. The network architecture (number of input, hidden and output nodes), and some parameters such as learning rate (η) and momentum (α) were also optimized for getting satisfactory results with minimum errors. The measuring range was 0.05-3.6 μg ml⁻¹ for both analytes. The proposed method has been successfully applied to the quantification of the sulfite and sulfide in different water samples.     

Fabrication and the electrochemical activation of network-like MnO<Subscript>2</Subscript> nanoflakes as a flexible and large-area supercapacitor electrode

Porous network-like MnO₂ thick films are successfully synthesized on a flexible stainless steel (SS) mesh using a simple and low-cost electrodeposition method followed by an electrochemical activation process. Morphology, chemical composition, and crystal structure of the prepared electrodes before and after the activation process are determined and compared by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) analyses. The results show that the implementation of the electrochemical activation process does not change the chemical composition and crystal structure of the films, but it influences the surface morphology of the MnO₂ thick layer to a flaky nanostructure. Based on the electrochemical data analysis, the maximum specific capacitance of 1400 mF (381 F g^?1) and 3700 mF (352 F g^?1) are measured for small (2.6 cm²) and large (10 cm²) surface area electrodes, respectively. In addition, a flexible symmetric MnO₂//MnO₂ solid-state supercapacitor shows a capacitance of 0.3 F with about 98% retention at different bending angles from 0 to 360°.     

The first study on enhanced photoresponsivity of ZnO-TiO2 nanocomposite thin films by anodic polarization

The physical and photoelectrochemical properties of the anodized ZnO-TiO(2) thin films were investigated in this study. Impedance spectroscopy revealed a decrease in charge transfer resistance and Tafel plots determined enhancement of about 200 times in the exchange current (i(0)) after anodization at high positive potential. It was found from XPS analysis that after applying the potential of 5 V to the ZnO-TiO(2) photoelectrode, the lattice oxygen (O(2-)) in the thin film is oxidized to molecular oxygen and then, cations such as Zn(2+) can be solved in the basic electrolyte and passed to the solution. Moreover, according to AFM analysis it was observed that the surface of the samples has been grooved by applying anodic voltage resulting in an increase of effective surface of the film. A mechanism for describing the significant enhancement in the photoresponse of the anodized layer is proposed.     

Electrochemical investigations of the various electrolytes for high energy density metal oxide supercapacitor

Journal of Solid State Electrochemistry - In this work, the asymmetric supercapacitor (ASC) devices with three different electrolytes including aqueous, organic, and gel polymer electrolytes have...     

Extragradient and linesearch methods for solving split feasibility problems in Hilbert spaces

Utilizing the Tikhonov regularization method and extragradient and linesearch methods, some new extragradient and linesearch algorithms have been introduced in the framework of Hilbert spaces. In the presented algorithms, the convexity of optimization subproblems is assumed, which is weaker than the strong convexity assumption that is usually supposed in the literature, and also, the auxiliary equilibrium problem is not used. Some strong convergence theorems for the sequences generated by these algorithms have been proven. It has been shown that the limit point of the generated sequences is a common element of the solution set of an equilibrium problem and the solution set of a split feasibility problem in Hilbert spaces. To illustrate the usability of our results, some numerical examples are given. Optimization subproblems in these examples have been solved by FMINCON toolbox in MATLAB.     

Hyers–Ulam–Rassias Stability of a Quadratic and Additive Functional Equation in Quasi-Banach Spaces

In this paper we establish the general solution of the functional equation