Solubilization of Ni Imidazole Complex in Micellar Media of Anionic Surfactants,Sodium Dodecyl Sulfate and Sodium Stearate

The solubilization and physicochemical behavior of a coordination complex of nickel, namely [Ni(im)₆]F₂·5H₂O [hexakis(imidazole)nickel(II) fluoride pentahydrate], in aqueous micellar media of anionic surfactants, i.e., sodium dodecyl sulfate (SDS) and sodium stearate (SS), were investigated by using UV–Vis spectroscopy and electrical conductivity measurements. Spectroscopic techniques were used for the computation of binding constant (K_b), partition coefficient (K_x), change in free energy of binding (ΔG_b), and change in free energy of partition (ΔG_p), whereas electrical conductivity data was helpful to calculate thermodynamic parameters of micellization of surfactants in the presence of the Ni complex, i.e., standard entropy of micellization (ΔS_m), free energy (ΔG_m), and enthalpy of micellization (ΔH_m). It is evident from the results that solubilization of the Ni complex takes place because of electrostatic as well as hydrophobic interactions. The presence of the Ni complex in micellar media increases the critical micelle concentration of both surfactants owing to the structure‐breaking effect.     

Influence of machine variables and tool profile on the tensile strength of dissimilar AA7075-AA6061 friction stir welds

Friction stir welding (FSW) of dissimilar alloys and materials is becoming progressively essential as it permits to take the benefits of both materials. Tensile strength is a measure of the weld quality, which mainly depends on machine variables and tool design. In this paper, FSW of dissimilar AA7075-AA6061 aluminium alloys was studied with respect to the welding speeds (rotational and axial), tool tilt angle and tool geometry by the response surface methodology (RSM) with central composite design (CCD). A reduced second-order polynomial equation was successfully developed and validated to adequately fit the observed results of the ultimate tensile strength (UTS). Respectable fitness and well agreement between the experimental and calculated values with an elevated regression coefficient and low deviation were detected for this model within the range of the operating variables. Five tools with concave shoulders and different probe profiles (cylindrical and tapered, smooth and threaded, flatted and non-flatted) and a self-designed backing plate and clamping system were fabricated for this study. It was found that the welding tool with a threaded truncated cone pin and single flat results in a sound weld with higher tensile strength, wide nugget area and smooth surface finish.     

Integration of instrumental neutron activation analysis and inductively coupled plasma-optical emission spectrometry with mathematical modeling for the elemental analysis of plants

Metals in fourteen plants were analyzed in parallel by instrumental neutron activation analysis (INAA) and inductively coupled plasma-optical emission spectrometry (ICP-OES) for the possible integration of the analytical techniques. INAA correlates well with ICP-OES for Ca, K, Fe, Mn, Mg, and Zn. Advantages of INAA include its nondestructive nature and ease of sample preparation. ICP-OES requires destructive sample digestion, but provides superior limits of detection. Therefore, ICP-OES is the method of the choice for low elemental concentrations. In general, ICP-OES is a better choice for Cr, Sr, and Cu in plant analysis for accuracy. On the other hand, a simple mathematical model was developed for predicting the concentrations of Cu and Cr that were measured by INAA. The predicted values of the elements showed consistency to their corresponding certified values as well as to the concentrations measured by ICP-OES, specifically for Cu or when the concentrations exceeded 5?mg/kg.     

A systematic approach to designing a wide‐current range,MOS capacitor‐based switched‐capacitor DC‐DC converter with an augmenting LDO

Switched‐capacitor DC‐DC converters (SC DC‐DC) are analyzed for loss sources, voltage regulation integrity, start‐up latency, and ripple size, while the trade‐offs between these metrics are derived. These analyses are used to design a SC DC‐DC that achieves high efficiency in a wide load current range. Four‐way interleaving was employed to reduce the output ripple and efficiency loss due to this ripple. The design can be reconfigured to achieve gains of 1/3 and 2/5 for inputs ranging between 1.4 and 3.6 V to generate output voltage range of 0.4 to 1.27 V and can supply peak load current of 22 mA. It uses thin‐oxide MOS capacitors for their high density and achieves 75.4% peak efficiency with an input frequency of 100 MHz and a load capacitor of 10 nF. An augmenting LDO that only regulates during sudden load transients helps the converter respond fast to these transients. The chip was implemented using a 65‐nm standard CMOS process.     

A generalized family of memristor‐based voltage controlled relaxation oscillator

Recently, memristive oscillators are a significant topic in the nonlinear circuit theory where there is a possibility to build relaxation oscillators without existence of reactive elements. In this paper, a family of voltage‐controlled memristor‐based relaxation oscillator including two memristors is presented. The operation of two memristors‐based voltage relaxation oscillator circuits is demonstrated theoretically with the mathematical analysis and with numerical simulations. The generalized expressions for the oscillation frequency and conditions are derived for different cases, where a closed form is introduced for each case. The effect of changing the circuit parameters on the oscillation frequency and conditions is investigated numerically. In addition, the derived equations are verified using several transient PSPICE simulations. The power consumption of each oscillator is obtained numerically and compared with its PSPICE counterpart. Furthermore, controlling the memristive oscillator with a voltage grants the design an extra degree of freedom which increases the design flexibility. The nonlinear exponential model of memristor is employed to prove the oscillation concept. As an application, two examples of voltage‐controlled memristor‐based relaxation oscillator are provided to elaborate the effect of the reference voltage on the output voltage. This voltage‐controlled memristor‐based relaxation oscillator has nano size with storage property that makes it more efficient compared with the conventional one. It would be helpful in many communication applications.     

Prediction of high-strength concrete: high-order response surface methodology modeling approach

In the concrete industry, compressive strength is the most essential mechanical property. Therefore, insufficient compressive strength may lead to dangerous failure and, thus, becomes very difficult to repair. Consequently, early, and precise prediction of concrete strength is a major issue facing researchers and concrete designers. In this study, high-order response surface methodology (HORSM) is used to develop a prediction model to accurately predict the compressive strength of high-strength concrete (HSC). Different polynomial degrees order ranging from 2 to 5 is used in this model. The HORSM, with five-order polynomial degree, model outperforms several artificial intelligence (AI) modeling approaches which are carried out widely in the prediction of HSC compression strength. Besides, support vector machine (SVM) model was developed in this study and compared with the HORSM. The HORSM models outperformed the SVM models according to different statistical measures. Additionally, HORSM models managed to perfectly predict the HSC compressive strength in less than one second to accomplish the learning processes. While, other AI models including SVM much longer time. Lastly, the use of HORSM for the first time in the concrete technology field provided much accurate prediction results and it has great potential in the field of concrete technology.

     

A gradient projection algorithm for relaxation methods

We consider a particular problem which arises when apply-ing the method of gradient projection for solving constrained optimiza-tion and finite dimensional variational inequalities on the convex set formed by the convex hull of the standard basis unit vectors. The method is especially important for relaxation labeling techniques applied to problems in artificial intelligence. Zoutendijk's method for finding feasible directions, which is relatively complicated in general situations, yields a very simple finite algorithm for this problem. We present an extremely simple algorithm for performing the gradient projection and an independent verification of its correctness.     

Kinetics of methyl tertiary butyl ether synthesis catalyzed by ion exchange resin

This paper presents the results of an experimental investigation of the kinetics of liquid phase reaction between methanol and isobutene, catalyzed by an acidic ion-exchange resin, to form methyl tertiary butyl ether (MTBE). A one litre Parr batch reactor was used. Experiments were carried out at 70, 80, 90 and 100°C and at pressures sufficient to maintain liquid phase at those temperatures. Initial methanol/isobutene mole ratios of 1.0 and 2.0 were used. The catalyst amount was also varied. These kinetic data were used to model the reaction kinetics, by non-linear least squares regression technique. The reaction was found to follow Rideal-Eley kinetics. The values of the rate constants are reported.