Hybrid nanocomposite membranes of sulfonated poly(ethersulfone)/1,1-carbonyl diimidazole/1-(3-aminopropyl)-silane/silica for direct methanol fuel cells

Composite membranes of sulfonated poly(ethersulfone)/1,1-carbonyl diimidazole/1-(3-aminopropyl)-silane/silica (SPES/CDI/AS/SiO₂) with silica of various contents (3, 5 and 8 wt%) were prepared as electrolytes for direct methanol fuel cells (DMFCs). Comparison was made with pure SPES and SPES/SiO₂. The properties of the composite membranes were studied by FTIR, TGA, XRD, water and methanol uptake, proton conductivity. SPES/CDI/AS/SiO₂ membranes were also characterized by scanning electron microscopy (SEM), which showed good adhesion between the modified sulfonic acid (-SO3H) groups of SPES and silica because of cross-linking with covalent bond formation and reduced cavities in the composites. This effect played an important role in reducing water uptake, methanol uptake and methanol permeability of the SPES/CDI/AS/SiO₂ composites. The water and methanol uptake and also methanol permeability of the SPES/CDI/AS/SiO₂ composite membrane with 8% SiO₂ were found in the order 3.58%, 2.48% and 1.91×10^?7 (cm²s^?1), lower than those of SPES and Nafion 117. In SPES membrane of 16.94% level of sulfonation, the proton conductivity was 0.0135 s/cm at 25 °C, which approached that of Nafion 117 under the same conditions. Also, the proton conductivity of the SPES/CDI/AS/SiO₂ 8% membrane was 0.0186 s/cm, which was higher than that of SPES at room temperature. The preparation of SPES/SiO₂ composites in the presence of AS and CDI, led to 63%, 56% and 64% reduction of water uptake, methanol uptake and methanol permeability, respectively without a sharp drop in proton conductivity of the composite membranes which featured a good balance between high proton conductivity, water and methanol uptake of SPES/CDI/AS/SiO₂ membranes.     

Application of energies of optimal frequency bands for fault diagnosis based on modified distance function

Low-dimensional relevant feature sets are ideal to avoid extra data mining for classification. The current work investigates the feasibility of utilizing energies of vibration signals in optimal frequency bands as features for machine fault diagnosis application. Energies in different frequency bands were derived based on Parseval's theorem. The optimal feature sets were extracted by optimization of the related frequency bands using genetic algorithm and a Modified distance function (MDF). The frequency bands and the number of bands were optimized based on the MDF. The MDF is designed to a) maximize the distance between centers of classes, b) minimize the dispersion of features in each class separately, and c) minimize dimension of extracted feature sets. The experimental signals in two different gearboxes were used to demonstrate the efficiency of the presented technique. The results show the effectiveness of the presented technique in gear fault diagnosis application.     

Weibull verification of reduced pressure test as a tool for assessing Al melt quality

The credibility of reduced pressure test (RPT) as a substitute for Weibull analysis for benchmarking bifilm defects in Al alloys was confirmed by comparing the RPT parameters (2D and 3D porosity, and Bifilm Index) with the Weibull moduli for UTS values for pure Al and Al-0.05Sr alloys. The porosity of RPT samples was found to have an exponential decay relationship with Weibull modulus. A reasonable trend for Bifilm Index could not be found. 3D porosity of RPT samples was found to be more favourable than 2D porosity or Bifilm Index. Some evidence was also found of connections occurring between the sides of bifilm defects at the surfaces of the fractured tensile test bars of Al-0.05Sr alloy which had a relatively high UTS.     

Practical Implementation of Novel Robust Position Control Scheme for Synchronous Reluctance Motor

A variable structure robust position controller is presented for a three-phase synchronous reluctance motor. Linear control and variable structure control and pulse-width modulation generation are combined. These provide robust, fast, and accurate position control without the penalty of high chattering. Schemes, including conventional sliding-mode control and the proposed scheme, are tested under parameter variations, and sudden perturbations are applied to the system at a specific time, then compared. This scheme uses both advantages of traditional variable structure control methods and linear methods. The disadvantages of each method, such as chattering and parameter sensitivity, are minimized. Results demonstrate that the proposed technique preserves the classical linear position control merits, while both the steady-state and transient behavior are significantly improved in terms of robustness, accuracy, and low ripple. The results also prove that the position reference command is perfectly tracked in spite of motor parameter uncertainties and load torque disturbance in control of the system that uses the new schemes.     

A theoretical study of the tautomerism kinetics of 4-amino-6-methyl-3-thioxo-3,4-dihydro-1,2,4-triazin-5(2H)-one in the gas phase: NBO population and NICS analysis

The tautomerization reactions of the 4-amino-6-methyl-3-thioxo-3,4-dihydro-1,2,4-triazin-5(2H)-one studied by means of M06-2x and CBS-QB3 theoretical methods. The measured energy profiles are complemented with kinetic rate coefficients calculations using transition state theory (TST). In line with the optimized tautomers geometries using the CBS-QB3 method, the natural bond orbital (NBO) analysis reveals that the stabilization energies of non-bonding LP(e)_S8 to the σ*_N2–C3 antibonding orbitals increase from tautomers 1 to 2. Furthermore, the delocalization energies of LP(e)_S8→σ*_N2–C3 could explain the increase of LP(e)_S8 non-bonding orbitals occupancies in the tautomers 1 and 2 (2?>?1). The increase of LP(e)_S8→σ*_N2–C3 delocalizations could fairly explicate the kinetics of tautomeric pathways 1 and 2 (k_2?>?k₁). Moreover, the HOMO–LUMO energy gap is increased parallel with the decreasing of activation energy barriers. NBO results also show that the kinetics of these processes controlled using LP→σ* resonance energies. Furthermore, nucleus-independent chemical shift (NICS) indices show the calculated reaction and energy barriers are involved by changes in aromaticity characters as well as electron transfer from LP(e)_S8 to σ*_N2–C3 orbitals, thus these reactions are controlled from both thermodynamic and kinetic viewpoints by the changes aromaticity characters.     

Developing an integrated model for the evaluation and selection of six sigma projects based on ANFIS and fuzzy goal programming

Six sigma is one of the most popular tools to eliminate waste in organizations, reduce the cost and improve quality. The process of creating and evaluating projects is an initial activity in implementing six sigma. This paper aims at proposing a comprehensive methodology for the evaluation and selection of the six sigma projects. For the evaluation of projects, reviewing the literature and decision team’s opinion, we identified three main categories of criteria including business criteria, technological & process criteria and financial criteria which contain eight sub-criteria. For deriving the overall utility of projects, we designed an adaptive neuro fuzzy inference system which is capable to consider interrelations among criteria. Then, applying a fuzzy weighted additive goal programming model, we obtained the optimal portfolio of projects which should be implemented. Finally, we applied the proposed model in a leading company in Iran to illustrate the applicability of the model.     

Short‐Time Linear Quadratic Form Technique for Estimating Fast‐Varying Parameters in Feedback Loops

The precision of a closed‐loop controller system designed for an uncertain plant depends strongly upon the maximum extent to which it is possible to track the trend of time‐varying parameters of the plant. The aim of this study is to describe a new parameter estimation algorithm that is able to follow fast‐varying parameters in closed‐loop systems. The short‐time linear quadratic form (STLQF) estimation algorithm introduced in this paper is a technique for tracking time‐varying parameters based on short‐time analysis of the regressing variables in order to minimize locally a linear quadratic form cost function. The established cost function produces a linear combination of errors with several delays. To meet this objective, mathematical development of the STLQF estimation algorithm is described. To implement the STLQF algorithm, the algorithm is applied to a planar mobile robot with fast‐varying parameters of inertia and viscous and coulomb frictions. Next, performance of the proposed algorithm is assessed against noise effects and variation in the type of parameters.     

Multivariable autopilot design for sounding rockets using intelligent Eigenstructure Assignment technique

When a sounding rocket rolls about its longitudinal axis, the role of angle of attack and sideslip angle exchange regularly. This interchange causes the aerodynamic moments to alternate between pitching and yawing moments, which, coupled with the moment of inertia effects, further aggravates the inertial cross-coupling. In this paper, first we analyze the cross-coupling phenomena and derive a Linear, Time-Invariant (LTI), multi input — multi output model of a spinning sounding rocket and then we design an autopilot for this system. An application of multivariable control technique is presented to the design of the autopilot. The involved controller is advanced by combining Eigenstructure Assignment (EA) approach with the Particle Swarm Optimization (PSO) algorithm. Results of linear and nonlinear simulations are reported to demonstrate the performance and stability margin of the considered autopilot.