Synthesis of silver chromate nanoparticles: Parameter optimization using Taguchi design

The Taguchi method of experimental design is very well suited to improving the production process of synthetic nanoparticles. The current application of the Taguchi method was successful in optimizing the experimental parameters affect on synthesis procedure of silver chromate nanoparticles. Ultrafine silver chromate particles were synthesied by precipitation method using addition of silver ion solution to the chromate reagent. The effect of reaction conditions such as: silver and chromate concentrations, flow rate of reagent addition and temperature on the particle size of synthesized silver chromate particles were investigated. The effect of these factors on the diameter of silver chromate particles were quantitavely evaluated by the analysis of variance (ANOVA). The results showed that silver chromate particles can be synthesized by controlling silver concentration, flow rate and temperature. Finally, the optimum conditions for synthesis of silver chromate particles by this simple and fast method were proposed. The results of ANOVA showed that 0.001 mol/l silver ion concentration, 40 ml/min flow rate for addition of silver reagent to the chromate solution and 0°C temperature are optimum conditions for producing silver chromate particles with 100 ± 33 nm width. On the other hand, the Ag₂CrO₄ nano-superstructures were synthesized by electrosynthesis method. The results showed that Ag₂CrO₄ nanoparticles synthesized by this method have 75 nm average diameter.     

Corrosion behavior of pure Mg and AZ31 magnesium alloy

Protection of Metals and Physical Chemistry of Surfaces - Purpose of this article is to study corrosion behavior of pure magnesium and AZ31 magnesium alloy in electrolyte containing different...     

Scalable architecture for a contention-free optical network on-chip

This paper proposes CoNoC (Contention-free optical NoC) as a new architecture for on-chip routing of optical packets. CoNoC is built upon all-optical switches (AOSs) which passively route optical data streams based on their wavelengths. The key idea of the proposed architecture is the utilization of per-receiver wavelength in the data network to prevent optical contention at the intermediate nodes. Routing optical packets according to their wavelength eliminates the need for resource reservation at the intermediate nodes and the corresponding latency, power, and area overheads. Since passive architecture of the AOS confines the optical contention to the end-points, we propose an electrical arbitration architecture for resolving optical contention at the destination nodes. By performing a series of simulations, we study the efficiency of the proposed architecture, its power and energy consumption, and the data transmission latency. Moreover, we compare the proposed architecture with electrical NoCs and alternative ONoC architectures under various synthetic traffic patterns. Averaged across different traffic patterns, the proposed architecture reduces per-packet power consumption by 19%, 28%, 29%, and 91% and achieves per-packet energy reduction of 28%, 40%, 20%, and 99% over Columbia, Phastlane, λ$\lambda$-router, and electrical torus, respectively.     

Modeling of first-order photobleaching kinetics using Krylov subspace spectral methods

We solve the first order 2-D reaction–diffusion equations which describe binding-diffusion kinetics using the photobleaching scanning profile of a confocal laser scanning microscope, approximated by a Gaussian laser profile. We show how to solve the first-order photobleaching kinetics partial differential equations (PDEs) using a time-stepping method known as a Krylov subspace spectral (KSS) method. KSS methods are explicit methods for solving time-dependent variable-coefficient partial differential equations. They approximate Fourier coefficients of the solution using Gaussian quadrature rules in the spectral domain. In this paper, we show how a KSS method can be used to obtain not only an approximate numerical solution, but also an approximate analytical solution when using initial conditions that come from pre-bleach steady states and also general initial conditions, to facilitate asymptotic analysis. Analytical and numerical results are presented. It is observed that although KSS methods are explicit, it is possible to use a time step that is far greater than what the CFL condition would indicate.     

Optimized performance data transmission in Mobile IP networks

In a Mobile IP network (MIPN), nodes move. When a node moves, it may go away from other nodes and this decreases available bandwidth and data rate and increases the propagation delay of links. Therefore, nodes’ movement can decrease data delivery and handoff latency; these will reduce network efficiency. Suppose that an MIPN uses an optimal routing algorithm and transmits data from a source node to a destination node optimally. Nodes’ movement can violate the optimality of the data transmission and this will waste bandwidth and network resources. In this paper we present a new parametric optimal unicast multichannel routing algorithm that computes a domain for a mobile node and this domain will hold the optimality of data transmission and prevent network efficiency failure. Our new method determines an optimal domain for each mobile node and does not allow nodes to exit from that optimal domain. Simulation results show that our new method increases data rate and network efficiency.     

Efficiency analysis of straight fin with variable heat transfer coefficient and thermal conductivity

In this study, one type of applicable analytical method, differential transformation method (DTM), is used to evaluate the efficiency and behavior of a straight fin with variable thermal conductivity and heat transfer coefficient. Fins are widely used to enhance heat transfer between primary surface and the environment in many industrial applications. The performance of such a surface is significantly affected by variable thermal conductivity and heat transfer coefficient, particularly for large temperature differences. General heat transfer equation related to the fin is derived and dimensionalized. The concept of differential transformation is briefly introduced, and then this method is employed to derive solutions of nonlinear equations. Results are evaluated for several cases such as: laminar film boiling or condensation, forced convection, laminar natural convection, turbulent natural convection, nucleate boiling, and radiation. The obtained results from DTM are compared with the numerical solution to verify the accuracy of the proposed method. The effects of design parameters on temperature and efficiency are evaluated by some figures. The major aim of the present study, which is exclusive for this article, is to find the effect of the modes of heat transfer on fin efficiency. It has been shown that for radiation heat transfer, thermal efficiency reaches its maximum value.     

Design of very thin wide band absorbers using modified local best particle swarm optimization

A method of using particle swarm optimization (PSO) algorithm to design electromagnetic absorber is presented. To demonstrate effectiveness of the PSO algorithm three different design cases are optimized. To reduce the local minimum traps, a modified local search strategy is employed. Each design problem is optimized using genetic algorithm (GA) and four variants of PSO algorithms, namely global PSO (gbest), local PSO (lbest), comprehensive learning PSO (CLPSO), and modified local PSO (MLPSO). The results clearly show that the MLPSO is a robust, fast, and useful optimization tool for designing absorbers. A seven-layer absorber achieved by this method has reflection coefficient below 18.7 dB from VHF to 20 GHz.     

Synthesis and investigation of anchored copper (II) complexes within MCM-41 as selective catalysts for epoxidation of olefins

In the present study, preparation, characterization and catalytic activity of encapsulated copper (II) complexes within MCM-41 were investigated. The mesoporous molecular sieve MCM-41 was synthesized and grafted with 3-(trimethoxysilyl)-1-propanethiol to give a thiol modified material (MCM-41-S). The prepared material successively was reacted with acrylic acid and acrylonitrile to give AA-MCM-41 and AN-MCM-41, respectively. Using hexamethyldisilazane and copper (II) chloride, copper (II) complexes in the cavities of MCM-41 (Cu-AA-MCM-41 and Cu-AN-MCM-41) were prepared. The presence of copper (II) complex on the surfaces of host matrix and the structure of prepared catalyst is investigated by FT-IR, inductively coupled plasma-optical emission spectroscopy (ICP-OES), powder X-ray diffraction (XRD) and BET nitrogen adsorption–desorption methods. The catalytic activities of the catalysts were studied in epoxidation of olefins. The results showed that activities of the prepared catalysts (Cu-AA-MCM-41 and Cu-AN-MCM-41) and their selectivity to corresponding epoxides were more than those of MCM-41. In addition, the synthesized heterogeneous catalysts were truly reusable.     

Taguchi robust design to optimize synthesis of lead oxalate nano-disks

Disk-shaped lead oxalate nanoparticles were synthesized via sol-precipitation in aqueous media without any surfactant, template or catalyst. Significance of reaction conditions such as: lead and oxalate concentrations, flow rate of reagent addition and temperature of reactor on diameter of synthesized lead oxalate disk-shaped particles were investigated and optimized. The participation of the studied variables in the particle size control of lead oxalate was quantitatively evaluated by analysis of variance. The results showed that lead oxalate nano-disks can be synthesized via controlling effective procedure parameters. Under optimum conditions, disk shaped nano-sized lead oxalate particles with two dimensions (95 nm diameter and 35 nm thickness) were synthesized. The structure and morphology of the lead oxalate nano-disks obtained under optimum conditions of synthesis process were characterized by scanning electron microscopy, X-ray diffraction, infrared spectroscopy and thermal analysis techniques. The Thermal analysis of the nanoparticles obtained under optimum conditions indicates that the main thermal degradation of the nano-disks occurs in the temperature range of 310–380 °C; while, submicron particles decomposed exothermally in more wider temperature range of 320–430 °C.     

Determination of models and optimization for the products of Fischer-Teropsch synthesis on Fe-Mn/K Catalyst

The Fischer-Tropsch synthesis produces the different clean energy, which fulfills the basic human needs in terms of the energy carriers. With attention to market needs, the production of certain products of this process is considered. To achieve this goal, multiple timed experiments are needed to increase the production of the desired product. In order to reduce the cost and time, the selectivity models were determined for the Fe-Mn/K catalyst. Using the response surface methodology based on three factors (reduction pressure, H₂/CO ratio, and space velocity) for three products—CO₂, C5-11, and C12+ — the selectivity models were obtained. In the models, the effect of each parameter and the interaction of the parameters with each other during the process of production was evaluated and analyzed. Finally, the optimal conditions were foreseen for each product.