A simple and accurate dynamical modeling of quantum‐dot semiconductor optical amplifiers

In this article, quantum‐dot semiconductor optical amplifiers (QD‐SOAs) have been modelled using state space method. To derive this model, we have manipulated the rate equation model of the QD‐SOA, where the average values of the occupation probabilities along the QD‐SOA cavity are considered as the state variables of the system. Using these variables, the distance dependence of the rate equations is eliminated. The derived state space model gives the optical gain and output signal of the amplifier with a high accuracy. Simulation results show that the derived model is not only much simpler and faster than conventional rate equation models, but also the optical gain and output signal of the investigated QD‐SOA are calculated with a higher precision compared to the rate equation model. Copyright © 2013 John Wiley & Sons, Ltd.     

Review of supplier diversification and pricing strategies under random supply and demand

Uncertainties of supply and demand are two major sources of risk in any supply chain. As a result, the companies are implementing different strategies to mitigate the effects of these risks. Supplier diversification and responsive pricing are two of the main strategies that are used to mitigate the supply and demand risks. In supplier diversification, a firm uses multiple channels of sourcing while in responsive pricing, a firm manipulates demand through pricing to mitigate supply and demand risks. In this paper, we review lot-sizing problems when supply and demand are random. We focus on studies that have considered supplier diversification or responsive pricing as a mitigation strategy. We classify the studies based on their main assumptions and summarise their major findings. Finally, we present some directions for future research. Part of what we have found is that most studies that use multiple decision makers have focused on cases where information is complete and non-cooperative. There is a need to consider more realistic situations when there is information asymmetry between the decision makers. In addition, we have found that there is a lack of studies that look at the impact of joint ordering and pricing in the existence of multiple suppliers.     

Improving Performance Criteria in the Water Resource Systems Based on Fuzzy Approach

Water Resources Management - Reliability, resilience, and vulnerability (RRV) have been widely used as the performance criteria of a water supply system in the studies conducted over the last three...     

A neural network decision-making model for job-shop scheduling

Scheduling in a job-shop system is a challenging task. Simulation modelling is a well-known approach for evaluating the scheduling plans of a job-shop system; however, it is costly and time-consuming, and developing a model and interpreting the results requires expertise. As an alternative, we have developed a neural network (NN) model focused on detailed scheduling that provides a versatile job-shop scheduling analysis framework for management to easily evaluate different possible scheduling scenarios based on internal or external constraints. A new approach is also proposed to enhance the quality of training data for better performance. Previous NN models in scheduling focus mainly on job sequencing and simple operations flow, and may not consider the complexities of real-world operations. The proposed model’s output proved statistically equivalent to the results of the simulation model. The study was accomplished using sensitivity analysis to measure the effectiveness of the input variables of the NN model and their impact on the output, revealing that the batch size variable had a significant impact on the scheduling results in comparison with other variables.     

An Electromagnetism-like algorithm for cell formation and layout problem

Implementation of cellular manufacturing systems (CMS) is thriving among manufacturing companies due to many advantages that are attained by applying this system. In this study CMS formation and layout problems are considered. An Electromagnetism like (EM-like) algorithm is developed to solve the mentioned problems. In addition the required modifications to make EM-like algorithm applicable in these problems are mentioned. A heuristic approach is developed as a local search method to improve the quality of solution of EM-like. Beside in order to examine its performance, it is compared with two other methods. The performance of EM-like algorithm with proposed heuristic and GA are compared and it is demonstrated that implementing EM-like algorithm in this problem can improve the results significantly in comparison with GA. In addition some statistical tests are conducted to find the best performance of EM-like algorithm and GA due to their parameters. The convergence diagrams are plotted for two problems to compare the convergence process of the algorithms. For small size problems the performances of the algorithms are compared with an exact algorithm (Branch & Bound).     

Supplier Selection Based on a Neural Network Model Using Genetic Algorithm

In this paper, a decision-making model was developed to select suppliers using neural networks (NNs). This model used historical supplier performance data for selection of vendor suppliers. Input and output were designed in a unique manner for training purposes. The managers' judgments about suppliers were simulated by using a pairwise comparisons matrix for output estimation in the NN. To obtain the benefit of a search technique for model structure and training, genetic algorithm (GA) was applied for the initial weights and architecture of the network. The suppliers' database information (input) can be updated over time to change the suppliers' score estimation based on their performance. The case study illustrated shows how the model can be applied for suppliers' selection.     

All‐optical multi‐wavelength header recognition using superimposed Bragg gratings based correlators

We have demonstrated that an optical correlator, based on superimposed Bragg gratings, can be used as all‐optical multi‐wavelength header recognition in optical packet switching networks. The proposed correlator is composed of two superimposed gratings in conjunction with variable delay lines. These superimposed Bragg gratings are used to demultiplex and multiplex the wavelength components of multi‐wavelength header bit patterns. The variable delay lines create a wavelength profile that can be matched with any arbitrary bit patterns. Simulation results for all optical recognition of four‐bit patterns at 10 Gbps are reported. The results show that when the header bit pattern matches the wavelength profile of the correlator, the generated auto‐correlation function will include a high amplitude peak; otherwise, a cross‐correlation function with low amplitude peaks will be generated in the output of the correlator. Considering this idea, multi‐wavelength header is recognized by using all‐optical processing method. Copyright © 2012 John Wiley & Sons, Ltd.     

Bose-Mesner algebra on finite <Emphasis Type="Italic">G</Emphasis>/<Emphasis Type="Italic">H</Emphasis> coset graphs and its application on continuous time quantum walks

Continuous-time quantum walk (CTQW) over finite group schemes is investigated, where it is shown that some properties of a CTQW over a group scheme defined on a finite group G induces a CTQW over group scheme defined on G/H, where H is a normal subgroup of G with prime index. This reduction can be helpful in analyzing CTQW on underlying graphs of group schemes. Even though this claim is proved for normal subgroups with prime index (using the Clifford’s theorem from representation theory), it is checked in some examples that for other normal subgroups or even non-normal subgroups, the result is also true! Moreover, it is shown that the Bose-Mesner (BM) algebra associated with the group scheme over G is isomorphic to the corresponding BM algebra of the association scheme defined over the coset space G/H up to the scale factor |H|. In fact, we show that the underlying graph defined over group G is a covering space for the quotient graph defined over G/H, so that CTQW over the graph on G, starting from any arbitrary vertex, is isomorphic to the CTQW over the quotient graph on G/H if we take the sum of the amplitudes corresponding to the vertices belonging to the same cosets.     

Biosynthesis of tin oxide (SnO2) nanoparticles using jujube fruit for photocatalytic degradation of organic dyes

In this study, tin oxide (SnO₂) nanoparticles were synthesized via a green route using jujube fruit as a non-toxic, renewable reducing agent, and excellent stabilizer. The biosynthesized SnO₂ nanoparticles were characterized by X-ray diffraction analysis (XRD), Fourier-Transform infrared (FT-IR), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). Moreover, the photocatalytic activity of the novel SnO₂ nanoparticles was investigated for degradation of two organic dyes which were named methylene blue (MB) and eriochrome black-T (EBT) under direct sunlight. An excellent performance was observed and about 90% and 83% of degradation efficiencies were achieved for MB and EBT, respectively. The high stability of the photocatalyst also makes SnO₂ nanoparticles easily to reuse at least four times without any remarkable loss in activity.