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We extend our previously-derived generalized closed-form representation for spectral dispersing performance of the Virtually- Imaged-Phased-Array (VIPA) based on a 3D vectorial Gaussian beam formulation to demultiplexing application. To analyze VIPA in the demultiplexer scheme, a spherical lens is added after the VIPA, so that the device plane is superimposed on the focal plane of the lens. The calculated output pro-le at previous step is reformulated ¿ in a matrix form in this step. Finally, the derived closed-form is simulated, and the numerical outcomes are compared with the previous results. The 3D output radiation of VIPA demultiplexer pattern is also depicted and found to be very... 

We have developed a generalized closed-form representation of the virtually imaged phased array (VIPA) output profile based on a 3D vectorial Gaussian beam formulation. Tracing the input vectorial elliptic Gaussian beam (GB), the output profile of the VIPA is represented as an array of virtual images. Furthermore, employing GB propagation and summing up all the virtual image profiles, the VIPA output profile has been calculated on a vertical plane at an arbitrary distance from the device. Finally, the derived closed-form representation is applied to the different sources (i.e., circular and elliptic GBs) and the results are compared with previous work. © 2009 Optical Society of America  

The Virtually-Imaged-Phased-Array (VIPA) is a modified version of etalon used as a hyperfine spectral disperser. We have developed an analytical Gaussian beam tracing formulation which can model the VIPA output pattern and the effects of polarization changes  

We propose a design algorithm for VIPA-based OCOMA encoder used in WOM-compatible COMA networks based on the problem requirements. Analyzing this device by our previous formulation leads to some useful suggestions to improve the device  

In this study, the authors propose a novel Filon-type integration method that uses error-controllable and frequency-independent closed-form expression to evaluate highly oscillatory physical optics (PO) surface integrals on smooth conducting surfaces. In this method, the phase and amplitude functions of PO integrals for a general parametric surface and incident wave are approximated by second order polynomials, first. Although there are some complicated closed-form expressions for these integrals in the literature, the authors present simple and computationally efficient closed-form expressions for them. For this end, the parametric domain of each resulted integral is meshed by triangular... 

In this paper, we propose a frequency-independent method for calculation of scattered electromagnetic (EM) fields by the human body in millimeter-wave (MMW) band. The surface of the body is accurately modeled by non-uniform rational B-spline (NURBS) surfaces and is illuminated by a plane wave. The scattered EM fields are formulated by physical optics (PO) approximation. This approximation yields PO surface highly oscillatory integrals that are solved by numerical steepest descent path (NSDP) method, frequency-independently. This paper provides an efficient and accurate method for considering human body in indoor propagation, surveillance and medical imaging, and detection of human body by... 

In this study, an efficient frequency-independent and error-controllable Filon-type solution of highly oscillatory physical optics (PO) integrals on the quadratic surfaces is presented. In this method first, PO surface integral is decomposed into some analytically solvable integrals and one highly oscillatory integral (HOI) which must be solved numerically. Then, by demodulating complementary error function, the integrand of this HOI is decomposed into an oscillatory part and a slowly varying part (demodulated part). The demodulated part can be easily approximated by various types of basis functions, especially in high frequencies. Therefore, after approximating the demodulated part using... 

One of the basic assumptions of classical production-inventory models is that all products are of perfect quality. However, in real manufacturing situations, the production of defective items is inevitable, and a fraction of the items produced may be naturally imperfect. In fact, items may be damaged due to production and/or transportation conditions in the manufacturing process. On the other hand, some reworkable items exist among imperfect items that can be made perfect by additional processing. In addition, the classical production-inventory models assume that there is only one product in the system and that there is an unlimited amount of resources. However, in many practical situations,... 

This paper designs a Scenario analysis approach to determine the joint production policy for two products under possible substitution. The Scenario analysis is designed to improve decision-making by considering possible outcomes and their implications. The traditional multi-product production models assume that there is no possible substitution between products. However, in real-world cases, there are many substitutable products where substitution may occur in the event of a product stock-out. The proposed model optimizes production quantities for two products under substitution with the aim of minimizing the total cost of the inventory system, including setup and holding costs, subject to a... 

High penetration of constant-power loads (CPL) in dc microgrids may cause a destabilizing effect on the system that can lead to severe voltage oscillations. This paper addresses stability problems of the CPLs and proposes a simple active damping technique to damp the oscillations caused by CPLs. The particle swarm optimization algorithm has been used to find the best values of the parameters of the proposed active damper to achieve maximum damping of the oscillations. The effectiveness of the proposed approach is verified by simulations  

Modeling of hybrid systems using mixed logical dynamical (MLD) systems is an art. The MLD framework often introduces numerous constraints and auxiliary binary and continuous variables, which, in turn, increase the computational complexity of the optimization problems. This paper presents an automaton-based realization for discrete-time hybrid automaton (DHA) with both controlled and uncontrolled switching phenomena by which it is attempted to develop efficient translation techniques to MLD systems and reduce the total number of decision variables in the MLD model. Based on this DHA model, a modified version of MLD systems, which is called extended MLD (EMLD) is formally defined and... 

Supply Chain (SC) coordination, quality requirements, and environmental issues are the main areas of interest within the field of inventory management. Few studies have integrated these concepts into an inventory problem despite its overwhelming necessity. In this direction, this paper deals with a vendor-buyer SC under the Vendor-Managed Inventory with Consignment Stock (VMI-CS) agreement. According to the agreement, the vendor bears the buyer's financial holding cost in return for the storage of products in the buyer's warehouse. Further, each shipment involves a random fraction of repairable items, which need to be withdrawn from the inventory system. Unlike the existing literature, when... 

Magnetic drug delivery is an effective method to decrease the side effects of traditional drug delivery methods. To enhance the efficiency of magnetic nanoparticle transport, a precise and cost-effective magnetic system is required. In this research, different arrangements of NdFeB magnets for drug delivery in human spinal cord were presented and then compared. Assummed magnetic nanoparticles are injected into the cerebrospinal fluid (CSF) and focused on the disease site with external magnets. The effects of these magnets on nanoparticles have been investigated. The results show that the arrangement of sharp magnets has a more accurate performance in delivering nanoparticles to the damage... 

Development of high frequency power electronic devices leads to high performance and flexible switch mode AC voltage stabilizers instead of traditional electromechanical types. This paper introduces a novel double stage topology for switch mode AC voltage regulators. The system produces a continuous adjustable isolated AC voltage providing a constant output voltage for sensitive loads. In order to simplify the control strategy, a symmetrical PWM is used. In contrast with conventional AC choppers, the proposed circuit does not need any snubber circuits or voltage and current sensors which leads to a simpler and more reliable circuit. Detailed analysis and simulation results show the... 

This paper presents a novel flexible control strategy for Unified Power Quality Conditioner (UPQC), which achieves more flexibility in compensation of power quality disturbances as compared to the existing methods. The proposed control strategy provides priority-based compensation as well as full and standard-based compensation considering the rating of series and shunt parts of a UPQC. The priority-based compensation is done based on the compensation priority among different power quality disturbances. In this control strategy, an on-line estimation of different voltage and current disturbances is required. For this purpose, a Unified Adaptive Power Quality Estimator (UAPQE) has been... 

This paper presents a control strategy for an islanded medium voltage microgrid to coordinate hybrid power source (HPS) units and to control interfaced multilevel inverters under unbalanced and nonlinear load conditions. The proposed HPS systems are connected to the loads through a cascaded H-bridge (CHB) multilevel inverter. The CHB multilevel inverters increase the output voltage level and enhance power quality. The HPS employs fuel cell (FC) and photovoltaic sources as the main and supercapacitors as the complementary power sources. Fast transient response, high performance, high power density, and low FC fuel consumption are the main advantages of the proposed HPS system. The proposed... 

This paper presents a new unified power-quality conditioning system (MC-UPQC), capable of simultaneous compensation for voltage and current in multibus/multifeeder systems. In this configuration, one shunt voltage-source converter (shunt VSC) and two or more series VSCs exist. The system can be applied to adjacent feeders to compensate for supply-voltage and load current imperfections on the main feeder and full compensation of supply-voltage imperfections on the other feeders. In the proposed configuration, all converters are connected back to back on the dc side and share a common dc-link capacitor. Therefore, power can be transferred from one feeder to adjacent feeders to compensate for... 

Sub-harmonic stability issues due to the interaction between a load-commutated motor drive and a synchronous turbo-generator train in a Liquefied Natural Gas (LNG) station are studied in this paper. The sub-harmonic current injected by motor drives may excite the mechanical torsional modes of turbogenerator train. In this paper, the electro-mechanical interaction phenomenon is investigated and an active damper is proposed to absorb the sub-harmonic currents of motor drives and increase the damping of the electro-mechanical system. Simulations and experiments validate the instability problem and effectiveness of the proposed solution. © 2018 EPE Association  

This paper discusses the application of unified power quality conditioner (UPQC) for improving power quality of a system supplying an electric arc furnace (EAF). The UPQC includes combined series and shunt active filters sharing a common DC link. It is used to mitigate voltage disturbances and compensate for reactive power, harmonics and interharmonics. A novel control strategy for the UPQC is presented. As voltages at the point of common coupling contain low-frequency interharmonics, conventional methods cannot be used for extracting voltage reference signals. In the proposed method, voltage references are extracted using a phase-locked loop to generate sinusoidal waveforms. Current... 

Advanced static VAR compensators (ASVCs) are used to improve the transient stability of electric power systems. In this paper we present a new control strategy, which has superior performances compared to the conventional control techniques for these systems. The proposed method utilizes a novel current reference based on the transient energy function (TEF) approach. It also includes the voltage limits in the optimizing process using the Lyapunov theory and linear programming. In addition, it is optimized considering the permissible system conditions. A continuous control of the reactive power flow is also achieved. The proposed ASVC is modeled in single-machine and multimachine systems. In...