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Goos–Hänchen shift via refractive index control of four-level quantum dot nanostructure

Jafarzadeh H.

Optica Applicata

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2018

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Vol. 48, nr 3

499--513

EN

In this paper, we will discuss the Goos–Hänchen shifts properties of reflected and transmitted light beams from the cavity with four-level InGaN/GaN quantum dots nanostructure. We find that the Goos–Hänchen shifts properties of reflected and transmitted light beams can be controlled via adjusting the refractive index of four-level quantum dot nanostructure. Here, we show that by tunable infrared laser field the negative refraction index can be possible at certain values of probe frequency. Therefore, the large Goos–Hänchen shifts for reflected and transmitted light beams are possible for negative refractive index condition.

2

An exact geometry-based algorithm for path planning

Jafarzadeh H., Fleming C. H.

International Journal of Applied Mathematics and Computer Science

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2018

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Vol. 28, no. 3

493--504

EN

A novel, exact algorithm is presented to solve the path planning problem that involves finding the shortest collision-free path from a start to a goal point in a two-dimensional environment containing convex and non-convex obstacles. The proposed algorithm, which is called the shortest possible path (SPP) algorithm, constructs a network of lines connecting the vertices of the obstacles and the locations of the start and goal points which is smaller than the network generated by the visibility graph. Then it finds the shortest path from start to goal point within this network. The SPP algorithm generates a safe, smooth and obstacle-free path that has a desired distance from each obstacle. This algorithm is designed for environments that are populated sparsely with convex and nonconvex polygonal obstacles. It has the capability of eliminating some of the polygons that do not play any role in constructing the optimal path. It is proven that the SPP algorithm can find the optimal path in O(nn’2) time, where n is the number of vertices of all polygons and n’ is the number of vertices that are considered in constructing the path network (n’ ≤ n). The performance of the algorithm is evaluated relative to three major classes of algorithms: heuristic, probabilistic, and classic. Different benchmark scenarios are used to evaluate the performance of the algorithm relative to the first two classes of algorithms: GAMOPP (genetic algorithm for multi-objective path planning), a representative heuristic algorithm, as well as RRT (rapidly-exploring random tree) and PRM (probabilistic road map), two well-known probabilistic algorithms. Time complexity is known for classic algorithms, so the presented algorithm is compared analytically.

3

Friction Stir Radial Backward Extrusion (FSRBE) as a new grain refining technique

Jafarzadeh H., Babaei A., Esmaeili-Goldarag F.

Archives of Civil and Mechanical Engineering

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2018

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Vol. 18, no. 4

1374--1385

EN

A new method entitled Friction Stir Radial Backward Extrusion (FSRBE) is presented for processing fine-grained tubes. In FSRBE technique, an initial pure copper billet is placed inside a cylindrical chamber. The billet is pushed toward a rotating tool which results in radial and backward flow of the material while is frictionally stirred. The microstructure evolution during FSRBE was investigated through experimental observations and cellular automaton (CA) modeling. The observations reveal that the microstructure with initial grain size of 75 μm was refined to a fine-grained structure with an average grain size of 12 μm. The results of tensile tests demonstrate slight improvement in the value of yield and ultimate strength, elongation and microhardness. The microstructural evolution during FSRBE processing in the micro-level was studied using a coupled cellular automaton algorithm and finite element model. First, the macroscopic plastic flow behavior of material during FSRBE was calculated using FEM simulation method. Next, by tracing the plastic strain, the strain rate and temperature, in the deformation domain of cellular automaton, the DRX kinetics of pure copper is obtained in a devised post-processing step. The microstructure observations showed that the proposed model predictions were in reasonably good agreement with the experimentally obtained results.