Scientia Iranica
Volume:30 Issue: 3, May-June 2023

A graph $G$ is called irregular if the degrees of all its vertices are not the same. A graph is said to be \textit{Stepwise Irregular} (SI) if the difference of the degrees of any two adjacent vertices is always 1 (one). This paper deals with \textit{2-Stepwise Irregular} (2-SI) graphs in which the degrees of every pair of adjacent vertices differ by 2. Here we discuss some properties of 2-SI graphs and generalize them for $k$-SI graphs for which the imbalance of every edge is $k$. Besides, we also compute bounds of irregularity for the Albertson index in any 2-SI graph.

During the COVID-19 pandemic, wearing a face mask has been known to be an effective way to prevent the spread of COVID-19. In lots of monitoring tasks, humans have been replaced with computers thanks to the outstanding performance of the deep learning models. Monitoring the wearing of a face mask is another task that can be done by deep learning models with acceptable accuracy. The main challenge of this task is the limited amount of data because of the quarantine. In this paper, we did an investigation on the capability of three state-of-the-art object detection neural networks on face mask detection for real-time applications. As mentioned, here are three models used, SSD, two versions of YOLO i.e., YOLOv4-tiny, and YOLOv4-tiny-3l from which the best was selected. In the proposed method, according to the performance of different models, the best model that can be suitable for use in real-world and mobile device applications in comparison to other recent studies was the YOLOv4-tiny model, with 85.31% and 50.66 for mAP and FPS, respectively. These acceptable values were achieved using two datasets with only 1531 images in three separate classes, “with mask”, “without mask”, and “incorrect mask”.

Community detection is a significant issue in extracting valuable information and ‎understanding complex network structures. Non-negative matrix factorization (NMF) methods ‎are the most remarkable topics in community detection. The modularized tri-factor NMF ‎‎(Mtrinmf) method was proposed as a new class of NMF methods that combines the modularized ‎information with tri-factor NMF. It has high computational complexity due to its dependence on ‎the choice of the initial value of the parameter and the number of communities (c). In other ‎words, the Mtrinmf method should search among different c candidates to find correct c. In this ‎paper, a novel hybrid adaptive Mtrinmf (Hamtrinmf) method is proposed to improve the ‎performance of Mtrinmf and reduce the computational complexity efficiently. In the proposed ‎method, computational complexity reduction is made by selecting the right c candidates and ‎tuning parameter. For this purpose, a hybrid algorithm including singular value decomposition ‎‎(SVD) and relative eigenvalue gap (REG) algorithms is suggested to estimate the set of c ‎candidates. Next, the Tpmtrinmf model is proposed to improve the performance of community ‎detection via employing a self-tuning β parameter. Moreover, experimental results confirm the ‎efficiency of the Hamtrinmf method with respect to other reference methods on artificial and ‎real-world networks.‎

Due to the lack of magnets and the suitable final price, synchronous reluctance motors are potential applicants for household electric appliances and so on. But in general, they suffer from high torque ripple. Optimized design of the synchronous reluctance rotor structure is presented for two different types of barrier shape with aiming to reduce the torque ripple along with increasing the average torque.In this paper, the optimization of rotor geometries with a fixed machine size for C-shaped barriers and circular barriers type is investigated. Most of the rotor parameters such as the width of iron parts, and the width of barriers along d and q axis are optimized by a new method using the PSO algorithm. Besides, the angle of end points for each barrier with constant rib and insulation factor are considered in optimization process. Minimizing the torque ripple without losing or even increasing the average torque is the most critical optimization achievement. Two prototypes of the optimized rotor with the C-shaped and circular barriers type have been fabricated and experimentally compared. The results obtained from the 2-D Finite Element Simulation of the recommended machine conform well to the experimental result.

Flux-switching permanent magnet (FSPM) machines are novel brushless machines having magnets in the stator and currently are under intensive research due to their novel features, such as simple and robust rotor, flux focusing effect, sinusoidal phase back-EMF, high torque/power density and high efficiency. In this paper, a sensorless high-frequency sinusoidal signal injection scheme for a novel yokeless and segmented armature axial flux-switching sandwiched permanent-magnet motor (YASA-AFFSSPM) is proposed. Firstly, pulsating voltage injection is investigated in detail. In addition, a simpler method (Direct signal process method) for position error signal processing is presented based on pulsating signal injection. The principle and the realization of this method are analyzed in depth. Through experiment, the traditional signal process method and direct signal process method with high-frequency pulsating sinusoidal signal injection are compared to verify the validity these methods.

In this paper harmonic resonance analysis of the grid comprising wind power plants (WPPs) with permanent magnet synchronous generators (PMSGs) is presented. Usually, Norton equivalent circuit is used as the wind turbine (WT) model for harmonic resonance studies, in which, WTs are simply modeled as ideal current and voltage sources and impacts of converters controls on the WTs output impedances are neglected. This paper deals with the harmonic resonance analysis of study WPP system taking the impacts of converters controls, and current and voltage measurement filters into account. In this way, harmonic impedance models of the WTs are presented for simple and detailed cases, and then WT harmonic impedance is extracted for the mentioned cases. Next, results of frequency scan and harmonic mode resonance analyses for different cases are given and compared, and then effects of the current and voltage measurements filters and WT converter control on harmonic resonance analysis of the study WPP system are presented. It is shown that increasing the bandwidth of the grid-side converter current control loop can not shift the resonant frequencies, but enhances the system damping, and consequently reduces the driving point impedances in the resonant frequencies.

This study aimed to provide the analytical design, optimization, and three-dimensional (3D) simulation through finite element method of a coreless stator axial field flux-switching motor (AFFSM). The motor consists of two indented rotors with a coreless stator between them consisting of a magnet and winding. First of the motor electrical and magnetic design was performed and its basic parameters were calculated. Then, the optimization of the machine was evaluated implementing the Taguchi algorithm in order to minimize the motor cogging torque. Some of the basic motor dimensions, such as the magnet length and width, the rotor tooth width and height, and the back iron thickness, were selected as optimization variables, and the best combination of these variables was obtained by changing them in a certain range to achieve the desired objective. Then, the accuracy of analytical design and optimization was evaluated through forming a 3D finite element method (FEM) of the motor and investigating its performance. Comparison of the optimized and primary motor revealed that the optimal design had a better performance than the initial. Finally, a prototype of the proposed motor was fabricated and tested, which indicated that the experimental results were largely similar to the analytical results.

In this paper, some hidden aspects of composite right-/left-handed (CRLH) transmission lines (TLs) and couplers are clarified. Complete and detailed dispersion analysis of an isolated CRLH TL is presented including lossless and lossy cases based on a conventional unit cell, devised formerly. Dispersion analysis of CRLH TLs is extended form the conventional to an accurate unit cell. Capability of TLs consisting of such unit cells in supporting RLH waves is demonstrated. A pure analytical strategy is proposed for parameter extraction of CRLH TLs and symmetric couplers based on accurate circuit models. It is shown that by including loss parameters in the circuit model, there is no need to make use of curve fitting methods for parameters extraction of said couplers.

In this paper, the robust gain-scheduled state-feedback controller problem is studied for uncertain linear parameter-varying systems whose state-space representations are the linear combination of the uncertain time-varying parameters including time-invariant parametric uncertainties (TIPU). It is supposed that these uncertainties are bounded by the given intervals and cannot be pulled out as an uncertain block. It is considered a serious challenge because the exact information about the plant dynamics cannot be extracted from the uncertain time-varying parameters. This is while; the gain-scheduled controllers need to have the exact information about the plant dynamics to satisfy the desired control purposes. To handle this challenge, we introduce a state-feedback gain, which is formed by a set of the new scheduling parameters and a secondary time-varying term. The stabilization conditions are obtained in terms of the linear matrix inequalities (LMIs). The effectiveness of the proposed method is shown using an example.