javad askari

Due to their extended use, nowadays, Multi-Agent Systems have attracted the attention of many researchers. Bipartite formation is one of the interesting fields of Multi-Agent Systems that has been raised within a decade. In this research, the distributed bipartite formation of Multi-Agent Systems was investigated by a leader-follower approach. Heterogeneous agents in this approach have second-order nonlinear dynamics, and the communication graph between the agents is also a structurally balanced signed directed graph. Because of the distributed approach of the controller and the lack of existing communication between the leader and all of the followers, a finite-time observer is used to estimate the leader's dynamic in finite time. Also, because a finite-time approach increases performance and efficiency in many practical applications, a terminal sliding mode controller provides finite-time formation. Finally, the validity of the theoretical results is illustrated by simulation examples.

In this paper, direct numerical methods for solving a class of the fractional optimal control problems (FOCP) with different fractional derivative order and boundary conditions based on Genocchi hybrid functions are presented. For this purpose, first the importance of fractional calculus, definitions and required properties are provided. Then the hybrid functions including the combination of Genocchi polynomials with the block pulse basic functions, the advantages and properties of these polynomials are expressed. A required property has been proven. By using the new methods, the two fractional operators including the left Caputo fractional derivative and left Riemann-Liouville fractional integral of the Genocchi hybrid functions, are calculated directly and without approximation. Subsequently, some of the methods for solving fractional optimal control problems are presented in the form of classification of the direct methods. In the proposed direct methods, the fractional optimal control problem becomes a system of algebraic equations by discretizing state and control variables based on Genocchi hybrid functions with using fractional operators, Legendre-Gaussian formula for integral approximation and Lagrange multipliers. From the solution of the resulting system, the unknown coefficients of the state and control variables are obtained. We extend these methods with the ideas for the FOCP, including the final point. Then, the error bound of the function approximation are determined. Also, the convergence analysis of hybrid functions is investigated in the direct methods. At last, the efficiency and effectiveness of the proposed methods and comparison of the obtained results with those reported in the previous studies are discussed in the final section by solving some test problems.

Performing primary percutaneous coronary intervention (PPCI) in a timely fashion is a crucial part of the management of ST-elevation myocardial infarction (STEMI). We aimed to evaluate the contributing factors to and the etiologies of a prolonged door-to-device (D2D) time. In 2016, the D2D time was measured in all patients who were treated with PPCI at Tehran Hear Center. The major causes of a prolonged D2D time (>90 min) were determined. The second phase was then started in 2017 by focusing on the determined causes, and direct feedback was given to anyone having contributed to the delayed D2D time. The D2D time was compared between these 2 years. The mean age of the patients was 59.54±11.82 years, and 82.2% of them were men. The median D2D time decreased from 55 minutes (IQR25-75%: 40–82) in 2016 to 46 minutes (IQR25-75%: 34–70) in 2017 (P<0.001). In the first year, 79.8% of the patients had a D2D time of below 90 minutes; the figure rose to 84.1% of the patients in the second year (P=0.017). The first cause of a prolonged D2D time was missed ST-elevation in the first electrocardiogram by physician or nurse (8.4% of the cases). Along with a declining rate of missed STE to 6.7%, the median D2D time in the missed patients also decreased from 205 minutes to 177 minutes (P=0.011). The rate of ambulance arrival increased from 10.2% to 20.7% of the cases, and the median D2D time also declined from 45 (IQR25-75%: 34–55) to 34 (IQR25-75%: 25–55) in these patients (P<0.001). Even in the setting of a 24/7 on-site interventionist in the hospital, the dispatch system and prehospital electrocardiograms, along with regular assessment and feedback, may improve the D2D time.

In this paper‎, ‎a modern method is presented to solve a class of fractional optimal control problems (FOCPs) indirectly‎. ‎First‎, ‎the necessary optimality conditions for the FOCP are obtained in the form of two fractional differential equations (FDEs)‎. ‎Then‎, ‎the unknown functions are approximated by the hybrid functions‎, ‎including Bernoulli polynomials and Block-pulse functions based on the spectral Ritz method‎. ‎Also‎, ‎two new methods are proposed for calculating the left Caputo fractional derivative and right Riemann-Liouville fractional derivative operators of the hybrid functions that are proportional to the Ritz method‎. ‎The FOCP is converted into a system of the algebraic equations by applying the fractional derivative operators and collocation method‎, ‎which determines the solution of the problem‎. ‎Error estimates for the hybrid function approximation‎, ‎fractional operators and‎, ‎the proposed method are provided‎. ‎Finally‎, ‎the efficiency of the proposed method and its accuracy in obtaining optimal solutions are shown by some test problems.

Quadrotors are types of Unmanned Aerial Vehicles (UAVs) which have unique features compared to conventional aircrafts because of its vertical take-off and landing capability, flying in small areas and its high maneuverability. Also the relatively simple, economical and easy flight system of quadrotors, makes it to widely used as a good platform for development, implementation and testing a variety of control methods. One of the robust control methods is sliding mode control. In spite of the high capabilities of this approach, it has a main problem which is high frequency switching of the control signal witch is known the chattering phenomenon. In the past several decades, fractional order differential equations have been implemented in engineering application field, including controllers design and provided the possibility of using controllers for improving the performance of system. In this paper, a fractional order sliding surface has been employed for designing sliding mode control rule for quadrotors. The main objective of this study is to improve the performance and reduce the chattering phenomenon in sliding mode method. In this regard, by introducing sliding 〖PD〗^α surface, the control rule is designed in two different modes of 0

Stabilization of switched linear systems is one of the most important problems in the area of switched systems. In this paper، a design method for robust stabilization of parametric uncertain switched linear systems is proposed in terms of linear matrix inequalities. First، a method is proposed assuming that all states are available. This method designs the state feedback gains، such that the closed-loop system to be robustly asymptotically stable under switching signals with the known minimum dwell time. Since the states are unmeasurable in some practical systems، the method is then extended to the practical cases، in which the outputs are just available. The observer-based stabilizing state feedback gains are designed to stabilize such systems robustly for dwell time switching signals. The asymptotic stability of the proposed methods is proved under the assumption that all the nominal subsystems are controllable and observable. Then، the method is also generalized for robust stabilization of uncertain switched linear systems under any arbitrary switching signal. The correctness and effectiveness of the results are illustrated by some numerical examples.

Singular systems naturally exist in many physicall and practical systems in control issues. Also, a big group of nonlinear systems which can not be estimated by linear systems are carfully estimated by bilinear systems. On the other hand, if the user in sensetive systems dose not detect the fault on time,a considerable amount of facilities and information will be damaged and destroyed; therefore,the fault detection and recognition in singular bilinear systems with unknown input disturbances and faults by using bilinear sliding mode observer, is done in this paper because of the importance that singular bilinear systems have in modeling physical systems and undesirable effect of fault on performances of systems. For this perpose, have at first singular bilinear system is decomposed, then a sliding mode observer is considered for it. More over, a method is given for fault detection and isolation base on sliding mode observer. And at the end, we have a simulation for a numeral example to illustrate the effect of given method.

This paper presents a New Hybrid Shuffled Frog Leaping (NHSFL) algorithm applied to solve Economic Load Dispatch (ELD) problem. Practical ELD has non-convex cost function and various equality and inequality constraints that convert the ELD problem as a nonlinear، non-convex and non-smooth optimization problem. In this paper، a new frog leaping rule is proposed to improve the local exploration and the performance of the conventional SFL algorithm. Also a genetic mutation operator is used for the creation of new frogs instead of random frog creation that improves the convergence. To show the efficiency of the proposed approach، the non-convex ELD problem is solved using conventional SFL and an improved SFL method proposed by other researchers. Then the results of SFL methods are compared to the results obtained by the proposed NHSFL algorithm. Simulation studies show that the results obtained by NHSFL are more effective and better compared with these algorithms.