No abstract

One of the main concerns during the COVID-19 pandemic was the protection of healthcare workers against the novel coronavirus. The critical role and vulnerability of healthcare workers during the COVID-19 pandemic leads us to derive a mathematical model to express the spread of coronavirus between the healthcare workers. In the first step, the SECIRH model is introduced, and then the mathematical equations are written. The proposed model includes eight state variables, i.e., Susceptible, Exposed, Carrier, Infected, Hospitalized, ICU admitted, Dead, and finally Recovered. In this model, the vaccination, protective equipment, and recruitment policy are considered as preventive actions. The formal confirmed data provided by the Iranian ministry of health is used to simulate the proposed model. The simulation results revealed that the proposed model has a high degree of consistency with the actual COVID-19 daily statistics. In addition, the roles of vaccination, protective equipment, and recruitment policy for the elimination of coronavirus among the healthcare workers are investigated. The results of this research help the policymakers to adopt the best decisions against the spread of coronavirus among healthcare workers.

The existence of a bubble in the vicinity of an elastic boundary appears in many situations such as medical and mechanical systems. On the other hand, bubble collapse is considered a source of energy loss in most systems and caused a lot of damages to it. This research is the first attempt to prevent bubble collapse in the vicinity of an elastic boundary by using control algorithms. In this paper, first, the nonlinear dynamic model of bubble in the vicinity of an elastic wall is introduced and then rewritten into state-space form. The second part of this paper is devoted to the design of the sliding mode controller for the bubble system, where the ultrasonic pressure plays the role of control input and the output is the bubble radius. Our main objective is to design a stabilizing controller that is able to regulate the radius of the bubble to the desired radius. At first, traditional sliding mode controller is proposed. Despite the successful tracking error, the chattering problem of this method leads us to introduce the boundary layer sliding mode control. Although the chattering phenomenon has been attenuated, it increases the steady-state error. Finally, robust integral sliding mode control is suggested to minimize the steady-state error while the chattering problem is removed. Numerical simulations including the case of parametric uncertainty are also presented. The results of this study are of immediate interest for medical applications such as ultrasound imaging and also industrial applications such as designing long-lasting pumps and valves.

In many industrial and medical systems, there is a bubble between two elastic walls. On the other hand, the collapse of bubbles is considered a constant source of energy lost and causes system damage. This research is the first attempt to prevent from bubble collapse between two elastic boundaries by using control algorithms. In this paper, first, the nonlinear dynamic model of the bubble between two elastic walls is introduced and then rewritten into a state-space form. The second part of this paper is devoted to the design of the sliding mode controller, where the ultrasonic pressure plays the role of control input and the output is bubble radius. At first, terminal sliding mode control is proposed. Although this method ensures finite-time convergence, its main drawback is singularity in the control input signal. The nonsingular terminal sliding mode control is proposed to solve the problem of singularity in the control input signal. A rigorous stability analysis is also presented using the Lyapunov theory to demonstrate the stability of nonsingular sliding manifold. The effect of controller parameters on the performance of the closed-loop system is investigated. Finally, some simulation results including the case of parametric uncertainty are also presented to demonstrate the efficiency of the proposed scheme. The results of this study are of immediate interest for industrial applications such as designing pumps and valves and medical applications such as targeted ultrasound imaging and cancer treatment.

In this research, a novel pulse-doubling circuit (PDC) is employed to upgrade the 28-pulse rectifier to the efficient 56-pulse rectifier. The main objective of this research is to reduce the power kVA rating. In the autotransformer with a 14-phase polygon structure, the kVA rating is approximately 39.5% of the load power. Since the pulse-doubling method is utilized, the rectifier with 56 pulses has benefited from a simpler structure. With a comparison to the other rectifiers, the harmonic mitigation is the clearest feature of the proposed rectifier. According to the experimental and theoretical results, in the proposed rectifier with 56 pulses, the input current THD is less than 3%. Finally, the volume and cost of the proposed rectifier with 56 pulses show a notable reduction. In other words, the proposed rectifier is an economical choice for most sectors of the industry.