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The aim of this research paper is to design a disturbance observer (DO)-based robust adaptive tracking control of uncertain nonlinear system subject to unknown nonlinear disturbance.

To achieve desired control objectives, i.e. nonlinear trajectory tracking and disturbance attenuation, firstly, a control scheme is designed based on the adaptive criteria integrated in sliding mode control (SMC). In the second step, the disturbance estimation criterion is designed followed by patching with the controller obtained in the first step. Following the control development, using the Lyapunov candidate function, the stability criterion is ensured by designing appropriate adaptive gains.

In this paper, a robust adaptive nonlinear tracking method is presented. The findings includes the design of adaptive gains for the control parameters involved in the robust SMC technique, i.e. adaptive criterion is designed for the switching gain as well as for the gain used in sliding mode surface. Furthermore, a disturbance estimation criterion is developed to attenuate nonlinear disturbances with variable frequency and magnitude. Finally, the disturbance estimation scheme is combined with the control technique to obtain DO-based control (DOBC) algorithm.

Sliding mode control is a powerful robust control method. And, combining it with the DO achieves the control objectives of plants subject to disturbances and uncertainties. However, usually the uncertainties and disturbances are unknown and time varying. Thus, during practical implementation, designing the standard SMC is a challenging task due to the constant gains involved in the control design. Hence, it is important to have a criterion which adapts to the varying dynamics of plants due to the uncertainties and disturbances for achieving practical implementation of the control system.

Sliding mode control has been widely used for achieving the desired control objectives and robustness in the close-loop nonlinear systems. Besides, the SMC technique has been combined with the DOs as well. However, mostly the ideal conditions were considered during these developments, which required the control gains to be designed simply by manual tuning appropriately. However, by considering the real-time dynamics, uncertainties and disturbances, the constant control gain criteria can fail. Furthermore, due to external and internal disturbances, the model plant can vary with time. Thus, it is important to design the adaptive criteria for the control gains in DOBC schemes.

The purpose of this research paper is to design a disturbance observer-based control based on the robust model reference adaptive backstepping sliding-mode control for attitude quadrotor model subject to uncertainties and disturbances.

To estimate and reject the disturbance, a disturbance observer is designed for the exogenous disturbances with perturbation while a control criterion is developed for the tracking of desired output. To achieve the control performance, backstepping and sliding-mode control techniques are patched together to obtain robust chattering-free controller. Furthermore, a model reference adaptive control criterion is also combined with the design of robust control for the estimation and rejection of uncertainties and unmodeled dynamics of the attitude quadrotor.

The findings of this research work includes the design of a disturbance observer-based control for uncertain attitude quadrotor system with the ability of achieving tracking control objective in the presence of nonlinear exogenous disturbance with and without perturbation.

In practice, the quadrotor flight is opposed by different kinds of the disturbances. In addition, being an underactuated system, it is difficult to obtain an accurate mathematical model of quadrotor for the control design. Thus, a quadrotor model with uncertainties and disturbances is inevitable. Hence, it is necessary to design a control system with the ability to achieve the control objectives in the presence of uncertainties and disturbances.

Designing the control methods for quadrotor control without uncertainties and disturbances is a common practice. However, investigating the uncertain quadrotor plant in the presence of nonlinear disturbances is rarely taken into consideration for the control design. Hence, this paper presents a control algorithm to address the issues of the uncertainties and disturbances as well as investigate a control algorithm to achieve tracking performance.

This paper aims to study a neural network-based fault-tolerant controller to improve the tracking control performance of an unmanned autonomous helicopter with system uncertainty, external disturbances and sensor faults, using the prescribed performance method.

To ensure that the tracking error satisfies the prescribed performance, the authors adopt an error transformation function method. A control scheme based on the neural network and high-order disturbance observer is designed to guarantee the boundedness of the closed-loop system. A simulation is performed to prove the validity of the control scheme.

The developed adaptive fault-tolerant control method makes the system with sensor fault realize tracking control. The error transformation function method can effectively handle the prescribed performance requirements. Sensor fault can be regarded as a type of system uncertainty. The uncertainty can be approximated accurately using neural networks. A high-order disturbance observer can effectively suppress compound disturbances.

The tracking performance requirements of unmanned autonomous helicopter system are considered in the design of sensor fault-tolerant control. The inequality constraint that the output tracking error must satisfy is transformed into an unconstrained problem by introducing an error transformation function. The fault state of the velocity sensor is considered as the system uncertainty, and a neural network is used to approach the total uncertainty. Neural network estimation errors and external disturbances are treated as compound disturbances, and a high-order disturbance observer is constructed to compensate for them.

This paper aims to present a novel structural reliability analysis scheme with considering the structural strength degradation for the wing spar of a generic hypersonic aircraft to guarantee flight safety and structural reliability.

A logarithmic model with strength degradation for the wing spar is constructed, and a reliability model of the wing spar is established based on stress-strength interference theory and total probability theorem.

It is demonstrated that the proposed reliability analysis scheme can obtain more accurate structural reliability and failure results for the wing spar, and the strength degradation cannot be neglected. Furthermore, the obtained results will provide an important reference for the structural safety of hypersonic aircraft.

The proposed reliability analysis scheme has not implemented in actual flight, as all the simulations are conducted according to the actual experiment data.

The proposed reliability analysis scheme can solve the structural life problem of the wing spar for hypersonic aircraft and meet engineering practice requirements, and it also provides an important reference to guarantee the flight safety and structural reliability for hypersonic aircraft.

To describe the damage evolution more accurately, with consideration of strength degradation, flight dynamics and material characteristics of the hypersonic aircraft, the stress-strength interference method is first applied to analyze the structural reliability of the wing spar for the hypersonic aircraft. The proposed analysis scheme is implemented on the dynamic model of the hypersonic aircraft, and the simulation demonstrates that a more reasonable reliability result can be achieved.

This study aims to achieve the post-stall pitching maneuver (PSPM) and decrease the deflection frequency of aircraft actuators controlled by the robust backstepping method based on event-triggered mechanism (ETM), nonlinear disturbance observer (NDO) and dynamic surface control (DSC) techniques.

To estimate unsteady aerodynamic disturbances (UADs) to suppress their adverse effects, the NDO is designed. To avoid taking the derivative of the virtual control law directly and eliminate the coupling term of the system states and dynamic surface errors in the stability analysis, an improved DSC is developed. Combined with the NDO and DSC techniques, a robust backstepping method is proposed to achieve the PSPM. Furthermore, to decrease the deflection frequency of the aircraft actuators, a state-dependent ETM is introduced.

An ETM-and-NDO-based backstepping method with an improved DSC technique is developed to achieve the PSPM and decrease the deflection frequency of aircraft actuators. And simulation results are presented to verify the effectiveness of the proposed paper.

Few studies have been conducted on the control of the PSPM in which the lateral and longitudinal attitude dynamics are coupled with each other considering the UADs. Moreover, the mechanism that can decrease the deflection frequency of aircraft actuators is rarely developed in existing research. This study proposes an ETM-and-NDO-based backstepping scheme to address these problems with satisfactory performance of the PSPM.

The purpose of this paper is to focus on the emerging phenomenon of medical tourism in the context of Iran from a customer experience management perspective and benchmark of their judgment including positive or negative, of the experience they have achieved of the Iranian health (medical) experience (CE) and suggest scenarios for the improvement of the Iranian customer experience management (CEM).

The research methodologies and research methods that are used in this descriptive-analytical research are based on an inspection of the remarkable literature related to medical tourism and customer experience management. The data gathering instrument is a researcher-made questionnaire based on the variables in the conceptual model extracted from the research literature. The study was conducted from May to August 2019. The population cohort of this study was the foreign patients calling selected Iranian hospitals and the sampling method was a purposive and snowball sample of prospective medical tourists. As the study was conducted throughout Iran, some important hospitals in Iran were selected by stratified sampling Yang et al. (2020b). The sample size and data saturation were 500 participants Lv and Song (2019). The collected data using the questionnaire were analyzed by SPSS software and statistical tests.

According to the results, the customer experience management statistical significance in the task aspect is (p = 0.0523), in the mechanical aspect is (p = 0.0563), in the human aspect is (p = 0.0544). The study showed positive customer experience among the patients who had been treated in the Iranian hospitals.

There is a lack of study that focuses on medical tourism and customer experience management in Iran. Therefore, based on the results of this study, the experience of medical tourists in Iran proved to be positive and satisfying. As little research has been conducted in the area of customer experience management (CEM) in Iranian medical tourism, future researchers can use these valuable results precisely and in more detail to benchmark more accurately the customer experience in all areas of medical and health tourism and other research areas in different aspects of CEM in Iran.

This chapter introduces EmoGenPath, an innovative machine learning-based model designed to deliver adaptive therapy to children and youth affected by the trauma of armed conflict. The model synthesizes advanced artificial intelligence (AI) techniques, including convolutional neural networks for emotion recognition and an advantage-actor critic-trained reinforcement learning model for therapeutic content tailoring toward goal achievement, to provide a dynamic and personalized therapeutic experience. Recognizing the importance of empathetic and culturally sensitive interventions, EmoGenPath offers a unique approach by prioritizing the emotional states and individual narratives of its users. In regions where conflict has impeded traditional mental health services, this model aims to bridge the gap, facilitating resilience and recovery through a virtual therapeutic environment that can be accessed via low-bandwidth internet connections, ensuring broader reach and impact. This chapter emphasizes the ethical implementation of AI in sensitive settings. It discusses the imperative of privacy, security, and inclusive design, ensuring that the model is responsive to diverse emotional expressions across different ethnicities and backgrounds. Additionally, it outlines the potential of such a model to scale therapeutic resources effectively, delivering tailored interventions with a compassionate approach.

The paper aims to study the effect of sintering temperature on the microstructure, shear strength and ratcheting fatigue life of nanosilver sintered lap shear joint. In addition, the Gerber model is used to predict the ratcheting fatigue lives of nanosilver sintered lap shear joints at different sintering temperatures.

In this paper, the nanosilver sintered lap shear joints were prepared at three sintering temperatures of 250 °C, 280 °C and 310 °C. The bonding quality was characterized by scanning electron microscopy, X-ray diffraction, transmission electron microscope and shear tests, and the long-term reliability was studied by conducting ratcheting fatigue tests. In addition, three modified models based on Basquin equation were used to predict the ratcheting fatigue life of nanosilver sintered lap shear joint and their accuracies were evaluated.

When the sintering temperature is 250°C, the nanosilver sintered lap shear joint shows the porosity of 22.9 ± 1.6 %, and the shear strength of 22.3 ± 2.4 MPa. Raising the sintering temperature enhances silver crystallite size, strengthens sintering necks, thus improves shear strength and ratcheting fatigue life in joints. In addition, the ratcheting fatigue lives of the joints sintered at different temperatures are effectively predicted by three equivalent force models, and the Gerber model shows the highest life prediction accuracy.

The sintered silver bondline is suffering a complex stress state. The study only takes the shear stress into consideration. The tensile stress and the combination of shear stress and tensile stress can to be considered in the future study.

The paper provides the experimental and theoretical support for robust bonding and long-term reliability of sintered silver structure.

The introduced model can predict the ratcheting fatigue lives of the joints sintered at different temperatures, which shows a potential in engineering applications.

The study revealed the relationship between the sintering temperature and the microstructure, the shear strength and the ratcheting fatigue life of the joint. In addition, the Gerber model can predict the ratcheting fatigue life accurately at different sintering temperatures.

The purpose of this paper is to examine the continuance intention of Alipay by proposing an integrated model. This paper highlights how the capacity of providing context-based information to the users plays significant role in determining the continuance intention of mobile payment like Alipay.

Data are collected from 336 Alipay users from Wuhan, P.R. China. To analyze the data, the authors apply structural equation modeling approach. Also, the authors perform importance-performance map analysis (IPMA) to identify the critical factors in explaining the continuance intention of Alipay.

The results of the study reveal that confirmation and perceived usefulness significantly influence the continuance intention of Alipay through satisfaction. Also, perceived usefulness, satisfaction, context and ubiquity have direct impact on the continuance intention of Alipay through attitude. According to IPMA, perceived ease of use, confirmation and context require special managerial consideration to improve their performance.

This research has proposed and validated an integrated model by incorporating context-awareness theory and technology continuance theory. This study provides significant insights that can assist respective decision-makers to formulate/adjust their strategies related to the retention of the existing users of mobile payment like Alipay.