Desired Position Research Articles

Some features satellite attitude control using quaternions

Algorithms using the kinematics equations in quaternions are widely used in the attitude control systems of modern spacecraft, primarily microsatellites. They ensure large-angle rotations and avoidance of singularity points characteristic of Euler-Krylov angles. However, the specificity of single quaternions as attitude representation parameters can create an "unwinding effect" in the control system, when turning the spacecraft to a desirable position is not performed by the shortest path and increases the electricity consumption, that is limited on board. This work, summarizing known publications, illustrates the causes of this effect and demonstrates a simple algorithm for its prevention. The effectiveness of this approach is shown on the MATLAB platform numerical simulation examples of the microsatellite control system with reaction wheels and a PD controller.

Finite-Time Neural Network-Based Hierarchical Sliding Mode Antiswing Control for Underactuated Dual Ship-Mounted Cranes With Unmatched Sea Wave Disturbances Suppression.

As typical mechanical transportation equipment, cooperative dual ship-mounted cranes are widely used to transport large goods or containers in the marine environment. However, the control problem of the dual ship-mounted crane system is much more complex due to its underactuated characteristic and persistent unmatched disturbances. To solve these problems, we propose a novel neural network (NN)-based hierarchical sliding mode adaptive (HSMA) control method in this article. More specifically, an appropriate hierarchical sliding mode surface is first designed to connect the actuated and underactuated system state variables effectively. At the same time, the NNs are constructed to compensate for the unmatched interference of ship motions induced by sea waves simultaneously. Not only can the booms and the rope lengths reach their desired positions in finite time, but also the synchronous swing angles of the payload can be effectively eliminated. The asymptotic convergence of the closed-loop system's equilibrium points is achieved through rigorous mathematical proofs. Furthermore, the stability of each sliding mode surface is also analyzed utilizing the Lyapunov technique and Barbalat's lemma. Finally, numerous groups of compared numerical simulation results are investigated to further show the effectiveness and strong robustness of the proposed NN-based HSMA controller.

Heat‐resistant and transparent polyimides derived from alicyclic dianhydrides and phthalazinone‐based diamine

AbstractAdvanced flexible display materials have drastically sparked considerable interest for heat‐resistant, low dielectric, and transparent polyimide (PI) materials. In light of this, our study aims to develop high‐performance semi‐aromatic PI films, followed by investigate the correlations between bridged‐alkyl/heteroaromatic ring structures and their thermal, dielectric, optical, and mechanical properties. Such PI films, namely AP‐PIs, were synthesized with a one‐step high‐temperature method between 4‐[4‐(4‐aminophenoxy) phenyl]‐2‐(4‐aminophenyl)‐1(2H)‐phthalazinone (DHPZDA) and various commercial alicyclic dianhydrides. The incorporation of rigid phthalazinone structures significantly enhanced thermal resistance and mechanical flexibility, while simultaneously reducing their dielectric constant (Dk), attributed to the large polymer internal free volume. Impressively, the prepared films exhibit exceptional glass transition temperature (Tg) as high as 419°C (DMTA tanδ peak), low Dk as low as 2.71, and elongation at break (ε %) up to 50.4%. Furthermore, AP‐PI films demonstrate reasonable solubility and optical transparency within the UV–visible region. The maximum optical transmittance at 550 nm (T550 nm) could reach 83.01%. These desirable properties position these materials as promising candidates for flexible substrate applications.

Islands in the City: Negotiating the Location of British Concessions Along the Yangtze River in 1861 China

In the second half of the nineteenth century, Britain signed treaties to secure the right to establish concessions along the Yangtze River in China. Despite extensive scholarly analysis of the history of British concessions, one aspect that is often overlooked is that these treaties did not specify the locations for these concessions. As a result, the British had to negotiate with local Chinese officials to acquire suitable sites. This essay aims to delve into the history of Sino-British relations and the spatial dynamics of occupation by examining the interactions between the British and Chinese in determining concession sites within Yangtze River port cities – specifically Zhenjiang, Hankou, and Jiujiang. It reveals that, following the Second Opium War, British arrivals and Chinese authorities established an implicit understanding. Despite diverse strategies employed by Chinese authorities in managing foreign affairs – ranging from appeasement to radical measures – the British consistently pursued potential advantages and preferred negotiation to maximize their respective interests. Consequently, these concessions were located in less desirable positions along the Yangtze River, surrounded by waterways. This strategic placement facilitated British cargo landings while enabling the Chinese to retain control over foreign arrivals, effectively transforming them into metaphorical islands within these cities.

Communication-Efficient and Collision-Free Motion Planning of Underwater Vehicles via Integral Reinforcement Learning.

Motion planning of underwater vehicles is regarded as a promising technique to make up the flexibility deficiency of underwater sensor networks (USNs). Nonetheless, the unique characteristics of underwater channel and environment make it challenging to achieve the above mission. This article is concerned with a communication-efficient and collision-free motion planning issue for underwater vehicles in fading channel and obstacle environment. We first develop a model-based integral reinforcement learning (IRL) estimator to predict the stochastic signal-to-noise ratio (SNR). With the estimated SNR, an integrated optimization problem for the codesign of communication efficiency and motion planning is constructed, in which the underwater vehicle dynamics, communication capacity, collision avoidance, and position control are all considered. In order to tackle this problem, a model-free IRL algorithm is designed to drive underwater vehicles to the desired position points while maximizing the communication capacity and avoiding the collision. It is worth mentioning that, the proposed motion planning solution in this article considers a realistic underwater communication channel, as well as a realistic dynamic model for underwater vehicles. Finally, simulation and experimental results are demonstrated to verify the effectiveness of the proposed approach.

Fixed-time coordination control for 6-DOF attitude-orbit coupled spacecraft formation flying

This paper presents a distributed fixed-time control protocol for 6-DOF(degree-of-freedom) attitude-orbit coupled spacecraft formation flying with external disturbances. Firstly, the 6-DOF attitude-orbit coupled dynamics is established. The communication topology between the spacecraft in the formation is described by a directed graph. Secondly, a fixed-time disturbance observer (FxTDO) is designed to ensure that the estimation errors of the unknown external disturbances can converge to zero in fixed time. Thirdly, based on non-singular fixed-time terminal sliding mode (NFFTSM) surface, the fixed-time coordination control protocol is proposed combined with the fixed-time disturbance observer, which can guarantee that each spacecraft can track their desirable positions and attitudes in fixed time. The stability of the closed-loop system is proved through Lyapunuov method. Finally, simulation results for a formation with one virtual leader and five followers demonstrate the effectiveness of the proposed control scheme.

Improvement of biomedical properties of PEO-treated titanium with flurbiprofen and exosome conjugation

Exosome (EXO)-based drug delivery systems have attained a desirable position among scientific researchers and in biomedical applications. In this study, an exosomal coating comprising the anti-inflammatory drug flurbiprofen (FLB) was applied on a commercially pure titanium (cp-Ti) substrate that had undergone surface treatment using plasma electrolytic oxidation (PEO) process. The samples were characterized through field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), and water contact angle (WCA) measurement. The results indicated that FLB was loaded onto the EXO and the formation of FLB.EXO was confirmed by FTIR, XRD, AFM and FESEM. Furthermore, FLB.EXO system was treated on PEO-treated substrates and FLB.EXO@PEO system demonstrated a considerable degree of roughness (Ra= 51.16 nm) and exceptional WCA (37.2 ± 0.7 ̊) in comparison to the other samples. The cellular inquiries were assessed through examination of the morphology of bone marrow mesenchymal stem cells (BMMSc) and the MTT assay. The cytotoxicity assessment showed that the FLB.EXO@PEO improved BMMSCs attachment without toxicity. The antibacterial efficacy was determined by means of bacterial adhesion testing against both gram-positive Staphylococcus aureus (S. aureus) and gram-negative Escherichia coli (E. coli) bacterial strains. FLB.EXO@PEO sample also revealed an excellent antibacterial rate of ∼ 86 % against S. aureus and ∼ 55 % against E. coli. Additionally, in vitro drug release evaluations indicated that sustained drug release was occurred and FLB released from FLB.EXO@PEO during 191 h that was lower than release time in FLB.EXO (120 h). Moreover, the prolonged release was confirmed by constant release rate in both of systems of FLB.EXO and FLB.EXO@PEO after 191 h and 167 h, respectively. The release kinetic of FLB.EXO and FLB.EXO@PEO followed the zero order and first-order model, respectively. Overall, the results indicate that the designed sustained release system have a high potential for development of advanced biomedical implants.

3D printing of hydrogels for flexible micro‐supercapacitors

AbstractAdvances in hydrogel technology have paved the way for novel and valuable capabilities that are being applied to a diverse spectrum of energy storage applications. Hydrogels, originally renowned for their biomedical applications, are now finding translation into the energy storage domain. These versatile materials exhibit promising potential for various energy‐related applications, including but not limited to acting as highly flexible electrolytes, facilitating the development of flexible supercapacitors, and contributing to advancements in energy conversion devices. The tunable properties of hydrogels, their high ion accessibility, and desirable mechanical characteristics position them as promising candidates for enhancing the performance and efficiency of energy storage systems. In this review, we emphasize the integration of hydrogels into flexible micro‐supercapacitors through 3D printing technology, unraveling the charge transport mechanisms inherent in hydrogels. We discuss methods for developing hydrogels with enhanced physicochemical properties, such as improved mechanical strength, flexibility, and charge transport, offering new prospects for next‐generation energy storage devices. With a deeper understanding of gelation chemistry, we showcase significant progress in fabricating stimuli‐responsive, self‐healing, and highly stretchable hydrogels. Furthermore, we present compelling examples highlighting the versatility of hydrogels, including tailorable architectures, conductive nanostructures, 3D frameworks, and multifunctionalities. The application of innovative 3D printing techniques in hydrogel design is poised to yield materials with immense potential in the realm of energy storage.

Reinforcement Learning-Based Switching Controller for a Milliscale Robot in a Constrained Environment

This work presents a reinforcement learning-based switching control mechanism to autonomously move a ferromagnetic object (representing a milliscale robot) around obstacles within a constrained environment in the presence of disturbances. This mechanism can be used to navigate objects (e.g., capsule endoscopy, swarms of drug particles) through complex environments when active control is a necessity but where direct manipulation can be hazardous. The proposed control scheme consists of a switching control architecture implemented by two sub-controllers. The first sub-controller is designed to employs the robot's inverse kinematic solutions to do an environment search of the to-be-carried ferromagnetic particle while being robust to disturbances. The second sub-controller uses a customized rainbow algorithm to control a robotic arm, i.e., the UR5 robot, to carry a ferromagnetic particle to a desired position through a constrained environment. For the customized Rainbow algorithm, Quantile Huber loss from the Implicit Quantile Networks (IQN) algorithm and ResNet are employed. The proposed controller is first trained and tested in a real-time physics simulation engine (PyBullet). Afterward, the trained controller is transferred to a UR5 robot to remotely transport a ferromagnetic particle in a real-world scenario to demonstrate the applicability of the proposed approach. The experimental results show an average success rate of 98.86\% calculated over 30 episodes for randomly generated trajectories.

Event-triggered adaptive vibration control for a flexible satellite with time-varying actuator faults

In this study, vibration control is studied for the flexible satellite through wireless communication, and given the fact that the actuators are prone to unknown faults, the input signal event-triggering and time-varying actuator faults are considered for the flexible satellite simultaneously. The satellite system is composed of two symmetrical flexible panels attached to a centrebody, which is a distributed parameter system and the established model is represented by partial differential equations (PDEs). Based on the PDEs model of the flexible satellite, the input event-triggered mechanism using the relative threshold strategy is designed firstly to lower the communication burden, and then the event-triggered-based adaptive fault-tolerant control laws are developed with the aid of the designed auxiliary signals for the system with time-varying actuator faults. With the proposed control scheme, the vibration of the system is controlled to the small neighborhood of zero, and the angle of the panels is regulated to the desired position. Finally, numerical simulation results are given to further show the effectiveness of the designed control scheme.

POSITION CONTROL OF A QUADCOPTER WITH PID AND FUZZY-PID CONTROLLER

In this study, PID based efficient control systems are designed and compared for position control of a quadcopter in six degrees of freedom. The main goal is to get the quadcopter to the desired position in three-dimensional space. Firstly, the desired position for the quadcopter to reach is determined. Then, the physical model of the system is selected, and mathematical model is derived according to the physical model. Initially, all external disturbances like drag force and wind are neglected. However, various external disturbances are then applied to the system to measure robustness of the designed controllers. Firstly, PID controller is implemented to the quadcopter system. Secondly, Fuzzy-PID controller is used. Necessary pitch and roll angles are found and control forces are calculated by using both controllers. Also, angular velocities of the motors and current values which are needed to be supplied to each motor are calculated and compared to evaluate performance and applicability of the proposed controllers. According to the results, it is observed that both controllers worked successfully, quadcopter is able to reach the desired location in three-dimensional space. However, Fuzzy-PID controller gives faster response and smaller overshoot levels than basic PID controller. In addition, it is seen that the Fuzzy-PID controller is less affected by external disturbances, and it recovers faster against these changes.

Collision-free automatic berthing of maritime autonomous surface ships via safety-certified active disturbance rejection control

This paper addresses the automatic berthing of a maritime autonomous surface ship operating in a confined water environment subject to static obstacles, dynamic obstacles, thruster constraints, and space constraints due to shorelines. A safety-certified active disturbance rejection control (ADRC) method is proposed for achieving the automatic berthing task of an MASS in the presence of model uncertainties and ocean disturbances. An extended state observer (ESO) based on a second-order robust exact differentiator (RED) is employed to estimate an extended state vector consisting of internal model uncertainties and external ocean disturbances. With the aid of the RED-based ESO, a nominal ADRC law is designed to achieve the position and heading stabilization. To avoid collisions with static obstacles, dynamic obstacles, and shorelines, input-to-state safe high-order control barrier functions are used to guarantee safety. Optimized control signals are obtained based on a constrained quadratic programming (QP) problem within safety constraints. In order to translate the control signals into the individual thruster command, a constrained QP problem is further used to search for optimized commands in real time. It is proven that the closed-loop automatic berthing system is input-to-state stable. By using the proposed method, the MASS is able to reach the desired position and heading with collision avoidance. Simulation results verify the effectiveness of the proposed safety-certified ADRC method for automatic berthing.

A Lyapunov based posture controller for a differential drive mobile robot

Driving a vehicle to a desired position and orientation is one of the most important problems that should be solved in most navigation systems. This paper describes a new complete design and hardware implementation of a two-level controller that will enable a differential drive mobile robot to reach any desired posture starting from any initial position. The first or low-level controller consists of a set of two proportional–integral–derivative (PID) controllers, running on an embedded system on board of the robot. These controllers provide the required voltages to the motors to make the left and right wheels of the robot rotate with the angular speeds computed by the second or high-level controller, running on a stationary PC system. This second controller is based on the Lyapunov stability theorem to derive two control laws for the kinematic model, used to transform the linear and angular speeds of the unicycle model in terms of left and right rotational speeds, required by the motors. As will be shown later, this architecture provides a very flexible way not only to tune the main controller parameters but also to get access and record all the system states.

DDPG-based reinforcement learning for controlling a spatial three-section continuum robot

This paper proposes an approach to controlling a spatial three-section continuum robot using reinforcement learning (RL). Rather than relying on traditional methods that use bending and orientation angles, this study utilizes the curvature of each section to achieve the desired position. The training process involves identifying a 3D workspace for the robot and utilizing a deep neural network to optimize its control policies. The results demonstrate that the robot’s end effector can follow a given trajectory with a maximum error of 1 [1/mm] based on the generated curvature for each section. The Deep Deterministic Policy Gradients (DDPG) algorithm is employed to optimize the robot’s control policies. Additionally, the developed DDPG algorithm is compared to the Deep Q-Network (DQN) from a precision standpoint, particularly during the tracking of a circular trajectory. This comparison highlights the superior accuracy of DDPG in managing the intricate movements required for continuum robotics, making it a promising tool for applications where precision is crucial, such as in medical and surgical robotics.

Deep Circumflex Iliac Artery-vascularized Iliac Bone Graft for Femoral Head Osteonecrosis: Computed Tomography Anatomical Study.

Deep circumflex iliac artery (DCIA)-vascularized iliac graft transposition is a method for treating femoral head osteonecrosis but with inconsistent efficacy. We aim to improve the method of this surgery by recommending the optimal location of the iliac pedicle to satisfy the vascular length for transposition and the blood supply of the vascularized iliac graft. The DCIA and its surrounding tissues were assessed on computed tomography angiography images for 100 sides (left and right) of 50 patients. The length of the vascular pedicle required for transposition and the length of the pedicle at different iliac spine positions were compared. The diameter and cross-sectional area of the DCIA and the distance between the DCIA and iliac spine were measured at different points to assess blood supply. We also compared differences in sex and left-right position. The diameter and cross-sectional area of the DCIA gradually decreased after crossing the anterior superior iliac spine (ASIS), and it approached the iliac bone. However, when the DCIA was 4 cm behind the ASIS (54 sides, 54%), it coursed posteriorly and superiorly away from the iliac spine. The vascular length of the pedicle was insufficient to transpose the vascularized iliac graft to the desired position when it was within 1 cm of the ASIS. The vascular length requirement was satisfied, and the blood supply was sufficient when the pedicle was positioned at 2 or 3 cm. To obtain a satisfactory pedicle length and sufficient blood supply, the DCIA pedicle of the vascularized iliac graft should be placed 2 to 3 cm behind the ASIS. The dissection of DCIA has slight differences in sex and left-right position due to anatomical differences.

Event-Based Secure Consensus Control for Multirobot Systems With Cooperative Localization Against DoS Attacks

In this article, we investigate the secure consensus control problem for multirobot systems with event-triggered communication strategy under aperiodic energy-limited denial-of-service (DoS) attacks, where DoS attacks prevent the transmission of information between robots. Each robot is equipped with onboard sensors to estimate its position cooperatively by taking relative measurements and exchanging the local positioning information with other robots through the unreliable communication network. In the meantime, each robot determines its consensus control based on transmitted position estimates and steers the robot to the desired consensus position. Therefore, our goal is to design a secure control scheme for each robot based on cooperative localization with an event-triggered mechanism and obtain a sufficient condition for the upper bound of duration and the maximum number of attacks such that <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$N$</tex-math></inline-formula> robots can move to the desired secure consensus position in the presence of DoS attacks. Finally, simulation and experimental results are presented to show the effectiveness of obtained theoretical results.

Technique for cementing screwmentable implant crowns to prevent misalignment.

The purpose of this article is to describe a technique to accurately cement implant crowns on an abutment extraorally and prevent misalignment that might change the desired position of the crown on the abutment when delivered. An implant-retained crown was tried-in and occlusal and interproximal contacts were adjusted for delivery. The cementation verification aid was fabricated using a polyvinylsiloxane bite registration material (Blu Mousse) to cement the crown onto the abutment extraorally to ensure proper alignment of the crown on the abutment. Cementation of the prosthesis occurred with no adjustments required to the interproximal or occlusal contacts during final delivery. This article provides a technique that aims to increase accuracy in the placement of the crown on the abutment when cementing screwmentable crowns.

Organizational corruption, test score manipulation, and teacher hiring in Romania

This study investigated the relationship between organized corruption and the irregularities observed in the score distribution of Romania's national teaching hiring and mobility test, which determines eligibility for fixed-term and open-ended teaching positions. Despite its strict scoring rules, there was a significant excess of scores at the critical cut-off values. Both bunching analyses and binomial generalized linear mixed models identified organizational but not individual corruption, as a significant predictor of scoring irregularities at the minimum value required for open-ended positions.Organizational corruption was also associated with a higher probability that scoring precisely at this threshold value would secure an open-ended position. The results further indicated that other factors may contribute to the scoring irregularities at the minimum value required for the less desirable fixed-term positions.

Adaptive multivariate reusable launch vehicles reentry attitude control with pre-specified performance in the presence of unmatched disturbances

This paper introduces a novel adaptive multivariable attitude control method for a reusable launch vehicle (RLV) to track desired attitude trajectories in the presence of unknown external disturbances and uncertainties. Unlike most existing designs that overlook mismatched disturbances, this method employs an adaptive finite-time observer (AFO) to estimate the unknown states. Based on the outputs of the AFO and the prescribed performance function, a time-varying adaptive gain that is not overestimated is designed to establish the adaptive multivariable attitude control for the RLV system. The simulations demonstrate that the proposed approach successfully guides the RLV to follow desired attitude signals despite the presence of unmatched disturbances and uncertainties.

Undesirable or slightly desirable social position of Iranian nurses: A rising cause for concern of the Iranian nursing community

The meaning of nursing is different between cultures, and it seems hard to integrate nursing concepts. However, many studies evaluate the process of professional socialization [1]. Nurses' social position is one of the major factors affecting their quality of life, which may alter their job competency [2]. Being recognized as a doctor's assistant is not only limited to nurses in Iran but also in other countries; even doctors have the same view of nurses and ignore their art in patient care [3]. A study in Iran showed that most Iranian nurses were concerned of culturally based ‘poor’ attitudes of their job [1, 4]. Another study on nurses' social well-being showed a lower score of social acceptance among other variables. Also, have been shown that the mean score of social well-being was higher in male participants who had more experience [5]. “Nursing is not well perceived as a profession within this community”, this is likely the best description of Iranian nurses' social position from a study by Valizadeh et al. [6]. On the other hand, nurses' high rate of burnout is also related to their social position [7]. With all of these, few studies are addressing how to change this social image of nurses. One way is to use them without distortion, portraying their profession in the media [3]. Others suggest extending community-based services and replacing the style of nursing practice from routine-oriented to knowledge-based [4].