Sliding mode control with self-adaptive parameters of a 5-DOF hybrid robot.

Due to the advantages of high stiffness, high precision, high load capacity and large workspace, hybrid robots are applicable to drilling and milling of complicated components with large sizes, for instance car panels. However, the difficulty in establishing an exact dynamic model and external disturbances affect the high accuracy control directly, which will decrease the machining accuracy and thereby affect the machining quality and efficiency of the system. Sliding mode control is an effective approach for high-order nonlinear dynamic systems since that it is very insensitive to disturbances and parameter variations. However, chattering may exist in traditional sliding mode control with fixed parameters, which results from a constant approaching speed. Besides, the approaching speed will affect the chattering strength directly. To solve these problems, a modified sliding mode controller with self-adaptive parameters is proposed to enhance the trajectory-tracking performance of a 5-degree-of-freedom hybrid robot. Firstly, the kinematic model of the robot is established. Then adopting the principle of virtual work, a rigid dynamic model of the robot is built. Based on the built dynamic model, a modified sliding mode control method is developed, of which the approaching speed is dependent on the system state. Finally, the sliding mode controller with self-adaptive parameters is created for a hybrid robot. The proposed sliding mode controller can achieve a rapid approaching speed and suppress chattering simultaneously. Simulation results demonstrate that the proposed modified sliding mode controller can achieve a comparatively accurate and smooth trajectory, which owns good robustness to external disturbances.

Frequency modulation increases the specificity of time-resolved connectivity: A resting-state fMRI study.

Representing data using time-resolved networks is valuable for analyzing functional data of the human brain. One commonly used method for constructing time-resolved networks from data is sliding window Pearson correlation (SWPC). One major limitation of SWPC is that it applies a high-pass filter to the activity time series. Therefore, if we select a short window (desirable to estimate rapid changes in connectivity), we will remove important low-frequency information. Here, we propose an approach based on single sideband modulation (SSB) in communication theory. This allows us to select shorter windows to capture rapid changes in the time-resolved functional network connectivity (trFNC). We use simulation and real resting-state functional magnetic resonance imaging (fMRI) data to demonstrate the superior performance of SSB+SWPC compared to SWPC. We also compare the recurring trFNC patterns between individuals with the first episode of psychosis (FEP) and typical controls (TC) and show that FEPs stay more in states that show weaker connectivity across the whole brain. A result exclusive to SSB+SWPC is that TCs stay more in a state with negative connectivity between subcortical and cortical regions. Based on all the results, we argue that SSB+SWPC is more sensitive for capturing temporal variation in trFNC.

Distinction between Pneumothorax and Pneumomediastinum Using Point of Care Ultrasound (POCUS): Role of Still Lung Point.

The rapid identification and management of air leak syndrome in the neonatal intensive care unit is critical to prevent and/or minimize short- and long-term complications. Traditionally, chest X-ray is used to diagnose pneumothorax or pneumomediastinum. However, point-of-care ultrasound is increasingly being used for procedural and diagnostic purposes. Current ultrasound guidelines recommend specific criteria to diagnose pneumothorax in newborns including sharp A-lines, absence of B-lines, lack of shimmering of the pleural line, and the presence of a lung point. Pneumomediastinum may have similar ultrasound characteristics. In this case report, we present two cases of pneumomediastinum in newborns, describe the associated ultrasound findings, and review some of the criteria to differentiate from pneumothorax, including the presence of a still lung point. A high index of suspicion for pneumomediastinum should be maintained when using ultrasound to diagnose air leak given the overlapping sonographic features with pneumothorax. This distinction is of particular importance if evacuation of air by needle thoracentesis or the placement of a chest tube is under consideration.

Molecular basis of global promoter sensing and nucleosome capture by the SWR1 chromatin remodeler.

The SWR1 chromatin remodeling complex is recruited to +1 nucleosomes downstream of transcription start sites of eukaryotic promoters, where it exchanges histone H2A for the specialized variant H2A.Z. Here, we use cryoelectron microscopy (cryo-EM) to resolve the structural basis of the SWR1 interaction with free DNA, revealing a distinct open conformation of the Swr1 ATPase that enables sliding from accessible DNA to nucleosomes. A complete structural model of the SWR1-nucleosome complex illustrates critical roles for Swc2 and Swc3 subunits in oriented nucleosome engagement by SWR1. Moreover, an extended DNA-binding α helix within the Swc3 subunit enables sensing of nucleosome linker length and is essential for SWR1-promoter-specific recruitment and activity. The previously unresolved N-SWR1 subcomplex forms a flexible extended structure, enabling multivalent recognition of acetylated histone tails by reader domains to further direct SWR1 toward the +1 nucleosome. Altogether, our findings provide a generalizable mechanism for promoter-specific targeting of chromatin and transcription complexes.

Quantized feedback integral sliding mode control for uncertain networked linear systems via event-triggered approach.

This paper investigates the design problem of quantized event-triggered (ET) integral sliding mode (ISM, SM) controller for uncertain networked linear systems. Firstly, this paper proposes a novel ISM surface constructed using only quantized ET states and applied to the design of the controller. The quantized ET ISM surface in this paper divides the integrals from t0 to t into the sum of adjacent ET intervals and replaces ET states with quantized ET states. Secondly, based on state error and quantized ET SM error, novel ET conditions are constructed to decide whether to update the current control signal or not. Thirdly, this paper proves the existence of minimum inter-event times under "zoom-out" and "zoom-in" phases respectively, avoiding Zeno phenomenon. Finally, to prove the validity of the proposed method, two comparative simulation results are given.

Picometer-Level In Situ Manipulation of Ferroelectric Polarization in Van der Waals layered InSe.

Ferroelectric 2D van der Waals (vdW) layered materials are attracting increasing attention due to their potential applications in next-generation nanoelectronics and in-memory computing with polarization-dependent functionalities. Despite the critical role of polarization in governing ferroelectricity behaviors, its origin and relation with local structures in 2D vdW layered materials have not been fully elucidated so far. Here, intralayer sliding of approximately six degrees within each quadruple-layer of the prototype 2D vdW ferroelectrics InSe is directly observed and manipulated using sub-angstrom resolution imaging and in situ biasing in an aberration-corrected scanning transmission electron microscope. The in situ electric manipulation further indicates that the reversal of intralayer sliding can be achieved by altering the electric field direction. Density functional theory calculations reveal that the reversible picometer-level intralayer sliding is responsible for switchable out-of-plane polarization. The observation and manipulation of intralayer sliding demonstrate the structural origin of ferroelectricity in InSe and establish a dynamic structural variation model for future investigations on more 2D ferroelectric materials.

Elderly trochanteric fracture outcomes: Unveiling the risks of excessive postoperative sliding - A retrospective multicenter (TRON group) investigation.

BACKGROUND: Intramedullary nailing (IMN) for femoral trochanteric fractures (FTF) is the primary surgical intervention. Excessive lag screw sliding (ES) of the femoral neck screw sometimes occurs. This multicenter investigation sought to 1) determine the prevalence of ES, 2) evaluate the relationship between ES and postoperative complications, and 3) identify the factors of ES in elderly patients with FTF undergoing IMN. METHODS: From 2016 to 2020, 1448 patients with FTF were treated using a short IMN across 11 institutions (TRON group). Upon applying exclusion criteria, 519 patients (127 men, 392 women; mean age, 84.4 years) were included. The postoperative sliding distance was measured immediately after surgery and at final follow-up. A sliding distance of ≥8 mm categorized patients as having ES. We identify the factors contributing to ES using the logistic regression analysis, with a p < 0.05 as statistical significance. RESULTS: ES was observed in 116 patients (22.4 %). Patients with ES had a higher incidence of postoperative cut-out and peri-implant fracture. Logistic regression analysis showed that achieving optimal reduction in both AP and lateral views (odds ratio (OR) 0.48, p = 0.0012) and the use of a double screw system or twin screws with integrated locking mechanism significantly reduced the risk of ES (OR 0.27, 0.17; p = 0.0027, <0.001). CONCLUSIONS: The incidence rate of ES was 22.4 %. ES was associated with a higher risk of postoperative complications. The surgeons should aim for optimal reduction and use a double screw or twin screws with an integrated interlocking mechanism as the implant of choice.

Ultrasensitive lab-on-paper electrochemical device via heterostructure copper/cuprous sulfide@N-doped C@Au hollow nanoboxes as signal amplifier for alpha-fetoprotein detection.

Rapid and accurate detection of tumor markers at extremely low levels is crucial for the early diagnosis of cancers. In this work, we developed a portable label-free sliding electrochemical paper-based analytical device (ePAD) using copper/cuprous sulfide@N-doped C@Au nanoparticles (Cu/Cu2S@NC@Au) hollow nanoboxes as the signal amplifier for the ultrasensitive detection of alpha-fetoprotein (AFP). Cu/Cu2S@NC nanoboxes were synthesized by sacrificial template and interface reaction methods, on which Au nanoparticles were electrodeposited to construct unique heterostructure for effectively capturing anti-AFP and serving as signal amplifier. The designed ePAD incorporates sliding microfluidic paper chips to form a flexible three-electrode system, enabling highly sensitive detection of AFP with a wide linear range of 0.005-50 ng mL-1 and a low detection limit of 0.62 pg mL-1. The practicality of the prepared ePAD was validated through AFP detection in clinical human serum, which was consistent with chemiluminescence immunoassay. In addition, the developed immunosensor demonstrates excellent specificity, repeatability and stability. This novel platform exhibits significant potential for rapid on-site analysis and point-of-care diagnosis.

Oblique sliding ulna osteotomy to treat paediatric neglected monteggia fracture dislocation.

INTRODUCTION: There have been osteotomy methods that corrected or overcorrected the ulna deformity as part of surgical treatment for chronic radial head dislocation. METHODOLOGY: We reported surgical technique and outcome of oblique sliding ulna osteotomy that created acute lengthening, deformity correction or both to assist open reduction of radiocapitellar joint in four patients with neglected Monteggia fracture dislocation. RESULT: Patients aged 3-12 years old had trauma duration of 4 weeks to 3 years. Two patients had Bado type I injury, and the other two had Bado type III. There was no acute nerve injury. During the final follow-up, all patients achieved union, with the limitation of motion range in the rotation arch being less than 20°. The radial head had no recurrent dislocation. CONCLUSION: This case series has shown sliding osteotomy safely, providing acute correction and lengthening of the ulna without requiring bone graft to facilitate stable reduction of the neglected Monteggia lesion.

Multifrequency operation of an intracavitary monopole with sliding broadband choke for delivering hyperthermia treatment with variable coverage.

Microwave applicators reported for intracavitary hyperthermia (HT) operate at single frequency and deliver fixed treatment coverage at the tumor target. In this work, we report multifrequency operation of a water-cooled monopole antenna with a sliding broadband ferrite choke for delivering intracavitary HT to the cervix with variable spatial coverage. Spatially varying treatment coverage is achieved by varying the choke position with respect to the monopole using a mechanical sliding arrangement and exciting the antenna at the modified resonant frequency. Multifrequency operation of the antenna prototype is demonstrated over 700-1000 MHz using a straight intrauterine cervix applicator. Numerical simulations confirm the ability to deliver targeted HT with axial extent varying between 35.4 and 62.0 mm by controlling the sliding choke and coupling water temperature. Applicator prototype measurements in tissue mimicking phantoms confirm multifrequency operation of the antenna and its ability to induce axially varying intracavitary HT coverage to match the tumor size using a single applicator.

Microwave devices used for targeted internal hyperthermia treatment typically operate at fixed frequency and provide fixed treatment coverage to the tumor. In this study, we introduce a new approach using a water-cooled monopole antenna with a sliding broadband ferrite choke to treat cervical cancer with varying tumor volumes. The proposed antenna can be operated at multiple frequencies to adjust the treatment volume. By sliding the choke along the antenna, the antenna can be tuned to different frequencies and deliver spatially varying treatment coverage to suit the clinical target volume. Laboratory assessment shows that this antenna can be operated over 700 to 1000 MHz to deliver treatment coverage with axial extent varying over 35.4 to 62.0 mm, depending on the choke position and water temperature. Experiments on tissue mimicking phantoms confirm that this method enables precise control of hyperthermia treatment coverage to match the tumor size using a single device.

Disturbance Estimation and Predefined-Time Control Approach to Formation of Multi-Spacecraft Systems.

Accurate sensing and control are important for high-performance formation control of spacecraft systems. This paper presents a strategy of disturbance estimation and distributed predefined-time control for the formation of multi-spacecraft systems with uncertainties based on a disturbance observer. The process begins by formulating a kinematics model for the relative motion of spacecraft, with the formation's communication topology represented by a directed graph for the formation system of the spacecraft. A disturbance observer is then developed to estimate the disturbances, and the estimation errors can be convergent in fixed time. Following this, a disturbance-estimation-based sliding mode control is proposed to guarantee the predefined-time convergence of the multi-spacecraft formation system, regardless of initial conditions. It allows each spacecraft to reach its desired position within a set time frame. The results of the analysis of the multi-spacecraft formation system are also provided. Finally, an example simulation of a five-spacecraft formation flying system is provided to demonstrate the presented formation control method.

Ultrasonic Obstacle Avoidance and Full-Speed-Range Hybrid Control for Intelligent Garages.

In the current study, which focuses on the operational safety problem in intelligent three-dimensional garages, an obstacle avoidance measurement and control scheme for the AGV parking robot is proposed. Under the premise of high-precision distance detection using Kalman filtering, a mathematical model of a brushless DC (BLDC) motor with full-speed range hybrid control is established. MATLAB/Simulink (R2022a) is used to build the control model, which has dual closed-loop vector-controlled motors in the low- to medium-speed range, with photoelectric encoders for speed feedback. The simulation results show that, at lower to medium speeds, the maximum overshoot of the output response curve is 1.5%, and the response time is 0.01 s. However, at higher speeds, there is significant jitter in the speed output waveform. Therefore, the speed feedback is switched to a sliding mode observer (SMO) instead of the original speed sensor at high speeds. Experiments show that, based on the SMO, the problem of speed waveform jitter at high motor speeds can be significantly improved, and the BLDC motor system has strong robustness. The above shows that the motor speed under the full-speed range hybrid control system can meet the AGV control and safety requirements.

Adaptive backstepping sliding mode control for single-inductor double-output boost converter.

To reduce the cross-regulation and improve the dynamic response performance of a single-inductor double-output Boost converter, an adaptive backstepping sliding mode control (ABSMC) strategy is proposed in this paper. The nonlinear mathematical model of the converter is established, an output function satisfying the exact feedback linearization (EFL) is constructed based on the inverse system theory, and the linearization and decoupling of the model are implemented. Meanwhile, the problem of EFL heavily relying on an exact model is solved by combining backstepping control with sliding mode control. Furthermore, an adaptive reaching law is proposed to adjust the gain of the switching function, and the chattering phenomenon of sliding mode control is reduced. The stability of the system is proven according to the Lyapunov stability theorem. Finally, compared with the existing control methods, both the simulation results and experimental results verify the effectiveness and superiority of the proposed ABSMC strategy.

ADP-based online compensation hierarchical sliding-mode control for partially unknown switched nonlinear systems with actuator failures.

This article investigates an adaptive dynamic programming-based online compensation hierarchical sliding-mode control problem for a class of partially unknown switched nonlinear systems with actuator failures and uncertain perturbations under an identifier-critic neural networks architecture. Firstly, by introducing a cost function related to hierarchical sliding-mode surfaces for the nominal system, the original control problem is equivalently converted into an optimal control problem. To obtain this optimal control policy, the Hamilton-Jacobi-Bellman equation is solved through an adaptive dynamic programming method. Compared with conventional adaptive dynamic programming methods, the identifier-critic network architecture not only overcomes the limitation on the unknown internal dynamic but also eliminates the approximation error arising from the actor network. The weights in the critic network are tuned via the gradient descent approach and the experience replay technology, such that the persistence of excitation condition can be relaxed. Then, a compensation term containing hierarchical sliding-mode surfaces is used to offset uncertain actuator failures without the fault detection and isolation unit. Based on the Lyapunov stability theory, all states of the closed-loop nonlinear system are stable in the sense of uniformly ultimately boundedness. Finally, numerical and practical examples are given to demonstrate the effectiveness of our presented online compensation control strategy.

Super-twisting ADRC for maximum power point tracking control of photovoltaic power generation system based on non-linear extended state observer.

This paper proposed a new method for maximum power point tracking in photovoltaic power generation systems by combining super-twisting sliding mode control and active disturbance rejection method. An incremental guidance method is used to find the point of maximum power. The non-linear extended state observer is applied to estimate the unmodeled dynamics and external disturbance. The ADRC based on a super-twisting sliding mode is designed to bring the state variables to the desired state. In the next step, the stability of NESO and ADRC are theoretically proved. Finally, the simulation results have been compared with the results of the PI controller, classical sliding mode control, and terminal sliding mode control (TSMC) presented in other articles. The results show the effectiveness and superiority of the proposed method. Also, to check the performance of the proposal method in real-time, real-time results have been compared with non-real-time results. The results obtained from the real-time and non-real-time simulations exhibited a minimal difference. This fact indicates the high accuracy of the modeling and simulations performed. Indeed, the mathematical models and non-real-time simulations have been able to accurately mimic the actual behavior of the photovoltaic system under various operating conditions.

Performance study of dual heart assisted control system based on SL-SMC physiological combination controller.

The main challenges of Biventricular Assist Devices (BiVAD) as a treatment modality for patients with Bicardiac heart failure heart failure are the balance of systemic blood flow during changes in physiological activity and the prevention of ventricular suction. In this study, a model of the Biventricular Circulatory System (BCS) was constructed and a physiological combination controller based on Starling-Like controller and Sliding Mode Controller (SMC) was proposed. The effects of the physiological controller on the hemodynamics of the BCS were investigated by simulating two sets of physiological state change experiments: elevated pulmonary artery resistance and resting-exercise, with constant speed (CS) control and combined Starling-like and PI control (SL-PI) as controllers. Simulation and experimental results showed that the Starling-like and Sliding Mode Control (SL-SMC) physiological combination controller was effective in preventing the occurrence of ventricular suction, providing higher cardiac output, maintain balance of systemic blood flow, and have higher response speed and robustness in the face of physiological state changes.

Advanced Necklace for Real-Time PPG Monitoring in Drivers.

Monitoring heart rate (HR) through photoplethysmography (PPG) signals is a challenging task due to the complexities involved, even during routine daily activities. These signals can indeed be heavily contaminated by significant motion artifacts resulting from the subjects' movements, which can lead to inaccurate heart rate estimations. In this paper, our objective is to present an innovative necklace sensor that employs low-computational-cost algorithms for heart rate estimation in individuals performing non-abrupt movements, specifically drivers. Our solution facilitates the acquisition of signals with limited motion artifacts and provides acceptable heart rate estimations at a low computational cost. More specifically, we propose a wearable sensor necklace for assessing a driver's well-being by providing information about the driver's physiological condition and potential stress indicators through HR data. This innovative necklace enables real-time HR monitoring within a sleek and ergonomic design, facilitating seamless and continuous data gathering while driving. Prioritizing user comfort, the necklace's design ensures ease of wear, allowing for extended use without disrupting driving activities. The collected physiological data can be transmitted wirelessly to a mobile application for instant analysis and visualization. To evaluate the sensor's performance, two algorithms for estimating the HR from PPG signals are implemented in a microcontroller: a modified version of the mountaineer's algorithm and a sliding discrete Fourier transform. The goal of these algorithms is to detect meaningful peaks corresponding to each heartbeat by using signal processing techniques to remove noise and motion artifacts. The developed design is validated through experiments conducted in a simulated driving environment in our lab, during which drivers wore the sensor necklace. These experiments demonstrate the reliability of the wearable sensor necklace in capturing dynamic changes in HR levels associated with driving-induced stress. The algorithms integrated into the sensor are optimized for low computational cost and effectively remove motion artifacts that occur when users move their heads.

A joint-threshold Filippov model describing the effect of intermittent androgen-deprivation therapy in controlling prostate cancer.

Intermittent androgen-deprivation therapy (IADT) can be beneficial to delay the occurrence of treatment resistance and cancer relapse compared to the standard continuous therapy. To study the effect of IADT in controlling prostate cancer, we developed a Filippov prostate cancer model with a joint threshold function: therapy is implemented once the total population of androgen-dependent cells (AC-Ds) and androgen-independent cells (AC-Is) is greater than the threshold value ET, and it is suspended once the population is less than ET. As the parameters vary, our model undergoes a series of sliding bifurcations, including boundary node, focus, saddle, saddle-node and tangency bifurcations. We also obtained the coexistence of one, two or three real equilibria and the bistability of two equilibria. Our results demonstrate that the population of AC-Is can be contained at a predetermined level if the initial population of AC-Is is less than this level, and we choose a suitable threshold value.

Band-Edge Mixture Engineered Giant and Switchable Shift Current Generation.

Two-dimensional materials have enormous development prospects in the bulk photovoltaic effect (BPVE). The enhancement and manipulation of the BPVE are some of the key roles of its various applications. Through a simplified Hamiltonian model, this work shows that a substantial band mixture between occupied and unoccupied states could produce a large optical absorption rate with trivial topological features, resulting in a significantly enhanced shift current generation. Furthermore, this mechanism is illustrated in a realistic C3B/C3N bilayer material based on density functional theory calculation and tight-binding model. As each layer of C3B/C3N is centrosymmetric, the in-plane shift current arises from the interfacial interaction. The electron transfer between the layers gives a controllable band mixture, which offers a giant shift current reaching over ∼1500 µA/V2. In addition, we propose that interlayer sliding could reverse the in-plane shift current. Our work suggests a feasible approach for giant and switchable nonlinear optical processes.

Thermostable Nucleoid Protein Cren7 Slides Along DNA and Rapidly Dissociates From DNA While Not Inhibiting the Sliding of Other DNA-binding Protein.

A nucleoid protein Cren7 compacts DNA, contributing to the living of Crenarchaeum in high temperature environment. In this study, we investigated the dynamic behavior of Cren7 on DNA and its functional relation using single-molecule fluorescence microscopy. We found two mobility modes of Cren7, sliding along DNA and pausing on it, and the rapid dissociation kinetics from DNA. The salt dependence analysis suggests a sliding with continuous contact to DNA, rather than hopping/jumping. The mutational analysis demonstrates that Cren7 slides along DNA while Trp (W26) residue interacts with the DNA. Furthermore, Cren7 does not impede the target search by a model transcription factor p53, implying no significant interference to other DNA-binding proteins on DNA. At high concentration of Cren7, the molecules form large clusters on DNA via bridging, which compacts DNA. We discuss how the dynamic behavior of Cren7 on DNA enables DNA-compaction and protein-bypass functions.