This paper studies the prescribed performance tracking problem for nonlinear leader-following multiagent systems by developing a data-driven cooperative adaptive sliding mode controller. First, the ...synchronization measurement error is transformed by combining prescribed performance function with sliding mode surface. Then, the agent’s dynamics are described as a linearization model by the pseudo-partial derivative, and a data-based cooperative adaptive sliding mode control approach is designed to achieve the synchronization of all agents. The synchronization measurement error can converge to the predefined zone. Moreover, the proposed controller only depends on the input/output data of the agents. The effectiveness and advantages of the proposed controller are verified by numerical simulations.
Objective
To investigate the feasibility of T
2
WI-based radiomics nomogram analysis to non-invasively predict normal-sized pelvic lymph node (LN) metastasis (LNM) in cervical cancer patients.
...Methods
Preoperative images of 219 normal-sized pathologically confirmed LNs from 132 cervical cancer patients admitted to our hospital between January 2013 and March 2020 were retrospectively reviewed. Regions of interests (ROIs) were separately delineated on whole LNs and tumors. The maximum-relevance and minimum-redundancy (mRMR) and least absolute shrinkage and selection operator (LASSO) methods were used for the construction of radiomics signature. Logistic regression modeling was employed to build models based on clinical features on LN T
2
WI (model 1), model 1 combined with LN radiomics features (model 2), and model 2 combined with tumor score (model 3). Diagnostic performance was assessed and compared.
Results
Both model 2 and model 3 showed higher diagnostic accuracy (training: model 2 0.75, model 3 0.78, model 1 0.72; validation: model 2 0.77, model 3 0.69, model 1 0.66) and AUC (training: model 2 0.77, model 3 0.82, model 1 0.74; validation: model 2 0.75, model 3 0.74, model 1 0.70) than clinical model 1. Diagnostic performance of model 3 was improved compared with model 2 in primary cohort, but reduced in validation cohort. However, the differences did not show obvious statistical difference (
p
= 0.05 and
p
= 0.15).
Conclusions
T
2
WI-based radiomics nomogram incorporating the LN radiomics signature with the clinical morphological LN features is promising for predicting the normal-sized pelvic LNM in cervical cancer patients. The original tumor radiomics analysis did not significantly improve the differential diagnosis of LNM.
Key Points
•
The combination of LN radiomics signature with LN clinical morphological features on T
2
WI could discriminate LNM relatively well.
•
The tumor radiomics analysis did not significantly improve the differential diagnosis of LNM.
Purpose
To explore the value of histogram analysis of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) quantitative parameters and apparent diffusion coefficient (ADC) values in ...predicting the neoadjuvant chemotherapy (NACT) response for cervical cancers.
Methods
Sixty-three patients with pathologically proved stage IB2–IIA2 cervical cancer from March 2013 to January 2017 were retrospectively analyzed. They were divided into two groups on the basis of therapeutic response: the significant response (SR) group, which contains complete response patients and partial response patients, and nonsignificant response (non-SR) group, which contains progressive diseases and stable diseases. Clinical characteristics, DCE-MRI parameters (
K
trans
,
K
ep
,
V
e
), and ADC values before NACT were analyzed and compared between the two groups.
Results
SR group and non-SR group were documented in 35 and 28 patients. The mean
K
trans
value, 90th percentile
K
trans
value, maximal
K
trans
value, and 90th percentile ADC value of tumors in SR were significantly higher than those in non-SR group (
P
= 0.012,
P
= 0.022,
P
= 0.005,
P
= 0.033, respectively), and the mean
V
e
value and 10th percentile
V
e
value of tumors were significantly lower in SR group (
P
= 0.041,
P
= 0.033, respectively).
K
ep
values did not significantly differ between SR and non-SR. The 90th percentile
K
trans
value combined with the 90th percentile ADC value had the highest area under the curve at 0.740 (
P
= 0.003) to predict NACT effectiveness.
Conclusion
Histogram analysis of DCE-MRI multi-parameters combined with ADC values may serve as sensitive indicators for predicting NACT effectiveness in cervical cancers.
The event-triggered tracking control for large-scale high order nonlinear uncertain systems, whose state information is immeasurable, is investigated via an observer-based approach. Firstly, a neural ...observer is designed to estimate the unmeasurable state information of high order nonlinear systems. Then, a relative threshold event-triggered strategy is proposed to reduce the communication burden between the actuator and the controller. On this basis, a novel observer-based adaptive event-triggered controller is designed to achieve the output tracking of the reference trajectory via the backstepping technique. Theoretical proof shows that the proposed controller guarantees the stability of the closed-loop systems and the Zeno-behavior can be excluded. Finally, some simulation examples are performed to illustrate the effectiveness of the proposed method.
To maintain a safe distance between the autonomous vehicle and the leader, ensure that the vehicle runs at its expected speed as far as possible, and achieve various control requirements such as ...speed, distance and collision avoidance, a model-free prescribed performance adaptive cruise control (ACC) algorithm based on funnel control is proposed. The contributions of this paper are that the designed ACC algorithm only requires the speed and position information and can constrain their tracking errors within a predetermined range. When the follower is far away from the leader, the speed-prescribed performance controller adjusts the follower vehicle’s speed to the reference velocity. When the follower vehicle approaches the leader vehicle, a distance-prescribed performance controller is designed to adjust the distance between the follower and the leader. On this basis, the prescribed performance function can expand the switching interval, thereby improving the robustness of the speed and distance control switching process. The effectiveness of the designed algorithm is demonstrated in three scenarios, such as approaching and following, emergency braking, and frequent starting and stopping. The results show that during the speed control stage, the designed algorithm allows the vehicle’s operating speed to vary within a predetermined spatial range; in the distance control stage, the designed algorithm strictly limits the distance error within the preset range. The speed and distance of the vehicle change smoothly, and there is no overshoot during the initial state adjustment, emergency braking, and frequent start and stop stages, demonstrating a good control effect.
This paper studies the model-free robust adaptive cruise control problem of a vehicle with unknown nonlinear dynamics and disturbances. First, under backstepping control framework, the position ...tracking errors with different spacing strategies are used to design a virtual control law, which provides a velocity reference. Then, a novel data-driven sliding surface whose parameters are updated by designing estimation algorithm is developed to handle the unknown uncertainties and disturbances. Finally, the model-free robust backstepping adaptive cruise control (MFRB-ACC) method including PI control, model-free control, and robust control is designed. The novelty of the proposed control technique lies in its strong robustness, which is not based on the precise vehicle model. The designed data-driven sliding surface releases the necessity for the accurate mathematical model of the vehicle and guarantees the inherent robustness of the controller, in particular to uncertainties, modelling error, or external disturbance. Moreover, the designed controller contains three terms such that it has an effective decoupling ability and strong robustness. The effectiveness and superiority of the designed MFRB-ACC method are validated on MATLAB, and the simulation results show that compared to the PID algorithm, the designed MFRB-ACC algorithm can track its preceding vehicle with lower tracking error under different spacing strategies, different operating conditions, and low sampling frequencies. Especially at a sampling frequency of 0.1 s, the error under the PID-ACC increases from 0.2 m at a sampling frequency of 0.01 s to 2 m, and the error under MFRB-ACC has little change compared to the error at a sampling frequency of 0.01 s.
This paper investigates the actuator fault detection and tolerant control problem for vehicle platoons with partial loss of effectiveness and bias faults. Considering the inherent coupling between ...the control input and the nonlinear term in the actuator, a decoupled observer based fault detection algorithm with time-varying threshold is developed to decide whether the actuator fault occurs in the platoon. Then, by employing radial basis function neural networks (RBF NNs) and backstepping control method, an adaptive robust fault-tolerant control (FTC) scheme is proposed, which is proved to be capable of achieving the safety, stability and tracking performance of vehicle platoons in the presence of actuator fault. Simulation studies illustrate the effectiveness of the proposed method.
In this paper, by incorporating the neural network into an adaptive dynamic surface control (DSC) framework, a neural adaptive DSC algorithm is developed for a class of uncertain nonlinear system to ...ensure the asymptotic output tracking. Neural network is used to approximate the unknown nonlinear term in the system such that the requirements for known nonlinear term in control laws design procedure are released. In order to eliminate the boundary layer effects, which are caused by the linear filters at each step in the DSC procedure, the nonlinear filters with the compensation term are designed skillfully. The proposed neural adaptive DSC algorithm not only avoids the inherent problem of “explosion of complexity” in the backstepping procedure, but also has its own advantages: (1) releasing the requirements for known nonlinear term in control laws design procedure; (2) holding the asymptotic output tracking performance. Some simulations are shown to demonstrate the effectiveness and advantages of the proposed controller.
This paper studies the adaptive control problem for unknown time-varying high-order nonlinear multiagent systems (MASs) with directed topology. A novel low-complexity distributed adaptive ...backstepping controller is developed to achieve the asymptotic synchronization. The designed controller regards the unknown system non-linearities as “disturbance-like” terms, which are guaranteed to be bounded by using the barrier functions, such that detail models of system nonlinearities are released. Then, the “disturbance-like” terms are compensated adaptively by designing the novel compensator at each step, such that the synchronization error is eliminated to zero eventually for each agent. In addition, unlike the existing backstepping-like synchronization approaches for high-order nonlinear MASs, the “explosion of complexity” issue is avoided without extra low-pass filters. Some simulations are shown to demonstrate the effectiveness and advantages of the developed method.
Silicon carbide (SiC) has a variety of applications because of its favorable chemical stability and outstanding physical characteristics, such as high hardness and high rigidity. In this study, a ...femtosecond laser with a spiral scanning radial offset of 5 μm and a spot radius of 6 μm is utilized to process micropillars on a SiC plate. The influence of pulsed laser beam energies and laser translation velocities on the micropillar profiles, dimensions, surface roughness
a, and material removal capability (MRC) of micropillars was investigated. The processing results indicate that the micropillar has the best perpendicularity, with a micropillar bottom angle of 75.59° under a pulsed beam energy of 50 μJ in the range of 10-70 μJ, with a pulsed repetition rate of 600 kHz and a translation velocity of 0.1 m/s. As the laser translation velocity increases between 0.2 m/s and 1.0 m/s under a fixed pulsed beam energy of 50 μJ and a constant pulsed repetition rate of 600 kHz, the micropillar height decreases from 119.88 μm to 81.79 μm, with the MRC value increasing from 1.998 μm
/μJ to 6.816 μm
/μJ, while the micropillar bottom angle increases from 68.87° to 75.59°, and the
a value diminishes from 0.836 μm to 0.341 μm. It is suggested that a combination of a higher pulsed laser beam energy with a faster laser translation speed is recommended to achieve micropillars with the same height, as well as an improved processing efficiency and surface finish.
