Full prescribed performance trajectory tracking control strategy of autonomous underwater vehicle with disturbance observer.

This paper investigates trajectory tracking control of the Autonomous Underwater Vehicle (AUV) with the general uncertainty consisting of model uncertainties and unknown ocean current disturbances. A full prescribed performance control strategy based on disturbance observer is developed, which ensures that the tracking error, the velocity error, and the observation error are all constrained. First, under the case of unmeasurable AUV acceleration, a fixed-time observer is constructed to estimate the general uncertainty, which constrains the observation error within the prescribed accuracy by a prescribed performance observer. Then, based on the performance function and corresponding error transformation, a prescribed performance protocol is designed to realize the trajectory tracking control, so that the observation error, the tracking error, and the velocity error are all constrained within the prescribed accuracy range. Simulation results demonstrate the efficiency of the full prescribed performance control strategy while the AUV tracking control with full state constraints is feasible. Moreover, compared with the other two relevant works, this study improves the observation performance by at least 10 %, both in case of deepwater disturbances and near-surface disturbances.

Provable Unrestricted Adversarial Training without Compromise with Generalizability.

Adversarial training (AT) is widely considered as the most promising strategy to defend against adversarial attacks and has drawn increasing interest from researchers. However, the existing AT methods still suffer from two challenges. First, they are unable to handle unrestricted adversarial examples (UAEs), which are built from scratch, as opposed to restricted adversarial examples (RAEs), which are created by adding perturbations bound by an lp norm to observed examples. Second, the existing AT methods often achieve adversarial robustness at the expense of standard generalizability (i.e., the accuracy on natural examples) because they make a tradeoff between them. To overcome these challenges, we propose a unique viewpoint that understands UAEs as imperceptibly perturbed unobserved examples. Also, we find that the tradeoff results from the separation of the distributions of adversarial examples and natural examples. Based on these ideas, we propose a novel AT approach called Provable Unrestricted Adversarial Training (PUAT), which can provide a target classifier with comprehensive adversarial robustness against both UAE and RAE, and simultaneously improve its standard generalizability. Particularly, PUAT utilizes partially labeled data to achieve effective UAE generation by accurately capturing the natural data distribution through a novel augmented triple-GAN. At the same time, PUAT extends the traditional AT by introducing the supervised loss of the target classifier into the adversarial loss and achieves the alignment between the UAE distribution, the natural data distribution, and the distribution learned by the classifier, with the collaboration of the augmented triple-GAN. Finally, the solid theoretical analysis and extensive experiments conducted on widely-used benchmarks demonstrate the superiority of PUAT.

ZmBSK1 positively regulates BR-induced H2O2 production via NADPH oxidase and functions in oxidative stress tolerance in maize.

Brassinosteroid (BR) has been indicated to induce the production of hydrogen peroxide (H2O2) in plants in response to various environmental stimuli. However, it remains largely unknown how BR induces H2O2 production. In this study, we found that BR treatment significantly raised the kinase activity of maize (Zea mays L.) brassinosteroid-signaling kinase 1 (ZmBSK1) using the immunoprecipitation kinase assay. ZmBSK1 could modulate the gene expressions and activities of nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (EC 1.6.3.1) to modulate BR-induced H2O2 production. BR could enhance the interaction between ZmBSK1 and maize calcium/calmodulin-dependent protein kinase (ZmCCaMK), a previously identified substrate of ZmBSK1. The BR-induced phosphorylation and kinase activity of ZmCCaMK are dependent on ZmBSK1. Moreover, we showed that ZmBSK1 regulated the NADPH oxidase gene expression and activity via directly phosphorylating ZmCCaMK. Genetic analysis suggested that ZmBSK1-ZmCCaMK module strengthened plant tolerance to oxidative stress induced by exogenous application of H2O2 through improving the activities of antioxidant defense enzyme and alleviating the malondialdehyde (MDA) accumulation and electrolyte leakage rate. In conclusion, these findings provide the new insights of ZmBSK1 functioning in BR-induced H2O2 production and the theoretical supports for breeding stress-tolerant crops.

Overexpression of a Zea mays Brassinosteroid-Signaling Kinase Gene ZmBSK1 Confers Salt Stress Tolerance in Maize.

Salinity has become a crucial environmental factor seriously restricting maize (Zea mays L.) growth, development and productivity. However, how plants respond to salt stress is still poorly understood. In this study, we report that a maize brassinosteroid-signaling kinase gene ZmBSK1 plays a significant role in salt stress response. Expression pattern analysis revealed that the transcript level of ZmBSK1 was upregulated by NaCl treatment both in maize leaves, roots, and stems. Phenotypic and physiological analysis showed that overexpression of ZmBSK1 in maize improved salt tolerance by reducing the malondialdehyde (MDA) content, the percentage of electrolyte leakage, O2 - and H2O2 accumulation under salt stress, relying on the increases of antioxidant defense enzyme activities and proline content. qRT-PCR analysis showed that overexpression of ZmBSK1 also positively modulated the expression levels of reactive oxygen species (ROS)-scavenging and proline biosynthesis-related genes under salt stress. Moreover, immunoprecipitation-mass spectrometry (IP-MS) assay and firefly luciferase complementation imaging (LCI) assay showed that ZmBSK1 could associate with heat shock protein ZmHSP8 and 14-3-3-like protein ZmGF14-6, and their gene expression levels could be significantly induced by NaCl treatment in different maize tissues. Our findings unravel the new function of ZmBSK1 in salt stress response, which provides the theoretical bases for the improvement of maize salt resistance.

Fault-tolerant trajectory tracking control for unmanned surface vehicle with actuator faults based on a fast fixed-time system.

In this paper, an observer-based fixed-time tracking control strategy is presented for unmanned surface vehicles (USVs) with model uncertainties, external disturbances, and actuator faults. Firstly, as the theory foundation, a fast fixed-time stable system that has a shorter settling time than the existing systems is proposed. According to this system and the motion characteristics of an USV, a fast fixed-time disturbance observer is developed to obtain the unknown effects caused by lumped uncertainties. By combining the estimated knowledge and a nonsingular fast fixed-time terminal sliding surface, a robust fast fixed-time trajectory tracking controller is designed for the USV. According to Lyapunov stability theory, the fast fixed-time convergence of the proposed controller is proved. Finally, the simulation results demonstrate the effectiveness of the developed control scheme.

An ERP study on the influence of mental abacus calculation on subthreshold arithmetic priming in children.

OBJECTIVE: The objective of this study was to investigate the influence of mental abacus calculation training (MACT) on subliminal cognitive processes. METHODS: Twenty children with intensive MACT (MACT group) and 20 children without MACT (non-MACT group) were selected. The two groups of children were matched in age, sex, handedness and academic grade. The participants were tested with subthreshold arithmetic priming task while their neural activities were recorded with a 32-channel electroencephalogram system. RESULTS: We found that MACT changed the subliminal cognitive mechanism of computational processing, speeding up the computation. MACT affected the computational processing mode. Specifically, in the identification stage, both groups of children adopted the visual space processing mode, while in the computing stage, the MACT group adopted a visual space processing mode, but the non-MACT group adopted a semantic processing mode. Moreover, MACT improved children's executive functions. CONCLUSION: These results yielded insights into the effect of early abacus training on children's cognitive processing, providing a theoretical basis for the development and promotion of abacus training.

Comparison between sustained effects of spray and injection thiamethoxam on apple aphids and non-target insects in apple orchard.

Spray application is considered to be the most common method of insecticide use in apple orchard, while trunk injection has often be used in labor-intensive areas. Here, a comparison of both methods in aphid control efficiency and non-target effects was conducted. We evaluated the effects of thiamethoxam by either spray or injection on apple aphid Aphis citricola, and examined the temporal dynamic of thiamethoxam in leaves by using residue analysis. Results showed that thiamethoxam had a remarkable suppression effect on Aphis citricola, and both application methods had obvious control efficiency with the highest value above 90%. The control effect of spray method on Aphis citricola reached the maximum at 7 days after application, while that of injection method reached the maximum at 14 days after application. Moreover, the control effect of injection after 14 days and that of spray after 7 days were not significant, suggesting the spray method had a higher quick-acting effect than the injection method, and the two methods had a similar persistence effect. The population dynamics of non-target insects (ladybugs, parasitoid wasps and predatory bugs) showed basically the same as that of blank controlled. The control effect evaluation of thiamethoxam on Aphis citricola suggest that injection treatment was more effective in protecting natural enemies than spray treatment, and thiamethoxam didn't interfere with natural enemies to control Aphis citricola with both two application methods.

Distributed tracking control for multiple Euler-Lagrange systems with communication delays and input saturation.

This study mainly investigates the problem of distributed tracking control for time-varying delay existing multiple Euler-Lagrange systems considering full-state constraints and input saturation under the directed graph. Specifically, the system under consideration consists of system uncertainties and external disturbances. In the control law design, a distributed observer is first designed that the followers can obtain the leader's time-varying information. Then the barrier Lyapunov function technique is used to make sure the system errors can converge to a certain range while the anti-windup method is utilized to overcome the influence of control input saturation. Further, in order to prevent chattering, an adaptive law is given. Numerical simulations are given to verify the proposed algorithms.

Synchronization control for bilateral teleoperation system with position error constraints: A fixed-time approach.

In this work, a novel exponential-type Barrier Lyapunov Function (EBLF) is proposed to address the synchronization control issue for a class of bilateral teleoperation systems with system uncertainties, external disturbances, and constraint requirement. The most prominent feature of the EBLF is that it can be used in a unified scheme, which deals with full state constrained and output constrained problems. Moreover, a novel control strategy is incorporated with the EBLF to achieve fixed-time convergence into a small set while the synchronization position tracking errors are guaranteed to never exceed the predefined constraints through the "adding a power integrator" technique, and the estimated settling time is shown to be independent of initial values. Simulation results demonstrate the effectiveness of the proposed control scheme.

Observer-based prescribed performance attitude control for flexible spacecraft with actuator saturation.

This paper investigates the prescribed performance attitude control problem for flexible spacecraft subject to external disturbances and actuator constraints. By using a new performance function and an error transformation, the attitude control system is transformed into an error system which will be kept bounded to ensure expected dynamic and steady-state responses. Compared with the commonly used performance function, the modified one has an explicit prespecified terminal time which determines the maximum convergence time of the attitude control system. A modal observer and a disturbance observer are designed to deal with the flexible vibration and disturbances, respectively. Furthermore, when considering actuator saturation, an improved control strategy is developed with an auxiliary system utilized to compensate the saturation. The stability of the closed-loop system is analyzed by Lyapunov theory. Simulation results show the effectiveness and performance of the proposed methods.

Distributed coordinated attitude tracking control for spacecraft formation with communication delays.

This paper investigates the distributed coordinated attitude tracking control problem for spacecraft formation with time-varying communication delays under the condition that the dynamic leader spacecraft is a neighbor of only a subset of follower spacecrafts. We consider two cases for the leader spacecraft: i) the attitude derivative is constant, and ii) the attitude derivative is time-varying. In the first case, a distributed estimator is proposed for each follower spacecraft by using its neighbors' information with communication delays. In the second case, to express the dynamic leader's attitude, an improved distributed observer is developed to estimate the leader's information. Based on the estimated values, adaptive coordinated attitude tracking control laws are designed to compensate for parametric uncertainties and unknown disturbances. By employing the Lyapunov-Krasovskii functional approach, the attitude tracking errors and estimation errors are proven to converge to zero asymptotically. Numerical simulations are presented to illustrate the effectiveness of theoretical results.

An event-related potential investigation of spatial attention orientation in children trained with mental abacus calculation.

The objective of this study was to investigate the effects of long-term mental abacus calculation training (MACT) on children's spatial attention orientation. Fifteen children with intensive MACT (MACT group) and 15 children without MACT (non-MACT group) were selected. The two groups of children were matched in age, sex, handedness, and academic grade. The participants were tested with a Posner spatial cueing task while their neural activities were recorded with a 32-channel electroencephalogram system. The participants' behavior scores (reaction time and accuracy) as well as early components of event-related potential (ERP) during the tests were statistically analyzed. The behavioral scores showed no significant difference between the two groups of children, although the MACT group tended to have a shorter reaction time. The early ERP components showed that under valid cueing condition, the MACT group had significantly higher P1 amplitude [F(1, 28)=5.06, P<0.05, effective size=0.72] and lower N1 amplitude [F(1, 28)=6.05, P<0.05, effective size=0.82] in the occipital region compared with the non-MACT group. In the centrofrontal brain region, the MACT group had lower N1 amplitude [F(1, 28)=4.89, P<0.05, effect size=0.70] and longer N1 latency [F(1, 28)=6.26, P<0.05, effect size=0.80] than the non-MACT group. In particular, the MACT group also showed a higher centrofrontal P2 amplitude in the right hemisphere [F(1, 28)=4.82, P<0.05, effect size 0.81] compared with the left hemisphere and the middle location. MACT enhances the children's spatial attention orientation, which can be detected in the early components of ERP.

[Chemical Constituents from Xanthium mongolicum].

Objective: To investigate the chemical constituents from Xanthium mongolicum. Methods: The constituents were isolated and purified by silicagel,Sephadex LH-20 column chromatography. Their structures were identified on the basis of spectral data and physiochemical characteristics. Results: Ten compounds were isolated and identified as hexadecanoic acid( 1), methyl 3, 4-dihydroxybenzoate ( 2), protocatechuic aldehyde( 3), caffeic acid methyl ester( 4), vanillic acid( 5), 4-hydroxybenzoic acid( 6), caffeic acid ethyl ester( 7), chlorogenic acid( 8), caffeic acid( 9), 3, 4-di-O-caffeoylquinic acid( 10). Conclusion: Compounds 1 ~ 5,7 and 10 are isolated from this plant for the first time.