State Saturation Research Articles

Impulsive consensus of nonlinear multi-agent systems with input and state saturation constraints

This work focus on the study of consensus problems of nonlinear second-order multi-agent system (MAS). By fully taking performance difference constrained by the locations of communication channel into account, and in view that impulsive control scheme can reduce control costs in some degree, input-saturation and state-saturation are integrated into the design of impulsive consensus control protocol, respectively. By doing that, some sufficient conditions that guarantee the consensus of nonlinear MAS are derived by using Lyapunov stability theory. Finally, by giving two examples, some simulation examples are presented to verify the theoretical results.

Disentangling the Impact of Point Defect Density and Carrier Localization-Enhanced Auger Recombination on Efficiency Droop in (In,Ga)N/GaN Quantum Wells.

The internal quantum efficiency of (In,Ga)N/GaN quantum wells can surpass 90% for blue-emitting structures at moderate drive current densities but decreases significantly for longer emission wavelengths and at higher excitation rates. This latter effect is known as efficiency "droop" and limits the brightness of light-emitting diodes (LEDs) based on such quantum wells. Several mechanisms have been proposed to explain efficiency droop including Auger recombination, both intrinsic and defect-assisted, carrier escape, and the saturation of localized states. However, it remains unclear which of these mechanisms is most important because it has proven difficult to reconcile theoretical calculations of droop with measurements. Here, we first present experimental photoluminescence measurements extending over three orders of magnitude of excitation for three samples grown at different temperatures that indicate that droop behavior is not dependent on the point defect density in the quantum wells studied. Second, we use an atomistic tight-binding electronic structure model to calculate localization-enhanced radiative and Auger rates and show that both the corresponding carrier density-dependent internal quantum efficiency and the carrier density decay dynamics are in excellent agreement with our experimental measurements. Moreover, we show that point defect density, Auger recombination, and the effect of the polarization field on recombination rates only limit the peak internal quantum efficiency to about 70% in the resonantly excited green-emitting quantum wells studied. This suggests that factors external to the quantum wells, such as carrier injection efficiency and homogeneity, contribute appreciably to the significantly lower peak external quantum efficiency of green LEDs.

The influence of loading speed on the bending strength of beech (Fagus sp.) and birch (Betula sp.) wood

The influence of loading speed on the bending strength of beech (Fagus sp.) and birch (Betula sp.) wood The subject of this paper was to investigate the effect of loading speeds from 20 mmˑmin-1 to 200 mmˑmin-1 on the flexural strength and deformation of beech (Fagus sp.) and birch (Betula sp.) wood with moisture content close to the absolutely dry state and fibre saturation point. A GOM Aramis measuring system, operating with Digital Image Correlation (DIC) technology, was used in the study to record the displacement and deformation of the elements in real time. The results obtained for flexural strength, flexural modulus and the amount of deformation observed showed a relationship between material properties and loading rate. At higher moisture content, the bending strength and modulus of elasticity decreased with increasing deflexion. The highest bending strength and modulus of elasticity were achieved by the tested wood species at a loading rate of 200 mmˑmin-1. Beech wood, compared to birch wood, showed higher bending strength and modulus of elasticity. Images obtained by means of DIC revealed, at moisture contents close to the dry state, a symmetrical distribution of compressive and tensile stresses relative to the neutral axis of the sample cross-section. At higher moisture contents, there was a significant asymmetry between the compressive and tensile stresses and an apparent shift of the neutral axis towards the tensile surface.

Optimal guaranteed cost control of discrete-time uncertain systems subjected to state saturation nonlinearity

This paper investigates the optimal guaranteed cost (GC) control problem for uncertain discrete-time (DT) systems with state saturation nonlinearities via static-state feedback. The parameter uncertainties in the system state and input matrix are considered to be norm bounded. Utilizing Lyapunov theory and sector-based characterization of saturation nonlinearities, a novel criterion for the existence of GC controllers is proposed. The criterion is expressed in the framework of linear matrix inequalities (LMIs) and is thus computationally tractable. The proposed GC controllers make the closed-loop (CL) system asymptotically stable and ensure an adequate level of performance for all admissible parameter uncertainties. To design an optimum GC controller, a convex optimization problem with LMI constraints is formulated. The effectiveness of the proposed approach is illustrated by examples.

Set membership filtering for discrete saturated time‐varying networked systems with incomplete measurements under round‐robin protocol

AbstractIn this paper, the set membership filtering problem is investigated for a class of discrete networked systems with time delay and state saturation under the round‐robin (RR) protocol, where the system noise is unknown but bounded. In order to reduce the communication burden, the RR protocol is used to schedule the measurement information of the system. In addition, the incompleteness of the measurement information is considered. A set membership filter is established based on incomplete measurements. The objective is to give a criterion that the filtering error is confined to the ellipsoidal set by using the recursive linear matrix inequality (RLMI) method. Moreover, a convex optimization method is proposed to minimize the obtained ellipsoids. Finally, a numerical simulation illustrates that the designed set membership filtering scheme is effective.

New Criterion for the Stability of Discrete-Time Systems with State Saturation and Time-Varying Delay

New Criterion for the Stability of Discrete-Time Systems with State Saturation and Time-Varying Delay

Event-Triggered Fault Estimation and Fault Tolerance for Cyber-Physical Systems with False Data Injection Attacks

This paper investigates an event-triggered framework for addressing fault estimation and fault tolerance issues in discrete-time cyber-physical systems (CPSs) with partial state saturations and random false data injection attacks (FDIAs). A stochastic variable is introduced to characterize the random FDIAs and to establish the corresponding model. A reduced-order fault estimator and an event condition are co-derived to reconstruct system states and actuator faults. The proposed event-triggered transmission scheme helps reduce network utilization in the sensor-to-estimator channel. A sufficient condition for the proposed event-triggered estimator is derived, which minimizes state and fault estimation errors even when the controlled plants are subject to exogenous disturbances, fault signals, and random attacks. Furthermore, a fault-tolerant compensation controller is proposed using the estimated states and faults, ensuring that the considered systems achieve mean-squared stability. Finally, a DC motor platform is developed to further demonstrate the effectiveness of the designed estimator-based fault-tolerant controller.

Maximum Correntropy Kalman Filtering for Non-Gaussian Systems With State Saturations and Stochastic Nonlinearities

Maximum Correntropy Kalman Filtering for Non-Gaussian Systems With State Saturations and Stochastic Nonlinearities

Consensus tracking control for time-varying delayed linear multi-agent systems under relative state saturation constraints

The consensus control with the leader of delayed linear multi-agent systems under the relative state saturations is investigated in this article. Using an incidence matrix, the consensus problem of delayed multi-agent systems (time-varying input delays) with relative state saturation is converted into the stability problem of edge dynamics on the closed sets. Then, a new linear control protocol is designed using a saturation function that guarantees stability for all agents under relative state saturation constraints. With the appropriate Lyapunov–Krasovskii functional definition, sufficient conditions are created for the consensus of the agents. Meanwhile, the relative state saturations do not happen. Also, the agents track the leader’s path well, while bounded delays can be time-varying and arbitrarily fast. This consensus and stability are achieved by maintaining graph connectivity. Finally, the correctness of the above content is confirmed by simulating a practical example.

Asynchronous sliding mode control of semi-Markovian jump systems with state saturation

This paper deals with the sliding mode control problem for semi-Markovian jump systems with state saturation, in which the controller may not be synchronized with the considered systems. A mode-detector is introduced to estimate the unavailable system mode, based on which an asynchronous sliding mode controller is designed. Then, both the μ-exponential mean-square stability and the reachability of sliding surface are analyzed. Furthermore, a solving algorithm is given to acquire the feasible controller gains. Finally, the proposed asynchronous sliding mode control approach under state-saturation is illustrated via simulation results.

Relationship between Obstructive Sleep Apnea Hypopnea Syndrome Complicated with Various Types of Hypertension and Plasma Homocysteine Level

To investigate the relationship between obstructive sleep apnea hypopnea syndrome complicated with various traditional Chinese medicine syndromes of hypertension and plasma homocysteine level, patients were divided into liver-fire excess syndrome, yin deficiency and yang excess syndrome, phlegm-blood stasis syndrome, yin deficiency and yang deficiency syndrome based on the traditional Chinese medicine syndrome type standard of hypertension complicated obstructive sleep apnea hypopnea syndrome. General data, body mass index values, apnea and hypopnea index, oxyhemoglobin saturation, Epworth sleepiness scale scores and homocysteine of patients were extracted and analyzed. The results revealed that the number of males was greater than that of females with a proportion of 1.5:1. The number of patients with body mass index ≥24.00 kg/m2 was obviously greater than that of patients with body mass index <24.00 kg/m2. The proportion of patients with body mass index >28.00 kg/m2 reached 59.18 %. In terms of the comparison of traditional Chinese medicine syndrome types, the proportion of patients suffering from phlegm-blood stasis syndrome was the highest, reaching 27.89 % and the proportion of patients suffering from yin deficiency and yang deficiency syndrome is the lowest, amounting to 22.45 %. In homocysteine examination, the homocysteine of syndrome was increased in order of yin deficiency and yang excess, phlegm-blood stasis, yin deficiency and yang deficiency and liver-fire excess. The results revealed that the syndrome type of phlegm-blood stasis was significant among patients with obstructive sleep apnea hypopnea syndrome in the distribution of traditional Chinese medicine syndrome types. This syndrome type showed significant statistical meaning in age, neck circumference, apnea and hypopnea index, average oxyhemoglobin saturation, triglyceride and overall difference in blood glucose fasting state. The severity of obstructive sleep apnea hypopnea syndrome was positively correlated with homocysteine and apnea, and hypopnea index was also positively correlated with homocysteine and was negatively correlated with lowest oxygen saturation. Lowest oxygen saturation was negatively correlated with homocysteine.

Pseudo-gap in RuGa3: A microscopic point of view

We report a detailed study of the nature of the RuGa3in-gap states by means of precision microscopic methods: nuclear quadrupole resonance (NQR), nuclear magnetic resonance (NMR), and pump-probe spectroscopy. We observe a pronounced splitting of 69Ga nuclear spin-lattice relaxation curves below ∼40 K and between 70 and 145 K, although the corresponding NQR lines remain narrow over the entire temperature range under study. The slow relaxing component behaves like a typical phonon-induced relaxation way, while the fast relaxing one demonstrates signatures of paramagnetic (below ∼40 K) and activation (between 70 and 145 K) mechanisms. Moreover, additional Ga’ and Ga’’ positions with anomalously low electric field gradient were revealed for the first time for IrIn3-type structure gallides, which stay almost unchanged, at least up to 77 K. The observed microscopic features are accompanied with in-gap states saturation or depleting, which is seen as the resistivity mechanism crossover at ∼180 K and electron localization below 145 K evidenced by pump-probe spectroscopy. Based on our experimental results, we associate this pseudo-gap like behavior with inhomogeneously distributed electronic density defects, which manifest at both micro- (nuclear spin and phonon dynamics) and macroscale (bulk transport properties such as resistivity).

Uncertain Disturbance Attenuation and Rejection for Interval Type-2 Fuzzy Systems via Disturbance Observer

This study is concerned with the composite anti-disturbance issue for nonlinear systems subject to state saturation and parameter uncertainties, including the unknown harmonic disturbance. First, an interval type-2 (IT2) Takagi–Sugeno fuzzy model is proposed herein to describe the nonlinear system with state saturation and parametric uncertainties. Next, a novel disturbance observer framework is designed to eliminate the unknown harmonic disturbance. By introducing the new framework, the expression of the unknown harmonic disturbance is transformed into a new expression having only an uncertain parameter, which is then estimated. The corresponding composite anti-disturbance control scheme is then put forward and the sufficient conditions guaranteeing the stochastically stable of the composite system are established. Finally, the simulations are conducted to confirm the availability of the this control scheme.

Recursive Minimum-Variance Filter Design for State-Saturated Complex Networks With Uncertain Coupling Strengths Subject to Deception Attacks.

In this article, the recursive filtering problem is investigated for state-saturated complex networks (CNs) subject to uncertain coupling strengths (UCSs) and deception attacks. The measurement signals transmitted via the communication network may suffer from deception attacks, which are governed by Bernoulli-distributed random variables. The purpose of the problem under consideration is to design a minimum-variance filter for CNs with deception attacks, state saturations, and UCSs such that upper bounds on the resulting error covariances are guaranteed. Then, the expected filter gains are acquired via minimizing the traces of such upper bounds, and sufficient conditions are established to ensure the exponential mean-square boundedness of the filtering errors. Finally, two simulation examples (including a practical application) are exploited to validate the effectiveness of our designed approach.

Distributed Edge Event-Triggered Control of Nonlinear Fuzzy Multiagent Systems With Saturation Constraint Hybrid Impulsive Protocols

In this article, we devote to solve the consensus problem for nonlinear multiagent system under energy consumption constraint. A novel control protocol which combines impulse control with event-triggered mechanism is proposed. By setting the event decision time at pulse time, it can not only reduce triggered times but also avoid the occurrence of “Zeno behavior.” In order to reduce the conservatism of control protocol, input saturation constraint and state saturation constraint are both discussed, for the limited receiving channel of the agent and limited sampling range of the sampler, respectively. Further, the dynamic model of multiagent systems with fuzzy information is proposed for the uncertain factors in actual environment. Finally, for the sake of proving the effectiveness about the control protocols, some simulation examples are presented.

Gas Fluxes and Steady State Saturation Anomalies at Very High Wind Speeds

AbstractGas exchange at high wind speeds is not well understood—few studies have been conducted at wind speeds above 20 ms−1 and significant disagreement exists between gas exchange models at high wind speeds. In this study, noble gases (He, Ne, Ar, Kr, and Xe) were measured in 35 experiments in the SUSTAIN wind‐wave tank where the wind speeds ranged from 20 to 50 m s−1 and mechanical waves were generated as monochromatic or with a short‐crested JONSWAP frequency spectrum. Bubble size spectra were determined using shadowgraph imagery and wave statistics were measured using a wave wire array. The steady state saturation anomalies and gas fluxes initially increased as wind speeds increased but then leveled off, similar to prior studies of heat and momentum flux coefficients. Noble gas fluxes and steady state saturation anomalies are correlated most strongly with bubble volumes for the less soluble noble gases and with wind speed and wave Reynolds number for the more soluble noble gases. In the JONSWAP experiments, significant wave height was the most important predictor for gas steady state saturation anomalies with correlation coefficients of greater than 0.92 for He, Ne, and Ar (P &lt; 0.05). Furthermore, invasion fluxes were larger than evasion fluxes when other conditions were similar. Taken together, these lab‐based experiments suggest more attention should be paid to parameterizations based on wave characteristics and bubbles and that current wind‐speed based gas exchange parameterizations should not be applied to conditions with very high wind speeds.

Intersystem crossing rates of violet-, green- and red-emitting DNA stabilized silver luminescent clusters

The dark states of DNA stabilized silver clusters are extensively used for upconversion fluorescence enhancement. This work probed the triplet state saturation of the violet-, green- and red-emitting AgN-DNA complexes through intersystem crossing rate constant DFT calculations. Our computations showed that DNA significantly affects the electronic structure of Ag3+1 and Ag4+2 clusters. It dramatically increases the ISC constants from value ca. ∼104 s−1 for free clusters up to ca. ∼108 s−1 for clusters bound to nucleobases. The results indicate that silver clusters in complex with DNA can actively transition to the triplet state upon excitation, ISC process can compete with fluorescence.

Microbial driving mechanism for simultaneous removal of nitrogen and phosphorus in a pure anammox reactor under ferrous ion exposure

The mechanisms of Fe2+ on nitrogen and phosphorus removal and functional bacterial competition in anammox systems was investigated. Under 0.12 mM Fe2+, the performance of nitrogen and phosphorus removal increased by 10.08 % and 151.91 %, respectively, compared with the control stage. Phosphorus removal was achieved through extracellular polymeric substance (EPS) induced biomineralization to form Fe-P minerals, and functional group COC in EPS played a critical role. T-EPSs was the major nucleation site due to it maintaining the supersaturated state (saturation index > 0) of Fe-P minerals for a long time. Population succession showed that Fe2+ weakened the competition between heterotrophic denitrifier (Denitrasoma) and anammox microbe (Candidatus Brocadia) for space and substrates, which was favorable for the enrichment of anammox biomass. Moreover, the variation in gene abundance (such as Hao, Cyt c, and Nir) indicated that Fe2+ improved electron behaviors (generation, transport, and consumption) during the nitrogen metabolism of anammox systems.

Event-triggered control of positive switched systems with randomly occurring state saturation

This paper is concerned with the event-triggered control of positive switched systems with randomly occurring state saturation. First, a vector-based event-triggering condition is established. Thus, interval and polytope approaches are used to deal with the positivity and stability of the systems and the saturation, respectively. An event-triggered controller and the corresponding domain of attraction are designed by decomposing gain matrix into the sum of non-negative and non-positive components. The proposed design approach is developed for the systems with input saturation. Finally, two examples are given to illustrate the effectiveness of the proposed design.

H ∞ state-feedback control for saturated 2-D Roesser systems: the event-triggered case

This work discusses the state-feedback control issue for a class of state saturated two-dimensional (2-D) Roesser systems under the event-triggered mechanism. Here, the state saturation is considered to cater the practical situation. First, an event-triggered strategy is exploited to make use of resources rationally in the communication network with finite capacity. Based on the Lyapunov method, the sufficient criterion is presented to achieve the desired performance of the corresponding closed-loop saturated 2-D system and the existence of event-triggered state-feedback (ET-SF) controller is ensured. Particularly, a positive scalar is introduced to cope with the state saturation term. With the aid of sufficient criterion and cone complementary linearisation (CCL) algorithm, the design problem of ET-SF controller can further be transformed into seeking the feasible solution to linear matrix inequalities. Eventually, a simulation example is implemented to reveal the usefulness of the presented control scheme.