Sedimentary studies at continental boundary show that the global sea level has hundreds of meters of change since the late Paleozoic. Long-term global sea-level change is closely related to the ...mantle convection. The deflection of the ocean basins caused by dynamic topography can change the container volume of the basin, thus inducing global sea-level change. However, the influence of dynamic topography on the global sea-level change during supercontinent cycles is not well understood. Based on dynamic topography from mantle convection models and past seafloor age from plate reconstructions, I studied the influence of dynamic topography on global sea-level change since 410 Ma. Model results show that the present-day dynamic topography contributes to ∼120 m of positive global sea level. Dynamic topography raises the sea level during the dispersal, assembly, and transition phases, and drops the sea level during period of supercontinent stability. Global sea-level change caused by the seafloor age distribution is the main factor that controls the long-term global sea-level change. Different methods to define the ocean basin have only a small influence on global sea level change due to the combined effects of seafloor age and dynamic topography. The combined effects of dynamic topography and seafloor age uplift the sea-level during Pangea dispersal and assembly phases, and decrease sea-level during stability and the transition phases.
•Present-day dynamic topography contributes to ∼120 m of positive global sea level.•Different definitions of ocean basin influence the sea-level from dynamic topography.•Effects of seafloor age and dynamic topography on sea level correlate with supercontinent Pangean cycle.•Sea-level rise during Pangea dispersal and assembly phases, and drop during other phases.
This paper is concerned with the input-to-state stabilizing control problem for cyber-physical systems (CPSs) with multiple transmission channels under denial-of-service (DoS) attacks. Under the data ...update policy with bounded update interval, a new control scheme that discards the outdated information is proposed, and the stability analysis of CPSs under DoS attacks is transformed into analyzing the stability of the system under a switched controller with the help of a class of linear matrix inequalities (LMIs). Then, inspired by the techniques for switched systems, sufficient conditions on the duration and frequency of the DoS attacks, under which the stability of the closed-loop systems is still guaranteed, are proposed. Compared with the existing method for the single-channel case, the considered multiple-channel case is more challenging, and the proposed LMI-based method is more flexible.
This paper investigates the secure state estimation problem of multiagent systems with misbehaving agents. Compared with the existing works which only consider malicious behaviors generated ...elaborately, a class of faulty behaviors generated randomly is also taken into account. By assuming that faulty behaviors cannot be altered by the adversaries, the notion of orthogonal complement matrix is introduced to characterize the state observability of the multiagent systems with both faulty and malicious agents. It is shown that more misbehaving agents can be tolerated by distinguishing faulty agents from malicious ones. Then, for single agent, two algorithms are provided to estimate the state based on its own value and the measurements obtained from its neighbors. Finally, two simulations are provided to illustrate the correctness and effectiveness of the proposed conditions and methods.
This article investigates the stealthy false data injection attack design problem for a class of cyber physical systems equipped with state estimators and attack detectors. The objective is to worsen ...the estimation performance without triggering any alarm. First, a necessary and sufficient condition for the existence of perfect attacks, which alter the state estimate without affecting residual signals, is provided. It is shown that the estimation error can be arbitrarily large under the well-designed perfect attacks. Second, if the perfect attacks do not exist, the existence of nonperfect attacks, which worsen the estimation performance with a degree influence on residual signals, is analyzed. It is shown that the desired nonperfect attack sequence can be designed by analyzing the maximum eigenvalue and the corresponding eigenvector of an auxiliary matrix. Compared with the existing methods, in this article, attacks are designed without knowledge of estimators and can be injected from any time point. Finally, a numerical simulation is provided to illustrate the effectiveness of the proposed methods.
This paper investigates the problem of distributed consensus control for multi-agent systems under denial-of-service (DoS) attacks. Different from the existing results where DoS attacks on all the ...channels are same, in this paper, the adversaries compromise each channel independently. The objective is to design distributed controllers such that the consensus is still achieved in the presence of DoS attacks. Both state-feedback and observer-based controllers are considered. First, the decay rates under different attack modes are obtained by solving a class of linear matrix inequalities. Second, sufficient conditions on the duration of the DoS attacks, under which the consensus is still achieved, are proposed. The difficulty that there is no one-to-one match between the obtained decay rates and DoS duration limitations, is overcome by introducing the equivalent decay rates corresponding to channels. Moreover, the computational complexity is reduced greatly by introducing a novel scaling method. Finally, two examples are presented to illustrate the effectiveness of the proposed approaches.
Secure state estimation for cyber-physical systems under sparse sensor attacks is the problem of estimating the state from the corrupted measurements. Although such problem can be addressed by brute ...force search, combinatorial candidates lead to excessive time requirement, which hinders the scalability. For reducing the computational complexity, this paper provides an alternative approach (called set cover approach) to reduce the number of candidates by at least half with the help of a greedy algorithm. Then, a switched observer, with less candidate observers, is designed to estimate the state from the corrupted measurements under the basic observability requirement. Meanwhile, a modified greedy algorithm is proposed to reduce the number of candidates further based on the observer design conditions. Finally, the effectiveness of the proposed set cover approach is demonstrated by two simulations showing an order of magnitude decrease in execution time.
We reviewed the recent advances of over 120 MOFs-based materials for photocatalytic hydrogen production from water splitting under UV, visible or even NIR light irradiation, and divided them into ...three categories: MOFs, MOFs composites and MOFs-derived photocatalysts. The relationship between high hydrogen production efficiency and possible hydrogen production mechanism of MOFs-based photocatalysts was discussed in detail, providing suggestions to explore new and efficient photocatalysts.
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•Reviews 123 MOFs-based catalysts for water-splitting by UV/Vis/NIR irradiation.•Elucidates photocatalytic H2 production efficiency and possible reaction mechanism.•Discusses the strategy of high H2 production efficiency by MOFs-based materials.
Owing to the structural controllability, pore modification and unique semiconductor property of metal-organic frameworks (MOFs), the investigation on MOFs as efficient photocatalysts for hydrogen production from water splitting under UV, visible or even NIR light irradiation have made great progress. In this review, we systematically summarized the recent advances of MOFs-based photocatalysts for hydrogen production from water, and divided them into three categories: MOFs, MOFs composites and MOFs-derived photocatalysts. The high hydrogen production efficiency and possible hydrogen production mechanism of MOFs-based photocatalysts were analyzed in detail. A brief perspective was given to achieve high effective and stable MOFs-based materials for photolysis of water, providing suggestions to explore new and efficient MOFs-based photocatalysts.
Hydrogenated amorphous carbon (a-C:H) is capable of providing a near-frictionless lubrication state when rubbed in dry sliding contacts. Nevertheless, the mechanisms governing superlubricity in a-C:H ...are still not well comprehended, mainly due to the lack of spatially resolved structural information of the buried contact surface. Here, we present structural analysis of the carbonaceous sliding interfaces at the atomic scale in two superlubricious solid lubricants, a-C:H and Si-doped a-C:H (a-C:H:Si), by probing the contact area using state-of-the-art scanning electron transmission microscopy and electron energy-loss spectroscopy. The results emphasize the diversity of superlubricity mechanisms in a-C:Hs. They suggest that the occurrence of a superlubricious state is generally dependent on the formation of interfacial nanostructures, mainly a tribolayer, by different carbon rehybridization pathways. The evolution of such anti-friction nanostructures highly depends on the contact mechanics and the counterpart material. These findings enable a more effective manipulation of superlubricity and developments of new carbon lubricants with robust lubrication properties.
This article investigates malicious attacks against distributed control systems. The objective of this article is to analyze the potential attack mechanisms, which worsen the estimation performance ...through compromising partial communication links. Two regimes of attacks (perfect and nonperfect attacks) are considered. First, a necessary and sufficient condition for the existence of perfect attack is provided in the form of null space. Based on the obtained conditions, a perfect attack design strategy is proposed. Second, for the case that the adversary cannot compromise enough communication links to implement the perfect attack, an offline nonperfect attack design strategy is proposed. Besides, by intercepting the system measurements, an online nonperfect attack design strategy is provided to enlarge the influence of the designed attacks. Finally, the simulation results demonstrate the correctness and effectiveness of the proposed conditions and methods.
Until now there has been no fundamental theory applicable for biodegradable metals (BMs). First, this paper optimizes the definition of BMs given in 2014. Second, the dual criteria of ...biodegradability and biocompatibility are proposed for BMs, and all metallic elements in the periodic table with accessible data are screened on the basis of these criteria. Regarding biodegradability, electrode potential, reactivity series, galvanic series, Pilling–Bedworth ratio, and Pourbaix diagrams are all adopted as parameters to classify the degradable and nondegradable nature of a material, especially in a physiological environment. Considering the biocompatibility at different levels, cellular biocompatibility, tissue biocompatibility, and human/clinical related biocompatibility parameters are put forward to comprehensively evaluate the biosafety of BMs. Third, for the material design of BMs, mechanical properties, chemical properties, physical properties and biological properties should be considered and balanced to guarantee that the degradation behavior of BMs match well with a tissue regeneration/repair procedure as the function of time and spatial location. Besides the selected metallic elements, some nonmetallic elements are selected as suitable alloying elements for BMs. Finally, five classification/research directions for future BMs are proposed: biodegradable pure metals, crystalline alloys, bulk metallic glasses, high entropy alloys, and metal matrix composites.
The fundamental theory of biodegradable metals are clarified in this review article, with the definition of biodegradable metals, biodegradability, and biocompatibility dual criteria for metallic elements in the periodic table being regarded as biodegradable metals. Key properties needed to be considered for materials design of biodegradable metals and future research and development directions for biodegradable metals are proposed.
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