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The multiple autonomous underwater vehicle (AUV) formation plays an important role in underwater missions, such as oceanographic sampling and water pollution monitoring. This article presents the mechatronic design, modeling, formation control, and experiments of multiple AUVs. The structure of the AUV and a simplified mathematical model for tracking control are described. To achieve formation control, we formulate a control framework for the multiple AUVs. The upper layer is a formation algorithm based on a novel leader-follower control law. The bottom layer is a dynamic controller based on active disturbance rejection control (ADRC). The formation algorithm is in charge of calculating reference values for the followers to maintain a desired pattern with the leader. The stability and convergence properties of the algorithm have been analyzed using the Lyapunov stability method. Meanwhile, an ADRC approach-based dynamic controller is established to track the reference values. Numerical simulations are carried out to analyze formation control and validate the control framework. The multiple AUVs can switch and maintain the formation between the one-line pattern and the V pattern. Finally, extensive formation field experiments involving the one-line pattern and the V pattern show the good motion ability of the self-designed AUVs and also verify the feasibility of the proposed control approach.

In this work, the impacts of OFF-state gate bias (VGS,OFF) on dynamic on-resistance (RON) are systematically investigated in commercial Schottky-type p-GaN Gate high-electron-mobility transistors (HEMTs). Double-pulse tester (DPT) and PIV system are adopted to evaluate the dynamic RON with various OFF-state gate and drain bias (VDS,OFF) under hard- and soft-switching conditions. More negative VGS,OFF can aggravate the dynamic RON degradation under both soft- and hard-switching, especially when switching with a high VDS,OFF. The impacts of VGS,OFF on switching transients and OFF-state stress are investigated separately to reveal the underlying mechanisms, which are found to be associated with the generation and movements of holes. OFF-state gate bias of the voltage-driving scheme needs to be carefully considered according to the identified mechanisms in terms of dynamic on-resistance degradation.

A fundamentally difficult problem to apply the orthogonal matching pursuit (OMP) to estimate the underwater acoustic (UWA) orthogonal frequency division multiplexing (OFDM) channel is designing a proper iteration termination condition. However, existing OMP-based algorithms that design termination conditions based on the physical sparsity suffer the limited estimation accuracy in high-level noise cases and the difficult balance between the accuracy and computational costs in low-level noise cases. We find that it is the recovery sparsity, a quantity related to but possibly significantly different from the physical sparsity, that should be utilized to devise termination conditions. Based on this observation, we first exploit the recovery sparsity to derive a closed-form expression for the termination condition to improve the estimation accuracy in high-level noise cases. Then, to balance the estimation accuracy and computational costs in low-level noise cases, we design another termination condition based on the residual vector and the observation vector. By embedding these two conditions into the OMP structure, we propose an innovative channel estimation algorithm for UWA-OFDM communication systems, referred to as the adaptive OMP (A-OMP). Simulation results show that, compared with the OMP, the A-OMP can achieve comparable or even higher estimation accuracy with smaller computational costs in all considered noise cases. Specially, the A-OMP can increase the estimation accuracy by 71.31% with only 13.48% CPU running time in high-level noise cases.

In a ${p}$ -channel field-effect-transistor ( ${p}$ -FET) bridge HEMT device recently realized on a commercial ${p}$ -GaN/AlGaN/GaN-on-Si power HEMT epi-wafer, it is revealed that the device’s reverse-conduction turn-on voltage ( ${V}_{\text {RT}}$ ) can be effectively decoupled from the forward threshold voltage ( ${V}_{\text {TH}}$ ) of Schottky-type ${p}$ -GaN gate HEMTs. Unlike the conventional Schottky-type ${p}$ -GaN gate HEMTs, of which ${V}_{\text {RT}}$ is closely linked to ${V}_{\text {TH}}$ , the ${p}$ -FET-bridge HEMT enables separate designs of ${V}_{\text {RT}}$ and $V_{\text {TH}}$ so that low-loss reverse conduction and high threshold voltage can be simultaneously realized. In addition, ${V}_{\text {RT}}$ can be further reduced by engineering the AlGaN barrier layer, which will also benefit a lower channel sheet resistance without lowering ${V}_{\text {TH}}$ .

With the development of robotics, the underwater robot platform has been widely used in the Internet of Underwater Things (IoUT). An underwater robot platform equipped with multiple sensors is used as a mobile collector to build a reliable information collection system for IoUT. This article presents the mechatronic design, fabrication, modeling, control, simulation, and experiments of a robot IoUT platform to enable the smart ocean. Inspired by the design of both fin-actuated swimming of fish and buoyancy-driven gliding of underwater glider, a novel multilink gliding fish robot is proposed. The multilink gliding fish robot, which is called FishBot in this article, can swim flexibly and glide energy efficiently in three dimensions. In the FishBot, the body and/or caudal fin (BCF) with three degrees of freedom and buoyancy-driven system was equipped as the main propulsion device. Besides, a pair of pectoral fins was equipped to assist in regulating the gliding attitude and enhance the FishBot maneuverability in the vertical plane. The dynamic model that consists of cruise swimming motion, pure-pitching swimming motion, and 3-D swimming motion for control is established. Moreover, a behavioral control framework is developed to achieve a variety of fish-like swimming behaviors and gliding motion. Meanwhile, we proved the stability of the linear quadratic regulation controller and the locomotion controller is provided with exponential stability. The validity of the proposed model and the designed controller is demonstrated by numerical simulations. Finally, a series of experiments involving different fish-like behaviors and gliding motion elucidates the powerful locomotion ability of the FishBot.

In this article, we systematically investigate the OFF-state drain-voltage-stress-induced threshold voltage ( $V_{\mathrm {TH}}$ ) instability in Schottky-type p-GaN gate high electron mobility transistors (HEMTs). OFF-state drain-voltage stress and recovery tests were conducted under various temperatures and different drain biases. A sharp increase in $V_{\mathrm {TH}}$ was observed at the beginning of the stress, and $V_{\mathrm {TH}}$ kept shifting positively during the stress until it reached saturation. Further experiments showed that two different mechanisms dominated the $V_{\mathrm {TH}}$ shift, which were distinguished by the temperature dependence, degradation/recovery process and affected locations in the gate region. The hole deficiency caused by hole emission from the p-GaN layer is suggested to be the dominant reason for the $V_{\mathrm {TH}}$ instability at the beginning of the stress, while with increasing stress time, electron trapping in the barrier and buffer layers gradually dominates the $V_{\mathrm {TH}}$ shift. Based on the identified mechanisms, physics-based analytical calculations and empirical fitting are conducted to describe the $V_{\mathrm {TH}}$ behavior during the OFF-state drain-voltage stress. The fundamental mechanisms can provide a guide to develop corresponding methods to address the drain-induced $V_{\mathrm {TH}}$ instability issue.

In this work, we study the gate leakage mechanisms of E-mode ${p}$ - ${n}$ junction/AlGaN/GaN (PNJ) high electron mobility transistors (HEMTs), which have been shown to deliver low gate leakage and wide safe operating gate-bias range. The intrinsic gate leakage through the PNJ-gate was found to be limited by the transport of holes through the ${p}$ -GaN layer, which occurs via Poole-Frenkel emission and phonon-assisted tunneling in low and high gate bias region, respectively. In addition, lateral leakage current and the role of variable hopping process (VRH) are also discussed. Gate leakage current models based on the revealed mechanisms can quantitatively reproduce the gate-leakage behavior in the entire relevant range of gate biases and temperatures.

Fog computing is considered to be an effective method to solve the problem of high latency and high energy consumption of IoT devices. A suitable computation offloading strategy can provide a low offloading cost to the user device. Most researches on computation offloading in fog computing focus on one or two targets to improve system performance, however, the actual system needs to meet a comprehensive demand. Therefore, the joint optimization of multi-objective in multiple scenarios is a very meaningful problem. Inspired by this, the paper highlights the joint optimization research for fog computing, which proposes a Joint Computation offloading, Data compression, Energy harvesting, and Application scenarios (JCDEA) algorithm. The related mathematical model is constructed and the cost expressions of local computing, fog computing, and cloud computing are derived. Through the proposed algorithm, solving the computation offloading strategy is transformed into solving the minimum cost and is simplified by controlling strategy factors. Moreover, five simulation experiments are conducted and the meaningful conclusions are drawn, which contain that (1) the cost of fog computing is lower than that of local and cloud computing in most time slots and cloud computing can compensate for fog computing in complex environments; (2) the cost increases approximately linear with the amount of offloaded data; (3) the number of user devices and the compression ratio affect the fog-to-cloud ratio (FCR), while the FCR affects the cost; and (4) the related offloading strategy distribution and the cost are obtained for different scenarios. The JCDEA algorithm always outperforms than that of the random selection algorithm in all scenarios.

This paper presents a study on bioinspired closed-loop Central Pattern Generator (CPG) based control of a robot fish for obstacle avoidance and direction tracking. The biomimetic robot fish is made of a rigid head with a pair of pectoral fins, a wire-driven active body covered with soft skin, and a compliant tail. The CPG model consists of four input parameters: the flapping amplitude, the flapping angular velocity, the flapping offset, and the time ratio between the beat phase and the restore phase in flapping. The robot fish is equipped with three infrared sensors mounted on the left, front and right of the robot fish, as well as an inertial measurement unit, from which the surrounding obstacles and moving direction can be sensed. Based on these sensor signals, the closed-loop CPG-based control can drive the robot fish to avoid obstacles and to track designated directions. Four sets of experiments are presented, including avoiding a static obstacle, avoiding a moving obstacle, tracking a designated direction and tracking a designated direction with an obstacle in the path. The experiment results indicated that the presented control strategy worked well and the robot fish can accomplish the obstacle avoidance and direction tracking effectively.

In this paper, aiming to drive the unmanned aerial vehicle (UAV) to the optimal position of the vertical plane in the close formation flight, a control method that is based on extended state observ...

Two-dimensional (2D) materials1–5 offer a unique platform from which to explore the physics of topology and many-body phenomena. New properties can be generated by filling the van der Waals gap of 2D materials with intercalants6,7; however, post-growth intercalation has usually been limited to alkali metals8–10. Here we show that the self-intercalation of native atoms11,12 into bilayer transition metal dichalcogenides during growth generates a class of ultrathin, covalently bonded materials, which we name ic-2D. The stoichiometry of these materials is defined by periodic occupancy patterns of the octahedral vacancy sites in the van der Waals gap, and their properties can be tuned by varying the coverage and the spatial arrangement of the filled sites7,13. By performing growth under high metal chemical potential14,15 we can access a range of tantalum-intercalated TaS(Se)y, including 25% Ta-intercalated Ta9S16, 33.3% Ta-intercalated Ta7S12, 50% Ta-intercalated Ta10S16, 66.7% Ta-intercalated Ta8Se12 (which forms a Kagome lattice) and 100% Ta-intercalated Ta9Se12. Ferromagnetic order was detected in some of these intercalated phases. We also demonstrate that self-intercalated V11S16, In11Se16 and FexTey can be grown under metal-rich conditions. Our work establishes self-intercalation as an approach through which to grow a new class of 2D materials with stoichiometry- or composition-dependent properties.

In this work, we demonstrate a GaN-based $\textit {p-n}$ junction gate (PNJ) HEMT featuring an ${n}$ -GaN/ ${p}$ -GaN/AlGaN/GaN gate stack. Compared to the more conventional ${p}$ -GaN gate HEMT with a Schottky junction between the gate metal and ${p}$ -GaN layer, the $\textit {p-n}$ junction can withstand higher reverse bias at the same peak electric-field as the depletion region extends to both the ${n}$ -side and ${p}$ -side, while exhibiting lower leakage current. The PNJ-HEMT shows a positive threshold voltage ( ${V}_{\text {TH}}$ ) of 1.78 V, a small gate leakage $(\sim 10^{-3}$ mA/mm @ ${V}_{\text {GS}} = {10}\,\, \text {V}$ ). In particular, a large forward gate breakdown voltage of 19.35 V at 25 °C and 19.70 V at 200 °C was achieved with the PNJ-gate HEMT.

Industry applications that support massive mobile nodes are an important part of 5G Narrow Band Internet of Things (NB-IoT). The mobile node is abstracted as a terminal scene with many shapes and complex behaviors in the cellular internet of things, which makes the network need a better radio resource management strategy to meet more mobility, larger connection requests and higher access rate services. Therefore, the feature extraction of the node trajectories will greatly facilitate the development of optimal algorithms for radio resource management in the large mobile scene of 5G NB-IoT networks. This paper presents a feature mining of the real trajectories from the urban operating vehicles in the city of Shenzhen, China. Meanwhile, the generated trajectories by four common mobility models are also handled as a comparison. The self-similarity, hot-spots, long-tails and travel time are evaluated due to the widely recognized four features of human traces. Mining results show that the vehicles to serve the daily trip of human in the city always take a short travel and activate in several hot-spots with randomly roaming, while the vehicles to serve the goods are showing the opposite characteristics. Moreover, the trajectory generated by the models does not have the characteristics of short travel and roaming in multiple hot spots, nor does it have different movement trends in various time periods.

a novel p-GaN gate topology is proposed to inherently increase threshold voltage (V TH ) and enhance V TH stability. The gate consists of a conventional Schottky-type p-GaN gate and a normally-on p-channel FET bridge connecting source and gate. By modulating the V TH of the p-channel FET, a wide-range positive V TH from 3.6 V to 8.2 V can be achieved without subthreshold voltage degradation. Owing to the well-grounded p-GaN through the normally-on p-FET channel, a stable V TH is also achieved without sacrificing the low gate leakage and large gate swing enabled by the Schottky gate metal/p-GaN contact.

This article proposes a model for threshold voltage (VTH) instability induced by reverse-bias stress (i.e. drain-to-source voltage at off-state) in Schottky gate p-GaN high electron mobility transistors (HEMTs). It is suggested that two different mechanisms would take place during the reverse-bias stress. At the beginning of the stress, a sudden VTH shift is observed, which is recognized to be dominated by hole-deficiency in the further experiments. While the gradually-increased VTH shift during the long-term stress could be mainly induced by electron trapping in both barrier and buffer layers.

Gate reliability and reverse-bias-stress-induced $V$ TH instability issues were investigated in the E-mode p-GaN gate HEMTs. A GaN-based p-n junction gate (PNJ) HEMT featuring an $n$ -GaN/ $p$ -GaN/AlGaN/GaN gate stack was proposed to effectively reduce the gate leakage and enlarge safe gate operation bias region of the p-GaN gate devices. The $V$ TH instability of the p-GaN gate HEMTs under reverse-bias stress has also been systematically investigated under various temperatures and different drain biases. Two different mechanisms are suggested to dominant the $V$ TH shifts during the short-and long-term stress, respectively.

in this work, we investigate the gate reliability of E-mode ${p-n}$ junction gate (PNJ) HEMT, which features an n GaN/p-GaN/AlGaN/GaN gate stack. Both electric-field and thermal-accelerated time-dependent gate breakdown (TDGB) tests were conducted on the PNJ-HEMTs with constant voltage stress (CVS). Compared with the Schottky-junction p-GaN gate HEMT (SJ-HEMT), the PNJ-HEMT delivers lower gate leakage, larger gate swing and longer TDDB lifetime. The estimated maximum applicable $V _{\mathbf{GS}}$ of PNJ-HEMT is 10 V for 10 years’ lifetime at 63% failure level.

A novel flight control method for a fixed-wing unmanned aerial vehicle (UAV) is provided, which uses only synthetic jet actuators (SJAs) to achieve thrust vector control of the fixed-wing UAV. Firstly, the fluid model of the engine jet (or primary jet) and the SJAs are built, and the relation between the deflection angle of the primary jet and the amplitude of vibrating membrane of the SJAs is obtained. Secondly, based on the relation, a SJAs-based thrust vector control pitching motion model of the UAV is built. Thirdly, considering parameter uncertainties, unmodeled dynamics and unknown external disturbance of the system, an adaptive back-stepping sliding mode control (ABSMC) law is proposed, and pitching motion of the UAV is achieved by using only the SJAs-based thrust vector control. Finally, some simulations are conducted to analyze and verify the effectiveness of the flight control method. The results show that the thrust vector produced by the SJAs can enable the pitch control of the UAV and the ABSMC performs well in the presence of parameter uncertainties, unmodeled dynamics and unknown external disturbance of the system.

Creation of guidance law is of central importance for the development of unmanned vehicles. In this paper, we introduce a novel guidance law for leader free circular multiagents unmanned formation flight. Instead of using an actual leader agent, current guidance law uses a virtual leader, of which the position is known by all other agents and other agents can obtain information about the relative model of leader-follower relation from their neighbor agents. The guidance law is designed to describe the preset time-varying formation, which controls the relative states of the followers and the leader in the directions both parallel to and orthogonal to the line-of-sight, as a replacement of the reference trajectories for the agents to follow. To confirm the validity and performance of current guidance law, a numerical simulation is performed.

The construction of novel guidance laws is critical for the field of unmanned vehicles navigation. Previous guidance laws assign an actual leading agent and describe the reference trajectories for agents to follow. By contrast, in this work, the distributed guidance law we proposed predetermines the time-varying formation by controlling the relative states between the following agents and the leading virtual agent in directions parallel to and orthogonal to the line-of-sight. The virtual leading agent's position is recognized by all following agents through a spanning-tree network. Theoretical prove and numerical simulation confirmed the validity of this guidance law.

The parasympathetic nervous system has been known to modify innate immune responses. In animal models, acetylcholine (Ach) released from the distal ends of nerves has been shown to inhibit inflammatory responses such as endotoxic shock, pancreatitis, intestinal inflammation, etc. However, its role in LPS-induced fulminant hepatitis remains to be elucidated. Here, we demonstrate that the vagus nerve acts as a suppressor in the liver after challenge with LPS plus D-gal. The vagus nerve acts through the α7 AchR expressed on the surface of Kupffer cells, inhibiting the production of the proinflammatory cytokines TNF and IL-6. A mechanism study revealed that the suppressive effect of Ach may occur through the activation of Src kinase and subsequent inhibition of the Myd88 signal pathway. Our study has suggested a suppressive role of vagus nerve in the modulation of liver inflammatory responses, which should be noticed during clinical massive hepatectomy and liver transplantation. The nicotinic anti-inflammatory pathway may also be a potential target for sepsis after liver transplantation.

Sepsis-associated immunosuppression (SAIS) is regarded as one of main causes for the death of septic patients at the late stage because of the decreased innate immunity with a more opportunistic infection. LPS-tolerized macrophages, which are re-challenged by LPS after prior exposure to LPS, are regarded as the common model of hypo-responsiveness for SAIS. However, the molecular mechanisms of endotoxin tolerance and SAIS remain to be fully elucidated. In addition, negative regulation of the Toll-like receptor (TLR)-triggered innate inflammatory response needs further investigation. Here we show that expression of immune responsive gene 1 (IRG1) was highly up-regulated in the peripheral blood mononuclear cells of septic patients and in LPS-tolerized mouse macrophages. IRG1 significantly suppressed TLR-triggered production of proinflammatory cytokines TNF-α, IL-6, and IFN-β in LPS-tolerized macrophages, with the elevated expression of reactive oxygen species (ROS) and A20. Moreover, ROS enhanced A20 expression by increasing the H3K4me3 modification of histone on the A20 promoter domain, and supplement of the ROS abrogated the IRG1 knockdown function in breaking endotoxin tolerance by increasing A20 expression. Our results demonstrate that inducible IRG1 promotes endotoxin tolerance by increasing A20 expression through ROS, indicating a new molecular mechanism regulating hypoinflammation of sepsis and endotoxin tolerance.

Effective recognition of viral infections and subsequent triggering of antiviral innate immune responses are essential for the host antiviral defense, which is tightly regulated by multiple regulators, including microRNAs (miRNAs). A previous study showed that miR-466l upregulates IL-10 expression in macrophages by antagonizing RNA-binding protein tristetraprolin-mediated IL-10 mRNA degradation. However, the ability of miR-466l to regulate antiviral immune responses remains unknown. Here, we found that interferon-alpha (IFN-α) expression was repressed in Sendai virus (SeV)- and vesicular stomatitis virus (VSV)-infected macrophages and in dendritic cells transfected with miR-466l expression. Moreover, multiple IFN-α species can be directly targeted by miR-466l through their 3′ untranslated region (3′UTR). This study has demonstrated that miR-466l could directly target IFN-α expression to inhibit host antiviral innate immune response.