A control method based on global fast dynamic terminal sliding mode control (TSMC) technique is proposed to design the flight controller for performing the finite-time position and attitude tracking ...control of a small quadrotor UAV. Firstly, the dynamic model of the quadrotor is divided into two subsystems, i.e., a fully actuated subsystem and an underactuated subsystem. Secondly, the dynamic flight controllers of the quadrotor are formulated based on global fast dynamic TSMC, which is able to guarantee that the position and velocity tracking errors of all system state variables converge to zero in finite-time. Moreover, the global fast dynamic TSMC is also able to eliminate the chattering phenomenon caused by the switching control action and realize the high precision performance. In addition, the stabilities of two subsystems are demonstrated by Lyapunov theory, respectively. Lastly, the simulation results are given to illustrate the effectiveness and robustness of the proposed control method in the presence of external disturbances.
•A control method is proposed for a quadrotor UAV.•The global fast dynamic terminal sliding mode control technique is used.•The technique can ensure the state tracking errors converge to zero in finite time.•The proposed control method can eliminate the chattering phenomenon on controller.
A synthesis control method is proposed to perform the position and attitude tracking control of the dynamical model of a small quadrotor unmanned aerial vehicle (UAV), where the dynamical model is ...underactuated, highly-coupled and nonlinear. Firstly, the dynamical model is divided into a fully actuated subsystem and an underactuated subsystem. Secondly, a controller of the fully actuated subsystem is designed through a novel robust terminal sliding mode control (TSMC) algorithm, which is utilized to guarantee all state variables converge to their desired values in short time, the convergence time is so small that the state variables are acted as time invariants in the underactuated subsystem, and, a controller of the underactuated subsystem is designed via sliding mode control (SMC), in addition, the stabilities of the subsystems are demonstrated by Lyapunov theory, respectively. Lastly, in order to demonstrate the robustness of the proposed control method, the aerodynamic forces and moments and air drag taken as external disturbances are taken into account, the obtained simulation results show that the synthesis control method has good performance in terms of position and attitude tracking when faced with external disturbances.
•A synthesis control method is proposed for a quadrotor UAV.•The novel robust terminal sliding mode control algorithm is used to converge state variables.•A second order sliding mode technique is used to avoid the chattering phenomenon.•The robustness of the synthesis control is demonstrated through simulation results.
In this brief, the problem of delay-dependent stability of recurrent neural networks with time-varying delays is studied. A newly augmented Lyapunov-Krasovskii functional (LKF) that considers the ...information of the nonzero lower bound of time-varying delays is developed. Moreover, the information of the delayed state terms is not considered as elements of augmented vectors when constructing the LKF. An improved stability criterion with the framework of linear matrix inequalities is derived by employing the integral inequality and reciprocally convex combination. With the comparison to the existing ones, the developed stability criterion for neural networks has less conservatism and complexity. Finally, two widely used numerical examples are given to show the effectiveness and superiority of the obtained stability criterion.
Recent advances with the type II clustered regularly interspaced short palindromic repeats （CRISPR） system promise an improved approach to genome editing. However, the applicability and efficiency of ...this system in model organisms, such as zebrafish, are little studied. Here, we report that RNA-guided Cas9 nuclease efficiently facilitates genome editing in both mammalian cells and zebrafish embryos in a simple and robust manner. Over 35% of site- specific somatic mutations were found when specific Cas/gRNA was used to target either etsrp, gata4 or gata5 in zebrafish embryos in vivo. The Cas9/gRNA efficiently induced biallelic conversion of etsrp or gata5 in the resulting somatic cells, recapitulating their respective vessel phenotypes in etsrpv11 mutant embryos or cardia bifida phenotypes in fautm236a mutant embryos. Finally, we successfully achieved site-specific insertion of mloxP sequence induced by Cas9/gRNA system in zebrafish embryos. These results demonstrate that the Cas9/gRNA system has the potential of becoming a simple, robust and efficient reverse genetic tool for zebrafish and other model organisms. Together with other genome-engineering technologies, the Cas9 system is promising for applications in biology, agriculture, envi- ronmental studies and medicine.
Implicit curve and surface reconstruction has wide applications in computer graphics, which attracts great attention of many researchers. In this paper, we propose the relaxed implicit randomized ...algebraic reconstruction technique (RIR-ART) for curve and surface reconstruction. The RIR-ART method generates a sequence of curves and surfaces by adjusting the control coefficients with the relaxation parameters iteratively. It is proved that the sequence of curves and surfaces generated by the RIR-ART method with the suitable relaxation parameters converge to the least-norm results in terms of the mean square error. The RIR-ART method can eliminate the extra zero-level sets effectively during its iterative process, and converge faster than the implicit progressive-iterative approximation method (Hamza et al. 2020). Numerical examples present the efficiency and effectiveness of the proposed method.
•The RIR-ART method converges in terms of the mean square error.•The extra zero-level sets are eliminated by the RIR-ART method effectively.•The RIR-ART method converges faster than the I-PIA method for the reconstruction.
A method based on second order sliding mode control (2-SMC) is proposed to design controllers for a small quadrotor UAV. For the switching sliding manifold design, the selection of the coefficients ...of the switching sliding manifold is in general a sophisticated issue because the coefficients are nonlinear. In this work, in order to perform the position and attitude tracking control of the quadrotor perfectly, the dynamical model of the quadrotor is divided into two subsystems, i.e., a fully actuated subsystem and an underactuated subsystem. For the former, a sliding manifold is defined by combining the position and velocity tracking errors of one state variable, i.e., the sliding manifold has two coefficients. For the latter, a sliding manifold is constructed via a linear combination of position and velocity tracking errors of two state variables, i.e., the sliding manifold has four coefficients. In order to further obtain the nonlinear coefficients of the sliding manifold, Hurwitz stability analysis is used to the solving process. In addition, the flight controllers are derived by using Lyapunov theory, which guarantees that all system state trajectories reach and stay on the sliding surfaces. Extensive simulation results are given to illustrate the effectiveness of the proposed control method.
•A method based on second order sliding mode control is proposed for a quadrotor UAV.•The nonlinear coefficients of the defined switching sliding manifolds are further explored via Hurwitz.•Second order sliding mode technique is used to avoid the chattering phenomenon.•The effectiveness and robustness of the proposed control method are demonstrated by the simulations.
Abstract
Suffering from COVID-19 and witnessing the suffering and deaths of patients with COVID-19 may place frontline healthcare workers (HCWs) at particularly high risk for posttraumatic stress ...disorder (PTSD); however, few data are available on the clinical characteristics of PTSD among frontline HCWs who survived COVID-19 (“surviving HCWs” hereafter). The present study examined the prevalence, correlates, and clinical symptoms of possible PTSD in surviving HCWs 6 months after the COVID-19 outbreak in China. A total of 291 surviving HCWs and 42 age- and gender-matched COVID-19-free frontline HCWs (control group) were recruited and administered the Chinese Essen Trauma Inventory, which was used to assess the presence of possible PTSD according to DSM-IV-TR criteria. Survivors’ clinical data and characteristics of exposure to COVID-19 were collected via self-report questionnaires. Surviving HCWs had significantly higher rates of possible PTSD than controls (19.9% vs. 4.8%,
P
= 0.017). Correlates of PTSD in survivors were ICU admission (OR = 8.73,
P
= 0.003), >10 respiratory symptoms during the most symptomatic period of COVID-19 (OR = 3.08,
P
= 0.006), the residual symptom of dizziness (OR = 2.43,
P
= 0.013), the residual symptom of difficult breathing (OR = 2.23,
P
= 0.027), life in danger due to COVID-19 (OR = 16.59,
P
= 0.006), and exposure to other traumatic events (OR = 2.94,
P
= 0.035). Less commonly seen PTSD symptoms in survivors were having nightmares about the event (34.5%), suddenly feeling like they were living through the event suddenly (25.9%), being unable to remember an important part of the event (32.8%), and overalertness (31.0%). Nearly one-fifth of the surviving HCWs had possible PTSD 6 months after the COVID-19 outbreak. Mental health services for this vulnerable population should include periodic screening for PTSD, expanded social support, and, when necessary, psychotherapy and psychopharmacological treatment.
•ECMO has been used as a rescue therapy for severe respiratory failure and ARDS for years and ECMO should also be considered as a rescue therapy for COVID-19 with refractory hypoxemia despite ...lung-protective ventilation according to WHO.•Although the clinical trials of ECMO for COVID-19 are lacking, its use in COVID-19 might also offer promise based on the previous experience.•In the current situation of pandemic outbreak, many issues of ECMO use deserve our attention.
The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has emerged since December 2019 in Wuhan city, and has quickly spread throughout China and other countries. To date, no specific treatment has been proven to be effective for SARS-CoV-2 infection. According to World Health Organization (WHO), management of coronavirus disease 19 (COVID-19) has mainly focused on infection prevention, case detection and monitoring, and supportive care. Given to the previous experience, extracorporeal membrane oxygenation (ECMO) has been proven to be an effective therapy in the treatment of respiratory failure or acute respiratory distress syndrome (ARDS). On the basis of similar principle, ECMO may be also an effective therapy in the treatment of severe COVID-19. In this study, we described and discussed the clinical outcomes of ECMO for ARDS patients, ECMO use for severe COVID-19 in China, the indications of ECMO use, and some important issues associated with ECMO.
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