14 research outputs found

    Robust control of uncertain nonlinear systems: a nonlinear DOBC approach

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    This paper advocates disturbance observer based control (DOBC) for uncertain nonlinear systems. Within this framework, a nonlinear controller is designed based on the nominal model in the absence of disturbance and uncertainty where the main design specifications are to stabilize the system and achieve good tracking performance. Then a nonlinear disturbance observer is designed to not only estimate external disturbance but also system uncertainty/ unmodelled dynamics. With described uncertainty, rigorous stability analysis of the closed-loop system under the composite controller is established in this paper. Finally, the robust control problems of a missile roll stabilization and a mass spring system are addressed to illustrative the distinct features of the nonlinear DOBC approach

    High-order sliding mode observer-based trajectory tracking control for a quadrotor UAV with uncertain dynamics

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    This paper investigates the trajectory tracking problem of the quadrotor unmanned aerial vehicles (UAV) with consideration of both attitude and position dynamics. First of all, the trajectory tracking problem is divided into the commands tracking in position and attitude loops by introducing the virtual attitude angle commands. Secondly, the high-order sliding mode observers (HSMOs) are introduced to estimate the lumped disturbances in position loop and the derivatives of the attitude angle tracking errors, the lumped disturbances in the attitude loop. And then the composite nonlinear dynamical inversion controller in position loop and the composite nonsingular terminal sliding mode controller in attitude loop are constructed by introducing the estimation information of HSMOs into controller design process. Finally, the simulations based on the data of a practical UAV are carried out to verify the effectiveness of the proposed method

    Nonlinear composite bilateral control framework for n-DOF teleoperation systems with disturbances

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    This paper proposes a new nonlinear composite bilateral control framework for n-degree-of-freedom (n-DOF) teleoperation systems with external disturbances. Different with the existing methods which usually regard the dynamics of the master and slave robots as linear impedance models, the proposed control framework fully considers the nonlinear dynamics of the n-DOF teleoperation systems. Central to the proposed framework is the utilization of nonlinear disturbance observers for estimating the disturbances in master and slave robot systems. The nonlinear composite bilateral controller is constructed by incorporating the disturbance estimations into the nonlinear feedback linearization controller. The proposed control method guarantees satisfactory position tracking performance and desired remote force haptic simultaneously for the n-DOF teleoperation systems with external disturbances. The effectiveness of the proposed control framework is validated by its applications on 2-DOF teleoperation systems

    Finite-time disturbance observer-based trajectory tracking control for flexible-joint robots

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    This paper proposes a robust finite-time control scheme for the high-precision tracking problem of (FJRs) with various types of unpredictable disturbances. Specifically, based on a flatness dynamic model, a finite-time disturbance observer (FTDO) with only link-side position measurements is firstly developed to estimate the lumped unknown time-varying disturbance and unmeasurable states. Then, through the information of the states and disturbances provided by the FTDO, a robust output feedback controller is constructed, which can accomplish the tasks of disturbance suppression and trajectory tracking in finite time. Moreover, a rigorous stability analysis of the closed-loop system based on a finite-time bounded (FTB) function is conducted. Finally, the simulation results validate the feasibility and superiority of the proposed control scheme against other existing control results

    Contributions of T Lymphocyte Abnormalities to Therapeutic Outcomes in Newly Diagnosed Patients with Immune Thrombocytopenia

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    <div><p>T cell abnormalities have been reported to play an important role in pathogenesis of immune thrombocytopenia (ITP) besides specific autoantibodies towards platelet. The aim of this study was to explore the clinical importance of T lymphocyte subsets in adult patients with newly diagnosed ITP before and after first-line treatment. Elderly ITP patients were also studied and we tried to analyze the relationships between these items and therapeutic outcomes. The patients were treated with intravenous immunoglobulin (IVIG) plus corticosteroids and therapeutic responses were evaluated. As a result, compared with the controls, absolute lymphocyte counts in ITP patients decreased significantly before treatment. After treatment, lymphocyte counts restored to control level regardless of their treatment outcomes. In addition, we observed increased IgG and CD19<sup>+</sup> cell expression and decreased CD4<sup>+</sup>/CD8<sup>+</sup> cell ratio in both whole ITP group and elderly group before treatment. After treatment, the increased IgG and CD19<sup>+</sup> cell expression could be reduced in both respond and non-respond group regardless of patient age, while CD4<sup>+</sup>/CD8<sup>+</sup> cell ratio could not be corrected in non-respond ITP patients. In non-respond ITP patients, increased CD8<sup>+</sup> cell expression was noticed and could not be corrected by first-line treatment. Furthermore, even lower NK cell expression was found in non-respond elderly patients after treatment when compared with that in controls. Our findings suggest that ITP patients usually had less numbers of peripheral lymphocytes and patients with higher levels of CD8<sup>+</sup> cells or lower levels of CD4<sup>+</sup>/CD8<sup>+</sup> cell ratio were less likely to respond to first-line treatment. Lower levels of NK cells made therapies in elderly ITP patients even more difficult.</p></div

    Absolute lymphocyte counts in different analyzing groups before and after treatment (×10<sup>9</sup>/L).

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    <p>*** P<0.001 compared with that before treatment.</p><p>* P<0.05 compared with that before treatment.</p><p>Absolute lymphocyte counts in different analyzing groups before and after treatment (×10<sup>9</sup>/L).</p

    IgG and T lymphocyte subsets expression in different groups.

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    <p>(A) The levels of serum IgG (mean±SD, 21.33±4.64 g/L, P<0.001) and CD19<sup>+</sup> cell percentage (17.27±9.14%, P<0.01) in ITP patients were higher than those in control group (11.15±4.61 g/L, 12.47±2.19%),respectively. And so did those in elderly ITP group when compared with the controls, which were 22.16±4.28 g/L (P<0.001) and 15.94±6.68% (P<0.05) respectively. Serum IgG and CD19<sup>+</sup> cell percentage did not differ significantly between the whole ITP patients and the elderly ITP patients. There were no remarkable differences in CD2<sup>+</sup>, CD3<sup>+</sup>,CD4<sup>+</sup>, CD8<sup>+</sup> and NK cell expression among the three groups. (B) A significant reduction in CD4<sup>+</sup>/CD8<sup>+</sup> cell ratio was seen in both ITP group (1.29±0.61, P<0.01) and elderly ITP group (1.32±0.62, P<0.05) compared with controls(1.56±0.29). CD4<sup>+</sup>/CD8<sup>+</sup> cell ratio did not differ significantly between the ITP patients and the elderly ITP patients.</p

    IgG and T lymphocyte subsets expression in both ITP and elderly ITP patients (NR) before and after first-line treatment(mean±SD).

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    <p>*** P<0.001 compared with the group before treatment.</p><p>* P<0.05 compared with the group before treatment.</p><p><b>#</b> P<0.05 compared with the control group.</p><p>IgG and T lymphocyte subsets expression in both ITP and elderly ITP patients (NR) before and after first-line treatment(mean±SD).</p

    IgG and T lymphocyte subsets expression in different outcome groups of ITP patients.

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    <p>(A) IgG levels in healthy controls, respond group (CR+R) and non-respond group (NR) were 11.15±4.61g/L, 22.07±4.65 g/L, 19.54±4.28 g/L, respectively. IgG expression in both respond and non-respond groups were remarkably higher than that in controls (P<0.001), but there was no significant difference between the respond group and the non-respond group. CD3<sup>+</sup> cell percentage in respond group was 59.00±12.08%, which was lower than that in controls (66.98±6.86%, P<0.05). CD19<sup>+</sup> cell percentage in respond group was 17.88±9.45%, which was higher than that in controls (12.47±2.19%, P<0.05). Increased CD8<sup>+</sup> cell expression was observed in non-respond group (32.42±8.07%, P<0.01) compared with that in controls (22.99±3.24%) and that in respond group (24.13±7.83%). There were no remarkable differences in CD2<sup>+</sup>, CD4<sup>+</sup> and NK cell expression among the three groups. (B) A significant reduction in CD4<sup>+</sup>/CD8<sup>+</sup> cell ratio was seen in non-respond group (0.98±0.50) compared with that in controls (1.56±0.29, P<0.001) and that in respond group (1.42±0.61, P<0.01).</p
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