This article presents an adaptive antisaturation prescribed-time control (AAPTC) scheme for the stable payload retrieval of a two-body tethered space system following the desired libration state. The ...tethered payload is retrieved at the analytical speed function corresponding to the desired stable libration state. At the same time, the thrust at the payload is applied with the proposed AAPTC scheme to closely track the desired state to eliminate any deviation from the desired libration state due to external disturbances. The influence of the thrust saturation is minimized by a neural dynamics-based adaptive antisaturation compensator (ASC) that quickly drives the control system away from the saturated region. The Lyapunov stability of the proposed control scheme is proved analytically. Numerical simulations validate the effectiveness of the proposed prescribed-time strategy and the adaptive ASC.
The mitochondrial pathway of apoptosis is initiated by mitochondrial outer membrane permeabilization (MOMP). The BCL-2 family effectors BAX and BAK are thought to be absolutely required for this ...process. Here, we report that BCL-2 ovarian killer (BOK) is a bona fide yet unconventional effector of MOMP that can trigger apoptosis in the absence of both BAX and BAK. However, unlike the canonical effectors, BOK appears to be constitutively active and unresponsive to antagonistic effects of the antiapoptotic BCL-2 proteins. Rather, BOK is controlled at the level of protein stability by components of the endoplasmic reticulum (ER)-associated degradation pathway. BOK is ubiquitylated by the AMFR/gp78 E3 ubiquitin ligase complex and targeted for proteasomal degradation in a VCP/p97-dependent manner, which allows survival of the cell. When proteasome function, VCP, or gp78 activity is compromised, BOK is stabilized to induce MOMP and apoptosis independently of other BCL-2 proteins.
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•BOK induces mitochondrial apoptosis in the absence of BAX and BAK•The proapoptotic activity of BOK is independent of other BCL-2 family proteins•BOK activity is regulated via endoplasmic-reticulum-associated degradation (ERAD)•ERAD components AMFR/gp78 and VCP/p97 and the proteasome carry out BOK degradation
The BCL-2 family member BOK offers a path to mitochondrial outer membrane permeabilization and apoptosis that can be executed in the absence of BAX and BAK and that is controlled at the level of protein stability by ER-associated degradation.
Self-powered electronic devices require energy harvesting systems to support their energy needs, but their energy harvesting efficiency seems still insufficient. In this paper, a flexoelectric energy ...harvester based on controllable wrinkling mechanism is theoretically proposed to enhance the energy harvesting efficiency. The dielectric film, partly bonded to a pre-stretched substrate, wrinkles after release to achieve controllable wavy shapes. A harmonic cyclic post-stretch is employed to stimulate the generation of electric charges. Meanwhile, an electrode-regrouping technique is resorted to optimize the energy harvesting efficiency. Formulation toward this problem includes both the flexoelectricity and piezoelectricity of dielectrics. Theoretical prediction indicates that electrode-regrouping technique can effectively act to relieve neutralization of the charges induced mainly by flexoelectricity and thus improve the energy harvesting efficiency of FEHs. A larger loading frequency and a lower resistance are preferred to optimize the effective power. The power density of the present FEHs is at least 1 orders of magnitude higher than that of vibrational FEHs under micro-scale. Meanwhile, with the scale shrinking below 100 nm, the energy density of the present FEHs may exceed 104W/m3 which is generally 2–4 orders of magnitude higher than that of most vibrational energy harvesters (including electrostatic, electromagnetic, piezoelectric types).
•A flexoelectric energy harvester based on controllable wrinkling mechanism is theoretically proposed.•An electrode-regrouping technique is resorted to improve energy harvesting efficiency.•A larger loading frequency and a lower resistance are preferred to optimize effective power.•Scale effects can greatly affect the energy harvesting efficiency.•The power density on a small scale is higher than that of most vibrational energy harvesters.
This article investigates the attitude control and stability analysis of an electric solar wind sail (E-sail) by considering elastic deflection of tethers while assuming main spacecraft and remote ...units as point masses. The attitude and orbital motion of the E-sail is analyzed by a high-order high-fidelity E-sail model derived from the nodal position finite-element method, where the attitude angles are implicitly described via the nodal coordinates. To overcome the difficulty in handling the stability analysis of high-order model under the Lyapunov framework, the E-sail's attitude dynamics is approximated explicitly by a reduced order analytical model with only three attitude angles. A sliding mode control law is proposed for the E-sail attitude control based on the reduced order analytical E-sail model and its stability is proved by the Lyapunov theory. Finally, two schemes are derived to map the control torque to either the control thrust at remote units or the voltages of main tethers respectively, which are applied to the high-fidelity E-sail model for attitude control. Numerical simulation demonstrates that the proposed control law performs similarly with the high-fidelity and reduced order analytical E-sail models if proper control gains are selected. It shows that the control law developed from the reduced order analytical E-sail model can stably control the attitude of a real E-sail. The investigation also indicates that the high-order flexible E-sail model provides an effective virtual testbed to evaluate the E-sail attitude control strategy derived from the reduced order attitude dynamics.
•Developed high-fidelity rigid-flexible coupling model for E-sail.•Studied rigid-flexible coupling effect on the attitude dynamics of E-sail.•Studied control strategy for spin rate control of E-sail.
...This paper investigates the modelling of rigid-flexible coupling effect on the attitude dynamics and spin control of an electric solar wind sail (E-sail) by developing a rigid-flexible coupling dynamic model. The model considers the attitude dynamics of the central spacecraft, the elastic deformation of the tethers and the rigid-flexible coupling between the spacecraft and the tether. The attitude and translation dynamics of the central spacecraft is described by the natural coordinate formulation, while the tether deformation is described by the high-fidelity nodal position finite element method. The latter enables a natural coupling between the motion of the flexible tethers and the rigid-body dynamics of the central spacecraft at the anchor points where the tethers connected to the spacecraft by Lagrange multipliers. Based on the model, the influence of the rigid-flexible coupling, E-sail orientation and geometrical configuration on the dynamic characteristics of the E-sail is investigated by a parametric analysis. It is found that the deformation motion of flexible tethers will cause the offset of centres of mass and thrust of E-sail, which generates disturbance torques on the central spacecraft. Through the nonlinear rigid-flexible coupling, the disturbance causes the tension fluctuations and the undesired fluctuations of the E-sail's attitude and spin rate. The parametric analysis indicates that the E-sail is more stable if the spin plane passes the centre of mass of the central spacecraft. Finally, the controllability of E-sail spin rate is investigated by applying simple feedback torque controls at the central spacecraft or at the central spacecraft and the remote units simultaneously. The analysis demonstrates the spin rate cannot be controlled by the central spacecraft along due to the rigid-flexible coupling and must be controlled at the remote units with finite control input.
•The fiticious node method based on the LRBFCM is further applied to 3D case.•The band structure of 3D phononic crystals can be quickly evaluated.•The boundary or interface condition of 3D case can ...be easily treated.•The improved LRBFCM is applied to the 3D phononic crystals for the first time.
In this paper, we further extend the local radial basis function collocation method (LRBFCM) for efficient computation of band structures of phononic crystals from 2D to 3D. The proposed LRBFCM uses one fictitious node to tackle instability problems caused by calculation of derivatives of the wave pressure. A few examples of sound pressure wave propagation are modelled to validate the developed method. Comparisons with finite element modeling demonstrate the high stability and efficiency of the new method in computation of band structures of 3D phononic crystals.
A lattice Boltzmann model for simulating multiphase flows with large density ratios is described in this paper. The method is easily implemented. It does not require solving the Poisson equation and ...does not involve the complex treatments of derivative terms. The interface capturing equation is recovered without any additional terms as compared to other methods M.R. Swift, W.R. Osborn, J.M. Yeomans, Lattice Boltzmann simulation of liquid–gas and binary fluid systems, Phys. Rev. E 54 (1996) 5041–5052; T. Inamuro, T. Ogata, S. Tajima, N. Konishi, A lattice Boltzmann method for incompressible two-phase flows with large density differences, J. Comput. Phys. 198 (2004) 628–644; T. Lee, C.-L. Lin, A stable discretization of the lattice Boltzmann equation for simulation of incompressible two-phase flows at high density ratio, J. Comput. Phys. 206 (2005) 16–47. Besides, it requires less discrete velocities. As a result, its efficiency could be greatly improved, especially in 3D applications. It is validated by several cases: a bubble in a stationary flow and the capillary wave. The numerical surface tension obtained from the Laplace law and the interface profile agrees very well with the respective analytical solution. The method is further verified by its application to capillary wave and the bubble rising under buoyancy with comparison to other methods. All the numerical experiments show that the present approach can be used to model multiphase flows with large density ratios.
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