Periodically driven non-Hermitian systems can exhibit rich topological band structure and non-Hermitian skin effect, without analogs in their static or Hermitian counterparts. In this work we ...investigate the exceptional band-touching points in the Floquet quasienergy bands, the topological characterization of such exceptional points and the Floquet non-Hermitian skin effect (FNHSE). Specifically, we exploit the simplicity of periodically quenched two-band systems in one dimension or two dimensions to analytically obtain the Floquet effective Hamiltonian as well as locations of the many exceptional points possessed by the Floquet bulk bands. Two different types of topological winding numbers are used to characterize the topological features. Bulk-boundary correspondence (BBC) is naturally found to break down due to FNHSE, which can be drastically different among different bulk states. Remarkably, given the simple nature of our model systems, recovering the BBC is doable in practice only for certain parameter regime where a low-order truncation of the characteristic polynomial (which determines the Floquet band structure) becomes feasible. Furthermore, irrespective of which parameter regime we work with, we find a number of intriguing aspects of Floquet topological zero modes and π modes. For example, under the open boundary condition, zero edge modes and π edge modes can individually coalesce and localize at two different boundaries. These anomalous edge states can also switch their accumulation boundaries when a certain system parameter is tuned. These results indicate that non-Hermitian Floquet topological phases, though more challenging to understand than their Hermitian counterparts, can be extremely rich in the presence of FNHSE.
The underlying circuit control is a key problem of the hybrid energy-storage system (HESS) in electric vehicles (EV). In this paper, a composite non-linear control strategy (CNC) is proposed for the ...accurate tracking current/voltage of the fully-active HESS by combining the exact feedback linearization method and the sliding mode variable structure control technology. Firstly, by analyzing the circuit characteristics of HESS, the affine non-linear model of fully-active HESS is derived. Then, a rule-based energy management strategy (EMS) is designed to generate the reference current value. Finally, the HESS is linearized by the exact feedback linearization method, and the proposed CNC strategy is developed combined with sliding mode variable structure control technology to ensure fast response, high performance, and robustness. At the same time, the stability proof based on the Lyapunov method is given. Moreover, the performance of the CNC strategy is thoroughly investigated and compared with simulation studies with the traditional PI control and a modified sliding mode control, and its effectiveness under different driving conditions is fully verified.
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The tissue engineering is a promising method for cartilage regeneration studies. The rough in vivo initial repair environment of articular cartilage is a challenge for the development ...of cartilage tissue engineering. Hereon, in this study, a silk fibroin/collagen type II scaffold was designed. The optimal mechanical environment for chondrocyte/scaffold complex in vitro maturation culture was determined and in vitro cultured mature artificial cartilage was evaluated for in vivo defect repair. Our research shows that the silk fibroin/collagen type II scaffold has good performance and can meet the special requirements of cartilage repair. 10 % compressive strain is the optimal compressive loading in vitro. Under optimal compression loading in vitro, chondrocytes can proliferate and grow rapidly on the scaffold to achieve better “maturation”. The in vitro cultured chondrocyte/scaffold complex effectively improves the cartilage repair effect after implantation. The compressive elastic modulus of the new tissue reached 0.682 ± 0.010 MPa after 12 weeks of repair (0.714 ± 0.011 MPa for the surrounding host cartilage). Therefore, this study not only enhance the effect of cartilage repair but also provides a promising strategy for mechanical stimulation to promote functional in situ regeneration of articular cartilage.
Path planning is a basic function for autonomous vehicle (AV). However, it is difficult to adapt to different velocities and different types of obstacles including dynamic obstacle and static ...obstacle (such as road boundary) for AV. To solve the problem of path planning under different velocities and different types of obstacles, a two potential fields fused adaptive path planning system (TPFF-APPS) which includes two parts, a potential field fusion controller and an adaptive weight assignment unit, is presented in this work. In the potential field fusion controller, a novel potential velocity field is built by velocity information and fused with a traditional artificial potential field for adapting various velocities. The adaptive weight assignment unit is designed to distribute adaptively the weights of two potential fields for adapting different types of obstacles at the same time, including road boundary and dynamic obstacles. The simulation is carried on the Carsim-Matlab co-simulation platform, and the simulation results indicate that the proposed TPFF-APPS has excellent performance for path planning adapting to different velocities and different types of obstacles.
•A path planning system adapting to various velocities is proposed.•And this system can also adapt to different types of obstacles.•A novel potential velocity field is designed for adapting to various velocities.•The weights of different types of obstacles can be distributed adaptively.
This paper proposes an efficient and robust control scheme for the position-sensorless electric vehicle (EV) with a brushless dc motor. The back electromotive force detection method is first adopted ...and improved to implement sensorless control of the motor. The equivalent circuits of the control system are depicted, and the mathematical models under normal driving and energy regeneration are then derived, respectively. By combining the advantages of nonsingular terminal sliding mode with the high-order sliding-mode method, a hybrid terminal sliding-mode (HTSM) control scheme for EV is put forward to guarantee both system performance and robust stability. Experimental results show that the scheme can perfectly implement position-sensorless control without Hall sensors and that the HTSM exhibits better performance and higher efficiency than the proportional-integral-differential (PID) controller. Furthermore, more energy is recovered, and by the proposed scheme, the driving range is improved 5.7% more than using the traditional controller.
The low power and narrow speed range remain bottlenecks that constrain the application of small-scale wind energy harvesting. This paper proposes a simple, low-cost, and reliable method to address ...these critical issues. A galloping energy harvester with the cooperative mode of vibration and collision (GEH-VC) is presented. A pair of curved boundaries attached with functional materials are introduced, which not only improve the performance of the vibration energy harvesting system, but also convert more mechanical energy into electrical energy during collision. The beam deforms and the piezoelectric energy harvester (PEH) generates electricity during the flow-induced vibration. In addition, the beam contacts and separates from the boundaries, and the triboelectric nanogenerator (TENG) generates electricity during the collision. In order to reduce the influence of the boundaries on the aerodynamic performance and the feasibility of increasing the working area of the TENG, a vertical structure is designed. When the wind speed is high, the curved boundaries maintain a stable amplitude of the vibration system and increase the frequency of the vibration system, thereby avoiding damage to the piezoelectric sheet and improving the electromechanical conversion efficiency, and the TENG works with the PEH to generate electricity. Since the boundaries can protect the PEH at high wind speeds, its stiffness can be designed to be low to start working at low wind speeds. The electromechanical coupling dynamic model is established according to the GEH-VC operating principle and is verified experimentally. The results show that the GEH-VC has a wide range of operating wind speeds, and the average power can be increased by 180% compared with the traditional galloping PEH. The GEH-VC prototype is demonstrated to power a commercial temperature sensor. This study provides a novel perspective on the design of hybrid electromechanical conversion mechanisms, that is, to combine and collaborate based on their respective characteristics.
•A novel autonomous tracking control of intelligent electric vehicles.•Modified Hough transform algorithm used to detect the lane marking.•Tracking error model from detected markings and preview ...steering geometry model.•The optimal preview sliding mode control to improve the tracking performance.
In this paper, a novel autonomous tracking control (ATC) of intelligent electric vehicles (IEVs) based on lane detection and sliding-mode control (SMC) is innovatively developed to implement accurate path tracking and optimal torque distribution between the motors of IEVs. Initially, the road image was captured by the camera and was processed to extract the lane markings and to calculate the desired steering angle by the lateral trajectory tracking error and the head tracking error. Then, to accurately track the desired path, an optimal preview linear quadratic regulator (OP_LQR) based on SMC approach with 2-DOF vehicle model was proposed. To prove the effectiveness of the proposed OP_LQR scheme, the marking recognition analysis and the optimization results of the traditional three controllers are obtained and compared. Results show that the lane marking identification algorithm has high accuracy. Moreover, the actual path with the proposed method can better track the desired trajectory and appropriate differential braking torques are allocated into four wheels.
Shockwave treatment promotes bone healing of nonunion fractures. In this study, we investigated whether this effect could be due to adenosine 5′‐triphosphate (ATP) release‐induced differentiation of ...human mesenchymal stem cells (hMSCs) into osteoprogenitor cells. Cultured bone marrow‐derived hMSCs were subjected to shockwave treatment and ATP release was assessed. Osteogenic differentiation and mineralization of hMSCs were evaluated by examining alkaline phosphatase activity, osteocalcin production, and calcium nodule formation. Expression of P2X7 receptors and c‐fos and c‐jun mRNA was determined with real‐time reverse transcription polymerase chain reaction and Western blotting. P2X7‐siRNA, apyrase, P2 receptor antagonists, and p38 MAPK inhibitors were used to evaluate the roles of ATP release, P2X7 receptors, and p38 MAPK signaling in shockwave‐induced osteogenic hMSCs differentiation. Shockwave treatment released significant amounts (∼7 μM) of ATP from hMSCs. Shockwaves and exogenous ATP induced c‐fos and c‐jun mRNA transcription, p38 MAPK activation, and hMSC differentiation. Removal of ATP with apyrase, targeting of P2X7 receptors with P2X7‐siRNA or selective antagonists, or blockade of p38 MAPK with SB203580 prevented osteogenic differentiation of hMSCs. Our findings indicate that shockwaves release cellular ATP that activates P2X7 receptors and downstream signaling events that caused osteogenic differentiation of hMSCs. We conclude that shockwave therapy promotes bone healing through P2X7 receptor signaling, which contributes to hMSC differentiation. STEM Cells 2013;31:1170–1180
MicroRNA (miRNA) is an endogenous regulatory small molecule RNA. Growing evidence shows that miRNA plays an important regulatory role in gene expression. Although miRNA is a more intensive regulatory ...noncoding RNA in recent years, few studies have investigated the regulation of targeting genes involved in bone repair. Meanwhile, as a negative bone regulator, previous studies showed that casein kinase 2-interacting protein 1 (CKIP-1) is closely associated with bone formation and regeneration. However, the gene knockout method may not be suitable for clinical application. Therefore, it was hypothesized that miRNA molecules can inhibit the expression of CKIP-1 and ultimately promote the osteogenesis process. The present study revealed that let-7i-5p plays an important role in the process of fracture healing by inhibiting the expression of CKIP-1. Related research provides a novel gene target for fracture healing.
Accurate short-term photovoltaic (PV) power forecasting can reduce the un- certainty of PV power generation, which is crucial for grid operation as well as energy dispatch. Considering the influence ...of seasonal and meteorological factors on short-term PV power prediction, a short-term PV power predic- tion method based on meteorological similarity day and sparrow search algo- rithm and bi-directional long and short-term memory network combination (SSA-BiLSTM) is proposed. Firstly, the correlation between meteorological factors and PV power generation is calculated by using Pearson coefficients, getting the strongly correlated meteorological factors affecting PV power generation; afterwards,the historical data of the strongly correlated meteorological factors are clustered by fuzzy C-means clustering to achieve meteorological similar day clustering; then, the best similar day is selected from the meteorological similar day according to the test day seasonal features and meteorological data, and Forming a training set with historical data, and training the original BiLSTM network. the SSA algorithm was used to find the optimal BiLSTM network parameters. Finally, Using the optimal parameters construct BiLSTM network to achieve short-term PV power prediction. The experiments were conducted with historical data from a PV power plant in Xinjiang, and also compared with existing prediction algorithms.The results show that the accuracy of PV power prediction in different weather conditions is 33.1 %, 31.9 % and 24.1 % higher than that under the same intelligent optimization algorithm and different neural networks, the accuracy of PV power prediction in different weather conditions is 27.9 %, 24.7 % and 18.0 % higher than that under the different intelligent algorithms and same neural network. Therefore, the algorithm in this paper has better accuracy in short-term PV power prediction under different seasons and different weather conditions.
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