In this paper, a unique 100kHz sampling and switching frequency shunt active power filter (SAPF), which is based on a dual-core DSP TMS320F28377D, is designed to achieve high control bandwidth for the potential market of wide frequency range harmonic suppression and resonance damping in future more electric aircraft (MEA) or high-speed railway power grid. By rearranging different computation segments, such as analog-to-digital conversion, recursive discrete Fourier transform (RDFT), inner-loop current and outer-loop voltage control, the traditional single pipeline code structure in DSP can be reformed as two parallel running groups. This multitasking strategy provides the proposed SAPF with huge advantages on higher frequency harmonic suppression compared to the mostly commercial SAPF with 10~20kHz switching frequency. Detailed parameter design of LCL filter, DC-side capacitor and deadtime are also presented. A 10kVA prototype utilizing CREE SiC power module CCS050M12CM2 is set up to verify the effectiveness of the proposed SAPF. The results show that the total harmonic distortion can be limited within 5%, which complies with the IEEE power quality standard 519-2014.
Abstract A 3D transformable model can be transformed into different shapes through folding operations to suit different needs, such as a table or a chair in daily life. Furthermore, the features of foldable structure and flat components allow it to be folded into a smaller stack for compact storage when not in use. To this end, this study applies a new foldable modular chain structure and proposes a novel method of constructing 3D models into 3D shapes based on this structure and guiding the transformation between shapes. For the construction of the model, that is, to find a module chain path that constructs the model shape, the divide-and-conquer method is adopted. The model is first divided into multiple units, and then the search for the linearly connected module sub-path is executed for each unit. This involves three major steps: unit-based segmentation of the model, search for the unit tree structure that can form the target 3D shape, and search for the modular chain path based on the unit tree. The experimental cases demonstrate the application of the square modular chain in the fields of furniture and toys and prove the effectiveness of the method in constructing and transforming the foldable chain-type modular configurations of the input 3D models.
The high self-diffusion barrier of lithium inevitably triggers catastrophic lithium dendrites, creating a safety hazard and hindering the practical application of lithium metal batteries. Experimental studies have observed thermal self-healing of lithium dendrites, but numerical simulations often ignore lithium-atom diffusion, which is detrimental to elucidating the mechanism of thermally induced dendrite self-healing. We develop a phase-field model with atom diffusion and heat transfer modules to investigate the role of atom diffusion in dendrite growth and thermally induced dendrite self-healing. The results show that atom diffusion can induce surface self-healing (weakening the protrusions) and bulk self-healing (dissipating the voids) and optimize the dendritic profile; thus, it should be incorporated. The atom diffusion accelerated by high temperature exhibits strong healing-dendrite properties and achieves the thermal self-healing of dendrites. Moreover, our model precisely predicts the threshold temperature of 55 °C above which the dendrites achieve thermal self-healing, consistent with the experimental observations. This work deeply describes the thermal self-healing mechanism of lithium dendrites, which provides potential strategies for managing temperature and effectively suppressing dendrite growth in lithium batteries.
Microblogs are considered as We-Media information with many real-time opinions.This paper presents a Twitter-OpinMiner system for Twitter sentiment analysis evaluation at SemEval 2015.Our approach stems from two different angles: topic detection for discovering the sentiment distribution on different topics and sentiment analysis based on a variety of features.Moreover, we also implemented intra-sentence discourse relations for polarity identification.We divided the discourse relations into 4 predefined categories, including continuation, contrast, condition, and cause.These relations could facilitate us to eliminate polarity ambiguities in compound sentences where both positive and negative sentiments are appearing.Based on the SemEval 2014 and SemEval 2015 Twitter sentiment analysis task datasets, the experimental results show that the performance of Twitter-OpinMiner could effectively recognize opinionated messages and identify the polarities.
Single nanowires (NWs) are of great importance for various optoelectronic applications, especially solar cells serving as powering nanoscale devices. However, weak off-resonant absorption can limit its light-harvesting capability. Here, we propose a single NW coated with the graded-index dual shells (DSNW). We demonstrate that with the proper thickness and refractive index of the inner shell, the DSNW exhibits significantly enhanced light trapping compared with the bare NW (BNW), and the NW only coated with the outer shell (OSNW) and inner shell (ISNW), which can be attributed to the optimal off-resonant absorption mode profiles due to the improved coupling between the reemitted light of the leak mode resonances of the Si core and the nanofocusing light from the dual shells with the graded refractive index. We found that the light absorption can be adjusted via tuning the thickness and refractive index of the inner shell, the photocurrent density is significantly enhanced by 134% (56%, 12%) in comparison with that of the BNW (OSNW, ISNW). This work advances our understanding of how to improve off-resonant absorption by applying graded dual shells and provides a new choice for designing high-efficiency single NW photovoltaic devices.
Cooperative driving at signal-free intersections, which aims to improve driving safety and efficiency for connected and automated vehicles, has attracted increasing interest in recent years. However, existing cooperative driving strategies either suffer from computational complexity or cannot guarantee global optimality. To fill this research gap, this paper proposes an optimal and computationally efficient cooperative driving strategy with the polynomial-time complexity. By modeling the conflict relations among the vehicles, the solution space of the cooperative driving problem is completely represented by a newly designed small-size state space. Then, based on dynamic programming, the globally optimal solution can be searched inside the state space efficiently. It is proved that the proposed strategy can reduce the time complexity of computation from exponential to a small-degree polynomial. Simulation results further demonstrate that the proposed strategy can obtain the globally optimal solution within a limited computation time under various traffic demand settings.
Series and parallel resonance tend to occur and cause harmonic distortion when the distribution system contains a shunt power capacitor to compensate inductive load and dynamic capacitor (D-CAP) to suppress harmonics. This study focuses on the series and parallel resonance active damping of three-phase buck-type D-CAP, so as to achieve better power quality control. Two virtual resistor damping methods for series resonance, D-CAP power capacitor voltage or D-CAP front-end buffer inductor current feedback, are introduced and compared. Then, parallel resonance is damped by generating certain harmonic currents in the phase with the selective harmonic voltage at the point of common coupling (PCC), equivalent to controlling the D-CAP as a virtual harmonic resistor. In addition, the power balance of D-CAP is interpreted to ensure no additional energy control loop is needed for the active damping. To further improve the parallel resonance damping, the self-adjusted damping gain is proposed by the closed-loop regulation of harmonics in PCC voltage. Finally, coordinated control between reactive and multiple harmonic currents is introduced for the whole combined control to avoid over-modulation. A wide variety of experimental results from a 33 kVar/220 V laboratory prototype are provided to demonstrate the validity of the combined control.
Rubik's Snake is an intellectual toy with a high degree of freedom, which can be changed and combined freely. This paper proposes a method for constructing and deforming 3D models, which can construct the 3D model into a Rubik's Snake configuration and realize the mutual deformation between different configurations with a straight chain as the intermediate state through standard folding steps. A detailed representation of the voxels of the 3D model is presented. Based on the refined voxels, a connection forest generation algorithm is developed, which is able to describe possible Rubik's Snake configurations. The foldability verification of the configuration and the generation of the folding sequence are realized by the folding rules. In addition, a collision detection algorithm based on encoding and projection is introduced to detect collisions in the process of generating folding sequences. In order to achieve mutual deformation between 3D models, the number of modules in their chain configuration is matched and adjusted. In this paper, an interactive platform is established, which enables users to calculate the deformation of the input model through simple operations, and obtain a simulation animation of the folding operations that can guide the deformation. The experimental cases prove the effectiveness of the method of constructing and deforming the Rubik's Snake configurations of the input 3D models.
To ensure structural sustainability, it is necessary to conduct steel bridge long-term performance study, including bridge design, evaluation, maintenance, and reinforcement technology. The research on steel bridge long-term performance is introduced in four aspects: (1) fatigue performance experimental study for full-scale orthotropic steel bridge decks in laboratory to study its fatigue failure mechanism, in order to improve fatigue design methodology and find rational reinforcement and maintenance method; (2) conducting steel bridge out-of-plane distortion-induced fatigue performance study, and developing cold reinforcement method; (3) performance study for base material and typical joint under long-term vehicle and environmental effect in aging steel bridges, and safety assessment and maintenance of existing steel bridge; (4) temperature gradient monitoring for steel box girder model to build the temperature design mode. Meantime, in-situ tests and monitoring are conducted for steel bridge long-term performance detection, assessment, and maintenance. The study results in this article build the research framework of steel bridge long-term performance preliminarily, which is the basis for steel bridge sustainable design, maintenance, and cold reinforcement methodology system.
Abstract The trusted sharing of Electronic Health Records (EHR) can realize the effiffifficient use of medical data resources. Generally speaking, EHR are stored inside the hospital, but their ownership is the patient, So every patient has the right to delete their own EHR stored in the hospital. However, after the deletion, it is diffiffifficult for the patient to have a record to share when he visits the hospital again. To solve this problem, we use the Medical Certifificate Blockchain and InterPlanetary File System (IPFS) to store Personal Health Records, which are generated by patients in difffferent medical institutions. We use cross-chain technology to interconnect the Medical Certifificate Blockchain and the Hospital blockchain to enable the recovery of deleted Electronic Health Record. In addition, We also combine digital watermarking technology to ensure the authenticity of the restored Electronic Health Record. System analysis and security analysis illustrate the completeness and feasibility of the scheme.
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