Search

The real-time transient stability assessment (TSA) is critical for emergency control of power systems. Accurate and fast TSA can provide an important basis for post-fault control of power systems. At present, the accuracy of the evaluation model based on machine learning is very high, but there are still some misjudgements in the results. In order to build a high-accuracy evaluation model, a novel frame based on the cost-sensitive method is proposed. Firstly, a deep belief network (DBN) is applied to build a TSA frame. The DBN is effectively trained by means of pre-training and fine tuning. Secondly, two models with the opposite preference are constructed based on the cost-sensitive method. Based on the output results of the two models, the deterministic or uncertain evaluation results are obtained. The samples that may be misclassified are divided into uncertain evaluation results. Thus, the accuracy of the deterministic evaluation results can be improved greatly. Through this design, the practicability of the evaluation model based on machine learning is greatly improved. The effectiveness of the proposed scheme is verified by the simulation results in the IEEE-39 bus system and a realistic regional system.

With the rapid development of machine learning technology, a new tool is provided for real-time stability evaluation in power systems. The training of a machine learning-based model is inseparable from a large number of training samples. However, compared with stable samples, unstable samples in power systems are infrequent. The results of the model evaluation are biased due to the imbalance of training samples. Faced with such a problem, a framework based on deep imbalanced learning is proposed. Firstly, for each sample, the samples nearby in the opposite class are applied to calculate its space information. Based on the space information of all samples, the spatial distribution characteristics of the training samples are obtained. And then, in order to obtain balanced training samples, unstable samples are generated according to their spatial distribution characteristics. Finally, stacked sparse denoising auto-encoder (SSDAE) based model, which has the ability of anti-noise, is established as the classifier. Simulation results in IEEE 39-bus system show the high performance of the proposed imbalanced correction scheme and evaluation scheme.

The grain boundary in copper-based electrocatalysts has been demonstrated to improve the selectivity of solar-driven electrochemical CO2 reduction toward multicarbon products. However, the approach to form grain boundaries in copper is still limited. This paper describes a controllable grain growth of copper electrodeposition via poly(vinylpyrrolidone) used as an additive. A grain-boundary-rich metallic copper could be obtained to convert CO2 into ethylene and ethanol with a high selectivity of 70% over a wide potential range. In situ attenuated total reflection surface-enhanced infrared absorption spectroscopy unveils that the existence of grain boundaries enhances the adsorption of the key intermediate (*CO) on the copper surface to boost the further CO2 reduction. When coupling with a commercially available Si solar cell, the device achieves a remarkable solar-to-C2-products conversion efficiency of 3.88% at a large current density of 52 mA·cm-2. This low-cost and efficient device is promising for large-scale application of solar-driven CO2 reduction.

Denial of Service (DoS) attack is a serious threat to Software Defined Network (SDN). Although many research efforts have been devoted to identify new features for DoS attack detection, the existing approaches are not able to detect various types of DoS attacks. In SDN, DoS attacks against data plane are mainly organized in two ways: 1) DoS attack with multiple flow entries (M-DoS) to exhaust the Ternary Content-Addressable Memory (TCAM) resource of the switch. 2) DoS attack with a single well-designed entry (S-DoS) to overwhelm the target link and further impact the controller. To detect these two attacks, we propose a new approach by extracting six features of flow table, and using the back propagation (BP) neural network to construct the classifier. Test results of test-bed experiments indicate that the accurate detection probability of proposed approach is 98.9%, which can effectively distinguish M-DoS flows and S-DoS flows without being affected by Flash crowd scene.

Due to the requirement of safety and reliability in power systems, unstable samples in the real system are rarely appeared. The evaluation results of the model trained by these imbalance samples have a certain preference. Generally, the imbalance in quantity is taken into account, while the imbalance in quality is ignored. Faced with such a problem, an imbalanced correction method based on support vector machine (SVM) is proposed. Firstly, the classification hyperplane trained by SVM and the normalized Euclidean distance between each sample and the classification hyperplane are calculated so as to obtain their fault severity. Based on this, training samples can be grouped to multilevel sets. Then, the original stacked sparse auto-encoder (SSAE) are pretrained to quantify the imbalance between two classes of samples in multilevel sets. Subsequently, in order to improve the imbalance of training samples, a cost-sensitive correction matrix is generated according to the imbalanced information of multilevel sets. Finally, the loss function of SSAE is modified by cost-sensitive correction matrix to establish the final classifier. Simulation results in IEEE 39-bus system and the realistic regional power system of Eastern China show the high performance of the proposed imbalanced correction method.

Hepatocellular carcinoma is one of the deadliest neoplasms around the world, and a major proportion of patients are diagnosed in an advanced state not amenable to curative treatment. Lenvatinib, a promising first-line targeted therapy, has shown antitumour activity in both preclinical studies and clinical trials. Emerging evidence indicates that a combination of lenvatinib plus anti-PD-1 inhibitors or locoregional therapies exerts a stronger antitumour effect than monotherapy and even offers the possibility of long-term survival while maintaining acceptable tolerability. Several studies have also shown the superiority of lenvatinib over sorafenib in combination strategies. This review addresses the rationale behind lenvatinib-based combination therapies and comprehensively summarizes various clinical studies investigating lenvatinib in combination with immune checkpoint inhibitors (ICIs), locoregional therapies, and other systemic treatments. We discuss the unsatisfactory search for suitable biomarkers and key ongoing trials in this field.

Improving the heat dissipation efficiency of electronic products is the key to the design of many modern electronic and mechanical systems. Herein, we combined the 3D network fabricating with the way of micron-nano reinforcement to prepare high thermal conductivity and excellent thermal stability composites. Epoxy resin was used as the matrix, while the silicon carbide foam (f-SiC) as skeleton and the BN/nano-SiC as thermally conductive fillers. The thermal conductivity of the EP/f-SiC/BN/nano-SiC composite reaches 3.5 W·m− 1·K− 1, which is about 16.6 times higher than that of pure epoxy resin. The characterization results of TC and infrared thermography images indicate that the EP/f-SiC/BN/nano-SiC composite possess superior heat transport performance. Meantime, the EP/f-SiC/BN/nano-SiC composite have excellent thermal stability, the THRI of EP/f-SiC/BN/nano-SiC reaches 195.8℃, which is 21.3℃ higher than that of pure EP. This work would provide a new strategy for improving the TC of polymers by using other 3D skeletons and micron-nano fillers, and is conducive to the development of high thermal conductivity and excellent thermal stability materials.

Water‐coal interactions have gained much recent attention, although few studies focus on the strength of coal under wetting‐drying cycles. This study investigates changes in the microstructure and mechanical strength of coal that are induced by water‐coal interactions, at the macroscale and microscale. Fourteen specimens after continuous wetting and fourteen specimens after wetting‐drying cycles were tested, indicating that peak stress and elastic modulus decrease with increasing continuous wetting time and number of wetting‐drying cycles, while peak strain increases. We analyzed changes in the coal microstructure using a scanning electron microscope (SEM) and the Image Pro Plus 6.0 (IPP 6.0) software. The regression model for cyclic wetting‐drying reveals that porosity and pore circularity are the main correlation indicators associated with uniaxial compressive strength. Therefore, different numbers of wetting‐drying cycles could induce different degrees of damage to coal, which increases progressively through gradual changes to its microstructure. These findings indicate that wetting‐drying cycles have a more significant impact on the stability of coal mass than continuous wetting. Our results are of use in determining the size of coal pillars, and expanding the knowledge base related to the mechanical properties of coal mass, water bursting, water recharge channels, and the stress‐crack‐permeability evolution law in mines.

Poly(urea–formaldehyde)/SiO2 hybrid microcapsules containing linseed oil are successfully fabricated in a SiO2 nanoparticles stabilized Pickering emulsion system by use of in situ polymerization. T...

Single-stage oil/water separation membranes usually suffer from weak chemical stability, susceptible mechanical damage and relatively low permeating flux, and the sophisticated preparation processes also limit their massive utilization. In this work, Cu(OH)2 nanoneedles coated copper mesh (CM) is prepared by simple and eco-friendly anodic oxidation at a current density of 4 mA/cm2 for 6 min, which is the most efficient route reported so far. The mesh exhibits outstanding superhydrophilicity and underwater superoleophobicity towards various oils with contact angles up to 164.9°, achieving superior oil/water separation efficiency of above 99.5% and ultrahigh permeating flux of 191 160 L·m−2h−1 solely driven by gravity. Impressively, the Cu(OH)2/CM demonstrates excellent chemical stability and anti-fouling performance when exposed to acidic and strongly alkaline solutions, saturated NaCl solution and various organic solvents. High durability to withstand mechanical challenges, e.g. high-power sonication and sand abrasion, is experimentally confirmed owing to strong cohesional strength of Cu(OH)2 nanoneedles on CM surface. Importantly, the Cu(OH)2/CM exhibits favorable long-term recyclability with stable microstructure morphologies even after 50 cycles. These distinct advantages endow the Cu(OH)2/CM to be an ideal candidate to efficiently separate oil pollutants from water. The oil/water separation mechanisms are proposed based on the concept of intrusion pressure.

Anti-corrosion polymer coatings are commonly used for metal to form a barrier against the corrosion medium. However the anti-corrosion performance of many polymer coatings is unavoidably degraded owing to the long-term permeation of corrosion media. Many researches have attempted to inhibit this permeation process and enhance the corrosive protecting performance. In this study, a novel polyethersulfone (PES) superhydrophobic coating with long-term anti-corrosion ability for carbon steel was developed by utilizing reduced potassium titanate whisker (RPTW), nano-SiO2 and 1H,1H,2H,2H-perfluorooctyltriethoxysilane (POTS). Oxygen vacancies were generated on the RPTW owing to the reducing reaction at a low temperature. Then, for the first time, the RPTW was used to passivate the carbon steel substrate in coating by generating and transferring atomic oxygen through oxygen vacancies, providing an additional protection layer to shield the metal substrate against the corrosion medium. Moreover, 6% RPTW and 3% nano-SiO2 formed an excellent superhydrophobic surface with the addition of POTS. The air film captured on the superhydrophobic surface inhibited the diffusion of water and ions. Therefore, in combination with the air film and the dense Fe3O4 passive film generated via a novel method, the PES superhydrophobic coating exhibited a stable impedance two orders of magnitude higher than that of the normal PTW reinforced PES coating.

Superhydrophobic surfaces with special wettability have a promising potential for self-cleaning, anti-fouling, and anti-corrosion applications. However, the practical applications of superhydrophobic coatings are currently limited by their poor mechanical strength and hydrophobic durability. Here, we report a superhydrophobic epoxy (EP) composite coating with improved durability, achieved by a dual interfacial enhancement. First, melt extrusion technology was used to enhance the bonding force between EP and polytetrafluorethylene (PTFE). Then, combining dopamine self-polymerization and sol-gel approaches, the interfacial strength between graphene-polydopamine (GP) and SiO2 was enhanced by in-situ growth of SiO2 on the GP surface. After modification with 1H,1H,2H,2H-perfluorooctyltriethoxysilane (POTS), the superhydrophobic EP-PTFE/GP-SiO2-POTS coating (WCA = 156.3 ± 1.5°, WSA = 3.5 ± 0.5°) was successfully prepared on a steel surface by electrostatic spraying. With the enhanced interfacial strength, the prepared composite coating demonstrated excellent mechanical performance, and could withstand 105 abrasion cycles with only 54.4 mg weight loss. Moreover, due to the induction effect of graphene, a special multilayered nano-micro-nano structure was formed by the evenly distributed nano-SiO2 particles on the coating surface, which is beneficial to extend its superhydrophobic duration. The prepared coating can maintain its superhydrophobicity even after being scratched or immersed in 3.5 wt% NaCl solution for 60 days. Therefore, the prepared superhydrophobic coating demonstrates great potential for application in anti-fouling, drag reduction, and other fields.

In this paper, a versatile low-cost and simple spraying process was reported for fabricating epoxy resin (EP)/fluorinated ethylene propylene (FEP)/modified ZnO (m-ZnO) superhydrophobic coating (EP/FEP/m-ZnO). The ZnO nanoparticles were modified by the low surface-energy material of stearic acid, and the pore-forming agent (NH4HCO3) was used to build micro/nano-structures. Results showed that the composite coating with 32 wt.% of m-ZnO, 5 wt.% of NH4HCO3 exhibits the optimum superhydrophobicity, with water contact angle (WCA) of 160° and sliding angle of 2°. More importantly, the WCA of the as-prepared composite coating still maintains more than 130° under strong acid or 3.5 wt.% NaCl aqueous solution for 270 h immersion, which demonstrates the excellent anti-corrosive performance of EP/FEP/m-ZnO superhydrophobic coating. The WCA of the EP/FEP/m-ZnO coating still kept 136° and only gained weight loss of 1.04% after being rubbed with 300 cycles, and the weight loss of EP/FEP coating is 18.85% under the same condition. All the above aspects are the direct evidences for the highest wear resistance of EP/FEP/m-ZnO superhydrophobic coating. Furthermore, the adhesive ability of the EP/FEP/m-ZnO composite coating was satisfied with the requirements of Grade 1, that standing for strong adhesion between the coating and substrate. Simultaneously, the soil and fly ash could be easily cleaned from the surface of superhydrophobic coating with flowing droplets, that showing unique self-cleaning property. Furthermore, the EP/FEP/m-ZnO superhydrophobic coating has excellent anti-corrosion performance. It is believed that the nano/micro structure formed by the inorganic filler m-ZnO and pore-forming agent of NH4HCO3 plays an important role. The suitable magnitude of pores has a positive meaning on fabricating the EP/FEP/m-ZnO superhydrophobic coating. The multifunctional coating has a high application value in condition of wear resistance, self-cleaning and anticorrosion, this facile and economic method may offer an effective strategy for surface and interface science and even industrial production.

A multifunctional super-hydrophobic polyethersulfone (PES)/1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane (POTS)/MoS2–polydopamine (PDA)–TiO2 coating was fabricated by a simple spraying method that involved two consecutive steps of dopamine (DA) self-polymerization on MoS2 sheet surface and in situ growth of TiO2 nano-particles. The coating possessed super-hydrophobicity with the water contact angle (WCA) of 159 ± 2° and excellent self-cleaning property. Remarkable mechanical stability was obtained with original super-hydrophobicity even after 10,000 abrasion cycles of damage under the load of 50 KPa. It also retained high WCA of 150° after exposure to strong acids (HCl, pH = 1) and bases (NaOH, pH = 14) for at least 30 h. Compared with the uncoated aluminum substrate, the corrosion resistance of the coating was significantly enhanced with lower corrosion current density of 2.7 × 10−9 A/cm2 and higher corrosion potential of −41 mV after immersion in a 3.5 wt% NaCl solution for 15 days. All these results suggest the super-hydrophobic PES/POTS/MoS2–PDA–TiO2 coating exhibits great potential as a functional surface in a wide range of practical applications.

Carbon nanotubes (CNTs), as a carrier of diethylenetriaminepenta(methylphosphonic acid) (DTPMPA), combining with flake zinc and PVDF powders, were used to fabricate a novel organosilicon epoxy resin-based (EP) composite coating (EP/iDCNTs/Zn/PVDF) for antiscaling and anti-corrosion purposes. Compared with EP coating, the EP/iDCNTs/Zn/PVDF composite coating exhibited unique antiscaling properties with the CaCO3 deposition on the coating surface decreased by 81.6%. It was mainly because the coating surface contains DTPMPA, and Zn2+released by corrosion of Zn powder, which jointly inhibited the deposition behavior of CaCO3. Meanwhile, the fabricated composite coating hardly adhered by CaCO3 crystals which was due to its higher hydrophobicity. Moreover, anti-corrosion tests proved that the prepared composite coating's impedance modulus was about 2 orders higher than that of the EP coating. This was ascribed to the improving shielding effect of fillers and high hydrophobicity of coating, preventing the water and oxygen molecules from penetrating into the composite coating.

Ionic liquids (ILs) are promising high-performance lubricants with remarkable lubrication and antiwear capabilities in tribology. In this article, first solid-state (at room temperature) IL-incorpo...

The inertia of the power system changes when the generators in the system are disturbed or tripped. However, in some systems, there is no control center or communication device falling behind. It makes real-time inertia difficult to obtain and affects the adaptive under frequency load shedding (UFLS) scheme. This paper proposes an adaptive decentralized UFLS scheme based on load information to overcome this problem. First, a calculation method is derived according to the load information after the disturbance to identify the real-time of load equivalent virtual inertia. Then, the power deficit of load is estimated and the optimal adaptive load shedding scheme is obtained. Finally, compared with conventional UFLS schemes, the proposed scheme can be performed merely by load information. Hence, the requirement of communication conditions and the dependence on the control center are reduced. The simulation is carried out on the island utilizing the IEEE39-bus system. Furthermore, the accuracy of real-time identification of load equivalent virtual inertia and the validity of the load shedding scheme are verified.

With the increasing capacity of new energy in the power system, new energy cannot provide support for the system frequency directly. This characteristic of new energy affects the frequency stability of the power system. Therefore the control strategy of a virtual synchronous generator (VSG) is proposed to improve the frequency stability of the system. An adaptive virtual inertia control strategy based on an improved bang-bang control strategy for a micro-grid is presented. On one hand, it can make full use of the variability of virtual inertia to reduce dynamic frequency deviation. On the other hand, the steady-state interval of frequency and the steady-state inertia are set to improve the system frequency stability. Then the stability analysis of the value range of the virtual inertia is performed by the small signal model of the VSG for the micro-grid. Meanwhile, the ranges of virtual inertia and steady-state inertia are determined. Finally, Matlab/Simulink is applied to accomplish simulation experiments to compare various virtual inertia control strategies. The results indicate the effectiveness of the proposed strategy.

Polyurethane (PU) microcapsules containing [BMIm]PF6 as a lubricant have been fabricated by interfacial polymerization. The stabilizing effect of 10 kinds of emulsifiers towards [BMIm]PF6 ionic liquid have been delineated. A Pickering emulsion stabilized by lignin showed the best emulsification effect on highly viscous [BMIm]PF6. The types and reactivities of monomers have an important influence on the formation of microcapsules. Three kinds of isocyanate (IPDI, MDI, TDI) were reacted with diamines or diols to prepare the PU microcapsules in this work. The optiaml [BMIm]PF6@PU microcapsules were obtained when using IPDI and TETA as monomers, under conditions of 5,000 rpm emulsifying rate, 0.5 wt% concentration of lignin Pickering emulsion, and a 3:1 mass ratio of [BMIm]PF6/IPDI. The synthesized microcapsules have a regular and compact spherical structure, smooth outer, and inner surfaces with a mean diameter of 43 ± 15 µm, and a thickness of 3.8 µm. The core content of [BMIm]PF6@PU microcapsules was determined as >70%, and the initial decomposition temperature was 300 °C. The [BMIm]PF6 ionic liquid shown excellent lubricating property, ultralow friction coefficient (decreased by 72.7%) and wear rate (decreased by 160 times) were obtained by embedding 30 wt% microcapsules into epoxy compared with pure epoxy.