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In this paper, we report in situ preparation of nickel hydroxide nanoflake array on carbon cloth (Ni(OH)2 NA/CC) by a rapid and simple microplasma method. Using this technique, Ni(OH)2 nanoflake can be prepared on carbon cloth in only 1.5 h at atmospheric pressure and ambient temperature. As an electrode with highly efficient catalytic and non-enzymatic sensor for detecting glucose, such a Ni(OH)2 NA/CC electrode showed excellent electrocatalytic activity with a short response time within 5 s, low detection limit (LOD) of 62 nM (S/N=3), and response sensitivity of 2216.2 mA mM−1 cm−2, meanwhile a satisfactory reproducibility and selectivity.

Antifreeze (glyco)proteins (AF(G)Ps) are naturally evolved ice inhibitors incomparable to any man-made materials, thus, they are gaining intensive interest for cryopreservation and beyond. AF(G)Ps depress the freezing temperature (Tf) noncolligatively below the melting temperature (Tm), generating a thermal hysteresis (TH) gap, within which the ice growth is arrested. However, the ice crystals have been reported to undergo a retaliatory and explosive growth beyond the TH gap, which is lethal to living organisms. Although intensive research has been carried to inhibit such an explosive ice growth, no satisfactory strategy has been discovered until now. Here, we report that crowded solutions mimicking an extracellular matrix (ECM), in which AF(G)Ps are located, can completely inhibit the explosive ice growth. The crowded solutions are the condensates of liquid-liquid phase separation consisting of polyethylene glycol (PEG) and sodium citrate (SC), which possess a nanoscale network and strong hydrogen bond (HB) forming ability, completely different to crowded solutions made of single components, that is, PEG or SC. Due to these unique features, the dynamics of the water is significantly slowed down, and the energy needed for breaking the HB between water molecules is distinctly increased; consequently, ice growth is inhibited as the rate of water molecules joining the ice is substantially reduced. The present work not only opens a new avenue for cryopreservation, but also suggests that the ECM of cold-hardy organisms, which also exhibit great water confining properties, may have a positive effect in protecting the living organisms from freezing damage.

In the past, most of the transient electromagnetic (EM) analyses focused on the scattering from the target. The transient scattering from rough surface was rarely studied, especially for the layered rough surface. When the target is above the rough surface, it needs to solve the composite transient scattering from the rough surface and the target above it. In this article, we mainly focus on the time-domain (TD) analysis for transient scattering from the target and layered rough surface based on time-domain ray tracing (TDRT) modeling. Applying geometrical optics (GO), the multiple bounces of the transient EM waves between layered rough surfaces and target are traced to obtain the incident field of the irradiated surfaces. Then considering the particularity of the layered rough surface, we modify TD Gordon integral and reduce the TD physical optics (TDPO) integral to closed-form expressions to improve the computing efficiency. To demonstrate the efficiency and accuracy of the proposed algorithm, the transient scattering simulations of the composite model involving target and layered rough surface are compared with frequency-domain ray tracing (FDRT) with inverse fast Fourier transform (IFFT), as well as the results obtained by the multilevel fast multipole algorithm (MLFMA) of FEKO in conjunction with IFFT (IFFT-MLFMA). The characteristics of transient scattering from the composite model are further studied to show the physical phenomenon of scattering mechanisms. Specifically, the transient scattering from the composite model for different parameters is simulated for sensitivity investigation of the transient scattering to the variations in the related parameters.

The utilization of demand response flexibility has become a significant method to cope with the intermittence of renewable energy sources in distributed systems. This paper proposed a new pricing method for demand response resources managed by a distribution system aggregator, which is deduced from analyzing the operating revenue within the timescale from hours to years. In the proposed model, the hourly decision-making of an aggregator is formulated as a newsvendor model and uncertainties in the long-term decisions are modelled by a backward valuation process. It maximizes the benefit of an aggregator by considering the price and quantity uncertainties of distributed load/generation in day-ahead and real-time wholesale electricity markets. Meanwhile, the coexistence of controllable and uncontrollable loads is also considered, where the former refers to electricity consumption from end-users who are equipped with smart devices for energy management, and the latter load demand of passive end-users who have no willingness or capability to participate in the demand response schemes. Finally, numerical studies are carried out to demonstrate the feasibility and effectiveness of the developed model and methods, and the impacts of active end-user percentage on the aggregator operation under the proposed pricing method are also compared and illustrated.

Replacing expensive IGBT with thyristor to design dc circuit breaker (dcCB) is attracting attention recently due to its advantages in terms of low investment and low conduction loss. However, due to the half-controlled characteristic of thyristor, the existing thyristor-based dcCBs (T-CBs) cannot be actively turned off . As a result, the opening process is not fully controllable and reliable. In this letter, a simple active T-CB (AT-CB) topology is proposed. The proposed AT-CB can interrupt both fault current and operation current actively, and the current breaking process is fast, reliable, and fully controllable. Moreover, the proposed AT-CB can be improved to be bidirectional without increasing the conduction loss, and the topology remains simple. Parameters design principle and operation process of AT-CB are presented. Scaled-down experiment verified the effectiveness of the proposed solution.

In electric motorcycles and light electric cars, permanent magnetic synchronous motor (PMSM) of outer-rotor type are preferred, due to its concise structure and flexible control. Since the body mass and road impact causes vertical eccentricity on shaft bearings, vibration and noise take place during vehicle cruising along with a torque and speed ripple. The torque ripples contain significant features closely related to eccentricity, and those special components can be compensated by an injection current with proper frequency, phase and amplitude. In this paper, a novel control method is used to regulate the injection current to restrain torque ripples. By coarse turning with quadratic spline curve fitting and fine turning with successive approximation, the method can response sudden disturbance and drive the specific torque ripple to minimum in a very short time, so that the performance on ride comfort and handling stability of the vehicle could be improved. Experimental tests show that the method performs favorably with rapid convergence and validity.

This paper proposed a method for exact selecting the optimal filter length of minimal entropy deconvolution (MED) to solve it recovering a single random pulse when the filter length is not improper. The energy ratio of autocorrelation between the filtered signal and the residual signal is adopted to measure the salience of periodic impulses. Then this index is used as an objective function of genetic algorithms (GA) to form an adaptive optimal selection method of filter length. The proposed method is verified by two different rolling bearing fault experiments. The results show that the proposed method reveals the periodic impulses successfully from the casing signals. Compared with other MED-based methods, the proposed method has better performance in detecting the weak fault signal.

Sudden increases in the dc-link voltage, caused by ac grid side voltage drops, can lead to potential damage in the equipment. Therefore, dc choppers are widely used in offshore wind power links to absorb the excess energy and keep the voltage within safe margins. This article investigates the existing chopper topologies and summarizes their advantages and disadvantages. On this basis, a novel dc chopper topology with both centralized and distributed resistances is proposed. It is a combination of two mainstream chopper topologies and gives the flexibility to tradeoff among the pros and cons of them. In this way, the proposed topology achieves great electromagnetic interference performance, precise power control, and very small system disturbance. In addition, the maximum power dissipation of the distributed resistance is reduced by 75%. The switching frequency and the loss of insulated gate bipolar transistors (IGBTs) are also decreased. Finally, the claimed attributes of the proposed topology are verified by test and simulation.

The in-wheel electric vehicle with distributed drive units has better stability and flexibility than traditional centralized drives, but may encounter a higher failure rate due to additional actuators and sensors, especially that the faults of the wheel-side position sensor make motor torque out of control. To overcome this problem, a fault-tolerant control strategy with a multi-states switching method is proposed. The strategy judges the sensor failure by verifying redundant speed information, realizes sensorless control schemes by flux-observer based algorithm in high-speed range and I-F control algorithm in low-speed range with low acoustic noise, and applies adaptive transition process between different control schemes. To pursuit high stability, the signal-to-noise analysis for fault judgment due to sensorless estimation accuracy is discussed. Meanwhile, the principle of I-F resonant oscillations during the transition process is initially deduced in detail, and the conclusion of stability condition is obtained. Finally, the influence of system parameters on resonance performance is analyzed by simulation, and the effectiveness and reliability of the proposed strategy for the risk-controlling process are verified by experiments.

SCR-based solid-state dc circuit breaker (SCR-DCCB) topologies have been widely studied for replacing the traditional expensive insulated-gate bipolar transistor (IGBT) based DCCB. Yet, the existing SCR-DCCB cannot be actively turned- off since SCR is a half-controlled device. In this letter, an active Z-source DCCB (AZ-DCCB) is proposed by the combination of IGBT and SCR. The proposed AZ-DCCB has advantages of simple and compact topology, economical design, low conduction losses, and active and bidirectional current breaking capacity. The operation process of the proposed AZ-DCCB is discussed in detail, and the designing principle of circuit parameters is also presented. Experimental results verified the effectiveness of the proposed AZ-DCCB.

In some cases, because of the complex internal structure of the machines, the positions of the vibration sensors are far away from the rolling bearings, such as in an aeroengine, causing the fault features to become extremely weak, which brings great challenge to the detection of rolling bearings. To address this problem, an integrated detection method is proposed. First, a method named MEDL is proposed to determine the optimal filter length in minimum entropy deconvolution (MED) to enhance the periodic fault impulse component in the weak signal, which accuracy is 1. After that, the MEDL is combined with variational mode decomposition (VMD) and autocorrelation to extract fault features from strong background noise. A series of fault simulation experiments for rolling bearings were conducted by using an aeroengine rotor experimental rig with casing. The results verify that the accuracy of the integrated detection method is 100 % in different measuring points, speeds and fault types. At the same time, it compared with spectral kurtosis (SK) and empirical wavelet transform (EWT). It proves that the integrated detection method is more robust in extracting the weak fault characteristic of rolling bearings from the casing signals effectively.

Smart home scheduling, facilitated by advanced metering, monitoring, and manipulation technology, plays an important role in the energy transition in terms of accommodating intermittent renewable energy and improving energy consumption efficiency. The key functionalities of home energy scheduling are usually implemented by leveraging the flexibility of household appliances, such as thermostatically controlled loads (TCLs) and energy storage units, to improve the peak-to-average ratio for utilities and reduce energy bills for customers. However, the consumption patterns of appliances are greatly influenced by a variety of factors, including real-time tariffs, ambient temperature profiles, indoor activities, and solar irradiance. Hence, smart home energy scheduling is a challenging task because most of these impacting factors are stochastic and difficult to predict. To properly model and manage the uncertainty factors associated with smart home appliance scheduling, an economic model predictive control (MPC)-based bilevel smart scheduling scheme is proposed in this paper. The comprehensive modeling of distributed generation and household appliances is performed at the single-household level. The home energy scheduling problem is formulated on two levels, with the upper level emphasizing the economic impact and the lower level focusing on capturing TCL responses. The correlations among different TCLs and their performance under the influence of various uncertainty factors, such as environmental impacts and user behaviors, are considered. The efficiency of the proposed MPC-based bilevel optimization model and the effectiveness of the home energy scheduling strategy in managing uncertainties are validated and illustrated in numerical studies.

Memtransistor, a hybrid structure that integrates the function of memristor and transistor, is a promising device prototype for the realization of complex neuromorphic learning owing to its diverse functionality and additional flexibility in emulating synaptic behaviors. Memtransistor of two-dimensional (2D) chalcogenide materials have received many interests as it has distinctive memristive mechanism quite different from conventional oxide memristors. Here, we report a memtransistor based on the two-dimensional thin films (2DTFs) of non-layered β-In2S3. The In2S3 2DTFs grown by physical vapor deposition method have microscopically visible grain boundaries (GBs) formed by the stacking and interconnecting of 2D In2S3 flakes. The memtransistors of In2S3 2DTFs show tunable bipolar resistive states with resistance ratio up to 105, endurance over 200 cycles, and a retention time of 104 s. Illumination of laser light from visible and near-infrared are able to induce intermediate resistance states in memtransistors, enabling optical-modulated multilevel memory storage. Also, the memtransistors are able to emulate the synaptic function of long-term potentiation (LTP) and long-term depression (LTD) with tunable synaptic weight in response to presynaptic stimuli of drain/gate pulses. Interestingly, the plasticity of LTP and LTD behavior can be switched in a highly tunable manner by simply varying the gate voltages. The diverse optoelectronic properties and controllable functionality of memtransistors based on the emerging 2D In2S3 offer a useful guide to potential application in electronic memory and artificial synapses.

The precise information of initial rotor position is very important to high performance Interior Permanent Magnet Synchronous Machine (IPMSM) adopting incremental encoder, which can normally be obtained by the high-frequency (HF) rotating or pulsating voltage injection methods. However, the demodulation procedure may confront with the challenge of constrained stability and limited accuracy. For improving estimation accuracy, an improved impulse injection method with merits of simple and fast is proposed. It is carried out by generating a series of phase-axial injections to calculate the probable rotor position, then injecting two reciprocal voltage pulses to obtain the rotor polarity, and finally injecting iterative voltage vectors to obtain the real position rapidly. During the estimation process, the filters to extract the high frequency current signals are not needed. The method effectiveness is validated by the measured results of IPMSM test platform. In the same time, its application limitation is deduced by comparison with the measured results between IPMSM and surface-mounted PMSM (SPMSM). It is shown that the estimation algorithm is compatible with motor parameter differences and can reduce the influence of inductance saturation and nonlinear voltage error. Therefore, the proposed method not only improves the accuracy and robustness of the PMSM sensorless startup control, but also ensures the fast response.

Although materials for ice recrystallization inhibition (IRI) are essential for the cryopreservation of cells and tissues, there exists no guiding mechanism for the design of such materials. Therefore, the construction of materials for IRI relies on the try-and-error strategy. Herein, through changing the tacticity of hydroxyl groups on poly(vinyl alcohol) (PVA) backbones with the affinities of PVAs to ice unchanged, we experimentally find IRI activity decreases significantly for isotactic PVA in comparison to that of atactic PVA. Molecular dynamics simulation shows atactic PVA spreads fully at the ice-water interface due to its much stronger interaction with water. This indicates atactic PVA can cover more ice surface and possess a higher IRI activity when the same amount of PVAs are used, which is consistent with the results that PVA can cover the same amount of ice surface more efficiently through experimentally measuring the adsorption of PVAs on the ice surface. A guiding mechanism of high active IRI materials can be obtained: only having affinity to ice is not enough to obtain high IRI activity ( i.e ., only small amount of materials is required to reduce the size of ice crystals to ca. (35± 10) μm), IRI agents must also have high affinity to water, i.e. , low interfacial energies, to both ice and water. The former is to guarantee the adsorption of the IRI agent on the ice surface, and the latter is required for the IRI agent to spread sufficiently at the ice-water interface. Therefore, each IRI molecule can effectively block the diffusion of water onto the ice surface, and consequently inhibits the growth of ice. A spreading coefficient of IRI agents is therefore introduced to quantitatively assess the capability of IRI agents to spread at the ice-water interface.

A dc–ac converter for voltage-source converter (VSC)-HVdc technology has a significant influence on the performance of the entire power transmission system. This paper introduces a new dc–ac converter composed of submodules and series insulated-gate bipolar transistor (IGBT) switches. The basic idea of this hybrid solution is to shape the ac voltage by submodules but, per half cycle, reconnect them to different electrical points by IGBT switches. This concept can help to reduce the quantities of submodules, thereby reducing the energy storage requirement significantly. Another advantage is that the IGBT switches can be soft switched by utilizing the high controllability of the submodules. This brings extra benefit of power losses reduction. In this paper, the operating principle of this hybrid converter is explained. Its performances are also presented in detail and compared with those popular VSC dc–ac converters. The feasibility of the new concept is also verified by simulation and experimental results.

Increasing deployment of distributed energy resources (DERs) is re-sculpturing the modern power systems in recent years. Future smart power distribution systems should be competent at accommodating extensive integration of DERs and managing the associated uncertainties at the distribution level. The electricity market has been proved to be an efficient way to employ market signals to direct behaviors of users and DERs with large capacity and homogeneous pattern. However, existing market frameworks cannot effectively handle a large number of small-scale DERs due to their diverse characteristics and arbitrary behavior patterns. In this context, an aggregated model which can represent and manage a diverse collection of DER, load, and storage is proposed. An additional trading platform, namely the energy sharing market, is established to reinforce the coordination and collaboration among various aggregators as well as operators. Energy sharing scheme is applied and a corresponding dynamic dispatch platform is designed to solve the crowdsource problem. The efficiency of the proposed model is validated by the numerical studies, and the market performance and impacts of energy sharing on the power systems are illustrated.

The benzene series is one type of volatile organic compounds (VOCs) which causes significant health and environmental issues. Adsorption is an energy-efficient technique for VOC treatment. With a combination of strong π–π interaction with the benzene series, large specific surface area (SSA), tunable nanostructure hierarchy and favourable hydrophobicity, three-dimensional porous graphene materials are potentially favorable for high adsorption capacity, low-energy regeneration and good resistance to high humidity. In this work, few-layered mesoporous graphene (FLMG) with a large SSA (1990 m2 g−1) is constructed by chemical vapor deposition on porous magnesium oxide templates. The as-prepared mesoporous graphene presents a high adsorption capacity (260.0 mg g−1) for toluene at low toluene concentration (∼120 ppm) and a high desorption ratio of 92% for regeneration even at mild heating conditions of 95 °C. Additionally, FLMG preserves 80.1% of the initial adsorption capacity even under high humidity (78%). The good adsorption performance of FLMG is due to its high SSA and high mesoporosity, which render a stronger adsorption ability, a larger adsorption accommodation and a more facile desorption behaviour. This work illustrates the further development of advanced graphene materials for enhanced VOC treatment and other environmental applications.

Prediction over heterogeneous data attracts much attention in urban computing. Recently, satellite imagery provides a new chance for urban perception but raises the problem of how to fuse visual and non-visual features. So far, the practice is to concatenate the multimodal features into a vector, which may suppress important features. Therefore, we propose a new ensemble learning framework: (1) An estimator is developed for each predictor to score its confidence, which is input adaptive. (2) By applying the output of each predictor to the input of the corresponding estimator as feedback, the estimator learns the performance of the predictor in the input-output space. When a new input is applied to produce a prediction, the similar situations will be recalled by the estimator to score the confidence of the prediction. (3) Using end-to-end training, the estimator learns the weights automatically to minimize the total loss of the neural networks. With the proposed method, data mining based urban computing and computer vision rendered urban perception can be bridged at the task of commercial activeness prediction, where the prediction based on satellite images and social context data are fused to yield better prediction than those based on single view data in the experiments.

It is vital of practical engineering significance to connect the isolated station into the DC grid smoothly without affecting other stations or triggering protective systems. To this end, an active charging method with damping control of the isolated station is proposed and will be used in a 500 kV-level DC grid in China. First, the analytical expression of starting current is calculated. The key factors influencing the starting current are analysed to provide theoretic evidence for simplifying the calculation model. Second, the selecting expression of start-up resistor is derived by simplifying the main circuit parameters, DC line parameters, control processes and so on. Third, the principle of active charging method is clarified, the selecting principle of decreasing slope and parameters of damping controller are presented, and the required time of charging process is calculated. This method does not need the start-up resistor any more but still ensure no oscillation and impulse during the active charging process. Meanwhile, it is also faster than the traditional method with a better economy. Finally, electromagnetic transient simulation models are built to verify the correctness of the resistor selecting expression and the effectiveness of the active charging strategy with damping control.

In this work, inorganic tin-doped perovskite quantum dots (PQDs) are incorporated into carbon-based perovskite solar cells (PSCs) to improve their photovoltaic performance. On the one hand, by controlling the content of Sn2+ doping, the energy level of the tin-doped PQDs can be adjusted, to realize optimized band alignment and enhanced separation of photogenerated electron–hole pairs. On the other hand, the incorporation of tin-doped PQDs provided with a relatively high acceptor concentration due to the self-p-type doping effect is able to reduce the width of the depletion region near the back surface of the perovskite, thereby enhancing the hole extraction. Particularly, after the addition of CsSn0.2Pb0.8I3 quantum dots (QDs), improvement of the power conversion efficiency (PCE) from 12.80 to 14.22% can be obtained, in comparison with the pristine device. Moreover, the experimental results are analyzed through the simulation of the one-dimensional perovskite/tin-doped PQDs heterojunction.

Because of the special low-dimensional physical properties of quantum dots (QDs) and the excellent optoelectronic properties of perovskite, the combination of perovskite solar cells (PSCs) and QDs may largely be one of the breakthroughs in device performance. However, little attention has been paid to the effect of the size of QDs on device performance except for bandgap tuning. In this work, non-toxic SnS QDs of different sizes were prepared by varying the reaction temperature of the thermal injection method. Their optical bandgaps with sizes were investigated, and they were implanted into the active layers of the carbon-based PSCs without hole transport layer. The effects of implanting SnS QDs with different sizes on the perovskite film quality and PSCs performance were studied. The cells implanted with SnS QDs of the best size (average 6.9 nm) achieved a photoelectric conversion efficiency of 14.26%, reaching a 12.42% improvement. The improved performance was mainly attributed to the presence of SnS QDs, which provided more nucleation sites for the growth of perovskite grains, and contributed to better quality perovskite films (including higher crystallinity, increased grain numbers and fewer surface defects), thus improving the light utilization, accelerating carrier transfer and reducing carrier recombination in the active layers. The successful implantation of QDs with different sizes in this paper has facilitated the development of the combination of perovskite and QDs in mesoporous PSC.

In this work, the groove depth of the vertical GaN trench MOSFETs have been investigated by TCAD simulation. The groove depth is found to have a crucial influence on the specific on-resistance and breakdown voltage. A deep enough groove is required to annihilate the build-in barrier between the p-body and the n-drift region close to the sidewall of the groove, in order to reduce the specific on-resistance. On the other hand, an increased groove depth will also cause electrical field peak and hence degrade the breakdown voltage. Therefore, there is a trade-off between the specific on-resistance and breakdown voltage, and optimization is required. This study has provided a quantitative analysis on the optimization scheme.

Partial fingerprint verification is a challenging task because of the few features contained in small area as well as the large rotation angle and translation between query images and template images. In this paper, we propose a new framework of partial fingerprint verification based on spatial transformer networks (STN) model, where a transform model, i.e., AlignNet network, is proposed to estimate the alignment parameters, and the verification is modeled as a binary classification task. The experimental results on the simulated datasets created from FVC2004 and the real-world dataset FVC2006 DB1 show that our method is invariant to rotation, and also robust to different kinds of scanners, and dramatically outperforms the rank-1 entry of FVC2006 participants. The EER on FVC2006 DB1 of the proposed algorithm is 3.587% compared to that of 5.564%, the best of FVC2006 DB1 entries.

In this paper, we propose a distributed source coding algorithm based on sampling for source symbols, which is implemented by arithmetic coding and context modeling. We propose an improved posterior probability calculation method for this algorithm. The proposed algorithm has the same or better performance than the original distributed arithmetic coding when coding a practical source sequence obtained from a binary image.

It is a challenging task to resist adversarial attacks due to the imperceptibility of adversarial examples. The passive defense method is developed based on a series of input transformations and has achieved a promising result, which however suffers from a high computation cost. In this paper, we design a new heatmap-aware method to defend adversarial attacks, leading to a significant decrease in the time cost. To be specific, we compute the classification importance from each part of the input to obtain the heatmap of the data, and the key areas of classification are extracted according to the heatmap. A series of transformations are applied to the key areas of the classification, which reduces the amount of data to be processed and thus reduces the time cost. A set of preliminary experiments are conducted to testify the effectiveness of the proposed approach.

The accretion of frost on heat exchanging surfaces through the freezing of condensed water in cold and humid environments significantly reduces the operating efficiency of air-source heat pumps, refrigerators and other cryogenic equipment. The construction of hierarchical micro-nanostructured SHSs, with the ability to timely remove condensed water before freezing via self-propelled droplet jumping, serves as a promising anti-frosting strategy. However, the actual relationship between microstructural features and water removal capability through droplet jumping is still not clear, hindering the further optimization of anti-frosting SHSs. Herein, a series of aluminum SHSs with different micro-cone arrays is designed and fabricated via ultrafast laser processing and chemical etching. The effect of microstructural features on water removal capability is elucidated by statistically analyzing the condensation process. As compared to nanostructured SHSs with the micro-cone size ranging from 10 to 40 μm, the water removal through droplet jumping is remarkably enhanced from 3.42 g m-2 to as much as 13.91 g m-2 over 10 minutes of condensation experiments due to the effective transition of condensed microdroplets from the initial high-adhesion partial wetting (PW) state to low-adhesion Cassie state, leading to significantly reduced water accumulation and improved anti-frosting performance. However, a further increase in the micro-cone size decreased the water removal amount due to greater droplet adhesion to the surface, which results in higher chances for immobile coalescence and the formation of large droplets. Herein, by rationally tuning the size scale of the structured micro-cones, the optimal SHSs display the least water accumulation and render excellent frosting delay of over 90 minutes under simulated harsh operating conditions.

Condensation freezing inhibition is of great practical importance for anti-icing applications; however, no coatings with this performance have been reported. Here, we report the inhibition of condensation freezing on patterned polyelectrolyte coatings, including polyelectrolyte brush (PB), polyelectrolyte multilayer (PEM), and polyelectrolyte hydrogel (PH) surfaces, benefiting from their feature in regulating ice nucleation and propagation via changing counterions. On the reported surfaces, ice nucleation can be initiated exclusively at the domains with the polyelectrolytes; moreover, spontaneous ice propagation can be achieved atop the patterned polyelectrolyte surface. Consequently, condensed water surrounding the frozen drops on the patterned polyelectrolyte surface evaporates due to the instantaneously released latent heat in the course of ice propagation. Afterward, ice grows specifically on polyelectrolyte surfaces via desublimation as the saturated vapor pressure of ice is smaller than that of condensed water drops. As such, an ice-free region up to 96% of the entire surface area can be accomplished. We demonstrate that various polyelectrolyte coatings can be easily introduced on almost all surfaces, revealing great promise for anti-icing applications.

Preventing condensation frosting is crucial for air conditioning units, refrigeration systems, and other cryogenic equipment. Coalescence-induced self-propelled jumping of condensed microdroplets on superhydrophobic surfaces serves as a favorable strategy against condensation frosting. In previous reports, efforts were dedicated to enhance the efficiency of self-propelled jumping by constructing appropriate surface structures on superhydrophobic surfaces. However, the incorporation of surface structures results in larger area available for condensation to occur, leading to an increase in total amount of condensed water on the surface and partially counteracts the effect of promoted jumping on removing condensed water from the surface. In this paper, we focus on the competing effects between condensing and self-propelled jumping on promoting and preventing water accumulation, respectively. A series of micro- and nanostructured superhydrophobic surfaces are designed and prepared. The condensation process and self-propelled jumping behavior of microdroplets on the surfaces are investigated. Thousands of jumping events are statistically analyzed to acquire a comprehensive understanding of antifrosting potential of superhydrophobic surfaces with self-propelled jumping of condensed microdroplets. Further frosting experiments shows that the surface with the lowest amount of accumulated water exhibits the best antifrosting performance, which validates our design strategy. This work offers new insights into the rational design and fabrication of antifrosting materials.

The determination and optimization of the rated capacitance of a capacitor voltage transformer (CVT) is very valuable for the optimal design of a CVT since it is a fundamental parameter for solving many problems such as minimizing the effect of stray capacitance (SC), ensuring a high accuracy of voltage measurement, and fast transient response. SC is known to seriously affect the capacitance of an ultra-high-voltage (UHV) CVT resulting in a larger additional measurement error and a higher false operation rate of relay protection; it is usually unknown or poorly quantified and cannot be measured directly. A new effective and reliable method for rated capacitance design of a new UHV equipotential shielding CVT under the interference of SCs is proposed and successfully demonstrated in this work. An equivalent mathematical model is established to derive the CVT rated capacitance and the SCs are extracted using a finite element method. The performance of this method is verified in the experiment to demonstrate the effectiveness of the method.

Ice formation on solid surfaces includes heterogeneous ice nucleation and ice propagation processes. However, no study has been focused on tuning of both ice nucleation and ice propagation via a simple anti-icing coating method. In this work, we have prepared multilayer hydrogels based on simple layer-by-layer (LBL) deposition approach and discover the ion-specific effect on both ice nucleation and ice propagation. A large ice nucleation temperature window of 11 °C is controlled via changing different counterions; meanwhile, the differences in ice propagation time can be tuned up to 4 orders of magnitude. Through synergistically controlling of ice nucleation and propagation delay times, we can tune the freezing delay time of water droplets on multilayer hydrogel surfaces up to 3 orders of magnitude via changing various counterions. Considering the application requirements, these multilayer hydrogels are stable under different conditions and can be coated on various materials without destroying the existing surface. This new insight can inspire the design of anti-icing surfaces based on regulating both ice nucleation and ice propagation.

In order to deal with the context dilution problem introduced in the lossless compression of M-ary sources, a lossless compression algorithm based on a context tree model is proposed. By making use of the principle that conditioning reduces entropy, the algorithm constructs a context tree model to make use of the correlation among adjacent image pixels. Meanwhile, the M-ary tree is transformed into a binary tree to analyze the statistical information of the source in more details. In addition, the escape symbol is introduced to deal with the zero-frequency symbol problem when the model is used by an arithmetic encoder. The increment of the description length is introduced for the merging of tree nodes. The experimental results show that the proposed algorithm can achieve better compression results.

This paper presents a comprehensive analysis and a novel solution for the discharge problem on the half-bridge submodules’ (HBSMs’) capacitors in the hybrid modular multilevel converter (MMC)-based high-voltage direct current transmission systems under a long-term (e.g., several minutes or longer) pole-to-ground fault condition. The mechanism of this issue is analyzed, and then a solution based on fundamental-frequency reactive circulating current (FFRCC) injection is proposed. The influence of FFRCC injection is analyzed in terms of the fluctuated arm capacitor energy and the current stress of semiconductors. Moreover, an enhanced arm voltage modulation method based on HBSMs and full-bridge submodules coordinate control is proposed to accelerate the capacitor voltage balance of HBSMs. Finally, the performance of the proposed control strategy is verified by the simulation results.

Reducing the capacitance of submodules (SM) and handling short-circuit faults in HVdc systems are crucial for economical and reliable operation of modular multilevel converters (MMC). This paper proposes an SM capacitance reduction method for full-bridge submodule (FBSM)-MMC, which combines circulating current injection and ac voltage boosting. An optimized circulating current control method considering the limitation of fixed semiconductor current rating is introduced. By adding second-harmonic voltage to the reference arm voltage, the capacitor voltage ripple can be controlled to be a targeted value under all operating conditions. To further decrease the SM capacitor voltage ripples, the negative voltage state of FBSM is fully utilized to boost the ac voltage under fixed dc voltage with the modulation index up to 1.414. Consequently, the capacitance requirement for ac voltage boosting FBSM-MMC can be significantly reduced as compared to the conventional FBSM-MMC. Experimental results confirm the feasibility and validity of the proposed SM capacitance reduction method.

Pole-to-ground (PTG) fault is one of the most common DC-side faults in multi-terminal high-voltage direct-current (HVDC) systems. During the PTG fault, the loss of system transmission power is a challenging issue. This study proposes a PTG fault ride through strategy for low-impedance grounded radial multi-terminal HVDC systems. It is realised by the coordinated operation between half-/full-bridge hybrid modular multilevel converters and mechanical DC switches. The mechanical DC switch is utilised to isolate the fault and a ground return path is formed to transmit the active power during PTG fault. If the fault is located at the sending terminal, half of the rated transmission power can be kept at the entire fault duration. If the fault is located at the receiving terminal, the successfully restarted active power regulator stations can further return to normal operation after the isolation of the PTG fault. With the proposed strategy, the loss of transmission power during PTG fault is minimised, which can improve the transient angle stability of the AC grid. PSCAD/EMTDC simulation is performed to verify the proposed strategy.

Control of heterogeneous ice nucleation (HIN) on foreign surfaces is of great importance for anti-ice-nucleation material design. In this work, we studied the HIN behaviors on various ion-modified poly(butylene succinate) (PBS) surfaces via chain-extension reaction. Inspired by antifreeze proteins (AFPs), the PBS-based polyampholytes, containing both negative and positive charge groups on a single chain, show excellent performance of ice nucleation inhibition and freezing delay. Unlike the extremely high price and low availability of AFPs, these PBS-based polyampholytes can be commercially synthesized under mild reaction conditions. Through water freezing tests on a wide range of substrates at different temperatures, these PBS-based polyampholytes have shown application value of tuning ice nucleation via a simple spin-coating method.

Ice propagation is of great importance to the accumulation of ice/frost on solid surfaces. However, no investigation has been reported on the tuning of ice propagation through a simple coating process. Herein, we study the ice propagation behavior on polyelectrolyte multilayer (PEM) surfaces coated with the layer-by-layer (LBL) deposition approach. We discover that ice propagation is strongly dependent on the amount of water in the outermost layer of PEMs, that is, the ice propagation rate increases with the amount of water in the outermost layer. The ice propagation rate can be tuned by up to three orders of magnitude by changing the polyelectrolyte pairs, counterions of the outermost polymer layer, or the salt concentration during the preparation of PEMs. Because the simple, versatile, and inexpensive LBL deposition approach is generally applicable to almost all available surfaces, the PEM coatings can tune ice propagation on a wide range of substrates.

Using voltage-source converter high-voltage direct current (VSC-HVDC) to interconnect weak ac power systems has drawn much attention. Under the traditional vector control for the VSC that the response of AC voltage loop cannot match that of the active power loop may limit power transmission capability of the VSCs that interconnect with weak power systems. To enhance the power transmission capability and stability, this paper proposes a power compensation control that is based on the analysis of characteristics of power–voltage (PV) curves. This method can improve the damping control performance of the active power and the ac voltage by adjusting the compensated values adaptively. A small-signal model of the integrated system is established to study the performance of the proposed control method. The impact of the compensation coefficients and steady-state operating points on the system stability is studied. Motivated by an on-going back-to-back project in China, corresponding electromagnetic transient simulation models are constructed in MATLAB/Simulink environment to verify the effectiveness of the proposed method on the performance of operating limits, damping performance, disturbance withstanding capability, and fault ride-through capability.

A series of Ce 3+ , Tb 3+ co-doped Na 6 Ca 3 Si 6 O 18 phosphors have been synthesized by traditional solid state reaction. The emission spectra of the Na 6 Ca 3 Si 6 O 18 :Ce 3+ ,Tb 3+ phosphors show a blue broad band at 450 nm of the Ce 3+ and a green line peaking at 550 nm. Energy transfer from Ce 3+ to Tb 3+ ions has been investigated. Results indicate that the color of these phosphors changes from blue to green by adjusting the ratio of Ce 3+ to Tb 3+ . In addition, the mechanism of the energy transfer from the Ce 3+ to Tb 3+ ions is demonstrated to be a dipole-quadrupole mechanism. The energy transfer efficiency as well as the critical distance is also estimated. By optimizing the Tb 3+ concentration, the absolute PL quantum yield as high as 43% can be achieved. The results show that this phosphor has potential applications as a single-phased phosphor for UV white-light LEDs.

Samples of the Ba9 (Lu2-x Yx )Si6 O24 :Ce3+ (x = 0-2) blue-green phosphors were synthesized by solid-state reactions. All the samples exhibited a rhombohedral crystal structure. As the Y3+ concentration increased, the diffraction peaks shifted to the small angle region and the lattice parameters increased due to the larger ionic radius of Y3+ (r = 0.900 A) compared with that of Lu3+ (r = 0.861 A). Under 400 nm excitation, samples exhibited strong blue-green emissions around 490 nm. The emission bands had a slight blue shift that resulted from weak crystal-field splitting with increasing Y3+ concentration. Luminescence intensity and quantum efficiency (QE) decreased with increasing Y3+ concentration. The internal QE decreased from 74 to 50% and the external QE decreased from 50 to 34% as x increased from 0 to 2. The thermal stability of the Lu series was better than that of the Y-series. The excitation band peak around 400 nm matched well with the emission light from the efficient near-ultraviolet (NUV) chip. These results indicate promising applications for these NUV-based white light-emitting diodes.

Ice propagation is an essential step when freezing happens on hydrated surfaces. In this work, we choose polyelectrolyte brushes (PB), whose hydration ability can be controlled by simply exchanging the counterions, to demonstrate the distinct ice propagation mechanism on differently hydrated surfaces.

Step test method is a commonly used system identification method in the plant advanced process control application. Bayesian forecasting method is a kind of method based on subjective experience information and historical data. In this paper, a model identification method based on Bayesian forecasting is proposed. Combining the operators experience information and historical model data, the Bayesian method is used to predict the process model, and the model monitoring is used to abandon the abnormal data. Finally, the MPC controller is designed and the practical application of the top temperature control of the nitrobenzene rectifying tower proves the effectiveness of this method.

Pole-to-ground (PTG) fault analysis is of vital importance for HVDC grid. However, many factors are not considered in the existing studies, such as the asymmetrical property of PTG fault, the coupling issue between dc transmission lines and the complexity of dc grid's structure. This paper presents a PTG fault analysis method, which is based on common- and differential-mode (CDM) transformation. Similar to the symmetrical component method in ac system, the transformation decomposes the HVDC grid into CDM networks at first. Then, under the perspective of CDM components, a transfer impedance based analysis is performed to obtain the analytical expressions of PTG fault characteristics. The proposed PTG fault analysis method is applicable to arbitrary HVDC grid topologies. And the analytical expressions can give theoretical guidance for fault protection. The validity of the proposed PTG fault analysis method is verified by comparison with the simulation results in PSCAD/EMTDC.

Energy-related occupant behaviour in buildings has demonstrated considerable energy-saving potential. However, the current modelling method of occupant behaviour does not give sufficient considerations on the implementation difficulty of behaviour and provide a holistic map from survey data to various behaviour models. This article proposes a holistic survey-and-simulation-based framework for estimating the energy-saving potential of occupant behaviour improvement. In the framework, seven typical categories of occupant behaviour models are identified based on the survey results. According to the implementation difficulty, the models are integrated into four behaviour styles (baseline, wasteful, moderate and austere) to represent different levels of energy-saving consciousness of occupants. Based on a case study with a nationwide survey in Singapore, there are remarkable energy savings potential if occupant behaviour is improved; the building energy consumption can be reduced by up to 9.5% with the moderate behaviour improvement, and up to 21.0% with the aggressive behaviour improvement. The simulation results accord well with the measured results within a reasonable range of deviation. The framework can be applied to estimate the energy-saving potential of occupant behaviour improvement in a building with affordable cost, and the findings can inform a behaviour improvement programme with effective and efficient measures.

As the increasing penetration of modular multilevel converter (MMC)-based high-voltage direct current (HVDC) into bulky power transmission systems, the performance of MMC on dealing with DC faults, especially on temporary DC fault in overhead transmission lines, has been becoming more and more significant. A comprehensive overview of MMC on DC fault ride-through (FRT) capability is discussed. Compared with DC fault blocking capability considered as a passive DC FRT strategy focusing on isolating DC fault from AC sides, the DC FRT capability emphasises remaining converters continuous operating during DC faults to regulate and support the connected AC grids. The principle and prerequisite of MMC on DC FRT are analysed, and then improved MMC topologies with DC fault handling capability are summarised and a corresponding comparison among them is conducted. Finally, applications of MMC with DC FRT capability on HVDC systems and its relative control strategies are presented.

The selective area growth (SAG) technique has been proved to be an effective method to achieve trench gate normally-off AlGaN/GaN MOSFET. In this paper, the two-dimensional electron gas (2DEG) transport properties of SAG AlGaN/GaN heterostructure are investigated for samples with different insertion layers. As the thickness of the GaN insertion layer increases, the mobility of 2DEG drops at first and then increases dramatically. This is explained by a shift of the location of the 2DEG from the GaN template into the GaN insertion layer. Interface contamination at the template/insertion layer interface is found to be the reason of the degradation of the transport properties. Through optimizing the thickness of the SAG GaN insertion layer, 2DEG mobility is similar to the value of as-grown AlGaN/GaN heterostructure. The proper thickness of SAG GaN insertion layer for device fabrication is 24 nm referring to the variation in 2DEG transport properties.

Due to the rapid development of the voltage-source converter (VSC), the demands for HVDC cables have increased significantly. Although more than ten VSC-HVDC projects are under construction and many more are in operations globally, the testing criteria for HVDC XLPE cables are mainly referenced to test guideline TB 496 recommended by CIGRE. Due to the large stray capacitance of the VSC-HVDC cables, the switching impulse overvoltage stress of the cables is the main electrical parameter concerned, a unified overvoltage factor of 2.1 p.u. being generally accepted. However, the switching impulse overvoltage stress of a VSC-HVDC cable system depends on not only the VSC topology but also the cable parameters and the volt-ampere characteristics of the dc cable surge arresters used. This paper studies the switching impulse overvoltage stresses for the dc cable system of a symmetrical monopole VSC-HVDC transmission system using the modular multilevel converter technology. The studies were performed according to the key technical parameters for a typical 1000-MW/320-kV VSC-HVDC transmission scheme, the XLPE dc cable links being assumed. The results show that a switching impulse overvoltage level of 2.3 p.u. should be applied during the type test of the overvoltage capability of the HVDC cables.

The hybrid multilevel voltage-source converter, combining semiconductor switches and power module cells, is a new family for VSC-HVDC applications. The hybrid multilevel converter in parallel arrangement (PHMC), in terms of converter investment, is very adaptable for cable transmission systems. However, the dc voltage of the converter, synthesized by the output voltage of three-phase cell stacks, is strongly coupled with ac voltage variations, which influences the stability of converter operation. This paper proposes a dc voltage compensation strategy for the parallel hybrid multilevel converter. This strategy, implemented by introducing an isolation period, can effectively cope with the dc voltage deviation, especially under ac network faults. Simulation results in PSCAD/EMTDC verify the effectiveness of the proposed strategy under various circumstances.

The influence of different AlGaN Impurity Blocking Layer (IBL) thickness in the GaN/Si (111) structure with GaN/AlN SLs buffer on the material and electrical properties of GaN/Si (111) system was studied in detail. It is found that the insertion of AlGaN IBL can increase the (102) FWHM and decrease the (002) FWHM. Meanwhile, AlGaN IBL with an optimized thickness can further improve the surface roughness and strain-state of GaN-Si (111) system. By using Secondary Ion Mass Spectroscopy, it is found that AlGaN IBL have a strong effect in blocking the Si donor impurities originating from the Si substrate during the high temperature growth, which can decrease the leakage current while the breakdown voltage can be dramatically increased.