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The non-volatile resistive switching process of a MoS2 based atomristor with a vertical structure is investigated by first-principles calculations. It is found that the monolayer MoS2 with S vacancy defects (Vs) could maintain an insulation characteristic and a high resistance state (HRS) is also remained. As an electrode metal atom adsorbed on MoS2 monolayer, the semi-conductive filament is formed with the assistance of Vs. Under this condition the atomristor presents a low resistance state (LRS). The ON state current of this semi-filament is increased close to two orders than that of without filament (HRS). The energy barrier for an Au-atom to penetrate the monolayer MoS2 via Vs is as high as 6.991 eV. When it comes to double S vacancy (Vs2), the energy barrier is still amounted to 3.554 eV, which manifests the bridge-like full conductive filaments cannot form in monolayer MoS2 based atomristor. The investigation here promotes the atomistic understanding of the resistive switching properties about the monolayer MoS2 based memristor. The physics behind should also work in atomristors based on other monolayer transitional metal dichalcogenides, like WeSe2 and MoTe2. The investigation here will promote the comprehension of these devices at atomic scale and be a reference for device design or optimization.

The flexible DC transmission technology proposed in recent years has significant technical advantages over other transmission methods for long-distance grid-connected transmission of large-capacity wind farms. However, as the scale of wind farms continues to expand, new problems have emerged, mainly in the form of start-up control as the basis for the reliable grid-connected operation of wind turbines. In this paper, a start-up control strategy for DFIG wind farms connected to the grid via MMC-HVDC is proposed for DFIG wind farms via flexible DC outgoing transmission scenarios, mainly including MMC-HVDC controlled rectifier start-up control and single DFIG start-up control. Finally, the correctness and feasibility of the proposed control strategy are verified by simulation.

With the increasing scale of wind farms and the increasing proportion of wind power generation in the energy system, the grid has higher and higher requirements for the voltage stability of wind farms. In this paper, we propose a hybrid reactive power compensation system and its control strategy for weakly connected asynchronous wind farms, which can effectively control the compensation cost while improving the continuity of reactive power regulation. It also verifies the correctness and feasibility of the proposed hybrid reactive power compensation system and its control strategy through simulation.

The braking indices of pulsars may contain important information about the internal physics of neutron stars (NSs), such as neutron superfluidity and internal magnetic fields. As a subsequent paper of Cheng et al., we perform the same analysis as that done in the previous paper to other young pulsars with a steady braking index, n. Combining the timing data of these pulsars with the theory of magnetic field decay, and using their measured magnetic tilt angles, we can set constraints on the number of precession cycles, ξ, which represents the interactions between superfluid neutrons and other particles in the NS interior. For the pulsars considered in this paper, the results show that ξ is within the range of a few ×103 to a few ×106. Interestingly, for the Crab and Vela pulsars, the constraints on ξ obtained with our method are generally consistent with that derived from modeling of the glitch rise behaviors of the two pulsars. Furthermore, we find that the internal magnetic fields of pulsar with n < 3 may be dominated by the toroidal components. Our results may not only help to understand the interactions between the superfluid neutrons and other particles in the interior of NSs but also be important for the study of continuous gravitational waves from pulsars.

In the process of industrial production cables and pipes, the precise measurement of the produced product line diameter parameters is very important. In the present paper, we propose an offset compensation diameter measurement system based on analytical geometry and spatial coordinate transformation. The right-angle coordinate system is established in the corresponding planes of the two sets of charge coupling devices and the corresponding laser light source, and the center coordinates of the measured cable are obtained by the analytical geometric method, and the spatial coordinate transformation is used to connect the two coordinate systems to build the offset compensation measurement system. In the actual test (taking θ=45° as an example), considering the overall measurement results of the cylinder standard bar, the overall absolute error is between ± 4 μm without offset, and the relative error is 0~0.05%; and the relative average error (deviation angle is more than 0° and less than 35°) can be maintained at less than 0.7%. The above results demonstrate the feasibility of accurate measurement of this offset-compensated measurement system.

To realize 5G network slicing, the virtual resource scheduling and allocation method based on NFV and SDN is designed. The scheme comprehensively considers 5G communication technology and network slice structure, and establishes the optimal mathematical model of network slice operation economy. Then the network functions and resources are virtualized by NFV and SDN, the greedy algorithm is adopted to solve the mapping problem of network slices, and the specific implementation algorithm is provided. The simulation results show that the allocation algorithm can customize the management of network slice resources, achieve flexible control and sharing of network traffic and resources, and significantly promote the construction, optimization and promotion of 5G mobile communication network architecture.

A solid-state pulse source is mainly formed by replacing the spark switch in a traditional pulse source with semiconductor switch device. Compared with conventional gas switch devices such as spark switches, semiconductor switch devices have the advantages of high work repetition frequency, long service life, small size, high efficiency, high reliability, easy control, and active shutdown. However, there are still problems, such as the solid-state switch being easily broken down by high voltage, the rising and falling edges of the pulse being slow, and the loss is enormous. In this paper, a solid-state pulse generator based on Marx with a chopping switch circuit is developed, which effectively solves the above problems. The pulse generator comprises DC power, a switching power circuit, a Marx circuit with a chopping switch, a serial port touch screen, and an optical fiber transmission circuit.

We investigate conventional photon blockade in a non-degenerate four wave mixing system with Kerr non-linearity. By analyzing the Hamiltonian of the system, we have acquired the corresponding condition to implement photon anti-bunching effect. And we solve the master equation with the purpose of obtaining solutions numerically. We find that the analytic conditions could be consistent with numerical results, and photon blockade could be realized in this system. Furthermore, we discuss the effect of several parameters on the realization of conventional photon blockade in detail. The results show that four wave mixing interaction and Kerr non-linearity could significantly enhance the conventional photon blockade effect, whereas the dissipation rate has a negative effect on implementing photon blockade.

The secondary electron emission coefficient of dielectric materials will have an important impact on the performance of electronic devices and equipment. In order to understand the secondary electron emission coefficient of common dielectric materials, the collection electrode negative bias method is introduced in this study. First, the measurement method of secondary electron emission coefficient of dielectric materials is analyzed, and 20 common dielectric materials are introduced, the secondary electron emission coefficients of 20 kinds of common dielectric materials were measured and analyzed, which laid the foundation for the subsequent application of dielectric materials. The results show that among common dielectric materials, the secondary electron emission coefficients of alumina, silica and muscovite are relatively high, while those of polyimide, polycarbonate and polyester are relatively low; The surface roughness of the material will also have an important impact on the secondary electron emission coefficient. With the gradual increase of the surface roughness of the material, the undulation of the material surface will have a shielding effect and absorption effect on the secondary electrons, which will eventually lead to the gradual reduction of the secondary electron emission coefficient of the material. The research results can provide data support for the establishment of the database of secondary electron emission characteristics of common dielectric materials.

We investigate the decays of B 0 → K 0 X(3872) and B + → K + X(3872) based on the picture where the X(3872) resonance is strongly coupled to the D D ¯ * + c . c . channel. In addition to the decay mechanism where the X(3872) resonance is formed from the c c ¯ pair hadronization with the short-distance interaction, we have also considered the D D ¯ * rescattering diagrams in the long-distance scale, where D and D ¯ * are formed from c and c ¯ separately. Because of the difference of the mass thresholds of charged and neutral D D ¯ * channels, and the rather narrow width of the X(3872) resonance, at the X(3872) mass, the loop functions of D 0 D ¯ * 0 and D + D ¯ * − are much different. Taking this difference into account, the ratio of ℬ [ B 0 → K 0 X ( 3872 ) ] / ℬ [ B + → K + X ( 3872 ) ] ≃ 0.5 can be naturally obtained. Based on this result, we also evaluate the decay widths of B s 0 → η ( η ′ ) X ( 3872 ) . It is expected that future experimental measurements of these decays can be used to elucidate the nature of the X(3872) resonance.

Machine learning is a novel and powerful technology and has been widely used in various science topics. We demonstrate a machine-learning-based approach built by a set of general metrics and rules inspired by physics. Taking advantages of physical constraints, such as dimension identity, symmetry and generalization, we succeed to approach the Gell-Mann–Okubo formula using a technique of symbolic regression. This approach can effectively find explicit solutions among user-defined observables, and can be extensively applied to studying exotic hadron spectrum.

With the wide application of new energy technologies, wind power has become one of the technologies with the largest development scale. Voltage Source Converter based High Voltage Direct Current Transmission system has unique advantages in its active and reactive power decoupling control, etc., and has become the main solution to solve the wind power transmission of large-scale wind farms. This paper studies the control characteristics and basic principles of new energy generation in the passive transmission system of DC island power grids, and proposes a frequency signal transmission scheme in the external transmission scenario. The simulation results verify the feasibility of the frequency signal transmission scheme between the sending-end wind farm and the receiving-end power grid in the DC islanding scenario, and that the VSC-HVDC system can quickly provide active power support and improve the dynamic frequency stability of the interconnected system.

With the construction of the energy internet, the demand for various sensing devices is increasing. Most of sensing devices need power source which limits their application in the wide spread distributed nodes of sensor network. Therefore, there is an urgent need to develop passive sensing devices which is more intelligent and convenient. This paper studies the magnetoelectric effect of layered magnetoelectric composites. Firstly, the physical process is analyzed by using the finite element method. Secondly, magnetoelectric response of the eddy current in the Cu-PZT layered composite material is investigated. Finally, the voltage variations of circular and rectangular samples are compared. It can be seen from the results that under the action of the eddy current, there is a u-shaped curve relationship between the induced voltage and the magnetic field. The energy conversion of metal-piezoelectric composite material without power source provides an effective path for developing passive magnetic sensor.

The synergistic influences of boron, oxygen, and titanium on growing large single-crystal diamonds are studied using different concentrations of B2O3 in a solvent–carbon system under 5.5 GPa–5.7 GPa and 1300 °C–1500 °C. It is found that the boron atoms are difficult to enter into the crystal when boron and oxygen impurities are doped using B2O3 without the addition of Ti atoms. However, high boron content is achieved in the doped diamonds that were synthesized with the addition of Ti. Additionally, boron–oxygen complexes are found on the surface of the crystal, and oxygen-related impurities appear in the crystal interior when Ti atoms are added into the FeNi–C system. The results show that the introduction of Ti atoms into the synthesis cavity can effectively control the number of boron atoms and the number of oxygen atoms in the crystal. This has important scientific significance not only for understanding the synergistic influence of boron, oxygen, and titanium atoms on the growth of diamond in the earth, but also for preparing the high-concentration boron or oxygen containing semiconductor diamond technologies.

Calcium bismuth niobate (CaBi2Nb2O9, CBN) is considered to be one of the most promising high-temperature (HT) piezoelectric materials owing to its high Curie temperature of ∼940 °C, however, its low electrical resistance and poor piezoelectric properties at elevated temperatures limit its applications at high temperatures. In this work, we report the significantly enhanced dc electrical resistivity and piezoelectric performance of CBN ceramics through rare-earth Nd-substitution. The crystal structure, microstructure, and dielectric, electrical, ferroelectric and piezoelectric properties of Nd-modified CBN with nominal compositions of Ca1−x Nd x Bi2Nb2O9 (CBN-100xNd) have been investigated in detail. The results indicate that the substitutions of Nd3+ ions for Ca2+ ions increase the piezoelectric properties, and reduce the dielectric loss tanδ at high temperatures. The dc and ac conduction mechanisms indicate that the conduction mechanism is closely related to oxygen vacancies that are reduced through the donor substitutions of Nd3+ for Ca2+, thereby resulting in a significant improvement in the dc electrical resistivity. The optimal composition of CBN-3Nd exhibits a high piezoelectric constant d 33 of 13.5 pC N−1, and a high Curie temperature T c of 948 °C. More importantly, the CBN-3Nd exhibits good thermal stability of the electrical properties (ρ= 2.6 × 107 Ω cm at 500 °C and 1.8 × 106 Ω cm at 600 °C, k p = 6.1%–6.2% at RT ∼ 500 °C), which demonstrates that the Nd-modified CBN ceramics are promising piezoelectric materials for use in HT piezoelectric sensors.

Determining the time-resolved three-dimensional (3D) three-component (3C) velocity is essential for complex turbulent flow measurements. The current study is an extension of a recently developed temporal-spatial three-dimensional particle tracking velocimetry (TS 3D-PTV) technique established for two-view imaging systems. Two improvements have been embedded in TS 3D-PTV algorithm to improve the accuracy at high particle image densities (up to 0.03 ppp). One is using the neighboring particle information to correct the predicted positions and select the temporal particles with higher probability; the other is to iteratively optimize the 2D particle positions during the tracking process using the temporal and image information. The synthetic particle tests indicate that the correctness can be increased by 4.7%–5.8%, to reach a value about 92% with the improved algorithm around 0.03 ppp. The comparative results also indicate that using an advanced particle identification algorithm can improve the correctness over 20%. Two experiments, including a buoyancy jet in water and a transient droplet splashing process, have been conducted with a two-view shadowgraph imaging system. Different tracking algorithms have been conducted to determine the 3D trajectories of seeding particles or secondary droplets comparatively. The new algorithm has shown the best performance with much longer and more reliable trajectories, which indicates the tracking interruption caused by particle overlapping is reduced. The newly developed algorithms have further improved the performance under high seeding density conditions, which makes the two-view shadowgraph 3D PTV system adaptable to more experimental conditions.

Cs2TiBr6 nanocrystals (NCs) are a type of promising optoelectronic materials, owing to their high photoelectric properties and non-toxicity. Here, we synthesize the colloidal Cs2TiBr6 NCs using a hot-injection approach. The temperature-dependent absorption data shows that its energy band changes about 30 meV with temperature, reflecting that its energy band structure is much stable. The excitation intensity-dependent transient absorption data confirms its linear absorption cross-sections and carrier recombination rate constants, involving monomolecular and bimolecular recombination, which are all superior to those of conventional perovskite bromide counterparts. In addition, its nonlinear absorption cross-sections are also measured based on femtosecond Z-scan. Our results suggest that Cs2TiBr6 NCs can be extensively applied in the field of optoelectronics, owing to its excellent carrier dynamics and nonlinear optical properties.

For power systems, the operation of concealed power equipment such as grounding grids and underground pipelines affects the system reliability. The ground penetrating radar with ultra-high frequency electromagnetic pulse can detect underground objects without stopping power equipment. It has the advantages of saving costs, improving construction efficiency and helping to improve the stability of the power system. This paper adopts the finite difference time domain method (FDTD) based on fourth-order accuracy which improves the accuracy of the numerical calculation to study the detection and location of concealed equipment in underground power. In this paper, electromagnetic echoes of common metal materials in the grounding grid are calculated. Moreover, the electromagnetic echo is further calculated when the outer layer material and the filling medium changed, and the change law of the waveform is systematically analyzed. The research results provide a theoretical basis for the application of ground penetrating radar technology in engineering practice.

SrRuO3 (SRO)-based heterostructures have attracted much attention for potential applications such as electrodes, oxide spintronics, topological electronics and electrocatalytic function mainly due to the strong spin–orbit coupling, itinerant ferromagnetism with 4d electrons, high metallic conductivity, perpendicular magnetic anisotropy and rich oxygen octahedral distortion of SRO. Here, this work aims to offer a timely and systematic review on SRO-based heterostructures for its emerging opportunities in oxide spintronic and topological electronic applications. We first present a brief summary of the current status in SRO-based heterostructures and describe the motivations of this review. We then briefly review the surface and interface modulation in SRO-based heterostructures, including oxygen octahedral distortions (antiferrodistortive mode and ferroelectric mode) engineering and ion defect engineering. In the third part, we discuss the spin-charge interconversion phenomena in SRO-based heterostructures, covering the inverse spin Hall effect and current-induced spin-orbit torques. Particularly, in the fourth part, we discuss the emergent topological Hall effect and underlying mechanism in SRO-based heterostructures, including the two-channel anomalous Hall effect and Berry phase manipulation. The fifth part presents the magnetic Weyl fermions and its electric-field control of SRO films. We finally conclude with a discussion of challenges and prospects of SRO-based heterostructures, which provides a guidance for exploring novel physical properties and designing multifunctional devices based on SRO.

When a short-circuit fault occurs on a power transformer, the windings of the transformer under the combined action of the short-circuit current and the leakage magnetic field, which is easy to deform the winding or damage the insulation of the transformer. Therefore, it is necessary to research on the force of the transformer under short-circuit situation, analyze and calculate the size and distribution characteristics of the electromagnetic force in different short-circuit modes. Based on the structural parameters of a transformer with a rated capacity of 200kVA, a three-dimensional model of a three-phase transformer is established by finite element simulation software. The axial and radial electromagnetic forces of windings in different short-circuit modes are analyzed by this model, comparing and analyzing the experimental results. In the simulation model, It can be known that the electromagnetic force of voltage zero-crossing closing phase when three-phase short-circuit occurs on low-voltage winding is basically the same as that of short-circuit phase electromagnetic force when single-phase short-circuit occurs. The analysis results have a certain reference value for improving transformer short-circuit withstand ability.

In the process of coalbed fracturing, the drag reducers absorbed on the surface of the coalbed causes water lock damage and decreases gas production efficiency of coalbed methane. Thus, research on low-damage coalbed drag reducers is of great significance. Aiming at four drag reducers with different molecular weights, the law of drag reducers adsorption was investigated through static adsorption test and contact angle tests. Afterwards, a core displacement experiment was carried out to study the damage rate of slick water to the coabed, and the nanoemulsion CND was used for competitive adsorption to relieve the influence of fracturing fluid adsorption on the core damage. Finally, through the static adsorption test results, combined with core SEM images before and after displacement, the internal relationship between adsorption and damage was revealed, and the optimal principles and control methods for reducing the damage of drag reducers to the coalbed were proposed. The results show that: the drag reducers with larger molecular weight are more likely to adsorb in the coalbed, which caused more severe damage to the coalbed reservoir. In contrast, drag reducers with lower molecular weight show a lower damage rate (less than 20%) to the reservoir, which is suitable for the preparation of low-damage slick water. Mechanistic studies have shown that the drag reducers is adsorbed on the surface of the organic matter in the coalbed, leading to the exposure of the hydrophilic end. Therefore, the hydrophilic area on the surface of the coal powder was enlarged, which forms the water film adhesion in the pore throat, causing the water lock to block the gas and liquid seepage channel, resulting in reduced permeability; Nanoemulsion and coal powder are more closely adsorbed, which can reduce the adsorption of drag reducers through competition with the adsorption matrix, reduce water lock damage, facilitating the subsequent drainage and gas collection process.

The short-circuit test is a test of the comprehensive technical ability of transformer manufacturing. The three-phase power supply is usually used for short-circuit test of transformer. To investigate the feasibility of using a single-phase power supply in the short-circuit test of transformer, in this paper, we modeled a 200 kVA power transformer in three dimensions, using the finite element method to calculate the short-circuit current and short-circuit electromagnetic force of the windings under different excitation modes when the three-phase short-circuit occurs in the low-voltage windings. Analyze and compare the short-circuit current and short-circuit electromagnetic force distribution characteristics of windings under different working conditions. The results show that when the three-phase short-circuit condition occurred in the low-voltage windings, regardless of the three-phase excitation or single-phase excitation exerted on the high-voltage windings, the short-circuit current and the short-circuit electromagnetic force of the voltage zero-crossing closing phase is basically the same. This proves that a single-phase power supply can be used instead of a three-phase power supply for short-circuit tests. the analysis result has certain reference significance for improving the short-circuit test of transformer.

We study the effects of higher-order deformations $\beta_\lambda$ ($\lambda=4,6,8,$ and $10$) on the ground state properties of superheavy nuclei (SHN) near the doubly magic deformed nucleus $^{270}$Hs by using the multidimensionally-constrained (MDC) relativistic mean-field (RMF) model with five effective interactions PC-PK1, PK1, NL3$^{*}$, DD-ME2, and PKDD. The doubly magic properties of $^{270}$Hs are featured by the large energy gaps at $N=162$ and $Z=108$ in the single-particle spectra. By investigating the binding energies and single-particle levels of $^{270}$Hs in multidimensional deformation space, we find that the deformation $\beta_6$ has the greatest impact on the binding energy among these higher-order deformations and influences the shell gaps considerably. Similar conclusions hold for other SHN near $^{270}$Hs. Our calculations demonstrate that the deformation $\beta_6$ must be considered when studying SHN by using MDC-RMF., Comment: accepted for publication in Chin. Phys. C

In recent years, the continuous acceleration of industrial and agricultural production has aggravated the deterioration of the environment and seriously affected people’s health. Gas pollutant index has become an important indicator to measure air quality. Taking a region of China as the study subject, this paper firstly uses the monitoring data of air pollutants in 5 years and meteorological data (rainfall, temperature and wind speed) of meteorological observation stations in the same period. Then, the autocorrelation function is selected to analyze the autocorrelation of pollutants, and on this basis, the significant correlation level between meteorological factors and pollutants is analyzed by Copula theory. The results show that the ACF values of pollutants are all higher than 0.6, which means that the autocorrelation of pollutants within 2 hours is relatively significant. PM2.5 has a significant negative correlation with wind speed in four seasons, but a low correlation with rainfall. SO2 is negatively correlated with most of the three meteorological factors. In addition, the study also finds that there are significant differences in the impact of meteorological factors on pollutants at different time scales. This paper proposes a correlation analysis method between meteorological factors and pollutants, which provides corresponding support and guarantee for China’s economic and environmental protection policies.

Cloud manufacturing adopts contemporary information cutting-edge technologies including advanced concepts such as cloud computing to support the manufacturing industry. Under a wide range of network resource manufacturing environments, it can add high value-added products, reduce costs, and meet globalization. The optimization of cloud manufacturing services is based on the attributes of cloud manufacturing services as evaluation indicators, and corresponding optimization strategies are formulated to ensure the selection process of manufacturing services. Taking into account the uncertainty of cloud service, rough set is used to assign the weight to each evaluation index and furthermore solve the cloud manufacturing service selection. Finally, an example is used to verify the effectiveness of the proposed method.

The effect of nitrogen flow and growth temperature on extension of GaN on Si substrate has been studied. By increasing the nitrogen flow whose outlet is located in the center of the MOCVD (metal–organic chemical vapor deposition) gas/particle screening flange and by increasing the growth temperature of HT-AlN and AlGaN buffer layers near the primary flat of the wafer, the GaN layer has extended more adequately on Si substrate. In the meantime, the surface morphology has been greatly improved. Both the AlN and GaN crystal quality uniformity has been improved. X-ray diffraction results showed that the GaN (0002) XRD FWHMs (full width at half maximum) decreased from 579 arcsec∼ 1655 arcsec to around 420 arcsec.

This paper investigates the operation inspection and anomaly diagnosis of transformers in substations, and carries out an application study of artificial intelligence-based sound recognition technology in transformer discharge diagnosis to improve the timeliness and diagnostic capability of intelligent monitoring of substation equipment operation. In this study, a sound parameterization technology in the field of sound recognition is used to implement automatic discharge sound detections. The sound samples are pre-processed and then Mel-frequency cepstrum coefficients (MFCCs) are extracted as features, which are used to train Gaussian mixture models (GMMs). Finally, the trained GMMs are used to detect discharge sounds in the place of transformers in substations. The test results demonstrate that the audio anomaly detection based on MFCCs and GMMs can be used to effectively recognize anomalous discharge in the high scenario of transformers.

This paper presents a method to determine the exhaust enthalpy of small steam turbine. Starting from the feed water pump group, the feed water pump and small steam turbine are studied as a whole. Based on the thermodynamic method, the efficiency of the feed water pump is obtained separately, and then the efficiency and exhaust enthalpy of the small steam turbine are deduced. This method only needs to measure the inlet and outlet pressure, temperature, feed water flow of feed water pump, inlet steam pressure, temperature and flow of small turbine. It has the advantages of less measurement parameters, low measurement cost and small measurement error. It provides a reliable basis for a comprehensive understanding of the performance of small steam turbine and guiding its economic and safe operation.

This paper presents a method for calculating the efficiency of steam feed pump, which fills the literature gap in calculating the efficiency of steam feed pump when the middle tap of feed pump is opened. This method has the advantages of convenient measurement and few measurement parameters. Combined with IFCIFC-97 industrial water and steam thermodynamic property model, the efficiency of feed pump can be calculated

This paper introduces the basic situation of thermal power units in Shandong power grid, the mode of unit heating transformation, the results of installed capacity and heating area after the transformation of heating, and the main work of Shandong power grid in ensuring people's livelihood heating and promoting the peak load adjustment of thermal power units.

Due to the late start of China's industrial simulation software, the current virtual simulation market is basically occupied by foreign products, and the emerging forces are accelerating to enter.In order to help China occupy a field of simulation market, promote the research and development of simulation software, and ensure the security and stability of simulation network operation,This paper analyzes the definition, classification and principle of data encryption technology, and discusses the application of some encryption technology in simulation software [1].