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In the operation of power grid, the low frequency subharmonics in power lines are easy to cause harmonic current problems. A harmonic current suppression method is constructed based on fuzzy sliding mode and virtual DC motor (VDC). First, the adaptive linear network is introduced to compare and analyze the output value and the actual value in the power line, and the possible harmonic current is obtained, which is detected and discretized. After that, this study adopts Fuzzy sliding mode control (FSMC) strategy for VDC, uses FSMC to participate in on-off control of VDC, and then realizes the suppression of harmonic current in VDC ports. In addition, the model also uses the circuit superposition theorem and the amount of harmonic data to be compensated by FSMC. The whole method uses VDC control technology to ensure the voltage stability of DC bus and load side when the load changes. In this physical experiment, harmonic current generated by load disturbance is eliminated by reducing DC harmonic voltage, so as to achieve the suppression of DC port harmonic current. Experimental results show that the third and fifth harmonics in power lines can be eliminated by this method to a large extent. Therefore, the proposed method can accurately detect and eliminate the harmonic current caused by sudden load change, and then realize the suppression of VDC harmonic current.

Abstract Before a wide range of enhanced oil recovery (EOR) techniques were implemented for an oilfield, the EOR potential and economic evaluation of the techniques should be evaluated in advance for each reservoir to determine which EOR technique was proper. In an oilfield developed with fluvial delta reservoirs, the complicated distribution of scattered small reservoirs in vertical and horizontal directions brought trouble for evaluation work. A rapid and reliable evaluation model for EOR techniques applicability was necessary to deal with the evaluation simulation for many small reservoirs of an oilfield. Combining fraction theory model with auxiliary equations, which describe the effect of formation heterogeneity and mechanism of different EOR technique on fractional flow rate, an evaluation analysis method for EOR techniques applicability of gas flooding, foam flooding and surfactant flooding was proposed. In the gas flooding model, the minimum miscible pressure of impure gas was introduced, and the relative permeability was modified by the minimum miscible factor. In the foam flooding model, changes in the mobility ratio and chemical adsorption were considered and a reduction factor of mobility ratio was introduced. In the surfactant flooding model, calculation formulas of viscosity and interfacial tension as well as the relative permeability were introduced. Finally, the model was simulated for a low permeability reservoir, and the simulation results were compared with that from Eclipse software. The similar results, little calculation time and feasibility of predicting optimal injection parameter had shown the reliability of the rapid evaluation model.

ObjectiveTo analyze the correlation between personality characteristics and family environment of undergraduate medical students taking psychology course.MethodsIn June 2017， a cross-sectional survey was conducted among 67 undergraduate medical students taking psychology course， and all the selected individuals were assessed using Minnesota Multiphasic Personality Inventory （MMPI） and Family Environment Scale-Chinese Version （FES-CV）. Then Pearson correlation analysis was performed between the original scores of MMPI subscales and the scores of FES-CV subscales.ResultsThe scores of hypochondriasis， depression， hysteria， psychopathic deviate， masculine-femininity， paranoia， psychasthenia and schizophrenia in MMPI of undergraduates were all higher than those of the national norm， with statistical differences （t=2.070~8.350， P

Cryo-electron microscopy (cryo-EM) has been widely used to reveal the structures of proteins at atomic resolution. One key challenge is that almost all proteins are predominantly adsorbed to the air-water interface during standard cryo-EM specimen preparation. The interaction of proteins with air-water interface will significantly impede the success of reconstruction and achievable resolution. Here, we highlight the critical role of impenetrable surfactant monolayers in passivating the air-water interface problems, and develop a robust effective method for high-resolution cryo-EM analysis, by using the superstructure GSAMs which comprises surfactant self-assembled monolayers (SAMs) and graphene membrane. The GSAMs works well in enriching the orientations and improving particle utilization ratio of multiple proteins, facilitating the 3.3-Å resolution reconstruction of a 100-kDa protein complex (ACE2-RBD), which shows strong preferential orientation using traditional specimen preparation protocol. Additionally, we demonstrate that GSAMs enables the successful determinations of small proteins (

Based on sol-gel method and spin coating process, TiO2 film doped with Li+ is prepared by utilizing analytical pure butyl titanate, lithium nitrate, absolute ethanol, glacial acetic acid, acetylacetone and deionized water as raw material. The Li+ ion which has equal radius as Ti4+ ion is chosen in experiments for doping and modification. Experimental results show certain increase of catalytic efficiency in TiO film doped with Li+. However, the increase level of catalytic efficiency gradually shows some decrease when the dopant amount changes from 0.025mol to 0.1mol. Catalytic efficiency is raised to 25.7% when the dopant amount is 0.025mol.

With the development of cryo-electron microscopy (cryo-EM), high-resolution structures of macromolecules can be reconstructed by the single particle method efficiently. However, challenges may still persist during the specimen preparation stage. Specifically, proteins tend to adsorb at the air-water interface and exhibit a preferred orientation in vitreous ice. To overcome these challenges, we have explored dual-affinity graphene (DAG) modified with two different affinity ligands as a supporting material for cryo-EM sample preparation. The ligands can bind to distinct sites on the corresponding tagged particles, which in turn generates various orientation distributions of particles and prevents the adsorption of protein particles onto the air-water interface. As expected, the DAG exhibited high binding specificity and affinity to target macromolecules, resulting in more balanced particle Euler angular distributions compared to single functionalized graphene on two different protein cases, including the SARS -CoV-2 spike glycoprotein. We anticipate that the DAG grids will enable facile and efficient three-dimensional (3D) reconstruction for cryo-EM structural determination, providing a robust and general technique for future studies.

Although single-particle cryogenic electron microscopy (cryo-EM) has been applied extensively for elucidating many crucial biological mechanisms at the molecular level, this technique still faces critical challenges, the major one of which is to prepare the high-quality cryo-EM specimen. Aiming to achieve a more reproducible and efficient cryo-EM specimen preparation, novel supporting films including graphene-based two-dimensional materials have been explored in recent years. Here we report a robust and simple method to fabricate EM grids coated with single- or few-layer reduced graphene oxide (RGO) membrane in large batch for high-resolution cryo-EM structural determination. The RGO membrane has decreased interlayer space and enhanced electrical conductivity in comparison to regular graphene oxide (GO) membrane. Moreover, we found that the RGO supporting film exhibited nice particle-absorption ability, thus avoiding the air-water interface problem. More importantly, we found that the RGO supporting film is particularly useful in cryo-EM reconstruction of sub-100-kDa biomolecules at near-atomic resolution, as exemplified by the study of RBD-ACE2 complex and other small protein molecules. We envision that the RGO membranes can be used as a robust graphene-based supporting film in cryo-EM specimen preparation.

This paper models and analyzes the Complementary Metal Oxide Semiconductor (CMOS) cross-coupled differential-drive (CCDD) rectifier for Ultra-Low-Power ambient radio-frequency energy harvesters (RFEHs) working in the subthreshold region. In this paper, two closed-form equations of CCDD rectifier output voltage and input resistance in the subthreshold region were derived based on BSIM4 models of NMOS and PMOS. The model give insight to specify circuit parameters according to different inputs, transistor sizes, threshold voltages, numbers of stages, load conditions and compensation voltages, which can be used to optimize the rectifier circuit. There is a good agreement between the simulation results and these models, and these models have a maximum deviation of 10% in comparison with the simulation results in the subthreshold region. The measurement results of a single-stage CCDD rectifier reported in a previous paper were adopted to verify the model. The output voltage and input resistance predicted by these models provide excellent consistency with corresponding measurement results. The model can be employed to optimize the CCDD rectifier without expensive calculation in the design stage. [ABSTRACT FROM AUTHOR]

The aim of this study was to examine the accuracy of electromagnetic radiation and microseismic signals in determining the anti-scour effect resulting from coal seam water injection. We established a simultaneous acquisition system of electromagnetic and microseismic full waveforms for coal rock damages under load, and an image acquisition system that captured the entire coal damage process was used. Uniaxial compression experiments of coal samples with different moisture contents were conducted, and the influence of water on the physical and mechanical properties of the coal samples and the generation of electromagnetic and microseismic signals were theoretically analyzed. The results showed that water reduced the adhesion and friction coefficient of particles in the coal body, promoted coal and rock fracture development, and weakened the generation of electromagnetic and microseismic signals. A significant positive correlation was found among stress drop, electromagnetic radiation signals, and microseismic signals, and the temporal distribution of the three variables was synchronous. As moisture content increased, the electromagnetic radiation and microseismic signal amplitude of the coal samples decreased, and the average signal of both signals exhibited an exponential downward trend. The relationship between the mean value of the signal and moisture content was obtained. To evaluate the water-injection effect of the coal samples, we also determined the theoretical percentage of the signal amplitude reduction corresponding to the increment in moisture content required by the on-site coal seam water injection and anti-erosion. [ABSTRACT FROM AUTHOR]

Differential evolution is capable of searching for the optimum for different types of optimization problems with a few inputs, which has gained worldwide popularity. In this paper, we propose a parameters adaptation scheme based on the stagnation ratio (PASR), which regards the stagnation ratio (STR) as the indicator for adjusting the control parameters and greediness parameter. To be specific, when the STR is larger than the predefined threshold, exploration is advocated. In this circumstance, larger control parameters and a greediness parameter are adopted. However, when the STR is smaller than the predefined threshold, exploitation is preferred. In this case, smaller control parameters and a greediness parameter are utilized. Further, when the stagnation lasts for a long period, a generation-based selection (GBS) scheme is developed to help it escape from the local optimum and stagnation. Comparative experiments have been implemented on the CEC2017 to testify the effectiveness of adaptive differential evolution with the stagnation termination mechanism (STMDE) and its components. The competitiveness of the STMDE is also verified via comparing it to top-performing DE variants in the practical optimization problem selected from the CEC2011. [ABSTRACT FROM AUTHOR]