Review of Three-phase Soft Switching Inverters and Challenges for Motor Drives

For electric vehicles (EVs),it is necessary to improve endurance mileage by improving the efficiency.There exists a trend towards increasing the system voltage and switching frequency,contributing to improve charging speed and power density.However,this trend poses significant challenges for high-voltage and high-frequency motor controllers,which are plagued by increased switching losses and pronounced switching oscillations as consequences of hard switching.The deployment of soft switching technology presents a viable solution to mitigate these issues.This paper reviews the applications of soft switching technologies for three-phase inverters and classifies them based on distinct characteristics.For each type of inverter,the advantages and disadvantages are evaluated.Then,the paper introduces the research progress and control methods of soft switching inverters (SSIs).Moreover,it presents a comparative analysis among the conventional hard switching inverters (HSIs),an active clamping resonant DC link inverter (ACRDCLI) and an auxiliary resonant commuted pole inverter (ARCPI).Finally,the problems and prospects of soft switching technology applied to motor controllers for EVs are put forward.

Antioxidant Activity of Different Solvent Extracts of Blumea Megacephala in Vitro

[Objectives] The aim was to study the antioxidant activity of different solvent extracts of Blumea Megacephala in vitro. [Methods] The removal rates of DPPH free radicals and ABTS free radicals and the reduction capacity of Fe^(3+) by ethanol extract( EE),acetone extract( AE) and ethyl acetate extract( EAE) of Blumea Megacephala were detected. [Results]The three extracts of Blumea Megacephala had certain antioxidant activity,of which the antioxidant activity of ethyl acetate extract was the strongest and has great potential for development.[Conclusions]The study can provide scientific reference for the deep research on the antioxidant activity of Blumea Megacephala.

Evaluation of Mine Geological Environment of Guqiao Coalmine

The geological environment is important for the development of coal enterprises. In the Guqiao coalmine, the information of coal mining subsidence, terrain landform, coal gangue utilization, mine water treatment and several on-site investigations have been analyzed. It holds that its geological environment can be evaluated from three aspects, i.e., geological disasters, terrain and landform destruction, and influence on water and soil environment. The results show that mining activities have serious impacts on geological disasters and terrain landform, while lighter impacts on the water and soil environment. According to the research results, a set of corresponding governance strategies are given. The findings can provide theoretical support for the geological environmental protection and restoration of the Guqiao coalmine.

Identification of Mine Water Inrush Source Based on PCA-BP Neural Network

It is of great significance to analyze the chemical indexes of mine water and develop a rapid identification system of water source, which can quickly and accurately distinguish the causes of water inrush and identify the source of water inrush, so as to reduce casualties and economic losses and prevent and control water inrush disasters. Taking Ca2+, Mg2+, Na+ + K+, , , Cl-, pH value and TDS as discriminant indexes, the principal component analysis method was used to reduce the dimension of data, and the identification model of mine water inrush source based on PCA-BP neural network was established. 96 sets of data of different aquifers in Panxie mining area were selected for prediction analysis, and 20 sets of randomly selected data were tested, with an accuracy rate of 95%. The model can effectively reduce data redundancy, has a high recognition rate, and can accurately and quickly identify the water source of mine water inrush.

面向垃圾焚烧炉应用的抗高温氯腐蚀涂层技术

焚烧是市政垃圾最为有效的处置方式。然而,垃圾焚烧气氛产生的腐蚀及磨损对锅炉安全运行存在极大的风险。采用功能涂层技术隔绝锅炉管与腐蚀气氛,从而实现对管壁的保护,是可行方案。本文对比了熔覆、耐火材料及热喷涂等防护方案,最终采用电弧喷涂制备耐氯腐蚀涂层,通过分析涂层的基本性能、锅炉内现场施工及实际焚烧环境运行等多方面,验证了采用电弧喷涂对垃圾焚烧炉管防护的可行性。

Clinical Significance of the Correlation between Changes in the Major Intestinal Bacteria Species and COVID-19 Severity

新冠病毒肺炎(COVID-19)是一种高度传染性疾病。与H7N9感染相似,COVID-19的典型临床表现是肺炎和细胞因子风暴。我们在既往研究中观察到H7N9患者存在肠道菌群失调。然而,肠道微生物菌群与COVID-19之间的关系尚未明确。本研究共纳入了57名COVID-19患者,其中包括20例普通型、19例重型以及18例危重型。本研究的目的是利用定量聚合酶链反应(q-PCR),研究COVID-19患者的10种主要肠道优势菌群的丰度变化,从而建立这些菌群与COVID-19临床指标之间的相关性。结果表明,COVID-19患者的10种主要肠道菌群丰度出现变化,这些肠道微生物菌群的变化与疾病严重程度和血液学指标有关。产丁酸菌,如普拉梭菌(Faecalibacterium prausnitzii),酪酸梭菌(Clostridium butyricum)、柔嫩梭菌(Clostridium leptum)、直肠真杆菌(Eubacteriumrectale)的丰度显著降低,细菌群落的这些变化有助于区分危重型与普通型和重型患者。此外,常见的条件致病菌肠球菌(Enterococcus,Ec)和肠杆菌科细菌(Enterobacteriaceae,E)的丰度在COVID-19患者中增加,尤其对于预后较差的危重型患者。这些结果表明,这些肠道优势菌群可作为COVID-19的诊断生物标志物,并且Ec/E值可用于预测危重型患者预后。

Opposed multi-burner gasification technology:Recent process of fundamental research and industrial application

Opposed multi-burner(OMB)gasification technology is the first large-scale gasification technology developed in China with completely independent intellectual property rights.It has been widely used around the world,involving synthetic ammonia,methanol,ethylene glycol,coal liquefaction,hydrogen production and other fields.This paper summarizes the research and development process of OMB gasification technology from the perspective of the cold model experiment and process simulation,pilotscale study and industrial demonstration.The latest progress of fundamental research in nozzle atomization and dispersion,mixing enhancement of impinging flow,multiscale reaction of different carbonaceous feedstocks,spectral characteristic of impinging flame and particle characteristics inside gasifier,and comprehensive gasification model are reviewed.The latest industrial application progress of ultralarge-scale OMB gasifier and radiant syngas cooler(RSC)combined with quenching chamber OMB gasifier are introduced,and the prospects for the future technical development are proposed as well.

岩石蠕变模型及蠕变参数识别研究综述

蠕变特性是岩石重要的力学特性之一。根据各种岩石蠕变模型的特点,总结了国内外学者对于岩石蠕变模型的研究进展,介绍了现有主要三种类型的蠕变模型和其适用性,即经验模型、元件组合模型和断裂损伤模型。对蠕变参数识别方法进行了介绍和总结。提出了建立蠕变模型和参数识别需要考虑的问题。

Mine Gas Emission Prediction Based on Grey Markov Prediction Model

This article puts forward the gray markov prediction model to predict mine gas emission by combining grey system theory and markov chain theory. And GM (1, 1) model is established in the first place for grey data by the model. To eliminate the error, and improve the prediction accuracy of the model, secondary parameters fitting was done on the basis of GM (1, 1) model. And we get second parameter fitting for trend prediction. Then using Markov state transfer probability matrix prediction method to do quadratic fitting for its predictive value, which can improve the prediction precision of the volatile random variables. It proves the prediction results of the model are satisfactory by analyzing history data of gas emission prediction. This conclusion broadens the application scope of grey forecast model and provides a new method for mine gas emission scientific forecast.

Application of Chemical Dynamics Method in Solving Hydro-Geological Parameters

With the increasing of coal mining depth, the coal seam floor is threatened more and more seriously with the limestone aquifer of Taiyuan Formation. In order to make the coal seam floor water inrush accident to be effectively prevented, it is very important to ascertain the hydro-geological condition of the research area and adequately gain hydro-geological parameters. Based on the theory of chemical dynamics, the chemical dynamical equation of the mineral was obtained. The chemical dynamical equation of the mineral and the Darcy’s Law were combined to derive the expression of permeability coefficient and transmissibility coefficient that was indicated by hydro-chemistry index. Based on the data of water quality analysis in the research area, the hydro-geology parameter of the aquifer of Taiyuan Formation was calculated. And it was compared with what the hydro-geology parameter was determined by the data of pumping test. The results show that the permeability coefficient (K) of the research area is 1.7512 m/d, and transmissibility coefficient (T) is 42.0282 m2/d. The calculated results of chemical dynamics and pumping test results are little different between them. And it has certain practical significance in the mine water control. It provides an effective method for obtaining hydro-geological parameters.

Lead-free bilayer heterometallic halide perovskite with reversible phase transition and photoluminescence properties

The layered heterometallic halide perovskites, as a newly explored material, have attracted great scientific attention. As one of the representatives of perovskite, lead-free or lead-substituted perovskite materials are widely applied in photovoltaic, sensors, catalysis, detectors and other fields. Therefore, it is urgent to carry out more systematic exploration and expand applicable preresearch, so as to make more interesting discoveries in this new hot spot. As an interesting candidate, heterometallic compounds will introduce more structural adjustability and novel physical properties, which is the main feature to be selected as the research hotspot. Here, we reported a lead-free bilayer heterometallic Ruddlesden-Popper(RP) type perovskite, [(MACH)_(2)CsAgBiBr_(7)](MACH = cyclohexanemethylamine), which possesses a reversible phase transition at 379.6 K/375.1 K during heating-cooling cycle. Besides, it exhibits reddish-brown light emission under 365 nm, meanwhile, CIE chromaticity coordinate is(0.32, 0.45) on the yellow side and correlated color temperature is about 6000 K. Moreover, both the experimental data and theoretical calculation results suggest that [(MACH)_(2)CsAgBiBr_(7)] shows indirect semiconducting characteristics. In summary, this work will inspire the design of lead-free heterometallic perovskite materials for the application of sensors and light-emitting diodes(LEDs) fields.

Investigation Method and Utilization Mode of Geothermal Resources in Abandoned Mines in Huainan and Huaibei

With the depletion of coal resources due to excessive exploitation and the increasing adjustment of the national energy structure, in response to the call of national policy, some mines are forced to close, and the reuse of abandoned mine resources plays an important role in the sustainable development of mining industry. This paper analyzes the general situation of abandoned mines in Huainan and Huaibei, elaborates the research methods of geothermal temperature and calculation methods of geothermal reserves in abandoned mines, analyzes and studies the utilization prospect of geothermal resources in abandoned mines in Huainan and Huaibei, and draws the following conclusions: the temperature of geothermal resources in abandoned mines in Huainan and Huaibei is 25℃- 60℃, which belongs to the moderate-hot water and warm water resources in low-temperature geothermal resources, and can be used for geothermal heating, industrial geothermal and entertainment industries. Based on the previous experience in geothermal resource utilization mode, this paper provides theoretical and technical support for the demonstration project of resource utilization and development of abandoned mines in the Huainan and Huaibei mining areas.

S-Trifluoroethyl Benzenesulfonothioate:A Bench-Stable Reagent for Electrophilic Trifluoroethylthiolation

of main observation and conclusion We report herein a practical approach for synthesis of an electrophilic trifluoroethylthiolation reagent PhSO2SCH2CF3(1)from easily available materials.The reaction proceeded through a protonation and nucleophilic substitution cascade of the in situ formed trifluorodiazoethane.This bench-stable reagent could easily be applied to introduce trifluoroethylthio group into small organic molecules.

Characterization of powder flow properties from micron to nanoscale using FT4 powder rheometer and PT-X powder tester

The rapid development of nanotechnology has led to a need to further understand the physical char-acteristics of nanoparticles.In this paper,the flow characteristics of micro-nano alumina particles with different particle sizes were characterized.The FT4 powder rheometer and the PT-X powder tester were used to measure the compression,friction,and dynamic properties of powders.Powder compressibility increased significantly as the particle size decreased from 27 μm to 30 nm.Pressure distribution in the silo was measured and predicted by Janssen's theory,with errors mostly less than 10%.The basic flow energy and the specific energy of the three powders were 4983,1734,and 244 mJ,and 6.80,11.70,and 6.70 mJ/g,respectively,indicating that there was no linear relationship between the change in flowability and particle size.The dynamic properties of the powders change from particle-dominated to agglomeration-dominated as the particle size decreases.The conclusion is supported by the results of field emission scanning electron microscopy.

基于第一性原理计算的低维功能材料分子设计

低维材料具有高比表面积以及独特的物理化学特性,是未来能源、信息等技术领域的重要研究内容,但如何实现特定结构和功能是其实际应用的基础.分子是保持化学结构和特性的最小单元,从分子基元出发,可以实现低维材料结构预测以及功能导向的理论设计.本文综述了低维功能材料理论设计方面的研究进展,结合分子设计策略和第一性原理电子结构计算方法,针对特定结构和性能开展理论设计,预测了复杂二维单质晶体结构以及一系列低维新型光催化材料和自旋电子学材料,并揭示了低维材料功能和分子基元物性之间的对应关系,总结和展望了低维功能材料分子设计的优势与挑战.

Treatment of soybean wastewater by a wild strain Rhodobacter sphaeroides and to produce protein under natural conditions

The conventional treatment method of soybean wastewater is expensive and generates waste sludge that requires further handling.Purple nonsulfur bacteria(PNSB)wastewater treatment is a clean technology and can generate single cell protein while degrading pollutants.A wild strain of PNSB,Rhodobacter sphaeroides Z08,was isolated from local soil and was used to treat soybean wastewater.To develop a cost-effective process,the work was performed under natural conditions without artificial light,aeration,nutrients addition,or pH and temperature adjustment.The results showed that the wild strain Rhodobacter sphaeroides Z08 could grow well under natural conditions.The growth curve showed two quickgrowth periods and a turning point.The Z08 treatment of soybean wastewater was zero order reaction and COD reduction was 96%after 10 d.The major byproducts of the process were C2-C5 organic acids,predominantly butyric acid.No alcohol was found in the effluent.The initial COD/bacterial-mass ratio(F/M)had a significant effect on soybean wastewater treatment efficiency.When the initial F/M was lower than 10 mg-COD/mg-bacteria,a sufficient amount of time to achieve 90%of COD reduction was only three days.The Z08 biomass yield was 0.28 g·g^(–1),and the bacterial protein content was 52%.

Structural shifts in the intestinal microbiota of rats treated with cyclosporine A after orthotropic liver transplantation

Understanding the effect of immunosuppressive agents on intestinal microbiota is important to reduce the mortality and morbidity from orthotopic liver transplantation (OLT). We investigated the relationship between the commonly used immunosuppressive agent cyclosporine A (CSA) and the intestinal microbial variation in an OLT model. The rat samples were divided as follows:(1) N group (normal control);(2) I group (isograft LT, Brown Norway [BN] rat to BN);(3) R group (allograft LT, Lewis to BN rat);and (4) CSA group (R group treated with CSA). The intestinal microbiota was assayed by denaturing gradient gel electrophoresis profiles and by using real-time polymerase chain reaction. The liver histopathology and the alanine/aspartate aminotransferase ratio after LT were both ameliorated by CSA. In the CSA group, the numbers of rDNA gene copies of Clostridium cluster I, Clostridium cluster XIV, and Enterobacteriaceae decreased, whereas those of Faecalibacterium prausnitzii increased compared with the R group. Cluster analysis indicated that the samples from the N, I, and CSA groups were clustered, whereas the other clusters contained the samples from the R group. Hence, CSA ameliorates hepatic graft injury and partially restores gut microbiota following LT, and these may benefit hepatic graft rejection.

Molecular imprinting and cladding produces antibody mimics with significantly improved affinity and specificity

Molecularly imprinted polymers(MIPs),as important mimics of antibodies,are chemically synthesized by polymerization in the presence of a target compound.MIPs have found wide applications in important fileds.However,the current molecular imprinting technology suffers from a dilemma;there is often a compromise between the best affinity and the best specificity for MIPs prepared under optimized condi-tions.Herein,we proposed a new strategy called molecular imprinting and cladding(MIC)to solve this issue.The principle is straightforward;after molecular imprinting,a chemically inert cladding thinlayer is generated to precisely cover non-imprinted area.We further proposed a special MIC approach for con-trollably engineering protein binders.The prepared cladded MIPs(cMIPs)exhibited significantly improved affinity and specificity.The general applicability of the proposed strategy and method was ver-ified by engineering of cMIPs for the recognition of a variety of different proteins.The feasibility of cMIPs for real applications was demonstrated by fluorescence imaging of cancer cells against normal cells and immunoassay of C-peptide in human urine.This study opened up a new avenue for controllably engi-neering protein-specific antibody mimics with excellent recognition properties,holding great prospective in important applications such as disease diagnosis and nanomedicine.

低维自旋电子材料的理论设计与调控

自旋电子器件利用电子的自旋进行信息的传递、处理与存储,是未来信息技术的重要载体.低维体系具有显著的量子耦合效应,是研究电荷/自旋相互作用机制、发展纳米自旋电子器件的重要载体.由于缺陷、杂质、界面以及边界效应等提供的冗余自由度,使得长程有序磁性体系的制备、维护和调控远无法达到器件化的基本条件,寻找具有高居里温度、高自旋极化率等特性的低维材料是目前面临的挑战.基于密度泛函理论、热动力学模拟等第一性原理方法的计算结果,应用合适的物理统计模型,可以加深对低维材料结构-机制-性能的认识,为自旋电子学材料的发展提供理论支持,并通过应力和电荷掺杂,对低维材料的磁性进行调控.