Investigation on Cracking in the Surfacing Welding Layer of Ni_3Al Based Alloy

Investigation has been made into the causes of cracking in the Surfacing welding layer of Ni3Al based alloy by analysing both the liqu id-to-solid transformation in the molten pool and the distribution of thermal stress within the surfacing welding layer. The results show that cracking in the surfacing welding layer is directly related to the producing of eutectic phase β' (NiAl) in the interdendritic region and high thermal stress within the surfacing welding layer. When the process of electric arc surfacing welding is changed from along straight line to along' Z' pattern, cracking in the surfacing welding layer of Ni3Al based alloy is prevented due to being reduced of both the cooling rate of liquid in the molten pool and the moving speed of the heat source. Reducing the melting volume of the substrate material by lowering the output power of electric arc welding would make the content of iron atoms in the molten pool decrease. and this also can reduce the trend of the eutectic reaction in the interdendfitic region and is helpful to Suppress cracking in the surfacing welding layer.

Three-Dimensional Planar Metallic Lenses Based on Concentric Rings with Modulated Subwavelength Width

A kind of Subwavelength Planar Metallic Lenses (SPMLs) is proposed to realize far-field optical focusing in the visible range based on concentric rings with modulated width in a silver film. The width of each metallic ring is mutative so that the radiation fields of surface plasmon polaritons can be controlled and the relevant phase retardations can be modulated to make a beam focus at the desired position. For comparison, the Subwavelength Planar Dielectric Lenses (SPDLs) structured on silica glass with the same concentric ring shapes as SPMLs are analyzed, although without opaque metal coating on SPDLs, the computational results show that SPMLs can support higher intensity focal spot, narrower full-width half-maximum beam width, and longer depth of focus at the focal region under certain lens thickness due to the coupling of surface plasomon polaritons, diffracted evanescent waves and propagated electromagnetic waves.

城市轨道交通车辆应答器传输模块电磁干扰原因及其应对措施

目的:实际运营中经常出现车载变流系统对车载BTM(应答器传输模块)天线产生电磁干扰、导致BTM天线无法正常工作的情况,需找出电磁干扰的原因,并制定干扰抑制措施。方法:先对干扰源进行定位,确定其干扰源是车载变流系统;阐述了变流系统产生电磁干扰的机理和传输路径,初步分析了变流系统产生的共模干扰分量与差模干扰分量对BTM天线正常工作产生的影响。建立了简化电路模型和理论计算公式,给出了所增设器件的参数范围。提出了抑制变流系统产生差模干扰和共模干扰的三个方案,对三个方案下变流系统对外端口产生的干扰幅值进行测试。结果及结论:增加共模干扰和差模干扰信号的流通路径后,实现了干扰信号在变流系统内的循环流通,减少了对变流系统外设备的传导干扰。方案三可以有效解决BTM天线受扰问题。

Effect of solidification mode on microstructure evolution and properties of magnesium alloy with long-period stacking ordered phase

The solidification methods of electromagnetic stirring(EMS)and non-electromagnetic stirring were employed to prepare Mg–6Gd–3Y–xZn–0.6Zr(x=1,1.5,2,3)alloys.The evolution of alloy microstructures and the changes in properties were analyzed for different Zn contents.It has been observed that in alloys without electromagnetic stirring,as the Zn content increases,the alloy structure gradually refines.The primary second phase transitions from Mg5RE phase to long-period stacking ordered(LPSO)phase,resulting in improved hardness and elongation.In alloys subjected to electromagnetic stirring,there is a relatively higher content of the second phase,primarily consisting of LPSO phase.After applying electromagnetic stirring,the quantity and the type of LPSO phase in the alloy change.The alloy structure becomes more uniform with electromagnetic stirring,resulting in increased hardness and reduced hardness gradients within the grains.The mechanical properties of alloys with electromagnetic stirring are superior to those without electromagnetic stirring.

添加La-Ce对Al-18Si-4Cu-0.5Mg合金显微组织和力学性能的影响

通过光学显微镜、扫描电镜、电子探针和拉伸测试研究添加镧铈稀土后Al-18Si-4Cu-0.5Mg合金的组织演变和力学性能。光学显微镜和扫描电镜结果表明,添加镧铈稀土后初晶硅颗粒由粗大块状和不规则多边形状明显细化为细片状,共晶硅由粗长针状细化为短棒状和珊瑚状。添加0.3%镧铈稀土时,合金具有最小初晶硅尺寸和最佳力学性能。此时,初晶硅平均尺寸由61μm细化至28μm,抗拉强度由222 MPa增大到242 MPa,伸长率由3.2%提高至6.3%。此外,还通过扫描电镜和电子探针探究合金的变质机制和断裂模式。

酶循环法定量检测血清同型半胱氨酸的技术性能评价

目的:评价酶循环法(ECM)定量检测血清同型半胱氨酸(Hcy)的技术性能。方法:参考NCCLS评价方案,评价ECM定量检测血清Hcy的准确度、精密度、线性范围和干扰因素。结果:ECM定量检测低、高水平定值质控血清Hcy的相对偏差分别为2.52%和4.28%;正常值和高值血清测定的批内变异系数(CV)和总CV分别为1.63%~1.58%和4.65%~3.88%;3.12~49.98 umol/L范围内测定的线性相关系数(r^(2))达到0.9971;胆红素(20 mg/dL)、乳糜(1000 mg/dL)和维生素C(10 mg/dL)对该检测方法无显著性干扰(P>0.05)。结论:酶循环法不仅实用性高,而且可靠性强,因此在各级医疗机构的检验科均可普及使用。

编码大鼠ENPP1蛋白的cDNA克隆及重组腺相关病毒构建

目的:克隆编码大鼠外核苷酸焦磷酸酶/磷酸二酯酶1(ENPP1)的全长cDNA片段,构建ENPP1重组腺相关病毒载体(AAV-ENPP1)。方法:以大鼠血管平滑肌细胞mRNA为模板,通过RT-PCR扩增获得大鼠ENPP1基因大片段并克隆至pCDH载体中,经过EcoR I/Xho I酶切、连接、转化将该片段克隆至腺相关病毒载体pAAV-MCS中,酶切及DNA测序对阳性克隆进行鉴定。重组AAV-ENPP1经包装后转染目的血管平滑肌细胞,Western blot检测目的蛋白ENPP1的表达。结果:RT-PCR成功克隆出2721 bp的大鼠ENPP1基因大片段,并最终获得测序正确的pAAV/ENPP1克隆,Western blot检测显示目的蛋白ENPP1的表达升高。结论:成功构建大鼠ENPP1重组腺相关病毒载体。

高职英语教学中批判性思维的培养模式探究

建立新型英语教学模式,以批判性思维为导向,文章从提高学生的学习品质、教学方法、教学活动、教学环境和评测形式方面,以培养学生的批判性思维,提高学生的英语学习能力。

翻转课堂助力高职英语教学改革

现如今高职院校的英语教学由于仍采用原有的教育模式,只针对眼前的各种专业或是学业考试,没有注重长远的发展与应用,使得学生在日后的工作中没有竞争优势,文章通过对翻转课堂的优势进行介绍,提出了翻转课堂的应用方法。

Evaluation on Tourism Ecological Security in Nature Heritage Sites——Case of Kanas Nature Reserve of Xinjiang,China

The nature heritages are the precious legacy of nature with outstanding scientific and aesthetic value. They are quite different from other common ecotourism areas, because of its original and unique system, sensitive and vulnerable landscape, and peripheral cultural features. Therefore, the tourism development in the nature heritage sites should be on the premise of ecological security. The evaluation index system of tourism ecological security in nature heritage sites was constructed in this article by AHP and Delphi methods, including nature ecological security, landscape visual security and local culture ecological security, and the security thresholds of indices were also established. In the indices' weights of the evaluation model, the nature ecological security ranked the highest, followed by tourist landscape visual security and culture ecological security, which reflected the influence degree of the limited factor to tourism ecological security. Then, this paper carried out an empirical study of Kanas of Xinjiang Uygur Autonomous Region, China, which has the potential to be the World Nature Heritage. On the basis of the data attained from survey and observation on the spot, as well as questionnaire answered by tourists and local communities, the ecological security status in Kanas was evaluated. The result showed that the status of Kanas tourism ecological security was better, but there had some limiting factors. Lastly, effective measures were put forward to ensure its ecological security.

Estimation on Aesthetic Value of Tourist Landscapes in a Natural Heritage Site:Kanas National Nature Reserve,Xinjiang,China

Most world natural heritage sites are designated partly by reason of their prominent aesthetic values in accordance with Article Ⅶ of World Natural Heritage Convention.In this paper, the aesthetic values of Kanas National Nature Reserve, which has potential for such designation, was analyzed quantitatively using scenic beauty estimation(SBE).The landscapes of 19 representative scenic spots in the Kanas National Nature Reserve in summer and autumn were selected as the objects of evaluation.The contributions of different landscape factors to the aesthetic value of the Kanas National Nature Reserve were revealed using a multivariate quantitative model.The main factors affecting the aesthetic value were waterscapes, vegetation, mountains, folk culture and the tourist environment.The t-test and F-test results are extremely significant.According to the results, some suggestions were given for conserving the landscapes in the Kanas National Nature Reserve.

Effects of conform continuous extrusion and heat treatment on the microstructure and mechanical properties of Al–13Si–7.5Cu–1Mg alloy

The effects of conform continuous extrusion and subsequent heat treatment on the mechanical and wear-resistance properties of high-alloying Al–13Si–7.5Cu–1Mg alloy were investigated.The microstructures of alloys before and after conform processing and aging were compared by transmission electron microscopy and scanning electron microscopy,respectively.The results reveal that the primary phases were broken and refined by intense shear deformation during conform processing.After the conform-prepared Al–13Si–7.5Cu–1Mg alloy was subjected to solid-solution treatment at 494℃for 1.5 h and aging at 180℃for 4 h,its hardness improved from HBS 115.8 to HBS 152.5 and its ultimate tensile strength increased from 112.6 to 486.8 MPa.Its wear resistance was also enhanced.The factors leading to the enhanced strength,hardness,and wear resistance of the alloy were discussed in detail.

玉米盐诱导型启动子克隆及其植物表达载体构建

首先提取B73玉米(Zea mays)的基因组DNA,以此为模板利用PCR的方法克隆Zea mays salt-inducible protein kinase(STY2)基因上游1675 bp,将其命名为STY。从网站PlantCARE上的启动子预测工具在线对克隆到的启动子进行分析,结果表明:STY启动子中含有多种调控元件,典型的调控元件有:TATA-box,CAAT-box等等。另外还有2个盐诱导顺式作用元件GT1-motif和一些冷、干旱胁迫诱导有关的顺式作用元件,以及功能未知的元件。然后将克隆到的基因与植物双元表达载体pCAMBIA1301连接,并将其转入根癌农杆菌EHA105中,然后利用农杆菌介导法转化烟草,经过GUS组织化学染色验证STY的诱导功能。研究表明:STY启动子片段具有启动活性,为解决东北地区农业生产中严重的多元逆境胁迫问题开辟了有效途径。

城市轨道交通车辆应急启动电路改进及控制方法优化方案

城市轨道交通列车在应急启动模式下,如在蓄电池亏电工况下直接带载启动,会发生充电机过流停机问题,其在启动过程中还存在应急启动电源停机的问题。基于列车应急启动模式工作原理,针对性地提出优化的应急启动电路并对相应控制方法进行优化,实现了应急启动模式的一键激活列车。优化后的应急启动电路及优化控制方法已在济南轨道交通R2线上进行了试验。试验效果良好,验证了优化应急启动电路及优化控制方法的可用性和有效性。

基于改进层次分析法的信息安全风险评估

以智能船舶项目建设为背景,研究可能导致信息安全风险的27种因素,分别采用故障树分析法、层次分析法和改进层次分析法对典型网络环境信息安全架构进行评估。根据逻辑门原理,将故障树的基本要素和层次分析法基本要素建立联系,分别建立其判断矩阵并计算各基本要素的权重,在此基础上求得综合权重并进行排序。通过与实际环境对比,发现改进层次分析法较之另外两种方法具有更高的可靠性。通过改进层次分析法找出系统薄弱点和风险点并进行改进,可系统全面地保护关键设备和数据,将智能船岸基信息安全风险降低到可接受的水平,从根本上保证业务的连续性。

Study on the adaptability of augmented reality smartglasses for astigmatism based on holographic waveguide grating

Background Augmen ted reality(AR)smartglasses are considered as the next generation of smart devices to replace mobile phones,and are widely concerned.But at present,AR smartglasses are usually designed according to the human normal eyes.In order to experience AR smartglasses perfectly,abnormal eye users must first wear diopters.Methods For people with astigmatism to use AR smartglasses without wearing a diopter lens,a cylindrical lens waveguide grating is designed in this study based on the principle of holographic waveguide grating.First,a cylindrical lens waveguide substrate is constructed for external light deflection to satisfy the users'normal viewing of the real world.Further,a variable period grating structure is established based on the cylindrical lens waveguide substrate to normally emit the light from the virtual world in the optical machine to the human eyes.Finally,the structural parameters of grating are optimized to improve the diffraction efficiency.Results The results show that the structure of cylindrical lens waveguide grating allows people with astigmatism to wear AR smartglasses directly.The total light utilization rate reaches 90%with excellent imaging uniformity.The brightness difference is less than 0.92%and the vertical field of view is 10°.Conclusions This research serves as a guide for AR product designs for people with long/short sightedness and promotes the development of such products.

Vitamin A deficiency suppresses CEACAM1 to impair colonic epithelial barrier function via downregulating microbial-derived short-chain fatty acids

Vitamin A (VA) plays an essential role in modulating both the gut microbiota and gut barrier function.Short-chain fatty acids (SCFAs),as metabolites of the gut microbiota,protect the physiological intestinal barrier;however,they are compromised when VA is deficient.Thus,there is an urgent need to understand how and which SCFAs modulate colonic epithelial barrier integrity in VA deficiency (VAD).Herein,compared with normal VA rats (VAN),at the beginning of pregnancy,we confirmed that the colonic desmosome junction was impaired in the VAD group,and the amounts of acetate,propionate,and butyrate declined because of the decreased abundance of SCFA-producing bacteria (Romboutsia ,Collinsella ,and Allobaculum ).The differentially expressed genes correlated with the gut barrier and the histone deacetylase complex between the VAD and VAN groups were enriched by RNA sequencing.In the VAD group,the expression levels of colonic CEA cell adhesion molecule 1 (CEACAM1) were down-regulated,and the levels of histone deacetylase 1 (HDAC1) and HDAC3 were up-regulated.Intriguingly,the above changes in the VAD groups were rescued by VA supplementation in the early postnatal period.Further study indicated that in Caco-2 cells,butyrate treatment significantly repressed the enrichment of HDAC3 on the promoter of the CEACAM1 gene to induce its expression.Our findings support that butyrate intervention can alleviate the impairment of colonic barrier function caused by VAD,and timely postnatal VA intervention may reverse the damage caused by VAD on gut barrier integrity during pregnancy.

Hot workability characteristics of Rene88DT superalloy with directionally solidified microstructure

The hot deformation characteristics of Rene88DT superalloy with directionally solidified micro- structure produced by electroslag remelting continuous directionally solidification （ESR-CDS） were studied in the temperature range of 1,040-1,140 ℃ and strain rate range of 0.001-1.000 s-1 by hot compression tests. Flow curves for Rene88DT alloy with initial directionally solidified （DS） microstructure exhibit pronounced peak stresses at the early stage of deformation followed by the occurrence of dynamic softening phenomenon. Rene88DT alloy with DS micro- structure shows higher flow peak stresses compared with HIPed P/M superalloy FGH4096, but the disparities in peak stresses between ESR-CDSed Rene88DT and HIPed P/M superalloy FGH4096 reduce as temperature increases. The improvement of hot workability of DS alloy with columnar grains avoiding the maximum shear stress comes true. A hot deformation constitutive equation as a function of strain that describes the dependence of flow stress on strain rate and temperature is established. Hot deformation apparent acti- vation energy （Q） varies not only with the strain rate and temperature but also with strain. The strain rate sensitivity exponent （m） map is established at the strain of 0.8, which reveals that global dynamic recrystallization （DRX） shows a relatively high m value in a large strain compression. Optimum parameters are predicted in two regions： T = 1,100-1,130 ℃, ε = 0.100-1.000 s-1 and T = 1,080- 1,100 ℃, ε = 0.010-100 s-1, which is based on pro- cessing maps and deformation microstructure observations.

Effects of slurry viscosity and particle additive size on filter cake formation in highly permeable sand

Filter cake is critical to maintaining the stability of the excavation face of an underwater shield tunnel in a high-permeability stratum.In a high-permeability formation,generating an effective filter cake on the excavation face is difficult with a pure bentonite slurry,which penetrates the ground and may not achieve the required suspension pressure.Determining how to efficiently and quickly form a thin and low-permeability filter cake on the tunnel working face has become a key engineering problem in the construction of slurry shield tunnels in high-permeability strata.In this study,the relationship between slurry viscosity and the slurry pressure gradient of pure bentonite was established by performing slurry permeability experiments.The influence of slurry viscosity on the formation of the filter cake in a high-permeability formation was studied under different pressure gradients.In addition,the effect of additive particle size on the slurry filter cake formation was analyzed by introducing additives with different particle sizes to pure bentonite slurries with different viscosities.The test results indicate that(1)for the pure bentonite slurry,the critical initial pressure gradient can be used as a rough indicator of the formation of the filter cake,and the relationship between the critical maximum pore diameter and the average pore diameter of the for-mation can be compared to establish and analyze the formation law of the slurry filter cake;(2)adding particles to the slurry can enhance the effect of the pure bentonite slurry;and(3)adding coarse-grained materials can effectively improve the film-forming effect.The slurry is more compact when the particle size is close to the average pore size of the formation.

Effect of extrusion temperature on microstructure and tensile properties of Mg-Gd-Er-Zn-Zr alloy containing LPSO phase

The Mg-1Gd-0.75Er-0.5Zn-0.18Zr(at.%)alloy with long-period stacking ordered(LPSO)phase was prepared by metal mold casting and hot extrusion.The extruded samples had a typical bimodal microstructure.The different fractions of equiaxed grains were observed in annealed samples.The percentage of fine grains decreased in the extruded Mg alloys with and without annealing treatment when the extrusion temperature was increased.The LPSO phases promote recrystal-lization behavior in the samples through particle-stimulated nucleation(PSN)mechanism.The Mg alloys extruded at 300℃ with or without annealing treatment obtained the best tensile properties.At the low extrusion temperature,more finely equiaxed grains with random texture are formed through PSN,and more LPSO phase kink bands are formed,which could improve the mechanical properties of the extruded Mg alloys.