A Possible Mechanism of the Impact of Atmosphere-Ocean Interaction on the Activity of Tropical Cyclones Affecting China

In this study, tropical cyclone data from China Meteorological Administration （CMA） and the ECMWF reanalysis data for the period 1958-2001 was used to propose a possible mechanism for the impacts of air- sea interaction on the activity of tropical cyclones （TCs） affecting China. The frequency of TCs affecting China over past 40 years has trended downward, while during the same period, the air sea interaction in the two key areas of the Pacific region has significantly weakened. Our diagnoses and simulations suggest that air sea interactions in the central North Pacific tropics and subtropics （Area 1） have an important role in adjusting typhoon activities in the Northwest Pacific in general, and especially in TC activity affecting China. On the contrary, impacts of the air-sea interaction in the eastern part of the South Pacific tropics （Area 2） were found to be rather limited. As both observational analysis and modeling studies show that, in the past four decades and beyond, the weakening trend of the latent heat released from Area 1 matched well with the decreasing Northwest Pacific TC frequency derived from CMA datasets. Results also showed that the weakening trend of latent heat flux in the area was most likely due to the decreasing TC frequency over the Northwest Pacific, including those affecting China. Although our preliminary analysis revealed a possible mechanism through which the air sea interaction may adjust the genesis conditions for TCs, which eventually affect China, other relevant questions, such as how TC tracks and impacts are affected by these trends, remain unanswered. Further in-depth investigations are required.

MICROSTRUCTURE AND MECHANICAL PROPERTY DEVELOPMENT IN THE SIMULATED HEAT AFFECTED ZONE OF V TREATED HSLA STEELS

The simulated heat affected zone （HAZ） of the high strength low alloy （HSLA） steels containing 0%, 0.047%, 0.097% and 0.151% vanadium, respectively, were studied with Gleeble-2000 thermomechanical simulator to determine the influence of vanadium addition on the mechanical properties of the HAZ. The HAZ simulation involved reheating the samples to 1350℃, and then cooling to ambient temperature at a cooling rate of 5℃/s ranging from 800 to 500℃ （△8/5=60s）. The mechanical properties including tensile strength and -20℃ impact toughness were conducted. The microstructures of the base steel and the simulated HAZs were investigated using optical microscope, scanning electron microscope （ SEM ） and transmission electron microscope （TEM）. Based on the systemutic examination, the present work confirmed that about 0.05% vanadium addition to low carbon low alloy steels resulted in expected balance of strength and toughness of the HAZ. And more than 0.10% levels addition led to detrimental toughness of the HAZ SEM study showed that the simulated 0.097% and 0.151%V HAZs consisted of more coarse ferrite plates with greater and more M-A constituents along austenite grain and ferrite plate bound- aries. The impact fracture surfaces of the simulated 0.097% and 0.151%V HAZs showed typically brittle mode with predominant cleavages. The size of the facet in the fracture surface increased with increasing vanadium level from 0.097% to 0.151%.As a result, the simulated 0.151% V HAZ has the lowest impact toughness of the four specimens.

Microstructure and mechanical properties of heat affected zone in multi-pass GMA welded Al-Zn-Mg-Cu alloy

Microstructure and mechanical properties of the heat affected zone(HAZ)in multi-pass gas metal arc(GMA)welded Al Zn Mg Cu alloy plates were investigated,based upon which the mechanical anisotropy and fracture mechanism were analyzed.The microstructure and composition were analyzed by scanning electron microscope(SEM)and energy dispersive spectroscope(EDS).X-ray diffractometer(XRD),transmission electron microscope(TEM)and selective area electron diffraction(SAED)were used to analyze the phase composition.The distribution of microhardness was identified as gradual transition and tensile strength had a tendency to decrease first and then increase.The distribution of nano-sizedη(MgZn2)particles in theα(Al)matrix and Al2MgCu phase determined the tensile performances along the thickness direction and led to the formation of ductile/brittle composite fracture in the HAZ.The continuous distribution of Al2MgCu phase in the strip intergranular precipitates gave birth to premature cracks and the brittle fracture region.The precipitated particles coarsening also led to the deterioration of mechanical properties.

Crushing Mechanism of Spherical Tungsten Alloy Fragments Penetrate Thick Steel Plate Target

Against protection requirements for high-speed fragments on the ground weapons,we carried out the research work of crushing mechanism at different impact speeds ofφ8.7 mm spherical tungsten alloy,the penetration to 603 armor steel was completed by 20 mm ballistic gun,and the ANSYS/LS-DYNA software was used to complete the numerical calculation of the penetration.We find that there are different crushing mechanisms of spherical tungsten alloy with different speeds and low speed,the crushing mechanism of fragment is mainly controlled by overall plastic deformation,shearing stripping,and squeezing at a high pressure and a high speed.The crushing mechanism will have a spallation phenomenon in addition to the crushing mechanism under high pressure.

MICROSTRUCTURE AND INCLUSION CHARACTERIZATION IN THE SIMULATED COARSE-GRAIN HEAT AFFECTED ZONE WITH LARGE HEAT INPUT OF A Ti-Zr-MICROALLOYED HSLA STEEL

The microstructure and the characteristics of the inclusions embedded in ferrite matrix in simulated coarse-grain heat affected zone (CGHAZ) of a Ti-Zr-treated high strength low alloy (HSLA) steel have been investigated. The microstructure of the simulated CGHAZ dominantly consisted of intragranular acicular ferrite (IAF) combining with a small amount of polygonal ferrite (PF), widmanst tten ferrite (WF), bainite ferrite (BF), pearlite and martensite-austenite (M-A) islands. The PF, WF and BF were generally observed at the prior austenite grain boundaries and the interlocking acicular ferrite was usually found intragranularly. It was found that the inclusions were composed of Ti2O3, ZrO2, Al2O3 locating at the center of the particles and MnS lying on the surface layer of the inclusions. The intragranular complex inclusions promoted the acicular ferrite formation and the refinement of microstructure whilst those at prior austenite grain boundaries caused PF formation on the inclusions. The simulated CGHAZ consisting of such complicated microstructure exhibited desired mechanical properties.

Heterogeneous Fenton-like discoloration of methyl orange using Fe3O4/MWCNTs as catalyst： combination mechanism and affecting parameters

Multi-walled carbon nanotubes （MWCNTs） can act not only as a support for Fe3O4 nanoparticles （NPs） but also as a coworker with synergistic effect, accordingly improving the heterogeneous Fenton-like efficiency of Fe3O4 NPs. In this study, Fe3O4 NPs were in situ anchored onto MWCNTs by a moderate co-precipitation method and the as-prepared Fe3O4/MWCNTs nanocomposites were employed as the highly efficient Fenton-like catalysts. The analyses of XRD, FTIR, Raman, FESEM, TEM and HRTEM results indicated the formation of Fe3O4 crystals in Fe3O4/MWCNTs nanocomposites prepared at different conditions and the interaction between Fe3O4 NPs and MWCNTs. Over a wide pH range, the surface of modified MWCNTs possessed negative charges. Based on these results, the possible combination mechanism between Fe3O4 NPs and MWCNTs was discussed and proposed. Moreover, the effects of preparation and catalytic conditions on the Fenton-like catalytic efficiency were investigated in order to gain further insight into the heterogeneous Fenton-like reaction catalyzed by Fe3O4/MWCNTs nanocomposites.

A decoupled method to identify affecting mechanism of crosswind on performance of a natural draft dry cooling tower

The natural draft dry cooling tower(NDDCT)has been increasingly used for cooling in power generation in arid area.As crosswind affects the performance of a NDDCT in a complicated way,and the basic affecting mechanism is unclear,attempts have been made to improve the performance of a NDDCT based on limited experiences.This paper introduces a decoupled method to study the complicated crosswind effects on the inlet and outlet of a NDDCT separately by computational fluid dynamics(CFD)modeling and hot state experiments.Accordingly,the basic affecting mechanism of crosswind on the NDDCT performance is identified.Crosswind changes the inlet flow field of a NDDCT and induces mainstream vortices inside the tower,so as to degrade the ventilation.Besides,low crosswind deflects the upward plume at the outlet to further degrade the ventilation,while high crosswind induces the low pressure area at the outlet to reduce the ventilation degradation.

Study on laser welded heat-affected zone in new ultralow carbon bainitic steel

800 MPa grade ultralow carbon bainitic （NULCB） steel is the recently developed new generation steel, which was produced by thermo mechanical controlled processing ＆ relaxation-precipitation controlling transformation （TMCP＆RPC） tech- nique. The microstructure and the mechanical properties of the heat-affected zone （HAZ） in NULCB steel under laser welding conditions were investigated by using a Gleeble-1500 thermal simulator. The experimental results indicate that the simplex microstructure in the HAZ is granular bainite that consists of bainite-ferrite （BF） lath and M-A constituent when the cooling time from 800 to 500℃ （t8/5） is 0.3-30 s, and the M-A constituent consists of twinned martensite and residual austenite. As t8/5 increases, the hardness and tensile strength of HAZ decreases, but they are higher than that of the base metal, indicating the absence of softened zone after laser welding. The impact toughness of HAZ increases at first and then decreases when t8/5 increases. The impact energy of HAZ is much higher than that of the base metal when t8/5 is between 3 and 15 s. It indicates that excellent low temperature toughness can be obtained under appropriate laser welding conditions.

新能源汽车政策下居民出行意向多群组分析

为研究新能源汽车政策对不同群体居民出行意向影响存在的差异性问题,提出新能源汽车政策下居民出行意向多群组模型.以计划行为理论为基础,整合居民对新能源汽车政策的态度、响应程度以及低碳理念,构建新能源汽车政策下居民出行意向模型,并对模型进行检验及修正,划分多群组,对修正后的模型进行多群组分析,研究新能源汽车政策对不同出行方式偏好群体影响机理的差异性.研究结果表明:居民对新能源汽车政策的态度、响应以及低碳理念对出行态度、主观规范、知觉行为控制以及行为意向的影响在不同出行方式偏好下存在显著差异;居民对新能源汽车政策的态度越积极、低碳理念越强,则选择新能源汽车或公共交通出行的意向越强;居民对新能源汽车政策的响应越积极,则选择新能源汽车出行的意向越强;改善居民对新能源汽车政策的态度、响应,可促进新能源汽车的使用;通过提升居民的低碳理念,可提高居民采用公共交通或新能源汽车出行的意向.研究可为通过交通政策调整居民出行意向以及制定交通政策提供参考.

基于句法依赖增强图的方面级情感分析

方面级情感分析旨在分析句子中特定方面的情感极性,现有研究侧重于利用图神经网络建模上下文与方面的依赖信息,忽略了对上下文中情感词及其词性的挖掘和利用。为此,提出一种基于句法依赖的增强图(syntactic dependency enhancement graph, SDEG)模型,在原始句法依赖图上引入情感知识和词性信息,增强情感词权重和相关词性单词在上下文中的作用。使用双向长短期记忆网络和卷积神经网络捕捉句子的重点语义信息,通过图卷积神经网络建模句法依赖增强图,通过交互注意力机制生成特定方面的上下文语义和语法表示以进行情感极性分类。在多个公共基准数据集上的实验结果表明,所提模型在性能上有明显提升。

在流动中走向融合:推动城乡融合发展的实现机制——基于陕西省F县的案例考察

能否在人口快速流动的城乡社会转型发展中加快推进城乡融合发展,是实现农业农村现代化不容忽视的问题。基于城乡融合发展的流动性增强和空间转向的双重基础,通过陕西省F县城乡融合发展实践的案例分析,探究流动情境下城乡融合发展的实现逻辑。研究发现,流动性内嵌于城乡融合发展过程,通过人口流动的表征对传统城乡二元结构带来地域性变化和社会关系转变;在“乡—城”流动、“城—乡”流动和“城乡两栖”的多元人口流动样态下,城乡融合发展实现过程呈现跨域协同机制、关系协调机制和情感维系机制,表现出在流动中走向融合的内在逻辑。推进城乡融合发展,要突破传统二元结构对城乡融合发展研究的单一图解,在流动性引致的城乡社会变迁中,加强城乡物理空间、社会空间和情感空间的融合,进而促进城乡秩序均衡。

地聚合物复合材料断裂性能研究进展

混凝土的断裂性能直接影响着结构的安全性和耐久性。研究裂缝在混凝土中的扩展规律,是分析混凝土断裂性能的基础。具有非均质和非线性特性的混凝土是一种多相材料,在其内部存在大量初始裂缝,因此混凝土的断裂机理十分复杂,影响因素颇多。目前,普通混凝土断裂性能的分析方法比较成熟,针对混凝土的非线性特性已经建立了两类模型:便于数值分析的缝面软化模型和便于解析计算的等效弹性裂缝模型。此外,地聚合物是一种低碳环保的建筑材料,具有优异的机械性能、耐久性能和耐高温性能。因此,对于地聚合物复合材料(geopolymer composite, GPC)的断裂性能研究是推广其工程应用的必要前提。地聚合物与普通混凝土具有相似的脆性,研究者们基于普通混凝土断裂力学的分析方法,开展了GPC断裂性能的研究。本综述梳理了混凝土断裂力学发展历程,概括了GPC性能的主要影响因素,总结了原材料组成、碱激发剂和纤维对GPC断裂性能的影响,并对GPC断裂性能的未来研究方向进行了展望。

国产P91钢焊接接头热影响区各亚区域的热处理模拟

采用不同温度(800,850,950,1 300℃)×25 min的正火+755℃×60 min回火处理分别模拟P91钢接头热影响区不同亚区域,采用650℃×200 h高温加速时效热处理工艺模拟服役50 000 h工况,通过对比热模拟和实际接头试样研究了服役50 000 h后P91钢焊接接头热影响区不同亚区域的组织及性能。结果表明:粗晶区、细晶区服役态热模拟试样的马氏体板条形态以及MX相、M_(23)C_(6)碳化物和Laves相的数量、分布、颗粒尺寸与实际接头相应亚区域均十分接近;除粗晶区外,热影响区各亚区域服役态热模拟试样和实际服役接头相应区域的平均晶粒尺寸十分接近,相对误差不超过12.5%,显微硬度和微型杯突力学性能相近,强度、韧度和断裂挠度率相对误差均在5%以内,断口呈典型微孔聚集型韧性断裂特征;热影响区部分相变区显微硬度最小,为191 HV,在细晶区和粗晶区硬度大幅上升,在熔合线处达到最大,为314 HV;热影响区粗晶区的微型杯突强度最大,塑性最差,部分相变区的强度最低,塑性最好;相比粗晶区,部分相变区的颈缩程度更高,韧窝更大更深。

开放式创新平台激励与约束机制对用户创新行为的影响

平台的开放共享特征促使用户更主动地参与到价值创造活动中,企业吸纳用户参与创新过程成为其提升创新能力的重要途径。从认知—情感双重视角出发,以创新自我效能感、情感承诺为中介变量,以主动型人格为调节变量,探究开放式创新平台激励与约束机制对用户创新行为的影响机制及边界条件。结果显示,开放式创新平台激励机制、约束机制对用户创新行为均具有正向影响;创新自我效能感与情感承诺分别在开放式创新平台激励机制、约束机制与用户创新行为间发挥部分中介作用;主动型人格分别在开放式创新平台激励机制、约束机制与用户创新行为间发挥正向调节作用。

多道焊接热循环对6082-T6铝合金接头热影响区显微组织及力学性能的影响

采用ER5087铝合金焊丝在6082-T6铝合金板上进行四道双脉冲熔化极惰性气体保护堆焊,在焊接热影响区不同位置取样进行显微组织观察和力学性能测试,结合焊接温度场数值模拟研究了多道焊接热循环对热影响区不同位置显微组织及力学性能的影响。结果表明:根据试验测得的热影响区截面硬度变化和模拟得到的热影响区截面峰值温度变化规律,结合材料热处理工艺将6082-T6铝合金焊接接头热影响区按照距熔合线由远到近分为过时效区(A区)、严重过时效区(B区)和固溶区(C区)。随着焊接道次的增加,热影响区晶粒粗化,A区析出相发生β″相+β'相→β'相+U2相→β相+β'相+半溶解相→β'相+半溶解相转变;不同道次焊接后B区析出相基本呈半溶解状态,C区有序析出相完全溶解,析出大量GP区;随着焊接道次的增加,热影响区A区、B区的析出相逐渐粗化和溶解,C区的GP区数量减少。四道焊接后,热影响区整体力学性能下降,热影响区B区的软化现象最严重。热影响区软化的主要原因是析出相的演变而非晶粒的粗化。

Ti_(2)AlNb合金热模拟焊接热影响区的组织与力学性能

Ti_(2)AlNb合金因其较高的比强度和高温抗氧化能力,是先进航空发动机热端部件的重要候选材料。但作为金属间化合物材料,其焊接性能是一重要挑战。为了解焊接热循环对合金组织性能的影响规律,使用Gleeble3500热模拟试验机模拟了Ti_(2)AlNb合金焊缝附近热影响区的热循环,研究了冷却速度对焊接热影响区组织与性能的影响;根据热膨胀-温度曲线,结合不同冷速下合金的显微组织,建立了Ti_(2)AlNb合金焊接热影响区连续冷却转变(SH-CCT)曲线。结果表明:在快速加热至B2单相区后的连续冷却过程中Ti_(2)AlNb合金中主要析出相为O相,α_(2)相的析出量很少。随着冷却速度的增加,析出相的数量逐渐减少、尺寸降低,且α_(2)相的析出率先被抑制,B2相向O相转变的温度区间缩小。冷却速度低,合金中析出相数量多,强度高,但塑性低。反之,随着冷速的增加,残留B2相增多,合金的塑性得到改善。

配FRP矩形箍混凝土梁的受剪承载力研究现状

钢筋在恶劣环境中极易发生腐蚀,导致混凝土构件的力学性能退化,而采用纤维增强复合材料(FRP)箍代替钢筋能有效规避这个问题。但FRP箍较低的弹性模量使得梁易产生脆性的剪切破坏,同时其各向异性的特点使得FRP箍筋的弯折强度大大低于直线段强度,导致配FRP矩形箍混凝土梁的受剪承载力低于钢筋混凝土梁。近20年来,国内外学者为了探究配FRP矩形箍混凝土梁的实际应用价值,进行了一系列实验研究及理论推导,提出了受剪承载力以及FRP箍筋弯拉强度的计算方法。本文全面总结了上述有关研究成果,并对今后的研究方向进行了展望,以期为该类结构构件的应用发展提供参考。

铜及其合金在海洋环境中的腐蚀机理研究进展

铜及其合金以其良好的耐蚀性、导电性、导热性、机械性能、可成形性,已成为船舶工业和海洋工程的关键结构和部件的不可或缺的材料,在螺旋桨、海水管道、泵、阀门以及冷却系统上都具有广泛而重要的应用。然而,复杂严酷的海洋环境和不断提升的使用强度使得铜合金的服役条件日益苛刻,关键结构和部件的安全可靠性面临巨大威胁。基于此,本文综述了海洋环境常用铜合金的分类、应用,着重总结了纯铜、黄铜、白铜、青铜海洋环境腐蚀机理及其影响因素的研究进展,对新型铜合金及其制备和应用的未来发展进行了展望。

焊接热输入对1000 MPa级马氏体钢焊接接头组织和性能的影响

采用熔化极气体保护焊的方法对1.8 mm厚1000 MPa级马氏体钢进行了焊接,系统地研究了焊接热输入对焊接接头硬度分布、组织演变及力学性能的影响规律。结果表明:与母材相比,焊缝及热影响区的硬度均发生了不同程度的软化现象,细晶区软化现象最为显著;随着焊接热输入增加,焊接接头的强度及塑性均降低,韧性提高,焊缝区、临界区及亚临界区的硬度略有降低,粗晶区和细晶区的硬度略有升高,焊缝及热影响区的冲击性能无明显变化,接头断裂位置由细晶区变为亚临界区。

In-field harvest loss of mechanically-harvested maize grain and affecting factors in China

Field harvest loss is a common problem of maize grain mechanical harvesting in China and abroad.From 2012 to 2019,2987 groups of samples for the quality of mechanical grain harvesting in field were obtained in 21 major maize-producing provinces,cities,and regions of China.The analysis performed in this study showed that the average harvest loss of fallen ears was equivalent to 76.5%of the total harvest loss,indicating that the harvest loss in the mechanical harvesting of maize grain mainly came from the loss of fallen ears.Meanwhile,statistical analysis of the harvest loss in different ranges of grain moisture contents showed that,when the grain moisture content fell below 20%,the harvest loss rate of fallen ears and the total harvest loss rate both increased sharply,and the harvest loss of fallen ears increased faster than the harvest loss of fallen grain with a decreasing grain moisture content.Moreover,the results of multi-point experiments and harvest experiments in different periods showed that,during harvesting time,the harvest loss of fallen ears caused by lodging was the main reason for in-field harvest losses in the mechanical harvesting of maize grain.Apart from the above mentioned,the test results of 35 groups of harvesters for the in-field mechanical harvesting of maize grain showed that the harvester types and their operating parameters were important factors affecting the harvest loss in the mechanical harvesting of maize grain.Therefore,the principal paths to reduce harvest loss in the mechanical harvesting of maize grain are to breed lodging-resistant maize varieties,adopt reasonable planting densities,cultivate healthy plants,develop harvesters with low harvesting loss,intensify the training of operators,and harvest at an appropriate time.