2011,Wang(PTL)Widely Tunable Ultra-Wideband Signals Generation Utilizing Optically Injected Semicond

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基于超表面的超宽带隐身天线罩的仿真设计

现代电子技术Modern Electronics Technique2023年12月1日第46卷第23期Dec. 2023Vol. 46 No. 230 引言频率选择表面（Frequency Selective Surface, FSS ）是一种由周期性排列的金属片或任意几何形状的孔径元件组成的周期结构[1⁃2]，因其具有独特的频率选择特性而引起研究者们的广泛关注，它广泛应用于空间滤波器[3]、偏振器[4]、隐身天线罩[5⁃6]。

在隐身领域，由于天线通常是强散射源，因此降低整个天线系统的雷达横截面（Radar Scattering Section, RCS ）至关重要。

当外部电磁波照射天线系统时，将天线工作波段外的电磁信号反射到某些方向，缩减了天线的单站RCS 。

同时，FSS 天线罩对天线工作频率范围内的信号具有全传输特性，保证了工作频段内天线的正常通信。

然而，这种反射带外电磁波的方法仅适用于单站雷达，对于双站或多站雷达而言并没有较好的隐身效果。

近年来形成了一种结合FSS 和吸波器的设计思路，它被称为频率选择性吸波体（FSA ）。

FSA 通常能够吸收带外的入射电磁波，并且由一个传输波段来传输通信信号。

FSA 的概念首先在文献[5]中被提到，它一般由两层结构组成，即上层的吸波结构和下层的FSS 结构。

上层的吸波结构通常由金属结构和损耗元件构成，下层的FSS 由孔径元件组成。

根据吸波波段与传输波段位置基于超表面的超宽带隐身天线罩的仿真设计熊杰，杨宝平（黄冈师范学院物理与电信学院，湖北黄冈 438000）摘要：为了减小飞行器的多基站雷达散射截面，增加天线系统的隐身功能，提出一种基于超表面的超宽带隐身天线罩模型，该模型具有低频吸收、高频传输的特性。

提出的天线罩由位于上层的吸波结构和位于下层的频率选择结构组成。

上层由两个π型金属结构与工型金属结构组合而成，中间通过电阻元件连接，下层由“X ”字型周期缝隙结构组成，每个周期结构中一个电阻层结构对应4个“X ”字型FSS 结构。

前驱体转化法制备超高温陶瓷粉体研究进展　

第42卷第8期2023年8月硅㊀酸㊀盐㊀通㊀报BULLETIN OF THE CHINESE CERAMIC SOCIETY Vol.42㊀No.8August,2023前驱体转化法制备超高温陶瓷粉体研究进展孙楚函,王洪磊,周新贵(国防科技大学空天科学学院,新型陶瓷纤维及其复合材料重点实验室,长沙㊀410073)摘要:超高温陶瓷(UHTC)在航空航天的热防护领域具有重要作用,高质量的UHTC 粉体是制备高性能UHTC 的重要原料㊂在制备UHTC 粉体的工艺中,前驱体转化法制备的粉体纯度高㊁粒径小㊁各组分分布均匀,具有广阔的应用前景㊂本文根据前驱体合成机理将UHTC 前驱体转化法分为金属醇盐配合物合成法㊁基于格氏反应合成法以及引入支链合成法,综述了近年来通过三种方法制备UHTC 粉体的研究进展,分析总结了三种方法的优缺点,指出了UHTC 前驱体转化法目前存在的问题以及未来发展方向㊂关键词:前驱体转化法;超高温陶瓷粉体;反应机理;碳热还原;陶瓷产率;微观结构中图分类号:TH145㊀㊀文献标志码:A ㊀㊀文章编号:1001-1625(2023)08-2865-16Research Progress on Ultra-High Temperature Ceramics Powder Prepared by Precursor-Derived MethodSUN Chuhan ,WANG Honglei ,ZHOU Xingui(Science and Technology on Advanced Ceramic Fibers and Composites Laboratory,College of Aerospace Science and Engineering,National University of Defense Technology,Changsha 410073,China)Abstract :Ultra-high temperature ceramics (UHTC)plays an important role in the field of thermal protection in aerospace.High quality UHTC powder is important raw material for the preparation of high performance UHTC.In the process of preparing UHTC powder,the powder prepared by precursor-derived method has high purity,small particle size and uniform distribution of component,so it has broad application prospects.According to the synthesis mechanism of precursor,the precursor-derived methods of UHTC were divided into metal alkoxides complex synthesis method,synthesis based on Grignard reaction method and synthesis by introducing branch chains method.The research progress of preparation of UHTCby three methods in recent years was reviewed.The advantages and disadvantages of three methods were analyzed and summarized.The existing problems and future development direction of the UHTC powder prepared by precursor-derived method were pointed out.Key words :precursor-derived method;ultra-high temperature ceramics powder;reaction mechanism;carbothermic reduction;ceramic yield;microstructure 收稿日期:2023-04-12;修订日期:2023-05-30作者简介:孙楚函(2001 ),男,硕士研究生㊂主要从事超高温陶瓷的研究㊂E-mail:151****6953@通信作者:王洪磊,博士,副教授㊂E-mail:honglei.wang@0㊀引㊀言近年来,航空航天技术快速发展,先进飞行器正朝着高机动㊁轻质化㊁低成本和可重复使用等方向发展[1],其发动机热端㊁鼻锥和机翼前缘等部件往往要承受2000ħ甚至3000ħ以上的高温,同时还将处于高温氧化㊁热疲劳和高应力等恶劣服役条件下[2-5],传统的难熔合金材料难以满足使用要求,而超高温陶瓷(ultra-high temperature ceramics,UHTC)因其优良的性能已成为该领域的研究重点[6-8]㊂超高温陶瓷一般是指熔点超过3000ħ,且在高温㊁高载荷等极端环境下仍能保持物理及化学性能稳定的过渡金属化合物,主要包括第IVB 族和第VB 族的钛(Ti)㊁锆(Zr)㊁铪(Hf)和钽(Ta)的硼化物㊁氮化物和碳化物[9-10]㊂表1列出了常见UHTC 的物理及力学性能[10-29](HCP 为密排六方结构,FCC 为面心立方结构)㊂2866㊀陶㊀瓷硅酸盐通报㊀㊀㊀㊀㊀㊀第42卷表1㊀常见超高温陶瓷的物理及力学性能Table1㊀Physical and mechanical properties of common ultra-high temperature ceramicsMaterial Crystalstructure Meltingpoint/ħDensity/(g㊃cm-3)CTE/(10-6㊃K-1)Thermalconductivity/(W㊃m-1㊃K-1)Elasticmodulus/GPaHardness/GPa ReferenceTaB2HCP304012.58.54155126[12-15] TiB2HCP3225 4.58.66556025[11-13,16] ZrB2HCP3245 6.1 6.26048923[12-13,17-18] HfB2HCP338011.2 6.610448028[12-13,17-18] TiC FCC3100 4.97.41740026[13,16,19-20] ZrC FCC3530 6.6 6.72036933[17,19-23] TaC FCC388014.5 6.32250322[17,24-25] HfC FCC389012.7 6.62245229[17,19-23] TaN FCC308713.4 3.2849010[10,26-27] TiN FCC2950 5.49.32946021[10,13,19,26,28] ZrN FCC29507.37.22039016[10,13,19,26,28-29] HfN FCC338513.9 6.92138516[10,13,19,26,28]㊀㊀Note:CTE,coefficient of thermal expansion.高质量UHTC粉体是制备高性能UHTC的关键,UHTC粉体的传统合成工艺是利用相应的金属氧化物粉体经碳热还原反应实现的㊂但原料颗粒的尺寸较大㊁反应物无法充分接触以及可能存在杂质等因素,导致反应温度较高㊁产物晶粒尺寸过大㊁纯度不高等问题,使其应用存在较大的局限性㊂近年来被广泛研究的前驱体转化法是通过化学手段在溶液体系中合成一类包括合成陶瓷时所需元素的金属有机聚合物,再将前驱体在一定温度范围进行交联㊁热解,最终得到陶瓷粉体产物的方法㊂前驱体转化法可对前驱体分子结构进行设计,且在制备过程中具有很好的加工性,可应用于制备陶瓷粉体㊁纤维㊁涂层和复合材料等[30]㊂由于原料组分可以在分子层面均匀混合,缩短元素间的扩散距离,进而降低热解温度,这避免了晶粒粗大的问题,且使产物的相组成分布均匀㊂前驱体转化为陶瓷粉体主要包含两个过程:1)在100~400ħ低温条件下的交联过程中,前驱体分子将交联形成不熔的网状结构;2)在600~1400ħ高温条件下的热解过程中,在600~1000ħ时交联的前驱体发生有机-无机转变,生成非晶陶瓷,继续升高热解温度则会发生相分离与结晶化过程,最终得到多晶陶瓷㊂含氧前驱体会额外发生碳热还原反应,将氧化物陶瓷转化为碳化物陶瓷[31]㊂目前合成UHTC前驱体的工艺按照反应机理可大致分为三类:一是采用金属醇盐配合物经水解缩合形成聚合物前驱体;二是以格氏反应为核心合成单体,再经缩合反应得到聚合物前驱体;三是将有机金属化合物单体作为支链引入聚合物,从而得到目标前驱体㊂1㊀金属醇盐配合物前驱体制备UHTC粉体在制备金属醇盐配合物前驱体的过程中,主要采用过渡金属氯化物作为金属源,通过与醇的取代反应得到金属醇盐㊂由于金属醇盐水解剧烈,利用乙酰丙酮等配体与金属醇盐反应形成配合物以实现可控水解缩合,得到聚合物前驱体㊂同时为保证后续碳热还原反应充分,往往还需向前驱体溶液中加入碳源㊂该方法既可以利用单种金属醇盐配合物制备单相高纯UHTC粉体,也可以通过引入多种金属醇盐配合物制备UHTC 固溶体粉体,或引入含Si聚合物制备复相UHTC粉体㊂1.1㊀金属醇盐配合物前驱体制备单相UHTC粉体TaC具有高熔点㊁高硬度和高强度等诸多优点,是超高温碳化物陶瓷的研究热点之一㊂Jiang等[32]以TaCl5为钽源,酚醛树脂为碳源,乙醇和乙酰丙酮为溶剂,混合得到TaC的前驱体溶液㊂随后在80ħ下固化, 200ħ下保温2h除去溶剂,在1000ħ时开始发生碳热还原反应,1200ħ时反应完全,得到的TaC陶瓷粉体元素分布均匀,平均晶粒尺寸为40nm,但陶瓷产率为57%(质量分数),仍有提升空间㊂图1为前驱体合成和热解过程中可能发生的反应(Hacac为乙酰丙酮;acac为失去一个H原子的乙酰丙酮根)㊂第8期孙楚函等:前驱体转化法制备超高温陶瓷粉体研究进展2867㊀图1㊀TaC 前驱体制备可能发生的反应机理[32]Fig.1㊀Possible reaction mechanism for preparation of TaC precursor [32]常规的前驱体碳热还原法包括前驱体合成㊁固化㊁惰性气氛热解以及最终的碳热还原处理等多个步骤,存在反应时间长㊁生产效率低的问题㊂为优化生产工艺,Cheng 等[33]通过高温喷雾热解(high temperature spray pyrolysis,HTSP)工艺,低成本㊁单步合成了纳米TaC 粉体㊂TaC 前驱体溶液由TaCl 5和酚醛树脂溶解在乙醇和1-戊醇中得到,然后通过喷雾器将其破碎成细小的液滴,液滴处在Ar 气氛的高温管式炉中,再经过溶剂一次性去除㊁热解和1650ħ的快速原位碳热还原,在几分钟内即可制得纳米TaC 粉体㊂但由于采用的是医用雾化器,难以产生足够细小的液滴,且部分产物附着在管式炉内壁上,所以生成的TaC 颗粒存在团聚现象,产率较低,工艺流程需要继续改进㊂图2为高温喷雾热解示意图(CTR 为碳热还原反应)㊂图2㊀高温喷雾热解示意图[33]Fig.2㊀Schematic diagram of high temperature spray pyrolysis [33]单相UHTC 的高温抗氧化能力较弱,尤其是过渡金属碳化物表面被氧化后,无法生成致密氧化膜来阻止内部被进一步氧化㊂例如,当HfC 暴露在空气中时,400ħ以上就开始氧化[34],TaC 在850ħ时即会被完全氧化[35]㊂在实际应用过程中,使用单相UHTC 的情况较少㊂1.2㊀金属醇盐配合物前驱体制备UHTC 固溶体粉体为改善TaC 和HfC 的抗氧化性能,Zhang 等[36]系统地研究了Ta-Hf-C 三元陶瓷在1400~1600ħ等温条件下各种成分的氧化机理,研究表明氧化过程取决于成分㊂与单相TaC 和HfC 陶瓷相比,1TaC-1HfC 和1TaC-3HfC 的抗氧化性显著提高,这是因为氧化生成的三维共晶Hf 6Ta 2O 17-Ta 2O 5结构和致密纯Hf 6Ta 2O 17层都能够抑制O 2扩散,改善抗氧化性㊂因此,与单相UHTC 相比,使用钽醇盐配合物与铪醇盐配合物混合得到前驱体所制备的UHTC 固溶体具有更好的抗高温氧化能力[37]㊂在碳热还原过程中,多相氧化物由于各相反应活化能不同,往往会发生某相优先析出㊁碳化物之间固溶不充分和碳源过剩等问题㊂为解决以上问题,蒋进明[38]以Ta㊁Hf㊁Zr 的氯化物为金属源,乙酰丙酮多齿配体为螯合剂,酚醛树脂为碳源,经200ħ溶剂热处理12h,合成出具有多层核壳结构的前驱体㊂前驱体中心区富含Ta㊁次外层富含Hf(Zr),外壳由树脂包覆㊂该结构的前驱体在热解过程中可以实现外层碳原子向内核逐层扩散,使元素分布均匀,得到粒径为200~300nm 的Ta-Hf(Zr)-C 三元陶瓷纳米粉体㊂图3为Ta-Hf(Zr)-C 碳热还原转化机理示意图㊂2868㊀陶㊀瓷硅酸盐通报㊀㊀㊀㊀㊀㊀第42卷图3㊀Ta-Hf(Zr)-C 碳热还原转化机理示意图[38]Fig.3㊀Schematic diagram for carbothermal reduction synthesis of Ta-Hf(Zr)-C [38]TaC 和HfC 晶体结构相同(均为NaCl 结构)且晶格常数相近(分别为0.445和0.464nm),可以形成不同比例的固溶体,其中Ta 4HfC 5具有目前已知物质中的最高熔点4215ħ[39],是一种极具发展前景的耐超高温陶瓷㊂Cheng 等[40]等以酚醛树脂作为碳源,与摩尔比为4ʒ1的TaCl 5和HfCl 4溶解在乙醇和乙酰丙酮的混合溶剂中,经过磁力搅拌得到Ta 4HfC 5前驱体溶液,随后在Ar 气氛中200ħ油浴交联固化2h,再通过真空蒸馏除去剩余溶剂,接下来在Ar 气氛中进行热解,Ta 2O 5的碳热还原在1000ħ左右开始,1200~1400ħ时,Hf 6Ta 2O 17的碳热还原以及TaC 和HfC 之间的固溶反应同时发生,最后HfC 和TaC 在1800ħ下固溶充分反应,得到粒度为200~300nm㊁元素分布均匀的Ta 4HfC 5粉体㊂高温下生成的熔融Hf 6Ta 2O 17层可作为氧扩散屏障,使得陶瓷具有优秀的高温抗烧蚀性能㊂但1800ħ的固溶温度过高,不利于得到晶粒细小的高质量粉体㊂图4㊀Ta 4HfC 5粉体TEM 照片[42]Fig.4㊀TEM image of Ta 4HfC 5powder [42]改进前驱体合成工艺可以降低HfC 和TaC 发生固溶反应的温度㊂Lu 等[41]利用摩尔比4ʒ1的TaCl 5和HfCl 4与三乙胺㊁甲基叔丁基醚和乙酰丙酮反应后缩聚,得到聚钽铪氧烷(polytantahafnoxane,PTHO),再将其与含烯丙基的树脂混合即得到Ta 4HfC 5前驱体,固化后在1600ħ下热解制备得到了Ta 4HfC 5粉体㊂孙娅楠等[42]则将含烯丙基的树脂替换为酚醛树脂,与PTHO 混合后得到了Ta 4HfC 5前驱体,将前驱体在250ħ下保温2h 以固化,随后在Ar 气氛中1350~1450ħ热解1.5~3.0h,得到粒径为100~200nm㊁晶粒尺寸为25~50nm 的Ta 4HfC 5粉体㊂图4为Ta 4HfC 5粉体的TEM 照片㊂综合以上研究发现,固溶反应发生的温度普遍高于碳热还原反应㊂与Cheng 等[40]和Lu 等[41]相比,孙娅楠等[42]将固溶反应完成温度从1800ħ降至1450ħ,且所得陶瓷粉体粒径更小㊂通过金属醇盐配合物前驱体制备的超高温陶瓷粉体多为碳化物,也可以通过向前驱体溶液中加入硼酸以制备硼化物复相陶瓷粉体㊂IVB 族硼化物陶瓷ZrB 2和HfB 2在高于1200ħ的氧化环境中,表面的B 2O 3保护层将蒸发,因此主要依赖于ZrO 2或HfO 2层作为抗氧化屏障[43-44]㊂在向ZrB 2和HfB 2中添加高价阳离子Ta 5+后,氧化生成的Ta 2O 5可以填充氧晶格空位以减缓O 2传输速率,并与ZrO 2或HfO 2形成中间相,从而增强相稳定性[45]㊂Xie 等[46]采用乙酰丙酮与Zr(OPr)4通过回流生成Zr(OPr)4-x (acac)x ,得到ZrO 2前驱体㊂类似地,使用Ta(OC 2H 5)4作为Ta 源合成Ta 2O 5前驱体,然后在溶液中分别加入酚醛树脂和硼酸,将溶液浓缩㊁干燥获得前驱体粉末后,在800~1800ħ的Ar 气氛中热解,热解过程中金属氧化物优先进行碳热还原生成金属碳化物,在硼源过量的情况下会继续反应生成金属二硼化物㊂图5为ZrB 2-TaB 2在1300ħ热第8期孙楚函等:前驱体转化法制备超高温陶瓷粉体研究进展2869㊀图5㊀ZrB 2-TaB 2在1300ħ热处理2h 的SEM 照片[46]Fig.5㊀SEM image of ZrB 2-TaB 2after heat treated at 1300ħfor 2h [46]处理2h 的SEM 照片㊂ZrB 2和TaB 2之间的固溶反应从1400ħ开始,1800ħ时TaB 2相完全消失㊂与由ZrB 2和TaB 2两相混合的陶瓷粉体相比,固溶体陶瓷粉体在性能上具有哪些差异值得继续研究㊂1.3㊀金属醇盐配合物前驱体制备复相UHTC 粉体另一种提高UHTC 抗氧化性能的方法则是引入SiC,高温下SiC 氧化生成的玻璃相SiO 2可提高多孔结构的金属氧化物致密度,具有良好的抗高温氧化和抗烧蚀性[47]㊂同时两种成分在结晶过程中的相互抑制效应可以起到细化晶粒的作用㊂聚碳硅烷(polycarbosilane,PCS)是一种以Si 和C 交替排列作为聚合物骨架的有机硅化合物,常被用来作为制备SiC 的前驱体[48]㊂Lu 等[49]以三乙胺为共沉淀剂,用TaCl 5㊁正丁醇和乙酰丙酮反应制备得到Ta 2O 5前驱体溶液,将其与PCS 混合后蒸馏得到TaC-SiC 前驱体溶液,前驱体充分交联固化后,在1600ħ的Ar 气氛中热解2h,得到了平均晶粒尺寸50nm 的TaC-SiC 陶瓷粉体㊂图6为1800ħ热解的TaC-SiC 陶瓷粉体的HR-TEM 照片(标尺101/nm 为10个1/nm,下文图17㊁18中标尺含义类似)㊂由图6可知,TaC 和SiC 晶粒以接近球形的形态均匀分散,同时还有少量无定形碳嵌在晶界位置㊂该前驱体合成方法同样适用于IVB 族UHTC,可推广用于制备ZrC-SiC 和HfC-SiC㊂图6㊀1800ħ热解的TaC-SiC 陶瓷粉体的HR-TEM 照片[49]Fig.6㊀HR-TEM images of TaC-SiC ceramics powder pyrolyzed at 1800ħ[49]PCS 的交联主要依靠硅氢化反应,通过向前驱体中加入如二乙烯基苯(divinylbenzene,DVB)等含不饱和C C 键的物质可以进一步提升前驱体的交联程度㊂Cai 等[50]利用该原理,以HfCl 4与异丙醇和乙酰丙酮反应得到铪醇盐配合物,再通过水解得到HfO 2前驱体(polyhafnoxane,PHO),随后将PHO 与PCS 和DVB 混合,控制n (Hf)/n (Si)摩尔比为1ʒ1,交联后在1600ħ下碳热还原得到了元素分布均匀㊁结晶质量高㊁粒径分布窄的HfC-SiC 复相陶瓷粉末㊂图7为HfC-SiC 复相陶瓷的TEM 照片,可以观察到分别属于HfC 和SiC 的晶格条纹㊂由于PHO 的弱极性,其与PCS 和DVB 具有良好的相容性,可以大范围改变n (Hf)/n (Si)摩尔比来调控陶瓷粉体成分㊂合成前驱体的单体中交联位点越多,前驱体越易形成高度交联的三维网状结构㊂每个四乙氧基硅烷(tetraethoxysilane,TEOS)分子中含有四个Si O C 键可供交联,是另一种理想的制备含Si 前驱体的原料㊂Patra 等[51]采用TEOS 与HfCl 4㊁乙酰丙酮㊁对苯二酚反应合成HfC-SiC 前驱体㊂经过回流和固化后,在1500ħ的Ar 气氛中发生碳热还原反应,生成HfC-SiC 陶瓷粉体㊂图8为1500ħ热解的HfC-SiC 前驱体亮场TEM 照片和平均粒径㊂由图8可知,碳热还原所生成的球形HfC 和SiC 颗粒平均尺寸为25~50nm㊂由于对苯二酚和四乙氧基硅烷具有较高的C㊁Si 含量,因此前驱体在热解过程中质量损失较少,1600ħ时陶瓷产率高达65%,具有很好的应用前景㊂PCS 作为SiC 前驱体的缺陷在于其常温下为固态,需要利用二甲苯等有机溶剂将其配制成溶液使用,增2870㊀陶㊀瓷硅酸盐通报㊀㊀㊀㊀㊀㊀第42卷加了前驱体合成的复杂程度㊂Wang 等[52]采用常温下为液态的低分子量SiC 前驱体(LPVCS)与HfCl 4㊁乙酰丙酮和1,4-丁二醇反应合成了HfC-SiC 前驱体(PHCS)㊂HfO 2和SiO 2的碳热还原主要发生在1400~1600ħ,生成的HfC-SiC 复相陶瓷粉体的SEM 照片和EDS 分析如图9所示㊂与PCS 相比,LPVCS 结构中引入的V4分子具有 CH CH 2基团,可在较低温度下实现自交联,有利于陶瓷产率的提升[53]㊂同时LPVCS 中较高的碳含量可以补偿PHCO 热解产物中碳含量的不足,制备出不含HfO 2和微量游离碳的高性能HfC-SiC 陶瓷㊂图7㊀1600ħ热解的HfC-SiC 粉末TEM 照片[50]Fig.7㊀TEM images of HfC-SiC powder pyrolyzed at 1600ħ[50]图8㊀1500ħ热解的HfC-SiC 前驱体亮场TEM 照片和平均粒径[51]Fig.8㊀Bright-field TEM image and average particle size of HfC-SiC precursor pyrolyzed at 1500ħ[51]第8期孙楚函等:前驱体转化法制备超高温陶瓷粉体研究进展2871㊀图9㊀HfC-SiC 粉末的SEM 照片和EDS 分析[52]Fig.9㊀SEM images and EDS analysis of HfC-SiC powder [52]㊀㊀综上可见,合成金属醇盐配合物前驱体所需的原料结构简单,反应时间较短㊂但由于前驱体中存在氧元素,有可能会导致生成的UHTC 粉体中有氧残留,使陶瓷高温抗氧化性能和机械性能下降㊂另外为防止金属醇盐水解,该反应需全程在惰性气氛中进行,对设备要求较高㊂2㊀基于格氏反应的前驱体制备UHTC 粉体基于格氏反应的前驱体制备工艺主要采用茂金属化合物和含不饱和键的格氏试剂合成单体,再通过与非金属源分子的聚合反应得到前驱体㊂金属醇盐配合物前驱体的各目标元素由不同种聚合物提供,多数通过机械搅拌的方法实现分子间的混合㊂不同的是,基于格氏反应的前驱体中金属源与非金属源在同种聚合物分子中,实现了分子内的混合㊂所合成的聚合物分子包括线型聚合物与网状聚合物㊂2.1㊀线型聚合物前驱体制备UHTC 粉体合成线型聚合物前驱体的原料通常依靠分子两端的基团发生缩聚反应,交联程度相较于网状聚合物更低,可以通过在主链上插入交联位点来减少热解过程中的质量损失㊂Cheng 等[54]在四氢呋喃(tetrahydrofuran,THF)溶剂中利用反-1,4-二溴-2-丁烯与镁反应制备格氏试剂,再与Cp 2HfCl 2和氯甲基三甲基硅烷通过缩聚合成了主链包含Hf C㊁Si C 和 CH CH 基团的线性PHCS 前驱体聚合物,图10为前驱体合成过程中可能发生的化学反应㊂前驱体在经过1600ħ热解后得到了元素分布均匀的HfC-SiC 纳米复合陶瓷粉体㊂前驱体主链中的不饱和 CH 2CH CHCH 2 基团提供了潜在的交联位点或反应位点,可用于后续固化或改性㊂图10㊀PHCS 前驱体合成过程中可能发生的反应[54]Fig.10㊀Reactions that may occur during synthesis of PHCS precursors [54]基于格氏反应的MC-SiC(M =Zr,Hf)前驱体分子结构中往往含有M C Si 键,普遍认为该键是由格氏反应所致㊂Gao 等[55]提出了一种新的前驱体合成机制,该机制基于㊃MgCl 辅助下的活性物质Cp 2Zr(II)的自由基聚合,合成过程如图11所示,首先将二氯二茂锆Cp 2ZrCl 2与Mg 和四氢呋喃在60ħ下搅拌混合2872㊀陶㊀瓷硅酸盐通报㊀㊀㊀㊀㊀㊀第42卷4h 后冷却,得到活性物质双环戊二烯基锆Cp 2Zr (II),再将Cp 2Zr (II)分别与CH 3Si (CH CH 2)Cl 2和(CH 3)2Si(CH 2Cl)2在110ħ下反应16h,经过冷却过滤并真空浓缩得到了含有[ Zr C Si ]n 主链结构的单源聚合物前驱体聚锆碳硅烷(PZCS-1,PZCS-2)㊂随后将前驱体在N 2气氛中进行热解,SiO 2和ZrO 2相在1000ħ时析出,随着温度继续升高转化为SiC 和ZrC 相,且均匀分布在自由碳基体中,形成ZrC /SiC /C 复合陶瓷㊂由于该前驱体为线型聚合物且不含可作为交联位点的不饱和基团,热解过程中质量损失较为严重,900ħ时陶瓷产率仅有43.9%㊂图11㊀PZCS-2前驱体合成过程[55]Fig.11㊀Synthesis process of the PZCS-2precursor [55]2.2㊀网状聚合物前驱体制备UHTC 粉体与线型聚合物前驱体相比,合成网状聚合物前驱体的原料多含有三个以上的交联位点,前驱体交联程度高,质量损失较少,有利于陶瓷产率的提高㊂Wang 等[56]通过格氏反应将Cp 2ZrCl 2和CH 2 CHMgCl 制成Cp 2Zr(CH CH 2)2,然后将其与B 源H 3B㊃SMe 2混合,利用氢化反应得到网状结构的大分子前驱体聚锆碳硼烷(polyzirconcarborane,PZCB),合成机理如图12所示㊂随后将前驱体放置于Ar 气氛的石墨管式炉中进行热解,1600ħ时碳热还原完全,得到充分结晶且分布均匀的ZrC-ZrB 2陶瓷粉体,继续加热至2200ħ,产物失重仅为2.5%,说明该复相陶瓷粉体具有良好的耐热性㊂在该合成过程中,利用了硼烷分子具有三个反应位点的特征,以其作为骨架合成了网状大分子,使得前驱体充分交联㊂SiBNC 非晶陶瓷在2000ħ仍具有很好的高温稳定性,而引入过渡金属元素可以进一步抑制其在高温下的结晶与氧化[57]㊂龙鑫[58]将锆源(Cp 2ZrCl 2)与格氏试剂(CH 2 CHCH 2MgCl)反应制备得到双官能度的活性单体(PZC),然后引入低分子量聚硼硅氮烷(LPBSZ),PZC 中的C C 键与LPBSZ 中的Si H 发生硅氢化反应,ZrC /SiBNC 前驱体合成机理如图13所示(Me 3Si 为三甲基亚砜)㊂未参与反应的C C 键则为后续交联提供活性位点,最终形成网状结构的ZrC /SiBNC 前驱体㊂随后将前驱体置于Ar 气氛中经过1200ħ热解生成ZrC /SiBNC 陶瓷粉体,其中ZrC 纳米颗粒均匀分散在无定形SiBNC 基体中㊂ZrC 相提高了SiBNC 的第8期孙楚函等:前驱体转化法制备超高温陶瓷粉体研究进展2873㊀热稳定性,经过1800ħ以上高温处理后,ZrC /SiBNC 仍能够保持均匀细小的纳米晶结构,同时SiBNC 也改善了ZrC 的耐高温氧化性能㊂但该前驱体的不足之处在于碳含量过高导致陶瓷粉体产物中含有过量的碳,影响UHTC 的高温抗氧化性能㊂图12㊀PZCB 前驱体合成机理[56]Fig.12㊀Synthesis mechanism of PZCB precursor[56]图13㊀ZrC /SiBNC 前驱体合成机理[58]Fig.13㊀Synthesis mechanism of ZrC /SiBNC precursor [58]基于格氏反应的前驱体制备工艺实现了各目标元素在聚合物分子内的混合,比金属醇盐配合物前驱体混合更加充分,能更好地避免陶瓷产物中元素偏析现象的发生㊂同时原料中不含氧元素,热解过程中不会发生碳热还原反应,能降低热解温度㊂但该工艺的原料结构较为复杂,反应时间较长,为避免合成过程中引入空气中的氧等杂质,反应必须在保护气氛中进行,对设备要求较高㊂3㊀引入支链的前驱体制备UHTC 粉体在制备引入支链的前驱体过程中,需以一种聚合物分子作为主链,再将其他含目标元素的小分子通过反应作为支链连接到主链上㊂常见的作为主链的大分子有聚碳硅烷和聚硅氮烷等,其分子结构中包含大量可与含目标元素的小分子发生交联反应的基团,同时自身足够大的分子量可避免在热处理过程中分解挥发㊂3.1㊀以聚碳硅烷作主链制备UHTC 粉体聚碳硅烷的主链由Si 和C 交替组成,Si 和C 上连接有H 或 CH 2 CH CH 2等基团作为交联位点[48],通过向主链上引入UHTC 组分,热解后可原位生成含SiC 的UHTC 粉体㊂Amorós 等[59]系统性地研究2874㊀陶㊀瓷硅酸盐通报㊀㊀㊀㊀㊀㊀第42卷图14㊀1350ħ热解的SiC-TiC-C 陶瓷粉体的SEM 照片[59]Fig.14㊀SEM image of SiC-TiC-C ceramics powder pyrolyzed at 1350ħ[59]了采用聚二甲基硅烷(polydimethylsiloxane,PDMS)和PCS 与Cp 2MCl(M =Ti,Zr,Hf)反应制备SiC-MC-C 陶瓷粉体的机理和工艺流程㊂与PDMS 相比,PCS 中的Si H 键促进了前驱体的交联,提高了陶瓷产率,金属配合物则通过取代反应连接在前驱体的网状结构中㊂经过900ħ热解后,前驱体转变为非晶态陶瓷,结晶化在1350ħ下基本完成,生成由β-SiC㊁MC 以及自由碳组成的复相陶瓷粉体,但仍有部分非晶态物质存在㊂图14是1350ħ热解所得的SiC-TiC-C 陶瓷粉体的SEM 照片㊂该研究采用同种前驱体转化工艺成功制备出了含IVB 族三种元素碳化物的复相UHTC 粉体,但对热解过程的探究不够深入,1350ħ时结晶尚未完成㊂通过对PCS 进行改性,可以进一步提高前驱体交联程度㊂Yu 等[60]以含烯丙基的聚碳硅烷AHPCS(商品名SMP10)为SiC 源,与TaCl 5的CHCl 3溶液混合后,在真空中加热至160ħ脱除溶剂得到前驱体,前驱体合成过程如图15所示,随后将前驱体在Ar 气氛下的管式炉中进行热解,得到SiC-TaC-C 陶瓷粉体㊂研究发现,随着热解温度升高,前驱体由于发生脱氢耦合反应而失重,在900ħ时聚合物完全转化为非晶陶瓷粉末,1200ħ时TaC 相开始析出,并被非晶态碳薄壳所包裹,形成核壳结构的TaC@C 纳米颗粒,而β-SiC 相则在1400ħ下结晶㊂所得的β-SiC 和TaC 的晶粒尺寸均小于30nm㊂前驱体热解后的游离碳需要通过生成TaC 来消耗,由于没有额外添加碳源,所以需要准确掌握TaCl 5和AHPCS 的比例以保证陶瓷产物中有少量包裹在TaC 晶粒表面的游离碳㊂图15㊀SiC-TaC-C 前驱体合成过程[60]Fig.15㊀Synthesis of SiC-TaC-C precursor [60]在利用引入支链的前驱体制备含N 原子的超高温陶瓷粉体时,Wen 等[61]以AHPCS 为SiC 源,四(二甲氨基)铪(TDMAH)为Hf 源和N 源合成SiHfCN 陶瓷前驱体㊂AHPCS 中的Si H 键可与TDMAH 中的N CH 3键反应生成Si N Hf 键,使Hf 连接到大分子上㊂Si H 键还会与AHPCS 侧链上的烯丙基发生硅氢化反应以增加前驱体交联程度,可能发生的化学反应如图16所示㊂热解后所得UHTC 组分为HfC 0.87N 0.13,其被碳层包裹镶嵌在SiC 基体中,两相的晶粒尺寸均小于100nm㊂2~4nm 厚的碳层可作为扩散屏障,有效。

ultra-long Ag2Te nanowires

Simple synthesis of ultra-long Ag 2Te nanowires through solvothermal co-reduction methodFeng Xiao,Gang Chen n ,Qun Wang,Lin Wang,Jian Pei,Nan ZhouDepartment of Applied Chemistry,Harbin Institute of Technology,Harbin 150001,People’s Republic of Chinaa r t i c l e i n f oArticle history:Received 11March 2010Received in revised form 27May 2010Accepted 12July 2010Keywords:Silver telluride Solvothermal NanowiresElectrical transport propertya b s t r a c tUltra-long single crystal b -Ag 2Te nanowires with the diameter of about 300nm were fabricated through a solvothermal route in ethylene glycol (EG)system without any template.The long single crystal wires were curves,with high purity,well-crystallized,and dislocation-free and characterized by using X-ray powder diffraction (XRD),Differential scanning calorimetry (DSC)analysis,X-ray photoelectron spectroscope (XPS),ﬁeld emission scanning electron microscopy (FE-SEM),transmission electron microscopy (TEM)and high-resolution transmission microscopy (HRTEM).The detailed topotactic transformation process from particles into single crystal wires was studied.Furthermore,the electrical conductivity and Seebeck coefﬁcient have been systematically studied between 300and 600K.Crown Copyright &2010Published by Elsevier Inc.All rights reserved.1.IntroductionMetal tellurides have drawn considerable attention because of their unique physical properties and potential applications in fabricating sensors for detection of low energy gamma-ray detection [1],low-dimensional phase-change nanomaterials for information storage [2,3],thermoelectric materials [4,5],ﬁeld sensing devices,etc.[6].Among these tellurides,silver tellurides are a series of compounds with variable stoichiometries,and the four typical stable silver telluride phases are AgTe [7,8],Ag 2Te [9],Ag 5Te 3[10],and Ag 7Te 4[11].These silver telluride materials may ﬁnd applications in manufacture of magnetic ﬁeld measurements [12–15],memory devices [16],and optics materials [17].Recently,silver telluride (Ag 2Te)has received great attentions due to its interesting and useful characteristics [18].The low-temperature phase of monoclinic silver telluride is a kind of semiconductor with a narrow band gap,high carrier mobility,and low lattice thermal conductivity,whereas its high-temperature phase gives rise to superionic conductivity because Ag +cations can easily move through the cubic sublattice formed with tellurium anions [19,20].Generally,Ag 2Te bulk material was prepared by the solid reaction between elemental Ag and Te at elevated temperature in evacuated tubes [21],or by the aqueous reaction of metal–salt solutions with toxic gaseous H 2Te [22].Recently,low-dimensional nanostructures,including nanowires,nanorods,and nanosheets,are of importance because they exhibit promising mechanical,electrical,optical,and magnetic properties different from those of corresponding polycrystalline powders.A number of methods for the synthesis of Ag 2Te with nanostructures have been explored.For example,Ag 2Te nanowires were obtained by cathodic electrolysis from dimethyl sulfoxide (DMSO)solution containing AgNO 3and TeCl 4in porous anodic alumina membranes [20].Ag 2Te nanorods were prepared by the reaction between AgCl and elemental Te in the mixed solvent of ethylenediamine and hydrazine hydrate [23].A room-temperature solution-phase route for the preparation of one-dimensional silver telluride nanowires (Ag 2Te NWs)has been reported [24].Silver telluride nanotubes have been prepared by the solvothermal process without a template or a surfactant [25].Template-engaged method in which the Te nanorods were used as template reagents has been developed for the synthesis of the Ag 2Te nanorods [26].However,most objects of these syntheses have to use templates which served as a physical scaffold and hard to obtain long wires (420m m in length).Herein,we have developed a general strategy to grow large scale,ultra-long Ag 2Te nanowires through solvothermal co-reduction method without any template.Moreover,the formation mechanism of the nanostruc-tured silver telluride has been elucidated on the basis of the experimental observations.2.Experimental section 2.1.SynthesisUltra-long Ag 2Te nanowires were prepared from AgNO 3(99.99%)and Na 2TeO 3(99.98%)by a solvothermal co-reductionContents lists available at ScienceDirectjournal homepage:/locate/jsscJournal of Solid State Chemistry0022-4596/$-see front matter Crown Copyright &2010Published by Elsevier Inc.All rights reserved.doi:10.1016/j.jssc.2010.07.020nCorresponding author.Fax:+8645186413753.E-mail address:gchen@ (G.Chen).Journal of Solid State Chemistry ](]]]])]]]–]]]method.In a typical experiment,the aqueous solutions of 0.2208g AgNO 3(1.3mmol)and 0.2215g Na 2TeO 3(1mmol)were prepared by adding 5mL deionized water.1g (2.68mmol)dis-odium salt of ethylenediaminetetraacetic acid (Na 2(EDTA)Á2H 2O)was added into the solution of AgNO 3.After a vigorous stirring of 5min,they were transferred into Teﬂon lined stainless steel autoclave of capacity 40mL in sequence.Then 10mL 1M NaOH and 5mL ethylene glycol (EG)were added immediately,which result in a few brownish-black spots ﬂoating on the surface of the mixed solution and the white milky liquid could be obtained by vigorous stirring.The ﬁnal volume of the solution mixture was adjusted to 30mL with deionized water and the autoclave was heated at 513K.After 24h,the vessel was taken out and allowed to cool to room temperature naturally,and the black cloudy precipitate found inside the autoclave was separated by centri-fugation,washed with deionized water and ethanol several times,and dried in a vacuum at 323K for 10h.Moreover,the experimental conditions with different reaction time were also investigated in order to understand the growth mechanism of the ultra-long single crystal Ag 2Te wires.Table 1summarizes these typical conditions and the corresponding morphologies and phases evolution of the products.2.2.CharacterizationX-ray diffraction data were collected at ambient temperaturefrom 51to 901with a step of 0.021on Rigaku D/max diffractometer working with Cu K a radiation.Differential scanning calorimetry (DSC)analysis was carried out up to a temperature of 500K,using a SETARAM DSC-141under a stream of nitrogen and a heating rate of 10K/min.The XPS spectra were collected on an American Electronics physical PHI5700ESCA system,X-ray photoelectron spectroscope using Al K a radiation (1486.6eV).The source was operated at 12.5kV and the anode power was 250W.The binding energy (BE)was calibrated with the C 1s peak.The morphology of particles was studied by ﬁeld emission scanning electron microscopy (FE-SEM,FEI QUANTA 200F).Transmission electron micrographs were obtained by employing an FEI Tecnai G2S-Twin transmission electron microscope,using an accelerat-ing voltage of 300kV.The powder specimens were prepared in air.Rectangular shape specimens of about 15.7Â4.6Â0.7mm 3were obtained under a pressure of 15MPa.The measurements of the electrical conductivity and Seebeck coefﬁcient were carried out using a laboratory-designed apparatus under an argon atmosphere.The electrical conductivity of the samples were measured by four probe method with the increase in temperature of about 2.51C/min.For the measurement of Seebeck coefﬁcient,thermo-electromotive force measured as a function of tempera-ture gives a straight line and its slope is Seebeck coefﬁcient.The detailed procedure for the measurement of Seebeck coefﬁcient is described below.The sample with a pair of Pt/Rh thermocouples attached to two ends (bar-shaped sample)was heated to a certain temperature,and then one of the ends was heated by an extrathermal source to produce the temperature gradient;the temperature and voltage signals were collected by a commercial data acquisition system (Keithley 2700,Keithley Instruments Inc.,America).3.Results and discussion3.1.Structure,formation,and morphologyThe crystallinity of as-prepared samples was analyzed using X-ray diffraction (XRD)as shown in Fig.1.It reveals that the product is composed of monoclinic Ag 2Te,which is consistent with those of bulk monoclinic Ag 2Te [space group:P 2n /c (no.13)](JCPDS 34-0142).The calculated lattice constants a ¼8.1586˚A,b ¼8.9339˚A,andc ¼8.0100˚Awere in agreement with the standard literature.No other diffraction peaks were detected such as Ag or Te crystalline phases.From the results of XRD,it can be concluded that high purity of Ag 2Te was obtained by the present synthetic method.In addition,Brownish-black Ag 2O which resulted from unstable intermediate product AgOH can be obtained in alkaline solution [27].On the other hand,there was a strong complexing action between silver (I)ions and EDTA.So the black spots may be Ag 2O phase and the brownish-black precipitate disappeared because of the strong complexing action between silver (I)ions and EDTA.To understand the chemical situation of elements in the product,the XPS test was performed,and the results are shown in Fig.2.It can be found that a little oxides and carbon are present on the surface of the product.The oxides may result from the surface oxidation reaction of the Ag 2Te nanowires with O 2[26].The binding energies obtained from the XPS spectrum are 367.7and Table 1Summary of the synthesis of typical products under various experimental parameters.Sample T (K)t (h)PhaseMorphologySample15132Ag and Ag 2Te Straight nanotubes and particles Sample25136Ag,Te,and Ag 2Te Straight nanotubes and particlesSample35138Ag 2Te,Ag,and Te Straight nanotubes,bent wires,and particles Sample451312Ag 2Te,Te,and Ag Straight nanotubes,bent wires,and particles Sample551316Ag 2Te,Te,and Ag Straight nanotubes,bent wires,and particles Sample651320Main Ag 2Te Bent wires and particles Sample751324Pure b -Ag 2TeBent wires2002004006008001000(113) (004) (110)⎯(213)(410)⎯(504) (400)⎯(123)⎯(314) ⎯(402)(021)⎯(313) ⎯(311) ⎯(312)(112)(210)(111)⎯(112)⎯(212)(200)I n t e n s i t y (c p s )25303540455055602 (degree)Fig.1.The XRD pattern for Ag 2Te sample prepared at 513K for the mol ratio of Ag/Te ¼1.30.F.Xiao et al./Journal of Solid State Chemistry ](]]]])]]]–]]]2573.3eV for Ag 3d 5/2and Te 3d 5/2in Fig.2a,respectively,which means that the product is composed of Ag (I+)and Te (II À).The peaks at 367.7and 373.7eV correspond to Ag 3d 5/2and Ag 3d 3/2,respectively (Fig.4b),and those at 573.3and 583.5eV correspond to Te 3d 5/2and Te 3d 3/2,respectively (Fig.4c).In addition,two small peaks are observed at 577.1and 587.5eV,which can be attributed to Te(IV)oxide.According to the quantiﬁcation of XPS peaks,the molar ratio of Ag to Te is 2.05:1.00.Morphological features of the samples were investigated by FE-SEM as shown in Fig.3.The low-magniﬁcation FE-SEM image (Fig.3a)reveals that the typical products consist of a large quantity of wire-like structures with the lengths in the range of several tens to several hundred micrometers.The high-magniﬁcation FE-SEM image (Fig.3b)shows that the diameter of wire-like structures is 300À500nm.To the best of our knowledge,the synthesis of ultra-long silver telluride nanowires have never previously been reported.In order to further understand the morphology and micro-structure of the wire-like Ag 2Te,a detailed investigation was performed using high-resolution TEM (HRTEM).Fig.3c shows the low-magniﬁcation TEM image of a single ultra-long Ag 2Te wire with diameters between 200and 400nm,lengths ranging from 8to 10m m.In addition,from the TEM iamge,we found that the ultra-long silver telluride wires can be destroyed by ultrasound during the TEM sample preparation.Fig.3d shows a typical HRTEM image of a single nanowire and reveals the single-crystalline nature of the nanowires,and free of dislocation.The interplanar spacing of 0.372and 0.685nm are consistent with the (110)and (100)plane of Ag 2Te.Moreover,the FFT pattern (left inset in Fig.3d)further substantiates that the Ag 2Te nanowire is a monoclinic phase.A series of experiments were carried out to study the inﬂuence of the ratio of AgNO 3to Na 2TeO 3and Na 2(EDTA)Á2H 2O as well as NaOH on the synthesis of products.It can be seen in Fig.4a–d that the phases in the samples prepared at 513K for different ratios of AgNO 3to Na 2TeO 3are composed of monoclinic phase Ag 2Te (JCPDS:34-0142)and Ag (JCPDS:04-0783)or Te (JCPDS:65-3370).As the ratio of AgNO 3to Na 2TeO 3decreases,the amount of the Ag phase decreases gradually,then Te phase appears (Fig.4d).Here another point to be noted is that pure Ag 2Te shown in Fig.1is for the ratio 1.30.It means that the ratio of 1.30for AgNO 3to Na 2TeO 3is required for the preparation of pure long wire Ag 2Te under solvothermal synthesis at 513K.In addition,Na 2(EDTA)Á2H 2O and NaOH played a key role in this solvothermal co-reduction process.It can be seen in Fig.4e and f that the phases Ag 7Te 4(JCPDS:18-1187)and Ag (JCPDS:04-0783)appeared in the samples prepared at 513K and Ag/Te ¼1.30for 24h in the absence of NaOH and Na 2(EDTA)Á2H 2O,respectively.First of all,the pH value played an important role during this reaction,which inﬂuenced on the purity of samples.Ag 7Te 4phase would appear without NaOH added,which implied that NaOH could inﬂuence the reaction greatly.A branch reaction for elemental Te would occur in an alkaline environment to formboth positive ions (Te occurs as +4valence in TeO 2À3)and negative ions (Te 2À)simultaneously [28].The disproportionation of a little Te in alkaline environment may be essential for the purity of samples.There would be a little surplus Te to produce Ag 7Te 4phase without the disproportionation.On the other hand,E Ag +/Ag20004000600080001000012000AgMNNTeMNNTe3dO1sAg3dC1sBinding Energy (eV)I n t e n s i t y (c p s )Te4d365200040006000800010000Ag3d 3/2Ag3d 5/2Binding Energy (eV)I n t e n s i t y (c p s )57002000400060008000100001200014000Binding Energy (eV)I n t e n s i t y (c p s )oxides oxidesTe3d 3/2Te3d 5/2200400600800100012001400370375380385575580585590595Fig.2.XPS spectrum of the as-prepared pure Ag 2Te sample:(a)the survey spectrum,(b)narrow spectrum for Ag 3d ,and (c)narrow spectrum for Te 3d .F.Xiao et al./Journal of Solid State Chemistry ](]]]])]]]–]]]3was so high [29]to produce Ag phase easily in a short time that it could not react with Te phase completely which was produced relatively slowly.Consequently,pH value could adjust E Ag +/Ag to a proper value in order to obtain a pure phase.Similarly,Batabyal and Vittal [16]has approved that the pH value inﬂuenced the Ag +reduction.Then,the role of Na 2(EDTA)Á2H 2O was also investigated.Sample S2which contained both Ag phase and Ag 2Te phase was obtained when no Na 2(EDTA)Á2H 2O was added.Na 2(EDTA)Á2H 2O played a critical role in the formation of theAg 2Te nanowires.Na 2(EDTA)Á2H 2O could not only stabilize Ag +at the beginning stage,but also release Ag +gradually when main reaction consumes Ag phase.In aqueous solution,the strong complexing action between silver (I)ions and Na 2(EDTA)Á2H 2O resulted in the formation of Ag-EDTA complexes.The formation of the complexes could reduce the concentration of free Ag +in the solution,and slow the reaction rate,which is favorable for the growth of Ag 2Te nanowires.While if no Na 2(EDTA)Á2H 2O was added,Ag +would be quickly reduced by EG at 2401C,which resulted in Ag impurity in samples [30].It is known that silver telluride exhibits a structural phase transition from low-temperature monoclinic phase (a -Ag 2Te)to cubic phase (b -Ag 2Te)[18].DTA,TG,and DSC analyses have been carried out to determine transformation temperature of our sample and to apply to subsequent test of electrical conductivity and Seebeck coefﬁcient,and the results are shown in Fig.5a.A distinct endothermic peak can be seen at 421K in Fig.5a,which corresponds to the phase transformation temperature (a -Ag 2Te -b -Ag 2Te)[18].According to the DSC plot in Fig.5b,the latent heat of the phase transition is 29.34J g À1.This value is much different from that reported by Li (3.93J g À1)[31]but close to the calculated results of the thin ﬁlm (25.75J g À1)and the bulk (23.12J g À1)of Ag 2Te [32,33].3.2.Growth mechanism of Ag 2Te nanowiresTo understand the growth mechanism of Ag 2Te nanowires prepared in an solvothermal system,the silver tellurium nanos-tructures at various stages of the growth process were character-ized using FE-SEM.Fig.6shows the images of the samples that were taken from the reaction mixture after an aging time of (a)2h,(b)4h,(c)6h,(d)8h,(e)12h,(f)16h,(g)18h,(h)20h,andFig.3.SEM images of the as-prepared Ag 2Te samples synthesized at 513K for 24h with 1.30(a)and (b)for the ratio of AgNO 3to Na 2TeO 3,(c)TEM image of the Ag 2Te wire.(d)HRTEM image recorded on the edge of this wire.Inset:FFT image of the HRTEM image (left).20I n t e n s i t y (a .u .)2 (degree)25303540455055606570Fig.4.The XRD patterns for Ag 2Te samples for (a)Ag/Te ¼1.70,(b)Ag/Te ¼1.58,(c)Ag/Te ¼1.44,(d)Ag/Te ¼1.00,and Ag/Te ¼1.30for (e)no NaOH and (f)no Na 2(EDTA)Á2H 2O.F.Xiao et al./Journal of Solid State Chemistry ](]]]])]]]–]]]4(i)24h at 513K.These images clearly show the evolution of silver tellurium nanostructures from particles into ultra-long wire-like morphology over time at 513K.For the transformation of the nanowires,topotactic transformation mechanisms can be considered.Based on the experimental results,the formation process of ultra-long Ag 2Te wires is proposed as follows:First of all,Ag,Te,Ag 2Te nucleation:Fig.6a shows that the samples were comprised of numerous smaller crystallites of about 100–500nm and we can believe that in this step,Ag phase,highly anisotropic Te phase and a little amount of Ag 2Te phase proceeded through nucleation and coexisted.To the best of our knowledge,Ag core and Te core could be easily nucleated and can be grown in EG solvents at appropriate temperature [34].In addition,Na 2(EDTA)Á2H 2O and NaOH could reduce the concen-tration of free Ag +and E Ag +/Ag effectively,which played a crisis role in this reduction condition.Then,Te nanotubes and Ag 2Te wires Growth:In this step,highly anisotropic Te nanotubes can be easily and directly grown along c -axis from Te seeds without the use of any physical templates [34,35].But how Te tubes transform to Ag 2Te wires?Consulting the literature,two possible mechanisms can be considered.The one is that active Ag atom in supersaturated solution adsorbed on the surface of Te nanotubes inner and outer,and then rearranged,reaction.Similarly,the copper and silver chalcogenides have been prepared by this topotactic transforma-tion mechanism [32–35].Another one is the split of Ag 2Te tubes and half-tubes formed by inward diffusion of Ag on surface of Tetubes,which is similar with the report of Purkayastha et al.[36]for the preparation of single-crystal lead telluride nanorods.It should be mentioned that there were some bent Ag 2Te nanowires as indicated in Fig.6b–e because of the mechanical stress resulted from the change of atom radius and band length in the conversion of Te to Ag 2Te [26,37].In addition,Na 2(EDTA)Á2H 2O could not only stabilize Ag +at the beginning stage,but also releases Ag +gradually when main reaction consume Ag phase,which was a very important factor to obtain pure samples.Finally,Ostwald Ripening of Ag 2Te nanowires:As soon as Ag 2Te crystallites existed,there was a balance between Ag 2Te nanowires and smaller Ag 2Te crystallites.As indicated in Fig.6f–i,Ag 2Te wires grown at the expense of the smaller ones [38]and it can be seen there is only wire-like morphology for the sample prepared for 24h.This mechanism is totally different from the work of Qin et al.[25]and Zuo et al.[26]for the preparation of silver telluride.Furthermore,XRD and TEM results have proved that Ag 2Te phase existed in samples prepared for 8and 16h.Experimental studies with X-ray diffraction for the samples that were taken from the reaction mixture after an aging time of (a)4h,(b)8h (c)16h,and (d)24h at 513K have also provided evidence to support this proposed mechanism.In this process,the ethylene glycol could serve as both solvent and reducing reagent [34].The XRD investigation shown in Fig.7indicates that all of the sample prepared in the present work can be indexed to the monoclinic Ag 2Te phase.Almost only Te phase and Ag phase could be obtained by reaction for 4h,which can be seen in Fig.7a.In particular,the intensity of Te crystallographic phase in the products is indeed increased gradually with the reaction time from 8to 16h in Fig.7b and c which indicates that preferential orientation of Te nanotubes occurred [34].It is easy to understand that the relative amount of Ag 2Te,Ag,and Te phase would change gradually which depended on the reaction time.Finally,pure and ultra-long Ag 2Te wires could be obtained as reaction time went to 24h in Fig.7d.On the basis of the experimental results,the whole process for the formation of Ag 2Te wires can be schematically illustrated in Fig.8.In the early stage,the intermediate products indicate the coexistence of Ag particles and Te particles.As the reaction continued,it can be noted that the particles gradually disappear with the dramatical increase in the production of Te nanotubes.For the transformation process from Te nanotubes to Ag 2Te wires during 8–24h,we can understand this interesting phenomenon by topotactic transformation.3.3.The electrical conductivity and Seebeck coefﬁcient of Ag 2Te nanowiresThe thermoelectric properties of the bulk and ﬁlm silver telluride have been studied by many researchers.From these studies,they have observed abrupt changes of the Hall coefﬁcient,the Seebeck coefﬁcient,and the electrical conductivity at 1401C,a consequence of the structural phase transition.Fujikane et al.[39,40]have studied the thermoelectric properties of silver telluride in bulk form over a wide temperature range from 4to 450K.Around 1501C,Das et al.[41]have observed the maximum Seebeck coefﬁcient of the thin ﬁlm to be À110m V K À1in the thickness of 58nm.Gnanadurai et al.[32]have also found the maximum Seebeck coefﬁcient of the thin ﬁlm to be 130m V K À1in the optimal thickness of 41nm during the cooling process.The temperature-dependent Seebeck coefﬁcient of as-prepared wire-like Ag 2Te (Fig.9a)also demonstrates the structural phase transition.The two standard error bars stands for the maximum and minimum values include the uncertainties in measuring electrical conductivity as well as Seebeck coefﬁcient.The maximum value observed for the Seebeck coefﬁcient (S )320-10-8-6-4-20Temperature (K)D T A (μV )4.04.24.44.64.85.05.25.45.65.86.0T G (m g )340-36-34-32-30-28-26-24-22-20Temperature (K)D S C (m W )340360380400420440460480360380400420440460480Fig.5.(a)DTA-TG analysis and (b)DSC analysis of the Ag 2Te samples heated with 10K/min up to 493K.F.Xiao et al./Journal of Solid State Chemistry ](]]]])]]]–]]]5was À70m V K À1,which was lower than the reported value (À160m V K À1)[18].It can be observed distinctly that the Seebeck coefﬁcient greatly decreases at 426K,implying that sample’s structure and the carrier concentration changes greatly.Fig.9b shows the behavior of the electrical conductivity in thetemperature range of 300–673K.The electrical conductivity increases with increasing temperature below 373K,which is consistent with the property of semiconductor’s electrical conductivity.From 373to 423K,the s (T )curve greatly decreases with increase in temperature,which indicated the structure of Ag 2Te changes greatly as results of phase transition of b -Ag 2Te to a -Ag 2Te.Then s (T )curve slowly increases with increase in temperature above 423K.Because the electronic conductivity is strongly dependent on Seebeck coefﬁcient (S )[42],it is easy to explain the abrupt decrease of the value of the electrical conductivity in the temperature range between about 373and 423K.The maximum value observed for the electrical conductivity s was 30S cm À1,which was much higher than reported value (0.7S cm À1)for wire-like Ag 2Te [18].This is possibly due to interconnection in the NW network and the length (420m m)of the single crystal NWs are higher than the mean free path of electron in Ag 2Te far away [43,44].The interconnection in the NW network can reduce the interface electron scattering while ultra-long single crystal nanowires morphology can provide a good 1-D transporting channels.Further investigation is currently undergoing to verify this.4.ConclusionsIn summary,ultra-long single crystal b -Ag 2Te nanowires have been successfully synthesized by one-pot solvothermal co-reduc-tion method at moderate temperatures and ratio of AgNO 3toFig.6.FE-SEM images of the Ag 2Te samples hydrothermal treated at 513K for (a)2h,(b)4h,(c)6h,(d)8h,(e)12h,(f)16h,(g)18h,(h)20h,and (i)24h.252 (degree)I n t e n s i t y (a .u .)303540Fig.7.The XRD patterns of the Ag 2Te samples treated hydrothermally for (a)4h,(b)8h,(c)16h,and (d)24h.F.Xiao et al./Journal of Solid State Chemistry ](]]]])]]]–]]]6Na 2TeO 3.The phenomenon of phase transitions of the as-prepared long wire-like Ag 2Te from monoclinic structure (b -Ag 2Te)to face-centered cubic structure (a -Ag 2Te)around 421K are obviously observed.In our experiment,reaction time and mol ratio of AgNO 3to Na 2TeO 3were found to have more inﬂuence on the morphology of the products.Based on our experimental results,anisotropic Te nanotubes grow and transform the nanotubes into single-crystal b -Ag 2Te wires via reaction with an Ag salt.AcknowledgmentThis work was supported by the National Natural Science Foundation of China (Project no.20871036)and the Development Program for Outstanding Young Teachers in Harbin Institute of Technology (HITQNJS.2009.001).References[1]T.Gandhi,K.S.Raja,I.Chatterjee,M.Misra,X.Luo,P.Dzurella,Int.J.Nanotechnol.5(2008)519.[2]X.H.Sun,B.Yu,G.Ng,M.Meyyappan,J.Phys.Chem.C 111(2007)2421.[3]S.Meister,D.T.Schoen,M.A.Topinka,A.M.Minor,Y.Cui,Nano 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i t y (S c m -1)-90-80-70-60-50-40-30-20S e e b e c k c o e f f i c i e n t ( V K -1)400500600700800Fig.9.(a)Temperature dependence of the Seebeck coefﬁcient (b)Electrical conductivity for pure Ag 2Te samples.The two standard error bars include the uncertainties in measuring Seebeck coefﬁcient and electrical conductivity.F.Xiao et al./Journal of Solid State Chemistry ](]]]])]]]–]]]7。

2021届高考英语中国元素之阅读理解中国科技二

高中2021届高考英语“中国元素”之阅读理解中国科技（二）.2019 World Conference on VR Industry was held in Nanchang, China, with the goal of further satisfying people's growing demand for a better life, accelerating the modernization of China's economic system and its transformation into an innovation-oriented country, and promoting breakthroughs in the economic and social development of Jiangxi Province. The theme of the conference is "VR Adorns（装扮）the World - VR + 5G for a New Era of Perception（观念）".The virtual reality industry in Nanchang, capital city of East China's Jiangxi province, is expecting a boom when China grows in a new era of 5G this year, experts and industry insiders said at the conference.The Conference attracted experts, scholars and company leaders from more than 30 countries, including the us, Germany, Britain, Russia, India and Israel, discussing the development and application of VR, especially as 5G, the next generation technology for network on devices like cellphones, unlocks the potential of VR. With a focus on the new era of perception enabled by 5G, this year's conference showed leading-edge VR technologies and the latest outcomes of the global VR industry.Miao Wei, head of the Ministry of Industry and Information Technology, said in the opening address that with China officially getting 5G; commercial licenses on June 6th 2019, the co-development of VR and 5G promises a huge market in future. “China takes the lead in VR innovations. And the wide popularity of high-tech in our country guarantees the potential of this market,” said Miao.China is building its VR industry into one with the most dynamic environments for innovation and entrepreneurship, highest market acceptance, and the greatest growth potential in the world.1.What is one of the aims of 2019 World Conference on VR Industry?A.To promote 5G technology.B.To make Chinese people more creative.C.To improve the economic development of Jiangxi.D.To change the world into a modern one.高中高中2.What is the relationship between 5G and VR?B.VR,s application would unlock 5G.C.5G makes VR a business.D.VR is made up of 5G.3.What is the best title for the text?A.Technology Revolution in JiangxiB.New Era Marked by 5G and VRC.VR, Technology for the FutureD.VR Conference in Nanchang一、Everyone has a quarrel or two with friends, co-workers and family members,but library goers in Nanchang, East China,s Jiangxi Province got a surprise when a person unintentionally started an argument between two robots.The two robots, named Tutu and Wangbao, are supposed to offer assistance to visitors in the hall of the Jiangxi Provincial Library. When a library goer scanned Tutu's QR code, Wangbao seemingly became annoyed, which brought a great amusement to the library goer who posted a video of the exchange that occurred on December 30 and has gone viral on social media.“Tutu, let,s stop fighting,OK?”said Wangbao.“Your mood sure swings a lot!" Tutu said.Wangbao raved, “Aren’t you a drama queenjm giving you an out. Stop being petulant!”The library goer was even more amused, as the two robots grew noisier and angrier with each other, and finally, abruptly turning away from each other like naughty children.“It looks like how you quarrel with your girlfriend,ha-ha." one netizen posted.“I see myself from the quarrel,〃wrote another on Sina Weibo,which was echoed by many others.“It's annoying to hear people arguing,and I didn,t expect I,d have to listen to robots arguing,〃another netizen wrote.The online video was widely circulating on Sina Weibo, with some 500, 000 views as of press time on Saturday. Tutu and Wangbao became internet hot figures, even attracting attention高中高中When the two online celebrities were interviewed by reporters on Friday, the two seems already forgave each other after three days.“It was a thing last year…Isn’t it normal to have quarrels between friends?”Wangbao said in video posted by the Xinhua News Agency on Saturday.1.What's the purpose of paragraph one ?A.To show how smart the two robots are.B.To increase our awareness of Al technology.C.To introduce the following parts.D.To criticize the quarrel between the two robots.2.What was the library goer,s attitudetowards the argument?A.Amazed.B.Entertained.C.Puzzled.D.Excited.3.By presenting some netizens, comments,the author intends to tell us.A.the fight draws the public,s great attentionB.the fight has an awful effect on people/s lifeC.the fight takes place on a regular basisD.the fight feels like a real one4.Where is the text most likely from?A.A textbook.B.A diary.C.A magazine.D.A website.二、A 1.6-metre-tall robot may soon become the best friend for lonely elderly people, as Chinese scientists are making the final sprint（冲刺）towards its market launch（投放），said a senior researcher on the robot project on Saturday."We are working on testing the exact functions and ways to reduce the cost in preparations for an expected market launch of the robot in two to three years," said Li Ruifeng, a member of the project.He said the team hoped to reduce the cost so that the robot can be priced at 30, 000 to 50, 000 yuan, which is expected to be an affordable price for most of China's better-off families.The robot has been developed with the functions of fetching food and medicine, sounding alarms in case of water or gas leakage, sending texts or video images via wireless communications,高中and even singing a song or playing chess to entertain its masters.Li said that the robot, developed independently in China, has technology at the same level as those in Western labs.China set about the research of the robot in 2007, when it was listed as a national key project. It is backed by government funding（拨款）.China has the world's largest elderly population with 159 million people over 60, accounting for 12 percent of its total population. According to a survey by the Ministry of Civil Affairs, more than 10 million caregivers and nurses are needed to attend the elderly, as most of Chinese elderly prefer to live their retired lives at home.1.The underlined word "backed" in the last paragraph means.A. supportedB. suggestedC. controlledD. stopped2.From the last paragraph we know that.A.our government pays no attention to the elderly peopleB.China has the world's largest elderly populationC.Chinese elderly people prefer to be looked after by robot caregiversD.robots are the best friends for the lonely elderly people3.Which of the following is true according to the passage?A.Robot caregivers will appear in the market in 2 to 3 years.B.Robot caregivers can help elderly people to do everything.C.China needs some technical support from Western labs.D.The robot is expected to be bought by every person.4.The author wrote the passage to.A.advertise a robot caregiver to the elderlyB.tell Chinese elderly not to worry about their livesC.explain how robot caregivers work in the futureD.introduce a newly-developed robot caregiver四、On Tuesday, China announced it had grown the first ever plants on the moon, days after landing on the moon's “far side” Von Karman crater. The cotton seed sprouts （新芽）seemed to have withstood the tough lunar conditions: freezing temperatures, lower gravity levels, and radiation.高中But by Thursday, the new cotton seed sprouts had dead already, according to Liu Hanlong, the experiment leader, in a government press conference statement.After Chang,e-4 landed on the far side of the moon earlier this month, the probe （探测器）was sent a command to remotely water the plants and start the growing process. A tube directed natural light on the surface of the moon into the small container to allow the plants to grow. The probe entered a sleep mode on Sunday, the first lunar night after the probe,s landing.Professor Xie Gengxin, professor at Chongqing University and chief designer of the experiment, told CNN that it ended after nine days when the control team shut down the power. Xie said temperatures inside the biosphere had grown too abnormal and reached extremes that would likely kill all life, including the seeds and eggs during the lunar night. Xie didn,t confirm why temperatures had risen to levels unbearable for the plants in spite of the measures taken by the research team.Even though the experiment was quickly terminated, Xie considered it a success. The cotton were the only seeds to sprout, however, and despite many assumptions about the future possibility of moon clothes, the cotton plant,s main purpose this time was to give researchers the valuable data on how to cultivate life in the moon/s tough conditions. The eventual ability to grow plants on the moon could prove useful for long-term space missions, like a trip to Mars. Astronauts could theoretically harvest their own food in space, avoiding the need to return to Earth to resupply.Aside from the apparent failure of the biological or plant experiment, the rest of China's mission to the far side of the moon appeared on track as of Thursday. The historic mission is intended to accomplish a range of tasks, including conducting the first lunar low-frequency radio astronomy experiment and exploring whether there is water at the moon/s poles.Chang,e-4 is the latest step in China/s robotic lunar-exploration program, named after a moon goddess in Chinese mythology. China plans to launch the Chang,e-5 sample-return mission sometime this year.l.What does the underlined word “withstood” mean?A.Appreciated.B.Suffered from.C.Tolerated.D.Been subject to.2.What is the fourth paragraph mainly about?A.The measures of the research team.B.The cause of ceasing the experiment.高中高中C.The reason for the extreme temperature. D.The failure and impact of the experiment. 3.What isthe major target of the plant experiment?A.To make moon clothes possible.B.To ensure its value for long-term space missions.C.To enable astronauts to harvest their own food without returning to Earth to resupply.D.To accumulate the priceless data on how to grow lifeiii the moon,s severe conditions.4.What is the best title for the text?A.China,s moon plants have diedB.China,s mission to the far side of the moonC.The Chang,e-5 sample-return missionD.Astronauts, efforts to cultivate life in the moon五、China became the first country to clone a monkey using non-reproductive cells, scientists said on Thursday. By December 2017, the Chinese Academy of Sciences had created two clone macaques （猕猴）named "Zhong Zhong" and "Hua Hua" by nuclear transfer （核移植）of body cells —any cell in the organism other than reproductive cells. This was the similar technology used to create the famous clone sheep Dolly in 1996.Tetra, a monkey born in 1999, is the world's first ever-cloned monkey, but it was done using a simpler method called embryo splitting, and cannot be genetically modified （改造）to suit experimental needs, said Pu Muming, a leading researcher at the Chinese Academy of Sciences. Cloning a monkey using body cells has been a world-class challenge because it is a primate （灵长类）that shares its genetic make-up with humans, he said.For drug and other lab tests, scientists have to purchase monkeys from all over the world, which is costly, bad for the environment and produces inaccurate results because each monkey might have different genes, Pu said."By cloning monkeys using body cells, we can reproduce a large number of genetically identical monkeys in a short amount of time, and we can even change their genes to suit our needs," he added. "This can save time, cut down experiment costs, and produce more accurate results, leading to more effective medicine."Sun Qiang, director of the non-human primate research facility at the institute, said most of 高中高中the drug tests are currently done on lab mice. However, drugs that work on mice might not work or even have severe side effects on humans because the two species are so different.Monkeys and humans are both primates, so they are much closely related and testing on monkeys is supposed to be as effective as testing on humans. This achievement will help China lead the world research in an international science project related to study of primate brains.1.Which description of the two clone macaques is true?A.They were the first monkeys ever-cloned in the world.B.They were created using reproductive cells.C.They would not be fed to suit experimental needs.D.The technology used to create them was similar to that of creating Dolly.2.Cloning monkeys using body cells for drug and other lab tests is.A.time-consumingB.very expensiveC.more efficientD.inaccurate 3.What can be learned from the passage?A.Pu Muming and Sun Qiang were doing most work in cloning the two macaques.B.Genetic research on monkeys can be seen as effective as that on humans.C.Most drug tests have been done on mice because mice share the same genetic make-up with humans.D.Scientists mass reproduce clone monkeys only to cut down experiment costs.4.This passage above can be most probably read in.A.a science magazineB.a travel guidebookC.an imaginary fictionD.a lab brochure 六、China successfully sent the 52nd and 53rd satellites of its domestically developed BeiDou Navigation Satellite System (BDS—the last two medium Earth orbit (MEO) satellites for the BDS-3 constellation (星座)一into space on Monday, marking the completion of the global navigation system,s core constellation deployment 部署)and this year,s BDS satellite launch campaign.Launched from Xichang Satellite Launch Center, Sichuan Province, on board a Long March-3B carrier rocket with an Expedition-1 upper stage, the two satellites were injected into planned orbits after more than three hours, flight.Since the first BDS-3 satellite was launched on November 5, 2017, China has conducted 18 BDS satellite launch missions, successfully sending 30 into their planned orbit, setting a national 高中高中record for highest mission frequency and success rate.In-orbit tests will be carried out before the two MEO satellites are commissioned ( 正式委托).By then the core constellation for the Chinese global navigation satellite system will be successfully completed.Wang Ping, chief designer of the BDS-3 system, said that the hybrid constellation design, in which three groups of satellites—the Inclined Geo Synchronous Orbit (IGSO), MEO and geosynchronous Earth orbit (GEO)—work in concert in different orbits, was an exclusive BDS innovation and a world first. “Existing global navigation satellite systems, such as the US GPS and Russia,s GLONASS, only have a MEO satellite constellation,” said Wang.The MEO satellites, in orbit 20,000 kilometers above Earth, are a special type of satellite providing global service, while the IGSO and GEO satellites, in an orbit 360,000 kilometers above Earth, mainly enhance regional service quality, according to Wang. That explained why completion of the MEO constellation was significant, marking the completion of the core network for BDS-3, meaning a stable BDS-3 global coverage without weak points has been carried out.Feedback shows that the BDS service quality was already comparable to GPS since the end of 2018, and after completing BDS-3, “We will be as good as any GNSS.” Wang said.1.How many BDS satellites were sent into their planned orbit successfully?A.3.B.18.C.30.D.36.2.What's the advantage of BDS compared with GPS and GLONASS?A.The diverse functions.B.The excellent service quality.C.The lower cost of designing it.D.The ability to work in different orbits.3.Why are the MEO satellites important?A.They enhance regional service quality.B.They can be put into use immediately.C.They can enter farther orbits.D.They can serve the world.4.What may be the best title for the text?A.China Becomes the First Country to Launch a MEO Satellite高中高中B.The Core Constellation of BDS-3 CompletesDeploymentC.The BDS-3 System Has Benefited Many CountriesD.Exploring Space Is Very Important to the World高中答案以及解析、答案：1.C; 2.A; 3.D解析:1.根据第一段可知,VR大会的目的有很多。

211114970_纯钽表面微弧氧化“类骨小梁”状多孔涂层的细胞相容性

第52卷第4期表面技术2023年4月SURFACE TECHNOLOGY·363·纯钽表面微弧氧化“类骨小梁”状多孔涂层的细胞相容性王伟强，王舒月，于凤云，王轶农（大连理工大学，辽宁大连 116024）摘要：目的提高医用纯钽的生物活性，利用微弧氧化（MAO）技术在其表面制备出“类骨小梁”状分级多孔涂层，并对比该涂层与传统“火山坑”状MAO涂层以及机械抛光纯钽表面在表面粗糙度、亲水性以及细胞相容性方面的差异。

方法使用0.1 mol/L Na2B4O7和0.05 mol/L Na3PO4电解液在纯钽表面分别制备出“类骨小梁”状及“火山坑”状多孔涂层（分别命名为B-MAO和P-MAO涂层）。

采用扫描电镜、X射线衍射以及X射线光电子能谱对不同结构涂层进行形貌观察和相组成分析，使用十字划格法评价涂层结合强度，使用激光共聚焦显微镜测定涂层的表面粗糙度，使用接触角仪测量其亲水性，并将小鼠前成骨细胞（MC3T3-E1）接种于材料表面，对比不同形貌状态对细胞铺展、增殖以及成骨分化的影响。

结果 MAO 涂层物相主要为Ta2O5。

B-MAO涂层由于内部孔隙度高，应力释放充分，涂层结合强度高，而P-MAO涂层则因具有分层现象和较大的残余应力，易从基体剥落。

抛光纯钽表面、P-MAO、B-MAO涂层表面的粗糙度分别为0.06、1.50、1.58 μm，与之相应的接触角分别为42.6°、15.5°、7.2°。

细胞初期粘附结果表明，MAO 涂层表面细胞数量多于抛光纯钽表面，且B-MAO涂层细胞铺展能力优于P-MAO涂层和抛光钽表面。

CCK-8测试结果表明，细胞数量随时间逐渐增加，MAO组细胞增殖能力好于抛光组，B-MAO组细胞增殖能力最优。

ALP活性方面，B-MAO组也高于P-MAO和抛光组。

结论 MAO涂层相较于抛光纯钽表面具有更高的粗糙度以及亲水性，从而具有高的细胞粘附和增殖能力。

四级真题：2011年6月四级阅读理解解析

英语类考试频道为友整理⼤学英语四六级考试，供⼤家参考学习。

Passage One Questions 57 to 61 are based on the following passage. Global warming may or may not be the great environmental crisis of the 21st century, but—regardless of whether it is or isn’t - we won’t do much about it. We will argue over it and may even, as a nation, make some fairly solemn-sounding commitments to avoid it. But the more dramatic and meaningful these commitments seem, the less likely they are to be observed. Al Gore calls global warming an “inconvenient truth,” as if merely recognizing it could put us on a path to a solution. But the real truth is that we don’t know enough to relieve global warming, and—without major technological breakthroughs—we can’t do much about it. From 2003 to 2050, the world’s population is projected to grow from 6.4 billion to 9.1 billion, a 42% increase. If energy use per person and technology remain the same, total energy use and greenhouse gas emissions (mainly, CO2) will be 42% higher in 2050. But that’s too low, because societies that grow richer use more energy. We need economic growth unless we condemn the world’s poor to their present poverty and freeze everyone else’s living standards. With modest growth, energy use and greenhouse emissions more than double by 2050. No government will adopt rigid restrictions on economic growth and personal freedom (limits on electricity usage, driving and travel) that might cut back global warming. Still, politicians want to show they’re “doing something.” Consider the Kyoto Protocol (京都议定书). It allowed countries that joined to punish those that didn’t. But it hasn’t reduced CO2 emissions (up about 25% since 1990), and many signatories (签字国) didn’t adopt tough enough policies to hit their 2008-2012 targets. The practical conclusion is that if global warming is a potential disaster, the only solution is new technology. Only an aggressive research and development program might find ways of breaking our dependence on fossil fuels or dealing with it. The trouble with the global warming debate is that it has become a moral problem when it’s really an engineering one. The inconvenient truth is that if we don’t solve the engineering problem, we’re helpless. 注意：此部分试题请在答题卡2上作答。

基于模拟曝光融合的非均匀光照图像增强

第61卷第3期吉林大学学报(理学版)V o l .61 N o .3 2023年5月J o u r n a l o f J i l i nU n i v e r s i t y (S c i e n c eE d i t i o n )M a y 2023d o i :10.13413/j .c n k i .jd x b l x b .2022080基于模拟曝光融合的非均匀光照图像增强王若状,臧景峰,张朋朋(长春理工大学电子信息工程学院,长春130022)摘要:针对非均匀光照图像存在的场景细节被掩盖㊁图像信息获取较难的问题,提出一种基于模拟曝光融合的非均匀光照图像增强方法.首先,在H S V 颜色空间下使用改进的自适应伽马校正算法处理亮度分量,将其作为中等曝光图像;其次,对亮度分量通过动态阈值划分过曝光像素集,对其使用最大信息熵估计及相机响应模型合成模拟的过曝光图像;再次,对原图像㊁中等曝光图像㊁过曝光图像组成的多曝光图像序列使用改进的质量度量方法以及基于导向滤波的权重优化方法得到融合图像;最后,融合结果经过多尺度细节增强处理得到最终的图像增强结果.实验结果表明,该算法能有效改善非均匀光照图像的视觉效果,通过主客观评价的数据对比,表明本文算法优于同类算法.关键词:非均匀光照;自适应伽马校正;模拟曝光图像;多曝光融合;导向滤波中图分类号:T P 391 文献标志码:A 文章编号:1671-5489(2023)03-0601-11N o n -u n i f o r mI l l u m i n a t i o n I m a g eE n h a n c e m e n t B a s e d o nS i m u l a t e dE x po s u r eF u s i o n WA N G R u o z h u a n g ,Z A N GJ i n g f e n g ,Z H A N GP e n g p e n g(S c h o o l o f E l e c t r o n i c a n dI n f o r m a t i o nE n g i n e e r i n g ,C h a n g c h u nU n i v e r s i t y o f S c i e n c e a n dT e c h n o l o g y ,C h a n g c h u n 130022,C h i n a )收稿日期:2022-03-03.第一作者简介:王若状(1997 ),男,汉族,硕士研究生,从事图像融合与图像增强的研究,E -m a i l :3347570691@q q.c o m.通信作者简介:臧景峰(1976 ),男,汉族,博士,教授,从事计算机视觉和嵌入式系统的研究,E -m a i l :z a n g j i n g f e n g@c u s t .e d u .c n .基金项目:吉林省教育厅科学技术研究项目(批准号:J J K H 20210839K J ).A b s t r a c t :A i m i n g a tt h e p r o b l e m so fs c e n ed e t a i l sb e i n g c o v e r e du p a n di m a g ei n f o r m a t i o nb e i n g d i f f i c u l t t oo b t a i n i nn o n -u n i f o r mi l l u m i n a t i o n i m a g e s ,w e p r o p o s e d an o n -u n i f o r mi l l u m i n a t i o n i m a g e e n h a n c e m e n tm e t h o db a s e do ns i m u l a t e de x p o s u r ef u s i o n .F i r s t l y ,a ni m p r o v e da d a p t i v e G a mm a c o r r e c t i o na l g o r i t h m w a s u s e d i nH S Vc o l o r s p a c e t o p r o c e s s t h eb r i g h t n e s s c o m p o n e n t a s am e d i u m e x p o s u r e i m a g e .S e c o n d l y ,t h eo v e r -e x p o s u r e p i x e ls e t w a sd i v i d e db y d y n a m i ct h r e s h o l df o rt h e b r i g h t n e s s c o m p o n e n t ,a n dt h es i m u l a t e do v e r -e x p o s u r e i m a g ew a ss y n t h e s i z e db y u s i n g m a x i m u m i n f o r m a t i o n e n t r o p y e s t i m a t i o n a n d c a m e r a r e s p o n s e m o d e l .T h i r d l y ,t h e i m p r o v e d q u a l i t ym e a s u r e m e n tm e t h o d a n d t h ew e i g h t o p t i m i z a t i o n m e t h o db a s e do n t h e g u i d e d f i l t e r i n g w e r eu s e d t o o b t a i n t h e f u s e d i m a g e f o r t h em u l t i -e x p o s u r e i m a g e s e q u e n c e s c o m p o s e dof t h eo r ig i n a l i m a g e s ,th e m e di u m -e x p o s u r e i m a g e s a n d t h eo v e r -e x p o s u r e i m a g e s .F i n a l l y ,t h e f u s i o nr e s u l tw a s p r o c e s s e db y m u l t i -s c a l e d e t a i l e n h a n c e m e n t t o o b t a i n t h e f i n a l i m a g e e n h a n c e m e n t r e s u l t .T h e e x p e r i m e n t a l r e s u l t s s h o wt h a t t h e p r o p o s e d a l g o r i t h mc a n e f f e c t i v e l y i m p r o v e t h e v i s u a l e f f e c t o f n o n -u n i f o r mi l l u m i n a t i o n i m a g e s .T h e c o m p a r i s o n o f s u bj e c t i v e a n d o b j e c t i v e e v a l u a t i o n d a t a s h o w s t h a t t h e p r o p o s e d a l go r i t h m206吉林大学学报(理学版)第61卷i s s u p e r i o r t o s i m i l a r a l g o r i t h m s.K e y w o r d s:n o n-u n i f o r m i l l u m i n a t i o n;a d a p t i v e G a mm a c o r r e c t i o n;s i m u l a t e d e x p o s u r e i m a g e; m u l t i-e x p o s u r e f u s i o n;g u i d e d f i l t e r i n g非均匀光照图像通常指由于拍摄时光照不均或曝光不当等原因产生的低质量图像,常见的如逆光㊁低光照㊁非均匀照明等场景,这些图像普遍存在亮度不均㊁对比度低㊁图像细节信息被掩盖等问题.为改善这类图像的视觉效果,复原图像信息,许多研究者针对该问题提出了图像增强方案.目前,关于非均匀光照的图像增强主要包括以下几类算法:1)基于直方图均衡(h i s t o g r a me q u a l i z a t i o n,H E)的增强算法,基于图像直方图改变像素值的分布情况,扩宽图像的动态范围,从而达到照度增强的目的,该类方法较简单,但其作用范围是图像全局,存在色彩失真㊁放大噪声等问题;2)基于大气散射模型(a t m o s p h e r i c d i s p e r s i o nm o d e l,A D M)的算法,该模型最初源于暗通道去雾模型[1],之后基于非均匀光照图像取反后与雾天图像在亮度分布上具有相似性理论,衍生出基于单通道和双通道先验的非均匀光照图像增强算法,但该类方法的理论假设在物理上并不合理,因此增强后需要进行后处理强化[2];3)基于照度反射模型R e t i n e x理论,认为图像成像值可表示为场景光照分量和场景反射分量的乘积,传统基于R e t i n e x的增强方法通过去除光照分量并增强反射分量达到增强效果[3-4],但存在易出现过度增强及细节失真等问题;4)基于深度学习(d e e p l e a r n i n g,D L)的方法,该类方法需要设计合理的网络模型,且依赖于非均匀光照图像数据集资源和较强的计算能力,也是近年较热门的研究方法[5].此外,多曝光融合(m u l t i e x p o s u r e f u s i o n)的方法,多用于实现高动态范围(h i g hd y n a m i c r a n g e, H D R)显示,通过融合在不同曝光时间下捕获的场景细节,能有效扩展图像的动态范围,该技术目前也较多用于非均匀光照图像增强.H u a n g等[6]对曝光图像序列的单张图像分别进行对比度提取㊁结构保持和强度调整操作,并使用局部权重㊁全局权重和显著性权重融合结构保持和强度调整的图块,最终将三部分进行融合得到增强图像,但存在色彩失真的问题;Y a n g等[7]借助强度映射函数将两张图像生成曝光时间相同的两张虚拟中间图像,使用权重合并两张图像为最终的虚拟图像,使用质量因子权重估计对两张初始图像和合成的虚拟图像,但会出现色彩失真㊁视觉效果略差的问题;L e e等[8]根据每张图像与曝光图像序列的其他图像的整体亮度关系及全局梯度范围大小分别确定权重,将两类权重结合作为该图像在融合过程的最终权重,能取得较好的融合效果,但具有一定的计算复杂度,且会出现光晕现象;L i等[9]提出了改进的曝光融合权重计算方法,使用结合自适应直方图均衡的L a p l a c e滤波结果作为对比度权重,并提出将图像信息熵作为一种新的权重代替传统权重中的饱和度权重,最终的融合结果与传统权重度量方法相比在主观视觉上增强效果并不显著;Lü[10]通过对传统权重图使用函数映射构建加权的高斯金字塔,根据图像差和二维信息熵优化权重图以消除运动伪影,并基于图像对比度进行自适应细节增强,取得了较好的融合效果;L i u等[11]提出一种注意力引导的全局-局部对抗性曝光融合学习网络,先通过注意力权重获取粗融合结果,再使用边缘损失函数改进融合过程增强边缘信息,并通过全局-局部学习纠正颜色失真,取得了较好的融合效果.传统使用拍摄的曝光序列融合方法需要场景相对稳定,否则在融合后会出现伪影.本文基于相机响应模型可由单张图像直接生成模拟的曝光序列,避免了该问题,同时结合改进的自适应伽马校正㊁动态曝光区域分割阈值和曝光融合方法,有效解决了非均匀光照图像视觉效果较差的问题.本文算法的流程如图1所示.图1 本文算法流程F i g .1 F l o wc h a r t o f p r o p o s e da l go r i t h m 1 模拟曝光融合图像增强算法1.1 颜色空间转换从像素水平分析,相同场景下不同曝光度的图像颜色信息基本不变,只是亮度差异显著,因此对多曝光图像序列只需处理图像的亮度信息而保留颜色信息,以保证在增强图像亮度细节的基础上不改变图像的原始色彩信息,而通常计算机处理的彩色图像都是用R G B 颜色空间表示的,其主要问题是三通道彩色分量高度线性相关,不适于分离亮度与颜色信息.H S V 颜色空间是根据人对颜色的感知特性进行描述的,由色调(H )㊁饱和度(S )和明度(V )三个分量合成,其中明度V 是对物体发光或光照辐射进行描述,能反映图像场景的亮度信息,同时与两个颜色描述分量具有良好的独立性,符合本文对颜色空间的设计要求,因此本文将待处理图像转换至H S V 空间并对V 分量进行增强处理.1.2 相机响应模型相机响应函数(c a m e r a r e s p o n s e f u n c t i o n ,C R F )可描述为相机传感器辐照度与图像像素之间的非线性映射关系:P (x ,y )=f (E (x ,y )),(1)其中P (x ,y )表示成像像素值,E (x ,y )表示场景辐射强度,f (㊃)表示相机响应函数.文献[12]提出用亮度变换函数(b r i g h t t r a n s f o r mf u n c t i o n ,B M F )间接估计C R F ,是目前应用较广的一种C R F 模型,表示为P N =g (P M ,k ),(2)并有P N =f (k E ),(3)其中P N 和P M 为仅曝光不同的两张图像,g (㊃)为B M F 函数,k 为由P M 生成P N 的曝光率,E 为场景辐射强度.参照伽马校正,将g (㊃)拟合为P N =βP γM ,(4)其中β,γ为参数因子.由式(2)~(4)有β=e x p {b (1-k a )},γ=ka {,(5)即B T F 可表示为P x =βx P γx0=e x p {b (1-k a x )}P k a x 0,(6)其中P x 表示基础图像为P 0㊁曝光率为k x 时对应的模拟曝光图像.实验表明,满足参数a =-0.3293,b =1.1258时,该模型可适用于大部分相机.1.3 模拟曝光序列由于原图像可以包含场景最多的细节信息,而模拟曝光图像将不可避免地导致图像细节损失,因此直接使用原图像作为曝光序列的一张图像,能补偿曝光序列中其他图像在细节上的不足,下面通过自适应伽马校正和相机响应模型分别生成中等曝光与过曝光图像.306 第3期王若状,等:基于模拟曝光融合的非均匀光照图像增强1.3.1 自适应伽马校正传统的伽马校正由于其参数固定,对不同的图像采用相同参数的非线性变换,即对不同图像的亮度校正程度不变,这对后续的图像增强处理显然不合适.因此,本文改进文献[13]的自适应伽马校正方法,对待增强图像的V 分量进行处理.首先,需对图像的对比度及明暗度进行划分,根据划分属性进行针对性的校正处理,本文采用离散L a p l a c e 滤波绝对值的均值췍T 作为对比度度量,相比文献[13]使用均值与标准差度量的方法,该方法能更好地反映像素点之间的空间关系:T =V *h L ,(7)C =C 1,췍T <1/θ,C 2,其他{,(8)其中:h L 为3ˑ3离散L a p l a c e 滤波核;T 为对比度度量值;C 1为划分的低对比度图像集,C 2为划分的中等对比度图像集,V ɪC ;θ为阈值参数,取θ=50.其次,使用对比度决定伽马值,相比于文献[13],本文对低对比度图像伽马值进行补偿,即γ=-l o g 2(μ+σ),V ɪC 1,e x p {[1-(μ+σ)]/2},V ɪC 2{,(9)其中γ为计算的伽马值,μ,σ分别为V 的均值和标准差.最后,使用均值μ作为明暗度度量,决定伽马校正系数K ,即K =1/[V γ+(1-V γ)μγ],μ<0.5,1,其他{.(10) 因此,自适应伽马校正结果为V *=K V γ.(11)经自适应伽马校正的处理结果V *整体上已具备了良好的曝光水平,将其作为中等曝光图像.1.3.2 过曝光图像用自适应阈值划分过曝光区域,对于曝光度较好的像素点,其归一化均值接近于0.5.本文采用的动态过曝光划分阈值表示为t =1/(1+e x p {-6췍V +3}),(12)其中t 为过曝光阈值,췍V为亮度分量V 的均值.经上述计算,过曝光阈值自适应地提高,以获取图像中的更多亮度像素;当图像偏亮时,过曝光阈值自适应地降低,以获取更多的亮度像素;相比文献[14]采用的固定阈值,本文获取的过曝光集合特征性更强.因此获得的过曝光集合V ᶄ为V ᶄ={(x ,y )V (x ,y )>t }.(13) 由于用最佳曝光率拍摄的图像将包含最大的信息量,因此采用最大信息熵表征最多的图像信息量,计算最佳曝光值,根据式(6)生成过曝光图像的曝光率为k ᶄ=a r g m a x k H (g (V ᶄ,k ))=a r g m a x k H (V ᵡ),(14)其中H (㊃)为信息熵函数.由上述计算可得中等曝光亮度V *和过曝光亮度V ᵡ,再结合颜色分量H ,S 转换为R G B 空间,并与原图像I 组成曝光图像序列{I ,I *,I ᵡ}.逆光场景下模拟合成的曝光序列如图2所示.1.4 曝光融合曝光融合的目的是利用多曝光序列之间亮度的互补关系,按照权重分配融合不同曝光度的图像,最终使图像各区域呈现出适宜曝光条件下的成像效果.文献[15]采用了基于质量度量和双金字塔融合框架的曝光融合方法,但该方法获得的融合图像可能会在明暗交界等亮度变化明显的区域出现光晕现象.本文使用改进的质量度量方法构建权重图,并使用改进导向滤波优化权重,最终结合细节增强得到没有光晕影响的融合图像.1.4.1 基于质量度量的权重合成本文用对比度㊁饱和度和良好曝光度作为图像质量度量指标计算多曝光序列{I k }的权重图.使用406 吉林大学学报(理学版) 第61卷图2 逆光场景下模拟合成的曝光序列F i g .2 E x p o s u r e s e q u e n c e o f s i m u l a t e d s y n t h e s i s i nb a c k l i gh t s c e n e 离散L a p l a c e 滤波器提取{I k }的边缘细节,并取响应的绝对值表征图像的边缘变化,作为对比度度量,根据式(7)有ωc ,k =13ði I i ,k ˑh ()L ,(15)其中:ωc ,k 为对比度度量;i 为颜色通道值,i ={R ,G ,B };由于过曝光和欠曝光区域在色彩上通常表现为欠饱和,因此使用R G B 颜色通道的标准平方差度量饱和度,即ωs ,k (x ,y )=(C 2R +C 2G +C 2B )/3,(16)其中:ωc ,k 为饱和度度量;C i (x ,y )=I i ,k (x ,y )-췍I k (x ,y ),췍I k 为颜色通道均值.用高斯曲线度量像素值与最佳曝光像素值的接近程度度量曝光度,对于归一化亮度分量,一般取最佳曝光值为0.5,标准差σ=0.2.本文为增强曝光度度量的特征性,在原曝光度量基础上添加补偿参数,即ωe ,k =ᵑi A +B 2ˑe x p -(I i ,k (x ,y )-0.5)22σ{}æèçöø÷2,(17)经实验验证,取参数A =0.5,B =췍I k 时,式(17)具有良好的曝光度度量能力.综合式(15)~(17),I k 的归一化权重图构建为W k =ωc ,k ˑωs ,k ˑωe ,k ð3k =1(ωc ,k ˑωs ,k ˑωe ,k )+η,(18)其中η=5ˑ10e -6.1.4.2 基于导向滤波的权重优化用上述方法得到初始权重直接融合的结果具有严重的斑块效应,因此需对初始权重进行优化.导向滤波[16]基于滤波结果在局部与导向图像保持一定线性关系的关键假设,构建自适应滤波核,当导向图像为输入图像本身时,滤波结果在平滑的同时能保持图像边缘,本文采用导向滤波优化权重图,即Q i =a k W i +b k , ∀i ɪφk ,(19)其中:a k ,b k 为以i 为像素中心㊁半径为r 的局部窗体φk 上的常量线性系数;Q i 为初始权重的导向滤波结果,可知Q i 的边缘信息只来自于初始权重W i .基于最小二乘法进行系数拟合,即E (a k ,b k )=ði ɪφk [(Q i -^W i )2+εa 2k ],(20)其中E (a k ,b k )为误差函数,ε为正则化参数,用以约束平滑力度a k .由于传统导向滤波中参数ε是固定的,即对于边缘强弱的约束能力不变,会导致部分区域过平滑而出现光晕,因此本文根据导向图像的梯度图获取纹理信息,对参数ε进行自适应调整[17],即εᶄ=0.25,G (x ,y )<0.2,0.25ˑe x p {-3ˑ(G (x ,y )-0.2)},G (x ,y )ȡ0.2{,(21)506 第3期王若状,等:基于模拟曝光融合的非均匀光照图像增强其中G (x ,y )为梯度函数.经式(20),(21)计算得:a k =φ-1ði ɪφk (W 2i -μk 췍W k )δk +εᶄ,(22)b k =췍W k -a k μk ,(23)其中췍W k 为原始权重均值,μk ,δk 分别为导向图在局部窗体上的均值和标准差.由于所有重叠窗口中均包含像素i ,需进行取均值处理,因此最终的优化权重为Q i =φ-1ði ɪφk(a k W i +b k ).(24)从而融合图像表示为췍I (x ,y )=ð3i =1Q i (x ,y )ˑI i (x ,y ),(25) 实验结果表明,经过上述融合过程得到的增强结果相比于原图像会出现一定程度上的细节损失,因此本文使用基于高斯滤波差分的多尺度细节[18]提升算法,得到输入图像的细节图像:D =(1-λ1ˑs g n (D 1))ˑD 1+λ2ˑD 2+λ3ˑD 3,(26)其中D 为根据输入图像计算的细节图像,D i (i =1,2,3)为对应高斯核循环计算的差分图像,权重λ1=λ2=0.5,λ3=0.25.因此,最终经过细节增强处理的增强结果为^I =D ˑX +췍I ,(27)其中D 为细节图像,췍I 为细节增强前图像,X 为增强系数,本文取X =1.图像光晕消除前后结果对比如图3所示.图3 图像光晕消除前后结果对比F i g .3 C o m p a r i s o no f r e s u l t s b e f o r e a n da f t e r i m a ge h a l o e l i m i n a t i o n 2 实验与分析本文基于P C 平台(W i n d o w s 10系统,I n t e l (R )C o r e (TM )i 5-7200U C P U@2.70G H z 处理器,8G B 内存)上的MA T L A B 2016b 进行实验验证,并与L I M E [19],C R M [12],C E A [14],B I M E F [20],N P L I E [21]几类经典算法从主观和客观方面对实验结果进行对比分析.低照度场景图像增强结果及细节对比如图4和图5所示.逆光场景图像增强结果及细节对比如图6~图9所示.由图4~图9可见,在不同场景下本文算法的效果均最好.2.1 主观因素对于图4场景,由于L I E M 算法亮度提升的程度过大,因此使得场景相对并不自然,C R M ,C E A ,B I M E F 和N P L I E 算法整体仍偏暗,树叶㊁墙壁㊁白色建筑等部分颜色信息和对比度不突出,本文算法场景相对自然,图像细节信息相对突出.对于图5场景,L I M E 算法对云的形态细节㊁轮廓及颜色过606 吉林大学学报(理学版) 第61卷图4 低照度场景图像增强结果及细节对比1F i g .4 I m a g e e n h a n c e m e n t r e s u l t s a n dd e t a i l c o m pa r i s o n1i n l o wi l l u m i n a t i o n s c e n es 图5 低照度场景图像增强结果及细节对比2F i g .5 I m a g e e n h a n c e m e n t r e s u l t s a n dd e t a i l c o m pa r i s o n2i n l o wi l l u m i n a t i o n s c e n e s 分突出,场景不自然,C R M 算法在图像边缘出现了大面积光晕,C E A 算法细节保留较好,但图像偏暗,N P L I E 和本文算法在颜色㊁场景轮廓等细节信息上更丰富.对于图6场景,L I M E 算法同样增强过度,C R M 算法也出现了一定的光晕,C E A 和N P L I E 算法在建筑体上相对较暗,本文算法在保留图像细节信息的基础上,图像饱和度较好,颜色信息更突出.对于图7场景,几类算法处理结果相近,相比之下L I M E 算法仍增强过度,C R M 算法仍出现了光晕,C E A 和B I M E F 算法在墙体建筑区域偏暗,N P L I E 与本文算法在对应区域颜色饱和,细节清楚.对于图8场景,几类算法对窗体亮光区域没有过度放大,C R M ,C E A 和B I M E F 算法表现得偏暗,本文算法色彩饱和,在吊灯等场景的边缘细节突出.对于图9场景,C E A ,B I M E F 和N P L I E 算法能复原场景的细节信息,但相对偏暗,L I M E 算法仍增强过度,本文算法则相对自然.主观评价指标包括清晰度㊁细节保持度㊁场景自然效果3个维度,评价者对每张图像在3个指标上打分并计算算术平均值.表1为选取的10位评价者对数据集M L L P -S e t [22]上测试结果的主观评价平均值(10分为满分);表2为10位评价者对数据集V V -S e t (h t t p s ://s i t e s .g o o gl e .c o m /s i t e /v o n i k a k i s /d a t a s e t s /c h a l l e n g i n g -d a t a s e t -f o r -e n h a n c e m e n t )上测试结果的主观评价平均值(10分为满分).706 第3期王若状,等:基于模拟曝光融合的非均匀光照图像增强图6 逆光场景图像增强结果及细节对比1F i g .6 I m a g e e n h a n c e m e n t r e s u l t s a n dd e t a i l c o m p a r i s o n1i nb a c k l i gh t s c e n es 图7 逆光场景图像增强结果及细节对比2F i g .7 I m a g e e n h a n c e m e n t r e s u l t s a n dd e t a i l c o m p a r i s o n2i nb a c k l i gh t s c e n e s 表1 数据集M L L P -S e t 上测试结果的平均主观评价指标T a b l e 1 A v e r a g e s u b je c t i v e e v a l u a t i o n i n d e x of t e s t r e s u l t s o n M L L P -S e t d a t a s e t 算法清晰度细节保持度场景自然度综合平均值L I M E 8.27.57.57.73C R M 8.17.87.47.77C E A 8.08.07.87.93B I M E F 8.28.58.08.23N P L I E 8.38.58.18.30本文8.58.68.18.40表2 数据集V V -S e t 上测试结果的平均主观评价指标T a b l e 2 A v e r a g e s u b je c t i v e e v a l u a t i o n i n d e x of t e s t r e s u l t s o nV V -S e t d a t a s e t 算法清晰度细节保持度场景自然度综合平均值L I M E 7.97.87.27.63C R M 7.97.67.57.67C E A 8.07.97.97.93B I M E F 8.28.18.28.17N P L I E 8.38.38.28.27本文8.48.48.28.33806 吉林大学学报(理学版) 第61卷图8 逆光场景图像增强结果及细节对比3F i g .8 I m a g e e n h a n c e m e n t r e s u l t s a n dd e t a i l c o m p a r i s o n3i nb a c k l i gh t s c e n es 图9 逆光场景图像增强结果及细节对比4F i g .9 I m a g e e n h a n c e m e n t r e s u l t s a n dd e t a i l c o m p a r i s o n4i nb a c k l i gh t s c e n e s 由表1和表2可见,10位评价者认为在几种算法中,L I M E 和C R M 算法综合得分较低,即对两类算法增强结果的认可度较低,B I M E F 算法综合得分好于C E A 算法,N P L I E 算法与本文算法最接近,但本文算法综合得分更高,表明10位评价者对本文算法的增强结果最认可.2.2 客观因素主观因素分析可能带有评价者主观意识下的偏好,且评价结果可能受多种因素的影响,因此仅通过主观分析不足以说明问题,需通过图像处理领域广泛使用的图像质量评价指标对图像质量和信息量进行客观度量.本文采用结构相似性(S S I M )㊁平均信息熵(A I E )和视觉信息保真度(V I F )指标对同类算法的处理结果进行评价.S S I M 用于度量结果图像与原始图像在结构上的差异性,通过在局部区域上的像素统计量构造亮度㊁对比度和结构估计,并作为影响因子构建相似度度量函数,综合局部相似性指标作为最终的相似度度量,其值范围为[0,1].该值越接近1,表明结果图像与原始图像的相似度越高.A I E 即通过平均信息熵计算度量图像所包含的平均信息量,该值越大表明图像所包含的信息量越丰富,在图像质量上表现为图像的清晰度㊁对比度较好,细节信息较丰富.V I F 认为人的视觉系统也是一种失真通道,即原始图像和失真图像在被人捕捉为视觉信息的过程中同样存在信息损失,并将人眼获得的失真图像信906 第3期王若状,等:基于模拟曝光融合的非均匀光照图像增强016吉林大学学报(理学版)第61卷息与原始图像信息的比值定义为视觉信息保真度,表征失真图像相对于原始图像信息保留的完整性,其值范围为[0,1].该值越接近1,表明信息完整性越好.数据集M L L P-S e t和V V-S e t上测试结果的平均客观评价指标分别列于表3和表4.表3数据集M L L P-S e t上测试结果的平均客观评价指标T a b l e3A v e r a g e o b j e c t i v e e v a l u a t i o n i n d e x o f t e s t r e s u l t s o n M L L P-S e t d a t a s e tT a b l e4A v e r a g e o b j e c t i v e e v a l u a t i o n i n d e x o f t e s t r e s u l t s o nV V-S e t d a t a s e t由表可见:和算法值较低,表明对于原图像,增强图像在结构信息上发生了较大改变,本文算法在S S I M指标上略低于C E A算法,并与N P L I E算法相近,表明这3种算法对原始图像结构属性保留的能力大致相同;L I M E和C R M算法的A I E值较高,但亮度增强过度,存在细节失真的问题,本文算法A I E值则高于其他三类算法,在清晰度㊁对比度㊁细节信息等方面的表达较好.对于V I F指标,本文算法最高,表明对图像原始信息的保留能力较好,C E A和N P L I E算法则相对较弱.由表4可见,在数据集V V-S e t上的测试结果与表3数据中各种算法的指标数据差异性大致相同,表明本文算法的增强结果在视觉保真度上优于其他算法.实验结果表明,客观分析与主观分析在结论上具有一致性,证明了本文算法在处理非均匀光照图像增强方面的有效性.综上所述,本文针对非均匀光照图像的低质量问题提出了一种模拟多曝光融合的图像增强算法,具有以下特点:1)基于相机响应函数,使用单张低质量图像模拟合成多曝光图像序列,避免了拍摄的多曝光序列因场景变化可能导致的融合后出现伪影.2)用动态阈值分割过曝光区域,针对不同的低质量图像提取特征性更强的过曝光像素集合;用改进的自适应伽马校正获得中等曝光图像,对不同的低质量图像具有针对性的校正能力.3)对质量度量时的曝光度度量指标进行了修正,使用改进的导向滤波方法进行权重优化,避免了金字塔融合可能出现的光晕现象;最终使用基于高斯滤波差分的多尺度细节增强方法修复了因融合过程出现的图像细节丢失问题.本文算法经实验验证及主客观分析,能解决一般场景下的非均匀光照图像的增强问题,增强后的图像质量优于同类算法.参考文献[1] H EK M,S U NJ,T A N GXO.S i n g l e I m a g eH a z eR e m o v a lU s i n g D a r kC h a n n e l P r i o r[J].I E E ET r a n s a c t i o n s o nP a t t e r nA n a l y s i s a n d M a c h i n e I n t e l l i g e n c e,2011,33(12):2341-2353.[2] Z HA O X Y,HU A N GFZ.A N o v e l L o w-I l l u m i n a t i o n I m a g eE n h a n 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fI m a ge sa n dP a t t e r n s (C A I P ).B e r l i n :S p r i n ge r ,2017:36-45.[15] M E R T E N ST ,K A U T ZJ ,V A NR E E T H F ,e t a l .E x p o s u r eF u s i o n :AS i m p l e a n dP r a c t i c a lA l t e r n a t i v e t oH i g h D y n a m i cR a n g eP h o t o g r a p h y [J ].C o m p u t e rG r a ph i c sF o r u m ,2009,28:161-171.[16] H EK M ,S U NJ ,T A N G X O.G u i d e d I m a g eF i l t e r i n g [C ]//E u r o p e a nC o n f e r e n c eo nC o m p u t e rV i s i o nL e c t u r e N o t e s i nC o m p u t e r S c i e n c e .B e r l i n :S p r i n ge r ,2010:1-14.[17] Y A N GZ ,WA N G QC ,D E N G Y ,e t a l .M u l t i -e x p o s u r eF u s i o nw i t hA d a p t i v e W e l l -E x p o s e d n e s s W e i g h tF a c t o r a n dE n h a n c e dG u i d e dF i l t e r i n g [C ]//2021I E E E9t hI n t e r n a t i o n a lC o nf e r e n c eo nC o m p u t e rS c i e n c ea n dN e t w o r k T e c h n o l og y (I C C S N T ).P i s c a t a w a y ,N J :I E E E ,2021:105-109.[18] K I M YB ,K OH YJ ,L E EC ,e t a l .D a r k I m a g eE nh a n c e m e n t B a s e dO n p ai r w i s eT a r g e t C o n t r a s t a n dM u l t i -s c a l e D e t a i l B o o s t i n g [C ]//P r o c e e d i n g s I n t e r n a t i o n a l C o n f e r e n c e o n I m a g eP r o c e s s i n g (I C I P ).P i s c a t a w a y,N J :I E E E ,2015:1404-1408.[19] G U O XJ ,L IY ,L I N G H B ,e t a l .L I M E :L o w -L i g h t I m a g eE n h a n c e m e n t v i a I l l u m i n a t i o nM a p E s t i m a t i o n [J ].I E E ET r a n s a c t i o n s o n I m a g eP r o c e s s i n g,2017,26(2):982-993.[20] Y I N GZQ ,L IG ,G A O W.AB i o -I n s p i r e dM u l t i -e x p o s u r eF u s i o nF r a m e w o r k f o r L o w -L i g h t I m a g eE n h a n c e m e n t [E B /O L ].(2017-11-02)[2022-02-01].h t t p s ://a r x i v .o r g /a b s /1711.00591.[21] K A V I N D E RS ,P A R I HA R A S .I l l u m i n a t i o nE s t i m a t i o nf o rN a t u r eP r e s e r v i n g L o w -L i g h t I m a g eE n h a n c e m e n t [J ].T h eV i s u a l C o m pu t e r ,2020,36(3):649-665.[22] WA N GSH ,L U O G.N a t u r a l n e s sP r e s e r v e d I m a g eE n h a n c e m e n tU s i n g aP r i o r iM u l t i -l a y e rL i g h t n e s sS t a t i s t i c s [J ].I E E ET r a n s a c t i o n s o n I m a g eP r o c e s s i n g ,2018,27(2):938-948.(责任编辑:韩啸)116 第3期王若状,等:基于模拟曝光融合的非均匀光照图像增强 Copyright ©博看网. 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构建下转换荧光-适配体的免疫层析试纸条用于快速检测黄曲霉毒素B_(1)

构建下转换荧光-适配体的免疫层析试纸条用于快速检测黄曲霉毒素B1王邹璐琪1，李立煌1，李丹阳1，艾超超1，任磊1,*，孙本强2,*（1.厦门大学材料学院，福建厦门361005；2.厦门医学院附属口腔医院，福建厦门361005）摘要：构建下转换荧光-适配体免疫层析试纸条用于食品中黄曲霉毒素B1（aflatoxin B1，AFB1）的快速高效检测。

体系中AFB1存在会减弱下转换荧光-适配体纳米颗粒层析至T线时与AFB1半抗原的结合能力，从而导致下转换荧光信号衰减，进而实现对AFB1的高效检测。

该方法在AFB1质量浓度1～40 ng/mL范围内与荧光信号呈良好的线性关系，线性相关系数为0.994，检测限为0.287 ng/mL。

该方法利用稀土掺杂荧光纳米颗粒的长寿命发光及近红外荧光特性，有效降低了生物背景荧光干扰并提高了检测体系的特异性。

该方法在AFB1的快速高灵敏检测中具有良好的应用前景。

关键词：稀土掺杂荧光纳米颗粒；荧光免疫层析；黄曲霉毒素B1；快速检测Construction of Down-conversion Fluorescence-Aptamer Immunochromatographic Strip for Rapid Detection of Aﬂatoxin B1 WANG Zouluqi1, LI Lihuang1, LI Danyang1, AI Chaochao1, REN Lei1,*, SUN Benqiang2,*(1. College of Materials, Xiamen University, Xiamen361005, China;2. Stomatological Hospital of Xiamen Medical College, Xiamen361005, China)Abstract: In this study, a down-conversion fluorescence-aptamer immunochromatographic strip was constructed for the rapid and efficient detection of aflatoxin B1 (AFB1) in foods. The presence of AFB1 in the system will weaken the binding ability of down-conversion-aptamer fluorescent nanoparticles to the hapten AFB1 when down-conversion-aptamer fluorescent nanoparticles reach the T-line, thus leading to the attenuation of down-conversion fluorescence signal and consequently highly efficient detection of AFB1. In the range of 1–40 ng/mL, the concentration of AFB1 had a good linear relationship with the fluorescence signal, showing a correlation coefficient of 0.994, and the detection limit for AFB1 was0.287 ng/mL. By taking advantage of the long-lived luminescence and the near infrared fluorescence characteristics of rareearth doped fluorescent nanoparticles, this method effectively reduced the interference of biological background fluorescence and improved the specificity of the detection system, making it a promising candidate for application in the rapid and sensitive detection of AFB1.Keywords: rare earth doped fluorescent nanoparticles; fluorescence immunochromatographic assay; aflatoxin B1; rapid detection DOI:10.7506/spkx1002-6630-20191030-337中图分类号：TS201.2 文献标志码：A 文章编号：1002-6630（2021）12-0295-07引文格式：王邹璐琪, 李立煌, 李丹阳, 等. 构建下转换荧光-适配体的免疫层析试纸条用于快速检测黄曲霉毒素B1[J]. 食品科学, 2021, 42(12): 295-301. DOI:10.7506/spkx1002-6630-20191030-337. WANG Zouluqi, LI Lihuang, LI Danyang, et al. Construction of down-conversion fluorescence-aptamer immunochromatographic strip for rapid detection of aﬂatoxin B1[J]. Food Science, 2021, 42(12): 295-301. (in Chinese with English abstract) DOI:10.7506/spkx1002-6630-20191030-337. 收稿日期：2019-10-30基金项目：福建省自然科学基金项目（2017Y0078）；国家自然科学基金面上项目（31870994）第一作者简介：王邹璐琪（1996—）（ORCID: 0000-0002-7715-1267），女，硕士研究生，研究方向为生物医学材料。

高精度、高驱动电流、双运算放大器AD826说明书

REV.BInformation furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication oraAD826One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.Tel: 781/329-4700World Wide Web Site: High-Speed, Low-Power Dual Operational AmplifierCONNECTION DIAGRAM8-Lead Plastic Mini-DIP and SO Package12348765AD826V+OUT2–IN2+IN2OUT1–IN1+IN1V–The AD826 features high output current drive capability of 50mA min per amp, and is able to drive unlimited capacitive loads. With a low power supply current of 15 mA max for both amplifiers, the AD826 is a true general purpose operational amplifier.The AD826 is ideal for power sensitive applications such as video cameras and portable instrumentation. The AD826 can operate from a single +5 V supply, while still achieving 25 MHz of band-width. Furthermore the AD826 is fully specified from a single +5 V to ±15 V power supplies.The AD826 excels as an ADC/DAC buffer or active filter in data acquisition systems and achieves a settling time of 70 ns to 0.01%, with a low input offset voltage of 2 mV max. The AD826 is available in small 8-lead plastic mini-DIP and SO packages.10901000%500ns5V5VC L = 100pFC L = 1000pFFEATURES High Speed:50 MHz Unity Gain Bandwidth 350 V/␮s Slew Rate70 ns Settling Time to 0.01%Low Power:7.5 mA Max Power Supply Current Per Amp Easy to Use:Drives Unlimited Capacitive Loads50 mA Min Output Current Per AmplifierSpecified for +5 V, ؎5 V and ؎15 V Operation 2.0 V p-p Output Swing into a 150 ⍀ Load (V S = +5 V)Good Video PerformanceDifferential Gain & Phase Error of 0.07% & 0.11؇Excellent DC Performance:2.0 mV Max Input Offset Voltage APPLICATIONSUnity Gain ADC/DAC Buffer Cable Drivers8- and 10-Bit Data Acquisition Systems Video Line Driver Active FiltersPRODUCT DESCRIPTIONThe AD826 is a dual, high speed voltage feedback op amp. It is ideal for use in applications which require unity gain stability and high output drive capability, such as buffering and cable driving. The 50 MHz bandwidth and 350 V/µs slew rate make the AD826 useful in many high speed applications including:video, CATV, copiers, LCDs, image scanners and fax machines.TEKTRONIX P6201 FET PROBE HP PULSE GENERATOR1/2AD8261k ⍀50⍀1k ⍀C LV OUTV INTEKTRONIX 7A24 FET PREAMP؉V S0.01␮F3.3␮F0.01␮F–V S3.3␮F132Driving a Large Capacitive Load查询AD826AR-REEL供应商捷多邦，专业PCB打样工厂，24小时加急出货AD826–SPECIFICATIONS(@ T A = +25؇C, unless otherwise noted)Parameter Conditions V S Min Typ Max Unit DYNAMIC PERFORMANCEUnity Gain Bandwidth±5 V3035MHz±15 V4550MHz0, +5 V2529MHz Bandwidth for 0.1 dB Flatness Gain = +1±5 V1020MHz±15 V2555MHz0, +5 V1020MHz Full Power Bandwidth1V OUT = 5 V p-pR LOAD = 500 Ω±5 V15.9MHzV OUT = 20 V p-pR LOAD = 1 kΩ±15 V 5.6MHz Slew Rate R LOAD = 1 kΩ±5 V200250V/µsGain = –1±15 V300350V/µs0, +5 V150200V/µs Settling Time to 0.1%–2.5 V to +2.5 V±5 V45ns0 V–10 V Step, A V = –1±15 V45nsto 0.01%–2.5 V to +2.5 V±5 V70ns0 V–10 V Step, A V = –1±15 V70ns NOISE/HARMONIC PERFORMANCETotal Harmonic Distortion F C = 1 MHz±15 V–78dB Input Voltage Noise f = 10 kHz±5 V, ±15 V15nV/√Hz Input Current Noise f = 10 kHz±5 V, ±15 V 1.5pA/√Hz Differential Gain Error NTSC±15 V0.070.1% (R1 = 150 Ω)Gain = +2±5 V0.120.15%0, +5 V0.15% Differential Phase Error NTSC±15 V0.110.15Degrees (R1 = 150 Ω)Gain = +2±5 V0.120.15Degrees0, +5 V0.15Degrees DC PERFORMANCEInput Offset Voltage±5 V to ±15 V0.52mVT MIN to T MAX3mV Offset Drift10µV/°C Input Bias Current±5 V, ±15 V 3.3 6.6µAT MIN10µAT MAX 4.4µA Input Offset Current±5 V, ±15 V25300nAT MIN to T MAX500nA Offset Current Drift0.3nA/°C Open-Loop Gain V OUT = ±2.5 V±5 VR LOAD = 500 Ω24V/mVT MIN to T MAX 1.5V/mVR LOAD = 150 Ω 1.53V/mVV OUT = ±10 V±15 VR LOAD = 1 kΩ 3.56V/mVT MIN to T MAX25V/mVV OUT = ±7.5 V±15 VR LOAD = 150 Ω (50 mA Output)24V/mV INPUT CHARACTERISTICSInput Resistance300kΩInput Capacitance 1.5pF Input Common-Mode Voltage Range±5 V+3.8+4.3V–2.7–3.4V±15 V+13+14.3V–12–13.4V0, +5 V+3.8+4.3V+1.2+0.9V Common-Mode Rejection Ratio V CM = ±2.5 V, T MIN–T MAX±5 V80100dBV CM = ±12 V±15 V86120dBT MIN to T MAX±15 V80100dBAD826 ABSOLUTE MAXIMUM RATINGS1Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .±18 VInternal Power Dissipation2Plastic (N) . . . . . . . . . . . . . . . . . . . . . See Derating CurvesSmall Outline (R) . . . . . . . . . . . . . . . . See Derating CurvesInput Voltage (Common Mode) . . . . . . . . . . . . . . . . . . .±V SDifferential Input Voltage . . . . . . . . . . . . . . . . . . . . . . .±6 VOutput Short Circuit Duration . . . . . . . See Derating Curves Storage Temperature Range (N, R) . . . . . . . –65°C to +125°C Operating Temperature Range . . . . . . . . . . –40°C to +85°C Lead Temperature Range (Soldering 10 seconds) . . . +300°C NOTES1Stresses above those listed under Absolute Maximum Ratings may cause perma-nent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability .2Specification is for device in free air: 8-lead plastic package, θJA= 100°C/watt; 8-lead SOIC package, θJA = 155°C/watt.ORDERING GUIDETemperature Package Package Model Range Description Option AD826AN–40°C to +85°C8-Lead Plastic DIP N-8AD826AR–40°C to +85°C8-Lead Plastic SOIC SO-8 AD826AR-REEL7–40°C to +85°C7” Tape & Reel SOIC SO-8Parameter Conditions V S Min Typ Max Unit OUTPUT CHARACTERISTICSOutput Voltage Swing R LOAD = 500 Ω±5 V 3.3 3.8±VR LOAD = 150 Ω±5 V 3.2 3.6±VR LOAD = 1 kΩ±15 V13.313.7±VR LOAD = 500 Ω±15 V12.813.4±VR LOAD = 500 Ω0, +5 V+1.5,+3.5V Output Current±15 V50mA±5 V50mA0, +5 V30mA Short-Circuit Current±15 V90mA Output Resistance Open Loop8ΩMATCHING CHARACTERISTICSDynamicCrosstalk f = 5 MHz±15 V–80dB Gain Flatness Match G = +1, f = 40 MHz±15 V0.2dB Slew Rate Match G = –1±15 V10V/µs DCInput Offset Voltage Match T MIN–T MAX±5 V to ±15 V0.52mV Input Bias Current Match T MIN–T MAX±5 V to ±15 V0.060.8µA Open-Loop Gain Match V O = ±10 V, R LOAD = 1 kΩ,T MIN–T MAX±15 V0.150.01mV/V Common-Mode Rejection Ratio Match V CM = ±12 V, T MIN–T MAX±15 V80100dB Power Supply Rejection Ratio Match±5 V to ±15 V, T MIN–T MAX80100dB POWER SUPPLYOperating Range Dual Supply±2.5±18VSingle Supply+5+36V Quiescent Current/Amplifier±5 V 6.67.5mAT MIN to T MAX±5 V7.5mA±15 V7.5mAT MIN to T MAX±15 V 6.87.5mA Power Supply Rejection Ratio V S = ±5 V to ±15 V, T MIN to T MAX7586dB NOTES1Full power bandwidth = slew rate/2π VPEAK. Specifications subject to change without notice.ESD SUSCEPTIBILITYESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 volts, which readily accumulate on the human body and on test equipment, can discharge without detection. Although the AD826 features proprietary ESD protection cir-cuitry, permanent damage may still occur on these devicesif they are subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid any performance degradation or loss of functionality.2.0–50901.50.5–301.050703010–1080–40406020–20AMBIENT TEMPERATURE –؇CMAXIMUMPOWERDISSIPATION–WattsMaximum Power Dissipation vs. Temperature for Different Package TypesAD8262000201555101015I N P U T C O M M O N -M O D E R A N G E – ؎V o l t sSUPPLY VOLTAGE – ؎Volts–V CM+V CMFigure mon-Mode Voltage Range vs. Supply2000201555101015SUPPLY VOLTAGE – ؎VoltsO U T P U T V O L T A G E S W I N G – ؎V o l tsFigure 2.Output Voltage Swing vs. Supply 30010k1551001010201k25LOAD RESISTANCE – ⍀O U T P U T V O L T A G E S W I N G – V o l t s p -pFigure 3.Output Voltage Swing vs. Load Resistance7.75.70207.26.256.71015SUPPLY VOLTAGE – ؎VoltsQ U I E S C E N T S U P P L Y C U R R E N T P E R A M P – m AFigure 4.Quiescent Supply Current per Amp vs. Supply Voltage for Various TemperaturesS L E W R A T E – V /␮s20501510SUPPLY VOLTAGE– ؎Volts200300350400250Figure 5.Slew Rate vs. Supply Voltage10010.011k10k100M10M1M100k0.110FREQUENCY – HzC L O S ED -L O O P O U T P U T I M PE D A N C E – ⍀Figure 6.Closed-Loop Output Impedance vs. Frequency– Typical CharacteristicsAD8267114042–403–6065120806040100200–20TEMPERATURE – ؇CI N P U T B I A S C U R R E N T – ␮AFigure 7.Input Bias Current vs. Temperature130301409050–4070–60110120100806040200–20TEMPERATURE – ؇CS H O R T C I R C U I T C U R R E N T – m AFigure 8.Short Circuit Current vs. Temperature 10020–601408040–4060100120806040200–20TEMPERATURE – ؇CP H A S E M A R G I N – D e g r e e s20804060U N I T Y G A I N B A N D W I D T H – M HzFigure 9.Unity Gain Bandwidth and Phase Margin vs. Temperature100–201G4010k201k 8060100M 10M1M 100k FREQUENCY – Hz+100+40+20+80+60P H A S E M A R G I N – D e g r e e sO P E N -L O O P G A I N – d BFigure 10.Open-Loop Gain and Phase Margin vs. Frequency411001k10k2356LOAD RESISTANCE – ⍀O P E N -L OO P G A I N – V /m V7Figure 11.Open-Loop Gain vs. Load Resistance10010100M30201k 10040506070809010M 1M 100k10k FREQUENCY – HzP S R – d BFigure 12.Power Supply Rejection vs. FrequencyAD826140601k 10M1208010k 100100k 1M FREQUENCY – HzC M R – dBFigure mon-Mode Rejection vs. Frequency 30100100k1M 100M10M 20FREQUENCY – HzO U T P U T V O L T A G E – V o l t s p -pFigure rge Signal Frequency Response 10–10160–4–820–602–20468140120100806040SETTLING TIME – ns O U T P U T S W I N G F R O M 0 T O ؎V0.01%0.1%1%1%0.01%0.1%Figure 15.Output Swing and Error vs. Settling Time –40–10010M–70–901k –80100–50–601M 100k 10k FREQUENCY – HzH A R M O N I C D I S T O R T I O N – dBFigure 16. Harmonic Distortion vs. Frequency50010M301010203401M100k 10k 1k 100FREQUENCY – HzI N P U T V O L T A G E N O I S E – nV / H zFigure 17. Input Voltage Noise Spectral Density380300–60140360320–40340100120806040200–20TEMPERATURE – ؇CS L E WR A T E – V /␮sFigure 18. Slew Rate vs. TemperatureAD826FREQUENCY – HzG A I N – d B50–5100k1M100M10M–1–2–3–41234Figure 19. Closed-Loop Gain vs. Frequency SUPPLY VOLTAGE – Volts0.130.070.10D I F FE R E N T IA L P H A S E – D e g r e e sD I F FE R E N T I A L G A I N – P e r c e n t0.10؎150.130.110.12؎5؎10Figure 20. Differential Gain and Phase vs. Supply Voltage –30–70–110100k100M10M1M10k–90–50–60–80–100–40FREQUENCY – HzC R O S S T A L K – d BFigure 21. Crosstalk vs. Frequency FREQUENCY – HZ50–5100k1M 100M10M –1–2–3–41234G A I N – dBFigure 22. Closed-Loop Gain vs. Frequency, Gain = –1FREQUENCY – HzG A I N – d B1.00–1.0100k1M 100M10M –0.2–0.4–0.6–0.80.20.40.60.8Figure 23. Gain Flatness Matching vs. Supply, G = +1USE GROUND PLANEPINOUT SHOWN IS FOR MINIDIP PACKAGEV R L = 150⍀ FOR ؎V S = 5V, 1k ⍀ FOR ؎V S = 15VFigure 24. Crosstalk Test CircuitAD826Figure 25. Noninverting Amplifier ConfigurationFigure 26. Noninverting Large Signal Pulse Response, R L = 1 k ΩFigure 27. Noninverting Large Signal Pulse Response,R L = 150ΩFigure 28. Noninverting Small Signal Pulse Response, R L = 1 k ΩFigure 29.Noninverting Small Signal Pulse Response, R L = 150 ΩAD826Figure 30.Inverting Amplifier ConfigurationFigure 31.Inverting Large Signal Pulse Response,R L = 1 kΩFigure 32.Inverting Large Signal Pulse Response,R L = 150ΩFigure 33.Inverting Small Signal Pulse Response,R L = 1 kΩFigure 34.Inverting Small Signal Pulse Response,R L = 150 ΩAD826THEORY OF OPERATIONThe AD826 is a low cost, wide band, high performance dual operational amplifier which can drive heavy capacitive and resistive loads. It also achieves a constant slew rate, bandwidth and settling time over its entire specified temperature range. The AD826 (Figure 35) consists of a degenerated NPN differen-tial pair driving matched PNPs in a folded-cascode gain stage. The output buffer stage employs emitter followers in a class AB amplifier which delivers the necessary current to the load while maintaining low levels of distortion.–INNULL 1NULL 8S–VSFigure 35. Simplified SchematicThe capacitor, C F, in the output stage mitigates the effect of capacitive loads. With low capacitive loads, the gain from the compensation node to the output is very close to unity. In this case, C F is bootstrapped and does not contribute to the overall compensation capacitance of the device. As the capacitive load is increased, a pole is formed with the output impedance of the output stage. This reduces the gain, and therefore, C F is incompletely bootstrapped. Effectively, some fraction of C F contributes to the overall compensation capacitance, reducing the unity gain bandwidth. As the load capacitance is further increased, the bandwidth continues to fall, maintaining the stability of the amplifier.INPUT CONSIDERATIONSAn input protection resistor (R IN in Figure 25) is required in circuits where the input to the AD826 will be subjected to transient or continuous overload voltages exceeding the ±6 V maximum differential limit. This resistor provides protection for the input transistors by limiting their maximum base current. For high performance circuits, it is recommended that a “bal-ancing” resistor be used to reduce the offset errors caused by bias current flowing through the input and feedback resistors. The balancing resistor equals the parallel combination of R IN and R F and thus provides a matched impedance at each input terminal. The offset voltage error will then be reduced by more than an order of magnitude.APPLYING THE AD826The AD826 is a breakthrough dual amp that delivers precision and speed at low cost with low power consumption. The AD826 offers excellent static and dynamic matching characteristics, combined with the ability to drive heavy resistive and capacitive loads.As with all high frequency circuits, care should be taken to main-tain overall device performance as well as their matching. The following items are presented as general design considerations. Circuit Board LayoutInput and output runs should be laid out so as to physically isolate them from remaining runs. In addition, the feedback resistor of each amplifier should be placed away from the feedback resistor of the other amplifier, since this greatly reduces inter-amp coupling.Choosing Feedback and Gain ResistorsIn order to prevent the stray capacitance present at each amplifier’s summing junction from limiting its performance, the feedback resistors should be ≤ 1 kΩ. Since the summing junction capaci-tance may cause peaking, a small capacitor (1 pF–5pF) may be paralleled with R F to neutralize this effect. Finally, sockets should be avoided, because of their tendency to increase interlead capacitance.Power Supply BypassingProper power supply decoupling is critical to preserve the integrity of high frequency signals. In carefully laid out designs, decoupling capacitors should be placed in close proximity to the supply pins, while their lead lengths should be kept to a mini-mum. These measures greatly reduce undesired inductive effects on the amplifier’s response.Though two 0.1µF capacitors will typically be effective in decoupling the supplies, several capacitors of different values can be paralleled to cover a wider frequency range.AD826؎SINGLE SUPPLY OPERATIONAn exciting feature of the AD826 is its ability to perform well in a single supply configuration (see Figure 37). The AD826 is ideally suited for applications that require low power dissipation and high output current and those which need to drive large capacitive loads, such as high speed buffering and instrumentation. Referring to Figure 36, careful consideration should be given to the proper selection of component values. The choices for this particular circuit are: (R1 + R3)ʈR2 combine with C1 to form a low frequency corner of approximately 30 Hz.OUT0.1VFigure 36. Single Supply Amplifier Configuration R3 and C2 reduce the effect of the power supply changes on the output by low-pass filtering with a corner at12πR3C2.The values for R L and C L were chosen to demonstrate the AD826’s exceptional output drive capability. In this configura-tion, the output is centered around 2.5 V. In order to eliminate the static dc current associated with this level, C3 was inserted in series with R L.Figure 37.Single Supply Pulse Response, G = +1,R L = 150Ω, C L = 200 pFPARALLEL AMPS PROVIDE 100 mA TO LOADBy taking advantage of the superior matching characteristics ofthe AD826, enhanced performance can easily be achieved byemploying the circuit in Figure 38. Here, two identical cells areparalleled to obtain even higher load driving capability than thatof a single amplifier (100 mA min guaranteed). R1 and R2 areincluded to limit current flow between amplifier outputs thatwould arise in the presence of any residual mismatch.LFigure 38.Parallel Amp ConfigurationAD826SINGLE-ENDED TO DIFFERENTIAL LINE DRIVEROutstanding CMRR (> 80 dB @ 5 MHz), high bandwidth, wide supply voltage range, and the ability to drive heavy loads, make the AD826 an ideal choice for many line driving applications.In this application, the AD830 high speed video difference amp serves as the differential line receiver on the end of a back terminated, 50 ft., twisted-pair transmission line (see Figure 40).The overall system is configured in a gain of +1 and has a –3 dB bandwidth of 14 MHz. Figure 39 is the pulse response with a 2 V p-p, 1 MHz signal input.Figure 39.Pulse ResponseFigure 40.Differential Line DriverLOW DISTORTION LINE DRIVERThe AD826 can quickly be turned into a powerful, low distor-tion line driver (see Figure 41). In this arrangement the AD826can comfortably drive a 75Ω back-terminated cable, with a 5MHz, 2 V p-p input; all of this while achieving the harmonic distortion performance outlined in the following table.Configuration 2nd Harmonic 1.No Load –78.5 dBm 2.150 Ω R L Only –63.8 dBm 3.150Ω R L 7.5Ω R C–70.4 dBmIn this application one half of the AD826 operates at a gain of 2.1 and supplies the current to the load, while the other pro-vides the overall system gain of 2. This is important for two reasons: the first is to keep the bandwidth of both amplifiers the same, and the second is to preserve the AD826’s ability to oper-ate from low supply voltages. R C varies with the load and must be chosen to satisfy the following equation:R C = MR Lwhere M is defined by [(M+ 1) G S = G D ] and G D = Driver ’s Gain,Figure 41.Low Distortion AmplifierAD826HIGH PERFORMANCE ADC BUFFERFigure 42 is a schematic of a 12-bit high speed analog-to-digital converter. The AD826 dual op amp takes a single ended input and drives the AD872 A/D converter differentially, thus reduc-ing 2nd harmonic distortion. Figure 43 is a FFT of a 1MHz input, sampled at 10 MHz with a THD of –78 dB. The AD826can be used to amplify low level signals so that the entire range of the converter is used. The ability of the AD826 to perform on a ±5 volt supply or even with a single 5 volts combined with its rapid settling time and ability to deliver high current to compli-cated loads make it a very good flash A/D converter buffer as well as a very useful general purpose building block.V Figure 42.A Differential Input Buffer for High Bandwidth ADCsFigure 43.FFT, Buffered A/D ConverterAD826OUTLINE DIMENSIONSDimensions shown in inches and (mm).8-Lead Plastic Mini-DIP (N) Package8-Lead SO (R) Package45؇All brand or product names mentioned are trademarks or registered trademarks of their respective holders.C 1807a –0–6/00 (r e v . B ) 00877P R I N T ED I N U .S .A .。

The COST 2100 MIMO channel model

I NTRODUCTIONMultiple-input multiple-output (MIMO) is an enabling technology in order to meet the grow-ing demands for faster and more reliable trans-missions over harsh wireless channels. Overrecent years, research on MIMO technology has covered the gamut from theory to applications, and the technology is now included as a key component in standards such as Third Genera-tion Partnership Project Long Term Evolution (3GPP LTE) and WiMAX 802.16e.In MIMO systems, multiple collocated or dis-tributed antenna arrays replace the traditional single-antenna units, enabling the system to exploit the spatial dimension of radio channels.The technology can be used to increase the channel capacity by spatial multiplexing, to miti-gate multipath fading by spatial diversity, and to achieve a better signal-to-noise (SNR) level by directional transmission (i.e., beamforming) [1].As new wireless applications have become more and more sophisticated, the need for more accurate channel models has increased accord-ingly. For instance, in the planning of conven-tional GSM networks, simple path loss models were sufficient for sensible coverage prediction, whereas nowadays, the channel models needed in the development of MIMO systems have to represent the signal dispersion in the angular, delay, and Doppler domains simultaneously. The emergence of multi-user MIMO and cooperative communication techniques also calls for realistic multi-link channel models.Stochastic MIMO channel models rely on a limited number of parameters to efficiently describe the channel statistics in different domains. The computational complexity of the model depends on the scope of the systems. In this respect, there are two major approaches. On one hand, analytical (non-physical) models char-acterize the MIMO channel matrix, including the antenna effects, by a mathematical descrip-tion. Examples include the 802.11n tapped angu-lar-delay line model, the correlation-based Kronecker model, and the eigenspace-based Weichselberger model [2]. On the other hand, physical models characterize the radio waves by their delay, directions of departure (DoD), directions of arrival (DoA), and complex path weight for different polarizations. Physical mod-els are antenna-independent; hence, they can be directly combined with the antenna array responses to synthesize the MIMO channel matrix. Geometry-based stochastic channel mod-els (GSCMs) further constitute a group of advanced stochastic physical MIMO channel models that statistically describe the explicit locations of the scatterers.The COST 2100 MIMO channel model is a GSCM that was built on the framework of the earlier COST 259 and 273 models [3]. The COST 259 channel model [4] was the first GSCM con-sidering multi-antenna base stations, while full MIMO systems were later targeted by the COST 273 model. The COST 2100 channel model extends the COST 273 model to cover MIMO systems at large, including multi-user, multicellu-lar, and cooperative aspects, without requiring a fundamental shift in the original modeling phi-losophy.This article aims to give a concise overview of the COST 2100 channel model, covering the overall structure as well as the individual key elements constituting the model framework. TheL INGFENG L IU AND C LAUDE O ESTGES, U NIVERSITÉCA THOLIQUE DE L OUV AINJ UHO P OUTANEN, K A TSUYUKI H ANEDA, AND P ERTTI V AINIKAINEN, A ALTO U NIVERSITY S CHOOLOF E LECTRICAL E NGINEERINGF RANÇOIS Q UITIN, U NIVERSITY OF C ALIFORNIA A T S ANTA B ARBARAF REDRIK T UFVESSON, L UND U NIVERSITYP HILIPPE D E D ONCKER, U NIVERSITÉLIBRE DE B RUXELLESA BSTRACTThe COST 2100 channel model is a geome-try-based stochastic channel model (GSCM) thatcan reproduce the stochastic properties ofMIMO channels over time, frequency, and space.In contrast to other popular GSCMs, the COST2100 approach is generic and flexible, making itsuitable to model multi-user or distributedMIMO scenarios. In this article a conciseoverview of the COST 2100 channel model ispresented. Main concepts are described, togeth-er with useful implementation guidelines. Recentdevelopments, including dense multipath compo-nents, polarization, and multi-link aspects, arealso discussed.T HE COST 2100 MIMO C HANNEL M ODELmost recent achievements, including multi-link aspects, are presented, while considerations about parameterization, implementation, and validation are discussed later.R EVIEW OF G EOMETRY-B ASEDS TOCHASTIC C HANNEL M ODELSThe principle of GSCMs is to model the stochas-tic properties of wireless channels, with respect to the delay and double-directional domains, by analyzing the geometric distribution of the inter-acting objects (or scatterers) in the environment that contribute scattering to the radio channels. In GSCMs, a radio channel results from the superposition of different propagation paths, known as the multipath components (MPCs). Those MPCs are caused by the interaction between the radio waves and the objects in the environment, where each scattered contribution is characterized in both delay and direction domains. These scattering mechanisms may con-sist of a single interaction, that is, with one object (single-bounce), or of a number of con-secutive interactions with multiple objects (mul-tiple-bounce). The MPCs generated by either ofthese scattering mechanisms are representedthrough a geometric description of their proper-ties in three parameter space domains: delay,DoD, and DoA.Experimentally, it was observed that MPCstend to appear in packets in these domains.Intuitively, this makes sense: if a building acts asan interacting object, it is likely that the buildingwill create several reflected paths, caused bywindows, balconies, and so on, with similardelays and directions, given the finite size of thebuilding. In addition to being experiment-based,grouping MPCs with similar delays and direc-tions into packets (or clusters, as they are usuallyknown) enables the number of modeling param-eters to be significantly reduced. This explainswhy clusters constitute the basis of all recentGSCMs, from COST 259 to WINNER II.Whereas clusters are the parameterized quan-tities, it is important that overall models reflectreality. In particular, the channel large-scaleparameters (LSPs), such as the global delay andangular spreads, as synthesized from GSCMs,should be statistically reliable and consistent withexperimental observations. This means that clus-ters should be parameterized individually, yet insuch way that the global accuracy is guaranteed.This is where two main approaches can be used:a system-level approach, such as the widelyknown 3GPP Spatial Channel Model (SCM) [5]and the recent WINNER II model [6], or a clus-ter-level approach, such as the COST family ofchannel models. Both approaches rely on essen-tially different simulation processes. In system-level GSCMs (taking WINNER II as anexample), the modeling process is specified foreach instance of the channel between a base sta-tion (BS) and a mobile station (MS) by:•Defining the LSPs by their stochastic distribu-tion for each channel instance•Generating the clusters and MPCs accordingto these LSPs for any given locations of bothBS and MSBy contrast, in the cluster-level COST 2100model, the modeling process is specified oncefor the entire environment by:•Defining a large quantity of clusters with con-sistent stochastic parameters throughout thesimulation environment based on the BS loca-tion (yet not all clusters are visible at any timeinstant)•Defining the MS location and determining thescattering from the so-called visible clusters ateach channel instance•Synthesizing the LSPs based on the clusterscatteringThe advantage of such a system-level channelmodel is that the LSP statistics in a specific sce-nario are always guaranteed in each series ofchannel instances. However, forcing the statisti-cal consistency of the LSPs brings two criticallimitations:•The rigid structure of the approach does notspontaneously support continuous channeldescriptions over intervals larger than theauto-correlation distance, hence hamperingthe simulation of larger MS motions.•As the propagation environment is describedfrom the original LSPs only, adding new LSPs(e.g., the inter-link correlation) requires thatwe redefine the entire initialization of theenvironment, thereby hindering a straightfor-ward extension of the model.By contrast, the cluster-level COST 2100model is not constrained by the LSPs, and theenvironment is described independent of the MSlocation. This allows for smoother modeling oftime-variant channels. Basically, it is the MSmotion through the environment that will causethe channel statistics to vary, even over periodslarger than the auto-correlation distance. Fur-thermore, accounting for new LSPs, such as thecorrelation properties of multi-link channels, canbe carried out in a flexible fashion (i.e., withoutmodifying the model structure) by exploringadvanced properties of the clusters. Naturally, inany single realization of the channel, a cluster-level GSCM is expected to exhibit larger devia-tions of the LSP statistics than system-levelGSCMs, as these statistics are not expresslyforced by the model. Nevertheless, the averageLSP statistics remain typically consistent withmeasurements, as illustrated later.Regarding complexity, both system- and clus-ter-level GSCMs are similar as far as simulationsare concerned, as they both rely on adding con-tributions from a number of MPCs. Arguably,the cluster-level COST 2100 model probablyrelies on a more complex representation of theclusters, making their identification, estimation,and parameterization from measurements a criti-cal task.G ENERAL S TRUCTURE OF THECOST 2100 C HANNEL M ODELThe COST 2100 channel model was originallyproposed for simulating the radio channelbetween a static multiple-antenna BS and a mul-tiple-antenna MS. In most cases, the MPCs aremapped to the corresponding scatterers, and arecharacterized by their delay, azimuth of depar-Arguably, thecluster-level COST2100 modelprobably relies on amore complexrepresentation of theclusters, makingtheir identification,estimation, andparameterizationfrom measurementsa critical task.K ATSUYUKI H ANEDA(katsuyuki.haneda@aalto.fi) received his Doctor of Engineering from the Tokyo Institute of Technol-ogy, Japan, in 2007. He has been a post-doctoral researcher at the SMARAD Centre of Excellence in the Aalto University (former Helsinki University of Technology) School of Electri-cal Engineering, Espoo, Finland, since 2007. He was the recipient of the Student Paper Award presented at the 7th International Symposium on Wireless Personal Multimedia Communications. He has been serving as a co-chair of the Topical Working Group Indoor of the Euro-COST Action IC1004 “Cooperative Radio Communications for Green Smart Environments”. His research expertise includes radio wave propagation measurements and modeling, ultrawide-band radio, and multiple-input multiple-output radio com-munications, radio sensors and antennas, and applied electromagnetics for medical scenarios. Since 2012, he has been serving as an Associate Editor of IEEE Transactions on Antennas and Propagation.P HILIPPE D E D ONCKER(pdedonck@ulb.ac.be) received his engineering and Ph.D. degrees from ULB in 1996 and 2001, respectively. He is currently a professor with ULB. His research interests focus on wireless communications andelectromagnetics.F REDRIK T UFVESSON(fredrik.tufvesson@eit.lth.se) received hisM.S. degree in electrical engineering in 1994, his Licentiatedegree, in 1998 and his Ph.D. degree in 2000, all fromLund University, Sweden. After almost two years at a start-up company, Fiberless Society, he is now an associate pro-fessor at the Department of Electrical and InformationTechnology. His main research interests are channel mea-surements and modeling for wireless communication,including channels for both MIMO and UWB systems.Besides this, he also works with research projects on radio-based positioning as well as on his company on wirelesssearch and rescue equipment.P ERTTI V AINIKAINEN(pertti.vainikainen@aalto.fi) received hisM.S. in technology, Licentiate of Science in technology,and Doctor of Science in technology from Helsinki Universi-ty of Technology (TKK) in 1982, 1989, and 1991, respec-tively. Since 1998 he has been a professor in radioengineering in the Radio Laboratory (since 2008 theDepartment of Radio Science and Engineering) of TKK(since 2010, Aalto University School of Science and Tech-nology). His main fields of interest are antennas and prop-agation in radio communications and industrialmeasurement applications of radio waves. He is the authoror coauthor of six books or book chapters and about 380refereed international journal or conference publications,and the holder of 11 patents.C LAUDE O ESTGES(claude.oestges@uclouvain.be) receivedM.S. and Ph.D. degrees in electrical engineering from UCLin 1996 and 2000. In January 2001, he joined as a post-doctoral scholar the Smart Antennas Research Group(Information Systems Laboratory), Stanford University, Cali-fornia. He is presently a research associate of the BelgianFonds de la Recherche Scientifique and assistant professorwith the Electrical Engineering Department, Institute forInformation and Communication Technologies, Electronicsand Applied Mathematics, UCL. He also currently serves asan Associate Editor for IEEE Transactions on Antennas andPropagation and IEEE Transactions on Vehicular Technolo-gy. He is the author or co-author of two books and morethan 170 journal papers and conference communications,and was the recipient of the 1999-2000 IET Marconi Premi-um Award and the 2004 IEEE Vehicular Technology SocietyNeal Shepherd Award.。

分形阵列螺旋仿生超宽带天线设计

收稿日期:2017-08-15基金项目:福建省自然科学基金(2016J01318)。

作者简介:林斌(1984-),男,福建漳州人,厦门大学嘉庚学院信息科学与技术学院讲师,研究方向:微波射频器件设计、太赫兹波段器件设计。

分形阵列螺旋仿生超宽带天线设计林斌,刘泽泰,张颖,蔡沅坤,叶广雅,张培涛(厦门大学嘉庚学院,福建漳州363105)摘要:文章针对移动通信系统、射频识别系统、超宽带通信系统对天线的性能要求,使用耳蜗螺旋仿生辐射结构作为阵元天线,谢尔宾斯基分形结构作为阵列排布结构,设计了一款分形阵列螺旋仿生超宽带天线,并对其工作性能进行了测试。

测试结果表明,该款天线的工作频带范围为0.537~13.158GHz ,工作带宽为12.621GHz ,带宽倍频程为24.51,回波损耗最小值为-32.08dB 。

该款天线完全覆盖了移动通信系统所有工作频段、射频识别系统频段、超宽带系统频段。

因此,它是一款性能很好的超高兼容性通信天线。

关键词:移动通信系统;射频识别系统;超宽带通信系统;耳蜗螺旋仿生天线;谢尔宾斯基分形阵列中图分类号:TN 828.6文献标识码:A 文章编号:1671-2250(2018)01-0088-040引言移动通信是无线技术的最重要应用之一,目前我国第二代、第三代、第四代移动通信长期共存,第五代移动通信已在研发之中,将于2020年投入使用。

不同制式、多个频段的移动通信无线信号将长期共存,这就需要移动通信天线具有很好的多频段兼容能力,能够同时覆盖GSM 0.905~0.915GHz 、0.950~0.960GHz 、1.710~1.785GHz 、1.805~1.880GHz 频段,TD-SCDMA 1.880~1.920GHz 、2.010~2.025GHz 、2.300~2.400GHz 频段,WCDMA 1.920~1.980GHz 、2.110~2.170GHz 频段,TD-LTE 2.570~2.620GHz 频段,第五代移动通信3.300~3.400GHz 、4.400~4.500GHz 、4.800~4.990GHz 候选频段,尺寸较小且有足够的性能冗余[1,2,3]。

NaturePhotonics报道本刊编委黄维院士团队首例多彩有机“夜明珠”研究新成果

62南京邮电大学学报（自然科学版）2019年Simulation-based computation of information rates forchannels with memory[J J.IEEE Transactions on Information Theory,2006,52(8)：3498-3508.[11]BARBIERI A,FERTONANI D,COLAVOLPE G.Timefrequency packing for linear modulations:spectral efficiency and practical detection schemes[J].IEEE Transactionson Communications,2009,57(10)：2951-2959.[12]BUZZI S,RISI C,COLAVOLPE G.Green and fast DSLvia joint processing of multiple lines and time-frequencypacked modulation[C]〃IEEE International Conferenceon Communications Workshops.2013：538-542.[13]KANNAN M,SRIVATSA S.Hardware implementation lowpower high speed FFT core[J].Optimization,2009,6(1):1-15.[14]BUZZI S.CHIH-LIN I,KLEIN T E,et al.A survey of energy-efficient techniques for5G networks and challengesahead[J].IEEE Journal on Selected Areas in Communications,2016,34(4)：697-709.[15]BUZZI S,DANDREA C.Are mmwave low-complexitybeamforming structures energy-efficient?analysis of the downlink MU-MIMO[C]〃GLOBECOM Workshops.2017：l-6.[16]UGOLINI A,RICCIULLI M.Advanced transceiverschemes for next generation high-rate telemetry[C]〃Advanced Satellite Multimedia Systems Conference&the Signal Processing for Space CommunicationsWorkshop.2016.[17]SRIDHARAN A,VIJI A.Low power hardware implementation of high speed FFT core[C]〃International Conference on Advances in Computer Engineering.2010：223-227.Nature Photonics报道本刊编委黄维院士团队首例多彩有机“夜明珠”研究新成果近日，本刊编委、我校信息材料与纳米技术研究院、省部共建有机电子与信息显示国家重点实验室培育基地黄维院士，新加坡国立大学化学系刘小钢教授和南京工业大学安众福教授带领的团队在有机长余辉发光领域再次取得重大突破。

紧急倒车模式下螺旋桨诱导环状涡的发展机理

第41卷第12期2020年12月哈㊀尔㊀滨㊀工㊀程㊀大㊀学㊀学㊀报Journal of Harbin Engineering UniversityVol.41ɴ.12Dec.2020紧急倒车模式下螺旋桨诱导环状涡的发展机理王超1,李鹏1,王文全2,孙帅1(1.哈尔滨工程大学船舶工程学院,黑龙江哈尔滨150001;2.中国船舶及海洋工程设计院,上海200011)摘㊀要:为了解诱导环状涡的产生机理和发展过程,本文采用有限体积法结合大涡模拟湍流模型,对E1619桨紧急倒车模式下的流场进行仿真计算㊂经网格和时间步长的收敛性分析,确保结果的可信性,并分析了不同载荷工况下环状涡变形㊁演化和脱落与其载荷变化㊂结果表明:紧急倒车模式下螺旋桨的水动力载荷分为极限载荷和平均载荷,极限载荷又可分为重载和轻载;诱导环状涡的结构变形与其外环突起的脱落会改变螺旋桨的水动力载荷;螺旋桨排出流和自由来流的挤压和剪切促使诱导环状涡的形成,而流场速度脊线的出现驱动环状涡发生变形和突起脱落㊂螺旋桨附近流场3个方向(轴向㊁径向和切向)速度的不同耦合作用是造成环状涡变形㊁演化和脱落的原因㊂关键词:紧急倒车;E1619桨;大涡模拟;载荷工况;环状涡;变形;脱落;速度脊线DOI :10.11990/jheu.201904064网络出版地址:http :// /kcms /detail /23.1390.u.20201203.0957.002.html 中图分类号:U661.31㊀文献标志码:A㊀文章编号:1006-7043(2020)12-1742-08Deformation ,evolution and shedding of the annular vortex ofpropeller in crash-back modelWANG Chao 1,LI Peng 1,WANG Wenquan 2,SUN Shuai 1(1.College of Shipbuilding Engineering,Harbin Engineering University,Harbin 150001,China;2.No.708Research Institute,ChinaShipbuilding Industry Corporation,Shanghai 200011,China)Abstract :The induced annular vortex is an important characteristic of the flow field around the propeller under the crash-back mode,and the induced annular vortex is significant for the security of the emergency navigation of ships.To determine how the annular vortex forms and develops,we combined the finite volume method and large-eddy simu-lation to simulate the flow field near the E1619propeller in the crash-back mode.The convergence of the spatial and temporal resolutions was studied to prove the result reliability.By comparing different load cases,the link between loads of the propeller and the deformation,evolution,and shedding of the annular vortex was confirmed.The results showed that the hydrodynamic load of the propeller in the crash-back mode was divided into extreme load and average load,while the extreme load included high loads and low loads.The hydrodynamics of the propeller was affected by the structure deformation and the shedding of the annular vortex,which is the result of the extrusion and shearing of the free stream and discharge flow.The ridge of velocities drives the deformation and the shedding of the annular vortex.Different coupling effects of the velocities in three directions (axial,radial,and tangential)in the flow field near the propeller are the causes of deformation,evolution,and shedding of the annular vortex.Keywords :crash back;E1619propeller;large-eddy simulation;load cases;ring-vortex;deformation;shedding;ridge of velocities收稿日期:2019-04-19.网络出版日期:2020-12-03.基金项目:国家重点实验室基金项目(61422230203182223010);国家自然科学基金项目(51679052).作者简介:王超,男,教授,博士生导师;李鹏,男,博士研究生.通信作者:王超,E-mail:wangchao806@.㊀㊀以转速ω㊁自由来流速度U 为变量可将螺旋桨工作模式分为4种[1]:正车前进㊁正车倒退㊁倒车前进和倒车倒退㊂正车前进,ω和U 固定时,螺旋桨产生的推力㊁扭矩不随时间变化;其余3种工作模式用于舰船操纵,此时,螺旋桨工作流场较正车前进复杂,紧急倒车模式更甚,产生急剧变化的水动力载荷,威胁螺旋桨结构强度,甚至发生塑性变形或损坏其结构,进而造成桨的效率降低㊁丧失等危险㊂研究紧急倒车模式下螺旋桨流场特性能全面掌握螺旋桨的性能,同时能指导舰船的安全操纵,亦对指导在非设计工况下保证螺旋桨结构强度安全有重要意义㊂第12期王超,等:紧急倒车模式下螺旋桨诱导环状涡的发展机理HECKER 等[2-3]对P4381螺旋桨紧急倒车模式下的载荷㊁流场开展了实验,螺旋桨盘面附近存在的1个环状旋涡,为后续的理论研究提供了验证基础;文献[4-7]基于不同的湍流模型对螺旋桨非设计工况下的流场进行数值计算分析,验证了环状涡的存在;他们的研究还将紧急倒车模式下螺旋桨流场特征分为4个阶段:射流环附着阶段㊁稳定环状涡阶段㊁环状涡摆动阶段㊁环状涡脱落及尾流分离阶段,并对每类流场与螺旋桨载荷之间的关系进行探讨;王贵彪[8]对导管桨紧急倒车模式下的水动力性能进行数值模拟计算,结果表明导管和螺旋桨的推力变化趋势始终保持一致且变化剧烈;陈进[9]采用LES 模拟对螺旋桨紧急倒车和停船正车的螺旋桨性能进行了数值模拟计算㊂目前,紧急倒车模式下螺旋桨的推进性能已有较多研究,但针对影响其性能的环状涡仍缺乏系统的研究成果㊂本文以E1619桨为研究对象,以Star CCM +为工具,基于大涡模拟(LES)对该桨紧急倒车模式下的流场进行计算,系统分析在重载㊁均载和轻载状态下螺旋桨附近的流场特征,总结得出环状涡的形成原因以及环状涡变形㊁演化和脱落与3向速度之间的关系㊂1㊀数值计算方法1.1㊀理论方法和湍流模型紧急倒车过程中,流向相反的流场耦合存在大量的不稳定流动和分离旋涡㊂大涡模拟[10-11](large eddy simulation,LES)是对紊流脉动(紊流涡)的1种空间平均,通过过滤函数将大尺度涡和小尺度涡分离开,大尺度涡进行直接模拟,小尺度涡用模型来封闭㊂大涡模拟成立的理论基础是在高雷诺数紊流中存在惯性尺度的涡,该尺度的涡具有统计意义上的各项同性的性质,理论上它既不含能量也不耗散能量,它将含能尺度的涡的能量传递给耗散尺度的涡㊂LES 中,次格子尺度模型较RANS 包含更少的经验系数和定义系数,大涡模拟中用于过滤变量的连续性和动量方程如式(1)所示,当流体计算的网格尺寸足够小的时候,次格子尺度模型对流动的影响会降至最低,更小范围内的流体流动,即小于网格尺寸的湍流流动会被次格子尺度模型移除模拟结果㊂∂ρ∂t +u ∂ρ u i ∂x i =0∂ρ∂t (ρ u i )+∂∂x i (ρu i u j )=∂∂x j μu ∂ u i∂x j ()-∂ p ∂x j -∂τij ∂x j ìîíïïïïï(1)式中:x i ㊁x j 是单元中心的坐标分量;u i 和u j 是速度分量的平均值;p 是平均压强;μ是流体粘性系数;ρ是流体密度;τij 是网格应力值:τij =ρu i u j -ρu i u j (2)1.2㊀计算模型的建立1.2.1㊀计算域及网格划分E1619桨[12]是七叶大侧斜螺旋桨,该桨是意大利INSEAN 水池为潜艇设计的专用螺旋桨,其正车运转时为右旋桨.如图1(b)所示,螺旋桨直径D 为485mm,毂径比0.226,桨叶0.7倍半径处螺距为1.15,0.75倍半径处弦长为6.8mm㊂本文参考Pontarelli [6]的研究设置计算域尺寸及其边界条件,如图2所示㊂图1㊀E1619桨几何模型Fig.1㊀E1619Propellermodel图2㊀紧急倒车仿真计算域及边界条件Fig.2㊀Emergency reversing simulation calculation domainand boundary conditions计算采用3套网格,并借此进行网格收敛性分析,从而降低或者避免网格划分对仿真计算结果的影响㊂网格最小尺寸以2为比例逐渐增加,3套网格的最大尺寸相同;网格划分方式统一采用切割体网格;3套网格选取的y +值均为10;3套网格的边界层设置层数均为15层,边界层厚度分别为0.001㊁0.0015㊁0.002m㊂3套网格具体划分信息如表1所示,图3是细网格的桨叶网格和流场网格加密㊁桨叶边界层示意图㊂图3㊀用于收敛性计算的细网格划分Fig.3㊀Fine grid for convergency calculations㊃3471㊃哈㊀尔㊀滨㊀工㊀程㊀大㊀学㊀学㊀报第41卷表1㊀收敛性计算的网格数量分布Table 1㊀The distribution of the number of the number of grids calculated for convergence位置单个桨叶桨毂小域大域合计尺寸(1.2R +0.8R )ˑ1.2R(12R +16R )ˑ14R粗网格1820021500254700023620004909000中网格2012024010307000029300006000000细网格23800264103004000350600065100001.2.2㊀计算工况设定文献[1-5]的研究中,以螺旋桨倒转即螺旋桨角速度ω为负㊁自由来流速度与正车运转相同即来流速度U 为正时定义为紧急倒车运转㊂此时E1619桨的运转模式如图4所示㊂紧急倒车模式螺旋桨转速和来流速度表示无量纲化J 为[3-5]:J =U nD(3)式中:U 是来流速度,m /s;n 是紧急倒车螺旋桨转速,r /s;D 是螺旋桨直径,m㊂图4㊀螺旋桨紧急倒车运转Fig.4㊀Crashback for propeller同时,JESSUP 等[4-5]的研究发现,紧急倒车过程中,有3个的载荷作用于螺旋桨,即轴向推力㊁扭矩和侧向力㊂为区别于正车运转时螺旋桨载荷,本文以T ㊁T S ㊁Q 3个力学元素,利用式(4)~(6)进行无量纲化获得3个系数K T ㊁K T S ㊁K Q :K T =T ρn 2D 4(4)K T S =T Sρn 2D 4(5)K Q =Qρn 2D 5(6)㊀㊀在J =-0.5时,螺旋桨环状涡的变形㊁演化和脱落与其自身性能变化很具有代表性[4-5],因此本文选定这一特殊的工况进行螺旋桨紧急倒车流场特性的研究㊂E1619桨的正车额定转速为23.15r /s [13],螺旋桨紧急倒车时的额定转速均为对应额定转速的65%~75%[6],本文中将紧急倒车模式下E1619桨的转速定为16r /s,约为正车额定转速的70%,因此J =-0.5时的自由来流的速度为3.88m /s㊂2㊀收敛性分析CFD 仿真计算的不确定度主要有3个来源:网格分辨率,时间步长分辨率和迭代次数㊂文献[14-16]的研究表明,网格分辨率相对于其他2项对计算结果的影响大1个数量级㊂本节用3套网格和3个时间步长(Δt /2㊁Δt 和2Δt ,Δt 为螺旋桨倒转1ʎ的时间)对J =-0.5时3个力学分量(K T ㊁K T S ㊁K Q )的平均值㊁最大值和最小值共9个分量进行网格㊁时间步长收敛性计算㊂图5给出J =-0.5不同网格和时间步长时上述9个分量的计算结果,可以看出,9个分量对网格和时间步长的敏感性不高㊂网格收敛性验证方法用STERN 等[14-16]的论述过程进行㊂网格收敛率R G 为:R G =S 3-S 2S 2-S 1(7)式中S i (i =1,2,3)分别代表粗㊁中和细网格对应的计算结果㊂图5㊀不同网格和时间步长计算结果对比Fig.5㊀Comparison of results from different grids and timesteps㊃4471㊃第12期王超,等:紧急倒车模式下螺旋桨诱导环状涡的发展机理㊀㊀表2是网格收敛性验证的计算结果,可以看出,针对K T ㊁K T S ㊁K Q 的平均值㊁最大值和最小值等9个变量的计算结果得出网格收敛率R G 均小于1,同样基于Fine 网格进行的时间步长的收敛率R T 同样均小于1㊂综上,本次计算采用的网格和时间步长呈单调收敛,网格及时间步长收敛性很好㊂另外,本文还基于Fine 网格㊁Δt 时间步长进行了E1619桨正车敞水性能的计算,计算结果同实验值和Di 等[13]的仿真结果进行了对比,如图6所示,可以看出,本文的计算结果和实验值的吻合程度很高,相比于Di 等[13]的计算更为贴近实验值㊂表2㊀网格收敛性分析Table 2㊀Convergence analysis of mesh变量统计量R GR TK T 平均值0.6890.141最大值0.6670.638最小值0.5310.327K TS平均值0.8240.104最大值0.5020.282最小值0.6080.000K Q平均值0.5890.542最大值0.5870.179最小值0.7400.807图6㊀E1619桨正车敞水性能Fig.6㊀Open water curver of propeller E16193㊀水动力及流场仿真结果分析3.1㊀水动力载荷本次计算中,为避免计算不收敛,螺旋桨共旋转30圈,采用最后20圈的数据进行分析,图7是最后20圈的载荷(横轴为螺旋桨圈数,即旋转圈数)的3个分量时历曲线㊂可以看出螺旋桨的载荷曲线波动很大,在旋转20圈的过程中没有出现明显的周期性循环,K T 和K Q 的变化趋势除数值外基本相同,但K T 的变化较两者有着明显区别,由此可推断K T S 的变化较K T 和K Q 的影响为微量;将载荷时历数据进行数学方法处理,可以获得其平均值㊁标准差(如表3)㊂参考文献[17-19]的研究方法,以1倍标准差为单位,可以看出载荷时历曲线在平均值周围的波动情况,如图7所示㊂本文将位于平均值ʃ标准差外的载荷称为极限载荷,反之为平均载荷,极限载荷按绝对值大小分为重载和轻载㊂可以看出,3个力学分量的变化趋势基本相同,在对应的时刻均出现极限载荷或平均载荷,为后续分析提供了途径㊂图7㊀载荷时历曲线Fig.7㊀Load time domain curves表3㊀载荷统计数据Table 3㊀Load statistics统计量K TK TSK Q 平均值-0.076-0.009-0.181标准差0.2090.0050.345平均值+标准差0.133-0.0040.164平均值-标准差-0.285-0.014-0.5263.2㊀全局流场分析螺旋桨载荷分为极限载荷和平均载荷,图7中表明在20圈左右时,螺旋桨的3个载荷分量均出现了重载㊁均载和轻载的循环,本文针对这一过程进行分析㊂如图8所示以K T 为例,对应图7中矩形虚线框中部分,A ㊁B ㊁C 对应了3.1节中的轻载㊁均载和重载3个工况,图9是3种工况下螺旋桨盘面附近低压等值面的轴向速度云图㊂图8㊀K T 时历曲线中的极限载荷㊁平均载荷Fig.8㊀Time domain curve of K T consisting high-load ,mean-load and low-load㊃5471㊃哈㊀尔㊀滨㊀工㊀程㊀大㊀学㊀学㊀报第41卷在1个载荷循环内,螺旋桨周围存在1个明显的环状流场涡结构,下文简称环状涡㊂可以看出:环状涡结构紧凑㊁直径较小且变形微弱时的水动力载荷最小,如图9(a)所示;环状涡结构紧凑,但其内环中心发生偏移,外环出现低压凸起,此时螺旋桨载荷循环的均值,如图9(b)所示;环状涡内环部分完全脱离桨叶,其结构发生明显的变形,同时其外环凸起即将发生或发生脱落时,螺旋桨处于载荷循环的极大值;外环凸起脱落完成后,环状涡的结构再次回归完整紧凑㊂环状涡的桨叶叶面的低压区没有明显的变化,但叶背的低压区面积与桨叶载荷呈正比例变化,即变形㊁演化对应螺旋桨的水动力载荷变化,同时桨叶表面的低压区亦表现出这样的趋势,图9中可以看出,无论是哪种载荷工况,载荷增加,低压区面积有明显增加,且低压区不断向叶根处扩展㊂图9㊀不同载荷工况下螺旋桨附近流场(低压-25kPa 等值面的轴向速度云图)Fig.9㊀Flow field near propeller under different load cases (isosurface of P =-25kPa colored by axial velocity )㊀㊀紧急倒车模式下,螺旋桨的排出流和自由来流流向相反,在螺旋桨上游流场产生挤压㊁剪切,从而沿螺旋桨径向流动,形成上游的汇聚流;螺旋桨吸入流同样和自由来流流向相反,在螺旋桨下游形成分离流;汇聚流和分离流的流动在螺旋桨盘面附近形成了旋涡状的流场流动,如图10(a)所示,在三维空间内对应形成如图9所示的环状涡㊂图10(b)是J =-0.5时,不同载荷工况螺旋桨上下游5个轴向位置的流场速度曲线,可以看出不同载荷工况下,流场的轴向速度发生较大的变化,推断汇聚流和分离流形成的旋涡大小㊁位置会有所不同,进而形成三维空间内环状涡的变形㊁演化,甚至是脱落㊂图10㊀环状涡的形成原理Fig.10㊀A schematic diagram of the formation of the ring-vortex3.3㊀局部流场分析紧急倒车时极限载荷和环状涡的变形演化有着密切的关系,而环状涡的形成㊁变形和演化均与流场速度相关㊂图11是环状涡近后方(螺旋桨下游)㊁环状涡中心处及近前方1.5倍半径内流场(依次对应图10(a)中从左向右3条垂直实线对应的切面)的轴向㊁径向和切向速度㊂轻载时环状涡的直径明显小于重载,此时近前方径向速度为正值㊁近后方切面的径向速度为负值,且绝对值明显较小,对应图10(a)可知,在同一来流速度下,轻载时的汇聚流和分离流速度相对于来流的速度要小于重载,由此形成了较小的环状涡㊂重载时,在环状涡出现脱落的地方,如图11(a)中所示2处,2项速度在涡脱落的对应径向投影位置出现了符号相反,即速度矢量相反的流场,称之为流场速度脊线 ;对比轻载工况,径向速度㊁切向速度等值线更加的完整和紧凑,且未出现流场速度脊线 ,对应环状涡更加的完整和紧凑,推断环状涡的脱落与流场速度脊线的出现有关㊂紧急倒车模式下,螺旋桨处于高雷诺数流场中,而流场速度脊线处相反的轴向速度和切向速度迫使环状涡的凸起发生剪切,从而形成了环状涡的脱落,如图12(a)所示;结合对环状涡3个截面的3个方向速度分析可知,环状涡的变形与其附近流场径向速度的不均匀分布有关,轻载时径向速度分布均匀㊁大小相似,重载则相反,对应于环状涡的变形㊂㊃6471㊃第12期王超,等:紧急倒车模式下螺旋桨诱导环状涡的发展机理图11㊀不同载荷工况3个轴向切面的3向速度Fig.11㊀Different velocities at 3axial locations under different cases㊀㊀图13是3个不同半径切面,波动最为剧烈的桨叶附近流场矢量图㊂可以看出,沿螺旋桨径向方向,桨叶附近的流场波动程度逐渐降低,且随边处出现了不同程度的湍流旋涡,但重载工况时更为明显,尤其在0.4倍半径处㊂结合图9推断这可能是造成桨叶表面低压区不同扩展程度的原因㊂另外,随边处波动剧烈的流场也能造成桨叶受力的波动,由此推断也是紧急倒车模式螺旋桨载荷波动的原因㊂表4㊃7471㊃哈㊀尔㊀滨㊀工㊀程㊀大㊀学㊀学㊀报第41卷是1倍半径环状涡中心处平面(下文称中面)紧急倒车时,重载工况和轻载的转换造成中面内的流场通量不同(流场面积分量),另外中面3向速度的标准差也有不同程度的波动情况,在较大的通量和波动程度下,即重载时,螺旋桨的载荷必然大于通量和波动程度较小,即轻载工况㊂另外,3向速度分量中,切向速度的波动程度最大,结合图12中的环状涡脱落简图可推断,切向速度对于环状涡的脱落较轴向速度有较大的作用,而环状涡表面的凸起或脱落涡多沿其周向较长亦说明了这一点㊂图12㊀环状涡变形演化原理Fig.12㊀Sketch of the deformation and evolution ofring-vortex图13㊀不同半径处桨叶局部流场矢量Fig.13㊀Vector velocity of local field at different radial lo-cations表4㊀螺旋桨中心平面流场主要参数Table 4㊀Main parameters of the field in the middle planeof the propeller变量轴向速度径向速度切向速度积分变量/(m 3㊃s -1)标准差积分变量/(m 3㊃s -1)标准差积分变量/(m 3㊃s -1)标准差重载96.448 1.41150.188 1.66440.087 2.349轻载56.5641.35130.4791.43235.2671.8544㊀结论1)通过网格㊁时间步长收敛性的验证分析发现,以Star CCM +为工具,基于LES 湍流模型计算紧急倒车模式下螺旋桨性能具有可行性和正确性㊂2)紧急倒车模式下,螺旋桨的K T ㊁K T S ㊁K Q 变化剧烈且无规律㊁周期,且螺旋桨盘面附近存在1个不断变形㊁演化和脱落的环状涡;环状涡的形成是螺旋桨排出流和自由来流挤压㊁剪切而引发的汇聚流和分离流共同作用的结果㊂3)极限载荷和平均载荷的变化与螺旋桨附近环状涡的变形和演化有关,环状涡附近流场的速度脊线是造成切向速度和轴向速度的剪切形成了其凸起和脱落,径向速度的不均匀性造成其变形㊂本文对紧急倒车模式过程的流场进行了准定常计算分析,即特定J 时的流场特性,初步得出螺旋桨附近环状涡的存在是该过程中的重要特征;另外,环状涡的变形㊁演化和脱落影响螺旋桨的载荷的变化㊂但未来仍需要进行更细致的工作,即对不同J 下螺旋桨盘面附近的流场及其变化规律进行深入的探讨㊂参考文献:[1]HECKER R,REMMERS K.Four quadrant open-water per-formance of propellers 3710,4024,4086,4381,4382,4383,4384and 4426[R].Bethesda,USA:David Taylor Naval Ship Research and Development Center,1971.[2]HAMPTON G A.Open water force and moment characteris-tics on three propellers in a crashback condition,432-H07[R].Bethesda,USA:David Taylor Naval Ship Research and Development Center,1995.[3]JIANG C W,DONG R,LIU H L,et al.24-inch water tun-nel flow field measurements during propeller crashback [C]//In Proceedings of the 21st Symposium on Naval Hy-drodynamics.Trondheim,Norway,National Academies Press,1997:34-56.[4]JESSUP S,CHESNAKAS C,FRY D,et al.Propeller per-formance at extreme off design conditions [C]//In Pro-ceedings of the 25th Symposium on Naval Hydrodynamics.Newfoundland,Canada,National Academies Press.2004:281-294.[5]JESSUP S D,FRY D,DONNELLY M.Unsteady propeller㊃8471㊃第12期王超,等:紧急倒车模式下螺旋桨诱导环状涡的发展机理performance in crashback conditions with and without a duct [C]//In Proceedings of the26th Symposium on Naval Hydrodynamics.Rome,Italy,National Academies Press. 2006:238-249.[6]PONTARELLI M.Flow regimes and instabilities of propel-ler crashback[D].Iowa,USA:University of Iowa,2017: 1-167.[7]CHEN B,STERN putational fluid dynamics of four-quadrant marine-propuisor flow[J].Journal of ship research,1999,43(4):218-228.[8]王贵彪,谢永和,许颂捷.导管螺旋桨四象限水动力性能研究[J].船舶工程,2015,37(10):26-28,53. WANG Guibiao,XIE Yonghe,XU Songjie.Research on ducted propellerᶄs hydrodynamic performance in four quad-rants[J].Ship engineering,2015,37(10):26-28,53.[9]陈进,邹早建.紧急制动及紧急向前时螺旋桨绕流的大涡模拟[J].船舶力学,2018,22(3):296-310. CHEN Jin,ZOU Zaojian.LES simulations of the flow around a propeller in crash back and crash ahead[J].Jour-nal of ship mechanics,2018,22(3):296-310. [10]贾晓荷,刘桦.双圆柱绕流的大涡模拟[J].水动力学研究与进展,2008,23A(6):625-632.JIA Xiaohe,LIU rge eddy simulation of flow around two circular cylinders[J].Chinese journal of hydrodynam-ics,2008,23A(6):625-632.[11]王玲玲.大涡模拟理论及其应用综述[J].河海大学学报(自然科学版),2004,32(3):261-265.WANG rge eddy simulation theory and its application[J].Journal of Hohai University(Natural Sci-ences),2004,32(3):261-265.[12]CHASE N,CARRICA P M.Submarine propeller compu-tations and application to self-propulsion of DARPA suboff [J].Ocean engineering,2013,60:68-80. [13]DI FELICE F,FELLI M,LIEFVENDAHL M,et al.Nu-merical and experimental analysis of the wake behavior ofa generic submarine propeller[C]//Proceedings of the1stInternational Symposium on Marine Propulsors.Trond-heim,Norway,2009:301-321.[14]王超.螺旋桨水动力性能㊁空泡及噪声性能的数值预报研究[D].哈尔滨:哈尔滨工程大学,2010.WANG Chao.The research on performance of propellerᶄs hydrodynamics,cavitation and noise[D].Harbin:Harbin Engineering University,2010.[15]STERN F,WILSON R V,COLEMAN H W,et -prehensive approach to verification and validation of CFD simulations Part1:methodology and procedures[J].Journal of fluids engineering,2001,123(4):793-802.[16]WILSON R V,STERN F,COLEMAN H W,et -prehensive approach to verification and validation of CFD simulations-Part2:application for RANS simulation of a cargo/container ship[J].Journal of fluids engineering, 2001,123(3):803-810.[17]VERMA A,JANG H,MAHESH K.The effect of anupstream hull on a propeller in reverse rotation[J].Jour-nal of fluid mechanics,2012,704:61-88. [18]JANG H,MAHESH rge eddy simulation of flowaround a reverse rotating propeller[J].Journal of fluid mechanics,2013,729:151-179.[19]DI MASCIO A,MUSCARI R,DUBBIOSO G.On thewake dynamics of a propeller operating in drift[J].Jour-nal of fluid mechanics,2014,754:263-307.本文引用格式:王超,李鹏,王文全,等.紧急倒车模式下螺旋桨诱导环状涡的发展机理[J].哈尔滨工程大学学报,2020,41(12):1742-1749. WANG Chao,LI Peng,WANG Wenquan,et al.Deformation,evolution and shedding of the annular vortex of propeller in crash-back model[J].Journal of Harbin Engineering University,2020,41(12):1742-1749.㊃9471㊃。

基于神经网络遗传算法的超疏水涂层优化

表面技术第51卷第1期 ·240· SURFACE TECHNOLOGY 2022年1月收稿日期：2021-07-29；修订日期：2021-11-21 Received ：2021-07-29；Revised ：2021-11-21基金项目：国家重点研发计划（2020YFC1910100）Fund ：National Key Research and Development Plan of China (2020YFC1910100) 作者简介：苑昭阔（1989—），男，博士研究生，主要研究方向为换热和涂层。

Biography ：YUAN Zhao-kuo (1989—), Male, Doctoral candidate, Research focus: heat transfer and coatings. 通讯作者：吴俐俊（1965—），男，博士，教授，主要研究方向为强化换热、有机朗肯循环、表面工程。

Corresponding author ：WU Li-jun (1965—), Male, Doctor, Professor, Research focus: enhanced heat transfer, ORC, surface engineering. 引文格式：苑昭阔，吴俐俊，王骏，等. 基于神经网络遗传算法的超疏水涂层优化[J]. 表面技术, 2022, 51(1): 240-246.YUAN Zhao-kuo, WU Li-jun, WANG Jun, et al. Optimization of Superhydrophobic Coatings Based on Neural Network and Genetic Algorithm [J]. Surface Technology, 2022, 51(1): 240-246.基于神经网络遗传算法的超疏水涂层优化苑昭阔1，吴俐俊1，王骏2，张萍1，韦增志1（1.同济大学机械与能源工程学院，上海 201804； 2.南京同诚节能环保装备研究院，南京 211100）摘要：目的探究超疏水涂层各成分的含量对涂层水接触角和导热系数的影响，找到最优成分组合，使涂层水接触角和导热系数同时获得最大值。

蝠鲼仿生型多模块UUV_的水动力分析及能量捕获效能研究

本文网址：/cn/article/doi/10.19693/j.issn.1673-3185.03019期刊网址：引用格式：王佳茂, 杨鹏, 李静茹. 蝠鲼仿生型多模块UUV 的水动力分析及能量捕获效能研究[J]. 中国舰船研究, 2023, 18(6):106–118.WANG J M, YANG P, LI J R. Hydrodynamic analysis and energy capture efficiency of multi-module bionic manta ray UUV[J]. Chinese Journal of Ship Research, 2023, 18(6): 106–118.蝠鲼仿生型多模块UUV 的水动力分析及能量捕获效能研究扫码阅读全文王佳茂1，杨鹏*2，李静茹11 海南大学机电工程学院，海南海口 5702282 华中科技大学船舶与海洋工程学院，湖北武汉 430074摘要:［目的］针对无人值守型航行器存在电能续航力不足的瓶颈，开展蝠鲼仿生型无人潜航器（UUV ）的构型设计、运动性能和能量捕获效率分析。

［方法］基于浮体液压缸捕获波浪能原理，首先提出一型蝠鲼仿生型长续航UUV 的构型，并推导获得蝠鲼式多模块UUV 的运动及其能量捕获机理。

然后基于多模块浮体理论和三维势流理论编制程序进行水动力计算分析，揭示蝠鲼式多模块UUV 在不同浪向、不同液压缸连接刚度和阻尼环境下运动响应和波浪能捕获规律。

［结果］最后结合最优的液压缸刚度和阻尼研究了蝠鲼式多模块UUV 在波浪中的波浪能捕获效能。

［结论］可见，推导的蝠鲼式多模块UUV 的运动方程及其能量捕获公式可被用于有效分析其波浪能捕获特性。

关键词：蝠鲼仿生；多模块UUV ；波浪能；运动；能量捕获中图分类号: U661.1文献标志码: ADOI ：10.19693/j.issn.1673-3185.03019Hydrodynamic analysis and energy capture efficiency of multi-module bionicmanta ray UUVWANG Jiamao 1, YANG Peng *2, LI Jingru11 School of Mechanics and Electrics Engineering, Hainan University, Haikou 570228, China2 School of Naval Architecture and Ocean Engineering, Huazhong University of Science and Technology,Wuhan 430074, ChinaAbstract : ［Objectives ］Aiming at the bottleneck of the insufficient electric endurance of unattended vehicles, the configuration design, motion performance and energy capture efficiency analysis of a manta ray bionic unmanned underwater vehicle (UUV) are carried out. ［Methods ］The configuration of a multi-module bionic long-endurance manta ray UUV is proposed, and its motion and energy capture mechanism are deduced and obtained under the principle of wave energy capture by a floating hydraulic cylinder. Next, based on the multi-module floating body theory and three-dimensional potential theory, hydrodynamic calculation and analysis are carried out, and the motion response and wave energy capture law of the multi-module manta ray UUV are revealed under different wave directions and different connected stiffness and damping of the UUV. ［Results ］Finally, the wave energy capture efficiency of the multi-module manta ray UUV in waves is studied in combination with the optimal stiffness and damping of the hydraulic cylinder.［Conclusions ］It is concluded that the wave energy capture characteristics of a multi-module manta ray UUV can be analyzed by its motion equations and energy capture formula.Key words : bionic manta rays ；multi-module UUV ；wave energy ；motion ；energy capture收稿日期: 2022–08–03 修回日期: 2022–12–08 网络首发时间: 2023–03–18 10:36基金项目: 海南省自然科学基金资助项目（520RC539）；船舶总体性能创新研究开放基金资助项目（31122115）作者简介: 王佳茂，男，1998年生，硕士生。

2011年高考英语最富有创新的题及理由全国通用-真题在线

2011年高考英语最富有创新的试题及理由河北省易县育英高级中学（074200）庞永升1.（2011·北京卷）开放作文题请根据下面提示，写一篇短文。

词数不少于50。

In your spoken English class, your teacher shows you the following picture. You are asked to describe the picture and explain how you understand it.（请务必将开放作文写在答题卡指定区域内）One possible version:In the picture,there stands a tree full of fruit on one side of the stream.Across the stream ,a man is trying to reach out on the edge of the bank for the fruit with a net attached to a pole.Not far away there is a bridge that can lead him to the tree for more fruit.The message conveyed in the picture is clear.In pursuing a dream ,we might focus on only one way of making it come true ,forgetting that there may be alternatives.As indicated in the picture ,if the man is willing to look for other possibilities,he can find a better and more rewarding way to achieve his goal.All he has to do is to turn around,cross the bridge and walk to the tree.【上榜理由】北京卷的开放作文真正做到了以语言为载体，考查学生的创新能力。

专利大棒下的Android

专利大棒下的Android
老王
【期刊名称】《中文信息》
【年(卷),期】2011(000)009
【摘要】在过去三年中，谷歌培育的Android系统从无到有，创造了前所未有的市场奇迹。

在它的领导下，庞大的Android智能军团不仅成功制衡了iOS系统不断提升的市场份额，并且在欧美市场将诺基亚赶下王座。

但今日以来，一场围绕着Android终端的专利风暴开始聚集。

诺基亚与微软联手，开始计划向谷歌“征税”，黑莓、英特尔等也磨刀霍霍。

在市场上无法得到的东西，在这场专利之争中能够获得吗？
【总页数】1页(P22-22)
【作者】老王
【作者单位】不详
【正文语种】中文
【中图分类】TP278
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2.中国大陆LED企业如何防范专利“大棒”？ [J],
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4.彩电业要对垒专利大棒先得戒掉"拿来主义" [J], 凤飞伟
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因版权原因，仅展示原文概要，查看原文内容请购买。

破译科技文阅读密码

破译科技文阅读密码
王志耀
【期刊名称】《发明与创新（中学时代）》
【年(卷),期】2008(000)006
【摘要】@@ 科技文阅读试题是每年高考的一道必考题,学生在解答此类试题时,
往往摸不着头脑.解答这类阅读试题可以从排除干扰项人手,所以要了解干扰项的设
置方法,找出干扰项.下面结合2007年高考试题分别作解说.
【总页数】1页(P17)
【作者】王志耀
【作者单位】无
【正文语种】中文
【相关文献】
1.密码的编制与破译：破译时间的研究
2.年轻、梦想、改变——多媒体破译奥巴
马蓝色军团成功密码——我型我秀：奥巴马的“年轻密码”3.有没有破译上古文化的密码本？──《中国文化的人类学破译》系列几副标本的考察4.《四川教育》(理论)“成长密码”栏目“名师”征集:寻找本土“名师”,破译成长“密码”5.《四川教育》(理论)“成长密码”栏目“名师”征集:寻找本土“名师”,破译成长“密码”
因版权原因，仅展示原文概要，查看原文内容请购买。

【华人频道】王光雷

王光雷：世界首个物种分类“字典”王老师：主持人好！观众朋友们大家好！网友朋友们大家好！主持人：王先生，您看刚开始我就提到了这个物种身份证编码系统，那么我感觉可能这个名字当中，物种两个字是比较重要的，是关键词，那么您先给我们介绍一下，什么是物种？物种的概念是什么？再一个在世界上到底有多少物种？王老师：物种是我们人类认识世界，研究世界获得的一些宝贵资料。

这个物种就是在地球上它具有形态学方面比较一致，而且具有一定的群体。

它并且具有良好的遗传性，这样一类生物呢，我们就把它叫做物种。

据文献报导呢，有五千万到一亿种，但是具有文字记载呢，大概有二百万种。

主持人：那王先生，刚才我们就提到这个物种，您也给我们介绍了这个物种，那您跟我们说一下吧，这个物种在记录方面它有什么样的意义？王老师：物种这个研究呢，前人都研究的它比较简单，是逐步的完善的，随着科学技术水平的提高，我们就把这些资料归纳、总结、完整，以便能够让后人进行借鉴。

主持人：您接下来就给我们介绍您这个系统，您这个系统是不是就针对这个物种开发研发的呢？王老师：是的，我这个系统就是为了。

在物种的分类和物种的资料的保存、记录上为主要内容的。

主持人：那您现在就给我们简单的先介绍一下您的这个系统。

王老师：只要我们输入物种身份证五个汉字的拼音字头加上.com就可以进入我这个网站了。

我们这个网站有两种查法，第一种查法呢就是盲查，就是按节元查询，单击界门纲这个按钮，它就会出现生物。

世界上生物的分类，6个系统。

比方说我们要查一个扩张莫尼茨绦虫，我们就知道它是动物，我们就点动物界，单击到动物界以后呢，它会出现33个门，那么绦虫它属于扁形动物门，单击扁形动物门以后呢，它就会出现了以下3个纲，那么绦虫呢它就属于绦虫纲了。

单击到绦虫纲以后会出现绦虫纲隶属的14个目。

第二种查法，如果我们比较专业，知道这个物种的汉文或者是拉丁文名称呢，我们可以在这个地方呢直接输入就可以查询，比方说我们查一下禽流感，我们输入禽流感病毒，然后我们单击搜索，它就会出现禽流感病毒这个物种的形态学描述和图片。