AN AGGLOMERATION-BASED MULTILEVEL-TOPOLOGY CONCEPT WITH APPLICATION TO 3D-FE MESHES
聚苯胺的制备
随着社会科技的发展，绿色能源成为人类可持续发展的重要条件，而风能、太阳能等非可持性能源的开发和利用面临着间歇性和不稳定性的问题，这就催生了大量的储能装置，其中比较引人注目的包括太阳能电池、锂子电池和超级电容器等。
超级电容器作为一种新型化学储能装置，具有高功率密度、快速充放电、较长循环寿命、较宽工作温度等优秀的性质，目前在储能市场上占有很重要的地位，同时它也广泛应用于军事国防、交通运输等领域。
目前，随着环境保护观念的日益增强，可持续性能源和新型能源的需求不断增加，低排放和零排放的交通工具的应用成为一种大势，电动汽车己成为各国研究的一个焦点。
超级电容器可以取代电动汽车中所使用的电池，超级电容器在混合能源技术汽车领域中所起的作用是十分重要的，据英国《新科学家》杂志报道，由纳米花和纳米草组成的纳米级牧场可以将越来越多的能量贮存在超级电容器中。
随着能源价格的不断上涨，以及欧洲汽车制造商承诺在1995年到2008年之间将汽车CO2的排放量减少25%，这些都促进了混合能源技术的发展，宝马、奔驰和通用汽车公司已经结成了一个全球联盟，共同研发混合能源技术。
2002年1月，我国首台电动汽车样车试制成功，这标志着我国在电动汽车领域处于领先地位。
而今各种能源对环境产生的负面影响很大，因此对绿色电动车辆的推广提出了迫切的要求，一项被称为Loading-leveling(负载平衡)的新技术应运而生，即采用超大容量电容器与传统电源构成的混合系统“Battery-capacitor hybrid”(Capacitor-battery bank) [1]。
目前对超级电容器的研究多集中于开发性能优异的电极材料，通过掺杂与改性，二氧化锰复合导电聚合物以提高二氧化锰的容量[1、2、3]。
生瑜(是这个人吗？)等[4]通过原位聚合法制备了聚苯胺/纳米二氧化锰复合材料，对产物特性进行细致分析。
因导电高分子具有可逆氧化还原性能，通过导电高分子改性，这对于提高二氧化锰的性能和利用率是很有意义的。
纳米纤维素基多层级孔道结构碳气凝胶的制备及在锂电池中的应用
纳米纤维素基多层级孔道结构碳气凝胶的制备及在锂电池中的应用孔雪琳;卢芸;叶贵超;李道浩;孙瑾;杨东江;殷亚方【摘要】采用纳米精磨法对商品桉木浆进行纳米纤丝化处理,得到了高长径比、尺寸均一的纳米纤丝化纤维素(NFC),平均直径为230.10 nm,长度达数十微米.将其组装、干燥后制得具有大量介孔的纳米纤丝化纤维素气凝胶(NFCA).将NFCA在氮气氛围下高温碳化制得碳气凝胶(CNFA),或在氢氧化钾条件下辅助碳化制得具有多层级孔道结构的碳气凝胶(CNFA-A),在保留的碳气凝胶骨架结构上进行孔洞构建.通过扫描电子显微镜(SEM)、透射电子显微镜(TEM)表征及Nanomeasure?统计分析,发现NFC的平均直径经碳化后减小到53.16 nm.利用X射线衍射(XRD)、BET 比表面积测试和拉曼光谱揭示了碳化处理对纳米纤维素结构、比表面积、石墨化程度和缺陷的影响.结果表明,KOH辅助碳化处理后的碳气凝胶不仅保留了纤维素气凝胶前驱体的网络结构,还在其骨架上二次构建了更多的微孔和介孔,其比表面积高达488.92 m2/g,总孔容为0.404 cm3/g,所得的碳骨架被部分石墨化,具有良好的导电性.这类源于生物质的高比表面积碳气凝胶在被用作锂离子电池(LIB)负极材料时表现出优异的电化学性能,在电流密度1 A/g下连续充放电1000次后比容量达到409 mA·h/g,在电流密度高达20 A/g下,比容量还能维持在219 mA·h/g.%The nanofibrillated cellulose ( NFC ) with large aspect ratio and uniform size ( mean diameter is 230. 10 nm) was fabricated from commercial eucalyptus pulps by scale-up nano-grinding. Then the NFC was assembled to NFC aerogels(NFCA) with three-dimensional(3D) frameworks. After carbonization of NFCA under N2 atmosphere, the carbon nanofiber aerogels( CNFA) were generated with the inherited 3D network structure.With futher KOH-assisted annealing of CNFA, the hierarchical porous carbon aerogels( denoted as CNFA-A) were finally obtained. CNFA-A combined the inherited original 3D network from NFCA and the secondary constructed micropore-mesopore structure. The mean diameter of CNFA-A was diminished to 53. 16 nm. The structures of three kinds of cellulose-based aerogels were characterized by scanning electron microsco-py(SEM) and transmission electron microscopy ( TEM), and the statistic diameter of nanofibril building-blocks was obtained by Nanomeasure ?. The graphitization degree of cellulose-based aerogels was investigated by X-ray diffraction( XRD) and Raman spectroscopy, and the specific surface area was measured through BET specific surface area test. The specific surface area of CNFA-A is as high as 488. 92 m2/g and the total pore volume can reach up to 0. 404 cm3/g. In addition, as anode material for lithium ion battery, the CNFA-A exhibits a high reversible capacity ( 448 mA · h/g at 1 A/g ) , an excellent rate capability ( 219 mA · h/g at 20 A/g) and an outstanding cycling performance(409 mA·h/g at 1 A/g after 1000 cycles).【期刊名称】《高等学校化学学报》【年(卷),期】2017(038)011【总页数】6页(P1941-1946)【关键词】纳米纤丝化纤维素;气凝胶;碳化;多层级结构;锂离子电池【作者】孔雪琳;卢芸;叶贵超;李道浩;孙瑾;杨东江;殷亚方【作者单位】青岛大学材料科学与工程学院,青岛266071;中国林业科学研究院木材工业研究所,北京100091;中国林业科学研究院木材工业研究所,北京100091;青岛大学材料科学与工程学院,青岛266071;青岛大学材料科学与工程学院,青岛266071;青岛大学环境科学与工程学院,青岛266071;青岛大学环境科学与工程学院,青岛266071;中国林业科学研究院木材工业研究所,北京100091【正文语种】中文【中图分类】O613.71;O636.1纤维素是一种由β-(1→4)糖苷键连接脱水-D-葡萄糖单元构成的高分子, 广泛存在于植物中, 是植物细胞壁最主要的成分之一, 是地球上最丰富的天然高聚物. 如今, 人们已经从细胞壁中成功制备了环境友好的纳米纤丝化纤维素(NFC)[1,2]. 通过精细盘磨、高频超声[3,4]、高压均质等简单的机械处理, 可以用较低的成本制备出尺寸均一的NFC. 通过一定的组装手段, 可将NFC构建成具有三维网络结构的纳米纤丝化纤维素气凝胶(NFCA). 这类仅含C, H, O的绿色新型气凝胶是新型碳材料的理想前驱体[5], 可以通过热解直接成为碳气凝胶. 最重要的是, 高温碳化后的碳气凝胶不仅保持了NFCA的三维网状结构, 还具有良好的机械性、疏水性和导电性等新功能, 可将NFCA原本局限在亲水或极性介质中的应用拓展到新能源储存与转化等领域[6].碳气凝胶是最具有前景的高性能材料之一, 是一种密度可调的轻质多孔碳材料, 具有多孔道网状结构, 其孔隙率可以高达80%～99%, 具有网络连续、电导率高、比表面积大及密度变化范围大等特点. 传统的碳气凝胶通常是由有机气凝胶(如间苯二酚-甲醛气凝胶、间苯二酚-甲醛(RF)气凝胶、三聚氰胺-甲醛气凝胶)经高温碳化后制得[7～10]. 这类有机气凝胶存在易碎、密度相对较高、孔隙率低、原料或生产过程毒性较高等缺陷. 相比之下, NFC作为碳气凝胶前驱体具有来源广泛、产量巨大、制备绿色、可再生、机械性能优异、可生物降解、生物相容性好[11,12]和改性位点多等显著优点, 是一种极具开发潜力的碳气凝胶前驱体[13], 有利于推动探索环境友好、成本低廉的碳气凝胶的大规模生产.碳材料在能源储存与转化等领域具有广泛应用, 但传统的碳材料理论容量和能量密度低、活性位点少, 限制了其在锂电池、超级电容器以及电催化方面的应用. 在追求提高碳材料的电化学性能而不降低其稳定性和功率密度的解决方案中, 具有特殊纳米结构的新型碳材料是人们探索的主要热点[14]. 目前, 对碳基纳米材料的研究还大多集中在化学还原和分离的石墨烯、碳纳米管(CNF)和炭黑等导电性好、比表面积高的碳材料上. 碳纳米管、碳纳米纤维、空心碳纳米球, 石墨烯等不同纳米结构的碳材料已被证明可增强锂离子电池(LIB)的性能[15～18]. 然而, 制备技术复杂、前驱体成本高、石油基原料不可再生等因素严重限制了纳米碳的工业化生产. 本研究中, 我们将由纳米精磨桉木浆制备的一维NFC可控组装成具有贯通孔道结构和三维网络结构的气凝胶, 在高温碳化后保留了其三维网络骨架结构, 并进行了二次孔道构建. 这种方法得到的碳气凝胶具有可控的多层级孔道结构和比表面积高、孔隙率高、机械性能优异、导电性良好等特点, 其连贯的三维网络结构上还具有大量的微孔, 是典型的微孔-介孔-大孔气凝胶. 这样的多孔道结构有助于缩短Li离子的插入-脱嵌过程的扩散路径, 为Li离子的传输提供更多的路径[19]. 较高的比表面积可以加快电子传导且能够束缚更多的Li离子, 有极高的稳定性; 同时其连贯的网络结构保证了电子/离子的定向传输途径和应力变化的强耐性, 作为阳极材料具有优异的物理性能和电化学性能. 由该碳气凝胶组装的LIB显示出优异的循环性能和良好的倍率性能, 为低成本锂电池的研究提供了新的思路.1.1 试剂与仪器桉木浆(Eucalyptus pulps)由中国林业科学研究院林产化学研究所提供; 氢氧化钾、N-甲基吡咯烷酮和六氟磷酸锂(分析纯)购自国药集团化学试剂品有限公司; 乙炔黑(分析纯)购自长沙电池厂; 聚偏氟乙烯(PVDF, 分析纯)购自武汉荟谱化学新材料有限公司; 透析袋(直径76 mm)购自美国Sigma-Aldrich公司; 氮气(纯度99.999%)购自北京市亚南气体科技有限公司; 实验用水均为去离子水.NoVaTMNano SEM 250型场发射扫描电子显微镜和FEI Tecnai G20型透射电子显微镜(美国FEI公司); Magna-IR 750型傅里叶变换红外光谱仪(美国Nicolet 公司); HR800型拉曼光谱仪(法国Horiba Jobin Yvon Lab RAM公司); NOVA 1200e比表面积分析仪(美国康塔仪器公司); CT2001A型电池测试系统(武汉蓝电电子有限公司); MKSS1-1012-B079型超级净化手套箱(德国米开罗那有限公司).1.2 实验过程1.2.1 机械法制备NFC 先将桉木浆分散在去离子水中, 形成固含量为2.5%(质量分数)的分散液. 采用盘磨机进行初步纳米纤丝化, 盘磨机的转速设定为2000 r/min, 磨盘间距设定为-20 μm. 分散液经盘磨后重新倒入物料槽, 如此往复3次在磨盘间进行纳米纤丝化, 将盘磨后的湿态纤维素分散在去离子水中, 得到浓度为1.0%(质量分数)的水分散液.1.2.2 纳米纤丝化纤维素气凝胶及碳气凝胶的制备将制得的纤维素上清液装入透析袋中, 然后放入叔丁醇中置换24 h, 并用磁力搅拌器进行机械搅拌, 剩余悬浮液体积约为原体积的1/3, 收集剩余的悬浮液装入瓶中后在超低温冰箱(-80 ℃)中冷冻, 然后转入冷冻干燥仪中干燥72 h(-55 ℃, 10 Pa)得到干燥的NFCA. 将NFCA放入管式炉中, 在空气中由室温加热至250 ℃(升温速率为2 ℃/min), 保温2 h后在氮气氛围下继续升温至800 ℃(升温速率为5 ℃/min), 保温1 h, 即得到相应的碳纳米纤丝化纤维素气凝胶(CNFA). 此外, 将CNFA在管式炉中用氢氧化钾进行辅助碳化, 控制氮气的流速为80 mL/min, 得到孔道结构二次构建的气凝胶CNFA-A.1.2.3 电化学测试将样品、乙炔黑和聚偏氟乙烯按照质量比为8∶1∶1的比例溶解在N-甲基-2-吡咯烷酮中, 研磨形成膏状. 然后将悬浮液均匀地涂抹在Cu箔基底上, 放入真空烘箱中, 在120 ℃下干燥10 h制成电极片. 电解液为1 mol/L六氟磷酸锂(LiPF6)的碳酸亚乙酯(EC)/碳酸二甲酯(DMC)/碳酸二乙酯(DEC)(质量比为1∶1∶1)溶液. 在手套箱中组装成CR2016型纽扣电池. 在LAND CT2001A电池测试系统上进行充放电性能测试, 限制电压为0.01～3.0 V.2.1 纳米纤丝化纤维素的结构表征通过XRD和FTIR对按木浆原料和NFC进行晶体结构与化学结构的表征. 由图1(A)可见, 桉木浆和NFC均呈现典型的天然纤维素Iβ型结构, 在14.3°, 16.8°和22.5°出现了和(002)晶面的衍射峰. 可见纳米纤丝化处理并没有改变纤维素的晶型. 图1(B)中桉木浆和NFC的FTIR图均在3300～3450 cm-1附近和2910 cm-1附近出现强吸收峰, 归属于分子链上羟基O—H和C—O的伸缩振动; 1636 cm-1处的明显吸收峰来自于CO伸缩振动. 此外, 桉木浆和NFC在1430和1030 cm-1处均出现较明显的纤维素Iβ特征峰[20], 说明纳米精磨机械处理不会改变纤维素的化学结构.2.2 碳化处理与孔结构二次构建对气凝胶骨架结构的影响图2分别为NFCA、 CNFA及CNFA-A的SEM照片和相应的直径分布统计图(对200个纤维直径进行数值测量统计). 由图2(A)和(D)可见, NFCA的形貌均匀细长, 表面光滑, 平均直径为230.10 nm. 碳化后的CNFA直径大幅度减小, 平均直径为90.92 nm[图2(B), (E)]. 这是因为高温碳化过程中发生了脱氢脱氧, 其结构发生了重组[21]. 碳化孔道构建后的CNFA-A的纳米纤丝相互交错成网状结构, 较二次构建前的直径进一步减小[图2(C)及其插图], 统计分析显示其平均直径仅为53.16 nm[图2(F)].2.3 纤维素气凝胶的孔径分布与结构表征为进一步观察处理过程中气凝胶孔结构的变化, 采用N2吸附-脱附来分析材料孔道分布的微观结构. 如图3所示, 根据IUPAC气体吸附等温线的分类标准, NFCA,CNFA和CNFA-A的N2吸附-脱附等温线均属于IV型吸附曲线. 其中, 由NFC组装而成的NFCA的比表面积为111.69 m2/g, 总孔容为0.283 cm3/g. 由于纤维网络在热解过程中形成了大量孔隙, 高温热解后的碳纤维气凝胶的比表面积发生了显著提升, 但由于高温热解导致NFCA中部分介孔孔洞坍塌, 碳化后比表面积为423.77 m2/g, 总孔容为0.317 cm3/g. KOH辅助的高温二次构建后的CNFA-A 比表面积高达488.92 m2/g, 总孔容为0.404 cm3/g. 这是因为KOH高温下通过氧化还原反应腐蚀碳气凝胶网络结构, 在K渗入石墨层的过程中生成大量孔结构[22]. 通过非定域密度函数理论(NLDFT)分析[23], 孔结构二次构建后的CNFA-A增加了少量的微孔及部分介孔.通过Raman测试表征了CNFA及CNFA-A的石墨化程度. 图4(A)中出现了2个明显的峰, 一个是由C—C键的振动形成的D带(1335～1350cm-1), 对应样品的无序部分或有缺陷的石墨结构; 另一个峰是碳原子的sp2电子排布形成的G带(1585～1590 cm-1), 为样品石墨相的特征峰. ID/IG强度比可用于表征样品的石墨化程度[24,25]. CNFA-A的ID/IG值CNFA更高, 且G峰和D峰的半峰宽增加, 揭示了CNFA-A的石墨化程度更低, 无序缺陷结构更多. XRD谱[图4(B)]在2θ=25°处较宽的衍射峰也表明碳化后生成了无定形碳.2.4 纤维素碳气凝胶的锂电性能为了研究样品作为锂离子电池负极材料的电化学性能, 对CNFA-A进行了恒电流充放电测试. 图5(A)是CNFA-A的1～3次充放电循环的恒电流充放电曲线, 电流密度为1 A/g, 电压范围0.01～3.0 V(vs. Li+/Li). 第1次恒电流放电曲线在1.2 V处有1个放电平台, 首次的充、放电比容量分别为994和448 mA·h/g, 库仑效率为45%, 第1次充放电过程中产生不可逆容量的原因是材料表面的电解液与多孔碳气凝胶电极材料反应生成了固体电解质界面膜(SEI). SEI的形成消耗了部分锂离子, 使得首次充放电的不可逆容量增加, 降低了负极材料的库仑效率[26]. 随后的第2次和第3次的充放电循环过程中, 材料的充电比容量分别为437和423 mA·h/g, 变化不大, 说明材料性能稳定.锂离子电池负极材料的使用寿命是很重要的电化学性能指标. 图5(B)示出了材料的比容量和循环稳定性能, 测试在0.01～3.0 V的电位窗口、 1 A/g的电流密度下进行. 结果表明, 循环1000周后, CNFA的比容量为279 mA·h/g, CNFA-A的比容量达到409 mA·h/g, 且二者均具有良好的稳定性, 容量保持率均在80%以上. 由图5(C)可见, CNFA和CNFA-A均具有非常好的倍率性能. 同一电流密度下, 材料的比容量保持稳定; 随着电流密度的增加, 材料的比容量逐渐变小. CNFA-A在2, 5和10 A/g 3个不同电流密度下的比容量分别为416, 323和260 mA·h/g. CNFA在1 A/g电流密度下的比容量为310 mA·h/g, 经过倍率性能循环后, 电池的容量几乎未发生变化. 而CNFA-A在经过倍率循环后, 比容量同样未发生变化, 但倍率性能稍有衰减. 在电流密度为20 A/g时, CNFA-A电池的平均容量约为219 mA·h/g, 说明这种碳材料具备大电流快速充放电的潜力, 这得益于材料较大的比表面积及本身多层级的孔洞结构有利于增加与电解液的接触面积. 而微孔结构较多的热解碳材料会形成更加稳定的SEI膜[27], 从而避免了溶剂分子对电极材料的破坏, 因而此气凝胶作为电极材料具有优异的循环稳定性能.通过采用纳米精磨法对按木浆进行纤丝化处理, 制备出直径均一、高长径比的NFC(平均直径为230.10 nm). 将NFC组装成具有3D网络结构的气凝胶后进行高温碳化处理, 并在保留的碳气凝胶骨架结构上进行了孔道二次构建, 得到具有多层级孔道结构的高比表面积碳气凝胶. 其内部网络纤维的平均直径为53.16 nm, 比表面积高达488.92 m2/g. 该新型碳材料在被用作锂离子电池负极材料时表面出较高的容量、良好的循环稳定性及理想的倍率性能. 在电流密度为1 A/g下连续充放电1000次后比容量达到409 mA·h/g, 在电流密度高达20 A/g下比容量还能维持在219 mA·h/g.† Supported by the National Natural Science Foundation of China(No. 31500468) and the Fundamental Research Funds for the Central Non-profit Research Institution of CAF(No. CAFYBB2016QB012).【相关文献】[1] Arioli T., Peng L., Betzner A. S., Sci., 1998, 279(5351), 717—720[2] Zhu H., Luo W., Ciesielski P. N., Fang Z., Zhu J. Y., Henriksson G., Himmel M. E., Chem. Rev., 2016, 116(16), 9305—9374[3] Zhao H. P., Feng X. Q., Gao H., Appl. 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L., Esparza J. M., Campero A., Phys. Chem. Chem. Phys., 2003, 5(9), 1859—1866[24] Zhang B., Qin X., Li G. R., Gao X. P., Energy Environ. Sci., 2010, 3(10), 1531—1537[25] Wu Z. S., Ren W., Xu L., Li F., Cheng H. M., ACS Nano, 2011, 5(7), 5463—5471[26] Zhang K. L., Li X. N., Liang J., Zhu Y. C., Hu L., Cheng Q. S., Guo C., Lin N., Qian Y. T., Electrochimica Acta, 2015, 155, 174—182[27] Kong F., Kostecki R., Nadeau G., J. Power Sources, 2001, 97, 58—66。
基于MEMS技术的三维触觉感知阵列研究
基 于ＭＥ 技术 的三维触 觉感知阵列研 究 ＭＳ
王辉 静
（ 深圳信息职业技术学院计算机应用 系，广东 深圳 ５ ８２ １０９）
摘 要 ： 本 文 设 计 了一 种 基 于 ＭＥ 技 术 的 柔性 触 觉 感 知 阵 列 。 通 过 将 Ｍ ＭＳ 感 器 单 元 与 柔 性 基 板 相 结 合 ， 实 现 三维 ＭＳ Ｅ 传
板 厚ｈ ＝８ ［ ｎ ０ｔ ． ｍ
：
ｌ ＿０ ５： 一 ３ ２ ｎ ． ０．６ ７
１ ‘ 一
第６ 第２ 卷 期 ２０年６ ０ ８ 月
深圳信息 职业技 术学 院学报
Ｊ ｕｎ ｌ ｆ ｈ ｎ ｈ ｎＩ ｓｉ ｌ ｆ ｎｏｍａｉｎＴ ｃ ｎ ｌｇ ｏ ｒ ａ ｏ ｅ ｚ ｅ ｎ ｌｕｅｏ ｆｒ ｔ ｅ ｈ ｏｏ ｙ Ｓ ｔ Ｉ ｏ
．
Ｖｏ ． ２ Ｉ６ Ｎｏ．
Ｊｎ ２０ ｕ ．０ ８
取物体形状 、位置和姿态信息 、实现智能操作物体
提 供 了有效 的手段 。
１触觉感知阵列柔性化的实现
由于 ｉ维 力 触 觉 传 感 器 必 须 是 以刚 性 材 料 制
［ 收稿 日期】 ０ ８ ０ — ５ ２０ — ３ １
具体方案是以柔性电路板作为柔性基底，将分
离 的三维 力触 觉传 感 器焊 接在 柔性 电路 板上 。 由于
【 作者简介】 王辉静 （９ ６ ），女 （ １７ － 汉），河北石家庄市 人，讲师，Ｅ— ａｈ１ ｍｉ
维普资讯
深 圳 信 息 职 业 技 术 学 院学 报
第６ 卷
柔性 电路板 的柔性 特性 ，传感 器 阵列就 可 以实现柔
性 的要 求 ，同时 由于柔性 电路 板 的机械 强度 、引线
基于三维尺度不变特征的肺结节良恶性诊断
图像来挖掘，因此利用肺部CT序列图像的特点，提出三 维尺度不变特征点的选取方法。
(1)特征点的初步检测 在肺结节CT序列图像中,p"x#$)指点坐标， 指坐标系的3个维度，其中$指第$张CT图像，特征点的 尺度不变性可以通过将每个像素点与一个尺度可变的高斯 核函数卷积来实现，这样生成了病灶区域的尺
度空间L(x#,,)
Software , Shanxi Agricultural University & Jinzhong 030801 , China； 4. PET/CT Center , Shanxi Provincial People?s Hospital , Taiyuan 030024 , China)
Abstract： In the traditional method of benign and malignant diagnosis of pulmonary nodules& it is difficult to extract the nodular features with significant and discriminating characteristics & resulting in low diagnostic accuracy of nodules and high misdiagnosis rate.Adiagnosticmethodforbenignandmalignantpulmonarynodulesbasedonthree-dimensionalscaleinvariantfeatureswas thenproposed.Consideringthethree-dimensionalfeaturesandlocaldetailsofclinicalnodules &scaleinvariantfeaturepointsof bining3DSIFTdescriptorandgrayscalediferencecumulativehistogram&thescale invariantdescriptorofeachfeaturepointwasobtainedtofulycharacterizethelocaldetailsofthelesion.Thefeaturerepresentation of the nodule was calculated usingDFCM clustering algorithm and BoW model.SVM was trained to diagnose the benign and malignant nodules. Experimental results show that & the proposed method achieves excellent diagnostic results. Compared with themethodsindiferentliterature thismethodhasobviousadvantages and it is found that nodules with malignancy of3are moresimilartobenignnodules. Keywords： pulmonary nodules; sequence images； scale-invariant features； three-dimensional ； benign and malignant diagnosis
切换拓扑结构下多智能体系统的一致性研究
收稿日期：2021年7月13日，修回日期：2021年8月23日基金项目：国家自然科学基金项目（编号：61573230）资助。
作者简介：罗俊芝，女，博士，讲师，研究方向：导航、制导与控制。
詹环，女，硕士，讲师，研究方向：应用数学。
张雪飞，女，硕士，助教，研究方向：基础数学。
闵祥娟，女，硕士，副教授，研究方向：应用数学。
∗1引言多智能体系统（Multi-agent systems ）是指由大量局部相互作用的简单个体（称为Agent ）组成的复杂系统［1］。
多智能体系统有广泛的应用背景，其理论运用到了车辆编队、无人机协调飞行、物流供应链系统控制等实际问题。
尤其是随着科学技术的发展，多智能体系统的应用研究变得日益重要，近些年来成为控制界学者的关注的焦点［2~11］。
一致性控制问题是多智能体系统研究的重要方面，所谓一致性控制是指基于多智能体系统中个体之间有限的信息交换，设计一致性协议，使得所有智能体的某一个状态量或是所有状态量趋于相等，即使得智能体之间能够达到协调一致性，最终完成复杂任务。
如Wen G H ［2］针对具有无向连通拓扑结构的多智能体系统，假设每个Agent 的状态方程为连续线性模型，研究了系统的分布式一致性控制问题。
Liu S ［3］则针对有向拓扑结构的智能体系统，考虑了带有虚拟的Leader Agent 情形，设计了含有时滞的一致性控制协议，给出了多智能体系统的一致性控制的条件。
Zhang J ［4］利用滑模控制对非线性多智能体系统一致性控制问题进行了研究。
Li Z K 等［5］考虑了系统在有向拓扑结构下，分析了在带有界输入下的分布式一致性跟踪问题。
Shen Q K 等［6］研究了固定拓扑结构下的多智能体系统的自适应一致性控制问题。
注意到文献［2~6］研究中，智能体之间采用的是固定拓扑结构，但是在实际问题中，如车辆编队控制问题，车辆的相对位置关系可能随时间的演变发生变化，从而各智能体之间的拓扑结构相应也会切换拓扑结构下多智能体系统的一致性研究∗罗俊芝詹环张雪飞闵祥娟（陆军装甲兵学院基础部北京100072）摘要针对一类多智能体系统，研究了系统在切换拓扑结构下的一致性控制问题。
基于空洞卷积与多尺度特征融合的室内场景单图像分段平面三维重建
传感技术学报CHINESE JOURNAL OF SENSORS AND ACTUATORS Vol.34No.3 Mar.2021第34卷第3期2021年3月Piecewise Planar3D Reconstruction for Indoor Scenes from a Single Image Based on Atrous Convolution and Multi-Scale Features Fusion*SUN Keqiang,MIAO Jun*9JIANG Ruixiang,HUANG Shizhong,ZHANG Guimei (Computer Vision Institute of Nanchang Hongkong University,Nanchang Jiangxi33Q063f China)Abstract:It is hard for pixel-level and regional-level3D reconstruction algorithms to recover details of indoor scenes due to luminous changes and lack of texture.A piecewise planar3D reconstruction method is proposed based on the convolution residual connection of the holes and the multi-scale feature fusion network.This model uses the shallow high-resolution detail features generated by the ResNet-101network with the added hole convolution to reduce the loss impact of spatial information as network structure deepens on the detail reconstruction,so that this model can learn more abundant features and by coupling positioning accuracy optimized by the fiilly connected conditional random field(CRF)with the recognition ability of deep convolutional neural network,which keeps better boundary smoothness and details・Experimental results show that the proposed method is robust to the plane prediction of indoor scenes with complex backgrounds,the plane segmentation results are accurate,and the depth prediction accuracy can reach92.27%on average.Key words:3D reconstruction of indoor scene；deep convolutional neural network;conditional random field;atrous convolution；multi-scale feature fusionEEACC:6135；6135E doi:10.3969/j.issn.l004-1699.2021.03.012基于空洞卷积与多尺度特征融合的室内场景单图像分段平面三维重建*孙克强，缪君*,江瑞祥，黄仕中，张桂梅(南昌航空大学计算机视觉研究所，江西南昌330063)摘要:受光照变化和纹理缺乏等因素的影响，基于单幅室内场景图像的像素级和区域级三维重建算法很难恢复场景结构细节。
基于连续顶点分区的混凝土3D打印路径规划算法
基于连续顶点分区的混凝土3D打印路径规划算法
崔衡;马宗方;宋琳;刘超;韩怡萱
【期刊名称】《工程设计学报》
【年(卷),期】2024(31)3
【摘要】针对混凝土3D打印构件成形质量差和打印时间长的问题,提出了一种基于连续顶点分区的路径规划算法。
首先,采用基于哈密顿回路的连续顶点分区方法,将打印区域划分为多个连续的区域,以确保在打印过程中打印喷头不会多次经过同一顶点,从而避免了重复打印和成形质量差的问题。
然后,使用遗传算法搜索每个区域,通过迭代和优化来确定最短的打印路径。
实验结果表明,与其他路径规划算法相比,所提出的算法能够显著减少打印喷头的空行程和启停次数,且缩短打印时间10%以上,有效地提升了混凝土构件的成形质量与打印效率。
基于连续顶点分区的混凝土3D打印路径规划算法通过有效划分打印区域、智能搜索最短路径以及合并优化路径的方式,解决了混凝土3D打印构件成形质量差和打印时间长的问题,这可为混凝土3D打印技术的发展和应用提供有力的技术支持。
【总页数】9页(P271-279)
【作者】崔衡;马宗方;宋琳;刘超;韩怡萱
【作者单位】西安建筑科技大学信息与控制工程学院
【正文语种】中文
【中图分类】TP3-05
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2.碳纤维长纤3D打印的连续性路径规划算法
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4.基于蚁群的环境分区目标偏置RRT算法路径规划
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减反结构 综述
highlights
• Colloidal self-assembly enables selfcleaning broadband anti-reflection (AR) coatings.
• Bioinspired moth-eye AR coatings show much better AR performance than quarter-wavelength AR coatings.
1.1. Quarter-wavelength AR coatings
The antireflection performance of traditional quarterwavelength AR coatings depends on both the coating thickness and the refractive index of the material. Carefully controlling both
1.1.1. Vacuum deposition of AR coatings Some of the most popular vacuum-based technologies for
generating AR coatings include plasma-enhanced chemical vapor deposition (PECVD) [13–19], electron-beam (E-beam) evaporation [20–22], and sputtering [23,24]. For crystalline silicon substrates, which have been widely used in fabricating solar cells, the typical AR coatings are quarter-wavelength titanium dioxide (TiO2) and silicon nitride (SiNx) films [25]. Silicon has a high refractive index of ∼3.5 [26], therefore when light travels from air to a silicon substrate, the amount of light reflected will be about 30% from each air/silicon interface. This could significantly impact the conversion efficiencies of crystalline silicon solar cells as an ideal solar cell should adsorb all useful photons. Therefore it is essential to utilize AR coatings to maximize the amount of light adsorbed by a solar cell [27].
高分子论文参考文献
Published:May 12,2011COMMUNICATION /JACSInterface-Directed Assembly of One-Dimensional Ordered Architecture from Quantum Dots Guest and Polymer HostShengyang Yang,Cai-Feng Wang,and Su Chen*State Key Laboratory of Materials-Oriented Chemical Engineering,and College of Chemistry and Chemical Engineering,Nanjing University of Technology,Nanjing 210009,P.R.ChinabSupporting Information ABSTRACT:Assembly of inorganic semiconductor nano-crystals into polymer host is of great scienti fic and techno-logical interest for bottom-up fabrication of functional devices.Herein,an interface-directed synthetic pathway to polymer-encapsulated CdTe quantum dots (QDs)has been developed.The resulting nanohybrids have a highly uniform fibrous architecture with tunable diameters (ranging from several tens of nanometers to microscale)and enhanced optical performance.This interfacial assembly strategy o ffers a versatile route to incorporate QDs into a polymer host,forming uniform one-dimensional nanomaterials po-tentially useful in optoelectronic applications.Similar to the way that atoms bond to form molecules and complexes,inorganic nanoparticles (NPs)can be combined to form larger ensembles with multidimensional ordered hier-archical architecture,evoking new collective functions.To this end,the development of the controlled self-assembly method for well-de fined structures of these ensembles is signi ficant for creating new and high-performance tunable materials and hence has aroused appealing scienti fic and industrial interest.1Particu-larly,much e ffort has been devoted to the construction of one-dimensional (1D)structures of NPs,owing in part to their application as pivotal building blocks in fabricating a new generation of optoelectronic devices.2In this context,directed host Àguest assembly of NPs into polymer matrices is an e ffective “bottom-up ”route to form 1D ordered functional materials with advantageous optical,electrical,magnetic,and mechanical properties.3Some typical routes have been developed for the generation of these 1D hybrids so far,involving template-assisted,4seeding,5and electro-static approaches.6However,the challenge still remains to precisely manipulate assembly of aqueous NPs and water-insoluble polymers into uniform 1D nanocomposites with a high aspect ratio because of phase separation and aggregation.7Moreover,facile synthetic strate-gies are highly needed to fabricate homogeneous 1D composites in which each component still preserves favorable properties to produce optimal and ideal multifunctional materials.A liquid Àliquid interface o ffers an ideal platform to e fficiently organize NPs into ordered nanostructures driven by a minimiza-tion of interfacial energy.8While much of this research has been directed toward NP hybrids with diverse morphologies based on small organic ligand-directed assembly,9some success has also been achieved in polymer-based NPs nanocomposites.10Russelland co-workers developed ultrathin membranes and capsules of quantum dots (QDs)stabilized by cross-linked polymers at the toluene/water interface.10a,11Brinker ’s group reported the fab-rication of free-standing,patternable NP/polymer monolayer arrays via interfacial NP assembly in a polymeric photoresist.12Herein,a simple host Àguest assembly route is developed to facilely create homogeneous 1D CdTe/polymer hybrids without any indication of phase separation at the aqueous/organic inter-face for the first time.The CdTe nanocrystal is a semiconductor that has been used extensively for making thin film for solar cells.13Some elegant studies have been made in synthesizing pure inorganic 1D CdTe nanowires via assembly from corre-sponding individual CdTe nanocrystals.14In this work,CdTe QDs are covalently grafted with poly(N -vinylcarbazole-co -glycidylmethacrylate)(PVK-co -PGMA)to form uniform fibrous fluorescent composites at the water/chloroform interface via the reaction between epoxy groups of PVK-co -PGMA and carboxyl groups on the surface of CdTe QDs (Scheme 1).15These 1D composite fibers can be allowed to grow further in the radial direction by “side-to-side ”assembly.Additionally,this type of interfacial QD Àpolymer assembly can observably improve the fluorescence lifetime of semiconductor QDs incorporated in theScheme 1.Schematic Representation of the Synthesis of PVK-co -PGMA/CdTe QDs Composite Nano fibersReceived:February 8,2011polymeric matrix.It can be expected that this example of both linear axial organization and radial assembly methodology can be applied to fabricate spatial multiscale organic Àinorganic com-posites with desired properties of NPs and polymers.Figure 1a shows a typical scanning electron microscope (SEM)image of PVK-co -PGMA/CdTe QDs composite nano fi-bers obtained at the water/chloroform interface after dialysis.The as-prepared fibers have uniform diameters of about 250nm and typical lengths in the range of several tens to several hundreds of micrometers (Figures 1a and S4Supporting In-formation [SI]).Interestingly,PVK-co -PGMA/CdTe composite fibers can randomly assemble into nestlike ring-shaped patterns (Figures 1b and S5[SI]).Given the interaction among epoxy groups,the formation of nestlike microstructures could be attributed to incidental “head-to-tail ”assembly of composite fibers.Moreover,in order to establish the relationship between the role of epoxy groups and the formation of composite nano fibers,control experiments were performed,in which pure PGMA or PVK was used to couple CdTe QDs.The PGMA/CdTe composites could be obtained with fibrous patterns (Figure S6[SI]),but no fibrous composites were achieved at the biphase interface with the use of PVK under the same conditions.The microstructures and fluorescence properties of PVK-co -PGMA/CdTe composite fibers were further character-ized using laser confocal fluorescence microscopy (LCFM).Confocal fluorescence micrographs of composite fibers show that the di fferently sized QDs have no obvious in fluence on the morphology of composites (Figure 1c Àe).Clearly,uniform and strong fluorescence emission is seen throughout all the samples,and the size-dependent fluorescence trait of CdTe QDs in PVK-co -PGMA matrix remains well.In order to verify the existence and distribution of CdTe QDs in the fibers,transmission electron microscopy (TEM)was employed to examine the assembled structures.Figure 2a shows a TEM image of PVK-co -PGMA/CdTe QDs composite nano fi-bers,indicating each composite fiber shown in Figure 1a was assembled from tens of fine nano fibers.An individual fine nano fiber with the diameter of about 30nm is displayed in Figure 2b,from which we can see that CdTe QDs have been well anchored into the fiber with polymeric protection layer,revealing this graft-form process at the interface e ffectively avoidednon-uniform aggregation in view of well-dispersed CdTe QDs within the composite fiber,consistent with the LCFM observa-tion.Unlike previous works where the nanoparticles were ad-sorbed onto the polymer fibers,16CdTe QDs were expelled from the surface of fibers (∼2.5nm)in our system (Figure 2c),albeit the high percentage of QDs in the polymer host (23wt %)was achieved (Figure S7[SI]).This peculiarity undoubtedly confers CdTe QDs with improved stability.The clear di ffuse rings in the selected area electron di ffraction (SAED)pattern further indicate excellent monodispersion and finely preserved crystalline struc-ture of QDs in the nano fibers (Figure 2d).The SAED data correspond to the cubic zinc blende structure of CdTe QDs.A possible mechanism for the assembly of 1D nanostructure was proposed,as illustrated in Figure S8[SI].The hydrophilic epoxy groups of the PVK-co -PGMA chain in the oil phase orient toward the biphase interface and then react with carboxyl groups on the surface of CdTe QDs in the aqueous phase to a fford premier PVK-co -PGMA/CdTe QDs composites.Such nanocomposites will reverse repeatedly,resulting from iterative reaccumulation of epoxy groups at the interface and the reaction between the active pieces (i.e.,epoxy or carboxyl groups)in the composites with intact CdTe QDs or PVK-co -PGMA,forming well-de fined nano-fibers.The control experiments showing that the diameter of composite fibers increases with the increase in the concentration of PVK-co -PGMA are in agreement with the proposed mechan-ism (Figure S9[SI]).In addition,it is expected that the pure polymeric layer on the surface of the fibers (red rectangular zone in Figure 2c)will allow further assembly of fine fibers into thick fibers,and these fibers also could randomly evolve into rings,forming nestlike microstructures when the “head ”and “tail ”of fibers accidentally meet (Figure 1b).To further examine the assembly behavior of composite fibers,the sample of PVK-co -PGMA/CdTe QDs composite nano fibers were kept at the water/chloroform interface for an additional month in a close spawn bottle at room temperature (Figure S10[SI]).With longer time for assembly,thicker composite fibers with tens of micrometers in diameter were obtained (Figure 3a).These micro-fibers have a propensityto form twisted morphology (Figure 3a,b),Figure 1.(a,b)SEM images of PVK-co -PGMA/CdTe QDs composite nano fibers.(c Àe)Fluorescence confocal microscopy images of PVK-co -PGMA/CdTe QDs composite nano fibers in the presence of di fferently sized QDs:(c)2.5nm,(d)3.3nm,and (e)3.6nm.The excitation wavelengths are 488(c),514(d),and 543nm (e),respectively.Figure 2.(a,b)TEM images of PVK-co -PGMA/CdTe QDs composite nano fibers,revealing composite nano fiber assemblies.(c)HRTEM image and (d)SAED pattern of corresponding PVK-co -PGMA/CdTe QDs composite nano fibers.while their re fined nanostructures still reveal relatively parallel character and con firm the micro fibers are assembled from countless corresponding nano fibers (Figure 3c).The corresponding LCFM image of an individual micro fiber is shown in Figure 3d (λex =488nm),indicating strong and homogeneous green fluorescence.Another indication is the fluorescent performance of PVK-co -PGMA/CdTe QDs composite micro fibers (Figure 4a).The fluorescent spectrum of composite fibers takes on emission of both PVK-co -PGMA and CdTe QDs,which suggests that this interfacial assembly route is e ffective in integrating the properties of organic polymer and inorganic nanoparticles.It is worth noting that there is a blue-shift (from 550to 525nm)and broadening of the emission peak for CdTe QDs upon their incorporation into polymeric hosts,which might be ascribed to the smaller QD size and less homogeneous QD size distribution resulting from the photooxidation of QD surfaces.17Since the emission spectra of PVK-co -PGMA spectrally overlap with the CdTe QD absorption (Figure S11[SI]),energy transfer from the copolymer to the CdTe QDs should exist.18However,the photoluminescence of PVK-co -PGMA does not vanish greatly in the tested sample in comparison with that of polymer alone,revealing inferior energy transfer between the polymer host and the QDs.Although e fficient energy transfer could lead to hybrid materials that bring together the properties of all ingredients,18it is a great hurdle to combine and keep the intrinsic features of all constituents.19In addition,by changing the polymeric compo-nent and tailoring the element and size of QDs,it should be possible to expect the integration of organic and inorganic materials with optimum coupling in this route for optoelectronic applications.Finally,to assess the stability of CdTe QDs in the composite micro fibers,time-resolved photoluminescence was performed using time-correlated single-photon counting (TCSPC)parative TCSPC studies for hybrid PVK-co -PGMA/CdTe QDs fibers and isolated CdTe QDs in the solid state are presented in Figure 4b.We can see that the presence of PVK-co -PGMA remarkably prolongs the fluorescence lifetime (τ)of CdTe QDs.Decay traces for the samples were well fittedwith biexponential function Y (t )based on nonlinear least-squares,using the following expression.20Y ðt Þ¼R 1exp ðÀt =τ1ÞþR 2exp ðÀt =τ2Þð1Þwhere R 1,R 2are fractional contributions of time-resolved decaylifetimes τ1,τ2and the average lifetime τhcould be concluded from the eq 2:τ¼R 1τ21þR 2τ22R 1τ1þR 2τ2ð2ÞFor PVK-co -PGMA/CdTe QDs system,τh is 10.03ns,which is approximately 2.7times that of isolated CdTe QDs (3.73ns).Photooxidation of CdTe QDs during the assembly process can increase the surface states of QDs,causing a delayed emission upon the carrier recombination.21Also,the polymer host in this system could prevent the aggregation of QDs,avoid self-quench-ing,and delay the fluorescence decay process.22The increased fluorescence lifetime could be also ascribed to energy transfer from PVK-co -PGMA to CdTe QDs.18c The result suggests that this host Àguest assembly at the interface could find signi ficant use in the fabrication of QDs/polymer hybrid optoelectronic devices.In summary,we have described the first example of liquid/liquid interfacial assembly of 1D ordered architecture with the incorporation of the QDs guest into the polymer host.The resulting nanohybrids show a highly uniform fibrous architecture with tunable diameter ranging from nanoscale to microscale.The procedure not only realizes the coexistence of favorable properties of both components but also enables the fluorescence lifetime of QDs to be enhanced.This interesting development might find potential application for optoelectronic and sensor devices due to high uniformity of the 1D structure.Further e fforts paid on optimal regulation of QDs and polymer composition into 1D hybrid nanostructure could hold promise for the integration of desirable properties of organic and inorganic compositions for versatile dimension-dependent applications.In addition,this facile approach can be easily applied to various semiconductor QDs and even metal NPs to develop highly functional 1D nanocomposites.’ASSOCIATED CONTENTbSupporting Information.Experimental details,FT-IR,GPC,UV Àvis,PL,SEM,TGA analysis,and complete ref 9c.This material is available free ofcharge via the Internet at .Figure 3.(a,b)SEM and (c)FESEM images of PVK-co -PGMA/CdTe QDs composite micro fibers.(d)Fluorescence confocal microscopy images of PVK-co -PGMA/CdTe QDs composite micro fibers inthe presence of green-emitting QDs (2.5nm).Figure 4.(a)Fluorescence spectra of PVK-co -PGMA,CdTe QD aqueous solution,and PVK-co -PGMA/CdTe QDs composite micro-fibers.(b)Time-resolved fluorescence decay curves of CdTe QDs (2.5nm diameter)powders (black curve)and the corresponding PVK-co -PGMA/CdTe QDs composite micro fibers (green curve)mea-sured at an emission peak maxima of 550nm.The samples were excited at 410nm.Biexponential decay function was used for satisfactory fitting in two cases (χ2<1.1).’AUTHOR INFORMATIONCorresponding Authorchensu@’ACKNOWLEDGMENTThis work was supported by the National Natural Science Foundation of China(21076103and21006046),National Natural Science Foundation of China-NSAF(10976012),the Natural Science Foundations for Jiangsu Higher Education Institutions of China(07KJA53009,09KJB530005and10KJB5 30006),and the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD).’REFERENCES(1)(a)Kashiwagi,T.;Du,F.;Douglas,J.F.;Winey,K.I.;Harris, R.H.;Shields,J.R.Nat.Mater.2005,4,928.(b)Shenhar,R.;Norsten, T.B.;Rotello,V.M.Adv.Mater.2005,17,657.(c)Akcora,P.;Liu,H.; Kumar,S.K.;Moll,J.;Li,Y.;Benicewicz,B.C.;Schadler,L.S.;Acehan, D.;Panagiotopoulos,A.Z.;Pryamitsyn,V.;Ganesan,V.;Ilavsky,J.; Thiyagarajan,P.;Colby,R.H.;Douglas,J.F.Nat.Mater.2009,8,354.(d)Dayal,S.;Kopidakis,N.;Olson,D.C.;Ginley,D.S.;Rumbles,G. 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α-MnO2
Journal of Solid State Chemistry 179(2006)1757–1761A simple method of fabricating large-area a -MnO 2nanowires and nanorodsYi Liu a,b ,Meng Zhang a ,Junhao Zhang a ,Yitai Qian a,ÃaHefei National Laboratory for Physical Sciences at Microscale,Department of Chemistry,University of Science &Technology of China,Hefei 230026,PR ChinabDepartment of Chemistry,Zaozhuang University,Zaozhuang 277100,PR ChinaReceived 20December 2005;received in revised form 14February 2006;accepted 17February 2006Available online 6March 2006Abstracta -MnO 2nanowires or nanorods have been selectively synthesized via the hydrothermal method in nitric acid condition.The a -MnO 2nanowires hold with average diameter of 50nm and lengths ranging between 10and 40m m,using MnSO 4ÁH 2O as manganese source;meanwhile,a -MnO 2bifurcate nanorods with average diameter of 100nm were obtained by adopting MnCO 3as starting material.The morphology of a -MnO 2bifurcate nanorods is the first one to be reported in this paper.X-ray powder diffraction (XRD),field scanning electron microscopy (FESEM),transmission electron microscopy (TEM),selected area electron diffraction (SAED)and high-resolution transmission electron microscopy (HRTEM)were used to characterize the products.Experimental results indicate that the concentrated nitric acid plays a crucial role in the phase purity and morphologies of the products.The possible formation mechanism of a -MnO 2nanowires and nanorods has been discussed.r 2006Elsevier Inc.All rights reserved.Keywords:a -MnO 2;Nanowires and nanorods;Hydrothermal reaction;X-ray powder diffraction (XRD);Field scanning electron microscopy (FESEM);Transmission electron microscope (TEM);Selected area electron diffraction (SAED);High-resolution transmission electron microscope (HRTEM)1.IntroductionIn the past few years,controlling the shape of nanostructures at the mesoscopic level is one of challenging issues presently faced by material scientists [1].Nanowires and nanorods,which are one-dimensional (1-D)objects,have stimulated great interest among synthetic material operators due to their peculiar properties and potential application [2–9].Several techniques for the preparation of nanowires or nanorods have been reported,such as the solid–vapor process [2],laser ablation [3],arc discharge [4],electrochemical techniques [5],virus-templating [6],exfo-liating method [7,8],and hydrothermal method [9].As a popular inorganic-function material,manganese dioxide and derivative compound have attracted special attention and been widely used not only as catalysts,molecular sieves[10,11],but also as promising candidate materials for cathodes in lithium ion batteries [12–15].Generally speak-ing,a -and g -MnO 2can be converted by electrochemical Li +intercalation into cubic spinel,Li 1Àx Mn 2O 4,which has channels through which Li +can move [13,14].Recently,many efforts have been focused on preparing manganese oxide 1-D nanostructures,and their synthesis methods are generally based on the redox reactions of MnO 4Àand/orMn 2+[16–23].For example:Y.D.Li et al.[20,21]reported a selected-control low-temperature hydrothermal method of synthesizing 1-D MnO 2nanostructure through theoxidation of Mn 2+by S 2O 82À,MnO 4Àor ClOÀwithout any existence of catalysts or templates;Z.Q.Li et al.[22]provided a simple room-temperature solution-based cata-lytic route to fabricate a novel hierarchical structure of a -MnO 2core-shell spheres with spherically aligned nanor-ods on a large scale.The previous experimental results indicated that a -MnO 2tended to form in acidic conditions,the pH of solution had crucial effect on the formation of 1-D nanostructural a -MnO 2[23].The influence of the/locate/jssc0022-4596/$-see front matter r 2006Elsevier Inc.All rights reserved.doi:10.1016/j.jssc.2006.02.028ÃCorresponding author.Fax:+865513607402.E-mail addresses:liuyi67@ (Y.Liu),ytqian@ (Y.Qian).anion on growth of the products had been investigated by Kijima et al.[19],and their results showed that a -MnO 2could be prepared in concentrated H 2SO 4rather than HCl or HNO 3.Thus far,the synthesis of a -MnO 2nanowires or nanorods has seldom been reported under concentrated nitric acidic conditions.Here we report a novel,large-area synthesis method for obtaining nanowires and nanorods with uniform sizes.The a -MnO 2nanowires have average diameter of 50nm and lengths of 10–40m m,using MnSO 4ÁH 2O as manganese source;meanwhile,a -MnO 2bifurcate nanorods with average diameter of 100nm were obtained by adopting MnCO 3as starting material.In our presentation,we choose concentrated nitric acid as acid source to tune the pH of the system.Our experiments show that pure-phase a -MnO 2can be readily obtained in a wide range of nitric acid concentrations.This result may be a useful comple-mentarity to previous experimental results that a -MnO 2could be only produced in H 2SO 4surroundings.2.Experimental procedureAll the reagents of analytical grade were purchased from Shanghai Chemical Reagent Company and used without further purification.In a typical procedure,1mmol MnSO 4ÁH 2O or MnCO 3and 2mmol KClO 3powders were successively put into a beaker with 15mL concen-trated nitric acid,the solution was magnetically stirred for 20min at 801C to form brown colloid.The slurry solution was transferred into a 50mL stainless-steel autoclave with a Teflon-liner,the beaker was washed with 25–30mL distilled water,and washing solution was put into above-mentioned Teflon-liner.The autoclave was sealed and maintained at 1201C for 12h,then air cooled to room temperature.The brown products were filtered off,washed several times with distilled water and absolute ethanol,and then dried in vacuum at 801C for 1h.The X-ray powder diffraction (XRD)pattern of the as-prepared samples was determined using a Philips X’Pert PRO SUPER X-ray diffractometer equipped with graphitemonochromatized Cu K a radiation (l ¼1:541874A)in the 2y ranging from 101to 701.The morphology and size of the final products were determined by field scanning electron microscopy (FESEM)images,taken with JEOL-6700F scanning electronic microanalyzer.Transmission electron microscope (TEM)image and selected area electrondiffraction (SAED)pattern,which were characterized by Hitachi H-800TEM with a tungsten filament and an accelerating voltage of 200kV.High-resolution transmis-sion electron microscope (HRTEM)image was recorded on a JEOL 2010microscope.The samples used for TEM and HRTEM characterization were dispersed in absolute ethanol and were ultrasonicated before observation.3.Results and discussionThe synthesis of a -MnO 2nanowires and nanorods is based on the hydrothermal method in a strong acidic (nitric acid)circumstance.The experimental results by using nitric acid as acidification agent,different manganese sources,and KClO 3as the oxidizer are summarized in Table 1.Under our experimental conditions,the different size and morphological products can be obtained by varying the concentration of nitric acid.From this table we can see that only under concentrated nitric acid condition pure a -MnO 2can be obtained.The volume of concentrated nitric acid can be in the range of 3–20mL.The yields and morphology change greatly when different amounts of nitric acid were introduced.We found that the most optimal conditions of obtaining uniform a -MnO 2nanowires were fixed on 15mL concentrated nitric acid and reaction temperature of 1201C.Moreover,when different Mn compounds were selected as starting materi-als,the size and morphologies can be changed greatly,as shown in the lines 1and 4of Table 1.The result of experiments clearly indicates concentrated nitric acid plays a crucial role in the formation of a -MnO 2with 1-D structure.The phase and purity of the products were firstly examined by XRD.Fig.1shows a typical XRD pattern of the as-synthesized samples at 1201C for 12h,all the reflection peaks can be readily indexed to body-centered tetragonal a -MnO 2phase (space group I 4/m ),with latticeconstants of a ¼9:816A,and c ¼2:853A,which are in agreement with the standard values (JCPDS 72-1982,a ¼9:815A;c ¼2:847A Þ.No other phase was detected in Fig.1indicating the high purity of the final products.The morphologies and structure information were further obtained from FESEM,TEM and SAED.Fig.2provides FESEM images of the as-prepared a -MnO 2single-crystal nanowires.Figs.2(a)and (b)are the low-and high-magnification FESEM images of the as-prepared a -MnO 2Table 1Summary of the results on the products obtained under different manganese sources,the content of concentrated nitric acid and reaction temperature for 12h,using KClO 3as the oxidizer Sample no.Manganese source Concentrated nitric acid (mL)Reaction temperature (1C)Product morphology 1MnSO 4ÁH 2O 15120a -MnO 2nanowires 2MnSO 4ÁH 2O 0120Nonexistence of MnO 23MnSO 4ÁH 2O 0180Minor b -MnO 24MnCO 315120Flowery a -MnO 2nanorods 5MnCO 3120Nonexistence of MnO 2Y.Liu et al./Journal of Solid State Chemistry 179(2006)1757–17611758single-crystal nanowires when MnSO 4ÁH 2O served as manganese source.These images show that the products of a -MnO 2consisted of a large quantity of uniform nanowires,with diameters of 50nm and lengths up to several hundreds of micrometers.Fig.3(a)shows the TEM image of as-prepared a -MnO 2nanowires,and the TEM images further demonstrate that the obtained product has a uniform wire-like morphology.The results reveal the product of a -MnO 2was composed of nanowires.The diameters and lengths of nanowires were consistent with(541)(002)(521)(600)(411)(510)(321)(301)(420)(330)(211)(400)(310)(220)(101)(200)(110)i n t e n s i t y2θ/degreeFig.1.Typical XRD pattern of as-prepared a -MnO 2.Fig.2.Low-magnification FESEM image (a)and high-magnification FESEM image (b)of a -MnO 2nanowires (MnSO 4ÁH 2O as manganesesource).Fig.3.TEM images of as-prepared single-crystal a -MnO 2nanowires (a),TEM image (b),SAED pattern (c)and HRTEM image (d)of the single a -MnO 2nanowire.Y.Liu et al./Journal of Solid State Chemistry 179(2006)1757–17611759those of FESEM results.The TEM image (Fig.3(b))of representative single nanowires and HRTEM observation for individual nanowire provide additional insight into the structure of a -MnO 2with MnSO 4ÁH 2O as manganese source.The typical SAED pattern of the single a -MnO 2nanowire is shown in the inset of Fig.3(c).Fig.3(d)is the HRTEM image taken from the single a -MnO 2nanowire,which shows the clearly resolved lattice fringes.Theseparated spacings of 2.73and 3.12Acorrespond to ð101Þand (310)planar of a -MnO 2,respectively.This image clearly reveals that the as-synthesized nanowire has no defect of dislocation and further substantiates that the nanowires are single crystalline,which is consistent with the SAED pattern.According to HRTEM image and SAED pattern recorded on the single a -MnO 2nanowire,the deduced growth direction of nanowire is ½101 .If MnCO 3was introduced into the reaction system,the products are mainly composed of nanorods,as revealed by the corresponding FESEM images.Figs.4(a)and (b)are the low-and high-magnification FESEM images of the as-prepared a -MnO 2nanorods with MnCO 3as manganese source.The low-magnification FESEM image (Fig.4(a))reveals that the product of a -MnO 2is consisted of a large quantity of flowery nanorods with average diameter of 100nm.Fig.4(b)is the high-magnification FESEM image of the as-prepared a -MnO 2,in which we seem to observe obvious features of bifurcate rod-like structure.It is worth to note that the morphology of a -MnO 2bifurcate nanorods has never been reported paring Figs.4(a)and (b)to Figs.2(a)and (b),it can be found that the nanowires with MnSO 4ÁH 2O as manganese source are much slenderer than the bifurcate nanorods with MnCO 3as manganese source.Generally,pH is believed to have great impact on the crystal forms of final products [17,19,24,25].In our experiment,a series of hydrothermal synthesis were carried out in a wide range of acidity with pH value less than 7,we found that the final products to be a -MnO 2nanowires or nanorods with 1-D morphology whether MnSO 4ÁH 2O or MnCO 3as manganese source.Therefore,this method is very effective for the large-scale synthesis of a -MnO 2with 1-D nanostructures.The influence of the reaction time on the growth of the nanowires and nanorods was investigated.The correspond-ing samples were tested by FESEM.Fig.5shows FESEM images of the as-obtained samples measured (a)after 0.5h,(b)after 3h,(c)after 6h,(d)after 12h,and other conditions kept constant at the same time.Thereinto,Figs.5(a)–(d)are FESEM images of the products with MnSO 4ÁH 2O as manganese source.As can be seen,the reaction lasted for 0.5h;the products were composed of aggregated particles (see Fig.5(a)).When the reaction timeFig.4.Low-magnification FESEM image (a)and high-magnification FESEM image (b)of a -MnO 2nanorods (MnCO 3as manganesesource).Fig.5.The FESEM images of products obtained by heating in the acidic solution for various reaction times,MnSO 4ÁH 2O (a–d)as manganese source:(a)0.5h,(b)3h,(c)6h,(d)12h and MnCO 3(e–h)as manganese source:(e)0.5h,(f)3h,(g)6h,(h)12h.Y.Liu et al./Journal of Solid State Chemistry 179(2006)1757–17611760prolonged to3h,on the surfaces of these particles,lamellar structures appeared,and some of these lamellar split to tiny nanowires,indicating the beginning of the formation of a-MnO2nanowires(see Fig.5(b)).This process continued and more nanowires formed after6h(see Fig.5(c)).Until the reaction time was extended to12h,most of the products are nanowires with average diameter of50nm and lengths ranging between10and40m m,as shown in Fig.5(d).Further elongating the reaction time shows little effects on the size and phase-purity of the products. This growth process is similar to the results of C.Z.Wu et al.[26],we call this a‘‘rolling-broken-growth’’process. According to above results and previous research [20,21,27],the possible formation mechanism of a-MnO2 nanowires by adopting MnSO4ÁH2O as manganese source could be explained as follows:(1)when temperature was maintained at801C,the interaction of KClO3and manganese source with Mn2+ion happened only when concentrated nitric acid exists.In the synthetic process,a large number of the MnO2colloidal particles had been formed in concentrated nitric acid before hydrothermal operation.(2)Under hydrothermal conditions,owing to the absence of surfactants,the MnO2colloidal particles are prone to aggregate and form bigger particles.(3)The surface of aggregated big particles grows gradually into sheets of a-MnO2with lamellar structure through an elevated temperature and pressure,and then these sheets of a-MnO2will curl by extending reaction time to form a-MnO21-D nanostructres.(4)Much evidence has demonstrated that the lamellar structure had a strong tendency to form1-D nanostructures[20,27].The structure of a-MnO2comprises a macromolecular lamellar net with octahedral[MnO6]units coordinated Mn and O atoms [20],which can give rise to formation of1-D nanostruc-tures.As the layer structure of a-MnO2is in a metastable state,these sheets of a-MnO2with lamellar structure split into nanowires.(5)Anisotropic nature of crystal growth makes thefinal products turn into a large number of uniform a-MnO2nanowires.Moreover,we found when MnCO3serves as manganese source,a similar growth procedure was observed,as shown in Figs.5(e)–(h).We believe this a-MnO21-D nanostructural formation process is universal despite different manganese sources were involved in the hydrothermal process.This observation may spread to other nanomaterials synthesis.The above mechanism is in good agreement with our experiment results.4.ConclusionIn summary,a-MnO2nanowires and nanorods with a uniform diameter have been successfully synthesized on a large scale via a simple nitric-acid-assisted hydrothermal process at low temperature.It belongs tofirstly report that the morphology of a-MnO2bifurcate nanorods can be acquired when MnCO3serves as manganese source.The concentrated nitric acid plays a crucial role in the formation of a-MnO2nanowires and nanorods.This experimental result is different from the previous conclu-sion that the concentrated nitric acid seems to be an unfavorable condition to form a-MnO2.This observation may be expanded to synthesize other nanomaterials. AcknowledgmentsFinancial support from the National Natural Science Foundation of China and the973Project of China is greatly appreciated.References[1]A.P.Alivisatos,Science271(1996)933.[2]Y.Wu,P.Yang,Chem.Mater.12(2000)605.[3](a) A.M.Morales,C.M.Lieber,Science279(1998)208;(b)M.S.Gudiken,C.M.Lieber,J.Am.Chem.Soc.122(2000)8801.[4](a)S.Iijima,Nature354(1991)56;(b)T.Seeger,P.Kohler-Redlich,M.Ruhle,Adv.Mater.12(2000)279.[5]Y.Zhou,S.H.Yu,X.P.Cui,C.Y.Wang,Z.Y.Chen,Chem.Mater.11(1999)545.[6]C.Mao,D.J.Solis,B.D.Reiss,S.T.Kottmann,R.Y.Sweeney,A.Hayhurst,G.Georgiou,B.Iverson,A.M.Belcher,Science303(2004) 213.[7]G.H.Du,L.-M.Peng,Q.Chen,S.Zhang,W.Z.Zhou,Appl.Phys.Lett.83(2003)1638.[8]G.H.Du,Q.Chen,Y.Yu,S.Zhang,W.Z.Zhou,L.M.Peng,J.Mater.Chem.14(2004)1437.[9]G.H.Du,Q.Chen,R.C.Che,L.M.Peng,Appl.Phys.Lett.79(2001)3702.[10]M.M.Thackeray,Prog.Solid State Chem.25(1997)1.[11]A.R.Armstrong,P.G.Bruce,Nature381(1996)499.[12]B.Ammundsen,J.Paulsen,Adv.Mater.13(2001)943.[13]Q.Feng,H.Kanoh,K.Ooi,J.Mater.Chem.9(1999)319.[14]L.I.Hill,A.Verbaere,D.Guyomard,J.Power Sources226(2003)119.[15]M.M.Thackeray,J.Am.Ceram.Soc.82(1999)3347.[16]Y.F.Shen,R.P.Zerger,S.L.Suib,L.McCurdy,D.I.Potter,C.L.O’Young,Science260(1993)511.[17]R.N.DeGuzman,Y.F.Shen,h,S.L.Suib,C.L.O’Young,S.Levine,J.M.Newsam,Chem.Mater.6(1994)815.[18]M.Benaissa,M.Jose-Yacaman,T.D.Xiao,P.R.Strutt,Appl.Phys.Lett.70(1997)2120.[19]N.Kijima,H.Yasuda,T.Sato,Y.Yoshimura,J.Solid State Chem.159(2001)94.[20]Y.D.Li,X.L.Li,R.R.He,J.Zhu,Z.X.Deng,J.Am.Chem.Soc.124(2002)1411.[21]X.Wang,Y.D.Li,Chem.Eur.J.9(2003)300.[22](a)Z.Q.Li,Y.Ding,Y.J.Xiong,Q.Yang,Y.Xie,mun.(2005)918;(b)Z.Q.Li,Y.Ding,Y.J.Xiong,Y.Xie,Cryst.Growth Des.5(2005)1953.[23](a)Y.Q.Gao,Z.H.Wang,J.X.Wan,G.F.Zou,Y.T.Qian,J.Cryst.Growth279(2005)415;(b)Y.Chen,C.Liu,F.Liu,H.M.Cheng,J.Alloy Compd.19(2005)282.[24]J.Luo,S.L.Suib,J.Phys.Chem.B101(1997)10403.[25]T.D.Xiao,P.R.Strutt,M.Benaissa,H.Chen, B.H.Kear,Nanostruct.Mater.10(1998)1051.[26]C.Z.Wu,Y.Xie,D.Wang,J.Yang,T.W.Li,J.Phys.Chem.B107(2003)13583.[27]Y.D.Li,X.L.Li,Z.X.Deng,B.C.Zhou,S.S.Fan,J.W.Wang,X.M.Sun,Angew Chem.Int.Ed.Engl.41(2002)333.Y.Liu et al./Journal of Solid State Chemistry179(2006)1757–17611761。
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ANAGGLOMERATION-BASEDMULTILEVEL-TOPOLOGYCONCEPTWITHAPPLICATIONTO3D-FEMESHES
JOHANNESK.KRAUSANDJOSEFSYNKAAbstract.Inthispaperwefocusongeneratinghierarchiesoftopologicalrelationsforunstructuredthree-dimensional(3D)finiteelement(FE)meshes.Therelatedtopologicalelementsareagglomerates,faces,edges,andvertices.Weprovidepracti-caldefinitionsandproposeefficientprocedures,inparticularforthesetupofcoarsefacesandcoarseedges.Moreover,weexaminetheagglomerationalgorithmin-troducedbyJonesandVassilevski[3]andsuggestapropergeneralizationfor3Dmeshes.Thissettingallowsforarecursiveconstructionofasequenceofnestedcoarsetopologies,whichcanbeusedindifferentareasoffiniteelementcomputations,e.g.,loadbalancingforparallelprocessing,domaindecompositionmethods,algebraicmultigridormultilevelpreconditioningmethodsbasedonincompletefactorization.
1.IntroductionThenumericalsolutionofpartialdifferentialequationsbythemethodoffiniteele-mentsinvolveslargestructuredorunstructuredmeshesfordiscretization.RegardingthequalityofanFEapproximation(differencebetweennumericalandexactsolu-tionmeasuredinsomenorm),therearemanysituationswhereasignificantportionofdegreesoffreedomintheFEmodelcanbesavediftheunderlyingmeshiswelladaptedtotheproblem.Duetocomplicatedshapesofthecomputationaldomainand/orthenecessityoflocalmeshrefinementthisadaptationoftencausesalossofstructureinthemesh.InmanyFEsimulationsunstructuredmeshesareusedrightfromthebeginning.Nowfordifferentreasonsonemightliketosubdivideameshintosmall(er)parts;mainlyfortheefficientiterativesolutionofthearisingsystemoflinearalgebraicequations,techniqueslikeloadbalancingforparallelprocessing,domaindecomposi-tionmethodsoralgebraicmultigridareused,whichstronglydependonpropermeshpartitionings,aquestionwewanttodealwithinthispaper.Usually,onedemandscertainpropertiesofthepartitioning:
•Onedesirablepropertyisthattheresultingsubsets(blocks)ofelementsarestronglyconnectedinthesensethatforeachpairofelementsinoneblock(partition)thereisapathalongelementfaces,possiblyviaotherelements(in
Date:August20th,2004.1991MathematicsSubjectClassification.65M55,65M60,65N30,65N55.Keywordsandphrases.agglomerationtechniques,3Dfiniteelementmeshes,multileveltopolog-icalrelations,graphpartitioning.ThisworkwassupportedbytheAustrianAcademyofSciences.12JOHANNESK.KRAUSANDJOSEFSYNKAthesameblock),thatconnectsthetwoelementstoeachother;(Notethattwoelementsshareafaceifftheshortestconnectingpathhaslengthone.)•Anotherfavoredpropertyofthepartitioningisthatallormostoftheparti-tionscontainapproximatelythesamenumberofelements.•Athirdcommonaimistokeepthenumberoffacessharedbyelementsbe-longingtodifferentblocksassmallaspossible;(Thisisequivalenttoalowedgecutwhenpartitioningtheverticesofadualgraph.Inthisdualgrapheveryelementcorrespondstoonevertex;twoofitsverticesareconnectedviaanedgeifandonlyifthecorrespondingelementsintheFEmeshshareaface.)
WehavetheserequirementsinmindwhenconstructingpartitioningsofFEmeshesviaelementagglomeration.Sinceanymeshpartitioningproblemdefinesanequivalent(constrained)graphpartitioningproblem(foradualgraph)varioustechniquesfromthisareaapply[1,2,4,5,6,7].Asummaryofthefunctionalityofanumberofpublicallyavailablesoftwarepackagesforgraphpartitioningwasgivenin[9].Otherpartitioningmethodsforunstructuredmeshesbasedonagglomerationandaggregationtechniqueshavebeeninvestigatedinthecontextofalgebraicmultigrid[3,10,11,12].However,wewillfocusonageneralmultilevel-topologyconceptfor3Dfiniteele-mentmeshesinthispaper.Thisincludestheconstructionofasequenceofnestedagglomeratedelements,referredtoasagglomerateshereafter,andthesetupaswellasthetransferofcertaintopologicalrelationsbetweenagglomerates,faces,andedges,fromonelevel(ofagglomeration)tothenext.ThedefinitionofthesetopologicalelementsandtheirrelationswillbepresentedinSection2.Givenanarbitraryparti-tioningoffine-levelagglomerates,i.e.,acoarse-agglomerate-fine-agglomeraterelation,Section3isconcernedwiththeconstructionofacoarsetopology,i.e.,coarsefaces,coarseedges,coarsevertices,andtheirrelations.Sections4and5dealwithagglomer-ationalgorithms:Averyfastalgorithm–linearcomplexity(inthenumberoffaces)–hasbeenintroducedin[3].Forunstructured2Dmeshesthisalgorithmproduceswell-shapedandsuitablymatchedagglomerates.Moreover,uptoboundaryeffects,itcorrectlyreproducesstructuredtriangularandquadrilateralmeshesoncoarserlevels.Wewillrecallthisalgorithm,which,inprinciple,isnotlimitedto2Dapplications,inSection4.However,itwillbeshownthatthequalityofagglomeratescanbeimprovedconsiderablybyintroducingsomemajormodificationsinthe3Dcase.Wethuspro-poseanimprovedalgorithm,describedinSection5,tobeusedfortheagglomerationprocess(in3Dspace),whichourmultilevel-topologyconceptisbasedon.Finally,wewilldiscusssomeresultsobtainedfor3Dunstructured(tetrahedral)meshesinSection6.