Prediction of the Aging of HTV Silicone Rubber Using Chemical Concentration and Polynomial
FactSage_热力学计算在耐火材料抗渣侵蚀性中的应用
第43卷第3期2024年3月硅㊀酸㊀盐㊀通㊀报BULLETIN OF THE CHINESE CERAMIC SOCIETY Vol.43㊀No.3March,2024FactSage 热力学计算在耐火材料抗渣侵蚀性中的应用郭伟杰1,2,朱天彬1,2,李亚伟1,2,廖㊀宁1,2,桑绍柏1,2,徐义彪1,2,鄢㊀文1,2(1.武汉科技大学省部共建耐火材料与冶金国家重点实验室,武汉㊀430081;2.武汉科技大学高温材料与炉衬技术国家地方联合工程研究中心,武汉㊀430081)摘要:商用热力学计算软件FactSage 在耐火材料抗渣侵蚀性研究中起到重要作用,因此在耐火材料研究中应用越来越广泛㊂本文总结了近15年来热力学计算在耐火材料抗渣侵蚀性研究中的应用,重点介绍了耐火材料抗渣侵蚀研究中常用的热力学计算模型,分析了各种模型的原理㊁特点㊁适用情景㊁精确度与局限性,并给出了详细的运用实例㊂此外,本文介绍了热力学计算与其他方法相结合运用的实例,包含ANSYS㊁动力学分析㊁分子动力学模拟等方法,规避热力学计算的局限性,更加全面地分析熔渣对耐火材料的侵蚀行为㊂最后,本文对热力学计算存在的问题进行了归纳,并基于现有研究现状对其发展前景与方向进行了展望㊂关键词:耐火材料;热力学计算;抗渣侵蚀性;FactSage;热力学模型中图分类号:TQ175㊀㊀文献标志码:A ㊀㊀文章编号:1001-1625(2024)03-1110-13Application of FactSage Thermodynamic Calculation on Slag Corrosion Resistance of RefractoriesGUO Weijie 1,2,ZHU Tianbin 1,2,LI Yawei 1,2,LIAO Ning 1,2,SANG Shaobai 1,2,XU Yibiao 1,2,YAN Wen 1,2(1.The State Key Laboratory of Refractories and Metallurgy,Wuhan University of Science and Technology,Wuhan 430081,China;2.National-Provincial Joint Engineering Research Center of High Temperature Materials and Lining Technology,Wuhan University of Science and Technology,Wuhan 430081,China)Abstract :Commercial thermodynamic calculation software FactSage plays an important role in the analysis of slag corrosion process,therefore it has been widely used in the research of refractories.Application of thermodynamic calculation on slag corrosion resistance of refractories and thermodynamic calculation models which are commonly used in the slag corrosionresistance of refractories were introduced.The mechanisms,characteristics,applicable situations,accuracy and limitations of every model were discussed,and the detailed examples were given.Furthermore,the application examples of FactSage combined with other methods including ANSYS,kinetic analysis and MD simulation were given,aiming to avoid the limitations of thermodynamic calculation and comprehensively analyze the slag corrosion stly,the common problems of thermodynamic calculation were summarized,and the direction of further development was proposed.Key words :refractory;thermodynamic calculation;slag corrosion resistance;FactSage;thermodynamic model 收稿日期:2023-09-27;修订日期:2023-12-06基金项目:国家自然科学基金联合基金重点项目(U21A2058,U1908227,52272071);湖北省自然科学基金项目(2022CFB024)作者简介:郭伟杰(1998 ),男,硕士研究生㊂主要从事耐火材料抗渣性能的研究㊂E-mail:1099255596@通信作者:朱天彬,博士,副教授㊂E-mail:zhutianbin@ 0㊀引㊀言随着计算机技术的高速发展,集成了大量热力学数据的商用热力学计算软件成为研究者的重要工具㊂FactSage [1]最早于1976年提出,2001年加拿大蒙特利尔综合工业大学的FACT-win 软件与德国GTT 公司的ChemSage 软件整合为FactSage,这是目前应用最为广泛的热力学计算软件之一㊂该软件集成了大量热力学数据库,包括溶液㊁化合物㊁纯物质㊁熔盐㊁合金的数据,并整合了以多元相平衡计算为代表的多种功能,是一㊀第3期郭伟杰等:FactSage热力学计算在耐火材料抗渣侵蚀性中的应用1111个综合性集成热力学计算软件[2-3],已在全球800多所大学㊁实验室和企业中应用[4]㊂在耐火材料领域,FactSage热力学计算同样占据着重要地位,已被应用于相图绘制㊁熔渣侵蚀分析㊁液相含量分析㊁黏度计算㊁复杂条件下多元多相体系平衡㊁体系热力学函数计算等诸多方面[5-8]㊂其中,热力学计算能够较好地分析耐火材料抗渣侵蚀性,在熔渣性质㊁热力学平衡相㊁液相组成等方面提供重要参考㊂因此,本文综述了近15年来FactSage热力学计算在耐火材料抗渣侵蚀研究进展,给出了基于热力学计算的抗渣侵蚀性研究案例,以期为相关科研工作者使用热力学计算分析耐火材料抗渣侵蚀机理提供参考和借鉴㊂同时,基于近年来的研究现状,总结FactSage热力学计算在耐火材料抗渣侵蚀性的发展趋势,并对其发展前景进行了展望㊂1㊀耐火材料抗渣侵蚀研究中的热力学计算模型热力学计算中,FactSage的Equilib模块是模拟熔渣与耐火材料反应过程的最常用工具㊂该模块通过原ChemSage的算法,基于吉布斯自由能最低原理[9-10],能够较好地预测熔渣对耐火材料侵蚀过程中的热力学平衡相与液相组成变化㊂使用该模块进行耐火材料抗渣侵蚀性研究的常用过程如图1所示㊂图1㊀使用FactSage的Equilib模块对熔渣-耐火材料侵蚀过程进行分析的主要步骤Fig.1㊀Main steps during the analysis of slag corrosion resistance of refractories using Equilib module of FactSage选择合适的热力学计算模型是获取准确的热力学计算结果的前提㊂不同的热力学计算模型具有不同的侧重点,应当基于当前研究体系的特点,选取合适的模型以达到较好的模拟效果㊂目前,经过国内外研究者的长期研究,以界面反应模型为代表的热力学计算模型被广泛开发,并经过了大量实验验证,具有较高的准确度与可信度㊂下面对常用的热力学计算模型分别进行介绍㊂1.1㊀物相-温度模型图2为物相-温度模型的示意图㊂物相-温度模型是一种常用的计算模型,能够较好地反映物相随温度的变化情况㊂物相-温度模型的示意图如图2(a)所示,熔渣与耐火材料的质量恒定(常设定为100gʒ100g),在该模型中温度是唯一的变量,通过计算得到物相-温度曲线(见图2(b)),从而反映物相随温度的变化过程㊂该模型常用于分析温度对耐火材料抗渣侵蚀性的影响以及高熔点相在耐火材料内的生成温度等情况㊂此外,该模型变量较少㊁上手门槛较低,适用于大多数耐火材料抗渣侵蚀性分析㊂图2㊀物相-温度模型的示意图Fig.2㊀Schematic diagram of phase-temperature thermodynamic model在Gehre等[11]关于含硫渣对尖晶石耐火材料的侵蚀行为的研究中,通过设定30g熔渣与10g耐火材料在强还原气氛下进行反应,得到了尖晶石㊁CaMg2Al16O27相在800~1450ħ的变化趋势(见图3),较好地描述了固相随温度降低逐渐析出的过程㊂类似地,在刚玉尖晶石浇注料体系中,Ramult等[12]在1112㊀耐火材料硅酸盐通报㊀㊀㊀㊀㊀㊀第43卷图3㊀矿物相与熔渣含量与温度的函数关系[11]Fig.3㊀Functional relationship between mineral phase,slag content and temperature [11]1200~1700ħ设定50%(文中均为质量分数)耐火材料与50%钢渣反应,比较了三种不同碱度的熔渣对浇筑料侵蚀后的产物区别㊂该方法同样在铜工业用无铬耐火材料中运用,Jastrzębska 等[13]通过将50g 的不同种类铜渣与50g 的Al 2O 3-MgAl 2O 4耐火材料进行计算,发现尖晶石能够在较大温度范围内稳定存在,证实了该种耐火材料对铜渣具有较好的抵抗能力㊂而在炉渣的固相分数分析中,Anton 等[14]则使用该模型计算了熔渣的完全融化温度,发现碱度不随固体析出而变化㊂物相-温度模型对熔渣-耐火材料体系内固相的析出温度具有良好的精确度,并能够准确判断固相在高温下的稳定情况,且可以确定产生液相的温度点㊂此外,这种热力学模型以温度作为变量,适合于描述较大温度范围内的熔渣侵蚀情况,能够提供从升温到降温的全过程熔渣侵蚀产物分析㊂然而,该种模型具有明显的局限性㊂众所周知,熔渣侵蚀耐火材料的过程中,熔渣含量变化导致系统物相组成不断变化,熔渣侵蚀耐火材料的过程是一个渐进的过程㊂使用温度-物相模型时,由于熔渣与耐火材料组分未引入变量,采用了固定值进行计算,导致其计算结果是对熔渣侵蚀最终结果的预测,而无法渐进㊁全面地展现熔渣对耐火材料的侵蚀过程㊂侵蚀过程描述的缺失使得中间相的产生机理无法较好地被描述(如浇注料体系中二铝酸钙(CA 2)与六铝酸钙(CA 6)相的含量变化),导致复杂体系的精确度较差㊂1.2㊀溶解模型图4为溶解模型示意图,图5为不同气氛下镁铬耐火材料-冰铜渣系统的热力学平衡相㊂溶解模型也是耐火材料抗渣侵蚀研究中一种常用的模型,如图4(a)所示,该模型设定耐火材料的质量恒定不变,熔渣质量线性增加㊂在该模型中,定义质量比A =m S /m R (m S 为熔渣质量,m R 为耐火材料质量),对系统内各组分使用表达式<m R +m S ˑA >进行描述,即随着A 值的增加,在耐火材料质量不变的情况下,熔渣质量从0开始不断线性增加,从而模拟熔渣量从少到多的侵蚀过程㊂如图4(b)所示,该模型较好地反映了组分在熔渣内的溶解速率情况与稳定程度,通过物相质量-A 曲线的斜率定性反映溶解速率,通过曲线归零时所需A 的绝对值反映该物相在熔渣内的稳定程度㊂图4㊀溶解模型示意图Fig.4㊀Schematic diagrams of dissolution model 溶解模型由于具有较好的普适性而被广泛运用于耐火材料抗渣侵蚀研究中㊂在Liu 等[15]㊁王恭一等[16]和程艳俏等[17]针对镁铬质耐火材料抗渣侵蚀性的研究中,根据如图5所示的热力学计算,发现镁铬尖晶石㊁镁铁尖晶石以及镁橄榄石在系统内可以稳定存在;而在还原气氛下(见图5(b)),镁橄榄石的含量明显下㊀第3期郭伟杰等:FactSage热力学计算在耐火材料抗渣侵蚀性中的应用1113降,且生成了Pb(g),从而解释了还原气氛下耐火材料抗渣侵蚀性下降的原因㊂在评价耐火骨料抗渣侵蚀性的研究中,金胜利等[18]分别计算了高炉钛渣对棕刚玉㊁电熔刚玉㊁亚白刚玉㊁镁铝尖晶石以及特级矾土的侵蚀,通过比较刚玉相完全消失时的A值分析了五种常见骨料的抗侵蚀能力㊂桑绍柏等[19]通过热力学计算发现SiC能够与含Ti熔渣反应生成稳定的FeSi与TiC相,且SiC在A=4.5时才完全消耗,证明了SiC在该体系内具有良好的稳定性㊂吕晓东等[20]通过该模型计算发现SiC㊁钛尖晶石在钛渣中具有较好的稳定性,这与静态坩埚法得到的结果一致㊂马三宝等[21]也计算了钢包渣对轻质方镁石-尖晶石耐火材料的侵蚀,得出尖晶石的溶解速率大于方镁石㊂而李真真等[22]使用该模型研究了氧化钛对镁砂抗渣渗透性能的影响,发现生成的CaTiO3在熔渣内比镁砂更加稳定㊂图5㊀不同气氛下镁铬耐火材料-冰铜渣系统的热力学平衡相[15]Fig.5㊀Equilibrium phases of magnesia chromite refractories-matte slag system under different atmospheres[15]该模型对高熔点物相在熔渣体系内的稳定度预测展现出较为良好的精确度㊂由于该模型中引入了变量A=m S/m R,特定物相消失时的A值反映了该物相在熔渣内的稳定程度,因此该模型能够较好地发现特定熔渣体系内的高熔点相(如尖晶石相㊁CaTiO3相与方镁石相),为针对性地开发具有优异抗渣侵蚀性的耐火材料提供依据㊂并且,该种模型能够有效地对比不同耐火材料体系在特定熔渣下的稳定程度,从而针对酸性渣㊁碱性渣㊁富钛渣㊁富锰渣等不同熔渣体系挑选对应的耐火材料,满足特定条件的需求㊂然而,该种模型仍具有一定局限性,虽然能够良好地预测高熔点㊁高稳定相的生成,却缺乏定性地描述这些物相在侵蚀区域相对位置的能力,例如其能够精确地预测刚玉骨料外侧生成CA2与CA6相,但难以定性地描述两相在骨料外侧的位置㊂因此,使用该种模型时需结合SEM㊁EDS等表征手段进行深入分析㊂此外,在真实的熔渣侵蚀过程中,由于耐火材料组分向熔渣中逐渐溶解,熔渣的组分受到耐火材料的影响而不断改变,因此熔渣组分处于 不断更新 的状态㊂而该模型中熔渣组分恒定不变,即恒定保持初始化学组分㊁仅逐步提升熔渣的质量,无法精确地描述熔渣与耐火材料之间的组分交换㊂因此,该种模型适合对静态坩埚抗渣法等熔渣组分变化不大的情景进行分析,对感应炉抗渣㊁回转窑抗渣㊁钢包渣线抗渣等组分交换剧烈㊁熔渣处于动态情景的模拟精确度较低㊂1.3㊀界面反应模型界面反应模型能够有效地模拟熔渣-耐火材料界面处的相互作用过程,被广泛应用于多种耐火材料体系中,其计算结果经过了广泛验证,是目前常用㊁可信的模型之一㊂该模型最早由Berjonneau等[23]于2009年提出,最初用于模拟恒定温度㊁压力条件下二次冶金钢包渣对Al2O3-MgO耐火材料的侵蚀㊂界面反应模型的示意图如图6所示,在该模型中定义了反应度B=w R/(w S+w R),并满足w R+w S=1,其中w R为耐火材料质量分数,w S为熔渣的质量分数,对系统内的组分采用表达式<m S-(m S-m R)ˑB>进行描述㊂B反映了耐火材料-熔渣界面的反应程度,当B接近0时,系统中熔渣比例较高,反应程度较低,反之B接近1时,系统中耐火材料占比较高,反应程度越高㊂如图6(b)所示,反应度B可以近似为熔渣-耐火材料接触的界面层的相对位置,B趋近于1时,生成的物相越接近耐火材料表层,而其趋近于0时物相靠近熔渣侧㊂这一特性使得该模型能较好地反映了侵蚀过程中固相的相对位置与生成量,因此尤其适合模拟保护层的生成情况㊂1114㊀耐火材料硅酸盐通报㊀㊀㊀㊀㊀㊀第43卷图6㊀界面反应模型的示意图[21]Fig.6㊀Schematic diagrams of interlayer reaction model[21]溶解模型在耐火材料抗渣领域得到了广泛应用,并被大量实验证明具有良好的精确度㊂Berjonneau 等[23]通过实验验证了该模型的精确度,计算结果与实际侵蚀区域的微观结构呈良好的对应关系(见图7(a)),并得出了CA2和CA6相的形成机理(图7(b))㊂Tang等[24]使用该模型对Al2O3坩埚的侵蚀行为进行了分析和实验验证,发现热力学计算预测的熔渣㊁CA2㊁CA6㊁尖晶石以及刚玉骨料的位置与实际实验结果一致㊂在蒋旭勇等[25]的研究中,通过该模型计算了铝镁质浇注料对不同Al2O3含量的CaO-SiO2-Al2O3渣的物相生成量,发现高Al2O3含量的熔渣能够促进形成更厚的隔离层㊂在高纯度镁质耐火材料对富铁渣的抗渣侵蚀性研究中,Betsis等[26]利用该模型发现,富铁渣将方镁石转化为MgO-Fe x O,且发现液相中FeO含量上升㊂类似地,Oh等[6]也观测到了MgO-Fe x O层,且MgO㊁FeO相对含量与显微结构观察一致㊂李艳华等[27]使用该模型对LF渣对ρ-Al2O3结合铝镁质浇注料的侵蚀行为进行了分析,通过FactSage软件得到了尖晶石的组成,结果显示生成的尖晶石中含有一定量的MnAl2O4和FeAl2O4,即熔渣中的Mn2+㊁Fe2+生成了复合尖晶石㊂Guo等[28]使用该模型计算了熔渣侵蚀钙镁铝酸盐(CMA)骨料产生的热力学平衡相,发现CMA骨料内的一铝酸钙(CA)㊁CA2相在高温下转化为液相,提高了熔渣的Al2O3含量㊂图7㊀熔渣对刚玉骨料的侵蚀的热力学计算结果[21]Fig.7㊀Thermodynamic calculation results of corrosion of slag to corundum aggregate[21]㊀第3期郭伟杰等:FactSage热力学计算在耐火材料抗渣侵蚀性中的应用1115溶解模型不仅可以预测物相组成的变化,还常用于预测熔渣侵蚀过程中液相组成的变化与黏度变化[29]㊂Wang等[30]使用该模型对ZrO2耐火材料对高碱度精炼渣的侵蚀行为进行了研究,图8为ZrO2耐火材料的侵蚀过程的热力学计算结果㊂EDS线扫描中ZrO2含量从耐火材料到过渡层逐渐降低,CaO含量随着渣层到过渡层逐渐降低,其趋势与热力学计算结果一致㊂鄢文等[31]研究了熔渣对刚玉尖晶石浇注料侵蚀的热力学模型,结果显示,侵蚀层到耐火材料内部SiO2㊁CaO含量逐渐降低,而SiO2的含量则先降低后增加,这与A值介于0.66至0.84之间的曲线相吻合㊂此外,Peng等[32]计算了轻质方镁石-尖晶石浇注料与熔渣反应过程中的液相黏度变化,证明了该种耐火材料优秀的抗渣渗透性能㊂图8㊀ZrO2耐火材料侵蚀过程的热力学计算结果[27]Fig.8㊀Thermodynamic calculation results of corrosion process of ZrO2refractories[27]作为最常用的抗渣模型之一,界面反应模型最大的优势为能够生动地描述物相的生成机理㊁生成位置㊂由于变量B=w R/(w S+w R)的引入,界面反应模型能够细致地描述熔渣对耐火材料侵蚀的全过程,详细地展现各热力学平衡相的含量变化,其良好的精确度与泛用性使得其被广大研究者所使用,助力了许多研究成果的产出,并得到了广泛的实验验证㊂然而,该模型同样具有一定的局限性㊂如前文所述,熔渣对耐火材料侵蚀是一个动态的过程,渣组分会随侵蚀程度的改变不断变化,Zhang等[33]指出,该模型忽略了耐火材料溶解对熔渣化学组分变化,使得其对动态渣蚀的模拟存在一定的误差㊂在真实熔渣侵蚀过程中,耐火材料的损毁常是由溶解㊁化学反应与渗透共同导致的㊂该模型虽然能够较好地描述熔渣-耐火材料界面上的化学反应,却不能很好地胜任熔渣渗透过程的模拟㊂此外,受制于热力学计算的局限性,界面反应模型无法展现耐火材料表面形貌㊁扩散速率㊁熔体冲刷等因素对抗渣侵蚀性的影响㊂1.4㊀逐步迭代模型在实际侵蚀过程中,熔渣化学组分会随着熔渣与耐火材料的反应而发生变化,从而影响熔渣的侵蚀能力,而溶解模型与界面反应模型忽略了这一变化,且两者均不能较好地模拟熔渣的渗透过程㊂针对以上问题,Luz等[34]设计了一个新的模型,迭代模型的示意图如图9所示㊂该模型具有一个迭代程序,其原理如图9(a)所示,设定第一反应阶段初始耐火材料质量与熔渣质量均为100g(S为熔渣,R为耐火材料),将反应后将得到的改性渣(S1)再次与相同质量的耐火材料进行二次迭代计算得到新的改性渣(S2),不断重复该过程直至熔渣量归零或达到饱和,通过该迭代程序,每一次循环后熔渣组分都会改变㊂该模型同样可以用于描述熔渣对耐火材料的渗透过程(图9(b)),即更大的迭代计算次数对应更长的熔渣渗透距离[31]㊂Calvo等[35]在钢包用铝碳质耐火材料的用后分析中使用该模型分析了熔渣对耐火材料的渗透,其热力学计算结果与用后耐火材料的显微结构如图10所示(MA为镁铝尖晶石)㊂热力学计算结果显示,随着熔渣渗透深度的增加,尖晶石和六铝酸钙将会依次生成㊂从侵蚀区图像中可以看出,从工作面到耐火材料内部依次为镁铝尖晶石㊁二铝酸钙和六铝酸钙,基本与热力学计算一致㊂类似地,在Muñoz等[36]对铝镁碳耐火材料抗渣侵蚀性研究中,该模型计算结果与熔渣渗透区的显微结构吻合程度较高㊂此外,该模型仍可以较为精确1116㊀耐火材料硅酸盐通报㊀㊀㊀㊀㊀㊀第43卷地预测物相的生成情况,并非专用于描述熔渣对耐火材料的渗透情况㊂在Luz等[37]针对尖晶石浇注料的熔渣侵蚀研究中,该模型预测了CA2和CA6相的存在,并通过显微结构验证了热力学计算的准确性㊂Han 等[38]使用该模型计算得到了MgO-Fe x O层,这与侵蚀后试样的显微结构一致㊂在Luz等[39]对镁碳质耐火材料的抗渣侵蚀的研究中,通过该模型计算发现MgO溶解量随着熔渣碱度降低而增加,证明了低碱度渣对镁碳质耐火材料的侵蚀更加强烈㊂图9㊀迭代模型的示意图[31]Fig.9㊀Schematic diagram of the iterative corrosion model[31]图10㊀用后铝碳质耐火材料的热力学计算结果[32]Fig.10㊀Thermodynamic calculation results of spent Al2O3-C refractories[32]与溶解模型㊁界面反应模型相比,迭代模型能够模拟耐火材料组分对熔渣侵蚀能力的影响㊂每次迭代时,熔渣组分都会被耐火材料所改变,改性渣再次与新的耐火材料反应,这个过程模拟熔渣组分更新,因此该模型对动态渣蚀具有更加良好的模拟精确度㊂此外,该种模型能够定性地描述渗透过程,反映熔渣渗透过程中熔渣组分的变化与物相的变化,从而为耐火材料用后分析㊁熔渣渗透行为分析提供重要的参考㊂在真实的熔渣渗透过程中,熔渣的渗透行为除了受到熔渣的组分和黏度的影响外,还会受到接触角㊁气孔孔径㊁晶界渗透㊁渗透时间等诸多因素的影响,而该模型仅能从热力学的角度预测熔渣组分变化㊁黏度变化和物相变化,对物理过程缺乏描述的能力㊂因此将该模型用于描述熔渣渗透过程时,迭代次数仅能够定性地反映渗透深度,不能够精确地给出渗透距离㊂此外,随着熔渣深入耐火材料内部,耐火材料工作面与内部之间的温度梯度也会影响熔渣的渗透行为,而该种模型设定耐火材料内外温度恒定,导致对耐火材料深处的物相的预测存在一定的偏差㊂并且,该种模型中引入了迭代程序,使得计算量大幅增加,部分体系中甚至需要十几次以上的循环计算才能使熔渣完全耗尽或达到饱和,对模型使用者造成了较重的负担㊂这些因素制约了该模型的普及与发展,因此较少研究使用该种模型进行热力学模拟㊂1.5㊀其他热力学计算模型除上述四种最常用的热力学计算模型外,国内外研究者针对不同熔渣侵蚀过程的特点,针对性地开发了新的热力学计算模型,从而更加精确地预测耐火材料侵蚀过程㊂㊀第3期郭伟杰等:FactSage热力学计算在耐火材料抗渣侵蚀性中的应用1117针对迭代模型的局限性,Sagadin等[40]使用FactSage与SimuSage[41]开发了一种新型耐火材料侵蚀模型,用于模拟镍铁渣对镁质耐火材料的侵蚀,并对气孔率和温度梯度的影响进行了模拟,具体如图11所示㊂如图11(a)所示,该模型将耐火材料分为了十个区域,温度从外到内线性递减,每个区域均含有定量的耐火材料与气孔㊂图11(b)为该模型单个区域的运算流程,耐火材料与熔渣首先进行计算,产物被 物相分离器 分离为固体与熔体㊂由于耐火材料的气孔仅能允许一部分熔渣向深处渗透,因此研究者使用SimuSage设计了 熔体分离器 ,将熔体分离为可以进入下一区域的熔体A与被阻碍在该区域的熔体B㊂熔体B与固体氧化物组成混合体并在该区域内再次计算,而熔体A则进入下一区域㊂该模型不仅能够描述熔渣化学组分的变化,还考虑了耐火材料气孔率对熔渣渗透的影响[42]㊂并且,由于温度梯度的存在,橄榄石等能够在材料深处的低温区域稳定存在,这在恒定温度的模型中是无法实现的㊂图11㊀基于FactSage与SimuSage的耐火材料侵蚀模型[37]Fig.11㊀Corrosion model based on FactSage and SimuSage[37]在感应炉抗渣法中,熔渣由于电磁场的作用剧烈地冲刷耐火材料,熔渣的组分由于耐火材料的损毁和熔渣的对流运动而不断混合和改变,并且耐火材料基质与骨料的侵蚀速率不同,导致两者对熔渣组分的改变能力不同,因此需要新的热力学计算模型描述动态条件下的熔渣侵蚀过程㊂在轻量化MgO-Al2O3浇注料的抗渣侵蚀性研究中,邹阳[43]提出了一种新的热力学计算模型,这种模型中熔渣组分受到耐火材料侵蚀的影响,并可以反映骨料与基质的侵蚀速率差别㊂该模型将熔渣侵蚀过程分为了n个相等的时间段,在每个Δt内,熔渣分别与骨料㊁基质进行计算,得到新的液相加和,即为 更新 后的熔渣组分㊂图12为动态熔渣侵蚀下的热力学计算模型㊂相较于其他模型,该模型能够形象地显示骨料㊁基质抗侵蚀能力的差异,且由于受到了骨料㊁基质的共同影响而不断 更新 ,其具有更高的精确度,更加符合动态熔渣条件下熔渣受到对流而不断混合的实际情况㊂图12㊀动态熔渣侵蚀下的热力学计算模型[40]Fig.12㊀Thermodynamic calculation model of dynamic slag corrosion condition[40]综合来看,以上模型在现有的经典模型基础上进行了一定程度的改进,使之能够更好地描述熔渣侵蚀过程,展现熔渣侵蚀模型的改进潜力㊂然而,这些改进模型计算方式复杂,或需要使用其他软件,导致其难以掌握㊂同时,这些模型提出较晚,未在大量研究中被广泛使用,缺乏实验数据的验证㊂受制于热力学计算本身的局限性,这些模型还是仅能从热力学角度描述化学反应过程㊁物相变化,对湍流㊁扩散等现象造成的影响无法给出预测㊂。
The Role of CRISPR-Cas in Gene Editing and Beyond
The Role of CRISPR-Cas in Gene Editingand BeyondCRISPR-Cas technology has revolutionized the field of gene editing, offering unprecedented precision and efficiency in the manipulation of genetic material. This powerful tool has the potential to not only treat genetic disorders but also to transform various industries, including agriculture and biotechnology. However, the widespread application of CRISPR-Cas raises ethical, social, and regulatory concerns that must be carefully considered. In this essay, we will explore therole of CRISPR-Cas in gene editing and its implications beyond the realm of science. At its core, CRISPR-Cas is a bacterial immune system that has been repurposed for gene editing. The system consists of two main components: the Cas9 protein, which acts as molecular scissors, and a guide RNA, which directs the Cas9 to a specific target sequence in the genome. This precise targeting ability allows researchers to make changes to the DNA with unprecedented accuracy, whether it involves correcting a mutation, introducing a new gene, or disrupting aproblematic gene. The potential applications of this technology are vast, ranging from the development of novel therapeutics to the creation of genetically modified organisms with desirable traits. One of the most promising aspects of CRISPR-Casis its potential to treat genetic disorders. By correcting disease-causing mutations at the genetic level, CRISPR-Cas could offer hope to millions of people suffering from conditions that were previously considered untreatable. For example, researchers have already made significant progress in using CRISPR-Cas to treat genetic disorders such as sickle cell anemia and muscular dystrophy in preclinical studies. These advancements bring a sense of optimism and possibility toindividuals and families affected by genetic diseases, offering the potential for improved quality of life and longevity. Beyond the realm of human health, CRISPR-Cas also holds immense promise for agricultural and environmental applications. The ability to precisely modify the genomes of plants and animals could lead tothe development of hardier crops, livestock with improved disease resistance, and environmentally friendly bioengineered solutions. For instance, CRISPR-Cas couldbe used to create crops that are more resilient to climate change, therebyaddressing food security concerns in a rapidly changing world. Additionally, the technology could enable the conservation of endangered species by mitigating the genetic factors contributing to their decline. However, the widespread use of CRISPR-Cas also raises significant ethical and societal considerations. The potential for heritable changes to the human genome, often referred to as "germline editing," has sparked intense debate within the scientific community and beyond. The prospect of altering the genetic makeup of future generations carries profound implications, including concerns about unintended consequences, equity in access to genetic enhancements, and the potential for exacerbating existing social inequalities. These ethical dilemmas underscore the importance of thoughtful and inclusive dialogue surrounding the responsible use of CRISPR-Cas technology. Moreover, the regulatory landscape surrounding CRISPR-Cas remains complex and variable across different jurisdictions. While some countries have established clear guidelines for the use of gene editing technologies, others have yet to develop comprehensive regulatory frameworks. This lack of uniformity presents challenges for researchers and companies seeking to navigate the ethical and legal considerations associated with CRISPR-Cas. Harmonizing international regulations and fostering transparent communication will be essential in ensuring that the potential benefits of CRISPR-Cas are realized in a manner that prioritizes safety, equity, and societal well-being. In conclusion, CRISPR-Cas has emerged as a transformative tool with far-reaching implications for human health, agriculture, and the environment. Its precision and versatility offer unprecedented opportunities for addressing genetic disorders, enhancing food security, and advancing conservation efforts. However, the ethical, social, and regulatory considerations surrounding its use are equally significant and demand careful reflection and engagement. As we continue to harness the potential of CRISPR-Cas, it is imperative that we approach its applications with humility, empathy, and a commitment to the well-being of present and future generations.。
高压SiC功率半导体器件的发展现状与解决措施
智能控制技术今 日 自 动 化2020.7 今日自动化 | 15Intelligent control technologyAutomation Today2020年第7期2020 No.7本文分析的半导体材料碳化硅在进行相关产品的制造以及实际使用期间存在较为明显的特性,例如击穿场强高饱和、电子漂移速率快以及诱导率高等等。
而这些数据可以满足现代功率期间在大功率场合高频高温工作状态下的应用。
所以从整体的情况来看,典型的宽禁带半导体材料的发展前景相对较好,但在实际发展期间仍然存在较多的问题,如市场拓展问题,技术问题等等限制着它的深入发展。
那么本次研究主要以开关电源,电动汽车新能源发电,交通轨道以及智能电网等多个领域作为背景,探讨碳化硅功率器件的实际应用现状,以及在未来的发展走向。
1 碳化硅器件与硅器件的性能比较近几年,人们对碳化硅器件的研究力度相对较高,因为它与传统的碳化硅器件相比,其性能相对较好,能够在多种类型的工况下进行产品的生产工作,也可以满足人们在日常生产工作中的各项需求。
例如碳化硅器件在高电压额定值以及地导通电阻和快速开关速度工作中,都可以达到人们的相关标准,这些良好的性能为人们的日常生产工作提供了极大的便利。
之所以它的性能远远高于硅器件,其主要原因是碳化硅材料内部的结构存在多种晶体结构,这些晶体结构因为具有较高的电子迁移率和较低的参杂电离,所以很多功率器件的选择开始偏向于碳化硅器件。
那么从整体的角度来看,碳化硅器件与传统的硅器件相比,其性能优势主要表现在带隙、熔点、电子迁移率、电子饱和速度、击穿电场、介电常数和诱导率这7个指标方面。
通过对这些指标进行分析,可发现碳化硅的相关指标中的数据占有更大的优势,首先SIC 具有更宽的近代宽度,其次,碳化硅具有更低的导通损耗和开关损耗,其三碳化硅的散热性能相对较高,几乎是碳的三倍,最后碳化硅具有更快的开关速度。
2 碳化硅功率器件的研究进展目前市场上出现的碳化硅半导体包括的类型相对较多,常见的主要有二极管、金属氧化物、半导体场效应、晶体管、晶闸管、结算场、效应晶体管等等这些不同类型的碳化硅器件,单元结构和漂移区参杂以及厚度之间存在较为明显的差异。
Predictions and Trends for the Next Decade
Predictions and Trends for the Next DecadeThe constant evolution of technology has transformed our lives in numerous ways, and as we enter a new decade, it's fascinating to speculate on what the future holds. In this article, we will explore some predictions and trends that are likely to shape the next ten years.Artificial Intelligence (AI) is expected to continue its rapid advancement. With machine learning algorithms becoming increasingly sophisticated, AI will become more integrated into our daily lives. From voice assistants to autonomous vehicles, AI will revolutionize various industries, enhancing efficiency and convenience.The Internet of Things (IoT) will also play a significant role in the coming decade. The ability to connect everyday devices and appliances to the internet will create a seamless network of interconnected devices. Smart homes will become the norm, with automated systems controlling everything from lighting to security.5G technology will bring about a significant transformation in the way we communicate and access information. The increased speed and bandwidth offered by 5G networks will enable faster download and upload speeds, making tasks such as video streaming and online gaming even more immersive. Additionally, the Internet of Things will rely heavily on 5G connectivity, enabling real-time communication between devices.The healthcare industry is poised for a technological revolution. With advancements in medical research and technology, we can expect breakthroughs in personalized medicine, gene editing, and regenerative medicine. Wearable devices will become more prevalent, allowing individuals to monitor their health in real-time and enabling early detection of potential health issues.Renewable energy sources will gain even greater prominence in the next decade due to increased awareness of climate change and the need for sustainable alternatives. Solar and wind power will become more accessible and efficient, leading to a reduction in greenhouse gas emissions and a shift towards a greener future.Cryptocurrencies and blockchain technology will continue to disrupt traditional financial systems. As more businesses and individuals embrace cryptocurrencies, we can expect an increase in digital transactions and a decrease in reliance on traditional banking systems. Blockchain technology will also find applications beyond finance, such as supply chain management and voting systems, ensuring transparency and security.Virtual reality (VR) and augmented reality (AR) will revolutionize various industries, including gaming, entertainment, and education. VR will offer immersive experiences, allowing users to explore virtual worlds and interact with digital environments. AR, on the other hand, will enhance the real world by overlaying digital information, creating endless possibilities for education and training.Space exploration will take giant leaps in the next decade, with plans for manned missions to Mars and beyond. Private space companies will play a crucial role inexpanding our understanding of the universe and making space travel more accessible. These advancements will not only fuel scientific discoveries but also open up new opportunities for commercial space ventures.In conclusion, the next decade promises to be an exciting time filled with technological advancements and transformative changes. From AI and IoT to renewable energy and space exploration, our world is on the cusp of a new era. Embracing these predictions and trends will undoubtedly shape the future and propel us into a more connected, sustainable, and innovative world.。
乙酸蒸汽催化重整制氢的研究进展
CHEMICAL INDUSTRY AND ENGINEERING PROGRESS 2017年第36卷第5期·1658·化 工 进展乙酸蒸汽催化重整制氢的研究进展王东旭1,肖显斌2,李文艳1(1华北电力大学能源动力与机械工程学院,北京 102206;2华北电力大学生物质发电成套设备国家工程实验室,北京 102206)摘要:通过生物油蒸汽重整制备氢气可以减少环境污染,降低对化石燃料的依赖,是一种极具潜力的制氢途径。
乙酸是生物油的主要成分之一,常作为模型化合物进行研究。
镍基催化剂是乙酸蒸汽重整过程中常用的催化剂,但容易因积炭失去活性,降低了制氢过程的经济性。
本文首先分析了影响乙酸蒸汽重整制氢过程的各种因素,阐述了在这一过程中镍基催化剂的积炭原理,讨论了优化镍基催化剂的方法,包括优化催化剂的预处理过程、添加助剂和选择合适的载体,最后对乙酸蒸汽重整制氢的热力学分析研究进展进行了总结。
未来应重点研究多种助剂复合使用时对镍基催化剂积炭与活性的影响,分析多种助剂的协同作用机理,得到一种高活性、高抗积炭能力的用于生物油蒸汽重整制氢的镍基催化剂。
关键词:生物油;乙酸;制氢;催化剂;热力学中图分类号:TK6 文献标志码:A 文章编号:1000–6613(2017)05–1658–08 DOI :10.16085/j.issn.1000-6613.2017.05.014A review of literatures on catalytic steam reforming of acetic acid forhydrogen productionWANG Dongxu 1,XIAO Xianbin 2,LI Wenyan 1(1 School of Energy ,Power and Mechanical Engineering ,North China Electric Power University ,Beijing 102206,China ;2 National Engineering Laboratory for Biomass Power Generation Equipment ,North China Electric PowerUniversity ,Beijing 102206,China )Abstract :Hydrogen production via steam reforming of bio-oil ,a potential way to produce hydrogen , can reduce environmental pollution and dependence on fossil fuels. Acetic acid is one of the main components of bio-oil and is often selected as a model compound. Nickel-based catalyst is widely used in the steam reforming of acetic acid ,but it deactivates fast due to the carbon deposition. In this paper ,the affecting factors for the steam reforming of acetic acid are analyzed. The coking mechanism of nickel-based catalyst in this process is illustrated. Optimization methods for nickel-baed catalyst are discussed ,including optimizing the pretreatment process ,adding promoters ,and choosing appropriate catalyst supports. Research progresses in the thermodynamics analyses for steaming reforming of acetic acid are summarized. Further studies should be focused on the effects of a combination of a variety of promoters on carbon deposition. Catalytic activity and the synergy mechanism should be analyzed to produce a novel nickel-based catalyst with high activity ,high resistance to caborn deposition for hydrogen production via steam reforming of bio-oil. Key words :bio-oil ;acetic acid ;hydrogen production ;catalyst ;thermodynamics第一作者:王东旭(1994—),男,硕士研究生,从事生物质能利用技术研究。
一种从大熊猫粪便中提取DNA的改进方法
动物学报49 (5) :670~674 , 2003Acta Zoologica S i nica一种从大熊猫粪便中提取D NA 的改进方法3钟华①赖旭龙②魏荣平③刘中来①33( ①华中师范大学生命科学学院, 武汉430079)( ②中国地质大学地球科学学院, 武汉430074) ( ③中国保护大熊猫研究中心, 四川卧龙623006)摘要本研究描述一个改进的方法, 使从大熊猫粪便中提取DNA 用于PCR 扩增变得更加容易。
在粪便DNA 的提取过程中采用一个新的预处理方法, 将粪便用预冷的丙酮洗2~3 次, 除去粪便中含有的大量PCR 抑制物, 然后用蛋白酶K 裂解、酚- 氯仿抽提, 能提取到纯度很高的DNA 供PCR 扩增。
本实验PCR 扩增了大熊猫脑源性神经营养因子(BDNF) 基因和线粒体细胞色素 b 基因片段, 并进行测序分析, 证实了提取的可靠性。
对比本方法和未经丙酮预处理的方法提取的DNA 进行PCR 扩增, 前者的扩增结果明显优于后者[ 动物学报49 (5) : 670~674 , 2003 ] 。
关键词大熊猫粪便DNA 丙酮DNA 抽提非损伤性取样An improved protocol for D NA extraction from the faeces of the giant panda 3 ZHON G Hua ① LA I Xu2Long ② W EI Rong2Ping ③ L IU Zhong2Lai ①33( ①College of L if e S cience , Cent ral China Nor mal U niversit y , W uh an430079 , China)( ②Faculty of Earth Sciences , China U niversit y of Geosciences , W uhan430074 , China)( ③China Cons ervation and Res earch Center f or th e Gi ant Pan da , W olong623006 , S ichuan , China) Abstract An improved method that facilitates the extraction of PCR2compatible faecal DNA from giant pand a’s faeces is described. The method involved a novel preprocessing step in DNA extraction. The faeces was washed two or three timeswith precooled acetone , which removed numerous potential PCR inhibitors , and then digested with proteinase K. The DNA was purified with phenol/ chloroform. The faecal DNA obtained was sufficiently pure to support reliable amplifica2 tion , and was applied as template DNA to amplify a portion of the giant panda brain derived neurotrophic factor (BDNF) gene and mitochondrial cytochrome b gene. The sequenced results of PCR products confirmed that the extracted DNA was from the giant panda. Comparison with the PCR products demonstrated that the faecal DNA extracted b y the improved protocol was better than the faecal DNA extracted without acetone preprocessing. [ Acta Zoologica S inica 49 (5) : 670 - 674 , 2003 ] .K ey words Giant panda ( A il uropoda melanoleuca) , Faecal DNA , Acetone , DNA extraction , Noninvasive sampling在大熊猫的遗传多样性、种群数量调查、进化和分类、亲子鉴定等研究中, DNA 分析是重要的研究手段。
光气化反应技术生产异氰酸酯的研究进展
2017年第36卷第5期 CHEMICAL INDUSTRY AND ENGINEERING PROGRESS·1565·化 工 进展光气化反应技术生产异氰酸酯的研究进展毕荣山,胡明明,谭心舜,郑世清(青岛科技大学计算机与化工研究所,山东 青岛 266042)摘要:光气化反应技术是目前工业化规模生产有机异氰酸酯最主要的工艺技术,具有工艺成熟、反应收率高等优点,但由于反应过程涉及剧毒物质光气和生产副产物氯化氢,使其存在安全和环保等隐患。
本文首先结合光气化反应机理,分析了光气化反应技术的本质缺点,总结了目前针对其本质缺点进行改进的研究现状,认为随着科技地进步,光气化反应技术的两个缺点可以逐步克服。
其次,回顾了光气化反应技术从最初的小规模实验室工艺到目前大规模先进生产工艺的发展历程,从反应工程的角度总结了光气化反应技术逐步改进的内在机理,并在此基础上提出了今后光气化技术进一步发展的趋势和研究方向;最后,论文对非光气化异氰酸酯生产技术的研究进行了总结,指出非光气化技术是将来的发展趋势,但在相当长的时间内,还难以在工业装置上取代光气化技术。
因此,对光气化反应技术进行进一步的研究,对目前异氰酸酯工业的节能减排和提高效率具有重要的现实意义。
关键词:异氰酸酯;光气化;反应器中图分类号:TQ226 文献标志码:A 文章编号:1000–6613(2017)05–1565–08 DOI :10.16085/j.issn.1000-6613.2017.05.002Research progress on development of phosgenation reaction technology inisocyanate industryBI Rongshan ,HU Mingming ,TAN Xinshun ,ZHENG Shiqing(Research Center for Computer and Chemical Engineering ,Qingdao University of Science and Technology ,Qingdao266042,Shandong ,China )Abstract :Phosgenation reaction is the main technology to produce isocyanate in industrialization scale at present ,which has advantages of mature process and high yields. However,there are still existing some potential hazards in safety and environmental protection because of phosgene and HCl as reactant and product in phosgenation reaction. This paper analyzed firstly the intrinsic defects of phosgenation reaction technology ,combined with the phosgenation mechanism ,and summarized the present states of improvements to the defects and concluded that two shortcomings of the technology can be solved step by step. Next ,this paper retrospected the development history of phosgenation technology and summarized the internal mechanism of phosgenation progress based on reaction engineering ,as well as presented the development tendency of phosgenation process. Finally ,this paper briefly introduced some non-phosgenation technologies and agreed with that some of them will replace the present technology in the future but not in a short term while we compared the each features. Therefore ,the further researches on phosgenation technology are necessary in promoting the technology of isocyanate industry and for the energy-saving and cost-reducing. Key words :isocyanate ;phosgenation ;reactor收稿日期:2016-09-26;修改稿日期:2016-11-28。
材料科学与工程基础(英文)_南京航空航天大学中国大学mooc课后章节答案期末考试题库2023年
材料科学与工程基础(英文)_南京航空航天大学中国大学mooc课后章节答案期末考试题库2023年1.The driving force for steady-state diffusion is the __________.答案:concentration gradient2.Diffusion coefficient is with the increasing diffusion temperature.答案:exponentially increased;3.Due to , alloys are usually than pure metals of the solvent.答案:solid solution strengthening, stronger;4.The finer the grains, the larger the , and .答案:strength, hardness, toughness;5.With plastic deformation,the increase of dislocationdensity will result in .答案:higher strength;6.In general, Brinell Hardness test is to measure thematerial’s hardness.答案:relatively softer7.Yield strength is corresponding to the occurrenceof deformation.答案:noticeable plastic8.Strain Hardening is also named as .答案:work hardening9.Vacancy diffusion is usually interstitial one.答案:slower than10.Edge and screw dislocations differ in what way?答案:angle between Burgers vector and line direction.11. A ____ may form when impurity atoms are added to a solid, in which case theoriginal crystal structure is retained and no new phases are formed.答案:solid solution12.One explanation for why graphite powder acts so well as a “solid lubricant”is .答案:carbon atoms in graphite are covalently bonded within planar layers but have weaker secondary bonds between layers13.Substitutional atom (impurity) is an example of ______.答案:point defect14.Interstitial solid solution belongs to .答案:finite solid solution;15.The atomic packing factor for FCC is .答案:0.7416.The coordination number of BCC crystal structure is .答案:817.The crystal structure of Cu is ?答案:FCC18.How many atoms does the face centered cubic unit cell contain?答案:Four19.If the electron configuration of Fe is 1s2 2s2 2p6 3s2 3p6 3d6 4s2, then theelectron configurations for the Fe3+ is 1s2 2s2 2p6 3s2 _____.答案:3p6 3d520.Bonds in most metals are referred to as ______.答案:Non-directional21.Covalent bonding occurs as a result of _________ sharing.答案:electron22.Which of the following is NOT an example of primary bonding?答案:Van der Waals23.Atomic weight (A) of an element corresponds to the weighted average of theatomic masses of the atom’s naturally occurring ___________.答案:isotopes24.The point on a phase diagram where the maximum number of allowablephases are in equilibrium is .答案:eutectic point25.Sterling silver (92.5%Ag/7.5%Cu) is an example of ___________.答案:Solid solution26.Engineering stress-strain curve and true stress-strain curve are equal up to .答案:Yeild point27.Among thefollowingtypical transformations of austenite in steels,____________transformation is diffusionless.答案:martensitic28.The heat-treatable aluminum alloy can be strengthened by .答案:Both of above29.In the as-quenched state, martensite is very hard and so brittle that a heattreatment known as must be accomplished sequently.答案:tempering30.During heat treatment of steel, austenite transforms into martensite by .答案:quenching31.Which of the following plane has the highest planar density for fcc.答案:(111)32.Which of the following describes recrystallization?答案:Diffusion dependent with no change in phase composition33.Heating the cold-worked metal progresses in three stages: .答案:recovery, recrystallization, grain growth;34.Strength is increased by making dislocation motion .答案:difficult35.The boundary above which only liquid phase exist is called _________.答案:liquidus36.We have an annealed carbon steel which has hardness of 150HBS. Supposewe know the hardness of Pearlite is 200HBS and the hardness of Ferrite is 80HBS, determine the carbon amount of this steel.答案:0.45%37.The maximum solubility of C in γ-austenite - solid solution is .答案:2.1438.In a plain steel that contains 0.2 percentage carbon, we should expect: .答案:a 25% pearlite and 75% pro-eutectoid ferrite39. A copper-nickel alloy is high-temperature heat treated; the diffusion of Cuinto Ni and Ni into Cu regions is referred to as _____________________.答案:Inter-diffusion40.The phase diagram of Sn-Pb alloy is called .答案:Eutectic phase diagram。
考研英语二阅读真题及答案
考研英语二阅读真题及答案2017考研英语二阅读真题及答案引导语:为了帮助大家更好地准备考研,以下是店铺为大家整理的2017考研英语二阅读真题及答案,欢迎阅读!英语二Section 1 Use of English1. [标准答案][C]how[考点分析]连词辨析[选项分析]? 根据语境,“新发现表明:快乐可能会影响工作__的稳定。
”[A] 为什么 [B] 哪里 [C] 怎样,多么 [D] 当…时候。
根据语义分析,C选项填入原文,译为“快乐可能会影响工作是有多么稳定”,C为正确选项。
2. [标准答案][B]In particular[考点分析]上下文语义以及短语辨析[选项分析][A] 反过来 [B] 尤其是 [C] 相反 [D] 总的来说根据前文语境,第二段第一句译为“根据近期的研究,拥有更多快乐的人的公司会投资更多”。
而第二句“_______那些在快乐氛围中的公司会做更多的研发以及发展。
“第二句是在第一句的基础上进一步强调说明,因此B选项更符合语境要求。
3. [标准答案] [D]necessary[考点分析]上下文语义及形容词词义辨析[选项分析][A]充足的 [B] 著名的 [C] 完美的 [D] 必要的首先,根据本句题干“That’s?because happiness is linked to the kind of longer-term thinking 3 for making investments for the future.”译为“因为快乐与对未来投资有______长远考虑相联系。
”要求填写形容词, 我们要考虑其搭配与其修饰成分。
空格处搭配介词for, 并且修饰“长远考虑”。
因此D选项最符合语境要求。
4. [标准答案][C]optimism[考点分析]上下文语义及名词词义辨析[选项分析][A]个人主义[B] 现代主义[C] 乐观主义[D] 现实主义本题考查同后缀的名词辨析。
根据原文主旨,探讨“happy people”与公司的关系。
热红外传感史
History of infrared detectorsA.ROGALSKI*Institute of Applied Physics, Military University of Technology, 2 Kaliskiego Str.,00–908 Warsaw, PolandThis paper overviews the history of infrared detector materials starting with Herschel’s experiment with thermometer on February11th,1800.Infrared detectors are in general used to detect,image,and measure patterns of the thermal heat radia−tion which all objects emit.At the beginning,their development was connected with thermal detectors,such as ther−mocouples and bolometers,which are still used today and which are generally sensitive to all infrared wavelengths and op−erate at room temperature.The second kind of detectors,called the photon detectors,was mainly developed during the20th Century to improve sensitivity and response time.These detectors have been extensively developed since the1940’s.Lead sulphide(PbS)was the first practical IR detector with sensitivity to infrared wavelengths up to~3μm.After World War II infrared detector technology development was and continues to be primarily driven by military applications.Discovery of variable band gap HgCdTe ternary alloy by Lawson and co−workers in1959opened a new area in IR detector technology and has provided an unprecedented degree of freedom in infrared detector design.Many of these advances were transferred to IR astronomy from Departments of Defence ter on civilian applications of infrared technology are frequently called“dual−use technology applications.”One should point out the growing utilisation of IR technologies in the civilian sphere based on the use of new materials and technologies,as well as the noticeable price decrease in these high cost tech−nologies.In the last four decades different types of detectors are combined with electronic readouts to make detector focal plane arrays(FPAs).Development in FPA technology has revolutionized infrared imaging.Progress in integrated circuit design and fabrication techniques has resulted in continued rapid growth in the size and performance of these solid state arrays.Keywords:thermal and photon detectors, lead salt detectors, HgCdTe detectors, microbolometers, focal plane arrays.Contents1.Introduction2.Historical perspective3.Classification of infrared detectors3.1.Photon detectors3.2.Thermal detectors4.Post−War activity5.HgCdTe era6.Alternative material systems6.1.InSb and InGaAs6.2.GaAs/AlGaAs quantum well superlattices6.3.InAs/GaInSb strained layer superlattices6.4.Hg−based alternatives to HgCdTe7.New revolution in thermal detectors8.Focal plane arrays – revolution in imaging systems8.1.Cooled FPAs8.2.Uncooled FPAs8.3.Readiness level of LWIR detector technologies9.SummaryReferences 1.IntroductionLooking back over the past1000years we notice that infra−red radiation(IR)itself was unknown until212years ago when Herschel’s experiment with thermometer and prism was first reported.Frederick William Herschel(1738–1822) was born in Hanover,Germany but emigrated to Britain at age19,where he became well known as both a musician and an astronomer.Herschel became most famous for the discovery of Uranus in1781(the first new planet found since antiquity)in addition to two of its major moons,Tita−nia and Oberon.He also discovered two moons of Saturn and infrared radiation.Herschel is also known for the twenty−four symphonies that he composed.W.Herschel made another milestone discovery–discov−ery of infrared light on February11th,1800.He studied the spectrum of sunlight with a prism[see Fig.1in Ref.1],mea−suring temperature of each colour.The detector consisted of liquid in a glass thermometer with a specially blackened bulb to absorb radiation.Herschel built a crude monochromator that used a thermometer as a detector,so that he could mea−sure the distribution of energy in sunlight and found that the highest temperature was just beyond the red,what we now call the infrared(‘below the red’,from the Latin‘infra’–be−OPTO−ELECTRONICS REVIEW20(3),279–308DOI: 10.2478/s11772−012−0037−7*e−mail: rogan@.pllow)–see Fig.1(b)[2].In April 1800he reported it to the Royal Society as dark heat (Ref.1,pp.288–290):Here the thermometer No.1rose 7degrees,in 10minu−tes,by an exposure to the full red coloured rays.I drew back the stand,till the centre of the ball of No.1was just at the vanishing of the red colour,so that half its ball was within,and half without,the visible rays of theAnd here the thermometerin 16minutes,degrees,when its centre was inch out of the raysof the sun.as had a rising of 9de−grees,and here the difference is almost too trifling to suppose,that latter situation of the thermometer was much beyond the maximum of the heating power;while,at the same time,the experiment sufficiently indi−cates,that the place inquired after need not be looked for at a greater distance.Making further experiments on what Herschel called the ‘calorific rays’that existed beyond the red part of the spec−trum,he found that they were reflected,refracted,absorbed and transmitted just like visible light [1,3,4].The early history of IR was reviewed about 50years ago in three well−known monographs [5–7].Many historical information can be also found in four papers published by Barr [3,4,8,9]and in more recently published monograph [10].Table 1summarises the historical development of infrared physics and technology [11,12].2.Historical perspectiveFor thirty years following Herschel’s discovery,very little progress was made beyond establishing that the infrared ra−diation obeyed the simplest laws of optics.Slow progress inthe study of infrared was caused by the lack of sensitive and accurate detectors –the experimenters were handicapped by the ordinary thermometer.However,towards the second de−cade of the 19th century,Thomas Johann Seebeck began to examine the junction behaviour of electrically conductive materials.In 1821he discovered that a small electric current will flow in a closed circuit of two dissimilar metallic con−ductors,when their junctions are kept at different tempera−tures [13].During that time,most physicists thought that ra−diant heat and light were different phenomena,and the dis−covery of Seebeck indirectly contributed to a revival of the debate on the nature of heat.Due to small output vol−tage of Seebeck’s junctions,some μV/K,the measurement of very small temperature differences were prevented.In 1829L.Nobili made the first thermocouple and improved electrical thermometer based on the thermoelectric effect discovered by Seebeck in 1826.Four years later,M.Melloni introduced the idea of connecting several bismuth−copper thermocouples in series,generating a higher and,therefore,measurable output voltage.It was at least 40times more sensitive than the best thermometer available and could de−tect the heat from a person at a distance of 30ft [8].The out−put voltage of such a thermopile structure linearly increases with the number of connected thermocouples.An example of thermopile’s prototype invented by Nobili is shown in Fig.2(a).It consists of twelve large bismuth and antimony elements.The elements were placed upright in a brass ring secured to an adjustable support,and were screened by a wooden disk with a 15−mm central aperture.Incomplete version of the Nobili−Melloni thermopile originally fitted with the brass cone−shaped tubes to collect ra−diant heat is shown in Fig.2(b).This instrument was much more sensi−tive than the thermometers previously used and became the most widely used detector of IR radiation for the next half century.The third member of the trio,Langley’s bolometer appea−red in 1880[7].Samuel Pierpont Langley (1834–1906)used two thin ribbons of platinum foil connected so as to form two arms of a Wheatstone bridge (see Fig.3)[15].This instrument enabled him to study solar irradiance far into its infrared region and to measure theintensityof solar radia−tion at various wavelengths [9,16,17].The bolometer’s sen−History of infrared detectorsFig.1.Herschel’s first experiment:A,B –the small stand,1,2,3–the thermometers upon it,C,D –the prism at the window,E –the spec−trum thrown upon the table,so as to bring the last quarter of an inch of the read colour upon the stand (after Ref.1).InsideSir FrederickWilliam Herschel (1738–1822)measures infrared light from the sun– artist’s impression (after Ref. 2).Fig.2.The Nobili−Meloni thermopiles:(a)thermopile’s prototype invented by Nobili (ca.1829),(b)incomplete version of the Nobili−−Melloni thermopile (ca.1831).Museo Galileo –Institute and Museum of the History of Science,Piazza dei Giudici 1,50122Florence, Italy (after Ref. 14).Table 1. Milestones in the development of infrared physics and technology (up−dated after Refs. 11 and 12)Year Event1800Discovery of the existence of thermal radiation in the invisible beyond the red by W. HERSCHEL1821Discovery of the thermoelectric effects using an antimony−copper pair by T.J. SEEBECK1830Thermal element for thermal radiation measurement by L. NOBILI1833Thermopile consisting of 10 in−line Sb−Bi thermal pairs by L. NOBILI and M. MELLONI1834Discovery of the PELTIER effect on a current−fed pair of two different conductors by J.C. PELTIER1835Formulation of the hypothesis that light and electromagnetic radiation are of the same nature by A.M. AMPERE1839Solar absorption spectrum of the atmosphere and the role of water vapour by M. MELLONI1840Discovery of the three atmospheric windows by J. HERSCHEL (son of W. HERSCHEL)1857Harmonization of the three thermoelectric effects (SEEBECK, PELTIER, THOMSON) by W. THOMSON (Lord KELVIN)1859Relationship between absorption and emission by G. KIRCHHOFF1864Theory of electromagnetic radiation by J.C. MAXWELL1873Discovery of photoconductive effect in selenium by W. SMITH1876Discovery of photovoltaic effect in selenium (photopiles) by W.G. ADAMS and A.E. DAY1879Empirical relationship between radiation intensity and temperature of a blackbody by J. STEFAN1880Study of absorption characteristics of the atmosphere through a Pt bolometer resistance by S.P. LANGLEY1883Study of transmission characteristics of IR−transparent materials by M. MELLONI1884Thermodynamic derivation of the STEFAN law by L. BOLTZMANN1887Observation of photoelectric effect in the ultraviolet by H. HERTZ1890J. ELSTER and H. GEITEL constructed a photoemissive detector consisted of an alkali−metal cathode1894, 1900Derivation of the wavelength relation of blackbody radiation by J.W. RAYEIGH and W. WIEN1900Discovery of quantum properties of light by M. PLANCK1903Temperature measurements of stars and planets using IR radiometry and spectrometry by W.W. COBLENTZ1905 A. EINSTEIN established the theory of photoelectricity1911R. ROSLING made the first television image tube on the principle of cathode ray tubes constructed by F. Braun in 18971914Application of bolometers for the remote exploration of people and aircrafts ( a man at 200 m and a plane at 1000 m)1917T.W. CASE developed the first infrared photoconductor from substance composed of thallium and sulphur1923W. SCHOTTKY established the theory of dry rectifiers1925V.K. ZWORYKIN made a television image tube (kinescope) then between 1925 and 1933, the first electronic camera with the aid of converter tube (iconoscope)1928Proposal of the idea of the electro−optical converter (including the multistage one) by G. HOLST, J.H. DE BOER, M.C. TEVES, and C.F. VEENEMANS1929L.R. KOHLER made a converter tube with a photocathode (Ag/O/Cs) sensitive in the near infrared1930IR direction finders based on PbS quantum detectors in the wavelength range 1.5–3.0 μm for military applications (GUDDEN, GÖRLICH and KUTSCHER), increased range in World War II to 30 km for ships and 7 km for tanks (3–5 μm)1934First IR image converter1939Development of the first IR display unit in the United States (Sniperscope, Snooperscope)1941R.S. OHL observed the photovoltaic effect shown by a p−n junction in a silicon1942G. EASTMAN (Kodak) offered the first film sensitive to the infrared1947Pneumatically acting, high−detectivity radiation detector by M.J.E. GOLAY1954First imaging cameras based on thermopiles (exposure time of 20 min per image) and on bolometers (4 min)1955Mass production start of IR seeker heads for IR guided rockets in the US (PbS and PbTe detectors, later InSb detectors for Sidewinder rockets)1957Discovery of HgCdTe ternary alloy as infrared detector material by W.D. LAWSON, S. NELSON, and A.S. YOUNG1961Discovery of extrinsic Ge:Hg and its application (linear array) in the first LWIR FLIR systems1965Mass production start of IR cameras for civil applications in Sweden (single−element sensors with optomechanical scanner: AGA Thermografiesystem 660)1970Discovery of charge−couple device (CCD) by W.S. BOYLE and G.E. SMITH1970Production start of IR sensor arrays (monolithic Si−arrays: R.A. SOREF 1968; IR−CCD: 1970; SCHOTTKY diode arrays: F.D.SHEPHERD and A.C. YANG 1973; IR−CMOS: 1980; SPRITE: T. ELIOTT 1981)1975Lunch of national programmes for making spatially high resolution observation systems in the infrared from multielement detectors integrated in a mini cooler (so−called first generation systems): common module (CM) in the United States, thermal imaging commonmodule (TICM) in Great Britain, syteme modulaire termique (SMT) in France1975First In bump hybrid infrared focal plane array1977Discovery of the broken−gap type−II InAs/GaSb superlattices by G.A. SAI−HALASZ, R. TSU, and L. ESAKI1980Development and production of second generation systems [cameras fitted with hybrid HgCdTe(InSb)/Si(readout) FPAs].First demonstration of two−colour back−to−back SWIR GaInAsP detector by J.C. CAMPBELL, A.G. DENTAI, T.P. LEE,and C.A. BURRUS1985Development and mass production of cameras fitted with Schottky diode FPAs (platinum silicide)1990Development and production of quantum well infrared photoconductor (QWIP) hybrid second generation systems1995Production start of IR cameras with uncooled FPAs (focal plane arrays; microbolometer−based and pyroelectric)2000Development and production of third generation infrared systemssitivity was much greater than that of contemporary thermo−piles which were little improved since their use by Melloni. Langley continued to develop his bolometer for the next20 years(400times more sensitive than his first efforts).His latest bolometer could detect the heat from a cow at a dis−tance of quarter of mile [9].From the above information results that at the beginning the development of the IR detectors was connected with ther−mal detectors.The first photon effect,photoconductive ef−fect,was discovered by Smith in1873when he experimented with selenium as an insulator for submarine cables[18].This discovery provided a fertile field of investigation for several decades,though most of the efforts were of doubtful quality. By1927,over1500articles and100patents were listed on photosensitive selenium[19].It should be mentioned that the literature of the early1900’s shows increasing interest in the application of infrared as solution to numerous problems[7].A special contribution of William Coblenz(1873–1962)to infrared radiometry and spectroscopy is marked by huge bib−liography containing hundreds of scientific publications, talks,and abstracts to his credit[20,21].In1915,W.Cob−lentz at the US National Bureau of Standards develops ther−mopile detectors,which he uses to measure the infrared radi−ation from110stars.However,the low sensitivity of early in−frared instruments prevented the detection of other near−IR sources.Work in infrared astronomy remained at a low level until breakthroughs in the development of new,sensitive infrared detectors were achieved in the late1950’s.The principle of photoemission was first demonstrated in1887when Hertz discovered that negatively charged par−ticles were emitted from a conductor if it was irradiated with ultraviolet[22].Further studies revealed that this effect could be produced with visible radiation using an alkali metal electrode [23].Rectifying properties of semiconductor−metal contact were discovered by Ferdinand Braun in1874[24],when he probed a naturally−occurring lead sulphide(galena)crystal with the point of a thin metal wire and noted that current flowed freely in one direction only.Next,Jagadis Chandra Bose demonstrated the use of galena−metal point contact to detect millimetre electromagnetic waves.In1901he filed a U.S patent for a point−contact semiconductor rectifier for detecting radio signals[25].This type of contact called cat’s whisker detector(sometimes also as crystal detector)played serious role in the initial phase of radio development.How−ever,this contact was not used in a radiation detector for the next several decades.Although crystal rectifiers allowed to fabricate simple radio sets,however,by the mid−1920s the predictable performance of vacuum−tubes replaced them in most radio applications.The period between World Wars I and II is marked by the development of photon detectors and image converters and by emergence of infrared spectroscopy as one of the key analytical techniques available to chemists.The image con−verter,developed on the eve of World War II,was of tre−mendous interest to the military because it enabled man to see in the dark.The first IR photoconductor was developed by Theodore W.Case in1917[26].He discovered that a substance com−posed of thallium and sulphur(Tl2S)exhibited photocon−ductivity.Supported by the US Army between1917and 1918,Case adapted these relatively unreliable detectors for use as sensors in an infrared signalling device[27].The pro−totype signalling system,consisting of a60−inch diameter searchlight as the source of radiation and a thallous sulphide detector at the focus of a24−inch diameter paraboloid mir−ror,sent messages18miles through what was described as ‘smoky atmosphere’in1917.However,instability of resis−tance in the presence of light or polarizing voltage,loss of responsivity due to over−exposure to light,high noise,slug−gish response and lack of reproducibility seemed to be inhe−rent weaknesses.Work was discontinued in1918;commu−nication by the detection of infrared radiation appeared dis−tinctly ter Case found that the addition of oxygen greatly enhanced the response [28].The idea of the electro−optical converter,including the multistage one,was proposed by Holst et al.in1928[29]. The first attempt to make the converter was not successful.A working tube consisted of a photocathode in close proxi−mity to a fluorescent screen was made by the authors in 1934 in Philips firm.In about1930,the appearance of the Cs−O−Ag photo−tube,with stable characteristics,to great extent discouraged further development of photoconductive cells until about 1940.The Cs−O−Ag photocathode(also called S−1)elabo−History of infrared detectorsFig.3.Longley’s bolometer(a)composed of two sets of thin plati−num strips(b),a Wheatstone bridge,a battery,and a galvanometer measuring electrical current (after Ref. 15 and 16).rated by Koller and Campbell[30]had a quantum efficiency two orders of magnitude above anything previously studied, and consequently a new era in photoemissive devices was inaugurated[31].In the same year,the Japanese scientists S. Asao and M.Suzuki reported a method for enhancing the sensitivity of silver in the S−1photocathode[32].Consisted of a layer of caesium on oxidized silver,S−1is sensitive with useful response in the near infrared,out to approxi−mately1.2μm,and the visible and ultraviolet region,down to0.3μm.Probably the most significant IR development in the United States during1930’s was the Radio Corporation of America(RCA)IR image tube.During World War II, near−IR(NIR)cathodes were coupled to visible phosphors to provide a NIR image converter.With the establishment of the National Defence Research Committee,the develop−ment of this tube was accelerated.In1942,the tube went into production as the RCA1P25image converter(see Fig.4).This was one of the tubes used during World War II as a part of the”Snooperscope”and”Sniperscope,”which were used for night observation with infrared sources of illumination.Since then various photocathodes have been developed including bialkali photocathodes for the visible region,multialkali photocathodes with high sensitivity ex−tending to the infrared region and alkali halide photocatho−des intended for ultraviolet detection.The early concepts of image intensification were not basically different from those today.However,the early devices suffered from two major deficiencies:poor photo−cathodes and poor ter development of both cathode and coupling technologies changed the image in−tensifier into much more useful device.The concept of image intensification by cascading stages was suggested independently by number of workers.In Great Britain,the work was directed toward proximity focused tubes,while in the United State and in Germany–to electrostatically focused tubes.A history of night vision imaging devices is given by Biberman and Sendall in monograph Electro−Opti−cal Imaging:System Performance and Modelling,SPIE Press,2000[10].The Biberman’s monograph describes the basic trends of infrared optoelectronics development in the USA,Great Britain,France,and Germany.Seven years later Ponomarenko and Filachev completed this monograph writ−ing the book Infrared Techniques and Electro−Optics in Russia:A History1946−2006,SPIE Press,about achieve−ments of IR techniques and electrooptics in the former USSR and Russia [33].In the early1930’s,interest in improved detectors began in Germany[27,34,35].In1933,Edgar W.Kutzscher at the University of Berlin,discovered that lead sulphide(from natural galena found in Sardinia)was photoconductive and had response to about3μm.B.Gudden at the University of Prague used evaporation techniques to develop sensitive PbS films.Work directed by Kutzscher,initially at the Uni−versity of Berlin and later at the Electroacustic Company in Kiel,dealt primarily with the chemical deposition approach to film formation.This work ultimately lead to the fabrica−tion of the most sensitive German detectors.These works were,of course,done under great secrecy and the results were not generally known until after1945.Lead sulphide photoconductors were brought to the manufacturing stage of development in Germany in about1943.Lead sulphide was the first practical infrared detector deployed in a variety of applications during the war.The most notable was the Kiel IV,an airborne IR system that had excellent range and which was produced at Carl Zeiss in Jena under the direction of Werner K. Weihe [6].In1941,Robert J.Cashman improved the technology of thallous sulphide detectors,which led to successful produc−tion[36,37].Cashman,after success with thallous sulphide detectors,concentrated his efforts on lead sulphide detec−tors,which were first produced in the United States at Northwestern University in1944.After World War II Cash−man found that other semiconductors of the lead salt family (PbSe and PbTe)showed promise as infrared detectors[38]. The early detector cells manufactured by Cashman are shown in Fig. 5.Fig.4.The original1P25image converter tube developed by the RCA(a).This device measures115×38mm overall and has7pins.It opera−tion is indicated by the schematic drawing (b).After1945,the wide−ranging German trajectory of research was essentially the direction continued in the USA, Great Britain and Soviet Union under military sponsorship after the war[27,39].Kutzscher’s facilities were captured by the Russians,thus providing the basis for early Soviet detector development.From1946,detector technology was rapidly disseminated to firms such as Mullard Ltd.in Southampton,UK,as part of war reparations,and some−times was accompanied by the valuable tacit knowledge of technical experts.E.W.Kutzscher,for example,was flown to Britain from Kiel after the war,and subsequently had an important influence on American developments when he joined Lockheed Aircraft Co.in Burbank,California as a research scientist.Although the fabrication methods developed for lead salt photoconductors was usually not completely under−stood,their properties are well established and reproducibi−lity could only be achieved after following well−tried reci−pes.Unlike most other semiconductor IR detectors,lead salt photoconductive materials are used in the form of polycrys−talline films approximately1μm thick and with individual crystallites ranging in size from approximately0.1–1.0μm. They are usually prepared by chemical deposition using empirical recipes,which generally yields better uniformity of response and more stable results than the evaporative methods.In order to obtain high−performance detectors, lead chalcogenide films need to be sensitized by oxidation. The oxidation may be carried out by using additives in the deposition bath,by post−deposition heat treatment in the presence of oxygen,or by chemical oxidation of the film. The effect of the oxidant is to introduce sensitizing centres and additional states into the bandgap and thereby increase the lifetime of the photoexcited holes in the p−type material.3.Classification of infrared detectorsObserving a history of the development of the IR detector technology after World War II,many materials have been investigated.A simple theorem,after Norton[40],can be stated:”All physical phenomena in the range of about0.1–1 eV will be proposed for IR detectors”.Among these effects are:thermoelectric power(thermocouples),change in elec−trical conductivity(bolometers),gas expansion(Golay cell), pyroelectricity(pyroelectric detectors),photon drag,Jose−phson effect(Josephson junctions,SQUIDs),internal emis−sion(PtSi Schottky barriers),fundamental absorption(in−trinsic photodetectors),impurity absorption(extrinsic pho−todetectors),low dimensional solids[superlattice(SL), quantum well(QW)and quantum dot(QD)detectors], different type of phase transitions, etc.Figure6gives approximate dates of significant develop−ment efforts for the materials mentioned.The years during World War II saw the origins of modern IR detector tech−nology.Recent success in applying infrared technology to remote sensing problems has been made possible by the successful development of high−performance infrared de−tectors over the last six decades.Photon IR technology com−bined with semiconductor material science,photolithogra−phy technology developed for integrated circuits,and the impetus of Cold War military preparedness have propelled extraordinary advances in IR capabilities within a short time period during the last century [41].The majority of optical detectors can be classified in two broad categories:photon detectors(also called quantum detectors) and thermal detectors.3.1.Photon detectorsIn photon detectors the radiation is absorbed within the material by interaction with electrons either bound to lattice atoms or to impurity atoms or with free electrons.The observed electrical output signal results from the changed electronic energy distribution.The photon detectors show a selective wavelength dependence of response per unit incident radiation power(see Fig.8).They exhibit both a good signal−to−noise performance and a very fast res−ponse.But to achieve this,the photon IR detectors require cryogenic cooling.This is necessary to prevent the thermalHistory of infrared detectorsFig.5.Cashman’s detector cells:(a)Tl2S cell(ca.1943):a grid of two intermeshing comb−line sets of conducting paths were first pro−vided and next the T2S was evaporated over the grid structure;(b) PbS cell(ca.1945)the PbS layer was evaporated on the wall of the tube on which electrical leads had been drawn with aquadag(afterRef. 38).。
飞秒激光烧蚀晶体硅的改性阈值和微观形态(英文)
Appl.Phys.A74,19–25(2002)/Digital Object Identifier(DOI)10.1007/s003390100893Applied Physics AMaterialsScience&ProcessingFemtosecond laser ablation of silicon–modification thresholds and morphologyJ.Bonse∗,S.Baudach,J.Krüger,W.Kautek,M.LenznerLaboratory for Thin Film Technology,Federal Institute for Materials Research and Testing(BAM),Unter den Eichen87,12205Berlin,Germany Received:4December2000/Revised version:29March2001/Published online:20June2001– Springer-Verlag2001Abstract.We investigated the initial modification and abla-tion of crystalline silicon with single and multiple Ti:sapphire laser pulses of5to400fs duration.In accordance with earlier established models,we found the phenomena amorphization, melting,re-crystallization,nucleated vaporization,and abla-tion to occur with increasing laserfluence down to the short-est pulse durations.We noticed new morphological features (bubbles)as well as familiar ones(ripples,columns).A nearly constant ablation thresholdfluence on the order of0.2J/cm2 for all pulse durations and multiple-pulse irradiation was ob-served.For a duration of≈100fs,significant incubation can be observed,whereas for5fs pulses,the ablation threshold does not depend on the pulse number within the experimental error.For micromachining of silicon,a pulse duration of less than500fs is not advantageous.PACS:79.20D;42.70.QMicromachining with ultrashort laser pulses has attracted growing interest even in industry and medicine since the ap-propriate lasers were made readily available for a wide set of parameters[1,2].It has been demonstrated that ultrashort pulses bear the potential for precise micromachining(later-ally and vertically)in transparent dielectrics[3].In the course of investigations with femtosecond pulses,it became obvious that the detailed mechanisms of damage to solids caused by laser light are far from fully understood.A number of phenomena concerning photo-induced mod-ification of silicon surfaces have been explored in different ranges of wavelength,intensity and duration of the applied laser pulses.In this paper,we want to extend the existing investigations on laser-induced surface damage in silicon to pulse durations as short as5fs.We also observed several different phenomena;we try to methodically“file”these ob-servations into a physical overview.We will demonstrate that the so-far-assumed sequence of physical processes,namely amorphization[4],melting[5, 6],re-crystallization[4,7],nucleated vaporization[8],andfi-nally ablation[9],can also account for these experimental re-∗Corresponding author.(Fax:+49-30/8104-1827,E-mail:joern.bonse@bam.de)sults.Various well-known features,for example,ripples[10] and columns[11],could be realized and appropriately ex-plained as well.In Sect.1,the current knowledge about the interaction between laser pulses and silicon is reviewed. Our experimental results are shown and compared to this in Sect.2.1Physical considerationsThe deposition of the laser energy into a solid is usually viewed in the quantum-mechanical formalism of particle in-teraction.The incident pulse energy is absorbed by the elec-trons,dependent on the peak intensity,by one-,two-or more-photon absorption.Absorption by free carriers(sometimes called inverse bremsstrahlung)depends on the number of al-ready existing carriers and is therefore a subsequent process. The same applies to collisional ionization,which utilizes part of the energy of highly excited carriers to generate new free electrons.These carriers then thermalize to a Fermi–Dirac distribution while transferring their excess energy to phonons, typically on a time scale of100fs.These phonons afterwards recombine to a Bose–Einstein distribution in a few picosec-onds[12].During the detailed exploitation of pulsed-laser annealing(PLA,typically done with nanosecond pulses),a “plasma-annealing”model was established,which stated that a non-thermal“bond softening”was responsible for the loss of the crystal structure[13,14].Recently,this non-thermal model was shown to be applicable for several semiconductors irradiated with femtosecond pulses[15–18].So far,no spatial transport of energy out of the excitation region has been considered.In order to treat the subsequent processes,including melting,boiling,and ablation of mate-rial,one usually uses either a two-temperature model[19,20], which distinguishes between electron and lattice(ion)tem-peratures,or a completely classical model of thermal trans-port in a continuum[8,21].The latter one describes phase changes from the molten phase to a gas,considering the ex-istence of transient thermodynamical states(such as super-heated liquids)due to the rapid action of the ultrashort laser pulses.The physical mechanisms that are involved in photo-excitation of the solid are manifested also in irreversible20changes of the irradiated surface.These changes can be used for identification of some of the processes and also for deter-mination of their thresholdfluences.After irradiation with short laser pulses,re-solidification of molten material was observed to happen in two stages: amorphization and re-crystallization[4].The difference was simply attributed to the amount of energy deposited in the ma-terial(the temperature)and the consequent cooling velocity. At lower temperatures,the material has not enough time to re-crystallize from the melt,thus leaving the semiconductor in an amorphous state.In regions with higher temperatures, cooling is sufficiently slow to allow re-crystallization.Already in previous experiments,a rather mysterious phe-nomenon has been discovered after the solids have been ir-radiated with multiple subsequent pulses[22].Finally termed “ripples”,these periodic surface structures appear as lines orthogonal to the direction of the electricfield vector of the incident light and show a period on the order of the wave-length of the generating light[10,23].The generally accepted explanation of these ripples is an interference between the in-cident light and a surface wave(generated by scattering).This interference leads to periodic modulation of the absorbed in-tensity and consequently to modulated ablation.Column formation in crystalline silicon as a result of multi-pulse laser irradiation has been observed in the past at different laser wavelengths(UV–NIR),for different pulse durations(fs–ns),and in different environments(vacuum, air,different gases).A certain number of laser pulses is re-quired to initiate the self-organized growth process of Si microcolumns in the irradiated region.This phenomenon is of major importance because it can limit the precision of laser ablation.For the treatment with ultrashort(fs) laser pulses,the Si-column formation was observed by sev-eral groups under different experimental conditions(λ= 248nm,τ=105fs,vacuum[24];λ=390nm,τ=250fs, vacuum[9];λ=620nm,τ=300fs,air[25];λ=780nm,τ=100fs,SF6,Cl2,N2,He,vacuum[11]).The phenomenon was also found for short-pulse(ns)excimer-laser irradiation (λ=193nm,τ=23ns,air[26];λ=248nm,τ=25ns, SF6,N2,O2,Ar[27];λ=248nm,τ=12ns,vacuum[28];λ=308nm,τ=28ns,vacuum[29]).The process strongly depends on the number of pulses ap-plied to the same spot and the laserfluence.A further key parameter for the formation process and the shape of the microstructures seems to be the ambient environment.Ox-idizing or halogen-containing atmospheres such as air,O2 or SF6support the generation of high-aspect-ratio pillars, whereas the formation of sharp spikes can be reduced in vac-uum,N2or He[11].On the other hand,column formation is rather insensitive to the laser wavelength[9,11,24,25]and the pulse duration[30,31].Influences of the doping concen-tration have not been observed[11,27].For these reasons, a chemical control of the dimensions of microcolumns seems to be possible[31].2Experimental results and analysisExperiments were carried out with two different Ti:sap-phire laser systems,a commercial CPA system(SPECTRA PHYSICS,Spitfire)at the BAM Berlin and the Vienna sys-tem,comprised of an amplifier and hollowfiber compressor,which is capable of producing5-fs pulses with a maximum energy of500µJ[32].The pulse duration of the latter one was changed between5fs and400fs by inserting dispersive material(glass blocks)in the beam path.The experimen-tal conditions were kept similar.The center wavelengths of the linearly polarized laser pulses differed by only20nm (BAM:800nm,Vienna:780nm).The different repetition rates(BAM:10Hz,Vienna:1kHz)should have no influence on the experimental results because every physical process known to be important here is terminated after1ms.An im-portant measurement–actually the one that dominates the overall error–is the energy detection.Here we used a py-roelectric detector BESTEC PM200(BAM)and the OPHIR pulse energy detector NOV A(Vienna),respectively.Different pulse numbers with varying energy were fo-cused to a diameter on the order of several10µm(BAM: f=60mm plano-convex lens,Vienna:R=100mm spher-ical silver mirror)onto the polished(111)surface of n-doped silicon samples.On these samples,a native oxide layer of about2.7nm thickness has been found from ellip-sometric measurements.For higher appliedfluences(in the single-pulse case for5-fs pulses),the sample was placed in a slightly evacuated chamber(p≈10−4mbar)in order to pre-vent ionization or non-linear effects in air and resulting pulse distortions.Inspection of the irradiated surface regions was performed using an optical microscope(Reichert–Jung,Polyvar)in No-marski mode.A more detailed characterization of morpho-logical changes of the laser-modified areas was done by means of a scanning electron microscope(SEM)equipped with a cold-field electron emission cathode(Hitachi,S-4100, accelerating voltage10kV)and an atomic force microscope (AFM,Digital Instruments,Dimension3000SPM)operated in tapping mode.Anticipating the results of our investigations,we outline the principal physical processes occurring on the Si surface after a Gaussian laser pulse was incident in Fig.1.For com-parison,a damage spot on the silicon surface generated by a single laser pulse is shown in Fig.2exhibiting different cir-cular regions of modification,annealing,and ablation.The formation of ripples cannot be seen in this picture because it only occurs after irradiation with multiple pulses onto the same sample spot.In the following section,these thresholds will be further investigated and classified quantitatively.2.1Modification thresholdsSome of the early experiments on laser-induced modification of silicon surfaces distinguish regions of amorphization and crystallization[4].We observed the same phenomena in our experiments,but the zone of amorphization showed a fur-ther substructure which we believe is related to oxidation of the surface layers of silicon.The thresholds of oxidation and amorphization are so close together that unambiguous iden-tification is hardly possible.However,in order to take this fact into account,we call the physical process in this region modification rather than amorphization.The thresholdfluences for these phenomena can be de-termined similar to the ablation thresholdfluence,namely measuring the diameter of the modified areas versus the pulse fluence and extrapolating to zero[33].In Fig.3,the square of21/xFig.1.Physical processes during the modification of silicon with femtosec-ond laser pulses and their threshold fluencesFig.2.Nomarski optical micrograph of the silicon sample surface treated with a single laser pulse in air (λ=800nm,τ=130fs,Φ0=1.5J /cm 2).The outermost ring has a diameter of 45µmthe diameter (corresponding to a modified area)is depicted versus increasing peak fluence of the laser pulses.Extending the regression of this line to zero yields the threshold values to Φmod =0.26J /cm 2and Φann =0.55J /cm 2,respectively.Forthe applied pulse duration,this is identical to the single-pulse threshold measured by Pronko et al.[20].The ablation thresholds of multi-shot experiments in air for different pulse durations are shown in Fig.4.For pulse durations below 100fs,the threshold becomes constant,a be-havior that is well known for metals [34].For higher pulse numbers,one can find no more evidence for crystallization or oxidation/amorphization.A clean edge of ablation as in Fig.9a can be recognized.From the dimen-sions of these craters,an ablation threshold is determined which cannot be distinguished from other thresholds due to morphological changes in the irradiated surface region.The values in Fig.4are significantly lower than the single-pulse thresholds evaluated from Fig.3,because the thresholds of modification and ablation depend on the number of applied laser pulses.This incubation effect rests on a non-ablating modification of the sample material by the laser pulses in such a manner that the threshold for damage decreases.This effect has been extensively studied at the surface of single-crystal metals [35].A dependence in the form of a power law was found:Φmod (N )=Φmod (1)·N ξ−1.(1)Φmod (N )denotes the modification threshold fluence for N laser pulses,and ξis a material-dependent coefficient.In-cubation is related to an accumulation of energy (i.e.non-complete dissipation of the deposited energy)into plastic stress–strain of the metal.However,this formula has also suc-cessfully been employed in the case of indium phosphide (InP)[36],where it is unclear whether intermediate storage of laser energy is mechanical or,for example,chemical (as in several glasses by F-center formation [37]).In Fig.5,the dependence of N ·Φmod (N )on the number of pulses is plot-ted for our data.The fit according to (1)(solid line)yields a coefficient ξof 0.84.From Fig.5,one can conclude that there is significant in-cubation in silicon for pulses with a duration of ≈100fs.Laser fluence Φ0[ J/cm 2]1S q u a r e d d i a m e t e r D 2[µm 2]1000200030000.50.35Fig.3.Diameter (squared)of modification and re-crystallization of the sili-con surface versus the incident peak fluence of the laser pulse (λ=800nm,τ=130fs,N =1,in air).Squares belong to the areas of modification,whereas circles belong to the re-crystallization regions.Solid lines are lin-ear regressions within the semi-logarithmic plot.The deviation of the data from the regression for high fluences is attributed to a slightly non-Gaussian beam profile (caused by apertures)22T h r e s h o l d f l u e n c e [J /c m 2]Fig.4.Ablation threshold fluence of n-Si(111)for several pulse durations,100pulses per spot,in air.Values measured at λ=780nm,except the solid circle (λ=800nm)Number of pulses N110100N ∗Φm o d (N ) [ J /c m 2]110Fig.5.Threshold fluence of laser-induced damage of silicon versus num-ber of laser pulses with a duration of τ=130fs and λ=800nm in an air environment.The solid line represents a least-squares-fit with (1),where ξ=0.84Fig.6.AFM picture of damage in silicon generated with a single Ti:sapphire laser pulse (λ=780nm,τ=5fs,Φ0=7.7J /cm 2).Dark areas indicate more ablated material.The inset at the bottom of the picture is a line-scan along the dotted white line ,the depth scale is indicated in blackThe precise nature of this effect,whether energy is stored in the form of chemical modification or by mechanical stress (as in the case of metals),cannot be deduced from these results.Interestingly,single-shot measurements with 5-fs pulses yield a damage threshold of 0.20±0.05J /cm 2,which agrees with the threshold achieved with multiple pulses within the experimental error (compare Fig.4).Obviously –for these short pulses –there is no such intermediate storage of energy below the damage threshold as it was found,for example,in fused silica [38].2.2Single-pulse experimentsSurface images taken with an atomic force microscope (AFM)and a scanning electron microscope (SEM)reveal in-teresting morphological features of the damaged areas.TheFig.7a,b.SEM picture (0◦)of damage in silicon generated with Ti:sap-phire laser pulses in air (λ=780nm,τ=5fs,Φ0=2.5J /cm 2,N =5).Three different regions of modification (ablation including ripples,re-crystallization,and amorphization)can be recognized.a Full view,b detail23formation of circular substructures (holes)within the cavities can be observed (see Fig.6).These holes vanish or are ob-scured by other morphological features when the same spot is illuminated with subsequent pulses.With increasing laser fluence,the size of these holes increases.Phenomena such as these are frequently attributed to a locally enhanced car-rier density generated either by an inhomogeneous laser beam profile or by locally enhanced absorption (scratches,crystal defects,dust).An initialization of inhomogeneous surface structures due to “hot spots”in the beam profile can be ruled out because –due to the efficient spatial filtering by guiding in a hollow fiber –the Vienna system exhibits an extremely smooth beam profile [32].External surface impurities (dust,scratches due to pol-ishing)cannot be significant,as we will see in the follow-ing argument.We consider indirect two-photon absorption with a coefficient of only 1cm /GW [39]as the domin-ant carrier-generating mechanism.Calculating the penetra-tion depth induced by this mechanism,one finds that the number of absorbing atoms in the excited volume is far smaller than the number of photons supposedly absorbed in this volume.Thus,even the indirect two-photon absorp-tion is already strongly saturated.Virtually all available electrons are excited and it is hardly conceivable that the carrier density exhibits local spikes (e.g.by absorption of defects)so distinct that locally enhanced ablation could occur.Although an enhancement of surface absorption is no appropriate explanation for the observed substructures,en-hancement of absorption at depth in the semiconductor (where the light intensity already dropped one or moreordersFig.9a–f.SEM pictures (60◦)of damage in silicon generated with Ti:sapphire laser pulses in air.a Φ0=1.0J /cm 2,b 1.3J /cm 2,c 1.8J /cm 2(λ=780nm,τ=100fs,N =100).d Φ0=2.0J /cm 2,e 2.8J /cm 2,f 4.1J /cm 2(λ=800nm,τ=130fs,N =100)of magnitude)could account for an evolving inhomogeneous energy deposition.Consequently,after the strongly saturated and overheated surface layer was removed by phase explosion,normal boil-ing including inhomogeneous nucleation of bubbles occurs in the remaining liquid layer [21].This scenario is sup-ported by the fact that larger bubbles are formed in regions of higher fluences,i.e.regions of higher temperature (and therefore slower cooling)where bubbles have more time togrow.Fig.8.SEM picture (0◦)of damage in silicon generated with Ti:sapphire laser pulses in air (λ=800nm,τ=130fs,Φ0=0.42J /cm 2,N =5)242.3Ablation with multiple pulsesThe application of a moderate number(N≈5)of laser pulses leads to characteristic laser-induced periodic surface struc-tures(ripples).In single-pulse experiments,these highly ori-ented structures were not observed,indicating that a feed-back mechanism is involved during the formation of the sur-face patterns.Fig.7shows typical surface damage in silicon(λ=800nm,τ=5fs)at afluence of2.5J/cm2.Three dif-ferent modified zones are clearly visible(compare Fig.1): ablation and ripple-formation in the central region,anneal-ing in thefirst annular structure,and modification in the outer annular border.It is interesting to note,that all these surface modifications known from longer pulses also occur at this ul-trashort pulse duration of5fs.A magnified view(Fig.7b) reveals average lateral ripple periods between650nm and 750nm which is comparable to the laser wavelength.The rip-ples were always oriented perpendicular to the electric-field vector of the incident radiation.Thus,we attribute this phe-nomenon to the well-known mechanism of interference andsubsequent localfield enhancement[10].Small globules of re-deposited material were observed on the top of the surface corrugations.The same characteristic ripple morphology was detected in the central crater region at an≈25times longer pulse duration(λ=800nm,τ=130fs,Φ0=0.42J/cm2,N=5, see Fig.8).Additionally,some outspread periodic patterned(triangular)regions are seen in the direction of the electric field.A further increased number of laser pulses(N≈100) leads to another characteristic surface morphology:the columns or pillars,already introduced in Sect.1.A certain pulse number is required to nucleate the column growth pro-cess.The evolution of silicon microcones and mirocolumns in a series of laser-generated craters,obtained with a con-stant number of100Ti:sapphire laser pulses(τ=100fs at λ=780nm,andτ=130fs atλ=800nm)at varying peak fluences in air is shown in Fig.9.At a comparatively lowfluence of1.0J/cm2(which is ≈5−6times above the ablation threshold),a uniformly ablated crater with a rough,but featureless bottom can be seen as well as highly directed nearly wavelength-sized rip-ple structures in the border region(Fig.9a).With increas-ing laserfluence,small conical structures arise from the bottom of the craters to form the initial stages of micro-columns(Fig.9b,c).The lateral and vertical extent of the columns and the spacing between them strongly depends on the localfluence.In the center of the irradiated area, the columns are wider,taller and more sparse.In the bor-der region they are packed closer together.Up to afluence of≈2J/cm2,the columns are formed in the middle of the crater(Fig.9d),while at higherfluences(Φ0=2.8J/cm2) the morphology appears crown-like.At this stage of devel-opment,the columns can protrude above the original surface plane(Fig.9e),which provides conclusive evidence for the redeposition/re-crystallization origin of these columns.At further increased laserfluences ofΦ0≈4.1J/cm2,a volcano-like structure is observed within the ablated region(Fig.9f). It is probably formed by not completely ejected mate-rial,which is redeposited at the crater walls when the crater depth exceeds a certain value.The height of the columns grows with an increasing number of laser pulses.If a critical size is reached,a destruction of the Si pillars occurs[24].Concerning the formation mechanism of the silicon columns,we suggest a similar explanation as Lowndes et al.[31].Initial surface corrugation inhomogeneously nucle-ates from local vaporization(bubble ejection from the melt layer)and/or ripple formation and subsequently re-deposited material.On the edges of these corrugations,the absorbed local laserfluence is reduced due to an altered angle of inci-dence of the laser radiation.Therefore,ablation takes place preferably at the minima and maxima of the surface topog-raphy.The silicon-rich vapor which is formed at the grooves cools during the material transport(expansion of the vapor plume)and can be re-deposited at the protruding features of the surface.During a large number of these transport cycles,a highly protruding column can be formed.Addi-tionally,the effect can be enhanced by multiple reflections of the incident laser radiation on the bodies of thecolumns, Fig.10a,b.Cross-sectional SEM picture of damage in silicon gener-ated with Ti:sapphire laser pulses in air(λ=800nm,τ=130fs,Φ0= 0.65J/cm2,N=500).a Full view,b detail25Fig.11.Scheme of the different morphological phenomena after irradiation of the silicon surface with linearly polarized femtosecond laser pulses of typically 100fs durationwhich “guides”the light into the grooves.Therefore,the re-gions between the columns again act as emitters of ablated material.A cross-section through a crater (depth ≈9µm)in silicon obtained after the application of 500subsequent laser pulses in air (λ=800nm,τ=130fs,Φ0=0.65J /cm 2)is shown in Fig.10a.A detail of the crater wall can be seen in Fig.10b.Besides an irregular surface morphology and remaining parts of small columns,only a thin thermally or chemically modi-fied layer (depth <500nm)is visible.Figure 11summarizes the different morphological fea-tures (bubbles,ripples,microcolumns)formed after irradi-ation of silicon surfaces with linearly polarized laser pulses for pulse durations of approximately 100fs.3ConclusionWe investigated laser-induced modification and ablation of silicon surfaces with laser pulse durations in the range be-tween 5fs and 400fs.The multi-pulse ablation threshold flu-ence is almost constant around 0.2J /cm 2.We found several physical processes resulting in clearly distinguishable mor-phological features.These are (from lower to higher fluences)oxidation,amorphization,re-crystallization,the formation of bubbles due to boiling below the surface,and finally ablation.Other features occur while treating the sample with multiple subsequent pulses,namely ripple formation,column growth,and crater formation due to material removal.Although these phenomena can limit the precision of micromachining,there are potential applications of controlled manufactured sili-con microcolumns and needles,for example,field-emission sources in the display technology [40].With respect to the feasibility of using femtosecond pulses for microstructuring of semiconductors one can state that –in contrast to transpar-ent materials –a reduction of the pulse duration below 500fs does not offer significant advantage,because of the nearly constant ablation threshold fluence and the similarity of the observed surface morphologies.Acknowledgements.We thank Birgid Strauss,Sigrid Benemann,and Marion Männ (all at BAM)for their technical assistance.M.L.acknowledges sup-port by the Austrian Science Foundation (FWF)under grant No.P-12762.We are grateful to Harald Bergner and Gabriele Pfeiffer from the Fach-hochschule Jena for help with the AFM.References1.R.Haigh,D.Hayden,P.Longo,T.Neary,A.Wagner:Proc.SPIE 3546,477(1998)2.M.H.Niemz:Laser–Tissue Interactions (Springer,Berlin,Heidelberg 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WC5(Invited)
Silicon Photonic Crystal Waveguide ModulatorsLanlan Gu 1, Wei Jiang 2, Xiaonan Chen 1, Ray T. Chen 1*Microelectronic Research Center, Department of Electrical and Computer Engineering,1. The University of Texas at Austin, Austin, TX 78758, USA2. Omega Optics Inc, Austin, TX 78758, USA*Email:***************.eduAbstractUltra-compact silicon-photonic-crystal-waveguide-based thermo-optic and electro-opticalMach-Zehnder interferometers have been proposed and fabricated. Thermal and electricalsimulations have been performed. Experimental results were in a good agreement with thetheoretical prediction.IntroductionThe driving force behind the development of silicon photonics is the monolithic integration of optics and microelectronics. Silicon remains the dominant material for microelectronics ever since the invention of the integrated circuit. Silicon-on-insulator (SOI) has been identified as a promising material for integrated optoelectronics. CMOS circuits fabricated on SOI benefit from reduced parasitics and absence of latch-up problem, which enable high-speed and low-power operations. SOI also provides strong optical confinement for the telecommunication wavelengths serving as an ideal platform to realize the guided-wave micro- and nano- photonic devices. Silicon microelectronic devices have undergone numerous generations of feature size reduction. However, there has been little progress made in the miniaturization of the silicon based optical components. Photonic crystal provides a promising platform to build ultra-compact and high-performance photonic devices [1]. It has been demonstrated that the light propagation in a photonic crystal waveguide (PCW) can have much slower group velocity than that in the conventional waveguides [2]. Such a slow-photon effect greatly enhances the interaction between the light wave and the wave-guiding materials, namely, it amplifies the optical response of materials to the external fields, such as thermal and electrical fields. It thus potentially leads to a significant reduction in size and power consumption. In this paper, we present the simulation and experimental results for ultra-compact silicon-PCW-based thermo-optic (TO) and electro-optical (EO) Mach-Zehnder interferometers (MZIs).Results and discussionFor low-cost and low-frequency applications, the TO effect is considered an attractive alternative to the free-carrier EO effect for realization of optical switching and modulation [3, 4]. Silicon is an ideal material for implementing TO MZIs operating at 1.5µm mainly because: (1) silicon is transparent at this communication wavelength, (2) the TO coefficient is high in silicon, which is approximately 1.86 X10-4 K -1 , two times greater than polymers and twenty times greater than SiO 2 and Si 3N 4; (3) the thermal conductivity of silicon is also high, which is 100 times higher than SiO 2, and therefore it provides a comparatively fast switching speed. The microscope image of the fabricated silicon-PCW-based TO MZI is shown in Fig. 1 (a). This device was fabricated on a SOI wafer with a 220 nm-thick top silicon layer and a 2 µm-thick buried oxide layer. The pitch size of the hexagonal photonic crystal lattice is a = 400 nm. The normalized air hole diameter is designed to be (a)(b) Fig. 1 (a) Microscope image of the TO MZI;(b) Scanning electron microscope (SEM) image of a PCW at the 45o viewing angle.WC5 (Invited)18:00 – 18:30d/a = 0.53. Details of the fabrication were published in [5]. A Scanning electron microscope (SEM) image of the 45o -view of the PCW in conjunction with an input strip waveguide is shown in Fig. 1 (b). The length of photonic crystal waveguides is 80 µm. An aluminum thin-film micro-heater with the dimension of 8µm X100 µm was deposited on the silicon layer. It was on one side of the active arm of the MZI. A static thermal analysis of such a device was performed using a finite element modeling software, ANSYS. The simulated temperature profile across the device showed a temperature rise of 9o C in the line-defect region under an input ohmic heating power of 70 mW. It can be calculated, in a conventional silicon TO MZI, it requires an active region at least of 460 µm to obtain the π phase shift of the optical signal at 1.55 µm for a 9 o C temperature increase. Details of the calculation were previously reported [5]. However, in the PCW based MZI, the required length of the active region could be reduced significantly due to the amplification of TO effect in photonic crystals, which is intrinsically associated with the high-dispersion property of the PCW. We have experimentally demonstrated a size reduction of the silicon-PCW-based MZI by almost one order of magnitude compared with conventional TO MZIs [6].The modulation measurements were performed on afully-automated Newport Photonics Alignment/Packaging Station. The input and output lensed fibers canbe accurately aligned with silicon waveguides by twofive-axis high-precision stages with computerizedcontrol. TE waves were used for the opticalmeasurements. We chose wavelength at 1548nm, whichis at the edge of the defect mode, for the switchingproperty characterization. Switching characteristics wereobtained through a digital communication analyzer. Themeasured 3dB bandwidth was 30 kHz, which is a typicalvalue of a TO switch. The modulation curves at 1 kHzand 30 kHz are shown in Fig. 2 (a) and (b), respectively.The rise (10% to 90%) time and fall (90% to 10%) timewere measured to be 19 µs and 11 µs, respectively. It wasone order of magnitude faster than that was reported in aconventional structure with the micro-heater placed onthe top of the PCW region [7]. The maximummodulation depth of 84% was achieved at the switchingpower of 78 mW. The power consumption can bereduced by optimizing the heater geometry. It waspreviously shown by the ANSYS thermal simulation, asmall temperature variation of 9 o C was obtained in thePCW region with a supplied heat power of 70 mW. Itwould require an active region at least 460 µm to achieveπ phase shift in a conventional rib or strip waveguide based silicon TO MZI. Our experiments demonstrated almost a one-order of magnitude reduction in the lengthof the device active region, which obviously benefitedfrom the slow group-velocity of the PCW.The main drawback of the TO modulator is itscomparative low switching speed. A feasible way torealize high-speed optical modulation in the GHz domainis to utilize the EO effect instead of the TO effect. MostEO silicon modulators operate based on plasmadispersion effect. The relation between the variation ofthe refractive index and perturbation of free-carrierconcentration was studied by Scorf [8]. Here, wepropose a lateral p-i-n configuration for a PCW based EOMZI, which has a different structure from as previouslyreported [9]. In this device, index tuning was achieved using a forward biasing voltage to inject free carriers into photonic crystal region of the active arm. The switchingspeed of such a p-i-n diode based device is usually determined by the carrier recombination time or carrier transit time depending on which one is larger. The transient characteristics of the p-i-n diode were simulated using a (a) (b)Fig. 2 Modulation curves at (a) 1 kHz and (b) 30 kHz. Fig. 3 Transient free-carrier distributions along lateral distance of the p-i-n diode.two-dimensional semiconductor device simulator MEDICI. Thesimulated p-i-n device has an n-type background dopingconcentration of 1015 /cm 3 in the i region, whereas a uniformdoping concentration of 2X1019 /cm 3 was assumed for both p +and n + regions. The lateral electrodes were defined on top of thep + and n + regions, separated by 2µm from the PCW line defect.It is clearly shown in Fig. 3 that the minority carrier injection inthe intrinsic region, which is also the PCW region, is fairlyuniform. A carrier concentration perturbation of around 3X1017/cm 3, which induced a real refractive-index change of siliconabout -0.001, was predicted within 0.63ns under a forward biasing voltage of 2V. Further decrease of response time can be achieved by reducing the separation distance between the two lateral electrodes. For an index variation about 0.001, it usuallyrequires one-half to several millimeters active region to obtain the required π phase shift in the conventional rib waveguide based MZIs [10]. However, in our proposed PCW based MZI modulators, an active PCW region with a few tens of microns in length is long enough to achieve sufficient phase shift [9]. The microscope image of the fabricated p-i-n diode based silicon PCW MZI is shown in Fig. 4. As shown in Fig. 4, the p + and n + regions were carefully designed to avoid electrical breakdown at the fragile edges of photonic crystal waveguides and the advantages of such a design have been demonstrated in experiments. Extensive electrical and optical measurements is currently under investigation. More detailed experimental results will be presented at the conference.SummaryIn summary, we have proposed and fabricated ultra-compact silicon-PCW-based EO and TO MZIs. Device configurations were carefully designed based on the thermal and electrical simulations. The size of the silicon modulators was significantly reduced by incorporating the PCW into to MZIs. Both TO and EO devices have been fabricated and characterized.AcknowledgementsThis research is supported by AFOSR, DARPA’s AP2C program and NSF’s NNIN program. Technical advices from Dr. Gernot Pomrenke and Dr. Richard Soref are acknowledged.References[1]J. D. Joannopoulos, R. D. Meade, and J. Winn, Photonic Crystals , Princeton University Press, 1995. [2]M. Notomi, K. Yamada, A. Shinya, J. Takahashi, C. Takahashi, and I. Yokohama, “Extremely Large Group-Velocity Dispersion of Line-defect Waveguides in Photonic Crystal Slabs,” Phys. Rev. Lett ., 87, 253902 (2001). [3] G. Cocorullo, M. Iodice, I. Rendina, and P. M. Sarro, “Silicon thermaloptical micromodulator with 700-kHz-3-dBbandwidth ,” IEEE. Photonic technology letters , 7, 363 (1995).[4] Y. A. Vlasov, Martin O’Boyle, Hendrik F. Hamann, and S. J. McNab, “Active control of slow light on achip with photonic crystal waveguides,” Nature , 438, 65 (2005).[5]Lanlan Gu, Yongqiang Jiang, Wei Jiang, Xiaonan Chen, Ray T. Chen, “Silicon-on-insulator-based photonic-crystal Mach-Zehnder interferometers, ” Proceedings of SPIE, 6128, 261-268 (2006). [6]U. Fischer, T. Zinker, B. Schuppert and K. Petermann, “Singlemode optical switches based on SOI waveguides with large cross-section,” Electronics Letters , 30, 406 (1994). [7] Tao Chu, Hirohito Yamada, Satomi Ishida, and Yasuhiko Arakawa, “Thermooptic switch based on photonic-crystalline-defect waveguides,” IEEE. Photonic technology letters , 17, 2083 (2005).[8] R. A. Soref, B. R. Bennett, “Electrooptical effects in silicon,” IEEE J. Quantum Electron. QE-23, 123(1987).[9] Yongqiang Jiang, Wei Jian, Lanlan GU, Xiaonan Chen, Ray T. Chen, “80-micron interaction length silicon nano-photonic crystal waveguide modulator,” Applied Physics Letters , 87, 221105 (2005).[10] G.V. Treyz, P.G. May and J.M. Halbout, “Silicon Mach-Zehnder waveguide interferometers based on theplasma dispersion effect,” Appl. Phys. Lett ., 59, 771 (1991).Fig. 4 Microscope image of the top view of a p-i-n diode based photonic crystal silicon MZI.。
二氧化硅气相的英文
二氧化硅气相的英文English:"Silicon dioxide in the gas phase is commonly referred to as silicon dioxide vapor or silicon dioxide gas. In this state, silicon dioxide exists as individual molecules or small clusters of molecules dispersed in the gas medium. The gas phase of silicon dioxide is primarily encountered in high-temperature environments, such as in certain industrial processes like chemical vapor deposition (CVD) or thermal oxidation. Silicon dioxide vapor is crucial in these processes for depositing thin films of silicon dioxide onto substrates, enabling the fabrication of various electronic and optical devices. The properties of silicon dioxide gas, including its reactivity and transport characteristics, play a significant role in determining the quality and properties of the deposited films. Understanding the behavior of silicon dioxide in the gas phase is thus essential for optimizing these deposition processes and achieving desired material properties."中文翻译:"气相中的二氧化硅通常被称为二氧化硅蒸气或二氧化硅气体。
It is time to view John Searle’s Chinese Room thought
The Chinese Room: Just Say “No!”To appear in the Proceedings of the 22nd Annual Cognitive Science Society Conference, (2000), NJ: LEARobert M. FrenchQuantitative Psychology and Cognitive ScienceUniversity of Liège4000 Liège, Belgiumemail: rfrench@ulg.ac.beAbstractIt is time to view John Searle’s Chinese Room thought experiment in a new light. The main focus of attention has always been on showing what is wrong (or right) with the argument, with the tacit assumption being that somehow there could be such a Room. In this article I argue that the debate should not focus on the question “If a person in the Room answered all the questions in perfect Chinese, while not understanding a word of Chinese, what would the implications of this be for strong AI?” Rather, the question should be, “Does the very idea of such a Room and a person in the Room who is able to answer questions in perfect Chinese while not understanding any Chinese make any sense at all?” And I believe that the answer, in parallel with recent arguments that claim that it would be impossible for a machine to pass the Turing Test unless it had experienced the world as we humans have, is no.IntroductionAlan Turing’s (1950) classic article on the Imitation Game provided an elegant operational definition of intelligence. His article is now exactly fifty years old and ranks, without question, as one of the most important scientific/philosophical papers of the twentieth century. The essence of the test proposed by Turing was that the ability to perfectly simulate unrestricted human conversation would constitute a sufficient criterion for intelligence. This way of defining intelligence, for better or for worse, was largely adopted as of the mid-1950’s, implicitly if not explicitly, as the overarching goal of the nascent field of artificial intelligence (AI).Thirty years after Turing’s article appeared, John Searle (1980) put a new spin on Turing’s original arguments. He developed a thought experiment, now called “The Chinese Room,” which was a reformulation of Turing’s original test and, in so doing, produced what is undoubtedly the second most widely read and hotly discussed paper in artificial intelligence. While Turing was optimistic about the possibility of creating intelligent programs in the foreseeable future, Searle concluded his article on precisely the opposite note:“...no [computer] program, by itself, is sufficient for intentionality.” In short, Searle purported to have shown that real (human-like) intelligence was impossible for any program implemented on a computer. In the present article I will begin by briefly presenting Searle’s well-known transformation of the Turing’s Test. Unlike other critics of the Chinese Room argument, however, I will not take issue with Searle’s argument per se. Rather, I will focus on the argument’s central premise and will argue that the correct approach to the whole argument is simply to refuse to go beyond this premise, for it is, as I hope to show, untenable.The Chinese RoomInstead of Turing’s Imitation Game in which a computer in one room and a person in a separate room both attempt to convince an interrogator that they are human, Searle asks us to begin by imagining a closed room in which there is an English-speaker who knows no Chinese whatsoever. This room is full of symbolic rules specifying inputs and outputs, but, importantly, there are no translations in English to indicate to the person in the room the meaning of any Chinese symbol or string of symbols. A native Chinese person outside the room writes questions — any questions — in Chinese on a piece of paper and sends them into the room. The English-speaker receives each question inside the Room then matches the symbols in the question with symbols in the rule-base. (This does not have to be a direct table matching of the string of symbols in the question with symbols in the rule base, but can include any type of look-up program, regardless of its structural complexity.) The English-speaker is blindly led through the maze of rules to a string of symbols that constitutes an answer to the question. He copies this answer on a piece of paper and sends it out of the room. The Chinese person on the outside of the room would see a perfect response, even though the English-speaker understood no Chinese whatsoever. The Chinese person would therefore be fooled into believing that the person inside the room understood perfect Chinese.Searle then compares the person in the room to a computer program and the symbolic rules that fill the room to the knowledge databases used by the computer program. In Searle’s thought experiment the person who is answering the questions in perfect written Chinese still has no knowledge of Chinese. Searle then applies the conclusion of his thought experiment to the general question of machine intelligence. He concludes that a computer program, however perfectly it managed to communicate in writing, thereby fooling all humanquestioners, would still not understand what it was writing, any more than the person in the Chinese Room understood any Chinese. Ergo, computer programs capable of true understanding are impossible.Searle’s Central PremiseBut this reasoning is based on a central premise that needs close scrutiny.Let us begin with a simple example. If someone began a line of reasoning thus: “Just for the sake of argument, let’s assume that cows are as big as the moon,” you would most likely reply, “Stop right there, I’m not interested in hearing the rest of your argument because cows are demonstrably NOT as big as the moon.” You would be justified in not allowing the person to continue to his conclusions because, as logical as any of his subsequent reasoning might be, any conclusion arising from his absurd premise would be unjustified.Now let us consider the central premise on which Searle’s argument hangs — namely, that there could be such a thing as a “Chinese Room” in which an English-only person could actually fool a native-Chinese questioner. I hope to show that this premise is no more plausible than the existence of lunar-sized cows and, as a result, we have no business allowing ourselves to be drawn into the rest of Searle’s argument, any more than when we were asked to accept that all cows were the size of the moon.Ironically, the arguments in the present paper support Searle’s point that symbolic AI is not sufficient to produce human-like intelligence, but do so not by comparing the person in the Chinese Room to a computer program, but rather by showing that the Chinese Room itself would be an impossibility for a symbol-based AI paradigm.Subcognitive Questioning andthe Turing TestTo understand why such a Room would be impossible, which would mean that the person in the Room could never fool the outside-the-Room questioner, we must look at an argument concerning the Turing Test first put forward by French (1988, 1990, 2000). French’s claim is that no machine that had not experienced life as we humans had could ever hope to pass the Turing Test. His demonstration involves showing just how hard it would be for a computer to consistently reply in a human-like manner to what he called “subcognitive”questions. Since Searle’s Chinese Room argument is simply a reformulation of the Turing Test, we would expect to be able to apply these arguments to the Chinese Room as well, something which we will do this later in this paper.It is important to spend a moment reviewing the nature and the power of “subcognitive” questions.These are questions that are explicitly designed to provide a window on low-level (i.e., unconscious) cognitive or physical structure. By "low-level cognitive structure", we mean the subconscious associative network in human minds that consists of highly overlapping activatable representations of experience (French, 1990). Creating these questions and, especially, gathering the answers to them require a bit of preparation on the part of the Interrogator who will be administering the Turing Test.The Interrogator in the Turing Test (or the Questioner in the Chinese Room) begins by preparing a long list of these questions — the Subcognitive Question List. To get answers to these questions, she ventures out into an English-language population and selects a representative sample of individuals from that population. She asks each person surveyed all the questions on her Subcognitive Question List and records their answers. The questions along with the statistical range of answers to these questions will be the basis for her Human Subcognitive Profile. Here are some of the questions on her list (French, 1988, 1990). Questions using neologisms:"On a scale of 0 (completely implausible) to 10 (completely plausible):- Rate Flugblogs as a name Kellogg's would giveto a new breakfast cereal.- Rate Flugblogs as the name of start-up computercompany- Rate Flugblogs as the name of big, air-filled bagsworn on the feet and used to walk acrossswamps.- Rate Flugly as the name a child might give to afavorite teddy bear.- Rate Flugly as the surname of a bank accountantin a W. C. Fields movie.- Rate Flugly as the surname of a glamorous femalemovie star.“Would you like it if someone called you atrubhead? (0= not at all, ..., 10 = very much)”“Which word do you find prettier: blutch orfarfaletta?”Note that the words flugblogs, flugly, trubhead, blutch and farfaletta are made-up. They will not be found in any dictionary and, yet, because of the uncountable influences, experiences and associations of a lifetime of hearing and using English, we are able to make judgments about these neologisms. And, most importantly, while these judgments may vary between individuals, their variation is not random. For example, the average rating of Flugly as the surname of a glamorous actress will most certainly fall below the average rating of Flugly as the name for a child’s teddy bear. Why? Because English speakers, all of us, havegrown up surrounded by roughly the same sea of sounds and associations that have gradually formed our impressions of the prettiness (or ugliness) of particular words or sounds. And while not all of these associations are identical, of course, they are similar enough to be able to make predictions about how, on average, English-speaking people will react to certain words and sounds. This is precisely why Hollywood movie moguls gave the name “Cary Grant” to a suave and handsome actor born “Archibald Alexander Leach” and why “Henry Deutschendorf, Jr.” was re-baptised “John Denver.”Questions using categories:- Rate banana splits as medicine.- Rate purses as weapons.- Rate pens as weapons.- Rate dry leaves as hiding places.No dictionary definition of “dry leaves” will include in its definition “hiding place,” and, yet, everyone who was ever a child where trees shed their leaves in the fall knows that that piles of dry leaves make wonderful hiding places. But how could this information, and an infinite amount of information just like it that is based on our having experienced the world in a particular way, ever be explicitly programmed into a computer? Questions relying on human physical sensations: - Does holding a gulp of Coca-Cola in your mouthfeel more like having pins-and-needles in yourfoot or having cold water poured on your head?- Put your palms together, fingers outstretched andpressed together. Fold down your two middlefingers till the middle knuckles touch. Move theother four pairs of fingers. What happens to yourother fingers? (Try it!)We can imagine many more questions that would be designed to test not only for subcognitive associations, but for internal physical structure. These would include questions whose answers would arise, for example, from the spacing of a human’s eyes, would be the results of little self-experiments involving tactile sensations on their bodies or sensations after running in place, and so on.People’s answers to subcognitive questions are the product of a lifetime of experiencing the world with our human bodies, our human behaviors (whether culturally or genetically engendered), our human desires and needs, etc. (See Harnard (1989) for a discussion of the closely related symbol grounding problem.)I have asked people the question about Coca-Cola and pins-and-needles many times and they overwhelmingly respond that holding a soft-drink in their mouth feels more like having pins and needles in their foot than having cold water poured on them. Answering this question is dead easy for people who have a head and mouth, have drunk soft-drinks, have had cold water poured on their head, and have feet that occasionally fall asleep. But think of what it would take for a machine that had none of these to answer this question. How could the answer to this question be explicitly programmed into the machine? Perhaps (after reading this article) a programmer could put the question explicitly into the machine’s database, but there are literally infinitely many questions of this sort and to program them all in would be impossible. A program that could answer questions like these in a human-like enough manner to pass a Turing Test would have had to have experienced the world in a way that was very similar to the way in which we had experienced the world. This would mean, among many other things, that it would have to have a body very much like ours with hands like ours, with eyes where we had eyes, etc. For example, if an otherwise perfectly intelligent robot had its eyes on its knees, this would result in detectably non-human associations for such activities as, say, praying in church, falling when riding a bicycle, playing soccer, or wearing pants.The moral of the story is that it doesn’t matter if we humans are confronted with made-up words or conceptual juxtapositions that never normally occur (e.g., dry leaves and hiding place), we can still respond and, moreover, our responses will show statistical regularities over the population. Thus, by surveying the population at large with an extensive set of these questions, we draw up a Human Subcognitive Profile for the population. It is precisely this subcognitive profile that could not be reproduced by a machine that had not experienced the world as the members of the sampled human population had. The Subcognitive Question List that was used to produce the Human Subcognitive Profile gives the well-prepared Interrogator a sure-fire tool for eliminating machines from a Turing test in which humans are also participating. The Interrogator would come to the Turing Test and ask both candidates the questions on her Subcognitive Question List. The candidate most closely matching the average answer profile from the human population will be the human.The English RoomNow let us see how this technique can be gainfully applied to Searle’s Chinese Room thought experiment. We will start by modifying Searle’s original Gedankenexperiment by switching the languages around. This, of course, has no real bearing on the argument itself, but it will make our argument easier to follow. We will assume that inside the Room there is a Chinese person (let’s call him Wu) who understands not a word of written English and outside the Room is a native speaker/writer of English (Sue). Sue sends into the Room questions written in English and Wu must produce the answers to these questions in English.Now, it turns out that Sue is not your average naive questioner, but has read many articles on the Turing Test, knows about subcognitive questions and is thoroughly familiar with John Searle’s argument. She also suspects that the person inside the (English) Room might not actually be able to read English and she sets out to prove her hunch.Sue will not only send into the Room questions like, “What is the capital of Cambodia?”, “Who painted The Mona Lisa?” or “Can fleas fly?” but will also ask a large number of “subcognitive questions.” Because the Room, like the computer in the Turing Test, had not experienced the world as we had and because it would be impossible to explicitly write down all of the rules necessary to answer subcognitive questions in general, the answers to the full range of subcognitive questions could not be contained in the lists of symbolic rules in the Room. Consequently, the person in the Room would be revealed not to speak English for exactly the same reason that the machine in the Turing Test would be revealed not to be a person.Take the simple example of non existent words like blutch or trubhead. These words are neologisms and would certainly be nowhere to be found in the symbolic rules in the English Room. Somehow, the Room would have to contain, in some symbolic form, information not only about all words, but also non-words as well. But the Room, if it is to be compared with a real computer, cannot be infinitely large, nor can we assume infinite fast search of the rule base (see Hofstadter & Dennett, 1981, for a discussion of this point). So, we have two closely related problems: First, and most crucially, how could the rules have gotten into the Room in the first place (a point that Searle simply ignores)? And secondly, the number of explicit symbolic rules would require essentially an infinite amount of space. And while rooms in thought experiments can perhaps be infinitely large, the computers that they are compared to cannot be.In other words, the moral of the story here, as it was for the machine trying to pass the Turing Test, is that no matter how many symbolic rules were in the English Room they would not be sufficient for someone who did not understand written English to fool a determined English questioner. And this is where the story should rightfully end. Searle has no business taking his argument any further — and, ironically, he doesn’t need to, since the necessary inadequacy of an such a Room, regardless of how many symbolic rules it contains, proves his point about the impossibility of achieving artificial intelligence in a traditional symbol-based framework. So, when Searle asks us to accept that the English-only human in his Chinese Room could reply in perfect written Chinese to questions written in Chinese, we must say, “That’s strictly impossible, so stop right there.”Shift in Perception of the Turing Test Let us once again return to the Turing Test to better understand the present argument.It is easy to forget just how high the optimism once ran for the rapid achievement of artificial intelligence. In 1958 when computers were still in their infancy and even high-level programming languages had only just been invented, Simon and Newell, two of the founders of the field of artificial intelligence, wrote, “...there are now in the world machines that think, that learn and that create. Moreover, their ability to do these things is going to increase rapidly until – in a visible future – the range of problems they can handle will be coextensive with the range to which the human mind has been applied.” (Simon & Newell, 1958). Marvin Minsky, head of the MIT AI Laboratory, wrote in 1967, “Within a generation the problem of creating ‘artificial intelligence’ will be substantially solved” (Minsky, 1967).During this period of initial optimism, the vast majority of the authors writing about the Turing Test tacitly accepted Turing’s premise that a machine might actually be able to be built that could pass the Test in the foreseeable future. The debate in the early days of AI, therefore, centered almost exclusively around the validity of Turing’s operational definition of intelligence — namely, did passing the Turing Test constitute a sufficient condition for intelligence or did it not? But researchers’ views on the possibility of achieving artificial intelligence shifted radically between the mid-1960’s and the early 1980’s. By 1982, for example, Minsky’s position regarding achieving artificial intelligence had undergone a radical shift from one of unbounded optimism 15 years earlier to a far more sober assessment of the situation: “The AI problem is one of the hardest ever undertaken by science” (Kolata, 1982). The perception of the Turing Test underwent a parallel shift. At least in part because of the great difficulties being experienced by AI, there was a growing realization of just how hard it would be for a machine to ever pass the Turing Test. Thus, instead of discussing whether or not a machine that had passed the Turing Test was really intelligent, the discussion shifted to the question of whether it would even be possible for any machine to pass such a test (Dennett, 1985; French, 1988, 1990; Crockett 1994; Harnad, 1989; for a review, see French, 2000).The Need for a Corresponding Shift in the Perception of the Chinese RoomA shift in emphasis identical to the one that has occurred for the Turing Test is now needed for Searle’s Chinese Room thought experiment. Searle’s article was published in pre-connectionist 1980, when traditional symbolic AI was still the dominant paradigm in the field. Many of the major difficulties facing symbolic AI had come to light, but in 1980 there was still little emphasis on the “sub-symbolic” side of things.But the growing difficulties that symbolic AI had in dealing with “sub-symbolic cognition” were responsible, at least in part, for the widespread appeal of the connectionist movement of the mid-1980’s. While several of the commentaries of Searle’s original article (Searle, 1980) briefly touch on the difficulties involved in actually creating a Chinese Room, none of them focus outright on the impossibility of the Chinese Room as described by Searle and reject the rest of the argument because of its impossible premise. But this rejection corresponds precisely to rejecting the idea that a machine (that had not experienced the world as we humans have) could ever pass the Turing Test, an idea that many people now accept. We are arguing for a parallel shift in emphasis for the Chinese Room Gedankenexperiment.Can the “Robot Reply” Help?It is necessary to explore for a moment the possibility that one could somehow fill the Chinese Room with all of the appropriate rules that would allow the non-Chinese-reading person to fool a non-holds-barred Chinese questioner. Where could rules come from that would allow the person in the Chinese Room to answer all of the in-coming questions in Chinese perfectly? One possible reply is a version of the Robot Reply (Searle, 1980). Since the rules couldn’t have been symbolic and couldn’t have been explicitly programmed in for the reasons outlined above (also see French, 1988, 1990), perhaps they could have been the product of a Robot that had experienced and interacted with the world as we humans would have, all the while generating rules that would be put in the Chinese Room.This is much closer to what would be required to have the appropriate “rules,” but still leaves open the question of how you could ever come up with such a Robot. The Robot would have to be able to interact seamlessly with the world, exactly as a Chinese person would, in order to have been able to produce all the “rules” (high-level and subcognitive) that would later allow the person in the Room to fool the Well-Prepared Questioner. But then we are back to square one, for creating such a robot amounts to creating a robot that would pass the Turing Test.The Chinese Room: a Simple Refutation It must be reiterated that when Searle is attacking the “strong AI” claim that machines processing strings of symbols are capable of doing what we humans call thinking, he is explicitly talking about programs implemented on computers. It is important not to ignore the fact, as some authors unfortunately have (e.g., Block, 1981), that computers are real machines of finite size and speed; they have neither infinite storage capacity nor infinite processing speed.Now consider the standard Chinese Room, i.e., the one in which the person inside the Room has no knowledge of Chinese and the Questioner outside the Room is Chinese. Now assume that the last character of the following question is distorted in an extremely phallic way, but in a way that nonetheless leaves the character completely readable to any reader of Chinese:“Would the last character of this sentence embarrass a very shy young woman?” In order to answer this question correctly — a trivially easy task for anyone who actually reads Chinese — the Chinese Room would have to contain rules that would not only allow the person to respond perfectly to all strings of Chinese characters that formed comprehensible questions, but also to the infinitely many possible legible distortions of those strings of characters. Combinatorial explosion brings the house down around the Chinese Room. (Remember, we are talking about real computers that can store a finite amount information and must retrieve it in a finite amount of time.)One might be tempted to reply, “The solution is to eliminate all distortions. Only standard fonts of Chinese characters are permitted.” But, of course, there are hundreds, probably thousands, of different fonts of characters in Chinese (Hofstadter, 1985) and it is completely unclear what would constitute “standard fonts.” In any event, one can sidestep even this problem.Consider an equivalent situation in English. It makes perfect sense to ask, “Which letter could be most easily distorted to look like a cloud: an ‘O’ or an ‘X’?”An overwhelming majority of people would, of course, reply “O”, even though clouds, superficially and theoretically, have virtually nothing in common with the letter “O”. But how could the symbolic rules in Searle’s Room possibly serve to answer this perfectly legitimate question? A theory of clouds contained in the rules certainly wouldn’t be of any help, because that would be about storms, wind, rain and meteorology. A theory or database of cloud forms would be of scant help either, since clouds are anything but two dimensional, much less round. Perhaps only if the machine/Room had grown up scrawling vaguely circular shapes on paper and calling them clouds in kindergarten and elementary school, then maybe it would be able to answer this question. But short of having had that experience, I see little hope of an a priori theory of correspondence between clouds and letters that would be of any help.ConclusionThe time has come to view John Searle’s Chinese Room thought experiment in a new light. Up until now, the main focus of attention has been on showing what is wrong (or right) with the argument, with the tacit assumption being that somehow there could be such a Room. This parallels the first forty years of discussionson the Turing Test, where virtually all discussion centered on the sufficiency of the Test as a criterion for machine intelligence, rather than whether any machine could ever actually pass it. However, as the overwhelming difficulties of AI gradually became apparent, the debate on the Turing Test shifted to whether or not any machine that had not experience the world as we had could ever actually pass the Turing Test. It is time for an equivalent shift in attention for Searle’s Chinese Room. The question should not be, “If a person in the Room answered all the questions in perfect Chinese, while not understanding a word of Chinese, what would the implications of this be for strong AI?"” Rather, the question should be, “Does the very idea of such a Room and a person actually be able to answer questions in perfect Chinese while not understanding any Chinese make any sense at all?” And I believe that the answer, in parallel with the impossibility of a machine passing the Turing Test, is no.AcknowledgmentsThe present paper was supported in part by research grant IUAP P4/19 from the Belgian government.ReferencesBlock, N. (1981) Psychologism and behaviourism.Philosophical Review, 90, 5-43Crockett, L. (1994) The Turing Test and the Frame Problem: AI's Mistaken Understanding of Intelligence. AblexDavidson, D. (1990) Turing's test. In Karim A. Said et al. (eds.), Modelling the Mind. Oxford University Press, 1-11.Dennett, D. (1985) Can machines think? In How We Know. (ed.) M. Shafto. Harper & RowFrench, R. M. (1988). Subcognitive Probing: Hard Questions for the Turing Test. Proceedings of the Tenth Annual Cognitive Science Society Conference, Hillsdale, NJ: LEA. 361-367.French, R. M. (1990). Subcognition and the Limits of the Turing Test. Mind, 99(393), 53-65. Reprinted in: P. Millican & A. Clark (eds.). Machines and Thought: The Legacy of Alan Turing Oxford, UK: Clarendon Press, 1996.French, R. M. (2000). Peeking Behind the Screen: The Unsuspected Power of the Standard Turing Test.Journal of Experimental and Theoretical Artificial Intelligence. (in press).French, R. M. (2000). The Turing Test: The First Fifty Years. Trends in Cognitive Sciences, 4(3), 115-122. Harnad, S. (1989) Minds, machines and Searle. Journal of Experimental and Theoretical Artificial Intelligence, 1, 5-25Hofstadter, D. (1985). Variations on a Theme as the Crux of Creativity. In Metamagical Themas. New York, NY: Basic Books. p. 244.Hofstatder, D. & Dennett, D. (1981). The Mind’s I.New York, NY: Basic Books.Kolata, G. (1982) How can computers get common sense? Science, 217, p. 1237Minsky, M. (1967) Computation: Finite and Infinite Machines. Prentice-Hall, p. 2Searle, J. R. (1980). Minds, brains, and programs.Behavioral and Brain Sciences, 3, 414-424. Simon, H. and Newell, A. (1958) Heuristic problem solving: The next advance in operations research.Operations Research, 6。
大环多胺
New1H-Pyrazole-Containing Polyamine Receptors Able ToComplex L-Glutamate in Water at Physiological pH ValuesCarlos Miranda,†Francisco Escartı´,‡Laurent Lamarque,†Marı´a J.R.Yunta,§Pilar Navarro,*,†Enrique Garcı´a-Espan˜a,*,‡and M.Luisa Jimeno†Contribution from the Instituto de Quı´mica Me´dica,Centro de Quı´mica Orga´nica Manuel Lora Tamayo,CSIC,C/Juan de la Cier V a3,28006Madrid,Spain,Departamento de Quı´mica Inorga´nica,Facultad de Quı´mica,Uni V ersidad de Valencia,c/Doctor Moliner50, 46100Burjassot(Valencia),Spain,and Departamento de Quı´mica Orga´nica,Facultad deQuı´mica,Uni V ersidad Complutense de Madrid,A V plutense s/n,28040Madrid,SpainReceived April16,2003;E-mail:enrique.garcia-es@uv.esAbstract:The interaction of the pyrazole-containing macrocyclic receptors3,6,9,12,13,16,19,22,25,26-decaazatricyclo-[22.2.1.111,14]-octacosa-1(27),11,14(28),24-tetraene1[L1],13,26-dibenzyl-3,6,9,12,13,16,-19,22,25,26-decaazatricyclo-[22.2.1.111,14]-octacosa-1(27),11,14(28),24-tetraene2[L2],3,9,12,13,16,22,-25,26-octaazatricyclo-[22.2.1.111,14]-octacosa-1(27),11,14(28),24-tetraene3[L3],6,19-dibenzyl-3,6,9,12,13,-16,19,22,25,26-decaazatricyclo-[22.2.1.111,14]-octacosa-1(27),11,14(28),24-tetraene4[L4],6,19-diphenethyl-3,6,9,12,13,16,19,22,25,26-decaazatricyclo-[22.2.1.111,14]-octacosa-1(27),11,14(28),24-tetraene5[L5],and 6,19-dioctyl-3,6,9,12,13,16,19,22,25,26-decaazatricyclo-[22.2.1.111,14]-octacosa-1(27),11,14(28),24-tetra-ene6[L6]with L-glutamate in aqueous solution has been studied by potentiometric techniques.The synthesis of receptors3-6[L3-L6]is described for the first time.The potentiometric results show that4[L4]containing benzyl groups in the central nitrogens of the polyamine side chains is the receptor displaying the larger interaction at pH7.4(K eff)2.04×104).The presence of phenethyl5[L5]or octyl groups6[L6]instead of benzyl groups4[L4]in the central nitrogens of the chains produces a drastic decrease in the stability[K eff )3.51×102(5),K eff)3.64×102(6)].The studies show the relevance of the central polyaminic nitrogen in the interaction with glutamate.1[L1]and2[L2]with secondary nitrogens in this position present significantly larger interactions than3[L3],which lacks an amino group in the center of the chains.The NMR and modeling studies suggest the important contribution of hydrogen bonding andπ-cation interaction to adduct formation.IntroductionThe search for the L-glutamate receptor field has been andcontinues to be in a state of almost explosive development.1 L-Glutamate(Glu)is thought to be the predominant excitatory transmitter in the central nervous system(CNS)acting at a rangeof excitatory amino acid receptors.It is well-known that it playsa vital role mediating a great part of the synaptic transmission.2However,there is an increasing amount of experimentalevidence that metabolic defects and glutamatergic abnormalitiescan exacerbate or induce glutamate-mediated excitotoxic damageand consequently neurological disorders.3,4Overactivation ofionotropic(NMDA,AMPA,and Kainate)receptors(iGluRs)by Glu yields an excessive Ca2+influx that produces irreversible loss of neurons of specific areas of the brain.5There is much evidence that these processes induce,at least in part,neuro-degenerative illnesses such as Parkinson,Alzheimer,Huntington, AIDS,dementia,and amyotrophic lateral sclerosis(ALS).6In particular,ALS is one of the neurodegenerative disorders for which there is more evidence that excitotoxicity due to an increase in Glu concentration may contribute to the pathology of the disease.7Memantine,a drug able to antagonize the pathological effects of sustained,but relatively small,increases in extracellular glutamate concentration,has been recently received for the treatment of Alzheimer disease.8However,there is not an effective treatment for ALS.Therefore,the preparation of adequately functionalized synthetic receptors for L-glutamate seems to be an important target in finding new routes for controlling abnormal excitatory processes.However,effective recognition in water of aminocarboxylic acids is not an easy task due to its zwitterionic character at physiological pH values and to the strong competition that it finds in its own solvent.9†Centro de Quı´mica Orga´nica Manuel Lora Tamayo.‡Universidad de Valencia.§Universidad Complutense de Madrid.(1)Jane,D.E.In Medicinal Chemistry into the Millenium;Campbell,M.M.,Blagbrough,I.S.,Eds.;Royal Society of Chemistry:Cambridge,2001;pp67-84.(2)(a)Standaert,D.G.;Young,A.B.In The Pharmacological Basis ofTherapeutics;Hardman,J.G.,Goodman Gilman,A.,Limbird,L.E.,Eds.;McGraw-Hill:New York,1996;Chapter22,p503.(b)Fletcher,E.J.;Loge,D.In An Introduction to Neurotransmission in Health and Disease;Riederer,P.,Kopp,N.,Pearson,J.,Eds.;Oxford University Press:New York,1990;Chapter7,p79.(3)Michaelis,E.K.Prog.Neurobiol.1998,54,369-415.(4)Olney,J.W.Science1969,164,719-721.(5)Green,J.G.;Greenamyre,J.T.Prog.Neurobiol.1996,48,613-63.(6)Bra¨un-Osborne,H.;Egebjerg,J.;Nielsen,E.O.;Madsen,U.;Krogsgaard-Larsen,P.J.Med.Chem.2000,43,2609-2645and references therein.(7)(a)Shaw,P.J.;Ince,P.G.J.Neurol.1997,244(Suppl2),S3-S14.(b)Plaitakis,A.;Fesdjian,C.O.;Shashidharan,S Drugs1996,5,437-456.(8)Frantz,A.;Smith,A.Nat.Re V.Drug Dico V ery2003,2,9.Published on Web12/30/200310.1021/ja035671m CCC:$27.50©2004American Chemical Society J.AM.CHEM.SOC.2004,126,823-8339823There are many types of receptors able to interact with carboxylic acids and amino acids in organic solvents,10-13yielding selective complexation in some instances.However,the number of reported receptors of glutamate in aqueous solution is very scarce.In this sense,one of the few reports concerns an optical sensor based on a Zn(II)complex of a 2,2′:6′,2′′-terpyridine derivative in which L -aspartate and L -glutamate were efficiently bound as axial ligands (K s )104-105M -1)in 50/50water/methanol mixtures.14Among the receptors employed for carboxylic acid recogni-tion,the polyamine macrocycles I -IV in Chart 1are of particular relevance to this work.In a seminal paper,Lehn et al.15showed that saturated polyamines I and II could exert chain-length discrimination between different R ,ω-dicarboxylic acids as a function of the number of methylene groups between the two triamine units of the receptor.Such compounds were also able to interact with a glutamic acid derivative which has the ammonium group protected with an acyl moiety.15,16Compounds III and IV reported by Gotor and Lehn interact in their protonated forms in aqueous solution with protected N -acetyl-L -glutamate and N -acetyl-D -glutamate,showing a higher stability for the interaction with the D -isomer.17In both reports,the interaction with protected N -acetyl-L -glutamate at physiological pH yields constants of ca.3logarithmic units.Recently,we have shown that 1H -pyrazole-containing mac-rocycles present desirable properties for the binding of dopam-ine.18These polyaza macrocycles,apart from having a highpositive charge at neutral pH values,can form hydrogen bonds not only through the ammonium or amine groups but also through the pyrazole nitrogens that can behave as hydrogen bond donors or acceptors.In fact,Elguero et al.19have recently shown the ability of the pyrazole rings to form hydrogen bonds with carboxylic and carboxylate functions.These features can be used to recognize the functionalities of glutamic acid,the carboxylic and/or carboxylate functions and the ammonium group.Apart from this,the introduction of aromatic donor groups appropriately arranged within the macrocyclic framework or appended to it through arms of adequate length may contribute to the recognition event through π-cation interactions with the ammonium group of L -glutamate.π-Cation interactions are a key feature in many enzymatic centers,a classical example being acetylcholine esterase.20The role of such an interaction in abiotic systems was very well illustrated several years ago in a seminal work carried out by Dougherty and Stauffer.21Since then,many other examples have been reported both in biotic and in abiotic systems.22Taking into account all of these considerations,here we report on the ability of receptors 1[L 1]-6[L 6](Chart 2)to interact with L -glutamic acid.These receptors display structures which differ from one another in only one feature,which helps to obtain clear-cut relations between structure and interaction(9)Rebek,J.,Jr.;Askew,B.;Nemeth,D.;Parris,K.J.Am.Chem.Soc.1987,109,2432-2434.(10)Seel,C.;de Mendoza,J.In Comprehensi V e Supramolecular Chemistry ;Vogtle,F.,Ed.;Elsevier Science:New York,1996;Vol.2,p 519.(11)(a)Sessler,J.L.;Sanson,P.I.;Andrievesky,A.;Kral,V.In SupramolecularChemistry of Anions ;Bianchi,A.,Bowman-James,K.,Garcı´a-Espan ˜a,E.,Eds.;John Wiley &Sons:New York,1997;Chapter 10,pp 369-375.(b)Sessler,J.L.;Andrievsky,A.;Kra ´l,V.;Lynch,V.J.Am.Chem.Soc.1997,119,9385-9392.(12)Fitzmaurice,R.J.;Kyne,G.M.;Douheret,D.;Kilburn,J.D.J.Chem.Soc.,Perkin Trans.12002,7,841-864and references therein.(13)Rossi,S.;Kyne,G.M.;Turner,D.L.;Wells,N.J.;Kilburn,J.D.Angew.Chem.,Int.Ed.2002,41,4233-4236.(14)Aı¨t-Haddou,H.;Wiskur,S.L.;Lynch,V.M.;Anslyn,E.V.J.Am.Chem.Soc.2001,123,11296-11297.(15)Hosseini,M.W.;Lehn,J.-M.J.Am.Chem.Soc.1982,104,3525-3527.(16)(a)Hosseini,M.W.;Lehn,J.-M.Hel V .Chim.Acta 1986,69,587-603.(b)Heyer,D.;Lehn,J.-M.Tetrahedron Lett.1986,27,5869-5872.(17)(a)Alfonso,I.;Dietrich,B.;Rebolledo,F.;Gotor,V.;Lehn,J.-M.Hel V .Chim.Acta 2001,84,280-295.(b)Alfonso,I.;Rebolledo,F.;Gotor,V.Chem.-Eur.J.2000,6,3331-3338.(18)Lamarque,L.;Navarro,P.;Miranda,C.;Ara ´n,V.J.;Ochoa,C.;Escartı´,F.;Garcı´a-Espan ˜a,E.;Latorre,J.;Luis,S.V.;Miravet,J.F.J.Am.Chem.Soc .2001,123,10560-10570.(19)Foces-Foces,C.;Echevarria,A.;Jagerovic,N.;Alkorta,I.;Elguero,J.;Langer,U.;Klein,O.;Minguet-Bonvehı´,H.-H.J.Am.Chem.Soc.2001,123,7898-7906.(20)Sussman,J.L.;Harel,M.;Frolow,F.;Oefner,C.;Goldman,A.;Toker,L.;Silman,I.Science 1991,253,872-879.(21)Dougherty,D.A.;Stauffer,D.A.Science 1990,250,1558-1560.(22)(a)Sutcliffe,M.J.;Smeeton,A.H.;Wo,Z.G.;Oswald,R.E.FaradayDiscuss.1998,111,259-272.(b)Kearney,P.C.;Mizoue,L.S.;Kumpf,R.A.;Forman,J.E.;McCurdy,A.;Dougherty,D.A.J.Am.Chem.Soc.1993,115,9907-9919.(c)Bra ¨uner-Osborne,H.;Egebjerg,J.;Nielsen,E.;Madsen,U.;Krogsgaard-Larsen,P.J.Med.Chem.2000,43,2609-2645.(d)Zacharias,N.;Dougherty,D.A.Trends Pharmacol.Sci.2002,23,281-287.(e)Hu,J.;Barbour,L.J.;Gokel,G.W.J.Am.Chem.Soc.2002,124,10940-10941.Chart 1.Some Receptors Employed for Dicarboxylic Acid and N -AcetylglutamateRecognitionChart 2.New 1H -Pyrazole-Containing Polyamine Receptors Able To Complex L -Glutamate inWaterA R T I C L E SMiranda et al.824J.AM.CHEM.SOC.9VOL.126,NO.3,2004strengths.1[L1]and2[L2]differ in the N-benzylation of the pyrazole moiety,and1[L1]and3[L3]differ in the presence in the center of the polyamine side chains of an amino group or of a methylene group.The receptors4[L4]and5[L5]present the central nitrogens of the chain N-functionalized with benzyl or phenethyl groups,and6[L6]has large hydrophobic octyl groups.Results and DiscussionSynthesis of3-6.Macrocycles3-6have been obtained following the procedure previously reported for the preparation of1and2.23The method includes a first dipodal(2+2) condensation of the1H-pyrazol-3,5-dicarbaldehyde7with the corresponding R,ω-diamine,followed by hydrogenation of the resulting Schiff base imine bonds.In the case of receptor3,the Schiff base formed by condensation with1,5-pentanediamine is a stable solid(8,mp208-210°C)which precipitated in68% yield from the reaction mixture.Further reduction with NaBH4 in absolute ethanol gave the expected tetraazamacrocycle3, which after crystallization from toluene was isolated as a pure compound(mp184-186°C).In the cases of receptors4-6, the precursor R,ω-diamines(11a-11c)(Scheme1B)were obtained,by using a procedure previously described for11a.24 This procedure is based on the previous protection of the primary amino groups of1,5-diamino-3-azapentane by treatment with phthalic anhydride,followed by alkylation of the secondary amino group of1,5-diphthalimido-3-azapentane9with benzyl, phenethyl,or octyl bromide.Finally,the phthalimido groups of the N-alkyl substituted intermediates10a-10c were removed by treatment with hydrazine to afford the desired amines11a-11c,which were obtained in moderate yield(54-63%).In contrast with the behavior previously observed in the synthesis of3,in the(2+2)dipodal condensations of7with 3-benzyl-,3-phenethyl-,and3-octyl-substituted3-aza-1,5-pentanediamine11a,11b,and11c,respectively,there was not precipitation of the expected Schiff bases(Scheme1A). Consequently,the reaction mixtures were directly reduced in situ with NaBH4to obtain the desired hexaamines4-6,which after being carefully purified by chromatography afforded purecolorless oils in51%,63%,and31%yield,respectively.The structures of all of these new cyclic polyamines have been established from the analytical and spectroscopic data(MS(ES+), 1H and13C NMR)of both the free ligands3-6and their corresponding hydrochloride salts[3‚4HCl,4‚6HCl,5‚6HCl, and6‚6HCl],which were obtained as stable solids following the same procedure previously reported18for1‚6HCl and2‚6HCl.As usually occurs for3,5-disubstituted1H-pyrazole deriva-tives,either the free ligands3-6or their hydrochlorides show very simple1H and13C NMR spectra,in which signals indicate that,because of the prototropic equilibrium of the pyrazole ring, all of these compounds present average4-fold symmetry on the NMR scale.The quaternary C3and C5carbons appear together,and the pairs of methylene carbons C6,C7,and C8are magnetically equivalent(see Experimental Section).In the13C NMR spectra registered in CDCl3solution, significant differences can be observed between ligand3,without an amino group in the center of the side chain,and the N-substituted ligands4-6.In3,the C3,5signal appears as a broad singlet.However,in4-6,it almost disappears within the baseline of the spectra,and the methylene carbon atoms C6and C8experience a significant broadening.Additionally,a remark-able line-broadening is also observed in the C1′carbon signals belonging to the phenethyl and octyl groups of L5and L6, respectively.All of these data suggest that as the N-substituents located in the middle of the side chains of4-6are larger,the dynamic exchange rate of the pyrazole prototropic equilibrium is gradually lower,probably due to a relation between proto-tropic and conformational equilibria.Acid-Base Behavior.To follow the complexation of L-glutamate(hereafter abbreviated as Glu2-)and its protonated forms(HGlu-,H2Glu,and H3Glu+)by the receptors L1-L6, the acid-base behavior of L-glutamate has to be revisited under the experimental conditions of this work,298K and0.15mol dm-3.The protonation constants obtained,included in the first column of Table1,agree with the literature25and show that the zwitterionic HGlu-species is the only species present in aqueous solution at physiological pH values(Scheme2and Figure S1of Supporting Information).Therefore,receptors for(23)Ara´n,V.J.;Kumar,M.;Molina,J.;Lamarque,L.;Navarro,P.;Garcı´a-Espan˜a,E.;Ramı´rez,J.A.;Luis,S.V.;Escuder,.Chem.1999, 64,6137-6146.(24)(a)Yuen Ng,C.;Motekaitis,R.J.;Martell,A.E.Inorg.Chem.1979,18,2982-2986.(b)Anelli,P.L.;Lunazzi,L.;Montanari,F.;Quici,.Chem.1984,49,4197-4203.Scheme1.Synthesis of the Pyrazole-Containing MacrocyclicReceptorsNew1H-Pyrazole-Containing Polyamine Receptors A R T I C L E SJ.AM.CHEM.SOC.9VOL.126,NO.3,2004825glutamate recognition able to address both the negative charges of the carboxylate groups and the positive charge of ammonium are highly relevant.The protonation constants of L 3-L 6are included in Table 1,together with those we have previously reported for receptors L 1and L 2.23A comparison of the constants of L 4-L 6with those of the nonfunctionalized receptor L 1shows a reduced basicity of the receptors L 4-L 6with tertiary nitrogens at the middle of the polyamine bridges.Such a reduction in basicity prevented the potentiometric detection of the last protonation for these ligands in aqueous solution.A similar reduction in basicity was previously reported for the macrocycle with the N -benzylated pyrazole spacers (L 2).23These diminished basicities are related to the lower probability of the tertiary nitrogens for stabilizing the positive charges through hydrogen bond formation either with adjacent nonprotonated amino groups of the molecule or with water molecules.Also,the increase in the hydrophobicity of these molecules will contribute to their lower basicity.The stepwise basicity constants are relatively high for the first four protonation steps,which is attributable to the fact that these protons can bind to the nitrogen atoms adjacent to the pyrazole groups leaving the central nitrogen free,the electrostatic repulsions between them being therefore of little significance.The remaining protonation steps will occur in the central nitrogen atom,which will produce an important increase in the electrostatic repulsion in the molecule and therefore a reduction in basicity.As stated above,the tertiary nitrogen atoms present in L 4-L 6will also contribute to this diminished basicity.To analyze the interaction with glutamic acid,it is important to know the protonation degree of the ligands at physiological pH values.In Table 2,we have calculated the percentages ofthe different protonated species existing in solution at pH 7.4for receptors L 1-L 6.As can be seen,except for the receptor with the pentamethylenic chains L 3in which the tetraprotonated species prevails,all of the other systems show that the di-and triprotonated species prevail,although to different extents.Interaction with Glutamate.The stepwise constants for the interaction of the receptors L 1-L 6with glutamate are shown in Table 3,and selected distribution diagrams are plotted in Figure 1A -C.All of the studied receptors interact with glutamate forming adduct species with protonation degrees (j )which vary between 8and 0depending on the system (see Table 3).The stepwise constants have been derived from the overall association constants (L +Glu 2-+j H +)H j LGlu (j -2)+,log j )provided by the fitting of the pH-metric titration curves.This takes into account the basicities of the receptors and glutamate (vide supra)and the pH range in which a given species prevails in solution.In this respect,except below pH ca.4and above pH 9,HGlu -can be chosen as the protonated form of glutamate involved in the formation of the different adducts.Below pH 4,the participation of H 2Glu in the equilibria has also to be considered (entries 9and 10in Table 3).For instance,the formation of the H 6LGlu 4+species can proceed through the equilibria HGlu -+H 5L 5+)H 6LGlu 4+(entry 8,Table 3),and H 2Glu +H 4L 4+)H 6LGlu 4(entry 9Table 3),with percentages of participation that depend on pH.One of the effects of the interaction is to render somewhat more basic the receptor,and somewhat more acidic glutamic acid,facilitating the attraction between op-positely charged partners.A first inspection of Table 3and of the diagrams A,B,and C in Figure 1shows that the interaction strengths differ markedly from one system to another depending on the structural features of the receptors involved.L 4is the receptor that presents the highest capacity for interacting with glutamate throughout all of the pH range explored.It must also be remarked that there are not clear-cut trends in the values of the stepwise constants as a function of the protonation degree of the receptors.This suggests that charge -charge attractions do not play the most(25)(a)Martell,E.;Smith,R.M.Critical Stability Constants ;Plenum:NewYork,1975.(b)Motekaitis,R.J.NIST Critically Selected Stability Constants of Metal Complexes Database ;NIST Standard Reference Database,version 4,1997.Table 1.Protonation Constants of Glutamic Acid and Receptors L 1-L 6Determined in NaCl 0.15mol dm -3at 298.1KreactionGluL 1aL 2aL 3bL 4L 5L 6L +H )L H c 9.574(2)d 9.74(2)8.90(3)9.56(1)9.25(3)9.49(4)9.34(5)L H +H )L H 2 4.165(3)8.86(2)8.27(2)8.939(7)8.38(3)8.11(5)8.13(5)L H 2+H )L H 3 2.18(2)7.96(2) 6.62(3)8.02(1) 6.89(5)7.17(6)7.46(7)L H 3+H )L H 4 6.83(2) 5.85(4)7.63(1) 6.32(5) 6.35(6) 5.97(8)L H 4+H )L H 5 4.57(3) 3.37(4) 2.72(8) 2.84(9) 3.23(9)L H 5+H )L H 6 3.18(3) 2.27(6)∑log K H n L41.135.334.233.634.034.1aTaken from ref 23.b These data were previously cited in a short communication (ref 26).c Charges omitted for clarity.d Values in parentheses are the standard deviations in the last significant figure.Scheme 2.L -Glutamate Acid -BaseBehaviorTable 2.Percentages of the Different Protonated Species at pH 7.4H 1L aH 2LH 3LH 4LL 11186417L 21077130L 3083458L 4083458L 51154323L 6842482aCharges omitted for clarity.A R T I C L E SMiranda et al.826J.AM.CHEM.SOC.9VOL.126,NO.3,2004outstanding role and that other forces contribute very importantly to these processes.26However,in systems such as these,which present overlapping equilibria,it is convenient to use conditional constants because they provide a clearer picture of the selectivity trends.27These constants are defined as the quotient between the overall amounts of complexed species and those of free receptor and substrate at a given pH[eq1].In Figure2are presented the logarithms of the effective constants versus pH for all of the studied systems.Receptors L1and L2with a nonfunctionalized secondary amino group in the side chains display opposite trend from all other receptors. While the stability of the L1and L2adducts tends to increase with pH,the other ligands show a decreasing interaction. Additionally,L1and L2present a close interaction over the entire pH range under study.The tetraaminic macrocycle L3is a better(26)Escartı´,F.;Miranda,C.;Lamarque,L.;Latorre,J.;Garcı´a-Espan˜a,E.;Kumar,M.;Ara´n,V.J.;Navarro,mun.2002,9,936-937.(27)(a)Bianchi,A.;Garcı´a-Espan˜a,c.1999,12,1725-1732.(b)Aguilar,J.A.;Celda,B.;Garcı´a-Espan˜a,E.;Luis,S.V.;Martı´nez,M.;Ramı´rez,J.A.;Soriano,C.;Tejero,B.J.Chem.Soc.,Perkin Trans.22000, 7,1323-1328.Table3.Stability Constants for the Interaction of L1-L6with the Different Protonated Forms of Glutamate(Glu) entry reaction a L1L2L3L4L5L6 1Glu+L)Glu L 3.30(2)b 4.11(1)2HGlu+L)HGlu L 3.65(2) 4.11(1) 3.68(2) 3.38(4) 3Glu+H L)HGlu L 3.89(2) 4.48(1) 3.96(2) 3.57(4) 4HGlu+H L)H2Glu L 3.49(2) 3.89(1) 2.37(4) 3.71(2)5HGlu+H2L)H3Glu L 3.44(2) 3.73(1) 2.34(3) 4.14(2) 2.46(4) 2.61(7) 6HGlu+H3L)H4Glu L 3.33(2) 3.56(2) 2.66(3) 4.65(2) 2.74(3) 2.55(7) 7HGlu+H4L)H5Glu L 3.02(2) 3.26(2) 2.58(3) 4.77(2) 2.87(3) 2.91(5) 8HGlu+H5L)H6Glu L 3.11(3) 3.54(2) 6.76(3) 4.96(3) 4.47(3) 9H2Glu+H4L)H6Glu L 2.54(3) 3.05(2) 3.88(2) 5.35(3) 3.66(4) 3.56(3) 10H2Glu+H5L)H7Glu L 2.61(6) 2.73(4) 5.51(3) 3.57(4) 3.22(8) 11H3Glu+H4L)H7Glu L 4.82(2) 4.12(9)a Charges omitted for clarity.b Values in parentheses are standard deviations in the last significantfigure.Figure1.Distribution diagrams for the systems(A)L1-glutamic acid, (B)L4-glutamic acid,and(C)L5-glutamicacid.Figure2.Representation of the variation of K cond(M-1)for the interaction of glutamic acid with(A)L1and L3,(B)L2,L4,L5,and L6.Initial concentrations of glutamate and receptors are10-3mol dm-3.Kcond)∑[(H i L)‚(H j Glu)]/{∑[H i L]∑[H j Glu]}(1)New1H-Pyrazole-Containing Polyamine Receptors A R T I C L E SJ.AM.CHEM.SOC.9VOL.126,NO.3,2004827receptor at acidic pH,but its interaction markedly decreases on raising the pH.These results strongly suggest the implication of the central nitrogens of the lateral polyamine chains in the stabilization of the adducts.Among the N-functionalized receptors,L4presents the largest interaction with glutamate.Interestingly enough,L5,which differs from L4only in having a phenethyl group instead of a benzyl one,presents much lower stability of its adducts.Since the basicity and thereby the protonation states that L4and L5 present with pH are very close,the reason for the larger stability of the L4adducts could reside on a better spatial disposition for formingπ-cation interactions with the ammonium group of the amino acid.In addition,as already pointed out,L4presents the highest affinity for glutamic acid in a wide pH range,being overcome only by L1and L2at pH values over9.This observation again supports the contribution ofπ-cation inter-actions in the system L4-glutamic because at these pH values the ammonium functionality will start to deprotonate(see Scheme2and Figure1B).Table4gathers the percentages of the species existing in equilibria at pH7.4together with the values of the conditional constant at this pH.In correspondence with Figure1A,1C and Figure S2(Supporting Information),it can be seen that for L1, L2,L5,and L6the prevailing species are[H2L‚HGlu]+and[H3L‚HGlu]2+(protonation degrees3and4,respectively),while for L3the main species are[H3L‚HGlu]+and[H4L‚HGlu]2+ (protonation degrees4and5,respectively).The most effective receptor at this pH would be L4which joins hydrogen bonding, charge-charge,andπ-cation contributions for the stabilization of the adducts.To check the selectivity of this receptor,we have also studied its interaction with L-aspartate,which is a competitor of L-glutamate in the biologic receptors.The conditional constant at pH7.4has a value of3.1logarithmic units for the system Asp-L4.Therefore,the selectivity of L4 for glutamate over aspartate(K cond(L4-glu)/K cond(L4-asp))will be of ca.15.It is interesting to remark that the affinity of L4 for zwiterionic L-glutamate at pH7.4is even larger than that displayed by receptors III and IV(Chart1)with the protected dianion N-acetyl-L-glutamate lacking the zwitterionic charac-teristics.Applying eq1and the stability constants reported in ref17,conditional constants at pH7.4of 3.24and 2.96 logarithmic units can be derived for the systems III-L-Glu and IV-L-Glu,respectively.Molecular Modeling Studies.Molecular mechanics-based methods involving docking studies have been used to study the binding orientations and affinities for the complexation of glutamate by L1-L6receptors.The quality of a computer simulation depends on two factors:accuracy of the force field that describes intra-and intermolecular interactions,and an adequate sampling of the conformational and configuration space of the system.28The additive AMBER force field is appropriate for describing the complexation processes of our compounds,as it is one of the best methods29in reproducing H-bonding and stacking stabiliza-tion energies.The experimental data show that at pH7.4,L1-L6exist in different protonation states.So,a theoretical study of the protonation of these ligands was done,including all of the species shown in5%or more abundance in the potentiometric measurements(Table4).In each case,the more favored positions of protons were calculated for mono-,di-,tri-,and tetraprotonated species.Molecular dynamics studies were performed to find the minimum energy conformations with simulated solvent effects.Molecular modeling studies were carried out using the AMBER30method implemented in the Hyperchem6.0pack-age,31modified by the inclusion of appropriate parameters. Where available,the parameters came from analogous ones used in the literature.32All others were developed following Koll-man33and Hopfinger34procedures.The equilibrium bond length and angle values came from experimental values of reasonable reference compounds.All of the compounds were constructed using standard geometry and standard bond lengths.To develop suitable parameters for NH‚‚‚N hydrogen bonding,ab initio calculations at the STO-3G level35were used to calculate atomic charges compatible with the AMBER force field charges,as they gave excellent results,and,at the same time,this method allows the study of aryl-amine interactions.In all cases,full geometry optimizations with the Polak-Ribiere algorithm were carried out,with no restraints.Ions are separated far away and well solvated in water due to the fact that water has a high dielectric constant and hydrogen bond network.Consequently,there is no need to use counteri-ons36in the modelization studies.In the absence of explicit solvent molecules,a distance-dependent dielectric factor quali-tatively simulates the presence of water,as it takes into account the fact that the intermolecular electrostatic interactions should vanish more rapidly with distance than in the gas phase.The same results can be obtained using a constant dielectric factor greater than1.We have chosen to use a distance-dependent dielectric constant( )4R ij)as this was the method used by Weiner et al.37to develop the AMBER force field.Table8 shows the theoretical differences in protonation energy(∆E p) of mono-,bi-,and triprotonated hexaamine ligands,for the (28)Urban,J.J.;Cronin,C.W.;Roberts,R.R.;Famini,G.R.J.Am.Chem.Soc.1997,119,12292-12299.(29)Hobza,P.;Kabelac,M.;Sponer,J.;Mejzlik,P.;Vondrasek,put.Chem.1997,18,1136-1150.(30)Cornell,W.D.;Cieplak,P.;Bayly,C.I.;Gould,I.R.;Merz,K.M.,Jr.;Ferguson,D.M.;Spelmeyer,D.C.;Fox,T.;Caldwell,J.W.;Kollman,P.A.J.Am.Chem.Soc.1995,117,5179-5197.(31)Hyperchem6.0(Hypercube Inc.).(32)(a)Fox,T.;Scanlan,T.S.;Kollman,P.A.J.Am.Chem.Soc.1997,119,11571-11577.(b)Grootenhuis,P.D.;Kollman,P.A.J.Am.Chem.Soc.1989,111,2152-2158.(c)Moyna,G.;Hernandez,G.;Williams,H.J.;Nachman,R.J.;Scott,put.Sci.1997,37,951-956.(d)Boden,C.D.J.;Patenden,put.-Aided Mol.Des.1999, 13,153-166.(33)/amber.(34)Hopfinger,A.J.;Pearlstein,put.Chem.1984,5,486-499.(35)Glennon,T.M.;Zheng,Y.-J.;Le Grand,S.M.;Shutzberg,B.A.;Merz,K.M.,put.Chem.1994,15,1019-1040.(36)Wang,J.;Kollman,P.A.J.Am.Chem.Soc.1998,120,11106-11114.Table4.Percentages of the Different Protonated Adducts[HGlu‚H j L](j-1)+,Overall Percentages of Complexation,andConditional Constants(K Cond)at pH7.4for the Interaction ofGlutamate(HGlu-)with Receptors L1-L6at Physiological pH[H n L‚HGlu]an)1n)2n)3n)4∑{[H n L‚HGlu]}K cond(M-1)L13272353 2.44×103L2947763 4.12×103L31101324 3.99×102L423737581 2.04×104L51010222 3.51×102L6121224 3.64×102a Charges omitted for clarity.A R T I C L E S Miranda et al. 828J.AM.CHEM.SOC.9VOL.126,NO.3,2004。
2024考博英语预测英语作文
2024考博英语预测英语作文英文回答:In the contemporary era, the advent of technological advancements has brought about profound transformations in various aspects of human life. Education, being a crucial realm shaping individuals and societies, has also undergone significant reconfigurations in response to these technological upheavals. However, amidst the rapid strides made in educational technology, concerns have emerged regarding the potential consequences for traditional forms of face-to-face learning. This essay aims to delve into the complexities of this issue, examining the possible impacts of educational technology on face-to-face learning while exploring ways to harness the benefits of technology while mitigating its potential drawbacks.On the one hand, educational technology offers a plethora of advantages that can potentially enhance face-to-face learning experiences. By incorporatingtechnological tools into classrooms, educators can create more interactive and engaging learning environments. Interactive whiteboards, virtual reality simulations, and other digital resources can stimulate students' curiosity, foster collaboration, and provide personalized learning experiences tailored to individual needs. Technology also enables access to vast repositories of educational content, including online courses, videos, and interactive simulations, which students can utilize to supplement their classroom learning.Furthermore, educational technology can break down geographical barriers and make education more accessible to diverse populations. Online learning platforms and virtual classrooms allow students from remote areas or with limited mobility to participate in educational programs. Additionally, educational technology can facilitate the creation of blended learning models, combining online and face-to-face instruction to provide a flexible and adaptive learning experience.On the other hand, there are potential drawbacksassociated with the integration of educational technology into face-to-face learning that warrant careful consideration. One concern is the potential for technologyto become a distraction in the classroom, divertingstudents' attention from the learning task. Furthermore,the use of technology may exacerbate existing inequalities, as students from disadvantaged backgrounds may lack accessto necessary devices or reliable internet connectivity.Another concern relates to the potential impact of educational technology on the social and emotional development of students. Face-to-face interactions are essential for building relationships, developing communication skills, and fostering a sense of community within the classroom. Excessive reliance on technology may limit opportunities for students to engage in these crucial interactions, which are vital for their overall well-being and development.To address these concerns and harness the benefits of educational technology while mitigating its potential drawbacks, a balanced and thoughtful approach is imperative.Educators should carefully consider the appropriate uses of technology in the classroom, ensuring that it complements and enhances face-to-face learning rather than replacing it entirely. It is also crucial to ensure equitable access to technology and provide necessary support to students from disadvantaged backgrounds.Moreover, educators should prioritize the developmentof digital literacy skills among students, equipping them with the knowledge and skills to navigate the complexitiesof the digital landscape. By cultivating critical thinking, problem-solving, and effective communication skills, students can harness the power of technology to enhancetheir learning and become active and responsible digital citizens.中文回答:随着科技的进步,教育技术对传统面对面授课方式产生了深远的影响。
药物结晶中的经典与非经典结晶路径
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人工智能gpt的影响专八英语作文
人工智能gpt的影响专八英语作文English: The impact of artificial intelligence, particularly GPT, is vast and far-reaching. GPT, or Generative Pre-trained Transformer, has revolutionized the way we interact with technology. It has significantly improved natural language processing, allowing for more accurate and human-like conversations between humans and machines. GPT has the potential to streamline various industries, from customer service to healthcare, by automating repetitive tasks and providing quick and accurate responses. However, the rise of GPT also raises concerns about data privacy, job displacement, and the ethical implications of relying on AI for decision-making. Furthermore, there are potential risks of misinformation and manipulation through the use of GPT-generated content. Despite these challenges, the development and integration of GPT and other forms of AI are inevitable, and society must find ways to harness the benefits while mitigating the negative consequences.中文翻译: 人工智能,特别是GPT的影响是巨大而深远的。