Tunneling or proppin Evidence from connected transactions in China
基于对应分析模型的隧道纵向裂缝主成因分析
更大 , 其 开 裂 成 因分 析 也 显 得 至 关 重 要 。根 据 已有 的 关 于 隧 道 纵 向 裂 缝 成 因分 析 的 文 献 资 料 , 建 立 隧 道 衬 砌 结 构 纵 向 裂 缝 统 计 样 本 与成 因变 量 的 列 联 表 并 对 其 进 行 矩 阵规 范 化 处 理 , 最 后 基 于对 应 分 析 模 型进 行 R型 和 Q 型 因 子 分 析 。若 前 2维惯 量 累 积 解释 百 分 比 P ≥7 5 %, 二 维 条 件 下 分 析 主 成 因 满足 收 敛 性 要 求 , 否 则 需要 通 过 剔 除 特 殊
a b o u t t h e r e a s o n a n a l y s i s o f l o n g i t u d i n a l c r a c k o f t un n e l l i n i n g s t r u c t u r e, a c o n t i n g e n c y t a b l e wa s e s t a b l i s h e d be t we e n t h e s t a t i s t i c a l s a mpl e s a n d t h e r e a s o n v a r i a b l e s o f t h e l o n g i t ud i n a l c r a c k o f t u n n e l l i n i n g s t r u c t u r e;s u bs e q ue n t l y t h e c o n t i n g e n c y t a b l e wa s n o r ma l i z e d wi t h ma t r i x me t h o d; a n d in f a l l y t h e
应用地球化学元素丰度数据手册-原版
应用地球化学元素丰度数据手册迟清华鄢明才编著地质出版社·北京·1内容提要本书汇编了国内外不同研究者提出的火成岩、沉积岩、变质岩、土壤、水系沉积物、泛滥平原沉积物、浅海沉积物和大陆地壳的化学组成与元素丰度,同时列出了勘查地球化学和环境地球化学研究中常用的中国主要地球化学标准物质的标准值,所提供内容均为地球化学工作者所必须了解的各种重要地质介质的地球化学基础数据。
本书供从事地球化学、岩石学、勘查地球化学、生态环境与农业地球化学、地质样品分析测试、矿产勘查、基础地质等领域的研究者阅读,也可供地球科学其它领域的研究者使用。
图书在版编目(CIP)数据应用地球化学元素丰度数据手册/迟清华,鄢明才编著. -北京:地质出版社,2007.12ISBN 978-7-116-05536-0Ⅰ. 应… Ⅱ. ①迟…②鄢…Ⅲ. 地球化学丰度-化学元素-数据-手册Ⅳ. P595-62中国版本图书馆CIP数据核字(2007)第185917号责任编辑:王永奉陈军中责任校对:李玫出版发行:地质出版社社址邮编:北京市海淀区学院路31号,100083电话:(010)82324508(邮购部)网址:电子邮箱:zbs@传真:(010)82310759印刷:北京地大彩印厂开本:889mm×1194mm 1/16印张:10.25字数:260千字印数:1-3000册版次:2007年12月北京第1版•第1次印刷定价:28.00元书号:ISBN 978-7-116-05536-0(如对本书有建议或意见,敬请致电本社;如本社有印装问题,本社负责调换)2关于应用地球化学元素丰度数据手册(代序)地球化学元素丰度数据,即地壳五个圈内多种元素在各种介质、各种尺度内含量的统计数据。
它是应用地球化学研究解决资源与环境问题上重要的资料。
将这些数据资料汇编在一起将使研究人员节省不少查找文献的劳动与时间。
这本小册子就是按照这样的想法编汇的。
北京大学光华管理学院金融学系研究生导师 刘俏
北京大学光华管理学院金融学系研究生导师刘俏刘俏系别:金融学系职称:教授办公电话:86-10-62767993Email:qiao_liu@刘俏现任北京大学光华管理学院金融学和经济学教授、博士生导师、嘉茂荣聘教授、和主管国际事务和职业发展的院长助理。
他也是深圳证劵交易所专家评审委员会委员和中国证监会、中国金融期货交易所、民生银行、及深交所博士后站指导导师。
刘俏主要教授公司金融,收购与兼并,和国际金融管理课程。
他在公司金融,实证资产定价、实际期权、市场微观结构和中国经济研究等方面拥有众多著述,并且由《金融经济学期刊》(Journal of Financial Economics), 《管理科学》(Management Science),《会计研究期刊》(Journal of Accounting Research), 《金融和数量分析期刊》(Journal of Financial and Quantitative Analysis),《经济学期刊》(Economic Journal),《企业金融》(Journal of Corporate Finance)、《经济探究》(Economic Inquiry), 《比较经济学期刊》(Journal of Comparative Economics), 《会计,审计和金融学期刊》(Journal of Accounting, Auditing and Finance), 《金融分析师期刊》( Financial Analysts Journal), 《经济学通信》(Economics Letter),《亚太商业评论》(Asia-Pacific Business Review)等国际著名金融与经济杂志出版。
他与他人合作编撰一本关于亚洲债券市场的书Asia’s Debt Markets: Prospects and Strategies for Development 于2006年由国际著名出版商- New York: Springer- 出版。
10-会议日程安排
3. Hua Dai and Al Salam
Developing Trust and Service Strategies in Electronic Mediated Environment
Understanding Consumers' Online Search and Purchase Behaviors: A Social-Psychological Perspective Session 3C: E-commerce and E-markets, Enterprise and Economic Issues (miscellaneous session) 分会场3C:电子商务与电子市场, 企业与经济问题(其它研究分会)
3. JunYing Zhong
Dynamic cross-industry business models of mobile payment
4. Long Li
Exploring the Role of Human Nature in the Adoption of Mobile Banking
1. Qi Li and YuanYuan Cao
Study of Acceptance and Adoption Model of Mobile Payment User under Pervasive Services Based on UTAUT Model
2. Zheng Wang
DSME: a Data Synchronization Algorithm of Mobile E-commerce
量子隧道效应博士生对物理学中奇特现象的研究
量子隧道效应博士生对物理学中奇特现象的研究量子隧道效应(Quantum Tunneling Effect)作为量子力学中的一个奇特现象,一直以来都备受物理学家们的关注。
这种现象发生在微观尺度下,当一个粒子在能量较高的势垒之前时,它有可能以非经典的方式穿过这个势垒,而不需要具备足够的能量克服它。
近年来,量子隧道效应引起了博士生们的广泛研究兴趣,他们通过实验和理论分析,深入探索了这个奇特现象的本质以及它对物理学领域的重要意义。
一、量子隧道效应的基本概念量子隧道效应最早由著名物理学家里奇特(Richard Feynman)在20世纪50年代提出。
它与经典物理学中的障碍物穿透不同,后者需要具备足够的能量才能越过障碍物。
而量子隧道效应则是通过量子力学的奇特性质,让粒子在概率上以某种方式通过势垒。
二、量子隧道效应的机理量子隧道效应的机理可以通过波动-粒子二象性来解释。
根据量子力学的基本原理,微观粒子既可以表现为粒子,也可以表现为波动。
当一束波动经过势垒时,它的一部分穿过势垒,一部分被反射回来。
而粒子的位置则无法明确确定,它具有概率分布。
因此,量子隧道效应可以看作是粒子经过势垒的一种概率性过程。
三、博士生对量子隧道效应的研究近年来,越来越多的博士生参与到对量子隧道效应的研究中。
他们通过实验和理论模拟,深入探索量子隧道效应的性质、特点以及应用前景。
以下是一些具体的研究方向:1. 量子隧道效应在电子器件中的应用研究。
随着电子器件尺寸的逐渐缩小,经典物理学的规律已经无法完全描述器件中的电子运动。
博士生们研究了量子隧道效应在纳米尺度电子器件中的应用,例如隧道二极管(Tunneling Diode)和隧道场效应晶体管(Tunneling Field-Effect Transistor),这些器件利用了量子隧道效应的特性,实现了新型电子器件的设计与制造。
2. 量子隧道效应在量子通信中的应用研究。
量子通信是一种利用量子隧道效应传输信息的新型通信方式,具有信息传输安全性高、传输速率快等优点。
光滑平行板高速非达西渗流实验研究
光 滑 平 行 板 高速 非达 西渗 流 实 验研 究
秦 峰 王 媛 顾 智 刚
(. 1 河海 大学 岩土 力 学与堤 坝 工程教 育部 重点 实验 室 , 南京 2 0 9 ;. 1 0 8 2 河海 大学 岩土 工程研 究所 , 南京 2 0 9 ) 1 0 8
摘 要 : 于深埋 隧洞 , 对 由于 高地应 力和 高水压 环境 , 洞通 过较 宽 的裂 隙就 可能发 生较 大 的突 水 和 隧
Ab t a t For t e p t ne ,u e g te s a g r s ur nv r nme t,wa e nr s ma C sr c he d e un l nd r hi h s r s nd hi h p e s e e io n t ri u h y be O — c r d wh n t u e hr u he wi r c u e;a d wat rfo i he fa t e wa n a no i e r s a e u e e he t nn lt o gh t de fa t r n e l w n t r c ur s i nln a t t .So, t m o t a a l lpl t x rm e t ls ud fhi pe d n — r y fow s d e he s o h p r le a e e pe i n a t y o gh s e on Da c l wa on .The e p rme t ls t p x e i n a e u a x e i nt lpr c dur r e c i e . U tlzng For hheme q a i n o g pe d no — r y fow — nd e p rme a o e e we e d s rb d iii c i r e u to fhi h s e n Da c l e q a i f mo i n, t nfue e oe fce f o Da c l ,pe me b lt nd v ra i n f e c r c u e u ton o to he i l nc c fi int o n n— r y fow r a iiy a a ito o a h f a t r we e o a ne hr ug he e pe i nt ld t n u ve ft i g.The e pr s i ft nfu n e c fiinto r bt i d t o h t x rme a a a a d c r itn x e son o he i l e c oe fc e f n n Da c l w nd pe m e biiy wa t i e o hi xp rme t o — r y fo a r a lt sob a n d f rt s e e i n .Fi a l n ly,t e s n fe r n t i xp r— he r a o s o r ori h s e e i
1973年诺贝尔物理学奖隧道现象和约瑟夫森效应的发现
1973年诺贝尔物理学奖——隧道现象和约瑟夫森效应的发现1973年诺贝尔物理学奖一半授予美国纽约州约克城高地(YorktownHeights)IBM瓦森研究中心的江崎玲於奈(Leo Esaki,1925—),美国纽约州斯琴奈克塔迪(Schenectady)通用电器公司的贾埃沃(IvarGiaever,1929—),以表彰他们分别在有关半导体和超导体中的隧道现象的实验发现;另一半授予英国剑桥大学的约瑟夫森(BrianJosephson,1940—),以表彰他对穿过隧道壁垒的超导电流所作的理论预言,特别是关于普遍称为约瑟夫森效应的那些现象。
江崎玲於奈1925年3月12日出生于日本大阪的一个建筑师家庭里,1938年,江崎进入同志社中学,三年后父亲去世。
江崎自幼就表现出对科学的浓厚兴趣,喜欢阅读科学家传记故事,立志要作像爱迪生和马可尼那样的发明家,小时自己动手制作电动火车和汽车模型。
1940年,他以优异成绩越级进入京都第三高等学校。
1944年初提前毕业。
同年10月,江崎进入东京帝国大学攻读实验物理。
在大学期间,为维持生计勤工俭学,做晚间家庭教师。
他认真学习了数学和物理课程,并自学物理学专著。
1947年,江崎获硕士学位,有机会进入神户工业股份有限公司研究真空管热电子发射现象。
他由此接触到固体表面物理化学性质和真空管材料技术。
由于这项研究与强外电场作用下的冷金属表面电子发射现象有关,他对固体中的隧道效应发生了兴趣。
1950年,他转入对半导体材料和晶体管的研究。
这时,晶体管刚刚发明。
1956年江崎辞去神户公司的工作转入索尼公司。
在索尼公司领导了一个小组对半导体二极管内电场发射机理进行研究。
这项研究主要考查窄宽度p-n结的导电机制。
p-n结中内电场分布取决于杂质的分布。
当时许多研究者都把提取含杂质少的高纯半导体材料当作目标,而江崎选择了相反的路线,他尝试制备高掺杂的锗p-n结器件。
1957年初江崎首先获得了掺有高浓度杂质的锗精制单晶体做成了薄p-n结。
文献导读
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Behavior Finance★ Nicholas Baeberis, and Richard Thaler, 2002. Survey of Behavioral Finance.○Graham, J.F., Harvey, C.R., 2001. The theory and practice of corporate finance: evidence from the field. Journal of Financial Economics 60, 187-243.★ Alti, A., 2006. How persistent is the impact of market timing on capital structure? Journal of Finance 61, 1681-1710.○ Baker, M., Wurgler, J., 2002. Market Timing and capital structure. Journal of Finance 57,1-32.○Kayhan, A., Titman, S., 2007. Firms’ histories and their capital structures. Journal ofFinancial Economics 83, 1-32.★ Fama, E.F., French, K.R., 2001. Disappearing dividends: changing firm characteristics or lower propensity to pay? Journal of Financial Economics 60, 3-43.○ DeAngelo, H., DeAngelo, L., Skinner, D.J., 2004. Are dividends disappearing? Dividendconcentration and the consolidation of earnings? Journal of Financial Economics 72, 425-456.★ Billett, M., Qian, Y., 2006. Are overconfident CEOs born or make? Evidence ofself-attribution bias from frequent acquirers. Unpublished working paper, Henry B, TippieCollege of Business, University of Iowa.○ Doukas, J., Petmezas, D., 2006. Acquisitions, overconfident managers and self-attributionbias.Unpublished working paper, Department of Finance, Graduate School of Business, OldDominion University.○ Malmendier, U., Tate, G., 2005. CEO overconfidence and corporate investment. Journal ofFinance 60, 2661-2700.10. The Board of DirectorsWeisbach, M., 1988, Outsider directors and CEO turnovers, Journal of Financial Economics 20, 431-460.Yermack, D., 1996, Higher market valuation of companies with a small board of directors, Journal of Financial Economics 40, 185-211.Rosenstein, S. and J. Wyatt, 1997, Inside Directors, Board Effectiveness, and Shareholder Wealth, Journal of Financial Economics 44, 229-250.Hermalin, B. and M. Weisbach, 1988, The determinants of board composition, Rand Journal of Economics 19, 589-606.Warner, J., R. Watts, and K. Wruck, 1988, Stock prices and top management changes, Journal of Financial Economics 20, 461-492.Johnson, Bruce, Robert Magee, Nandu Nagarajan and Henry Newman, 1985, An Analysis of the Stock Price Reaction to Sudden Executive Deaths: Implications for the Management Labor Model, Journal of Accounting and Economics 7, 151-174.11. Talent, Incentives, and Executive CompensationsBaumol, W., 1990, Entrepreneurship: Productive, Unproductive, and Destructive, Journal of Political Economy 98, 893-921.Murphy, K., A. Shleifer, and R. Vishny, 1991, The allocation of talent: Implications for growth, Quarterly Journal of Economics, 503-530.Jensen, Michael, and Kevin Murphy, 1990, Performance Pay and Top Management Incentives, Journal of Political Economy 98, 225-264.Core, John, Robert Holthausen and David Larcker, 1999, Corporate Governance, Chief Executive Officer Compensation, and Firm Performance, Journal of Financial Economics 51, 371-406.Rose, Nancy, and Andrea Shepard, 1997, Firm Diversification and CEO Compensation: Managerial Ability or Executive Entrenchment? RAND Journal of Economics 28, 489-514. 12. Corporate RestructuringDesai, H. and P. Jain, 1999, Firm performance and focus: Long-run stock market performance following spinoffs, Journal of Financial Economics 54, 75-101.Daley, L., V. Mehrotra and R. Sivakumar, 1997, Corporate focus and value creation: Evidence from spinoffs, Journal of Financial Economics 45, 257-281.Chen, P., V. Mehrotra, R. Sivakumar, and W. Yu, 2001, Layoffs, shareholders’ wealth, and corporate performance, Journal of Empirical Finance 8, 171-199.Servaes, H., 1996, The Value of Diversification During the Conglomerate Merger Wave, Journal of Finance 51, 1201-1225.Berger, P. and E. Ofek, 1996, Bustup Takeovers of Value-Destroying Diversified Firms,Journal of Finance 51, 1175-1200.Lamont, O. A. and C. Polk, 2002, Does diversification destroy value? Evidence from the industry shocks, Journal of Financial Economics 63, 51-77.Gillian, S., J. Kensinger, and J. Martin, 2000, Value creation and corporate diversification: the case of Sears, Roebuck & Co., Journal of Financial Economics 55, 103-137.Cusatis, P., J. Miles and J. Woolridge, Some new evidence that spinoffs create value, in NCF, 592-599.Mansi, S and D. M. Reeb, 2002 Corporate diversification: What gets discounted, Journal of Finance, 2167-2183Graham J. R., M. L. Lemmon and J. G. Wolf, 2002, Does corporate diversification destroy value? Journal of Finance , LVII, 695-720.Schoar, A, 2002, Effects of corporate diversification on productivity, Journal of Finance, LVII, 2379-2403.Campa, J. M. and S. Kedia, 2002, Explaining the diversification discount, Journal of Finance, 1731-1762.Aggarwal, R. and A. A. Samwick, 2003, Why do managers diversify their firms? Agency reconsidered. Journal of Finance, LVIII, 71-118.13. Risk ManagementGuay, W.R., 1999, The impact of derivatives on Þrm risk: An empirical examination of new derivative, Journal of Accounting and Economics 26 , 319-351Allayannis, G., and Weston, J.P., 2001, The use of foreign currency derivatives and firm market value, The Review of Financial Studies 14, 243-276.Guaya, W., and Kothari, S.P., 2003, How much do firms hedge with derivatives? Journal of Financial Economics 70, 423–461.Tufano, P., 1996, Who manage risks: An empirical examination of risk manage practices in gold mining industry, The Journal of Finance, 1097-1137.。
tpo61三篇托福阅读TOEFL原文译文题目答案背景知识
tpo61三篇托福阅读TOEFL原文译文题目答案背景知识阅读-1 (2)原文 (2)译文 (5)题目 (7)答案 (13)背景知识 (15)阅读-2 (18)原文 (19)译文 (22)题目 (24)答案 (32)背景知识 (34)阅读-3 (39)原文 (39)译文 (42)题目 (45)答案 (53)背景知识 (54)阅读-1原文Physical Properties of Minerals①A mineral is a naturally occurring solid formed by inorganic processes. Since the internal structure and chemical composition of a mineral are difficult to determine without the aid of sophisticated tests and apparatus , the more easily recognized physical properties are used in identification.②Most people think of a crystal as a rare commodity, when in fact most inorganic solid objects are composed of crystals. The reason for this misconception is that most crystals do not exhibit their crystal form: the external form of a mineral that reflects the orderly internal arrangement of its atoms. Whenever a mineral forms without space restrictions, individual crystals with well-formed crystal faces will develop. Some crystals, such as those of the mineral quartz, have a very distinctive crystal form that can be helpful in identification. However, most of the time, crystal growth is interrupted because of competition for space, resulting in an intergrown mass of crystals, none of which exhibits crystal form.③Although color is an obvious feature of a mineral, it is often anunreliable diagnostic property. Slight impurities in the common mineral quartz, for example, give it a variety of colors, including pink, purple (amethyst), white, and even black. When a mineral, such as quartz, exhibits a variety of colors, it is said to possess exotic coloration. Exotic coloration is usually caused by the inclusion of impurities, such as foreign ions, in the crystalline structure. Other minerals —for example, sulfur, which is yellow, and malachite, which is bright green —are said to have inherent coloration because their color is a consequence of their chemical makeup and does not vary significantly.④Streak is the color of a mineral in its powdered form and is obtained by rubbing a mineral across a plate of unglazed porcelain. Whereas the color of a mineral often varies from sample to sample, the streak usually does not and is therefore the more reliable property.⑤Luster is the appearance or quality of light reflected from the surface of a mineral. Minerals that have the appearance of metals, regardless of color, are said to have a metallic luster. Minerals with a nonmetallic luster are described by various adjectives, including vitreous (glassy) pearly, silky, resinous, and earthy (dull).⑥One of the most useful diagnostic properties of a mineral is hardness, the resistance of a mineral to abrasion or scratching. This property is determined by rubbing a mineral of unknown hardness against one ofknown hardness, or vice versa. A numerical value can be obtained by using Mohs' scale of hardness, which consists of ten minerals arranged in order from talc, the softest, at number one, to diamond, the hardest, at number ten. Any mineral of unknown hardness can be compared with these or with other objects of known hardness. For example, a fingernail has a hardness of 2.5, a copper penny 5, and a piece of glass 5.5. The mineral gypsum, which has a hardness of two, can be easily scratched with your fingernail. On the other hand, the mineral calcite which has a hardness of three, will scratch your fingernail but will not scratch glass. Quartz, the hardest of the common minerals, will scratch a glass plate.⑦The tendency of a mineral to break along planes of weak bonding is called cleavage. Minerals that possess cleavage are identified by the smooth, flat surfaces produced when the mineral is broken. The simplest type of cleavage is exhibited by the micas. Because the micas have excellent cleavage in one direction, they break to form thin, flat sheets. Some minerals have several cleavage planes, which produce smooth surfaces when broken, while others exhibit poor cleavage, and still others exhibit no cleavage at all. When minerals break evenly in more than one direction, cleavage is described by the number of planes exhibited and the angles at which they meet. Cleavage should not be confused with crystal form. When a mineral exhibits cleavage, itwill break into pieces that have the same configuration as the original sample does. By contrast, quartz crystals do not have cleavage, and if broken, would shatter into shapes that do not resemble each other or the original crystals. Minerals that do not exhibit cleavage are said to fracture when broken. Some break into pieces with smooth curved surfaces resembling broken glass. Others break into splinters or fibers, but most fracture irregularly.译文矿物的物理性质①矿物质是由无机过程形成的天然固体。
清华大学经济管理学院硕士生导师简介-杨之曙
清华大学经济管理学院硕士生导师简介-杨之曙杨之曙金融系教授办公室伟伦楼540凯程教育是五道口金融学院和清华经管考研黄埔军校,在2014年,凯程学员考入五道口金融学院28人,清华经管11人,五道口状元武xy出自凯程, 在2013年,凯程学员考入五道口金融学院29人,清华经管5人,状元李少h出在凯程, 在凯程网站有很多凯程学员成功经验视频,大家随时可以去查看. 2016年五道口金融学院和清华经管考研保录班开始报名!个人简介研究成果研究项目工作经历:2001-2004年,清华大学经济管理学院讲师;2004年-2009年,清华大学经济管理学院副教授,2009年至今,清华大学经济管理学院教授。
2001年,香港科技大学管理学院访问学者;2007年,麻省理工学院斯隆管理学院访问学者。
期刊论文:研究成果发表在JournalofFinance,JournalofFinancialQuantitativeandAnalysis,JournalofFinancialMarkets,Journalo fCorporateFinance,ChinaEconomicReview等国际顶尖和一流学术期刊。
研究项目:多项科研项目获得了国家自然基金,清华大学人文社科研究基金,汇丰银行等基金支持。
获奖情况:2009,研究论文“WhyInvestorsDonotBuyCheaperSecurities?-AnAnalysisofTradingbyIndividualInvestorsinChine seStockMarket"获得2009TheChinaFinanceAssociation(TCFA)AnnualConference最佳论文奖;2006,国家自然科学基金资助项目“中国股票市场微观结构研究”(项目编号:70103002)结题“优秀”;2003,研究论文"EvidenceontheForeignShareDiscountPuzzleinChina:LiquidityorInformationAsymmetry"获得美国2003EasternFinanceAssociation(EFA)AnnualConference最佳论文奖;2002,研究论文"OwnershipStructure,Bid-AskSpreads,andMarketLiquidity-EvidencefromChineseStockMarkets"获得2002年GlobalFinanceAnnualConference最佳论文奖;2002,获得清华大学优秀博士论文。
公司治理结构与财务困境相关性实证——以2008-2010年上市公司数据为例
·综—以2008-2010年上市公司数据为例——一、引言作为现代企业的一个重要特征,所有权和控制权分离使得经营者在追求自身利益最大化的同时,可能会损害公司及股东利益,从而产生代理成本。
要降低这种代理成本,就需要对公司的治理结构及其机制进行设计。
与此同时,安然公司、美国世通等案例均表明,财务失败的企业无一例外地出现了公司治理上的问题。
因此,市场监管者、投资者等也开始更多地关注公司治理结构与财务困境的研究,关注如何提高和促进公司治理的透明度,改善公司治理的效率,进而避免企业陷入财务困境。
本文基于已有研究基础,结合我国上市公司的实际情况,对财务困境的界定遵循多数学者的处理方法(Rose,2000),将“特别处理(ST)”的上市公司界定为财务困境公司(陈静、吴世农等)。
通过运用我国2008年至2010年上市公司的数据,对公司治理结构与财务困境进行具体分析。
二、文献综述(一)国外文献Fitzpartrick(1932)最先使用净资产收益率和股东权益负债比率来判别企业破产,随后,Beaver(1966)、Altman(1968)及Ohlson(1980)等分别提出了一元判别模型、多元判别模型和Logistic回归模型,直到M.Odom和R.Sharda(1990)提出以神经网络模型为代表的非参数预警模型。
在此基础上,Panayiotis(1996)等将管理的有效性作为解释变量引入预测模型,得出了无效管理与财务困境公司被并购的概率正相关的结论。
Gary&Anne(1998)、Elloumi&Gueyie(2001)和AimornJaikengkit(2004)等学者就董事会结构、特征、所有权集中度、管理者所有权及其他股权因素对财务困境的影响进行了检验,发现董事会组成与财务困境相关。
(二)国内文献相对而言,国内学者以吴世农(2001)等的研究最具有代表性。
姜秀华等(2001、2004)研究了弱化的公司治理与公司财务困境可能性的关系,发现主营业务利润水平和第一大股东持股比例显著地影响着公司在2003年被“ST”的可能性;王克敏等(2004)指出公司治理弱化是公司陷入财务困境的主要原因;黄辉、崔飚(2007)的研究表明,股权制衡度增加了财务困境的成本,而国有股比例的提高和股权的相对集中有助于财务困境成本的降低。
(成都七中)四川省成都市第七中学2023-2024学年高二上学期第二次月考模拟试卷一(解析版)
2023外研版-高二上册-成都第七中学
(第二次月考模拟试卷)
(本试卷不含听力)
考试时间:120分钟总分:150分
养成良好的答题习惯,是决定成败的决定性因素之一。做题前,要认真阅读题目要求、题干和选项,并对答案内容作出合理预测;答题时,切忌跟着感觉走,最好按照题目序号来做,不会的或存在疑问的,要做好标记,要善于发现,找到题目的题眼所在,规范答题,书写工整;答题完毕时,要认真检查,查漏补缺,纠正错误。
【3题详解】
细节理解题。根据最后一段“It is a social networking application for dogs. Users can share with other people what’s going on in their dog’s life, share photos, and find great animal-friendly places to meet up.”(这是一款狗狗社交网络应用。用户可以与其他人分享他们的狗狗生活中发生的事情,分享照片,并找到适合动物的地方见面。)可知,用户可以在Dogbook上交流养狗经验。故选D项。
B篇
Multitasking (多任务处理) refers to performing different activities at the same time,such as editing a document or replying to emails while participating in a teleconference. People think that they are capable of doing many things at once. However, the fact remains that they are merely switching from one job to the other.
“岩溶水文地质与生态系统”国际会议暨IGCP598项目国际工作组会议在美国西肯塔基大学召开
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New Perspectives on the Structure of Graphitic Carbons
Critical Reviews in Solid State and Materials Sciences,30:235–253,2005 Copyright c Taylor and Francis Inc.ISSN:1040-8436printDOI:10.1080/10408430500406265New Perspectives on the Structure of Graphitic CarbonsPeter J.F.Harris∗Centre for Advanced Microscopy,University of Reading,Whiteknights,Reading,RG66AF,UKGraphitic forms of carbon are important in a wide variety of applications,ranging from pollutioncontrol to composite materials,yet the structure of these carbons at the molecular level ispoorly understood.The discovery of fullerenes and fullerene-related structures such as carbonnanotubes has given a new perspective on the structure of solid carbon.This review aims toshow how the new knowledge gained as a result of research on fullerene-related carbons canbe applied to well-known forms of carbon such as microporous carbon,glassy carbon,carbonfibers,and carbon black.Keywords fullerenes,carbon nanotubes,carbon nanoparticles,non-graphitizing carbons,microporous carbon,glassy carbon,carbon black,carbonfibers.Table of Contents INTRODUCTION (235)FULLERENES,CARBON NANOTUBES,AND CARBON NANOPARTICLES (236)MICROPOROUS(NON-GRAPHITIZING)CARBONS (239)Background (239)Early Models (241)Evidence for Fullerene-Like Structures in Microporous Carbons (242)New Models for the Structure of Microporous Carbons (242)Carbonization and the Structural Evolution of Microporous Carbon (243)GLASSY CARBON (244)CARBON FIBERS (245)CARBON BLACK (248)Background (248)Structure of Carbon Black Particles (249)Effect of High-Temperature Heat Treatment on Carbon Black Structure (250)CONCLUSIONS (250)ACKNOWLEDGMENTS (251)REFERENCES (251)INTRODUCTIONUntil quite recently we knew for certain of just two allotropes of carbon:diamond and graphite.The vast range of carbon ma-∗E-mail:p.j.f.harris@ terials,both natural and synthetic,which have more disordered structures have traditionally been considered as variants of one or other of these two allotropes.Because the great majority of these materials contain sp2carbon rather than sp3carbon,their struc-tures have been thought of as being made up from tiny fragments235236P.J.F.HARRISFI G.1.(a)Model of PAN-derived carbon fibres from the work of Crawford and Johnson,1(b)model of a non-graphitizing carbon by Ban and colleagues.2of crystalline graphite.Examples of models for the structures of carbons in which the basic elements are graphitic are reproduced in Figure 1.The structure shown in Figure 1(a)is a model for the structure of carbon fibers suggested by Crawford and Johnson in 1971,1whereas 1(b)shows a model for non-graphitizing car-bon given by Ban and colleagues in 1975.2Both structures are constructed from bent or curved sheets of graphite,containing exclusively hexagonal rings.Although these models probably provide a good first approximation of the structures of these car-bons,in many cases they fail to explain fully the properties of the materials.Consider the example of non-graphitizing carbons.As the name suggests,these cannot be transformed into crystalline graphite even at temperatures of 3000◦C and above.I nstead,high temperature heat treatments transform them into structures with a high degree of porosity but no long-range crystalline order.I n the model proposed by Ban et al.(Figure 1(b)),the structure is made up of ribbon-like sheets enclosing randomly shaped voids.It is most unlikely that such a structure could retain its poros-ity when subjected to high temperature heat treatment—surface energy would force the voids to collapse.The shortcomings of this and other “conventional”models are discussed more fully later in the article.The discovery of the fullerenes 3−5and subsequently of re-lated structures such as carbon nanotubes,6−8nanohorns,9,10and nanoparticles,11has given us a new paradigm for solid car-bon structures.We now know that carbons containing pentago-nal rings,as well as other non-six-membered rings,among the hexagonal sp 2carbon network,can be highly stable.This new perspective has prompted a number of groups to take a fresh look at well-known forms of carbon,to see whether any evidence can be found for the presence of fullerene-like structures.12−14The aim of this article is to review this new work on the structure of graphitic carbons,to assess whether models that incorporate fullerene-like elements could provide a better basis for under-standing these materials than the conventional models,and to point out areas where further work is needed.The carbon ma-terials considered include non-graphitizing carbon,glassy car-bon,carbon fibers,and carbon black.The article begins with an outline of the main structural features of fullerenes,carbon nanotubes,and carbon nanoparticles,together with a brief dis-cussion of their stability.FULLERENES,CARBON NANOTUBES,AND CARBON NANOPARTICLESThe structure of C 60,the archetypal fullerene,is shown in Figure 2(a).The structure consists of twelve pentagonal rings and twenty hexagons in an icosahedral arrangement.I t will be noted that all the pentagons are isolated from each other.This is important,because adjacent pentagonal rings form an unstable bonding arrangement.All other closed-cage isomers of C 60,and all smaller fullerenes,are less stable than buck-minsterfullerene because they have adjacent pentagons.For higher fullerenes,the number of structures with isolated pen-tagonal rings increases rapidly with size.For example,C 100has 450isolated-pentagon isomers.16Most of these higher fullerenes have low symmetry;only a very small number of them have the icosahedral symmetry of C 60.An example of a giant fullerene that can have icosahedral symmetry is C 540,as shown in Figure 2(b).There have been many studies of the stability of fullerenes as a function of size (e.g.,Refs.17,18).These show that,in general,stability increases with size.Experimentally,there is evidence that C 60is unstable with respect to large,multiwalled fullerenes.This was demonstrated by Mochida and colleagues,who heated C 60and C 70in a sublimation-limiting furnace.19They showed that the cage structure broke down at 900◦C–1000◦C,although at 2400◦C fullerene-like “hollow spheres”with diameters in the range 10–20nm were formed.We now consider fullerene-related carbon nanotubes,which were discovered by Iijima in 1991.6These consist of cylinders of graphite,closed at each end with caps that contain precisely six pentagonal rings.We can illustrate their structure by considering the two “archetypal”carbon nanotubes that can be formed by cutting a C 60molecule in half and placing a graphene cylinder between the two halves.Dividing C 60parallel to one of the three-fold axes results in the zig-zag nanotube shown in Figure 3(a),whereas bisecting C 60along one of the fivefold axes produces the armchair nanotube shown in Figure 3(b).The terms “zig-zag”and “armchair”refer to the arrangement of hexagons around the circumference.There is a third class of structure in which the hexagons are arranged helically around the tube axis.Ex-perimentally,the tubes are generally much less perfect than the idealized versions shown in Figure 3,and may be eitherNEW PERSPECTIVES ON GRAPHITIC CARBONS STRUCTURE237FI G.2.The structure of (a)C 60,(b)icosahedral C 540.15multilayered or single-layered.Figure 4shows a high resolu-tion TEM image of multilayered nanotubes.The multilayered tubes range in length from a few tens of nm to several microns,and in outer diameter from about 2.5nm to 30nm.The end-caps of the tubes are sometimes symmetrical in shape,but more often asymmetric.Conical structures of the kind shown in Fig-ure 5(a)are commonly observed.This type of structure is be-lieved to result from the presence of a single pentagon at the position indicated by the arrow,with five further pentagons at the apex of the cone.Also quite common are complex cap struc-tures displaying a “bill-like”morphology such as thatshownFI G.3.Drawings of the two nanotubes that can be capped by one half of a C 60molecule.(a)Zig-zag (9,0)structure,(b)armchair (5,5)structure.20in Figure 5(b).21This structure results from the presence of a single pentagon at point “X”and a heptagon at point “Y .”The heptagon results in a saddle-point,or region of negative curvature.The nanotubes first reported by Iijima were prepared by va-porizing graphite in a carbon arc under an atmosphere of helium.Nanotubes produced in this way are invariably accompanied by other material,notably carbon nanoparticles.These can be thought of as giant,multilayered fullerenes,and range in size from ∼5nm to ∼15nm.A high-resolution image of a nanopar-ticle attached to a nanotube is shown in Figure 6(a).22In this238P.J.F.HARRISFI G.4.TEM image of multiwalled nanotubes.case,the particle consists of three concentric fullerene shells.A more typical nanoparticle,with many more layers,is shown in Figure 6(b).These larger particles are probably relatively im-perfect instructure.FI G.5.I mages of typical multiwalled nanotube caps.(a)cap with asymmetric cone structure,(b)cap with bill-like structure.21Single-walled nanotubes were first prepared in 1993using a variant of the arc-evaporation technique.23,24These are quite different from multilayered nanotubes in that they generally have very small diameters (typically ∼1nm),and tend to be curledNEW PERSPECTIVES ON GRAPHITIC CARBONS STRUCTURE239FI G.6.I mages of carbon nanoparticles.(a)small nanoparticle with three concentric layers on nanotube surface,22(b)larger multilayered nanoparticle.and looped rather than straight.They will not be considered further here because they have no parallel among well-known forms of carbon discussed in this article.The stability of multilayered carbon nanotubes and nanopar-ticles has not been studied in detail experimentally.However,we know that they are formed at the center of graphite electrodes during arcing,where temperatures probably approach 3000◦C.I t is reasonable to assume,therefore,that nanotubes and nanopar-ticles could withstand being re-heated to such temperatures (in an inert atmosphere)without significant change.MICROPOROUS (NON-GRAPHITIZING)CARBONS BackgroundIt was demonstrated many years ago by Franklin 25,26that carbons produced by the solid-phase pyrolysis of organic ma-terials fall into two distinct classes.The so-called graphitizing carbons tend to be soft and non-porous,with relatively high den-sities,and can be readily transformed into crystalline graphite by heating at temperatures in the range 2200◦C–3000◦C.I n con-trast,“non-graphitizing”carbons are hard,low-densitymateri-FI G.7.(a)High resolution TEM image of carbon prepared by pyrolysis of sucrose in nitrogen at 1000◦C,(b)carbon prepared bypyrolysis of anthracene at 1000◦C.I nsets show selected area diffraction patterns.30als that cannot be transformed into crystalline graphite even at temperatures of 3000◦C and above.The low density of non-graphitizing carbons is a consequence of a microporous struc-ture,which gives these materials an exceptionally high internal surface area.This high surface area can be enhanced further by activation,that is,mild oxidation with a gas or chemical pro-cessing,and the resulting “activated carbons”are of enormous commercial importance,primarily as adsorbents.27−29The distinction between graphitizing and non-graphitizing carbons can be illustrated most clearly using transmission elec-tron microscopy (TEM).Figure 7(a)shows a TEM image of a typical non-graphitizing carbon prepared by the pyrolysis of sucrose in an inert atmosphere at 1000◦C.30The inset shows a diffraction pattern recorded from an area approximately 0.25µm in diameter.The image shows the structure to be disordered and isotropic,consisting of tightly curled single carbon layers,with no obvious graphitization.The diffraction pattern shows symmetrical rings,confirming the isotropic structure.The ap-pearance of graphitizing carbons,on the other hand,approxi-mates much more closely to that of graphite.This can be seen in the TEM micrograph of a carbon prepared from anthracene,240P.J.F.HARRI Swhich is shown in Figure 7(b).Here,the structure contains small,approximately flat carbon layers,packed tightly together with a high degree of alignment.The fragments can be considered as rather imperfect graphene sheets.The diffraction pattern for the graphitizing carbon consists of arcs rather than symmetrical rings,confirming that the layers are preferentially aligned along a particular direction.The bright,narrow arcs in this pattern correspond to the interlayer {0002}spacings,whereas the other reflections appear as broader,less intense arcs.Transmission electron micrographs showing the effect of high-temperature heat treatments on the structure of non-graphitizing and graphitizing carbons are shown in Figure 8(note that the magnification here is much lower than for Figure 7).I n the case of the non-graphitizing carbon,heating at 2300◦C in an inert atmosphere produces the disordered,porous material shown in Figure 8(a).This structure is made up of curved and faceted graphitic layer planes,typically 1–2nm thick and 5–15nm in length,enclosing randomly shaped pores.A few somewhat larger graphite crystallites are present,but there is no macroscopic graphitization.n contrast,heat treatment of the anthracene-derived carbon produces large crystals of highly or-dered graphite,as shown in Figure 8(b).Other physical measurements also demonstrate sharp dif-ferences between graphitizing and non-graphitizing carbons.Table 1shows the effect of preparation temperature on the sur-face areas and densities of a typical graphitizing carbon prepared from polyvinyl chloride,and a non-graphitizing carbon prepared from cellulose.31It can be seen that the graphitizing carbon pre-pared at 700◦C has a very low surface area,which changes lit-tle for carbons prepared at higher temperatures,up to 3000◦C.The density of the carbons increases steadily as thepreparationFI G.8.Micrographs of (a)sucrose carbon and (b)anthracene carbon following heat treatment at 2300◦C.TABLE 1Effect of temperature on surface areas and densities of carbonsprepared from polyvinyl chloride and cellulose 31(a)Surface areas Specific surface area (m 2/g)for carbons prepared at:Starting material 700◦C 1500◦C 2000◦C 2700◦C 3000◦C PVC 0.580.210.210.710.56Cellulose 4081.601.172.232.25(b)Densities Helium density (g/cm 3)for carbons prepared at:Starting material 700◦C 1500◦C 2000◦C 2700◦C 3000◦C PVC 1.85 2.09 2.14 2.21 2.26Cellulose1.901.471.431.561.70temperature is increased,reaching a value of 2.26g/cm 3,which is the density of pure graphite,at 3000◦C.The effect of prepara-tion temperature on the non-graphitizing carbon is very different.A high surface area is observed for the carbon prepared at 700◦C (408m 2/g),which falls rapidly as the preparation temperature is increased.Despite this reduction in surface area,however,the density of the non-graphitizing carbon actually falls when the temperature of preparation is increased.This indicates that a high proportion of “closed porosity”is present in the heat-treated carbon.NEW PERSPECTIVES ON GRAPHITIC CARBONS STRUCTURE241FI G.9.Franklin’s representations of(a)non-graphitizing and(b)graphitizing carbons.25Early ModelsThefirst attempt to develop structural models of graphitizingand non-graphitizing carbons was made by Franklin in her1951paper.25In these models,the basic units are small graphitic crys-tallites containing a few layer planes,which are joined togetherby crosslinks.The precise nature of the crosslinks is not speci-fied.An illustration of Franklin’s models is shown in Figure9.Using these models,she put forward an explanation of whynon-graphitizing carbons cannot be converted by heat treatmentinto graphite,and this will now be summarized.During car-bonization the incipient stacking of the graphene sheets in thenon-graphitizing carbon is largely prevented.At this stage thepresence of crosslinks,internal hydrogen,and the viscosity ofthe material is crucial.The resulting structure of the carbon(at ∼1000◦C)consists of randomly ordered crystallites,held to-gether by residual crosslinks and van der Waals forces,as inFigure9(a).During high-temperature treatment,even thoughthese crosslinks may be broken,the activation energy for themotion of entire crystallites,required for achieving the struc-ture of graphite,is too high and graphite is not formed.Onthe other hand,the structural units in a graphitizing carbon areapproximately parallel to each other,as in Figure9(b),and thetransformation of such a structure into crystalline graphite wouldbe expected to be relatively facile.Although Franklin’s ideason graphitizing and non-graphitizing carbons may be broadlycorrect,they are in some regards incomplete.For example,thenature of the crosslinks between the graphitic fragments is notspecified,so the reasons for the sharply differing properties ofgraphitizing and non-graphitizing carbons is not explained.The advent of high-resolution transmission electron mi-croscopy in the early1970s enabled the structure of non-graphitizing carbons to be imaged directly.n a typical study,Ban,Crawford,and Marsh2examined carbons prepared frompolyvinylidene chloride(PVDC)following heat treatments attemperatures in the range530◦C–2700◦C.I mages of these car-bons apparently showed the presence of curved and twistedgraphite sheets,typically two or three layer planes thick,enclos-ing voids.These images led Ban et al.to suggest that heat-treatednon-graphitizing carbons have a ribbon-like structure,as shownin Figure1(b).This structure corresponds to a PVDC carbonheat treated at1950◦C.This ribbon-like model is rather similar to an earlier model of glassy carbon proposed by Jenkins andKawamura.32However,models of this kind,which are intendedto represent the structure of non-graphitizing carbons follow-ing high-temperature heat treatment,have serious weaknesses,as noted earlier.Such models consist of curved and twistedgraphene sheets enclosing irregularly shaped pores.However,graphene sheets are known to be highlyflexible,and wouldtherefore be expected to become ever more closely folded to-gether at high temperatures,in order to reduce surface energy.Indeed,tightly folded graphene sheets are quite frequently seenin carbons that have been exposed to extreme conditions.33Thus,structures like the one shown in Figure1(b)would be unlikelyto be stable at very high temperatures.It has also been pointed out by Oberlin34,35that the modelsput forward by Jenkins,Ban,and their colleagues were basedon a questionable interpretation of the electron micrographs.In most micrographs of partially graphitized carbons,only the {0002}fringes are resolved,and these are only visible when they are approximately parallel to the electron beam.Therefore,such images tend to have a ribbon-like appearance.However,because only a part of the structure is being imaged,this appear-ance can be misleading,and the true three-dimensional structuremay be more cagelike than ribbon-like.This is a very importantpoint,and must always be borne in mind when analyzing imagesof graphitic carbons.Oberlin herself believes that all graphiticcarbons are built up from basic structural units,which comprisesmall groups of planar aromatic structures,35but does not appearto have given a detailed explanation for the non-graphitizabilityof certain carbons.The models of non-graphitizing carbons described so farhave assumed that the carbon atoms are exclusively sp2and arebonded in hexagonal rings.Some authors have suggested thatsp3-bonded atoms may be present in these carbons(e.g.,Refs.36,37),basing their arguments on an analysis of X-ray diffrac-tion patterns.The presence of diamond-like domains would beconsistent with the hardness of non-graphitizing carbons,andmight also explain their extreme resistance to graphitization.Aserious problem with these models is that sp3carbon is unsta-ble at high temperatures.Diamond is converted to graphite at1700◦C,whereas tetrahedrally bonded carbon atoms in amor-phousfilms are unstable above about700◦C.Therefore,the242P.J.F.HARRI Spresence of sp 3atoms in a carbon cannot explain the resistance of the carbon to graphitization at high temperatures.I t should also be noted that more recent diffraction studies of non-graphitizing carbons have suggested that sp 3-bonded atoms are not present,as discussed further in what follows.Evidence for Fullerene-Like Structures in Microporous CarbonsThe evidence that microporous carbons might have fullerene-related structures has come mainly from high-resolution TEM studies.The present author and colleagues initiated a series of studies of typical non-graphitizing microporous carbons using this technique in the mid 1990s.30,38,39The first such study in-volved examining carbons prepared from PVDC and sucrose,after heat treatments at temperatures in the range 2100◦C–2600◦C.38The carbons subjected to very high temperatures had rather disordered structures similar to that shown in Figure 8(a).Careful examination of the heated carbons showed that they often contained closed nanoparticles;examples can be seen in Figure 10.The particles were usually faceted,and often hexagonal or pentagonal in shape.Sometimes,faceted layer planes enclosed two or more of the nanoparticles,as shown in Figure 10(b).Here,the arrows indicate two saddle-points,similar to that shown in Figure 5(b).The closed nature of the nanoparticles,their hexagonal or pentagonal shapes,and other features such as the saddle-points strongly suggest that the parti-cles have fullerene-like structures.I ndeed,in many cases the par-ticles resemble those produced by arc-evaporation in a fullerene generator (see Figure 6)although in the latter case the particles usually contain many more layers.The observation of fullerene-related nanoparticles in the heat treated carbons suggested that the original,freshly prepared car-bons may also have had fullerene-related structures (see next section).However,obtaining direct evidence for this is diffi-cult.High resolution electron micrographs of freshly prepared carbons,such as that shown in Figure 7(a),are usuallyratherFI G.10.(a)Micrograph showing closed structure in PVDC-derived carbon heated at 2600◦C,(b)another micrograph of same sample,with arrows showing regions of negative curvature.38featureless,and do not reveal the detailed structure.Occasion-ally,however,very small closed particles can be found in the carbons.30The presence of such particles provides circumstan-tial evidence that the surrounding carbon may have a fullerene-related structure.Direct imaging of pentagonal rings by HRTEM has not yet been achieved,but recent developments in TEM imaging techniques suggest that this may soon be possible,as discussed in the Conclusions.As well as high-resolution TEM,diffraction methods have been widely applied to microporous and activated carbons (e.g.,Refs.40–44).However,the interpretation of diffraction data from these highly disordered materials is not straightforward.As already mentioned,some early X-ray diffraction studies were interpreted as providing evidence for the presence of sp 3-bonded atoms.More recent neutron diffraction studies have suggested that non-graphitizing carbons consist entirely of sp 2atoms.40It is less clear whether diffraction methods can establish whether the atoms are bonded in pentagonal or hexagonal rings.Both Petkov et al .42and Zetterstrom and colleagues 43have interpreted neutron diffraction data from nanoporous carbons in terms of a structure containing non-hexagonal rings,but other interpreta-tions may also be possible.Raman spectroscopy is another valuable technique for the study of carbons.45Burian and Dore have used this method to analyze carbons prepared from sucrose,heat treated at tem-peratures from 1000◦C–2300◦C.46The Raman spectra showed clear evidence for the presence of fullerene-and nanotube-like elements in the carbons.There was also some evidence for fullerene-like structures in graphitizing carbons prepared from anthracene,but these formed at higher temperatures and in much lower proportions than in the non-graphitizing carbons.New Models for the Structure of Microporous Carbons Prompted by the observations described in the previous section,the present author and colleagues proposed a model for the structure of non-graphitizing carbons that consists ofNEW PERSPECTIVES ON GRAPHITIC CARBONS STRUCTURE243FI G.11.Schematic illustration of a model for the structure of non-graphitizing carbons based on fullerene-like elements.discrete fragments of curved carbon sheets,in which pentagons and heptagons are dispersed randomly throughout networks of hexagons,as illustrated in Figure11.38,39The size of the micropores in this model would be of the order of0.5–1.0nm, which is similar to the pore sizes observed in typical microp-orous carbons.The structure has some similarities to the“ran-dom schwarzite”network put forward by Townsend and col-leagues in1992,47although this was not proposed as a model for non-graphitizing carbons.I f the model we have proposed for non-graphitizing carbons is correct it suggests that these carbons are very similar in structure to fullerene soot,the low-density, disordered material that forms on walls of the arc-evaporation vessel and from which C60and other fullerenes may be ex-tracted.Fullerene soot is known to be microporous,with a sur-face area,after activation with carbon dioxide,of approximately 700m2g−1,48and detailed analysis of high resolution TEM mi-crographs of fullerene soot has shown that these are consis-tent with a structure in which pentagons and heptagons are dis-tributed randomly throughout a network of hexagons.49,50It is significant that high-temperature heat treatments can transform fullerene soot into nanoparticles very similar to those observed in heated microporous carbon.51,52Carbonization and the Structural Evolutionof Microporous CarbonThe process whereby organic materials are transformed into carbon by heat treatment is not well understood at the atomic level.53,54In particular,the very basic question of why some organic materials produce graphitizing carbons and others yield non-graphitizing carbons has not been satisfactorily answered. It is known,however,that both the chemistry and physical prop-erties of the precursors are important in determining the class of carbon formed.Thus,non-graphitizing carbons are formed, in general,from substances containing less hydrogen and more oxygen than graphitizing carbons.As far as physical properties are concerned,materials that yield graphitizing carbons usu-ally form a liquid on heating to temperatures around400◦C–500◦C,whereas those that yield non-graphitizing carbons gen-erally form solid chars without melting.The liquid phase pro-duced on heating graphitizing carbons is believed to provide the mobility necessary to form oriented regions.However,this may not be a complete explanation,because some precursors form non-graphitizing carbons despite passing through a liquid phase.The idea that non-graphitizing carbons contain pentagons and other non-six-membered rings,whereas graphitizing car-bons consist entirely of hexagonal rings may help in understand-ing more fully the mechanism of carbonization.Recently Kumar et al.have used Monte Carlo(MC)simulations to model the evo-lution of a polymer structure into a microporous carbon structure containing non-hexagonal rings.55They chose polyfurfuryl al-cohol,a well-known precursor for non-graphitizing carbon,as the starting material.The polymer was represented as a cubic lattice decorated with the repeat units,as shown in Figure12(a). All the non-carbon atoms(i.e.,hydrogen and oxygen)were then removed from the polymer and this network was used in the。
你最喜欢的房间及原因的英语作文
你最喜欢的房间及原因的英语作文全文共3篇示例,供读者参考篇1My Favorite RoomMy favorite room in our whole house is the basement. I just love going down there to play and explore. The basement is my own special world away from my brothers and sisters. Down there, I'm the queen of the castle!The basement isn't finished like the rest of the house. It has concrete floors and the walls are just bare concrete blocks. Some people might think it looks ugly and boring, but I think it's perfect! The plain walls and floors are like a blank canvas for my imagination to run wild.My favorite part is all the nooks and crannies to discover. There are little cubbyholes along the walls that are perfect for pretending to be a explorer searching for treasure or hidden civilizations. Sometimes I take a flashlight and crawl along poking my head into each little space, wondering what fantastic discoveries I'll make around the next corner.Behind the furnace is a really spooky area that's quite dark. Me and my friends like to dare each other to go sit alone back there while we turn off all the lights. It feels like you're being transported to the heart of a haunted castle or deep cave system.I try to be brave, but I'll admit that eerie groaning noises from the furnace pipes give me goosebumps!If you look up, you can see all the pipes and wires running along the low ceiling. I pretend they are pathways through a dense jungle or the inner workings of a spaceship's engine room. My friend Alex and I make up all kinds of stories about them leading to secret laboratories or untold civilizations.Along the back wall are some old shelves filled with random boxes and gear that no one uses anymore. To me, they look like artifacts from ancient cultures, just waiting to be explored and documented. I spend hours carefully going through each box, finding treasures like rusty old tools, tarnished picture frames, neatly coiled ropes, and many other mysterious items. I put on a pith helmet (actually an old sun hat) and carry a little notebook where I keep sketches and details about each unique find.Under the stairs is my top secret headquarters where no brothers are allowed. I've made it into a little hideout just for me using old boards and sheets. Inside I have all my most preciousartifacts and treasures arranged around the walls. Sometimes I bring a snack down and settle in on my ratty old bedspread on the floor and just admire my collection of "antiquities." It's a museum and fortress all in one!The basement also amplifies all sounds in a deliciously eerie and echoey way. If you whisper or shuffle your feet, it creates all these curious sounds that seem to come from every direction. When Alex and I play down there, we always end up whispering and tiptoeing around, jumping at every little creak or groan of the house settling. It adds so much atmosphere and suspense to our adventures and explorations!Last week, my friend Aisha came over and we found a whole new area that we never knew existed before! We pulled aside an old cabinet along the back wall and discovered a little room behind it that looks like it was walled off for some reason. It was pitch black inside and just just big enough for one of us to crawl in at a time. The other had to hold the cabinet open and shine a flashlight inside. Can you imagine how my heart was pounding as I was the first to make my way into that mysterious space? I felt like a real-life archaeologist happening upon an undiscovered tomb! Who knows what ancient artifacts or fossils could be in there?Well, it turned out to be just a small empty room with bare walls. But that didn't stop us from imagining all kinds of wild stories about what it could have been used for and who might have been trapped in there long ago. Aisha thought it was where they hid treasures or kept prisoners during the Revolutionary War. I thought it could have been an underground bunker from World War 2 that got sealed up and forgotten about. We spent the whole afternoon down there pretending and adding to our ongoing narratives about discoveries and expeditions.For me, the basement is the most wonderfully creepy, spooky, and imaginative place in our entire house. I look forward to spending as much time as I can down there all year long, but it's even better in the fall and winter months. That's when the basement really comes alive with sinister shadows and goosebump-inducing chill. The flickering light from a lonely camping lantern left on in the corner seems to make the walls move and shift. Strange scratching noises could either be ancient spectors or tiny mammals tunneling through. Who knows?If it were up to me, we would never clean or organize the basement. I love having dust, cobwebs, mysterious stains, and clutter everywhere you look. It keeps things deliciously unsettling and ripe for make-believe. If the basement looked allclean and tidy, it would ruin the atmosphere completely. It needs to look lived in, but not inhabited - if you know what I mean.I hope my parents never decide to remodel or finish the basement either. That would absolutely break my heart. All the charm and character would be stripped away in the interest of making it look like every other boring room. They'd put up drywall over the concrete blocks, install wood paneling, lay down laminate flooring, and suddenly it would become just another generic playroom. Please no! I want it to stay delightfully rough and unfinished forever.Who cares if we can't really use the basement for anything other than storage? To me, it serves the most important purpose of all: being a blank canvas where I can exercise my imagination and creativity to the fullest. Down there, I can be anyone or go anywhere my mind dreams up - an adventurer, scientist, archaeologist, or anthropologist. Each time I descend those creaky wooden stairs, it's like being transported into another world full of mystery and excitement.All the other rooms in our house are practical spaces for grown-ups. But the basement is my own private fantasy land. As long as I can explore it safely, it will always be my favorite room. I just hope I can hold onto the magic for as long as possiblebefore growing up inevitably strips it all away. I know I'll miss it tremendously when I'm older. But for now, I'm just going to keep on pretending!篇2My Favorite RoomMy favorite room in our whole house is my bedroom. It's the place where I spend most of my time when I'm at home. My bedroom is like my own tiny kingdom where I'm the ruler! I decorated it mostly by myself with the help of my mom and dad, so it feels totally me.What makes my bedroom so special? Well, first of all, I just love the colors. The walls are painted a sunny yellow, which always makes me feel happy and cheerful when I walk in the room. It's like having a little bit of sunshine surrounding me all the time. The curtains, bedspread, and area rug have a pretty blue and green pattern that reminds me of the outdoors. I picked those colors because they make me think of a bright, clear sky and fresh green grass. Just looking around my room puts me in a good mood.My bedroom isn't huge, but it feels nice and cozy. Mytwin-sized bed fits perfectly along one wall. The pale woodheadboard has curves that make it look almost like a princess bed or something from a fairy tale. Getting into my bed at night feels extra special, like I'm tucking myself into a magical story world. Next to the bed is my nightstand with a reading lamp and a drawer to store books, my diary with the locked cover, and other treasures. Across from the bed is my dresser where I can see my favorite stuffed animals sitting on top, keeping watch over the room. Being surrounded by my cuddly friends makes me feel safe and comforted.One of the best parts of my room is the big window with a cheerful window seat. Iyla padding and lots of bright pillows so it's a perfect reading nook. I love curling up in the window seat, propping open a book, and getting lost in another world. Sometimes I'll spend an entire rainy afternoon getting deliciously creeped out by a scary story or giggling over the silly adventures of a book's characters. The window looks out onto the big backyard with its trees, flowers, and butterflies. I enjoy watching the seasons change and bunnies munching on the green grass in spring.Of course, my bedroom also has plenty of space to keep all of my toys organized but within easy reach for playtime fun. My shelves display my beloved doll collection, coloring books, boardgames, and more. My pride and joy is my playhouse in one corner, big enough for me to sit inside. I've stuffed it with mini furniture, dishes, and all kinds of tiny treasures. I'll spend hours brushing my dollies' hair and creating imaginative storylines for them. My room is the perfect place for creative play and letting my fantasies run wild.Maybe my very favorite part of my bedroom is my art area. It's a cheery green kid-sized table and chair setup where I can craft, color, paint, and make all kinds of projects. The tabletop is covered in funky stains from my messiest artistic efforts. I'm not a tidy crafter at all, but that's okay because this space is just for me to express myself freely. Whenever I'm in an artistic mood, I can grab my supplies and go wild. Then I can decorate my room's walls with my latest masterpieces. Seeing my own artwork surrounding me gives me a sense of pride and happiness.When it's time to go to bed, I feel lucky to have such a cheerful, comfortable, personalized place to sleep. My room represents all the things I love most - books, art, toys, bright colors, and coziness. It's truly my own special, one-of-a-kind space. I hope I never outgrow the joy and contentment I feel inmy beloved bedroom kingdom! To me, it's the absolute best room in the whole house, no contest.篇3My Favorite Place: The PlayroomDo you have a favorite place in your house? A special room that makes you feel happy and safe? For me, that magical place is the playroom! It's where I spend most of my time after school and on weekends, lost in adventures and make-believe worlds. Let me tell you all about this wonderful room and why I love it so much.The playroom is downstairs, right next to the kitchen. It has big windows that let in lots of warm sunlight during the day. The room is painted a cheerful yellow color that reminds me of sunshine. Whenever I walk in, I instantly feel brighter and happier. The floors are covered in soft blue carpet that's perfect for sitting, crawling around on, and building forts and castles.But the best part is all the toys and games! There are more toys in this room than you could ever imagine. Shelves line the walls, overflowing with plastic bins stuffed full of treasures. Building blocks, action figures, dolls, puzzles, board games, stuffed animals - you name it, it's probably in the playroomsomewhere! Every time I look, I discover something new that I forgot I had.My favorite toys are the dress-up clothes. There's a huge trunk full of sparkly tutus, silly wigs and hats, fancy shoes, colorful capes, and more. I love putting on costume after costume, transforming into different characters and bringing their stories to life. One minute I'm a brave knight rescuing a princess, the next I'm a famous chef whipping up an imaginary feast!That reminds me of the play kitchen - it's the centerpiece of the room. This thing is amazing, with a working oven and microwave that really light up. The fridge even makes ice cube cracking sounds when you open it! The cupboards are packed with plates, pots and pans, and plastic food like hamburgers and pizza. Whenever my friends come over, we host pretend dinner parties and take turns being the chef, waiter, and restaurant guests.Next to the kitchen is the arts and crafts zone. We have drawers and boxes exploding with crayons, markers, paints, colored pencils, stickers, pipe cleaners - all the supplies for making masterpieces! I've created countless drawings, paintings, and craft projects here at the big kid-sized table with the colorfulplastic chairs. I get so lost in my creative projects that time seems to fly by.On rainy days when we're stuck inside, I'm never bored thanks to the dress-up trunk, play kitchen, and crafts. We can act out stories, cook pretend feasts, and make all kinds of artworks. But when the weather is nice, the playroom is the perfect home base for our backyard adventures. The sliding glass doors lead right out to the patio, yard, and our awesome playset. We can run in and out, grabbing toys like squirt guns, bubbles, sidewalk chalk, balls, and frisbees to bring outside.After getting all messy and sweaty from digging in the dirt, climbing on the swing set, and ambushing friends in water balloon fights, the playroom is the place to recharge. I'll settle onto one of the beanbag chairs with a book and a snack, maybe wearing one of my dress-up capes as a cozy blanket. Or sometimes I'll put a movie into the DVD player and cuddle up on the pullout couch with my stuffed animals.As you can probably tell, this special space is more than just a room - it's a doorway to endless adventures and possibilities! Behind that yellow door lies a whole world of imagination and creativity. I can go anywhere, be anyone, and do anything I can dream up. That's why the playroom is my absolute favorite place.No matter how old I get, this room will always hold a special place in my heart. It's a vibrant, joyful space overflowing with tokens from my childhood. Even when I'm all grown up, I'll remember the magic of disappearing into carefree worlds of make-believe here in the playroom. The dress-up clothes, the kitchen set, the crafts - they all spark that youthful sense of wonder and possibility.Maybe that's why this room means so much to me. As a kid, the playroom is a sanctuary, a safe space just for fun and freedom. It's a place without rules, responsibilities, or any of the pressures of the outside world. In this room, I don't have to follow a schedule or meet expectations. I can simply be present and immerse myself fully in whichever story or game I choose that day. The playroom is where creativity and imagination run wild and free.For all these reasons, the playroom is my happy place - a little slice of paradise right in the heart of our home. No matter what kind of day I'm having, I know I can escape into this cheerful, sun-filled space and leave my worries at the door. I cherish the endless hours I've spent exploring, pretending, and playing here more than I can put into words. That's why theplayroom is, and always will be, my very favorite room in the whole wide world.。
WS2812B-Mini智能外部控制LED说明书
Integrated light source Features and Benefits●The IC’s control circuit and the LED share the same power supply.●Control circuit and RGB chip are integrated in a package of3535component,to form a complete external controlpixel.●Built-in signal reshaping circuit,any pixel receives the signal,and then re-export after waveform reshaping toensure that the waveform distortion of the circuit will not accumulate.●Built-in Power-on reset and Power-off reset circuits.●The three primary color of each pixel can achieve256level Gray scale,and to fulfill16777216colors full-colordisplay,its scan frequency is higher than2KHz.●The reception and decoding of cascading data can be completed by a Serial Interface.●Any two transmission distance not more than3Meters,without adding any circuit.●When the refresh rate is of30fps,the cascade numbers are not less than1024pixels.●Data transfer speeds up to800Kbps.●Highly brightness consistency,and cost-effective.Applications●Full-color module,Full-color flexible strip.●LED decorative lighting,Indoor/outdoor LED video irregular screen.General descriptionWS2812B-Mini is an intelligent control LED light source that the control circuit and RGB chip are integrated in a package of3535component.It internal include intelligent digital port data latch and signal reshaping amplification drive circuit.It also includes a high-precision internal oscillator and a programmable constant current control part to ensure high color consistency.The data transfer protocol use single NZR communication mode.After the pixel power-on reset,the DIN port receive data from controller,the first pixel collect initial24bit data then sent to the internal data latch,the other data which reshaping by the internal signal reshaping amplification circuit sent to the next cascade pixel through the DO port.After transmission for each pixel,the signal to reduce24bit.pixel adopt auto reshaping transmit technology,making the pixel cascade number is not limited the signal transmission,only depend on the speed of signal transmission.RESET time>280μs,it won't cause wrong reset while interruption,it supports the lower frequency and inexpensive MCU.Refresh Frequency updates to2KHz,Low Frame Frequency and No Flicker appear in HD Video Camera,it improve excellent display effect.LED with low driving voltage,environmental protection and energy saving,high brightness,scattering angle is large, good consistency,low power,long life and other advantages.The control chip integrated in LED above becoming more simple circuit,small volume,convenient installation.Integrated light source Mechanical DimensionsPIN ConfigurationsPIN FunctionsNO.Symbol Function description1VDD LED Power supply2DOUT Control data signal output3VSS Ground4DIN Control data signal inputAbsolute Maximum RatingsParameter Symbol Ratings Unit Power supply voltage V DD+3.7~+5.3VLogical Input Voltage V I VDD-0.7~VDD+0.7V Operation junction temperature Topt-25~+85℃Storage temperature range Tstg-40~+105℃Integrated light source Electrical Characteristics(T A=-20~+70℃,V DD=4.5~5.5V,V SS=0V,unless otherwise specified)Parameter Symbol Min Tpy Max Unit ConditionInput current I I————±1µA V I=V DD/V SSInput voltage level V IH0.7V DD————V D IN,SET V IL————0.3V DD V D IN,SETHysteresis voltage V H——0.35——V D IN,SETLED Lifespan tled50000————H Test Current:16mATest Temperature:Room Temp.(25℃±5℃)Switching Characteristics(T A=-20~+70℃,V DD=4.5~5.5V,V SS=0V,unless otherwise specified) Parameter Symbol Min Tpy Max Unit Condition Transmission delay time T PLZ————300ns CL=15pF,DIN→DOUT,RL=10KΩFall time T THZ————120µs CL=300pF,OUTR/OUTG/OUTB Input capacity C I————15pF——LED CharacteristicsRef.ValueQuiescent Current0.7mARGB Channel Constant Current16mARED Brightness(Central Value)600mcdGREEN Brightness(Central Value)1200mcdBLUE Brightness(Central Value)300mcdWHITE Brightness(Central Value)2100mcdRED Wavelength620-630nmGREEN Wavelength520-530nmBLUE Wavelength465-475nmData Transfer TimeT0H0code,high voltage time220ns~380nsT1H1code,high voltage time580ns~1µsT0L0code,low voltage time580ns~1µsT1L1code,low voltage time220ns~420nsRES low voltage time>280µsIntegrated light sourceSequence chartCascade Method0code 1code RET codeT0HT0LT1H T1LTresetDIN DIN DIN DODODOPIX1D1D2D3D4PIX2PIX3Data Transmission MethodNote:The data of D1is sent by MCU,and D2,D3,D4through pixel internal reshaping amplification to position of 24bit DataG7G6G5G4G3G2G1G0R7R6R5R4R3R2R1R0B7B6B5B4B3B2B1B0Note:Follow the order of GRB to send data and the high bit sent at first.Typical Application CircuitRemarks:C1is external filter capacitor,its value of 100NF.Integrated light source Top SMD LED Using Instructions1.SummaryTo make the best use of WORLDSEMI’s LED,please refer to the below precautions,they are of same usage method as other electronic components.2.Cautions2.1.Dust&CleaningThe surface of the LED is encapsulated with modified epoxy resin because it plays a very good role in protecting the optical performance and aging resistance.The modified epoxy resin is easy to stick with dust and must be kept clean.When there’s a certain amount of dust on the surface of the LED,it won’t affect brightness,but dust proof should be taken care of.Promoting the use of unsealed package in preference to others and the assembled LEDs should be placed in a clean container.Avoid using the organic solvents to clean the dust on the LED surface and it’s necessary to confirm whether the cleaning fluid will dissolve the LED.Do not clean the LEDs by the ultrasonic.Some parameters affecting the LED performance must be evaluated if have no alternative but to the ultrasonic cleaning method,such as ultrasonic power,baking time and assembly conditions,etc.2.2.Moisture-proof packagingTOP SMD LEDs are moisture sensitive components.LEDs are packaged in aluminum foil bag to prevent the from absorbing moisture during transport and storage.A desiccant is placed in the bags to absorb moisture.If the LED absorbs moisture,then it evaporates and expands when in reflow process,which may break the colloid from the bracket and damage the optical performance of LED.For this reason,moisture-proof packaging is to prevent the from absorbing moisture during transport and storage.The moisture resistance rating of WORLDSEMI’s LED is: LEVEL6.Tabel I-IPC/JEDEC J-STD-020Moisture/Reflow Sensitivity ClassificationMSL Level Workshop LifeTime ConditionsLEVEL1Unlimited≤30℃/85%RHLEVEL21Year≤30℃/60%RHLEVEL2a4Weeks≤30℃/60%RHLEVEL3168Hours≤30℃/60%RHLEVEL472Hours≤30℃160%RHLEVEL548Hours≤30℃/60%RHLEVEL5a24Hours≤30℃/60%RHLEVEL6Take-out and Use immediately≤30℃/60%RHIntegrated light source2.3.Management after unpackingIt’s recommend to perform SMT assembly as soon as possible after opening the moisture-proof bag,and reflow soldering should be completed within 4hours after SMT assembly;for the remaining LEDs,they should be re-packed in seal package and placed in moisture-proof cabinet (Please note that it’s necessary to rebake at “70℃-75℃/48hours ”before next SMT process).3.Dehumidification Operation (Non-leakage of air,baking temperature:70℃-75℃)a.MD within 2weeks,baking time:24hours.b.MD exceeds 2weeks,baking time:48hours.4.Management of secondary SMT processIt’s necessary to do moisture-proof treatment when the secondary reflow carried out that followed the first reflow.It can’t be more than 2hours to be exposed at condition of “<30℃/60%RH”and dehumification operation is requested for a longer interval reflow.For instance,place in a drying box or a container with desiccant,and dehumidify it before the secondary reflow(Low temperature baking operation:70℃-75℃,≥12hours ).5.SMT ReflowRefer to the parameters listed below,the experimental results prove that the TOP SMD LED meets the JEDEC J-STD-020C standards.As a general guideline,it is recommended to follow the SMT reflow temperature curve recommended by the solder paste manufacturer.Remarks:1.These general guidelines may not apply to all PCB designs and reflow soldering configurations.2.All temperatures referred are measured on the surface of the package body.Curve DescriptionLead-free Reflow The lowest preheat temperature (Tsmin)150℃The highest preheat temperature (Tsmax)200℃Preheating time (Tsmin to Tsmax)(ts)60-180S Average rate of temperature rise (Tsmax to Tp)<3℃/S LIQUID REGION temperature (TL)217℃LIQUID REGION Holding Time (tL)60-150S Peak Temperature (Tp)240℃High Temperature Region(Tp=-5℃)Holding Time (tp)<10S Cooling Rate<6℃/S Room Temperature to Peak Holding Time<6minIntegrated light source 6.Assembly Precautions1.Clip the LED from its side.2.Neither directly touch the gel surface with the handor sharp instrument,it may damage its internal circuit.3.Not to be double stacked,it may damage its internal circuit.4.Can not be stored in or applied in the acidic sites of PH<7.Modify RecordVersion№Status Bar Modify Content Summary Date Reviser Approved V1.0N New20170523Shen JinGuo Yin HuaPing V1.1M Absolute Maximum Ratings、MechanicalDimensions20171009Shen JinGuo Yin HuaPing V1.2M Maximum ratings,Timing20180207Shen JinGuo Yin HuaPing V1.3M Electrical Parameters20180412Shen JinGuo Yin HuaPingV1.4M Logical Input Voltage;Brightness adjustment;Precautions20180719沈金国尹华平Remarks:Initial version:V1.0;Version number plus"0.1"after each revision;Status bar:N--New,A--Add,M--Modify,D--Delete.。
单电子晶体管
一、单电子晶体管定义及构造 二、单电子晶体管工作原理 三、单电子晶体管特征 四、单电子晶体管进展概况 五、单电子晶体管的应用及展望
一、定义及构造
定义:单电子晶体管是 基于库仑堵塞效应和单 电子隧道效应的根本物 理原理的一种新型纳米 电子器件。 构造:一般它由以下5局 部组成,〔1〕库仑岛或 量子点;〔2〕隧道势垒; 〔3〕势垒区;〔4〕栅 氧化层;〔5〕源、漏、 极。如右图1所示。
图 3 单电子晶体管与通常晶体管比照图
四、单电子晶体管进展概况
1968 年,Zeller 和Giaever 争论了Al-Al2O3-Al 构 造的导电特性。结果显示,当电压较低时,电流较小 ,而电压超过某一临界电压Vs 时,电导趋向于饱和 。Vs 猛烈地依靠于Sn颗粒的大小。据此,他们指出 ,在低温时,对于单隧道结,只有当V>e/2C 时才有 电流,并将这一电压值称为库仑抑制势。1969 年, Lambe 和Jaklevic 的试验说明,金属颗粒中的平均 电荷数随附加电压的增加而增加。Shekhter据此分析 预言,此种构造中,I -V 曲线将随电压的变化作周 期性的振荡。此预言后来被试验所证明。这个结论激 发起人们的灵感,人们开头设想,可以通过周期性地 转变中间金属颗粒的电压来掌握单个电子的通过与截 断。单电子晶体管的概念就这样产生。
五、单电子晶体管的应用及展望
• 由于SET具有高频、高速、功耗小、集成度高和适用作多 值规律等特性,所以SET可广泛用于高速高密度IC、超高 灵敏度静电计、单光子器件、高灵敏度红外辐射探测器 、超高速微功耗特大规模量子功能器件、电路和系统、 量子功能计算机等。如日本电信 公司于1999年12月研 制成功承受多个单电子晶体管的电子计算机规律电路, 最初的电路是一个加法器。2023年4月又研制成功基于硅 衬底可高密度集成化的单电子晶体管和单电子元件。假 设把各种技术相结合,有望不久将实现高密度集成化单电 子规律电路。但是,目前大多数单电子晶体管和IC的工 作温度都较低,通常在液氮温度〔77K〕。目前,人们正 在探究室温工作的SET及其IC。
自然界中的量子隧道现象
自然界中的量子隧道现象Quantum tunneling phenomenon in the natural world自然界中的量子隧道现象量子隧道现象是指量子力学中一种非常奇特的现象,即粒子可以越过势垒在不具备足够能量的情况下移到势垒的另一面。
在人类的科学研究中,这种现象被广泛应用于各种领域。
但其实,自然界中比我们想象的还要多的现象也是由这种量子隧道效应所主导的。
量子隧道现象最早被发现于核物理实验中。
20世纪50年代,物理学家Lester Germer发现电子可以在金属表面反射和干涉。
这启示了他在实验中发现电子可以通过单层石墨,即只有一层碳原子的材料,而这种材料相当的薄,对于电子来说相当于没有障碍。
这是因为在这种情况下,电子的波长已经越过势垒。
这种奇妙的现象被称为“量子隧道效应”。
许多鸟类揭示了量子隧道现象。
2012年,英国牛津大学的科学家们发现了欧洲文化乌鸦(Corvus corone corone)使用顶部弯曲成弯曲形状的钢线来掀开一个装有食物的密封容器,这种鸟类面对食物囤积者的方式非常聪明。
钢丝的上部远离接触口,没有牵动板导致钢丝开发。
观察证明,乌鸦使用了量子隧道现象来寻找钢丝温度上的物理变化,通过顶部弯曲的钢丝描绘动态人物,发现该物品的放置位置,从而找到食物。
在小到沙漠蜻蜓等昆虫,大到鲸鱼等海洋生物中,量子隧道现象也有着广泛的应用。
沙漠蜻蜓(Sympetrum danae)在表面温度低于自身时便知道停止飞行,以避免体温过快下降。
在过热时,昆虫可以通过量子隧道现象,透过神经反应使自己停止飞行。
同时,鲸鱼深海生存的巨大压力和盐度也可以通过量子隧道的方式缓冲。
在水下深处,物体常常需要经过压缩,使得它们变得更加稠密。
鲸鱼可以通过量子隧道现象,在深海压力下,进行不同骨骼、血液和脂肪组织的更好移动和平衡。
此外,量子隧道现象的应用还不仅仅限于物种对环境的适应,随着技术的发展和人类认识的深入,我们也已经利用量子隧道现象在新型材料制造等领域做出了不少贡献。
principal-principal problem_Oct30 (1)
Earnings management
Avoid losses or smooth earnings
Among Chinese listed firms to obtain a qualification for rights issues and/or to maintain their listing status (Jian and Wong, 2010)
They argue that in such instances, a firm’s board structure could serve as an important indicator of whether the controlling shareholder is committed to good corporate governance or is entrenched.
These studies also focus on how to mitigate minority-investor expropriation, thereby indicating that different solutions are required than for resolving the traditional agency problem.
10
Empirical evidence – M&A
Bae et al. (2002) report evidence that acquisitions by Korean business groups are used as a way for controlling shareholders to increase their own wealth at the expense of minority shareholders through tunneling. When a business-group-affiliated firm makes an acquisition, its stock price on average falls, but the controlling shareholder of that firm on average benefits because the acquisition enhances the value of other firms in the group, evidence consistent with the tunneling hypothesis.
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Tunneling or propping:Evidence from connected transactions in ChinaWinnie Qian Peng a ,K.C.John Wei a,⁎,Zhishu Yang baSchool of Business and Management,Hong Kong University of Science and Technology,Hong Kong b School of Economics and Management,Tsinghua University,Chinaa r t i c l ei n f o a b s t r a c t Available online xxxxFriedman et al.(2003)develop a model in which,in equilibrium,controlling shareholders may choose either tunneling or propping of their listed companies depending on the magnitude of an adverse shock and the magnitude of the private bene fits of control.In this paper,we employ connected transaction data from China to test the implications of their model.We hypothesize that,when listed companies are financially healthy (in financial distress),their controlling shareholders are more likely to conduct connected transactions to tunnel (prop up)their listedcompanies and the market reacts unfavorably (favorably)to the announcement of thesetransactions.Our empirical findings strongly support our hypotheses.We also find that all ofthe transaction types in our sample can be used for tunneling or propping depending ondifferent financial situations of the firms.Finally,political connection is negatively associatedwith the announcement effect.Overall,our analysis supports Friedman et al.'s (2003)model byfurnishing clear evidence for propping and tunneling to occur in the same company but atdifferent times.©2010Elsevier B.V.All rights reserved.JEL classi fication:G34G32G38Keywords:Connected transactions Tunneling Propping Chinese listed firms1.IntroductionA large body of empirical evidence has shown that controlling shareholders may take advantage of minority shareholdersthrough connected transactions,especially in emerging markets where legal protection of minority shareholders is Portaet al.(1997,1998,1999,2000),Johnson et al.(2000),Glaeser et al.(2001),and Chang (2003)have found that controllingshareholders extract private bene fits from minority shareholders through “tunneling.”Expropriation from minority shareholdersincludes outright theft and selling (buying)assets or products at lower (higher)than market price to (from)a firm in which thecontrolling shareholder has a high stake.Since the Asian Financial Crisis in 1997–1998,evidence has suggested that controlling shareholders also sometimes use privateresources to “prop up ”a troubled listed firm.1More speci fically,they may temporarily transfer resources to the listed firm to boostits performance so that a default or delisting can be avoided.Tunneling and propping are the two major behaviors of controllingshareholders when they engage in connected transactions within a group of af filiated firms.2Tunneling and propping can occur inJournal of Corporate Finance xxx (2010)xxx –xxx⁎Corresponding author.Department of Finance,Hong Kong University of Science and Technology,Clear Water Bay,Kowloon,Hong Kong.Tel.:+85223587676;fax:+852********.E-mail addresses:pengq@ust.hk (W.Q.Peng),johnwei@ust.hk (K.C.J.Wei),yangzhsh@ (Z.Yang).1The Salim group,once the biggest conglomerate in Indonesia,sold its privately held assets in the Netherlands in order to bail out its publicly listed operationsin the Philippines and Indonesia.It also injected funds from a publicly listed Hong Kong firm into a publicly listed Indonesian firm (Tasker,1998;Borsuk andHilsenrath,1999).The chairman of Samsung Electronics,Lee Kun Hee,who was also the head of the controlling family,donated part of his personal wealth to payoff the debts of Samsung Motors Inc.,which was facing bankruptcy in summer 1999(Fairclough,1999).2Besides tunneling and propping,there is also a “value-added ”view of the connected transactions in the literature,which suggests that connected transactionscan reduce transaction costs and facilitate the ef ficient allocation of resources within the group (Shin and Park,1999;Khanna and Palepu,1997,2000;Bae et al.,2002;Claessens et al.,2006).“Propping ”is not the same as “value-added ”because propping is used to boost performance temporarily and it is usually not able toadd real value to the firm in the long run.CORFIN-00474;No of Pages 200929-1199/$–see front matter ©2010Elsevier B.V.All rights reserved.doi:10.1016/j.jcorp fin.2010.08.002Contents lists available at ScienceDirectJournal of Corporate Financej o u r n a l h om e p a g e :w w w.e l sev i e r.c o m /l oc a t e /j c o r pfi n2W.Q.Peng et al./Journal of Corporate Finance xxx(2010)xxx–xxxthe samefirm but during different time periods.The questions are when and to what extent are controlling shareholders likely to choose tunneling or propping.Friedman et al.(2003)develop a model in which it is optimal for controlling shareholders to prop when there is a moderate adverse shock.If there is no shock or the shock is very small,controlling shareholders choose to tunnel.Looting(meaning that controlling shareholders take everything out of thefirm causing it to collapse),the extreme form of tunneling,occurs when the negative shock is very large.3To test the predictions of their model,Friedman et al.examine the stock price performance during the Asian Financial Crisis.They argue that issuing debt is a credible proxy for“propping”and that it is easy for Asianfirms in pyramidal structures to prop.Theyfind thatfirms in pyramids with more debt experienced smaller stock price declines during the Crisis than otherfirms,which is consistent with the existence of propping.Friedman et al.'s model facilitates our understanding of the fundamental nature of tunneling and propping.However,as they have noted,direct empirical evidence of propping is lacking.In addition,they do not provide any evidence of tunneling.Continuing their study,we analyze connected transaction data from China to test the predictions of their model directly.Connected transactions are a direct means for controlling shareholders in China to engage in tunneling or propping.The uniqueness of the ownership structures of listedfirms in China and the stock market regulations there allow us to identify both the timing and the extent of tunneling or propping in the samefirm,which is difficult if not impossible to observe or to quantify infirms in other countries.In China,afirm faces two types of risk after its listing that are unique to the Chinese stock market:(1)delisting and(2)losing the right to issue new shares.If a listedfirm reports a net loss for two consecutive years(return on equity(ROE)b0%),it will be designated as a special treatment(ST)firm and will face various trading andfinancial restrictions.If thefirm continues to make losses for one more year,it will be designated as a particular transfer(PT)firm which entails virtual suspension of trading.Further, if a PTfirm does not become profitable in the following year,it becomes completely delisted.A listedfirm also faces the risk of losing its right to issue new shares if the average ROE over the three-year period prior to issuing new shares is less than10%.4 Because it is very difficult to list afirm in China,afirm's controlling shareholders would suffer substantial losses of the private benefits of control from delisting or from the loss of the right to issue new shares.The controlling shareholders have strong incentives to prop up the listedfirms when they are facing the risks mentioned above so that they can continue to enjoy the private benefits of control of a listedfirm or the access to thefinancial market over the long run.With China's regulations on delisting and on the right to issue new shares,we are able to distinguish betweenfirms that are in soundfinancial condition for which controlling shareholders have strong incentives to tunnel andfirms that are in poorfinancial condition for which controlling shareholders have incentives to prop up.In general,since the listedfirms in China rarely go into bankruptcy,when a listedfirm is designated as ST or PT,it can be regarded as in poorfinancial condition and it is facing the risk of delisting.In contrast,if afirm has already successfully obtained the right to issue new shares,it must be in a healthyfinancial condition since neither the risk of delisting nor the risk of losing the right to issue new shares exists.It is important to note that, during other periods when afirm does not face the risk of delisting or the risk of losing the right to issue new shares,the incentive for tunneling or propping is less easily to identify.If afirm does not need or intend to issue new shares,tunneling is likely to occur. If afirm wishes to issue new shares in the near future,it is more likely for controlling shareholders to prop up rather than to tunnel in order to meet the requirements for issuing new shares.Based on the above classifications of listedfirms,we can examine the tunneling or propping behavior of controlling shareholders by using the information from the announcements of connected or non-connected transactions in China.We classify the listedfirms that are engaged in connected or non-connected transactions during the period1998–2004into three categories: soundfinancial condition,poorfinancial condition,and the rest.We also classify the transactions into connected and non-connected transactions.There arefive types of transactions included in our study:asset acquisitions,asset sales,asset displacements,equity transfers,and cash payments.We examine the market reactions to each of these types of transactions.Our results in general support our hypotheses.In particular,wefind that there is a negative market reaction to announcements of connected transactions by listedfirms that have successfully obtained the right to issue new shares,which indicates that investors perceive controlling shareholders as having incentives to tunnel.In contrast,wefind a positive market reaction to announcements of connected transactions by listedfirms that face the risk of delisting which indicates that investors perceive controlling shareholders as having incentives to prop.All of the transaction types in our sample can be used for tunneling or propping depending on thefinancial situations of thefirms.Political connection seems to be negatively associated with the announcement effect,which suggests thatfirms with political connections appear to be more likely to conduct tunneling-motivated connected transactions.This is consistent with thefinding by Fan et al.(2007)that government intervention is negatively associated with firm performance and governance quality.Finally,affiliated-groupfirms are more likely to use connected transactions to prop up listedfirms with high leverage than listedfirms with low leverage,which is consistent with Friedman et al.'s(2003)hypothesis.We note that there are two contemporaneous and independent studies that are directly related to ours.Jiang et al. (forthcoming)report that controlling shareholders in China use inter-corporate loans(a type of connected transaction)to tunnel from their listed companies.Jian and Wong(2010)document that controlling shareholders in China also prop up earnings by using abnormal related sales(another type of connected transaction),when their listedfirms are at the threshold for the right to issue new shares or for delisting.They alsofind significant cash transfers via related lending from listedfirms back to the controlling owners after the propping.We also note that there are two earlier studies that are also related to ours.Liu and Lu3Evidence of looting is also shown in La Porta et al.(2003).4For a detailed description of the ST policy and the right to issue new shares,please refer to Section2.(2007)find that earnings management in Chinese listed firms is mainly induced by the controlling owners'tunneling activities.Cheung et al.(2006)study a sample of connected transactions in Hong Kong listed companies and find that firms announcingconnected transactions earn signi ficantly more negative excess returns than firms announcing non-connected transactions.Theyalso find that mainland Chinese companies listed in Hong Kong are more likely to use connected transactions to expropriateminority shareholders.Our study is different from these previous studies in several ways.First,our study provides direct evidence to Friedman et al.'s(2003)model by identifying both the timing and the extent of tunneling or propping in the same firm.Speci fically,we find that,insome cases,controlling shareholders in China prop up their listed firms in bad times,while they tunnel from these same listedfirms in good times.Second,the transactions included in our study all have signi ficant economic impacts on listed firms.Onaverage,the transaction value is greater than 10%of a firm's total assets.Smaller transactions are not included,as timelyannouncements are not required.Third,the types of transactions studied in this paper are mainly asset and equity transactions,while the earlier studies focus on the related sales,related lending,among other types of transactions.We find that all types oftransactions in our sample can be used for tunneling or propping depending on the financial situation of a firm,while the earlierstudies document speci fic types of transactions that might be more likely to result in tunneling or propping.Finally,we find thatpolitical connection has a negative effect on announcement returns,suggesting that firms with political connections seem to bemore likely to conduct tunneling-motivated connected transactions.The rest of the paper proceeds as follows.Section 2details the background of our study and the hypothesis development.Section 3describes the data and the methodology.Section 4reports empirical results from simple t -statistic tests and cross-sectional regressions.Section 5summarizes and concludes the paper.2.Background and hypothesis development2.1.Unique features of the Chinese stock marketThe Chinese stock market was initially organized by the government to privatize its state-owned enterprises (SOEs)to raisecapital and to improve operating performance.Since its inception in 1991,the Chinese stock market (Shanghai Stock Exchangeand Shenzhen Stock Exchange jointly)has grown exponentially to become one of the largest stock markets in the world with amarket capitalization of around US$3.5trillion at the end of 2009.There were 870firms listed on the Shanghai Stock Exchange and830on the Shenzhen Stock Exchange with a combined total of 1700firms at the end of 2009.The Shanghai Stock Exchange alonewas the sixth largest stock exchange in the world,ranking just below the London Stock Exchange and just above the Hong KongStock Exchange at the end of 2009.The listed (tradable)shares in China are classi fied according to the residency of their owners asdomestic (A-shares)or foreign (B-,H-and N-shares).5In China,a country with a centrally planned economy,the China Securities Regulatory Committee (the CSRC)has the authorityto set listing and delisting policies for the listed firms in the Shanghai and Shenzhen Stock Exchanges,a situation that is differentfrom the United States,in that the stock exchanges have the authority to set their own rules.The ST policy and the policy on theright to issue new shares are the ones that are very unique and have a big impact on the Chinese stock market.Starting from April 1998,the CSRC mandated that if a listed firm reports a net loss (i.e.,a negative ROE)in two consecutiveyears,it will be designated as a special treatment (ST)firm.In 1999,the CSRC introduced the particular transfer designation (PT)for an ST firm if it suffers net losses for three consecutive years.There are various restrictions for an ST firm,the shares of which istraded with a 5%price change limit each day compared with a 10%limit for a normal firm.In addition,its midterm financial reportsmust be audited and it cannot raise additional capital from the stock market.A PT stock can be traded only on Friday,with amaximum 5%upside limit to the previous Friday's close,but no restriction on the downside.PT itself entails virtual suspension oftrading.Further,if a PT firm does not become pro fitable in the following year,it becomes completely delisted.In 2002,the PTdesignation was abolished by the CSRC.Afterwards,if a firm suffers losses for three consecutive years,it will be delisted without aPT transitional period.To replace the old “ST ”designation,the CSRC introduced a new designation called “*ST ”in 2003.An *ST firmis one that reports net losses for two consecutive years.It is similar to ST,but without the transitional PT period.That is,if an *STfirm suffers losses for one more year,it will be delisted.During 1998and 2004,250listed firms in the Shanghai and ShenzhenStock Exchanges were designated as ST or *ST firms,35of which were delisted eventually.6The ST policy is still effective as of June2010.It is set by regulators in the hope of protecting investors'interest.However,as addressed by Jiang and Wang (2008),the STpolicy has serious unintended consequences.For example,it could drive healthy firms out of the stock markets for temporaryaccounting losses,and it also induces listed firms to engage in earnings manipulation to avoid being delisted.In order to obtain the right to issue new shares in the form of rights issues or seasoned equity offerings,starting from 1996,alisted firm in China is required by the CSRC to maintain a minimum return on equity (ROE)of 10%for each of the three consecutive5A-shares are available exclusively to domestic Chinese investors and are denominated in the Chinese currency,the RMB.Originally,B-shares,which aredenominated in U.S.dollars on the Shanghai Stock Exchange and in Hong Kong dollars on the Shenzhen Stock Exchange,were only available for trading by non-residents.However,the B-share market was opened up to individual domestic investors in 2001if they had foreign currencies.Chinese firms have beenpermitted to list their stocks on the Stock Exchange of Hong Kong (SEHK)as H shares since 1993.N-shares are traded on U.S.stock exchanges,normally the NewYork Stock Exchange,in the form of American Depository Receipts (ADRs).6There were 851listed firms at the end of 1998and 1373listed firms at the end of 2004.3W.Q.Peng et al./Journal of Corporate Finance xxx (2010)xxx –xxx4W.Q.Peng et al./Journal of Corporate Finance xxx(2010)xxx–xxxyears prior to the offering.In1999,the policy was modified to an average ROE of no less than10%and at the same time a minimum ROE of no less than6%in each of the three years.In2001,the policy was further modified to an average ROE of no less than6%in the previous three years before the offering.Between1998and2004,1021listedfirms in the Shanghai and Shenzhen Stock Exchanges have issued new shares at least once.As documented by many previous studies such as Jiang and Wei(1998),Chen et al.(2001),and Haw et al.(2005),the policy on the right to issue new shares also has unintended consequences in that the listed firms tend to manage their earnings in order to reach the ROE thresholds.Ding et al.(2007),Liu and Lu(2007),Jian and Wong(2010),and others have documented that controlling shareholders in listedfirms have strong incentives to use real transaction-based techniques to“prop up”a listedfirm that is in danger of being delisted or losing its right to issue new shares.Those real transactions include connected transactions,restructuring,or fraudulent activities,which equally often result in tunneling by controlling shareholders when the listedfirms are out of danger.The above studies indicate that the ST policy and the policy on the right to issue new shares might provide timing and opportunities for controlling shareholders to prop up or tunnel from the listedfirms in China.Moreover,there are several other unique features of the Chinese listedfirms that are quite helpful for us to understand the incentives of controlling shareholders' tunneling and propping behavior.First,the ownership of Chinese listedfirms is highly concentrated,and more than80%of the listed companies are state-owned enterprises.On average,state-owned shares and legal person shares(indirectly owned by the government)account for70%of the total number of shares in Chinese listedfirms during our sample period1998–2004.7Furthermore,the largest shareholders(in 80%of the cases)control more than40%of the listedfirms'shares,while the second largest shareholders own less than10%of these shares.In some cases,CEOs of the listed companies are directly appointed by the local or central government or have close ties with the government.Fan et al.(2007)find that almost27%of the CEOs in their sample of790newly partially privatizedfirms in China are former or current government bureaucrats.The controlling shareholders are rarely challenged by other shareholders on important issues.Minority shareholders cannot take listedfirms to court,due to limitations in the civil law system and to the lack of punishment associated with the current securities laws.Second,a majority of A-shares owned by the government or its agencies are not tradable.State and legal person non-tradable shares cannot be traded on the exchanges,but can be transferred to domestic corporations,typically another government agency, if approved by the CSRC.At the end of2004,non-tradable shares accounted for more than60%of the outstanding stocks.Since most of their shares are non-tradable,the controlling shareholders could not benefit from the share price appreciation associated with improving operating performance,which leads to their tunneling behavior through other channels such as connected transactions and fraudulent activities.In2005,the Chinese government initiated a reform,called the share structure resolution,to resolve the issue of non-tradable shares.To make non-tradable A-shares tradable,the holders of non-tradable A-shares have to give part of their shares free of charge to the holders of the corresponding tradable A-shares.A typical holder of tradable A-shares will receive2–3shares per10 shares that the tradable A-shares holder own from holders of non-tradable shares.8The reform had been mostly completed by 2007,which caused an unprecedented wave of stock price boom during the reform period.Due to this structural change which may affect the incentives of controlling shareholder,our sample does not include the period after the reform.Third,the group-controlled ownership structure in China is very common.A large number of listedfirms have been restructured from existing SOEs through“carve outs,”meaning that the productive operation of afirm is carved-out to set up a firm to be listed and the unproductive operation remains in the parentfirm.After the listing,the government still controls the majority of the shares of these partially privatized SOEs through different local or central government agencies.Other than solely for profit maximization,the SOEs have other objectives such as to maintain employment,to directly control industries that are strategically important,and to extract various private benefits as well.As a result,there is a natural tendency for the SOEs to tunnel from listedfirms.According to Claessens et al.(2002),tunneling becomes more severe when the controlling shareholders' controlling right exceeds their ownership right.Fourth,it is very difficult forfirms to get listed in China.Since the primary objective for the development of the equity markets in China is to facilitate externalfinancing for the partially privatized SOEs,regulations have been asymmetrically in favor of the SOEs orfirms with close ties to the central or local governments.Specifically,until recently,access to listing on the Chinese stock market was strictly administered by the government.For example,listing quotas were allocated to provinces or ministries according to certain criteria.9Firms in protected industries or with close ties to the government had a great advantage over otherfirms in winning the right to go public.Because of policy constraints,the competition for the right to have a low listing via initial public offerings(IPOs)isfierce.As a result,the listing status of a publicfirm carries a significant value. Thus,the controlling shareholders have strong incentives to prop up the listedfirms in times offinancial distress in order to avoid delisting.Given the above reasons,the Chinese stock market offers a natural and unique setting for our study on tunneling and propping.7The percentage has been slightly reduced since the share structure resolution in2005.8In some cases,instead of giving out shares for free,the non-tradable shareholders pay a certain amount of cash to tradable shareholders.9The listing quota system was canceled and the quotas werefinally used up by2001.Afterwards,a series of reform plans were adopted by regulators. However,it was still difficult forfirms to get listed and the government's approval was still needed.At the end of2005,the government(i.e.,the CSRC)decided to give the exchanges the power to decide if afirm is qualified for listing,while the government still keeps the power to decide if afirm is qualified for issuing new shares after listing.In essence,the government still has the most influential power in making the issuing decision.2.2.Connected transactions in ChinaA connected transaction is generally de fined as any transaction between a firm or any of its subsidiaries and a connectedperson.Connected persons are the listed firm's or the subsidiary's substantial shareholders,the directors,the chief executive andtheir associates,including any firms that hold substantial shares of the listed firm.The de finition also applies to any person who is aclose relative (such as spouses,parents,step-parents,brothers/sisters,step-brothers/sisters,and in-laws)of the connected person.A listed firm's major connected parties include its shareholders (the parent firm usually is the largest shareholder and also thecontrolling shareholder),its shareholders'af filiates and its own af filiates.Another important connected party is the af filiated firmsin which the listed firms own a 5%–50%share and thus can exert signi ficant in fluence over but do not consolidate them into theirfinancial statements.There are many different forms of connected transactions in China,including asset acquisitions,asset sales,assetdisplacements,equity transfers,cash payments,cash receipts,asset leases,loan guarantees,trademark rights transfers,etc.Common transactions are tangible assets and equity transactions.Intangible asset transactions,such as trademark rights transfers,have become popular recently.Since 1997,the Ministry of Finance and the CSRC have issued several accounting rules and regulations regarding connectedtransactions.Connected transactions between a listed firm and its connected person amounting to a total value of greater thanRMB300,000(US$36,300),and connected transactions between a listed firm and its connected party amounting to a total value ofgreater than RMB3million (US$363,000)or 0.5%of net assets,whichever is higher,must be reported to the exchange within twoworking days following the signing of the transaction agreement,and must be disclosed in the footnotes of the firm's annualreport.For the connected transactions of a total value of greater than RMB30million (US$3.63million)or 5%of net assets,which ishigher,the transaction price must be appraised or audited by professionals,and approved in the general meeting of shareholders.For non-connected transactions,transactions amounting to a total value of greater than 10%of total assets or generating operatingrevenue greater than 10%of the total revenue must also be reported to the exchange within two working days following thetransaction agreement.However,enforcement of the rules is weak because the CSRC lacks the necessary investigative andprosecuting power and resources.Due to the unique ownership structure and weak governance mechanisms in China,listed firms become the nexus of a series ofconnected transactions carried out for the bene fit of controlling shareholders.Statistics show that out of 719listed firms in 1997,84.6%(i.e.,609firms)were involved in different degrees of connected transactions.In 2000,this number reached 93.2%.Amongthose connected transactions,more than 70%were conducted between the controlling shareholders and their listed firms.2.3.HypothesesAs stated earlier,the ST policy and the policy on the right to issue new shares might provide timing and opportunities forcontrolling shareholders to prop up or tunnel from the listed firms in China.In addition,several unique features of the Chineselisted firms give incentives for controlling shareholders'tunneling and propping behavior.Tunneling is related to the agencyproblem between controlling shareholders and minority shareholders.Corporate governance is designed to alleviate the agencyproblem.However,the corporate governance mechanisms are very weak in China.Chinese listed firms are mostly owned by thegovernment,meaning that controlling shareholders care less about minority shareholders and pay more attention to their owninterests.As the majority of shares owned by the government or its agencies are not tradable during our sample period,thecontrolling shareholders would have had to find alternative channels such as connected transactions to tunnel from listed firmsbecause they cannot bene fit from the share price appreciation associated with improving operating performance.In addition,thegroup-controlled ownership structure in China enables controlling shareholders to tunnel from listed companies for purposesother than wealth maximization or to bene fit themselves.Thus,when a listed firm is in sound financial condition and faces no risk of delisting or losing the right to issue new shares,connected transactions can provide controlling shareholders with direct opportunities to tunnel.Tunneling includes activities such asextracting cash from the listed firm (by selling assets,goods,or services to the firm through self-dealing transactions),obtaining loanson preferential terms,transferring assets from the listed firm to other group-af filiated firms,or diluting the interests of minorityshareholders by acquiring additional shares at a preferential price.The above discussions lead to the following hypothesis:H1.When a listed firm is in a sound financial condition,the market will react negatively to the firm's announcement of connectedtransactions.Controlling shareholders do not always tunnel.As the listing status is very valuable for Chinese listed firms,when a listed firmis in financial distress,controlling shareholders have incentives to prop up the firm in order to maintain its listing status so thatthey can continue to control the firm and to protect their private bene fits of control.Thus,when a listed firm is in poor financialcondition,its controlling shareholder is likely to provide temporary support for the firm,such as buying assets from the firm at ahigher price,exchanging good assets for bad assets in return,and providing loans with favorable interest rates.Through theseconnected transactions,the listed firm can turn a loss into a pro fit so that it can remove its special designation status.We thereforeexpect a positive market reaction to an announcement of a connected transaction when it is made between a listed firm in poorfinancial health and its controlling shareholders.However,this “propping ”behavior should not last long.The controllingshareholders would “help ”a listed firm temporarily,because they are afraid of losing the private bene fits of control or the ability to5W.Q.Peng et al./Journal of Corporate Finance xxx (2010)xxx –xxx。