Analysis of the Disturbances in Distribution using matlab

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tpo32三篇托福阅读TOEFL原文译文题目答案译文背景知识

tpo32三篇托福阅读TOEFL原文译文题目答案译文背景知识阅读-1 (2)原文 (2)译文 (5)题目 (7)答案 (16)背景知识 (16)阅读-2 (25)原文 (25)译文 (28)题目 (31)答案 (40)背景知识 (41)阅读-3 (49)原文 (49)译文 (53)题目 (55)答案 (63)背景知识 (64)阅读-1原文Plant Colonization①Colonization is one way in which plants can change the ecology of a site.Colonization is a process with two components:invasion and survival.The rate at which a site is colonized by plants depends on both the rate at which individual organisms(seeds,spores,immature or mature individuals)arrive at the site and their success at becoming established and surviving.Success in colonization depends to a great extent on there being a site available for colonization–a safe site where disturbance by fire or by cutting down of trees has either removed competing species or reduced levels of competition and other negative interactions to a level at which the invading species can become established.For a given rate of invasion,colonization of a moist,fertile site is likely to be much more rapid than that of a dry, infertile site because of poor survival on the latter.A fertile,plowed field is rapidly invaded by a large variety of weeds,whereas a neighboring construction site from which the soil has been compacted or removed to expose a coarse,infertile parent material may remain virtually free of vegetation for many months or even years despite receiving the same input of seeds as the plowed field.②Both the rate of invasion and the rate of extinction vary greatly among different plant species.Pioneer species-those that occur only in the earliest stages of colonization-tend to have high rates of invasion because they produce very large numbers of reproductive propagules(seeds,spores,and so on)and because they have an efficient means of dispersal(normally,wind).③If colonizers produce short-lived reproductive propagules,they must produce very large numbers unless they have an efficient means of dispersal to suitable new habitats.Many plants depend on wind for dispersal and produce abundant quantities of small,relatively short-lived seeds to compensate for the fact that wind is not always a reliable means If reaching the appropriate type of habitat.Alternative strategies have evolved in some plants,such as those that produce fewer but larger seeds that are dispersed to suitable sites by birds or small mammals or those that produce long-lived seeds.Many forest plants seem to exhibit the latter adaptation,and viable seeds of pioneer species can be found in large numbers on some forest floors. For example,as many as1,125viable seeds per square meter were found in a100-year-old Douglas fir/western hemlock forest in coastal British Columbia.Nearly all the seeds that had germinated from this seed bank were from pioneer species.The rapid colonization of such sites after disturbance is undoubtedly in part a reflection of the largeseed band on the forest floor.④An adaptation that is well developed in colonizing species is a high degree of variation in germination(the beginning of a seed’s growth). Seeds of a given species exhibit a wide range of germination dates, increasing the probability that at least some of the seeds will germinate during a period of favorable environmental conditions.This is particularly important for species that colonize an environment where there is no existing vegetation to ameliorate climatic extremes and in which there may be great climatic diversity.⑤Species succession in plant communities,i.e.,the temporal sequence of appearance and disappearance of species is dependent on events occurring at different stages in the life history of a species. Variation in rates of invasion and growth plays an important role in determining patterns of succession,especially secondary succession. The species that are first to colonize a site are those that produce abundant seed that is distributed successfully to new sites.Such species generally grow rapidly and quickly dominate new sites, excluding other species with lower invasion and growth rates.The first community that occupies a disturbed area therefore may be composed of specie with the highest rate of invasion,whereas the community of the subsequent stage may consist of plants with similar survival ratesbut lower invasion rates.译文植物定居①定居是植物改变一个地点生态环境的一种方式。

不要以貌取人英语作文

In the English composition titled Do Not Judge a Book by Its Cover,we can explore the theme of not making assumptions about people based on their appearance.Here is a detailed outline for such an essay:Introduction:Introduce the proverb Do not judge a book by its cover,explaining its relevance to human interactions.State the importance of looking beyond appearances to understand a persons true character.Body Paragraph1:The Dangers of Superficial JudgmentsDiscuss how quick judgments based on appearance can lead to misunderstandings and missed opportunities.Provide examples of famous individuals who have overcome initial judgments based on their looks,such as Albert Einstein or Steve Jobs.Body Paragraph2:The Psychological Basis for First ImpressionsExplain the psychological phenomenon of first impressions and why humans are inclined to make them.Discuss the role of cognitive biases in forming quick judgments about people.Body Paragraph3:The Importance of Character Over AppearanceArgue that a persons character,values,and actions are more important than their physical appearance.Use examples of individuals who have made significant contributions to society despite not fitting societal beauty standards.Body Paragraph4:The Impact of Media and Society on PerceptionAnalyze how media and societal standards influence our perceptions of beauty and worth. Discuss the negative effects of these influences,such as low selfesteem and discrimination.Body Paragraph5:Strategies for Overcoming Prejudice Based on Appearance Suggest practical steps individuals can take to avoid making superficial judgments,such as engaging in meaningful conversations and seeking to understand others experiences. Encourage the development of empathy and openmindedness.Conclusion:Reiterate the message that appearances can be deceiving and that true understanding comes from deeper interactions.End with a call to action for readers to challenge their own biases and to treat others with kindness and respect,regardless of their appearance.Sample Composition:In the everevolving tapestry of human interaction,the adage Do not judge a book by its cover stands as a timeless reminder of the importance of looking beyond the superficial. This essay aims to delve into the perils of superficial judgments and advocate for a deeper understanding of individuals based on their character and actions.The first impressions we form are often swift and influenced by appearances.However, these judgments can be misleading,as they may not reflect the true essence of a person. For instance,the unkempt appearance of Albert Einstein did not detract from his genius, nor did the casual attire of Steve Jobs diminish his innovative spirit. Psychologically,humans are hardwired to make quick assessments based on visual cues, a trait that has evolutionary roots in our need for rapid decisionmaking.Yet,this instinct can lead to cognitive biases that cloud our judgment.It is crucial to recognize these biases and actively work to overcome them.Character,defined by ones values,integrity,and actions,holds far more significance than physical appearance.The world has been enriched by the contributions of individuals who defied conventional attractiveness,proving that beauty is not a prerequisite for success or worth.The media and societal norms play a significant role in shaping our perceptions of beauty. These influences can be detrimental,fostering unrealistic expectations and leading to discrimination against those who do not conform.It is essential to challenge these standards and recognize the diversity of beauty in all its forms.To combat prejudice based on appearance,we must engage in meaningful dialogues that reveal the stories and experiences of others.Developing empathy and an open mind can help us see past the facade and appreciate the unique qualities each person possesses.In conclusion,while appearances may capture our initial attention,it is the substance of a persons character that truly defines them.Let us strive to look beyond the surface and embrace the rich diversity of human experience.By doing so,we not only enrich our own lives but also contribute to a more inclusive and compassionate society.。

写作业不正确的方式英语

1.Procrastination:Putting off the task until the last minute,which can lead to rushed and poorly thoughtout work.ck of Preparation:Starting the assignment without fully understanding the topic or requirements,resulting in confusion and errors.3.Distraction:Allowing external factors such as social media,television,or noisy environments to divert attention from the task at hand.4.Poor Time Management:Not allocating sufficient time for research,drafting,and revising the work,leading to incomplete or hastily done assignments.5.Copying from Others:Plagiarizing or copying work from classmates or online sources, which is unethical and can lead to academic penalties.6.Irrelevant Information:Including information in the assignment that does not pertain to the topic or question,which can dilute the focus and quality of the work.ck of Citation:Failing to properly cite sources,which can lead to accusations of plagiarism and a lack of credibility in the work.8.Poor Grammar and Spelling:Submitting work with numerous grammatical and spelling errors,which can detract from the overall quality and professionalism of the assignment.9.Inadequate Research:Relying on superficial or insufficient research,which can result in a lack of depth and understanding in the assignment.10.Not Following Instructions:Ignoring specific instructions given by the teacher or professor,such as formatting requirements,word count,or specific topics to be covered.11.Rushing the Conclusion:Ending the assignment abruptly or without a proper conclusion,which can leave the reader with an incomplete understanding of the argument or analysis.12.Overloading with Jargon:Using too much technical language or jargon without proper explanation,which can make the work difficult to understand for the intended audience.13.Not Proofreading:Failing to proofread the work for errors or inconsistencies beforesubmission,which can lead to a lower grade due to avoidable mistakes.ck of Personal Insight:Writing an assignment that lacks original thought or personal interpretation,making it generic and less engaging.15.Inappropriate Tone:Using an informal or overly casual tone in an academic assignment,which can undermine the seriousness and credibility of the work.。

高英课文翻译

THE MIDDLE EASTERN BAZAAR 中文翻译文: 中东的集市The Middle Eastern bazaar takes you back hundreds --- even thousands --- of years. The one I am thinking of particularly is entered by a Gothic - arched gateway of aged brick and stone. You pass from the heat and glare of a big, open square into a cool, dark cavern which extends as far as the eye can see, losing itself in the shadowy distance. Little donkeys with harmoniously tinkling bells thread their way among the throngs of people entering and leaving the bazaar. The roadway is about twelve feet wide, but it is narrowed every few yards by little stalls where goods of every conceivable kind are sold. The din of the stall-holder; crying their wares, of donkey-boys and porters clearing a way for themselves by shouting vigorously, and of would-be purchasers arguing and bargaining is continuous and makes you dizzy.中东的集市仿佛把你带回到了几百年、甚至几千年前的时代。

高级英语(第三版)第一册第十二课 Ships in the Desert

Para.1 typical example of environmental destruction
The Aral sea
•The Aral Sea:
*located in Uzbekistan and Kazakhstan *historically a saline lake *In 1960 the world’s fourth largest lake, the size of the entirety of Southern California *in the center of a large, flat desert basin •a prime example of a dynamic environment
–theater: scene of operation –e.g. This was the Pacific theatre of
World War II. –这里是第二次世界大战的太平洋战
2. Detailed study of the text
• Questions
What’s the meaning of the title? What does the author try to tell us through his article? Why did the writer go to the Aral Sea? What did he see there?
Michigan, Lake Huron, Lake Erie, and Lake Ontario • HOMES—H stands for Huron, O for Ontario, M for Michigan, E for Erie and S for Superior.

基于CPTED理论和空间句法的住区街道空间规划设计与犯罪防控——以西安市瓦胡同小区、雁鸣小区为例

基于CPTED理论和空间句法的住区街道空间规划设计与犯罪防控——以西安市瓦胡同小区、雁鸣小区为例Residential Street Space Planning and Design and Crime PreventionBased on CPTED Theory and Space Syntax------Taking Wahhutong Community and Yanming Community in Xi'an as Examples强靖淇，杜雅星，陈正英QIANG Jing-qi,DU Ya-xing,CHEN Zheng-ying(西北大学城市与环境学院)(School of Urban and Environmental Sciences,Northwest University)【摘要】随“新型城镇化”战略的实施，不仅繁荣了我国的经济、提高了人们的生活品质，也带来了资源消耗、城市犯罪行为日益凸显等“城市病"。

住区街道空间集聚周边居民的各项公共活动，更易产生犯罪行为。

文章基于CPTED理论的六大类空间要素，运用空间句法从宏观的街道轴线连接值、全局整合度和微观的街道节点视域进行分析，以西安市两个城中村改造社区为例，对比分析住区周边街道空间犯罪行为发生与规划设计之间的关系，从节点视线渗透、后期监管方面对住区街道空间提出对策，以达到犯罪防控的目的。

[Abstract]With the implementation of the"new urbanization'*strategy,it has not only continuously prospered China's economy and improved people*s quality of life,but also brought"urban diseases1'such as resource consumption and increasingly prominent urban criminal behaviors.The street space of the residential area gathers various public activities of the surrounding residents,and it is more likely to produce illegal and criminal acts.Based on the six major spatial elements of CPTED theory,this article uses spatial syntax to analyze the macroscopic street axis connection value,the global integration degree and the microscopic street node perspective.Taking the transformation of t wo urban villages in Xi'an as an example,it makes a comparative analysis of the relationship between the occurrence of illegal crimes and the planning and design of neighborhood space around the residential areas,and proposes countermeasures from the perspective of the node penetration and post-supervision of residential street space,so as to achieve the purpose of crime prevention and control.【关键词】CPTED理论；空间句法；街道空间；犯罪防控；规划设计；[Keywords]CPTED theory;space syntax;street space;crime prevention and control;planning and design1引言我国对于城市住区犯罪防控问题，主要采取的是建设后期的法律制约和治安管理，而对于住区建设前期的住区规划设计缺乏关注。

森林干扰生态研究_朱教君

森林干扰生态研究＊朱教君1,2＊＊　刘足根1,2(1中国科学院沈阳应用生态研究所,沈阳110016;2中国科学院研究生院,北京100039)【摘要】　陆地上80%的生态系统都已受到了来自人类和自然的各种干扰,森林生态系统也不例外.在各种干扰作用下,尤其是人类不合理的干扰导致世界范围内的森林退化/衰退已成为一个十分严峻的事实,因此,以维持、恢复森林生态系统固有的多种功能为基础,实现高效、稳定、可持续就成为经营森林生态系统的总目标.随着干扰的加剧,近年来生态学界更加关注的是“受干扰”生态系统的研究.干扰对森林生态系统主要生态过程的影响以及森林生态系统对干扰的响应等问题,已成为森林生态研究领域的国际前沿与热点.因此,系统地研究干扰条件下森林生态系统的生态过程,并在此基础上确立干扰森林的经营理论与技术,对中国天然林资源保护等林业工程实施及国家生态安全建设具有重要的科学和现实意义.本文在广泛收集国内外有关森林干扰研究结果的基础上,总结了森林干扰的基本概念,分析了干扰与森林经营的关系,探讨了森林干扰研究领域所涉及的内容和关注的基础问题,提出了森林干扰生态研究的主要内容与方向,对今后干扰森林生态研究和中国天然林保护等林业工程建设具有参考价值.关键词　干扰　森林干扰　干扰生态　生态过程文章编号　1001-9332(2004)10-1703-08　中图分类号　S757.1　文献标识码　AA review on disturbance ecolo gy of forest .ZHU Jiaojun 1,2,LI U Zugen 1,2(1Institute of Applied Ecolo gy ,ChineseAcademy of Sciences ,Shenyang 110016,China ;2Graduate Scho ol of Chinese Academy of Sciences ,Beijing 100039).-Chin .J .Appl .Ecol .,2004,15(10):1703～1710.M ore than 80%of terrestrial ecosy stems have been influenced by natural disasters ,human activities and the com -bination of bo th natural and human disturbances .F orest ecosystem ,as one of the most impo rtant terrestrial e -cosy stems ,has also been disturbed without exception .U nder the disturbance from natural disasters and human ac -tivities ,particularly from the unreasonable activities of human beings ,forest decline or forest deg radation has be -come more and mo re severe .F or this reason ,sustaining o r recovering fo rest service functions is one of the current purposes for managing forest ecosystems .In recent decades ,the studies on disturbed ecosystems hav e been carried out frequently ,especially on their ecological processes and their respo nses to the disturbances .T hese studies play a very impor tant role in the projects of natural forest conservation and the construction o f ecological environment in China .Based on a wide range of literatures collection on forest disturbance research ,this paper discussed the fun -damental co ncepts of disturbance ecolo gy ,the relationships between forest management and disturbance ,and the study contents o f forest disturbance ecology .The major research topics of forest disturbance ecology may include :1)the basic characteristics of disturbed forests ;2)the processes of natural and human disturbances ;3)the re -sponses of fo rests ecosy stem to the disturbances ;4)the main ecological processes or the consequential results of disturbed fo rests ,including the change of biodiversity ,soil nutrient and w ater cy cle ,eco -physiolo gy and carbo n cy cle ,regeneratio n mechanism of disturbed forests and so on ;5)the relationships between disturbances and forest management ;and 6)the principles and techniques for the management of disturbed forests .T his review may be helpful to the management of disturbed forest ecosy stem ,and to the projects of natural fo rest conserva tio n in Chi -na .Key words Disturbance ,Forest disturbance ,Disturbance ecology ,Ecological processes .＊中国科学院百人计划项目(BR0301)和国家自然科学基金资助项目(30371149).＊＊通讯联系人.2004-05-09收稿,2004-06-22接受.1　引言陆地上80%的生态系统都已受到了来自人类和自然的各种干扰,森林生态系统也不例外.广义上讲,森林干扰是普遍的,内在的和不可避免的,干扰影响到森林的各个水平.人类社会发展的历史可以认为是人类对森林干扰的历史[36],因为人类在自然界中所处的地位是其他任何生物所不能比拟的,是自然生态系统一个组成部分,并且通过自身的活动对其所处的环境产生巨大的影响力.由于近代人类对森林不合理、甚至是掠夺性的开发利用(干扰),使人为干扰远大于自然干扰,因此,在绝大多数情况应用生态学报　2004年10月　第15卷　第10期 CHI NESE JO U RNA L OF A PPL IED ECOLO GY ,Oct .2004,15(10)∶1703～1710DOI :10.13287/j .1001-9332.2004.0356下,人类干扰和破坏是联系在一起的[11].起源于传统林业资源管理的森林生态系统管理,最初更多的是关心干扰的破坏性、危害性以及如何防止干扰.近些年,随着森林科学理论和技术的发展,使多学科、大尺度和长期监测研究成为可能,人们逐渐认识到各种干扰在森林生态管理中的生态意义,并强调了人类活动作为一种合理的干扰的重要性.实际上,自然干扰作为驱动力之一,在维持森林生态系统物种多样性、群落稳定性和景观异质性等方面一直起着极其重要的作用,它是森林生态系统的正常行为,是森林的重要特征[51],甚至是种群维持的机制之一[2,54,65,67].我国天然林面积为8.726×107hm2,占森林总面积的70%;除自然保护区、森林公园、未开发的西藏林区、已实施保护的热带雨林和零散分布的原始林外(3.769×107hm2),其余全为经干扰后形成的次生林[70,73],即干扰条件下森林的经营问题是中国林业发展中最重要的主题之一[25].面对森林退化、被干扰森林面积的快速增加使这一问题更显突出[71].因此,弄清森林生态系统干扰与森林经营的关系,并通过研究对干扰进行合理控制,使其有利于森林生态系统的正向转化,对国家林业重点工程的实施及国家生态安全建设具有重大意义.由于干扰的形式不同,森林演替进程不一,群落结构千变万化;但如能根据森林结构特点和干扰的影响机理或机制实施合理经营,则可使被破坏的森林生态系统迅速恢复[25,30].为此,本文在广泛收集国内外有关森林干扰研究结果的基础上,总结森林干扰研究领域中的基本概念,对干扰与森林经营的相互关系进行分析,探讨森林干扰研究领域所涉内容及其关注的基础问题,提出森林干扰生态学研究的主要内容与方向,旨在对今后干扰森林生态学研究和中国天然林保护等林业工程建设有一定的指导作用.2　森林干扰的基本概念2.1　干扰与干扰生态随着人们对自然认识的提高和社会发展的需要,干扰有不同的定义.如White[65]对干扰的内涵分析指出:任何群落和生态系统都是动态变化和空间异质的,干扰是天然群落结构和动态时空异质性的主要来源.Pickett等[47]则把干扰定义为使生态系统、群落或物种结构遭受破坏,使基质和物理环境的有效性发生显著变化的一种离散性事件.对于人类生产活动,一般不称为干扰,这是因为在人们的想象中干扰总是与破坏联系在一起的,但对于自然生态系统来说,人类的一切行为均是干扰[8].干扰生态已成为当代生态学研究的活跃领域[67],干扰生态学是以研究影响生态系统自然干扰事件为主的科学,重点研究影响生态系统结构与功能的自然现象,开发能够预测长期或景观水平的经营管理活动对自然干扰发生频度、强度影响模型.对于森林生态系统而言,重点研究自然干扰在森林生态系统的可持续经营中的地位、意义,为森林资源的保护、森林生态系统的可持续经营提供必要的信息和策略.从干扰生态学的角度出发,森林生态系统的演替不一定要朝着固定的方向发展,相反,它强调随机性和非预定性.随着干扰生态学的发展,生态学家发现自然生态系统展示了植被变化的多个途径以及常常有多个稳定的状态,而不是一个共同的演替顶极[21].自然干扰在影响物种的相似性和演替途径中起到了重要作用[46],因此,根据自然干扰的作用,关心人类干扰对生态系统的影响也是必不可少的.2.2　森林干扰类型划分森林干扰从不同的角度可有不同的划分方法,按干扰起因分为自然干扰和人为干扰.森林中常见的自然干扰有生物性与非生物性(aboitic)之分,火、风、雪、洪水、土壤侵蚀、地滑、山崩、冰川、火山活动等属于非生物性自然干扰,动物危害和病虫害等则属于生物性自然干扰;其中研究较多的是森林火灾和风倒、雪害等干扰[74].自人类社会出现以后,除自然干扰以外,又增加了人为干扰,其影响远远超过了自然干扰,因为人为干扰彻底改变原来的森林景观.人类对森林的干扰多种多样,主要包括毁林、采伐、修枝、砍伐下木、扫除枯落物、放牧、采集果实、开矿、旅游、工业污染等等.随着人类社会和经济的高速发展,一些新的人为干扰不断出现,干扰强度也会日益增大.就人为干扰而言,按其性质分为破坏性干扰和增益性干扰.破坏性干扰多指导致森林结构破坏,生态平衡失调和生态功能退化的行为,这些人为干扰有时甚至是毁灭性的,如自20世纪30年代以来国内外对中国东北森林掠夺性的乱砍滥伐.增益性干扰则是指促进森林生态系统正向演替的人为活动,如合理采伐、人工更新和低产、低效林分改造等(表1).2.3　森林干扰特征描述在森林生态系统中,干扰特征由干扰类型决定,一般用干扰频率、恢复速率、干扰事件影响的空间范1704应　用　生　态　学　报 15卷表1　森林干扰的主要类型及其生态意义Table1Major types of forest disturbances and their ecological significance划分依据Division 干扰种类Type具体表现方式Example生态意义Ecological significance干扰起因Caus es 自然干扰Natural火灾Fire,地震Earthquake、病虫害等Diseaseand ins ect etc.森林生态系统结构破坏,甚至消失Destroythe structure of forest ecos ystem人类干扰Human毁林Forest des troying、采伐Cu tting、抚育Caring、放牧Pasturing、采集Picking、开矿M ining、旅游Traveling、工业污染Poll ution破坏森林生态系统自然生态过程Destroy thenatural ecol ogical process of forest ecos ystem干扰来源Origination 内部干扰Interior倒木Fall en w ood、机械摩擦Abrading、种间竞争Competition、他感作用Allel opathy对生态系统演替起到重要的作用Significantto the succession of ecos ystem外部干扰Exterior强烈的外界干扰及人为砍伐、放牧Largescale of natural and human distu rbances打破自然生态系统演替过程Destroy the suc-cession process of natural ecosystem干扰性质Properties 破坏性干扰Destroy乱砍滥伐等S poliatorily exploitation etc.森林正常结构破坏、平衡失调和功能退化Forest structure are destroyed,functions aredeclined增益性干扰Benefit合理采伐R easonably cutting、人工更新Artifi-cial regeneration促进发育和繁衍,延续生态功能发挥Im-prove the development and breeding and sustainthe ecological functions干扰传播特征Characteristics 局部干扰Partial倒木Fall en w ood、择伐Sel ective cutting生态系统能正常演替或危害性小Keeps thesuccession of forest ecos ystems跨边界干扰E-border强烈气候干扰Strongly climate disturbance、传染性病虫害Contagious dis ease and ins ect影响生态系统正常演替Influence the succes-s ion of forest ecosystems干扰机制M echanism 物理干扰Physical机械运输木材Logging破坏生态系统结构,影响正常演替Destroythe structu re and influence the success ion of theforest ecos ystems化学干扰Chemical土壤侵蚀酸雨S oil erosion acid rain、臭氧O-zone生物干扰Biological病虫害爆发Breaking out、外来种入侵Extra-species干扰程度Degree 可恢复干扰Restorable虫害Insect bursting,砍伐Cutting,火灾Fire逐步演替后,有可能得到恢复Restore afterlong-term success ion不可恢复干扰Un-restorable人为修建水库和建筑物等Buildings永久性破坏Destroy the structure and infl u-ence the succession of the forest ecosystems表2　描述干扰特征的概念及其含义Table2Usual concepts of distu rbance and their significance主要项目Item定　义Definition分布Distribution空间分布,包括与地理的、地形的、环境的以及群落梯度的关系Spatial distributions,including the rela-tionships betw een geography,topography,environment and communities频度Frequency在一个时间段内事件发生的平均次数Average times of matters being happened between in tervals重发间隔Return interval cycl e or turnover time 频度的倒数,两次扰动之间的平均时间Reciprocal of frequency,average time of interval between tw o dis-tu rbances周转期限Rotation period将整个研究区域扰动一遍所需的平均时间Average time of disturbing the whole region for one time预期性Predictability重发间隔方差的反函数Variance of re-occu rrence面积或大小Area or size每个时间段中的面积,每个时间段,每次干扰类型的总面积Area in an interval,total area of each type ofdisturbance强度值M agnitude of intensity每次每单位面积上该事件的物理力(对火因素来说,每个时间段、每单位面积所释放的热量)Physicalpow ers in unit time and unit area(e.g.,fire,the energy in unit time and unit area)严重程度M agnitude of severity对有机体、群落或生态系统的影响Effects on communities or ecosystems协同效应Synergism其他扰动对该事件的效应(如干旱会提高火的作用强度,昆虫损害会提高植物对风暴的敏感性Impactsof other disturbances on ecosystem(e.g.,drought can increase the intens ity of fire,insect damage can increasethe resistance of plant to w ind storm)围、形状以及景观范围等说明干扰特征.另外,也有应用一般干扰特征进行组合形成时间参数(干扰频率/恢复频率)和空间参数(干扰影响范围/景观范围)用来描述森林干扰的特征[32].研究表明,认识干扰特征必须以一定的尺度为前提,因为干扰是在自然条件下存在的普遍现象,生态系统内中小尺度的干扰可以被大尺度的系统消化,大尺度的干扰往往掩盖小尺度的干扰事件[32].描述干扰特征的一个重要概念是干扰状况(表2),正确理解这些概念,有利于加深对干扰的认识.3　主要森林干扰类型3.1　火干扰火是最活跃的生态因子之一,经常作用于森林生态系统,其干扰作用具有双重性.一方面由于高强度火突然释放大量能量,导致森林生态系统内各种生物死亡,破坏了森林生态系统的平衡;同时,由于高强度火灾发生后与其它因素的协同作用,易遭受病虫的危害,加速森林生态系统的破坏.高强度火的作用会使低价值的树种取代珍贵树种;萌生树种取170510期朱教君等:森林干扰生态研究代实生长树种;生产力低的林分取代生产力高的林分.另一方面低强度、小面积的火或局部火的作用,有利于改善森林环境,对维持森林生态系统的平衡、促进森林进展演替具有积极作用.因此,火可以作为加速森林演替的工具和手段[72].由于火干扰的偶发性及人为不可控性,有关火干扰发生的过程研究目前国内外报道较少;但火干扰后的有关森林生态系统的生态过程的研究则较多[51,52,59,60,64].3.2　风干扰风干扰是森林干扰中最常见的一种,已有研究表明,风害折断林木顶枝或疏开林冠,改变林内光照,使林分内土壤温度昼夜变幅加大,形成的风倒木,对林地土壤和风倒木范围的植被产生明显影响,从而引起小尺度的生境异质性;环境因子的改变导致林冠层树种更新格局发生变化[17,48].风干扰过程的研究比较多,自20世纪90年代初至今在国际林联(IUFRO)已召开3次有关风干扰国际研讨会[74],从风害产生的原因、机制到风对森林造成的危害、对树木的生长、形态以及森林生态的影响等进行了全面研究.有关风干扰过程的基本结论认为,风干扰是在大的气候条件作用下,由于海拔、地形、地势和林型等共同作用下产生的[9,45,50].3.3　病虫害干扰病虫害是一种重要的干扰,常引起林木损伤与死亡,如松毛虫专以松树的针叶为食,当虫害爆发严重时,受害松树的针叶会被松毛虫取食殆尽,使树木的光合作用能力彻底丧失,最终导致死亡.但病虫害在森林演替、物质循环和能量流动、食物来源、创造野生动物生境等方面都做出了积极的贡献,而且在森林生态系统发展中,对于生物多样性、土壤肥力、森林的稳定性等方面起着重要的作用[41].3.4　抚育和采伐干扰抚育是人类对森林生态系统的一种经营性干扰,一般包括整地、施肥、灌溉、除草、林地清理、整枝和间伐等.这些人为干扰的目的是改善土壤的物理性质和养分状况,促进养分的循环和利用,增加林地的光照条件,最终是为了提高林地和森林的生产力以及防止有危害的自然干扰发生.目前,以抚育为主的人为干扰多数是在人工林生态系统中进行的,而对于天然林生态系统,这种干扰的过程、结果等目前尚不清楚[73].森林采伐是人类为获得木材而进行的一种森林经营活动,这种干扰不可避免地对森林生态系统产生较大的扰动.由于林木的采伐,植被破坏,以及人、畜、机械和木材在林地上运行,集运材道路和贮木场等土木工程,使林地土遭受到不同程度的损害.大量具有生产能力的土壤将流失,养分、水分、空气在土壤中的传输受阻,土壤中菌根和微生物的活动受到限制,从而引起地力衰退.决定土壤破坏程度的最主要因素是采伐强度,集运材方式,以及所使用的机械设备类型.采伐干扰方式对森林生态系统的影响很大,采伐促进林木生长发育、改善林分组分、有利更新恢复、动植物多样性的维护和合理开发利用,以及环境与美学效益等.另外,森林中常见的其它干扰方式还有污染、林内生物采集、采樵、狩猎和捕捞等.随着人类社会的发展,人为干扰也在不断出现新的方式,如旅游、探险活动等,这些干扰也都对森林生态系统造成了不同程度的影响.4　干扰对森林生态系统的影响4.1　干扰对森林更新、演替的影响自然干扰被认为是生态系统的正常行为,森林生态系统通常受自然干扰的作用,影响森林环境,使森林结构和功能发生改变,进而成为森林生态系统演替/变化的驱动力之一[63].已有的研究认为,受自然干扰后的林地可以进行更新,因此,自然干扰在维持植被组成、演替过程和加速改变植被组成等方面具有无可替代的作用.Timo[58]认为掌握森林干扰和演替的生态过程、森林建群种的种群动态以及他们相互的生态过程是森林生态系统可持续经营的前提.干扰程度也影响森林更新、演替.极端类型的干扰(冰川活动、滑坡、严重侵蚀、大面积严重火灾等)发生后,森林冠层、树木个体、土壤表层结构、土壤营养及其他理化性质等都发生强烈变化,从而改变森林的物种结构;而较弱度的干扰(风倒、疏伐、突发性病虫害等)则可能促进多个树种、多种机制的更新[32].Waldrop等[60]在研究不同火干扰强度对森林更新影响时认为,低强度火干扰可以丰富森林更新的内容,但不能使更多的上层林木消失;高强度火干扰虽然可以使上层林木消失,但同时也使种子库受损;而中强度火干扰对更新最有利,在消除上层木的同时促进了更新.侯向阳等[24]对长白山风干扰迹地后的森林更新与恢复研究中发现,风干扰迹地的土壤水分及碳、氮、有机质含量有所降低,耐荫树种优势度趋于降低,阳性树种优势度逐年增加.4.2　干扰对物种多样性的影响1706应　用　生　态　学　报 15卷干扰对生物多样性变化很重要,因为干扰影响了森林生态系统的结构和功能,进而决定生境镶嵌性的特征,影响森林建群种的种群动态.很多研究表明,中度的干扰可增加森林生态系统的总体生物多样性,如Palmer等[43]调查了风害14年后的松林和橡胶林生物多样性的变化,结果表明维管植物物种丰富度大幅度增加;Niemelä等[40]在研究北方森林小尺度异质性表明,干扰使林内土壤内无脊椎动物多样性增加.Lindenmayer等[33]在对山地木岑树(Ash)森林皆伐干扰和自然火灾干扰后的生物多样性进行了比较研究后认为,森林皆伐后很多对后续植被发育起关键作用的生物遗留物均已消失,而自然火灾却可以很完整地把对后续植被发育起关键作用的生物保留下来,这有利于保护山地森林生态系统的生物多样性.另外,干扰的出现及干扰之间的间隔也是影响森林生态系统生物多样性变化程度主要因子.4.3　干扰对森林生态系统稳定性的影响干扰是生态系统空间异质性产生的主要来源,是决定生态系统组成和结构的主要外部动力[66].由于干扰影响树木个体,形成不同大小的斑块,改变原来的格局结构,从而影响树种之间的竞争和树木的生长环境[28].干扰一般使森林生态系统发生以下变化:在斑块范围内引起优势树种或个体死亡[3],造成格局结构和生境发生变化[13],限制了某些植物的生物量,从而为某些树种创造了新的生态位[57],维持生物地球化学循环[5].多数强烈的自然干扰和人为干扰会破坏森林现存结构,打破已有的生态平衡、改变生态功能,从而引起生态系统稳定性下降.但中度干扰或弱度干扰可以增加生态系统的生物多样性,常利于生态系统稳定性的提高[37].5　自然干扰与人为干扰比较掌握自然干扰与人为干扰的关系对培育森林具有重要的意义[31],目前该方面的研究多集中在营林实验中.Mo tta等[39]在观测长期和短期营林效果中发现,人为经营干扰不是改变森林功能,而是维持其状况,并认为通过营林技术和模拟森林自然变化过程可以提高森林的自然性和生物多样性.Attiw ill[2]研究原木搬运干扰对林内生物多样性影响表明,在自然干扰方式弹性范围内,原木搬运对生物多样性的影响最小,但这需要搬运原木的操作产生的干扰在空间尺度包括林分水平和景观水平上与自然干扰达到高度的一致性.Lindenmayer等[33]、Fries等[16]在研究自然干扰后林地残留生物特征的类型、数量和空间分布特点时发现,自然干扰林地残留物对后续植被的发育起关键作用,如果能够区分人为干扰事件如原木搬运与自然干扰后林地残留物的差异,并修正营林系统使其与自然干扰方式一致,那么就可以更好地保护生物多样性.森林经营者在设计营林系统时,要从生态与经济角度综合考虑天然林的发育过程,包括很好地理解天然林的自然干扰过程及其生物遗留物,如自然干扰后活立木、木桩、原木的结构等,因为天然林的结构发育远比传统林学家认为的复杂的多,而且自然干扰产生的结构遗迹将成为林分发展、演替、构成物种多样性等的关键因素[15,68].在实际营林操作时最主要的困难是按自然干扰的原理,确定需要保留管理目标的结构种类、数量和空间格局[7].因此,在进行人为干扰的同时,如何根据自然干扰原理利用人为干扰引导森林管理,掌握自然干扰和人类干扰的关系是十分重要的[40].5.1　自然干扰和人类干扰的区别如以人为干扰中木材生产与自然干扰中火灾为例,自然干扰和人类干扰的主要区别可以归纳总结如下:第一,木材采伐的周期比自然干扰短,短期森林轮作的结果是过熟林的结构类型和森林的特征没有足够的时间去发展[12,61],第二,自然干扰和人为干扰的空间布局不同,如森林火灾覆盖面积较大,但在其影响范围内,燃烧仅形成一些斑块或保留完整,即自然干扰(火、风)通常比人为干扰(木材采伐)产生不同类型的异质性;第三,自然干扰后,更多的有机质被保存下来,风灾的枯立木、火灾留下了大量燃烧的树木[19],而采伐作业后,土壤的化学特性发生了变化,如土壤中的总碳量、总氮量下降,C/N值下降,土壤酸性增加,pH值和置换酸度降低,阳离子交换量降低等;第四,火灾后的炭木是许多物种生长发育需要的生境[12],而人为干扰很难产生类似环境;第五,采伐迹地与自然干扰林地有不同的树种更新.一般认为,低强度、小面积的火或局部火没有烧毁原有物种,容易使一些喜光植物得以侵入,增加了森林物种的多样性,有利于维持和促进森林生态系统的平衡与稳定,促进森林正向演替.与传统的营林方法相比,自然干扰造成的格局和过程在时间和空间上展示更大的变异性,且留下遗迹(枯立木或倒木),直接影响干扰后森林发展的格局[14],因而倾向于形成更复杂的森林类型.另外,自然干扰方式的时空异质性也影响森林中林木年龄结构的变化,决定着枯死170710期朱教君等:森林干扰生态研究。

英语学术论文写作30题

英语学术论文写作30题1. In the introduction of an academic paper, which of the following is the best way to attract readers' attention?A. Presenting a long list of previous studies.B. Starting with a controversial statement.C. Using complex sentence structures.D. Describing personal experiences.答案：B。

解析：选项 A 呈现一长串以往的研究可能会让读者感到枯燥；选项 C 使用复杂的句子结构可能会增加读者的理解难度；选项 D 描述个人经历在学术论文引言中不太常见。

而选项 B 以有争议的陈述开头能够激发读者的兴趣和好奇心，从而吸引他们的注意力。

2. When elaborating the research background in the introduction, which of the following should be avoided?A. Citing recent and relevant studies.B. Overemphasizing minor details.C. Explaining the significance of the research.D. Connecting the research to existing theories.答案：B。

解析：选项 A 引用近期相关研究是必要的；选项 C 解释研究的重要性有助于突出研究价值；选项D 将研究与现有理论相联系能体现研究的科学性。

而选项B 过度强调次要细节会使重点不突出，分散读者注意力。

3. Which of the following is an appropriate opening sentence for the introduction of an academic paper?A. "This paper will discuss an important topic."B. "In recent years, there has been a growing interest in this field."C. "I have always been interested in this subject."D. "The aim of this study is to solve a long-standing problem."答案：D。

专八英语阅读

英语专业八级考试TEM-8阅读理解练习册（1）(英语专业2012级)UNIT 1Text AEvery minute of every day, what ecologist生态学家James Carlton calls a global ―conveyor belt‖, redistributes ocean organisms生物.It’s planetwide biological disruption生物的破坏that scientists have barely begun to understand.Dr. Carlton —an oceanographer at Williams College in Williamstown,Mass.—explains that, at any given moment, ―There are several thousand marine species traveling… in the ballast water of ships.‖ These creatures move from coastal waters where they fit into the local web of life to places where some of them could tear that web apart. This is the larger dimension of the infamous无耻的，邪恶的invasion of fish-destroying, pipe-clogging zebra mussels有斑马纹的贻贝.Such voracious贪婪的invaders at least make their presence known. What concerns Carlton and his fellow marine ecologists is the lack of knowledge about the hundreds of alien invaders that quietly enter coastal waters around the world every day. Many of them probably just die out. Some benignly亲切地，仁慈地—or even beneficially — join the local scene. But some will make trouble.In one sense, this is an old story. Organisms have ridden ships for centuries. They have clung to hulls and come along with cargo. What’s new is the scale and speed of the migrations made possible by the massive volume of ship-ballast water压载水— taken in to provide ship stability—continuously moving around the world…Ships load up with ballast water and its inhabitants in coastal waters of one port and dump the ballast in another port that may be thousands of kilometers away. A single load can run to hundreds of gallons. Some larger ships take on as much as 40 million gallons. The creatures that come along tend to be in their larva free-floating stage. When discharged排出in alien waters they can mature into crabs, jellyfish水母, slugs鼻涕虫，蛞蝓, and many other forms.Since the problem involves coastal species, simply banning ballast dumps in coastal waters would, in theory, solve it. Coastal organisms in ballast water that is flushed into midocean would not survive. Such a ban has worked for North American Inland Waterway. But it would be hard to enforce it worldwide. Heating ballast water or straining it should also halt the species spread. But before any such worldwide regulations were imposed, scientists would need a clearer view of what is going on.The continuous shuffling洗牌of marine organisms has changed the biology of the sea on a global scale. It can have devastating effects as in the case of the American comb jellyfish that recently invaded the Black Sea. It has destroyed that sea’s anchovy鳀鱼fishery by eating anchovy eggs. It may soon spread to western and northern European waters.The maritime nations that created the biological ―conveyor belt‖ should support a coordinated international effort to find out what is going on and what should be done about it. (456 words)1.According to Dr. Carlton, ocean organism‟s are_______.A.being moved to new environmentsB.destroying the planetC.succumbing to the zebra musselD.developing alien characteristics2.Oceanographers海洋学家are concerned because_________.A.their knowledge of this phenomenon is limitedB.they believe the oceans are dyingC.they fear an invasion from outer-spaceD.they have identified thousands of alien webs3.According to marine ecologists, transplanted marinespecies____________.A.may upset the ecosystems of coastal watersB.are all compatible with one anotherC.can only survive in their home watersD.sometimes disrupt shipping lanes4.The identified cause of the problem is_______.A.the rapidity with which larvae matureB. a common practice of the shipping industryC. a centuries old speciesD.the world wide movement of ocean currents5.The article suggests that a solution to the problem__________.A.is unlikely to be identifiedB.must precede further researchC.is hypothetically假设地，假想地easyD.will limit global shippingText BNew …Endangered‟ List Targets Many US RiversIt is hard to think of a major natural resource or pollution issue in North America today that does not affect rivers.Farm chemical runoff残渣, industrial waste, urban storm sewers, sewage treatment, mining, logging, grazing放牧,military bases, residential and business development, hydropower水力发电,loss of wetlands. The list goes on.Legislation like the Clean Water Act and Wild and Scenic Rivers Act have provided some protection, but threats continue.The Environmental Protection Agency (EPA) reported yesterday that an assessment of 642,000 miles of rivers and streams showed 34 percent in less than good condition. In a major study of the Clean Water Act, the Natural Resources Defense Council last fall reported that poison runoff impairs损害more than 125,000 miles of rivers.More recently, the NRDC and Izaak Walton League warned that pollution and loss of wetlands—made worse by last year’s flooding—is degrading恶化the Mississippi River ecosystem.On Tuesday, the conservation group保护组织American Rivers issued its annual list of 10 ―endangered‖ and 20 ―threatened‖ rivers in 32 states, the District of Colombia, and Canada.At the top of the list is the Clarks Fork of the Yellowstone River, whereCanadian mining firms plan to build a 74-acre英亩reservoir水库，蓄水池as part of a gold mine less than three miles from Yellowstone National Park. The reservoir would hold the runoff from the sulfuric acid 硫酸used to extract gold from crushed rock.―In the event this tailings pond failed, the impact to th e greater Yellowstone ecosystem would be cataclysmic大变动的，灾难性的and the damage irreversible不可逆转的.‖ Sen. Max Baucus of Montana, chairman of the Environment and Public Works Committee, wrote to Noranda Minerals Inc., an owner of the ― New World Mine‖.Last fall, an EPA official expressed concern about the mine and its potential impact, especially the plastic-lined storage reservoir. ― I am unaware of any studies evaluating how a tailings pond尾矿池，残渣池could be maintained to ensure its structural integrity forev er,‖ said Stephen Hoffman, chief of the EPA’s Mining Waste Section. ―It is my opinion that underwater disposal of tailings at New World may present a potentially significant threat to human health and the environment.‖The results of an environmental-impact statement, now being drafted by the Forest Service and Montana Department of State Lands, could determine the mine’s future…In its recent proposal to reauthorize the Clean Water Act, the Clinton administration noted ―dramatically improved water quality since 1972,‖ when the act was passed. But it also reported that 30 percent of riverscontinue to be degraded, mainly by silt泥沙and nutrients from farm and urban runoff, combined sewer overflows, and municipal sewage城市污水. Bottom sediments沉积物are contaminated污染in more than 1,000 waterways, the administration reported in releasing its proposal in January. Between 60 and 80 percent of riparian corridors (riverbank lands) have been degraded.As with endangered species and their habitats in forests and deserts, the complexity of ecosystems is seen in rivers and the effects of development----beyond the obvious threats of industrial pollution, municipal waste, and in-stream diversions改道to slake消除the thirst of new communities in dry regions like the Southwes t…While there are many political hurdles障碍ahead, reauthorization of the Clean Water Act this year holds promise for US rivers. Rep. Norm Mineta of California, who chairs the House Committee overseeing the bill, calls it ―probably the most important env ironmental legislation this Congress will enact.‖ (553 words)6.According to the passage, the Clean Water Act______.A.has been ineffectiveB.will definitely be renewedC.has never been evaluatedD.was enacted some 30 years ago7.“Endangered” rivers are _________.A.catalogued annuallyB.less polluted than ―threatened rivers‖C.caused by floodingD.adjacent to large cities8.The “cataclysmic” event referred to in paragraph eight would be__________.A. fortuitous偶然的，意外的B. adventitious外加的，偶然的C. catastrophicD. precarious不稳定的，危险的9. The owners of the New World Mine appear to be______.A. ecologically aware of the impact of miningB. determined to construct a safe tailings pondC. indifferent to the concerns voiced by the EPAD. willing to relocate operations10. The passage conveys the impression that_______.A. Canadians are disinterested in natural resourcesB. private and public environmental groups aboundC. river banks are erodingD. the majority of US rivers are in poor conditionText CA classic series of experiments to determine the effects ofoverpopulation on communities of rats was reported in February of 1962 in an article in Scientific American. The experiments were conducted by a psychologist, John B. Calhoun and his associates. In each of these experiments, an equal number of male and female adult rats were placed in an enclosure and given an adequate supply of food, water, and other necessities. The rat populations were allowed to increase. Calhoun knew from experience approximately how many rats could live in the enclosures without experiencing stress due to overcrowding. He allowed the population to increase to approximately twice this number. Then he stabilized the population by removing offspring that were not dependent on their mothers. He and his associates then carefully observed and recorded behavior in these overpopulated communities. At the end of their experiments, Calhoun and his associates were able to conclude that overcrowding causes a breakdown in the normal social relationships among rats, a kind of social disease. The rats in the experiments did not follow the same patterns of behavior as rats would in a community without overcrowding.The females in the rat population were the most seriously affected by the high population density: They showed deviant异常的maternal behavior; they did not behave as mother rats normally do. In fact, many of the pups幼兽，幼崽, as rat babies are called, died as a result of poor maternal care. For example, mothers sometimes abandoned their pups,and, without their mothers' care, the pups died. Under normal conditions, a mother rat would not leave her pups alone to die. However, the experiments verified that in overpopulated communities, mother rats do not behave normally. Their behavior may be considered pathologically 病理上，病理学地diseased.The dominant males in the rat population were the least affected by overpopulation. Each of these strong males claimed an area of the enclosure as his own. Therefore, these individuals did not experience the overcrowding in the same way as the other rats did. The fact that the dominant males had adequate space in which to live may explain why they were not as seriously affected by overpopulation as the other rats. However, dominant males did behave pathologically at times. Their antisocial behavior consisted of attacks on weaker male,female, and immature rats. This deviant behavior showed that even though the dominant males had enough living space, they too were affected by the general overcrowding in the enclosure.Non-dominant males in the experimental rat communities also exhibited deviant social behavior. Some withdrew completely; they moved very little and ate and drank at times when the other rats were sleeping in order to avoid contact with them. Other non-dominant males were hyperactive; they were much more active than is normal, chasing other rats and fighting each other. This segment of the rat population, likeall the other parts, was affected by the overpopulation.The behavior of the non-dominant males and of the other components of the rat population has parallels in human behavior. People in densely populated areas exhibit deviant behavior similar to that of the rats in Calhoun's experiments. In large urban areas such as New York City, London, Mexican City, and Cairo, there are abandoned children. There are cruel, powerful individuals, both men and women. There are also people who withdraw and people who become hyperactive. The quantity of other forms of social pathology such as murder, rape, and robbery also frequently occur in densely populated human communities. Is the principal cause of these disorders overpopulation? Calhoun’s experiments suggest that it might be. In any case, social scientists and city planners have been influenced by the results of this series of experiments.11. Paragraph l is organized according to__________.A. reasonsB. descriptionC. examplesD. definition12．Calhoun stabilized the rat population_________.A. when it was double the number that could live in the enclosure without stressB. by removing young ratsC. at a constant number of adult rats in the enclosureD. all of the above are correct13.W hich of the following inferences CANNOT be made from theinformation inPara. 1?A. Calhoun's experiment is still considered important today.B. Overpopulation causes pathological behavior in rat populations.C. Stress does not occur in rat communities unless there is overcrowding.D. Calhoun had experimented with rats before.14. Which of the following behavior didn‟t happen in this experiment?A. All the male rats exhibited pathological behavior.B. Mother rats abandoned their pups.C. Female rats showed deviant maternal behavior.D. Mother rats left their rat babies alone.15. The main idea of the paragraph three is that __________.A. dominant males had adequate living spaceB. dominant males were not as seriously affected by overcrowding as the otherratsC. dominant males attacked weaker ratsD. the strongest males are always able to adapt to bad conditionsText DThe first mention of slavery in the statutes法令，法规of the English colonies of North America does not occur until after 1660—some forty years after the importation of the first Black people. Lest we think that existed in fact before it did in law, Oscar and Mary Handlin assure us, that the status of B lack people down to the 1660’s was that of servants. A critique批判of the Handlins’ interpretation of why legal slavery did not appear until the 1660’s suggests that assumptions about the relation between slavery and racial prejudice should be reexamined, and that explanation for the different treatment of Black slaves in North and South America should be expanded.The Handlins explain the appearance of legal slavery by arguing that, during the 1660’s, the position of white servants was improving relative to that of black servants. Thus, the Handlins contend, Black and White servants, heretofore treated alike, each attained a different status. There are, however, important objections to this argument. First, the Handlins cannot adequately demonstrate that t he White servant’s position was improving, during and after the 1660’s; several acts of the Maryland and Virginia legislatures indicate otherwise. Another flaw in the Handlins’ interpretation is their assumption that prior to the establishment of legal slavery there was no discrimination against Black people. It is true that before the 1660’s Black people were rarely called slaves. But this shouldnot overshadow evidence from the 1630’s on that points to racial discrimination without using the term slavery. Such discrimination sometimes stopped short of lifetime servitude or inherited status—the two attributes of true slavery—yet in other cases it included both. The Handlins’ argument excludes the real possibility that Black people in the English colonies were never treated as the equals of White people.The possibility has important ramifications后果，影响.If from the outset Black people were discriminated against, then legal slavery should be viewed as a reflection and an extension of racial prejudice rather than, as many historians including the Handlins have argued, the cause of prejudice. In addition, the existence of discrimination before the advent of legal slavery offers a further explanation for the harsher treatment of Black slaves in North than in South America. Freyre and Tannenbaum have rightly argued that the lack of certain traditions in North America—such as a Roman conception of slavery and a Roman Catholic emphasis on equality— explains why the treatment of Black slaves was more severe there than in the Spanish and Portuguese colonies of South America. But this cannot be the whole explanation since it is merely negative, based only on a lack of something. A more compelling令人信服的explanation is that the early and sometimes extreme racial discrimination in the English colonies helped determine the particular nature of the slavery that followed. (462 words)16. Which of the following is the most logical inference to be drawn from the passage about the effects of “several acts of the Maryland and Virginia legislatures” (Para.2) passed during and after the 1660‟s?A. The acts negatively affected the pre-1660’s position of Black as wellas of White servants.B. The acts had the effect of impairing rather than improving theposition of White servants relative to what it had been before the 1660’s.C. The acts had a different effect on the position of white servants thandid many of the acts passed during this time by the legislatures of other colonies.D. The acts, at the very least, caused the position of White servants toremain no better than it had been before the 1660’s.17. With which of the following statements regarding the status ofBlack people in the English colonies of North America before the 1660‟s would the author be LEAST likely to agree?A. Although black people were not legally considered to be slaves,they were often called slaves.B. Although subject to some discrimination, black people had a higherlegal status than they did after the 1660’s.C. Although sometimes subject to lifetime servitude, black peoplewere not legally considered to be slaves.D. Although often not treated the same as White people, black people,like many white people, possessed the legal status of servants.18. According to the passage, the Handlins have argued which of thefollowing about the relationship between racial prejudice and the institution of legal slavery in the English colonies of North America?A. Racial prejudice and the institution of slavery arose simultaneously.B. Racial prejudice most often the form of the imposition of inheritedstatus, one of the attributes of slavery.C. The source of racial prejudice was the institution of slavery.D. Because of the influence of the Roman Catholic Church, racialprejudice sometimes did not result in slavery.19. The passage suggests that the existence of a Roman conception ofslavery in Spanish and Portuguese colonies had the effect of _________.A. extending rather than causing racial prejudice in these coloniesB. hastening the legalization of slavery in these colonies.C. mitigating some of the conditions of slavery for black people in these coloniesD. delaying the introduction of slavery into the English colonies20. The author considers the explanation put forward by Freyre andTannenbaum for the treatment accorded B lack slaves in the English colonies of North America to be _____________.A. ambitious but misguidedB. valid有根据的but limitedC. popular but suspectD. anachronistic过时的，时代错误的and controversialUNIT 2Text AThe sea lay like an unbroken mirror all around the pine-girt, lonely shores of Orr’s Island. Tall, kingly spruce s wore their regal王室的crowns of cones high in air, sparkling with diamonds of clear exuded gum流出的树胶; vast old hemlocks铁杉of primeval原始的growth stood darkling in their forest shadows, their branches hung with long hoary moss久远的青苔;while feathery larches羽毛般的落叶松,turned to brilliant gold by autumn frosts, lighted up the darker shadows of the evergreens. It was one of those hazy朦胧的, calm, dissolving days of Indian summer, when everything is so quiet that the fainest kiss of the wave on the beach can be heard, and white clouds seem to faint into the blue of the sky, and soft swathing一长条bands of violet vapor make all earth look dreamy, and give to the sharp, clear-cut outlines of the northern landscape all those mysteries of light and shade which impart such tenderness to Italian scenery.The funeral was over,--- the tread鞋底的花纹/ 踏of many feet, bearing the heavy burden of two broken lives, had been to the lonely graveyard, and had come back again,--- each footstep lighter and more unconstrained不受拘束的as each one went his way from the great old tragedy of Death to the common cheerful of Life.The solemn black clock stood swaying with its eternal ―tick-tock, tick-tock,‖ in the kitchen of the brown house on Orr’s Island. There was there that sense of a stillness that can be felt,---such as settles down on a dwelling住处when any of its inmates have passed through its doors for the last time, to go whence they shall not return. The best room was shut up and darkened, with only so much light as could fall through a little heart-shaped hole in the window-shutter,---for except on solemn visits, or prayer-meetings or weddings, or funerals, that room formed no part of the daily family scenery.The kitchen was clean and ample, hearth灶台, and oven on one side, and rows of old-fashioned splint-bottomed chairs against the wall. A table scoured to snowy whiteness, and a little work-stand whereon lay the Bible, the Missionary Herald, and the Weekly Christian Mirror, before named, formed the principal furniture. One feature, however, must not be forgotten, ---a great sea-chest水手用的储物箱,which had been the companion of Zephaniah through all the countries of the earth. Old, and battered破旧的，磨损的, and unsightly难看的it looked, yet report said that there was good store within which men for the most part respect more than anything else; and, indeed it proved often when a deed of grace was to be done--- when a woman was suddenly made a widow in a coast gale大风，狂风, or a fishing-smack小渔船was run down in the fogs off the banks, leaving in some neighboring cottage a family of orphans,---in all such cases, the opening of this sea-chest was an event of good omen 预兆to the bereaved丧亲者;for Zephaniah had a large heart and a large hand, and was apt有…的倾向to take it out full of silver dollars when once it went in. So the ark of the covenant约柜could not have been looked on with more reverence崇敬than the neighbours usually showed to Captain Pennel’s sea-chest.1. The author describes Orr‟s Island in a(n)______way.A.emotionally appealing, imaginativeB.rational, logically preciseC.factually detailed, objectiveD.vague, uncertain2.According to the passage, the “best room”_____.A.has its many windows boarded upB.has had the furniture removedC.is used only on formal and ceremonious occasionsD.is the busiest room in the house3.From the description of the kitchen we can infer that thehouse belongs to people who_____.A.never have guestsB.like modern appliancesC.are probably religiousD.dislike housework4.The passage implies that_______.A.few people attended the funeralB.fishing is a secure vocationC.the island is densely populatedD.the house belonged to the deceased5.From the description of Zephaniah we can see thathe_________.A.was physically a very big manB.preferred the lonely life of a sailorC.always stayed at homeD.was frugal and saved a lotText BBasic to any understanding of Canada in the 20 years after the Second World War is the country' s impressive population growth. For every three Canadians in 1945, there were over five in 1966. In September 1966 Canada's population passed the 20 million mark. Most of this surging growth came from natural increase. The depression of the 1930s and the war had held back marriages, and the catching-up process began after 1945. The baby boom continued through the decade of the 1950s, producing a population increase of nearly fifteen percent in the five years from 1951 to 1956. This rate of increase had been exceeded only once before in Canada's history, in the decade before 1911 when the prairies were being settled. Undoubtedly, the good economic conditions of the 1950s supported a growth in the population, but the expansion also derived from a trend toward earlier marriages and an increase in the average size of families; In 1957 the Canadian birth rate stood at 28 per thousand, one of the highest in the world. After the peak year of 1957, thebirth rate in Canada began to decline. It continued falling until in 1966 it stood at the lowest level in 25 years. Partly this decline reflected the low level of births during the depression and the war, but it was also caused by changes in Canadian society. Young people were staying at school longer, more women were working; young married couples were buying automobiles or houses before starting families; rising living standards were cutting down the size of families. It appeared that Canada was once more falling in step with the trend toward smaller families that had occurred all through theWestern world since the time of the Industrial Revolution. Although the growth in Canada’s population had slowed down by 1966 (the cent), another increase in the first half of the 1960s was only nine percent), another large population wave was coming over the horizon. It would be composed of the children of the children who were born during the period of the high birth rate prior to 1957.6. What does the passage mainly discuss?A. Educational changes in Canadian society.B. Canada during the Second World War.C. Population trends in postwar Canada.D. Standards of living in Canada.7. According to the passage, when did Canada's baby boom begin?A. In the decade after 1911.B. After 1945.C. During the depression of the 1930s.D. In 1966.8. The author suggests that in Canada during the 1950s____________.A. the urban population decreased rapidlyB. fewer people marriedC. economic conditions were poorD. the birth rate was very high9. When was the birth rate in Canada at its lowest postwar level?A. 1966.B. 1957.C. 1956.D. 1951.10. The author mentions all of the following as causes of declines inpopulation growth after 1957 EXCEPT_________________.A. people being better educatedB. people getting married earlierC. better standards of livingD. couples buying houses11.I t can be inferred from the passage that before the IndustrialRevolution_______________.A. families were largerB. population statistics were unreliableC. the population grew steadilyD. economic conditions were badText CI was just a boy when my father brought me to Harlem for the first time, almost 50 years ago. We stayed at the hotel Theresa, a grand brick structure at 125th Street and Seventh avenue. Once, in the hotel restaurant, my father pointed out Joe Louis. He even got Mr. Brown, the hotel manager, to introduce me to him, a bit punchy强力的but still champ焦急as fast as I was concerned.Much has changed since then. Business and real estate are booming. Some say a new renaissance is under way. Others decry责难what they see as outside forces running roughshod肆意践踏over the old Harlem. New York meant Harlem to me, and as a young man I visited it whenever I could. But many of my old haunts are gone. The Theresa shut down in 1966. National chains that once ignored Harlem now anticipate yuppie money and want pieces of this prime Manhattan real estate. So here I am on a hot August afternoon, sitting in a Starbucks that two years ago opened a block away from the Theresa, snatching抓取，攫取at memories between sips of high-priced coffee. I am about to open up a piece of the old Harlem---the New York Amsterdam News---when a tourist。

平均驻留时间方法——Disturbance attenuation properties of time controlled switched systems

Journal of the Franklin Institute338(2001)765–779Disturbance attenuation propertiesof time-controlled switched systemsGuisheng Zhai a,*,Bo Hu b,Kazunori Yasuda a,Anthony N.Michel ba Faculty of Systems En g ineerin g,Wakayama Uni v ersity,930Sakaedani,Wakayama640-8510,Japanb Department of Electrical En g ineerin g,Uni v ersity of Notre Dame,Notre Dame,IN46556,USAReceived2August2001AbstractIn this paper,we investigate the disturbance attenuation properties of time-controlled switched systems consisting of several linear time-invariant subsystems by using an average dwell time approach incorporated with a piecewise Lyapunov function.First,we show that when all subsystems are Hurwitz stable and achieve a disturbance attenuation level smaller than a positive scalar g0;the switched system under an average dwell time scheme achieves a weighted disturbance attenuation level g0;and the weighted disturbance attenuation approaches normal disturbance attenuation if the average dwell time is chosen suﬃciently large.We extend this result to the case where not all subsystems are Hurwitz stable,by showing that in addition to the average dwell time scheme,if the total activation time of unstable subsystems is relatively small compared with that of the Hurwitz stable subsystems, then a reasonable weighted disturbance attenuation level is guaranteed.Finally,a discussion is made on the case for which nonlinear norm-bounded perturbations exist in the subsystems. r2001Published by Elsevier Science Ltd.on behalf of The Franklin Institute. Keywords:Switched system;Switching law;Disturbance attenuation;Average dwell time;Piecewise Lyapunov function;Perturbations1.IntroductionBy a switched system,we mean a hybrid dynamical system that is composed of a family of continuous-time subsystems and a rule orchestrating the switching between *Corresponding author.Tel.:+81-73-457-8187;fax:+81-73-457-8201.E-mail addresses:zhai@sys.wakayama-u.ac.jp(G.Zhai),bo.hu.7@(B.Hu),kyasuda@sys. wakayama-u.ac.jp(K.Yasuda),anthony.n.michel.1@(A.N.Michel).0016-0032/01/$20.00r2001Published by Elsevier Science Ltd.on behalf of The Franklin Institute. PII:S0016-0032(01)00030-8the subsystems.Recently,there has been increasing interest in the stability analysis and switching control design of such systems (see,e.g.,[1–15]and the references cited therein).The motivation for studying such switched systems comes from the fact that many practical systems are inherently multimodal in the sense that several dynamical systems are required to describe their behavior which may depend on various environmental factors [1–3],and from the fact that the methods of intelligent control design are based on the idea of switching between diﬀerent controllers [1,4,5].In this paper,we consider the following linear switched system:’x ðt Þ¼A s x ðt ÞþB s w ðt Þ;x ð0Þ¼x 0;z ðt Þ¼C s x ðt Þ;ð1:1Þwhere x ðt ÞA R n is the state with x 0being the initial state,w ðt ÞA R m is the disturbance input and z ðt ÞA R p is the controlled output.s ðt Þ:½0;N Þ-I N ¼f 1;y ;N g is a piecewise constant function of time,called a switchin g si g nal ,which will be determined later,and thus A s ;B s and C s are also piecewise constant functions since ðA s ;B s ;C s Þ:½0;N Þ-fðA 1;B 1;C 1Þ;y ;ðA N ;B N ;C N Þg :Here,A i ;B i ;C i ði A I N Þare constant matrices of appropriate dimensions denoting the subsystems,and N >1is the number of subsystems.We ﬁrst introduce some notation and review several existing results concerning stability properties of system (1.1)(when w ¼0),where the dwell time approach was used.Given a positive constant t d ;let S d ½t d denote the set of all switching signals with time interval between consecutive switchings being no smaller than t d :The constant t d is called the ‘‘dwell time’’[4].It has been shown in [4]that when all subsystem matrices A i are Hurwitz stable (A matrix or the corresponding system is called Hurwitz stable if all its eigenvalues have negative real part),we can choose t d suﬃciently large so that switched system (1.1)without the disturbance input is exponentially stable for every s A S d ½t d :In [6],a dwell time scheme is analyzed for local asymptotic stability of nonlinear switched systems with the activation time being used as a dwell time.In [7],Hespanha extends the concept of ‘‘dwell time’’to ‘‘average dwell time’’.For any switching signal s and any t >t X 0;we let N s ðt ;t Þdenote the number of switchings of s over the interval ðt ;t Þ;and for given t a >0;we let S a ½t a denote the set of all switching signals satisfying for all t >0N s ð0;t Þp t t a;ð1:2Þwhere the positive constant t a is called the ‘‘average dwell time’’.The idea is that there may exist consecutive switchings separated by less than t a ;but the average time interval between consecutive switchings is not less than t a :It has been shown in [7]that if t a is suﬃciently large,then switched system (1.1)without the disturbance input is exponentially stable for any switching signal s A S a ½t a :In a recent paper [8],the authors extended the above stability results to the case where both Hurwitz stable and unstable subsystems exist,by showing that if the average dwell time is chosen suﬃciently large and the total activation time of unstable subsystems is relatively small compared with that of the Hurwitz stable subsystems,then global exponential stability of a desired decay rate is guaranteed.G.Zhai et al./Journal of the Franklin Institute 338(2001)765–779766In the present paper,we extend the above existing stability results to the analysis of disturbance attenuation for system(1.1).More precisely,when switched system(1.1)is controlled by an average dwell time scheme,we discuss quantitatively how the L2norm of zðtÞchanges for any wðtÞA L2½0;NÞ:Here,the L2norm of atime-varying vector v is deﬁned normally as jj v jj L2¼ﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃR Nv TðtÞvðtÞd tq:When allsubsystems are Hurwitz stable and achieve a disturbance attenuation level smaller than g0;we show that the switched system under an average dwell time scheme achieves a weighted disturbance attenuation level g0;and the weighted disturbance attenuation approaches the normal disturbance attenuation if the average dwell time is chosen suﬃciently large.In the special case,that all subsystems have a common Lyapunov function in the sense of disturbance attenuation,we show that the switched system achieves the normal disturbance attenuation level g0under arbitrary switching.A piecewise Lyapunov function is used to analyze the weighted L2gain from the disturbance input w to the controlled output z in the switched system.It is well known that Lyapunov function theory is the most general and useful approach for studying stability of various control systems.Recently,instead of traditional single Lyapunov functions,the use of piecewise Lyapunov functions(or multiple Lyapunov functions)has been proposed in many references[9–12].Since it is nearly impossible toﬁnd a single Lyapunov function for us to discuss the disturbance attenuation for switched system(1.1),we construct a piecewise Lyapunov function using the solutions of a set of matrix inequalities concerning all subsystems’disturbance attenuations separately.We show next that even when not all subsystems are Hurwitz stable,a reasonable weighted disturbance attenuation level can be guaranteed for the switched system under the average dwell time scheme,if the total activation time of unstable subsystems is relatively small compared with that of Hurwitz stable subsystems.It is noted here that the idea of specifying the total activation time ratio between Hurwitz stable subsystems and unstable ones is motivated by[8,13].Finally,we discuss the case for which nonlinear norm-bounded vanishing perturbations exist in the subsystems,and propose a switching law which ensures that the nonlinear switched system under the average dwell time scheme also achieves a reasonable weighted disturbance attenuation level.2.Disturbance attenuation analysis under average dwell timeIn this section,we consider two classes of switched systems:(a)all subsystems are Hurwitz stable;(b)not all subsystems are Hurwitz stable.For theﬁrst class of switched systems,we analyze the disturbance attenuation properties when the subsystems are switched by an average dwell time scheme.For the second class of switched systems,in addition to the average dwell time scheme,we propose a switching condition so as for the switched system to achieve a reasonable weighted disturbance attenuation level,where the total activation time ratio between unstable subsystems and Hurwitz stable subsystems is required to be smaller than a speciﬁed constant.G.Zhai et al./Journal of the Franklin Institute338(2001)765–7797672.1.Case ða Þ:all subsystems are Hurwitz stableIn this subsection,we assume that all subsystems in (1.1)are Hurwitz stable and achieve a disturbance attenuation level smaller than g 0:Here,the assumption of the same disturbance attenuation level g 0does not lose generality since we can set g 0¼max i f g i g if the i th subsystem’s disturbance attenuation level is smaller than g i (i A I N )(noting that a subsystem achieving a disturbance attenuation level smaller than g i also achieves a disturbance attenuation level smaller than max i f g i g ).In the present case,there exist a set of positive deﬁnite matrices P i ;i A I N ;such thatA T i P i þP i A i þg À20P iB i B T i P i þC T i C i o 0ð2:1Þholds (for example [16]).It is well known that the above inequality can be converted into an LMI [17]with respect to P i ;and thus is easily solved using any existing software,such as the LMI Control Toolbox [18].Also,there always exists a scalar l 0>0such thatA T i P i þP i A i þg À20P iB i B T i P i þC T i C i þl 0P i o 0ð2:2Þis satisﬁed for all i A I N :Using the solution P i ’s of (2.2),we deﬁne the following piecewise Lyapuno v function candidate:V ðt Þ¼V s ðx Þ¼x T P s x ð2:3Þfor switched system (1.1),where P s is switched among the solution P i ’s of (2.2)in accordance with the piecewise constant switching signal s :Then,the following properties are obtained for (2.3):1.Each V i ¼x T P i x in (2.3)is continuous and its derivative along the solutions of the corresponding subsystem satisﬁes’V i ¼q V i q xðA i x þB i w Þ¼x T P i ðA i x þB i w ÞþðA i x þB i w ÞT P i x ¼x T ðP i A i þA T i P i Þx þx T P i B i w þw T B T i P i xp Àl 0V i Àz T z Àðg À10B T i P i x Àg 0w ÞT ðg À10B T i P i x Àg 0w Þþg 20w T wp Àl 0V i Àz T z þg 20w T w :ð2:4Þ2.There exist constant scalars a 1>0;a 2>0such thata 1jj x jj 2p V i ðx Þp a 2jj x jj 28x A R n 8i A I N :ð2:5Þ3.There exists a constant scalar m X 1such thatV i ðx Þp m V j ðx Þ8x A R n 8i ;j A I N :ð2:6ÞG.Zhai et al./Journal of the Franklin Institute 338(2001)765–779768The ﬁrst property is based on matrix inequality (2.2),while the second and third properties hold,for example,with a 1¼inf i A I N l m ðP i Þ;a 2¼sup i A I N l M ðP i Þ;and m ¼sup k ;l A I N l M ðP k Þ=l m ðP l Þ;respectively.Here,l M ðP Þ(l m ðP Þ)denotes the largest (smallest)eigenvalue of the symmetric matrix P :Now,for an arbitrary piecewise constant switching signal s and any given t >0;we let t 1o ?o t i ði >1Þdenote the switching points of s over the interval ð0;t Þ:Then,using the diﬀerential inequality theory (for example [19])for (2.4),we obtain by induction thatV ðt Þp V ðt i Þe Àl 0ðt Àt i ÞÀZt t ie Àl 0ðt Àt ÞG ðt Þd t p m V ðt Ài Þe Àl 0ðt Àt i ÞÀZ tt i e Àl 0ðt Àt ÞG ðt Þd t p m V ðt i À1Þe Àl 0ðt i Àt i À1ÞÀZ t it i À1e Àl 0ðt i Àt ÞG ðt Þd t e Àl 0ðt Àt i ÞÀZt t i e Àl 0ðt Àt ÞG ðt Þd t^p m i e Àl 0t V ð0ÞÀm i Zt 10e Àl 0ðt Àt ÞG ðt Þd t Àm i À1Z t 2t 1e Àl 0ðt Àt ÞG ðt Þd t À?Àm0Z t t i e Àl 0ðt Àt ÞG ðt Þd t ¼m N s ð0;t Þe Àl 0t V ð0ÞÀZ t0m N s ðt ;t Þe Àl 0ðt Àt ÞG ðt Þd t¼e Àl 0t þN s ð0;t Þln m V ð0ÞÀZ t 0e Àl 0ðt Àt ÞþN s ðt ;t Þln m G ðt Þd t ;ð2:7Þwhere G ðt Þ:¼z T ðt Þz ðt ÞÀg 20w T ðt Þw ðt Þ;and the third property (2.6)was used at theswitching points in some of the inequalities.When m ¼1;which is a trivial case,we get from V ðt ÞX 0and (2.7)thatZt 0e Àl 0ðt Àt ÞG ðt Þd t p V ðt ÞþZ t 0e Àl 0ðt Àt ÞG ðt Þd t p e Àl 0t V ð0Þ:ð2:8ÞNote in the above inequality that R t 0e Àl 0ðt Àt Þz T ðt Þz ðt Þd t is integrable from t ¼0to N ;since e Àl 0t V ð0Þþg 20R t 0e Àl 0ðt Àt Þw T ðt Þw ðt Þd t is integrable for any w A L 2½0;N Þinthe same interval.Next,we integrate (2.8)from t ¼0to N to obtain (by rearranging G.Zhai et al./Journal of the Franklin Institute 338(2001)765–779769the double-integral area)Z N 0Z t0e Àl 0ðt Àt ÞG ðt Þd t d t¼Z N 0G ðt ÞZ N t e Àl 0ðt Àt Þd t d t ¼1l 0Z N 0G ðt Þd t p Z N 0e Àl 0t V ð0Þd t ¼1l 0V ð0Þ;ð2:9Þwhich means that jj z jj 2L 2p g 20jj w jj 2L 2þV ð0Þ;and thus the disturbance attenuation level g 0is achieved for switched system (1.1)under arbitrary switchings.Since m ¼1is a quite special case,we consider from now on the case of m >1:First,we multiply both sides of (2.7)by e ÀN s ð0;t Þln m to gete ÀN s ð0;t Þln m V ðt Þp e Àl 0t V ð0ÞÀZ t 0e Àl 0ðt Àt ÞÀN s ð0;t Þln m G ðt Þd t ;ð2:10Þwhich is equivalent toe ÀN s ð0;t Þln m V ðt ÞþZt 0e Àl 0ðt Àt ÞÀN s ð0;t Þln m z T ðt Þz ðt Þd tp e Àl 0t V ð0Þþg 20Z t0e Àl 0ðt Àt ÞÀN s ð0;t Þln m w T ðt Þw ðt Þd t :ð2:11ÞNow,we choose a positive scalar l smaller than l 0to consider the following average dwell time scheme:for any t >0;N s ð0;t Þp t t n a ;t n a ¼ln m l :ð2:12ÞFrom (2.12),we know that N s ð0;t Þln m p lt holds for any t >0:Then,from (2.11)and V ðt ÞX 0;we obtainZ t 0e Àl 0ðt Àt ÞÀlt z T ðt Þz ðt Þd t p e Àl 0t V ð0Þþg 20Z t 0e Àl 0ðt Àt Þw T ðt Þw ðt Þd t :ð2:13ÞSimilar to (2.9),we integrate the above inequality from t ¼0to N to get 1l 0Z N0e Àlt z T ðt Þz ðt Þd t p 1l 0V ð0Þþg 20l 0Z N 0w T ðt Þw ðt Þd t ð2:14Þand thus,Z N0e Àlt z T ðt Þz ðt Þd t p V ð0Þþg 20Z N 0w T ðt Þw ðt Þd t ð2:15Þholds for any w ðt ÞA L 2½0;N Þ:We conclude the above discussion in the following theorem.Theorem 1.Assume that all subsystems in ð1:1Þare Hurwitz stable and achie v e a disturbance attenuation le v el smaller than g 0;and switched system ð1:1Þis controlled by the a v era g e dwell time scheme ð2:12Þwith l o l 0:Then ;the switched system achie v es aG.Zhai et al./Journal of the Franklin Institute 338(2001)765–779770wei g hted disturbance attenuation le v el g0in the sense ofð2:15Þo v er S a½t a for any a v era g e dwell time t a X t na:Inequality(2.15)describes a weighted disturbance attenuation level from wðtÞto zðtÞdue to the existence of eÀl t:When l¼0;which means no switching between subsystems,(2.15)shrinks to normal disturbance attenuation for a single subsystem. When l is small enough,which means the average dwell time is chosen suﬃciently large,obviously inequality(2.15)approaches the normal disturbance attenuation. We note here that L2induced norm of switched systems which are composed of Hurwitz stable subsystems was also considered in Hespanha’s Ph.D.thesis[14]using piecewise Lyapunov function technique,and a weighted norm bound of wðtÞto zðtÞwas declaimed under the condition of large dwell time.However,we found that there was a mistake in the proof of the main theorem(Theorem4:1)there,and thus Theorem4:1in[14]is not correct in its present form.Moreover,the average dwell time scheme(2.12)includes the case of dwell time,and the weighted disturbance attenuation result(2.15)does not need large(average)dwell time at the present point.As explained in the above paragraph,our weighted disturbance attenuation result(2.15)seems to have a better interpretation of the average dwell time. Though we have discussed the case of m¼1in the proof of Theorem1,we did not include the result clearly in the theorem because it is a special case.Noting that the case of m¼1is equivalent to the existence of a common Lyapunov function for all subsystems in the sense of normal disturbance attenuation,we state the following corollary,which can be considered as an extension of the stability result under arbitrary switching[13,20].Corollary1.Assume that all subsystems inð1:1Þare Hurwitz stable and achie v e a disturbance attenuation le v el smaller than g0:If there exists a common Lyapuno v function satisfyin gð2:2Þfor all subsystems;then the switched system achie v es the disturbance attenuation le v el g0under arbitrary switchin g.The following are some remarks on Theorem1.Remark1.When w¼0;we get from(2.8)and(2.11)under(2.12)that VðtÞp eÀl0t Vð0Þand VðtÞp eÀðl0ÀlÞt Vð0Þ;which means that switched system(1.1)without the disturbance input is exponentially stable with decay rates l0and l0Àl; respectively.The same is true for the class of switched systems considered in the next subsection.In this way,the disturbance attenuation discussion in this paper covers the existing results[4,7,8]concerning exponential stability of linear switched systems if these are controlled by average dwell time schemes.Remark2.In the proof of Theorem1,we assumed tacitly that there are no state jumps when switching from one subsystem to another.However,there is no diﬃculty considering state jumps in our framework.It is reasonable to assume for state jumpsthat there exists a positive scalar J such that jj xðt iÞjj p J jj xðtÀi Þjj holds at all theswitching points t i:If J p1;the discussion upto now is the same.f J>1;thenG.Zhai et al./Journal of the Franklin Institute338(2001)765–779771V ðx ðt i ÞÞp J 2m V ðx ðt Ài ÞÞholds according to (2.6),and thus the remaining discussion is valid if we replace m with J 2m :As will be seen later,state jumps can also be considered in the discussion of the next subsection.Remark 3.Theorem 1can be theoretically extended to the case of the nonlinear switched system’x ðt Þ¼f s ðx ðt ÞÞþG s ðx ðt ÞÞw ðt Þ;z ðt Þ¼h s ðx ðt ÞÞ;ð2:16Þwhere x ðt Þ;w ðt Þ;z ðt Þand s are the same as in (1.1),each f i ðx Þis locally Lipschitz continuous and G i ðx Þ;h i ðx Þare continuous over R n :The idea is to consider for each subsystem a positive deﬁnite and proper function V i ðx Þsatisfying the following Hamilton–Jacobi inequality [21,22]:q V i q x ðx Þf i ðx Þþ12g 0q V i q xðx ÞG i ðx ÞG T i ðx Þq T V i q x ðx Þþ12h T i ðx Þh i ðx Þþl 0V i ðx Þp 0ð2:17Þinstead of matrix inequality (2.2).In this case,the piecewise Lyapunov function candidate V s ðx Þsatisﬁes the ﬁrst property (2.4)and the second property (2.5)with some small modiﬁcation,but the third property may not hold globally in the state space.If the inequality m :¼sup V p ðx ÞV q ðx Þ:x A R n ;p ;q A I N o N ð2:18Þholds,the same result as Theorem 1can be obtained for the nonlinear switched system (2.16).However,since we still lack eﬀective methodologies for solving the Hamilton–Jacobi inequalities (2.17),we will consider a special case of switched system (2.16)by perturbation methods,later in Section 3.Remark 4.It is easy to see that Theorem 1can be used to analyze robust stability properties of the following time-controlled switched system:’x ðt Þ¼A s x ðt ÞþB s F ðx ;t ÞC s x ðt Þ;ð2:19Þwhere x ðt Þand s are the same as in (1.1),and F ðx ;t Þdescribes norm-bounded uncertainties.Roughly speaking,if each subsystem is quadratically stable for any F ðx ;t Þsatisfying jj F ðx ;t Þjj p 1=g 0;then the entire switched system (2.19)is robustly asymptotically stable for any jj F ðx ;t Þjj p 1=g 0if the average dwell time between the activated subsystems is chosen suﬃciently large.2.2.Case ðb Þ:not all subsystems are Hurwitz stableIn this subsection,we assume that not all subsystems are Hurwitz stable.Without loss of generality,we suppose that the subsystem A i ’s (1p i p r )are Hurwitz stableG.Zhai et al./Journal of the Franklin Institute 338(2001)765–779772and achieve a disturbance attenuation level smaller than g0;where the positive integer r satisﬁes1p r o N;and the other subsystems are not Hurwitz stable.For the Hurwitz stable subsystems,similar to(2.2),there exist a positive scalar lÀand a set of positive deﬁnite matrices P i such thatA T i P iþP i A iþgÀ2P i B i B TiP iþC TiC iþlÀP i o0;1p i p r:ð2:20ÞFor the unstable subsystems,since there always exists a scalar l i>0making A iÀl i I Hurwitz stable,we assume that there exist a positive scalar lþand a set of positive matrices P i such thatA T i P iþP i A iþgÀ2P i B i B TiP iþC TiC iÀlþP i o0;r o i p N:ð2:21ÞNote that the assumption of the same disturbance attenuation level g0in(2.21)as the one in(2.20)does not lose generality either.Next,for the piecewise Lyapunov function candidate(2.3)with P i being the solutions of(2.20)and(2.21),the second property(2.5)and the third property(2.6) hold as before,while theﬁrst property(2.4)becomes:each V i is continuous and its derivative along the solutions of the corresponding subsystem satisﬁes’V i ¼q V iq xðA i xþB i wÞpÀlÀV iÀz T zþg2w T w if i p r;lþV iÀz T zþg2w T w if i>r:(ð2:22ÞFor any switching signal and any0p t o t;we let Tþðt;tÞ(resp.,TÀðt;tÞ)denote the total activation time of Hurwitz unstable subsystems(resp.,Hurwitz stable subsystems)during½t;tÞ:Then,we choose a scalar l n Að0;lÀÞarbitrarily and propose the following switchin g law:(S1)Let0¼t0o t1o t2o?ðlim j-N t j¼NÞbe a speciﬁed sequence of time instants satisfying sup j f t jþ1Àt j g¼T o N:Determine the switching signal sðtÞsuch that the inequality TÀðt j;t jþ1Þ=Tþðt j;t jþ1ÞXðlþþl nÞ=ðlÀÀl nÞholds on every time interval½t j;t jþ1Þ(j¼0;1;yÞ:Remark5.The idea of specifying the activation time period ratio between Hurwitz stable subsystems and unstable ones has appeared in[8,13].As is also shown there, the switching condition TÀðt j;t jþ1Þ=Tþðt j;t jþ1ÞXðlþþl nÞ=ðlÀÀl nÞon each time interval½t j;t jþ1Þis quite easy to satisfy.For example,we canﬁrst activate the Hurwitz stable subsystems with a time period of about2ðlþþl nÞT0;and then activate the unstable subsystems with a time period of aboutðlÀÀl nÞT0;where T0>0is a positive time unit satisfying the average dwell time requirement,which will be described later.Now,for an arbitrary piecewise constant switching signal s under the switching law(S1)and any given t>0;we let t1o?o t i denote the switching points of s over the intervalð0;tÞ:From(2.22),we know that the piecewise Lyapunov functionG.Zhai et al./Journal of the Franklin Institute338(2001)765–779773candidate (2.3)satisﬁesV ðt Þp e Àl Àðt Àt i ÞV ðt i ÞÀR t t i e Àl Àðt Àt ÞG ðt Þd t if i p r ;e l þðt Àt i ÞV ðt i ÞÀR t t i e l þðt Àt ÞG ðt Þd t if i >r :(ð2:23ÞSince V ðt i Þp m V ðt Ài Þholds on every switching point t i according to (2.6),we obtain by induction thatV ðt Þp m N s ð0;t Þe l þT þð0;t ÞÀl ÀT Àð0;t ÞV ð0ÞÀZ t 0m N s ðt ;t Þe l þT þðt ;t ÞÀl ÀT Àðt ;t ÞG ðt Þd t¼e l þT þð0;t ÞÀl ÀT Àð0;t ÞþN s ð0;t Þln m V ð0ÞÀZt 0e l þT þðt ;t ÞÀl ÀT Àðt ;t ÞþN s ðt ;t Þln m G ðt Þd t :ð2:24ÞUnder the switching law(S1),we see that for any t ;t satisfying t j À1o t p t j o t j þ1o ?o t k p t ;e l þT þðt ;t ÞÀl ÀT Àðt ;t Þp e l þðt Àt k Þe P k À1q ¼j ½l þT þðt q ;t q þ1ÞÀl ÀT Àðt q ;t q þ1Þ el þðt j Àt Þp e l þðt Àt k Þe Àl n ðt k Àt j Þe l þðt j Àt Þ¼e ðl þþl n Þðt Àt k Þe Àl n ðt Àt Þe ðl þþl n Þðt j Àt Þ:ð2:25ÞSince on any interval ½t j ;t j þ1Þthe total activation time period of unstable subsystems satisﬁes T þðt j ;t j þ1Þp ½ðl ÀÀl n Þ=ðl þþl ÀÞ ðt j þ1Àt j Þaccording to the requirement in (S1),we get from (2.25)thate l þT þðt ;t ÞÀl ÀT Àðt ;t Þp e c Àl n ðt Àt Þ;c ¼2ðl þþl n Þðl ÀÀl n Þl þþl ÀT :ð2:26ÞIt is not diﬃcult to see that (2.26)is also valid for any t ;t satisfying t q p t o t o t q þ1(q X 0).For the trivial case of m ¼1;we get easily from (2.24)and (2.26)thatZ t 0e Àl Àðt Àt Þz T ðt Þz ðt Þd t p e c Àl n t V ð0Þþg 20Z t 0e c Àl n ðt Àt Þw T ðt Þw ðt Þd t ð2:27Þand by integrating the above inequality from t ¼0to N ;1l ÀZ N 0z T ðt Þz ðt Þd t p e c l n V ð0Þþe c g 20l n ZN 0w T ðt Þw ðt Þd t ;ð2:28Þwhich means jj z jj 2L 2p ðe c l À=l n Þg 20jj w jj 2L 2þðe c l À=l n ÞV ð0Þ:Thus,the disturbance attenuation level ﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃðe c l À=l n Þp g 0is achieved under the switching law (S1)withoutconsidering the average dwell time.G.Zhai et al./Journal of the Franklin Institute 338(2001)765–779774。

城市公园可达性研究_方法与关键问题

生态学报2010,30(19):5381 5390Ac ta Ecologica S inica城市公园可达性研究方法与关键问题刘常富1,*,李小马1,韩东2(1.沈阳农业大学林学院,沈阳 110161;2.北京市延庆县园林绿化局,北京 102100)摘要:城市公园是城市居民主要的休闲游憩场所,对促进其身心健康,建设和谐可持续社会具有重要意义。

伴随快速城市化,城市居民对城市公园的需求与日俱增,不仅仅关注城市公园的数量,更关心能否方便快捷地进入公园进行游憩活动。

这对城市公园的评价和合理规划提出了新要求。

基于G IS的可达性研究从公园与市民相互关系角度出发,能够较好地评价城市公园的空间分布,是评价城市公园空间分布合理性和服务公平性的主要手段。

多种可达性计算方法的出现为城市公园可达性研究中方法的选择提供了充分的余地,但不同的方法基于不同的理论,对数据要求不同,反映可达性的不同方面,对各种可达性计算方法的理解是选择适宜可达性计算方法进行城市公园可达性研究的前提。

将城市公园可达性研究中常用的可达性计算方法分为4类6种,分别评述了其原理和优缺点,为城市公园可达性研究中方法的选择提供参考。

同时分析了城市公园可达性研究中的关键问题,探讨了未来城市公园可达性研究的重点。

关键词:城市公园;城市绿地;城市游憩;可达性;空间分布;G ISA ccessi bility anal ysis of urban parks:m ethods and key issuesLIU Chang fu1,*,LI X iao m a1,HAN Dong21F orest ry C olle ge,S he nyang Ag ri cult ura l Un iversit y,S he nyang110161,China2Yanqi ng L and scap e G ree n i ng Bu reau,Be i jing102100,Ch i naAbstract:U r ba n parks are the m ain places for le i sure and recreation f or urban resi de nts and play significa nt r o les i n beautify i ng the cities a nd har mon i zi ng the ur ba n residents&nature.W ith the rap i d ur ba n ization a nd fast increasi ng of people s li v i ng sta ndard,ur ban residents not only year n for more ur ba n parks,but also e xpect to enjoy the m conve n i ently. T hese changes present great challe nges for urban park evaluati ng and pl ann i ng.A ccessibility analysis is a feasi b le cho i ce to address this quest i on.A ccessibility is defi ned here as ur ban parks can be reac hed or obta i ned easily or not,whic h also can be regarded as an m i portant eval uating i ndicator o f urban par k spatial distri bution eff i c i enc y.A s the m ai n m ethod to eval uate distribut i on efficiency and serv ice equity of ur ban par ks, accessibility can be ana l yze d by m any methods.H o wever,different m ethods are based on differe nt theories and data require m ents,reflecting different aspects of accessi b ility.U nderstandi ng these m ethods a nd the ir characteristics exactl y w ill hel p us c hoose the suitablem et hod for ur ban park accessi bility ana l ysi s.W e categorized thesem et hods i nto four groups and si x types and rev ie w ed the ir theoretical basis,adva ntages and disadvantages.A lthough stat i st i c i ndex m et hod is the most w i dely used,it can only acquire so m e basic i nfor mation of ur ban par ks(e.g.percent of ur ba n par k area,urban par k area per capital)and neglect the spatial distri bution of urban par ks.Sm i ple BufferingM et hod andM i nm i um d i sta nce method are sm i ple m ethodswh i ch concern the l ocation of urban parks.The m ain disadvantage of these methods i s that they ignore the barriers bet w een ur ban parks a nd residents.Cost weighted distance m ethod m easures the total or average distance bet w een cit izens and urban par ks.U suall y distance is calculated as c ost w ei ghte d distance based on classified landscape.It assi gns基金项目:国家自然科学基金资助项目(30940013,30600482);辽宁省自然科学基金资助项目(20092065);辽宁省教育厅科研项目计划(L2010502)收稿日期:2010 03 16; 修订日期:2010 07 02*通讯作者C orres pond i ng author.E m ai:l li ucf898@163.co m5382 生态学报 30卷eac h landscape type a relat i ve travelli ng cost and then gener ates a map of accu mu l ated cost distance.Thism ethod depends on classifi ed landscape and rel ative travelling cost but t hese val ues are usually assi gne d ar b itrarily.G rav ity M odel is based on the la w of t he grav ity.T hism et hod calc u l ates relative valueswhich are proport i ona l to recreati on opportunities of urban parks(area,recreational fac ilities)and inversely proportional to distance bet ween ur ba n parks and residents.T hese relative values spatiall y display the ease w ith which urban par ks can be reached.H o wever it i s difficult to descri be the distance decay factor exactly.N et wor k A nalysisM ethod calculates the actual distance or t m i e cost bet ween ur ban parks and resi de nts base d on the actua l road.This method sm i ulates t he pr ocess peopl e reach ur ba n par ksmore exactl y.T here are four crit ical issues wh ic h need to be solve d duri ng ur ba n park accessi bility a nalysis:(1)sm i plifyi ng the ur ban par ks and ur ban citizens exactly,(2)sm i ulati ng t he actual resistance that peop l e w ill overco m e when reachi ng urban parks,(3)reflecting recreational attraction of ur ban parks objectively,and(4)c hoosi ng the su itable max m i u m ser v ice distance of ur ba n par ks especi a lly for differe nt groups of people.W e reco mm end that m ore effective m ethods,which not onl y take the above issues i nto acc ount,but also i nte grate the advantages o f the previous m ethods,shou l d be designed to provide m ore valuable and direct i nfor m at i on for urban par k planni ng.K eyW ords:ur ban par k;ur ban greenspace;urban recreation;accessi bility;spat i al distri bution;G IS目前世界城市人口已经超过总人口的一半,预计到2050年全球城市化将接近70%[1]。

生命周期视角下健康城市的主动式规划干预路径

ISSUE 5 AUG. 2020 / JOURNAL OF HUMAN SETTLEMENTS IN WEST CHINA / 048Abstract : With the rapid expansion of urban population and the rapid development of urbanization, “urban diseases” such as air pollution, energy shortage, water quality deterioration and traffic congestion are becoming increasingly serious, which are seriously endangering the health of all mankind. As an effective means to cure the urban disease, healthy city construction has aroused the common concern of mankind. In the international healthy city movement actively, starting from the theoretical level of planning to explore the healthy city system framework, construction level, focus and direction, active prevention of various chronic diseases of the significant role, Chinese planners have done a lot of researches to realize healthy cities. It is worth noting that due to the insufficient attention to the city as a system of the influence of the operation of the law, the study of healthy city construction lack of the overall system thinking.From the perspective of system theory, the paper analyzes the life cycle phenomenon of urban system development. Urban systems do not always develop in an orderly manner. With external interference or endogenous qualitative changes, the whole life cycle will be replaced. When a city develops to a certain stage, it will experience different degrees of “urban disease”. The occurrence of “urban disease” will stimulate the endogenous feedback regulation mechanism of the system, and the feedback will have a minimum impact on the system in time, so as to move towards “urban rehabilitation” and complete a virtuous cycle. Improper feedback results in maximized decomposition of the system and leads to “urban development disorder”.The construction of healthy cities should focus on the characteristics of three important stages in the whole life cycle to realize a virtuous cycle. The first stage is called the external disturbance stage in which the urban system suffers external disturbance, from “orderly urban development” to the emergence of “urban disease”. At this stage, the urban system is continuously disturbed by the external environment, which leads to the shift from the steady state of the system to the abnormal state, and finally the migration of the internal steady state. The second stage is called the continuous feedback stage, the city system of which experienced from “urban disease” to “urban rehabilitation”. In this stage, in order to avoid the overall collapse of the system, subsystems feedback the imbalance of each other. In accordance with the principle of minimizing the impact, subsystems assist each other to balance, and then give feedback until the overall system tends to be stable. The third stage is called the self-coupling adjustment stage, the city system of which experienced from “urban rehabilitation” to “orderly development”. In this stage, based on the continuous feedback of the subsystem, the system as a whole adjusts the combination mode of the subsystem according to the inertia of self-coupling until the system operation efficiency reaches the highest level to avoid falling into collapse again.In order to realize the life-cycle characteristics of healthy cities, urban and rural planning should comprehensively consider the progressive relationship of the whole cycle from “urban disease” to “urbanDOI: 10.13791/ki.hsfwest.20200507何琪潇, 谭少华. 生命周期视角下健康城市的主动式规划干预路径[J]. 西部人居环境学刊, 2020, 35(5): 48-55.HE Q X, TAN S H. Active Planning Intervention Paths for Healthy Cities from the Perspective of Life Cycle[J]. Journal of Human Settlements in West China, 2020, 35(5): 48-55.摘　要：健康城市建设作为对“城市病”蔓延的积极响应，引起全人类的共同关注。

Romeo Ortega

L 2 L 1x ? 1 x x2 = (1 ? v) C 1 RC 2 _
1
1 for tk t < tk + (tk )T 0 for tk + (tk )T t < tk + T where tk represents a sampling instant de ned by tk+1 = tk + T; k = 0; 1; : : :,; the parameter T > 0 is the xed sampling period, also called the duty cycle. The duty ratio function, ( ), ranging on the closed interval 0; 1], is the control input to the average PWM model given by 13] z_ = ?u 1 z + E + !
where x1 and x2 represent, respectively, the input inductor current and the output capacitor voltage variables; E > 0 represents the nominal constant value of the external voltage source and ! is an unknown disturbance, which satis es j! j < E ; v , which takes values in the discrete set f0; 1g, denotes the switch position function, and acts as a control input. The regulated output is x2 which should be driven to some constant desired value Eo > E . A Pulse Width Modulation (PWM) policy regulating the switch position function v , may 2

宿舍问题的英语作文

Living in a dormitory is a common experience for many students,but it can also present a variety of challenges.Here are some common issues that students might encounter and how they can be addressed in an English essay about dormitory problems:1.Noise Disturbances:One of the most frequent complaints in dormitories is noise from other residents.This can disrupt study time and sleep.To address this issue,students might propose setting quiet hours or establishing a community agreement on noise levels.2.Shared Spaces:Dormitories often have shared common areas like kitchens and bathrooms.The cleanliness and maintenance of these spaces can be a concern.An essay could discuss the importance of communal responsibility and suggest the implementation of a cleaning schedule.3.Privacy Concerns:With multiple roommates,maintaining personal privacy can be difficult.The essay could explore the concept of personal space and propose solutions such as designated quiet zones or private study areas within the dorm.4.Conflict Resolution:Disagreements between roommates are inevitable.The essay could discuss strategies for effective communication and conflict resolution,such as mediation services or roommate agreements.5.Safety Issues:Dormitories should be safe environments,but sometimes safety concerns arise,such as unauthorized access or fire safety.The essay might suggest improvements in security measures or regular safety drills.6.Internet and Connectivity:In the digital age,reliable internet access is crucial for students.Issues with connectivity can hinder academic work.The essay could propose solutions like upgrading the network infrastructure or providing tech support.7.Cultural Differences:Dormitories often house students from diverse backgrounds. Cultural misunderstandings can lead to tension.The essay could advocate for cultural sensitivity training or social events that promote understanding and integration.8.Health and Hygiene:Living in close quarters can increase the risk of illness.The essay might discuss the importance of personal hygiene and propose measures such as regular health checks or health education sessions.9.Study Environment:A conducive environment for studying is essential for academic success.The essay could suggest creating designated study rooms or implementing policies that promote a distractionfree environment.10.Mental Health Support:The stress of living away from home and the pressures of academic life can affect students mental health.The essay could call for increased access to counseling services and stress management workshops.In conclusion,addressing dormitory problems requires a collaborative approach that involves both the administration and the students.By identifying these issues and proposing thoughtful solutions,an essay can contribute to creating a more harmonious and supportive living environment for all dormitory residents.。

扭曲人们心态英语作文

扭曲人们心态英语作文Title: Distorting People's Mindsets。

In today's world, the distortion of people's mindsets has become a prevalent issue, permeating various aspects of society. This distortion manifests in different forms, from skewed perceptions of success to warped ideologies that breed prejudice and division. Understanding the root causes and implications of this phenomenon is crucial for addressing its adverse effects and fostering a healthier collective mentality.One prominent factor contributing to the distortion of mindsets is the influence of mass media. Through carefully crafted narratives and sensationalized content, media platforms often manipulate public opinion, shaping individuals' beliefs and values. The incessant bombardment of idealized images and unrealistic standards exacerbates feelings of inadequacy and fosters a culture of comparison and competition. As a result, people may develop distortedperceptions of themselves and others, leading to a host of psychological issues such as low self-esteem and anxiety.Furthermore, the proliferation of social media has amplified the phenomenon of distorted mindsets. Platforms like Instagram and Facebook serve as breeding grounds for curated self-presentations, where individuals meticulously construct and project an idealized version of their lives. This curated reality, often characterized by staged moments of happiness and success, creates unrealistic expectations and fosters feelings of envy and dissatisfaction among users. Consequently, many people fall into the trap of constantly seeking validation and approval online, neglecting genuine connections and experiences in favor of superficial gratification.Another significant factor contributing to the distortion of mindsets is societal pressure and cultural norms. From a young age, individuals are inundated with societal expectations and norms that dictate what constitutes success, beauty, and happiness. These rigid standards not only limit personal freedom but alsoperpetuate harmful stereotypes and biases. For instance, the relentless pursuit of material wealth and external validation may lead individuals to prioritize superficial goals over genuine fulfillment and self-actualization.Moreover, the prevalence of echo chambers and confirmation bias in the digital age further exacerbates the distortion of mindsets. With the rise of personalized algorithms, individuals are increasingly exposed to information that aligns with their existing beliefs and biases. This phenomenon creates a polarized society where dissenting opinions are dismissed, and critical thinking is stifled. As a result, people become entrenched in their own echo chambers, reinforcing narrow-minded perspectives and inhibiting meaningful dialogue and understanding.Addressing the issue of distorted mindsets requires a multi-faceted approach that encompasses education, media literacy, and societal change. Firstly, promoting critical thinking skills and media literacy is essential for empowering individuals to discern fact from fiction and resist manipulation. By teaching individuals to questionand analyze the information they encounter, we can mitigate the influence of biased media narratives and propaganda.Secondly, fostering a culture of authenticity and self-acceptance is crucial for combating the pressures of social media and societal norms. Encouraging individuals to embrace their unique identities and pursue genuine passions can help counteract the pervasive culture of comparison and competition. Additionally, promoting diversity andinclusivity in media representation can challenge narrow beauty standards and foster a more inclusive society.Lastly, fostering open dialogue and empathy isessential for bridging divides and overcoming echo chambers. By engaging in respectful discourse with those who hold different perspectives, we can broaden our understandingand cultivate empathy towards others. Building connections based on shared values and mutual respect is fundamentalfor fostering a more cohesive and empathetic society.In conclusion, the distortion of people's mindsets is a complex issue with far-reaching implications for society.By addressing the root causes of this phenomenon and implementing targeted interventions, we can foster a healthier collective mentality characterized by authenticity, empathy, and critical thinking. Only by challenging distorted perceptions and fostering genuine connections can we create a more inclusive and compassionate society for future generations.。

Distributed_Adaptive_Asymptotic_Tracking_of_2-D_Ve

LetterDistributed Adaptive Asymptotic Tracking of 2-D Vehicular Platoon Systems With ActuatorFaults and Spacing ConstraintsJiayi Lei, Yuan-Xin Li, and Shaocheng TongDear Editor,This letter investigates the adaptive asymptotic tracking sliding-mode control for nonlinear 2-D vehicular platoon systems subject to actuator faults. Firstly, by using the Nussbaum function, the disad-vantageous factors brought by the unknown direction actuator faults can be attenuated. Then, a new neural network (NN) asymptotic tracking control method is presented based on the sliding-mode con-trol and bounded estimation approach. By constructing a barrier Lya-punov function, it can be guaranteed that all signals of the corre-sponding closed-loop systems are bounded, and constraints are not violated. Finally, a numerical simulation is given to verify the obtained results.In the past few decades, the research on the vehicular platoon sys-tems has received growing interests due to its great anti-interference characteristics and string stability. A plenty of representative control algorithms in this area have been developed in [1]–[4]. Although the aforementioned studies can achieve the string stability, the issue of spacing constraints was not considered. To circumvent this problem, an interesting control scheme was proposed in [5], which can guaran-tee not only the safe distance but also communication connectivity. Besides, it is desirable for vehicles to guarantee the collision avoid-ance in some chaotic environments. The distributed tracking control method was proposed for vehicle systems to deal with the problem of obstacle avoidance in [6] by means of the NN. On the basis of exist-ing researches, a vehicle model on a two-dimensional (2-D) plane was first considered in [7], which can simulate the more realistic driving scene. Besides, there were many related results on asymp-totic tracking control problem, which provided asymptotic stable tracking error systems with zero errors in [8]–[10].It is worth noting that, the aforementioned results do not consider the issue of actuator faults, which will lead to deteriorative and insta-ble performance of the system. To ensure the controlled systems’security and dependability, various advanced methods on fault-toler-ant control have been reported in [11]–[13]. Recently, the authors have turned the research direction to the fault-tolerant control of the vehicular platoon systems since various types of actuator faults trig-ger risks to vehicle mechanism. In [14]–[16], the sliding-mode con-trol method and adaptive control technique were used to eliminate the impact of faults for platoon systems. Although lots of significant progress on adaptive fault-tolerant control for vehicular platoon sys-tems have been proposed, the following defects are inevitable in the existing control strategies. 1) The disadvantageous factors brought by the unknown direction actuator faults should be considered, which widely exist in practice and can not be ignored in controller designed.2) There is no work focusing on the asymptotic tracking control for vehicular platoon systems with unknown direction actuator faults to provide tracking performance with zero-error tracking.d i(t)Motivated by the above considerations, this letter addresses the adaptive asymptotic tracking sliding-mode control problem for non-linear 2-D vehicular platoon systems subject to actuator faults with unknown directions. The main contributions lie in the following: 1) Different from the traditional control methods [1]–[6], where the pro-posed control method do not obey principle owing to the existence of unknown direction actuator faults. To solve this problem, we design a Nussbaum function to eliminate disadvantageous factors brought by the unknown direction actuator faults. 2) An asymptotic tracking control for nonlinear 2-D vehicular platoon systems with unknown direction actuator faults is first proposed in this work. Based on the sliding-mode control, we design a novel asymptotic tracking con-troller to ensure that the practical distance tracks the desired dis-tance d asymptotically.Problem formulation:Consider a nonlinear i th follower system expressed as the following form:i iψi(t)v i(t)a i(t)u Fi(t)g i(x i,y i,v i,t)r i(t)ωi(t)ϵi(t)position respectively; is the angle between the speed direction and the X-axis direction; and , respectively, the vehicle’s velocity and acceleration; denotes the actuator faults;is uncertainty under nonlinear unmodeled dynamic; represents external disturbance; is the angular rate and is the acceleration of the velocity direction deflection angle.The actuator faults in our research are modeled as follows:iγ,i i n,itγ,i t n,iwhere denote the fault factors and are the bias faults. and are unknown fault time instants.r i(t)|r i(t)|≤¯r i,i=1,2,...,nAssumption 1: The external disturbances are unknown and bounded satisfying.γi(t,tγ,i)n i(t,t n,i)0<γi≤|γi(t,tγ,i)|≤γi<∞|n i(t,t n,i)|≤¯n i,i=1,2,...,nAssumption 2: The unknown parameters and referring to (3) satisfy the following conditions:and .min max i i are respectively the distance and the velocity direction deflection0<∆min<d i(t)<∆max∆min∆maxthe spacing restrictions are given as: , where is the minimum distance to ensure safety, while is the maximum distance to maintain effective communication.In addition,to guarantee the distance restrictions, the followinga minb maxChoose the following sliding surfaces:s i(t)=˙e i(t)+ρ1e i(t)+ρ2|e i(t)|a b sgn(e i(t))(8)12ρ3where a and b are positive constants satisfying , and and are positive constants.u i(t)Then, the controller is established asCorresponding author: Yuan-Xin Li.Citation: J. Y. Lei, Y.-X. Li, and S. C. Tong, “Distributed adaptiveasymptotic tracking of 2-D vehicular platoon systems with actuator faults andspacing constraints,” IEEE/CAA J. Autom. Sinica, vol. 10, no. 5, pp.1352–1354, May 2023.The authors are with the College of Science, Liaoning University of Techno-logy, Jinzhou 121001, China (e-mail: yxinly@126.Color versions of one or more of the figures in this paper are availableonline at .Digital Object Identifier 10.1109/JAS.2023.1231501352 IEEE/CAA JOURNAL OF AUTOMATICA SINICA, VOL. 10, NO. 5, MAY 2023D i (t )=ρ1˙ei (t )+ρ2ab |e i (t )|ab −1˙e i (t )+i i d i (t ),G i (t )=s i (t )×(ˆθi ζT 1,i (X i )ζ1,i (X i )√s 2i ζT 1,i (X i )ζ1,i (X i )+σ2i +ˆφi ζT 2,i (X i )ζ2,i (X i )√s 2i ζT 2,i (X i )ζ2,i (X i )+σ2i +ηi √s 2i +σ2i)H i (t )=1−sgn(e i (t ))νi ×e i (t )k a 2−e 2i (t )+1+sgn(e i (t ))νi e i (t )k b 2−e 2i (t )where , and the adaptive update laws are pro-i i σi (t )σi (t )>0,lim t →∞ tt 0σi (ϵ)d ϵ≤σi <+∞,σi Here, , and l are positive parameters. The Nussbaum function can be chosen as [7] to attenuate the disadvantageous factors brought by unknown direction actuator faults. In addition, is any uni-form boundedness continuous function expressed as: with being an unknown positive constant.Theorem 1: Consider the 2-D vehicular platoon systems (1) satisfy-ing Assumptions 1 and 2. The controller (10) and the adaptive laws (11) can ensure that the tracking errors converge to zero asymptoti-cally, and all the signals of closed-loop system are bounded.Then, by considering (1), (4) and (8), we can obtainV (t )From (12) and Lemma in [7], the derivative of givesi i i i ˜θi (t )=θ∗i−ˆθi (t )˜φi (t )=φ∗i −ˆφi (t )where and represent the estimation of and . Defineand .W ∗Tj ,i ζj ,i (X i ),j =1,2,Referring to [12], the NN are employed to 1,i 2,i 1,i ε1,i |ε2,i (t )|≤ε2,i W ∗1,i W ∗2,i and , and are the given optimal weight vectors.µ=14θi +14φi +θi +φi +ηi where .0µσi with .V (0)∑N i =1 t0[(ςN +1)˙ξi ]d τ[0,+∞)V (t )e i ,˜θi ,˜φi ˆθi ˆφ[0,+∞)This together with Lemma in [17], it can be shown that and are bounded on . In view of the defini-tion of , the boundedness of can be achieved. Besides,we can obtain that and are bounded. Therefore, we can conclude that all the signals of the controlled system are bounded on .Next, we prove the asymptotic tracking performance of the sliding t →∞i lim t →∞e i (t )=0From that, we know . Together with (8), we canget . Therefore, the asymptotic convergence is achieved. In addition, to prove the stability of sliding surfaces, the ψi ˙Vψ(t )<0, which implies that the object of this letter is ensured that sliding surfaces are asymptotically stable.d =15m ∆min =7m ∆max =22m a 0(t )=0.6t m /s 2,2.3m /s 2,−5m /s 20s ≤t <5s ,5s ≤t <9s ,14s ≤t <15s Numerical example: A platoon of vehicles with 1 leader vehicle and 4 follower vehicles are taken into account. The desired vehicle distances are set as , and , . The ex-pected acceleration of leader is while , respectively.To verify the above results, the system parameters used for simula-LEI et al .: DISTRIBUTED ADAPTIVE ASYMPTOTIC TRACKING OF 2-D VEHICULAR PLATOON SYSTEMS 1353αi =10βi =0.0009σi =10e −5t ˆθi (t )=1ˆφi (t )=1ρ1=1.5ρ2=0.3ρ3=6a =6b =4l =170g i (x i ,y i ,v i ,t )=−a 0,i −a 1,i v i (t )−a 2,i v 2i (t )a 0,i =0.01176a 1,i =0.00077616a 2,i =0.000016n i (t ,t n ,i )=sin(it +i π)γi (t ,t γ,i )n i (t ,t n ,i )γ1(t ,t γ,1)=1.2−0.2cos(t )γ2(t ,t γ,2)=0.5−0.2cos(t )γ3(t ,t γ,3)=−0.9−0.2cos(t )γ4(t ,t γ,4)=−0.4+0.2sin(0.01t )n i (t ,t n ,i )=0.3+0.2cos(t )m =3n =0.001tions are given as: , , , ,, , , , , , . In the simu-lation, is used with , , . In addition, the distur-bance enters into the system at the beginning.Consider the fault efficiency factors and bias fault as: , , , , . For the Nussbaum function, we select , .d i (t )ψi −1(t )ψi u i Simulation results under the proposed scheme are depicted in Figs. 1(a)−1(d), Figs. 1(a) and 1(b) show the performance of output variable and and the desired reference d and , respec-tively. It can be observed from these two figures that the tracking errors converge to zero asymptotically despite of unknown direction faults occurring on the actuators, which means that the proposed con-trol scheme can completely compensate for the influence by the fault to the system. Fig. 1(c) shows the practical positions of four vehicles,which can be seen that all followers move to the line, and 2-D driv-ing scene is achieved. Fig. 1(d) shows the curve of control input .Generally, according to the simulation results, it is obvious that the tracking errors converge to zero asymptotically while the whole sig-nals of closed-loop systems are bounded.To better exhibit the effectiveness of the presented scheme, we make a comparison on convergence results between the presented scheme in this letter and existing control scheme in [7]. From the comparison in Fig. 2, it is very clear that the tracking errors in this letter are much more satisfactory than those in [7].Conclusion: In this letter, 2-D vehicular platoon asymptotic track-ing sliding-mode control under unknown directions actuator faults has been investigated. By using the Nussbaum function, the disad-vantageous factors brought by the unknown direction actuator faults can be attenuated effectively. Based on the sliding-mode control and bounded estimation approach, a new asymptotic tracking controlmethod is presented to realize the asymptotic convergence of track-ing errors. Simulations verify the performance of the proposed approach.Acknowledgment: This work was supported in part by the Funds of National Science of China (61973146, 62173172), the Distin-guished Young Scientific Research Talents Plan in Liaoning Province (XLYC1907077, JQL201915402), and the Applied Basic Research Program in Liaoning Province (2022JH2/101300276)ReferencesY. Li, C. Tang, S. Peeta, and Y. Wang, “Nonlinear consensus-basedconnected vehicle platoon control incorporating car-following interactions and heterogeneous time delays,” IEEE Trans. Intelligent Transportation Syst., vol. 20, no. 6, pp. 2209–2219, Jun. 2019.[1]G. Guo and D. Li, “Adaptive sliding mode control of vehicular platoonswith prescribed tracking performance,” IEEE Trans. Vehicular Techno -logy , vol. 68, no. 8, pp. 7511–7520, Aug. 2019.[2]X. Ge, S. Xiao, Q.-L. Han, X. M. Zhang, and D. Ding, “Dynamic event-triggered scheduling and platooning control co-design for automated vehicles over vehicular ad-hoc networks,” IEEE/CAA J. Autom. Sinica ,vol. 9, no. 1, pp. 31–46, Jan. 2022.[3]Z. Zuo, C. Liu, Q.-L. Han, and J. Song, “Unmanned aerial vehicles:Control methods and future challenges,” IEEE/CAA J. Autom. Sinica ,vol. 9, no. 4, pp. 601–614, Apr. 2022.[4]J. Wang, X. Luo, W. Wong, and X. Guan, “Specified-time vehicularplatoon control with flexible safe distance constraint,” IEEE Trans.Vehicular Technology , vol. 68, no. 11, pp. 10489–10503, Nov. 2019.[5]X. Ge, Q.-L. Han, J. Wang, and X. M. Zhang, “A scalable adaptiveapproach to multi-vehicle formation control with obstacle avoidance,”IEEE/CAA J. Autom. Sinica , vol. 9, no. 6, pp. 990–1004, Jun. 2022.[6]X. G. Guo, W. D. Xu, J. L. Wang, and J. H. Park, “Distributedneuroadaptive fault-tolerant sliding-mode control for 2-D plane vehicular platoon systems with spacing constraints and unknown direction faults,” Automatica , vol. 129, p. 109675, 2021.[7]Z. Zhang, S. Xu, and B. Zhang, “Asymptotic tracking control ofuncertain nonlinear systems with unknown actuator nonlinearity,” IEEE Trans. Autom. Control , vol. 59, no. 5, pp. 1336–1341, May 2014.[8]Z. Zhang, S. Xu, and B. Zhang, “Exact tracking control of nonlinearsystems with time delays and dead-zone input,” Automatica , vol. 52,pp. 272–276, 2015.[9]W. Wang, J. Huang, C. Wen, and H. Fan, “Distributed adaptive controlfor consensus tracking with application to formation control of nonholonomic mobile robots,” Automatica , vol. 4, no. 50, pp. 1254–1263, 2014.[10]S. Y. Xiao and J. X. Dong, “Distributed fault-tolerant containmentcontrol for nonlinear multi-agent systems under directed network topology via hierarchical approach,” IEEE/CAA J. Autom. Sinica , vol. 8,no. 4, pp. 806–816, Apr. 2021.[11]X. Jin, X. Zhao, J. Yu, X. Wu, and J. Chi, “Adaptive fault-tolerantconsensus for a class of leader-following systems using neural network learning strategy,” Neural Networks , vol. 121, pp. 474–483, 2020.[12]H. Wang, W. Bai, and P. X. Liu, “Finite-time adaptive fault-tolerantcontrol for nonlinear systems with multiple faults,” IEEE/CAA J.Autom. Sinica , vol. 6, no. 6, pp. 1417–1427, Nov. 2019.[13]G. Guo, P. Li, and L. Y. Hao, “Adaptive fault-tolerant control ofplatoons with guaranteed traffic flow stability,” IEEE Trans. Vehicular Technology , vol. 69, no. 7, pp. 6916–6927, Jul. 2020.[14]C. Pan, Y. Chen, and I. Ali, “Adaptive fault-tolerant control forautonomous vehicle platoon against fault,” in Proc. CAA Symp. Fault Detection, Supervision, Safety Technical Processes , 2021, pp. 1–5.[15]L. Y. Hao, H. Zhang, H. Li, and T. S. Li, “Sliding mode fault-tolerantcontrol for unmanned marine vehicles with signal quantization and time-delay,” Ocean Engineering , vol. 215, p. 107882, 2020.[16]Z. T. Ding, “Adaptive consensus output regulation of a class ofnonlinear systems with unknown high-frequency gain,” Automatica ,vol. 51, no. 7, pp. 348–355, 2015.[17]J. J. Slotine and W. Li. “Applied nonlinear control,” in EnglewoodCliffs , New Jersey, USA: Prentice Hall, 1991, vol. 199, no. 1, pp.1–461.[18]1050−5−10e (t ),i = 1, 2, 3, 45L 0F F F F t (s)(a) Spacing errors e i (t )1015Δ−Δ−e (t )e (t )e (t )e (t )0.20−0.2−0.4e (t ),i = 1, 2, 3, 4t (s)(b) Deflection angle errors e ψi (t )33323130292827y (t ),i = 1, 2, 3, 450100150200250300350400x (t ), i = 1, 2, 3, 4(c) 2-D driving scene 450500400020000−2000−4000u (t ),i = 1, 2, 3, 45t (s)(d) Control input u i (t )1015u (t )u (t )u (t )u (t )Fig. 1. Simulation results of this letter.1050−5−10e (t ),i = 1, 2, 3, 41050−5−10e (t ),i = 1, 2, 3, 41050−5−10e (t ),i = 1, 2, 3, 4t1050−5−10e (t ),i = 1, 2, 3, 45t (s)(a) e 1(t )10155t (s)(b) e 2(t )1015(c) e 3(t )5t (s)(d) e 4(t )10155t (s)1015e (t ) in this letter e (t ) in [7]e (t ) in this letter e (t ) in [7]e (t ) in this letter e (t ) in [7]e (t ) in this letter e (t ) in [7]e i (t )Fig. 2. Comparison results of .1354IEEE/CAA JOURNAL OF AUTOMATICA SINICA, VOL. 10, NO. 5, MAY 2023。

如何远离极端伴侣英语作文

如何远离极端伴侣英语作文How to Avoid an Extremist Partner。

Having an extremist partner can be a challenging and even dangerous situation. Whether it's their extreme views, behavior, or actions, being in a relationship with someone who is extreme can have negative effects on your mental and emotional well-being. In this essay, we will discuss some strategies for avoiding an extremist partner and maintaining a healthy and balanced relationship.First and foremost, it's important to recognize the signs of extremism in a partner. This can include extreme political or religious views, controlling behavior, aggression, or a lack of empathy. If you notice any of these signs in your partner, it's important to take them seriously and consider whether the relationship is healthy for you.One strategy for avoiding an extremist partner is toset clear boundaries from the beginning of the relationship. This means being upfront about your own values and beliefs, and making it clear that you will not tolerate extreme or abusive behavior. By setting these boundaries early on, you can avoid getting involved with someone who has extremist tendencies.Another strategy is to seek support from friends, family, or a therapist. If you are in a relationship withan extremist partner, it's important to have a support system in place to help you navigate the challenges that may arise. This can include seeking advice from trusted friends and family members, or seeking professional help from a therapist who can provide guidance and support.It's also important to prioritize self-care and self-love. If you find yourself in a relationship with an extremist partner, it's easy to lose sight of your ownwell-being. It's important to take care of yourself and prioritize your own mental and emotional health. This can include engaging in activities that bring you joy, seeking out positive and supportive relationships, and settingboundaries to protect yourself from any harmful behavior.If you find yourself in a relationship with an extremist partner and feel that you are in danger, it's important to seek help immediately. This can include reaching out to a trusted friend or family member, seeking support from a domestic violence hotline, or contacting law enforcement if necessary. Your safety should always be the top priority, and it's important to take action if you feel threatened in any way.In conclusion, being in a relationship with an extremist partner can be challenging and even dangerous. By recognizing the signs of extremism, setting clear boundaries, seeking support, prioritizing self-care, and taking action if necessary, you can avoid getting involved with an extremist partner and maintain a healthy and balanced relationship. Remember that your safety and well-being should always be the top priority, and don't hesitate to seek help if you feel that you are in danger.。

睡眠障碍与多囊卵巢综合征相关性的Meta分析

顾方韵，侯丽辉，夏小焱，孙淼，李妍，郝松莉【摘要】目的：系统评价睡眠障碍与多囊卵巢综合征（PCOS）的相关性。

方法：计算机检索中国期刊全文数据库（CNKI）、万方数据库、PubMed、Web of Science、The Cochrane Library、Embase数据库，搜集关于睡眠障碍与PCOS的病例-对照研究，检索时限为建库至2020年1月1日。

由2位研究者独立筛选文献、提取资料并评价纳入研究的偏倚风险，采用Stata12.0软件进行Meta分析。

结果：共纳入8个研究，包括1735例PCOS患者和1671例对照者。

Meta分析结果显示：PCOS组匹兹堡睡眠质量指数（PSQI）评分（WMD=2.89，95%CI：0.13～5.64，P=0.040）及睡眠障碍发生率（OR=2.26，95%CI：1.02～4.97，P=0.044）均高于对照组。

结论：睡眠障碍与PCOS有一定相关性，受纳入研究的数量和质量的限制，尚待更多高质量研究予以验证。

【关键词】多囊卵巢综合征；睡眠障碍；病例对照研究；Meta分析；偏倚（流行病学）Association of Sleep Disturbances and Polycystic Ovary Syndrome:A Meta-Analysis GU Fang-yun，HOULi-hui，XIA Xiao-yan，SUN Miao，LI Yan，HAO Song-li.Heilongjiang University of Chinese Medicine，Harbin150040，China（GU Fang-yun，XIA Xiao-yan）；First Affiliated Hospital，Heilongjiang University of ChineseMedicine，Harbin150040，China（HOU Li-hui，SUN Miao，LI Yan，HAO Song-li）Corresponding author：HOU Li-hui，E-mail：*********************【Abstract】Objective:To review the association of sleep disturbances and polycystic ovary syndrome(PCOS).Methods：PubMed,Web of Science,The Cochrane Library,Embase,CNKI and Wan Fang Data databaseswere electronically searched to collect the case-control studies on the association of sleep disturbances and PCOS.Two reviewers independently screened literatures,extracted data and assessed the risk of bias of included studies.Then,meta-analysis was performed using Stata12.0software.Results：A total of8case-control studies wereincluded,in which1735patients were in the case group and1671in the control group.The results of meta-analysis showed:there were significant differences between the two groups in PSQI scores(WMD=2.89,95%CI:0.13-5.64,P=0.040)and sleep disturbances frequency(OR=2.26,95%CI:1.02-4.97,P=0.044).Conclusions：Thecurrent evidence shows that sleep disturbances is associated with PCOS.Due to the limited quality and quantity ofthe included studies,more high quality studies are required to verify above conclusion.【Keywords】Polycystic ovary syndrome；Sleep disorders；Case-control studies；Meta-analysis；Bias(epidemiology)（ＪＩｎｔＲｅｐｒｏｄＨｅａｌｔｈ蛐ＦａｍＰｌａｎ，2020，39：276-279）·论著·基金项目：国家中医药管理局2014年全国名老中医药专家传承工作室建设项目（2014-9-10）；国家自然科学基金（81804138）；国家中医药管理局2015年度国家中医临床研究基地业务建设科研专项课题（JDZX2015059）作者单位：150040哈尔滨，黑龙江中医药大学（顾方韵，夏小焱）；黑龙江中医药大学附属第一医院（侯丽辉，孙淼，李妍，郝松莉）通信作者：侯丽辉，E-mail：*********************多囊卵巢综合征（polycystic ovarian syndrome，PCOS）是一种复杂的内分泌失调性疾病，其发病原因尚未明确，症状和体征具有高度异质性，影响女性生殖、内分泌、代谢和心理等多方面健康状态[1]。

CollectiveDisturbance

Collective DisturbanceSandra L. Bloom, M.D.A “collective disturbance” is a common groupphenomenon representing a profounddisturbance in the communication network,unfolding when conflict higher in a hierarchy isbeing actually played out lower in the hierarchy,without anyone recognizing that there is adestructive parallel process going on. The level ofimmediate stress, collective emotionalintelligence and health of the communicationsystem in an organization is likely to determinehow rapidly and effectively a group manages this common but largely unconscious phenomenon. The level of emotional intelligence in an organization is likely to determine how rapidly and effectively a group manages a collective disturbance, a specific form of parallel process.Stanton and Schwartz wrote the first sociological study of the mental hospital in 1954. One of their most valuable observations centered on the role of covert conflict. They demonstrated that a covert conflict on the part of one subgroup, i.e. the staff, influenced another subgroup or the entire group in ways that were not ascribable to the individual interactions and that could lead to severe and pathological dysfunctions unless the conflict were surfaced (Stanton and Schwartz, 1954). It became clear to researchers that individual patients who became the focus of attention on a psychiatric unit were those who were the subject of unexpressed staff conflict and that as soon as the staff conflict was surfaced, the individual patients’ behavior improved [1].Similarly, collective disturbances involving several patients or an entire unit could be traced to conflicts originating near the top of the institutional hierarchy and the intensity of emotional interpersonal conflict could be followed down through the staff and into the patient community. These originating conflicts usually seemed to revolve around disagreements between the priorities of institutional purposes or incompatibility between a given purpose and some institutional need. The signs of an impending collective crisis were abundant: errors in technique, doors left unlocked, messages forgotten, increased absenteeism frequently due to functional illness, staff preoccupation with problems of or with other staff, increased withdrawal by key staff members, increased sense of helplessness, breakdown in communication, missing or canceling meetings, inability to make decisions and finally, a sense that “something bad is going to happen”.If the evolving crisis was not attended to and resolved, violence on the part of several, although not all, patients would be the result If the managers and staff members were able to confront their ownunspoken conflicts they could prevent or at least terminate a collective disturbance and in doing so, reduce the level of violence within the therapeutic community.In the therapeutic community literature, this phenomenon has been remarked upon repeatedly. Caudill observed that there seemed to be a “covert emotional structure” in the psychiatric hospital that could not be explained by the underlying emotional reactions of separate individuals, nor by the emotional contagion effect that takes over a mob. He noted that these “fields” were primarily emotional and led to the collective disturbances that Stanton and Schwartz had noted. He observed that these collective disturbances proceeded in a four-step fashion. First there would be a period of mutual withdrawal which would be followed by open collective disturbances, dividing the patients and the staff. In the next part of the sequence, the group would form a “paired role group response” in which different parts of the community created paired alliances with another subgroup. Finally, this unstable balance of forces would give way to restitution in which conflict was surfaced, aired, and adequately resolved. What is of great interest is that throughout this sequence emotional communication between the various role groups, of which there were four - senior staff, residents, nurses, and patients - was maintained while cognitive communication broke down, than re-formed and finally re-established. This description is reminiscent of the individual nonverbal-verbal split that occurs as a result of an overwhelming and highly conflictual experience [2].Excerpt from William Caudill, “Occurrence of Collective Disturbances” in The Psychiatric Hospital as a Small Society, 1958,In a general way, a collective disturbance usually refers to a situation in which the majority of patients on a ward become upset at one time, although as will be seen later the disturbance is probably much wider and includes the staff.In the months preceding the outbreak of the collective disturbance, the senior staff members were engaged in trying to define their own roles, in determining therapeutic policy, and in finding ways to formalize the routines of the hospital so that these would serve to implement therapeutic goals. The residents tended to see therapeutic problems in terms of their individual patients and were opposed to formalized routine. Such disagreement placed the nurses in confusion about their responsibilities and what were the rules to be followed. In line with the effort at transition, a new activities program headed by a professional group worker, was started on the wards.This new program was felt as a threat by the occupational therapist and as another area of confusion in routine by the nurses. This unsettled state among the staff was reflected in the patients in a lack of certainty about what were correct and permitted actions. These questions of disagreement among role groups tend to remain covert and were not openly discussed at such expected points as the daily administrative conference. Such disagreements were, however, very often implicit in the discussion of plans for individual patients, who then became the vehicle through which differences of opinion were expressed.Some two months before the collective disturbance, the observations clearly indicate that the various role groups had attempted to ease the difficulty of the situation by a process of mutual withdrawal in which each role group concentrated on the tasks which it felt were most sharply defined for its members and limited its interaction with other role groups to ‘neutral’ activities.What appeared to have happened was that an adjustive process of defense against the stresses of change and reorganization in the hospital policy was taking place within each group and looked at from the point of view of each separate group was reduced by the defenses used; but, looked at from the point of view of the hospital system as a whole, stress was increased, because all groups were still part of the hospital.In such a state of mutual withdrawal, cognitive communication had been disrupted, while affective communication was still going on, although the members of various groups were not aware of precisely why they seemed to be sharing certain feelings.The second type of balance of forces which occurred was initiated by the peak of acute difficulties and may be called the period of open collective disturbance. Just prior to the open collective disturbance two key members of the patient group were discharged, and this resulted in a fragmentation of the group structure on the ward. At the same time, two patients who were very upsetting to the patient group were admitted. The patients could not, at this point, reform adequate companionable groups, and, in various ways, appealed to the staff for greater control over their activities. Because of the state of mutual withdrawal, the patients’ attempts at communication did not get through in a meaningful way to the staff, and the open collective disturbance ensued.During the open collective disturbance, the patients were unable to maintain a state of relative equilibrium in the face of events on the ward, and the integration of the patient group was shattered. Following the outbreak of open disturbance on the ward, the staff were at first bewildered and then were divided in their efforts to help the patients… a situation was created in which the residents identified themselves with the patients, and the nurses with the senior physicians. This forms the third type in the sequence of structural balances – and may be called a paired role group response which was taking place in a social field that was seriously split apart.During this time, cognitive communication was somewhat better between the role groups which were paired with each other, but the two sets of pairs were not in communication on a cognitive basis – indeed, there was active resistance to this type of communication, as when the residents withheld information from the administrative conferences. Affective communication, however, in the sense of emotional discharge, continued to spread throughout all role groups in the hospital system as it had done during the preceding periods of mutual withdrawal and open collective disturbance.Two other matters of importance can be seen: (1) the expression of disagreement indirectly through the medium of the individual patient; and (2) the concentration on the ‘defiance and rebellion’ within the patient group, without bringing out the possibility of similar feelings present among the residents and nurses.Such an unstable balance of forces could not persist and, after several weeks, the discrepancies between the procedures followed by the residents in granting privileges to patients and the general policy of the hospital on this matter were ‘discovered’. This led to several conferences in which the real disagreements between the various staff role groups were openly discussed, and the operation of the hospital returned to a more stable equilibrium. This process of restitution comprises the fourth type in the sequence of balance of forces.In subsequent conferences a great many further topics were discussed. These included: (1) the difficulties the resident staff had in presenting their cases to the senior staff; (2) the senior staff’s supervision of the therapy done by the residents; (3) the whole area of the administrative management of patients and its effect upon therapeutic progress; (4) the financial situation of the patient and the meaning of this both therapeutically and administratively; and (5) the practical and emotional needs of ward personnel and residents which had to be satisfied in order for them to function effectively in the hospital.During all four phases of the collective disturbance outlined in this chapter, affective communication between the various role groups was maintained, but the lines of cognitive communication were at first broken, then re-formed rather strangely in the period of paired role group response, and only finally re-established during the period of restitution. Thus the covert emotional structure of the hospital was operative throughout the three-months’ cycle that included the acute period of the open collective disturbance, but the spread of emotions in the system was not supported by the effective operation of the overt social structure, which was fractured and twisted in many ways before it returned to normalcy.The process referred to here as a collective disturbance is not necessarily bad, and, in fact, much good can come of it. A hospital (or any other organization for work) which did not have some rhythm in its activities would not be a good hospital, it would be a dead one. The opposite is also obviously true – the ups and downs in everyday life can reach too great proportions for adequate functioning. In between a state of extreme oscillation and one of dead calm there is much to be learned from such processes and many ways in which they can be put to use for truly therapeutic ends.Rapaport (1956)…indicates that “these tension states need not be seen as antitherapeutic and therefore categorically to be avoided. On the contrary, they may have therapeutic value”. He proposes the term ‘sociotherapy” for the activities associated with the didactic, beneficial resolution of these tension states. Concerning this he says: “The resolution of a hidden staff conflict might alleviate a patient’s disturbance and thus be beneficial but it would only become sociotherapeutic if it were done to the accompaniment of an analysis of the patterned personal significance of the development and alleviation of discordant relationships for those concerned.The conclusion would appear to be that rather than attempting to do away with the processes that make up a collective disturbance (at bottom an impossible task because of the nature of both staff and patients as human beings), what is needed is the development of methods for studying the covertemotional structure in its relation to the overt social structure with the goal of first coming to some understanding and then perhaps bringing about changes in both.References1. Stanton, A.H. and M.S. Schwartz, The Mental Hospital: A Study of Institutional Participation inPsychiatric Illness and Treatment. 1954, New York: Basic Books.2. Caudill, W., The Psychiatric Hospital as a Small Society. 1958, Cambridge, MA: Harvard UniversityPress.。