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土地可持续利用的动态度量于金方1,周 鹏2,任建兰1(1.山东师范大学人口 资源与环境学院,山东济南250014;2.济南市国土资源局,山东济南250014)摘要:完善土地持续利用的定量评价指标体系和评价方法乃是今后土地持续利用的重要课题,度量土地利用的可持续性应该遵循动态延续、面向区域、显示过程和突出目标的原则,据此建立一个动态地度量土地利用可持续性的指标体系,包括生产性、结构性、效率性、公平性、稳定性、协调性、恢复性和可控性8个准则层,每一个准则层选择一个综合指标。
关键词:土地可持续利用;动态度量;过程中图分类号:F301 文献标识码:A 文章编号:1005-8141(2005)04-0289-03Dynamic Measurem ent of Land -use Sustainability YU Jing -fang 1,ZHO U Peng 2,REN Jian-lan 1(1.Shandong Normal U niversit y,College of Population Resource and Envir onment,Jinan 250014;2.Bureau of Land and Resources in Jinan,Jinan 250014)Abstract:I t w as an impor tant task to build a perfect comprehensive indicators and met hod aiming at the measurement of land-use sus tainability.T his ar ticle g av e four important principles to measure the land use sustainability:dy namic and continuance,looking on regio n,r epresenting progress and bulging the tar get.As a result,an indicator including eight criterions was build up,and each one was measured by a compr ehensive index es.T hey w er e productiv ity,str ucture,efficiency ,equality ,stability,harmonizing capacit y,restorability and ad justing capacit y.Key words:land-use sustainability;dynamic measurement;prog ress收稿日期:2005-06-10;修改日期:2005-07-02作者简介:于金方(1981-),女,山东省潍坊市人,在读研究生,研究方向为区域可持续发展。
考研英语经济类文章常识及词汇表达考研英语经济类文章常识及词汇表达随着考研英语的考试时间越来越近，我们需要了解清楚经济类文章常识及词汇表达的重点知识。
店铺为大家精心准备了考研英语经济类文章知识点及词汇表达的指南，欢迎大家前来阅读。
考研英语阅读：经济类文章的知识和词汇表达1. 产能利用率(Capacity Utilization)产能利用率，也叫设备利用率，是工业总产出(total industrial output)对生产设备的比率。
简单的理解，就是实际生产能力到底有多少在运转发挥生产作用。
当产能利用率超过 95% 以上，代表设备使用率接近全部，通货膨胀(inflation)的压力将随产能无法应付而急速升高，在市场预期利率(market expected interest rate)可能升高情况下，对该国货币是利多。
反之如果产能利用率在 90% 以下，且持续下降，表示设备闲置过多，经济有衰退的现象，在市场预期利率可能降低情况下，对该国货币是利空。
2. 自然失业率(Natural Rate of Unemployment)自然失业率指充分就业下的失业率。
自然失业率即是一个不会造成通货膨胀的失业率(Non-accelerating Inflation Rate of Unemployment，NAIRU )，也是劳动市场处于供求稳定状态的失业率。
从整个经济看来，任何时候都会有一些正在寻找工作的人，经济学家把在这种情况下的失业称为自然失业率，所以，经济学家对自然失业率的定义，有时被称作"充分就业状态下的失业率"，有时也被称作无加速通货膨胀下的失业率。
例：America’s capacity utilization, for example, hit historically high levels earlier this year, and its jobless rate (5.6% in August) has fallen bellow most estimates of the natural rate of unemployment -- the rate below which inflation has taken off in the past. (1997年T ext5)译文：例如，美国的生产力利用率在今年前段时间创下了历史高水平，而它的失业率(8月份为5.6%)已降至低于对自然失业率的大多数估测——过去当比率低于自然失业率时，通货膨胀率已急剧上升。
Capacity：治理能力的“能力”，如何译成英文？近日落幕的四中全会，就实现治理体系和治理能力现代化，提出了“三步走”的总体目标。
近年来，“治理能力”在官方媒体上频繁出现，引起了国际上的关注，开始把治理体系和治理能力现代化，称为中国的第五个现代化。
在用英文表述“治理能力”时，国外的报刊网站上，有的称为Governance Capability，有些则使用Governance Capacity的说法。
中国的官方文件，似乎倾向于使用后一种译法，也就是Governance Capacity；十九大报告的英文版本，采用的就是这种译法。
英语中的“能力”在英语中，表示“能力”的词语，数量很多，常见的包括：Ability, Aptitude, Acumen, Capability, Capacity, Competence, Expertise, Facility, Proficiency, Talent…英语中的这些“能力”，来源出处各不相同，同时也各有不同的含义和用法，很多时候不能互换通用。
Capacity这种“能力”，偏向于表示“抽象的能力”；和其它的各种“能力”比起来，更适合传达“治理能力”这个概念。
Capacity是英语中的常用词汇，在新闻媒体和图书出版的内容中，都能经常读到看到。
从学习英语的角度来说，Capacity这个词语值得全面理解并学会如何使用。
Capacity 的来源和用法Capacity这个词语，来源于古罗马的拉丁语，是通过法语进入英语词汇的。
在拉丁语中，Capacity的本来含义，是“包含、容纳”，同时还用来表示“掌握、持有”的意思。
在今天的英语词典中，Capacity除了表示“能力”，还有多种不同用法，都是源于“容纳、容积”的这种意象概念。
Capacity最常用的含义，是指一个空间所能够容纳的物品数量，这里的“空间”包含各种广义和狭义的空间，既包括小型的瓶罐容器，也包括大型的房屋建筑。
辩论：能力比责任重要英文回答：Capability is undoubtedly a crucial attribute for individuals and societies alike. It empowers us to achieve our goals, overcome challenges, and make meaningful contributions to the world. However, while capability is essential, I firmly believe that responsibility holds greater significance in shaping our lives and the well-being of others.Responsibility encompasses a sense of duty, accountability, and the willingness to answer for our actions. It reminds us that our choices and behaviors have consequences, not only for ourselves but also for those around us. As responsible individuals, we recognize the impact we have on our communities and strive to act in ways that benefit the greater good.Consider the example of a talented artist who possessesexceptional painting skills. While their capability enables them to create beautiful works of art, it is their sense of responsibility that drives them to use their talent for meaningful purposes. They may choose to paint murals in underprivileged neighborhoods, inspiring young minds and bringing joy to the community. Their art becomes a vehicle for social change and personal growth.In contrast, individuals who prioritize capability over responsibility may face moral dilemmas and ethical conflicts. They may possess great knowledge or abilities but lack the integrity to use them wisely. History is replete with examples of brilliant minds who succumbed to the temptations of power and wealth, ultimately causing harm to others.Moreover, responsibility fosters a sense of community and belonging. When individuals embrace their responsibilities, they contribute to the collective well-being of society. They volunteer their time, participate in local organizations, and work towards common goals. By taking ownership of our actions and decisions, we create amore cohesive and supportive social fabric.In the realm of technology, the debate betweencapability and responsibility becomes particularly relevant. Advances in artificial intelligence (AI) have created immense potential for progress and innovation. However, itis our responsibility as users and developers to ensurethat AI systems are deployed ethically and sustainably. We must consider the societal implications and potential risks associated with AI and act responsibly to prevent any negative consequences.In conclusion, while capability provides us with the means to act, it is responsibility that guides our actions, ensuring that we use our powers for good. Responsibility cultivates moral character, promotes social harmony, and empowers us to make meaningful contributions to society. By embracing responsibility as the guiding principle of our lives, we create a world where talent and abilities are harnessed for the betterment of humanity.中文回答：在我看来，责任比能力更重要，它塑造着我们的生活和影响着他人。
2021年考研《英语二》考前冲刺试卷及解析2021年考研《英语(二)》模拟试卷Section I Use of EnglishDirections:Read the following text. Choose the best word(s) for each numbered blank and mark A, B, C or D on ANSWER SHEET 1. (10 points) Use of EnglishDirections:Read the following text. Choose the best word(s)for each numbered blank and mark A, B, C, or D on ANSWER SHEET 1.(10 points)Among the thousands of business schools now operating around the world you would be hard-pressed to find one that doesn't believe it can teach the skills of entrepreneurship. However, of the people who immediately 1 to mind when one thinks of entrepreneurs——Bill Gates, Richard Branson or Oprah Winfrey, for example—few have done more than 2 a speech at a business school. 3 , a recent study by King's College in London has suggested what many intuitively 4 : that entrepreneurship may actually be in the blood—more to do with genes than classroom experience. All of which 5 the question—does anentrepreneur really need a business-school education?Not surprisingly some of the best-known schools in the field have a 6 answer to this: they don't actually profess to create entrepreneurs, 7 they nurture innate ability. Or as Timothy Faley of the entrepreneurial institute at Michigan's Ross School of Business 8 it: “A good idea is not enough. You need to know how to 9 a good idea into a good business.”Schools do this in a number of ways. One is to 10 that faculty are a mix of classic academics and businesspeople with experience of 11 their own successful firms. They can also create “incubators” where students 12 ideas and rub shoulders on a day-to-day basis with the external business world, receiving both advice and hard cash in the form of investment.Arguably such help is now more important than ever. The modern entrepreneur is faced with a more 13 world than when Richard Branson began by selling records out of a phone box. According to Patrice Houdayer, head of one of Europe's best-known entrepreneurship schools, EMIYON in France, new businesses used to move through a 14 series of growth steps —what he terms garage, local, national and international. Now however, 15 the communications revolution, they can leapfrog these stages and go global more or less straightaway—encountering a whole new 16 of problems and challenges. In this 17 Professor Houdayer maintains that the increasingly 18 nature of MBA classes can help the nascent entrepreneur in three ways: by plugging them into an international network of contacts and advisors, by preparing them for the pitfalls and opportunities 19 with dealing across different cultures and by 20 them to the different ways that business is conducted around the globe.1.[A]bring [B]call [C]spring [D]apply2.[A]report [B]deliver [C]prepare [D]compose3.[A]Indeed [B]Likewise [C]Therefore [D]Furthermore4.[A]conclude [B]assume [C]neglect [D]suspect5.[A]stirs [B]arouses [C]proves [D]invites6.[A]ready [B]unique [C]positive [D]favorable7.[A]yet [B]rather [C]nor [D]nevertheless8.[A]states [B]makes [C]puts [D]interprets9.[A]shift [B]transfer [C]modify [D]transform10.[A]ensure [B]assure [C]affirm [D]enlighten11.[A]carrying on [B]setting up [C]working out [D]turning around1 2. [A]convey [B]cherish [C]nurture [D]impart13.[A]complex [B]complicated [C]complementary[D]fantastic14.[A]variable [B]obvious [C]imperative [D]distinct15.[A]thanks to [B]but for [C]for all [D]next to1 6. [A]bulk [B]host [C]set [D]magnitude1 7. [A]position [B]context [C]perspective [D]dimension18.[A]similar [B]differential [C]diverse [D]versatile1 9. [A]interacted [B]combined [C]confronted[D]associated20.[A]entitling [B]exposing [C]leading [D]committing1234567 2021年考生必读：·2021年考研考前一周必看精华收藏·临考必备生活及学习建议·考前准备手册 | 考前注意事项 | 答题时间分配 | 考场规则 | 考试流程·作文：作文预测及热门话题摘要写作范文高分范文作文真题及范文·政治：考点预测时事政治形势与政策热门考点经典资料终极预测卷历年真题·英语：命题特点与规律分析专项冲刺必备终极预测卷历年真题·数学：命题趋势预测点题最后冲刺题21套历年真题·专业课：历年真题命题规律分析临考提醒·[2021年国内时政冲刺要点归纳] [考研考前三天公共课备考策略及必读资料]2021年公共课答题技巧和建议 | 免费：考研各科在线预测题100套·2021年考研考前必备十大临场技巧 | 2021年考研初试应考必读实用宝典·考后第一时间发布试题答案 | 2021年1月考研成绩查询短信免费提醒·2021，又是一年考研时，写心愿，送祝福! | 准考证发放、领取及查收通知汇总Section II Reading ComprehensionPart ADirections:Read the following four texts. Answer the questions below each text by choosing A, B, C or D. Mark your answers on ANSWER SHEET 1. (40 points)Text 1What's a label worth? A lot, it seems. Michael Hiscox and Nicholas Smyth, two Harvard University researchers, conducted an experiment on two sets of towels in an upmarket New York shop. One lot carried a label with the logo “Fair and Square” and the following message: These towels have been made under fair labour conditions, in a safe and healthy working environment which is free of discrimination, and where management has committed to respecting the rights and dignity of workers.The other set had no such label. Over five months, the researchers observed the impact of making various changes such as switching the label to the other set of towels and raising prices. The results were striking: not only did sales of towels increase when they carried the Fair and Square label, they carried on increasing each time the price was raised.No wonder companies are keen to appeal to ethically (i.e. morally)minded consumers, whether on labour standards or greencredentials. Timberland, a New Hampshire outdoor-gear company, is introducing detailed "Green Index” labels on its shoes. Tesco, M&S and Wal-Mart have all launched initiatives that bet on the rise of the ethical consumer.M&S estimates that about three-quarters of British consumers are interested in the green theme in some way. But even the keenest ethical consumer faces complicated situations, and sometimes the apparently obvious ethical choice turns out to be the wrong one. Surely it must be greener for Britons to buy roses from the Netherlands than ones air-freighted from Kenya? In fact, a study showed that related green house gas to the Dutch roses to be six times as large because they had to be grown in heated greenhouses.Joel Makower, editor of , says that, given a choice, most consumers will choose the greener product—provided it does not cost any more, comes from a trusted maker, requires no special effort to buy or use and is at least as good as the alternative. “That's almost an impossible barrier for any product,” he notes.So shoppers will still flock to shops selling cheap products of decent quality, ignoring how these are made. They will often buy more if a product is attractively presented,never mind that the packaging may be wasteful. And when companies try to do the right thing, consumers will not always go along with them.The lesson for companies is that selling green is hard work. And it is no good getting too far ahead of the customer. Half a step ahead is about right. Much more, and you won't sell. Any less, and you won't lead.21.The experiment on the towels indicated that ______.[A]consumers liked to purchase labeled products[B]consumers would buy goods when prices rose[C]consumption was influenced by green labels[D]ethical concern may influence consumption22.According to the text, consumers’ ethical choice ______.[A]determines the production of commodities[B]forces companies to sell green products only[C]leads companies to modify business activities[D]leads to higher labour and green standards23.We may infer from the fourth paragraph that ______.[A]green buying may be at higher environment cost[B]green production is actually complicated business[C]Dutch rose growth is greener than Kenya ones[D]British consumers actually oppose green farming24.According to Joel Makower, most consumers will ______.[A]buy greener products when given a choice[B]reject greener products for various reasons[C]pay more attention to the price of a product[D]refuse to follow the activities of companiespanies may learn the lesson that ______.[A]it is not worthwhile leading the customers[B]the customers are not easily to be misled[C]green policy is not effective for marketing[D]companies need a balanced green policyText 2There are various ways in which individual economic units can interact with one another. Three basic ways may be described as the market system, the administered system and the traditional system.In a market system individual economic units are free to interact among each other in the marketplace. It is possible to buy commodities from other economic units or sell commodities to them. In a market, transactions may take place via barter or money exchange. In a barter economy, real goods such as automobiles, shorts, and pizzas are traded against each other. Obviously, finding somebody who wants to trade my oldcar in exchange for a sailboat may not always be an easy task. Hence the introduction of money as a medium of exchange eases transactions considerably. In the modern market economy, goods and services are bought or sold for money.An alternative to the market system is administrative control by some agency over all transactions. This agency will issue edicts or commands as to how much of each good and service should be produced, exchanged, and consumed by each economic unit. Central planning may be one way of administering such an economy. The central plan, drawn up by the government, shows the amounts of each commodity produced by the various firms and allocated to different households for consumption. This is an example of complete planning of production consumption, and exchange for the whole economy.In a traditional society, production and consumption patterns are governed by tradition: every person's place within the economic system is fixed by parentage, religion and custom. Transactions take place on the basis of tradition, too. People belonging to a certain group or caste may have an obligation to care for other persons, provide them with food and shelter, care for their health, and provide their education. Clearly, in a system where every decision made on the basis of traditionalone, progress may be difficult to achieve. A stagnant society may result.26.What is the main purpose of the passage?[A]To outline contrasting types of economic.[B]To explain the science of economic systems.[C]To argue for the superiority of one economic system.[D]To compare barter and money-exchange markets.27.In the second paragraph, the word “real” in “real goods” could best be replaced by which of the following?[A]High quality. [B]Concrete.[C]Utter. [D]Authentic.28.According to the passage, a barter economy can lead to ______.[A]rapid speed of transactions[B]misunderstandings[C]inflation[D]difficulties for the traders29.According to the passage, who has the greatest degree of control in an administered system?[A]Individual households. [B]Small businesses.[C]Major corporations. [D]The government.30.Which of the following is not mentioned by the authoras a criterion for determining a person's place in a traditional society?[A]Family background. [B]Age.[C]Religious beliefs. [D]Custom.Text 3If sustainable competitive advantage depends on work-force skills, American firms have a problem. Human-resource management is considered an individual responsibility. Labour is simply another factor of production to be hired—rented at the lowest possible cost—much as one buys raw materials or equipment.The lack of importance attached to human-resource management can be seen in the corporate hierarchy. In an American firm the chief financial officer is almost always second in command. The post of head of human-resource management is usually a specialized job, off at the edge of the corporate hierarchy. The executive who holds it is never consulted on major strategic decisions and has no chance to move up to Chief Executive Officer(CEO). By way of contrast, in Japan the head of human-resources management is central—usually the second most important executive, after the CEO, in the firm'shierarchy.While American firms often talk about the vast amounts spent on training their work forces, in fact they invest less in the skills of their employees than do either Japanese of German firms. The money they do invest is also more highly concentrated on professional and managerial employees. And the limited investments that are made in training workers are also much more narrowly focused on the specific skills necessary to do the next job rather than on the basic background skills that make it possible to absorb new technologies.As a result, problems emerge when new breakthrough technologies arrive. If American workers, for example, take much longer to learn how to operate new flexible manufacturing stations than workers in Germany(as they do), the effective cost of those stations is lower in Germany than it is in the United States. More time is required before equipment is up and running at capacity, and the need for extensive retraining generates costs and creates bottlenecks that limit the speed with which new equipment can be employed. The result is a slower pace of technological change. And in the end the skills of the population affect the wages of the top half. If the bottom half can't effectively staff the processes that have to be operated,the management and professional jobs that go with these processes will disappear.31.Which of the following applies to the management of human resources in American companies?[A]They hire people at the lowest cost regardless of their skills.[B]They see the gaining of skills as their employees' own business.[C]They attach more importance to workers than equipment.[D]They only hire skilled workers because of keen competition.32.What is the position of the head of human-resource management in an American firm?[A]He is one of the most important executives in the firms.[B]His post is likely to disappear when new technologies are introduced.[C]He is directly under the chief financial executive.[D]He has no say in making important decisions in the firm.33.The money most American firms put in training mainly goes to ______.[A]workers who can operate new equipment[B]technological and managerial staff[C]workers who lack basic background skills[D]top executives34.According to the passage, the decisive factor in maintaining a firm's competitive advantage is ______.[A]the introduction of new technologies[B]the improvement of worker's basic skills[C]the rational composition of professional and managerial employees[D]the attachment of importance to the bottom half of the employees35.What is the main idea of the passage?[A]American firms are different from Japanese and German firms in human-resource management.[B]Extensive retraining is indispensable to effective human-resource management.[C]The head of human-resource management must be in the central position in a firm's hierarchy.[D]The human-resource management strategies of American firms affect their competitive capacity.Text 4The public holiday on the last Monday of August marks, in most British minds, the unofficial end of summer. A vastmigration takes place, as millions take advantage of the long weekend to visit seaside resorts or fly to Europe in a final sun-seeking cheer. Once the festivities are over, gloom descends: workers face four months of uninterrupted labor until Christmas Eve, their next official day off.This depression often provokes calls for more public holidays, and this year the clamor has been louder than usual. David Cameron's new Conservatives have been forced to deny rumors that they would recommend three new public holidays. Earlier in the summer, two ministers suggested a worthy sounding “Britain Day”, intended to inspire civil pride. On August 27th the Institute for Public Policy Research, a worthy think-tank, called for a new day off to “celebrate community heroes”.To the idlers, the case for more time off looks persuasive. By European standards at least, Britain is a nation of workaholics, with only the Austrians labouring as many hours per week. Workers are entitled to 20 working days of leave a year, the European Union's required minimum. Other countries are more generous. France and Denmark give at least 25 days in leave, and many Finns get 30. Britons celebrate a miserably eight national holidays a year; in Europe only the Romanians,with five, have fewer. Even significant national events are celebrated grudgingly. ： the British were given two days off to celebrate the queen's Golden Jubilee in 2002, but had to forfeit an existing public holiday to make up for it.National holidays are illogical as well as scarce. The queen's official birthday(a moveable holiday unrelated to her date of birth)is seen as a good excuse for a holiday in most of Britain's former colonies, but not in Her Majesty's homeland. Distribution is also badly distorted: seven of the eight holidays fall between December and May, leaving only August's to break up the rest of the year.There are plenty of things that a new holiday might celebrate. Patriots suggest that England should honour St George(the patron saint of the place), just as Scotland takes time off for St Andrew. The historically minded argue for a Magna Carta(The charter of liberties)day, whereas the politically correct suggest holidays celebrating “communities” and “volunteering”.Sadly, not everyone is keen on increasing public holidays. The CBI, a business lobbying group, points out that legal leave is already planned to rise to 28 working days by 2021, and says that an extra public holiday would cost up to ￡6 billion($ 12.1billion). In the face of such tough objections, concerns about leisure and the quality of life may seem vague and idealistic.36.What is the passage mainly talking about?[A]Different attitudes towards public holidays in Britain.[B]The increase of national holidays in Britain.[C]The problem of public holidays in Britain.[D]The call for more public holidays in Britain.37.The calls for more public holidays in Britain could be the results of ______.[A]the economic depression[B]the 4-month work without a rest[C]the long wait for an official day off[D]recommendation of two ministers38.What does the word “workaholics”most probably mean(Line 2, Paragraph 3)?[A]Compulsive workers.[B]Idle workers.[C]Lazy workers.[D]Irrational workers.39.According to the passage, the increase of British working days of leave ______.[A]is supported by all British people[B]is planned by CBI to be carried out by 2021[C]is challenged by some opponents[D]is likely to result in economic recession40.Which of the following conclusions can we draw from the text?[A]From June to December, there is only one British national holiday.[B]British national holidays are unsatisfactory for the quantity and the allocation.[C]The queen’s official birthday is celebrated in England.[D]People suggest new holidays for their own convenience.Part BDirections:Read the following text and answer questions by finding information from the right column that corresponds to each of the marked details given in the left column. There are two extra choices in the right column. Mark your answer on ANSWER SHEET 1.(10 points)Most people may drink only two liters of water a day, but they consume about 3,000 liters a day if the water that goes into their food is taken into account. The rich gulp down farmore, since they tend to eat more meat, which takes far more water to produce than grains. So as the world's population grows and incomes rise, farmers will need a great deal more water to keep everyone fed: 2,000 more cubic kilometers a year by 2030, according to the International Water Management Institute(IWMI). Yet in many farming regions, water is scarce and likely to get scarcer as global warming worsens. The world is facing not so much a food crisis as a water crisis, argues Colin Chartres, IWMI's director-general.The solution, Mr Chartres and others contend, is more efficient use of water or, as the sloganeers put it, “more crop per drop”. Some 1.2 billion people live in places that are short of water. Farming accounts for roughly 70% of human water consumption. So when water starts to run out, farming tends to offer the best potential for thrift. But governments rarely charge farmers a market price for water. So they are usually more wasteful than other consumers—even though the value they create from the water is often less than households or industry would be willing to pay for it.The pressing need is to make water go further. Antoine Fr érot, the head of the water division of Veolia Environment, promotes recycling of city wastewater to be used in industryor agriculture. This costs less and cuts pollution.Yet as Mr Frérot himself concedes, there are many even cheaper ways to save water. As much as 70% of water used by farmers never gets to crops, perhaps lost through leaky irrigation channels or by draining into rivers or groundwater. Investment in drip irrigation, or simply repairing the worst leaks, could bring huge savings.Farmers in poor countries can usually afford such things only if they are growing cash crops, says David Molden of IWMI. Even basic kit such as small rainwater tanks can be lacking. Ethiopia, for example, has only 38 cubic meters of storage capacity per inhabitant, compared to almost 5,000 in Australia. Yet modest water storage can hugely improve yields in rain-fed agriculture, by smoothing over short dry spells. Likewise, pumping water into natural aquifers for seasonal storage tends to be much cheaper than building a big dam, and prevents the great waste of water through evaporation.Agronomists are beginning to devise tools to help monitor the efficiency of water use. Some have designed algorithms that use satellite data on surface temperatures to calculate the rate at which plants are absorbing and transpiring water. That allows governments and development agencies to concentratetheir efforts on the most prodigal areas.Raising yields does not always involve greater water consumption, especially when farms are inefficient. It would take little extra water to double cereal output in many parts of Africa, Mr Molden argues. IWMI reckons that some three-quarters of the extra food the world needs could be provided simply by bringing yields in poor countries closer to those of rich ones. That is more realistic than the absolute alternative: giving up meat and other thirsty products altogether.[A]cultivating cash crops41.The world is meeting with challenges more from[B]leaking irrigation system42.Farmers waste more water due to[C]expenses and efficiency43.Farmers in poor countries can pay for irrigation improvement by[D]surface temperature data44.Building big dams is less effective for their[E]low water price45.The water use rate of plants is computed with[F]water shortage[G]food crisisPart CDirections:In this section there is a text in English. Translate the text into Chinese. Write your translation on ANSWER SHEET 2.(15 points )The objective of any advertisement is to convince people that it is in their best interests to take the action the advertiser is recommending. The action may be to purchase a product or use a service.Advertising as a business developed most rapidly in the United States, the country that uses it to the greatest extent. In 1980 advertising expenditure in the U.S. exceeded 55 billion dollars, or approximately 2 percent of the gross national product.While advertising brings the economics of mass selling to the manufacturer, it produces benefits for the consumer as well. Some of those economies are passed along to the purchaser so that the cost of a product sold primarily through advertising is usually far less than one sold through personal sales people. Advertising brings people immediate news about products that have just come on the market. Finally, advertising pays for the programs on commercial television and radio and for about twothirds of the cost of publishing magazines and newspapers.Section III WritingPart A47Write a letter to invite your best friend Jane to take part in your mother's 60-year-old birthday and inform her of your arrangement.Begin your letter as follows:Dear Jane,You should write about 100 words on ANSWER SHEET 2. Do not sign your own name, using "Li Ming" instead. Do not write the address. (10 points)Part B48. Directions:In this section, you are asked to write an essay based on the following table. In your essay, you should1)describe the table and,2)state your opinions drawn from it.You should write at least 150 words.You should write neatly on ANSWER SHEET 2.(15 points)Financial Sources of College StudentsFinancial SourcesAmerican studentsChinese studentsParents50％90％Part-time jobs35％5％Scholarship15％5％2021年考研英语(二)模拟试卷答案Section I Use of English1.【答案】[C]spring【解析】上下文含义题。
普通词替换为高级词一、名词篇1.characteristic特征→attribute属性2.wealth→capital资本；财产；大写字母3.detail→chapter and verse详细内容；具体细节4.work together→in collaboration with与....合作5.all→comprehensive综合的；全部的；所有的(拓展：~ quality综合素质）、6.thought→consensus一致的意见；共识(拓展：reach a ~达成共识)7.responsibility→capacity职责、生产能力、办事能力(拓展：processing ~加工能力、heat ~热量、handling ~处置能力、承载力;financial ~财力）8.class→curriculum课程(拓展：core ~基础课程、~ vitae简历）9.consideration→construct/concept观念、概念、建筑物10.hospital→medial clinic医疗诊所、11.agreement→consent同意12.conflict→clash/dispute冲突、不协调；分歧；矛盾13.permission→charter许可证；豁免权；给予...特权(拓展：a ~ for纵容；~ fight 包机）14.copy→contribution稿件；捐款；促成作用(拓展：significant ~重大贡献；senda ~寄稿件）15.social attention→social concerns社会关注；社会关心16.environment problem→environment concerns环境问题17.meal→cuisine饭菜；菜肴(拓展：Haute~高级烹饪）18.promise→commitment承诺；保证；献身；投入(拓展：firm~坚定的信仰；prior ~首要义务；~ to someone对某人的忠诚）19.skill→craft手艺；技巧；诡计；骗术(拓展：~ brother同行；space ~太空船；art and ~工艺品）mon things→commonplace常见的事情；老生常谈21.power→competence能力；胜任；技能；本领22.serious→crisis危机；决定性时刻；关键阶段；转折点(拓展：home ~住房危机；~management危机处理）23.element→component/ingredient成分；部件24.behavior→conduct行为；经营方式；管理方法(拓展：~business做生意；code of ~行为准则）25.accommodation→compromise和解；妥协(拓展：~ between someone and someone else某人与某人之间的妥协；reach a~达成和解）26.awareness→consciousness意识；观念；看法(拓展：legal ~法律意识；nation ~国家意识；safety ~安全意识）27.protection→conservation保护、文物保护、28.rule→discipline训练；纪律；自制力；惩罚v；自我控制v(拓展：academic~学科；labour ~劳动纪律；sever~）28.disease→illness/condition疾病29.happiness→delight高兴；愉快；使高兴v（拓展：delight in sth以....为乐）30.tend→leaning/penchant嗜好；倾向；偏好31.dull→sameness千篇一律；单调32.shortcoming→downside负面；底侧35.character→trait特性36.many→a slew of许多37.supporter→proponent支持者二、动词篇1.finish→accomplish完成2.adapt→acclimate适应3.with→accompany by在...的陪伴下4.arrange→assign布置5.arrival→advent到来6.draw attention→appeal吸引7.improve→boost促进8.mix up→blend混合e→apply利用；应用10.e xplain—account for解释11.m eet…need→cater to满足某人的需要12.e nchant→captivate使…着迷13.g et over→conquer克服14.i mage→conceive想出，想象15.p rotection→conservation（文物）保护16.a rgument→contradiction矛盾;对立;不一致17.t ry→attempt尝试18.p unish→accuse指责19.p lant→cultivate种植;培养20.e xchange→convert转换;改变观点;归附、21.b uild→construct建筑;修建;创建22.m ake friend→cultivate建立(拓展：友谊）；获得(拓展：支持）;逐渐形成23.a gree→consent同意；允许(拓展：by common ~经过一致同意）24.m ix up→confuse(拓展：be confused with混淆)使...混淆；使.....迷惑25.j udge→criticize/dish out批评；责备(拓展：criticism against something对....的批评；criticism from something来自.....的批评）26.a rgue→clash公开整编；不协调；不相容27.p ursuit→chase追捕；镂刻；争取得到(拓展：~ after someone/something）、make up→compensate补偿、worry about→concern over为.....担心28.w rite→compose撰写讲稿、诗歌等；组成；作曲；使...镇静(拓展：compose music 作曲）29.r each a collaboration→sign a contract签订合同30.s uffer from a disease→contract a disease感染疾病31.s mall→compact小型的；紧密的32.r aise money→chip in凑钱；捐助33.s ort out→classify分类；将....分界34.f it→correspond相一致；符合；相当于35.s ave→conserve/maintain/preserve保存；节约；保藏36.g et over a difficulty→conquer difficulties克服困难37.c onsider→contend竞争；争夺；主张；认为38.d iscuss→deliberation商议；审议；从容；审慎39.d ifficulty→dilemma困境(拓展：moral~道德困境）40.r efuse to recognize→deny/restraint否认；克制；拒绝(拓展：~entry拒绝进入）、41.prove→demonstrate证明；证实；显露；演示41.d raw→depict描绘；刻画42.d evote→delicate奉献43.g ain→derive得到；获得(拓展：~ from sth 从获得；be ~from sth起源于）、44.purposely→consciously自觉地；有意识地44.o n time→on the dot按时的(拓展：the year dot很久以前）45.f ail→collapse突然失败；倒塌；贬值n/v(拓展：collapse strength破坏强度）、46.spread→permeate思想、情感等的传播(拓展：~through渗透入）46.a ct→execute实行；执行47.s uggest→propose提出；建议48.k eep→stick to坚持49.a ccept→take sb up on sth接受50.r educe→mitigate缓和；减轻51.r eplace→supplant取代52.c reate→usher开创53.c oncentrate on→be preoccupied with全神贯注于54.i nfluence→have an impact on对....有影响55.reflect→embody体现三、形容词篇1.enough→adequate足够的2.unknowable→vague未知的3.talktive→articulate善于表达的4.kind→benevolent有善心的5.can→be capable of6.strange→bizarre奇怪的7.honourable→glorious光荣的8.rude→crude粗鲁的、粗略的9.think→contend主张10.a ware→conscious有意识的，慎重的11.s erious→critical严重的、关键的、批评的、挑剔的12.s elf→control→continent自制的;节欲的13.i mportant→crucial关键的，重要的(拓展：crucial decision重要决策；crucial role 关键作用；crucial stage重要阶段）14.s pecial→unique/distinctive独特的15.n ormal→conventional墨守成规的；习惯的；平常的16.l ong→term→chronic长期患病的；拙劣的；难以根除的17.p ersonal→civil公民的；国民的；民事的(拓展：civil right公民权）18.c entre on→centralized集中的(拓展：centralized management集中管理）、19.energetic→dynamic动态的；精力充沛的；个性强的19.f irm→decisive果断的；坚决的；关键的20.w onderful→delicate食物美味的；光柔和的；令人愉快的；易碎的；纤弱的；细微的；体贴的(拓展：~ touch妙笔生花)21.b rave→desperate不惜冒险的；绝望的；孤注一掷的(拓展：~ act孤注一掷的举动；~ measures铤而走险的方法）22.i mmediate→direct直接的23.p urpose→deliberate故意的；存心的；仔细思考v24.n ational→domestic本国的；国内的；家用的；佣人n;家庭n(~market国内市场；~product本地商品；~industry国内行业）、25.d ifferent→diverse不同的；各种各样的26.c lever→flexible能适应新情况的；灵活的27.b asic→fundamental基本的28.e legant→grace优雅的29.k ind→gracious和蔼可亲的30.e nthusiasm→hospitable热情的；好客的31.m odest→humbly谦逊的32.s trong→intense强烈的33.p olite→respectable恭敬的；有礼貌的34.q uiet→static静止的35.f inally→ultimate最后的；最终的36.d evote oneself→give oneself to为...献身37.b e used to doing→be attuned to习惯；适应；熟悉38.f ruitful→productive富有成效的39.l ong→term→standing长期存在的40.v ery→a hell of非常；及其41.e ssential→radical彻底的；根本的42.s udden→abrupt突然的43.o ther→alternative可供替代的副词篇1.remarkably→dramatically显著的；戏剧的(~reduce急剧减少）2.almost→practically几乎连词篇1.about→be to do with与什么有关2.because→underlie成为......的原因；构成....的基础(拓展：these ideas underlie much of his work他的作品大部分是以这些主题思想为基础）3.according to→on the basis of根据4.because of→by the reason of由于5.so far→thus far到现在位置；迄今介词篇in→within the scope of在...的范围内英语作文常见错误1.主谓不一致：谓语动词的时态、语态、主谓一致等，如people后面用are而非is2.定冠词缺失,如enjoy the high consumption model；the center of the world;the Internet、in the BC13 century、where the climate and environment、protect the heart The majority大多数、the development of the Chinese economy、introduce the fame...3.特定称谓使用大写，如Moonlight group月光族、Dear Sir or Madam、Sincerely、festival Eve、Reunion meal以及国家名称4.年份表示错误，In the late 1990s上世纪90年代5.单词后面空格遗失或多出6.句子中要加因此，用therefore用逗号隔开7.单词的特殊过去分词，例如become→became→become8.名词单复数变化，例如the design s are made in European and American countries.、tea gardens茶园、one of the+复数9.名词单数复数变化，例如company→companies、different cultures、these days10.介词使用错误，例如the majority of China、with the help of、introduce sb sth to do sth、have a long history of 5000 years、the goal of doing sth、improve the efficiency of work、lose the competence to arrangement、the water in the system、the most important dinner of the year、a hole in the sheepfold11.常见拼写错误：certainly、environment、Though、other、writing、necessary、people、through、Nowadays、language、two、countries、cause、accompany、between、although、studying、challenges、decision、recommend、modern、opportunities、sincerely、popular、service、approaches、financial、support、increase、useful、question、library、business、the use of something、computer、ourselves Quickly、a lot of、natural、sound、neighbor、season、especially、draw、drink、healthy12.固定搭配错误，例如good for the economy 而非good to the economy、adapt to、at midnight13.句号后面使用大写14.定冠词多余，例如the technology中the多余、improve the people ‘s communication中的the 多余、satisfy the people ‘s request中the多余、improve the ability中the多余15.冠词缺失，例如it contributes to an increase in efficiency.(表示在某方面用in)It is an inconvenience to.......、a long time ago16.动词使用不当，例如表示提升写作能力用improve writing ability而非develop writing ability；表示取得进步用make progress而非get progress;表示在国外学习用learn abroad而非study17.平衡结构形式一致，如and连接的两个词语词性一致18.固定跟v+ing形式的词语:mean、instead of、prevent to doing…19.从句要用完整的结构，如When he is sick or has trouble.20.固定句型错误：It is said that而非there is said that、The first time the building was constructed.没有when20.缺少代词，如the water seeped into underground and introduce it to the face...21.从句缺少连接词，例如There are many places in China、where dumpling is an significant cuisine.Once upon a time, there was a man who raised a group of sheep.22.固定表达不当，例如one morning一个早上、the next day第二天、large loss 巨大损失。
Capacity Efficiency and Restorability of Path Protection and Rerouting in WDM Networks Subject to Dual FailuresDominic A.Schupke,Robert G.PrinzMunich University of TechnologyInstitute of Communication NetworksD-80290Munich,GermanyPhone:+498928923500,Fax:+498928923523Contact author:Dominic A.SchupkeE-mail:schupke,prinz@lkn.ei.tum.deAbstractResilient optical networks are predominately designed to protect against single failures offiber links.But in larger networks,operators also see dual failures.As the capacity was planned for single failures,disconnections can occur by dual failures even if enough topological connectivity is provided.In our approach the design of the network minimizes the average loss caused by dual failures,while single failures are still fully survived.High dual failure restorability is the primary aim,capacity isoptimized in a second step.For WDM networks with full wavelength conversion,we formulate mixed integer linear program-ming models for dedicated path protection,shared(backup)path protection,and path rerouting with andwithout stub-release.For larger problem instances in path rerouting,we propose two heuristics.Computational results indicate that the connectivity is of much more importance for high restorability values than the overall protection capacity.Shared protection has similar restorability levels as dedicatedprotection while the capacity is comparable to rerouting.Rerouting surpasses the protection mechanismsin restorability and comes close to100%dual failure pared to single failure planning,both shared path protection and rerouting need significantly more capacity in dual failure planning.Keywords:Multiple Failures,Path Protection,Rerouting,Path Restoration,WDM Networks.This paper has been revised and accepted for publication in PHOTONIC NETWORK COMMUNICA-TIONS.Citations to and quotations from this work should reference that publication.If you cite this work, please check that the published form contains precisely the material to which you intend to refer.1IntroductionOptical networks are subject to many kinds of disruptions,especially environmental disruptions and those caused by hardware failures and operational errors.The most important failure type is regarded as thefiber1cut,e.g.,caused by a backhoe.As such a cut typically breaks allfibers of afiber link,the end-nodes which were previously neighbors become disconnected.In order to re-establish the connectivity of disrupted paths, appropriate protection and restoration mechanisms are deployed in the network.Often these networks are designed to protect against single failures of suchfiber links at a time.But for larger and more connected networks dual failures—though much less probable than single failures—should be taken into account[1,2].This can be made plausible by the following calculation. Consider a network withfiber links of equal length,with km.Then afiber link has the availability of:MTBFshowing the details for dual failures and building the basis for the following evaluations is developed in Section3.Section4proposes two solving heuristics for one of the optimization models.Section5containsa performance evaluation based on different network instances.Finally,Section6concludes this article.1.1Related WorkTo the best of our knowledge,this is thefirst contribution on the design of path-level protected networks, taking dual failure states into account.References[1,3,4,5,6,7,8,9,10,11,12]deal with dual failures in networks with link restoration where the adjacent nodes restore a failed link,while we consider end-to-end path recovery.References[1,2,4,10]point out the significance of multiple failures and develop frameworks to classify recovery of multiple failures.Capacity and availability performance in presence of dual failures are also investigated in[13]for1+1protection,link restoration,and path restoration.The case study networks are not dimensioned under direct consideration of dual failures.For path rerouting,link overprovisioning is suggested to alleviate dual failure loss.The restorability of dedicated and shared path protection is also part of the study in[4],where the primary path and the protection path are found by an algorithm which reduces capacity costs,whereas we use mixed integer linear programming methods with inclusion of costs and dual failures.1.2Definitions and Failure ScenariosThe physical level is described by a graph with nodes and edges.The network’s nodes are interconnected byfiber links which are the edges,i.e.,an edge comprises allfibers between adjacent physical nodes,and will therefore be the entity which is subject to failure.A transmission channel link,or briefly link,denotes an individual transmission wavelength-channel between two adjacent nodes on an edge.In the networks, a path is a sequence of edges,while a connection,following a path,is described as a sequence of links.A demand-unit between two nodes is a request to carry a bidirectional client wavelength-channel over the network.Depending on the protection mechanism,a single demand-unit needs one or more connections within the network.The total number of demand-units between two nodes is called demand.Edges,links, connections,and paths are undirected to model bidirectional communications.The degree of a node is the number of its incident edges.A network is two-edge-connected(two-node-connected),if two edge-disjoint (node-disjoint)paths between any node pair in the network exist.We assume that edges fail independently,i.e.,the edges are mutually disjoint(enough)such that a single failure intrusion does not affect multiple edges.Since the recovery time of protection and rerouting is much shorter than the mean time between failures,we also assume that the second failure does not occur when thefirst failure(with recovery time)has not yet been recovered.Thereby,double failures are treated as ordered events(,),which means a failure of edge at some time and failure of edge at some time with and.32Considered Path-based Recovery MechanismsWefix our attention to dedicated path protection,shared(backup)path protection,and path rerouting.The reason for this focus is that thefirst recovery mechanism is widely employed today,and the latter two become attractive as the need for efficient recovery strategies emerges.Path rerouting is also an important candidate for networks requiring high multiple failure survivability.For comparability of the mechanisms,we make a set of assumptions:One type of recovery mechanism is used in the network and all connections are protected by this method.The paths are chosen based on a(central)global view on the network,such that optimal solutions can be found.In this way we can make comparisons for the best-case performance of the mechanisms.The networks are two-node-connected.2.1Dedicated Path ProtectionUsing dedicated path protection,two disjoint paths are selected for a demand-unit in the network.Dedicated path protection can be classified in1+1protection and1:1protection.In1+1protection the capacity on both paths is reserved exclusively for the corresponding demand-unit. See Figure1(a)for two dedicated protection demands,one between A-F,and one between C-D.The sender sends the signal and a copy of the signal on the two paths,respectively.The receiver selects one of the paths which is called the working path(solid line)in the failureless case,and switches to the other path,the protection path(dotted line)if a failure occurs on the working path.1:1protection is similar to1+1protection,except that the protection path does not transport a copy of the signal.Instead,upon a failure on the working path,sender and receiver switch to the protection path, which then carries the traffic.When no failure is present on one of the paths,the protection path can carry “low-priority”traffic,i.e.,traffic that will be pre-empted if a failure on the working path occurs.Note that the connection is lost if there is one failure on the working path and at the same time one failure on the protection path.In mesh networks with a noticeable level of dual failure probability,1+1pro-tection or1:1protection can thereby attain less availability than,e.g.,restoration[1].It is obvious that any chronological order of a double failure leads to the same result,i.e.,failure events and have the same loss value.2.2Shared Path ProtectionFor shared(backup)path protection a working path is provided,and additionally a backup path which is disjoint from the working path.The backup path can be shared with other connections,as long as the working paths are disjoint,e.g.,see Figure1(b)where the longer paths are shared.After a failure on the working path,the reserved protection path has to be configured(cross-connected)in the passed nodes before traffic can be carried along the protection path.4It claims attention that a connection can be lost,even if a failure pair does not simultaneously hit the working path and the protection path.This is caused,e.g.,in situations where the(shared)protection ca-pacity is optimized for single failures only.Figure2depicts an example network with four connections which should be provided by dedicated and shared path protection.Dedicated path protection in Figure2(a) needs most capacity,but is able to survive any dual failure,except for those which hit both disjoint con-nections simultaneously.Shared path protection as in Figure2(b)requires less capacity.However,as the capacity is planned for single failures,it cannot survive a double failure,e.g.,on edges A-B and C-D,since the shared diagonal edge has not sufficient reversed capacity.If more capacity is reserved on that edge, see Figure2(c),this dual failure can be pared to dedicated path protection,the shared path protection optimized for dual failures still needs less capacity.Unlike dedicated path protection,the order of a dual failure cannot be ignored.For example,the network in Figure3carries three working connections(solid lines),which are protected by protection paths(dotted lines).Assume at most one connection can be carried by all edges except for edge E-H which can carry two. Then a failure(A-B,H-E)effects a loss for two demand-units(F-H and D-H),whereas a failure(H-E,A-B) causes a loss for one demand-unit(A-B)only.For dual failures,a stub-release mechanism is conceivable in shared path protection.After thefirst failure,active backup paths can be disrupted by a second failure.These backup paths can be torn-down so that,afterwards,other backup paths can access the freed capacity.As this stub-release mechanism adds signaling complexity and is only needed for dual failures,we do not expect it to be implemented in the networks,and disregard stub-release for shared path protection in this article.Note that for path rerouting (Section2.3)the same stub-release mechanism works for both single and dual failures.2.3Path ReroutingUsing path rerouting,demand-units are served by single connections.If a failure disrupts a connection,it will be re-setup after the failure has been signaled to the end-nodes.Figure4shows an example offive connections between nodes A and D,which are disrupted by a failure.The subsequent re-setup restores the connection on two different paths.To allow the re-setup of affected connections,spare capacity is needed in the network.For the ease of comparison to path protection,we denote this additional capacity also as“protection capacity.”For rerouting featuring stub-release,affected paths are torn down before re-setup to make the used resources available again.Without stub-release,the paths maintain the reserved capacity.The former option allows for better capacity sharing,the latter offers faster restoration,and simple path reversion after failure repair.In a similar fashion,if enough capacity is available,any double failure can be survived,except if the network becomes disconnected,e.g.,by failures around nodes with degree two.The order of dual failure events is important to determine the paths after failure rerouting.Figure5 exemplifies this with a network having one capacity unit per edge and routed connections between A-F, B-E,and C-D(solid lines).If edge B-E fails,the B-E connection can be rerouted over B-F-E.If then edge A-F fails,the A-F connection cannot be rerouted,since edge B-F is unavailable.Hence,using B-F-E as rerouting path,a failure(B-E,A-F)yields a lost connection,but a failure(A-F,B-E)has no loss,since5rerouting paths A-B-F and B-D-E can be taken for A-F and B-E,respectively.Obviously,if we use for failure(B-E,A-F)path B-D-E as rerouting path of thefirst failure,this blocking could have been avoided. However,by symmetry,it will lead to a loss for the dual failure(B-E,C-D),since edge B-D is not available for the rerouting path C-B-D.3Optimization Models Including Dual Failure StatesFor the three recovery mechanisms we formulate mixed integer linear programming models taking double failures into account.Given connection-demands from nodes to nodes have to be fully provided and protected against single edge failures.We assume homogeneous transmission systems with wavelengths. An edge carriesfibers.A used link on edge has a cost.If not mentioned otherwise,the primary objective will be to minimize the average double failure loss of connections.The average is taken over all double edge failure occurrences.This planning objective puts an emphasis on highly available network designs.With secondary priority we aim to minimize the total cost.The optimization models are composed of given indexing sets,given parameters,solution variables,the objective,and constraints.First,we describe a simple provisioning model without protection in Figure6. This model is also a basis for the models in the following three subsections,since we just point out which different or additional formulations to the provisioning model are needed.The optimization procedure works with the set,the set of node pairs which have a demand relation, and the set of edges.For every,a set of paths is precomputed,where each path(of a total of paths)is described by the set of edges.The variable counts how many connections go over path. We introduce the auxiliary variable for the number of required links on edge.Constraints(4)ensure the demand is carried by the connections over the paths.For the edges,Equations(5)calculate the number of links,for which the capacity Constraints(6)apply.3.1Dedicated Path Protection ModelIn contrast to the unprotected provisioning model with one connection per demand-unit,in dedicated path protection two disjoint connections have to be set up for every demand unit.See the model in Figure7 which relates to the provisioning model in Figure6.We generate a set which stores for every demand pair the pairs of disjoint paths.Hence,for a path combination,one of and in is working path,and the other protection path.In the evaluation (Section5),we interpret the shorter path as working path,the longer as protection path.We introduce variables which count for each demand pair the number of connections taking path pair.The variables are the number of lost demand-units of pair,when the dual failure of edges and occurs.Objective(7)minimizesfirst of all the sum of the demands lost by all the dual failures(first sum). This objective also minimizes the average double failure loss of connections,since the average is just the sum scaled by the constantthat this objective is the primary objective and does not interfere with the by-objective(second sum)which minimizes the total cost.In other words,among the solutions with least average lost demands,we take the minimal-cost solution.Constraints(4)of the provisioning model are substituted by Equations(8),since connection pairs are re-quired.Constraints(9)determine the number of connections on path.Per failure and per pair,Con-straints(10)determine the number of lost demand-units by adding the traffic of those path-pairs which are simultaneously affected by the failure.As the chronological order of the dual failure events does not matter in dedicated path protection,Equations(11)can be introduced,to allow for substitutions of variables(e.g.,in a presolving step)and thus,to make the computation faster.3.2Shared Path Protection ModelThe shared path protection model,as depicted in Figure8,relates to the provisioning model in Figure6and the dedicated path protection model in Figure7.We generate a set which stores for every demand pair the pairs of disjoint paths.Hence,the path variation assigns the path in to the working path, and path to the protection path which can be shared.As a path can have the role of a working path or a shared protection path,the set has twice as much entries as the path pair set in dedicated protection. From the capacity and survivability point-of-view,the distinction between working and protection path is not necessary in dedicated protection.(Therefore,we deal with path variations here,rather than with path combinations.)We introduce variables which count for each demand pair the number of demand-units which take the path-pair.Variables represent the shared protection capacity on edge.Variables denote the capacity of protection path for demand-pair,if the second failure hits the working path and the protection mechanism has not been activated because of thefirst failure,i.e.,did not hit the working path.The variables,as in dedicated path protection,are the number of lost demand-units of pair if the failed edges are both on working and protection paths.For shared protection additionally the variables are necessary,which denote the number of lost demand-units of pair because of insufficient capacity on the shared protection path.Objective(12)minimizes the demand lost by dual failures,which has a portion due to joint working and protection path hits,and a portion caused by insufficient capacity.Again,the by-objective minimizes the total cost.The Constraints(8-10)from the dedicated path protection model apply also for shared path protection. We augment them by the capacity sharing constraints.In Constraints(13),we obtain the shared capacity on edge by amounts from single and dual failures.Thefirst sum also accounts for backup paths which become disrupted by second failures,since these paths are not stub-released(Section2.2).Since will be minimized using Constraints(14),which determine the required capacity on an edge,and Objective(12), these constraints determine the actually required capacity(minimax-relation).For double failures,Con-straints(15)equate the number of working connections which are affected by the second failure only and which do not have a failure on the corresponding protection connection,to the required number of protection connections for the second failure plus the number of lost connections due to insufficient capacity.7Shared path protection becomes coincident to path rerouting,since we can regard the former as a special case of the latter,where rerouted connections are restricted to take the same path for each failure.However, the corresponding model becomes more complex than the one in Figure8.3.3Path Rerouting ModelThe path rerouting model,again relating to the provisioning model in Figure6,is shown in Figure9.For the failureless state wefind connections to serve the demands,as well as rerouting paths for all connections which are affected by single edge failures and,where possible,by dual edge failures.The parameter indicates if stub-release is employed.Variables measure the amount of capacity on path for demand-pair if edge fails.Analogously does this for the dual edge-failure. On edge,and are working capacity and spare capacity,respectively.counts the number of lost demand-units of pair because of dual failure.Again with highest priority,Objective(16)minimizes the sum of the demands lost by all the dual failures, then it minimizes the total cost.By Equations(17),the total capacity on an edge is the sum of working and spare capacity.Equations(18)determine the working capacity.Constraints(19)and(20)calculate the minimum spare capacity on a link,needed to survive any single failure and dual failure,respectively.With stub-release(),less spare capacity may be required than without sub-release(),since paths passing the edge and being affected by the(single or dual)failure are torn down,and thus,free capacity. Equations(21)determine the reroute connections of a demand-pair for each single failure on basis of the affected connections.For any two-failure case,Constraints(22)equate the number connections which are affected by the second failure(right part)to the number of reroutable connections plus the number of lost connections(left part).The connections affected by the second failure are working connections and connections rerouted after thefirst failure.Equations(23)and(24)prohibit to take reroute paths which are subject to single failures and dual failures,respectively.4Solving HeuristicsAs the path rerouting mixed integer linear programming(MILP)problem(Section3.3)can become complex, we propose the two solving heuristics“decomposition”and“rounding.”As with any heuristic,we can tackle the problem computationally,but may not attain(globally)optimal solutions,or we might even obtain infeasible problems.4.1DecompositionThefirst heuristic is the straightforward approach where we decompose the problem into three steps.In each step we solve a subpart of the overall MILP problem andfix variables obtained in the previous steps.In the first step,we minimize the working capacity for which the Constraints(19-24)of the model in Figure9are dropped.Afterfixing and,we compute in the second step the protection capacity needed to protect8against single failures by adding Constraints(19),(21),and(23)to the model.Finally,based on thefixedvariables,,and we solve the complete model in Figure9.In steps one and two we do not offer the entire capacity in the network(by modifying the right-handside of Constraints(6)).For example,in Step1and2we allow60%and80%of the capacity,respectively,thereby allowing a capacity margin for the subsequent steps.The overall computation of the three steps ismuch faster than solving the problem in a whole.4.2RoundingThe second heuristic is based on linear programming(LP)relaxation.The path rerouting problem PRP isdescribed as a MILP model,which works on the integer vector variable.In thefirst step,the computationof its LP relaxation PRP’returns a continuous solution vector,which may be infeasible for the MILP.Ina subsequent rounding step we add the rounding constraints to the PRP MILP and solve it.Note that if an entry of is integer,these constraints will keep it pared to solving the PRPMILP,solving the LP and the more restricted MILP is faster.5EvaluationIn this section we evaluate the performance of the recovery methods using several study networks.Perfor-mance measures are capacity efficiency and double failure restorability:The capacity of the network is the sum of reserved links in allfibers in the network.For this we set in the optimization model for all edges.The restorability of a double failure is defined in this article(similar to[1])as the portion of all working paths on the edges and that are simultaneously affected by a double failure and survive this failure.The average dual failure restorability(or short restorability)is the average taken over all double failures in the network:(1)where is the total loss in the network if and fail.We compute the number ofworking paths on and in path protection by(2)and in path rerouting by(3)9Note that restorability could also be an objective for the optimization models in Section3.However, by the definition of,this results in non-linear mixed integer linear programming models.5.1Topology GeneratorIn order to investigate different network instances,we use a random topology generator(for)which tries to reflect the structure of optical networks.It is based on the the generator by Salama[14],which we enhanced to ensure two-node-connectivity and degree bounds,to come close to the optical networks’connectivity.The generator takes the number of nodes,a rectangle of size,a distance parameter,and linking parameters and as input.In thefirst loop,points with coordinates and are generated at random.If, at an iteration,a point is not nearer than to any present node,a new node is placed on this point. The loopfinishes after nodes are positioned.Then,links are generated with the intention that node-pairs having shorter distance will be connected with a higher probability than those having longer distance.Specifically,two nodes and are linked with probabilityor more connected than a maximum degree,and5.3Comparison of Recovery MechanismsFigure10depicts the results for the considered recovery mechanisms.The average computation times are 2seconds for dedicated path protection,21minutes for shared path protection,and(using the rounding heuristic in Section4)24minutes and58minutes for path rerouting without and with stub-release,respec-tively.The restorability in Figure10(a)becomes higher for all mechanisms as the number of edges increases, since the network becomes more connected.Rerouting(using stub-release)outperforms the other protection alternatives by approximately10-15%and reaches very high values of more than98%.Therefore,rerouting proves to be the best mechanism for high restorability.Due to the inflexible path assignment,shared path protection and dedicated path protection achieve91% restorability at best.Shared path protection often has shorter protection paths(because of the sharing)than dedicated path protection.Therefore,the restorability is slightly higher,because less edges are needed for a connection and thus,less dual failure events affect the connection.The total capacity consumption(for21and more edges)in Figure10(b)decreases for all recovery mechanisms as the network becomes more connected,since paths can become shorter.Also,for shared path protection and rerouting,as shorter working paths are available,less protection capacity is needed.Each recovery mechanism requires about the same working capacity.The protection capacity for dedicated path protection is on average1.5as much as the working ing shared path protection,the protection capacity drops to an average of75%of the working capacity.The entire capacity for rerouting is slightly higher than the capacity for shared path protection,since more failures are protected yielding in better restorability(see Figure10(a)).For path rerouting,an interesting detail-question is if capacity can control restorability().In our investigations more capacity does not take direct influence on,but high-levels are reached anyway. Different topologies having a capacity range of400to500yield similar-values(in the range of99.1% to99.8%).In other words,one topology can have approximately the same-performance as another one, but needs25%more capacity.Therefore,the topology rules the outcome much more than the deployed capacity(Figure10(a)).Similar results have also been found for several link-restoration mechanisms in[1].The gain of stub-release effects approximately6%better capacity efficiency for rerouting,as depicted in Figure11.On average,the working capacity is slightly higher with stub release than without,since longer working paths help to reduce the(shared)protection capacity.With a growing number of edges,the total capacity decreases,because less protection capacity is needed,while the restorability increases.The restorability of rerouting with and without stub-release(not depicted)is comparable.We attribute this to the phenomenon that again,the additional capacity offered by stub-release cannot be exploited for better restorability.5.4Double Failures in Networks Planned for Single FailuresFigures12-13compare capacity and restorability of networks planned for double failures with those planned for single failures.Planning for single failures means that the(primary)aim,which is to reduce the sum of11。
